External noise distinguishes attention mechanisms.

Science.gov (United States)

Lu, Z L; Dosher, B A

1998-05-01

We developed and tested a powerful method for identifying and characterizing the effect of attention on performance in visual tasks as due to signal enhancement, distractor exclusion, or internal noise suppression. Based on a noisy Perceptual Template Model (PTM) of a human observer, the method adds increasing amounts of external noise (white gaussian random noise) to the visual stimulus and observes the effect on performance of a perceptual task for attended and unattended stimuli. The three mechanisms of attention yield three "signature" patterns of performance. The general framework for characterizing the mechanisms of attention is used here to investigate the attentional mechanisms in a concurrent location-cued orientation discrimination task. Test stimuli--Gabor patches tilted slightly to the right or left--always appeared on both the left and the right of fixation, and varied independently. Observers were cued on each trial to attend to the left, the right, or evenly to both stimuli, and decide the direction of tilt of both test stimuli. For eight levels of added external noise and three attention conditions (attended, unattended, and equal), subjects' contrast threshold levels were determined. At low levels of external noise, attention affected threshold contrast: threshold contrasts for non-attended stimuli were systematically higher than for equal attention stimuli, which were, in turn, higher than for attended stimuli. Specifically, when the rms contrast of the external noise is below 10%, there is a consistent 17% elevation of contrast threshold from attended to unattended condition across all three subjects. For higher levels of external noise, attention conditions did not affect threshold contrast values at all. These strong results are characteristic of a signal enhancement, or equivalently, an internal additive noise reduction mechanism of attention.

Dynamic analysis of scraper conveyor operation with external loads

Directory of Open Access Journals (Sweden)

Świder Jerzy

2017-01-01

Full Text Available A load to an armoured face conveyor (AFC during coal mining is changeable and very difficult or even impossible to be predicted. Changes of the load to the upper scraper chain affect the load of the driving motor and generate changes in a scraper chain tension. Impact of increasing the external load to the upper scraper chain on the operation of electric motors and on the scraper chain tension is presented. The developed numerical model of the Rybnik 850 conveyor enabled identifying the places of the scraper chain high tension or places of its loosening. An impact of changing frequency of driving motor voltage on AFC’s operational conditions was tested and analysed using the AFC’s numerical model. During tests, tension of the scraper chain on the discharge end and the return end was recorded. High tension of the scraper chain and its loosening during the changeable load were also recorded on upward and downward transportation of run-of-mine material.

Effects of external pressure loading on human skin blood flow measured by 133Xe clearance

International Nuclear Information System (INIS)

Holloway, G.A. Jr.; Daly, C.H.; Kennedy, D.; Chimoskey, J.

1976-01-01

Forearm skin blood flow was measured during external pressure loading in normal human subjects using 133 Xe washout from intracutaneous injection sites. Pressures ranging between 5 and 150 mmHg were applied through a 3-cm-diameter disc placed over the site of flow determination. The pressure was maintained constant by a servo-controlled loading mechanism. Flow decreased with pressures from 5 to 10 and 30 to 150 mmHg, but remained constant with pressures from 10 to 30 mmHg. Reactive hyperemia occurred following removal of pressures of 90 mmHg or greater, but did not occur following removal of lower pressures. The pressure-flow curve for parasacral skin of paraplegic subjects closely paralleled the pressure-flow curve of normal skin at pressures tested: 5 to 15 mmHg. These data are interpreted to demonstrate autoregulation of skin blood flow. Autoregulation in parasacral skin of paraplegic subjects suggests a peripheral mechanism. The occurrence of hyperemia at pressures which exceed the ability of skin to autoregulate suggests that both autoregulation and post occlusion hyperemia may have the same mechanism

Effects of external loads on postural sway during quiet stance in adults aged 20-80 years.

Science.gov (United States)

Hill, M W; Duncan, M J; Oxford, S W; Kay, A D; Price, M J

2018-01-01

The purpose of this study was to investigate the effects of holding external loads on postural sway during upright stance across age decades. Sixty-five healthy adults (females, n = 35), aged 18-80 years were assessed in four conditions; (1) standing without holding a load, holding a load corresponding to 5% body mass in the (2) left hand, (3) right hand and (4) both hands. The centre of pressure (COP) path length and anteroposterior and mediolateral COP displacement were used to indirectly assess postural sway. External loading elicited reductions in COP measures of postural sway in older age groups only (P  0.05). Holding external loads during standing is relevant to many activities of daily living (i.e. holding groceries). The reduction in postural sway may suggest this type of loading has a stabilising effect during quiet standing among older adults. Copyright © 2017 Elsevier Ltd. All rights reserved.

Relationships Between the External and Internal Training Load in Professional Soccer: What Can We Learn From Machine Learning?

Science.gov (United States)

Jaspers, Arne; Beéck, Tim Op De; Brink, Michel S; Frencken, Wouter G P; Staes, Filip; Davis, Jesse J; Helsen, Werner F

2017-12-28

Machine learning may contribute to understanding the relationship between the external load and internal load in professional soccer. Therefore, the relationship between external load indicators and the rating of perceived exertion (RPE) was examined using machine learning techniques on a group and individual level. Training data were collected from 38 professional soccer players over two seasons. The external load was measured using global positioning system technology and accelerometry. The internal load was obtained using the RPE. Predictive models were constructed using two machine learning techniques, artificial neural networks (ANNs) and least absolute shrinkage and selection operator (LASSO), and one naive baseline method. The predictions were based on a large set of external load indicators. Using each technique, one group model involving all players and one individual model for each player was constructed. These models' performance on predicting the reported RPE values for future training sessions was compared to the naive baseline's performance. Both the ANN and LASSO models outperformed the baseline. Additionally, the LASSO model made more accurate predictions for the RPE than the ANN model. Furthermore, decelerations were identified as important external load indicators. Regardless of the applied machine learning technique, the group models resulted in equivalent or better predictions for the reported RPE values than the individual models. Machine learning techniques may have added value in predicting the RPE for future sessions to optimize training design and evaluation. Additionally, these techniques may be used in conjunction with expert knowledge to select key external load indicators for load monitoring.

Novel instrument for characterizing comprehensive physical properties under multi-mechanical loads and multi-physical field coupling conditions

Science.gov (United States)

Liu, Changyi; Zhao, Hongwei; Ma, Zhichao; Qiao, Yuansen; Hong, Kun; Ren, Zhuang; Zhang, Jianhai; Pei, Yongmao; Ren, Luquan

2018-02-01

Functional materials represented by ferromagnetics and ferroelectrics are widely used in advanced sensor and precision actuation due to their special characterization under coupling interactions of complex loads and external physical fields. However, the conventional devices for material characterization can only provide a limited type of loads and physical fields and cannot simulate the actual service conditions of materials. A multi-field coupling instrument for characterization has been designed and implemented to overcome this barrier and measure the comprehensive physical properties under complex service conditions. The testing forms include tension, compression, bending, torsion, and fatigue in mechanical loads, as well as different external physical fields, including electric, magnetic, and thermal fields. In order to offer a variety of information to reveal mechanical damage or deformation forms, a series of measurement methods at the microscale are integrated with the instrument including an indentation unit and in situ microimaging module. Finally, several coupling experiments which cover all the loading and measurement functions of the instrument have been implemented. The results illustrate the functions and characteristics of the instrument and then reveal the variety in mechanical and electromagnetic properties of the piezoelectric transducer ceramic, TbDyFe alloy, and carbon fiber reinforced polymer under coupling conditions.

Relationships Between Internal and External Match-Load Indicators in Soccer Match Officials.

Science.gov (United States)

Castillo, Daniel; Weston, Matthew; McLaren, Shaun J; Cámara, Jesús; Yanci, Javier

2017-08-01

The aims of this study were to describe the internal and external match loads (ML) of refereeing activity during official soccer matches and to investigate the relationship among the methods of ML quantification across a competitive season. A further aim was to examine the usefulness of differential perceived exertion (dRPE) as a tool for monitoring internal ML in soccer referees. Twenty field referees (FRs) and 43 assistant referees (ARs) participated in the study. Data were collected from 30 competitive matches (FR = 20 observations, AR = 43 observations) and included measures of internal (Edwards' heart-rate-derived training impulse [TRIMP EDW ]) ML, external (total distance covered, distance covered at high speeds, and player load) ML, and ML differentiated ratings of perceived respiratory (sRPE res ) and leg-muscle (sRPE mus ) exertion. Internal and external ML were all greater for FRs than for ARs (-19.7 to -72.5), with differences ranging from very likely very large to most likely extremely large. The relationships between internal-ML and external-ML indicators were, in most cases, unclear for FR (r internal and external ML. Moreover, dRPE represents distinct dimensions of effort and may be useful in monitoring soccer referees' ML during official matches.

Cost minimization of generation, storage, and new loads, comparing costs with and without externalities

DEFF Research Database (Denmark)

Noel, Lance Douglas; Brodie, Joseph; Kempton, Willett

2017-01-01

G) technology, and building heat) are modeled within the PJM Interconnection. The corresponding electric systems are then operated and constrained to meet the load every hour over four years. The total cost of each energy system is calculated, both with and without externalities, to find the least...... cost energy systems. Using today’s costs of conventional and renewable electricity and without adding any externalities, the cost-minimum system includes no renewable generation, but does include EVs. When externalities are included, however, the most cost-effective to system covers 50% of the electric...... load with renewable energy and runs reliably without need for either new conventional generation or purpose-built storage. The three novel energy policy implications of this research are: (1) using today’s cost of renewable electricity and estimates of externalities, it is cost effective to implement...

Relationships Between Results Of An Internal And External Match Load Determining Method In Male, Singles Badminton Players.

