Thermo-mechanical response and fatigue behavior of shape memory alloy

Energy Technology Data Exchange (ETDEWEB)

Kusagawa, Masaki; Asada, Yasuhide; Nakamura, Toshiya [Tokyo Univ. (Japan). Dept. of Mechanical Engineering

1998-11-01

Mechanical, thermo-mechanical and fatigue behaviors of Ni-Ti-Nb shape memory alloy (SMA) have been studied to prepare material data for a design purpose. Presented are testing devices, testing procedure and test results of monotonic tensile, recovery of inelastic deformation due to post heating (thermo-mechanical recovery) and fatigue for future use of the SMA as a structural material of nuclear incore structures. (orig.)

Thermo-mechanical response and fatigue behavior of shape memory alloy

International Nuclear Information System (INIS)

Kusagawa, Masaki; Asada, Yasuhide; Nakamura, Toshiya

1998-01-01

Mechanical, thermo-mechanical and fatigue behaviors of Ni-Ti-Nb shape memory alloy (SMA) have been studied to prepare material data for a design purpose. Presented are testing devices, testing procedure and test results of monotonic tensile, recovery of inelastic deformation due to post heating (thermo-mechanical recovery) and fatigue for future use of the SMA as a structural material of nuclear incore structures. (orig.)

Application of a unified fatigue modelling to some thermomechanical fatigue problems

International Nuclear Information System (INIS)

Dang, K. van; Maitournam, H.; Moumni, Z.

2005-01-01

Fatigue under thermomechanical loadings is an important topic for nuclear industries. For instance, thermal fatigue cracking is observed in the mixing zones of the nuclear reactor. Classical computations using existing methods based on strain amplitude or fracture mechanics are not sufficiently predictive. In this paper an alternative approach is proposed based on a multiscale modelling thanks to shakedown hypothesis. Examples of predictive results are presented. Finally an application to the RHR problem is discussed. Main ideas of the fatigue modelling: Following an idea of Professor D. Drucker who wrote in 1963 'when applied to the microstructure there is a hope that the concept of endurance limit and shakedown are related, and that fatigue failure can be related to energy dissipated in idealized material when shakedown does not occur.' we have developed a theory of fatigue based on this concept which is different from classical fatigue approaches. Many predictive applications have been already done particularly for the automotive industry. Fatigue resistance of structures undergoing thermomechanical loadings in the high cycle regime as well as in the low cycle regime are calculated using this modelling. However, this fatigue theory is until now rarely used in nuclear engineering. After recalling the main points of the theory, we shall present some relevant applications which were done in different industrial sectors. We shall apply this modelling to the prediction of thermal cracking observed in the mixing zones of RHR. (authors)

Two scale damage model and related numerical issues for thermo-mechanical high cycle fatigue

International Nuclear Information System (INIS)

Desmorat, R.; Kane, A.; Seyedi, M.; Sermage, J.P.

2007-01-01

On the idea that fatigue damage is localized at the microscopic scale, a scale smaller than the mesoscopic one of the Representative Volume Element (RVE), a three-dimensional two scale damage model has been proposed for High Cycle Fatigue applications. It is extended here to aniso-thermal cases and then to thermo-mechanical fatigue. The modeling consists in the micro-mechanics analysis of a weak micro-inclusion subjected to plasticity and damage embedded in an elastic meso-element (the RVE of continuum mechanics). The consideration of plasticity coupled with damage equations at micro-scale, altogether with Eshelby-Kroner localization law, allows to compute the value of microscopic damage up to failure for any kind of loading, 1D or 3D, cyclic or random, isothermal or aniso-thermal, mechanical, thermal or thermo-mechanical. A robust numerical scheme is proposed in order to make the computations fast. A post-processor for damage and fatigue (DAMAGE-2005) has been developed. It applies to complex thermo-mechanical loadings. Examples of the representation by the two scale damage model of physical phenomena related to High Cycle Fatigue are given such as the mean stress effect, the non-linear accumulation of damage. Examples of thermal and thermo-mechanical fatigue as well as complex applications on real size testing structure subjected to thermo-mechanical fatigue are detailed. (authors)

Stress-strain time-dependent behavior of A356.0 aluminum alloy subjected to cyclic thermal and mechanical loadings

Science.gov (United States)

Farrahi, G. H.; Ghodrati, M.; Azadi, M.; Rezvani Rad, M.

2014-08-01

This article presents the cyclic behavior of the A356.0 aluminum alloy under low-cycle fatigue (or isothermal) and thermo-mechanical fatigue loadings. Since the thermo-mechanical fatigue (TMF) test is time consuming and has high costs in comparison to low-cycle fatigue (LCF) tests, the purpose of this research is to use LCF test results to predict the TMF behavior of the material. A time-independent model, considering the combined nonlinear isotropic/kinematic hardening law, was used to predict the TMF behavior of the material. Material constants of this model were calibrated based on room-temperature and high-temperature low-cycle fatigue tests. The nonlinear isotropic/kinematic hardening law could accurately estimate the stress-strain hysteresis loop for the LCF condition; however, for the out-of-phase TMF, the condition could not predict properly the stress value due to the strain rate effect. Therefore, a two-layer visco-plastic model and also the Johnson-Cook law were applied to improve the estimation of the stress-strain hysteresis loop. Related finite element results based on the two-layer visco-plastic model demonstrated a good agreement with experimental TMF data of the A356.0 alloy.

Thermomechanical fatigue and damage mechanisms in Sanicro 25 steel

Czech Academy of Sciences Publication Activity Database

Petráš, Roman; Škorík, Viktor; Polák, Jaroslav

2016-01-01

Roč. 650, JAN (2016), s. 52-62 ISSN 0921-5093 R&D Projects: GA MŠk(CZ) EE2.3.30.0063; GA ČR(CZ) GA13-23652S Institutional support: RVO:68081723 Keywords : thermomechanical fatigue * Sanicro 25 steel * damage mechanism * FIB cutting * localized oxidation-cracking Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 3.094, year: 2016

Prediction of thermal and mechanical stress-strain responses of TMC's subjected to complex TMF histories

Science.gov (United States)

Johnson, W. S.; Mirdamadi, M.

1994-01-01

This paper presents an experimental and analytical evaluation of cross-plied laminates of Ti-15V-3Cr-3Al-3Sn (Ti-15-3) matrix reinforced with continuous silicon-carbide fibers (SCS-6) subjected to a complex TMF loading profile. Thermomechanical fatigue test techniques were developed to conduct a simulation of a generic hypersonic flight profile. A micromechanical analysis was used. The analysis predicts the stress-strain response of the laminate and of the constituents in each ply during thermal and mechanical cycling by using only constituent properties as input. The fiber was modeled as elastic with transverse orthotropic and temperature-dependent properties. The matrix was modeled using a thermoviscoplastic constitutive relation. The fiber transverse modulus was reduced in the analysis to simulate the fiber-matrix interface failures. Excellent correlation was found between measured and predicted laminate stress-strain response due to generic hypersonic flight profile when fiber debonding was modeled.

Thermomechanical fatigue of shape memory alloys

International Nuclear Information System (INIS)

Lagoudas, D C; Kumar, P K; Miller, D A; Rong, L

2009-01-01

As shape memory alloys (SMAs) gain popularity as high energy density actuators, one characteristic that becomes particularly important is the thermomechanical transformation fatigue life, in addition to maximum transformation strain and stability of actuation cycles. In this paper, a novel test frame design and testing protocol are discussed, for investigating the thermally activated transformation fatigue characteristics of SMAs under various applied loads for both complete and partial phase transformation. A Ni 50 Ti 40 Cu 10 (at.%) SMA was chosen for this investigation and the effects of various heat treatments on the transformation temperatures and the transformation fatigue lives of actuators were studied. For selected heat treatments, the evolution of recoverable and irrecoverable strains up to failure under different applied stress levels was studied in detail. The influence of complete and partial transformation on the fatigue life is also presented. The irrecoverable strain accumulation as a function of the number of cycles to failure for different stress levels is presented by a relationship similar to the Manson–Coffin law for both partial and complete transformations

Influence of Pt-aluminide coating on the oxidation and thermo-mechanical fatigue behaviour of the single crystal superalloy CMSX-4

Energy Technology Data Exchange (ETDEWEB)

Jargelius-Pettersson, R F.A.; Andersson, H C.M.; Lille, C; Haenstroem, S; Liu, L [Swedish Institute for Metals Research, Stockholm (Sweden)

2001-10-01

Oxidation and thermo-mechanical fatigue studies have been performed on a single crystal nickel base superalloy, CMSX-4, with and without an MDC150L Pt-modified diffusional aluminide coating. Oxidation for up to 500 hours at 900, 1050 and 1150 deg C revealed formation of mixed nickel-aluminium oxides, with a pronounced spalling tendency, on the base material, but parabolic growth of aluminium oxide on the coated material. The effect of water vapour and SO{sub 2} on the oxidation rate has also been investigated, and attempts have been made to apply thermodynamic and kinetic modelling to microstructural evolution in the interdiffusion zone between coating and substrate. Thermo-mechanical fatigue testing was performed on both coated and uncoated specimens. The temperature was cycled between 400 and 1050 deg C and mechanical strain ranges between 0.7 and 2.0% were used. Some specimens were cycled from a raised lower temperature estimated to be above the brittle transition temperature of the coat. Both in-phase and out-of-phase test conditions were used. No significant difference in fatigue life was detected between coated specimens cycled in-phase and out-of-phase. An improvement in fatigue life was observed with uncoated specimens tested out-of-phase. Coated specimens cycled above the transition temperature exhibited the longest fatigue life of all tested specimens. In the uncoated specimens the cracks started at the surface of the specimens. Initial cracks in the coated specimens may have started in the bond interface between the coat and the substrate or on the surface of the coat. The damage mechanism in all specimens is characterised by an initial strain hardening followed by crack initiation and crack propagation until final collapse. The load versus number of cycles curve features a maximum followed by a slow load drop and then a fast final load drop. The maxima is associated with crack initiation and the final fast load drop with plastic collapse of the specimen

Damage evolution of TBC system under in-phase thermo-mechanical tests

International Nuclear Information System (INIS)

Kitazawa, R.; Tanaka, M.; Kagawa, Y.; Liu, Y.F.

2010-01-01

In-phase thermo-mechanical tests (TMF) of EB-PVD Y 2 O 3 -ZrO 2 thermal barrier coating (TBC) system (8 wt% Y 2 O 3 -ZrO 2 /CoNiCrAlY/IN-738 substrate) were done under a through-the-thick-direction thermal gradient from TBC surface temperature at 1150 deg. C to substrate temperature at 1000 deg. C. Deformation and failure behaviors of the TBC system were observed at the macroscopic and microscopic scales and damage evolution of the system under in-phase thermo-mechanical test was discussed. Special attention was paid to TBC layer cracking, thermally grown oxide (TGO) layer formation and void formation in bond coat and substrate. Effect of TMF conditions on the damage evolution behaviors was also discussed.

Damage evolution of TBC system under in-phase thermo-mechanical tests

Energy Technology Data Exchange (ETDEWEB)

Kitazawa, R.; Tanaka, M.; Kagawa, Y. [Research Center for Advanced Science and Technology, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904 (Japan); Liu, Y.F., E-mail: yfliu@hyper.rcast.u-tokyo.ac.jp [Research Center for Advanced Science and Technology, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904 (Japan)

2010-10-15

In-phase thermo-mechanical tests (TMF) of EB-PVD Y{sub 2}O{sub 3}-ZrO{sub 2} thermal barrier coating (TBC) system (8 wt% Y{sub 2}O{sub 3}-ZrO{sub 2}/CoNiCrAlY/IN-738 substrate) were done under a through-the-thick-direction thermal gradient from TBC surface temperature at 1150 deg. C to substrate temperature at 1000 deg. C. Deformation and failure behaviors of the TBC system were observed at the macroscopic and microscopic scales and damage evolution of the system under in-phase thermo-mechanical test was discussed. Special attention was paid to TBC layer cracking, thermally grown oxide (TGO) layer formation and void formation in bond coat and substrate. Effect of TMF conditions on the damage evolution behaviors was also discussed.

Energy-based fatigue model for shape memory alloys including thermomechanical coupling

Science.gov (United States)

Zhang, Yahui; Zhu, Jihong; Moumni, Ziad; Van Herpen, Alain; Zhang, Weihong

2016-03-01

This paper is aimed at developing a low cycle fatigue criterion for pseudoelastic shape memory alloys to take into account thermomechanical coupling. To this end, fatigue tests are carried out at different loading rates under strain control at room temperature using NiTi wires. Temperature distribution on the specimen is measured using a high speed thermal camera. Specimens are tested to failure and fatigue lifetimes of specimens are measured. Test results show that the fatigue lifetime is greatly influenced by the loading rate: as the strain rate increases, the fatigue lifetime decreases. Furthermore, it is shown that the fatigue cracks initiate when the stored energy inside the material reaches a critical value. An energy-based fatigue criterion is thus proposed as a function of the irreversible hysteresis energy of the stabilized cycle and the loading rate. Fatigue life is calculated using the proposed model. The experimental and computational results compare well.

Cyclic life of superalloy IN738LC under in-phase and out-of-phase thermo-mechanical fatigue loading

International Nuclear Information System (INIS)

Chen Hongjun; Wahi, R.P.; Wever, H.

1995-01-01

The cyclic life of IN738LC, a widely used nickel base superalloy for blades in stationary gas turbines, was investigated under thermo-mechanical fatigue loading using a temperature variation range of 1023 to 1223 K, with temperature variation rate in the range of 6 to 15 K/min. Simple thermo-mechanical cycles with linear sequences corresponding to in-phase (IP) and out-of-phase (OP) tests were performed. Both the IP and OP tests were carried out at different constant mechanical strain ranges varied between 0.8 to 2.0% and at a constant mechanical strain rate of 10 -5 s -1 . Thermo-mechanical fatigue lives under both test conditions were compared with each other and with those of isothermal LCF tests at a temperature of 1223 K. The results show that the life under thermo-mechanical fatigue is strongly dependent on the nature of the test, i.e. stress controlled or strain controlled. (orig.)

Thermal-mechanical and isothermal fatigue of IN 792 CC

International Nuclear Information System (INIS)

Beck, T.; Pitz, G.; Lang, K.-H.; Loehe, D.

1997-01-01

The cyclic deformation and lifetime behaviour of the cast Ni-base superalloy IN 792 CC was investigated both under thermal-mechanical fatigue (TMF) and isothermal fatigue (IF) conditions. During TMF the phase relations between temperature and mechanical strain were in-phase and out-of-phase, respectively. For both phase relations a similar cyclic deformation behaviour is observed. In all cases out-of-phase TMF causes tensile mean stresses, whereas in-phase TMF leads to compressive mean stresses. At T max below 800 C out-of-phase cycling results in smaller lifetimes than in-phase loading. In spite of the rather high compressive mean stresses developing at T max above 800 C, at these temperatures in-phase loading causes shorter lifetimes than out-of-phase TMF. This effect is due to the different damage mechanisms caused by in-phase and out-of-phase loadings: at higher T max considerable intergranular damage caused by in-phase loading reduces the lifetime below the respective values measured during out-of-phase TMF, after which no intergranular damage could be detected. A comparison of the TMF data with the cyclic deformation and lifetime behaviour under IF conditions shows that the material's reactions under TMF cannot be assessed satisfactorily by the results obtained from isothermal fatigue tests. (orig.)

Energy-based fatigue model for shape memory alloys including thermomechanical coupling

International Nuclear Information System (INIS)

Zhang, Yahui; Zhu, Jihong; Moumni, Ziad; Zhang, Weihong; Van Herpen, Alain

2016-01-01

This paper is aimed at developing a low cycle fatigue criterion for pseudoelastic shape memory alloys to take into account thermomechanical coupling. To this end, fatigue tests are carried out at different loading rates under strain control at room temperature using NiTi wires. Temperature distribution on the specimen is measured using a high speed thermal camera. Specimens are tested to failure and fatigue lifetimes of specimens are measured. Test results show that the fatigue lifetime is greatly influenced by the loading rate: as the strain rate increases, the fatigue lifetime decreases. Furthermore, it is shown that the fatigue cracks initiate when the stored energy inside the material reaches a critical value. An energy-based fatigue criterion is thus proposed as a function of the irreversible hysteresis energy of the stabilized cycle and the loading rate. Fatigue life is calculated using the proposed model. The experimental and computational results compare well. (paper)

A computational approach for thermomechanical fatigue life prediction of dissimilarly welded superheater tubes

Energy Technology Data Exchange (ETDEWEB)

Krishnasamy, Ram-Kumar; Seifert, Thomas; Siegele, Dieter [Fraunhofer-Institut fuer Werkstoffmechanik (IWM), Freiburg im Breisgau (Germany)

2010-07-01

In this paper a computational approach for fatigue life prediction of dissimilarly welded superheater tubes is presented and applied to a dissimilar weld between tubes made of the nickel base alloy Alloy617 tube and the 12% chromium steel VM12. The approach comprises the calculation of the residual stresses in the welded tubes with a multi-pass dissimilar welding simulation, the relaxation of the residual stresses in a post weld heat treatment (PWHT) simulation and the fatigue life prediction using the remaining residual stresses as initial condition. A cyclic fiscoplasticity model is used to calculate the transient stresses and strains under thermocyclic service loadings. The fatigue life is predicted with a damage parameter which is based on fracture mechanics. The adjustable parameters of the model are determined based on LCF and TMF experiments. The simulations show, that the residual stresses that remain after PWHT further relax in the first loading cycles. The predicted fatigue lives depend on the residual stresses and, thus, on the choice of the loading cycle in which the damage parameter is evaluated. It the first loading cycle, where residual stresses are still present, is considered, lower fatigue lives are predicted compared to predictions considering loading cycles with relaxed residual stresses. (orig.)

Thermomechanical fatigue of Sn-37 wt.% Pb model solder joints

International Nuclear Information System (INIS)

Liu, X.W.; Plumbridge, W.J.

2003-01-01

The fatigue of Sn-37 wt.% Pb model solder joints has been investigated under thermomechanical and thermal cycling. Based upon an analysis of displacements during thermomechancial cycling, a model solder joint has been designed to simulate actual joints in electronic packages. The strain-stress relationship, characterised by hysteresis loops, was determined during cycling from 30 to 125 deg. C, and the stress-range monitored throughout. The number of cycles to failure, as defined by the fall in stress range, was correlated to strain range and strain energy. The strain hardening exponent, k, varied with the definition of failure and, when a stress-range drop of 50% was used, it was 0.46. Cracks were produced during pure thermal cycling without external strains applied. These arose due to the local strains caused by thermal expansion mismatches between the solder and Cu 6 Sn 5 intermetallic layer, between the phases of solder, and due to the anisotropy of the materials. The fatigue life under thermomechanical cycling was significantly inferior to that obtained in isothermal mechanical cycling. A factor contributing to this inferiority is the internal damage produced during temperature cycling

Effect of thermo-mechanical loading histories on fatigue crack growth behavior and the threshold in SUS 316 and SCM 440 steels. For prevention of high cycle thermal fatigue failures

International Nuclear Information System (INIS)

Okazaki, Masakazu; Muzvidziwa, Milton; Iwasaki, Akira; Kasahara, Naoto

2014-01-01

High cycle thermal fatigue failure of pipes induced by fluid temperature change is one of the interdisciplinary issues to be concerned for long term structural reliability of high temperature components in energy systems. In order to explore advanced life assessment methods to prevent the failure, fatigue crack propagation tests were carried out in a low alloy steel and an austenitic stainless steel under typical thermal and thermo-mechanical histories. Special attention was paid to both the effect of thermo-mechanical loading history on the fatigue crack threshold, as well as to the applicability of continuum fracture mechanics treatment to small or short cracks. It was shown experimentally that the crack-based remaining fatigue life evaluation provided more reasonable assessment than the traditional method based on the semi-empirical law in terms of 'usage factor' for high cycle thermal fatigue failure that is employed in JSME Standard, S017. The crack propagation analysis based on continuum fracture mechanics was almost successfully applied to the small fatigue cracks of which size was comparable to a few times of material grain size. It was also shown the thermo-mechanical histories introduced unique effects to the prior fatigue crack wake, resulting in occasional change in the fatigue crack threshold. (author)

Design Analysis and Thermo-Mechanical Fatigue of a Polyimide Composite for Combustion Chamber Support

Science.gov (United States)

Thesken, J. C.; Melis, M.; Shin, E.; Sutter, J.; Burke, Chris

2004-01-01

Polyimide composites are being evaluated for use in lightweight support structures designed to preserve the ideal flow geometry within thin shell combustion chambers of future space launch propulsion systems. Principles of lightweight design and innovative manufacturing techniques have yielded a sandwich structure with an outer face sheet of carbon fiber polyimide matrix composite. While the continuous carbon fiber enables laminated skin of high specific stiffness; the polyimide matrix materials ensure that the rigidity and durability is maintained at operation temperatures of 316 C. Significant weight savings over all metal support structures are expected. The protypical structure is the result of ongoing collaboration, between Boeing and NASA-GRC seeking to introduce polyimide composites to the harsh environmental and loads familiar to space launch propulsion systems. Design trade analyses were carried out using relevant closed form solutions, approximations for sandwich beams/panels and finite element analysis. Analyses confirm the significant thermal stresses exist when combining materials whose coefficients of thermal expansion (CTEs) differ by a factor of about 10 for materials such as a polymer composite and metallic structures. The ramifications on design and manufacturing alternatives are reviewed and discussed. Due to stringent durability and safety requirements, serious consideration is being given to the synergistic effects of temperature and mechanical loads. The candidate structure operates at 316 C, about 80% of the glass transition temperature T(sub g). Earlier thermomechanical fatigue (TMF) investigations of chopped fiber polyimide composites made this near to T(sub g), showed that cyclic temperature and stress promoted excessive creep damage and strain accumulation. Here it is important to verify that such response is limited in continuous fiber laminates.

Influence of dwell times on the thermomechanical fatigue behavior of a directionally solidified Ni-base superalloy

Czech Academy of Sciences Publication Activity Database

Guth, S.; Petráš, Roman; Škorík, Viktor; Kruml, Tomáš; Man, Jiří; Lang, K. H.; Polák, Jaroslav

2015-01-01

Roč. 80, NOV (2015), s. 426-433 ISSN 0142-1123 R&D Projects: GA MŠk(CZ) EE2.3.30.0063 Institutional support: RVO:68081723 Keywords : Nickel base superalloy * Thermomechanical fatigue * Dwell time * Lifetime behavior * Damage mechanisms Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.162, year: 2015

Service life prediction. Development of models for predicting the service life of power plant components subject to thermomechanical creep fatigue; Lebensdauervorhersage. Entwicklung von Modellen zur Lebensdauervorhersage von Kraftwerksbauteilen unter thermisch-mechanischer Kriechermuedungsbeanspruchung. Abschlussbericht

Energy Technology Data Exchange (ETDEWEB)

Cui, L.; Scholz, A. [Technische Univ. Darmstadt (Germany). Institut fuer Werkstoffkunde; Hartrott, P. von; Schlesinger, M. [Fraunhofer-Institut fuer Werkstoffmechanik (IWM), Freiburg im Breisgau (Germany)

2009-07-01

Extensive use is made of massive components of heat resistant and highly heat resistant materials in installations of the power and heating industry. These components are exposed to varying thermomechanical stress as a result of ramping-up and down processes. In this research project two computer-assisted methods of predicting service life until crack initiation were extended to include cases of thermomechanical multi-axis stress conducive to creep fatigue and of superposition of high-cycle stress on power plant components. Investigations were limited to rotor steel of type X12CrMoWVNbN10-1-1. Complex thermomechanical multi-axis experiments were performed on round, notched and cruciform test specimens of close-to-life dimensions in order to demonstrate by experiment the validity of these models. The results of these calculations showed an acceptable degree of agreement between experiment and simulation for both models. Calculations on earlier TMF experiments performed at IfW on hollow specimens of 1%CrMoNiV showed good predictability for both the SARA and the ThoMat programme. Calculations on experiments performed at MPA Stuttgart on model bodies consisting of the same 1%CrMoNiV showed a predictability of acceptable variability considering the complexity of the stresses involved. A further outcome of this project is that the use of SARA appears universally suitable for the construction of new plants and in the service area, while the use of ThoMat appears suited for detail optimisation in the development process.

Reliable high-power diode lasers: thermo-mechanical fatigue aspects

Science.gov (United States)

Klumel, Genady; Gridish, Yaakov; Szafranek, Igor; Karni, Yoram

2006-02-01

High power water-cooled diode lasers are finding increasing demand in biomedical, cosmetic and industrial applications, where repetitive cw (continuous wave) and pulsed cw operation modes are required. When operating in such modes, the lasers experience numerous complete thermal cycles between "cold" heat sink temperature and the "hot" temperature typical of thermally equilibrated cw operation. It is clearly demonstrated that the main failure mechanism directly linked to repetitive cw operation is thermo-mechanical fatigue of the solder joints adjacent to the laser bars, especially when "soft" solders are used. Analyses of the bonding interfaces were carried out using scanning electron microscopy. It was observed that intermetallic compounds, formed already during the bonding process, lead to the solders fatigue both on the p- and n-side of the laser bar. Fatigue failure of solder joints in repetitive cw operation reduces useful lifetime of the stacks to hundreds hours, in comparison with more than 10,000 hours lifetime typically demonstrated in commonly adopted non-stop cw reliability testing programs. It is shown, that proper selection of package materials and solders, careful design of fatigue sensitive parts and burn-in screening in the hard pulse operation mode allow considerable increase of lifetime and reliability, without compromising the device efficiency, optical power density and compactness.

Review on structural fatigue of NiTi shape memory alloys: Pure mechanical and thermo-mechanical ones

Directory of Open Access Journals (Sweden)

Guozheng Kang

2015-11-01

Full Text Available Structural fatigue of NiTi shape memory alloys is a key issue that should be solved in order to promote their engineering applications and utilize their unique shape memory effect and super-elasticity more sufficiently. In this paper, the latest progresses made in experimental and theoretical analyses for the structural fatigue features of NiTi shape memory alloys are reviewed. First, macroscopic experimental observations to the pure mechanical and thermo-mechanical fatigue features of the alloys are summarized; then the state-of-arts in the mechanism analysis of fatigue rupture are addressed; further, advances in the construction of fatigue failure models are provided; finally, summary and future topics are outlined.

Probabilistic Simulation of Combined Thermo-Mechanical Cyclic Fatigue in Composites

Science.gov (United States)

Chamis, Christos C.

2011-01-01

A methodology to compute probabilistically-combined thermo-mechanical fatigue life of polymer matrix laminated composites has been developed and is demonstrated. Matrix degradation effects caused by long-term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress-dependent multifactor-interaction relationship developed at NASA Glenn Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability-integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability-based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/-45/90)s graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical-cyclic loads and low thermal-cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical-cyclic loads and high thermal-cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

Thermal-mechanical fatigue of high temperature structural materials

Science.gov (United States)

Renauld, Mark Leo

Experimental and analytical methods were developed to address the effect of thermal-mechanical strain cycling on high temperature structural materials under uniaxial and biaxial stress states. Two materials were used in the investigation, a nickel-base superalloy of low ductility, IN-738LC and a high ductility material, 316 stainless steel. A uniaxial life prediction model for the IN-738LC material was based on tensile hysteresis energy measured in stabilized, mid-life hysteresis loops. Hold-time effects and temperature cycling were incorporated in the hysteresis energy approach. Crack growth analysis was also included in the model to predict the number of TMF cycles to initiate and grow a fatigue crack through the coating. The nickel-base superalloy, IN-738LC, was primarily tested in out-of-phase (OP) TMF with a temperature range from 482-871sp°C (900-1600sp°F) under continuous and compressive hold-time cycling. IN-738LC fatigue specimens were coated either with an aluminide, NiCoCrAlHfSi overlay or CoNiCrAlY overlay coating on the outer surface of the specimen. Metallurgical failure analysis via optical and scanning electron microscopy, was used to characterize failure behavior of both substrate and coating materials. Type 316 SS was subjected to continuous biaxial strain cycling with an in-phase (IP) TMF loading and a temperature range from 399-621sp°C (750-1150sp°F). As a result, a biaxial TMF life prediction model was proposed on the basis of an extended isothermal fatigue model. The model incorporates a frequency effect and phase factors to assess the different damage mechanisms observed during TMF loading. The model was also applied to biaxial TMF data generated on uncoated IN-738LC.

Microstructural modeling of fatigue fracture of shape memory alloys at thermomechanical cyclic loading

Science.gov (United States)

Belyaev, Fedor S.; Evard, Margarita E.; Volkov, Aleksandr E.

2018-05-01

A microstructural model of shape memory alloys (SMA) describing their deformation and fatigue fracture is presented. A new criterion of fracture has been developed which takes into account the effect of hydrostatic pressure, deformation defects and material damage. It is shown that the model can describe the fatigue fracture of SMA under various thermomechanical cycling regimes. Results of calculating the number of cycles to failure at thermocycling under a constant stress, at symmetric two-sided cyclic deformation, at straining-unloading cycles, at cycling in the regime of the thermodynamic cycles of a SMA working body in the hard (strain controlled) and soft (stress controlled) working cycles, is studied. Results of calculating the number of cycles to failure are presented for different parameters of these cycles.

Service-cycle component-feature specimen TMF testing of steam turbine rotor steels

Energy Technology Data Exchange (ETDEWEB)

Radosavljevic, M.; Holdsworth, S.R. [Eidgenoessische Materialpruefungs- und Forschungsanstalt, Duebendorf (Switzerland); Mazza, E. [Eidgenoessische Materialpruefungs- und Forschungsanstalt, Duebendorf (Switzerland); Eidgenoessische Technische Hochschule (ETH), Zurich (Switzerland); Grossmann, P.; Ripamonti, L. [ALSTOM Power (Switzerland) Ltd., Baden (Switzerland)

2010-07-01

This paper reviews the methodology adopted in a Swiss Research Collaboration to devise a component-feature representative specimen geometry and the TMF cycle parameters necessary to closely simulate arduous steam turbine operating duty. Implementation of these service-like experimental conditions provides a practical indication of the effectiveness of deformation and crack initiation endurance predictions. Comprehensive post test inspection provides evidence to demonstrate the physical realism of the laboratory simulations in terms of the creep-fatigue damage generated during the benchmark tests. Mechanical response results and physical damage observations are presented and their practical implications discussed for the example of a 2%CrMoNiWV rotor service cycle. (orig.)

Reduced softening of EUROFER 97 under thermo-mechanical and multiaxial fatigue loading and its impact on the design rules

International Nuclear Information System (INIS)

Aktaa, J.; Weick, M.; Petersen, C.

2007-01-01

Full text of publication follows: Toward test blanket module (TBM) in ITER and DEMO fusion power plants design rules for components built from EUROFER 97 get more and more in the midpoint of interest. One of the specific characteristic of EUROFER 97 as a ferritic-martensitic steel is its cyclic softening yielding to lower stresses under strain controlled fatigue loading and thus longer lifetimes. However our thermo-mechanical and multiaxial fatigue tests showed lifetimes remarkably lower than those expected on the base of isothermal uniaxial fatigue tests. Reduced cyclic softening observed in these experiments is believed as one of the reasons of the shorter fatigue lifetimes. When applying the design rules, derived for EUROFER 97 on the base of isothermal uniaxial data considering the recommendations in the ASME and RCC-MR code, to our thermo-mechanical and multiaxial fatigue tests for verification strong loss in their conservatism has been found. The lifetimes observed in a part of the multiaxial experiments are even lower than the design lifetimes supposed to be sufficiently conservative. To overcome this problem new design rules are proposed among others on the base of damage and lifetime prediction model developed lately for EUROFER 97. In this paper the experimental findings as well as the new design approaches will be presented and discussed. (authors)

Equipment for the investigation of the thermomechanical fatigue of metallic materials

International Nuclear Information System (INIS)

Wolter, F.; Petersen, C.

1992-01-01

Within the framework of the European research program on nuclear fusion, a question is to be answered which is of great importance for the design of a fusion reactor, namely: To what extent is the 'First Wall structure' damaged by the pulsating mode of operation in this reactor type. This pulsating mode of operation leads to a thermal and mechanical cyclic stress in the metal support structure of the reactor. Thermomechanical cyclic stresses of a similar kind also occur in aircraft turbines, rocket drive units, and heat generating systems. For simulation of such stresses, a facility was developed in the Karlsruhe Nuclear Research Center which permits to produce thermomechanical cyclic stresses in uniaxial metallic materials specimens. The results of investigations with a martensitic 12%-Cr steel are explained. The stress range variations show a degressive behavior at the onset of fatigue and develop into a linear decline. The plastic strain reached a plateau after a number of cycles which was dependent on the mechanical strain (linear behavior). Relationships can be described by a simple transformation of number of cycles to failure between mechanical strain and number of stress cycles to failure. (orig./MM) [de

Fatigue behaviour of coke drum materials under thermal-mechanical cyclic loading

Directory of Open Access Journals (Sweden)

Jie Chen

2014-01-01

Full Text Available Coke drums are vertical pressure vessels used in the delayed coking process in petroleum refineries. Significant temperature variation during the delayed coking process causes damage in coke drums in the form of bulging and cracking. There were some studies on the fatigue life estimation for the coke drums, but most of them were based on strain-fatigue life curves at constant temperatures, which do not consider simultaneous cyclic temperature and mechanical loading conditions. In this study, a fatigue testing system is successfully developed to allow performing thermal-mechanical fatigue (TMF test similar to the coke drum loading condition. Two commonly used base and one clad materials of coke drums are then experimentally investigated. In addition, a comparative study between isothermal and TMF lives of these materials is conducted. The experimental findings lead to better understanding of the damage mechanisms occurring in coke drums and more accurate prediction of fatigue life of coke drum materials.

Anisotropic TGO rumpling in EB-PVD thermal barrier coatings under in-phase thermomechanical loading

Energy Technology Data Exchange (ETDEWEB)

Balint, D.S., E-mail: d.balint@imperial.ac.uk [Department of Mechanical Engineering, Imperial College London, London SW7 2AZ (United Kingdom); Kim, S.-S.; Liu Yufu; Kitazawa, R.; Kagawa, Y. [Research Center for Advanced Science and Technology, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8409 (Japan); Evans, A.G. [College of Engineering, University of California, Santa Barbara, CA 93106 (United States)

2011-04-15

An electron beam physical vapor deposited (EB-PVD) Y{sub 2}O{sub 3}-ZrO{sub 2} thermal barrier system has been tested under in-phase thermomechanical fatigue (TMF) conditions with thermal gradient in the through-thickness direction. Undulations in the thermally grown oxide (TGO) were observed to have clear anisotropic behavior with respect to the directions parallel and perpendicular to the loading axis. It was found that undulation wavelengths were nearly the same in both directions but the amplitude in the perpendicular direction was much larger than in the parallel direction. A recent model of TGO rumpling was adapted and used to analyze and explain the origins of the observed rumpling behavior under TMF conditions. Methods for deducing variation in the coefficient of thermal expansion with temperature and in the creep properties of the substrate from the experimental strain data are also presented in the course of the derivations. Model results show that tensile stress applied in the loading direction can overcome the compression occurring from lateral expansion during oxide formation, causing undulations to flatten; undulations perpendicular to the loading axis are unaffected. However, ratcheting in the strain cycle experienced by the substrate, which occurs naturally by substrate creep, is necessary for anisotropic rumpling under cyclic stress conditions. Model predictions for constant applied stress are also presented, demonstrating a reversal in the direction of undulation alignment under compression. A threshold stress is identified, in both tension and compression, sufficient to produce appreciable anisotropic rumpling. The model predictions provide a clear mechanism for the anisotropy and further evidence that the lateral expansion strain in the oxide is the driving force for oxide rumpling.

Anisotropic TGO rumpling in EB-PVD thermal barrier coatings under in-phase thermomechanical loading

International Nuclear Information System (INIS)

Balint, D.S.; Kim, S.-S.; Liu Yufu; Kitazawa, R.; Kagawa, Y.; Evans, A.G.

2011-01-01

An electron beam physical vapor deposited (EB-PVD) Y 2 O 3 -ZrO 2 thermal barrier system has been tested under in-phase thermomechanical fatigue (TMF) conditions with thermal gradient in the through-thickness direction. Undulations in the thermally grown oxide (TGO) were observed to have clear anisotropic behavior with respect to the directions parallel and perpendicular to the loading axis. It was found that undulation wavelengths were nearly the same in both directions but the amplitude in the perpendicular direction was much larger than in the parallel direction. A recent model of TGO rumpling was adapted and used to analyze and explain the origins of the observed rumpling behavior under TMF conditions. Methods for deducing variation in the coefficient of thermal expansion with temperature and in the creep properties of the substrate from the experimental strain data are also presented in the course of the derivations. Model results show that tensile stress applied in the loading direction can overcome the compression occurring from lateral expansion during oxide formation, causing undulations to flatten; undulations perpendicular to the loading axis are unaffected. However, ratcheting in the strain cycle experienced by the substrate, which occurs naturally by substrate creep, is necessary for anisotropic rumpling under cyclic stress conditions. Model predictions for constant applied stress are also presented, demonstrating a reversal in the direction of undulation alignment under compression. A threshold stress is identified, in both tension and compression, sufficient to produce appreciable anisotropic rumpling. The model predictions provide a clear mechanism for the anisotropy and further evidence that the lateral expansion strain in the oxide is the driving force for oxide rumpling.

Thermo-mechanical fatigue behavior of reduced activation ferrite/martensite stainless steels

International Nuclear Information System (INIS)

Petersen, C.; Rodrian, D.

2002-01-01

The thermo-mechanical cycling fatigue (TMCF) behavior of reduced activation ferrite/martensite stainless steels is examined. The test rig consists of a stiff load frame, which is directly heated by the digitally controlled ohmic heating device. Cylindrical specimens are used with a wall thickness of 0.4 mm. Variable strain rates are applied at TMCF test mode, due to the constant heating rate of 5.8 K/s and variable temperature changes. TMCF results of as received EUROFER 97 in the temperature range between 100 and 500-600 deg. C show a reduction in life time (a factor of 2) compared to F82H mod. and OPTIFER IV. TMCF-experiments with hold times of 100 and 1000 s show dramatic reduction in life time for all three materials

The Transportable Measurements Facility (TMF) System Description.

Science.gov (United States)

1980-05-23

sites using different antennas, antenna/site characterization, ATCRBS-mode and DABS-mode processor evaluation, and DABS-based ATC and ATARS system...conditions met. 34 TABLE 3 TMF DATA RECORDED DURING EXPERIMENTS By Word Type 1) By Parameter Word No. of Bits Experiment Number 8 Physical Location Number of

Life prediction of advanced materials for gas turbine application

Energy Technology Data Exchange (ETDEWEB)

Zamrik, S.Y.; Ray, A.; Koss, D.A. [Pennsylvania State Univ., University Park, PA (United States)

1995-10-01

Most of the studies on the low cycle fatigue life prediction have been reported under isothermal conditions where the deformation of the material is strain dependent. In the development of gas turbines, components such as blades and vanes are exposed to temperature variations in addition to strain cycling. As a result, the deformation process becomes temperature and strain dependent. Therefore, the life of the component becomes sensitive to temperature-strain cycling which produces a process known as {open_quotes}thermomechanical fatigue, or TMF{close_quotes}. The TMF fatigue failure phenomenon has been modeled using conventional fatigue life prediction methods, which are not sufficiently accurate to quantitatively establish an allowable design procedure. To add to the complexity of TMF life prediction, blade and vane substrates are normally coated with aluminide, overlay or thermal barrier type coatings (TBC) where the durability of the component is dominated by the coating/substrate constitutive response and by the fatigue behavior of the coating. A number of issues arise from TMF depending on the type of temperature/strain phase cycle: (1) time-dependent inelastic behavior can significantly affect the stress response. For example, creep relaxation during a tensile or compressive loading at elevated temperatures leads to a progressive increase in the mean stress level under cyclic loading. (2) the mismatch in elastic and thermal expansion properties between the coating and the substrate can lead to significant deviations in the coating stress levels due to changes in the elastic modulii. (3) the {open_quotes}dry{close_quotes} corrosion resistance coatings applied to the substrate may act as primary crack initiation sites. Crack initiation in the coating is a function of the coating composition, its mechanical properties, creep relaxation behavior, thermal strain range and the strain/temperature phase relationship.

Thermomechanical fields measurement for fatigue investigation under cyclic thermal shocks

International Nuclear Information System (INIS)

Charbal, Ali

2017-01-01

Thermal fatigue occurs in nuclear power plant pipes. The temperature variations are due to the turbulent mixing of fluids that have different temperatures. Many experimental setups have been designed but the measured temperatures have only been punctual and out of the zone of interest (e.g., via thermocouples). The equivalent strain variation in the crack initiation region is calculated with numerical thermomechanical simulations. In many cases, the comparisons between numerical and experimental results have shown that the crack initiation predictions in thermal fatigue are non-conservative. a new testing setup is proposed where thermal shocks are applied with a pulsed laser beam while the thermal and kinematic fields on the specimen surface are measured with infrared (IR) and visible cameras, respectively. Experimental testings are performed and different measurement techniques for temperature and kinematic fields are used. IR camera and pyrometers allow to measure the temperature variations in the zone impacted by the laser beam. To estimate the absolute temperature, the surface emissivities at the respective wavelengths are determined by different methods. The absolute temperature field is then used to apply the actual thermal loading in a decoupled FE model after an identification process of the parameters of the laser beam. Once the thermal loading is generated based upon the experimental data, the stress and strain fields can be computed in the region of interest with an elastoplastic law.The experimental strain variations calculated from the DIC measurements are compared with the predictions obtained with the FE simulation. (author) [fr

Marginal and internal fit of heat pressed versus CAD/CAM fabricated all-ceramic onlays after exposure to thermo-mechanical fatigue

Science.gov (United States)

Guess, Petra C.; Vagopoulou, Thaleia; Zhang, Yu; Wolkewitz, Martin; Strub, Joerg R.

2015-01-01

Objectives The aim of the study was to evaluate the marginal and internal fit of heat-pressed and CAD/CAM fabricated all-ceramic onlays before and after luting as well as after thermo-mechanical fatigue. Materials and Methods Seventy-two caries-free, extracted human mandibular molars were randomly divided into three groups (n=24/group). All teeth received an onlay preparation with a mesio-occlusal-distal inlay cavity and an occlusal reduction of all cusps. Teeth were restored with heat-pressed IPS-e.max-Press* (IP, *Ivoclar-Vivadent) and Vita-PM9 (VP, Vita-Zahnfabrik) as well as CAD/CAM fabricated IPS-e.max-CAD* (IC, Cerec 3D/InLab/Sirona) all-ceramic materials. After cementation with a dual-polymerizing resin cement (VariolinkII*), all restorations were subjected to mouth-motion fatigue (98N, 1.2 million cycles; 5°C/55°C). Marginal fit discrepancies were examined on epoxy replicas before and after luting as well as after fatigue at 200x magnification. Internal fit was evaluated by multiple sectioning technique. For the statistical analysis, a linear model was fitted with accounting for repeated measurements. Results Adhesive cementation of onlays resulted in significantly increased marginal gap values in all groups, whereas thermo-mechanical fatigue had no effect. Marginal gap values of all test groups were equal after fatigue exposure. Internal discrepancies of CAD/CAM fabricated restorations were significantly higher than both press manufactured onlays. Conclusions Mean marginal gap values of the investigated onlays before and after luting as well as after fatigue were within the clinically acceptable range. Marginal fit was not affected by the investigated heat-press versus CAD/CAM fabrication technique. Press fabrication resulted in a superior internal fit of onlays as compared to the CAD/CAM technique. Clinical Relevance Clinical requirements of 100 μm for marginal fit were fulfilled by the heat-press as well as by the CAD/CAM fabricated all-ceramic onlays

Effect of thermo-mechanical treatments on creep and fatigue properties of 9% Cr martensitic steels

International Nuclear Information System (INIS)

Hollner, S.; Fournier, B.; Le Pendu, J.; Caes, C.; Tournie, I.; Pineau, A.

2011-01-01

In the framework of the development of Generation IV nuclear reactors and fusion nuclear reactors, materials with high mechanical properties up to 550 C are required. In service the materials will be subjected to high-temperature creep and cyclic loadings. 9-12%Cr martensitic steels are candidate materials for these applications; however, they show a pronounced cyclic softening effect under cyclic loadings. This softening effect is linked to the coarsening of the martensitic microstructure. In order to refine its microstructure and its precipitation state, the commercial P91 steel has been submitted to a thermo-mechanical treatment including warm-rolling at 600 C and a tempering stage at 700 C. Microstructural observations confirm that this thermo-mechanical treatment led to a finer martensite with smaller MX-type precipitates. This evolution has an effect on the high-temperature mechanical properties: the optimized P91 steel is 100 Hv harder than the as-received P91, and its yield strength is 430 MPa higher at 20 C and 220 MPa higher at 550 C. Its lifetime under creep (at 650 C under 120 MPa) is at least 14 times longer; and the fatigue test at 650 C under 0.7% strain shows a slightly slower cyclic softening effect for the optimized P91. (authors)

Quality expectations and tolerance limits of trial master files (TMF) - Developing a risk-based approach for quality assessments of TMFs.

Science.gov (United States)

Hecht, Arthur; Busch-Heidger, Barbara; Gertzen, Heiner; Pfister, Heike; Ruhfus, Birgit; Sanden, Per-Holger; Schmidt, Gabriele B

2015-01-01

This article addresses the question of when a trial master file (TMF) can be considered sufficiently accurate and complete: What attributes does the TMF need to have so that a clinical trial can be adequately reconstructed from documented data and procedures? Clinical trial sponsors face significant challenges in assembling the TMF, especially when dealing with large, international, multicenter studies; despite all newly introduced archiving techniques it is becoming more and more difficult to ensure that the TMF is complete. This is directly reflected in the number of inspection findings reported and published by the EMA in 2014. Based on quality risk management principles in clinical trials the authors defined the quality expectations for the different document types in a TMF and furthermore defined tolerance limits for missing documents. This publication provides guidance on what type of documents and processes are most important, and in consequence, indicates on which documents and processes trial team staff should focus in order to achieve a high-quality TMF. The members of this working group belong to the CQAG Group (Clinical Quality Assurance Germany) and are QA (quality assurance) experts (auditors or compliance functions) with long-term experience in the practical handling of TMFs.

Fatigue behaviour of the austenitic steel 1.4550 under mechanical and thermal cyclic loading

Energy Technology Data Exchange (ETDEWEB)

Siegele, D.; Fingerhuth, J.; Varfolomeev, I.; Moroz, S. [Fraunhofer Institute for Mechanics of Materials (IWM), Freiburg (Germany)

2014-07-01

Fatigue behaviour of the austenitic steel 1.4550 (X6CrNiNb18-10) under low-cycle fatigue and high-cycle thermal fatigue was investigated with in two research projects supported by the Federal Ministry of Economic Affairs and Energy and the Ministry of Education and Research. The objectives of the projects were the gain of deep understanding of the damage mechanisms under mechanical and thermal cyclic loading and the development of material models and simulation procedures for an improved lifetime assessment. In comparison to the advanced mechanism based material models engineering computational procedures were proven with respect to their applicability and conservatisms. For thermal cyclic loading, test equipment and technique were developed which allow for cyclic thermal loading with temperature ranges between 1 00 C and 300 C and frequencies between 0.1 and 1 Hz. As a result, tests with a temperature range of 150 C and lower showed no crack formation up to 300,000 cycles. For temperature ranges of 200 C and higher multiple crack patterns were observed with the deepest crack of about 1.3 mm after 1,000,000 cycles, whereas the difference in crack depth between 300,000 and 1,000,000 cycles was negligibly small. To model the fatigue lifetime, the D{sub TMF} damage parameter was applied to the low-cycle fatigue and the thermal, high frequent fatigue tests. For thermal fatigue, the analyses predicted in agreement with the tests crack initiation followed by crack propagation, subsequent retardation and arrest. This behaviour can be explained qualitatively and quantitatively using the methods of linear-elastic fracture mechanics, whereas the consideration of the interaction of multiple cracks is essential to describe the experimentally observed crack retardation. The results for thermal fatigue are in the scatterband of the mechanical p and thermo-mechanical fatigue results and the cycles to failure are 10 times higher than those estimated according to the KTA fatigue

Fatigue life prediction of Ni-base thermal solar receiver tubes

Energy Technology Data Exchange (ETDEWEB)

Hartrott, Philipp von; Schlesinger, Michael [Fraunhofer-Institut fuer Werkstoffmechanik (IWM), Freiburg im Breisgau (Germany); Uhlig, Ralf; Jedamski, Jens [DLR Deutsches Zentrum fuer Luft- und Raumfahrt e.V., Stuttgart (Germany)

2010-07-01

Solar receivers for tower type Solar Thermal Power Plants are subjected to complex thermo-mechanical loads including fast and severe thermo-mechanical cycles. The material temperatures can reach more than 800 C and fall to room temperature very quickly. In order to predict the fatigue life of a receiver design, receiver tubes made of Alloy 625 with a wall thickness of 0.5 mm were tested in isothermal and thermo-cyclic experiments. The number of cycles to failure was in the range of 100 to 100,000. A thermo-mechanical fatigue life prediction model was set up. The model is based on the cyclic deformation of the material and the damage caused by the growth of fatigue micro cracks. The model reasonably predicts the experimental results. (orig.)

Thermomechanical fatigue life prediction for several solders

Science.gov (United States)

Wen, Shengmin

Since solder connections operate at high homologous temperature, solders are high temperature materials. This feature makes their mechanical behavior and fatigue phenomena unique. Based on experimental findings, a physical damage mechanism is introduced for solders. The mechanism views the damage process as a series of independent local damage events characterized by the failure of individual grains, while the structural damage is the eventual percolation result of such local events. Fine's dislocation energy density concept and Mura's microcrack initiation theory are adopted to derive the fatigue formula for an individual grain. A physical damage metric is introduced to describe the material with damage. A unified creep and plasticity constitutive model is adopted to simulate the mechanical behavior of solders. The model is cast into a continuum damage mechanics framework to simulate material with damage. The model gives good agreement with the experimental results of 96.5Pb-3.5Sn and 96.5Sn-3.5Ag solders under uniaxial strain-controlled cyclic loading. The model is convenient for implementation into commercial computational packages. Also presented is a fatigue theory with its failure criterion for solders based on physical damage mechanism. By introducing grain orientation into the fatigue formula, an m-N curve (m is Schmid factor) at constant loading condition is suggested for fatigue of grains with different orientations. A solder structure is defined as fatigued when the damage metric reaches a critical threshold, since at this threshold the failed grains may form a cluster and percolate through the structure according to percolation theory. Fatigue data of 96.5Pb-3.5Sn solder bulk specimens under various uniaxial tension tests were analyzed. Results show that the theory gives consistent predictions under broad conditions, while inelastic strain theory does not. The theory is anisotropic with no size limitation to its application, which could be suitable for

Quality expectations and tolerance limits of trial master files (TMF) – Developing a risk-based approach for quality assessments of TMFs

Science.gov (United States)

Hecht, Arthur; Busch-Heidger, Barbara; Gertzen, Heiner; Pfister, Heike; Ruhfus, Birgit; Sanden, Per-Holger; Schmidt, Gabriele B.

2015-01-01

This article addresses the question of when a trial master file (TMF) can be considered sufficiently accurate and complete: What attributes does the TMF need to have so that a clinical trial can be adequately reconstructed from documented data and procedures? Clinical trial sponsors face significant challenges in assembling the TMF, especially when dealing with large, international, multicenter studies; despite all newly introduced archiving techniques it is becoming more and more difficult to ensure that the TMF is complete. This is directly reflected in the number of inspection findings reported and published by the EMA in 2014. Based on quality risk management principles in clinical trials the authors defined the quality expectations for the different document types in a TMF and furthermore defined tolerance limits for missing documents. This publication provides guidance on what type of documents and processes are most important, and in consequence, indicates on which documents and processes trial team staff should focus in order to achieve a high-quality TMF. The members of this working group belong to the CQAG Group (Clinical Quality Assurance Germany) and are QA (quality assurance) experts (auditors or compliance functions) with long-term experience in the practical handling of TMFs. PMID:26693218

Quality expectations and tolerance limits of trial master files (TMF – Developing a risk-based approach for quality assessments of TMFs

Directory of Open Access Journals (Sweden)

Hecht, Arthur

2015-12-01

Full Text Available This article addresses the question of when a trial master file (TMF can be considered sufficiently accurate and complete: What attributes does the TMF need to have so that a clinical trial can be adequately reconstructed from documented data and procedures? Clinical trial sponsors face significant challenges in assembling the TMF, especially when dealing with large, international, multicenter studies; despite all newly introduced archiving techniques it is becoming more and more difficult to ensure that the TMF is complete. This is directly reflected in the number of inspection findings reported and published by the EMA in 2014. Based on quality risk management principles in clinical trials the authors defined the quality expectations for the different document types in a TMF and furthermore defined tolerance limits for missing documents. This publication provides guidance on what type of documents and processes are most important, and in consequence, indicates on which documents and processes trial team staff should focus in order to achieve a high-quality TMF.The members of this working group belong to the CQAG Group (Clinical Quality Assurance Germany and are QA (quality assurance experts (auditors or compliance functions with long-term experience in the practical handling of TMFs.

Fatigue crack threshold relevant to stress ratio, crack wake and loading histories

International Nuclear Information System (INIS)

Okazaki, Masakazu; Iwasaki, Akira; Kasahara, Naoto

2013-01-01

Fatigue crack propagation behavior was investigated in a low alloy steel which experienced several kind of loading histories. Both the effects of stress ratio, test temperature on the fatigue crack threshold, and the change in the threshold depending on the thermo-mechanical loading histories, were experimentally investigated. It was shown that the thermo-mechanical loading history left its effect along the prior fatigue crack wake resulting in the change of fatigue crack threshold. Some discussions are made on how this type of loading history effect should be treated from engineering point of view. (author)

Thermo-mechanical lifetime assessment of components for 700 °C steam turbine applications

International Nuclear Information System (INIS)

Ehrhardt, F.

2014-01-01

ranges and hold periods. The effectiveness of the deformation model was verified in a Thermo-Mechanical Fatigue (TMF) experiment. The cycle definition was determined from a lifetime-limiting location in a 700°C high-pressure steam turbine rotor. The CF lifetime assessment methodology for Alloy 617 was verified with the help of post-test microstructural investigations. CF experiments with representative strain ranges and sufficiently long hold durations are to be performed to further investigate the apparent CF damage mechanism. The post-test metallographic investigation on the TMF test has revealed extensive creep damage development. The second main objective of this work was the identification of the maximum application temperatures of dissimilar metal welded (DMW) joints between the Ni-base Alloy 617 and a 1% CrMoV low alloy bainitic rotor steel as well as a higher-alloyed 10% Cr martensitic rotor steel. A testing procedure for the static creep and cyclic testing of the DMW joints was developed. The fatigue and CF endurance characteristics have been determined as well as the creep rupture (CR) strength curves, whereas CR strength extrapolation was only possible up to maximum rupture times of 30 kh. Post-test metallographic investigations revealed Type IV creep damage in the fine grained heat affected zone of the steels. Fusion line cracking associated with a Type I precipitate condition at the interface between Alloy 617 weld metal and the steel heat-affected zone was observed in the investigated Alloy 617 -1% CrMoV and Alloy 617 - 10% Cr DMW joints. Whereas the Type I carbide layer was apparent in Alloy 617 - 1% CrMoV DMW joint specimens even after short duration high temperature exposure, the situation was not clearly visible within the Alloy 617 - 10% Cr DMW joint. One major reason for the development of these Type I precipitates are the cross fusion line chemical composition gradients, mainly for the constituents C and Cr, which are obviously larger for the low

Thermo-mechanical lifetime assessment of components for 700 °C steam turbine applications

Energy Technology Data Exchange (ETDEWEB)

Ehrhardt, F.

2014-07-01

ranges and hold periods. The effectiveness of the deformation model was verified in a Thermo-Mechanical Fatigue (TMF) experiment. The cycle definition was determined from a lifetime-limiting location in a 700°C high-pressure steam turbine rotor. The CF lifetime assessment methodology for Alloy 617 was verified with the help of post-test microstructural investigations. CF experiments with representative strain ranges and sufficiently long hold durations are to be performed to further investigate the apparent CF damage mechanism. The post-test metallographic investigation on the TMF test has revealed extensive creep damage development. The second main objective of this work was the identification of the maximum application temperatures of dissimilar metal welded (DMW) joints between the Ni-base Alloy 617 and a 1% CrMoV low alloy bainitic rotor steel as well as a higher-alloyed 10% Cr martensitic rotor steel. A testing procedure for the static creep and cyclic testing of the DMW joints was developed. The fatigue and CF endurance characteristics have been determined as well as the creep rupture (CR) strength curves, whereas CR strength extrapolation was only possible up to maximum rupture times of 30 kh. Post-test metallographic investigations revealed Type IV creep damage in the fine grained heat affected zone of the steels. Fusion line cracking associated with a Type I precipitate condition at the interface between Alloy 617 weld metal and the steel heat-affected zone was observed in the investigated Alloy 617 -1% CrMoV and Alloy 617 - 10% Cr DMW joints. Whereas the Type I carbide layer was apparent in Alloy 617 - 1% CrMoV DMW joint specimens even after short duration high temperature exposure, the situation was not clearly visible within the Alloy 617 - 10% Cr DMW joint. One major reason for the development of these Type I precipitates are the cross fusion line chemical composition gradients, mainly for the constituents C and Cr, which are obviously larger for the low

Experimental investigation on the initial expansion stage of vacuum arc on cup-shaped TMF contacts

Science.gov (United States)

Wang, Ting; Xiu, Shixin; Liu, Zixi; Zhang, Yanzhe; Feng, Dingyu

2018-02-01

Arc behavior and measures to control it directly affect the properties of vacuum circuit breakers. Nowadays, transverse magnetic field (TMF) contacts are widely used for medium voltages. A magnetic field perpendicular to the current direction between the TMF contacts makes the arc move, transmitting its energy to the whole contact and avoiding excessive local ablation. Previous research on TMF arc behavior concentrated mainly on the arc movement and less on the initial stage (from arc ignition to an unstable arc column). A significant amount of experiment results suggest that there is a short period of arc stagnation after ignition. The duration of this arc stagnation and the arc characteristics during this stage affect the subsequent arc motion and even the breaking property of interrupters. The present study is of the arc characteristics in the initial stage. Experiments were carried out in a demountable vacuum chamber with cup-shaped TMF contacts. Using a high-speed camera, both single-point arc ignition mode and multiple-point arc ignition (MPAI) mode were observed. The experimental data show that the probability of MPAI mode occurring is related to the arc current. The influences of arc-ignition mode, arc current, and contact diameter on the initial expansion process were investigated. In addition, simulations were performed to analyze the multiple arc expansion process mechanically. Based on the experimental phenomena and simulation results, the mechanism of the arc expansion motion was analyzed.

Thermomechanical fatigue life prediction of high temperature components

Energy Technology Data Exchange (ETDEWEB)

Seifert, Thomas; Hartrott, Philipp von; Riedel, Hermann; Siegele, Dieter [Fraunhofer-Inst. fuer Werkstoffmechanik (IWM), Freiburg (Germany)

2009-07-01

The aim of the work described in this paper is to provide a computational method for fatigue life prediction of high temperature components, in which the time and temperature dependent fatigue crack growth is a relevant damage mechanism. The fatigue life prediction is based on a law for microcrack growth and a fracture mechanics estimate of the cyclic crack tip opening displacement. In addition, a powerful model for nonisothermal cyclic plasticity is employed, and an efficient laboratory test procedure is proposed for the determination of the model parameters. The models are efficiently implemented into finite element programs and are used to predict the fatigue life of a cast iron exhaust manifold and a notch in the perimeter of a turbine rotor made of a ferritic/martensitic 10%-chromium steel. (orig.)

I Want My MTV, We Want Our TMF: The Music Factory, MTV Europe, and Music Television in the Netherlands, 1995-2011

NARCIS (Netherlands)

Kooijman, Jaap

2017-01-01

textabstractLaunched in 1995, the Dutch music television channel The Music Factory (TMF) presented a local alternative to MTV Europe, owned by the US-based conglomerate Viacom. In 2001, Viacom took over TMF, which by then proved to be far more popular than MTV Europe among the Dutch young viewers.

Mechanical properties of thermomechanical treated hyper-eutectic Al-Si-(Fe, Mn, Cu) materials

OpenAIRE

Umezawa, Osamu

2005-01-01

Tensile and high-cycle fatigue behavior of thermomechanical treated hyper-eutectic Al-Si-(Fe, Mn, Cu) materials were studied. Through the repeated thermomechanical treatment (RTMT) which is a repeat of the multi steps cold-working followed by heat treatment, Si crystals and/or intermetallic compounds were broken into some fragments and dispersed in the aluminum matrix. Fine dispersion of the second phase particles exhibited good ductility, since early fracture was overcome. A few large Si cry...