Science.gov (United States)

Abdullahi, Yahaya; Coetzee, Ben; Van den Berg, Linda

2017-07-03

The study purpose was to determine relationships between results of internal and external match load determining methods. Twenty-one players, who participated in selected badminton championships during the 2014/2015 season served as subjects. The heart rate (HR) values and GPS data of each player were obtained via a fix Polar HR Transmitter Belt and MinimaxX GPS device. Moderate significant Spearman's rank correlations were found between HR and absolute duration (r = 0.43 at a low intensity (LI) and 0.44 at a high intensity (HI)), distance covered (r = 0.42 at a HI) and player load (PL) (r = 0.44 at a HI). Results also revealed an opposite trend for external and internal measures of load as the average relative HR value was found to be the highest for the HI zone (54.1%) compared to the relative measures of external load where average values (1.29-9.89%) were the lowest for the HI zone. In conclusion, our findings show that results of an internal and external badminton match load determining method are more related to each other in the HI zone than other zones and that the strength of relationships depend on the duration of activities that are performed in especially LI and HI zones. Overall, trivial to moderate relationships between results of an internal and external match load determining method in male, singles badminton players reaffirm the conclusions of others that these constructs measure distinctly different demands and should therefore be measured concurrently to fully understand the true requirements of badminton match play.

Simulation of fatigue damage in ferroelectric polycrystals under mechanical/electrical loading

Science.gov (United States)

Kozinov, S.; Kuna, M.

2018-07-01

The reliability of smart-structures made of ferroelectric ceramics is essentially reduced by the formation of cracks under the action of external electrical and/or mechanical loading. In the current research a numerical model for low-cycle fatigue in ferroelectric mesostructures is proposed. In the finite element simulations a combination of two user element routines is utilized. The first one is used to model a micromechanical ferroelectric domain switching behavior inside the grains. The second one is used to simulate fatigue damage of grain boundaries by a cohesive zone model (EMCCZM) based on an electromechanical cyclic traction-separation law (TSL). For numerical simulations a scanning electron microscope image of the ceramic's grain structure was digitalized and meshed. The response of this mesostructure to cyclic electrical or mechanical loading is systematically analyzed. As a result of the simulations, the distribution of electric potential, field, displacement and polarization as well as mechanical stresses and deformations inside the grains are obtained. At the grain boundaries, the formation and evolution of damage are analyzed until final failure and induced degradation of electric permittivity. It is found that the proposed model correctly mimics polycrystalline behavior during poling processes and progressive damage under cyclic electromechanical loading. To the authors' knowledge, it is the first model and numerical analysis of ferroelectric polycrystals taking into account both domain reorientation and cohesive modeling of intergranular fracture. It can help to understand failure mechanisms taking place in ferroelectrics during fatigue processes.

Internal cycling, not external loading, decides the nutrient limitation in eutrophic lake: A dynamic model with temporal Bayesian hierarchical inference.

Science.gov (United States)

Wu, Zhen; Liu, Yong; Liang, Zhongyao; Wu, Sifeng; Guo, Huaicheng

2017-06-01

Lake eutrophication is associated with excessive anthropogenic nutrients (mainly nitrogen (N) and phosphorus (P)) and unobserved internal nutrient cycling. Despite the advances in understanding the role of external loadings, the contribution of internal nutrient cycling is still an open question. A dynamic mass-balance model was developed to simulate and measure the contributions of internal cycling and external loading. It was based on the temporal Bayesian Hierarchical Framework (BHM), where we explored the seasonal patterns in the dynamics of nutrient cycling processes and the limitation of N and P on phytoplankton growth in hyper-eutrophic Lake Dianchi, China. The dynamic patterns of the five state variables (Chla, TP, ammonia, nitrate and organic N) were simulated based on the model. Five parameters (algae growth rate, sediment exchange rate of N and P, nitrification rate and denitrification rate) were estimated based on BHM. The model provided a good fit to observations. Our model results highlighted the role of internal cycling of N and P in Lake Dianchi. The internal cycling processes contributed more than external loading to the N and P changes in the water column. Further insights into the nutrient limitation analysis indicated that the sediment exchange of P determined the P limitation. Allowing for the contribution of denitrification to N removal, N was the more limiting nutrient in most of the time, however, P was the more important nutrient for eutrophication management. For Lake Dianchi, it would not be possible to recover solely by reducing the external watershed nutrient load; the mechanisms of internal cycling should also be considered as an approach to inhibit the release of sediments and to enhance denitrification. Copyright © 2017 Elsevier Ltd. All rights reserved.

External representation of argumentation in CSCL and the management of cognitive load

NARCIS (Netherlands)

Bruggen, J.M.; Kirschner, P.A.; Jochems, W.

2002-01-01

Computer-supported collaborative learning (CSCL) environments, particularly environments where students share external representations, are discussed as an interesting area for the application of cognitive load theory (CLT). CSCL environments share a number of characteristics that will induce

External Load Affects Ground Reaction Force Parameters Non-uniformly during Running in Weightlessness

Science.gov (United States)

DeWitt, John; Schaffner, Grant; Laughlin, Mitzi; Loehr, James; Hagan, R. Donald

2004-01-01

Long-term exposure to microgravity induces detrimefits to the musculcskdetal system (Schneider et al., 1995; LeBlanc et al., 2000). Treadmill exercise is used onboard the International Space Station as an exercise countermeasure to musculoskeletal deconditioning due to spaceflight. During locomotive exercise in weightlessness (0G), crewmembers wear a harness attached to an external loading mechanism (EL). The EL pulls the crewmember toward the treadmill, and provides resistive load during the impact and propulsive phases of gait. The resulting forces may be important in stimulating bone maintenance (Turner, 1998). The EL can be applied via a bungee and carabineer clip configuration attached to the harness and can be manipulated to create varying amounts of load levels during exercise. Ground-based research performed using a vertically mounted treadmill found that peak ground reaction forces (GRF) during running at an EL of less than one body weight (BW) are less than those that occur during running in normal gravity (1G) (Davis et al., 1996). However, it is not known how the GRF are affected by the EL in a true OG environment. Locomotion while suspended may result in biomechanics that differ from free running. The purpose of this investigation was to determine how EL affects peak impact force, peak propulsive force, loading rate, and impulse of the GRF during running in 0G. It was hypothesized that increasing EL would result in increases in each GRF parameter.

Cost minimization of generation, storage, and new loads, comparing costs with and without externalities

International Nuclear Information System (INIS)

Noel, Lance; Brodie, Joseph F.; Kempton, Willett; Archer, Cristina L.; Budischak, Cory

2017-01-01

Highlights: • The study models a large regional transmission organization, with various amounts of renewable energy. • The cost of 86 million iterations of energy systems is calculated, with and without externalities. • When including externalities, society should implement 50% renewable energy. - Abstract: The goal of this research is to understand the economics of anticipated large-scale changes in the electric system. 86 million different combinations of renewable generation (wind and solar), natural gas, and three storage types (hydrogen storage, electric vehicles equipped with vehicle-to-grid (V2G) technology, and building heat) are modeled within the PJM Interconnection. The corresponding electric systems are then operated and constrained to meet the load every hour over four years. The total cost of each energy system is calculated, both with and without externalities, to find the least cost energy systems. Using today’s costs of conventional and renewable electricity and without adding any externalities, the cost-minimum system includes no renewable generation, but does include EVs. When externalities are included, however, the most cost-effective to system covers 50% of the electric load with renewable energy and runs reliably without need for either new conventional generation or purpose-built storage. The three novel energy policy implications of this research are: (1) using today’s cost of renewable electricity and estimates of externalities, it is cost effective to implement 240 GW of renewable electricity to meet 50% of the total electric load; (2) there is limited need to construct new natural gas power plants, especially from a system-wide perspective; and (3) existing coal plants may still be useful to the energy system, and instead of being retired, should be repurposed to occasionally provide generation.

Experimental proof of a load resilient external matching solution for the ITER ICRH system

International Nuclear Information System (INIS)

Vervier, M.; Messiaen, A.; Dumortier, P.; Lamalle, P.

2005-01-01

A reliable load resilient external matching scheme for the ITER ICRH system has been successfully tested on the mock-up of the external matching system with variable plasma load simulation. To avoid the deleterious mutual coupling effects the power has been passively distributed among the upper half and the bottom half of the 24 radiating straps of the antenna plug. In this plug the straps are grouped in 8 triplets by 4-ports junctions. The 4 top and 4 bottom triplets are respectively put in parallel outside the antenna plug near a voltage anti-node by means of T junctions. The load resilient matching is then obtained by a 4 parameters single 'conjugate T' (CT) configuration. For an antenna loading variation of about 1 to 8 Ω/m the VSWR at the power source remains below 1.3. The maximum voltage along the line remains equal to the one in the antenna plug and there is a fair power share between the straps. A π0π0 toroidal phasing is easily obtained. The poloidal phasing between the top and bottom triplets is determined by the loading. A straightforward matching procedure is described. Good load resilience is also obtained by replacing the CT by one hybrid

Energy cost and mechanical work of walking during load carriage in soldiers.

Science.gov (United States)

Grenier, Jordane G; Peyrot, Nicolas; Castells, Josiane; Oullion, Roger; Messonnier, Laurent; Morin, Jean-Benoit

2012-06-01

In the military context, soldiers carry equipments of total mass often exceeding 30%-40% of their body mass (BM) and complexly distributed around their body (backpack, weapons, electronics, protections, etc.), which represents severe load carrying conditions. This study aimed to better understand the effects of load carriage on walking energetics and mechanics during military-type walking. Ten male infantrymen recently retired from the French Foreign Legion performed 3-min walking trials at a constant speed of 4 km·h(-1) on an instrumented treadmill, during which walking pattern spatiotemporal parameters, energy cost (C(W)), external mechanical work (W(ext)), and the work done by one leg against the other during the double-contact period (W(int,dc)) were specifically assessed. Three conditions were tested: (i) light sportswear (SP, reference condition considered as unloaded), (ii) battle equipment (BT, ∼22 kg, ∼27% of subjects' BM, corresponding to a military intermediate load), and (iii) road march equipment (RM, ∼38 kg, ∼46% of subjects' BM, corresponding to a military high load). Repeated-measures ANOVA showed that military equipment carriage significantly (i) altered the spatiotemporal pattern of walking (all P < 0.01), (ii) increased absolute gross and net CW (P < 0.0001), and (iii) increased both absolute and mass-relative W(ext) (P < 0.01) and W(int,dc) (P < 0.0001) but did not alter the inverted pendulum recovery or locomotor efficiency. Military equipments carriage induced significant changes in walking mechanics and energetics, but these effects appeared not greater than those reported with loads carried around the waist and close to the center of mass. This result was not expected because the latter has been hypothesized to be the optimal method of load carriage from a metabolic standpoint.

Factors related to external loads in buried pipelines; Consideracoes quanto as variaveis relacionadas ao carregamento externo em dutos enterrados

Energy Technology Data Exchange (ETDEWEB)

Provenzano, Carlos E.C.; Silva, Breno S.; Fernandes, Lincoln F.; Santos Junior, Sergio J.F. [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil); Louzada, Carlos H.C.M.

2005-07-01

Work of heavy equipment or vehicles above existent right-of-ways, may cause undesired external overload at buried pipelines in operation. The effect of these loads shall be analyzed considering the deflections and stresses on the pipelines. The major variables, nominal diameter, thickness, material, soil parameters, operation pressure and external loads shall be related and verified according to the limits from original project. Cases when the external loads cause higher efforts, the traffic over the pipelines shall be restricted in order to avoid damages. In other cases, it may be adapted to any technical alternatives to modify the parameters in such a way to make possible work above the right-of-way, such as increase the machine support area, increase backfill covering, a reduction in the internal operation pressure in a short time, etc. This work presents the study on the parameters used to establish the maximum allowable external loads over buried pipelines in operation. (author)

Transient behavior of high-interaction MHD generator following external loading faults

International Nuclear Information System (INIS)

Ishikawa, Motoo

1983-01-01

Transient behavior consequent to external loading faults is studied numerically on four configurations of high-interaction MHD generators-subsonic Faraday, supersonic Faraday, subsonic diagonal and supersonic diagonal, to provide a variable data base to serve in selecting the type of large-scale MHD generator. Time-dependent one-dimensional Navier-Stokes equations are solved with the 1969 MacCormack method, in combination with the Maxwell equations and the generalized Ohm's law. An artificial viscosity term is added to the Navier-Stokes equations to maintain numerical stability. It is shown that, with both supersonic and subsonic flows, the Faraday generator is liable to sustain more harmful effect from short than from open faults of the external loading circuit. For large-scale diagonal types, on the other hand, open faults are more dangerous. With subsonic flow, a shock wave propagating upstream is induced by short fault in the Faraday, and by open fault in the diagonal-type generator. In the case of supersonic flow, propagation upstream of the disturbance is completely obstructed. Larger electrical stress is foreseen for Faraday than for diagonal configuration. (author)

The Relationships Between Internal and External Measures of Training Load and Intensity in Team Sports: A Meta-Analysis.

Science.gov (United States)

McLaren, Shaun J; Macpherson, Tom W; Coutts, Aaron J; Hurst, Christopher; Spears, Iain R; Weston, Matthew

2018-03-01

The associations between internal and external measures of training load and intensity are important in understanding the training process and the validity of specific internal measures. We aimed to provide meta-analytic estimates of the relationships, as determined by a correlation coefficient, between internal and external measures of load and intensity during team-sport training and competition. A further aim was to examine the moderating effects of training mode on these relationships. We searched six electronic databases (Scopus, Web of Science, PubMed, MEDLINE, SPORTDiscus, CINAHL) for original research articles published up to September 2017. A Boolean search phrase was created to include search terms relevant to team-sport athletes (population; 37 keywords), internal load (dependent variable; 35 keywords), and external load (independent variable; 81 keywords). Articles were considered for meta-analysis when a correlation coefficient describing the association between at least one internal and one external measure of session load or intensity, measured in the time or frequency domain, was obtained from team-sport athletes during normal training or match-play (i.e., unstructured observational study). The final data sample included 122 estimates from 13 independent studies describing 15 unique relationships between three internal and nine external measures of load and intensity. This sample included 295 athletes and 10,418 individual session observations. Internal measures were session ratings of perceived exertion (sRPE), sRPE training load (sRPE-TL), and heart-rate-derived training impulse (TRIMP). External measures were total distance (TD), the distance covered at high and very high speeds (HSRD ≥ 13.1-15.0 km h -1 and VHSRD ≥ 16.9-19.8 km h -1 , respectively), accelerometer load (AL), and the number of sustained impacts (Impacts > 2-5 G). Distinct training modes were identified as either mixed (reference condition), skills, metabolic, or

Mechanical loading regulates human MSC differentiation in a multi-layer hydrogel for osteochondral tissue engineering.

Science.gov (United States)

Steinmetz, Neven J; Aisenbrey, Elizabeth A; Westbrook, Kristofer K; Qi, H Jerry; Bryant, Stephanie J

2015-07-01

A bioinspired multi-layer hydrogel was developed for the encapsulation of human mesenchymal stem cells (hMSCs) as a platform for osteochondral tissue engineering. The spatial presentation of biochemical cues, via incorporation of extracellular matrix analogs, and mechanical cues, via both hydrogel crosslink density and externally applied mechanical loads, were characterized in each layer. A simple sequential photopolymerization method was employed to form stable poly(ethylene glycol)-based hydrogels with a soft cartilage-like layer of chondroitin sulfate and low RGD concentrations, a stiff bone-like layer with high RGD concentrations, and an intermediate interfacial layer. Under a compressive load, the variation in hydrogel stiffness within each layer produced high strains in the soft cartilage-like layer, low strains in the stiff bone-like layer, and moderate strains in the interfacial layer. When hMSC-laden hydrogels were cultured statically in osteochondral differentiation media, the local biochemical and matrix stiffness cues were not sufficient to spatially guide hMSC differentiation after 21 days. However dynamic mechanical stimulation led to differentially high expression of collagens with collagen II in the cartilage-like layer, collagen X in the interfacial layer and collagen I in the bone-like layer and mineral deposits localized to the bone layer. Overall, these findings point to external mechanical stimulation as a potent regulator of hMSC differentiation toward osteochondral cellular phenotypes. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Hydrodynamic interactions induce movement against an external load in a ratchet dimer Brownian motor.

Science.gov (United States)

Fornés, José A

2010-01-15

We use the Brownian dynamics with hydrodynamic interactions simulation in order to describe the movement of a elastically coupled dimer Brownian motor in a ratchet potential. The only external forces considered in our system were the load, the random thermal noise and an unbiased thermal fluctuation. For a given set of parameters we observe direct movement against the load force if hydrodynamic interactions were considered.

The impact of cognitive control, incentives, and working memory load on the P3 responses of externalizing prisoners.

Science.gov (United States)

Baskin-Sommers, Arielle R; Krusemark, Elizabeth A; Curtin, John J; Lee, Christopher; Vujnovich, Aleice; Newman, Joseph P

2014-02-01

The P3 amplitude reduction is one of the most common correlates of externalizing. However, few studies have used experimental manipulations designed to challenge different cognitive functions in order to clarify the processes that impact this reduction. To examine factors moderating P3 amplitude in trait externalizing, we administered an n-back task that manipulated cognitive control demands, working memory load, and incentives to a sample of male offenders. Offenders with high trait externalizing scores did not display a global reduction in P3 amplitude. Rather, the negative association between trait externalizing and P3 amplitude was specific to trials involving inhibition of a dominant response during infrequent stimuli, in the context of low working memory load, and incentives for performance. In addition, we discuss the potential implications of these findings for externalizing-related psychopathologies. The results complement and expand previous work on the process-level dysfunction contributing to externalizing-related deficits in P3. Copyright © 2013 Elsevier B.V. All rights reserved.

Damage mechanisms in PBT-GF30 under thermo-mechanical cyclic loading

International Nuclear Information System (INIS)

Schaaf, A.; De Monte, M.; Hoffmann, C.; Vormwald, M.; Quaresimin, M.

2014-01-01

The scope of this paper is the investigation of damage mechanisms at microscopic scale on a short glass fiber reinforced polybutylene terephthalate (PBT-GF30) under thermo-mechanical cyclic loading. In addition the principal mechanisms are verified through micro mechanical FE models. In order to investigate the fatigue behavior of the material both isothermal strain controlled fatigue (ISCF) tests at three different temperatures and thermo-mechanical fatigue (TMF) tests were conducted on plain and notched specimens, manufactured by injection molding. The goal of the work is to determine the damage mechanisms occurring under TMF conditions and to compare them with the mechanisms occurring under ISCF. For this reason fracture surfaces of TMF and ISCF samples loaded at different temperature levels were analyzed using scanning electron microscopy. Furthermore, specimens that failed under TMF were examined on microsections revealing insight into both crack initiation and crack propagation. The findings of this investigation give valuable information about the main damage mechanisms of PBT-GF30 under TMF loading and serve as basis for the development of a TMF life estimation methodology

Experimental results of superconducting magnet behaviour during discharging into the external load

Directory of Open Access Journals (Sweden)

Ladislav Grega

2008-12-01

Full Text Available The basic part of every SMES (Superconducting magnetic energy storage system is a superconducting magnet. All eventsof electrical nature which happen during its charging,, bypassing and discharging are transient. The article deals with experimentalresults of the superconducting magnet behaviour, especially during the period of its discharging into the prepared external load.

Surface Damage Mechanism of Monocrystalline Si Under Mechanical Loading

Science.gov (United States)

Zhao, Qingliang; Zhang, Quanli; To, Suet; Guo, Bing

2017-03-01

Single-point diamond scratching and nanoindentation on monocrystalline silicon wafer were performed to investigate the surface damage mechanism of Si under the contact loading. The results showed that three typical stages of material removal appeared during dynamic scratching, and a chemical reaction of Si with the diamond indenter and oxygen occurred under the high temperature. In addition, the Raman spectra of the various points in the scratching groove indicated that the Si-I to β-Sn structure (Si-II) and the following β-Sn structure (Si-II) to amorphous Si transformation appeared under the rapid loading/unloading condition of the diamond grit, and the volume change induced by the phase transformation resulted in a critical depth (ductile-brittle transition) of cut (˜60 nm ± 15 nm) much lower than the theoretical calculated results (˜387 nm). Moreover, it also led to abnormal load-displacement curves in the nanoindentation tests, resulting in the appearance of elbow and pop-out effects (˜270 nm at 20 s, 50 mN), which were highly dependent on the loading/unloading conditions. In summary, phase transformation of Si promoted surface deformation and fracture under both static and dynamic mechanical loading.