Damage behavior of SnAgCu/Cu solder joints subjected to thermomechanical cycling

International Nuclear Information System (INIS)

Xiao, H.; Li, X.Y.; Hu, Y.; Guo, F.; Shi, Y.W.

2013-01-01

Highlights: •A creep–fatigue damage model based on CDM was proposed. •Designed system includes load frame, strain measure device and damage test device. •Damage evolution of solder joints was a function of accumulated inelastic strain. •Damage of solder joints is an interaction between creep and low-cycle fatigue. -- Abstract: Thermomechanical fatigue damage is a progressive process of material degradation. The objective of this study was to investigate the damage behavior of SnAgCu/Cu solder joints under thermomechanical cycling. A damage model was proposed based on continuum damage mechanics (CDM). Based upon an analysis of displacements for flip-chip solder joints subjected to thermal cycling, a special bimetallic loading frame with single-solder joint samples was designed to simulate the service conditions of actual joints in electronic packages. The assembly, which allowed for strain measurements of an individual solder joint during temperature cycling, was used to investigate the impact of stress–strain cycling on the damage behavior of SnAgCu/Cu solder joints. The characteristic parameters of the damage model were determined through thermomechanical cycling and strain measurement tests. The damage variable D = 1 − R 0 /R was selected, and values for it were obtained using a four-probe method for the single-solder joint samples every dozen cycles during thermomechanical cycling tests to verify the model. The results showed that the predicted damage was in good agreement with the experimental results. The damage evolution law proposed here is a function of inelastic strain, and the results showed that the damage rate of SnAgCu/Cu solder joints increased as the range of the applied strain increased. In addition, the microstructure evolution of the solder joints was analyzed using scanning electron microscopy, which provided the microscopic explanation for the damage evolution law of SnAgCu/Cu solder joints

Damage behavior of SnAgCu/Cu solder joints subjected to thermomechanical cycling

Energy Technology Data Exchange (ETDEWEB)

Xiao, H., E-mail: xiaohui2013@yahoo.com.cn; Li, X.Y.; Hu, Y.; Guo, F.; Shi, Y.W.

2013-11-25

Highlights: •A creep–fatigue damage model based on CDM was proposed. •Designed system includes load frame, strain measure device and damage test device. •Damage evolution of solder joints was a function of accumulated inelastic strain. •Damage of solder joints is an interaction between creep and low-cycle fatigue. -- Abstract: Thermomechanical fatigue damage is a progressive process of material degradation. The objective of this study was to investigate the damage behavior of SnAgCu/Cu solder joints under thermomechanical cycling. A damage model was proposed based on continuum damage mechanics (CDM). Based upon an analysis of displacements for flip-chip solder joints subjected to thermal cycling, a special bimetallic loading frame with single-solder joint samples was designed to simulate the service conditions of actual joints in electronic packages. The assembly, which allowed for strain measurements of an individual solder joint during temperature cycling, was used to investigate the impact of stress–strain cycling on the damage behavior of SnAgCu/Cu solder joints. The characteristic parameters of the damage model were determined through thermomechanical cycling and strain measurement tests. The damage variable D = 1 − R{sub 0}/R was selected, and values for it were obtained using a four-probe method for the single-solder joint samples every dozen cycles during thermomechanical cycling tests to verify the model. The results showed that the predicted damage was in good agreement with the experimental results. The damage evolution law proposed here is a function of inelastic strain, and the results showed that the damage rate of SnAgCu/Cu solder joints increased as the range of the applied strain increased. In addition, the microstructure evolution of the solder joints was analyzed using scanning electron microscopy, which provided the microscopic explanation for the damage evolution law of SnAgCu/Cu solder joints.

Tee-junction of LMFR secondary circuit involving thermal, thermomechanical and fracture mechanics assessment on a striping phenomenon

International Nuclear Information System (INIS)

Lee, H.-Y.; Kim, J.-B.; Yoo, B.

2002-01-01

This paper presents the thermomechanical and fracture mechanics evaluation procedure of thermal striping damage on the secondary piping of LMFR using Green's function method and standard FEM. The thermohydraulic loading conditions used in the present analysis are simplified sinusoidal thermal loads and the random type thermal loads. The thermomechanical fatigue damage was evaluated according to ASME code subsection NH. The results of fatigue analysis for the sinusoidal and random type load cases showed that fatigue failure would occur at a welded joint during 90 000 hours of operation. The assessment for the fracture behavior of the welded joint showed that the crack would be initiated at an early stage of the operation. The fatigue crack was evaluated to propagate up to 5 mm along the thickness direction during the first 940.7 and 42 698.9 hours of operation for the sinusoidal and the random loading cases, respectively. However, it was evaluated that the crack would be arrested because of the low level of the primary stresses. The fatigue and crack propagation analyses for the random type loads were performed by Green's function method. (author)

ITER baffle module small-scale mock-ups: first wall thermo-mechanical testing results

International Nuclear Information System (INIS)

Severi, Y.; Giancarli, L.; Poitevin, Y.; Salavy, J.F.; Le Marois, G.; Roedig, M.; Vieider, G.

1998-01-01

The EU-home team is in charge of the R and D related to the ITER baffle first wall. Five small-scale mock-ups, using Be, CFC and W tiles and different armour/heat-sink material joints under development, have been fabricated and thermomechanically tested in FE200 (Le Creusot) and JUDITH (Juelich) electron beam facilities. The small-scale mock-ups have been submitted to thermo-mechanical fatigue tests (up to failure using accelerating techniques). The objective was to determine the performances of the armour material joints under high heat flux cycles. (orig.)

Improvement of high temperature fatigue lifetime in AZ91 magnesium alloy by heat treatment

International Nuclear Information System (INIS)

Mokhtarishirazabad, Mehdi; Azadi, Mohammad; Hossein Farrahi, Gholam; Winter, Gerhard; Eichlseder, Wilfred

2013-01-01

In the present paper, an improvement in high temperature fatigue properties of the AZ91 magnesium alloy with rare earth elements has been obtained by a typical heat treatment, denoted by T6. For this objective, out-of-phase thermo-mechanical fatigue, room temperature and high temperature low cycle fatigue tests are performed to compare lifetimes. Several rare earth elements are initially added to the AZ91 alloy during a gravity casting process in permanent molds. Also, the type of the heat treatment is examined. Results of specimens with only the solution (the T4 heat treatment) and the solution with the ageing process (the T6 heat treatment) are compared under isothermal fatigue loadings. Microstructural investigations are carried out, before and after fatigue experiments to demonstrate the heat treatment effect. Results showed that both low cycle fatigue and thermo-mechanical fatigue of the alloy at high temperatures increases tremendously after the T6 heat treatment. This behavior attributes to the variation of the ductility, which was a result of microstructural changes during the heat treatment and the varying temperature in fatigue tests

Improvement of high temperature fatigue lifetime in AZ91 magnesium alloy by heat treatment

Energy Technology Data Exchange (ETDEWEB)

Mokhtarishirazabad, Mehdi [School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Azadi, Mohammad, E-mail: m_azadi@ip-co.com [Fatigue and Wear Workgroup, Irankhodro Powertrain Company (IPCO), Tehran (Iran, Islamic Republic of); Hossein Farrahi, Gholam [School of Mechanical Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Winter, Gerhard; Eichlseder, Wilfred [Chair of Mechanical Engineering, University of Leoben, Leoben (Austria)

2013-12-20

In the present paper, an improvement in high temperature fatigue properties of the AZ91 magnesium alloy with rare earth elements has been obtained by a typical heat treatment, denoted by T6. For this objective, out-of-phase thermo-mechanical fatigue, room temperature and high temperature low cycle fatigue tests are performed to compare lifetimes. Several rare earth elements are initially added to the AZ91 alloy during a gravity casting process in permanent molds. Also, the type of the heat treatment is examined. Results of specimens with only the solution (the T4 heat treatment) and the solution with the ageing process (the T6 heat treatment) are compared under isothermal fatigue loadings. Microstructural investigations are carried out, before and after fatigue experiments to demonstrate the heat treatment effect. Results showed that both low cycle fatigue and thermo-mechanical fatigue of the alloy at high temperatures increases tremendously after the T6 heat treatment. This behavior attributes to the variation of the ductility, which was a result of microstructural changes during the heat treatment and the varying temperature in fatigue tests.

Life prediction methodology for thermal-mechanical fatigue and elevated temperature creep design

Science.gov (United States)

Annigeri, Ravindra

Nickel-based superalloys are used for hot section components of gas turbine engines. Life prediction techniques are necessary to assess service damage in superalloy components resulting from thermal-mechanical fatigue (TMF) and elevated temperature creep. A new TMF life model based on continuum damage mechanics has been developed and applied to IN 738 LC substrate material with and without coating. The model also characterizes TMF failure in bulk NiCoCrAlY overlay and NiAl aluminide coatings. The inputs to the TMF life model are mechanical strain range, hold time, peak cycle temperatures and maximum stress measured from the stabilized or mid-life hysteresis loops. A viscoplastic model is used to predict the stress-strain hysteresis loops. A flow rule used in the viscoplastic model characterizes the inelastic strain rate as a function of the applied stress and a set of three internal stress variables known as back stress, drag stress and limit stress. Test results show that the viscoplastic model can reasonably predict time-dependent stress-strain response of the coated material and stress relaxation during hold times. In addition to the TMF life prediction methodology, a model has been developed to characterize the uniaxial and multiaxial creep behavior. An effective stress defined as the applied stress minus the back stress is used to characterize the creep recovery and primary creep behavior. The back stress has terms representing strain hardening, dynamic recovery and thermal recovery. Whenever the back stress is greater than the applied stress, the model predicts a negative creep rate observed during multiple stress and multiple temperature cyclic tests. The model also predicted the rupture time and the remaining life that are important for life assessment. The model has been applied to IN 738 LC, Mar-M247, bulk NiCoCrAlY overlay coating and 316 austenitic stainless steel. The proposed model predicts creep response with a reasonable accuracy for wide range of

Advanced Environmental Barrier Coating and SA Tyrannohex SiC Composites Integration for Improved Thermomechanical and Environmental Durability

Science.gov (United States)

Zhu, Dongming; Halbig, Michael; Singh, Mrityunjay

2018-01-01

The development of 2700 degF capable environmental barrier coating (EBC) systems, particularly, the Rare Earth "Hafnium" Silicon bond coat systems, have significantly improved the temperature capability and environmental stability of SiC/SiC Ceramic Matrix Composite Systems. We have specifically developed the advanced 2700 degF EBC systems, integrating the EBC to the high temperature SA Tyrannohex SiC fiber composites, for comprehensive performance and durability evaluations for potential turbine engine airfoil component applications. The fundamental mechanical properties, environmental stability and thermal gradient cyclic durability performance of the EBC - SA Tyrannohex composites were investigated. The paper will particularly emphasize the high pressure combustion rig recession, cyclic thermal stress resistance and thermomechanical low cycle fatigue testing of uncoated and environmental barrier coated Tyrannohex SiC SA composites in these simulated turbine engine combustion water vapor, thermal gradients, and mechanical loading conditions. We have also investigated high heat flux and flexural fatigue degradation mechanisms, determined the upper limits of operating temperature conditions for the coated SA composite material systems in thermomechanical fatigue conditions. Recent progress has also been made by using the self-healing rare earth-silicon based EBCs, thus enhancing the SA composite hexagonal fiber columns bonding for improved thermomechanical and environmental durability in turbine engine operation environments. More advanced EBC- composite systems based on the new EBC-Fiber Interphases will also be discussed.

Creep-fatigue interaction at high temperature; Proceedings of the Symposium, 112th ASME Winter Annual Meeting, Atlanta, GA, Dec. 1-6, 1991

Science.gov (United States)

Haritos, George K.; Ochoa, O. O.

Various papers on creep-fatigue interaction at high temperature are presented. Individual topics addressed include: analysis of elevated temperature fatigue crack growth mechanisms in Alloy 718, physically based microcrack propagation laws for creep-fatigue-environment interaction, in situ SEM observation of short fatigue crack growth in Waspaloy at 700 C under cyclic and dwell conditions, evolution of creep-fatigue life prediction models, TMF design considerations in turbine airfoils of advanced turbine engines. Also discussed are: high temperature fatigue life prediction computer code based on the total strain version of strainrange partitioning, atomic theory of thermodynamics of internal variables, geometrically nonlinear analysis of interlaminar stresses in unsymmetrically laminated plates subjected to uniform thermal loading, experimental investigation of creep crack tip deformation using moire interferometry. (For individual items see A93-31336 to A93-31344)

Isothermal and thermal–mechanical fatigue of VVER-440 reactor pressure vessel steels

Energy Technology Data Exchange (ETDEWEB)

Fekete, Balazs, E-mail: fekete.mm.bme@gmail.com [College of Dunaujvaros, Tancsics 1A, Dunaujvaros H-2400 (Hungary); Department of Applied Mechanics, Budapest University of Technology and Economics, Muegyetem 5, Budapest H-1111 (Hungary); Trampus, Peter [College of Dunaujvaros, Tancsics 1A, Dunaujvaros H-2400 (Hungary)

2015-09-15

Highlights: • We aimed to determine the thermomechanical behaviour of VVER reactor steels. • Material tests were developed and performed on GLEEBLE 3800 physical simulator. • Coffin–Manson curves and parameters were derived. • High accuracy of the strain energy based evaluation was found. • The observed dislocation evolution correlates with the mechanical behaviour. - Abstract: The fatigue life of the structural materials 15Ch2MFA (CrMoV-alloyed ferritic steel) and 08Ch18N10T (CrNi-alloyed austenitic steel) of VVER-440 reactor pressure vessel under completely reserved total strain controlled low cycle fatigue tests were investigated. An advanced test facility was developed for GLEEBLE-3800 physical simulator which was able to perform thermomechanical fatigue experiments under in-service conditions of VVER nuclear reactors. The low cycle fatigue results were evaluated with the plastic strain based Coffin–Manson law, and plastic strain energy based model as well. It was shown that both methods are able to predict the fatigue life of reactor pressure vessel steels accurately. Interrupted fatigue tests were also carried out to investigate the kinetic of the fatigue evolution of the materials. On these samples microstructural evaluation by TEM was performed. The investigated low cycle fatigue behavior can provide reference for remaining life assessment and lifetime extension analysis.

Implementation of creep-fatigue model into finite-element code to assess cooled turbine blade.

CSIR Research Space (South Africa)

Dedekind, MO

1994-01-01

Full Text Available Turbine blades which are designed with airfoil cooling are subject to thermo-mechanical fatigue as well as creep damage. These problems arise due to thermal cycling and high operating temperatures in service. An implementation of fatigue and creep...

Thermomechanical fatigue – Damage mechanisms and mechanism ...

Indian Academy of Sciences (India)

R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

varied linearly with time and synchronously in-phase (IP) and out-of-phase (OP) to the plas- tic strain. The tests were always started at the mean temperature and at zero plastic strain with the strain increasing. The majority of the fatigue tests were conducted in laboratory air; though some experiments were carried out in high ...

Fatigue Assessment of Nickel-Titanium Peripheral Stents: Comparison of Multi-Axial Fatigue Models

Science.gov (United States)

Allegretti, Dario; Berti, Francesca; Migliavacca, Francesco; Pennati, Giancarlo; Petrini, Lorenza

2018-02-01

Peripheral Nickel-Titanium (NiTi) stents exploit super-elasticity to treat femoropopliteal artery atherosclerosis. The stent is subject to cyclic loads, which may lead to fatigue fracture and treatment failure. The complexity of the loading conditions and device geometry, coupled with the nonlinear material behavior, may induce multi-axial and non-proportional deformation. Finite element analysis can assess the fatigue risk, by comparing the device state of stress with the material fatigue limit. The most suitable fatigue model is not fully understood for NiTi devices, due to its complex thermo-mechanical behavior. This paper assesses the fatigue behavior of NiTi stents through computational models and experimental validation. Four different strain-based models are considered: the von Mises criterion and three critical plane models (Fatemi-Socie, Brown-Miller, and Smith-Watson-Topper models). Two stents, made of the same material with different cell geometries are manufactured, and their fatigue behavior is experimentally characterized. The comparison between experimental and numerical results highlights an overestimation of the failure risk by the von Mises criterion. On the contrary, the selected critical plane models, even if based on different damage mechanisms, give a better fatigue life estimation. Further investigations on crack propagation mechanisms of NiTi stents are required to properly select the most reliable fatigue model.

Fatigue Assessment of Nickel-Titanium Peripheral Stents: Comparison of Multi-Axial Fatigue Models

Science.gov (United States)

Allegretti, Dario; Berti, Francesca; Migliavacca, Francesco; Pennati, Giancarlo; Petrini, Lorenza

2018-03-01

Peripheral Nickel-Titanium (NiTi) stents exploit super-elasticity to treat femoropopliteal artery atherosclerosis. The stent is subject to cyclic loads, which may lead to fatigue fracture and treatment failure. The complexity of the loading conditions and device geometry, coupled with the nonlinear material behavior, may induce multi-axial and non-proportional deformation. Finite element analysis can assess the fatigue risk, by comparing the device state of stress with the material fatigue limit. The most suitable fatigue model is not fully understood for NiTi devices, due to its complex thermo-mechanical behavior. This paper assesses the fatigue behavior of NiTi stents through computational models and experimental validation. Four different strain-based models are considered: the von Mises criterion and three critical plane models (Fatemi-Socie, Brown-Miller, and Smith-Watson-Topper models). Two stents, made of the same material with different cell geometries are manufactured, and their fatigue behavior is experimentally characterized. The comparison between experimental and numerical results highlights an overestimation of the failure risk by the von Mises criterion. On the contrary, the selected critical plane models, even if based on different damage mechanisms, give a better fatigue life estimation. Further investigations on crack propagation mechanisms of NiTi stents are required to properly select the most reliable fatigue model.

Thermo-mechanical properties and integrity of metallic interconnects in microelectronics

Science.gov (United States)

Ege, Efe Sinan

In this dissertation, combined numerical (Finite Element Method) and experimental efforts were undertaken to study thermo-mechanical behavior in microelectronic devices. Interconnects, including chip-level metallization and package-level solder joints, are used to join many of the circuit parts in modern equipment. The dissertation is structured into six independent studies after the introductory chapter. The first two studies focus on thermo-mechanical fatigue of solder joints. Thermo-mechanical fatigue, in the form of damage along a microstructurally coarsened region in tin-lead solder, is analyzed along with the effects of intermetallic morphology. Also, lap-shear testing is modeled to characterize the joint and to investigate the validity of experimental data from different solder and substrate geometries. In the third study, the effects of pre-machined holes on strain localization and overall ductility in bulk eutectic tin-lead alloy is examined. Finite element analyses, taking into account the viscoplastic response, were carried out to provide a mechanistic rationale to corroborate the experimental findings. The fourth study concerns chip-level copper interconnects. Various combinations of oxide and polymer-based low-k dielectric schemes, with and without the thin barrier layers surrounding the Cu line, are considered. Attention is devoted to the thermal stress and strain fields and their dependency on material properties, geometry, and modeling details. This study is followed by a chapter on atomistics of interface-mediated plasticity in thin metallic films. The objective is to gain fundamental insight into the underlying mechanisms affecting the mechanical response of nanoscale thin films. The final study investigates the effect of microstructural heterogeneity on indentation response, for the purpose of raising awareness of the uncertainties involved in applying indentation techniques in probing mechanical properties of miniaturized devices.

Straightforward Downsizing of Inclusions in NiTi Alloys: A New Generation of SMA Wires with Outstanding Fatigue Life

Science.gov (United States)

Coda, Alberto; Cadelli, Andrea; Zanella, Matteo; Fumagalli, Luca

2018-03-01

One of most debated aspects around Nitinol quality is microcleanliness, nowadays considered as the main factor affecting fatigue life. Recent results demonstrate that fatigue is undoubtedly associated with inclusions which can act as crack initiators. However, type, size, and distribution of such particles have been observed to strongly depend on Ni/Ti ratio as well as melting and thermo-mechanical processes. Therefore, if a general reduction of non-metallic inclusions is expected to generate a beneficial effect in improving lifetime of Nitinol, on the other hand this necessarily involves a hard review of both material melting and processing. In this work, the characterization of the fatigue behavior of SMA wires with diameter below 100 µm is presented. The wires were prepared by a peculiar, non-standard combination of melting and thermo-mechanical processes (Clean Melt technology). Thermo-mechanical cycling was carried out and the fracture surfaces of all failed wires were investigated by scanning electron microscopy. A robust set of data was collected and analyzed by using the statistics of extremes. Results clearly demonstrate that in the new NiTi Clean Melt alloy the maximum inclusion size and area fraction are significantly reduced compared to standard Nitinol. This offers meaningful improvement in fatigue resistance over standard wires.

Low cycle thermomechanical fatigue of reactor steels: Microstructural and fractographic investigations

Energy Technology Data Exchange (ETDEWEB)

Fekete, Balazs, E-mail: fekete.mm.bme@gmail.com [College of Dunaujvaros, Tancsics 1A, Dunaujvaros H-2400 (Hungary); Department of Applied Mechanics, Budapest University of Technology and Economics, Muegyetem 5, Budapest H-1111 (Hungary); Kasl, Josef; Jandova, Dagmar [Výzkumný a zkušební ústav Plzeň s.r.o., Tylova 1581/46, 316 00 Plzen (Czech Republic); Jóni, Bertalan [College of Dunaujvaros, Tancsics 1A, Dunaujvaros H-2400 (Hungary); Eötvös Loránd University, Egyetem tér 1-3, Budapest H-1053 (Hungary); Misják, Fanni [Centre for Energy Research, Institute of Technical Physics and Materials Science, Konkoly-Thege M. 29-33, Budapest H-1121 (Hungary); Trampus, Peter [College of Dunaujvaros, Tancsics 1A, Dunaujvaros H-2400 (Hungary)

2015-07-29

The fatigue life of the structural materials 15Ch2MFA (CrMoV-alloyed ferritic steel) and 08Ch18N10T (CrNi-alloyed austenitic steel) of a VVER-440 reactor pressure vessel were investigated under fully reversed total strain controlled low cycle fatigue tests. The measurements were carried out in isothermal conditions at 260 °C and with thermal-mechanical conditions in the range 150–270 °C using a GLEEBLE-3800 servo-hydraulic thermal-mechanical simulator. The low cycle fatigue results were evaluated with the Coffin–Manson law, and the parameters of the Ramberg–Osgood stress–strain relation were investigated. Fracture mechanics behavior was observed using scanning electron microscopic analysis of the crack shapes and fracture surfaces. Crack propagation was assessed in relation to the actual crack size and the loading level. Interrupted fatigue tests were also carried out to investigate the kinetics of the fatigue evolution of the materials. Microstructural evaluation of the samples was performed using light, scanning and transmission electron microscopy as well as X-ray diffraction, and measurement of dislocations was completed using TEM and XRD. The course of dislocation density in relation to cumulative usage factor was similar for both steels. However, the nature and distribution of dislocations were different in the individual steels and this resulted in different mechanical behaviors. The nature of the fracture surfaces of both steels appeared similar despite differences in dislocation arrangement. The distances between striation lines initially increased with increasing crack length and then became saturated. The low cycle fatigue behavior investigated can provide a reference for the remaining life assessment and lifetime extension analysis of nuclear power plant components.

Advances in fatigue lifetime predictive techniques; Proceedings of the Symposium, San Francisco, CA, Apr. 24, 1990

International Nuclear Information System (INIS)

Mitchell, M.R.; Landgraf, R.W.

1992-01-01

Recent progress in the development of methods to predict fatigue performance of materials and structures is reviewed. Attention is given to general approaches to fatigue mechanics, elevated temperature phenomena, spectrum loading, the multiaxial behavior, and applications. Particular attention is given to a fracture-mechanics-based model for cumulative damage assessment, thermo-mechanical fatigue life prediction methods, a probabilistic fracture mechanics approach for structural reliability assessment of space flight systems, a multiaxial fatigue life estimation technique, plasticity and fatigue damage modeling of severely loaded tubing, damage evaluation in composite materials using thermographic stress analysis, and fatigue lifetime monitoring in power plants

Grain size refinement of inconel 718 thermomechanical processing

International Nuclear Information System (INIS)

Okimoto, P.C.

1988-01-01

Inconel 718 is a Ni-Fe precipitation treated superalloy. It presents good thermal fatigue properties when the material has small grain size. The aim of this work is to study the grain size refinement by thermomechanical processing, through observations of the microstructural evolution and the influence of some of the process variables in the final grain size. The results have shown that this refinement occured by static recrystallization. The presence of precipitates have influenced the final grain size if the deformations are below 60%. For greater deformations the grain size is independent of the precipitate distribution in the matrix and tends to a limit size of 5 μm. (author)

Thermo-mechanical behavior of power electronic packaging assemblies: From characterization to predictive simulation of lifetimes

Science.gov (United States)

Dalverny, O.; Alexis, J.

2018-02-01

This article deals with thermo-mechanical behavior of power electronic modules used in several transportation applications as railway, aeronautic or automotive systems. Due to a multi-layered structures, involving different materials with a large variation of coefficient of thermal expansion, temperature variations originated from active or passive cycling (respectively from die dissipation or environmental constraint) induces strain and stresses field variations, giving fatigue phenomenon of the system. The analysis of the behavior of these systems and their dimensioning require the implementation of complex modeling strategies by both the multi-physical and the multi-scale character of the power modules. In this paper we present some solutions for studying the thermomechanical behavior of brazed assemblies as well as taking into account the interfaces represented by the numerous metallizations involved in the process assembly.

Mean stress and the exhaustion of fatigue-damage resistance

Science.gov (United States)

Berkovits, Avraham

1989-01-01

Mean-stress effects on fatigue life are critical in isothermal and thermomechanically loaded materials and composites. Unfortunately, existing mean-stress life-prediction methods do not incorporate physical fatigue damage mechanisms. An objective is to examine the relation between mean-stress induced damage (as measured by acoustic emission) and existing life-prediction methods. Acoustic emission instrumentation has indicated that, as with static yielding, fatigue damage results from dislocation buildup and motion until dislocation saturation is reached, after which void formation and coalescence predominate. Correlation of damage processes with similar mechanisms under monotonic loading led to a reinterpretation of Goodman diagrams for 40 alloys and a modification of Morrow's formulation for life prediction under mean stresses. Further testing, using acoustic emission to monitor dislocation dynamics, can generate data for developing a more general model for fatigue under mean stress.

Fatigue analysis of a structure with welds considering metallurgical discontinuities

International Nuclear Information System (INIS)

Cabrillat, M.T.; Lejeail, Y.

1995-01-01

Within the frameworks of a creep-fatigue experimental program, called EVASION, thermo-mechanical tests were conducted on two mock-ups, the first one was fully machined and the second one welded and then machined (in order to eliminate geometrical discontinuities, thus only leaving metallurgical discontinuities). These two mock-ups were submitted to exactly the same loading history. Plastic analyses with a correct description of mechanical properties and fatigue strength of materials are conducted and compared with experimental results in order to highlight the influence of the weld. (author). 3 refs., 4 figs., 3 tabs

Isothermal and thermal-mechanical fatigue of VVER-440 reactor pressure vessel steels

Science.gov (United States)

Fekete, Balazs; Trampus, Peter

2015-09-01

The fatigue life of the structural materials 15Ch2MFA (CrMoV-alloyed ferritic steel) and 08Ch18N10T (CrNi-alloyed austenitic steel) of VVER-440 reactor pressure vessel under completely reserved total strain controlled low cycle fatigue tests were investigated. An advanced test facility was developed for GLEEBLE-3800 physical simulator which was able to perform thermomechanical fatigue experiments under in-service conditions of VVER nuclear reactors. The low cycle fatigue results were evaluated with the plastic strain based Coffin-Manson law, and plastic strain energy based model as well. It was shown that both methods are able to predict the fatigue life of reactor pressure vessel steels accurately. Interrupted fatigue tests were also carried out to investigate the kinetic of the fatigue evolution of the materials. On these samples microstructural evaluation by TEM was performed. The investigated low cycle fatigue behavior can provide reference for remaining life assessment and lifetime extension analysis.

Thermo-mechanically induced texture evolution and micro-structural change of aluminum metallization

DEFF Research Database (Denmark)

Brincker, Mads; Walter, Thomas; Kristensen, Peter Kjær

2018-01-01

During operation of high power electronic chips the topside metallization is subjected to cyclic compressive and tensile stresses leading to unwanted thermo-mechanical fatigue of the metallization layer. The stress is caused by the difference in the thermal expansion coefficients...... are not yet fully understood. In this work, we investigate the microstructural evolution of an Al metallization on high power diode chips subjected to passive thermal cycling between 20 and 100ºC. The texture of the Al film is analyzed ex-situ by a combination of electron backscatter diffraction and X...

Fatigue behaviour of metals. 2. ed.; Ermuedungsverhalten metallischer Werkstoffe

Energy Technology Data Exchange (ETDEWEB)

Christ, H.J. [Siegen Univ. (Gesamthochschule) (Germany). Inst. fuer Werkstofftechnik

2009-07-01

The book presents an outline of the fatigue characteristics of metals. Interested students, engineers, scientists and users are provided with a basic understanding of the possible processes, from which they will get a feeling for the processes going on inside materials under fatigue stress which is indispensable for developing and testing modern constructional materials. Subjects: Introduction and outline - Material fatigue and microstructure - Cyclic stress-strain behaviour - Cracking - Electron microscopy - Fundamentals of fracture mechanics - Fatigue crack growth - Cyclic strength of steels - Thermomechanical fatigue - Operating strength of components - Fatigue of welded constructions. [German] In dem vorliegenden Buch wird ein Ueberblick ueber die Ermuedung metallischer Werkstoffe gegeben. Interessierten Studenten, Ingenieuren, Wissenschaftlern und Anwendern wird ein Grundverstaendnis fuer die moeglichen Prozesse vermittelt, aus dem sich ein Gefuehl fuer die Vorgaenge im Werkstoff bei zyklischer Beanspruchung entwickelt - unabdingbar fuer Entwicklung und Pruefung moderner Kontruktionswerkstoffe. Es enthaelt folgende Themen: Einfuehrung und Ueberblick - Materialermuedung und Mikrostruktur - Zyklisches Spannungs-Dehnungsverhalten - Rissbildung - Elektronenmikroskopische Untersuchungen - Grundlagen der Bruchmechanik - Ermuedungsrisswachstum - Schwingfestigkeit von Staehlen - Thermomechanisches Ermuedungsverhalten - Betriebsfestigkeit von Bauteilen - Ermuedung von Schweisskonstruktionen.

Thermophysical and Thermomechanical Properties of Thermal Barrier Coating Systems

Science.gov (United States)

Zhu, Dongming; Miller, Robert A.

2000-01-01

Thermal barrier coatings have been developed for advanced gas turbine and diesel engine applications to improve engine reliability and fuel efficiency. However, the issue of coating durability under high temperature cyclic conditions is still of major concern. The coating failure is closely related to thermal stresses and oxidation in the coating systems. Coating shrinkage cracking resulting from ceramic sintering and creep at high temperatures can further accelerate the coating failure process. The purpose of this paper is to address critical issues such as ceramic sintering and creep, thermal fatigue and their relevance to coating life prediction. Novel test approaches have been established to obtain critical thermophysical and thermomechanical properties of the coating systems under near-realistic temperature and stress gradients encountered in advanced engine systems. Emphasis is placed on the dynamic changes of the coating thermal conductivity and elastic modulus, fatigue and creep interactions, and resulting failure mechanisms during the simulated engine tests. Detailed experimental and modeling results describing processes occurring in the thermal barrier coating systems provide a framework for developing strategies to manage ceramic coating architecture, microstructure and properties.

Lifetime prediction of structures submitted to thermal fatigue loadings; Prediction de duree de vie de structures sous chargement de fatigue thermique

Energy Technology Data Exchange (ETDEWEB)

Amiable, S

2006-01-15

The aim of this work is to predict the lifetime of structures submitted to thermal fatigue loadings. This work lies within the studies undertaken by the CEA on the thermal fatigue problems from the french reactor of Civaux. In particular we study the SPLASH test: a specimen is heated continuously and cyclically cooled down by a water spray. This loading generates important temperature gradients in space and time and leads to the initiation and the propagation of a crack network. We propose a new thermo-mechanical model to simulate the SPLASH experiment and we propose a new fatigue criterion to predict the lifetime of the SPLASH specimen. We propose and compare several numerical models with various complexity to estimate the mechanical response of the SPLASH specimen. The practical implications of this work are the reevaluation of the hypothesis used in the French code RCC, which are used to simulate thermal shock and to interpret the results in terms of fatigue. This work leads to new perspectives on the mechanical interpretation of the fatigue criterion. (author)

Design of durability and lifetime assessment method under thermomechanical stress for thermal barrier coatings

Energy Technology Data Exchange (ETDEWEB)

Shin, Hyun Gyoo; Choi, Young Kue; Jeon, Seol; Lee, Hee Soo [Pusan National University, Busan (Korea, Republic of); Jeon, Min Seok [Korea Testing Laboratory, Seoul (Korea, Republic of)

2014-01-15

A durability testing method under thermo-mechanical stress for thermal barrier coatings (TBC) specimens was designed by a combination of an electric furnace and a tensile testing machine, which was done on TBCs on NIMONIC 263 substrates by an atmospheric plasma spraying (APS) deposition method. The testing conditions were chosen according to a preliminary experiment that identified the elastic deformation region of the top coating and the substrate during mechanical loading. Surface cracking and a decrease in the thickness of the top coating, which are typical degradation behaviors under conventional thermal shock testing, were observed after the designed thermal fatigue test, and delamination at the top coating-bond coating interface occurred by the mechanical load. Lifetime assessment was conducted by statistical software using life cycle data which were obtained after the thermal fatigue test.

Lifetime prediction of structures submitted to thermal fatigue loadings

International Nuclear Information System (INIS)

Amiable, S.

2006-01-01

The aim of this work is to predict the lifetime of structures submitted to thermal fatigue loadings. This work lies within the studies undertaken by the CEA on the thermal fatigue problems from the french reactor of Civaux. In particular we study the SPLASH test: a specimen is heated continuously and cyclically cooled down by a water spray. This loading generates important temperature gradients in space and time and leads to the initiation and the propagation of a crack network. We propose a new thermo-mechanical model to simulate the SPLASH experiment and we propose a new fatigue criterion to predict the lifetime of the SPLASH specimen. We propose and compare several numerical models with various complexity to estimate the mechanical response of the SPLASH specimen. The practical implications of this work are the reevaluation of the hypothesis used in the French code RCC, which are used to simulate thermal shock and to interpret the results in terms of fatigue. This work leads to new perspectives on the mechanical interpretation of the fatigue criterion. (author)

Damage evolution during actuation fatigue in shape memory alloys (SPIE Best Student Paper Award)

Science.gov (United States)

Phillips, Francis R.; Wheeler, Robert; Lagoudas, Dimitris C.

2018-03-01

Shape Memory Alloys (SMAs) are unique materials able to undergo a thermomechanically induced, reversible phase transformation. Additionally, SMA are subject to two types of fatigue, that is structural fatigue due to cyclic loading as experienced by most materials, as well as actuation fatigue due to repeated thermally induced phase transformation. The evolution of multiple material characteristics is presented over the actuation fatigue lifetime of NiTiHf actuators, including the accumulation of irrecoverable strain, the evolution of internal voids, and the evolution of the effective modulus of the actuator. The results indicate that all three of these material characteristics are clearly interconnected and careful analysis of each of these characteristics can help to understand the evolution of the others, as well as help to understand how actuation fatigue leads to ultimate failure of the actuator.

Experimentally Validated Combustion and Piston Fatigue Life Evaluation Procedures for the Bi-Fuel Engines, Using an Integral-Type Fatigue Criterion

Directory of Open Access Journals (Sweden)

M. Shariyat

Full Text Available Abstract A relatively complete procedure for high cycle fatigue life assessment of the engine components is outlined in the present paper. The piston is examined as a typical component of the engine. In this regard, combustion process and transient heat transfer simulations, determination of the instantaneous variations of the pressure and temperature in the combustion chamber, kinematic and dynamic analyses of the moving parts of the engine, thermoelastic stress analyses, and fatigue life analyses are accomplished. Results of the simulation are compared with the test data to verify the results. The heat transfer results are validated by the experimental results measured by the Templugs. The nonlinear multipoint contact constraints are modeled accurately. Results of the more accurate available fatigue criteria are compared with those of a fatigue criterion recently proposed by the first author. These results are also evaluated by comparing them with the experimental durability tests. The presented procedure may be used, e.g., to decide whether it is suitable to convert a gasoline-based engine to a bi-fuel one. Results of the various thermomechanical fatigue analyses performed reveal that the piston life decreases considerably when natural gas is used instead of gasoline.

Estimate the thermomechanical fatigue life of two flip chip packages

International Nuclear Information System (INIS)

Pash, R.A.; Ullah, H.S.; Khan, M.Z.

2005-01-01

The continuing demand towards high density and low profile integrated circuit packaging has accelerated the development of flip chip structures as used in direct chip attach (DCA) technology, ball grid array (BOA) and chip scale package (CSP). In such structures the most widely used flip chip interconnects are solder joints. The reliability of flip chip structures largely depends on the reliability of solder joints. In this work solder joint fatigue life prediction for two chip scale packages is carried out. Elasto-plastic deformation behavior of the solder was simulated using ANSYS. Two dimensional plain strain finite element models were developed for each package to numerically compute the stress and total strain of the solder joints under temperature cycling. These stress and strain values are then used to predict the solder joint lifetime through modified Coffin Manson equation. The effect of solder joint's distance from edge of silicon die on life of the package is explored. The solder joint fatigue response is modeled for a typical temperature cycling of -60 to 140 degree C. (author)

Thermomechanical behaviour of bolted assemblies

International Nuclear Information System (INIS)

Scliffet, L.

1995-01-01

This paper presents first results obtained in an R and D study on the thermomechanical behaviour of bolted assemblies. Thermal shocks during operating transients both severely distort such assemblies and cause variations in stud pre-loads. So during a hot shock, the thermal gradient in the flange induced over-tightening due to the differential thermal expansion involved. Over-tightening can reach 70% of the nominal value, usually after 10 to 15 mn, after which the stress relaxes as soon as the heating affects the stud. A series of hot shocks causes assembly fatigue, notably resulting in thread plasticization, making it impossible to tighten the studs. In the case of cold transients, the reverse phenomenon is observed. The hot flange contracts sharply upon contact with the cold fluid, causing stress relief in the expanded studs. The resulting loss of tensile stress, which reaches up to 50%, can then cause severe leakage, especially if the nominal tightening capacity is already impaired. The study presented is based on tests and modelling. (author). 16 figs

Thermo-mechanical design of the Plasma Driver Plate for the MITICA ion source

Energy Technology Data Exchange (ETDEWEB)

Pavei, Mauro, E-mail: mauro.pavei@igi.cnr.it [Consorzio RFX, EURATOM-ENEA Association, Corso Stati Uniti 4, I-35127 Padova (Italy); Palma, Mauro Dalla; Marcuzzi, Diego [Consorzio RFX, EURATOM-ENEA Association, Corso Stati Uniti 4, I-35127 Padova (Italy)

2010-12-15

In the framework of the activities for the development of the Neutral Beam Injector (NBI) for ITER, the detailed design of the Radio-Frequency (RF) negative ion source has been carried out. One of the most heated components of the RF source is the rear vertical plate, named Plasma Driver Plate (PDP), where the Back-Streaming positive Ions (BSI+) generated from stripping losses in the accelerator and back scattered on the plasma source impinge on. The heat loads that result are huge and concentrated, with first estimate of the power densities up to 60 MW/m{sup 2}. The breakdowns that occur into the accelerator cause such heat loads to act cyclically, so that the PDP is thermo-mechanically fatigue loaded. Moreover, the surface of the PDP facing the plasma is functionally required to be temperature controlled and to be molybdenum or tungsten coated. The thermo-hydraulic design of the plate has been carried out considering active cooling with ultra-pure water. Different heat sink materials, hydraulic circuit layout and manufacturing processes have been considered. The heat exhaust has been optimized by changing the channels geometry, the path of the heat flux in the heat sink, the thickness of the plate and maximizing the Heat Transfer Coefficient. Such optimization has been carried out by utilizing 3D Finite Element (FE) models. Afterwards all the suitable mechanical (aging, structural monotonic and cyclic) verifications have been carried out post-processing the results of the thermo-mechanical 3D FE analyses in accordance to specific procedures for nuclear components exposed to high temperature. The effect of sputtering phenomenon due to the high energy BSI+ impinging on the plate has been considered and combined with fatigue damage for the mechanical verification of the PDP. Alternative solutions having molybdenum (or tungsten coatings) facing the plasma, aiming to reduce the sputtering rate and the consequent plasma pollution, have been evaluated and related 3D FE

Multiscale Thermo-Mechanical Design and Analysis of High Frequency and High Power Vacuum Electron Devices

Science.gov (United States)

Gamzina, Diana

Diana Gamzina March 2016 Mechanical and Aerospace Engineering Multiscale Thermo-Mechanical Design and Analysis of High Frequency and High Power Vacuum Electron Devices Abstract A methodology for performing thermo-mechanical design and analysis of high frequency and high average power vacuum electron devices is presented. This methodology results in a "first-pass" engineering design directly ready for manufacturing. The methodology includes establishment of thermal and mechanical boundary conditions, evaluation of convective film heat transfer coefficients, identification of material options, evaluation of temperature and stress field distributions, assessment of microscale effects on the stress state of the material, and fatigue analysis. The feature size of vacuum electron devices operating in the high frequency regime of 100 GHz to 1 THz is comparable to the microstructure of the materials employed for their fabrication. As a result, the thermo-mechanical performance of a device is affected by the local material microstructure. Such multiscale effects on the stress state are considered in the range of scales from about 10 microns up to a few millimeters. The design and analysis methodology is demonstrated on three separate microwave devices: a 95 GHz 10 kW cw sheet beam klystron, a 263 GHz 50 W long pulse wide-bandwidth sheet beam travelling wave tube, and a 346 GHz 1 W cw backward wave oscillator.

Probabilistic and microstructural aspects of fatigue cracks initiation in Inconel 718

International Nuclear Information System (INIS)

Alexandre, F.

2004-03-01

Thermomechanical treatments have been recently developed to produce Inconel 718DA (Direct Aged). This alloy optimisation leads to an increase of the fatigue life but also the scatter. The aim of this study is on the one hand the understanding of the fatigue crack initiation mechanisms and on the other hand the modelling of the fatigue life and the scatter. An experimental study showed that the fatigue cracks were initiated from carbide particles in fine grain alloy. Interrupted tensile tests show that the particles cracking occurred at the first quarter of the fatigue cycle. Fatigue behaviour tests were also performed on various grain size 718 alloys. The last experimental part was devoted to measurements of the low cycle fatigue crack growth rates using a high focal distance microscope. For these tests, EDM micro-defects were used for the fatigue crack initiation sites. This method was also used to observe the small fatigue crack coalescence. A fatigue life model is proposed. It is based on the three fatigue crack initiation mechanisms competition: particle crack initiation on the surface, internal particle crack initiation and Stade I crack initiation. The particle fatigue crack initiation is supposed instantaneous at a critical stress level. The Tanaka and Mura model is used for analysing the Stage I crack initiation number of cycles. The fatigue crack growth rate was analysed using the Tomkins model identified on the small fatigue crack growth rate measurements. The proposed fatigue life model decomposed in three levels: a deterministic one and two probabilistic with and without crack coalescence. (author)

The numerical high cycle fatigue damage model of fillet weld joint under weld-induced residual stresses

Science.gov (United States)

Nguyen Van Do, Vuong

2018-04-01

In this study, a development of nonlinear continuum damage mechanics (CDM) model for multiaxial high cycle fatigue is proposed in which the cyclic plasticity constitutive model has been incorporated in the finite element (FE) framework. T-joint FE simulation of fillet welding is implemented to characterize sequentially coupled three-dimensional (3-D) of thermo-mechanical FE formulation and simulate the welding residual stresses. The high cycle fatigue damage model is then taken account into the fillet weld joints under the various cyclic fatigue load types to calculate the fatigue life considering the residual stresses. The fatigue crack initiation and the propagation in the present model estimated for the total fatigue is compared with the experimental results. The FE results illustrated that the proposed high cycle fatigue damage model in this study could become a powerful tool to effectively predict the fatigue life of the welds. Parametric studies in this work are also demonstrated that the welding residual stresses cannot be ignored in the computation of the fatigue life of welded structures.

Thermal fatigue. Materials modelling

International Nuclear Information System (INIS)

Siegele, D.; Fingerhuth, J.; Mrovec, M.

2012-01-01

In the framework of the ongoing joint research project 'Thermal Fatigue - Basics of the system-, outflow- and material-characteristics of piping under thermal fatigue' funded by the German Federal Ministry of Education and Research (BMBF) fundamental numerical and experimental investigations on the material behavior under transient thermal-mechanical stress conditions (high cycle fatigue V HCF and low cycle fatigue - LCF) are carried out. The primary objective of the research is the further development of simulation methods applied in safety evaluations of nuclear power plant components. In this context the modeling of crack initiation and growth inside the material structure induced by varying thermal loads are of particular interest. Therefore, three scientific working groups organized in three sub-projects of the joint research project are dealing with numerical modeling and simulation at different levels ranging from atomistic to micromechanics and continuum mechanics, and in addition corresponding experimental data for the validation of the numerical results and identification of the parameters of the associated material models are provided. The present contribution is focused on the development and experimental validation of material models and methods to characterize the damage evolution and the life cycle assessment as a result of thermal cyclic loading. The individual purposes of the subprojects are as following: - Material characterization, Influence of temperature and surface roughness on fatigue endurances, biaxial thermo-mechanical behavior, experiments on structural behavior of cruciform specimens and scatter band analysis (IfW Darmstadt) - Life cycle assessment with micromechanical material models (MPA Stuttgart) - Life cycle assessment with atomistic and damage-mechanical material models associated with material tests under thermal fatigue (Fraunhofer IWM, Freiburg) - Simulation of fatigue crack growth, opening and closure of a short crack under

On the fatigue behavior of friction stir welded AlSi 10 Mg alloy

International Nuclear Information System (INIS)

Alburquerque, J. M.; Ramos, P. A.; Gomes, M. A.; Cruz, A. C.

2005-01-01

The high cycle fatigue behaviour of friction stir welded AISi 10 Mg samples was investigated for a stress ratio R=0.1, ranging from 0.5 to 0.9 of the yield strength, in addition to tensile tests. The welds were produced with different tool rotation and travel speeds, and these welding parameters were correlated to residual stresses, measured by X-ray diffraction (sen''2Ψ method). Moreover, the residual stresses were measured during the fatigue testing, at fixed cycle intervals, being reported. It was observed that the residual (compressive)stresses within the nugget were smaller than in the interface regions (between the thermo-mechanically affected zone and the base metal) and stabilized above 4 x 10''5 cycles. Fatigue crack morphology and microstructural changes were characterized by optical and electron microscopy and the observations are discussed along with the fatigue results. (Author) 14 refs

Thermo-mechanical tests of a CFC divertor mock-up

International Nuclear Information System (INIS)

Cardella, A.; Akiba, M.; Duwe, R.; Di Pietro, E.; Suzuki, S.; Satoh, K.; Reheis, N.

1994-01-01

Thermo-mechanical tests have been performed on a divertor mock-up consisting of a metallic tube armoured with five carbon fibre composite tiles. The tube is inserted the tiles and brazed with TiCuSil braze (monoblock concept). The tube material is TZM, a molybdenum alloy, and the armour material is SEP CARB N112, a high conductivity carbon-carbon composite. Using special surface preparation consisting of laser drilling, small (≅ 500 μm) holes in the composite have been made to increase the surface wetted by the braze and the resistance. The mock-up has been tested at the JAERI 400 kW electron beam test facility JEBIS. The aim of the test was to assess the performance of the mock-up in screening and thermal fatigue tests with particular attention to the behaviour of the armour to heat sink joint. (orig.)

Thermoelastoviscoplastic modeling of RAFM steel JLF-1 using tensile and low cycle fatigue experiments

Energy Technology Data Exchange (ETDEWEB)

Msolli, S., E-mail: sabeur.msolli@univ-lorraine.fr

2014-08-01

In this paper, a modeling of the elastoviscoplastic behavior of a Reduced Activation Ferritic Martensitic (RAFM) steel JLF-1 is presented. The modeling of this material was based on various Low Cycle Fatigue (LCF) and tensile tests performed in air and vacuum using different imposed strain rates and temperature ranges going from ambient temperature to 873 K. The coupled viscoplastic model is coded in FORTRAN program, implemented into the finite elements code ABAQUS and used to predict the thermomechanical behavior of a fatigue specimen made of RAFM steel JLF-1. Good agreements were found between numerical results and experimental data.

Thermomechanical Modelling of Friction Stir Welding

DEFF Research Database (Denmark)

Hattel, Jesper Henri; Schmidt, Henrik Nikolaj Blicher; Tutum, Cem Celal

2009-01-01

Friction Stir Welding (FSW) is a fully coupled thermomechanical process and should in general be modelled as such. Basically, there are two major application areas of thermomechanical models in the investigation of the FSW process: i) Analysis of the thermomechanical conditions such as e.g. heat...... generation and local material deformation (often referred to as flow) during the welding process itself. ii) Prediction of the residual stresses that will be present in the joint structure post to welding. While the former in general will call for a fully-coupled thermomechanical procedure, however...... for the FSW process at hand, the heat generation must either be prescribed analytically or based on a fully coupled analysis of the welding process itself. Along this line, a recently proposed thermal-pseudo-mechanical model is presented in which the temperature dependent yield stress of the weld material...

Thermo-mechanical design of the SINGAP accelerator grids for ITER NB Injectors

International Nuclear Information System (INIS)

Agostinetti, P.; Dal Bello, S.; Palma, M.D.; Zaccaria, P.

2006-01-01

The SINGle Aperture - SINgle GAP (SINGAP) accelerator for ITER neutral beam injector foresees four grids for the extraction and acceleration of negative ions, instead of the seven grids of the Multi Aperture Multi Grid (MAMuG) reference configuration. Optimized geometry of the SINGAP grids (plasma, extraction, pre-acceleration, and grounded grid) was identified by CEA Association considering specific requirements for ions extraction and beam generation referring to experimental data and code simulations. This paper focuses on the thermo-hydraulic and thermo-mechanical design of the grids carried out by Consorzio RFX for the design of the first ITER NB Injector and the ITER NB Test Facility. The cooling circuit design (position and shape of the channels) and the cooling parameters (water coolant temperatures, pressure and velocity) were optimized with thermo-hydraulic and thermo-mechanical sensitivity analyses in order to satisfy the grid functional requirements (temperatures, in plane and out of plane deformations). A complete and detailed thermo-structural design assessment of the SINGAP grids was accomplished applying the structural design rules for ITER in-vessel components and considering both the reference load conditions and the maximum load provided by the power supplies. The design required a complete modelling of the grids and their support frames by means of 3D FE and CAD models. The grids were finally integrated with the support and cooling systems inside the beam source vessel. The main results of the thermo-hydraulic and thermo-mechanical analyses are presented. The open issues are then reported, mainly regarding the material properties characterization (static and fatigue tests) and the qualification of technologies for OFHC copper electro-deposition, brazing, and welding of heterogeneous materials. (author)

Probabilistic and microstructural aspects of fatigue cracks initiation in Inconel 718; Aspects probabilistes et microstructuraux de l'amorcage des fissures de fatigue dans l'alliage INCO 718

Energy Technology Data Exchange (ETDEWEB)

Alexandre, F

2004-03-15

Thermomechanical treatments have been recently developed to produce Inconel 718DA (Direct Aged). This alloy optimisation leads to an increase of the fatigue life but also the scatter. The aim of this study is on the one hand the understanding of the fatigue crack initiation mechanisms and on the other hand the modelling of the fatigue life and the scatter. An experimental study showed that the fatigue cracks were initiated from carbide particles in fine grain alloy. Interrupted tensile tests show that the particles cracking occurred at the first quarter of the fatigue cycle. Fatigue behaviour tests were also performed on various grain size 718 alloys. The last experimental part was devoted to measurements of the low cycle fatigue crack growth rates using a high focal distance microscope. For these tests, EDM micro-defects were used for the fatigue crack initiation sites. This method was also used to observe the small fatigue crack coalescence. A fatigue life model is proposed. It is based on the three fatigue crack initiation mechanisms competition: particle crack initiation on the surface, internal particle crack initiation and Stade I crack initiation. The particle fatigue crack initiation is supposed instantaneous at a critical stress level. The Tanaka and Mura model is used for analysing the Stage I crack initiation number of cycles. The fatigue crack growth rate was analysed using the Tomkins model identified on the small fatigue crack growth rate measurements. The proposed fatigue life model decomposed in three levels: a deterministic one and two probabilistic with and without crack coalescence. (author)

Influence of creep ductility on creep-fatigue behaviour of 20%Cr/25%Ni/Nb stainless steel

International Nuclear Information System (INIS)

Gladwin, D.; Miller, D.A.

1985-01-01

The influence of creep ductility on creep-fatigue endurance of 20%Cr/25%Ni/Nb stainless steel has been examined. In order to induce different creep ductilities in the 20/25/Nb stainless steel, three different thermo-mechanical routes were employed. These resulted in a range of ductilities (3-36%) being obtained at the strain rates of interest. Strain controlled slow-fast creep-fatigue cycles were used with strain rates of 10 -6 s -1 , 10 -7 s -1 in tension and 10 -3 s -1 in compression. It was found that creep ductility strongly influenced the creep-fatigue endurance of the 20/25/Nb stainless steel. When failure was creep dominated endurance was found to be directly proportional to the creep ductility. A ductility exhaustion model has been used to successfully predict creep-fatigue endurance when failure was creep dominated. (author)

Development of testing system for the thermo-mechanical fatigue crack analysis of nuclear power plant pipes

International Nuclear Information System (INIS)

Lee, Ho Jin; Kim, Maan Won; Lee, Bong Sang

2003-12-01

Fatigue crack growth analysis plays an important role in the structural integrity assessment or the service life calculation of the nuclear power plant pipes. To obtain the material properties as a basic data to achieve an accurate crack growth analysis, a lot of tests and numerical crack growth simulations have been done for decades. The BS 7910 or the ASME Boiler and Pressure Vessel Code Section XI, generally used to evaluate crack growth behavior, were made under the based on simple stress states or at the evaluated isothermal temperature. It is well known that the ASME code could sometimes give so conservative results in some cases of which the cracked components are experiencing with cyclic thermal shock. In this report, we suggested a method for the life assessment of a crack embedded in nuclear power plant pipes under the thermal-mechanical fatigue loads. We here use the numerical method to get the temperature history for thermal- mechanical fatigue crack growth test. And then we can calculate the remaining life time of the pipe by using the fracture mechanics and the test results together. For this purpose, we constructed a thermal-mechanical fatigue crack growth testing system. We also gave a lot of review about recent researches in the experimental field of thermal-mechanical fatigue analysis

Some aspects of thermal fatigue in stainless steel

International Nuclear Information System (INIS)

Iorio, A.F.; Crespi, J.C.

1987-01-01

This paper is concerned with the analysis of failures in a moderator circuit branch piping of the ATUCHA-I pressurized heavy water reactor (PHWR), made of austenitic steel to DIN 1.4550 specification (similar to AISI 347). These failures are considered to result from a thermal fatigue processes induced by fluctuations in a zone where stratified temperature layers occurred -the fluctuations being associated with variations in the heavy water flow. The first section evaluates the possibility of cracking due to thermal fatigue phenomena and concludes that under service conditions a crack may be initiated and growth through 7 mm of the wall thickness of the pipe. Laboratory thermal fatigue tests that simulated the thermomechanical conditions for such a component, showed that the number of cycles required to initiate a thermal fatigue crack in a notched modified standard fatigue specimen was about 10 3 . This value may be used to give a conservative prediction of the number of thermal cycles for crack initiation in actual station piping, including those who suffered a cold plug condition which is produced in some emergency shut-down and valve testing situations. It was also demonstrated that beyond a crack depth of 7 mm stress corrosion cracking has the main process in further crack propagation. The relevance of this prediction has been confirmed by microfractographic observations, since the brittle nature of the fracture surfaces under service conditions appears very different from the transgranular ductile striations found in both thermal and mechanical fatigue test specimens as a result of environmental effects. (Author)

Thermo-mechanical ratcheting in jointed rock masses

KAUST Repository

Pasten, C.

2015-09-01

Thermo-mechanical coupling takes place in jointed rock masses subjected to large thermal oscillations. Examples range from exposed surfaces under daily and seasonal thermal fluctuations to subsurface rock masses affected by engineered systems such as geothermal operations. Experimental, numerical and analytical results show that thermo-mechanical coupling can lead to wedging and ratcheting mechanisms that result in deformation accumulation when the rock mass is subjected to a biased static-force condition. Analytical and numerical models help in identifying the parameter domain where thermo-mechanical ratcheting can take place.

Thermo-mechanical ratcheting in jointed rock masses

KAUST Repository

Pasten, C.; Garcí a, M.; Santamarina, Carlos

2015-01-01

Thermo-mechanical coupling takes place in jointed rock masses subjected to large thermal oscillations. Examples range from exposed surfaces under daily and seasonal thermal fluctuations to subsurface rock masses affected by engineered systems such as geothermal operations. Experimental, numerical and analytical results show that thermo-mechanical coupling can lead to wedging and ratcheting mechanisms that result in deformation accumulation when the rock mass is subjected to a biased static-force condition. Analytical and numerical models help in identifying the parameter domain where thermo-mechanical ratcheting can take place.

Thermomechanical treatment of titanium alloys

International Nuclear Information System (INIS)

Khorev, A.K.

1979-01-01

The problems of the theory and practical application of thermomechanical treatment of titanium alloys are presented. On the basis of the systematic investigations developed are the methods of thermomechanical treatment of titanium alloys, established are the optimum procedures and produced are the bases of their industrial application with an account of alloy technological peculiarities and the procedure efficiency. It is found that those strengthening methods are more efficient at which the contribution of dispersion hardening prevails over the strengthening by phase hardening

Low-cycle fatigue of dissimilar friction stir welded aluminum alloys

Energy Technology Data Exchange (ETDEWEB)

Rodriguez, R.I. [The University of Alabama, Department of Mechanical Engineering, Tuscaloosa, AL 35487 (United States); Jordon, J.B., E-mail: bjordon@eng.ua.edu [The University of Alabama, Department of Mechanical Engineering, Tuscaloosa, AL 35487 (United States); Allison, P.G. [The University of Alabama, Department of Mechanical Engineering, Tuscaloosa, AL 35487 (United States); Rushing, T.; Garcia, L. [Engineering Research and Development Center, Army Corps of Engineers, Vicksburg, MS 39180 (United States)

2016-01-27

In this work, experiments were conducted to quantify structure-property relations of low-cycle fatigue behavior of dissimilar friction stir welding (FSW) of AA6061-to-AA7050 high strength aluminum alloys. In addition, a microstructure-sensitive fatigue model is employed to further elucidate cause-effect relationships. Experimental strain-controlled fatigue testing revealed an increase in the cyclic strain hardening and the number-of cycles to failure as the tool rotational speed was increased. At higher applied strain amplitudes (>0.3%), the corresponding stress amplitude increased and the plastic strain amplitude decreased, as the number of cycles increased. However, at 0.2% strain amplitude, the plastic strain decreased until it was almost negligible. Inspection of the hysteresis loops demonstrated that at low strain amplitudes, there was an initial stage of strain hardening that increased until it reached a maximum strain hardening level, afterwards a nearly perfect elastic behavior was observed. Under fully-reversed fatigue loading, all samples failed at the region between the heat-affected and thermomechanically-affected zones. Inspection of the fractured surfaces under scanning electron microscopy revealed that the cracks initiated at either the crown or the root surface of the weld, and from secondary intermetallic particles located near the free surface of the weld. Lastly, a microstructure-sensitive multistage fatigue model was employed to correlate the fatigue life of the dissimilar FSW of AA6061-to-AA7050 considering microstructural features such as grain size, intermetallic particles and mechanical properties.

Dual-phase ULCB steels thermomechanically processed

International Nuclear Information System (INIS)

Lis, A.K.; Lis, J.

2001-01-01

The design philosophy of the processing of dual-phase (D-P) ultra low carbon steels (ULCB) by thermomechanical treatment has been briefly discussed. Modelling of the structure evolution during thermomechanical rolling of ULCB steel was based upon the established empirical equations for yield flow at different conditions of: deformation temperatures, strain rates and stresses for applied amount of deformation during hot deformation compression tests. The critical amount of deformation needed for the occurrence of dynamic or static recrystallization was determined. The dependence of grain refinement of the acicular bainitic and polygonal ferrite of the accelerated cooling and amount of stored energy of deformation in steel has been evaluated. Effect of the decreasing of the finishing temperature of thermomechanical processing on the increase of the impact toughness of dual-phase microstructure consisted of the bainitie-martensite islands in the ferrite matrix has been shown. The effect of ageing process after thermomechanical rolling of heavy plates on fracture toughness values of J 0.2 for ULCB-Ni steels has been established from cod tests measurements. New low cost technology of rolling of ULCB steels dual-phase is proposed. (author)

Influence of UFG structure formation on mechanical and fatigue properties in Ti-6Al-7Nb alloy

Science.gov (United States)

Polyakova, V. V.; Anumalasetty, V. N.; Semenova, I. P.; Valiev, R. Z.