Russian standards and design practice of ensuring NPP reliability under severe external loading conditions

Energy Technology Data Exchange (ETDEWEB)

Birbraer, A N [St. Petersburg Research and Design Institute Atomenergoproject, St. Petersburt (Russian Federation)

1993-07-01

Russian Standards and design practice of ensuring NPP reliability under severe external loading conditions are described. The main attention is paid to the seismic design requirements. Explosions, aircraft impact, and tornado are briefly examined too (author)

Russian standards and design practice of ensuring NPP reliability under severe external loading conditions

International Nuclear Information System (INIS)

Birbraer, A.N.

1993-01-01

Russian Standards and design practice of ensuring NPP reliability under severe external loading conditions are described. The main attention is paid to the seismic design requirements. Explosions, aircraft impact, and tornado are briefly examined too (author)

Clinical Parameters and Crestal Bone Loss in Internal Versus External Hex Implants at One Year after Loading

Directory of Open Access Journals (Sweden)

HamidReza Arab

2015-09-01

Full Text Available Introduction: The survival of an implant system is affected by the choice of antirotational design, which can include an external or internal hex. Implant success also is affected by the maintenance of the crestal bone around implants. The aim of present study was to evaluate the crestal bone loss and clinical parameters related to bone loss in patients loaded with an external or internal hex 3i implant (3i Implant Innovation, Palm Beach Gardens, FL, USA. The evaluations were performed one year after loading. Materials and Methods: A total of 39 implants (23 external hex, 16 internal hex were placed randomly in 23 patients (10 male, 13 female by a submerged approach. None of patients had compromised conditions or parafunctional habits. At placement and at one year after loading, periapical radiographs were taken via the parallel method from the implant sites. Results: Crestal bone loss was -0.712±0.831 mm in implants with an internal hex connection and -0.139±0.505 mm in implants with an external hex connection (P≤0.05. No correlation was found between crestal bone loss and parameters such as age, gender, jaw, implant location (anterior, premolar, or molar, implant diameter, or implant length. Conclusions: Crestal bone loss was greater in patients with internal hex 3i implants than in those with external implants. Similar results in other clinical factors were found between the groups.

Propagation of steady-state vibration in periodic pipes conveying fluid on elastic foundations with external moving loads

Energy Technology Data Exchange (ETDEWEB)

Yu, Dianlong, E-mail: dianlongyu@yahoo.com.cn [Laboratory of Science and Technology on Integrated Logistics Support, National University of Defense Technology, Changsha 410073 (China); MOE Key Laboratory of Photonic and Phononic Crystals, National University of Defense Technology, Changsha 410073 (China); Wen, Jihong; Shen, Huijie; Wen, Xisen [Laboratory of Science and Technology on Integrated Logistics Support, National University of Defense Technology, Changsha 410073 (China); MOE Key Laboratory of Photonic and Phononic Crystals, National University of Defense Technology, Changsha 410073 (China)

2012-10-01

The propagation of steady-state vibration in a periodic pipe conveying fluid on elastic foundation with an external moving load is studied using wave propagation and attenuation theory. Wavenumbers and propagation properties in a moving coordinate system are investigated. The propagation constants are calculated using transfer matrix theory to determine whether the perturbation, which is introduced by an external moving load, can propagate through the pipe or not. The Bragg and locally resonant band gaps, corresponding to the velocity field, can exist in a periodic pipe system. In addition, the effects on both types of band gaps have been analysed.

Propagation of steady-state vibration in periodic pipes conveying fluid on elastic foundations with external moving loads

International Nuclear Information System (INIS)

Yu, Dianlong; Wen, Jihong; Shen, Huijie; Wen, Xisen

2012-01-01

The propagation of steady-state vibration in a periodic pipe conveying fluid on elastic foundation with an external moving load is studied using wave propagation and attenuation theory. Wavenumbers and propagation properties in a moving coordinate system are investigated. The propagation constants are calculated using transfer matrix theory to determine whether the perturbation, which is introduced by an external moving load, can propagate through the pipe or not. The Bragg and locally resonant band gaps, corresponding to the velocity field, can exist in a periodic pipe system. In addition, the effects on both types of band gaps have been analysed.

Conditions of external loading of nuclear power plant structures by vapor cloud explosions and design requirements

International Nuclear Information System (INIS)

Geiger, W.

1977-01-01

In the design of nuclear power plant structures in the Federal Republic of Germany (FRG) the external loading by pressure waves from unconfined vapor cloud explosions is taken into account. The loading conditions used are based on simplified model considerations for the sequence of events which generates the pressure wave. The basic assumption is that the explosion of unconfined vapor clouds can evolve only in the form of a deflagration wave with a maximum overpressure of 0.3 bar. The research on gas explosions conducted in the FRG with a view to external reactor safety just as similar work in other countries demonstrates that there are still various problems which need further clarification. The principal issues are the maximum conceivable load and the modes of structrual response. This paper presents the main results of a status report commissioned by the German Ministry of the Inertior in which the whole sequence of events leading to the external loading of nuclear power plants and the corresponding response of the structure was scrutinized. Constitutive in establishing the status report have been thorough discussions with experts of the various fields. The following problem areas are discussed in the paper. Incidents leading to the release of large amounts of liquefied gas; Formation of explosive vapor clouds, ignition conditions; Development of the explosion, generation of the pressure wave; Interaction between pressure wave and reactor building. It is outlined where definite statements are possible and where uncertainties and information gaps exist. (Auth.)

Robust Position Control of Electro-mechanical Systems

OpenAIRE

Rong Mei; Mou Chen

2013-01-01

In this work, the robust position control scheme is proposed for the electro-mechanical system using the disturbance observer and backstepping control method. To the external unknown load of the electro-mechanical system, the nonlinear disturbance observer is given to estimate the external unknown load. Combining the output of the developed nonlinear disturbance observer with backstepping technology, the robust position control scheme is proposed for the electro-mechanical system. The stabili...

The Effect of mechanical resistive loading on optimal respiratory signals and breathing patterns under added dead space and CO2 breathing

Directory of Open Access Journals (Sweden)

Lin Shyan-Lung

2016-01-01

Full Text Available Current study aims to investigate how the respiratory resistive loading affects the behaviour of the optimal chemical-mechanical respiratory control model, the respiratory signals and breathing pattern are optimized under external dead space loading and CO2 breathing. The respiratory control was modelled to include a neuro-muscular drive as the control output to derive the waveshapes of instantaneous airflow, lung volume profiles, and breathing pattern, including total/alveolar ventilation, breathing frequency, tidal volume, inspiratory/expiratory duration, duty cycle, and arterial CO2 pressure. The simulations were performed under various respiratory resistive loads, including no load, inspiratory resistive load, expiratory resistive load, and continuous resistive load. The dead space measurement was described with Gray’s derivation, and simulation results were studied and compared with experimental findings.

Stress analysis in a functionally graded disc under mechanical loads ...

Indian Academy of Sciences (India)

They have therefore attracted considerable attention in recent ... vessels subjected to internal pressure by using the small deformation theory. ..... sure (Pi = 50 MPa), external pressure (Po = 100 MPa), centrifugal load with a constant angular.

The effect of elbow angle and external moment on load sharing of elbow muscles

NARCIS (Netherlands)

Praagman, M.; Chadwick, E.K.J.; van der Helm, F.C.T.; Veeger, H.E.J.

2010-01-01

To study elbow muscle load sharing we investigated the effect of external flexion-extension (FE) and pronation-supination (PS) moments and elbow angle on muscle activation and oxygen consumption (V̇O2).Two data sets were obtained. First, (n=6) electromyography (EMG) of elbow flexors (long and short

Energy Evolution Mechanism and Confining Pressure Effect of Granite under Triaxial Loading-Unloading Cycles

Science.gov (United States)

Wang, Hao; Miao, Sheng-jun

2018-05-01

Rock mass undergoes some deformational failure under the action of external loads, a process known to be associated with energy dissipation and release. A triaxial loading-unloading cycle test was conducted on granite in order to investigate the energy evolution pattern of rock mass under the action of external loads. The study results demonstrated: (1) The stress peaks increased by 50% and 22% respectively and the pre-peak weakening became more apparent in the ascending process of the confining pressure from 10MPa to 30MPa; the area enclosed by the hysteresis loop corresponding to 30MPa diminished by nearly 60% than that corresponding to 10MPa, indicating a higher confining pressure prohibits rock mass from plastic deformation and shifts strain toward elastic deformation. (2) In the vicinity of the strength limit, the slope of dissipation energy increased to 1.6 from the original 0.7 and the dissipation energy grew at an accelerating rate, demonstrating stronger propagation and convergence of internal cracks. (3) At a pressure of 70% of the stress peak, the elastic energy of the granite accounted for 88% of its peak value, suggesting the rock mechanical energy from the outside mostly changes into the elastic energy inside the rock, with little energy loss.(4) Prior to test specimen failure, the axial bearing capacity dropped with a decreasing confining pressure in an essentially linear way, and the existence of confirming pressure played a role in stabilizing the axial bearing capacity.

The role of mechanical loading in ligament tissue engineering.

Science.gov (United States)

Benhardt, Hugh A; Cosgriff-Hernandez, Elizabeth M

2009-12-01

Tissue-engineered ligaments have received growing interest as a promising alternative for ligament reconstruction when traditional transplants are unavailable or fail. Mechanical stimulation was recently identified as a critical component in engineering load-bearing tissues. It is well established that living tissue responds to altered loads through endogenous changes in cellular behavior, tissue organization, and bulk mechanical properties. Without the appropriate biomechanical cues, new tissue formation lacks the necessary collagenous organization and alignment for sufficient load-bearing capacity. Therefore, tissue engineers utilize mechanical conditioning to guide tissue remodeling and improve the performance of ligament grafts. This review provides a comparative analysis of the response of ligament and tendon fibroblasts to mechanical loading in current bioreactor studies. The differential effect of mechanical stimulation on cellular processes such as protease production, matrix protein synthesis, and cell proliferation is examined in the context of tissue engineering design.

Effect of external viscous load on head movement

Science.gov (United States)

Nam, M.-H.; Lakshminarayanan, V.; Stark, L. W.

1984-01-01

Quantitative measurements of horizontal head rotation were obtained from normal human subjects intending to make 'time optimal' trajectories between targets. By mounting large, lightweight vanes on the head, viscous damping B, up to 15 times normal could be added to the usual mechanical load of the head. With the added viscosity, the head trajectory was slowed and of larger duration (as expected) since fixed and maximal (for that amplitude) muscle forces had to accelerate the added viscous load. This decreased acceleration and velocity and longer duration movement still ensued in spite of adaptive compensation; this provided evidence that quasi-'time optimal' movements do indeed employ maximal muscle forces. The adaptation to this added load was rapid. Then the 'adapted state' subjects produced changed trajectories. The adaptation depended in part on the differing detailed instructions given to the subjects. This differential adaptation provided evidence for the existence of preprogrammed controller signals, sensitive to intended criterion, and neurologically ballistic or open loop rather than modified by feedback from proprioceptors or vision.

Fourier series analysis of a cylindrical pressure vessel subjected to axial end load and external pressure

International Nuclear Information System (INIS)

Brar, Gurinder Singh; Hari, Yogeshwar; Williams, Dennis K.

2013-01-01

This paper presents the comparison of a reliability technique that employs a Fourier series representation of random axisymmetric and asymmetric imperfections in a cylindrical pressure vessel subjected to an axial end load and external pressure, with evaluations prescribed by the ASME Boiler and Pressure Vessel Code, Section VIII, Division 2 Rules. The ultimate goal of the reliability technique described herein is to predict the critical buckling load associated with the subject cylindrical pressure vessel. Initial geometric imperfections are shown to have a significant effect on the calculated load carrying capacity of the vessel. Fourier decomposition was employed to interpret imperfections as structural features that can be easily related to various other types of defined imperfections. The initial functional description of the imperfections consists of an axisymmetric portion and a deviant portion, which are availed in the form of a double Fourier series. Fifty simulated shells generated by the Monte Carlo technique are employed in the final prediction of the critical buckling load. The representation of initial geometrical imperfections in the cylindrical pressure vessel requires the determination of respective Fourier coefficients. Multi-mode analyses are expanded to evaluate a large number of potential buckling modes for both predefined geometries in combination with asymmetric imperfections as a function of position within the given cylindrical shell. The probability of the ultimate buckling stress exceeding a predefined threshold stress is also calculated. The method and results described herein are in stark contrast to the “knockdown factor” approach as applied to compressive stress evaluations currently utilized in industry. Further effort is needed to improve on the current design rules regarding column buckling of large diameter pressure vessels subjected to an axial end load and external pressure designed in accordance with ASME Boiler and

Fracture Toughness Evaluation of a Ni2MnGa Alloy Through Micro Indentation Under Magneto-Mechanical Loading

Science.gov (United States)

Goanţă, Viorel; Ciocanel, Constantin

2017-12-01

Ni2MnGa is a ferromagnetic alloy that exhibits the shape memory effect either induced by an externally applied magnetic field or mechanical stress. Due to the former, the alloy is commonly called magnetic shape memory alloy or MSMA. The microstructure of the MSMA consists of tetragonal martensite variants (three in the most general case) that are characterized by a magnetization vector which is aligned with the short side of the tetragonal unit cell. Exposing the MSMA to a magnetic field causes the magnetization vector to rotate and align with the external field, eventually leading to variant reorientation. The variant reorientation is observed macroscopically in the form of recoverable strain of up to 6% [1, 2]. As the magnetic field induced reorientation happens instantaneously [1, 3], MSMAs are suitable for fast actuation, sensing, or power harvesting applications. However, actuation applications are limited by the maximum actuation stress of the material that is about 3.5MPa at approximately 2 to 3% reorientation strain. During MSMA fatigue magneto-mechanical characterization studies [4, 5] it was observed that cracks nucleate and grow on the surface of material samples, after a relatively small number of cycles, leading to loss in material performance. This triggered the need for understanding the mechanisms that govern crack nucleation and growth in MSMAs, as well as the nature of the material, i.e. ductile or brittle. The experimental study reported in this paper was carried out to determine material's fracture toughness, the predominant crack growth directions, and the orientation of the cracks relative to the mechanical loading direction and to the material's microstructure. A fixture has been developed to allow Vickers micro indentation of 3mm by 3mm by 20mm Ni2MnGa samples exposed to different levels of magnetic field and/or mechanical stress. Using the measured characteristics of the impression generated during micro indentation, the lengths of

Crack assessment of pipe under combined thermal and mechanical load

International Nuclear Information System (INIS)

Song, Tae Kwang; Kim, Yun Jae

2009-01-01

In this paper, J-integral and transient C(t)-integral, which were key parameters in low temperature and high temperature fracture mechanics, under combined thermal and mechanical load were estimated via 3-dimensional finite element analyses. Various type of thermal and mechanical load, material hardening were considered to decrease conservatism in existing solutions. As a results, V-factor and redistribution time for combined thermal and mechanical load were proposed to calculate J-integral and C(t)-integral, respectively.

Breakup of free liquid jets influenced by external mechanical vibrations

Energy Technology Data Exchange (ETDEWEB)

Lad, V N; Murthy, Z V P, E-mail: vnl@ched.svnit.ac.in, E-mail: zvpm@ched.svnit.ac.in, E-mail: zvpm2000@yahoo.com [Chemical Engineering Department, Sardar Vallabhbhai National Institute of Technology—Surat, Surat—395007, Gujarat (India)

2017-02-15

The breakup of liquid jets has been studied with various test liquids using externally imposed mechanical vibrations. Images of the jets were captured by a high speed camera up to the speed of 1000 frames per second, and analyzed to obtain the profile of the jet and breakup length. The dynamics of the jets have also been studied to understand the effects of additives—a surfactant and polymer—incorporating externally imposed mechanical vibrations. Different types of breakup modes have been explored with respect to the Weber number and Ohnesorge number. The introduction of mechanical vibrations have caused jet breakup with separated droplets at a comparatively lower Weber number. The region of jet breakup by neck formation at constant jet velocities also contracted due to mechanical vibrations. (paper)

Coupling effects of chemical stresses and external mechanical stresses on diffusion

International Nuclear Information System (INIS)

Xuan Fuzhen; Shao Shanshan; Wang Zhengdong; Tu Shantung

2009-01-01

Interaction between diffusion and stress fields has been investigated extensively in the past. However, most of the previous investigations were focused on the effect of chemical stress on diffusion due to the unbalanced mass transport. In this work, the coupling effects of external mechanical stress and chemical stress on diffusion are studied. A self-consistent diffusion equation including the chemical stress and external mechanical stress gradient is developed under the framework of the thermodynamic theory and Fick's law. For a thin plate subjected to unidirectional tensile stress fields, the external stress coupled diffusion equation is solved numerically with the help of the finite difference method for one-side and both-side charging processes. Results show that, for such two types of charging processes, the external stress gradient will accelerate the diffusion process and thus increase the value of concentration while reducing the magnitude of chemical stress when the direction of diffusion is identical to that of the stress gradient. In contrast, when the direction of diffusion is opposite to that of the stress gradient, the external stress gradient will obstruct the process of solute penetration by decreasing the value of concentration and increasing the magnitude of chemical stress. For both-side charging process, compared with that without the coupling effect of external stress, an asymmetric distribution of concentration is produced due to the asymmetric mechanical stress field feedback to diffusion.

Bond-Slip Relationship for CFRP Sheets Externally Bonded to Concrete under Cyclic Loading.

Science.gov (United States)

Li, Ke; Cao, Shuangyin; Yang, Yue; Zhu, Juntao

2018-02-26

The objective of this paper was to explore the bond-slip relationship between carbon fiber-reinforced polymer (CFRP) sheets and concrete under cyclic loading through experimental and analytical approaches. Modified beam tests were performed in order to gain insight into the bond-slip relationship under static and cyclic loading. The test variables are the CFRP-to-concrete width ratio, and the bond length of the CFRP sheets. An analysis of the test results in this paper and existing test results indicated that the slope of the ascending segment of the bond-slip curve decreased with an increase in the number of load cycles, but the slip corresponding to the maximum shear stress was almost invariable as the number of load cycles increased. In addition, the rate of reduction in the slope of the ascending range of the bond-slip curve during cyclic loading decreased as the concrete strength increased, and increased as the load level or CFRP-to-concrete width ratio enhanced. However, these were not affected by variations in bond length if the residual bond length was longer than the effective bond length. A bilinear bond-slip model for CFRP sheets that are externally bonded to concrete under cyclic loading, which considered the effects of the cyclic load level, concrete strength, and CFRP-to-concrete ratio, was developed based on the existing static bond-slip model. The accuracy of this proposed model was verified by a comparison between this proposed model and test results.

Bond–Slip Relationship for CFRP Sheets Externally Bonded to Concrete under Cyclic Loading

Science.gov (United States)

Li, Ke; Cao, Shuangyin; Yang, Yue; Zhu, Juntao

2018-01-01

The objective of this paper was to explore the bond–slip relationship between carbon fiber-reinforced polymer (CFRP) sheets and concrete under cyclic loading through experimental and analytical approaches. Modified beam tests were performed in order to gain insight into the bond–slip relationship under static and cyclic loading. The test variables are the CFRP-to-concrete width ratio, and the bond length of the CFRP sheets. An analysis of the test results in this paper and existing test results indicated that the slope of the ascending segment of the bond–slip curve decreased with an increase in the number of load cycles, but the slip corresponding to the maximum shear stress was almost invariable as the number of load cycles increased. In addition, the rate of reduction in the slope of the ascending range of the bond–slip curve during cyclic loading decreased as the concrete strength increased, and increased as the load level or CFRP-to-concrete width ratio enhanced. However, these were not affected by variations in bond length if the residual bond length was longer than the effective bond length. A bilinear bond–slip model for CFRP sheets that are externally bonded to concrete under cyclic loading, which considered the effects of the cyclic load level, concrete strength, and CFRP-to-concrete ratio, was developed based on the existing static bond–slip model. The accuracy of this proposed model was verified by a comparison between this proposed model and test results. PMID:29495383

Protection against external impacts and missiles - Load assumption and effects on the plant design of a 1300 MW PWR-Plant

International Nuclear Information System (INIS)

Gremm, O.; Orth, K.H.