2014-08-01

Ultrafine-grained (UFG) Ti alloys have potential applications in osteosynthesis and orthopedics due to high bio-compatibility and increased weight-to- strength ratio. In current study, Ti6Al7Nb ELI alloy is processed through equal channel angular pressing-conform (ECAP-Conform) and subsequent thermomechanical processing to generate a UFG microstructure. The fatigue properties of UFG alloys are compared to coarse grained (CG) alloys. Our study demonstrates that the UFG alloys with an average grain size of ~180 nm showed 35% enhancement of fatigue endurance limit as compared to coarse-grained alloys. On the fracture surfaces of the UFG and CG samples fatigue striations and dimpled relief were observed. However, the fracture surface of the UFG sample looks smoother; fewer amounts of secondary micro-cracks and more ductile rupture were also observed, which testifies to the good crack resistance in the UFG alloy after high-cyclic fatigue tests.

Nitrogen-containing steels and thermomechanical treatment

International Nuclear Information System (INIS)

Kaputkina, L.; Prokoshkina, V.G.; Svyazhin, G.

2004-01-01

The strengthening of nitrogen-containing corrosion-resistant steels resulting from alloying and thermomechanical treatment have been investigated using X-ray diffraction analysis, light microscopy, hardness measurements and tensile testing. Combined data have been obtained for nitrogen interaction with alloying elements , peculiarities of deformed structure and short-range of nitrogen-containing steels of various structural classes. The higher nitrogen and total alloying element contents, the higher deformation strengthening. Prospects of use the steels with not high nitrogen content and methods of their thermomechanical strengthening are shown. High temperature thermomechanical treatment (HTMT) is very effective for obtaining high and thermally stable constructional strength of nitrogen-containing steels of all classes. The HTMT is most effective if used in a combination with dispersion hardening for aging steels or in the case of mechanically unstable austenitic steels. (author)

Decomposition and Precipitation Process During Thermo-mechanical Fatigue of Duplex Stainless Steel

Czech Academy of Sciences Publication Activity Database

Weidner, A.; Kolmorgen, R.; Kuběna, Ivo; Kulawinski, D.; Kruml, Tomáš; Biermann, H.

47A, č. 5 (2016), s. 2112-2124 ISSN 1073-5623 R&D Projects: GA MŠk(CZ) ED1.1.00/02.0068; GA ČR GA15-08826S Institutional support: RVO:68081723 Keywords : FE-CR ALLOYS * SPINODAL DECOMPOSITION * COMPUTER-MODELS * ATOMIC-LEVEL * AGING EMBRITTLEMENT * FERRITE * BEHAVIOR * TEMPERATURE Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.874, year: 2016 http://link.springer.com/article/10.1007/s11661-016-3392-z

The Potential of Self-Tempered Martensite and Bainite in Improving the Fatigue Strength of Thermomechanically Processed Steels

Directory of Open Access Journals (Sweden)

Krupp Ulrich

2018-01-01

Full Text Available In contrast to a two-stage hardening and tempering process, the definition of optimized cooling routes after hot working of low-alloy Cr steel allows the adjustments of high-strength microstructures with a sufficient degree of ductility at the same time without any additional heat-treatment. While compressed air cooling after hot forging of micro-alloyed steel grades leads to the formation of lower bainite with finedispersed cementite platelets, quenching by water spray down to the martensite start temperature results in the formation of martensite, that is self-tempered during the subsequent slow-cooling in air. The precipitation of nano-sized cementite precipitates result in superior mechanical properties with respect to impact and tensile testing. Cyclic deformation and crack propagation tests being carried out using resonance testing (100Hz and ultrasonic fatigue testing (20kHz systems revealed a pronounced increase in fatigue strength by about 150MPa of the self-tempered martensite condition as compared to the bainitic modification. For the latter one, a steady decrease of the fatigue strength is observed rather than the existence of a real fatigue limit.

Theoretical approach to the WWER core thermomechanical modelling

International Nuclear Information System (INIS)

Likhatchev, Y.; Troyanov, V.; Folomeev, V.; Demishonkov, A.

2003-01-01

The paper presents studies on the analysis of root causes of fuel assembly bowing under operating conditions; developing of a methodology for fuel assemblies thermomechanical simulation; developing of a calculation technique for thermomechanical modelling of the fuel assemblies bowing in operational conditions. Some examples of calculation results are given

Microstructure-sensitive Crystal Viscoplasticity for Ni-base Superalloys Targeting Long-term Creep-Fatigue Interaction Modeling

Energy Technology Data Exchange (ETDEWEB)

Neu, Richard W.

2017-09-30

The aim of this project is to develop a microstructure-sensitive crystal viscoplasticity (CVP) model for single-crystal Ni-base superalloys to model the behavior of the material and components in the hot gas path sections of industrial gas turbines (IGT). Microstructure degradation associated with aging critical to predicting long-term creep-fatigue interactions will be embedded into the model through the γ' precipitate morphology evolution by coupling the coarsening drivers and kinetics into the constitutive equations of the CVP model. Model parameters will be determined using new experimental protocols that involve systematically artificially aging the alloy under different stress conditions to determine the relationship between the size and morphology g' precipitates on the creep and thermomechanical fatigue response.

Microstructure-sensitive Crystal Viscoelasticity for Ni-base Superalloys Targeting Long-term Creep-Fatigue Interaction Modeling

Energy Technology Data Exchange (ETDEWEB)

Neu, Richard W

2016-09-30

The aim of this project is to develop a microstructure-sensitive crystal viscoplasticity (CVP) model for single-crystal Ni-base superalloys to model the behavior of the material and components in the hot gas path sections of industrial gas turbines (IGT). Microstructure degradation associated with aging critical to predicting long-term creep-fatigue interactions will be embedded into the model through the γ' precipitate morphology evolution by coupling the coarsening drivers and kinetics into the constitutive equations of the CVP model. Model parameters will be determined using new experimental protocols that involve systematically artificially aging the alloy under different stress conditions to determine the relationship between the size and morphology g' precipitates on the creep and thermomechanical fatigue response.

Crack initiation and propagation on the polymeric material ABS (Acrylonitrile Butadiene Styrene, under ultrasonic fatigue testing

Directory of Open Access Journals (Sweden)

G. M. Domínguez Almaraz

2015-10-01

Full Text Available Crack initiation and propagation have been investigated on the polymeric material ABS (Acrylonitrile Butadiene Styrene, under ultrasonic fatigue testing. Three controlled actions were implemented in order to carry out fatigue tests at very high frequency on this material of low thermal conductivity, they are: a The applying load was low to limit heat dissipation at the specimen neck section, b The dimensions of testing specimen were small (but fitting the resonance condition, in order to restraint the temperature gradient at the specimen narrow section, c Temperature at the specimen neck section was restrained by immersion in water or oil during ultrasonic fatigue testing. Experimental results are discussed on the basis of thermo-mechanical behaviour: the tail phenomenon at the initial stage of fatigue, initial shear yielding deformation, crazed development on the later stage, plastic strain on the fracture surface and the transition from low to high crack growth rate. In addition, a numerical analysis is developed to evaluate the J integral of energy dissipation and the stress intensity factor K, with the crack length

Thermomechanical behavior of mica layers with lenticular fissures

Science.gov (United States)

Yang, Michael Xinyi

The thermomechanical behavior of natural phlogopite mica specimens from seven different origins is characterized. An initial heat treatment, to a temperature between 300°C and 400°C, is found to form fissures that stabilize in the material. Following the initial heat treatment, all the phlogopite specimens, regardless of their origin and polytype, exhibit the extraordinarily large thermal expansion (intumescence), more than 200% at 600°C, in the direction perpendicular to the basal planes. This phenomenon is strictly reproducible when tested under a range of thermal conditions including thermal shock, multiple thermal fatigue cycles, varying heating or cooling rates and isothermal heating over an extensive period of time at different temperatures up to 585°C. The hysteresis, associated with the thermal cycle, is increased when the specimen is heated or cooled at a faster rate. The maximum coefficient of linear thermal expansion, approximately 10 -2°C-1, is observed over the temperature range 100--120°C. This is due to the non-structural water, entrapped within the layer structure, which undergoes a phase transition and causes the mica layers to expand abruptly. A model of lenticular fissures is developed based on thin-plate mechanics and thermodynamics assumptions. The state of a lenticular fissure with water vapor molecules is determined to correlate the experimental parameters with the material properties. The average density of water vapor molecules within a lenticular fissure is calculated to be ˜1025 m 3 for the temperature interval between 100°C and 275°C. The concentration of non-structure water, based on the model calculation, is less than 0.1% by weight. Acoustic emission (AE) signals have been reported by Pranevicius et al. (1995) to correspond to the microstructure changes as the internal lenticular fissures develop in phlogopite. This technique has also been proven feasible to characterize the thermomechanical behavior of other layer structures

Recent developments on SMA actuators: predicting the actuation fatigue life for variable loading schemes

Science.gov (United States)

Wheeler, Robert W.; Lagoudas, Dimitris C.

2017-04-01

Shape memory alloys (SMAs), due to their ability to repeatably recover substantial deformations under applied mechanical loading, have the potential to impact the aerospace, automotive, biomedical, and energy industries as weight and volume saving replacements for conventional actuators. While numerous applications of SMA actuators have been flight tested and can be found in industrial applications, these actuators are generally limited to non-critical components, are not widely implemented and frequently one-off designs, and are generally overdesigned due to a lack of understanding of the effect of the loading path on the fatigue life and the lack of an accurate method for predicting actuator lifetimes. In recent years, multiple research efforts have increased our understanding of the actuation fatigue process of SMAs. These advances can be utilized to predict the fatigue lives and failure loads in SMA actuators. Additionally, these prediction methods can be implemented in order to intelligently design actuators in accordance with their fatigue and failure limits. In the following paper, both simple and complex thermomechanical loading paths have been considered. Experimental data was utilized from two material systems: equiatomic Nickel-Titanium and Nickelrich Nickel-Titanium.

Effect of thermomechanical treatment of the stress corrosion cracking of metastable beta III titanium

International Nuclear Information System (INIS)

Seats, J.H.; Condit, D.O.

1974-01-01

Results of studies on the relations of microstructural changes with stress corrosion of Ti--11.5 Mo--6 Zr--4.5 Sn (Beta III) alloys are presented. It was found that this alloy is virtually immune to stress corrosion cracking if no imperfections in the surface are present. Specimens that had not been cold worked showed surface deterioration, but it was not serious enough to cause any marked reduction in yield strengths. The alloy is, however, susceptible to SCC if the surface contains an imperfection such as a fatigue crack where high stresses can concentrate during testing. These high stress levels at the crack tip may cause mechanical destruction of the passivating oxide and allow a higher concentration of chloride ions near the fresh metal surfaces. However, even with precracked specimens, crack propagation is slow as evidenced by no failures within the 720 hour test period. The extreme notch sensitivity of Beta III prevented initiation of fatigue cracks in the sections of the alloy with 20 and 50 percent cold work. More research must be done to test Beta III in this condition. However, on the basis of the research conducted thus far, SCC susceptibility of Beta III titanium alloy appears to be independent of thermomechanical pretreatment. (U.S.)

Acoustic events during fatigue test of structural steels

Energy Technology Data Exchange (ETDEWEB)

Por, Gabor; Fekete, Balazs; Csicso, Gabor; Trampus, Peter [College of Dunaujvaros (Hungary)

2014-11-01

Acoustic emission sensors were applied recording noises during low cycle fatigue tests in steel materials. The test specimens were machined from the base metal (15H2MFA) and the anticorrosive cladding metal (08H18N10T) of the VVER-440/V-213 (Russian designed PWR) reactor pressure vessel. During the first period, the measurements were carried out with isothermal condition at 260 C on GLEEBLE 3800 servo-hydraulic thermal-mechanical simulator. The tests were run under uniaxial tension-compression loading with total strain control. The programmed waveform was triangular for all the fatigue tests with the frequency of 0.08 Hz. The cyclic loading was started from the compressed side. It was observed that besides rare acoustic emission events regular 10 msec Acoustic Barkhausen Noise (ABN) burst were recorded due to 50Hz AC current drive for heating and maintaining the constant temperature. The amplitude of MABN was higher under pressure than during relaxing and drawing-out by a factor of 2-5. We have carried out also thermo-mechanical fatigue experiment with the same strain-controlled mechanical cycle and simultaneous thermal cycle between 150 C and 270 C. The total number of cycles was terminated, when the force level necessary for the original elongation had been reduced to 75% of its original value. Visual examination showed always some at least surface cracks after stopping the fatigue test. ABN events registered during the beginning cycle exhibited different spectra from the middle and especially from the last cycles before the end of the test, where also double ABN bursts could be recorded. At the end of the test explicit AE events could be found by a new technique. The most interesting result is the possibility to use ABN for testing reactor materials, which could have practical application for fatigue testing.

Concurrent material-fabrication optimization of metal-matrix laminates under thermo-mechanical loading

Science.gov (United States)

Saravanos, D. A.; Morel, M. R.; Chamis, C. C.

1991-01-01

A methodology is developed to tailor fabrication and material parameters of metal-matrix laminates for maximum loading capacity under thermomechanical loads. The stresses during the thermomechanical response are minimized subject to failure constrains and bounds on the laminate properties. The thermomechanical response of the laminate is simulated using nonlinear composite mechanics. Evaluations of the method on a graphite/copper symmetric cross-ply laminate were performed. The cross-ply laminate required different optimum fabrication procedures than a unidirectional composite. Also, the consideration of the thermomechanical cycle had a significant effect on the predicted optimal process.

PWR fuel thermomechanics

International Nuclear Information System (INIS)

Traccucci, R.; Leclercq, J.

1986-01-01

Fuel thermo-mechanics means the studies of mechanical and thermal effects, and more generally, the studies of the behavior of the fuel assembly under stresses including thermal and mechanical loads, hydraulic effects and phenomena induced by materials irradiation. This paper describes the studies dealing with the fuel assembly behavior, first in normal operating conditions, and then in accidental conditions. 43 refs [fr

High-Cycle Fatigue Resistance of Si-Mo Ductile Cast Iron as Affected by Temperature and Strain Rate

Science.gov (United States)

Matteis, Paolo; Scavino, Giorgio; Castello, Alessandro; Firrao, Donato

2015-09-01

Silicon-molybdenum ductile cast irons are used to fabricate exhaust manifolds of internal combustion engines of large series cars, where the maximum pointwise temperature at full engine load may be higher than 973 K (700 °C). In this application, high-temperature oxidation and thermo-mechanical fatigue (the latter being caused by the engine start and stop and by the variation of its power output) have been the subject of several studies and are well known, whereas little attention has been devoted to the high-cycle fatigue, arising from the engine vibration. Therefore, the mechanical behavior of Si-Mo cast iron is studied here by means of stress-life fatigue tests up to 10 million cycles, at temperatures gradually increasing up to 973 K (700 °C). The mechanical characterization is completed by tensile and compressive tests and ensuing fractographic examinations; the mechanical test results are correlated with the cast iron microstructure and heat treatment.

A micromechanical study of the damage mechanics of acrylic particulate composites under thermomechanical loading

Science.gov (United States)

Nie, Shihua

The main aim of this dissertation was to characterize the damage mechanism and fatigue behavior of the acrylic particulate composite. This dissertation also investigated how the failure mechanism is influenced by changes in certain parameters including the volume fraction of particle, the interfacial bonding strength, the stiffness and thickness of the interphase, and the CTE mismatch between the particle and the matrix. Monotonic uniaxial tensile and compressive testing under various temperatures and strain rates, isothermal low-cycle mechanical testing and thermal cycling of a plate with a cutout were performed. The influence of the interfacial bonding strength between the particle and the matrix on the failure mechanism of the ATH filled PMMA was investigated using in situ observations under uniaxial loading conditions. For composites with weak interfacial bonding, the debonding is the major damage mode. For composites with strong interfacial bonding, the breakage of the agglomerate of particles is the major damage mode. Experimental studies also demonstrated the significant influence of interfacial bonding strength on the fatigue life of the ATH filled PMMA. The damage was characterized in terms of the elastic modulus degradation, the load-drop parameter, the plastic strain range and the hysteresis dissipation. Identifying the internal state variables that quantify material degradation under thermomechanical loading is an active research field. In this dissertation, the entropy production, which is a measure of the irreversibility of the thermodynamic system, is used as the metric for damage. The close correlation between the damage measured in terms of elastic modulus degradation and that obtained from the finite element simulation results validates the entropy based damage evolution function. A micromechanical model for acrylic particulate composites with imperfect interfacial bonds was proposed. Acrylic particulate composites are treated as three

Adjoint sensitivity analysis of the thermomechanical behavior of repositories

International Nuclear Information System (INIS)

Wilson, J.L.; Thompson, B.M.

1984-01-01

The adjoint sensitivity method is applied to thermomechanical models for the first time. The method provides an efficient and inexpensive answer to the question: how sensitive are thermomechanical predictions to assumed parameters. The answer is exact, in the sense that it yields exact derivatives of response measures to parameters, and approximate, in the sense that projections of the response fo other parameter assumptions are only first order correct. The method is applied to linear finite element models of thermomechanical behavior. Extensions to more complicated models are straight-forward but often laborious. An illustration of the method with a two-dimensional repository corridor model reveals that the chosen stress response measure was most sensitive to Poisson's ratio for the rock matrix

Fatigue performance improvement in AISI 4140 steel by dynamic strain aging and dynamic precipitation during warm laser shock peening

Energy Technology Data Exchange (ETDEWEB)

Ye Chang [School of Industrial Engineering, Purdue University, West Lafayette, IN 47906 (United States); Suslov, Sergey; Kim, Bong Joong; Stach, Eric A. [School of Materials Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, IN (United States); Cheng, Gary J., E-mail: gjcheng@purdue.edu [School of Industrial Engineering, Purdue University, West Lafayette, IN 47906 (United States)

2011-02-15

Warm laser shock peening (WLSP) is a thermomechanical treatment technique combining the advantages of laser shock peening and dynamic strain aging (DSA). Through DSA, WLSP of steel increases the dislocation density and stabilizes the dislocation structure by pinning of mobile dislocations by carbon atoms. In addition, WLSP generates nanoscale carbide precipitates through strain-induced precipitation. The carbide precipitates stabilize the microstructure by dislocation pinning. This results in higher stability of the dislocation structure and thus improves the stability of the compressive residual stress. In this study the mechanism of fatigue performance improvement in AISI 4140 steel by WLSP is investigated. It is found that microstructures formed after WLSP lead to a higher stability of dislocation structures and residual stress, which are beneficial for fatigue performance.

Fatigue performance improvement in AISI 4140 steel by dynamic strain aging and dynamic precipitation during warm laser shock peening

International Nuclear Information System (INIS)

Ye Chang; Suslov, Sergey; Kim, Bong Joong; Stach, Eric A.; Cheng, Gary J.

2011-01-01

Warm laser shock peening (WLSP) is a thermomechanical treatment technique combining the advantages of laser shock peening and dynamic strain aging (DSA). Through DSA, WLSP of steel increases the dislocation density and stabilizes the dislocation structure by pinning of mobile dislocations by carbon atoms. In addition, WLSP generates nanoscale carbide precipitates through strain-induced precipitation. The carbide precipitates stabilize the microstructure by dislocation pinning. This results in higher stability of the dislocation structure and thus improves the stability of the compressive residual stress. In this study the mechanism of fatigue performance improvement in AISI 4140 steel by WLSP is investigated. It is found that microstructures formed after WLSP lead to a higher stability of dislocation structures and residual stress, which are beneficial for fatigue performance.

Comparison of orthorhombic and alpha-two titanium aluminides as matrices for continuous SiC-reinforced composites

International Nuclear Information System (INIS)

Smith, P.R.; Graves, J.A.; Rhodes, C.G.

1994-01-01

The attributes of an orthorhombic Ti aluminide alloy, Ti-21Al-22Nb (at. pct), and an alpha-two Ti aluminide alloy, Ti-24Al-11Nb (at. pct), for use as a matrix with continuous SiC (SCS-6) fiber reinforcement have been compared. Foil-fiber-foil processing was used to produce both unreinforced (''neat'') and unidirectional ''SCS-6'' reinforced panels. Microstructure of the Ti-24Al-11Nb matrix consisted of ordered Ti 3 Al (α 2 ) + disordered beta (β), while the Ti-21Al-22Nb matrix contained three phases: α 2 , ordered beta (β 0 ), and ordered orthorhombic (O). Fiber/matrix interface reaction zone growth kinetics at 982 C were examined for each composite system. Although both systems exhibited similar interface reaction products (i.e., mixed Ti carbides, silicides, and Ti-Al carbides), growth kinetics in the α 2 + β matrix composite were much more rapid than in the O + β 0 + α 2 matrix composite. Additionally, interfacial reaction in the α 2 + β composite resulted in a relatively large brittle matrix zone, depleted of beta phase, which was not present in the O + β 0 + α 2 matrix composite. Mechanical property measurements included room and elevated temperature tensile, thermal stability, thermal fatigue, thermomechanical fatigue (TMF), and creep. The three-phase orthorhombic-based alloy outperformed the α 2 + β alloy in all of these mechanical behavioral areas, on both an absolute and a specific (i.e., density corrected) basis

Bulletin of Materials Science | Indian Academy of Sciences

Indian Academy of Sciences (India)

The fatigue behaviour of 2014 Al-alloy has been studied in various thermomechanically aged conditions. It is observed that fatigue properties can be improved by a thermomechanical treatment, which would reduce the concentrations of dispersoids, provide a relatively uniform deformation structure and produce fine ...

Thermo-mechanical properties of SOFC components investigated by a combined method

DEFF Research Database (Denmark)

Teocoli, Francesca; Esposito, Vincenzo; Ramousse, Severine

, and differential thermo-mechanical behavior at each layer. The combination of such factors can have a critical effect on the final shape and microstructure, and on the mechanical integrity. Thermo-mechanical properties and sintering mechanisms of important SOFC materials (CGO, YSZ, ScYSZ) were systematically...

Effect of Crystal Orientation on Fatigue Failure of Single Crystal Nickel Base Turbine Blade Superalloys

Science.gov (United States)

Arakere, Nagaraj K.; Swanson, Gregory R.

2000-01-01

High Cycle Fatigue (HCF) induced failures in aircraft gas-turbine engines is a pervasive problem affecting a wide range of components and materials. HCF is currently the primary cause of component failures in gas turbine aircraft engines. Turbine blades in high performance aircraft and rocket engines are increasingly being made of single crystal nickel superalloys. Single-crystal Nickel-base superalloys were developed to provide superior creep, stress rupture, melt resistance and thermomechanical fatigue capabilities over polycrystalline alloys previously used in the production of turbine blades and vanes. Currently the most widely used single crystal turbine blade superalloys are PWA 1480/1493 and PWA 1484. These alloys play an important role in commercial, military and space propulsion systems. PWA1493, identical to PWA1480, but with tighter chemical constituent control, is used in the NASA SSME (Space Shuttle Main Engine) alternate turbopump, a liquid hydrogen fueled rocket engine. Objectives for this paper are motivated by the need for developing failure criteria and fatigue life evaluation procedures for high temperature single crystal components, using available fatigue data and finite element modeling of turbine blades. Using the FE (finite element) stress analysis results and the fatigue life relations developed, the effect of variation of primary and secondary crystal orientations on life is determined, at critical blade locations. The most advantageous crystal orientation for a given blade design is determined. Results presented demonstrates that control of secondary and primary crystallographic orientation has the potential to optimize blade design by increasing its resistance to fatigue crack growth without adding additional weight or cost.

Introduction to nonlinear thermomechanics of solids

CERN Document Server

Kleiber, Michał

2016-01-01

The first part of this textbook presents the mathematical background needed to precisely describe the basic problem of continuum thermomechanics. The book then concentrates on developing governing equations for the problem dealing in turn with the kinematics of material continuum, description of the state of stress, discussion of the fundamental conservation laws of underlying physics, formulation of initial-boundary value problems and presenting weak (variational) formulations. In the final part the crucial issue of developing techniques for solving specific problems of thermomechanics is addressed. To this aim the authors present a discretized formulation of the governing equations, discuss the fundamentals of the finite element method and develop some basic algorithms for solving algebraic and ordinary differential equations typical of problems on hand. Theoretical derivations are followed by carefully prepared computational exercises and solutions.

Efficient thermo-mechanical generation of electricity from the heat of radioisotopes

International Nuclear Information System (INIS)

Cooke-Yarborough, E.H.; Yeats, F.W.

1975-01-01

The thermomechanical generator uses a thermomechanical oscillator to convert heat efficiently into a mechanical oscillation which in turn excites a suitable transducer to generate alternating electricity. The thermomechanical oscillator used is based on the Stirling cycle, but avoids the need for rotary motion and for sliding pistons by having a mechanically-resonant, spring-suspended displacer, and by using an oscillating metal diaphragm to provide the mechanical output. The diaphragm drives an alternator consisting of a spring-suspended permanent magnet oscillating between fixed pole pieces which carry the electrical power output windings. Because a thermomechanical generator is much more efficient than a thermo-electric generator at comparable temperatures, it is particularly suitable for use with a radioisotope heat source. The amounts of radioisotope and of shielding required are both greatly reduced. A machine heated by radioisotopes and delivering 10.7W ac at 80Hz began operating in October, 1974. Operating experience with this machine is reported, and these results, together with those obtained with higher-powered machines heated by other means, are used to calculate characteristics and performance of thermo-mechanical radioisotope generators capable of using heat sources such as the waste-management 90 Sr radioisotope sources becoming available from the US nuclear waste management programme. A design to use one of these heat sources in a 52-W underwater generator is described

Thermomechanical response of a cross-ply titanium matrix composite subjected to a generic hypersonic flight profile

International Nuclear Information System (INIS)

Mirdamadi, M.; Johnson, W.S.

1993-01-01

Cross-ply laminate behavior of Ti-15V-3Cr-3AI-3Sn (Ti-15-3) matrix reinforced with continuous silicon-carbide fibers (SCS-6) subjected to a generic hypersonic flight profile was evaluated experimentally and analytically. Thermomechanical fatigue test techniques were developed to conduct a simulation of a generic hypersonic flight profile. A micromechanical analysis was used. The analysis predicts the stress-strain response of the laminate and of the constituents in each ply during thermal and mechanical cycling by using only constituent properties as input. The fiber was modeled as elastic with transverse orthotropic and temperature-dependent properties. The matrix was modeled using a thermoviscoplastic constitutive relation. The fiber transverse modulus was reduced in the analysis to simulate the fiber-matrix interface failure. Excellent correlation was found between measured and predicted laminate stress-strain response due to generic hypersonic flight profile when fiber debonding was modeled

Thermomechanical behavior of an Fe-based shape memory alloy: transformation conditions and hystereses

International Nuclear Information System (INIS)

Tanaka, K.; Nishimura, F.; Tobushi, H.; Oberaigner, E.R.; Fischer, F.D.

1995-01-01

Transformation/thermomechanical behavior in an Fe-9%Cr-5%Ni-14%Mn-6%Si polycrystalline shape memory alloy during thermomechanical loading is investigated. The transformation lines in the stress-temperature plane are strongly influenced by the parameters characterizing the thermomechanical loading. The transformation start condition, the martensite start stress and the austenite start temperature, is carefully measured to compare the results with the other experimental and theoretical observations. The stress-strain-temperature hysteresis loops, full and sub, are determined during cyclic loading. (orig.)

Damage and service life of nickel-base alloys under thermal-mechanical fatigue stress at different phase positions; Schaedigung und Lebensdauer von Nickelbasislegierungen unter thermisch-mechanischer Ermuedungsbeanspruchung bei verschiedenen Phasenlagen

Energy Technology Data Exchange (ETDEWEB)

Guth, Stefan

2016-07-01

This work considers the behaviour of two nickel-base alloys (NiCr22Co12Mo9 and MAR-M247 LC) under thermo-mechanical fatigue loading with varying phase angles between mechanical strain and temperature. The investigations focus on the characterisation of microstructures and damage mechanisms as a function of the phase angle. Based on the results, a life prediction model is proposed.

Thermomechanical Fatigue Behavior of a Silicon Carbide Fiber-Reinforced Calcium Aluminosilicate Glass-Ceramic Matrix Composite.

Science.gov (United States)

1992-08-01

Testing of Coated Monocrystalline Superalloys," in Low Cycle Fatigue. ASTM STP 942, Solomon, H.D., Hafford, G.R., Kaisand, L.R., and Keis, B.N. , eds...HOTOL) project is considering the use of CMCs on lower aeroshell panels , air intake leading edges, and the nose cone where temperatures may climb to...Works (Corning, NY). The composite was supplied in 16-ply, unidirectionally reinforced (10116) panels , measuring 152.4 cm x 152.4 cm (6 in x 6 in

Simulation of thermo-mechanical effect in bulk-silicon FinFETs

OpenAIRE

Burenkov, Alex; Lorenz, Jürgen

2016-01-01

The thermo-mechanical effect in bulk-silicon FinFETs of the 14 nm CMOS technology node is studied by means of numerical simulation. The electrical performance of such devices is significantly enhanced by the intentional introduction of mechanical stress during the device processing. The thermo-mechanical effect modifies the mechanical stress distribution in active regions of the transistors when they are heated. This can lead to a modification of the electrical performance. Numerical simulati...

Optimization in Friction Stir Welding - With Emphasis on Thermo-mechanical Aspects

DEFF Research Database (Denmark)

Tutum, Cem Celal

combined with classical single-objective and evolutionary multi-objective optimization algorithms (i.e. SQP and NSGA-II), to find the optimum process parameters (heat input, rotational and traverse welding speeds) that would result in favorable thermo-mechanical conditions for the process.......This book deals with the challenging multidisciplinary task of combining variant thermal and thermo-mechanical simulations for the manufacturing process of friction stir welding (FSW) with numerical optimization techniques in the search for optimal process parameters. The FSW process...... is characterized by multiphysics involving solid material flow, heat transfer, thermal softening, recrystallization and the formation of residual stresses. Initially, the thermal models were addressed since they in essence constitute the basis of all other models of FSW. Following this, several integrated thermo-mechanical...

Main factors of thermal fatigue failure induced by thermal striping and total simulation of thermal hydraulic and structural behaviors (research report)

International Nuclear Information System (INIS)

Kasahara, Naoto; Muramatsu, Toshiharu

1999-01-01

At incomplete mixing area of high temperature and low temperature fluids near the surface of structures, temperature fluctuation of fluid gives thermal fatigue damage to wall structures. This phenomenon is called thermal striping, which becomes sometimes a critical problem in LMFR plants. Since thermal striping phenomenon is characterized by the complex thermohydraulic and thermomechanical coupled problem, conventional evaluation procedures require mock-up experiments. In order to replace them by simulation-base methods, the authors have developed numerical simulation codes and applied them to analyze a tee junction of the PHENIX secondary circuit due to thermal striping phenomenon, in the framework of the IAEA coordinated research program (CRP). Through this analysis, thermohydraulic and thermomechanical mechanism of thermal striping phenomenon was clarified, and main factors on structural integrity was extracted in each stage of thermal striping phenomenon. Furthermore, simulation base evaluation methods were proposed taking above factors of structural integrity into account. Finally, R and D problems were investigated for future development of design evaluation methods. (author)

Thermomechanical Response of Self-Assembled Nanoparticle Membranes

Energy Technology Data Exchange (ETDEWEB)

Wang, Yifan [Department; James; Chan, Henry [Center; Narayanan, Badri [Center; McBride, Sean P. [Department; Sankaranarayanan, Subramanian K. R. S. [Center; Lin, Xiao-Min [Center; Jaeger, Heinrich M. [Department; James

2017-07-21

Monolayers composed of colloidal nanoparticles, with a thickness of less than 10 nm, have remarkable mechanical moduli and can suspend over micrometer-sized holes to form free-standing membranes. In this paper, we discuss experiment's and coarse-grained molecular dynamics simulations characterizing the thermomechanical properties of these self-assembled nanoparticle membranes. These membranes remain strong and resilient up to temperatures much higher than previous simulation predictions and exhibit an unexpected hysteretic behavior during the first heating cooling cycle. We show this hysteretic behavior can be explained by an asymmetric ligand configuration from the self assembly process and can be controlled by changing the ligand coverage or cross-linking the ligand molecules. Finally, we show the screening effect of water molecules on the ligand interactions can strongly affect the moduli and thermomechanical behavior.

Thermomechanical properties of radiation hardened oligoesteracrylates

International Nuclear Information System (INIS)

Lomonosova, N.V.; Chikin, Yu.A.

1984-01-01

Thermomechanical properties of radiation hardened oligoesteracrylates are studied by the methods of isothermal heating and thermal mechanics. Films of dimethacrylate of ethylene glycol, triethylene glycol (TGM-3), tetraethylene glycol, tridecaethylene glycol and TGM-3 mixture with methyl methacrylate hardened by different doses (5-150 kGy) using Co 60 installation with a dose rate of 2x10 -3 kGy/s served as a subject of the research. During oligoesteracrylate hargening a space network is formed, chain sections between lattice points of which are in a stressed state. Maximum of deformation is observed at 210-220 deg C on thermomechanical curves of samples hardened by doses > 5 kGy, which form and intensity is dependent on an absorbed dose. Presence of a high-temperature maximum on diaqrams of isometric heating of spatially cross-linked oligoesteracrylates is discovered. High thermal stability of three-dimensional network of radiation hardened oligoesteracrylates provides satisfactory tensile properties (40% of initial strength) in sample testing an elevated temperatures (200-250 deg C)

Enhancing the ABAQUS Thermomechanics Code to Simulate Steady and Transient Fuel Rod Behavior

International Nuclear Information System (INIS)

Williamson, R.L.; Knoll, D.A.

2009-01-01

A powerful multidimensional fuels performance capability, applicable to both steady and transient fuel behavior, is developed based on enhancements to the commercially available ABAQUS general-purpose thermomechanics code. Enhanced capabilities are described, including: UO2 temperature and burnup dependent thermal properties, solid and gaseous fission product swelling, fuel densification, fission gas release, cladding thermal and irradiation creep, cladding irradiation growth, gap heat transfer, and gap/plenum gas behavior during irradiation. The various modeling capabilities are demonstrated using a 2D axisymmetric analysis of the upper section of a simplified multi-pellet fuel rod, during both steady and transient operation. Computational results demonstrate the importance of a multidimensional fully-coupled thermomechanics treatment. Interestingly, many of the inherent deficiencies in existing fuel performance codes (e.g., 1D thermomechanics, loose thermo-mechanical coupling, separate steady and transient analysis, cumbersome pre- and post-processing) are, in fact, ABAQUS strengths.

A comprehensive energy approach to predict fatigue life in CuAlBe shape memory alloy

International Nuclear Information System (INIS)

Sameallah, S; Kadkhodaei, M; Legrand, V; Saint-Sulpice, L; Arbab Chirani, S

2015-01-01

Stabilized dissipated energy is an effective parameter on the fatigue life of shape memory alloys (SMAs). In this study, a formula is proposed to directly evaluate the stabilized dissipated energy for different values of the maximum and minimum applied stresses, as well as the loading frequency, under cyclic tensile loadings. To this aim, a one-dimensional fully coupled thermomechanical constitutive model and a cycle-dependent phase diagram are employed to predict the uniaxial stress-strain response of an SMA in a specified cycle, including the stabilized one, with no need of obtaining the responses of the previous cycles. An enhanced phase diagram in which different slopes are defined for the start and finish of a backward transformation strip is also proposed to enable the capture of gradual transformations in a CuAlBe shape memory alloy. It is shown that the present approach is capable of reproducing the experimental responses of CuAlBe specimens under cyclic tensile loadings. An explicit formula is further presented to predict the fatigue life of CuAlBe as a function of the maximum and minimum applied stresses as well as the loading frequency. Fatigue tests are also carried out, and this formula is verified against the empirically predicted number of cycles for failure. (paper)

A comprehensive energy approach to predict fatigue life in CuAlBe shape memory alloy

Science.gov (United States)

Sameallah, S.; Legrand, V.; Saint-Sulpice, L.; Kadkhodaei, M.; Arbab Chirani, S.

2015-02-01

Stabilized dissipated energy is an effective parameter on the fatigue life of shape memory alloys (SMAs). In this study, a formula is proposed to directly evaluate the stabilized dissipated energy for different values of the maximum and minimum applied stresses, as well as the loading frequency, under cyclic tensile loadings. To this aim, a one-dimensional fully coupled thermomechanical constitutive model and a cycle-dependent phase diagram are employed to predict the uniaxial stress-strain response of an SMA in a specified cycle, including the stabilized one, with no need of obtaining the responses of the previous cycles. An enhanced phase diagram in which different slopes are defined for the start and finish of a backward transformation strip is also proposed to enable the capture of gradual transformations in a CuAlBe shape memory alloy. It is shown that the present approach is capable of reproducing the experimental responses of CuAlBe specimens under cyclic tensile loadings. An explicit formula is further presented to predict the fatigue life of CuAlBe as a function of the maximum and minimum applied stresses as well as the loading frequency. Fatigue tests are also carried out, and this formula is verified against the empirically predicted number of cycles for failure.

Effect of ballistic electrons on ultrafast thermomechanical responses of a thin metal film

International Nuclear Information System (INIS)

Xiong Qi-lin; Tian Xin

2017-01-01

The ultrafast thermomechanical coupling problem in a thin gold film irradiated by ultrashort laser pulses with different electron ballistic depths is investigated via the ultrafast thermoelasticity model. The solution of the problem is obtained by solving finite element governing equations. The comparison between the results of ultrafast thermomechanical coupling responses with different electron ballistic depths is made to show the ballistic electron effect. It is found that the ballistic electrons have a significant influence on the ultrafast thermomechanical coupling behaviors of the gold thin film and the best laser micromachining results can be achieved by choosing the specific laser technology (large or small ballistic range). In addition, the influence of simplification of the ultrashort laser pulse source on the results is studied, and it is found that the simplification has a great influence on the thermomechanical responses, which implies that care should be taken when the simplified form of the laser source term is applied as the Gaussian heat source. (paper)

Effective thermo-mechanical properties and shape memory effect of CNT/SMP composites

Science.gov (United States)

Yang, Qingsheng; Liu, Xia; Leng, Fangfang

2009-07-01

Shape memory polymer (SMP) has been applied in many fields as intelligent sensors and actuators. In order to improve the mechanical properties and recovery force of SMP, the addition of minor amounts of carbon nanotubes (CNT) into SMP has attracted wide attention. A micromechanical model and thermo-mechanical properties of CNT/SMP composites were studied in this paper. The thermo-mechanical constitutive relation of intellectual composites with isotropic and transversely isotropic CNT was obtained. Moreover, the shape memory effect of CNT/SMP composites and the effect of temperature and the volume fraction of CNT were discussed. The work shows that CNT/SMP composites exhibit excellent macroscopic thermo-mechanical properties and shape memory effect, while both of them can be affected remarkably by temperature and the microstructure parameters.

Enhanced thermo-mechanical performance and strain-induced ...

Indian Academy of Sciences (India)

Enhanced thermo-mechanical performance and strain-induced band gap reduction of TiO2@PVC nanocomposite films ... School of Chemical Engineering, Yeungnam University, Gyeongsan 712-749, Republic of Korea; School of Mechanical Engineering, Yeungnam University, Gyeongsan 712-749, Republic of Korea ...

Enhancing the ABAQUS thermomechanics code to simulate multipellet steady and transient LWR fuel rod behavior

International Nuclear Information System (INIS)

Williamson, R.L.

2011-01-01

Highlights: → The ABAQUS thermomechanics code is enhanced to enable simulation of nuclear fuel behavior. → Comparisons are made between discrete and smeared fuel pellet analysis. → Multidimensional and multipellet analysis is important for accurate prediction of PCMI. → Fully coupled thermomechanics results in very smooth prediction of fuel-clad gap closure. → A smeared-pellet approximation results in significant underprediction of clad radial displacements and plastic strain. - Abstract: A powerful multidimensional fuels performance analysis capability, applicable to both steady and transient fuel behavior, is developed based on enhancements to the commercially available ABAQUS general-purpose thermomechanics code. Enhanced capabilities are described, including: UO 2 temperature and burnup dependent thermal properties, solid and gaseous fission product swelling, fuel densification, fission gas release, cladding thermal and irradiation creep, cladding irradiation growth, gap heat transfer, and gap/plenum gas behavior during irradiation. This new capability is demonstrated using a 2D axisymmetric analysis of the upper section of a simplified multipellet fuel rod, during both steady and transient operation. Comparisons are made between discrete and smeared-pellet simulations. Computational results demonstrate the importance of a multidimensional, multipellet, fully-coupled thermomechanical approach. Interestingly, many of the inherent deficiencies in existing fuel performance codes (e.g., 1D thermomechanics, loose thermomechanical coupling, separate steady and transient analysis, cumbersome pre- and post-processing) are, in fact, ABAQUS strengths.

Thermomechanics of composite structures under high temperatures

CERN Document Server

Dimitrienko, Yu I

2016-01-01

This pioneering book presents new models for the thermomechanical behavior of composite materials and structures taking into account internal physico-chemical transformations such as thermodecomposition, sublimation and melting at high temperatures (up to 3000 K). It is of great importance for the design of new thermostable materials and for the investigation of reliability and fire safety of composite structures. It also supports the investigation of interaction of composites with laser irradiation and the design of heat-shield systems. Structural methods are presented for calculating the effective mechanical and thermal properties of matrices, fibres and unidirectional, reinforced by dispersed particles and textile composites, in terms of properties of their constituent phases. Useful calculation methods are developed for characteristics such as the rate of thermomechanical erosion of composites under high-speed flow and the heat deformation of composites with account of chemical shrinkage. The author expan...

Correlation of microstructure and low cycle fatigue properties for 13.5Cr1.1W0.3Ti ODS steel

International Nuclear Information System (INIS)

He, P.; Klimenkov, M.; Möslang, A.; Lindau, R.; Seifert, H.J.

2014-01-01

Reduced activation oxide dispersion strengthened (ODS) steels are prospective structural materials for the blanket system and first wall components in Tokamak-type fusion reactors. Under the pulsed operation, these components will be predominantly subjected to cyclic thermal–mechanical loading which leads to inevitable fatigue damage. In this work, strain controlled isothermal fatigue tests were conducted for 13.5Cr1.1W0.3Ti ODS steel at 550 °C. The total strain range varied from 0.54% to 0.9%. After thermomechanical processing, 13.5CrWTi–ODS steel exhibits a remarkable lifetime extension with a factor of 10–20 for strain ranges Δε ⩽ 0.7%. 13.5Cr ODS steel shows no cyclic softening at all during the whole testing process irrespective of the strain range. TEM observations reveal ultrastable grain structure and constant dislocation densities around 10 14 m −2 , independent of the number of cycles or the applied strain amplitude. The presence of the stabilized ultrafine Y–Ti–O dispersoids enhances the microstructural stability and therefore leads to outstanding fatigue resistance for 13.5Cr1.1W0.3Ti–ODS steel

Correlation of microstructure and low cycle fatigue properties for 13.5Cr1.1W0.3Ti ODS steel

Energy Technology Data Exchange (ETDEWEB)

He, P., E-mail: pei.he@kit.edu; Klimenkov, M.; Möslang, A.; Lindau, R.; Seifert, H.J.

2014-12-15

Reduced activation oxide dispersion strengthened (ODS) steels are prospective structural materials for the blanket system and first wall components in Tokamak-type fusion reactors. Under the pulsed operation, these components will be predominantly subjected to cyclic thermal–mechanical loading which leads to inevitable fatigue damage. In this work, strain controlled isothermal fatigue tests were conducted for 13.5Cr1.1W0.3Ti ODS steel at 550 °C. The total strain range varied from 0.54% to 0.9%. After thermomechanical processing, 13.5CrWTi–ODS steel exhibits a remarkable lifetime extension with a factor of 10–20 for strain ranges Δε ⩽ 0.7%. 13.5Cr ODS steel shows no cyclic softening at all during the whole testing process irrespective of the strain range. TEM observations reveal ultrastable grain structure and constant dislocation densities around 10{sup 14} m{sup −2}, independent of the number of cycles or the applied strain amplitude. The presence of the stabilized ultrafine Y–Ti–O dispersoids enhances the microstructural stability and therefore leads to outstanding fatigue resistance for 13.5Cr1.1W0.3Ti–ODS steel.

Fast prediction of the fatigue behavior of short-fiber-reinforced thermoplastics based on heat build-up measurements: application to heterogeneous cases

Science.gov (United States)

Serrano, Leonell; Marco, Yann; Le Saux, Vincent; Robert, Gilles; Charrier, Pierre

2017-09-01

Short-fiber-reinforced thermoplastics components for structural applications are usually very complex parts as stiffeners, ribs and thickness variations are used to compensate the quite low material intrinsic stiffness. These complex geometries induce complex local mechanical fields but also complex microstructures due to the injection process. Accounting for these two aspects is crucial for the design in regard to fatigue of these parts, especially for automotive industry. The aim of this paper is to challenge an energetic approach, defined to evaluate quickly the fatigue lifetime, on three different heterogeneous cases: a classic dog-bone sample with a skin-core microstructure and two structural samples representative of the thickness variations observed for industrial components. First, a method to evaluate dissipated energy fields from thermal measurements is described and is applied to the three samples in order to relate the cyclic loading amplitude to the fields of cyclic dissipated energy. Then, a local analysis is detailed in order to link the energy dissipated at the failure location to the fatigue lifetime and to predict the fatigue curve from the thermomechanical response of one single sample. The predictions obtained for the three cases are compared successfully to the Wöhler curves obtained with classic fatigue tests. Finally, a discussion is proposed to compare results for the three samples in terms of dissipation fields and fatigue lifetime. This comparison illustrates that, if the approach is leading to a very relevant diagnosis on each case, the dissipated energy field is not giving a straightforward access to the lifetime cartography as the relation between fatigue failure and dissipated energy seems to be dependent on the local mechanical and microstructural state.

Cognitive and Physical Fatigue Tasks Enhance Pain, Cognitive Fatigue and Physical Fatigue in People with Fibromyalgia

Science.gov (United States)

Dailey, Dana L; Keffala, Valerie J; Sluka, Kathleen A

2014-01-01

Objective Fibromyalgia is a condition characterized by chronic widespread muscle pain and fatigue. The primary objective of this study was to determine if pain, perceived cognitive fatigue, and perceived physical fatigue were enhanced in participants with fibromyalgia compared to healthy controls during a cognitive fatigue task, a physical fatigue task and a dual fatigue task. Methods Twenty four people with fibromyalgia and 33 healthy controls completed pain, fatigue and function measures. A cognitive fatigue task (Controlled Oral Word Association Test) and physical fatigue task (Valpar peg test) were done individually and combined for a dual fatigue task. Resting pain, perceived cognitive fatigue and perceived physical fatigue were assessed during each task using visual analogue scales. Function was assessed with shoulder range of motion and grip. Results People with fibromyalgia had significantly higher increases in pain, cognitive fatigue and physical fatigue when compared to healthy controls after completion of a cognitive fatigue task, a physical fatigue task, or a dual fatigue task (pfatigue tasks, respectively. Conclusions These data show that people with fibromyalgia show larger increases in pain, perceived cognitive fatigue and perceived physical fatigue to both cognitive and physical fatigue tasks compared to healthy controls. The increases in pain and fatigue during cognitive and physical fatigue tasks could influence subject participation in daily activities and rehabilitation. PMID:25074583

On-chip detection of gel transition temperature using a novel micro-thermomechanical method.

Directory of Open Access Journals (Sweden)

Tsenguun Byambadorj

Full Text Available We present a new thermomechanical method and a platform to measure the phase transition temperature at microscale. A thin film metal sensor on a membrane simultaneously measures both temperature and mechanical strain of the sample during heating and cooling cycles. This thermomechanical principle of operation is described in detail. Physical hydrogel samples are prepared as a disc-shaped gels (200 μm thick and 1 mm diameter and placed between an on-chip heater and sensor devices. The sol-gel transition temperature of gelatin solution at various concentrations, used as a model physical hydrogel, shows less than 3% deviation from in-depth rheological results. The developed thermomechanical methodology is promising for precise characterization of phase transition temperature of thermogels at microscale.

Effect of the structure on the low-cycle fatigue behaviour of alloy 800

International Nuclear Information System (INIS)

Robert, G.; Mathiot, A.; Regnard, C.; Dessus, J.; Claret, J.

1982-04-01

Alloy 800 (grade I) is used for making the steam generators of liquid metal fast breeder reactors. At working temperature (525 0 C) alloy 800 is strengthned by γ' (Ni 3 (Ti,Al)) precipitation which occurs during thermal aging. The mechanical properties of this alloy depend on the parameters which define the γ' precipitation and obviously on the structural characteristics due to the thermomechanical treatments which govern the manufacture of the product. For one cast of alloy 800 this work aims to analyse the influence, on low cycle fatigue behaviour at 550 0 C, of structural and microstructural variations originating either in different elaboration procedures or in γ' precipitation obtained by a thermal aging of 3000h at 550 0 C with or without a preceeding cold working of 10% [fr

Identification of a Critical Time with Acoustic Emission Monitoring during Static Fatigue Tests on Ceramic Matrix Composites: Towards Lifetime Prediction

Directory of Open Access Journals (Sweden)

Nathalie Godin

2016-02-01

Full Text Available Non-oxide fiber-reinforced ceramic-matrix composites are promising candidates for some aeronautic applications that require good thermomechanical behavior over long periods of time. This study focuses on the behavior of a SiCf/[Si-B-C] composite with a self-healing matrix at intermediate temperature under air. Static fatigue experiments were performed below 600 °C and a lifetime diagram is presented. Damage is monitored both by strain measurement and acoustic emission during the static fatigue experiments. Two methods of real-time analysis of associated energy release have been developed. They allow for the identification of a characteristic time that was found to be close to 55% of the measured rupture time. This critical time reflects a critical local energy release assessed by the applicability of the Benioff law. This critical aspect is linked to a damage phase where slow crack growth in fibers is prevailing leading to ultimate fracture of the composite.

Thermomechanical evaluation of the fuel assemblies fabricated in the ININ

International Nuclear Information System (INIS)

Hernandez L, H.; Ortiz V, J.

2005-01-01

The pilot plant of fuel production of the National Institute of Nuclear Research (ININ) provided to the Laguna Verde Nuclear Power Plant (CNLV) four fuel assemblies type GE9B. The fuel irradiation was carried out in the unit 1 of the CNLV during four operation cycles, highlighting the fact that in their third cycle the four assemblies were placed in the center of the reactor core. In the Nuclear Systems Department (DSN) of the ININ it has been carried out studies to evaluate their neutron performance and to be able to determine the exposure levels of this fuels. Its also outlines the necessity to carry out a study of the thermomechanical behavior of the fuel rods that compose the assemblies, through computational codes that simulate their performance so much thermal as mechanical. For such purpose has been developing in the DSN the FETMA code, together with the codes that compose the system Fuel Management System (FMS), which evaluates the thermomechanical performance of fuel elements. In this work were used the FETMA and FEMAXI codes (developed by JAERI) to study the thermomechanical performance of the fuel elements manufactured in the ININ. (Author)

A thermomechanical crystal plasticity constitutive model for ultrasonic consolidation

KAUST Repository

Siddiq, Amir; El Sayed, Tamer S.

2012-01-01

We present a micromechanics-based thermomechanical constitutive model to simulate the ultrasonic consolidation process. Model parameters are calibrated using an inverse modeling approach. A comparison of the simulated response and experimental

Areva fatigue concept. Fast fatigue evaluation, a new method for fatigue analysis

International Nuclear Information System (INIS)

Heinz, Benedikt; Bergholz, Steffen; Rudolph, Juergen

2011-01-01

Within the discussions on the long term operation (LTO) of nuclear power plants the ageing management is on the focus of that analysis. The knowledge of the operational thermal cyclic load data on components of the power plants and their evaluation in the fatigue analysis is a central concern. The changes in fatigue requirements (e.g. the consideration of environmentally assisted fatigue - EAF) recently discussed and LTO efforts are a strong motivation for the identification of margins in the existing fatigue analysis approaches. These margins should be considered within new approaches in order to obtain realistic (or more accurate) analysis results. Of course, these new analysis approaches have to be manageable and efficient. The Areva Fatigue Concept (AFC) offers the comprehensive conceptual basis for the consideration of fatigue on different levels and depths. The combination of data logging and automated fatigue evaluation are important modules of the AFC. Besides the established simplified stress based fatigue estimation Areva develops a further automated fatigue analysis method called Fast Fatigue Evaluation (FFE). This method comprises highly automated stress analyses at the fatigue relevant locations of the component. Hence, a component specific course of stress as a function of time is determined based on FAMOS or similar temperature measurement systems. The subsequent application of the rain flow cycle counting algorithm allows for the determination of the usage factor following the rules of the design code requirements. The new FFE approach constitutes a cycle counting method based on the real stresses in the component, and determined as result a rule-conformity cumulative usage factor. (orig.)

Interfacial characteristics of hybrid nanocomposite under thermomechanical loading

Science.gov (United States)

Choyal, Vijay; Kundalwal, Shailesh I.

2017-12-01

In this work, an improved shear lag model was developed to investigate the interfacial characteristics of three-phase hybrid nanocomposite which is reinforced with microscale fibers augmented with carbon nanotubes on their circumferential surfaces. The shear lag model accounts for (i) radial and axial deformations of different transversely isotropic constituents, (ii) thermomechanical loads on the representative volume element (RVE), and (iii) staggering effect of adjacent RVEs. The results from the current newly developed shear lag model are validated with the finite element simulations and found to be in good agreement. This study reveals that the reduction in the maximum value of the axial stress in the fiber and the interfacial shear stress along its length become more pronounced in the presence of applied thermomechanical loads on the staggered RVEs. The existence of shear tractions along the RVE length plays a significant role in the interfacial characteristics and cannot be ignored.

Modelling the Thermomechanical Conditions in Friction Stir Welding

DEFF Research Database (Denmark)

Schmidt, Henrik Nikolaj Blich

Friction Stir Welding is a solid-state welding process invented by TWI in 1991. The FSW process is unique in the sense that joining of un-weldable alloys readily can be made. The thermomechanical conditions present in the workpiece during the welding process are of great interest since...... these control the properties of the weld. In the present work, a set of experimental, analytical and numerical analyses are carried out in order to evaluate the thermomechanical conditions descriptive for welding of aluminium, in this case AA2024-T3, under a specific set of welding parameters. Despite...... these specific data, the developed models can be applied for other alloys and welding parameters as well. A detailed experiment is carried out which constitutes the basis for the development and validation of the numerical and analytical models presented in this work. The contact condition at the tool...

Coupled thermomechanical behavior of graphene using the spring-based finite element approach

Energy Technology Data Exchange (ETDEWEB)

Georgantzinos, S. K., E-mail: sgeor@mech.upatras.gr; Anifantis, N. K., E-mail: nanif@mech.upatras.gr [Machine Design Laboratory, Department of Mechanical Engineering and Aeronautics, University of Patras, Rio, 26500 Patras (Greece); Giannopoulos, G. I., E-mail: ggiannopoulos@teiwest.gr [Materials Science Laboratory, Department of Mechanical Engineering, Technological Educational Institute of Western Greece, 1 Megalou Alexandrou Street, 26334 Patras (Greece)

2016-07-07

The prediction of the thermomechanical behavior of graphene using a new coupled thermomechanical spring-based finite element approach is the aim of this work. Graphene sheets are modeled in nanoscale according to their atomistic structure. Based on molecular theory, the potential energy is defined as a function of temperature, describing the interatomic interactions in different temperature environments. The force field is approached by suitable straight spring finite elements. Springs simulate the interatomic interactions and interconnect nodes located at the atomic positions. Their stiffness matrix is expressed as a function of temperature. By using appropriate boundary conditions, various different graphene configurations are analyzed and their thermo-mechanical response is approached using conventional finite element procedures. A complete parametric study with respect to the geometric characteristics of graphene is performed, and the temperature dependency of the elastic material properties is finally predicted. Comparisons with available published works found in the literature demonstrate the accuracy of the proposed method.

Thermomechanical characterization of thiol-epoxy shape memory thermosets for mechanical actuators design

Science.gov (United States)

Belmonte, Alberto; Fernández-Francos, Xavier; De la Flor, Silvia

2018-02-01

In this paper, shape-memory "thiol-epoxy" polymers are synthesized and characterized as potential thermomechanical actuators. Their thermomechanical properties are investigated through dynamo mechanical and tensile analyses and related to their network structural properties by using "thiol" and "epoxy" compounds of different functionality and structure. Their mechanical properties (resistance at break, elongation limits and strain energy) are related to their shape-memory response under free-recovery conditions and partially-constrained conditions, thus, establishing the connection between network relaxation (free-recovery) with the work output capabilities (partially-constrained). Results show high mechanical performance, achieving high elongation at break values (up to 100%) and stress at break values (up to 50 MPa). The shape-memory experiments reveal strong dependence of the programming conditions and network structure on the recovery efficiency at free-conditions, whereas under partially-constrained conditions, the controlling factors are the mechanical limits at high temperature. Moreover, some recommendations to achieve the maximum work output efficiency for a given operational design of a thermomechanical actuator are deduced.

Research and Progress of Thermomechanical Treatment of Al-Li Alloys

Directory of Open Access Journals (Sweden)

WU Xiuliang

2016-10-01

Full Text Available The strengthening and toughening mechanism of aluminum lithium alloy treated by thermo-mechanical processing have been summarized, and the effect on the evolution of microstructures, grain structure and precipitation, were discussed and analysed deeply. The precipitation sequence and behavior of the main precipitation phase were modified by the thermo-mechanical processing, stimulating the forming of fine dispersion combined particles of δ',θ"/θ', T1, and S"/S' phases, uniformly distributed in the matrix, which significantly improved the relationships of strength and the plastic toughness, with the inhibiting of broadening of precipitate free zones, and of the precipitation and coarsening of strengthening particles at the grain boundary.The density of solute atom and vacancies significantly raised up after solution treating, and retained as supersaturated solid solution after water quenching, which acted as the driving force for the precipitation during subsequent aging. Pre-deformation and pre-aging significantly increased the density of fine dispersion strengthening particles of δ' and G.P. zones,which uniformly nucleated in the matrix, and the combined strengthening phases of δ',θ"/θ', and T1 were obtained after high temperature second aging, controlling the size and volume fraction of these particles.Refined grain and optimal grain structure were achieved by new and typical thermo-mechanical processing, and the proportion, size, and oriented relationship of main strengthening particles of δ',θ"/θ', and T1 phases were optimized.At last, the research direction of new thermo-mechanical treatment on the large scale rolled plates and hot worked forgings is pointed out, such as age forming, to meet the need of light high performance of new aluminum lithium alloys used for the large aircrafs and heavy lift launch vehicles.

Improvement of thermo-mechanical properties of ceramic materials for nuclear applications

International Nuclear Information System (INIS)

Decroix, G.M.; Gosset, D.; Kryger, B.; Boussuge, M.; Burlet, H.

1994-01-01

In order to improve the thermo-mechanical properties of materials used as neutron absorbers in nuclear reactors, cermet or cercer have been produced with two original microstructures: micro- or macro-dispersed composites. The composites thermal shock resistance has been evaluated in an image furnace. The microstructures we obtained involve different reinforcement mechanisms, such as crack deflection, crack branching, crack bridging or microcrack toughening, and improvement of thermal conductivity. The results reveal a significant improvement of the thermo-mechanical properties of the boron base neutron absorbers whose fabrication process leads to a macro-dispersed microstructure. (authors). 8 refs., 8 figs., 2 tabs

Examination of the Thermo-mechanical Properties of E-Glass/Carbon Composites

Directory of Open Access Journals (Sweden)

Hande Sezgin

2017-12-01

Full Text Available Eight-ply E-glass, carbon and E-glass/carbon fabric-reinforced polyester based hybrid composites were manufactured in this study. A vacuum infusion system was used as the production method. Dynamic mechanical analysis, thermogravimetric analysis and differential scanning calorimetry analysis were conducted to examine the thermo-mechanical properties of composite samples. The effect of reinforcement type and different stacking sequences of fabric plies on the thermo-mechanical properties of composite samples were also investigated. Results showed that the type and alignment of reinforcement material has a signifi cant effect on the dynamic mechanical properties of composite samples.

Strengthening of stable Cr-Ni austenitic stainless steel under thermomechanical treatments

Science.gov (United States)

Akkuzin, S. A.; Litovchenko, I. Yu.; Tyumentsev, A. N.