1978-01-01

The load assumptions and effects of the external impacts are given. The fundamental properties of the KWU standard design according to these impacts and the consequences for the engineering safeguards are explained. The protection against external impacts includes the protection against all external missiles. The basic measure of protection against internal missiles is the strict separation of redundancies. (author)

Mechanism of crack initiation and crack growth under thermal and mechanical fatigue loading

Energy Technology Data Exchange (ETDEWEB)

Utz, S.; Soppa, E.; Silcher, H.; Kohler, C. [Stuttgart Univ. (Germany). Materials Testing Inst.

2013-07-01

The present contribution is focused on the experimental investigations and numerical simulations of the deformation behaviour and crack development in the austenitic stainless steel X6CrNiNb18-10 under thermal and mechanical cyclic loading in HCF and LCF regimes. The main objective of this research is the understanding of the basic mechanisms of fatigue damage and the development of simulation methods, which can be applied further in safety evaluations of nuclear power plant components. In this context the modelling of crack initiation and crack growth inside the material structure induced by varying thermal or mechanical loads are of particular interest. The mechanisms of crack initiation depend among other things on the type of loading, microstructure, material properties and temperature. The Nb-stabilized austenitic stainless steel in the solution-annealed condition was chosen for the investigations. Experiments with two kinds of cyclic loading - pure thermal and pure mechanical - were carried out and simulated. The fatigue behaviour of the steel X6CrNiNb18-10 under thermal loading was studied within the framework of the joint research project [4]. Interrupted thermal cyclic tests in the temperature range of 150 C to 300 C combined with non-destructive residual stress measurements (XRD) and various microscopic investigations, e.g. in SEM (Scanning Electron Microscope), were used to study the effects of thermal cyclic loading on the material. This thermal cyclic loading leads to thermal induced stresses and strains. As a result intrusions and extrusions appear inside the grains (at the surface), at which microcracks arise and evolve to a dominant crack. Finally, these microcracks cause a continuous and significant decrease of residual stresses. The fatigue behaviour of the steel X6CrNiNb18-10 under mechanical loading at room temperature was studied within the framework of the research project [5], [8]. With a combination of interrupted LCF tests and EBSD

Mechanism of crack initiation and crack growth under thermal and mechanical fatigue loading

International Nuclear Information System (INIS)

Utz, S.; Soppa, E.; Silcher, H.; Kohler, C.

2013-01-01

The present contribution is focused on the experimental investigations and numerical simulations of the deformation behaviour and crack development in the austenitic stainless steel X6CrNiNb18-10 under thermal and mechanical cyclic loading in HCF and LCF regimes. The main objective of this research is the understanding of the basic mechanisms of fatigue damage and the development of simulation methods, which can be applied further in safety evaluations of nuclear power plant components. In this context the modelling of crack initiation and crack growth inside the material structure induced by varying thermal or mechanical loads are of particular interest. The mechanisms of crack initiation depend among other things on the type of loading, microstructure, material properties and temperature. The Nb-stabilized austenitic stainless steel in the solution-annealed condition was chosen for the investigations. Experiments with two kinds of cyclic loading - pure thermal and pure mechanical - were carried out and simulated. The fatigue behaviour of the steel X6CrNiNb18-10 under thermal loading was studied within the framework of the joint research project [4]. Interrupted thermal cyclic tests in the temperature range of 150 C to 300 C combined with non-destructive residual stress measurements (XRD) and various microscopic investigations, e.g. in SEM (Scanning Electron Microscope), were used to study the effects of thermal cyclic loading on the material. This thermal cyclic loading leads to thermal induced stresses and strains. As a result intrusions and extrusions appear inside the grains (at the surface), at which microcracks arise and evolve to a dominant crack. Finally, these microcracks cause a continuous and significant decrease of residual stresses. The fatigue behaviour of the steel X6CrNiNb18-10 under mechanical loading at room temperature was studied within the framework of the research project [5], [8]. With a combination of interrupted LCF tests and EBSD

The contribution of experimental in vivo models to understanding the mechanisms of adaptation to mechanical loading in bone

Directory of Open Access Journals (Sweden)

Lee B Meakin

2014-10-01

Full Text Available Changing loading regimens by natural means such as exercise, with or without interference such as osteotomy, has provided useful information on the structure:function relationship in bone tissue. However, the greatest precision in defining those aspects of the overall strain environment that influence modeling and remodeling behavior has been achieved by relating quantified changes in bone architecture to quantified changes in bones’ strain environment produced by direct, controlled artificial bone loading.Jiri Heřt introduced the technique of artificial loading of bones in vivo with external devices in the 1960s using an electromechanical device to load rabbit tibiae through transfixing stainless steel pins. Quantifying natural bone strains during locomotion by attaching electrical resistance strain gauges to bone surfaces was introduced by Lanyon, also in the 1960s. These studies in a variety of bones in a number of species demonstrated remarkable uniformity in the peak strains and maximum strain rates experienced.Experiments combining strain gauge instrumentation with artificial loading in sheep, pigs, roosters, turkeys, rats and mice has yielded significant insight into the control of strain-related adaptive (remodeling. This diversity of approach has been largely superseded by non-invasive transcutaneous loading in rats and mice which is now the model of choice for many studies. Together such studies have demonstrated that; over the physiological strain range, bone’s mechanically-adaptive processes are responsive to dynamic but not static strains; the size and nature of the adaptive response controlling bone mass is linearly related to the peak loads encountered; the strain-related response is preferentially sensitive to high strain rates and unresponsive to static ones; is most responsive to unusual strain distributions; is maximized by remarkably few strain cycles and that these are most effective when interrupted by short periods of

The Contribution of Experimental in vivo Models to Understanding the Mechanisms of Adaptation to Mechanical Loading in Bone

Science.gov (United States)

Meakin, Lee B.; Price, Joanna S.; Lanyon, Lance E.

2014-01-01

Changing loading regimens by natural means such as exercise, with or without interference such as osteotomy, has provided useful information on the structure:function relationship in bone tissue. However, the greatest precision in defining those aspects of the overall strain environment that influence modeling and remodeling behavior has been achieved by relating quantified changes in bone architecture to quantified changes in bones’ strain environment produced by direct, controlled artificial bone loading. Jiri Hert introduced the technique of artificial loading of bones in vivo with external devices in the 1960s using an electromechanical device to load rabbit tibiae through transfixing stainless steel pins. Quantifying natural bone strains during locomotion by attaching electrical resistance strain gages to bone surfaces was introduced by Lanyon, also in the 1960s. These studies in a variety of bones in a number of species demonstrated remarkable uniformity in the peak strains and maximum strain rates experienced. Experiments combining strain gage instrumentation with artificial loading in sheep, pigs, roosters, turkeys, rats, and mice has yielded significant insight into the control of strain-related adaptive (re)modeling. This diversity of approach has been largely superseded by non-invasive transcutaneous loading in rats and mice, which is now the model of choice for many studies. Together such studies have demonstrated that over the physiological strain range, bone’s mechanically adaptive processes are responsive to dynamic but not static strains; the size and nature of the adaptive response controlling bone mass is linearly related to the peak loads encountered; the strain-related response is preferentially sensitive to high strain rates and unresponsive to static ones; is most responsive to unusual strain distributions; is maximized by remarkably few strain cycles, and that these are most effective when interrupted by short periods of rest between them

Comparative evaluation of in vitro mechanical properties of different designs of epoxy-pin external skeletal fixation systems.

Science.gov (United States)

Tyagi, Surbhi Kuldeep; Aithal, Hari Prasad; Kinjavdekar, Prakash; Amarpal; Pawde, Abhijit Motiram; Srivastava, Tuhin; Tyagi, Kanti Prakash; Monsang, Shongsir Warson

2014-03-01

To compare in vitro biomechanical properties of different designs of epoxy-pin external skeletal fixator (ESF) constructs. Mechanical testing study. Four epoxy-pin ESF design constructs (uniplanar [EU], multiplanar-I [EM-I], multiplanar-II [EM-II], and circular [EC]) were mechanically tested in compression, bending, and torsion. Four different designs of free-form epoxy-pin external fixator constructs were developed using 1.5 mm K-wires and epoxy resin mounted in an ultra-high density polyethylene rod (20 mm diameter). Three-point fixation was done in each fragment, and the distance between fixation wires, and between the rod and the side bars was kept constant in all the designs. A 5 mm gap was maintained at the center of the fixation rod to simulate an unstable fracture condition. The fixator constructs (n = 12 of each design) were subjected to mechanical testing in axial compression, bending, or torsion. Load-deformation curves were generated and mechanical properties were compared between construct types. EU was the weakest design. Under compression, constructs EM-I, EM-II, and EC were similar. Under bending, EM-I and EM-II had similar strength, whereas EC was strongest. Under torsion, EC was strongest, followed by EM-II, EM-I, and EU; EM-II provided double the rotational stability of EM-I. Overall, EC followed by EM-II epoxy-pin fixator designs had better mechanical strength. © Copyright 2014 by The American College of Veterinary Surgeons.

Paxillin localisation in osteocytes-Is it determined by the direction of loading?

International Nuclear Information System (INIS)

Vatsa, A.; Semeins, C.M.; Smit, T.H.; Klein-Nulend, J.

2008-01-01

External mechanical loading of cells aligns cytoskeletal stress fibres in the direction of principle strains and localises paxillin to the mechanosensing region. If the osteocyte cell body can indeed directly sense matrix strains, then cytoskeletal alignment and distribution of paxillin in osteocytes in situ will bear alignment to the different mechanical loading patterns in fibulae and calvariae. We used confocal microscopy to visualise the immunofluorescence-labelled actin cytoskeleton in viable osteocytes and paxillin distribution in fixated osteocytes in situ. In fibular osteocyte cell bodies, actin cytoskeleton and nuclei were elongated and aligned parallel to the principal (longitudinal) mechanical loading direction. Paxillin was localised to the 'poles' of elongated osteocyte cell bodies. In calvarial osteocyte cell bodies, actin cytoskeleton and nuclei were relatively more round. Paxillin was distributed evenly in the osteocyte cell bodies. Thus in osteocyte cell bodies in situ, the external mechanical loading pattern likely determines the orientation of the actin cytoskeleton, and focal adhesions mediate direct mechanosensation of matrix strains.

The mechanics of head-supported load carriage by Nepalese porters.