2017-12-01

The features of microstructure and mechanical properties of stable austenitic steel after thermomechanical treatment consisted of low-temperature deformation, deformation in the temperature range T = 273-873 K, and subsequent annealing were investigated. It is shown that under such treatment direct (γ → α')- and reverse (α'→γ)-martensitic transformations occur in the steel. As a result of the thermomechanical treatment submicrocrystalline structural states with high density of micro- and nanotwins and localized deformation bands are formed. The strength of the steel in these structural states is several times higher than that in the initial state.

Determination of Turbine Blade Life from Engine Field Data

Science.gov (United States)

Zaretsky, Erwin V.; Litt, Jonathan S.; Hendricks, Robert C.; Soditus, Sherry M.

2013-01-01

It is probable that no two engine companies determine the life of their engines or their components in the same way or apply the same experience and safety factors to their designs. Knowing the failure mode that is most likely to occur minimizes the amount of uncertainty and simplifies failure and life analysis. Available data regarding failure mode for aircraft engine blades, while favoring low-cycle, thermal-mechanical fatigue (TMF) as the controlling mode of failure, are not definitive. Sixteen high-pressure turbine (HPT) T-1 blade sets were removed from commercial aircraft engines that had been commercially flown by a single airline and inspected for damage. Each set contained 82 blades. The damage was cataloged into three categories related to their mode of failure: (1) TMF, (2) Oxidation/erosion (O/E), and (3) Other. From these field data, the turbine blade life was determined as well as the lives related to individual blade failure modes using Johnson-Weibull analysis. A simplified formula for calculating turbine blade life and reliability was formulated. The L10 blade life was calculated to be 2427 cycles (11 077 hr). The resulting blade life attributed to O/E equaled that attributed to TMF. The category that contributed most to blade failure was Other. If there were no blade failures attributed to O/E and TMF, the overall blade L(sub 10) life would increase approximately 11 to 17 percent.

Effects of Microstructural Variability on Thermo-Mechanical Properties of a Woven Ceramic Matrix Composite

Science.gov (United States)

Goldsmith, Marlana B.; Sankar, Bhavani V.; Haftka, Raphael T.; Goldberg, Robert K.

2013-01-01

The objectives of this paper include identifying important architectural parameters that describe the SiC/SiC five-harness satin weave composite and characterizing the statistical distributions and correlations of those parameters from photomicrographs of various cross sections. In addition, realistic artificial cross sections of a 2D representative volume element (RVE) are generated reflecting the variability found in the photomicrographs, which are used to determine the effects of architectural variability on the thermo-mechanical properties. Lastly, preliminary information is obtained on the sensitivity of thermo-mechanical properties to architectural variations. Finite element analysis is used in combination with a response surface and it is shown that the present method is effective in determining the effects of architectural variability on thermo-mechanical properties.

Going greener: Synthesis of fully biobased unsaturated polyesters for styrene crosslinked resins with enhanced thermomechanical properties

Directory of Open Access Journals (Sweden)

C. S. M. F. Costa

2017-11-01

Full Text Available The main goal of this work was the development of fully biobased unsaturated polyesters (UPs that upon crosslinking with unsaturated monomers (UM could lead to greener unsaturated polyester resins (UPRs with similar thermomechanical properties to commercial fossil based UPR. After the successful synthesis of the biobased UPs, those were crosslinked with styrene (Sty, the most commonly used monomer, and the influence of the chemical structure of the UPs on the thermomechanical characteristics of UPRs were evaluated. The properties were compared with those of a commercial resin (Resipur 9837©. The BioUPRs presented high gel contents and contact angles that are similar to the commercial resin. The thermomechanical properties were evaluated by dynamic mechanical thermal analysis (DMTA and it was found that the UPR synthesized using propylene glycol (PG, succinic acid (SuAc and itaconic acid (ItAc presented very close thermomechanical properties compared to the commercial resin.

Operating experience with the Harwell thermo-mechanical generators

International Nuclear Information System (INIS)

Cooke-Yarborough, E.H.

1980-06-01

The Stirling-cycle thermo-mechanical generator (TMG) provides small amounts of electrical power continuously over long periods, while requiring much less fuel than other power sources running from hydrocarbon fuel or radio-isotopes. Two of these 25-watt generators, fuelled by propane, have been used to power the UK National Buoy on two successive missions. A total of more than three years experience at sea has now been accumulated. In addition, a 60-watt version has provided the power for a major lighthouse for more than a year. An early development version of the Thermo-mechanical Generator, adapted to run from the heat of a radio-isotope source, was loaded with strontium 90 titanate in October 1974 and has run continuously in the laboratory ever since. The improvements and changes found necessary in the course of 90,000 generator-hours of running time are described, and the improvements in operational performance and reliability which have resulted are outlined. (author)

The Relationships Between Microstructure, Tensile Properties and Fatigue Life in Ti-5Al-5V-5Mo-3Cr-0.4Fe (Ti-5553)

Science.gov (United States)

Foltz, John W., IV

beta-titanium alloys are being increasingly used in airframes as a way to decrease the weight of the aircraft. As a result of this movement, Ti-5Al-5V-5Mo-3Cr-0.4Fe (Timetal 555), a high-strength beta titanium alloy, is being used on the current generation of landing gear. This alloy features good combinations of strength, ductility, toughness and fatigue life in alpha+beta processed conditions, but little is known about beta-processed conditions. Recent work by the Center for the Accelerated Maturation of Materials (CAMM) research group at The Ohio State University has improved the tensile property knowledge base for beta-processed conditions in this alloy, and this thesis augments the aforementioned development with description of how microstructure affects fatigue life. In this work, beta-processed microstructures have been produced in a Gleeble(TM) thermomechanical simulator and subsequently characterized with a combination of electron and optical microscopy techniques. Four-point bending fatigue tests have been carried out on the material to characterize fatigue life. All the microstructural conditions have been fatigue tested with the maximum test stress equal to 90% of the measured yield strength. The subsequent results from tensile tests, fatigue tests, and microstructural quantification have been analyzed using Bayesian neural networks in an attempt to predict fatigue life using microstructural and tensile inputs. Good correlation has been developed between lifetime predictions and experimental results using microstructure and tensile inputs. Trained Bayesian neural networks have also been used in a predictive fashion to explore functional dependencies between these inputs and fatigue life. In this work, one section discusses the thermal treatments that led to the observed microstructures, and the possible sequence of precipitation that led to these microstructures. The thesis then describes the implications of microstructure on fatigue life and

Thermo-mechanical stress analysis of cryopreservation in cryobags and the potential benefit of nanowarming.

Science.gov (United States)

Solanki, Prem K; Bischof, John C; Rabin, Yoed

2017-06-01

Cryopreservation by vitrification is the only promising solution for long-term organ preservation which can save tens of thousands of lives across the world every year. One of the challenges in cryopreservation of large-size tissues and organs is to prevent fracture formation due to the tendency of the material to contract with temperature. The current study focuses on a pillow-like shape of a cryobag, while exploring various strategies to reduce thermo-mechanical stress during the rewarming phase of the cryopreservation protocol, where maximum stresses are typically found. It is demonstrated in this study that while the level of stress may generally increase with the increasing amount of CPA filled in the cryobag, the ratio between width and length of the cryobag play a significant role. Counterintuitively, the overall maximum stress is not found when the bag is filled to its maximum capacity (when the filled cryobag resembles a sphere). Parametric investigation suggests that reducing the initial rewarming rate between the storage temperature and the glass transition temperature may dramatically decrease the thermo-mechanical stress. Adding a temperature hold during rewarming at the glass transition temperature may reduce the thermo-mechanical stress in some cases, but may have an adverse effect in other cases. Finally, it is demonstrated that careful incorporation of volumetric heating by means on nanoparticles in an alternating magnetic field, or nanowarming, can dramatically reduce the resulting thermo-mechanical stress. These observations display the potential benefit of a thermo-mechanical design of the cryopreservation protocols in order to prevent structural damage. Copyright © 2017 Elsevier Inc. All rights reserved.

Thermo-mechanical properties of polystyrene-based shape memory nanocomposites

NARCIS (Netherlands)

Xu, B.; Fu, Y.Q.; Ahmad, M.; Luo, J.K.; Huang, W.M.; Kraft, A.; Reuben, R.; Pei, Y.T.; Chen, Zhenguo; Hosson, J.Th.M. De

2010-01-01

Shape memory nanocomposites were fabricated using chemically cross-linked polystyrene (PS) copolymer as a matrix and different nanofillers (including alumina, silica and clay) as the reinforcing agents. Their thermo-mechanical properties and shape memory effects were characterized. Experimental

Assessment of thermo-mechanical behavior in CLAM steel first wall structures

International Nuclear Information System (INIS)

Liu Fubin; Yao Man

2012-01-01

Highlights: ► China Low Activation Martensitic steel (CLAM) as FW the structural material. ► The thermo-mechanical behavior of the FW was analyzed under the condition of normal ITER operation combined effect of plasma heat flux and neutron heating. ► The temperature dependence of the material physical properties of CLAM is summarized. - Abstract: The temperature and strain distributions of the mockup with distinct structural material (SS316L or China Low Activation Martensitic steel (CLAM)) in two-dimensional model were calculated and analyzed, based on a high heat flux (HHF) test recently reported with heat flux of 3.2 MW/m 2 . The calculated temperature and strain results in the first wall (FW), in which SS316L is as the structural material, showed good agreement with HHF test. By substituting CLAM steel for SS316L the contrast analysis indicates that the thermo-mechanical property for CLAM steel is better than that of SS316 at the same condition. Furthermore, the thermo-mechanical behavior of the FW was analyzed under the condition of normal ITER operation combined effect of plasma heat flux and neutron heating.

Assessment of thermo-mechanical behavior in CLAM steel first wall structures

Energy Technology Data Exchange (ETDEWEB)

Liu Fubin, E-mail: liufubin_1216@126.com [School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, Liaoning (China); Yao Man, E-mail: yaoman@dlut.edu.cn [School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, Liaoning (China)

2012-01-15

Highlights: Black-Right-Pointing-Pointer China Low Activation Martensitic steel (CLAM) as FW the structural material. Black-Right-Pointing-Pointer The thermo-mechanical behavior of the FW was analyzed under the condition of normal ITER operation combined effect of plasma heat flux and neutron heating. Black-Right-Pointing-Pointer The temperature dependence of the material physical properties of CLAM is summarized. - Abstract: The temperature and strain distributions of the mockup with distinct structural material (SS316L or China Low Activation Martensitic steel (CLAM)) in two-dimensional model were calculated and analyzed, based on a high heat flux (HHF) test recently reported with heat flux of 3.2 MW/m{sup 2}. The calculated temperature and strain results in the first wall (FW), in which SS316L is as the structural material, showed good agreement with HHF test. By substituting CLAM steel for SS316L the contrast analysis indicates that the thermo-mechanical property for CLAM steel is better than that of SS316 at the same condition. Furthermore, the thermo-mechanical behavior of the FW was analyzed under the condition of normal ITER operation combined effect of plasma heat flux and neutron heating.

Thermo-mechanical simulations of early-age concrete cracking with durability predictions

Science.gov (United States)

Havlásek, Petr; Šmilauer, Vít; Hájková, Karolina; Baquerizo, Luis

2017-09-01

Concrete performance is strongly affected by mix design, thermal boundary conditions, its evolving mechanical properties, and internal/external restraints with consequences to possible cracking with impaired durability. Thermo-mechanical simulations are able to capture those relevant phenomena and boundary conditions for predicting temperature, strains, stresses or cracking in reinforced concrete structures. In this paper, we propose a weakly coupled thermo-mechanical model for early age concrete with an affinity-based hydration model for thermal part, taking into account concrete mix design, cement type and thermal boundary conditions. The mechanical part uses B3/B4 model for concrete creep and shrinkage with isotropic damage model for cracking, able to predict a crack width. All models have been implemented in an open-source OOFEM software package. Validations of thermo-mechanical simulations will be presented on several massive concrete structures, showing excellent temperature predictions. Likewise, strain validation demonstrates good predictions on a restrained reinforced concrete wall and concrete beam. Durability predictions stem from induction time of reinforcement corrosion, caused by carbonation and/or chloride ingress influenced by crack width. Reinforcement corrosion in concrete struts of a bridge will serve for validation.

Thermomechanical modeling and data analysis for heating experiments at Stripa, Sweden

International Nuclear Information System (INIS)

Chan, T.; Littlestone, N.; Wan, O.

1979-11-01

Comparisons were made between predicted and measured thermomechanical displacements and stresses for in situ heating experiments at a depth of 340 m in a granite body at Stripa, Sweden. We found that taking into account the temperature dependence of the thermal expansion coefficient and the mechanical properties of the rock substantially improves the agreement between theory and experiment. In general, the displacements calculated using laboratory values of rock properties agree better with field data than in the case of stresses. This may be due to the difference between in situ and laboratory rock modulus. The significance of temperature-dependent rock properties and strength to thermomechanical failure is also discussed

Thermomechanical behavior of NiTiPdPt high temperature shape memory alloy springs

International Nuclear Information System (INIS)

Nicholson, D E; Vaidyanathan, R; Padula II, S A; Noebe, R D; Benafan, O

2014-01-01

Transformation strains in high temperature shape memory alloys (HTSMAs) are generally smaller than for conventional NiTi alloys and can be purposefully limited in cases where stability and repeatability at elevated temperatures are desired. Yet such alloys can still be used in actuator applications that require large strokes when used in the form of springs. Thus there is a need to understand the thermomechanical behavior of shape memory alloy spring actuators, particularly those consisting of alternative alloys. In this work, a modular test setup was assembled with the objective of acquiring stroke, stress, temperature, and moment data in real time during joule heating and forced convective cooling of Ni 19.5 Ti 50.5 Pd 25 Pt 5 HTSMA springs. The spring actuators were subjected to both monotonic axial loading and thermomechanical cycling. The role of rotational constraints (i.e., by restricting rotation or allowing for free rotation at the ends of the springs) on stroke performance was also assessed. Finally, recognizing that evolution in the material microstructure can result in changes in HTSMA spring geometry, the effect of material microstructural evolution on spring performance was examined. This was done by taking into consideration the changes in geometry that occurred during thermomechanical cycling. This work thus provides insight into designing with HTSMA springs and predicting their thermomechanical performance. (paper)

Fatigue

Science.gov (United States)

... to help you find out what's causing your fatigue and recommend ways to relieve it. Fatigue itself is not a disease. Medical problems, treatments, and personal habits can add to fatigue. These include Taking certain medicines, such as antidepressants, ...

Experimental study of thermo-mechanical behavior of a thermosetting shape-memory polymer

Science.gov (United States)

Liu, Ruoxuan; Li, Yunxin; Liu, Zishun

2018-01-01

The thermo-mechanical behavior of shape-memory polymers (SMPs) serves for the engineering applications of SMPs. Therefore the understanding of thermo-mechanical behavior of SMPs is of great importance. This paper investigates the influence of loading rate and loading level on the thermo-mechanical behavior of a thermosetting shape-memory polymer through experimental study. A series of cyclic tension tests and shape recovery tests at different loading conditions are performed to study the strain level and strain rate effect. The results of tension tests show that the thermosetting shape-memory polymer will behave as rubber material at temperature lower than the glass transition temperature (Tg) and it can obtain a large shape fix ratio at cyclic loading condition. The shape recovery tests exhibit that loading rate and loading level have little effect on the beginning and ending of shape recovery process of the thermosetting shape-memory polymer. Compared with the material which is deformed at temperature higher than Tg, the material deformed at temperature lower than Tg behaves a bigger recovery speed.

Evaluation of thermo-mechanical properties data of carbon-based plasma facing materials

International Nuclear Information System (INIS)

Ulrickson, M.; Barabash, V.R.; Matera, R.; Roedig, M.; Smith, J.J.; Janev, R.K.

1991-03-01

This Report contains the proceedings, results and conclusions of the work done and the analysis performed during the IAEA Consultants' Meeting on ''Evaluation of thermo-mechanical properties data of carbon-based plasma facing materials'', convened on December 17-21, 1990, at the IAEA Headquarters in Vienna. Although the prime objective of the meeting was to critically assess the available thermo-mechanical properties data for certain types of carbon-based fusion relevant materials, the work of the meeting went well beyond this task. The meeting participants discussed in depth the scope and structure of the IAEA material properties database, the format of data presentation, the most appropriate computerized system for data storage, retrieval, exchange and management. The existing IAEA ALADDIN system was adopted as a convenient tool for this purpose and specific ALADDIN labelling schemes and dictionaries were established for the material properties data. An ALADDIN formatted test-file for the thermo-physical and thermo-mechanical properties of pyrolytic graphite is appended to this Report for illustrative purposes. (author)

Effect of Water on the Thermo-Mechanical Behavior of Carbon Cloth Phenolic

Science.gov (United States)

Sullivan, Roy M.; Stokes, Eric; Baker, Eric H.

2011-01-01

The results of thermo-mechanical experiments, which were conducted previously by one of the authors, are reviewed. The strain in the direction normal to the fabric plane was measured as a function of temperature for a variety of initial moisture contents and heating rates. In this paper, the general features of the thermo-mechanical response are discussed and the effect of heating rate and initial moisture content are highlighted. The mechanical interaction between the phenolic polymer and water trapped within its free volumes as the polymer is heated to high temperatures is discussed. An equation for the internal stresses which are generated within the polymer due to trapped water is obtained from the total stress expression for a binary mixture of polymer and water. Numerical solutions for moisture diffusion in the thermo-mechanical experiments were performed and the results of these solutions are presented. The results of the moisture diffusion solutions help to explain the effects of heating rate and moisture content on the strain behavior normal to the fabric plane.

Fatigue and thermal fatigue of Pb-Sn solder joints

International Nuclear Information System (INIS)

Frear, D.; Grivas, D.; McCormack, M.; Tribula, D.; Morris, J.W. Jr.

1987-01-01

This paper presents a fundamental investigation of the fatigue and thermal fatigue characteristics, with an emphasis on the microstructural development during fatigue, of Sn-Pb solder joints. Fatigue tests were performed in simple shear on both 60Sn-40Pb and 5Sn-95Pb solder joints. Isothermal fatigue tests show increasing fatigue life of 60Sn-40Pb solder joints with decreasing strain and temperature. In contrast, such behavior was not observed in the isothermal fatigue of 5Sn-95Pb solder joints. Thermal fatigue results on 60Sn-40Pb solder cycled between -55 0 C and 125 0 C show that a coarsened region develops in the center of the joint. Both Pb-rich and Sn-rich phases coarsen, and cracks form within these coarsened regions. The failure mode 60Sn-40Pb solder joints in thermal and isothermal fatigue is similar: cracks form intergranularly through the Sn-rich phase or along Sn/Pb interphase boundaries. Extensive cracking is found throughout the 5Sn-95Pb joint for both thermal and isothermal fatigue. In thermal fatigue the 5Sn-95Pb solder joints failed after fewer cycles than 60Sn-40Pb

Thermomechanical controls on magma supply and volcanic deformation: application to Aira caldera, Japan

Science.gov (United States)

Hickey, James; Gottsmann, Joachim; Nakamichi, Haruhisa; Iguchi, Masato

2016-01-01

Ground deformation often precedes volcanic eruptions, and results from complex interactions between source processes and the thermomechanical behaviour of surrounding rocks. Previous models aiming to constrain source processes were unable to include realistic mechanical and thermal rock properties, and the role of thermomechanical heterogeneity in magma accumulation was unclear. Here we show how spatio-temporal deformation and magma reservoir evolution are fundamentally controlled by three-dimensional thermomechanical heterogeneity. Using the example of continued inflation at Aira caldera, Japan, we demonstrate that magma is accumulating faster than it can be erupted, and the current uplift is approaching the level inferred prior to the violent 1914 Plinian eruption. Magma storage conditions coincide with estimates for the caldera-forming reservoir ~29,000 years ago, and the inferred magma supply rate indicates a ~130-year timeframe to amass enough magma to feed a future 1914-sized eruption. These new inferences are important for eruption forecasting and risk mitigation, and have significant implications for the interpretations of volcanic deformation worldwide. PMID:27619897

Thermomechanical controls on magma supply and volcanic deformation: application to Aira caldera, Japan.

Science.gov (United States)

Hickey, James; Gottsmann, Joachim; Nakamichi, Haruhisa; Iguchi, Masato

2016-09-13

Ground deformation often precedes volcanic eruptions, and results from complex interactions between source processes and the thermomechanical behaviour of surrounding rocks. Previous models aiming to constrain source processes were unable to include realistic mechanical and thermal rock properties, and the role of thermomechanical heterogeneity in magma accumulation was unclear. Here we show how spatio-temporal deformation and magma reservoir evolution are fundamentally controlled by three-dimensional thermomechanical heterogeneity. Using the example of continued inflation at Aira caldera, Japan, we demonstrate that magma is accumulating faster than it can be erupted, and the current uplift is approaching the level inferred prior to the violent 1914 Plinian eruption. Magma storage conditions coincide with estimates for the caldera-forming reservoir ~29,000 years ago, and the inferred magma supply rate indicates a ~130-year timeframe to amass enough magma to feed a future 1914-sized eruption. These new inferences are important for eruption forecasting and risk mitigation, and have significant implications for the interpretations of volcanic deformation worldwide.

Thermal/thermomechanical analyses for the room region with horizontal and vertial modes of emplacement

International Nuclear Information System (INIS)

1988-01-01

Extensive thermal/thermomechanical analyses of the Site Characterization Plan-Conceptual Design at the Deaf Smith county Site, Texas, have been carried out for the room region with horizontal and vertical modes of emplacement. The main purpose of this study is to make a good comparison between these two modes of emplacement in this region. Homogeneous and nonhomogeneous strata under isothermal or transient temperature conditions cases were considered in the analyses. Furthermore, various pillar widths for the vertical mode emplacement were also taken into consideration. Only spent fuel (SF) waste was considered in this study. Finite element method was used throughout the analyses. The thermal responses were evaluated using SPECTROM-41 while the thermomechanical responses were calculated using SPECTROM-32. Thermal and thermomechanical comparisons between the two modes of emplacement for various cases were presented in this paper

Prediction of thermo-mechanical reliability of wafer backend processes

NARCIS (Netherlands)

Gonda, V.; Toonder, den J.M.J.; Beijer, J.G.J.; Zhang, G.Q.; van Driel, W.D.; Hoofman, R.J.O.M.; Ernst, L.J.

2004-01-01

More than 65% of IC failures are related to thermal and mechanical problems. For wafer backend processes, thermo-mechanical failure is one of the major bottlenecks. The ongoing technological trends like miniaturization, introduction of new materials, and function/product integration will increase

Prediction of thermo-mechanical integrity of wafer backend processes

NARCIS (Netherlands)

Gonda, V.; Toonder, den J.M.J.; Beijer, J.G.J.; Zhang, G.Q.; Hoofman, R.J.O.M.; Ernst, L.J.; Ernst, L.J.

2003-01-01

More than 65% of IC failures are related to thermal and mechanical problems. For wafer backend processes, thermo-mechanical failure is one of the major bottlenecks. The ongoing technological trends like miniaturization, introduction of new materials, and function/product integration will increase

Thermomechanical Treatments on High Strength Al-Zn-Mg(-Cu) Alloys

National Research Council Canada - National Science Library

Di Russo, E; Conserva, M; Gatto, F

1974-01-01

An investigation was carried out to determine the metallurgical properties of Al-Zn-Mg and Al-Zn-Mg-Cu alloy products processed according to newly developed Final Thermomechanical Treatments (FTMT) of T-AHA type...

Thermal and thermo-mechanical simulation of laser assisted machining

International Nuclear Information System (INIS)

Germain, G.; Dal Santo, P.; Lebrun, J. L.; Bellett, D.; Robert, P.

2007-01-01

Laser Assisted Machining (LAM) improves the machinability of materials by locally heating the workpiece just prior to cutting. The heat input is provided by a high power laser focused several millimeters in front of the cutting tool. Experimental investigations have confirmed that the cutting force can be decreased, by as much as 40%, for various materials (tool steel, titanium alloys and nickel alloys). The laser heat input is essentially superficial and results in non-uniform temperature profiles within the depth of the workpiece. The temperature field in the cutting zone is therefore influenced by many parameters. In order to understand the effect of the laser on chip formation and on the temperature fields in the different deformation zones, thermo-mechanical simulation were undertaken. A thermo-mechanical model for chip formation with and without the laser was also undertaken for different cutting parameters. Experimental tests for the orthogonal cutting of 42CrMo4 steel were used to validate the simulation via the prediction of the cutting force with and without the laser. The thermo-mechanical model then allowed us to highlight the differences in the temperature fields in the cutting zone with and without the laser. In particular, it was shown that for LAM the auto-heating of the material in the primary shear zone is less important and that the friction between the tool and chip also generates less heat. The temperature fields allow us to explain the reduction in the cutting force and the resulting residual stress fields in the workpiece

Proceedings of the first thermomechanical workshop for shale

International Nuclear Information System (INIS)

1986-03-01

Chapter 2 provides a description of the three federal regulations that pertain to the development of a high-level nuclear waste repository regardless of the rock type. Chapter 3 summarizes the reference shale repository conditions selected for this workshop. A room-and-pillar configuration was considered at an extraction ratio of about 0.25. The depth was assumed to be 700 m. Chapter 4 gives a summary of several case histories that were considered to be valuable in gaining an understanding of some of the design and construction features that might be unique in creating underground openings in shale. Chapter 5 assesses the data and information needs, availability, technology for acquisition, and the research and development necessary for analytical/numerical modeling in heat transfer, fluid flow, and thermomechanics. Chapter 6 assesses data and information needs in the laboratory and considerations associated with shale rock characterization. Chapter 7 assesses the data and information needs, availability, technology for acquisition, and the research and development necessary for field/in situ testing. Chapter 8 presents the consensus of the workshop participants that there is a definite need to advance the state of knowledge concerning the thermomechanical behavior of shales and to gain experience in applying this knowledge to the design of room-and-pillar excavations. Finally, Chapter 9 provides a summary of the research and development needs in the various interacting activities of repository development, including analytical/numerical modeling, laboratory testing, and field/in situ testing. The main conclusion of the workshop was that a need exists for an aggressive program in laboratory, field, numerical modeling, and design studies to provide a thermomechanical, technological base for comparison of shale types and shale regions/areas/sites

The Nature of Fatigue in Chronic Fatigue Syndrome.

Science.gov (United States)

Olson, Karin; Zimka, Oksana; Stein, Eleanor

2015-10-01

In this article, we report the findings of our study on the nature of fatigue in patients diagnosed with chronic fatigue syndrome. Using ethnoscience as a design, we conducted a series of unstructured interviews and card sorts to learn more about how people with chronic fatigue syndrome describe fatigue. Participants (N = 14) described three distinct domains: tiredness, fatigue, and exhaustion. Most participants experienced tiredness prior to diagnosis, fatigue during daily life, and exhaustion after overexertion. We also discuss participants' ability to adapt to a variety of stressors and prevent shifts to exhaustion, and relate our findings to stress theory and other current research. Primary strategies that promoted adaptation to stressors included pacing and extended rest periods. These findings can aid health care professionals in detecting impending shifts between tiredness, fatigue, and exhaustion and in improving adaptive strategies, thereby improving quality of life. © The Author(s) 2015.

Effect of cerium and thermomechanical processing on microstructure

Indian Academy of Sciences (India)

The effect of cerium content and thermomechanical processing on structure and properties of Fe–10.5 wt.%Al–0.8 wt%C alloy has been investigated. Alloys were prepared by a combination of air induction melting with flux cover (AIMFC) and electroslag remelting (ESR). The ESR ingots were hot-forged and hotrolled at ...

The thermomechanical stability of micro-solid oxide fuel cells fabricated on anodized aluminum oxide membranes

Science.gov (United States)

Kwon, Chang-Woo; Lee, Jae-Il; Kim, Ki-Bum; Lee, Hae-Weon; Lee, Jong-Ho; Son, Ji-Won

2012-07-01

The thermomechanical stability of micro-solid oxide fuel cells (micro-SOFCs) fabricated on an anodized aluminum oxide (AAO) membrane template is investigated. The full structure consists of the following layers: AAO membrane (600 nm)/Pt anode/YSZ electrolyte (900 nm)/porous Pt cathode. The utilization of a 600-nm-thick AAO membrane significantly improves the thermomechanical stability due to its well-known honeycomb-shaped nanopore structure. Moreover, the Pt anode layer deposited in between the AAO membrane and the YSZ electrolyte preserves its integrity in terms of maintaining the triple-phase boundary (TPB) and electrical conductivity during high-temperature operation. Both of these results guarantee thermomechanical stability of the micro-SOFC and extend the cell lifetime, which is one of the most critical issues in the fabrication of freestanding membrane-type micro-SOFCs.

A Numerical Model for the Thermomechanical Conditions During Hydration of Early-age Concrete

DEFF Research Database (Denmark)

Hattel, Jesper; Thorborg, Jesper

2003-01-01

In the present study, a macroscopic numerical model for the thermomechanical conditions during hydration of early-age concrete is presented. The formulation is based on a semi-coupled, incremental thermomechanical model where the heat production from the hydration process is expressed in terms...... of the maturity and the thermal activation is expressed by the Arrhenius principle. The material properties are assumed to depend on the hydration process via the maturity. The discretization of the governing equations is accomplished by a control volume formulation involving a time-splitting scheme for the heat...

Improving fatigue performance of rail thermite welds

Science.gov (United States)

Jezzini-Aouad, M.; Flahaut, P.; Hariri, S.; Winiar, L.

2010-06-01

Rail transport development offers economic and ecological interests. Nevertheless, it requires heavy investments in rolling material and infrastructure. To be competitive, this transportation means must rely on safe and reliable infrastructure, which requires optimization of all implemented techniques and structure. Rail thermite (or aluminothermic) welding is widely used within the railway industry for in-track welding during re-rail and defect replacement. The process provides numerous advantages against other welding technology commonly used. Obviously, future demands on train traffic are heavier axle loads, higher train speeds and increased traffic density. Thus, a new enhanced weld should be developed to prevent accidents due to fracture of welds and to lower maintenance costs. In order to improve such assembly process, a detailed metallurgical study coupled to a thermomechanical modelling of the phenomena involved in the thermite welding process is carried out. Obtained data enables us to develop a new improved thermite weld (type A). This joint is made by modifying the routinely specified procedure (type B) used in a railway rail by a standard gap alumino-thermic weld. Joints of type A and B are tested and compared. Based on experimental temperature measurements, a finite element analysis is used to calculate the thermal residual stresses induced. In the vicinity of the weld, the residual stress patterns depend on the thermal conditions during welding as it also shown by litterature [1, 2]. In parallel, X-Ray diffraction has been used to map the residual stress field that is generated in welded rail of types A and B. Their effect on fatigue crack growth in rail welds is studied. An experimental study based on fatigue tests of rails welded by conventional and improved processes adjudicates on the new advances and results will be shown.

Hydrogen embrittlement of thermomechanically treated 18Ni Maraging steel

International Nuclear Information System (INIS)

Munford, J.W.; Rack, H.J.; Kass, W.J.

1977-01-01

The influence of thermomechanical treatments on susceptibility to cracking in 100 percent relative humidity air and low pressure (93.3 KPa) gaseous hydrogen has been investigated for 18Ni (350 ksi) Maraging steel. Two thermomechanical treatments were studied, ausforming and marforming and compared with the standard solution treated and aged material. Although little difference exists for the strength and toughness values between these treatments, a two to five-fold increase in the stress intensity threshold for cracking was found for both the ausformed and marformed material. A dramatic difference in cracking kinetics was also apparent as shown by the failure times at comparable stress intensities. Fractographic analysis showed that the primary fracture mode was 100 percent intergranular for the solution treated and aged samples while the ausform and marform failures were predominately quasi-cleavage or intergranular depending on orientation. Finally, permeation and diffusion measurements were conducted on the above materials and these results are correlated with the environmental cracking behavior

Hydrogen embrittlement of thermomechanically treated 18Ni Maraging steel

Energy Technology Data Exchange (ETDEWEB)

Munford, J.W.; Rack, H.J.; Kass, W.J.

1977-01-01

The influence of thermomechanical treatments on susceptibility to cracking in 100 percent relative humidity air and low pressure (93.3 KPa) gaseous hydrogen has been investigated for 18Ni (350 ksi) Maraging steel. Two thermomechanical treatments were studied, ausforming and marforming and compared with the standard solution treated and aged material. Although little difference exists for the strength and toughness values between these treatments, a two to five-fold increase in the stress intensity threshold for cracking was found for both the ausformed and marformed material. A dramatic difference in cracking kinetics was also apparent as shown by the failure times at comparable stress intensities. Fractographic analysis showed that the primary fracture mode was 100 percent intergranular for the solution treated and aged samples while the ausform and marform failures were predominately quasi-cleavage or intergranular depending on orientation. Finally, permeation and diffusion measurements were conducted on the above materials and these results are correlated with the environmental cracking behavior.

Casting dimensional control and fatigue life prediction for permanent mold casting dies. Technical progress report, September 29, 1993-- September 30, 1994

Energy Technology Data Exchange (ETDEWEB)

NONE

1994-11-01

First year efforts as part of a three year program to address metal casting dimensional control and fatigue life prediction for permanent mold casting dies are described. Procedures have been developed and implemented to collect dimensional variability data from production steel castings. The influence of process variation and casting geometry variables on dimensional tolerances have been investigated. Preliminary results have shown that these factors have a significant influence on dimensional variability, although this variability is considerably less than the variability indicated in current tolerance standards. Gage repeatability and reproducibility testing must precede dimensional studies to insure that measurement system errors are acceptably small. Also initial efforts leading to the development and validation of a CAD/CAE model to predict the thermal fatigue life of permanent molds for aluminum castings are described. An appropriate thermomechanical property database for metal, mold and coating materials has been constructed. A finite element model has been developed to simulate the mold temperature distribution during repeated casting cycles. Initial validation trials have indicated the validity of the temperature distribution model developed.

Mechanical and thermomechanical properties of polycarbonate-based polyurethane-silica nanocomposites

Directory of Open Access Journals (Sweden)

Rafał Poręba

2011-09-01

Full Text Available In this work aliphatic polycarbonate-based polyurethane-silica nanocomposites were synthesized and characterized. The influence of the type and of the concentration of nanofiller differing in average particle size (7 nm for Aerosil 380 and 40 nm for Nanosilica 999 on mechanical and thermomechanical properties was investigated. DMTA measurements showed that Nanosilica 999, irrespective of its concentration, slightly increased the value of the storage shear modulus G’ but Aerosil 380 brings about a nearly opposite effect, the shear modulus in the rubber region decreases with increasing filler content. Very high elongations at break ranging from 800% to more than 1000%, as well as high tensile strengths illustrate excellent ultimate tensile properties of the prepared samples. The best mechanical and thermomechanical properties were found for the sample filled with 0.5 wt.% of Nanosilica 999.

Midwest Structural Sciences Center 2010 Annual Report

Science.gov (United States)

2011-06-01

producing a range of response depending on load and temperature. In the first TMF experiment, a dog bone specimen was held at a constant load, a little... why this is the case. The loss of closure as temperature increases would have profound implications for the thermo- mechanical fatigue life of this...cohesive fracture properties for mode-I fracture of quasi- brittle materials, Submitted to Inter- national Journal of Fracture. Kang W.-H., Y.-J. Lee

Modelling of the thermomechanical behaviour of salt rock

International Nuclear Information System (INIS)

Albers, G.; Graefe, V.; Korthaus, E.; Pudewillis, A.; Prij, J.

1986-01-01

The modelling of the thermomechanical behaviour of salt rock is examined, with respect to the disposal of radioactive waste in salt formations. The calculation methods and programmes currently available for the modelling are described. Some examples are given of calculations carried out in parallel with tests. Some results of modelling calculations for a repository are presented by way of illustration. (U.K.)

Uncertainty analysis of a one-dimensional constitutive model for shape memory alloy thermomechanical description

DEFF Research Database (Denmark)

Oliveira, Sergio A.; Savi, Marcelo A.; Santos, Ilmar F.

2014-01-01

The use of shape memory alloys (SMAs) in engineering applications has increased the interest of the accuracy analysis of their thermomechanical description. This work presents an uncertainty analysis related to experimental tensile tests conducted with shape memory alloy wires. Experimental data...... are compared with numerical simulations obtained from a constitutive model with internal constraints employed to describe the thermomechanical behavior of SMAs. The idea is to evaluate if the numerical simulations are within the uncertainty range of the experimental data. Parametric analysis is also developed...

Role of grain refinement in hardening of structural steels at preliminary thermomechanical treatment

International Nuclear Information System (INIS)

Bukhvalov, A.B.; Grigor'eva, E.V.; Davydova, L.S.; Degtyarev, M.V.; Levit, V.I.; Smirnova, N.A.; Smirnov, L.V.

1981-01-01

The hardening mechanism during preliminary thermomechanical treatment with deformation by cold rolling or hydroextrusion is studied on structural 37KhN3M1 and 38KhN3MFA steels. Specimens have been tested on static tension, impact strength and fracture toughness. It is shown that hydroextrusion application instead of rolling does not change the hardening effect of preliminary thermomechanical treatment (PTMT). It is established that the increase of preliminary deformation degree and the use of accelerated short term hardening heating provides a bett er grain refinement and the increase of PTMT hardening effect [ru

Perceived Fatigue Interference and Depressed Mood: Comparison of Chronic Fatigue Syndrome/Myalgic Encephalomyelitis Patients with Fatigued Breast Cancer Survivors.

Science.gov (United States)

Hall, Daniel L; Antoni, Michael H; Lattie, Emily G; Jutagir, Devika R; Czaja, Sara J; Perdomo, Dolores; Lechner, Suzanne C; Stagl, Jamie M; Bouchard, Laura C; Gudenkauf, Lisa M; Traeger, Lara; Fletcher, MaryAnn; Klimas, Nancy G

Persistent fatigue and depressive symptoms are both highly prevalent among patients with Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME) as well as breast cancer survivors. This study aimed to assess and directly compare perceptions of fatigue as highly interfering in one's daily functioning in both patient populations to better understand their relationships with depressed mood. Participants were 95 female CFS/ME patients and 67 females who were approximately 5 years post-treatment for stage 0-III breast cancer presenting with clinically elevated fatigue severity. Self-report measures were obtained on participants' fatigue-related interference in daily functioning and fatigue severity as well as depressed mood. Hierarchical regression was used to test effects controlling for relevant demographic, psychosocial, and medical covariates. CFS/ME patients endorsed greater depressed mood and fatigue interference than did fatigued breast cancer survivors, p's fatigued breast cancer survivors (β=.18, p =.19). CFS/ME patients reported elevated fatigue symptoms and depression relative to fatigued breast cancer survivors. In the former group, greater depressed mood was highly and significantly associated with greater fatigue-related inference in daily activities. Potential targets for cognitive behavioral interventions are discussed.

The Identification of Fatigue Resistant and Fatigue Susceptible Individuals

National Research Council Canada - National Science Library

Harrison, Richard; Chaiken, Scott; Harville, Donald; Fischer, Joseph; Fisher, Dion; Whitmore, Jeff

2008-01-01

The present study was designed to target two specific areas regarding fatigue. The primary purpose was to begin investigations into possible genetic markers linked to fatigue resistance and fatigue susceptibility...

Production of enzymes by a newly isolated Bacillus sp. TMF-1 in solid state fermentation on agricultural by-products: The evaluation of substrate pretreatment methods.

Science.gov (United States)

Salim, Abdalla Ali; Grbavčić, Sanja; Šekuljica, Nataša; Stefanović, Andrea; Jakovetić Tanasković, Sonja; Luković, Nevena; Knežević-Jugović, Zorica

2017-03-01

Study on potential of different agro-industrial waste residues for supporting the growth of newly isolated Bacillus sp. TMF-1 strain under solid-state fermentation (SSF) was conducted aiming to produce several industrially valuable enzymes. Since the feasibility of the initial study was confirmed, further objectives included evaluation of several pretreatments of the studied agricultural by-products (soybean meal, sunflower meal, maize bran, maize pericarp, olive oil cake and wheat bran) on the microbial productivity as means of enhancing the yields of produced proteases, α-amylases, cellulases and pectinases. Among acid/alkaline treatment, ultrasound and microwave assisted methods, chemical treatments superiorly affected most of the studied substrates. Highest yields of produced proteases (50.5IUg -1 ) and α-amylases (50.75IUg -1 ) were achieved on alkaline treated corn pericarp. Alkaline treatment also promoted the secretion of cellulases on maize bran (1.19IUg -1 ). Highest yield of pectinases was obtained on untreated soybean meal (64.90IUg -1 ). Copyright © 2016 Elsevier Ltd. All rights reserved.

Transformation-induced plasticity in multiphase steels subjected to thermomechanical loading

NARCIS (Netherlands)

Tjahjanto, D.D.; Turteltaub, S.R.; Suiker, A.S.J.; Zwaag, van der S.

2008-01-01

The behaviour of transformation-induced plasticity steels subjected to combined thermomechanical loading is studied at the microscale by means of numerical simulations. The microstructure is composed of an austenitic phase that may deform plastically and/or transform into martensite, and a ferritic

Thermomechanical Morphology of Peas and Its Relation to Fracture Behaviour

NARCIS (Netherlands)

Pelgrom, P.J.M.; Schutyser, M.A.I.; Boom, R.M.

2013-01-01

Milling and subsequent air classification can be exploited for production of functional protein-enriched fractions from legumes and grains. Fracture behaviour is of large relevance to optimal disentanglement of protein and starch and is determined by the thermomechanical morphology of the seeds.

Influence of Microstructure on the Fatigue Crack Growth of A516 in Hydrogen

Science.gov (United States)

Wachob, Harry F.; Nelson, Howard G.

1980-01-01

Some day hydrogen may be used as a viable energy storage and transport medium within the United States. Hydrogen gas may be used to dilute and extend our present methane supply as a blend or may even be used in its pure elemental form as a primary fuel. Independent of the methods of production, storage, and distribution, the interaction of hydrogen with its containment material will play an integral role in the success of a hydrogen energy program. Presently, the selection of hydrogen containment materials can be made such that the material will remain reasonably free from environmental degradation; however, costly alloying additions are required. Unfortunately, high alloy steels are economically prohibitive when large-scale hydrogen energy storage, transmission, and conversion systems are desired. Therefore, in order to implement such hydrogen energy systems in the future, existing low-cost materials must be improved via mechanical, thermal, or thermo-mechanical processing methods or new low-cost materials which are compatible with hydrogen must be developed. Originally, low strength, low alloy steels at room temperature were thought to be immune to hydrogen gas embrittlement, since no sustained load crack growth is observed. However, results of Clark in HY8O and Nelson in SAE 1020 have shown that the fatigue crack growth rate can be greatly accelerated in the presence of hydrogen gas. In recent results reported by Louthan and Mucci, the smooth bar fatigue life of an A1068 pipeline steel was reduced up to a factor of ten when the tests were performed in a 13.8 MPa hydrogen environment. These results suggest that the selection of material for structures designed to operate in hydrogen under cyclic loads must include consideration of hydrogen/metal fatigue interaction. Although the hydrogen/metal fatigue interaction can be severe in low strength low alloy steels, the degree of degradation may be altered by the underlying ferrous microstructure. At present, no

Fatigue testing of wood composites for aerogenerator blades. Pt. 11: Assessment of fatigue damage accumulation using a fatigue modulus approach

Energy Technology Data Exchange (ETDEWEB)

Hacker, C L; Ansell, M P [Bath Univ. (United Kingdom)

1996-12-31

Stress-strain hysteresis loops have been captured during fatigue tests performed at R=10 (compression-compression) and R=0.1 (tension-tension) on Khaya epoxy wood composites. A fatigue modulus approach, proposed by Hwang and Han in 1989, has been applied to the data and a relationship established between the initial change in fatigue modulus and fatigue life. By following changes in fatigue modulus during the first 100 test cycles it is possible to predict the life of the sample allowing rapid evaluation of the fatigue performance of wood composites. Fatigue modulus values have also been calculated for hysteresis loops captured during complex load - time history tests. Similar trends in change in fatigue modulus suggest that this approach could be used in complex loading conditions to evaluate fatigue damage accumulation and predict fatigue life. (Author)

Fracture mechanics in new designed power module under thermo-mechanical loads

Directory of Open Access Journals (Sweden)

Durand Camille

2014-06-01

Full Text Available Thermo-mechanically induced failure is a major reliability issue in the microelectronic industry. On this account, a new type of Assembly Interconnected Technology used to connect MOSFETs in power modules has been developed. The reliability is increased by using a copper clip soldered on the top side of the chip, avoiding the use of aluminium wire bonds, often responsible for the failure of the device. Thus the new designed MOSFET package does not follow the same failure mechanisms as standard modules. Thermal and power cycling tests were performed on these new packages and resulting failures were analyzed. Thermo-mechanical simulations including cracks in the aluminium metallization and intermetallics (IMC were performed using Finite Element Analysis in order to better understand crack propagation and module behaviour.

Perceived Fatigue Interference and Depressed Mood: Comparison of Chronic Fatigue Syndrome/Myalgic Encephalomyelitis Patients with Fatigued Breast Cancer Survivors

Science.gov (United States)

Hall, Daniel L.; Antoni, Michael H.; Lattie, Emily G.; Jutagir, Devika R.; Czaja, Sara J.; Perdomo, Dolores; Lechner, Suzanne C.; Stagl, Jamie M.; Bouchard, Laura C.; Gudenkauf, Lisa M.; Traeger, Lara; Fletcher, MaryAnn; Klimas, Nancy G.

2015-01-01

Objective Persistent fatigue and depressive symptoms are both highly prevalent among patients with Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME) as well as breast cancer survivors. This study aimed to assess and directly compare perceptions of fatigue as highly interfering in one’s daily functioning in both patient populations to better understand their relationships with depressed mood. Methods Participants were 95 female CFS/ME patients and 67 females who were approximately 5 years post-treatment for stage 0-III breast cancer presenting with clinically elevated fatigue severity. Self-report measures were obtained on participants’ fatigue-related interference in daily functioning and fatigue severity as well as depressed mood. Hierarchical regression was used to test effects controlling for relevant demographic, psychosocial, and medical covariates. Results CFS/ME patients endorsed greater depressed mood and fatigue interference than did fatigued breast cancer survivors, p’sfatigued breast cancer survivors (β=.18, p=.19). Conclusions CFS/ME patients reported elevated fatigue symptoms and depression relative to fatigued breast cancer survivors. In the former group, greater depressed mood was highly and significantly associated with greater fatigue-related inference in daily activities. Potential targets for cognitive behavioral interventions are discussed. PMID:26180660

First-principles study of thermal expansion and thermomechanics of single-layer black and blue phosphorus

International Nuclear Information System (INIS)

Sun, Hongyi; Liu, Gang; Li, Qingfang; Wan, X.G.

2016-01-01

The linear thermal expansion coefficients (LTEC) and thermomechanics of single-layer black and blue phosphorus are systematically studied using first-principles based on quasiharmonic approximation. We find the thermal expansion of black phosphorus is very anisotropic. The LTEC along zigzag direction has a turning from negative to positive at around 138 K, while the LTEC along armchair direction is positive (except below 8 K) and about 2.5 times larger than that along zigzag direction at 300 K. For blue phosphorus, the LTEC is negative in the temperature range from 0 to 350 K. In addition, we find that the Young's modulus and Poisson's ratio of black phosphorus along zigzag direction are 4 to 5 times larger than those along armchair direction within considered temperature range, showing a remarkable anisotropic in-plane thermomechanics property. The mechanisms of these peculiar thermal properties are also explored. This work provides a theoretical understanding of the thermal expansion and thermomechanics of this single layer phosphorus family, which will be useful in nanodevices. - Highlights: • The thermal properties of black and blue phosphorus are studied. • Black phosphorus shows remarkable anisotropic thermal expansion and thermomechanics properties. • Blue phosphorus shows novel negative thermal expansion. • The thermal expansion properties are well analyzed by grüneisen theory.

New three-dimensional far-field potential repository thermomechanical calculations

International Nuclear Information System (INIS)

Hardy, M.P.; Bai, M.; Goodrich, R.R.; Lin, M.; Carlisle, S.; Bauer, S.J.

1993-03-01

The thermomechanical effect on the exploratory ramps, drifts, and shafts as a result of high-level nuclear waste disposal is examined using a three-dimensional thermo-elastic model. The repository layout modeled is based on the use of mechanical mining of all excavations with equivalent waste emplacement areal power densities of 57 and 80 kW/acre. Predicted temperatures and stress changes for the north and south access drifts, east main drift, east-west exploratory drift, the north and south Calico Hills access ramps, the Calico Hills north-south exploratory drift, and the optional exploratory studies facility and man and materials shafts are presented for times 10, 35, 50, 100, 300, 500, 1000, 2000, 5000, and 10,000 years after the start of waste emplacement. The study indicates that the east-west exploratory drift at the repository horizon is subject to the highest thermomechanical impact because it is located closest the buried waste canisters. For most exploratory openings, the thermally induced temperatures and stresses tend to reach the maximum magnitudes at approximately 1000 years after waste emplacement

Proceedings of the specialists meeting on experience with thermal fatigue in LWR piping caused by mixing and stratification

International Nuclear Information System (INIS)

1998-01-01

This specialists meeting on experience with thermal fatigue in LWR piping caused by mixing and stratification, was held in June 1998 in Paris. It included five sessions. Session 1: operating experience (7 papers): Historical perspective; EDF experience with local thermohydraulic phenomena in PWRs: impacts and strategies; Thermal fatigue in safety injection lines of French PWRs: technical problems, regulatory requirements, concerns about other areas; US NRC Regulatory perspective on unanticipated thermal fatigue in LWR piping; Failure to the Residual Heat Removal system suction line pipe in Genkai unit 1 caused by thermal stratification cycling; Emergency Core Cooling System pipe crack incident at Tihange unit 1; Two leakages induced by thermal stratification at the Loviisa power plant). Session 2: thermal hydraulic phenomena (5 papers): Thermal stratification in small pipes with respect to fatigue effects and so called 'Banana effect'; Thermal stratification in the surge line of the Korean next generation reactor; Thermal stratification in horizontal pipes investigated in UPTF-TRAM and HDR facilities; Research on thermal stratification in un-isolable piping of reactor pressure boundary; Thermal mixing phenomena in piping systems: 3D numerical simulation and design considerations. Session 3: response of material and structure (5 papers): Fatigue induced by thermal stratification, Results of tests and calculations of the COUFAST model; Laboratory simulation of thermal fatigue cracking as a basis for verifying life models; Thermo-mechanical analysis methods for the conception and the follow up of components submitted to thermal stratification transients; Piping analysis methods of a PWR surge line for stratified flow; The thermal stratification effect on surge lines, The VVER estimation. Session 4: monitoring aspects (4 papers): Determination of the thermal loadings affecting the auxiliary lines of the reactor coolant system in French PWR plants; Expected and

A study of thermo-mechanical stress and its impact on through-silicon vias

International Nuclear Information System (INIS)

Ranganathan, N; Balasubramanian, N; Prasad, K; Pey, K L

2008-01-01

The BOSCH etch process, which is commonly used in microelectromechanical system fabrication, has been extensively investigated in this work for implementation in through-silicon via (TSV) technology for 3D-microsystems packaging. The present work focuses on thermo-mechanical stresses caused by thermal loading due to post-TSV processes and their impact on the electrical performance of through-silicon copper interconnects. A test vehicle with deep silicon copper-plated comb structure was designed to study and evaluate different deep silicon via etch processes and its effect on the electrical leakage characteristics under various electrical and thermal stress conditions. It has been shown that the leakage current between the comb interconnect structures increases with an increase in sidewall roughness and that it can be significantly lowered by smoothening the sidewalls. It was also shown that by tailoring a non-BOSCH etch process with the normal BOSCH process, a similar leakage current reduction can be achieved. It was also shown through thermo-mechanical simulation studies that there is a clear correlation between high leakage current behavior due to non-uniform Ta barrier deposition over the rough sidewalls and the thermo-mechanical stress induced by post-TSV processes

Thermomechanical behaviour of boom clay

International Nuclear Information System (INIS)

Sultan, N.; Delage, P.; Cui, Y.J.

2000-01-01

Special attention has been recently paid on temperature effects on the behaviour of deep saturated clays, in relation with nuclear deep waste storage. However, few experimental data are presently available, and existing constitutive models need to be completed. This note is aimed at completing, both experimentally and theoretically, the understanding of the effects of the over-consolidation ration on the thermal volume changes of Boom clay (Belgium). The experimental data obtained here are in a good agreement with existing data. As a complement to existing data, they are used to develop a new elastoplastic model. The adoption of a second coupled plastic mechanism provides good simulations on a complex thermo-mechanical path. (authors)

Fatigue data compilation and evaluation of fatigue on design

International Nuclear Information System (INIS)

Nyilas, A.

1985-05-01

The aim of this report is a review of the available fatigue data of various materials necessary for the design of large superconducting magnets for fusion. One of the primary objectives of this work is to present a broad outline of the low temperature fatigue data of relevant materials within the scope of available data. Besides the classical fatigue data of materials the fatigue crack propagation measurements are outlined widely. The existing recommendations for the design of cryogenic structures are described. A brief introduction of fracture mechanics as well as a historical background of the development of our present day understanding of fatigue has been done. (orig.) [de

Thermo-mechanical behavior of retro-reflector and resulting parallelism error of laser beams for Wendelstein 7-X interferometer

International Nuclear Information System (INIS)

Peng, X.B.; Hirsch, M.; Köppen, M.; Fellinger, J.; Bykov, V.; Schauer, F.; Vliegenthart, W.

2014-01-01

Highlights: • The criterion for thermo-mechanical design of W7-X interferometer retro-reflector. • Thermo-mechanical analysis of retro-reflector with two different methods. • The most flexible part in the retro-reflector is spring washer. • Calculation of parallelism error between the incoming and reflected laser beams. • The parallelism error is much lower than the design limit 28 arcs. - Abstract: A 10 channels interferometer will be used in the Wendelstein 7-X (W7-X) for plasma density control and density profile tracking with laser beams passing through the plasma. Due to complex shape of non-planar modular coils and divertor structure, there are no large poloidally opposite ports on the plasma vessel (PV). Therefore 10 in-vessel Corner Cube Retro-reflectors (CCRs) will be used. The CCRs are integrated in the water cooled heat shield and exposed directly to thermal loads from plasma radiation. Thermo-mechanical issues are very important for the design of the CCR because deformation and flatness as well as mutual angles of the three reflecting surfaces would affect the parallelism of the laser beams and the functionality of the interferometer. Intensive work has been done to explore a suitable design for the CCR concerning thermo-mechanical behavior. Previous studies Ye et al. (2008, 2009) and Köppen et al. (2011) focused on structural optimization to decrease thermal stress in the reflecting plates under the thermal loads, and on computation and check of curvature radii of the deformed reflecting surfaces with the design criterion that the curvature radius must be bigger than 200 m. The paper presents detailed thermo-mechanical analysis of the current improved CCR under thermal loads and bolt preloads. The results of the thermo-mechanical analysis were used for the study of the resulting parallelism error of the laser beams with newly developed and more reasonable design criterion

Thermo-mechanical behavior of retro-reflector and resulting parallelism error of laser beams for Wendelstein 7-X interferometer

Energy Technology Data Exchange (ETDEWEB)

Peng, X.B., E-mail: pengxb@ipp.ac.cn [Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, 230031 Hefei Anhui (China); Max Planck Institute for Plasma Physics, EURATOM Association, Wendelsteinstr. 1, 17491 Greifswald (Germany); Hirsch, M.; Köppen, M.; Fellinger, J.; Bykov, V.; Schauer, F. [Max Planck Institute for Plasma Physics, EURATOM Association, Wendelsteinstr. 1, 17491 Greifswald (Germany); Vliegenthart, W. [TNO, Stieltjesweg 1, P.O. Box 2600, 2628 CK Delft (Netherlands)

2014-04-15

Highlights: • The criterion for thermo-mechanical design of W7-X interferometer retro-reflector. • Thermo-mechanical analysis of retro-reflector with two different methods. • The most flexible part in the retro-reflector is spring washer. • Calculation of parallelism error between the incoming and reflected laser beams. • The parallelism error is much lower than the design limit 28 arcs. - Abstract: A 10 channels interferometer will be used in the Wendelstein 7-X (W7-X) for plasma density control and density profile tracking with laser beams passing through the plasma. Due to complex shape of non-planar modular coils and divertor structure, there are no large poloidally opposite ports on the plasma vessel (PV). Therefore 10 in-vessel Corner Cube Retro-reflectors (CCRs) will be used. The CCRs are integrated in the water cooled heat shield and exposed directly to thermal loads from plasma radiation. Thermo-mechanical issues are very important for the design of the CCR because deformation and flatness as well as mutual angles of the three reflecting surfaces would affect the parallelism of the laser beams and the functionality of the interferometer. Intensive work has been done to explore a suitable design for the CCR concerning thermo-mechanical behavior. Previous studies Ye et al. (2008, 2009) and Köppen et al. (2011) focused on structural optimization to decrease thermal stress in the reflecting plates under the thermal loads, and on computation and check of curvature radii of the deformed reflecting surfaces with the design criterion that the curvature radius must be bigger than 200 m. The paper presents detailed thermo-mechanical analysis of the current improved CCR under thermal loads and bolt preloads. The results of the thermo-mechanical analysis were used for the study of the resulting parallelism error of the laser beams with newly developed and more reasonable design criterion.

Thermomechanical treatment of welded joints of aluminum-lithium alloys modified by scandium

Science.gov (United States)

Malikov, A. G.

2017-12-01

At present, the aeronautical equipment manufacture involves up-to-date high-strength aluminum alloys of decreased density resulting from the lithium admixture. Various technologies of fusible welding of these alloys are being developed. The paper presents experimental investigations of the optimization of the laser welding of aluminum alloys with the scandium-modified welded joint after thermomechanical treatment. The effect of scandium on the micro- and macrostructure is studied along with strength characteristics of the welded joint. It is found that thermomechanical treatment allows us to obtain the strength of the welded joint 0.89 for the Al-Mg-Li system and 0.99 for the Al-Cu-Li system with the welded joint modified by scandium in comparison with the base alloy after treatment.

Fatigue approach for addressing environmental effects in fatigue usage calculation

Energy Technology Data Exchange (ETDEWEB)

Wilhelm, Paul; Rudolph, Juergen [AREVA GmbH, Erlangen (Germany); Steinmann, Paul [Erlangen-Nuremberg Univ., erlangen (Germany). Chair of Applied Mechanics

2015-04-15

Laboratory tests consider simple trapezoidal, triangle, and sinusoidal signals. However, actual plant components are characterized by complex loading patterns and periods of holds. Fatigue tests in water environment show, that the damage from a realistic strain variation or the presence of hold-times within cyclic loading results in an environmental reduction factor (Fen) only half that of a simple waveform. This study proposes a new fatigue approach for addressing environmental effects in fatigue usage calculation for class 1 boiler and pressure vessel reactor components. The currently accepted method of fatigue assessment has been used as a base model and all cycles, which have been comparable with realistic fatigue tests, have been excluded from the code-based fatigue calculation and evaluated directly with the test data. The results presented show that the engineering approach can successfully be integrated in the code-based fatigue assessment. The cumulative usage factor can be reduced considerably.

Fatigue approach for addressing environmental effects in fatigue usage calculation

International Nuclear Information System (INIS)

Wilhelm, Paul; Rudolph, Juergen; Steinmann, Paul

2015-01-01

Laboratory tests consider simple trapezoidal, triangle, and sinusoidal signals. However, actual plant components are characterized by complex loading patterns and periods of holds. Fatigue tests in water environment show, that the damage from a realistic strain variation or the presence of hold-times within cyclic loading results in an environmental reduction factor (Fen) only half that of a simple waveform. This study proposes a new fatigue approach for addressing environmental effects in fatigue usage calculation for class 1 boiler and pressure vessel reactor components. The currently accepted method of fatigue assessment has been used as a base model and all cycles, which have been comparable with realistic fatigue tests, have been excluded from the code-based fatigue calculation and evaluated directly with the test data. The results presented show that the engineering approach can successfully be integrated in the code-based fatigue assessment. The cumulative usage factor can be reduced considerably.

Application of an enriched FEM technique in thermo-mechanical contact problems

Science.gov (United States)

Khoei, A. R.; Bahmani, B.

2018-02-01

In this paper, an enriched FEM technique is employed for thermo-mechanical contact problem based on the extended finite element method. A fully coupled thermo-mechanical contact formulation is presented in the framework of X-FEM technique that takes into account the deformable continuum mechanics and the transient heat transfer analysis. The Coulomb frictional law is applied for the mechanical contact problem and a pressure dependent thermal contact model is employed through an explicit formulation in the weak form of X-FEM method. The equilibrium equations are discretized by the Newmark time splitting method and the final set of non-linear equations are solved based on the Newton-Raphson method using a staggered algorithm. Finally, in order to illustrate the capability of the proposed computational model several numerical examples are solved and the results are compared with those reported in literature.

Predictors and Trajectories of Morning Fatigue Are Distinct from Evening Fatigue

Science.gov (United States)

Wright, Fay; Melkus, Gail D’Eramo; Hammer, Marilyn; Schmidt, Brian L.; Knobf, M. Tish; Paul, Steven M.; Cartwright, Frances; Mastick, Judy; Cooper, Bruce A.; Chen, Lee-May; Melisko, Michelle; Levine, Jon D.; Kober, Kord; Aouizerat, Bradley E.; Miaskowski, Christine

2015-01-01

Context Fatigue is the most common symptom in oncology patients during chemotherapy (CTX). Little is known about the predictors of interindividual variability in initial levels and trajectories of morning fatigue severity in these patients. Objectives An evaluation was done to determine which demographic, clinical, and symptom characteristics were associated with initial levels as well as the trajectories of morning fatigue and to compare findings with our companion paper on evening fatigue. Methods A sample of outpatients with breast, gastrointestinal, gynecological, and lung cancer (N=586) completed demographic and symptom questionnaires a total of six times over two cycles of CTX. Fatigue severity was evaluated using the Lee Fatigue Scale. Hierarchical linear modeling (HLM) was used to answer the study objectives. Results A large amount of interindividual variability was found in the morning fatigue trajectories. A piecewise model fit the data best. Patients with higher body mass index (BMI), who did not exercise regularly, with a lower functional status, and who had higher levels of state anxiety, sleep disturbance and depressive symptoms, reported higher levels of morning fatigue at enrollment. Variations in the trajectories of morning fatigue were predicted by the patients’ ethnicity and younger age. Conclusion The modifiable risk factors that were associated with only morning fatigue were BMI, exercise, and state anxiety. Modifiable risk factors that were associated with both morning and evening fatigue included functional status, depressive symptoms, and sleep disturbance. Using this information, clinicians can identify patients at higher risk for more severe morning fatigue and evening fatigue, provide individualized patient education, and tailor interventions to address the modifiable risk factors. PMID:25828559

Thermomechanical and Environmental Durability of Environmental Barrier Coated Ceramic Matrix Composites Under Thermal Gradients

Science.gov (United States)

Zhu, Dongming; Bhatt, Ramakrishna T.; Harder, Bryan

2016-01-01

This paper presents the developments of thermo-mechanical testing approaches and durability performance of environmental barrier coatings (EBCs) and EBC coated SiCSiC ceramic matrix composites (CMCs). Critical testing aspects of the CMCs will be described, including state of the art instrumentations such as temperature, thermal gradient, and full field strain measurements; materials thermal conductivity evolutions and thermal stress resistance; NDE methods; thermo-mechanical stress and environment interactions associated damage accumulations. Examples are also given for testing ceramic matrix composite sub-elements and small airfoils to help better understand the critical and complex CMC and EBC properties in engine relevant testing environments.

Thermomechanical behavior of tin-rich (lead-free) solders

Science.gov (United States)

Sidhu, Rajen Singh

In order to adequately characterize the behavior of ball-grid-array (BGA) Pb-free solder spheres in electronic devices, the microstructure and thermomechanical behavior need to be studied. Microstructure characterization of pure Sn, Sn-0.7Cu, Sn-3.5Ag, and Sn-3.9Ag-0.7Cu alloys was conducted using optical microscopy, scanning electron microscopy, transmission electron microscopy, image analysis, and a novel serial sectioning 3D reconstruction process. Microstructure-based finite-element method (FEM) modeling of deformation in Sn-3.5Ag alloy was conducted, and it will be shown that this technique is more accurate when compared to traditional unit cell models for simulating and understanding material behavior. The effect of cooling rate on microstructure and creep behavior of bulk Sn-rich solders was studied. The creep behavior was evaluated at 25, 95, and 120°C. Faster cooling rates were found to increase the creep strength of the solders due to refinement of the solder microstructure. The creep behavior of Sn-rich single solder spheres reflowed on Cu substrates was studied at 25, 60, 95, and 130°C. Testing was conducted using a microforce testing system, with lap-shear geometry samples. The solder joints displayed two distinct creep behaviors: (a) precipitation-strengthening (Sn-3.5Ag and Sn-3.9Ag-0.7Cu) and (b) power law creep accommodated by grain boundary sliding (GBS) (Sn and Sn-0.7Cu). The relationship between microstructural features (i.e. intermetallic particle size and spacing), stress exponents, threshold stress, and activation energies are discussed. The relationship between small-length scale creep behavior and bulk behavior is also addressed. To better understand the damage evolution in Sn-rich solder joints during thermal fatigue, the local damage will be correlated to the cyclic hysteresis behavior and crystal orientations present in the Sn phase of solder joints. FEM modeling will also be utilized to better understand the macroscopic and local

Blanket Manufacturing Technologies : Thermomechanical Tests on HCLL Blanket Mocks Up

International Nuclear Information System (INIS)

Laffont, G.; Cachon, L.; Taraud, P.; Challet, F.; Rampal, G.; Salavy, J.F.

2006-01-01

In the Helium Cooled Lithium Lead (HCLL) Blanket concept, the lithium lead plays the double role of breeder and multiplier material, and the helium is used as coolant. The HCCL Blanket Module are made of steel boxes reinforced by stiffening plates. These stiffening plates form cells in which the breeder is slowly flowing. The power deposited in the breeder material is recovered by the breeder cooling units constituted by 5 parallel cooling plates. All the structures such as first wall, stiffening and cooling plates are cooled by helium. Due to the complex geometry of these parts and the high level of pressure and temperature loading, thermo-mechanical phenomena expected in the '' HCLL blanket concept '' have motivated the present study. The aim of this study, carried out in the frame of EFDA Work program, is to validate the manufacturing technologies of HCLL blanket module by testing small scale mock-up under breeder blanket representative operating conditions.The first step of this experimental program is the design and manufacturing of a relevant test section in the DIADEMO facility, which was recently upgraded with an He cooling loop (pressure of 80 bar, maximum temperature of 500 o C,flow rate of 30 g/s) taking the opportunity of synergies with the gas-cooled fission reactor R-and-D program. The second step will deal with the thermo-mechanical tests. This paper focuses on the program made to support the cooling plate mock up tests which will be carried out on the DIADEMO facility (CEA) by thermo-mechanical calculations in order to define the relevant test conditions and the experimental parameters to be monitored. (author)

SI:FatiguePro 4 Advanced Approach for Fatigue Monitoring

International Nuclear Information System (INIS)

Evon, Keith; Gilman, Tim; Carney, Curt

2012-01-01

Many nuclear plants are making commitments to implement fatigue monitoring systems in support of license renewal. Current fatigue monitoring systems use the methodology of ASME Code Subarticle NB-3200, which is a design code intended to compute a bounding cumulative usage factor (CUF). The first generation of fatigue monitoring software utilized a simplified, single stress term assumption and classical stress cycle-counting methods that take order into account such as Rainflow or Ordered Overall Range counting. Recently, the NRC has indicated in Regulatory Issue Summary 2008-30 that any fatigue analyses in support of License Renewal should use ASME Code Section III methodologies considering all six stress components. In addition, fatigue calculations for the license renewal term are required to consider the effects of environment. The implementation of a six stress term NB-3200 fatigue calculation to a Boiling Water Reactor (BWR) feedwater nozzle, including environmental effects, is the topic of this paper. Differences in results between the advanced methodology and the simplified methodology are discussed. (author)

Development of ultrafine ferritic sheaves/plates in SAE 52100 steel for enhancement of strength by controlled thermomechanical processing

Energy Technology Data Exchange (ETDEWEB)

Chakraborty, J. [Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Kharagpur, W.B. 721 302 (India); Scientific Services and Research and Development, Tata Steel, Jamshedpur 831 001, Jharkhand (India); Manna, I., E-mail: imanna@metal.iitkgp.ernet.in [Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Kharagpur, W.B. 721 302 (India); Central Glass and Ceramic Research Institute (CGCRI), Council of Scientific and Industrial Research (CSIR), 196 Raja S C Mullick Road, Jadavpur, Kolkata 700032 (India)

2012-06-30

Highlights: Black-Right-Pointing-Pointer Ultrafine bainite + martensite duplex microstructure developed in SAE 52100 steel. Black-Right-Pointing-Pointer Thermomechanical processing modifies size + morphology of bainitic ferrite. Black-Right-Pointing-Pointer Processing involves hot deformation prior to/during/after austenitizing. Black-Right-Pointing-Pointer Significant improvement in mechanical strength achieved. Black-Right-Pointing-Pointer Similar study on high carbon, low alloy steel not reported in the literature. - Abstract: The present study attempts to tailor the size, morphology and distribution of the ferrite needles/sheaves by thermomechanical processing and develop an ultrafine ferrite + martensite duplex microstructure for enhancement of strength and toughness in SAE 52100 steel. The thermo-mechanical routine included 5% hot deformation before, during or after austenitizing at 950 Degree-Sign C for 15 min followed by austempering at 270 Degree-Sign C for 30 min and subsequent water quenching to room temperature. Optical/electron microscopy along with X-ray diffraction was used to quantitatively monitor the size, morphology and distribution of the phase or phase aggregate. Significant improvement in nanohardness, wear resistance and elastic modulus and was observed in samples subjected to thermomechanical processing, as compared to that following the same austenitizing and austempering routine without hot deformation at any stage. However, improvement in the bulk mechanical property due to the present thermo-mechanical is lower than that obtained in our earlier study comprising cold deformation prior to austenitizing and austempering.

Are nurses able to assess fatigue, exertion fatigue and types of fatigue in residential home patients?

NARCIS (Netherlands)

Tiesinga, L.J.; Dijkstra, Ate; Dassen, T.W.N.; Halfens, R.J.G.; van den Heuvel, W.J.A.

Although fatigue is recognized as a subjective, generalized, extensive and disabling health care problem with a relatively high prevalence among the chronically ill, there have been no studies to show whether nurses caring for fatigued subjects are able to accurately assess the level of fatigue that

Thermomechanical cycling and two-way memory effect induced in Cu-Zn-Al

International Nuclear Information System (INIS)

Pons, J.

1999-01-01

The two-way shape memory effect (TWME) has been induced by thermomechanical cycling in Cu-Zn-Al alloys using a dedicated hydraulic mechanical testing soft machine with complete computer control of force, elongation and temperature. The results concerning single crystals (composition Cu-16.9 wt.% Zn-7.7 wt.% Al, nominal M s of 273 K) and polycrystals (Cu-15.8 wt.% Zn-8.3 wt.% Al, nominal M s of 230 K, mean grain size of 1 mm) are reported for two training protocols (sequence of one thermomechanical cycle of education followed by one stress free thermal cycle to check the TWME or twenty consecutive thermomechanical cycles followed by one or two checking thermal cycles). The capacity of the trained specimen for producing work under an antagonist compressive stress is also studied and the behaviour of the deformation of the specimen under such a condition at different temperatures is analysed in terms of a competition between the contributions of the different variants: trained variants with an intrinsic deformation in the direction of the tensile stress of the training process, trained variants with an intrinsic deformation which is not well orientated with respect to this direction (in the polycrystal) and new variants with an intrinsic deformation in the direction of the compressive stress which can replace the educated variants. (orig.)

Non-destructive thermo-mechanical behavior assessment of glass-ceramics for dental applications

Science.gov (United States)

Kordatos, E. Z.; Abdulkadhim, Z.; Feteira, A. M.

2017-05-01

Every year millions of people seek dental treatment to either repair damaged, unaesthetic and dysfunctional teeth or replace missing natural teeth. Several dental materials have been developed to meet the stringent requirements in terms of mechanical properties, aesthetics and chemical durability in the oral environment. Glass-ceramics exhibit a suitable combination of these properties for dental restorations. This research is focused on the assessment of the thermomechanical behavior of bio-ceramics and particularly lithium aluminosilicate glass-ceramics (LAS glass-ceramics). Specifically, methodologies based on Infrared Thermography (IRT) have been applied in order the structure - property relationship to be evaluated. Non-crystallized, partially crystallized and fully crystallized glass-ceramic samples have been non-destructively assessed in order their thermo-mechanical behavior to be associated with their micro-structural features.

Chronic Fatigue Syndrome (CFS) and Cancer Related Fatigue (CRF): two "fatigue" syndromes with overlapping symptoms and possibly related aetiologies.

Science.gov (United States)

Rovigatti, Ugo

2012-12-01

In July 2010, at the Muscle Fatigue Meeting, I presented an overview of Chronic Fatigue Syndrome and Cancer Related Fatigue, emphasizing a critical interpretation of the potential association between Chronic Fatigue Syndrome and Cancer Related Fatigue and a newly discovered retrovirus: Xenotropic Murine Related Virus. Since this association was hotly debated at that time, I suggested at the Meeting that it was wrong and most likely due to the identification of the wrong virus culprit. Today, 20 months after the Meeting, the first part of our prediction has turned out to be correct, as Xenotropic Murine Related Virus was shown to be a laboratory-created artefact. Still, the potential association of fatigue-syndromes with an infection (most likely viral) is sustained by a plethora of evidence and this overview will initially summarize data suggesting prior viral infection(s). The principal hypothesized mechanisms for both peripheral and central Chronic Fatigue Syndrome/Cancer Related Fatigue will be then summarized, also indicating plausible associations and triggering factors. All evidence accrued so far suggests that further research work should be performed in this interesting area and in order to identify an infectious agent for Chronic Fatigue Syndrome/Cancer Related Fatigue. One candidate RNA virus, Micro-Foci inducing Virus, will be described in this overview. Copyright © 2012 Elsevier B.V. All rights reserved.

Fatigue in adults with post-infectious fatigue syndrome: a qualitative content analysis.

Science.gov (United States)

Stormorken, Eva; Jason, Leonard A; Kirkevold, Marit

2015-01-01

Fatigue is a major problem among individuals with post-infectious fatigue syndrome (PIFS), also known as chronic fatigue syndrome or myalgic encephalomyelitis. It is a complex phenomenon that varies across illnesses. From a nursing perspective, knowledge and understanding of fatigue in this illness is limited. Nurses lack confidence in caring for these patients and devalue their professional role. The aim of this study was to explore in-depth the experiences of fatigue among individuals with PIFS. A detailed description of the phenomenon of fatigue is presented. Increased knowledge would likely contribute to more confident nurses and improved nursing care. A qualitative study with open interviews was employed. In-depth interviews with patients were fully transcribed and underwent a qualitative content analysis. A maximum variation sample of 26 affected adults between 26-59 years old was recruited from a population diagnosed at a fatigue outpatient clinic. The fatigue was a post-exertional, multidimensional, fluctuating phenomenon with varying degrees of severity and several distinct characteristics and was accompanied by concomitant symptoms. Fatigue was perceived to be an all-pervasive complex experience that substantially reduced the ability to function personally or professionally. A range of trigger mechanisms evoked or worsened the fatigue, but the affected were not always aware of what triggered it. There was an excessive increase in fatigue in response to even minor activities. An increase in fatigue resulted in the exacerbation of other concomitant symptoms. The term fatigue does not capture the participants' experiences, which are accompanied by a considerable symptom burden that contributes to the illness experience and the severe disability. Although some aspects of the fatigue experience have been reported previously, more were added in our study, such as the dimension of awakening fatigue and the characteristic beyond time, when time passes unnoticed

Study on the effect of prior fatigue and creep-fatigue damage on the fatigue and creep characteristics of 316 FR stainless steel. 2nd report. The effect of prior creep-fatigue damage on the creep and fatigue characteristics

International Nuclear Information System (INIS)

Yamauchi, Masafumi; Chuman, Yasuharu; Otani, Tomomi; Takahashi, Yukio

2001-01-01

The effect of prior creep-fatigue damage on the creep and the fatigue characteristics was studied to investigate the creep-fatigue life evaluation procedure of 316FR stainless steel. Creep and fatigue tests were conducted at 550degC by using the specimen exposed to prior creep-fatigue cycles at the same temperature and interrupted at 1/4 Nf, 1/2 Nf and 3/4 Nf cycle. The creep and fatigue strength of the pre-damaged material showed monotonic reduction with the prior creep-fatigue damage compared with the virgin material. The creep ductility also showed monotonic reduction with the prior creep-fatigue damage. These results were evaluated by the stress-based Time Fraction Rule and the strain-based Ductility Exhaustion Method. The result showed that the application of the Ductility Exhaustion Method to the creep-fatigue damage evaluation is more promising than the Time Fraction Rule. (author)

Seafarer fatigue

DEFF Research Database (Denmark)

Jepsen, Jørgen Riis; Zhao, Zhiwei; van Leeuwen, Wessel M. A.

2015-01-01

Background: The consequences of fatigue for the health and safety of seafarers has caused concern in the industry and among academics, and indicates the importance of further research into risk factors and preventive interventions at sea. This review gives an overview of the key issues relating...... to seafarer fatigue. Materials and methods: A literature study was conducted aiming to collect publications that address risk factors for fatigue, short-term and long-term consequences for health and safety, and options for fatigue mitigation at sea. Due to the limited number of publications that deals...... with seafarers, experiences from other populations sharing the same exposures (e.g. shift work) were also included when appropriate. Results: Work at sea involves multiple risk factors for fatigue, which in addition to acute effects (e.g., impaired cognition, accidents) contributes through autonomic, immunologic...

Thermomechanical interactions of particle bed-structural wall in a layered configuration. Pt. 1. Effect of particle bed thermal expansions

International Nuclear Information System (INIS)

Tehranian, F.

1995-01-01

Materials in the form of particle beds have been considered for shielding and tritium breeding as well as neutron multiplication in many of the conceptual reactor design studies. As the level of effort of the fusion blanket community in the area of out-of-pile and in-pile (ITER) testing of integrated test modules increases, so does the need for modelling capability for predicting the thermomechanical responses of the test modules under reactor environment.In this study, the thermomechanical responses of a particle bed-structural wall system in a layered configuration, subjected to bed temperature rise and/or external coolant pressure, were considered. Equations were derived which represent the dependence of the particle-to-particle and particle-to-wall contact forces and areas on the structural wall deformations and in turn on the thermomechanical loads. Using the derived equations, parametric analyses were performed to study the variations in the thermomechanical response quantities of a beryllium particle bed-stainless steel structural wall when subjected to thermomechanical loads. The results are presented in two parts. In Part I, presented in this paper, the derivation of the analytical equations and the effects of bed temperature rise are discussed. In Part II of this study, also presented in this symposium, the effects of external coolant pressure as well as the combined effects of bed temperature rise and coolant pressure on the thermomechanical responses are given.It is shown that, depending on the stiffness of the structural walls, uniform bed temperature rises in the range 100-400 C result in non-uniform effective thermal properties through the prticle bed and could increase the bed effective thermal conductivity by a factor of 2-5 and the bed-wall interface thermal conductance by even a larger factor. (orig.)

Thermomechanical Behavior of Monolithic SN-AG-CU Solder and Copper Fiber Reinforced Solders

National Research Council Canada - National Science Library

Reuse, Rolando

2005-01-01

.... The thermomechanical cycling in the solder causes numerous reliability challenges, mostly because of the mismatch of the coefficient of thermal expansion between the silicon chip and the substrate...

Surface finishing and levelling of thermomechanically hardened rolled steel

International Nuclear Information System (INIS)

Grosval'd, V.G.; Bashchenko, A.P.; Grishkov, A.I.; Gutnik, M.V.; Kanevskij, B.L.; Nikozov, A.I.; Sedov, N.D.; Prosin, K.A.; Safonov, L.I.

1975-01-01

The finishing of high-strength merchant shapes from alloy steel was tried out under industrial conditions with the equipment of metallurgical plants. After thermomechanical hardening in the production line of the rolling mill, 30KhGSN2A and 40Kh1NVA steel rounds 32 and 31 mm in diameter were straightened on a two-roller straightening machine designed by the All-Union Scientific Research Institute for Metallurgical Machinery (VNII Metmash). This made possible subsequent turning and grinding of the rods. The conditions of straightening, turning and grinding have been worked so as to obtain thermomechanically strengthened and ground rolled products approximating the gauged and ground metal in shape geometry and surface finish. It is shown that the labour-consuming operation of turning can be eliminated by reducing the machining pass of the rolled product, and this lowers the labour required for the finishing operations by 75%. After grinding with 40- and 25-grain abrasive wheels, high strength rolled shapes were obtained with a diameter of 30-0.20 mm and a surface finish of class 6-5 satisfying the technical specifications. (author)

Damage and fatigue crack growth of Eurofer steel first wall mock-up under cyclic heat flux loads. Part 1: Electron beam irradiation tests

Energy Technology Data Exchange (ETDEWEB)

You, J.H., E-mail: you@ipp.mpg.de [Max-Planck-Institut für Plasmaphysik, Euratom Association, Boltzmannstr. 2, 85748 Garching (Germany); Höschen, T. [Max-Planck-Institut für Plasmaphysik, Euratom Association, Boltzmannstr. 2, 85748 Garching (Germany); Pintsuk, G. [Forschungszentrum Jülich GmbH, IEK2, Euratom Association, 52425 Jülich (Germany)

2014-04-15

Highlights: • Clear evidence of microscopic damage and crack formation at the notch root in the early stage of the fatigue loading (50–100 load cycles). • Propagation of fatigue crack at the notch root in the course of subsequent cyclic heat-flux loading followed by saturation after roughly 600 load cycles. • No sign of damage on the notch-free surface up to 800 load cycles. • No obvious effect of the pulse time duration on the crack extension. • Slight change in the grain microstructure due to the formation of sub-grain boundaries by plastic deformation. - Abstract: Recently, the idea of bare steel first wall (FW) is drawing attention, where the surface of the steel is to be directly exposed to high heat flux loads. Hence, the thermo-mechanical impacts on the bare steel FW will be different from those of the tungsten-coated one. There are several previous works on the thermal fatigue tests of bare steel FW made of austenitic steel with regard to the ITER application. In the case of reduced-activation steel Eurofer97, a candidate structural material for the DEMO FW, there is no report on high heat flux tests yet. The aim of the present study is to investigate the thermal fatigue behavior of the Eurofer-based bare steel FW under cyclic heat flux loads relevant to DEMO operation. To this end, we conducted a series of electron beam irradiation tests with heat flux load of 3.5 MW/m{sup 2} on water-cooled mock-ups with an engraved thin notch on the surface. It was found that the notch root region exhibited a marked development of damage and fatigue cracks whereas the notch-free surface manifested no sign of crack formation up to 800 load cycles. Results of extensive microscopic investigation are reported.

Thermo-mechanical design of the extraction grids for RF negative ion source at HUST

Energy Technology Data Exchange (ETDEWEB)

Zuo, Chen; Liu, Kaifeng, E-mail: kfliuhust@hust.edu.cn; Li, Dong; Mei, Zhiyuan; Zhang, Zhe; Chen, Dezhi

2017-01-15

Highlights: • An extraction system with cooling channels has been designed for HUST negative ion source. • Corresponding heat loads onto three grids has been used in thermo-mechanical analysis. • The analysis results could be very useful for driving the engineering design. - Abstract: Huazhong University of Science and Technology (HUST) is developing a small radio frequency negative ion source experimental setup to promote research on neutral beam injection ion sources. The extraction system for the negative ion source is the key component to obtain the negative ions. The extraction system is composed of three grids: the plasma grid, the extraction grid and the grounded grid. Each grid is impacted by different heat loads. As the grids have to fulfil specific requirements regarding ion extraction, beam optics, and thermo-mechanical issues, grid cooling systems have been included for ensuring reliable operation. This paper focuses on the thermo-hydraulic and thermo-mechanical design of the grids. Finite element calculations have been carried out to analyse the temperature and deformation of the grids under heat loads using the fluid dynamics code CFX. Based on these results, the cooling circuit design and cooling parameters are optimised to satisfy the grid requirements.

Preliminary AD-Horn Thermomechanical and Electrodynamic Simulations

CERN Document Server

AUTHOR|(CDS)2095747; Horvath, David; Calviani, Marco

2016-01-01

As part of the Antiproton Decelerator (AD) target area consolidation activities planned for LS2, it has been necessary to perform a comprehensive study of the thermo-structural behaviour of the AD magnetic horn during operation, in order to detail specific requirements for the upgrade projects and testing procedures. The present work illustrates the preliminary results of the finite element analysis carried out to evaluate the thermal and structural behaviour of the device, as well as the methodology used to model and solve the thermomechanical and electrodynamic simulations performed in the AD magnetic horn.

Fatigue processes in thermoplastic fibres; Les mecanismes de fatigue dans les fibres thermoplastiques

Energy Technology Data Exchange (ETDEWEB)

Herrera Ramirez, J.M.

2004-09-15

The present study examines and compares the behaviour of the two types of PA66 fibres and two types of PET fibres under fatigue loading up to failure, and the correlation between the fibres (nano)structures and their structural heterogeneities, with fatigue lifetimes. Several techniques have been used to analyze the materials, such as scanning electron microscopy (SEM), microanalysis (EDS), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and micro-Raman spectroscopy. A meticulous analysis by scanning electron microscopy of the fracture morphology of fibres broken in tension and in fatigue, as well as a study of the fatigue life, were undertaken. The fatigue process occurs when the cyclic load amplitude is sufficiently large, however a condition for fatigue failure is that the minimum load each cycle must be lower than a threshold stress level. Failure under fatigue conditions leads to distinctive fracture morphologies which are very different from those seen after tensile or creep failure and this allows easy identification of the fatigue process. The fibres have been analyzed in the as received state and after fatigue failure in order to observe the microstructural changes resulting from the fatigue loading. The results will be compared with those obtained for fibres loaded under conditions where the fatigue process was hindered. The role of the microstructure of the fibres in determining fatigue will be discussed in this work and the possibility of improving their resistance to fatigue or eliminating the fatigue process will be discussed. (author)

A Thermomechanical Transport Approach and Application in Soil-Water System of Polluted Mining Areas considering the Three-Phase Coupling

Directory of Open Access Journals (Sweden)

Xuan Guo

2016-01-01

Full Text Available The thermomechanical transport approach includes the process of diffusing or the condition of being diffused, absorption/desorption, swell/shrink, equilibrium/nonequilibrium, and thermomechanical transport of contaminant in three phases of polluted mining soil which are discussed. The thermomechanical transport model of the contaminants transport in polluted soil is established, and its basic equations are given. Based on that, the distribution regularities of the contaminant seepage in water-soil system are discussed in detail and the sensitivities of parameters are analyzed. The study shows that the parameter has important influence on the contamination distribution and transportation in polluted soil-water system. The influence degree is also related to the action of seepage force directly.

Thermal and thermo-mechanical behavior of butyl based rubber exposed to silicon oil at elevated temperature

International Nuclear Information System (INIS)

Ali, S.; Ramzan, S.; Raza, R.; Ahmed, F.; Hussain, R.; Ullah, S.; Ali, S.

2013-01-01

Silica reinforced rubbers are used as chemical resistant seals at high temperature. In this study the effect of alkali and silicon oil on the thermal and thermo-mechanical properties of the silica reinforced butyl rubber exposed as an interface between two liquid media at elevated temperature is investigated. Rubber bladder containing alkaline solution was immersed in silicon oil at 195+-5 degree C for multiple cycles and loss in its thermal, thermo-mechanical and mechanical properties were studied by TGA, DMA and Tinius Olsen Testing Machine supported by FTIR and Optical microscopy. It was observed that the thermal and thermo-mechanical properties of butyl rubber were negatively affected due to leaching out of silica filler embedded in an organic matrix at elevated temperature. The thermal stability of exposed rubber was decreased around 200 degree C and the loss of storage modulus was observed up to 99.5% at -59 degree C. (author)

The role of central and peripheral muscle fatigue in postcancer fatigue: a randomized controlled trial.

Science.gov (United States)

Prinsen, Hetty; van Dijk, Johannes P; Zwarts, Machiel J; Leer, Jan Willem H; Bleijenberg, Gijs; van Laarhoven, Hanneke W M

2015-02-01

Postcancer fatigue is a frequently occurring problem, impairing quality of life. Little is known about (neuro)physiological factors determining postcancer fatigue. It may be hypothesized that postcancer fatigue is characterized by low peripheral muscle fatigue and high central muscle fatigue. The aims of this study were to examine whether central and peripheral muscle fatigue differ between fatigued and non-fatigued cancer survivors and to examine the effect of cognitive behavioral therapy (CBT) on peripheral and central muscle fatigue of fatigued cancer survivors in a randomized controlled trial. Sixteen fatigued patients in the intervention group (CBT) and eight fatigued patients in the waiting list group were successfully assessed at baseline and six months later. Baseline measurements of 20 fatigued patients were compared with 20 non-fatigued patients. A twitch interpolation technique and surface electromyography were applied, respectively, during sustained contraction of the biceps brachii muscle. Muscle fiber conduction velocity (MFCV) and central activation failure (CAF) were not significantly different between fatigued and non-fatigued patients. Change scores of MFCV and CAF were not significantly different between patients in the CBT and waiting list groups. Patients in the CBT group reported a significantly larger decrease in fatigue scores than patients in the waiting list group. Postcancer fatigue is neither characterized by abnormally high central muscle fatigue nor by low peripheral muscle fatigue. These findings suggest a difference in the underlying physiological mechanism of postcancer fatigue vs. other fatigue syndromes. Copyright © 2015 American Academy of Hospice and Palliative Medicine. Published by Elsevier Inc. All rights reserved.

Side Effects: Fatigue

Science.gov (United States)

Fatigue is a common side effect of many cancer treatments such as chemotherapy, radiation therapy, immunotherapy, and surgery. Anemia and pain can also cause fatigue. Learn about symptoms and way to manage fatigue.

Myoelectrical manifestation of fatigue less prominent in patients with cancer related fatigue.

Directory of Open Access Journals (Sweden)

Katarzyna Kisiel-Sajewicz

Full Text Available PURPOSE: A lack of fatigue-related muscle contractile property changes at time of perceived physical exhaustion and greater central than peripheral fatigue detected by twitch interpolation technique have recently been reported in cancer survivors with fatigue symptoms. Based on these observations, it was hypothesized that compared to healthy people, myoelectrical manifestation of fatigue in the performing muscles would be less significant in these individuals while sustaining a prolonged motor task to self-perceived exhaustion (SPE since their central fatigue was more prominent. The purpose of this study was to test this hypothesis by examining electromyographic (EMG signal changes during fatiguing muscle performance. METHODS: Twelve individuals who had advanced solid cancer and cancer-related fatigue (CRF, and 12 age- and gender-matched healthy controls performed a sustained elbow flexion at 30% maximal voluntary contraction till SPE. Amplitude and mean power frequency (MPF of EMG signals of the biceps brachii, brachioradialis, and triceps brachii muscles were evaluated when the individuals experienced minimal, moderate, and severe fatigue. RESULTS: CRF patients perceived physical "exhaustion" significantly sooner than the controls. The myoelectrical manifestation of muscular fatigue assessed by EMG amplitude and MPF was less significant in CRF than controls. The lower MPF even at minimal fatigue stage in CRF may indicate pathophysiologic condition of the muscle. CONCLUSIONS: CRF patients experience less myoelectrical manifestation of muscle fatigue than healthy individuals near the time of SPE. The data suggest that central nervous system fatigue plays a more important role in limiting endurance-type of motor performance in patients with CRF.

On the fatigue behavior of friction stir welded AlSi 10 Mg alloy

Directory of Open Access Journals (Sweden)

Ramos, R. A.

2005-04-01

Full Text Available The high cycle fatigue behavior of friction stir welded AlSi10Mg samples was investigated for a stress ratio R = 0.1, ranging from 0.5 to 0.9 of the yield strength, in addition to tensile tests. The welds were produced with different tool rotation and travel speeds, and these welding parameters were correlated to residual stresses, measured by X-Ray diffraction (sen² ψmethod. Moreover, the residual stresses were measured during the fatigue testing, at fixed cycle intervals, being reported. It was observed that the residual (compressive stresses within the nugget were smaller than in the interface regions (between the thermomechanically affected zone and the base metal and stabilized above 4x10⁵ cycles. Fatigue crack morphology and microstructural changes were characterized by optical and electron microscopy and the observations are discussed along with the fatigue results.

Se estudia el comportamiento a la fatiga de alto ciclo de muestras de AlSi10Mg soldadas por fricción lineal para relación de tensión R = 0,1 cubriendo el rango de 0,5 a 0,9 de la resistencia a tracción, además de los datos del ensayo de tracción. Las soldaduras ensayadas fueron producidas con diferentes velocidades de rotación y avance de la herramienta. Las variables de proceso han sido correlacionadas con el análisis de tensiones residuales por difracción de Rayos X (método sen² ψ. Además, se midieron las tensiones residuales durante la deformación en fatiga a intervalos regulares de ciclos. Se observa que las tensiones residuales (de compresión dentro del nugget son más reducidas que en la interfase entre la región afectada térmica y mecánicamente y el material base, y se mantuvieron estables de manera progresiva a partir de los 4 x 10 ⁵ciclos. Se ha empleado la microscopía óptica y de barrido para evaluar la morfología y microestructura de las grietas de fatiga. Estos resultados se analizan

Effect of Nb2O5 doping on improving the thermo-mechanical stability of sealing interfaces for solid oxide fuel cells.

Science.gov (United States)

Zhang, Qi; Du, Xinhang; Tan, Shengwei; Tang, Dian; Chen, Kongfa; Zhang, Teng

2017-07-13

Nb 2 O 5 is added to a borosilicate sealing system to improve the thermo-mechanical stability of the sealing interface between the glass and Fe-Cr metallic interconnect (Crofer 22APU) in solid oxide fuel cells (SOFCs). The thermo-mechanical stability of the glass/metal interface is evaluated experimentally as well as by using a finite element analysis (FEA) method. The sealing glass doped with 4 mol.% Nb 2 O 5 shows the best thermo-mechanical stability, and the sealing couple of Crofer 22APU/glass/GDC (Gd 0.2 Ce 0.8 O 1.9 ) remains intact after 50 thermal cycles. In addition, all sealing couples show good joining after being held at 750 °C for 1000 h. Moreover, the possible mechanism on the thermo-mechanical stability of sealing interface is investigated in terms of stress-based and energy-based perspectives.

A randomized controlled trial of qigong exercise on fatigue symptoms, functioning, and telomerase activity in persons with chronic fatigue or chronic fatigue syndrome.

Science.gov (United States)

Ho, Rainbow T H; Chan, Jessie S M; Wang, Chong-Wen; Lau, Benson W M; So, Kwok Fai; Yuen, Li Ping; Sham, Jonathan S T; Chan, Cecilia L W

2012-10-01

Chronic fatigue is common in the general population. Complementary therapies are often used by patients with chronic fatigue or chronic fatigue syndrome to manage their symptoms. This study aimed to assess the effect of a 4-month qigong intervention program among patients with chronic fatigue or chronic fatigue syndrome. Sixty-four participants were randomly assigned to either an intervention group or a wait list control group. Outcome measures included fatigue symptoms, physical functioning, mental functioning, and telomerase activity. Fatigue symptoms and mental functioning were significantly improved in the qigong group compared to controls. Telomerase activity increased in the qigong group from 0.102 to 0.178 arbitrary units (p chronic fatigue and chronic fatigue syndrome.

Thermo-mechanical response of rigid plastic laminates for greenhouse covering

Directory of Open Access Journals (Sweden)

Silvana Fuina

2016-09-01

Full Text Available Innovation in the field of protected crops represents an argument of great applied and theoretical research attention due to constantly evolving technologies and automation for higher quality flower and vegetable production and to the corresponding environmental and economic impact. The aim of this paper is to provide an analysis of some thermomechanical properties of rigid polymeric laminates for greenhouses claddings, including innovative tests such as the thermographic ones. Four types of laminates have been analysed: two polycarbonates, a polymethylmethacrylate and a polyethylene terephthalate (PET. The tests gave interesting results on different important properties, such as radiometric properties, limit stresses, strains and ductility. Moreover, a direct comparison of infrared images and force elongation curves gave important information on the relation of the (localised or homogeneous damage evolution, with both an applicative and theoretical implication. Finally, even if to the authors knowledge at present there are no examples of using PET for covering greenhouses, the results of this paper indicates the thermomechanical and radiometric characteristics of this material make it interesting for agricultural applications.

Thermo-mechanical analysis of RMP coil system for EAST tokamak

International Nuclear Information System (INIS)

Wang, Songke; Ji, Xiang; Song, Yuntao; Zhang, Shanwen; Wang, Zhongwei; Sun, Youwen; Qi, Minzhong; Liu, Xufeng; Wang, Shengming; Yao, Damao

2014-01-01

Highlights: • Thermal design requirements for EAST RMP coils are summarized. • Cooling parameters based on both theoretical and numerical solutions are determined. • Compromise between thermal design and structural design is made on number of turns. • Thermo-mechanical calculations are made to validate its structural performance. - Abstract: Resonant magnetic perturbation (RMP) has been proved to be an efficient approach on edge localized modes (ELMs) control, resistive wall mode (RWM) control, and error field correction (EFC), RMP coil system under design in EAST tokamak will realize the above-mentioned multi-functions. This paper focuses on the thermo-mechanical analysis of EAST RMP coil system on the basis of sensitivity analysis, both normal and off-normal working conditions are considered. The most characteristic set of coil system is chosen with a complete modelling by means of three-dimensional (3D) finite element method, thermo-hydraulic and thermal-structural performances are investigated adequately, both locally and globally. The compromise is made between thermal performance and structural design requirements, and the results indicate that the optimized design is feasible and reasonable

Random non-proportional fatigue tests with planar tri-axial fatigue testing machine

Directory of Open Access Journals (Sweden)

T. Inoue

2016-10-01

Full Text Available Complex stresses, which occur on the mechanical surfaces of transport machinery in service, bring a drastic degradation in fatigue life. However, it is hard to reproduce such complex stress states for evaluating the fatigue life with conventional multiaxial fatigue machines. We have developed a fatigue testing machine that enables reproduction of such complex stresses. The testing machine can reproduce arbitrary in-plane stress states by applying three independent loads to the test specimen using actuators which apply loads in the 0, 45, and 90 degree directions. The reproduction was tested with complex stress data obtained from the actual operation of transport machinery. As a result, it was found that the reproduced stress corresponded to the measured stress with an error range of less than 10 %. Then, we made a comparison between measured fatigue lives under random non-proportional loading conditions and predicted fatigue lives. It was found that predicted fatigue lives with cr, stress on critical plane, were over a factor of 10 against measured fatigue lives. On the other hand, predicted fatigue lives with ma, stress in consideration of a non-proportional level evaluated by using amplitude and direction of principal stress, were within a factor of 3 against measured fatigue lives

An overview of fatigue

International Nuclear Information System (INIS)

Mc Evily, A.J.

1987-01-01

Four topics are briefly discussed in this paper: fatigue crack initiation and growth in a nickel-base superalloy single crystal, the environment effect on near-threshold fatigue crack growth behaviour, the role of crack closure in load-interaction effects in fatigue crack growth, and the nature of creep-fatigue interactions, if any, during fatigue crack growth. (Author)

Fatigue with HIV/AIDS

Science.gov (United States)

... 21, 2014 Select a Language: Fact Sheet 551 Fatigue WHAT IS FATIGUE? IS FATIGUE IMPORTANT? HOW DO ... It can be physical or psychological. With physical fatigue , your muscles cannot do things as easily as ...

Multi-purpose fatigue sensor. Part 1. Uniaxial and multiaxial fatigue

Directory of Open Access Journals (Sweden)

M.V. Karuskevich

2016-10-01

Full Text Available The paper describes the key principles and results of preliminary experiments aimed at the development of new technique for the fatigue life prediction under conditions of biaxial cyclic tension. The foundations of the method were developed early by the numerous tests with monitoring the process of surface deformation relief formation, which is proved to be an indicator of accumulated fatigue damage under uniaxial fatigue. The employed phenomenon was early applied for the development of a family of uniaxial loading fatigue sensors. The formation of strain induced relief has been recently taken into consideration as a part of damage accumulation criteria under biaxial fatigue as well. The home-made testing machine has been designed to implement combined bending and torsion loading that simulates loads experienced by an aircraft wing skin. The experimental evidences on formation and evolution of the deformation relief revealed under conditions of combined loading, supports the proposed concept of biaxial fatigue sensor

Evidence for sensitized fatigue pathways in patients with chronic fatigue syndrome.

Science.gov (United States)

Staud, Roland; Mokthech, Meriem; Price, Donald D; Robinson, Michael E

2015-04-01

Patients with chronic fatigue syndrome (CFS) frequently demonstrate intolerance to physical exertion that is often reported as increased and long-lasting fatigue. Because no specific metabolic alterations have been identified in CFS patients, we hypothesized that sensitized fatigue pathways become activated during exercise corresponding with increased fatigue. After exhausting handgrip exercise, muscle metabolites were trapped in the forearm tissues of 39 CFS patients and 29 normal control (NC) by sudden occlusion for up to 5 minutes. A nonocclusive condition of similar duration was used as control. Repeated fatigue and pain ratings were obtained before and after exercise. Mechanical and heat hyperalgesia were assessed by quantitative sensory testing. All subjects fulfilled the 1994 Fukuda Criteria for CFS. Normal control and CFS subjects exercised for 6.6 (2.4) and 7.0 (2.7) minutes (P > 0.05). Forearm occlusion lasted for 4.7 (1.3) and 4.9 (1.8) minutes in NC and CFS subjects, respectively (P > 0.05). Although fatigue ratings of CFS subjects increased from 4.8 (2.0) to 5.6 (2.1) visual analogue scale (VAS) units during forearm occlusion, they decreased from 5.0 (1.8) to 4.8 (2.0) VAS units during the control condition without occlusion (P = 0.04). A similar time course of fatigue ratings was observed in NC (P > 0.05), although their ratings were significantly lower than those of CFS subjects (P fatigue in CFS patients consistent with sensitization of fatigue pathways. Future interventions that reduce sensitization of fatigue pathways in CFS patients may be of therapeutic benefit.

Application of Laser Pulse Heating to Simulate Thermomechanical Damage at Gun Bore Surfaces

National Research Council Canada - National Science Library

Cote, Paul

2003-01-01

Laser pulse heating experiments were performed to provide insights into the thermomechanical damage effects that occur at the surface of coated and uncoated gun steel under cyclic rapid heating and cooling...

Clinical neurophysiology of fatigue.

Science.gov (United States)

Zwarts, M J; Bleijenberg, G; van Engelen, B G M

2008-01-01

Fatigue is a multidimensional concept covering both physiological and psychological aspects. Chronic fatigue is a typical symptom of diseases such as cancer, multiple sclerosis (MS), Parkinson's disease (PD) and cerebrovascular disorders but is also presented by people in whom no defined somatic disease has been established. If certain criteria are met, chronic fatigue syndrome can be diagnosed. The 4-item Abbreviated Fatigue Questionnaire allows the extent of the experienced fatigue to be assessed with a high degree of reliability and validity. Physiological fatigue has been well defined and originates in both the peripheral and central nervous system. The condition can be assessed by combining force and surface-EMG measurements (including frequency analyses and muscle-fibre conduction estimations), twitch interpolation, magnetic stimulation of the motor cortex and analysis of changes in the readiness potential. Fatigue is a well-known phenomenon in both central and peripheral neurological disorders. Examples of the former conditions are multiple sclerosis, Parkinson's disease and stroke. Although it seems to be a universal symptom of many brain disorders, the unique characteristics of the concomitant fatigue also point to a specific relationship with several of these syndromes. As regards neuromuscular disorders, fatigue has been reported in patients with post-polio syndrome, myasthenia gravis, Guillain-Barré syndrome, facioscapulohumeral dystrophy, myotonic dystrophy and hereditary motor and sensory neuropathy type-I. More than 60% of all neuromuscular patients suffer from severe fatigue, a prevalence resembling that of patients with MS. Except for several rare myopathies with specific metabolic derangements leading to exercise-induced muscle fatigue, most studies have not identified a prominent peripheral cause for the fatigue in this population. In contrast, the central activation of the diseased neuromuscular system is generally found to be suboptimal. The

Towards thermomechanics of fractal media

Science.gov (United States)

Ostoja-Starzewski, Martin

2007-11-01

Hans Ziegler’s thermomechanics [1,2,3], established half a century ago, is extended to fractal media on the basis of a recently introduced continuum mechanics due to Tarasov [14,15]. Employing the concept of internal (kinematic) variables and internal stresses, as well as the quasiconservative and dissipative stresses, a field form of the second law of thermodynamics is derived. In contradistinction to the conventional Clausius Duhem inequality, it involves generalized rates of strain and internal variables. Upon introducing a dissipation function and postulating the thermodynamic orthogonality on any lengthscale, constitutive laws of elastic-dissipative fractal media naturally involving generalized derivatives of strain and stress can then be derived. This is illustrated on a model viscoelastic material. Also generalized to fractal bodies is the Hill condition necessary for homogenization of their constitutive responses.

Effect of oxygen on the thermomechanical behavior of tantalum thin films during the β-α phase transformation

International Nuclear Information System (INIS)

Knepper, Robert; Stevens, Blake; Baker, Shefford P.

2006-01-01

Tantalum thin films were prepared in the metastable β phase, and their thermomechanical behaviors were investigated in situ in an ultrahigh vacuum environment. Controlled levels of oxygen were incorporated into the films either during deposition, by surface oxidation after deposition, or during thermomechanical testing. The transformation from the β phase to the stable α phase takes place in conjunction with a distinct increase in tensile stress. The thermomechanical behavior is strongly affected by the amount of oxygen to which the film is exposed and the method of exposure. Increasing oxygen content inhibits the phase transformation, requiring higher temperatures to reach completion. It is shown that the phase transformation takes place by a nucleation and growth process that is limited by growth. Changes in the activation energy for the phase transformation due to solute drag are estimated as a function of oxygen content and the mechanisms behind the stress evolution are elucidated

Reduced Electromyographic Fatigue Threshold after Performing a Cognitive Fatiguing Task.

Science.gov (United States)

Ferris, Justine R; Tomlinson, Mary A; Ward, Tayler N; Pepin, Marie E; Malek, Moh H

2018-02-22

Cognitive fatigue tasks performed prior to exercise may reduce exercise capacity. The electromyographic fatigue threshold (EMGFT) is the highest exercise intensity that can be maintained without significant increase in the EMG amplitude versus time relationship. To date, no studies have examined the effect of cognitive fatigue on the estimation of the EMGFT. The purpose of this study, therefore, was to determine whether or not cognitive fatigue prior to performing exercise reduces the estimated EMGFT. Eight healthy college-aged men were recruited from a university student population and visited the laboratory on multiple occasions. In a randomized order, subjects performed either the cognitive fatigue task (AX Continuous Performance Test; AX-CPT) for 60 min on one visit (experimental condition) or watched a video on trains for 60 min on the other visit (control condition). After each condition, subjects performed the incremental single-leg knee-extensor ergometry test while the EMG amplitude was recorded from the rectus femoris muscle and heart rate was monitored throughout. Thereafter, the EMGFT was calculated for each participant for each visit and compared using paired samples t-test. For exercise outcomes, there were no significant mean differences for maximal power output between the two conditions (control: 51 ± 5 vs. fatigue: 50 ± 3 W), but a significant decrease in EMGFT between the two conditions (control: 31 ± 3 vs. fatigue: 24 ± 2 W; p = 0.013). Moreover, maximal heart rate was significantly different between the two conditions (control: 151 ± 5 vs. fatigue: 132 ± 6; p = 0.027). These results suggest that performing the cognitive fatiguing task reduces the EMGFT with a corresponding reduction in maximal heart rate response.

The Nature of Self-Regulatory Fatigue and "Ego Depletion": Lessons From Physical Fatigue.

Science.gov (United States)

Evans, Daniel R; Boggero, Ian A; Segerstrom, Suzanne C

2015-07-30

Self-regulation requires overriding a dominant response and leads to temporary self-regulatory fatigue. Existing theories of the nature and causes of self-regulatory fatigue highlight physiological substrates such as glucose, or psychological processes such as motivation, but these explanations are incomplete on their own. Historically, theories of physical fatigue demonstrate a similar pattern of useful but incomplete explanations, as recent views of physical fatigue emphasize the roles of both physiological and psychological factors. In addition to accounting for multiple inputs, these newer views also explain how fatigue can occur even in the presence of sufficient resources. Examining these newer theories of physical fatigue can serve as a foundation on which to build a more comprehensive understanding of self-regulatory fatigue that integrates possible neurobiological underpinnings of physical and self-regulatory fatigue, and suggests the possible function of self-regulatory fatigue. © 2015 by the Society for Personality and Social Psychology, Inc.

Continuous fatigue crack monitoring of bridges: Long-Term Electrochemical Fatigue Sensor (LTEFS)

Science.gov (United States)

Moshier, Monty A.; Nelson, Levi; Brinkerhoff, Ryan; Miceli, Marybeth

2016-04-01

Fatigue cracks in steel bridges degrade the load-carrying capacity of these structures. Fatigue damage accumulation caused by the repetitive loading of everyday truck traffic can cause small fatigue cracks initiate. Understanding the growth of these fatigue cracks is critical to the safety and reliability of our transportation infrastructure. However, modeling fatigue in bridges is difficult due to the nature of the loading and variations in connection integrity. When fatigue cracks reach critical lengths failures occur causing partial or full closures, emergency repairs, and even full structural failure. Given the aging US highway and the trend towards asset management and life extension, the need for reliable, cost effective sensors and monitoring technologies to alert bridge owners when fatigue cracks are growing is higher than ever. In this study, an innovative Long-Term Electrochemical Fatigue Sensor (LTEFS) has been developed and introduced to meet the growing NDT marketplace demand for sensors that have the ability to continuously monitor fatigue cracks. The performance of the LTEFS has been studied in the laboratory and in the field. Data was collected using machined specimens with different lengths of naturally initiated fatigue cracks, applied stress levels, applied stress ratios, and for both sinusoidal and real-life bridge spectrum type loading. The laboratory data was evaluated and used to develop an empirically based algorithm used for crack detection. Additionally, beta-tests on a real bridge structure has been completed. These studies have conclusively demonstrated that LTEFS holds great potential for long-term monitoring of fatigue cracks in steel structures

The influence of thermomechanical processing on microstructural evolution of Ti600 titanium alloy

International Nuclear Information System (INIS)

Han Yuanfei; Zeng Weidong; Qi Yunlian; Zhao Yongqing

2011-01-01

Highlights: → Temperature and strain rate have great influence on the microstructure features. → The formation of sub-grain and dislocation wall is the typically microstructure features observed in the β single-phase. → The elongated lamellar α platelets kinked increasingly and break up under the α + β processing conditions. → The softening mechanisms of the Ti600 alloy hot compressed at 1000-1100 deg. C are mainly dynamic recovery. - Abstract: The influences of thermomechanical processing on microstructural evolution of Ti600 alloy were studied in the temperature range of 800-1100 deg. C, and at the strain rate of 0.001-10 s -1 . During the isothermal compression experiment, the flow stress-strain curves are examined in the β single-phase and in the α + β two-phase regions. The results show that the thermomechanical processing parameters have significant influences on the microstructure of Ti600 alloy, especially on the grain size, morphologies of α phase. Moreover, the microstructural evolution was analyzed by optical microstructure (OM) and transmission electron microscopy (TEM). It was found that typical of dynamic recovery and dynamic recrystallization phenomenon occurring in the thermomechanical processing. These results will optimize the microstructural control for hot working of Ti600 alloy and deepen the understanding of the flow softening mechanism of near-α titanium alloy.

Fatigue Perceived by Multiple Sclerosis Patients Is Associated With Muscle Fatigue

NARCIS (Netherlands)

Steens, Anneke; de Vries, Astrid; Hemmen, Jolien; Heersema, Thea; Heerings, Marco; Maurits, Natasha; Zijdewind, Inge

Background. Fatigue is a debilitating symptom in multiple sclerosis (MS). Previous studies showed no association between fatigue as perceived by the patient and physiological measures of fatigability. Objective. The authors investigated associations between perceived fatigue and measures of

Global thermo-mechanical effects from a KBS-3 type repository

International Nuclear Information System (INIS)

Hakami, E.; Olofsson, Stig-Olof

1998-01-01

The objective of this study has been to identify the global thermo-mechanical effects in the bedrock hosting a nuclear waste repository. Numerical thermo-mechanical modeling using distinct element models was performed. The number of fracture zones, the heat intensity of the waste, the material properties of the rock mass and the boundary conditions of the models were varied. Different models for multi-level repositories were also analyzed and compared to the main single-level case. Further, the global influence from the excavation of repository tunnels and deposition holes was examined by introducing weaker rock mass material properties in the repository region of one model. The maximum compression stress obtained for the main model is 44 MPa and occurs at the repository level after about 100 years of deposition. Due to thermal expansion, the rock mass displaces upward, and the maximum heave at the ground surface after 1000 years is calculated to be 16 cm. In the area close to the ground surface the horizontal stresses reduce, causing the rock to yield in tension down to a depth of about 80 meters. The fracture zones show opening displacements at shallow depths and closing and shearing at the repository level. The maximum displacements are 0.3-2.5 cm for closing, 0.0-0.8 cm for opening and 0.2-2.2 cm for shearing. The resultant stresses and displacements depend in large part on the assumptions made concerning the heat intensity of the waste. In the main model, an initial heat intensity of 10 W/m 2 is assumed, which gives larger effects than the case with 6 W/m 2 . Another important input parameter for the analysis is the Young's modulus of the rock mass. In the main model, a value of 30 GPa is assumed. Higher values of Young's modulus give larger thermo-mechanical effects. All multi-level repository layouts give rise to higher temperatures than the single-level layout, causing the compressive stresses to increase more at the repository level. The multi

Exact solution for stresses/displacements in a multilayered hollow cylinder under thermo-mechanical loading

International Nuclear Information System (INIS)

Yeo, W.H.; Purbolaksono, J.; Aliabadi, M.H.; Ramesh, S.; Liew, H.L.

2017-01-01

In this study, a new analytical solution by the recursive method for evaluating stresses/displacements in multilayered hollow cylinder under thermo-mechanical loading was developed. The results for temperature distribution, displacements and stresses obtained by using the proposed solution were shown to be in good agreement with the FEM results. The proposed analytical solution was also found to produce more accurate results than those by the analytical solution reported in literature. - Highlights: • A new analytical solution for evaluating stresses in multilayered hollow cylinder under thermo-mechanical loading. • A simple computational procedure using a recursive method. • A promising technique for evaluating the operating axial and hoop stresses in pressurized composite vessels.

Cumulative fatigue and creep-fatigue damage at 3500C on recrystallized zircaloy 4

International Nuclear Information System (INIS)

Brun, G.; Pelchat, J.; Floze, J.C.; Galimberti, M.

1985-06-01

An experimental programme undertaken by C.E.A., E.D.F. and FRAGEMA with the aim of characterizing the fatigue and creep fatigue behaviour of zircaloy-4 following annealing treatments (recrystallized, stress-delived) is in progress. The results given below concern only recrystallized material. Cyclic properties, low-cycle fatigue curves and creep behaviour laws under stresses have been established. Sequential tests of pure fatigue and creep-fatigue were performed. The cumulative life fractions at fracture depend on the sequence of leading, stress history and number of cycles of prestressing. The MINER's rule appears to be conservative with regard to a low-high loading sequence whereas it is not for the reverse high-low loading sequences. Fatigue and creep damage are not interchangeable. Pre-creep improves the fatigue resistance. Pre-fatigue improves the creep strength as long as the beneficial effect of cyclic hardening overcomes the damaging effect of surface cracking. The introduction of a tension hold time into the fatigue cycle slightly increases cyclic hardening and reduces the number of cycles to failure. For hold times of less than one hour, the sum of fatigue and creep life fractions is closed to one

Fatigue and creep-fatigue in sodium of 316 L stainless-steel

International Nuclear Information System (INIS)

Ardellier, A.

1981-03-01

The present paper describes test-facility developed to perform low-cycle fatigue and creep-fatigue interaction in sodium on stainless steel - 316 L . Fatigue life in sodium and in air are compared. A beneficial effect in sodium is noted

Taltirelin alleviates fatigue-like behavior in mouse models of cancer-related fatigue.

Science.gov (United States)

Dougherty, John P; Wolff, Brian S; Cullen, Mary J; Saligan, Leorey N; Gershengorn, Marvin C

2017-10-01

Fatigue affects most cancer patients and has numerous potential causes, including cancer itself and cancer treatment. Cancer-related fatigue (CRF) is not relieved by rest, can decrease quality of life, and has no FDA-approved therapy. Thyrotropin-releasing hormone (TRH) has been proposed as a potential novel treatment for CRF, but its efficacy against CRF remains largely untested. Thus, we tested the TRH analog, taltirelin (TAL), in mouse models of CRF. To model fatigue, we used a mouse model of chemotherapy, a mouse model of radiation therapy, and mice bearing colon 26 carcinoma tumors. We used the treadmill fatigue test to assess fatigue-like behavior after treatment with TAL. Additionally, we used wild-type and TRH receptor knockout mice to determine which TRH receptor was necessary for the actions of TAL. Tumor-bearing mice displayed muscle wasting and all models caused fatigue-like behavior, with mice running a shorter distance in the treadmill fatigue test than controls. TAL reversed fatigue-like behavior in all three models and the mouse TRH 1 receptor was necessary for the effects of TAL. These data suggest that TAL may be useful in alleviating fatigue in all cancer patients and provide further support for evaluating TAL as a potential therapy for CRF in humans. Published by Elsevier Ltd.

Manufacturing and thermomechanical testing of actively cooled all beryllium high heat flux test pieces

International Nuclear Information System (INIS)

Vasiliev, N.N.; Sokolov, Yu.A.; Shatalov, G.E.

1995-01-01

One of the problems affiliated to ITER high heat flux elements development is a problem of interface of beryllium protection with heat sink routinely made of copper alloys. To get rid of this problem all beryllium elements could be used as heat receivers in places of enhanced thermal loads. In accordance with this objectives four beryllium test pieces of two types have been manufactured in open-quotes Institute of Berylliumclose quotes for succeeding thermomechanical testing. Two of them were manufactured in accordance with JET team design; they are round open-quotes hypervapotron typeclose quotes test pieces. Another two ones are rectangular test sections with a twisted tape installed inside of the circular channel. Preliminary stress-strain analysis have been performed for both type of the test pieces. Hypervapotrons have been shipped to JET where they were tested on JET test bed. Thermomechanical testing of pieces of the type of open-quotes swirl tape inside of tubeclose quotes have been performed on Kurchatov Institute test bed. Chosen beryllium grade properties, some details of manufacturing, results of preliminary stress-strain analysis and thermomechanical testing of the test pieces open-quotes swirl tape inside of tubeclose quotes type are given in this report

Welding thermal cycle-triggered precipitation processes in steel S700MC subjected to the thermo-mechanical control processing

OpenAIRE

Górka J.

2017-01-01

This study presents tests concerned with welding thermal process-induced precipitation processes taking place in 10 mm thick steel S700MC subjected to the Thermo-Mechanical Control Process (TMCP) with accelerated cooling. The thermomechanical processing of steel S700MC leads to its refinement, structural defects and solutioning with hardening constituents. Tests of thin foils performed using a transmission electron microscope revealed that the hardening of steel S700MC was primarily caused by...

THERMO-MECHANICALLY PROCESSED ROLLED WIRE FOR HIGH-STRENGTH ON-BOARD WIRE

Directory of Open Access Journals (Sweden)

V. A. Lutsenko

2011-01-01

Full Text Available It is shown that at twisting of wire of diameter 1,83 mm, produced by direct wire drawing of thermomechanically processed rolled wire of diameter 5,5 mm of steel 90, metal stratification is completely eliminated at decrease of carbon, manganese and an additional alloying of chrome.

Effects of mental fatigue on the development of physical fatigue: a neuroergonomic approach.

Science.gov (United States)

Mehta, Ranjana K; Parasuraman, Raja

2014-06-01

The present study used a neuroergonomic approach to examine the interaction of mental and physical fatigue by assessing prefrontal cortex activation during submaximal fatiguing handgrip exercises. Mental fatigue is known to influence muscle function and motor performance, but its contribution to the development of voluntary physical fatigue is not well understood. A total of 12 participants performed separate physical (control) and physical and mental fatigue (concurrent) conditions at 30% of their maximal handgrip strength until exhaustion. Functional near infrared spectroscopy was employed to measure prefrontal cortex activation, whereas electromyography and joint steadiness were used simultaneously to quantify muscular effort. Compared to the control condition, blood oxygenation in the bilateral prefrontal cortex was significantly lower during submaximal fatiguing contractions associated with mental fatigue at exhaustion, despite comparable muscular responses. The findings suggest that interference in the prefrontal cortex may influence motor output during tasks that require both physical and cognitive processing. A neuroergonomic approach involving simultaneous monitoring of brain and body functions can provide critical information on fatigue development that may be overlooked during traditional fatigue assessments.