Science.gov (United States)

Bastien, G J; Willems, P A; Schepens, B; Heglund, N C

2016-11-15

In the Everest valley of Nepal, because of the rugged mountain terrain, roads are nothing more than dirt paths and all material must be conveyed on foot. The Nepalese porters routinely carry head-supported loads, which often exceed their body mass, over long distances up and down the steep mountain footpaths. In Africa, women transport their loads economically thanks to an energy-saving gait adaptation. We hypothesized that the Nepalese porters may have developed a corresponding mechanism. To investigate this proposition, we measured the mechanical work done during level walking in Nepalese porters while carrying different loads at several speeds. Our results show that the Nepalese porters do not use an equivalent mechanism as the African women to reduce work. In contrast, the Nepalese porters develop an equal amount of total mechanical work as Western control subjects while carrying loads of 0 to 120% of their body mass at all speeds measured (0.5-1.7 m s -1 ), making even more impressive their ability to carry loads without any apparent mechanically determined tricks. Nevertheless, our results show that the Nepalese porters have a higher efficiency, at least at slow speeds and high loads. © 2016. Published by The Company of Biologists Ltd.

Effects of Holding an External Load on the Standing Balance of Older and Younger Adults With and Without Chronic Low Back Pain.

Science.gov (United States)

Shigaki, Leonardo; Vieira, Edgar Ramos; de Oliveira Gil, André Wilson; Araújo, Cynthia Gobbi Alves; Carmargo, Mariana Zingari; Sturion, Leandro Amaral; de Oliveira, Marcio Roǵerio; da Silva, Rubens A

2017-05-01

The purpose of this study was to assess the effect of holding an external load on the standing balance of younger and older adults with and without chronic low back pain (CLBP). Twenty participants with and 20 without CLBP participated in the study. Each group contained 10 younger (50% men) and 10 older adults (50% men). Participants were instructed to look straight ahead while standing on a force platform during two 120-second trials with and without holding an external load (10% of body mass). The center of pressure area, mean velocity, and mean frequency in the anteroposterior and mediolateral directions were measured. Older adults had worse standing balance than younger adults did (P external load significantly increased postural instability for both age groups and CLBP status, with mean effect size across center of pressure variables of d = 0.82 for older participants without CLBP and d = 2.65 for younger participants without CLBP. These effects for people with CLBP were d = 1.65 for subgroup of older and d = 1.60 for subgroup of younger participants. Holding an external load of 10% of body mass increased postural instability of both younger and older adults with and without CLBP. Copyright © 2017. Published by Elsevier Inc.

Flight Testing and Real-Time System Identification Analysis of a UH-60A Black Hawk Helicopter with an Instrumented External Sling Load

Science.gov (United States)

McCoy, Allen H.

1998-01-01

Helicopter external air transportation plays an important role in today's world. For both military and civilian helicopters, external sling load operations offer an efficient and expedient method of handling heavy, oversized cargo. With the ability to reach areas otherwise inaccessible by ground transportation, helicopter external load operations are conducted in industries such as logging, construction, and fire fighting, as well as in support of military tactical transport missions. Historically, helicopter and load combinations have been qualified through flight testing, requiring considerable time and cost. With advancements in simulation and flight test techniques there is potential to substantially reduce costs and increase the safety of helicopter sling load certification. Validated simulation tools make possible accurate prediction of operational flight characteristics before initial flight tests. Real time analysis of test data improves the safety and efficiency of the testing programs. To advance these concepts, the U.S. Army and NASA, in cooperation with the Israeli Air Force and Technion, under a Memorandum of Agreement, seek to develop and validate a numerical model of the UH-60 with sling load and demonstrate a method of near real time flight test analysis. This thesis presents results from flight tests of a U.S. Army Black Hawk helicopter with various external loads. Tests were conducted as the U.S. first phase of this MOA task. The primary load was a container express box (CONEX) which contained a compact instrumentation package. The flights covered the airspeed range from hover to 70 knots. Primary maneuvers were pitch and roll frequency sweeps, steps, and doublets. Results of the test determined the effect of the suspended load on both the aircraft's handling qualities and its control system's stability margins. Included were calculations of the stability characteristics of the load's pendular motion. Utilizing CIFER(R) software, a method for near

Comparison of External Load Effect on Lumbar Lordosis Among between Low Back Pain Patients and Healthy Individuals

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Neda Ershad

2007-10-01

Full Text Available Objective: Lumbar curvature is an important factor in posture and body movement that help us to understand low back pain problems. The aim of this study was evaluation of external load and trunk posture effect on lumbar curvature under static condition.  Materials & Methods: This study is an interventional, quasi-experimental and case-control study. Ten women with non specific chronic low back pain and ten matched without low back pain women were participated in this study. We used simple and non random method for sampling. Two clinometers sensors were used to evaluate lumbar curvature. Six static tasks while holding three levels of load (0, 6, 12 Kg and two levels of trunk position (neutral and 30 degree of flexion were simulated for subjects. Data were analyzed by using Kolmogroff-Smirnoff, ANOVA (Repeated Measurement and independent T-test. Results: Findings revealed lumbar lordosis in patients with low back pain does not change to kyphosis while increasing external load from 0kg to 6kg and 12kg in neutral trunk position (P<0.05. Conclusion: Dysfunction in passive system due to soft tissue disorder, afraid of pain, changes trunk muscles recruitment and reduction of moment arm are likely reasons for increased lumbar lordosis in patients with low back pain during loading.

Synthesis of polyoxometalate-loaded epoxy composites

Science.gov (United States)

Anderson, Benjamin J

2014-10-07

The synthesis of a polyoxometalate-loaded epoxy uses a one-step cure by applying an external stimulus to release the acid from the polyoxometalate and thereby catalyze the cure reaction of the epoxy resin. Such polyoxometalate-loaded epoxy composites afford the cured epoxy unique properties imparted by the intrinsic properties of the polyoxometalate. For example, polyoxometalate-loaded epoxy composites can be used as corrosion resistant epoxy coatings, for encapsulation of electronics with improved dielectric properties, and for structural applications with improved mechanical properties.

Single-source mechanical loading system produces biaxial stresses in cylinders

Science.gov (United States)

Flower, J. F.; Stafford, R. L.

1967-01-01

Single-source mechanical loading system proportions axial-to-hoop tension loads applied to cylindrical specimens. The system consists of hydraulic, pneumatic, and lever arrangements which produce biaxial loading ratios.

The effect of mechanical loads on the degradation of aliphatic biodegradable polyesters.

Science.gov (United States)

Li, Ying; Chu, Zhaowei; Li, Xiaoming; Ding, Xili; Guo, Meng; Zhao, Haoran; Yao, Jie; Wang, Lizhen; Cai, Qiang; Fan, Yubo

2017-06-01

Aliphatic biodegradable polyesters have been the most widely used synthetic polymers for developing biodegradable devices as alternatives for the currently used permanent medical devices. The performances during biodegradation process play crucial roles for final realization of their functions. Because physiological and biochemical environment in vivo significantly affects biodegradation process, large numbers of studies on effects of mechanical loads on the degradation of aliphatic biodegradable polyesters have been launched during last decades. In this review article, we discussed the mechanism of biodegradation and several different mechanical loads that have been reported to affect the biodegradation process. Other physiological and biochemical factors related to mechanical loads were also discussed. The mechanical load could change the conformational strain energy and morphology to weaken the stability of the polymer. Besides, the load and pattern could accelerate the loss of intrinsic mechanical properties of polymers. This indicated that investigations into effects of mechanical loads on the degradation should be indispensable. More combination condition of mechanical loads and multiple factors should be considered in order to keep the degradation rate controllable and evaluate the degradation process in vivo accurately. Only then can the degradable devise achieve the desired effects and further expand the special applications of aliphatic biodegradable polyesters.

Dynamic load-balancing-extended gradient mechanism: Graphic representation

International Nuclear Information System (INIS)

Muniz, Francisco J.

2017-01-01

Load-balancing methods are quite well described in the open literature (hundreds of articles can be found about this subject). In particularly, about the Dynamic Load-balancing mechanism Extended Gradient (EG), several articles of the author are available. Even though, there are some overlap, each one of them is focused on a particular aspect of the mechanism, in a complementary way. In this article, a graphic representation of the Extended Gradient mechanism is done: this representation way had not yet been explored. However, for an in-depth knowledge of the Extended Gradient mechanism, at least, some other articles should to be read. In the CDTN, Clusters are used, mainly, in deterministic methods (CFD) and non-deterministic methods (Monte Carlo). (author)

Dynamic load-balancing-extended gradient mechanism: Graphic representation

Energy Technology Data Exchange (ETDEWEB)

Muniz, Francisco J., E-mail: muniz@cdtn.br [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil)

2017-07-01

Load-balancing methods are quite well described in the open literature (hundreds of articles can be found about this subject). In particularly, about the Dynamic Load-balancing mechanism Extended Gradient (EG), several articles of the author are available. Even though, there are some overlap, each one of them is focused on a particular aspect of the mechanism, in a complementary way. In this article, a graphic representation of the Extended Gradient mechanism is done: this representation way had not yet been explored. However, for an in-depth knowledge of the Extended Gradient mechanism, at least, some other articles should to be read. In the CDTN, Clusters are used, mainly, in deterministic methods (CFD) and non-deterministic methods (Monte Carlo). (author)

Loading direction regulates the affinity of ADP for kinesin.

Science.gov (United States)

Uemura, Sotaro; Ishiwata, Shin'ichi

2003-04-01

Kinesin is an ATP-driven molecular motor that moves processively along a microtubule. Processivity has been explained as a mechanism that involves alternating single- and double-headed binding of kinesin to microtubules coupled to the ATPase cycle of the motor. The internal load imposed between the two bound heads has been proposed to be a key factor regulating the ATPase cycle in each head. Here we show that external load imposed along the direction of motility on a single kinesin molecule enhances the binding affinity of ADP for kinesin, whereas an external load imposed against the direction of motility decreases it. This coupling between loading direction and enzymatic activity is in accord with the idea that the internal load plays a key role in the unidirectional and cooperative movement of processive motors.