A 1D thermomechanical network transition constitutive model coupled with multiple structural relaxation for shape memory polymers

Science.gov (United States)

Zeng, Hao; Xie, Zhimin; Gu, Jianping; Sun, Huiyu

2018-03-01

A new thermomechanical network transition constitutive model is proposed in the study to describe the viscoelastic behavior of shape memory polymers (SMPs). Based on the microstructure of semi-crystalline SMPs, a new simplified transformation equation is proposed to describe the transform of transient networks. And the generalized fractional Maxwell model is introduced in the paper to estimate the temperature-dependent storage modulus. In addition, a neo-KAHR theory with multiple discrete relaxation processes is put forward to study the structural relaxation of the nonlinear thermal strain in cooling/heating processes. The evolution equations of the time- and temperature-dependent stress and strain response are developed. In the model, the thermodynamical and mechanical characteristics of SMPs in the typical thermomechanical cycle are described clearly and the irreversible deformation is studied in detail. Finally, the typical thermomechanical cycles are simulated using the present constitutive model, and the simulation results agree well with the experimental results.

Effect of low-temperature thermomechanical treatment on mechanical properties of low-alloying molybdenum alloys with carbide hardening

International Nuclear Information System (INIS)

Bernshtejn, L.M.; Zakharov, A.M.; Veller, M.V.

1978-01-01

Presented are results of testing low-temperature thermomechanical treatment of low-alloying molybdenum alloys, including quenching from 2100 deg C, 40% deformation by hydroextrusion and aging at the temperature of 1200-1400 deg C. Tensile tests at room temperature with the following processing of results have shown that low-temperature thermomechanical treatment of low-alloying molybdenum alloys of Mo-Zr-C and Mo-Zr-Nb-C systems leads to a significant increase in low-temperature mechanical properties (strength properties - by 30-35%, ductility - by 30-40%) as compared with conventional heat treatment (aging after quenching). The treatment proposed increases resistance to small, as well as large plastic deformations, and leads to a simultaneous rise of strength and plastic properties at all stages of tensile test. Alloying of the Mo-Zr-C system with niobium increases both strength and plastic characteristics as compared with alloys without niobium when testing samples, subjected to low temperature thermomechanical treatment and conventional heat treatment at room temperature

Drift-scale thermomechanical analysis for the retrievability systems study

International Nuclear Information System (INIS)

Tsai, F.C.

1996-01-01

A numerical method was used to estimate the stability of potential emplacement drifts without considering a ground support system as a part of the Thermal Loading Systems Study for the Yucca Mountain Site Characterization Project. The stability of the drift is evaluated with two variables: the level of thermal loading and the diameter of the emplacement drift. The analyses include the thermomechanical effects generated by the excavation of the drift, subsequently by the thermal loads from heat-emitting waste packages, and finally by the thermal reduction resulting from rapid cooling ventilation required for the waste retrieval if required. The Discontinuous Deformation Analysis (DDA) code was used to analyze the thermomechanical response of the rock mass of multiple blocks separated by joints. The result of this stability analysis is used to discuss the geomechanical considerations for the advanced conceptual design (ACD) with respect to retrievability. In particular, based on the rock mass strength of the host rock described in the current version of the Reference Information Base, the computed thermal stresses, generated by 111 MTU/acre thermal loads in the near field at 100 years after waste emplacement, is beyond the criterion for the rock mass strength used to predict the stability of the rock mass surrounding the emplacement drift

Modelling fatigue and the use of fatigue models in work settings.

Science.gov (United States)

Dawson, Drew; Ian Noy, Y; Härmä, Mikko; Akerstedt, Torbjorn; Belenky, Gregory

2011-03-01

In recent years, theoretical models of the sleep and circadian system developed in laboratory settings have been adapted to predict fatigue and, by inference, performance. This is typically done using the timing of prior sleep and waking or working hours as the primary input and the time course of the predicted variables as the primary output. The aim of these models is to provide employers, unions and regulators with quantitative information on the likely average level of fatigue, or risk, associated with a given pattern of work and sleep with the goal of better managing the risk of fatigue-related errors and accidents/incidents. The first part of this review summarises the variables known to influence workplace fatigue and draws attention to the considerable variability attributable to individual and task variables not included in current models. The second part reviews the current fatigue models described in the scientific and technical literature and classifies them according to whether they predict fatigue directly by using the timing of prior sleep and wake (one-step models) or indirectly by using work schedules to infer an average sleep-wake pattern that is then used to predict fatigue (two-step models). The third part of the review looks at the current use of fatigue models in field settings by organizations and regulators. Given their limitations it is suggested that the current generation of models may be appropriate for use as one element in a fatigue risk management system. The final section of the review looks at the future of these models and recommends a standardised approach for their use as an element of the 'defenses-in-depth' approach to fatigue risk management. Copyright © 2010 Elsevier Ltd. All rights reserved.

The nature of self-regulatory fatigue and “ego depletion”: Lessons from physical fatigue

Science.gov (United States)

Evans, Daniel R.; Boggero, Ian A.; Segerstrom, Suzanne C.

2016-01-01

Self-regulation requires overriding a dominant response, and leads to temporary self-regulatory fatigue. Existing theories of the nature and causes of self-regulatory fatigue highlight physiological substrates such as glucose or psychological processes such as motivation, but these explanations are incomplete on their own. Historically, theories of physical fatigue demonstrate a similar pattern of useful but incomplete explanations, as recent views of physical fatigue emphasize the roles of both physiological and psychological factors. In addition to accounting for multiple inputs, these newer views also explain how fatigue can occur even in the presence of sufficient resources. Examining these newer theories of physical fatigue can serve as a foundation on which to build a more comprehensive understanding of self-regulatory fatigue that integrates possible neurobiological underpinnings of physical and self-regulatory fatigue, and suggests the possible function of self-regulatory fatigue. PMID:26228914

Study of the Thermo-Mechanical Behavior of the CLIC Two-Beam Modules

CERN Document Server

Rossi, F; Riddone, G; Österberg, K; Kossyvakis, I; Gudkov, D; Samochkine, A

2013-01-01

The final luminosity target of the Compact LInear Collider (CLIC) imposes a micron-level stability requirement on the two-meter repetitive two-beam modules constituting the main linacs. Two-beam prototype modules are being assembled to extensively study their thermo-mechanical behaviour under different operation modes. The power dissipation occurring in the modules will be reproduced and the efficiency of the corresponding cooling systems validated. At the same time, the real environmental conditions present in the CLIC tunnel will be studied. Air conditioning and ventilation systems have been installed in the dedicated laboratory. The air temperature will be changed from 20 to 40°C, while the air flow rate will be varied up to 0.8 m/s. During all experimental tests, the alignment of the RF structures will be monitored to investigate the influence of power dissipation and air temperature on the overall thermo-mechanical behaviour. \

The concept of fatigue fracture toughness in fatigue delamination growth behavior

NARCIS (Netherlands)

Yao, L.; Alderliesten, R.C.; Benedictus, R.

2015-01-01

This paper provides a study on mode I fatigue delamination growth in composite laminates using energy principles. Experimental data has been obtained from fatigue tests conducted on Double Cantilever Beam (DCB) specimens at various stress ratios. A concept of fatigue fracture toughness is proposed

Mechanical integrity of thin inorganic coatings on polymer substrates under quasi-static, thermal and fatigue loadings

International Nuclear Information System (INIS)

Leterrier, Y.; Mottet, A.; Bouquet, N.; Gillieron, D.; Dumont, P.; Pinyol, A.; Lalande, L.; Waller, J.H.; Manson, J.-A.E.

2010-01-01

The interplay between residual stress state, cohesive and adhesive properties of coatings on substrates is reviewed in this article. Attention is paid to thin inorganic coatings on polymers, characterized by a very high hygro-thermo-mechanical contrast between the brittle and stiff coating and the compliant and soft substrate. An approach to determine the intrinsic, thermal and hygroscopic contributions to the coating residual stress is detailed. The critical strain for coating failure, coating toughness and coating/substrate interface shear strength are derived from the analysis of progressive coating cracking under strain. Electro-fragmentation and electro-fatigue tests in situ in a microscope are described. These methods enable reproducing the thermo-mechanical loads present during processing and service life, hence identifying and modeling the critical conditions for failure. Several case studies relevant to food and pharmaceutical packaging, flexible electronics and thin film photovoltaic devices are discussed to illustrate the benefits and limits of the present methods and models.

Experiences of Fatigue at Sea

DEFF Research Database (Denmark)

Zhao, Zhiwei; Jepsen, Jørgen Riis; Chen, Zhonglong

2016-01-01

Fatigue has negative impacts on the general working population as well as on seafarers. In order to study seafarers’ fatigue, a questionnaire-base survey was conducted to gain information about potential risk factors for fatigue and construct indexes indicating fatigue. The study applies T-test t......-test to compare strata of seafarers to analyse work and sleep patterns in global seafaring. Qualitative analysis are also employed to explore the impacts of fatigue on seafarer’s occupational health and safety.......Fatigue has negative impacts on the general working population as well as on seafarers. In order to study seafarers’ fatigue, a questionnaire-base survey was conducted to gain information about potential risk factors for fatigue and construct indexes indicating fatigue. The study applies T...

Thermomechanical analysis of an electrically assisted wire drawing process

OpenAIRE

Sánchez Egea, Antonio José; González Rojas, Hernan Alberto; Celentano, Diego Javier; Jorba Peiró, Jordi; Cao, Jia

2017-01-01

Electrically-assisted wire drawing process is a hybrid manufacturing process characterized by enhancement of the formability, ductility and elongation of the wire drawn specimen. A thermomechanical model to describe the change of the mechanical response due to the thermal contribution is proposed in this work. Additionally, a numerical simulation was conducted to study the potential and limitations of this hybrid process by using two different hardening laws: a phenomenological and a dislocat...

Finite elements for the thermomechanical calculation of massive structures

International Nuclear Information System (INIS)

Argyris, J.H.; Szimmat, J.; Willam, K.J.

1978-01-01

The paper examines the fine element analysis of thermal stress and deformation problems in massive structures. To this end compatible idealizations are utilized for heat conduction and static analysis in order to minimize the data transfer. For transient behaviour due to unsteady heat flow and/or inelastics material processes the two computational parts are interwoven in form of an integrated software package for finite element analysis of thermomechanical problems in space and time. (orig.) [de

A simple 1D model with thermomechanical coupling for superelastic SMAs

International Nuclear Information System (INIS)

Zaki, W; Morin, C; Moumni, Z

2010-01-01

This paper presents an outline for a new uniaxial model for shape memory alloys that accounts for thermomechanical coupling. The coupling provides an explanation of the dependence of SMA behavior on the loading rate. 1D simulations are carried in Matlab using simple finite-difference discretization of the mechanical and thermal equations.

Adrenal Fatigue

Science.gov (United States)

... Search Featured Resource New Mobile App DOWNLOAD Adrenal Fatigue October 2017 Download PDFs English Editors Irina Bancos, MD Additional Resources Mayo Clinic What is adrenal fatigue? The term “adrenal fatigue” has been used to ...

Neuromuscular fatigue during exercise: Methodological considerations, etiology and potential role in chronic fatigue.

Science.gov (United States)

Twomey, Rosie; Aboodarda, Saied Jalal; Kruger, Renata; Culos-Reed, Susan Nicole; Temesi, John; Millet, Guillaume Y

2017-04-01

The term fatigue is used to describe a distressing and persistent symptom of physical and/or mental tiredness in certain clinical populations, with distinct but ultimately complex, multifactorial and heterogenous pathophysiology. Chronic fatigue impacts on quality of life, reduces the capacity to perform activities of daily living, and is typically measured using subjective self-report tools. Fatigue also refers to an acute reduction in the ability to produce maximal force or power due to exercise. The classical measurement of exercise-induced fatigue involves neuromuscular assessments before and after a fatiguing task. The limitations and alternatives to this approach are reviewed in this paper in relation to the lower limb and whole-body exercise, given the functional relevance to locomotion, rehabilitation and activities of daily living. It is suggested that under some circumstances, alterations in the central and/or peripheral mechanisms of fatigue during exercise may be related to the sensations of chronic fatigue. As such, the neurophysiological correlates of exercise-induced fatigue are briefly examined in two clinical examples where chronic fatigue is common: cancer survivors and people with multiple sclerosis. This review highlights the relationship between objective measures of fatigability with whole-body exercise and perceptions of fatigue as a priority for future research, given the importance of exercise in relieving symptoms of chronic fatigue and/or overall disease management. As chronic fatigue is likely to be specific to the individual and unlikely to be due to a simple biological or psychosocial explanation, tailored exercise programmes are a potential target for therapeutic intervention. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

Optimal Fatigue Testing

DEFF Research Database (Denmark)

Faber, Michael Havbro; Sørensen, John Dalsgaard; Kroon, I. B.

1993-01-01

life experiments for the same purpose. The methodology is basedon modern probabilistic concepts amd classical decision theory. The special case where the fatigue life experiments are given in terms of SN curves is considered in Particular. The proposed techniques are illustrated by an example.......This paper considers the reassessment of the reliability of tubular joints subjected to fatigue load. The reassessment is considered in two parts namely the task of utilizing new experimental data on fatigue life to update the reliability of the tubular joint ant the task of planning new fatigue...

Fatigue-Arrestor Bolts

Science.gov (United States)

Onstott, Joseph W.; Gilster, Mark; Rodriguez, Sergio; Larson, John E.; Wickham, Mark D.; Schoonover, Kevin E.

1995-01-01

Bolts that arrest (or, more precisely, retard) onset of fatigue cracking caused by inelastic strains developed. Specifically developed to be installed in flange holes of unrestrained rocket engine nozzle. Fanges sometimes used to bolt nozzle to test stand; however, when rocket engine operated without this restraint, region around bolt holes experience severe inelastic strains causing fatigue cracking. Interference fits introduce compressive preloads that retard fatigue by reducing ranges of strains. Principle of these fatigue-arrestor bolts also applicable to holes in plates made of other materials and/or used for different purposes.

Relações entre /s/ e /z/ e entre /e/ e /e/ não vozeado ou áfono Relations between /s/ and /z/ and between /e/ and voiceless /e/

Directory of Open Access Journals (Sweden)

Carla Aparecida Cielo

2013-01-01

Full Text Available OBJETIVO: correlacionar os tempos máximos de fonação (TMF e as relações entre os fricativos /s/ e /z/ (s/z e entre /e/ não vozeado e a vogal /e/ (ė/e de mulheres sem afecções laríngeas. MÉTODO: participaram 60 mulheres com média de 21,56 anos de idade. Coletaram-se os TMF/ė/, /e/, /s/ e /z/ e calcularam-se a relação s/z e a relação ė/e, com padrão de normalidade para as relações de 0,8 a 1,2; para os TMF/s/ e /z/, entre 15,57 e 34,17s; para o TMF/ė/, entre 16 a 18s; e para o TMF/e/, entre 14,04 e 26,96s. Testes de Lilliefords, Spearmann, Binomial e Mann-Whitney com nível de significância de 5%. RESULTADOS: correlação positiva entre TMF/s/ e TMF/ė/, TMF/z/ e TMF/e/, TMF/s/ e TMF/z/, e TMF/ė/ e TMF/e/. Não houve correlação entre as relações s/z e ė/e, nem diferenças entre a relação ė/e, enquanto a relação s/z foi significantemente normal. TMF/ė/ e TMF/e/ significantemente diminuídos; TMF/s/ e TMF/z/ significantemente normais. TMF/ė/ significantemente menor do que TMF/s/; TMF/e/ significantemente menor do que TMF/z/. CONCLUSÃO: os fonemas /s/ e /z/ isolados e sua relação ficaram dentro da normalidade e as relações s/z e ė/e não apresentaram correlação. Os TMF/ė/ e TMF/e/ mostraram-se diminuídos em relação à normalidade. O TMF/ė/ foi menor do que TMF/s/ e o TMF/e/ foi menor do que TMF/z/, possivelmente devido ao modo articulatório dos fricativos ter aumentado o tempo de emissão, independentemente do controle do nível glótico e respiratório.PURPOSE: correlate the maximum phonation time (MPT and the relations between the fricative /s/ and /z/ (s/z and between the vowels /ė/ and /e/ (ė/e of women without laryngeal disorders. METHOD: participants were 60 women with a mean of 21.56 years old. Were collected MPT/ė/, /e/, /s/ and /z/ and calculated the relations ė/e and s/z, with normal pattern for the relationship from 0.8 to 1.2; for MPT/s/ and MPT/z/, between 15.57 and 34.17s; for the

Solvability of an unsaturated porous media flow problem with thermomechanical interaction

Czech Academy of Sciences Publication Activity Database

Detmann, B.; Krejčí, Pavel; Rocca, E.

2016-01-01

Roč. 48, č. 6 (2016), s. 4175-4201 ISSN 0036-1410 R&D Projects: GA ČR(CZ) GA15-12227S Institutional support: RVO:67985840 Keywords : porous media * hysteresis * thermomechanical interactions Subject RIV: BA - General Mathematics Impact factor: 1.648, year: 2016 http://epubs.siam.org/doi/abs/10.1137/16M1056365

Fatigue Reliability and Calibration of Fatigue Design Factors for Offshore Wind Turbines

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Sergio Márquez-Domínguez

2012-06-01

Full Text Available Consequences of failure of offshore wind turbines (OWTs is in general lower than consequences of failure of, e.g., oil & gas platforms. It is reasonable that lower fatigue design factors can be applied for fatigue design of OWTs when compared to other fixed offshore structures. Calibration of appropriate partial safety factors/Fatigue Design Factors (FDF for steel substructures for OWTs is the scope of this paper. A reliability-based approach is used and a probabilistic model has been developed, where design and limit state equations are established for fatigue failure. The strength and load uncertainties are described by stochastic variables. SN and fracture mechanics approaches are considered for to model the fatigue life. Further, both linear and bi-linear SN-curves are formulated and various approximations are investigated. The acceptable reliability level for fatigue failure of OWTs is discussed and results are presented for calibrated optimal fatigue design factors. Further, the influence of inspections is considered in order to extend and maintain a given target safety level.

Low cycle fatigue and creep fatigue behavior of alloy 617 at high temperature

International Nuclear Information System (INIS)

Cabet, Celine; Carroll, Laura; Wright, Richard

2013-01-01

Alloy 617 is the leading candidate material for an intermediate heat exchanger (IHX) application of the very high temperature nuclear reactor (VHTR), expected to have an outlet temperature as high as 950 C. Acceptance of Alloy 617 in Section III of the ASME Code for nuclear construction requires a detailed understanding of the creep-fatigue behavior. Initial creep-fatigue work on Alloy 617 suggests a more dominant role of environment with increasing temperature and/or hold times evidenced through changes in creep-fatigue crack growth mechanisms and failure life. Continuous cycle fatigue and creep-fatigue testing of Alloy 617 was conducted at 950 C and 0.3% and 0.6% total strain in air to simulate damage modes expected in a VHTR application. Continuous cycle fatigue specimens exhibited transgranular cracking. Intergranular cracking was observed in the creep-fatigue specimens and the addition of a hold time at peak tensile strain degraded the cycle life. This suggests that creep-fatigue interaction occurs and that the environment may be partially responsible for accelerating failure. (authors)

Effect of Low-Temperature Thermomechanical Treatment on the Structure and Mechanical, Fatigue and Corrosion Characteristics of Sheets from an Alloy of the Al - Mg - Si - Cu - Zn System

Science.gov (United States)

Makhsidov, V. V.; Kolobnev, N. I.; Kochubey, A. Ya.; Fomina, M. A.; Zamyatin, V. M.; Pushin, V. G.

2014-11-01

The effect of deformation on the structure, strength and fatigue properties, stresses on the surface and sensitivity to intercrystalline corrosion of sheets from alloy 1370 of the Al -Mg - Si - Cu - Zn system with one-side cladding is investigated. Application of deformation to sheets of alloy 1370 between the stages of artificial aging lowers the depth of penetration of ICC (≤ 0.10 mm) and raises the fatigue characteristics (by up to a factor of 2) at a high level of mechanical properties.

Random non-proportional fatigue tests with planar tri-axial fatigue testing machine

OpenAIRE

Inoue, T.; Nagao, R.; Takeda, N.

2016-01-01

Complex stresses, which occur on the mechanical surfaces of transport machinery in service, bring a drastic degradation in fatigue life. However, it is hard to reproduce such complex stress states for evaluating the fatigue life with conventional multiaxial fatigue machines. We have developed a fatigue testing machine that enables reproduction of such complex stresses. The testing machine can reproduce arbitrary in-plane stress states by applying three independent loads to the test specimen u...

Study of cast and thermo-mechanically strengthened chromium-nickel nitrogen-containing steel

International Nuclear Information System (INIS)

Prokoshkina, V.G.; Kaputkina, L.M.; Svyazhin, A.G.

2000-01-01

The effect of nitrogen on the structure and strength of corrosion-resistant chromium-nickel steels after thermal and thermomechanical treatment is studied. The 06Kh15N7AD and 07Kh15N7DAMB steels alloying by nitrogen was accomplished through the basic composition steels remelting in the molecular nitrogen atmosphere under the pressure of 0.1-2.5 MPa. The 02Kh15N5DAF and 05Kh15N5DAM steels ingots were obtained through melting in a plasma furnace under the nitrogen pressure of 0.4MPA. The high-temperature thermomechanical treatment (HTMT) was performed by rolling with preliminary blanks heating up to 1050 deg C and the rolling end temperature not below 950 deg C. It is shown, that the HTMT of the nitrogen-containing steels makes it possible to obtain strength characteristics by 1.5 times exceeding the properties of traditionally applicable corrosion-resistant steels, whereby sufficiently high plasticity of the nitrogen-containing steel is retained [ru

Thermo-mechanical design of the SINGAP accelerator grids for ITER NB injectors

Energy Technology Data Exchange (ETDEWEB)

Agostinetti, P. [Consorzio RFX, Euratom-ENEA Association, Corso Stati Uniti 4, I35127 Padova (Italy)], E-mail: piero.agostinetti@igi.cnr.it; Dal Bello, S.; Dalla Palma, M.; Zaccaria, P. [Consorzio RFX, Euratom-ENEA Association, Corso Stati Uniti 4, I35127 Padova (Italy)

2007-10-15

The SINGle Aperture-SINgle GAP (SINGAP) accelerator for ITER neutral beam injector foresees four grids for the extraction and acceleration of negative ions, instead of the seven grids of the Multi-Aperture Multi-Grid (MAMuG) reference configuration. The grids have to fulfil specific requirements coming from ion extraction, beam optics and thermo-mechanical issues. This paper focuses on the thermo-hydraulic and thermo-mechanical design of the grids carried out by Consorzio RFX for the design of the first ITER NB injector and the ITER NB Test Facility. The cooling circuit design (position and shape of the channels) and the cooling parameters (water coolant temperatures, pressure and velocity) were optimized with sensitivity analyses in order to satisfy the grid functional requirements (temperatures, stresses, in plane and out of plane deformations). The design required a complete modelling of the grids and their support frames by means of 3D FE and CAD models.

Analysis of Heat Generation Mechanism in Ultrasound Infrared Thermography

International Nuclear Information System (INIS)

Choi, Man Yong; Lee, Seung Seok; Park, Jeong Hak; Kang, Ki Soo; Kim, Won Tae

2009-01-01

Heat generation mechanism of ultrasound infrared thermography is still not well understood, yet and there are two reliable assumptions of heat generation, friction and thermo-mechanical effect. This paper investigates the principal cause of heat generation at fatigue crack with experimental and numerical approach. Our results show most of heat generation is contributed by friction between crack interface and thermo-mechanical effect is a negligible quantity

Thermo-mechanical design aspects of mercury bombardment ion thrusters.

Science.gov (United States)

Schnelker, D. E.; Kami, S.

1972-01-01

The mechanical design criteria are presented as background considerations for solving problems associated with the thermomechanical design of mercury ion bombardment thrusters. Various analytical procedures are used to aid in the development of thruster subassemblies and components in the fields of heat transfer, vibration, and stress analysis. Examples of these techniques which provide computer solutions to predict and control stress levels encountered during launch and operation of thruster systems are discussed. Computer models of specific examples are presented.

Mediators of the effects on fatigue of pragmatic rehabilitation for chronic fatigue syndrome.

Science.gov (United States)

Wearden, Alison J; Emsley, Richard

2013-10-01

To examine potential mediators of the effect of pragmatic rehabilitation on improvements in fatigue following a randomized controlled trial for patients with chronic fatigue syndrome (CFS/ME) in primary care (IRCTN 74156610). Patients fulfilled the Oxford criteria for CFS. Ninety-five patients were randomized to pragmatic rehabilitation and 100 to general practitioner (GP) treatment as usual. The outcome was the Chalder fatigue scale score (0123 scoring) at end of treatment (20 weeks) and 1-year follow up (70 weeks). First, the effect of treatment on potential mediators was assessed. Then fatigue was regressed on significant mediators, treatment allocation, and baseline measures of fatigue and significant mediators. Reduction in limiting activities at 20 weeks mediated the positive effect of pragmatic rehabilitation on fatigue at 70 weeks (mediated effect size = -2.64, SE = 0.81, p = .001, proportion of effect mediated = 82.0%). Reduction in catastrophizing at 20 weeks mediated the positive effect of pragmatic rehabilitation on fatigue at 70 weeks (mediated effect size = -1.39, SE = 0.61, p = .023, proportion of effect mediated = 43.2%). Reductions in 70-week measures of fear avoidance, embarrassment avoidance, limiting activities, and all-or-nothing behavior all mediated improvement in fatigue at 70 weeks, although the causal direction of these cross-sectional effects cannot be determined. There were no between-group differences on measures of exercise capacity (a timed step test). Improvements in fatigue following pragmatic rehabilitation are related to changes in behavioral responses to and beliefs about fatigue.

MODELS OF FATIGUE LIFE CURVES IN FATIGUE LIFE CALCULATIONS OF MACHINE ELEMENTS – EXAMPLES OF RESEARCH

Directory of Open Access Journals (Sweden)

Grzegorz SZALA

2014-03-01

Full Text Available In the paper there was attempted to analyse models of fatigue life curves possible to apply in calculations of fatigue life of machine elements. The analysis was limited to fatigue life curves in stress approach enabling cyclic stresses from the range of low cycle fatigue (LCF, high cycle fatigue (HCF, fatigue limit (FL and giga cycle fatigue (GCF appearing in the loading spectrum at the same time. Chosen models of the analysed fatigue live curves will be illustrated with test results of steel and aluminium alloys.

Self-positioning of polymer membranes driven by thermomechanically induced plastic deformation

DEFF Research Database (Denmark)

Häfliger, Daniel; Hansen, Ole; Boisen, Anja

2006-01-01

Stress in polymeric resins is tailored by a thermomechanical process. It allows for controlled self-positioning of membranes in microdevices (see Figure). The process makes specific use of plastic deformation that results from the low viscosity of the polymer. This demonstrates that polymers offer...... new approaches to microfabrication that cannot be realized for common semiconductor materials without severe difficulties....

[Research Progress on the Interaction Effects and Its Neural Mechanisms between Physical Fatigue and Mental Fatigue].

Science.gov (United States)

Zhang, Lixin; Zhang, Chuncui; He, Feng; Zhao, Xin; Qi, Hongzhi; Wan, Baikun; Ming, Dong

2015-10-01

Fatigue is an exhaustion state caused by prolonged physical work and mental work, which can reduce working efficiency and even cause industrial accidents. Fatigue is a complex concept involving both physiological and psychological factors. Fatigue can cause a decline of concentration and work performance and induce chronic diseases. Prolonged fatigue may endanger life safety. In most of the scenarios, physical and mental workloads co-lead operator into fatigue state. Thus, it is very important to study the interaction influence and its neural mechanisms between physical and mental fatigues. This paper introduces recent progresses on the interaction effects and discusses some research challenges and future development directions. It is believed that mutual influence between physical fatigue and mental fatigue may occur in the central nervous system. Revealing the basal ganglia function and dopamine release may be important to explore the neural mechanisms between physical fatigue and mental fatigue. Future effort is to optimize fatigue models, to evaluate parameters and to explore the neural mechanisms so as to provide scientific basis and theoretical guidance for complex task designs and fatigue monitoring.

Fatigue Damage in Wood

DEFF Research Database (Denmark)

Clorius, Christian Odin; Pedersen, Martin Bo Uhre; Hoffmeyer, Preben

1996-01-01

An investigation of fatigue failure in wood subjected to load cycles in compression parallel to grain is presented. Fatigue failure is found to depend both on the total time under load and on the number of cycles.Recent accelerated fatigue research on wood is reviewed, and a discrepancy between...... to 10 Hz are used. The number of cycles to failure is found to be a poor measure of the fatigue performance of wood. Creep, maximum strain, stiffness and work are monitored throughout the fatigue tests. Accumulated creep is suggested identified with damage and a correlation between stiffness reduction...

Chemotherapy-Induced Fatigue Correlates With Higher Fatigue Scores Before Treatment.

Science.gov (United States)

Araújo, José Klerton Luz; Giglio, Adriana Del; Munhoz, Bruna Antenusse; Fonseca, Fernando Luiz Affonso; Cruz, Felipe Melo; Giglio, Auro Del

2017-06-01

Cancer chemotherapy can induce fatigue in about 20% to 30% of patients. So far, there is very little information as to the predictors of chemotherapy-induced fatigue (CIF). We evaluated potential predictors of CIF in a sample of patients with cancer with several types of solid tumors scheduled to receive chemotherapy according to institutional protocols. Before their first and second chemotherapy cycles, patients answered to the Brief Fatigue Inventory (BFI), Chalder, Mini Nutritional Assessment (MNA), Stress thermometer, and HADS questionnaires as well as provided blood samples for inflammatory markers. We evaluated 52 patients, 37 (71%) were female and mean age was 53 years. The most common tumors were breast cancer 21 (40%) and gastrointestinal tumors 12 (23%). Although 14 (25.2%) patients had an increase in their fatigue BFI scores equal or above 3 points from baseline, we observed no significant overall differences between BFI scores before and after chemotherapy. The only 2 factors associated with an increase of 3 points in the BFI scores after chemotherapy were race and higher baseline BFI levels. By multivariate analysis, overall BFI and Chalder scores after chemotherapy also correlated significantly with their respective baseline scores before treatment. HADS scores before treatment correlated with overall BFI scores postchemotherapy, whereas MNA scores before chemotherapy and female sex correlated with higher Chalder scores after treatment. We conclude that fatigue induced by chemotherapy is common and consistently associated with higher fatigue scores before treatment. Screening for fatigue before chemotherapy may help to identify patients who are prone to develop CIF.

Modafinil May Alleviate Poststroke Fatigue

DEFF Research Database (Denmark)

Poulsen, Mai Bang; Damgaard, Bodil; Zerahn, Bo

2015-01-01

was randomized, double-blinded, and placebo-controlled. Patients were treated with 400-mg modafinil or placebo for 90 days. Assessments were done at inclusion, 30, 90, and 180 days. The primary end point was fatigue at 90 days measured by the Multidimensional Fatigue Inventory-20 general fatigue domain......BACKGROUND AND PURPOSE: Poststroke fatigue is common and reduces quality of life. Current evidence for intervention is limited, and this is the first placebo-controlled trial to investigate treatment of poststroke fatigue with the wakefulness promoting drug modafinil. METHODS: The trial....... Secondary end points included the Fatigue Severity Scale, the Montreal Cognitive Assessment, the modified Rankin Scale and the Stroke-specific quality of Life questionnaire. Adult patients with a recent stroke achieving a score of ≥12 on the Multidimensional Fatigue Inventory-20 general fatigue domain were...

The effect of creep cavitation on the fatigue life under creep-fatigue interaction

International Nuclear Information System (INIS)

Nam, S.W.

1995-01-01

Low cycle fatigue tests have been carried out with three different materials (1Cr-Mo-V steel, 12Cr-Mo-V steel and 304 stainless steel) for the investigation of the effect of surface roughness on the fatigue life. To see the effect systematically, we have chosen those materials which may or may not form grain boundary cavities.Test results show that the continuous fatigue life of 1Cr-Mo-V steel and aged 304 stainless steel with a rough surface is decreased compared with that of the specimens with a smooth surface. These two alloys are found to have no grain boundary cavities formed under creep-fatigue test conditions. On the contrary, the fatigue life of 12Cr-Mo-V steel and solutionized 304 stainless steel in which grain boundary cavities are formed under creep-fatigue test conditions is not influenced by the states of surface roughness.The characteristic test results strongly confirm that the fatigue life of the specimen under creep-fatigue interaction, during which creep cavities are forming, may be controlled by the cavity nucleation and growth processes rather than the process of surface crack initiation. ((orig.))

Nuclear, thermo-mechanical and tritium release analysis of ITER breeding blanket

International Nuclear Information System (INIS)

Kosaku, Yasuo; Kuroda, Toshimasa; Enoeda, Mikio; Hatano, Toshihisa; Sato, Satoshi; Miki, Nobuharu; Akiba, Masato

2003-06-01

The design of the breeding blanket in ITER applies pebble bed breeder in tube (BIT) surrounded by multiplier pebble bed. It is assumed to use the same module support mechanism and coolant manifolds and coolant system as the shielding blankets. This work focuses on the verification of the design of the breeding blanket, from the viewpoints which is especially unique to the pebble bed type breeding blanket, such as, tritium breeding performance, tritium inventory and release behavior and thermo-mechanical performance of the ITER breeding blanket. With respect to the neutronics analysis, the detailed analyses of the distribution of the nuclear heating rate and TBR have been performed in 2D model using MCNP to clarify the input data for the tritium inventory and release rate analyses and thermo-mechanical analyses. With respect to the tritium inventory and release behavior analysis, the parametric analyses for selection of purge gas flow rate were carried out from the view point of pressure drop and the tritium inventory/release performance for Li 2 TiO 3 breeder. The analysis result concluded that purge gas flow rate can be set to conventional flow rate setting (88 l/min per module) to 1/10 of that to save the purge gas flow and minimize the size of purge gas pipe. However, it is necessary to note that more tritium is transformed to HTO (chemical form of water) in case of Li 2 TiO 3 compared to other breeder materials. With respect to the thermo-mechanical analyses of the pebble bed blanket structure, the analyses have been performed by ABAQUS with 2D model derived from one of eight facets of a blanket module, based on the reference design. Analyses were performed to identify the temperature distribution incorporating the pebble bed mechanical simulation and influence of mechanical behavior to the thermal behavior. The result showed that the maximum temperature in the breeding material was 617degC in the first row of breeding rods and the minimum temperature was 328

Fatigue and fatigue-related symptoms in patients treated for different causes of hypothyroidism.

Science.gov (United States)

Louwerens, Marloes; Appelhof, Bente C; Verloop, Herman; Medici, Marco; Peeters, Robin P; Visser, Theo J; Boelen, Anita; Fliers, Eric; Smit, Johannes W A; Dekkers, Olaf M

2012-12-01

Research on determinants of well-being in patients on thyroid hormone replacement therapy is warranted, as persistent fatigue-related complaints are common in this population. In this study, we evaluated the impact of different states of hypothyroidism on fatigue and fatigue-related symptoms. Furthermore, the relationship between fatigue and the TSH receptor (TSHR)-Asp727Glu polymorphism, a common genetic variant of the TSHR, was analyzed. A cross-sectional study was performed in 278 patients (140 patients treated for differentiated thyroid carcinoma (DTC) and 138 with autoimmune hypothyroidism (AIH)) genotyped for the TSHR-Asp727Glu polymorphism. The multidimensional fatigue inventory (MFI-20) was used to assess fatigue, with higher MFI-20 scores indicating more fatigue-related complaints. MFI-20 scores were related to disease status and Asp727Glu polymorphism status. AIH patients scored significantly higher than DTC patients on all five MFI-20 subscales (P<0.001), independent of clinical and thyroid hormone parameters. The frequency of the TSHR-Glu727 allele was 7.2%. Heterozygous DTC patients had more favorable MFI-20 scores than wild-type DTC patients on four of five subscales. The modest effect of the TSHR-Asp727Glu polymorphism on fatigue was found in DTC patients only. AIH patients had significantly higher levels of fatigue compared with DTC patients, which could not be attributed to clinical or thyroid hormone parameters. The modest effect of the TSHR-Asp727Glu polymorphism on fatigue in DTC patients should be confirmed in other cohorts.

Thermo-mechanical Modelling of Pebble Beds in Fusion Blankets and its Implementation by a Return-Mapping Algorithm

International Nuclear Information System (INIS)

Gan, Yixiang; Kamlah, Marc

2008-01-01

In this investigation, a thermo-mechanical model of pebble beds is adopted and developed based on experiments by Dr. Reimann at Forschungszentrum Karlsruhe (FZK). The framework of the present material model is composed of a non-linear elastic law, the Drucker-Prager-Cap theory, and a modified creep law. Furthermore, the volumetric inelastic strain dependent thermal conductivity of beryllium pebble beds is taken into account and full thermo-mechanical coupling is considered. Investigation showed that the Drucker-Prager-Cap model implemented in ABAQUS can not fulfill the requirements of both the prediction of large creep strains and the hardening behaviour caused by creep, which are of importance with respect to the application of pebble beds in fusion blankets. Therefore, UMAT (user defined material's mechanical behaviour) and UMATHT (user defined material's thermal behaviour) routines are used to re-implement the present thermo-mechanical model in ABAQUS. An elastic predictor radial return mapping algorithm is used to solve the non-associated plasticity iteratively, and a proper tangent stiffness matrix is obtained for cost-efficiency in the calculation. An explicit creep mechanism is adopted for the prediction of time-dependent behaviour in order to represent large creep strains in high temperature. Finally, the thermo-mechanical interactions are implemented in a UMATHT routine for the coupled analysis. The oedometric compression tests and creep tests of pebble beds at different temperatures are simulated with the help of the present UMAT and UMATHT routines, and the comparison between the simulation and the experiments is made. (authors)

A Multi-objective Optimization Application in Friction Stir Welding: Considering Thermo-mechanical Aspects

DEFF Research Database (Denmark)

Tutum, Cem Celal; Hattel, Jesper Henri

2010-01-01

speed and traverse welding speed have been sought in order to achieve the goals mentioned above using an evolutionary multi-objective optimization (MOO) algorithm, i.e. non-dominated sorting genetic algorithm (NSGA-II), integrated with a transient, 2-dimensional sequentially coupled thermomechanical...

Modelling thermomechanical conditions at the tool/matrix interface in Friction Stir Welding

DEFF Research Database (Denmark)

Schmidt, Henrik Nikolaj Blich; Hattel, Jesper

2004-01-01

is obtained. A fully coupled thermo-mechanical 3D FE model has been developed in ABAQUS/Explicit using the ALE formulation and the Johnson-Cook material law. The contact forces are modelled by Coulomb’s law of friction making the contact condition highly solution dependent. The heat is generated by both...

Thermomechanical Behavior of Rotor with Rubbing

Directory of Open Access Journals (Sweden)

Jerzy T. Sawicki

2003-01-01

Full Text Available This article presents an analytical study of the dynamics and stability of rotors subjected to rubbing due to contact with seals, taking account of associated thermal effects. The seal interaction force acting on the shaft gives rise to a friction force, which is a source of heating and can induce so-called spiral vibrations. A mathematical model that has been developed couples the heat-conduction equation with the equations for motion of the rotor. Numerical simulations have been conducted that show the thermomechanical behavior of the rotor at various operating conditions. A procedure for analyzing the stability of multibearing rotors based on the system eigenvalue analysis and the state-space approach has been proposed. Finally, the experimental data related to full annular rub have been presented.

Comparison of Fatigue Properties and Fatigue Crack Growth Rates of Various Implantable Metals

Science.gov (United States)

Okazaki, Yoshimitsu

2012-01-01

The fatigue strength, effects of a notch on the fatigue strength, and fatigue crack growth rate of Ti-15Zr-4Nb-4Ta alloy were compared with those of other implantable metals. Zr, Nb, and Ta are important alloying elements for Ti alloys for attaining superior long-term corrosion resistance and biocompatibility. The highly biocompatible Ti-15Zr-4Nb-4Ta alloy exhibited an excellent balance between strength and ductility. Its notched tensile strength was much higher than that of a smooth specimen. The strength of 20% cold-worked commercially pure (C.P.) grade 4 Ti was close to that of Ti alloy. The tension-to-tension fatigue strength of an annealed Ti-15Zr-4Nb-4Ta rod at 107 cycles was approximately 740 MPa. The fatigue strength of this alloy was much improved by aging treatment after solution treatment. The fatigue strengths of C.P. grade 4 Ti and stainless steel were markedly improved by 20% cold working. The fatigue strength of Co-Cr-Mo alloy was markedly increased by hot forging. The notch fatigue strengths of 20% cold-worked C.P. grade 4 Ti, and annealed and aged Ti-15Zr-4Nb-4Ta, and annealed Ti-6Al-4V alloys were less than those of the smooth specimens. The fatigue crack growth rate of Ti-15Zr-4Nb-4Ta was the same as that of Ti-6Al-4V. The fatigue crack growth rate in 0.9% NaCl was the same as that in air. Stainless steel and Co-Cr-Mo-Ni-Fe alloy had a larger stress-intensity factor range (ΔK) than Ti alloy.

3-D electromagnetic and thermo-mechanical simulation of a RF cavity

CERN Document Server

Launay, F

2003-01-01

A 3-D thermo-mechanical study of the edge of entrance blade of IPHI's RFQ was conducted by means of I-DEAS code. The aim is to compare the temperatures reached, the constraints, and the deformations calculated on the basis of RF power density stored on the blade obtained by means of two different electromagnetic computational codes, SOPRANO and MAFIA.

Application of a new thermo-mechanical model for the study of the nuclear waste disposal in clay rocks

International Nuclear Information System (INIS)

Dizier, A.; Li, X.L.; Francois, B.; Collin, F.; Charlier, R.

2012-01-01

Document available in extended abstract form only. One of the cornerstones of the nuclear waste disposal researches concerns the evolution of the damaged zone which can offer a preferential path for migration of radionuclide through modifications of its mechanical and hydraulic properties. Even if the thermo-mechanical behaviour of clays is well documented in the literature, the development of the damaged zone induced by an excavation with temperature is not well known. To investigate this problem, a new thermo-mechanical constitutive law has been implemented in the non-linear finite element code LAGAMINE developed at ULg (Universite de Liege) and has been used to model the PRACLAY experiment (Preliminary demonstration test for clay disposal of vitrified high level radioactive waste) at Mol URL (Underground Research Laboratory). Though several models are being to reproduce the different phenomena met when a thermal loading is applied to a clay specimen, the applications of such thermo-mechanical models to simulate large scale in-situ experiment are rare. Based on the work of Sultan a new thermo-mechanical constitutive law has been implemented in combination with a Cap model in the code LAGAMINE. The Cap model is a combination of a frictional criterion, a Cam-Clay model and a traction criterion. The influence of the temperature is considered through the thermo-mechanical law developed by Cui et al. (2000). This law permits to reproduce common features of the thermo-mechanical behaviour of clay, such as the decrease of the pre-consolidation pressure with temperature, the volume change, the thermal hardening, the transition between thermal dilation and thermal contraction for over-consolidated clays. These aspects are modelled with two curves in the (p',T) plane. The first one is related to the generation of the thermal volumetric plastic strains (TY curve (Thermal Yield)). The second one reproduces the decrease of the pre-consolidation pressure with the temperature

[Epidemiology of fatigue in general practice].

Science.gov (United States)

Fuhrer, R

1994-11-01

The epidemiology of fatigue is not well known in France, and this study reports on factors associated with fatigue in a sample of 3,784 general practice patients. Prevalence rates according to several definitions of fatigue are presented and factors are examined that have been reported to be associated with fatigue. Although 41.2% of the sample report having experienced symptoms of fatigue for at least three days, only 7.6% declare fatigue as a reason for consulting a doctor. Women report more symptoms of fatigue, but they do not consult more often than men for this reason. Age is strongly correlated with fatigue, but this is found only for men. Socioprofessional category bears no relationship to fatigue as a reason for consultation, however, the diagnosis of fatigue is more often attributed to professionals and upper management than it is to office staff or skilled and unskilled workers. We do find a strong relationship between depressive symptomatology as measured by the Center for Epidemiologic Studies (CES-D) and fatigue; nonetheless, fatigue is neither sensitive nor specific to the diagnosis of depression.

Thermo-elastic-plastic analysis for elastic component under high temperature fatigue crack growth rate

Science.gov (United States)

Ali, Mohammed Ali Nasser

transient thermal stresses superimposed on cyclic mechanical loading results in hollow cylinder under thermal shock in heating case and down shock cooling case. The combination of stress and strain intensity factor theoretical calculations with the experimental output recorded data shows a similar behaviour with increasing temperature, and there is a fair correlation between the profiles at the beginning and then divergence with increasing the crack length. The transient influence of high temperature in case two, giving a very high thermal shock stress as a heating or cooling effects, shifting up the combined stress, when applied a cyclic mechanical load in fraction of seconds, and the reputations of these shocks, causing a fast failure under high thermal shock stress superimposed with mechanical loading.Finally, the numerical modelling analyses three cases studied were solved due to the types of loading and types of specimen geometry by using finite element models constructed through the ANSYS Workbench version 13.0. The first case is a low cyclic fatigue case for a solid cylinder specimen simulated by applying a cyclic mechanical loading. The second is an isothermal fatigue case for solid cylinder specimen simulated by supplying different constant temperatures on the outer surface with cyclic mechanical loading, where the two cases are similar to the experimental tests and the third case, is a thermo-mechanical fatigue for a hollow cylinder model by simulating a thermal up-shock generated due to transient heating on the outer surface of the model or down shock cooling on the inner surface with the cyclic mechanical loading. The results show a good agreement with the experimental data in terms of alternative stress and life in the first case. In case two results show the strain intensity factor is increases with increasing temperature similar to the theoretical solution due to the influence of the modulus of elasticity and the difference in life estimation with the

Thermomechanical Behavior of High Performance Epoxy/Organoclay Nanocomposites

Directory of Open Access Journals (Sweden)

Artur Soares Cavalcanti Leal

2014-01-01

Full Text Available Nanocomposites of epoxy resin containing bentonite clay were fabricated to evaluate the thermomechanical behavior during heating. The epoxy resin system studied was prepared using bifunctional diglycidyl ether of bisphenol A (DGEBA, crosslinking agent diaminodiphenylsulfone (DDS, and diethylenetriamine (DETA. The purified bentonite organoclay (APOC was used in all experiments. The formation of nanocomposite was confirmed by X-ray diffraction analysis. Specimens of the fabricated nanocomposites were characterized by dynamic mechanical analysis (DMA. According to the DMA results a significant increase in glass transition temperature and storage modulus was evidenced when 1 phr of clay is added to epoxy resin.

Microstructure history effect during sequential thermomechanical processing

International Nuclear Information System (INIS)

Yassar, Reza S.; Murphy, John; Burton, Christina; Horstemeyer, Mark F.; El kadiri, Haitham; Shokuhfar, Tolou

2008-01-01

The key to modeling the material processing behavior is the linking of the microstructure evolution to its processing history. This paper quantifies various microstructural features of an aluminum automotive alloy that undergoes sequential thermomechanical processing which is comprised hot rolling of a 150-mm billet to a 75-mm billet, rolling to 3 mm, annealing, and then cold rolling to a 0.8-mm thickness sheet. The microstructural content was characterized by means of electron backscatter diffraction, scanning electron microscopy, and transmission electron microscopy. The results clearly demonstrate the evolution of precipitate morphologies, dislocation structures, and grain orientation distributions. These data can be used to improve material models that claim to capture the history effects of the processing materials

Prolonged unexplained fatigue in paediatrics

NARCIS (Netherlands)

Bakker, R.J.

2010-01-01

Prolonged Unexplained Fatigue in Paediatrics. Fatigue, as the result of mental or physical exertion, will disappear after rest, drinks and food. Fatigue as a symptom of illness will recover with the recovering of the illness. But when fatigue is ongoing for a long time, and not the result of

Assessment of early onset of driver fatigue using multimodal fatigue measures in a static simulator.

Science.gov (United States)

Jagannath, M; Balasubramanian, Venkatesh

2014-07-01

Driver fatigue is an important contributor to road accidents. This paper reports a study that evaluated driver fatigue using multimodal fatigue measures, i.e., surface electromyography (sEMG), electroencephalography (EEG), seat interface pressure, blood pressure, heart rate and oxygen saturation level. Twenty male participants volunteered in this study by performing 60 min of driving on a static simulator. Results from sEMG showed significant physical fatigue (ρ fatigue. This will help us understand the influence of physical and mental fatigue on driver during monotonous driving. Copyright © 2014 Elsevier Ltd and The Ergonomics Society. All rights reserved.

Fatigue and fatigue-related symptoms in patients treated for different causes of hypothyroidism

NARCIS (Netherlands)

Louwerens, M.; Appelhof, B.C.; Verloop, H.; Medici, M.; Peeters, R.P.; Visser, T.J.; Boelen, A.; Fliers, E.; Smit, J.W.A.; Dekkers, O.M.

2012-01-01

OBJECTIVE: Research on determinants of well-being in patients on thyroid hormone replacement therapy is warranted, as persistent fatigue-related complaints are common in this population. In this study, we evaluated the impact of different states of hypothyroidism on fatigue and fatigue-related

Fatigue and fatigue-related symptoms in patients treated for different causes of hypothyroidism

NARCIS (Netherlands)

Louwerens, Marloes; Appelhof, Bente C.; Verloop, Herman; Medici, Marco; Peeters, Robin P.; Visser, Theo J.; Boelen, Anita; Fliers, Eric; Smit, Johannes W. A.; Dekkers, Olaf M.

2012-01-01

Objective: Research on determinants of well-being in patients on thyroid hormone replacement therapy is warranted, as persistent fatigue-related complaints are common in this population. In this study, we evaluated the impact of different states of hypothyroidism on fatigue and fatigue-related

Thermo-mechanical modeling of laser treatment on titanium cold-spray coatings

Science.gov (United States)

Paradiso, V.; Rubino, F.; Tucci, F.; Astarita, A.; Carlone, P.

2018-05-01

Titanium coatings are very attractive to several industrial fields, especially aeronautics, due to the enhanced corrosion resistance and wear properties as well as improved compatibility with carbon fiber reinforced plastic (CFRP) materials. Cold sprayed titanium coatings, among the others deposition processes, are finding a widespread use in high performance applications, whereas post-deposition treatments are often used to modify the microstructure of the cold-sprayed layer. Laser treatments allow one to noticeably increase the superficial properties of titanium coatings when the process parameters are properly set. On the other hand, the high heat input required to melt titanium particles may result in excessive temperature increase even in the substrate. This paper introduces a thermo-mechanical model to simulate the laser treatment effects on a cold sprayed titanium coating as well as the aluminium substrate. The proposed thermo-mechanical finite element model considers the transient temperature field due to the laser source and applied boundary conditions using them as input loads for the subsequent stress-strain analysis. Numerical outcomes highlighted the relevance of thermal gradients and thermally induced stresses and strains in promoting the damage of the coating.

Thermo-mechanical design and testing of a microbalance for space applications

Science.gov (United States)

Scaccabarozzi, Diego; Saggin, Bortolino; Tarabini, Marco; Palomba, Ernesto; Longobardo, Andrea; Zampetti, Emiliano

2014-12-01

This work focuses on the thermo-mechanical design of the microbalance used for the VISTA (Volatile In Situ Thermogravimetry Analyzer) sensor. VISTA has been designed to operate in situ in different space environments (asteroids, Mars, icy satellites). In this paper we focus on its application on Mars, where the expected environmental conditions are the most challenging for the thermo-mechanical design. The microbalance holding system has been designed to ensure piezoelectric crystal integrity against the high vibration levels during launch and landing and to cope with the unavoidable thermo-elastic differential displacements due to CTE and temperature differences between the microbalance elements. The crystal holding system, based on three symmetrical titanium supports, provides also the electrical connections needed for crystal actuation, microbalance heating and temperature measurement on the electrode area. On the microbalance crystal surfaces the electrodes, a micro film heater (optimized to perform thermo-gravimetric analysis up to 400 °C) and a resistive thermometer are deposited through a vacuum sputtering process. A mockup of the system has been manufactured and tested at the expected vibration levels and the thermal control effectiveness has been verified in thermo-vacuum environment.

Modelling the Thermo-Mechanical Behavior of Magnesium Alloys during Indirect Extrusion

International Nuclear Information System (INIS)

Steglich, D.; Ertuerk, S.; Bohlen, J.; Letzig, D.; Brocks, W.

2010-01-01

One of the basic metal forming process for semi-finished products is extrusion. Since extrusion involves complex thermo-mechanical and multiaxial loading conditions resulting in large strains, high strain rates and an increase in temperature due to deformation, a proper yield criterion and hardening law should be used in the numerical modelling of the process. A phenomenological model based on a plastic potential has been proposed that takes strain, strain rate and temperature dependency on flow behaviour into consideration. A hybrid methodology of experiment and finite element simulation has been adopted in order to obtain necessary model parameters. The anisotropy/asymmetry in yielding was quantified by tensile and compression tests of specimens prepared from different directions. The identification of the corresponding model parameters was performed by a genetic algorithm. A fully coupled thermo-mechanical analysis has been used in extrusion simulations for calculation of the temperature field by considering heat fluxes and heat generated due to plastic deformation. The results of the approach adopted in this study appeared to be successful showing promising predictions of the experiments and thus may be extended to be applicable to other magnesium alloys or even other hcp metals.

Hyperthermia and fatigue

DEFF Research Database (Denmark)

Nybo, Lars

2008-01-01

The present review addresses mechanisms of importance for hyperthermia-induced fatigue during short intense activities and prolonged exercise in the heat. Inferior performance during physical activities with intensities that elicit maximal oxygen uptake is to a large extent related to perturbation...... of the cardiovascular function, which eventually reduces arterial oxygen delivery to the exercising muscles. Accordingly, aerobic energy turnover is impaired and anaerobic metabolism provokes peripheral fatigue. In contrast, metabolic disturbances of muscle homeostasis are less important during prolonged exercise...... in the heat, because increased oxygen extraction compensates for the reduction in systemic blood flow. The decrease in endurance seems to involve changes in the function of the central nervous system (CNS) that lead to fatigue. The CNS fatigue appears to be influenced by neurotransmitter activity...

Thermomechanics of solid materials with application to the Gurson-Tvergaard material model

Energy Technology Data Exchange (ETDEWEB)

Santaoja, K. [VTT Manufacturing Technology, Espoo (Finland). Materials and Structural Integrity

1997-12-31

The elastic-plastic material model for porous material proposed by Gurson and Tvergaard is evaluated. First a general description is given of constitutive equations for solid materials by thermomechanics with internal variables. The role and definition of internal variables are briefly discussed and the following definition is given: The independent variables present (possibly hidden) in the basic laws for thermomechanics are called controllable variables. The other independent variables are called internal variables. An internal variable is shown always to be a state variable. This work shows that if the specific dissipation function is a homogeneous function of degree one in the fluxes, a description for a time-independent process is obtained. When damage to materials is evaluated, usually a scalar-valued or tensorial variable called damage is introduced in the set of internal variables. A problem arises when determining the relationship between physically observable weakening of the material and the value for damage. Here a more feasible approach is used. Instead of damage, the void volume fraction is inserted into the set of internal variables. This allows use of an analytical equation for description of the mechanical weakening of the material. An extension to the material model proposed by Gurson and modified by Tvergaard is derived. The derivation is based on results obtained by thermomechanics and damage mechanics. The main difference between the original Gurson-Tvergaard material model and the extended one lies in the definition of the internal variable `equivalent tensile flow stress in the matrix material` denoted by {sigma}{sup M}. Using classical plasticity theory, Tvergaard elegantly derived an evolution equation for {sigma}{sup M}. This is not necessary in the present model, since damage mechanics gives an analytical equation between the stress tensor {sigma} and {sigma}M. Investigation of the Clausius-Duhem inequality shows that in compression

Thermomechanics of solid materials with application to the Gurson-Tvergaard material model

International Nuclear Information System (INIS)

Santaoja, K.

1997-01-01

The elastic-plastic material model for porous material proposed by Gurson and Tvergaard is evaluated. First a general description is given of constitutive equations for solid materials by thermomechanics with internal variables. The role and definition of internal variables are briefly discussed and the following definition is given: The independent variables present (possibly hidden) in the basic laws for thermomechanics are called controllable variables. The other independent variables are called internal variables. An internal variable is shown always to be a state variable. This work shows that if the specific dissipation function is a homogeneous function of degree one in the fluxes, a description for a time-independent process is obtained. When damage to materials is evaluated, usually a scalar-valued or tensorial variable called damage is introduced in the set of internal variables. A problem arises when determining the relationship between physically observable weakening of the material and the value for damage. Here a more feasible approach is used. Instead of damage, the void volume fraction is inserted into the set of internal variables. This allows use of an analytical equation for description of the mechanical weakening of the material. An extension to the material model proposed by Gurson and modified by Tvergaard is derived. The derivation is based on results obtained by thermomechanics and damage mechanics. The main difference between the original Gurson-Tvergaard material model and the extended one lies in the definition of the internal variable 'equivalent tensile flow stress in the matrix material' denoted by σ M . Using classical plasticity theory, Tvergaard elegantly derived an evolution equation for σ M . This is not necessary in the present model, since damage mechanics gives an analytical equation between the stress tensor σ and σM. Investigation of the Clausius-Duhem inequality shows that in compression, states occur which are not

Fatigue Experiences Among OCD Outpatients.

Science.gov (United States)

Pasquini, Massimo; Piacentino, Daria; Berardelli, Isabella; Roselli, Valentina; Maraone, Annalisa; Tarsitani, Lorenzo; Biondi, Massimo

2015-12-01

Patients with OCD are impaired in multiple domains of functioning and quality of life. While associated psychopathology complaints and neuropsychological deficits were reported, the subjective experience of general fatigue and mental fatigue was scarcely investigated. In this single-center case-control study we compared 50 non-depressed OCD outpatients consecutively recruited and 50 panic disorder (PD) outpatients, to determine whether they experienced fatigue differently. Assessment consisted of structured clinical interview for DSM-IV criteria by using the SCID-I and the SCID-II. Symptom severity was assessed using the Yale-Brown Obsessive-Compulsive Scale, the Hamilton Anxiety Rating Scale, the Hamilton Depression Rating Scale, the Clinical Global Impressions Scale, severity and the Global Assessment of Functioning Scale. Fatigue was assessed by using the Multidimensional Fatigue Inventory (MFI). Regarding MFI physical fatigue, an OR of 0.196 (95 % CI 0.080-0.478) was found, suggesting that its presence is associated with lower odds of OCD compared to PD. The same can be said for MFI mental fatigue, as an OR of 0.138 (95 % CI 0.049-0.326) was found, suggesting that its presence is associated with lower odds of OCD. Notably, OCD patients with OCDP co-morbidity reported higher scores of mental fatigue. In this study fatigue, including mental fatigue, seems not to be a prominent experience among adult non-depressed OCD patients.

Fatigue Crack Topography.

Science.gov (United States)

1984-01-01

alloys (2). [--I Fig. 6. Fatigue fracture in Nitrile- butadien rubber ( NBR ). Fig. 7. The characteristic features of fatigue fracture in press moulded...in plastics and even in rubber . It follows therefore, that fatigue fractures must also occur in the mineral layers of our earth or in the rock on...effective until the weakest point yields and forms a crack. To get a feeling for this process, you can imagine that the stressed article is made of rubber

Stress management skills, neuroimmune processes and fatigue levels in persons with chronic fatigue syndrome.

Science.gov (United States)

Lattie, Emily G; Antoni, Michael H; Fletcher, Mary Ann; Penedo, Frank; Czaja, Sara; Lopez, Corina; Perdomo, Dolores; Sala, Andreina; Nair, Sankaran; Fu, Shih Hua; Klimas, Nancy

2012-08-01

Stressors and emotional distress responses impact chronic fatigue syndrome (CFS) symptoms, including fatigue. Having better stress management skills might mitigate fatigue by decreasing emotional distress. Because CFS patients comprise a heterogeneous population, we hypothesized that the role of stress management skills in decreasing fatigue may be most pronounced in the subgroup manifesting the greatest neuroimmune dysfunction. In total, 117 individuals with CFS provided blood and saliva samples, and self-report measures of emotional distress, perceived stress management skills (PSMS), and fatigue. Plasma interleukin-1-beta (IL-1β, IL-2, IL-6, IL-10, and tumor necrosis factor-alpha (TNF-α), and diurnal salivary cortisol were analyzed. We examined relations among PSMS, emotional distress, and fatigue in CFS patients who did and did not evidence neuroimmune abnormalities. Having greater PSMS related to less fatigue (p=.019) and emotional distress (pfatigue levels most strongly in CFS patients in the top tercile of IL-6, and emotional distress mediated the relationship between PSMS and fatigue most strongly in patients with the greatest circulating levels of IL-6 and a greater inflammatory (IL-6):anti-inflammatory (IL-10) cytokine ratio. CFS patients having greater PSMS show less emotional distress and fatigue, and the influence of stress management skills on distress and fatigue appear greatest among patients who have elevated IL-6 levels. These findings support the need for research examining the impact of stress management interventions in subgroups of CFS patients showing neuroimmune dysfunction. Copyright © 2012 Elsevier Inc. All rights reserved.

Influence of thermo-mechanical processing on the microstructure of Cu-based shape memory alloys produced by powder metallurgy

International Nuclear Information System (INIS)

Rodriguez, P.P.; Ibarra, A.; Iza-Mendia, A.; Recarte, V.; Perez-Landazabal, J.I.; San Juan, J.; No, M.L.

2003-01-01

Cu-Al-Ni shape memory alloys processed by powder metallurgy show very good thermo-mechanical properties, much better than those found in alloys produced by conventional casting. In this paper, we present the microstructural characterisation of these powder metallurgy alloys in order to find the microscopic mechanisms, linked to the powder metallurgy processing method, which are indeed responsible of such good thermo-mechanical behaviour. Electron microscopy studies [scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM)] show that powder metallurgy processing creates a sub-grain structure characterised by the presence of low angle sub-boundaries. These sub-boundaries are found to be lying on {1 1 0} and {1 1 2} lattice planes and are composed by an arrangement of superdislocations. These sub-boundaries may improve ductility in two ways: acting as a sink of dislocations which promotes plastic deformation and decreasing stress concentration at grain boundaries. Moreover, since sub-boundaries act as weak obstacles for the movement of martensite plates, the improvement on ductility is accomplished by an adequate thermo-mechanical behaviour

Thermal fatigue appears to be more damaging than uniaxial isothermal fatigue for the austentic stainless steels, and application of multiaxial fatigue criteria

Energy Technology Data Exchange (ETDEWEB)

Fissolo, Antoine; Gourdin, Cedric [DM2S/SEMT/LISN, Gif sur Yvette (France); Vincent, Ludovic [DMN/SRMA/LCD, Gif sur Yvette (France)

2009-07-01

For nuclear reactor components, uniaxial isothermal fatigue curves are used to estimate the crack initiation under thermal fatigue. However, such approach would be not sufficient in some cases where cracking was observed. To investigate differences between uniaxial and thermal fatigue damage, tests have been carried out at CEA using the thermal fatigue devices SPLASH and FAT3D: a bi-dimensional (2-D) loading status is obtained in SPLASH, whereas a tri-dimensional (3-D) loading status is obtained in FAT3D. All the analysed tests clearly show that crack initiation in thermal fatigue is faster than in uniaxial isothermal fatigue conditions: for identical levels of strain, the number of cycles required to achieve crack initiation is significantly lower. The enhanced damaging effect probably results from a pure mechanical origin: a nearly perfect biaxial state corresponds to an increased hydrostatic stress. Consequently, multiaxial fatigue criteria must be applied. The Zamrik's strain criterion and the energy criterion proposed by Ecole Polytechnique provide the best estimations. In that framework, the proposed new method coupling both RCC-MR strain estimations and Zamrik's criterion appears to be more promising for the designer. (orig.)

Thermal fatigue appears to be more damaging than uniaxial isothermal fatigue for the austentic stainless steels, and application of multiaxial fatigue criteria

International Nuclear Information System (INIS)

Fissolo, Antoine; Gourdin, Cedric; Vincent, Ludovic

2009-01-01

For nuclear reactor components, uniaxial isothermal fatigue curves are used to estimate the crack initiation under thermal fatigue. However, such approach would be not sufficient in some cases where cracking was observed. To investigate differences between uniaxial and thermal fatigue damage, tests have been carried out at CEA using the thermal fatigue devices SPLASH and FAT3D: a bi-dimensional (2-D) loading status is obtained in SPLASH, whereas a tri-dimensional (3-D) loading status is obtained in FAT3D. All the analysed tests clearly show that crack initiation in thermal fatigue is faster than in uniaxial isothermal fatigue conditions: for identical levels of strain, the number of cycles required to achieve crack initiation is significantly lower. The enhanced damaging effect probably results from a pure mechanical origin: a nearly perfect biaxial state corresponds to an increased hydrostatic stress. Consequently, multiaxial fatigue criteria must be applied. The Zamrik's strain criterion and the energy criterion proposed by Ecole Polytechnique provide the best estimations. In that framework, the proposed new method coupling both RCC-MR strain estimations and Zamrik's criterion appears to be more promising for the designer. (orig.)

Fatigue evaluation algorithms: Review

Energy Technology Data Exchange (ETDEWEB)

Passipoularidis, V.A.; Broendsted, P.

2009-11-15

A progressive damage fatigue simulator for variable amplitude loads named FADAS is discussed in this work. FADAS (Fatigue Damage Simulator) performs ply by ply stress analysis using classical lamination theory and implements adequate stiffness discount tactics based on the failure criterion of Puck, to model the degradation caused by failure events in ply level. Residual strength is incorporated as fatigue damage accumulation metric. Once the typical fatigue and static properties of the constitutive ply are determined,the performance of an arbitrary lay-up under uniaxial and/or multiaxial load time series can be simulated. The predictions are validated against fatigue life data both from repeated block tests at a single stress ratio as well as against spectral fatigue using the WISPER, WISPERX and NEW WISPER load sequences on a Glass/Epoxy multidirectional laminate typical of a wind turbine rotor blade construction. Two versions of the algorithm, the one using single-step and the other using incremental application of each load cycle (in case of ply failure) are implemented and compared. Simulation results confirm the ability of the algorithm to take into account load sequence effects. In general, FADAS performs well in predicting life under both spectral and block loading fatigue. (author)

Pilot trials of hemicelluloses extraction prior to thermomechanical pulp production: Part 1

Science.gov (United States)

Carl Houtman; Eric Horn

2011-01-01

Pilot data indicate that wood chip pretreatment with oxalic acid reduced the specific energy required to make thermomechanical pulp. A combined oxalic acid/bisulfite treatment resulted in 21% refiner energy savings and 13% increase in brightness for aspen. A low level of oxalic acid treatment was effective for spruce. Energy savings of 30% was observed with no...

Examining fatigue in COPD

DEFF Research Database (Denmark)

Al-Shair, Khaled; Muellerova, Hana; Yorke, Janelle

2012-01-01

ABSTRACT: INTRODUCTION: Fatigue is a disruptive symptom that inhibits normal functional performance of COPD patients in daily activities. The availability of a short, simple, reliable and valid scale would improve assessment of the characteristics and influence of fatigue in COPD. METHODS......: At baseline, 2107 COPD patients from the ECLIPSE cohort completed the Functional Assessment of Chronic Illness Therapy Fatigue (FACIT-F) scale. We used well-structured classic method, the principal components analysis (PCA) and Rasch analysis for structurally examining the 13-item FACIT-F. RESULTS: Four items...... were less able to capture fatigue characteristics in COPD and were deleted. PCA was applied to the remaining 9 items of the modified FACIT-F and resulted in three interpretable dimensions: i) general (5 items); ii) functional ability (2 items); and iii) psychosocial fatigue (2 items). The modified...

Thermomechanical Analysis (TMA) and its application to polymer systems

Energy Technology Data Exchange (ETDEWEB)

Adams, Jillian Cathleen [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2016-05-25

Thermomechanical analysis (TMA) instruments are used to measure dimensional changes as a sample is heated or cooled. Data obtained from these instruments can be used to calculate the glass transition (Tg) and the coefficient of thermal expansion (CTE). Commonly, materials expand when heated and contract when cooled; however, the rate of such changes depends largely on the type of material. In manufacturing, it is important to use components with similar CTE values to avoid product failure, leaks, or a build-up of thermal stress. Therefore, TMA is a straightforward, useful tool in research and industry.

Contribution of Brazil nut shell fiber and electron-beam irradiation in thermomechanical properties of HDPE

International Nuclear Information System (INIS)

Polato, Pamella; Lorusso, Leandro Alex; Souza, Clecia de Moura; Moura, Esperidiana Augusta Barretos de; Chinellato, Anne; Rosa, Ricardo de

2010-01-01

In the present work, the influence of electron-beam irradiation on thermo-mechanical properties of HDPE and HDPE/Brazil nut shell fiber composite was investigated. The materials were irradiated at radiation dose 50 kGy using a 1.5 MeV electron beam accelerator, at room temperature in presence of air. The irradiated and non-irradiated samples were submitted to thermo-mechanical tests and the correlation between their properties was discussed. The results showed that the incorporation of Brazil nut shell fiber represented a significant gain (p < 0,05) in tensile strength at break, flexural strength, flexural module, Vicat softening temperature and heat distortion temperature (HDT) properties of the HDPE. In addition, the irradiated HDPE/Brazil nut shell fiber composite presented a significant increase (p < 0.05) in this properties compared with irradiated HDPE. (author)

High temperature creep-fatigue design

International Nuclear Information System (INIS)

Tavassoli, A. A. F.; Fournier, B.; Sauzay, M.

2010-01-01

Generation IV fission and future fusion reactors envisage development of more efficient high temperature concepts where materials performances are key to their success. This paper examines different types of high temperature creep-fatigue interactions and their implications on design rules for the structural materials retained in both programmes. More precisely, the paper examines current status of design rules for the stainless steel type 316L(N), the conventional Modified 9Cr-1Mo martensitic steel and the low activation Eurofer steel. Results obtained from extensive high temperature creep, fatigue and creep-fatigue tests performed on these materials and their welded joints are presented. These include sequential creep-fatigue and relaxation creep-fatigue tests with hold times in tension, in compression or in both. Effects of larger plastic deformations on fatigue properties are studied through cyclic creep tests or fatigue tests with extended hold time in creep. In most cases, mechanical test results are accompanied with microstructural and fractographic observations. In the case of martensitic steels, the effect of oxidation is examined by performing creep-fatigue tests on identical specimens in vacuum. Results obtained are analyzed and their implications on design allowable and creep-fatigue interaction diagrams are presented. While reasonable confidence is found in predicting creep-fatigue damage through existing code procedures for austenitic stainless steels, effects of cyclic softening and coarsening of microstructure of martensitic steels throughout the fatigue life on materials properties need to be taken into account for more precise damage calculations. In the long-term, development of ferritic/martensitic steels with stable microstructure, such as ODS steels, is proposed. (authors)

High temperature creep-fatigue design

Energy Technology Data Exchange (ETDEWEB)

Tavassoli, A. A. F.; Fournier, B.; Sauzay, M. [CEA Saclay, DEN DMN, F-91191 Gif Sur Yvette (France)

2010-07-01

Generation IV fission and future fusion reactors envisage development of more efficient high temperature concepts where materials performances are key to their success. This paper examines different types of high temperature creep-fatigue interactions and their implications on design rules for the structural materials retained in both programmes. More precisely, the paper examines current status of design rules for the stainless steel type 316L(N), the conventional Modified 9Cr-1Mo martensitic steel and the low activation Eurofer steel. Results obtained from extensive high temperature creep, fatigue and creep-fatigue tests performed on these materials and their welded joints are presented. These include sequential creep-fatigue and relaxation creep-fatigue tests with hold times in tension, in compression or in both. Effects of larger plastic deformations on fatigue properties are studied through cyclic creep tests or fatigue tests with extended hold time in creep. In most cases, mechanical test results are accompanied with microstructural and fractographic observations. In the case of martensitic steels, the effect of oxidation is examined by performing creep-fatigue tests on identical specimens in vacuum. Results obtained are analyzed and their implications on design allowable and creep-fatigue interaction diagrams are presented. While reasonable confidence is found in predicting creep-fatigue damage through existing code procedures for austenitic stainless steels, effects of cyclic softening and coarsening of microstructure of martensitic steels throughout the fatigue life on materials properties need to be taken into account for more precise damage calculations. In the long-term, development of ferritic/martensitic steels with stable microstructure, such as ODS steels, is proposed. (authors)

Translating Fatigue to Human Performance

Science.gov (United States)

Enoka, Roger M.; Duchateau, Jacques

2016-01-01

Despite flourishing interest in the topic of fatigue—as indicated by the many presentations on fatigue at the 2015 annual meeting of the American College of Sports Medicine—surprisingly little is known about its impact on human performance. There are two main reasons for this dilemma: (1) the inability of current terminology to accommodate the scope of the conditions ascribed to fatigue, and (2) a paucity of validated experimental models. In contrast to current practice, a case is made for a unified definition of fatigue to facilitate its management in health and disease. Based on the classic two-domain concept of Mosso, fatigue is defined as a disabling symptom in which physical and cognitive function is limited by interactions between performance fatigability and perceived fatigability. As a symptom, fatigue can only be measured by self-report, quantified as either a trait characteristic or a state variable. One consequence of such a definition is that the word fatigue should not be preceded by an adjective (e.g., central, mental, muscle, peripheral, and supraspinal) to suggest the locus of the changes responsible for an observed level of fatigue. Rather, mechanistic studies should be performed with validated experimental models to identify the changes responsible for the reported fatigue. As indicated by three examples (walking endurance in old adults, time trials by endurance athletes, and fatigue in persons with multiple sclerosis) discussed in the review, however, it has proven challenging to develop valid experimental models of fatigue. The proposed framework provides a foundation to address the many gaps in knowledge of how laboratory measures of fatigue and fatigability impact real-world performance. PMID:27015386

High strength and high electrical conductivity Cu–Cr system alloys manufactured by hot rolling–quenching process and thermomechanical treatments

International Nuclear Information System (INIS)

Xia Chengdong; Zhang Wan; Kang Zhanyuan; Jia Yanlin; Wu Yifeng; Zhang Rui; Xu Genying; Wang Mingpu

2012-01-01

Highlights: ► HR–Q and thermomechanical treatments are successfully developed to manufacture Cu–Cr system alloys. ► Ordered fcc structure Cr precipitates are considered to be precursors of equilibrium bcc Cr precipitates. ► The Cr precipitates are responsible for the improvement of properties. ► Additions of Zr, Mg and Si bring about significant improvement in properties of Cu–Cr alloy. ► Good properties are ascribed to grain boundary strengthening, strain hardening and precipitation hardening. - Abstract: Cu–Cr system alloy strips were manufactured by an online hot rolling–quenching (HR–Q) process and subsequent thermomechanical treatments. The microstructure and properties of the alloys were investigated by observations of optical microscopy and transmission electron microscopy, and measurements of microhardness and electrical conductivity. The results show that the HR–Q process and thermomechanical treatments are successfully developed to manufacture Cu–Cr system alloy strips with good combinations of strength, conductivity and softening resistance. Ordered fcc structure Cr precipitates, which are decomposed from the thermomechanical treated alloys, are considered to be precursors to the formation of equilibrium bcc Cr precipitates and responsible for the improvement of properties during near peak aging. Small additions of Zr, Mg and Si effectively improve the hardness and softening resistance of Cu–Cr alloy, and slightly reduce the electrical conductivity. The achievement of high strength and high electrical conductivity in the alloys is ascribed to the interactions of grain boundary strengthening, strain hardening and precipitation hardening.

Preliminary thermal/thermomechanical analyses of the Site Characterization Plan's Conceptual Design for a repository containing horizontally emplaced waste packages at the Deaf Smith County site

International Nuclear Information System (INIS)

Ghantous, N.Y.; Raines, G.E.

1987-10-01

This report presents thermal/thermomechanical analyses of the Site Characterization Plan Conceptual Design for horizontal package emplacement at the Deaf Smith County site, Texas. The repository was divided into three geometric regions. Then two-dimensional finite-element models were set up to approximate the three-dimensional nature of each region. Thermal and quasistatic thermomechanical finite-element analyses were performed to evaluate the thermal/thermomechanical responses of the three regions. The exponential-time creep law was used to represent the creep behavior of salt rock. The repository design was evaluated by comparing the thermal/thermomechanical responses obtained for the three regions with interim performance constraints. The preliminary results show that all the performance constraints are met except for those of the waste package. The following factors were considered in interpreting these results: (1) the qualitative description of the analytical responses; (2) the limitations of the analyses; and (3) either the conclusions based on overall evaluation of limitations and analytical results or the conclusions based on the fact that the repository design may be evaluated only after further analyses. Furthermore, a parametric analysis was performed to estimate the effect of material parameters on the predicted thermal/thermomechanical response. 23 refs., 34 figs., 9 tabs

Determinants of seafarers’ fatigue

DEFF Research Database (Denmark)

Bøggild Dohrmann, Solveig; Leppin, Anja

2017-01-01

in the review. The main reason for exclusion was fatigue not being the outcome variable. Results: Most evidence was available for work time-related factors suggesting that working nights was most fatiguing, that fatigue levels were higher toward the end of watch or shift, and that the 6-h on–6-h off watch...

Influence of thermo-mechanical cycling on porcelain bonding to cobalt-chromium and titanium dental alloys fabricated by casting, milling, and selective laser melting.

Science.gov (United States)

Antanasova, Maja; Kocjan, Andraž; Kovač, Janez; Žužek, Borut; Jevnikar, Peter

2018-04-01

The aim has been to determine the effect of thermo-mechanical cycling on shear-bond-strength (SBS) of dental porcelain to Co-Cr and Ti-based alloys fabricated by casting, computer-numerical-controlled milling, and selective-laser-melting (SLM). Seven groups (n=22/group) of metal cylinders were fabricated by casting (Co-Cr and commercially pure-cpTi), milling (Co-Cr, cpTi, Ti-6Al-4V) or by SLM (Co-Cr and Ti-6Al-4V) and abraded with airborne-particles. The average surface roughness (R a ) was determined for each group. Dental porcelain was applied and each metal-ceramic combination was divided into two subgroups - stored in deionized water (24-h, 37°C), or subjected to both thermal (6000-cycles, between 5 and 60°C) and mechanical cycling (10 5 -cycles, 60N-load). SBS test-values and failure modes were recorded. Metal-ceramic interfaces were analyzed with a focused-ion-beam/scanning-electron-microscope (FIB/SEM) and energy-dispersive-spectroscopy (EDS). The elastic properties of the respective metal and ceramic materials were evaluated by instrumented-indentation-testing. The oxide thickness on intact Ti-based substrates was measured with Auger-electron-spectroscopy (AES). Data were analyzed using ANOVA, Tukey's HSD and t-tests (α=0.05). The SBS-means differed according to the metal-ceramic combination (p<0.0005) and to the fatigue conditions (p<0.0005). The failure modes and interface analyses suggest better porcelain adherence to Co-Cr than to Ti-based alloys. Values of R a were dependent on the metal substrate (p<0.0005). Ti-based substrates were not covered with thick oxide layers following digital fabrication. Ti-based alloys are more susceptible than Co-Cr to reduction of porcelain bond strength following thermo-mechanical cycling. The porcelain bond strength to Ti-based alloys is affected by the applied metal processing technology. Copyright © 2017 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved.

Food web accumulation of cyclic siloxanes in Lake Mjøsa, Norway.

Science.gov (United States)

Borgå, Katrine; Fjeld, Eirik; Kierkegaard, Amelie; McLachlan, Michael S

2012-06-05

The biomagnification of the cyclic volatile methyl siloxanes octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexatetrasiloxane (D6) was analyzed in the Lake Mjøsa food web in Norway from zooplankton and Mysis to planktivorous and piscivorous fish. The trophic magnification factor (TMF) for D5 was determined and compared with TMFs of several legacy contaminants: polychlorinated biphenyl (PCB) congeners 153 and 180, polybrominated diphenyl ether (PBDE) congeners 47 and 99, and p,p'-DDE. D5 showed TMF significantly greater than 1, implying food web biomagnification (TMF = 2.28, CI: 1.22-4.29). This contrasts with two studies that reported TMF < 1, which may reflect variability in TMF between food webs. The Lake Mjøsa D5 TMF was sensitive to the species included at the higher trophic level; whole food web TMF differed from TMF excluding smelt (Osmerus eperlanus) or brown trout (Salmo trutta) (TMF(-SMELT) = 1.62, CI: 0.96-2.72; TMF(-TROUT) = 3.58, CI: 1.82-7.03). For legacy contaminants (e.g., PCB-153 and PCB-180), the TMFs were less sensitive to the food web composition, and a better model fit was obtained compared to D5. The differences in biomagnification behavior between D5 and the legacy contaminants suggest that the biomagnification of D5 is being governed by species-specific properties such as biotransformation rate or tissue distribution that differ from those of legacy contaminants.

Are There Any Natural Remedies That Reduce Chronic Fatigue Associated with Chronic Fatigue Syndrome?

Science.gov (United States)

... natural remedies that reduce chronic fatigue associated with chronic fatigue syndrome? Answers from Brent A. Bauer, M.D. Researchers ... a variety of natural products for effectiveness against chronic fatigue syndrome. Most results have been disappointing. A few remedies — ...

Compressive Fatigue in Wood

DEFF Research Database (Denmark)

Clorius, Christian Odin; Pedersen, Martin Bo Uhre; Hoffmeyer, Preben

1999-01-01

An investigation of fatigue failure in wood subjected to load cycles in compression parallel to grain is presented. Small clear specimens of spruce are taken to failure in square wave formed fatigue loading at a stress excitation level corresponding to 80% of the short term strength. Four...... frequencies ranging from 0.01 Hz to 10 Hz are used. The number of cycles to failure is found to be a poor measure of the fatigue performance of wood. Creep, maximum strain, stiffness and work are monitored throughout the fatigue tests. Accumulated creep is suggested identified with damage and a correlation...

Research progress of exercise-induced fatigue

Directory of Open Access Journals (Sweden)

Peng-yi DAI

2016-12-01

Full Text Available Exercise-induced fatigue is a comprehensive response to a variety of physiological and biochemical changes in the body, and can affect people's quality of life to different extents. If no timely recovery after occurrence of fatigue, accumulated gradually, it can lead to "burnout", a "overtraining syndrome", "chronic fatigue syndrome", etc., which will cause endocrine disturbance, immune suppression, even physical illness. Exercise-induced fatigue becomes an important factor endangering human health. In recent years, many experts and scholars at home and abroad are committed to the research of exercise-induced fatigue, and have put forward a variety of hypothesis to explain the cause of exercise-induced fatigue. They expect to find out the methods for preventing and eliminating exercise-induced fatigue. This article discusses mainly the pathogenesis, model building, elimination/ relief, etc. of exercise-induced fatigue to point out the research achievements of exercise-induced fatigue and its existing problems. DOI: 10.11855/j.issn.0577-7402.2016.11.14

Fatigue after Stroke: The Patient's Perspective

Directory of Open Access Journals (Sweden)

Victoria Louise Barbour

2012-01-01

Full Text Available Background. Fatigue after stroke is common and distressing to patients. Aims. Our aims were to explore patients' perceptions of post-stroke fatigue, including the causes of fatigue and the factors that alleviate fatigue, in a mixed methods study. Results. We interviewed 15 patients who had had a stroke and were inpatients on stroke rehabilitation wards. A substantial proportion of patients reported that their fatigue started at the time of their stroke. Various different factors were reported to improve fatigue, including exercise, good sleep, rehabilitation and rest. Fatigue influences patients' sense of “control” after their stroke. Conclusion. Our results are consistent with the possibility that poststroke fatigue might be triggered by factors that occur at the time of the stroke (e.g., the stroke lesion itself, or admission to hospital and then exacerbated by poor sleep and boredom. These factors should be considered when developing complex interventions to improve post-stroke fatigue.

Fretting fatigue life estimation using fatigue damage gradient correction factor in various contact configurations

Energy Technology Data Exchange (ETDEWEB)

Hwang, Dong Hyeon; Cho, Sung-San [Hongik University, Seoul (Korea, Republic of)

2017-03-15

A fretting fatigue life estimation method that takes into account the stress gradient effect was developed by the authors [Journal of Mechanical Science and Technology, 28 (2014) 2153-2159]. In the developed method, fatigue damage value at the cracking location is corrected with fatigue damage gradient and the corrected value is compared directly with the plain fatigue data for life estimation. In other words, the correction factor is the ratio of plain fatigue damage to fretting fatigue damage at the same life and a function of fatigue damage gradient. Since reliability of the method was verified only for cylinder-on-flat contact configuration in the previous study, the present study extends application of the method to flat-on-flat contact configurations by developing the correction factor for both the contact configuration. Fretting fatigue experiments were conducted to obtain fatigue life data for various fretting pads. Finite element analyses were conducted to evaluate the Smith-Watson-Topper (SWT) fatigue damage parameter in the cracking region. It is revealed that the SWT parameter in fat-on-flat contact configuration decreases exponentially away from the surface as in cylinder-on-flat contact configuration, and thus the SWT gradient at the surface can be evaluated reliably. Moreover, it is found that decrease in the SWT parameter around the cracking location can be expressed by piecewise exponential curves. If the gradient of SWT at the surface is used as a representative value of SWT gradient, it is impossible to establish functional relationship between the SWT gradient and the correction factor for both the contact configurations although it was possible for cylinder-on-flat contact configuration. However, if weighted average of the SWT gradient values obtained from each exponential curve in the piecewise exponential curve is used as a representative value, the correction factor for both the contact configurations becomes a function of the SWT gradient

Fatigue in soccer

DEFF Research Database (Denmark)

Mohr, Magni; Krustrup, Peter; Bangsbo, Jens

2005-01-01

This review describes when fatigue may develop during soccer games and the potential physiological mechanisms that cause fatigue in soccer. According to time?-?motion analyses and performance measures during match-play, fatigue or reduced performance seems to occur at three different stages......, acidity or the breakdown of creatine phosphate. Instead, it may be related to disturbances in muscle ion homeostasis and an impaired excitation of the sarcolemma. Soccer players' ability to perform maximally is inhibited in the initial phase of the second half, which may be due to lower muscle...... concentrations in a considerable number of individual muscle fibres. In a hot and humid environment, dehydration and a reduced cerebral function may also contribute to the deterioration in performance. In conclusion, fatigue or impaired performance in soccer occurs during various phases in a game, and different...

Low cycle fatigue: high cycle fatigue damage accumulation in a 304L austenitic stainless steel

International Nuclear Information System (INIS)

Lehericy, Y.

2007-05-01

The aim of this study was to evaluate the consequences of a Low Cycle Fatigue pre-damage on the subsequent fatigue limit of a 304L stainless steel. The effects of hardening and severe roughness (grinding) have also been investigated. In a first set of tests, the evolution of the surface damage induced by the different LCF pre-cycling was characterized. This has permitted to identify mechanisms and kinetics of damage in the plastic domain for different surface conditions. Then, pre-damaged samples were tested in the High Cycle Fatigue domain in order to establish the fatigue limits associated with each level of pre-damage. Results evidence that, in the case of polished samples, an important number of cycles is required to initiate surface cracks ant then to affect the fatigue limit of the material but, in the case of ground samples, a few number of cycles is sufficient to initiate cracks and to critically decrease the fatigue limit. The fatigue limit of pre-damaged samples can be estimated using the stress intensity factor threshold. Moreover, this detrimental effect of severe surface conditions is enhanced when fatigue tests are performed under a positive mean stress (author)

Thermomechanical treatment of austempered ductile iron

Directory of Open Access Journals (Sweden)

A. A. Nofal

2007-11-01

Full Text Available The production of lightweight ferrous castings with increased strength properties became unavoidable facing the serious challenge of lighter aluminum and magnesium castings. The relatively new ferrous casting alloy ADI offers promising strength prospects, and the thermo-mechanical treatment of ductile iron may suggest a new route for production of thin-wall products. This work aims at studying the influence of thermomechanical treatment, either by ausforming just after quenching and before the onset of austempering reaction or by cold rolling after austempering. In the first part of this work, ausforming of ADI up to 25% reduction in height during a rolling operation was found to add a mechanical processing component compared to the conventional ADI heat treatment, thus increasing the rate of ausferrite formation and leading to a much finer and more homogeneous ausferrite product. The kinetics of ausferrite formation was studied using both metallographic as well as XRD-techniques. The effect of ausforming on the strength was quite dramatic (up to 70% and 50% increase in the yield and ultimate strength respectively. A mechanism involving both a refined microstructural scale and an elevated dislocation density was suggested. Nickel is added to ADI to increase hardenability of thick section castings, while ausforming to higher degrees of deformation is necessary to alleviate the deleterious effect of alloy segregation on ductility. In the second part of this work, the influence of cold rolling (CR on the mechanical properties and structural characteristics of ADI was investigated. The variation in properties was related to the amount of retained austenite (γr and its mechanically induced ransformation. In the course of tensile deformation of ADI, transformation induced plasticity (TRIP takes place, indicated by the increase of the instantaneous value of strain-hardening exponent with tensile strain. The amount of retained austenite was found to

Study of the thermo-mechanical performances of the IFMIF-EVEDA Lithium Test Loop target assembly

Energy Technology Data Exchange (ETDEWEB)

Di Maio, P.A., E-mail: dimaio@din.unipa.it [Dipartimento dell' Energia, Universita di Palermo, Viale delle Scienze, 90128 Palermo (Italy); Arena, P.; Bongiovi, G. [Dipartimento dell' Energia, Universita di Palermo, Viale delle Scienze, 90128 Palermo (Italy); Giammusso, R.; Micciche, G.; Tincani, A. [ENEA C. R. Brasimone, 40032 Camugnano, Bologna (Italy)

2012-08-15

Highlights: Black-Right-Pointing-Pointer IFMIF-EVEDA target assembly thermo-mechanical behavior has been investigated. Black-Right-Pointing-Pointer Finite element method has been followed and a commercial code has been used. Black-Right-Pointing-Pointer Nominal, design and pressure test steady state scenarios and start-up transient conditions have been investigated. Black-Right-Pointing-Pointer Steady state results have shown that back-plate yielding may occur only under the design scenario. Black-Right-Pointing-Pointer Transient analysis has indicated that TA start-up lasts for {approx}60 h. - Abstract: Within the framework of the IFMIF R and D program and in close cooperation with ENEA-Brasimone, at the Department of Energy of the University of Palermo a research campaign has been launched to investigate the thermo-mechanical behavior of the target assembly under both steady state and start-up transient conditions. A theoretical approach based on the finite element method (FEM) has been followed and a well-known commercial code has been adopted. A realistic 3D FEM model of the target assembly has been set-up and optimized by running a mesh independency analysis. A proper set of loads and boundary conditions, mainly concerned with radiation heat transfer between the target assembly external walls and the inner walls of its containment vessel, have been considered and the target assembly thermo-mechanical behavior under nominal, design and pressure test steady state scenarios and start-up transient conditions has been investigated. Results are herewith reported and discussed.

Thermomechanical behavior modeling and experimental validation of polymer-wound composite multi-layers. Hydrogen storage application

International Nuclear Information System (INIS)

Gentilleau, Benoit

2012-01-01

The purpose of this research is to study the thermomechanical behavior of the constituent materials of a type IV hydrogen storage tank: a composite, ensuring the strength, is wound around the polyurethane liner that ensures sealing of the tank and thermal insulation; at the extremities, stainless steel parts are used to allow the process connection. In this type of tank, during filling, there is a significant increase in hydrogen temperature, resulting in a gradual heating of the structure and the presence of temperature gradients. The purpose of this study is primarily to characterize the behavior of such a structure when subjects to complex thermomechanical loading. Initially, mechanical and thermal characterization tests have been made over the service life range of temperature of the tank to obtain the necessary data for the realization of a thermomechanical numerical model. Then, a behavior law of the composite, easily transferable to a complex structure such as the whole tank and taking into account the non-linearity, the matrix damage, the progressive loss of shear modulus, and the thermo-dependence of the materials parameters, is developed. The tests on technological representative specimens have been performed to better understand the mechanisms that can appear in the tank and to validate the model. Finally, a numerical study of a tank was performed. The coupled influence of temperature and damage matrix on the behavior of this structure is analyzed. (author)

Visual perception of fatigued lifting actions.

Science.gov (United States)

Fischer, Steven L; Albert, Wayne J; McGarry, Tim

2012-12-01

Fatigue-related changes in lifting kinematics may expose workers to undue injury risks. Early detection of accumulating fatigue offers the prospect of intervention strategies to mitigate such fatigue-related risks. In a first step towards this objective, this study investigated whether fatigue detection was accessible to visual perception and, if so, what was the key visual information required for successful fatigue discrimination. Eighteen participants were tasked with identifying fatigued lifts when viewing 24 trials presented using both video and point-light representations. Each trial comprised a pair of lifting actions containing a fresh and a fatigued lift from the same individual presented in counter-balanced sequence. Confidence intervals demonstrated that the frequency of correct responses for both sexes exceeded chance expectations (50%) for both video (68%±12%) and point-light representations (67%±10%), demonstrating that fatigued lifting kinematics are open to visual perception. There were no significant differences between sexes or viewing condition, the latter result indicating kinematic dynamics as providing sufficient information for successful fatigue discrimination. Moreover, results from single viewer investigation reported fatigue detection (75%) from point-light information describing only the kinematics of the box lifted. These preliminary findings may have important workplace applications if fatigue discrimination rates can be improved upon through future research. Copyright © 2012 Elsevier B.V. All rights reserved.

Corrosion fatigue of steels

International Nuclear Information System (INIS)

Spaehn, H.; Wagner, G.H.

1976-01-01

Corrosion fatigue phenomena can be classified into two main groups according to the electrochemical state of the metal surface in the presence of electrolytes: the active and the passive state with an important sub-group of corrosion fatigue in the unstable passive state. The allowable stress for structures exposed to the conjoint action of corrosion and fatigue is influenced by many factors: kind of media, number of cycles, frequency, mean stress, size, notches, loading mode, alloy composition and mechanical strength. A critical literature review shows contradictory results if a classification by the electrochemical surface state is not applied. Case histories and counter measures illustrate the practical importance of corrosion fatigue in many branches of industry as well as the urgent need for a better knowledge about the mutual influence of the phenomena to get rules by which the engineer can appraise the risk of corrosion fatigue. (orig.) [de

Thermomechanical modelling of laser surface glazing for H13 tool steel

Science.gov (United States)

Kabir, I. R.; Yin, D.; Tamanna, N.; Naher, S.

2018-03-01

A two-dimensional thermomechanical finite element (FE) model of laser surface glazing (LSG) has been developed for H13 tool steel. The direct coupling technique of ANSYS 17.2 (APDL) has been utilised to solve the transient thermomechanical process. A H13 tool steel cylindrical cross-section has been modelled for laser power 200 W and 300 W at constant 0.2 mm beam width and 0.15 ms residence time. The model can predict temperature distribution, stress-strain increments in elastic and plastic region with time and space. The crack formation tendency also can be assumed by analysing the von Mises stress in the heat-concentrated zone. Isotropic and kinematic hardening models have been applied separately to predict the after-yield phenomena. At 200 W laser power, the peak surface temperature achieved is 1520 K which is below the melting point (1727 K) of H13 tool steel. For laser power 300 W, the peak surface temperature is 2523 K. Tensile residual stresses on surface have been found after cooling, which are in agreement with literature. Isotropic model shows higher residual stress that increases with laser power. Conversely, kinematic model gives lower residual stress which decreases with laser power. Therefore, both plasticity models could work in LSG for H13 tool steel.

Muscle Deoxygenation Causes Muscle Fatigue

Science.gov (United States)

Murthy, G.; Hargens, A. R.; Lehman, S.; Rempel, D.

1999-01-01

Muscle fatigue is a common musculoskeletal disorder in the work place, and may be a harbinger for more disabling cumulative trauma disorders. Although the cause of fatigue is multifactorial, reduced blood flow and muscle oxygenation may be the primary factor in causing muscle fatigue during low intensity muscle exertion. Muscle fatigue is defined as a reduction in muscle force production, and also occurs among astronauts who are subjected to postural constraints while performing lengthy, repetitive tasks. The objectives of this research are to: 1) develop an objective tool to study the role of decreased muscle oxygenation on muscle force production, and 2) to evaluate muscle fatigue during prolonged glovebox work.

Effect of ratchet strain on fatigue and creep–fatigue strength of Mod.9Cr–1Mo steel

International Nuclear Information System (INIS)

Ando, Masanori; Isobe, Nobuhiro; Kikuchi, Koichi; Enuma, Yasuhiro

2012-01-01

Highlights: ► Uniaxial fatigue and creep–fatigue tests with superimposed strain were performed. ► Variety of superimposed strain were applied as ratchet strain in the tests. ► Effect of superimposed strain on fatigue and creep–fatigue life is negligible. ► A cyclic softening character reducing the effect of superimposed strain. - Abstract: The effect of ratcheting deformation on fatigue and creep–fatigue life in Mod.9Cr–1Mo steel was investigated. Uniaxial fatigue and creep–fatigue testing with superimposed strain were performed to evaluate the effect of ratcheting deformation on the failure cycle. In a series of tests, a specific amount of superimposed strain was accumulated in each cycle. The accumulated strain as ratcheting deformation, cycles to reach the accumulated strain, and test temperatures were varied in the tests. In the fatigue tests with superimposed strain at 550 °C, slight reductions of failure lives were observed. All of the numbers of cycles to failure in the fatigue tests with superimposed strain were within a factor of 1.5 of that of the fatigue test without superimposed strain at 550 °C. The apparent relationship between failure cycles and testing parameters was not observed. In fatigue tests with superimposed strain at 550 °C, maximum mean stress was insignificant and generated in early cycles because Mod.9Cr–1Mo steel exhibits cyclic softening characteristics. It was assumed that suppression of mean stress generation by cyclic softening reduces the effect of ratcheting strain. Conversely, failure lives were increased by accumulated strain in the test conducted at 450 °C because of stress–strain hysteresis loop shrinkage caused by cyclic softening induced by the accumulated strain. In the creep–fatigue tests with superimposed strain, test results indicated that the accumulated stain was negligible. It was concluded that the effect of ratcheting deformation on fatigue and creep–fatigue life is negligible as long

All Fatigue is Not Created Equal: The Association of Fatigue and Its Subtypes on Pain Interference in Orofacial Pain.

Science.gov (United States)

Boggero, Ian A; Rojas-Ramirez, Marcia V; Carlson, Charles R

2017-03-01

Fatigue is known to be a pathway through which depression, psychological distress, pain intensity, and sleep disturbance influence pain interference, but the independent effects of fatigue on pain interference after controlling for these variables remains unknown. In addition, no study to date has tested whether fatigue subtypes of general fatigue, mental fatigue, emotional fatigue, physical fatigue, or vigor differentially predict pain interference. The current study tested these associations using archival medical data of 2133 chronic orofacial pain patients, who completed a battery of psychological questionnaires at the time of their first appointment at an orofacial pain clinic. Hierarchical linear regression analysis revealed that after controlling for depression, psychological distress, sleep disturbance, pain intensity, and demographic variables, fatigue predicted higher pain interference (B=0.70, SE=0.17, Ppain interference after controlling for the aforementioned variables. The findings suggest that fatigue is an important independent predictor of pain interference and not merely a mediator. These findings also suggest that not all fatigue is created equal. Interventions aimed at reducing pain interference should target specific fatigue symptoms of physical fatigue and vigor. Future research investigating the independent associations of fatigue subtypes on pain outcomes may help clarify the nature of the interrelationships between pain and fatigue.

Atomistic modeling of thermomechanical properties of SWNT/Epoxy nanocomposites

Science.gov (United States)

Fasanella, Nicholas; Sundararaghavan, Veera

2015-09-01

Molecular dynamics simulations are performed to compute thermomechanical properties of cured epoxy resins reinforced with pristine and covalently functionalized carbon nanotubes. A DGEBA-DDS epoxy network was built using the ‘dendrimer’ growth approach where 75% of available epoxy sites were cross-linked. The epoxy model is verified through comparisons to experiments, and simulations are performed on nanotube reinforced cross-linked epoxy matrix using the CVFF force field in LAMMPS. Full stiffness matrices and linear coefficient of thermal expansion vectors are obtained for the nanocomposite. Large increases in stiffness and large decreases in thermal expansion were seen along the direction of the nanotube for both nanocomposite systems when compared to neat epoxy. The direction transverse to nanotube saw a 40% increase in stiffness due to covalent functionalization over neat epoxy at 1 K whereas the pristine nanotube system only saw a 7% increase due to van der Waals effects. The functionalized SWNT/epoxy nanocomposite showed an additional 42% decrease in thermal expansion along the nanotube direction when compared to the pristine SWNT/epoxy nanocomposite. The stiffness matrices are rotated over every possible orientation to simulate the effects of an isotropic system of randomly oriented nanotubes in the epoxy. The randomly oriented covalently functionalized SWNT/Epoxy nanocomposites showed substantial improvements over the plain epoxy in terms of higher stiffness (200% increase) and lower thermal expansion (32% reduction). Through MD simulations, we develop means to build simulation cells, perform annealing to reach correct densities, compute thermomechanical properties and compare with experiments.

Atomistic modeling of thermomechanical properties of SWNT/Epoxy nanocomposites

International Nuclear Information System (INIS)

Fasanella, Nicholas; Sundararaghavan, Veera

2015-01-01

Molecular dynamics simulations are performed to compute thermomechanical properties of cured epoxy resins reinforced with pristine and covalently functionalized carbon nanotubes. A DGEBA-DDS epoxy network was built using the ‘dendrimer’ growth approach where 75% of available epoxy sites were cross-linked. The epoxy model is verified through comparisons to experiments, and simulations are performed on nanotube reinforced cross-linked epoxy matrix using the CVFF force field in LAMMPS. Full stiffness matrices and linear coefficient of thermal expansion vectors are obtained for the nanocomposite. Large increases in stiffness and large decreases in thermal expansion were seen along the direction of the nanotube for both nanocomposite systems when compared to neat epoxy. The direction transverse to nanotube saw a 40% increase in stiffness due to covalent functionalization over neat epoxy at 1 K whereas the pristine nanotube system only saw a 7% increase due to van der Waals effects. The functionalized SWNT/epoxy nanocomposite showed an additional 42% decrease in thermal expansion along the nanotube direction when compared to the pristine SWNT/epoxy nanocomposite. The stiffness matrices are rotated over every possible orientation to simulate the effects of an isotropic system of randomly oriented nanotubes in the epoxy. The randomly oriented covalently functionalized SWNT/Epoxy nanocomposites showed substantial improvements over the plain epoxy in terms of higher stiffness (200% increase) and lower thermal expansion (32% reduction). Through MD simulations, we develop means to build simulation cells, perform annealing to reach correct densities, compute thermomechanical properties and compare with experiments. (paper)

Poly-Lactide/Exfoliated C30B Interactions and Influence on Thermo-Mechanical Properties Due to Artificial Weathering

Directory of Open Access Journals (Sweden)

Wendy Margarita Chávez-Montes

2016-04-01

Full Text Available Thermal stability as well as enhanced mechanical properties of poly-lactide (PLA can increase PLA applications for short-use products. The conjunction of adequate molecular weight (MW as well as satisfactory thermo-mechanical properties, together, can lead to the achievement of suitable properties. However, PLA is susceptible to thermal degradation and thus an undesired decay of MW and a decrease of its mechanical properties during processing. To avoid this PLA degradation, nanofiller is incorporated as reinforcement to increase its thermo-mechanical properties. There are many papers focusing on filler effects on the thermal stability and mechanical properties of PLA/nanocomposites; however, these investigations lack an explanation of polymer/filler interactions. We propose interactions between PLA and Cloisite30B (C30B as nanofiller. We also study the effects on the thermal and mechanical properties due to molecular weight decay after exposure to artificial weathering. PLA blank and nanocomposites were subjected to three time treatments (0, 176, and 360 h of exposure to artificial weathering in order to achieve comparable materials with different MW. MW was acquired by means of Gel Permeation Chromatography (GPC. Thermo-mechanical properties were investigated through Thermogravimetric Analysis (TGA, Differential Scanning Calorimetry (DSC, X-ray Diffraction (XRD, Dynamic Mechanical Thermal Analysis (DMTA and Fourier Transform Infrared Spectroscopy (FTIR.

Enhancement of the electrochemical behaviour and biological performance of Ti–25Ta–5Zr alloy by thermo-mechanical processing

Energy Technology Data Exchange (ETDEWEB)

Cimpean, Anisoara [Department of Biochemistry and Molecular Biology, University of Bucharest, Spl. Independentei, 91-95, 050095 Bucharest (Romania); Vasilescu, Ecaterina; Drob, Paula [Department of Electrochemistry and Corrosion, Institute of Physical Chemistry “Ilie Murgulescu” of Romanian Academy, Spl. Independentei 202, 060021 Bucharest (Romania); Cinca, Ion, E-mail: ion_cinca@hotmail.com [Faculty of Material Science and Engineering, Politehnica University, Spl. Independentei 313, 060042 Bucharest (Romania); Vasilescu, Cora; Anastasescu, Mihai [Department of Electrochemistry and Corrosion, Institute of Physical Chemistry “Ilie Murgulescu” of Romanian Academy, Spl. Independentei 202, 060021 Bucharest (Romania); Mitran, Valentina [Department of Biochemistry and Molecular Biology, University of Bucharest, Spl. Independentei, 91-95, 050095 Bucharest (Romania); Drob, Silviu Iulian [Department of Electrochemistry and Corrosion, Institute of Physical Chemistry “Ilie Murgulescu” of Romanian Academy, Spl. Independentei 202, 060021 Bucharest (Romania)

2014-05-01

A new Ti–25Ta–5Zr alloy based only on non-toxic and non-allergic elements was elaborated in as-cast and thermo-mechanical processed, recrystallized states (XRD and SEM) in order to be used as candidate material for implant applications. Its long-term interactions with Ringer–Brown and Ringer solutions of different pH values and its cytocompatibility were determined. The thermo-mechanically processed alloy has nobler electrochemical behaviour than as-cast alloy due to finer microstructure obtained after the applied treatment. Corrosion and ion release rates presented the lowest values for the treated alloy. Nyquist and Bode plots displayed higher impedance values and phase angles for the processed alloy, denoting a more protective passive film. SEM micrographs revealed depositions from solutions that contain calcium, phosphorous and oxygen ions (EDX analysis), namely calcium phosphate. An electric equivalent circuit with two time constants was modelled. Cell culture experiments with MC3T3-E1 pre-osteoblasts demonstrated that thermo-mechanically processed Ti–25Ta–5Zr alloy supports a better cell adhesion and spreading, and enhanced cell proliferation. Altogether, these data indicate that thermo-mechanical treatment endows the alloy with improved anticorrosion and biological performances. - Highlights: • Ti–25Ta–5Zr alloy exhibited noble electrochemical, passive behaviour in simulated biofluids. • An electric equivalent circuit with two time constants was modelled. • Corrosion rates show the lowest values for the recrystallized Ti–25Ta–5Zr alloy. • In vitro tests revealed good cytocompatibility of as-cast and processed alloy. • Recrystallized treatment endows the alloy with superior biological performances.

Enhancement of the electrochemical behaviour and biological performance of Ti–25Ta–5Zr alloy by thermo-mechanical processing

International Nuclear Information System (INIS)

Cimpean, Anisoara; Vasilescu, Ecaterina; Drob, Paula; Cinca, Ion; Vasilescu, Cora; Anastasescu, Mihai; Mitran, Valentina; Drob, Silviu Iulian

2014-01-01

A new Ti–25Ta–5Zr alloy based only on non-toxic and non-allergic elements was elaborated in as-cast and thermo-mechanical processed, recrystallized states (XRD and SEM) in order to be used as candidate material for implant applications. Its long-term interactions with Ringer–Brown and Ringer solutions of different pH values and its cytocompatibility were determined. The thermo-mechanically processed alloy has nobler electrochemical behaviour than as-cast alloy due to finer microstructure obtained after the applied treatment. Corrosion and ion release rates presented the lowest values for the treated alloy. Nyquist and Bode plots displayed higher impedance values and phase angles for the processed alloy, denoting a more protective passive film. SEM micrographs revealed depositions from solutions that contain calcium, phosphorous and oxygen ions (EDX analysis), namely calcium phosphate. An electric equivalent circuit with two time constants was modelled. Cell culture experiments with MC3T3-E1 pre-osteoblasts demonstrated that thermo-mechanically processed Ti–25Ta–5Zr alloy supports a better cell adhesion and spreading, and enhanced cell proliferation. Altogether, these data indicate that thermo-mechanical treatment endows the alloy with improved anticorrosion and biological performances. - Highlights: • Ti–25Ta–5Zr alloy exhibited noble electrochemical, passive behaviour in simulated biofluids. • An electric equivalent circuit with two time constants was modelled. • Corrosion rates show the lowest values for the recrystallized Ti–25Ta–5Zr alloy. • In vitro tests revealed good cytocompatibility of as-cast and processed alloy. • Recrystallized treatment endows the alloy with superior biological performances

Thermal fatigue strength estimation of 2.25Cr-1Mo steel under creep-fatigue interaction

International Nuclear Information System (INIS)

Kuwahara, Kazuo; Nitta, Akihito; Kitamura, Takayuki

1980-01-01

A 2-1/4Cr-1Mo steel is one of principal materials for high temperature equipments in nuclear and thermal power plants. The authors experimentally analyzed the high temperature fatigue strength and creep strength of a 2-1/4 Cr-1Mo steel main steam pipe which had been used in a thermal plant for operation up to 130,000 hours, and pointed out that the strain-range vs. life curves crossed each other due to the difference of temperature-strain phase in thermal fatigue. This suggests that it is difficult to estimate thermal fatigue life of steel materials having been subjected to different temperature-strain phase on the basis of isothermal low-cycle fatigue life at the upper limit temperature of thermal fatigue, and that it is urgently required to establish an appropriate method of evaluating thermal fatigue life. The authors attempted to prove that the strain range partitioning method used for the evaluation of thermal fatigue life in SUS 304 steels is applicable to this 2-1/4Cr-1Mo steel. Consequently, it was found that the thermal fatigue life could be estimated within a factor of 2.5 by the application of this method. (author)

Thermomechanical evaluation of BWR fuel elements for procedures of preconditioned with FEMAXI-V

International Nuclear Information System (INIS)

Hernandez L, H.; Lucatero, M.A.; Ortiz V, J.

2006-01-01

The limitations in the burnt of the nuclear fuel usually are fixed by the one limit in the efforts to that undergo them the components of a nuclear fuel assembly. The limits defined its provide the direction to the fuel designer to reduce to the minimum the fuel failure during the operation, and they also prevent against some thermomechanical phenomena that could happen during the evolution of transitory events. Particularly, a limit value of LHGR is fixed to consider those physical phenomena that could lead to the interaction of the pellet-shirt (Pellet Cladding Interaction, PCI). This limit value it is related directly with an PCI limit that can be fixed based on experimental tests of power ramps. This way, to avoid to violate the PCI limit, the conditioning procedures of the fuel are still required for fuel elements with and without barrier. Those simulation procedures of the power ramp are carried out for the reactor operator during the starting maneuvers or of power increase like preventive measure of possible consequences in the thermomechanical behavior of the fuel. In this work, the thermomechanical behavior of two different types of fuel rods of the boiling water reactor is analyzed during the pursuit of the procedures of fuel preconditioning. Five diverse preconditioning calculations were carried out, each one with three diverse linear ramps of power increments. The starting point of the ramps was taken of the data of the cycle 8 of the unit 1 of the Laguna Verde Nucleo electric Central. The superior limit superior of the ramps it was the threshold of the lineal power in which a fuel failure could be presented by PCI, in function of the fuel burnt. The analysis was carried out with the FEMAXI-V code. (Author)

Fatigue and radiotherapy. A literature review; Fatigue et radiotherapie. Revue de la litterature

Energy Technology Data Exchange (ETDEWEB)

Dilhuydy, J.M.; Ouhtatou, F.; Laporte, C.; Nguyen, T.V.F.; Vendrely, V. [Institut Bergonie Centre Regional de Lutte Contre le Cancer, 33 - Bordeaux (France); Dilhuydy, J.M. [Federation Nationale des Centres de Lutte Contre le Cancer, FNCLCC, Groupe Rehabilitation, 75 - Paris (France); Dilhuydy, M.S. [Hopital Saint-Andre, Service de Medecine Interne, 33 - Bordeaux (France)

2001-11-01

Fatigue is a common complaint for the cancer patient during and after radiotherapy, according to the published studies. Fatigue is a subjective symptom mostly underestimated by oncologists and other care givers. Etiology is complex, poorly understood in spite of obvious causes like insomnia, nausea, pain, depression, psychological distress, anemia, hypothyroidism, menopause disturbances, treatment adverse effects. Fatigue presents multi-factorial and multidimensional aspects. To evaluate it, many tools can be used as single-item, unidimensional and multidimensional instruments. Practically, the open discussion with the patient throughout radiotherapy is essential to define it. Taking charge fatigue requires its acknowledgement by radiotherapist, treatment of associated symptoms with a multidisciplinary approach. (authors)

Development and characterization of fatigue resistant aramid reinforced aluminium laminates (ARALL) for fatigue critical aircraft components

International Nuclear Information System (INIS)

Qaiser, M. H.; Umar, S.; Nauman, S.

2013-01-01

The structural weight of an aircraft has always been a controlling parameter that governs its fuel efficiency and transport capacity. In pursuit of achieving light-weight aircraft structures, high design stress levels have to be adopted and materials with high specific strength such as Aluminum etc. are to be deployed. However, an extensive spectrum of fatigue load exists at the aircraft wings and other aerodynamic components that may cause initiation and propagation of fatigue cracks and concludes in a catastrophic rupture. Fatigue is therefore the limiting design parameter in such cases and materials with high fatigue resistance are then required. A major improvement in the fatigue behavior was observed by laminating Kevlar fibers with Aluminum using epoxy. ARALL (Aramid Reinforced Aluminum Laminates) is a fatigue resistant hybrid composite that consists of layers of thin high strength aluminum alloy sheets surface bonded with aramid fibers. The intact aramid fibers tie up the fatigue cracks, thus reducing the stress intensity factor at the crack tip as a result of which the fatigue properties of can be enhanced with orders of magnitude as compared to monolithic high strength Aluminum alloy sheets. Significant amount of weight savings can be achieved in fatigue critical components in comparison with the traditional materials used in aircraft. (author)

Development and characterization of fatigue resistant Aramid reinforced aluminium laminates (ARALL) for fatigue Critical aircraft components

Science.gov (United States)

Qaiser, M. H.; Umar, S.; Nauman, S.

2014-06-01

The structural weight of an aircraft has always been a controlling parameter that governs its fuel efficiency and transport capacity. In pursuit of achieving light-weight aircraft structures, high design stress levels have to be adopted and materials with high specific strength such as Aluminum etc. are to be deployed. However, an extensive spectrum of fatigue load exists at the aircraft wings and other aerodynamic components that may cause initiation and propagation of fatigue cracks and concludes in a catastrophic rupture. Fatigue is therefore the limiting design parameter in such cases and materials with high fatigue resistance are then required. A major improvement in the fatigue behavior was observed by laminating Kevlar fibers with Aluminum using epoxy. ARALL (Aramid Reinforced ALuminum Laminates) is a fatigue resistant hybrid composite that consists of layers of thin high strength aluminum alloy sheets surface bonded with aramid fibers. The intact aramid fibers tie up the fatigue cracks, thus reducing the stress intensity factor at the crack tip as a result of which the fatigue properties of can be enhanced with orders of magnitude as compared to monolithic high strength Aluminum alloy sheets. Significant amount of weight savings can be achieved in fatigue critical components in comparison with the traditional materials used in aircraft.

Development and characterization of fatigue resistant Aramid reinforced aluminium laminates (ARALL) for fatigue Critical aircraft components

International Nuclear Information System (INIS)

Qaiser, M H; Umar, S; Nauman, S

2014-01-01

The structural weight of an aircraft has always been a controlling parameter that governs its fuel efficiency and transport capacity. In pursuit of achieving light-weight aircraft structures, high design stress levels have to be adopted and materials with high specific strength such as Aluminum etc. are to be deployed. However, an extensive spectrum of fatigue load exists at the aircraft wings and other aerodynamic components that may cause initiation and propagation of fatigue cracks and concludes in a catastrophic rupture. Fatigue is therefore the limiting design parameter in such cases and materials with high fatigue resistance are then required. A major improvement in the fatigue behavior was observed by laminating Kevlar fibers with Aluminum using epoxy. ARALL (Aramid Reinforced ALuminum Laminates) is a fatigue resistant hybrid composite that consists of layers of thin high strength aluminum alloy sheets surface bonded with aramid fibers. The intact aramid fibers tie up the fatigue cracks, thus reducing the stress intensity factor at the crack tip as a result of which the fatigue properties of can be enhanced with orders of magnitude as compared to monolithic high strength Aluminum alloy sheets. Significant amount of weight savings can be achieved in fatigue critical components in comparison with the traditional materials used in aircraft

Inflammatory fatigue and sickness behaviour - lessons for the diagnosis and management of chronic fatigue syndrome.

Science.gov (United States)

Arnett, S V; Clark, I A

2012-12-10

Persistent and severe fatigue is a common part of the presentation of a diverse range of disease processes. There is a growing body of evidence indicating a common inflammatory pathophysiology underlying many conditions where fatigue is a primary patient concern, including chronic fatigue syndrome. This review explores current models of how inflammatory mediators act on the central nervous system to produce fatigue and sickness behaviour, and the commonality of these processes in conditions as diverse as surgical trauma, infection, various cancers, inflammatory bowel disease, connective tissue diseases and autoimmune diseases. We also discuss evidence indicating chronic fatigue syndrome may have important pathophysiological similarities with cytokine mediated sickness behaviour, and what lessons can be applied from sickness behaviour to chronic fatigue syndrome with regards to the diagnosis and management. Copyright © 2012 Elsevier B.V. All rights reserved.

Effect of quinoa and potato flours on the thermomechanical and breadmaking properties ofwheat flour

Directory of Open Access Journals (Sweden)

E. Rodriguez-Sandoval

2012-09-01

Full Text Available The thermomechanical properties of dough and the physical characteristics of bread from quinoa-wheat and potato-wheat composite flours at 10 and 20% substitution level were evaluated. The functional properties of flours were measured by the water absorption index (WAI, water solubility index (WSI and swelling power (SP. The thermomechanical properties of wheat and composite flours were assessed using a Mixolab and the baking quality characteristics of breads were weight, height, width, and specific volume. The results showed that the higher values of WAI (4.48, WSI (7.45%, and SP (4.84 were for potato flour. The quinoa-wheat composite flour presented lower setback and cooking stability data, which are a good indicator of shelf life of bread. On the other hand, the potato-wheat composite flour showed lower stability, minimum torque and peak torque, and higher water absorption. Weight, height, width, and specific volume of wheat bread were most similar to samples of potato-wheat composite flour at 10% substitution level.

Experimental investigations on the state of the friction-welded joint zone in steel hybrid components after process-relevant thermo-mechanical loadings

Science.gov (United States)

Behrens, B.-A.; Bouguecha, A.; Vucetic, M.; Peshekhodov, I.; Matthias, T.; Kolbasnikov, N.; Sokolov, S.; Ganin, S.

2016-10-01

As a part of the newly established Collaborative Research Center 1153 (SFB 1153) "Process chain for the manufacturing of hybrid high-performance components by tailored forming" at the Leibniz Universität Hannover, the Institute of Forming Technology and Machines (IFUM) examines the influence of thermo-mechanical stresses on the reduced Young's modulus as well as the hardness of hybrid (steel-steel compound) joined semi-finished products. Currently the expertise in the production of bulk metal formed parts is limited to mono-materials. For manufacturing parts of hybrid materials and also for the methods of the new process routes, practical experience has to be gained. The subproject C1 within the collaborative research center 1153 with the short title "Failure Prediction" deals with the question, if the hybrid semi-finished products fulfill the thermo-mechanical demands or if they fail at the joining zone (JZ) during forging. For this purpose, stresses similar to those in the process were imposed on hybrid semi-finished products by torsion tests by using the thermo-mechanical test system Gleeble 3800. Afterwards, the specimens were examined metallographically and by nanoindentations with the help of a TriboIndenter TI950. Thus, first knowledge on the behaviour of thermo-mechanical stresses on the reduced Young's modulus and the hardness of hybrid joined semi-finished parts was gained.

Thermomechanical studies in granite at Stripa, Sweden

International Nuclear Information System (INIS)

Cook, N.G.W.; Myer, L.R.

1981-01-01

Media other than rock salt are being considered for the deep, geologic disposal of nuclear wastes. The disposal of high-level nuclear waste in a deep, underground repository will subject the rock to a thermal pulse that will induce displacements, strains, and stresses in the rock. Thermomechanical experiments, with electrical heaters simulating the thermal output of waste canisters, were carried out in granite at a depth of 340 m below surface adjacent to a defunct iron ore mine at Stripa, Sweden. Changes in temperature, displacement, and stress in the rock around these heaters were measured, and the measurements were compared with predictions calculated from the theory of linear thermoelasticity. Measured temperature changes agreed well with predictions, but measured displacements and stresses were consistently less than those predicted with constant values for the coefficient of thermal expansion and elastic properties of the rock. A laboratory test program to measure these coefficients over ranges of stress and temperature representing those in the field experiment has been initiated. Test specimens were taken from cores recovered from the instrumentation holes in the Stripa experiments. Preliminary results from laboratory tests on specimens free of joints indicate that the values of Young's modulus and Poisson's ratio increase from about 60 to 80 MPa and from 0.15 to 0.22, respectively, as the confining stress is increased from 2 to 55 MPa; these values decrease with increasing temperature, more so at 2 MPa than at 55 MPa. The linear coefficient of thermal expansion at a confining stress of 30 MPa increases from about 10 x 10 - 6 / 0 C at 40 0 C to about 14 x 10 - 6 / 0 C. The magnitudes of these changes are not sufficient to resolve the disparity between measured and predicted results. Perhaps the properties of test specimens containing joints will show greater variations in the values of the thermomechanical coefficients with temperature and pressure

Mental Fatigue Affects Visual Selective Attention

NARCIS (Netherlands)

Faber, Leon G.; Maurits, Natasha M.; Lorist, Monicque M.

2012-01-01

Mental fatigue is a form of fatigue, induced by continuous task performance. Mentally fatigued people often report having a hard time keeping their attention focussed and being easily distracted. In this study, we examined the relation between mental fatigue, as induced by time on task, and

Standard guide for fretting fatigue testing

CERN Document Server

American Society for Testing and Materials. Philadelphia

2010-01-01

1.1 This guide defines terminology and covers general requirements for conducting fretting fatigue tests and reporting the results. It describes the general types of fretting fatigue tests and provides some suggestions on developing and conducting fretting fatigue test programs. 1.2 Fretting fatigue tests are designed to determine the effects of mechanical and environmental parameters on the fretting fatigue behavior of metallic materials. This guide is not intended to establish preference of one apparatus or specimen design over others, but will establish guidelines for adherence in the design, calibration, and use of fretting fatigue apparatus and recommend the means to collect, record, and reporting of the data. 1.3 The number of cycles to form a fretting fatigue crack is dependent on both the material of the fatigue specimen and fretting pad, the geometry of contact between the two, and the method by which the loading and displacement are imposed. Similar to wear behavior of materials, it is important t...

Probabilistic Fatigue Damage Program (FATIG)

Science.gov (United States)

Michalopoulos, Constantine

2012-01-01

FATIG computes fatigue damage/fatigue life using the stress rms (root mean square) value, the total number of cycles, and S-N curve parameters. The damage is computed by the following methods: (a) traditional method using Miner s rule with stress cycles determined from a Rayleigh distribution up to 3*sigma; and (b) classical fatigue damage formula involving the Gamma function, which is derived from the integral version of Miner's rule. The integration is carried out over all stress amplitudes. This software solves the problem of probabilistic fatigue damage using the integral form of the Palmgren-Miner rule. The software computes fatigue life using an approach involving all stress amplitudes, up to N*sigma, as specified by the user. It can be used in the design of structural components subjected to random dynamic loading, or by any stress analyst with minimal training for fatigue life estimates of structural components.

A Simple FEM Formulation Applied to Nonlinear Problems of Impact with Thermomechanical Coupling

Directory of Open Access Journals (Sweden)

João Paulo de Barros Cavalcante

Full Text Available Abstract The thermal effects of problems involving deformable structures are essential to describe the behavior of materials in feasible terms. Verifying the transformation of mechanical energy into heat it is possible to predict the modifications of mechanical properties of materials due to its temperature changes. The current paper presents the numerical development of a finite element method suitable for nonlinear structures coupled with thermomechanical behavior; including impact problems. A simple and effective alternative formulation is presented, called FEM positional, to deal with the dynamic nonlinear systems. The developed numerical is based on the minimum potential energy written in terms of nodal positions instead of displacements. The effects of geometrical, material and thermal nonlinearities are considered. The thermodynamically consistent formulation is based on the laws of thermodynamics and the Helmholtz free-energy, used to describe the thermoelastic and the thermoplastic behaviors. The coupled thermomechanical model can result in secondary effects that cause redistributions of internal efforts, depending on the history of deformation and material properties. The numerical results of the proposed formulation are compared with examples found in the literature.

Classifying post-stroke fatigue: Optimal cut-off on the Fatigue Assessment Scale.

Science.gov (United States)

Cumming, Toby B; Mead, Gillian

2017-12-01

Post-stroke fatigue is common and has debilitating effects on independence and quality of life. The Fatigue Assessment Scale (FAS) is a valid screening tool for fatigue after stroke, but there is no established cut-off. We sought to identify the optimal cut-off for classifying post-stroke fatigue on the FAS. In retrospective analysis of two independent datasets (the '2015' and '2007' studies), we evaluated the predictive validity of FAS score against a case definition of fatigue (the criterion standard). Area under the curve (AUC) and sensitivity and specificity at the optimal cut-off were established in the larger 2015 dataset (n=126), and then independently validated in the 2007 dataset (n=52). In the 2015 dataset, AUC was 0.78 (95% CI 0.70-0.86), with the optimal ≥24 cut-off giving a sensitivity of 0.82 and specificity of 0.66. The 2007 dataset had an AUC of 0.83 (95% CI 0.71-0.94), and applying the ≥24 cut-off gave a sensitivity of 0.84 and specificity of 0.67. Post-hoc analysis of the 2015 dataset revealed that using only the 3 most predictive FAS items together ('FAS-3') also yielded good validity: AUC 0.81 (95% CI 0.73-0.89), with sensitivity of 0.83 and specificity of 0.75 at the optimal ≥8 cut-off. We propose ≥24 as a cut-off for classifying post-stroke fatigue on the FAS. While further validation work is needed, this is a positive step towards a coherent approach to reporting fatigue prevalence using the FAS. Copyright © 2017 Elsevier Inc. All rights reserved.

Fatigue Analysis of Large-scale Wind turbine

Directory of Open Access Journals (Sweden)

Zhu Yongli

2017-01-01

Full Text Available The paper does research on top flange fatigue damage of large-scale wind turbine generator. It establishes finite element model of top flange connection system with finite element analysis software MSC. Marc/Mentat, analyzes its fatigue strain, implements load simulation of flange fatigue working condition with Bladed software, acquires flange fatigue load spectrum with rain-flow counting method, finally, it realizes fatigue analysis of top flange with fatigue analysis software MSC. Fatigue and Palmgren-Miner linear cumulative damage theory. The analysis result indicates that its result provides new thinking for flange fatigue analysis of large-scale wind turbine generator, and possesses some practical engineering value.

Thermomechanical CSM analysis of a superheater tube in transient state

Science.gov (United States)

Taler, Dawid; Madejski, Paweł

2011-12-01

The paper presents a thermomechanical computational solid mechanics analysis (CSM) of a pipe "double omega", used in the steam superheaters in circulating fluidized bed (CFB) boilers. The complex cross-section shape of the "double omega" tubes requires more precise analysis in order to prevent from failure as a result of the excessive temperature and thermal stresses. The results have been obtained using the finite volume method for transient state of superheater. The calculation was carried out for the section of pipe made of low-alloy steel.

Thermo-mechanical process for treatment of welds

International Nuclear Information System (INIS)

Malik, R.K.

1980-03-01

Benefits from thermo-mechanical processing (TMP) of austenitic stainless steel weldments, analogous to hot isostatic pressing (HIP) of castings, most likely result from compressive plastic deformation, enhanced diffusion, and/or increased dislocation density. TMP improves ultrasonic inspectability of austenitic stainless steel welds owing to: conversion of cast dendrites into equiaxed austenitic grains, reduction in size and number of stringers and inclusions, and reduction of delta ferrite content. TMP induces structural homogenization and healing of void-type defects and thus contributes to an increase in elongation, impact strength, and fracture toughness as well as a significant reduction in data scatter for these properties. An optimum temperature for TMP or HIP of welds is one which causes negligible grain growth and an acceptable reduction in yield strength, and permits healing of porosity

Plasmonically enhanced thermomechanical detection of infrared radiation.

Science.gov (United States)

Yi, Fei; Zhu, Hai; Reed, Jason C; Cubukcu, Ertugrul

2013-04-10

Nanoplasmonics has been an attractive area of research due to its ability to localize and manipulate freely propagating radiation on the nanometer scale for strong light-matter interactions. Meanwhile, nanomechanics has set records in the sensing of mass, force, and displacement. In this work, we report efficient coupling between infrared radiation and nanomechanical resonators through nanoantenna enhanced thermoplasmonic effects. Using efficient conversion of electromagnetic energy to mechanical energy in this plasmo-thermomechanical platform with a nanoslot plasmonic absorber integrated directly on a nanobeam mechanical resonator, we demonstrate room-temperature detection of nanowatt level power fluctuations in infrared radiation. We expect our approach, which combines nanoplasmonics with nanomechanical resonators, to lead to optically controlled nanomechanical systems enabling unprecedented functionality in biomolecular and toxic gas sensing and on-chip mass spectroscopy.

Fatigue analysis of aluminum drill pipes

Directory of Open Access Journals (Sweden)

João Carlos Ribeiro Plácido

2005-12-01

Full Text Available An experimental program was performed to investigate the fundamental fatigue mechanisms of aluminum drill pipes. Initially, the fatigue properties were determined through small-scale tests performed in an optic-mechanical fatigue apparatus. Additionally, full-scale fatigue tests were carried out with three aluminum drill pipe specimens under combined loading of cyclic bending and constant axial tension. Finally, a finite element model was developed to simulate the stress field along the aluminum drill pipe during the fatigue tests and to estimate the stress concentration factors inside the tool joints. By this way, it was possible to estimate the stress values in regions not monitored during the fatigue tests.

Flexural fatigue life prediction of closed hat-section using materially nonlinear axial fatigue characteristics

Science.gov (United States)

Razzaq, Zia

1989-01-01

Straight or curved hat-section members are often used as structural stiffeners in aircraft. For instance, they are employed as stiffeners for the dorsal skin as well as in the aerial refueling adjacent area structure in F-106 aircraft. The flanges of the hat-section are connected to the aircraft skin. Thus, the portion of the skin closing the hat-section interacts with the section itself when resisting the stresses due to service loads. The flexural fatigue life of such a closed section is estimated using materially nonlinear axial fatigue characteristics. It should be recognized that when a structural shape is subjected to bending, the fatigue life at the neutral axis is infinity since the normal stresses are zero at that location. Conversely, the fatigue life at the extreme fibers where the normal bending stresses are maximum can be expected to be finite. Thus, different fatigue life estimates can be visualized at various distances from the neural axis. The problem becomes compounded further when significant portions away from the neutral axis are stressed into plastic range. A theoretical analysis of the closed hat-section subjected to flexural cyclic loading is first conducted. The axial fatigue characteristics together with the related axial fatigue life formula and its inverted form given by Manson and Muralidharan are adopted for an aluminum alloy used in aircraft construction. A closed-form expression for predicting the flexural fatigue life is then derived for the closed hat-section including materially nonlinear action. A computer program is written to conduct a study of the variables such as the thicknesses of the hat-section and the skin, and the type of alloy used. The study has provided a fundamental understanding of the flexural fatigue life characteristics of a practical structural component used in aircraft when materially nonlinear action is present.

Fatigue of vanadium--hydrogen alloys

International Nuclear Information System (INIS)

Lee, K.S.; Stoloff, N.S.

1975-01-01

Hydrogen contents near and above the room temperature solubility limit increase the high cycle fatigue life but decrease low cycle life of polycrystalline vanadium. Changes in endurance limit with hydrides may be a consequence of decreased cyclic strain hardening coefficient, n'. 132 ppM hydrogen in solution has only a slightly beneficial effect on stress controlled fatigue life and essentially no effect on low cycle fatigue life. Unalloyed vanadium exhibits profuse striations, while hydrides produce cleavage cracks in fatigued samples. 10 fig

Advance development of a technique for characterizing the thermomechanical properties of thermally stable polymers

Science.gov (United States)

Gillham, J. K.; Stadnicki, S. J.; Hazony, Y.

1974-01-01

The torsional braid experiment has been interfaced with a centralized hierarchical computing system for data acquisition and data processing. Such a system, when matched by the appropriate upgrading of the monitoring techniques, provides high resolution thermomechanical spectra of rigidity and damping, and their derivatives with respect to temperature.

Evaluation of micro fatigue crack growth under equi-biaxial stress by membranous pressure fatigue test

International Nuclear Information System (INIS)

Iida, Satoshi; Abe, Shigeki; Nakamura, Takao; Kamaya, Masayuki

2014-01-01

For preventing nuclear power plant (NPP) accidents, NPPs are required to ensure system safety in long term safe operation under aging degradation. Now, fatigue accumulation is one of major ageing phenomena and are evaluated to ensure safety by design fatigue curve that are based on the results of uniaxial fatigue tests. On the other hand, thermal stress that occurs in piping of actual components is not uniaxial but equi-biaxial. For accurate evaluation, it is required to conform real circumstance. In this study, membranous pressure fatigue test was conducted to simulated equi-biaxial stress. Crack initiation and crack growth were examined by replica investigation. Calculation result of equivalent stress intensity factor shows crack growth under equi-biaxial stress is faster than under uniaxial stress. It is concluded that equi-biaxial fatigue behavior should be considered in the evaluation of fatigue crack initiation and crack growth. (author)

Muscle injections with lidocaine improve resting fatigue and pain in patients with chronic fatigue syndrome

Directory of Open Access Journals (Sweden)

Staud R

2017-06-01

Full Text Available Roland Staud,1 Taylor Kizer,1 Michael E Robinson2 1Department of Medicine, College of Medicine, 2Department of Clinical and Health Psychology, University of Florida, Gainesville, FL, USA Objective: Patients with chronic fatigue syndrome (CFS complain of long-lasting fatigue and pain which are not relieved by rest and worsened by physical exertion. Previous research has implicated metaboreceptors of muscles to play an important role for chronic fatigue and pain. Therefore, we hypothesized that blocking impulse input from deep tissues with intramuscular lidocaine injections would improve not only the pain but also fatigue of CFS patients. Methods: In a double-blind, placebo-controlled study, 58 CFS patients received 20 mL of 1% lidocaine (200 mg or normal saline once into both trapezius and gluteal muscles. Study outcomes included clinical fatigue and pain, depression, and anxiety. In addition, mechanical and heat hyperalgesia were assessed and serum levels of lidocaine were obtained after the injections. Results: Fatigue ratings of CFS patients decreased significantly more after lidocaine compared to saline injections (p = 0.03. In contrast, muscle injections reduced pain, depression, and anxiety (p < 0.001, but these changes were not statistically different between lidocaine and saline (p > 0.05. Lidocaine injections increased mechanical pain thresholds of CFS patients (p = 0.04 but did not affect their heat hyperalgesia. Importantly, mood changes or lidocaine serum levels did not significantly predict fatigue reductions. Conclusion: These results demonstrate that lidocaine injections reduce clinical fatigue of CFS patients significantly more than placebo, suggesting an important role of peripheral tissues for chronic fatigue. Future investigations will be necessary to evaluate the clinical benefits of such interventions. Keywords: muscle injections, lidocaine, metaboreceptor, chronic fatigue 

Fatigue Analysis of a Mono-Tower Platform

DEFF Research Database (Denmark)

Kirkegaard, Poul Henning; Sørensen, John Dalsgaard; Brincker, Rune

In this paper, a fatigue reliability analysis of a Mono-tower platform is presented. The failure mode, fatigue failure in the butt welds, is investigated with two different models. The one with the fatigue strength expressed through SN relations, the other with the fatigue strength expressed thro...... of the natural period, damping ratio, current, stress Spectrum and parameters describing the fatigue strength. Further, soil damping is shown to be significant for the Mono-tower.......In this paper, a fatigue reliability analysis of a Mono-tower platform is presented. The failure mode, fatigue failure in the butt welds, is investigated with two different models. The one with the fatigue strength expressed through SN relations, the other with the fatigue strength expressed...... through linear-elastic fracture mechanics (LEFM). In determining the cumulative fatigue damage, Palmgren-Miner's rule is applied. Element reliability as well as systems reliability is estimated using first-order reliability methods (FORM). The sensitivity of the systems reliability to various parameters...

Global thermo-mechanical effects from a KBS-3 type repository. Summary report

International Nuclear Information System (INIS)

Hakami, E.; Olofsson, Stig-Olof; Hakami, H.; Israelsson, Jan

1998-04-01

The objective of this study has been to identify the global thermomechanical effects in the bedrock hosting a nuclear waste repository - i.e. the effects at large distances from the repository. Numerical thermomechanical modeling was performed in several steps, beginning with elastic continuum models and followed by distinct element models (3DEC), in which fracture zones are explicitly simulated. The number of fracture zones, the heat intensity of the waste, the material properties of the rock mass and the boundary conditions of the models were varied in different simulations. The results from the numerical modeling show that the principal stresses increase near the repository. The maximum stress obtained for the main model is 44 MPa and occurs at the repository level after about 100 years of deposition. Due to thermal expansion, the rock mass displaces upward, and the maximum heave at the ground surface after 1000 years is calculated to be 16 cm. In the area close to the ground surface, above the center of the repository, the horizontal stresses reduce, causing the rock to yield in tension down to a depth of about 80 m. In correspondence with the stress changes, the fracture zones show opening normal displacements at shallow depths and closing normal displacements and shearing at the repository level. The maximum displacements of the different fracture zones are 0.3-2.5 cm for closing, 0.0-0.8 cm for opening and 0.2-2.2 cm for shearing. Another important input parameter for the analysis is the Young's modulus of the rock mass. In the main model, a value of 30 GPa is assumed. Higher values of Young's modulus give larger thermo-mechanical effects. Other changes of the properties considered give minor changes of the rock mass behavior. All multi-level repository layouts give rise to higher temperatures than the single-level layout, causing the compressive stresses to increase more at the repository level. Fracture zone displacements caused by different layouts are

Thermomechanical Stress in Cryopreservation Via Vitrification With Nanoparticle Heating as a Stress-Moderating Effect.

Science.gov (United States)

Eisenberg, David P; Bischof, John C; Rabin, Yoed

2016-01-01

This study focuses on thermomechanical effects in cryopreservation associated with a novel approach of volumetric heating by means on nanoparticles in an alternating electromagnetic field. This approach is studied for the application of cryopreservation by vitrification, where the crystalline phase is completely avoided-the cornerstone of cryoinjury. Vitrification can be achieved by quickly cooling the material to cryogenic storage, where ice cannot form. Vitrification can be maintained at the end of the cryogenic protocol by quickly rewarming the material back to room temperature. The magnitude of the rewarming rates necessary to maintain vitrification is much higher than the magnitude of the cooling rates that are required to achieve it in the first place. The most common approach to achieve the required cooling and rewarming rates is by exposing the specimen's surface to a temperature-controlled environment. Due to the underlying principles of heat transfer, there is a size limit in the case of surface heating beyond which crystallization cannot be prevented at the center of the specimen. Furthermore, due to the underlying principles of solid mechanics, there is a size limit beyond which thermal expansion in the specimen can lead to structural damage and fractures. Volumetric heating during the rewarming phase of the cryogenic protocol can alleviate these size limitations. This study suggests that volumetric heating can reduce thermomechanical stress, when combined with an appropriate design of the thermal protocol. Without such design, this study suggests that the level of stress may still lead to structural damage even when volumetric heating is applied. This study proposes strategies to harness nanoparticles heating in order to reduce thermomechanical stress in cryopreservation by vitrification.

Biaxial fatigue of metals the present understanding

CERN Document Server

Schijve, Jaap

2016-01-01

Problems of fatigue under multiaxial fatigue loads have been addressed in a very large number of research publications. The present publication is primarily a survey of biaxial fatigue under constant amplitude loading on metal specimens. It starts with the physical understanding of the fatigue phenomenon under biaxial fatigue loads. Various types of proportional and non-proportional biaxial fatigue loads and biaxial stress distributions in a material are specified. Attention is paid to the fatigue limit, crack nucleation, initial micro crack growth and subsequent macro-crack in different modes of crack growth. The interference between the upper and lower surfaces of a fatigue crack is discussed. Possibilities for predictions of biaxial fatigue properties are analysed with reference to the similarity concept. The significance of the present understanding for structural design problems is considered. The book is completed with a summary of major observations.

Fatigue Strength of Weathering Steel

Czech Academy of Sciences Publication Activity Database

Kunz, Ludvík; Lukáš, Petr; Klusák, Jan

2012-01-01

Roč. 18, č. 1 (2012), s. 18-22 ISSN 1392-1320 Grant - others:GA MPO(CZ) FT/TA5/076 Institutional support: RVO:68081723 Keywords : fatigue of weathering steel * corrosion pits * fatigue notch factor Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 0.522, year: 2012

PECULIARITIES OF FORMATION OF STRUCTURE AND PROPERTIES AT THERMO-MECHANICAL PROCESSING OF ROLLED WIRE OF NICKEL

OpenAIRE

V. A. Lutsenko

2012-01-01

There are results of researches of the mechanical properties and structure of the wire rod made of low-carbon nickel molybdenum steel after reduction to toughness thermomechanical treatment in the stream of high-speed wire mill.

Importance of fatiguing, overtraining and chronic fatigue in athletes

Directory of Open Access Journals (Sweden)

Adam Piesik

2017-09-01

Full Text Available Each training that requires achieving a higher heart rate limit and/or increased concentration in time may cause fatigue, considered to be a natural defence mechanism of a body. In the case of excessive fatigue and insufficient time designated for rest and regeneration, an overtraining syndrome (OTS may develop. The main symptom of overtraining is increased fatigue that fails to become reversed in normal conditions of regeneration. Although authors are familiar with the overtraining syndrome and associated symptoms, as of today no diagnostic tool has been developed that may form a basis for a final diagnosis, and the diagnosis itself is frequently based on a subjective assessment of the athlete. Possible causes of the band overtraining syndrome are disorders of sodium, inflammatory processes resulting from physical activity and / or disorders of the autonomic nervous system.

Influence of thermomechanical treatment on microstructure and properties of electroslag remelted Cu–Cr–Zr alloy

International Nuclear Information System (INIS)

Kermajani, M.; Raygan, Sh.; Hanayi, K.; Ghaffari, H.

2013-01-01

Highlights: • Effect of ESR process on microstructure of Cu–Cr–Zr alloy was investigated. • The hardness, strength and electrical conductivity are sensitive to thermomechanical treatment. • The microstructure of the alloy can be optimized for obtaining the best combination of mechanical and electrical properties. - Abstract: Effect of thermomechanical treatment (TMT) on aging behavior of electroslag remelted Cu–Cr–Zr alloy was investigated. The relationship between microstructure, mechanical and electrical properties was clarified using hardness, tensile and electrical conductivity testing methods and optical and scanning electron microscopy techniques. The results showed that an appropriate processing and aging treatment may improve the properties of the alloy due to the formation of fine, dispersive and coherent precipitates within the matrix. Indeed, the optimum condition for electrical conductivity and mechanical properties was obtained after cold working of 40% followed by aging at 500 °C for 150 min

Comparing Fatigue Life Estimations of Composite Wind Turbine Blades using different Fatigue Analysis Tools

DEFF Research Database (Denmark)

Ardila, Oscar Gerardo Castro; Lennie, Matthew; Branner, Kim

2015-01-01

In this paper, fatigue lifetime prediction of NREL 5MW reference wind turbine is presented. The fatigue response of materials used in selected blade cross sections was obtained by applying macroscopic fatigue approaches and assuming uniaxial stress states. Power production and parked load cases...... suggested by the IEC 61400-1 standard were studied employing different load time intervals and by using two novel fatigue tools called ALBdeS and BECAS+F. The aeroelastic loads were defined thought aeroelastic simulations performed with both FAST and HAWC2 tools. The stress spectra at each layer were...... calculated employing laminated composite theory and beam cross section methods. The Palmgren-Miner linear damage rule was used to calculate the accumulation damage. The theoretical results produced by both fatigue tools proved a prominent effect of analysed design load conditions on the estimated lifetime...

Prevalence of fatigue and chronic fatigue syndrome in a primary care practice.

Science.gov (United States)

Bates, D W; Schmitt, W; Buchwald, D; Ware, N C; Lee, J; Thoyer, E; Kornish, R J; Komaroff, A L

1993-12-27

Our goals were to determine the prevalence of unusual, debilitating fatigue and the frequency with which it was associated with the chronic fatigue syndrome (CFS) or other physical or psychological illness in an outpatient clinic population. We prospectively evaluated a cohort of 1000 consecutive patients in a primary care clinic in an urban, hospital-based general medicine practice. The study protocol included a detailed history, physical examination, and laboratory and psychiatric testing. Five patients who came because of CFS studies were excluded. Of the remaining 995, 323 reported fatigue, and 271 (27%) complained of at least 6 months of unusual fatigue that interfered with their daily lives. Of the 271, self-report or record review revealed a medical or psychiatric condition that could have explained the fatigue in 186 (69%). Thus, 85 (8.5%) of 995 patients had a debilitating fatigue of at least 6 months' duration, without apparent cause. Of these patients, 48 refused further evaluation, and 11 were unavailable for follow-up; 26 completed the protocol. Three of the 26 were hypothyroid, and one had a major psychiatric disorder. Of the remaining 22 patients, three met Centers for Disease Control and Prevention criteria for CFS, four met British criteria, and 10 met the Australian case definition. The point prevalences of CFS were thus 0.3% (95% confidence interval [CI], 0% to 0.6%), 0.4% (95% CI, 0% to 0.8%), and 1.0% (95% CI, 0.4% to 1.6%) using the Centers for Disease Control and Prevention, British, and Australian case definitions, respectively. These estimates were conservative, because they assumed that none of the patients who refused evaluation or were unavailable for follow-up would meet criteria for CFS. While chronic, debilitating fatigue is common in medical outpatients, CFS is relatively uncommon. Prevalence depends substantially on the case definition used.

Work fatigue in urban bus drivers

Directory of Open Access Journals (Sweden)

Teresa Makowiec-Dąbrowska

2015-10-01

Full Text Available Background: Bus drivers are a special group of professional drivers who are at a very high risk of fatigue. The aim of the study was to examine whether the driver’s subjective assessment of fatigue allows for the determination of its level and identification of its causes. Material and Methods: The study group comprised 45 randomly selected bus drivers (mean age – 43.7±7.9 years, period of employment as drivers – 14.7±8.6 years. Examinations were performed in all subjects four times – before and after work on the “easy” route (outside the city center, small traffic intensity and before and after work on the “difficult” route (city center, heavy traffic. The fatigue test questionnaire, based on the list of symptoms of fatigue prepared by the Japan Research Committee of Fatigue, was used in the study. Results: The rating of fatigue after the work was significantly higher than that before the work. The profile of fatigue after work was not influenced by the type of route, but the assessment of most symptoms of fatigue reached a higher level after the “difficult” routes and the differences were statistically significant for 7 symptoms. Only the ratings of leg fatigue, feeling of heaviness, and the necessity to squint eyes and gaze with effort reached the higher levels after driving the “easy” routes. It has been found that the level of fatigue was significantly correlated with the job characteristics (driving time, the length of the route, number of stops, etc. and with the abundance of food ingested and type of beverage (coffee vs. others drunk prior to driving. Conclusions: The questionnaire used in our study to assess the subjective feeling of fatigue has proved to be a sensitive and useful tool for indicating the level and causes of fatigue. The relationship between the symptoms of fatigue and the characteristics of job and lifestyle shows that actions must be taken by both the employers and employees to prevent fatigue

Fatigue 󈨛. Volume 2,

Science.gov (United States)

1987-06-01

ROLAND STICKLER Absolute Fatigue Thresholds in Metallic 801 Materials - J.A. LEWIS Thermometrical Investigations on the Near 809 Threshold Fatigue...impurities reported by Semi- Alloys Inc. totaled less than 0.1%. Specimens were cast in a flat open aluminum mold. Each specimen was 6 mm thick and 12...and 2024-T351 Aluminum Alloy", in "Fatigue Crack Growth Threshold Concepts", D.L. Davidson, S. Suresh, editors, TMS-AIME. 1984, pp. 63-82. (2) Bailon

Thermal Acoustic Fatigue Apparatus

Data.gov (United States)

Federal Laboratory Consortium — The Thermal Acoustic Fatigue Apparatus (TAFA) is a progressive wave tube test facility that is used to test structures for dynamic response and sonic fatigue due to...

Factors related to fatigue; priority of interventions to reduce or eliminate fatigue and the exploration of a multidisciplinary research model for further study of fatigue

NARCIS (Netherlands)

Tiesinga, LJ; Dassen, TWN; Halfens, RJG; van den Heuvel, WJA

A growing interest in the health problem presented by fatigue, both in clinical practice and research, coupled with a decreasing number of reported studies on fatigue in the last decade, make an updated and systematic review of factors related to fatigue necessary. A search of the literature,

Fatigue and creep-fatigue strength of 304 steel under biaxial strain conditions

International Nuclear Information System (INIS)

Asayama, Tai; Aoto, Kazumi; Wada, Yusaku

1990-01-01

A series of fatigue and creep-fatigue tests were conducted with 304 stainless steel at 550degC under a variety of biaxial strain conditions. Fatigue life under nonproportional loading conditions showed a significant life reduction compared with that of proportional loading, and this life reduction was reasonably estimated by taking into account the strain paths along which the strain history is imposed. Furthermore, a marked life reduction was shown to occur under nonproportional loading by imposing a strain hold period at a peak tensile strain. This life reduction was evaluated by the linear damage rule. It was shown to be possible to estimate the fatigue damage and the creep damage under nonproportional loading by a linear damage rule by estimating a stress relaxation behavior by Mises-type equivalent stress or Huddleston-type equivalent stress. (author)

Inorganic fullerene-like IF-WS_2/PVB nanocomposites of improved thermo-mechanical and tribological properties

International Nuclear Information System (INIS)

Simić, Danica; Stojanović, Dušica B.; Kojović, Aleksandar; Dimić, Mirjana; Totovski, Ljubica; Uskoković, Petar S.; Aleksić, Radoslav

2016-01-01

The subject of this research is to explore the possibility of preparation of nanocomposite material of improved thermo-mechanical and tribological properties, using inorganic fullerene-like tungsten disulfide nanostructures (IF-WS_2) as reinforcement in poly(vinyl butyral) (PVB). This paper also reports investigation of the effects of using different solvents in preparation of PVB/IF-WS_2 nanocomposite on the thermo-mechanical behavior of the resulting material. PVB was dissolved in ethanol, isopropanol, n-butanol and ethyl acetate. IF-WS_2 nanoparticles were added to these PVB solutions and dispersed by different deagglomeration techniques. Samples were dried and thin films were obtained. Their microstructure and the quality of IF-WS_2 dispersion and deagglomeration in PVB matrix was analyzed by scanning electron microscope (SEM). The reinforcing effect of IF-WS_2 is examined by determining hardness, reduced modulus of elasticity and coefficient of friction, by nanoindentation and nanoscratch test, in terms of the different solvents applied in preparation of the samples, mode of stirring and different contents of IF-WS_2. The glass transition temperature (T_g) was determined for the prepared samples using differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMA). Storage modulus and mechanical loss factor were observed in a defined temperature range using DMA. - Highlights: • Poly(vinyl butyral)/tungsten disulfide nanocomposites were examined. • Different solvents and deagglomeration methods affect the properties of composites. • Nanoindentation and scratch test, PSD, SEM, DSC and DMTA were analyzed. • Thermo-mechanical and antifriction properties of composite material are improved.

A comparison of patients with Q fever fatigue syndrome and patients with chronic fatigue syndrome with a focus on inflammatory markers and possible fatigue perpetuating cognitions and behaviour.

Science.gov (United States)

Keijmel, Stephan P; Saxe, Johanna; van der Meer, Jos W M; Nikolaus, Stephanie; Netea, Mihai G; Bleijenberg, Gijs; Bleeker-Rovers, Chantal P; Knoop, Hans

2015-10-01

Comparison of Q fever fatigue syndrome (QFS) and chronic fatigue syndrome (CFS) patients, with a focus on markers of inflammation and fatigue-related cognitive-behavioural variables. Data from two independent prospective studies on QFS (n=117) and CFS (n=173), respectively, were pooled and analyzed. QFS patients were less often female, had a higher BMI, and had less often received treatment for depression before the onset of symptoms. After controlling for symptom duration and correcting for differences in diagnostic criteria for QFS and CFS with respect to the level of impairment and the presence of additional symptoms, differences in the proportion of females and BMI remained significant. After correction, QFS patients were also significantly older. In all analyses QFS patients were as fatigued and distressed as CFS patients, but reported less additional symptoms. QFS patients had stronger somatic attributions, and higher levels of physical activity. No differences were found with regard to inflammatory markers and in other fatigue-related cognitive-behavioural variables. The relationship between cognitive-behavioural variables and fatigue, previously established in CFS, could not be confirmed in QFS patients with the exception of the negative relationship between physical activity and fatigue. Differences and similarities between QFS and CFS patients were found. Although the relationship between perpetuating factors and fatigue previously established in CFS could not be confirmed in QFS patients, the considerable overlap in fatigue-related cognitive-behavioural variables and the relationship found between physical activity and fatigue may suggest that behavioural interventions could reduce fatigue severity in QFS patients. Copyright © 2015 Elsevier Inc. All rights reserved.

Hormone levels in radiotherapy treatment related fatigue

International Nuclear Information System (INIS)

Biswal, B.M.; Mallik, G.S.

2003-01-01

Radiotherapy is known to cause debilitating treatment related fatigue. Fatigue in general is a conglomeration of psychological, physical, hematological and unknown factors influencing the internal milieu of the cancer patient. Radiotherapy can add stress at the cellular and somatic level to aggravate further fatigue in cancer patients undergoing radiotherapy. Stress related hormones might be mediating in the development of fatigue. This is an ongoing prospective study to evaluate if the hormonal profile related to stress is influenced by radiotherapy treatment related fatigue. The study was conducted from September 2002 onwards in the division of Radiotherapy and Oncology of our Medical School. Previously untreated patients with histopathology proof of malignancy requiring external beam radiotherapy were considered for this study. Selection criteria were applied to exclude other causes of fatigue. Initial fatigue score was obtained using Pipers Fatigue Score questionnaire containing 23 questions, subsequently final fatigue score was obtained at the end of radiotherapy. Blood samples were obtained to estimate the levels of ACTH, TSH, HGH, and cortisol on the final assessment. The hormone levels were compared with resultant post radiotherapy fatigue score. At the time of reporting 50 patients were evaluable for the study. The total significant fatigue score was observed among 12 (24%) patients. The individual debilitating fatigue score were behavioral severity 14 (28%), affective meaning 14(28%), Sensory 13 (26%) and cognitive mood 10 (20%) respectively. From the analysis of hormonal profile, growth hormone level > 1 ng/mL and TSH <0.03 appears to be associated with high fatigue score (though statistically not significant); whereas there was no correlation with ACTH and serum cortisol level. In our prospective study severe radiotherapy treatment related fatigue was found among our patient population. Low levels of TSH and high levels of GH appear to be associated

Thermal fatigue of beryllium

International Nuclear Information System (INIS)

Deksnis, E.; Ciric, D.; Falter, H.

1995-01-01

Thermal fatigue life of S65c beryllium castellated to a geometry 6 x 6 x (8-10)mm deep has been tested for steady heat fluxes of 3 MW/m 2 to 5 MW/m 2 and under pulsed heat fluxes (10-20 MW/m 2 ) for which the time averaged heat flux is 5 MW/m 2 . These tests were carried out in the JET neutral beam test facility A test sequence with peak surface temperatures ≤ 600 degrees C produced no visible fatigue cracks. In the second series of tests, with T max ≤ 750 degrees C evidence for fatigue appeared after a minimum of 1350 stress cycles. These fatigue data are discussed in view of the observed lack of thermal fatigue in JET plasma operations with beryllium PFC. JET experience with S65b and S65c is reviewed; recent operations with Φ = 25 MW/m 2 and sustained melting/resolidification are also presented. The need for a failure criterion for finite element analyses of Be PFC lifetimes is discussed

Parametric optimization of the MVC desalination plant with thermomechanical compressor

Science.gov (United States)

Blagin, E. V.; Biryuk, V. V.; Anisimov, M. Y.; Shimanov, A. A.; Gorshkalev, A. A.

2018-03-01

This article deals with parametric optimization of the Mechanical Vapour Compression (MVC) desalination plant with thermomechanical compressor. In this plants thermocompressor is used instead of commonly used centrifugal compressor. Influence of two main parameters was studied. These parameters are: inlet pressure and number of stages. Analysis shows that it is possible to achieve better plant performance in comparison with traditional MVC plant. But is required reducing the number of stages and utilization of low or high initial pressure with power consumption maximum at approximately 20-30 kPa.

Fatigue and workload among Danish fishermen

DEFF Research Database (Denmark)

Remmen, Line Nørgaard; Herttua, Kimmo; Riss-Jepsen, Jørgen

2017-01-01

. Highest levels of fatigue were observed among fishermen at Danish seiners (mean 10.21), and fatigue scores decreased with more days at sea. However, none of these results were significant. Adjusted analyses showed that physical workload was significantly related to general fatigue (b = 0.20, 95% CI: 0...... was additionally significantly associated to the levels of physical and mental fatigue. Fishermen had a lower average score for all fatigue dimensions compared to those seen in general Danish working population. Prospective studies are required to assess whether the identified associations are causal....

Fatigue: Is it all neurochemistry?

Science.gov (United States)

Meeusen, Romain; Roelands, Bart

2018-02-01

Fatigue during exercise can be approached from different angles. Peripheral fatigue is usually described as an impairment located in the muscle and characterized by a metabolic end point, while central fatigue is defined as a failure of the central nervous system to adequately drive the muscle. The aim of the present narrative review paper is to look at the mechanisms involved in the occurrence of fatigue during prolonged exercise, predominantly from a brain neurochemical point of view. From studies in rodents it is clear that exercise increases the release of several neurotransmitters in different brain regions, and that the onset of fatigue can be manipulated when dopaminergic influx in the preoptic and anterior hypothalamus is increased, interfering with thermoregulation. This is however not as straightforward in humans, in which most studies manipulating brain neurotransmission failed to change the onset of fatigue in normal ambient temperatures. When the ambient temperature was increased, dopaminergic and combined dopaminergic and noradrenergic reuptake inhibition appeared to override a safety switch, allowing subjects to push harder and become much warmer, without changing their perception. In general, we can conclude that brain neurochemistry is clearly involved in the complex regulation of fatigue, but many other mediators also play a role.

Damage assessment of low-cycle fatigue by crack growth prediction. Fatigue life under cyclic thermal stress

International Nuclear Information System (INIS)

Kamaya, Masayuki

2013-01-01

The number of cycles to failure of specimens in fatigue tests can be estimated by predicting crack growth. Under a cyclic thermal stress caused by fluctuation of fluid temperature, due to the stress gradient in the thickness direction, the estimated fatigue life differs from that estimated for mechanical fatigue tests. In this paper, the influence of crack growth under cyclic thermal loading on the fatigue life was investigated. First, the thermal stress was derived by superposing analytical solutions, and then, the stress intensity factor was obtained by the weight function method. It was shown that the thermal stress depended not on the rate of the fluid temperature change but on the rise time, and the magnitude of the stress was increased as the rise time was decreased. The stress intensity factor under the cyclic thermal stress was smaller than that under the uniform stress distribution. The change in the stress intensity factor with the crack depth was almost the same regardless of the rise time. The estimated fatigue life under the cyclic thermal loading could be 1.6 times longer than that under the uniform stress distribution. The critical size for the fatigue life determination was assumed to be 3 mm for fatigue test specimens of 10 mm diameter. By evaluating the critical size by structural integrity analyses, the fatigue life was increased and the effect of the critical size on the fatigue life was more pronounced for the cyclic thermal stress. (author)

Fatigue, burnout, and chronic fatigue syndrome among employees on sick leave: do attributions make the difference?

NARCIS (Netherlands)

Huibers, M.J.H.; Beurskens, A.J.H.M.; Prins, J.B.; Kant, I.J.; Bazelmans, H.M.; Schayck, C.P. van; Knottnerus, J.A.; Bleijenberg, G.

2003-01-01

BACKGROUND: Persistent fatigue among employees, burnout, and chronic fatigue syndrome (CFS) are three fatigue conditions that share some characteristics in theory. However, these conditions have not been compared in empirical research, despite conceptual similarities. METHODS: This cross sectional

Fatigue property and fatigue cracks of ultra-fine grained copper processed by equal-channel angular pressing

Czech Academy of Sciences Publication Activity Database

Wang, Q.; Du, Z.; Liu, X.; Kunz, Ludvík

2011-01-01

Roč. 2011, č. 682 (2011), s. 231-237 ISSN 1013-9826 Institutional research plan: CEZ:AV0Z20410507 Keywords : ultrafine-grained copper * equal channel angular pressing * fatigue * fatigue cracks Subject RIV: JL - Materials Fatigue, Friction Mechanics

Design and verification of thermomechanical parameters of P/M Ti6Al4V alloy forging

Energy Technology Data Exchange (ETDEWEB)

Wojtaszek, Marek, E-mail: mwojtasz@metal.agh.edu.pl; Śleboda, Tomasz

2014-12-05

Highlights: • Thermomechanical parameters of P/M Ti6Al4V alloy processing were determined. • The use of the mixture of elemental powders allows reducing manufacturing costs. • Numerical modelling allowed to elaborate favourable parameters of forging. • The industrial trials of hot forging of P/M Ti6Al4V alloy were successful. - Abstract: This work is focused on the design of technology of forging high-quality Ti6Al4V alloy by means of powder metallurgy methods. A mixture of elemental powders, with the chemical composition of that of Ti6Al4V alloy, was used as a starting material for the investigation. Powder mixtures were fully densified by hot compaction under precisely controlled conditions. The mechanical properties of the obtained compacts were examined. The mechanical behaviour of the investigated alloy powder compacts was evaluated by compression test under various thermomechanical conditions using Gleeble simulator. The microstructure of powder compacts as well as P/M alloy samples deformed in compression tests was examined. All data obtained from the experimental tests were applied as boundary conditions for numerical simulation of forging of selected forgings. Basing on the results of both plastometric tests and simulations, thermomechanical parameters of the investigated alloy forging were determined. Designed parameters of forging technology were verified by forging trials performed in industrial conditions. The quality of the obtained forgings was examined by means of computed tomography.

Design and verification of thermomechanical parameters of P/M Ti6Al4V alloy forging

International Nuclear Information System (INIS)

Wojtaszek, Marek; Śleboda, Tomasz

2014-01-01

Highlights: • Thermomechanical parameters of P/M Ti6Al4V alloy processing were determined. • The use of the mixture of elemental powders allows reducing manufacturing costs. • Numerical modelling allowed to elaborate favourable parameters of forging. • The industrial trials of hot forging of P/M Ti6Al4V alloy were successful. - Abstract: This work is focused on the design of technology of forging high-quality Ti6Al4V alloy by means of powder metallurgy methods. A mixture of elemental powders, with the chemical composition of that of Ti6Al4V alloy, was used as a starting material for the investigation. Powder mixtures were fully densified by hot compaction under precisely controlled conditions. The mechanical properties of the obtained compacts were examined. The mechanical behaviour of the investigated alloy powder compacts was evaluated by compression test under various thermomechanical conditions using Gleeble simulator. The microstructure of powder compacts as well as P/M alloy samples deformed in compression tests was examined. All data obtained from the experimental tests were applied as boundary conditions for numerical simulation of forging of selected forgings. Basing on the results of both plastometric tests and simulations, thermomechanical parameters of the investigated alloy forging were determined. Designed parameters of forging technology were verified by forging trials performed in industrial conditions. The quality of the obtained forgings was examined by means of computed tomography

Noncontact fatigue crack evaluation using thermoelastic

Energy Technology Data Exchange (ETDEWEB)

Kim, Ji Min; An, Yun Kyu; Sohn, Hoon [KAIST, Daejeon (Korea, Republic of)

2012-12-15

This paper proposes a noncontact thermography technique for fatigue crack evaluation under a cyclic tensile loading. The proposed technique identifies and localizes an invisible fatigue crack without scanning, thus making it possible to instantaneously evaluate an incipient fatigue crack. Based on a thermoelastic theory, a new fatigue crack evaluation algorithm is proposed for the fatigue crack tip localization. The performance of the proposed algorithm is experimentally validated. To achieve this, the cyclic tensile loading is applied to a dog bone shape aluminum specimen using a universal testing machine, and the corresponding thermal responses induced by thermoelastic effects are captured by an infrared camera. The test results confirm that the fatigue crack is well identified and localized by comparing with its microscopic images.

Design fatigue curve for Hastelloy-X

International Nuclear Information System (INIS)

Nishiguchi, Isoharu; Muto, Yasushi; Tsuji, Hirokazu

1983-12-01

In the design of components intended for elevated temperature service as the experimental Very High-Temperature gas-cooled Reactor (VHTR), it is essential to prevent fatigue failure and creep-fatigue failure. The evaluation method which uses design fatigue curves is adopted in the design rules. This report discussed several aspects of these design fatigue curves for Hastelloy-X (-XR) which is considered for use as a heat-resistant alloy in the VHTR. Examination of fatigue data gathered by a literature search including unpublished data showed that Brinkman's equation is suitable for the design curve of Hastelloy-X (-XR), where total strain range Δ epsilon sub(t) is used as independent variable and fatigue life Nsub(f) is transformed into log(log Nsub(f)). (author)

Thermo-mechanical properties of mixed ion-electron conducting membrane materials

Energy Technology Data Exchange (ETDEWEB)

Huang, Bingxin

2011-07-01

The thesis presents thermo-mechanical properties of La{sub 0.58}Sr{sub 0.4}Co{sub 0.2}Fe{sub 0.8}O{sub 3-{delta}} (LSCF) and Ba{sub 0.5}Sr{sub 0.5}Co{sub 0.8}Fe{sub 0.2}O{sub 3-{delta}} (BSCF) perovskite materials, which are considered as oxygen transport membranes (OTM) for gas separation units. Ring-on-ring bending test with disk-shaped samples and depth-sensitive micro-indentation have been used as macroscopic and microscopic tests, respectively. In addition, the thermo-mechanical properties of a third OTM candidate material La{sub 2}NiO{sub 4+{delta}} (LNO) were investigated. The results of the thermo-mechanical measurements with the BSCF revealed an anomaly between 200 C and 400 C. In particular, the temperature dependence of Young's modulus shows a minimum at {proportional_to} 200 C. Fracture stress and toughness exhibit a qualitatively similar behavior with a minimum between 200 C and 400 C, before recovering between 500 C and 800 C. X-ray diffraction analyses verified that BSCF remains cubic in the relevant temperature range. Hence the anomalies were assumed to be related to the transition of Co{sup 3+} spin states reported for other Co-containing perovskites. This assumption could be experimentally confirmed by magnetic susceptibility measurements. The fracture surfaces of the specimens are not affected by the mechanical anomalies at intermediate temperatures, since only a transgranular fracture mode has been observed. Complementary to the mechanical characterization of BSCF, also the temperature dependency of fracture stress and elastic behavior of LSCF have been determined. Phase compositions of LSCF have been studied by in-situ high temperature XRD. Changes in phase composition with temperature are observed. At ambient temperature the LSCF perovskite material comprises two phases: rhombohedral and cubic symmetry. The ratio of the two phases depends on both cooling rate and atmosphere. The transition of rhombohedral to cubic occurs between 700 C and

Thermo-mechanical analysis of a user filter assembly for undulator/wiggler operations at the Advanced Photon Source

International Nuclear Information System (INIS)

Nian, H.L.T.; Kuzay, T.M.; Collins, J.; Shu, D.; Benson, C.; Dejus, R.

1996-01-01

This paper reports a thermo-mechanical study of a beamline filter (user filter) for undulator/wiggler operations. It is deployed in conjunction with the current commissioning window assembly on the APS insertion device (ID) front ends. The beamline filter at the Advanced Photon Source (APS) will eventually be used in windowless operations also. Hence survival and reasonable life expectancy of the filters under intense insertion device (ID) heat flu are crucial to the beamline operations. To accommodate various user requirements, the filter is configured to be a multi-choice type and smart to allow only those filter combinations that will be safe to operate with a given ring current and beamline insertion device gap. However, this paper addresses only the thermo-mechanical analysis of individual filter integrity and safety in all combinations possible. The current filter design is configured to have four filter frames in a cascade with each frame holding five filters. This allows a potential 625 total filter combinations. Thermal analysis for all of these combinations becomes a mammoth task considering the desired choices for filter materials (pyrolitic graphite and metallic filters), filter thicknesses, undulator gaps, and the beam currents. The paper addresses how this difficult task has been reduced to a reasonable effort and computational level. Results from thermo-mechanical analyses of the filter combinations are presented both in tabular and graphical format

Thermo-mechanical efficiency of the bimetallic strip heat engine at the macro-scale and micro-scale

International Nuclear Information System (INIS)

Arnaud, A; Boughaleb, J; Monfray, S; Boeuf, F; Skotnicki, T; Cugat, O

2015-01-01

Bimetallic strip heat engines are energy harvesters that exploit the thermo-mechanical properties of bistable bimetallic membranes to convert heat into mechanical energy. They thus represent a solution to transform low-grade heat into electrical energy if the bimetallic membrane is coupled with an electro-mechanical transducer. The simplicity of these devices allows us to consider their miniaturization using MEMS fabrication techniques. In order to design and optimize these devices at the macro-scale and micro-scale, this article proposes an explanation of the origin of the thermal snap-through by giving the expressions of the constitutive equations of composite beams. This allows us to evaluate the capability of bimetallic strips to convert heat into mechanical energy whatever their size is, and to give the theoretical thermo-mechanical efficiencies which can be obtained with these harvesters. (paper)

Fatigue sensation induced by the sounds associated with mental fatigue and its related neural activities: revealed by magnetoencephalography

OpenAIRE

Ishii, Akira; Tanaka, Masaaki; Iwamae, Masayoshi; Kim, Chongsoo; Yamano, Emi; Watanabe, Yasuyoshi

2013-01-01

Background It has been proposed that an inappropriately conditioned fatigue sensation could be one cause of chronic fatigue. Although classical conditioning of the fatigue sensation has been reported in rats, there have been no reports in humans. Our aim was to examine whether classical conditioning of the mental fatigue sensation can take place in humans and to clarify the neural mechanisms of fatigue sensation using magnetoencephalography (MEG). Methods Ten and 9 healthy volunteers particip...

PECULIARITIES OF FORMATION OF STRUCTURE AND PROPERTIES AT THERMO-MECHANICAL PROCESSING OF ROLLED WIRE OF NICKEL

Directory of Open Access Journals (Sweden)

V. A. Lutsenko

2012-01-01

Full Text Available There are results of researches of the mechanical properties and structure of the wire rod made of low-carbon nickel molybdenum steel after reduction to toughness thermomechanical treatment in the stream of high-speed wire mill.

Fatigue Life Analysis and Prediction of 316L Stainless Steel Under Low Cycle Fatigue Loading

Energy Technology Data Exchange (ETDEWEB)

Oh, Hyeong; Myung, NohJun; Choi, Nak-Sam [Hanyang Univ., Seoul (Korea, Republic of)

2016-12-15

In this study, a strain-controlled fatigue test of widely-used 316L stainless steel with excellent corrosion resistance and mechanical properties was conducted, in order to assess its fatigue life. Low cycle fatigue behaviors were analyzed at room temperature, as a function of the strain amplitude and strain ratio. The material was hardened during the initial few cycles, and then was softened during the long post period, until failure occurred. The fatigue life decreased with increasing strain amplitude. Masing behavior in the hysteresis loop was shown under the low strain amplitude, whereas the high strain amplitude caused non-Masing behavior and reduced the mean stress. Low cycle fatigue life prediction based on the cyclic plastic energy dissipation theory, considering Masing and non-Masing effects, showed a good correlation with the experimental results.

Exploring nurse leader fatigue: a mixed methods study.

Science.gov (United States)

Steege, Linsey M; Pinekenstein, Barbara J; Arsenault Knudsen, Élise; Rainbow, Jessica G

2017-05-01

To describe hospital nurse leaders' experiences of fatigue. Fatigue is a critical challenge in nursing. Existing literature focuses on staff nurse fatigue, yet nurse leaders are exposed to high demands that may contribute to fatigue and associated risks to patient, nurse and organisational outcomes. A mixed method approach comprising semi-structured interviews and the Occupational Fatigue Exhaustion Recovery scale with 21 nurse administrators (10 nurse managers and 11 nurse executives) from hospitals in a Midwestern state. Most nurse leaders experience fatigue; nurse managers reported higher levels of chronic fatigue. Participants identified multiple sources of fatigue including 24 h accountability and intensity of role expectations, and used a combination of wellness, restorative, social support and boundary setting strategies to cope with fatigue. The consequences of nurse leader fatigue include an impact on decision-making, work-life balance and turnover intent. The high prevalence of nurse leader fatigue could impact the turnover intent of nurse administrators and quality of care. This study highlights the significance and consequences of nurse leader fatigue. As health care organisations continue to raise awareness and establish systems to reduce nurse fatigue, policies and programmes must be adapted to address nurse leader fatigue. © 2017 John Wiley & Sons Ltd.

Variable amplitude fatigue, modelling and testing

International Nuclear Information System (INIS)

Svensson, Thomas.

1993-01-01

Problems related to metal fatigue modelling and testing are here treated in four different papers. In the first paper different views of the subject are summarised in a literature survey. In the second paper a new model for fatigue life is investigated. Experimental results are established which are promising for further development of the mode. In the third paper a method is presented that generates a stochastic process, suitable to fatigue testing. The process is designed in order to resemble certain fatigue related features in service life processes. In the fourth paper fatigue problems in transport vibrations are treated

Metabolomic markers of fatigue: Association between circulating metabolome and fatigue in women with chronic widespread pain.

Science.gov (United States)

Freidin, Maxim B; Wells, Helena R R; Potter, Tilly; Livshits, Gregory; Menni, Cristina; Williams, Frances M K

2018-02-01

Fatigue is a sensation of unbearable tiredness that frequently accompanies chronic widespread musculoskeletal pain (CWP) and inflammatory joint disease. Its mechanisms are poorly understood and there is a lack of effective biomarkers for diagnosis and onset prediction. We studied the circulating metabolome in a population sample characterised for CWP to identify biomarkers showing specificity for fatigue. Untargeted metabolomic profiling was conducted on fasting plasma and serum samples of 1106 females with and without CWP from the TwinsUK cohort. Linear mixed-effects models accounting for covariates were used to determine relationships between fatigue and metabolites. Receiver operating curve (ROC)-analysis was used to determine predictive value of metabolites for fatigue. While no association between fatigue and metabolites was identified in twins without CWP (n=711), in participants with CWP (n=395), levels of eicosapentaenoate (EPA) ω-3 fatty acid were significantly reduced in those with fatigue (β=-0.452±0.116; p=1.2×10 -4 ). A significant association between fatigue and two other metabolites also emerged when BMI was excluded from the model: 3-carboxy-4-methyl-5-propyl-2-furanpropanoate (CMPF), and C-glycosyltryptophan (p=1.5×10 -4 and p=3.1×10 -4 , respectively). ROC analysis has identified a combination of 15 circulating metabolites with good predictive potential for fatigue in CWP (AUC=75%; 95% CI 69-80%). The results of this agnostic metabolomics screening show that fatigue is metabolically distinct from CWP, and is associated with a decrease in circulating levels of EPA. Our panel of circulating metabolites provides the starting point for a diagnostic test for fatigue in CWP. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

Real-Time Assessment of Fatigue in Patients With Multiple Sclerosis: How Does It Relate to Commonly Used Self-Report Fatigue Questionnaires?

Science.gov (United States)

Heine, Martin; van den Akker, Lizanne Eva; Blikman, Lyan; Hoekstra, Trynke; van Munster, Erik; Verschuren, Olaf; Visser-Meily, Anne; Kwakkel, Gert

2016-11-01

(1) To assess real-time patterns of fatigue; (2) to assess the association between a real-time fatigue score and 3 commonly used questionnaires (Checklist Individual Strength [CIS] fatigue subscale, Modified Fatigue Impact Scale (MFIS), and Fatigue Severity Scale [FSS]); and (3) to establish factors that confound the association between the real-time fatigue score and the conventional fatigue questionnaires in patients with multiple sclerosis (MS). Cross-sectional study. MS-specialized outpatient facility. Ambulant patients with MS (N=165) experiencing severe self-reported fatigue. Not applicable. A real-time fatigue score was assessed by sending participants 4 text messages on a particular day (How fatigued do you feel at this moment?; score range, 0-10). Latent class growth mixed modeling was used to determine diurnal patterns of fatigue. Regression analyses were used to assess the association between the mean real-time fatigue score and the CIS fatigue subscale, MFIS, and FSS. Significant associations were tested for candidate confounders (eg, disease severity, work status, sleepiness). Four significantly different fatigue profiles were identified by the real-time fatigue score, namely a stable high (n=79), increasing (n=57), stable low (n=16), and decreasing (n=13). The conventional questionnaires correlated poorly (rquestionnaires, ranging from 15.4% to 35%. Perceived fatigue showed 4 different diurnal patterns in patients with MS. Severity of sleepiness is an important confounder to take into account in the assessment of fatigue. Copyright © 2016 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.

Research on driver fatigue detection

Science.gov (United States)

Zhang, Ting; Chen, Zhong; Ouyang, Chao

2018-03-01

Driver fatigue is one of the main causes of frequent traffic accidents. In this case, driver fatigue detection system has very important significance in avoiding traffic accidents. This paper presents a real-time method based on fusion of multiple facial features, including eye closure, yawn and head movement. The eye state is classified as being open or closed by a linear SVM classifier trained using HOG features of the detected eye. The mouth state is determined according to the width-height ratio of the mouth. The head movement is detected by head pitch angle calculated by facial landmark. The driver's fatigue state can be reasoned by the model trained by above features. According to experimental results, drive fatigue detection obtains an excellent performance. It indicates that the developed method is valuable for the application of avoiding traffic accidents caused by driver's fatigue.

Damage assessment of low-cycle fatigue by crack growth prediction. Fatigue life under cyclic thermal stress

International Nuclear Information System (INIS)

Kamaya, Masayuki

2013-01-01

The number of cycles to failure of specimens in fatigue tests can be estimated by predicting crack growth. Under a cyclic thermal stress caused by fluctuation of fluid temperature, due to the stress gradient in the thickness direction, the estimated fatigue life differs from that estimated for mechanical fatigue tests. In this paper, the influence of crack growth under cyclic thermal loading on the fatigue life was investigated. First, the thermal stress was derived by superposing analytical solutions, and then, the stress intensity factor was obtained by the weight function method. It was shown that the thermal stress depended not on the rate of the fluid temperature change but on the rise time, and the magnitude of the stress was increased as the rise time was decreased. The stress intensity factor under the cyclic thermal stress was smaller than that under the uniform stress distribution. The change in the stress intensity factor with the crack depth did not depend on the heat transfer coefficient and only slightly depended on the rise time. The estimated fatigue life under the cyclic thermal loading could be 1.6 times longer than that under the uniform stress distribution. The critical size for the fatigue life determination was assumed to be 3 mm for fatigue test specimens of 10 mm diameter. By evaluating the critical size by structural integrity analyses, the fatigue life was increased and the effect of the critical size on the fatigue life was more pronounced for the cyclic thermal stress. (author)

Thermomechanical analyses of conceptual repository designs for the Paradox and Permian Basins

International Nuclear Information System (INIS)

Loken, M.C.; Callahan, G.D.; Svalstad, D.K.; Wagner, R.A.

1987-11-01

The potential repositories are designed to accommodate all waste forms emplaced at various thermal loadings; specifically, commercial high-level waste (30 W/m 2 ), spent fuel (15 W/m 2 ), defense high-level waste (20 W/m 2 ), and remote-handled and contact-handled transuranic nonheat-generating waste. The study evaluates the design parameters, primarily thermal loading, based on a comparison of calculable thermomechanical parameters with prescribed performance constraints. This evaluation was accomplished by numerical simulation using finite element techniques of the canister, disposal room, and repository regions of each potential site. Important thermal and thermomechanical results were compared with their prescribed constraint or limit value. All of the performance constraints were satisfied at the Davis Canyon site in the Paradox Basin for commercial high-level waste, spent fuel, and defense high-level waste at areal thermal loadings of 20 W/m 2 , 15 W/m 2 , and 20 W/m 2 , respectively. Similarly, for the Deaf Smith County site in the Permian Basin, commercial high-level waste, spent fuel, and defense high-level waste thermal loadings of 13.5 W/m 2 , 8.5 W/m 2 , and 6.0 W/m 2 , respectively, satisfied all of the performance constraints. 89 refs., 64 figs., 22 tabs

Thermomechanical damage of nucleosome by the shock wave initiated by ion passing through liquid water

International Nuclear Information System (INIS)

Yakubovich, Alexander V.; Surdutovich, Eugene; Solov’yov, Andrey V.

2012-01-01

We report on the results of full-atom molecular dynamics simulations of the heat spike in the water medium caused by the propagation of the heavy ion in the vicinity of its Bragg peak. High rate of energy transfer from an ion to the molecules of surrounding water environment leads to the rapid increase of the temperature of the molecules in the vicinity of ions trajectory. As a result of an abrupt increase of the temperature we observe the formation of the nanoscale shock wave propagating through the medium. We investigate the thermomechanical damage caused by the shock wave to the nucleosome located in the vicinity of heavy ion trajectory. We observe the substantial deformation of the DNA secondary structure. We show that the produced shock wave can lead to the thermomechanical breakage of the DNA backbone covalent bonds and present estimates for the number of such strand brakes per one cell nucleus.