The Integration of Internal and External Training Load Metrics in Hurling

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Malone Shane

2016-12-01

Full Text Available The current study aimed to assess the relationship between the hurling player’s fitness profile and integrated training load (TL metrics. Twenty-five hurling players performed treadmill testing for VO2max, the speed at blood lactate concentrations of 2 mmol•L-1 (vLT and 4 mmol•L-1 (vOBLA and the heart rate-blood lactate profile for calculation of individual training impulse (iTRIMP. The total distance (TD; m, high speed distance (HSD; m and sprint distance (SD; m covered were measured using GPS technology (4-Hz, VX Sport, Lower Hutt, New Zealand which allowed for the measurement of the external TL. The external TL was divided by the internal TL to form integration ratios. Pearson correlation analyses allowed for the assessment of the relationships between fitness measures and the ratios to performance during simulated match play. External measures of the TL alone showed limited correlations with fitness measures. Integrated TL ratios showed significant relationships with fitness measures in players. TD:iTRIMP was correlated with aerobic fitness measures VO2max (r = 0.524; p = 0.006; 95% CI: 0.224 to 0.754; large and vOBLA (r = 0.559; p = 0.003; 95% CI: 0.254 to 0.854; large. HSD:iTRIMP also correlated with aerobic markers for fitness vLT (r = 0.502; p = 0.009; 95% CI: 0.204 to 0.801; large; vOBLA (r = 0.407; p = 0.039; 95% CI: 0.024 to 0.644; moderate. Interestingly SD:iTRIMP also showed significant correlations with vLT (r = 0.611; p = 0.001; 95% CI: 0.324 to 0.754; large. The current study showed that TL ratios can provide practitioners with a measure of fitness as external performance alone showed limited relationships with aerobic fitness measures.

Investigations On Crack Propagation Under Cyclical Isothermal And Thermo-mechanical Loadings For A Type 304-L Stainless Steel Used For Pressurized Water Reactor

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Gourdin Cédric

2018-01-01

Full Text Available The integrity of structures exhibiting flaws in Pressurized Water Reactor (PWR has to be assessed to meet safety criteria. This paper deals with crack-propagation under cyclic thermo-mechanical loadings, as encountered in class I austenitic pipes of PWR’s. To have a conservative and reliable assessment of the crack propagation due to the in-service loading, various codes and standards use simplified method. For example, the RSE-M Code introduces a plastic correction depending on the proportion of the mechanical loading. An improvement of the current method requires additional investigations. Moreover, components loaded with transient or thermal fluctuations are not really in loadcontrolled conditions. To this end, a device called PROFATH was designed. The specimen is a pre-cracked thick-walled tube undergoing a set of thermal cycles and loaded with a static mechanical force. During the first part of the thermal cycle, a high frequency induction coil heats the external wall of the tube. Then, the heating system stops and the specimen is cooled down by running water inside the tube. Finite element calculations show that only a region half-way along the tube should be heated to ensure adequate structural effect. In the heated zone, the machining of a sharp circumferential groove ensures the propagation of a unique crack. An electro-mechanical jack controls the level of the mechanical static load. Tests have been carried out, and these tests allow having an evaluation of the pertinence of the correction proposed by the RSE-M Code for a significant plasticity.

EXTERNAL CORPORATE GOVERNANCE MECHANISMS: MERGERS AND ACQUISITIONS ON THE BRAZILIAN MARKET

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Mario Augusto Parente Monteiro

2014-08-01

Full Text Available The research aims to answer the following question: What is the effectiveness of mergers and acquisitions in the Brazilian market as external corporate governance mechanism? The main objective of the study is to verify if mergers and acquisitions operations in Brazilian market may act as an external mechanism of corporate governance, replacing managers and, as a consequence of changes in management, improving financial performance. The study is exploratory, qualitative in its approach, supported by documentary research on secondary data concerning an intentional sample of Brazilian companies aiming to identify the effect of M&A operations on the corporate governance structure of the acquired firm and on its financial results. Data obtained on the website of the Brazilian Securities and Exchange Commission (CVM, related to Brazilian M&A operations in the period 2005-2010, were analyzed. Although M&A operations in Brazil were found to have disciplinary nature in our sample of firms in the studied period, our results are inconclusive regarding the effectiveness of these transactions and external governance mechanisms.

Influences of load characteristics on impaired control of grip forces in patients with cerebellar damage.

Science.gov (United States)

Brandauer, B; Timmann, D; Häusler, A; Hermsdörfer, J

2010-02-01

Various studies showed a clear impairment of cerebellar patients to modulate grip force in anticipation of the loads resulting from movements with a grasped object. This failure corroborated the theory of internal feedforward models in the cerebellum. Cerebellar damage also impairs the coordination of multiple-joint movements and this has been related to deficient prediction and compensation of movement-induced torques. To study the effects of disturbed torque control on feedforward grip-force control, two self-generated load conditions with different demands on torque control-one with movement-induced and the other with isometrically generated load changes-were directly compared in patients with cerebellar degeneration. Furthermore the cerebellum is thought to be more involved in grip-force adjustment to self-generated loads than to externally generated loads. Consequently, an additional condition with externally generated loads was introduced to further test this hypothesis. Analysis of 23 patients with degenerative cerebellar damage revealed clear impairments in predictive feedforward mechanisms in the control of both self-generated load types. Besides feedforward control, the cerebellar damage also affected more reactive responses when the externally generated load destabilized the grip, although this impairment may vary with the type of load as suggested by control experiments. The present findings provide further support that the cerebellum plays a major role in predictive control mechanisms. However, this impact of the cerebellum does not strongly depend on the nature of the load and the specific internal forward model. Contributions to reactive (grip force) control are not negligible, but seem to be dependent on the physical characteristics of an externally generated load.

The effect of external dynamic loads on the lifetime of rolling element bearings: accurate measurement of the bearing behaviour

International Nuclear Information System (INIS)

Jacobs, W; Boonen, R; Sas, P; Moens, D

2012-01-01

Accurate prediction of the lifetime of rolling element bearings is a crucial step towards a reliable design of many rotating machines. Recent research emphasizes an important influence of external dynamic loads on the lifetime of bearings. However, most lifetime calculations of bearings are based on the classical ISO 281 standard, neglecting this influence. For bearings subjected to highly varying loads, this leads to inaccurate estimations of the lifetime, and therefore excessive safety factors during the design and unexpected failures during operation. This paper presents a novel test rig, developed to analyse the behaviour of rolling element bearings subjected to highly varying loads. Since bearings are very precise machine components, their motion can only be measured in an accurately controlled environment. Otherwise, noise from other components and external influences such as temperature variations will dominate the measurements. The test rig is optimised to perform accurate measurements of the bearing behaviour. Also, the test bearing is fitted in a modular structure, which guarantees precise mounting and allows testing different types and sizes of bearings. Finally, a fully controlled multi-axial static and dynamic load is imposed on the bearing, while its behaviour is monitored with capacitive proximity probes.

Anterior cruciate ligament injuries in soccer: Loading mechanisms, risk factors, and prevention programs

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Boyi Dai

2014-12-01

Full Text Available Anterior cruciate ligament (ACL injuries are common in soccer. Understanding ACL loading mechanisms and risk factors for ACL injury is critical for designing effective prevention programs. The purpose of this review is to summarize the relevant literature on ACL loading mechanisms, ACL injury risk factors, and current ACL injury prevention programs for soccer players. Literature has shown that tibial anterior translation due to shear force at the proximal end of tibia is the primary ACL loading mechanism. No evidence has been found showing that knee valgus moment is the primary ACL loading mechanism. ACL loading mechanisms are largely ignored in previous studies on risk factors for ACL injury. Identified risk factors have little connections to ACL loading mechanisms. The results of studies on ACL injury prevention programs for soccer players are inconsistent. Current ACL injury prevention programs for soccer players are clinically ineffective due to low compliance. Future studies are urgently needed to identify risk factors for ACL injury in soccer that are connected to ACL loading mechanisms and have cause-and-effect relationships with injury rate, and to develop new prevention programs to improve compliance.

A complex study on the reliability assessment of the containment of a PWR. Part III.- Structural reliability assessment under internal and external loading conditions

International Nuclear Information System (INIS)

Bauer, J.; Schueller, G.I.

1977-01-01

The first part of the analysis is concerned with the determination of the failure probability of the steel hull under internal load conditions. Two independent failure criteria are the basis for this calculation; the first one being the ultimate yield which is actually an instability condition and the second one being the fracture condition as described in Part II of the paper. Both the global and the local failure probabilities are investigated. The second part of the analysis is concerned with the external load case of earthquake. As it has already been described in Part I the probability of occurrence of a LOCA, given an earthquake has been considered in connection with the probable damage which the steel hull might experience during the earthquake. In other words the survival probability of the hull with deteriorated resistance is calculated, taking into account the frequencies of occurrence of the various events. The third part of the analysis is concerned with the reliability determination of the reinforced concrete dome structure, which is supposed to protect, the steel hull against external load conditions such as airplane crash and external pressure waves (the latter covering the load case of tornado occurrence). The reliability analysis of the reinforced concrete structure under earthquake loading is performed by utilizing the time-history method. Some aspects of the drawbacks of the response spectra method -when used in a risk analysis- are pointed out. The probability distribution of the concrete strength as determined under intermediate strain rate as described in Part II is utilized in the analysis. Finally the remaining two external load cases are discussed in light of their use in a reliability analysis and with respect to their frequency of occurrence and the probability distribution of their load intensities. The reliability demonstration is performed using the containment structure of the PWR-plant 'Biblis B' which is locate

Vibration condition monitoring of planetary gearbox under varying external load

Energy Technology Data Exchange (ETDEWEB)

Bartelmus, W.; Zimroz, R. [Wroclaw University of Technology, Wroclaw (Poland)

2009-01-15

The paper shows that for condition monitoring of planetary gearboxes it is important to identify the external varying load condition. In the paper, systematic consideration has been taken of the influence of many factors on the vibration signals generated by a system in which a planetary gearbox is included. These considerations give the basis for vibration signal interpretation, development of the means of condition monitoring, and for the scenario of the degradation of the planetary gearbox. Real measured vibration signals obtained in the industrial environment are processed. The signals are recorded during normal operation of the diagnosed objects, namely planetary gearboxes, which are a part of the driving system used in a bucket wheel excavator, used in lignite mines. It has been found that the most important factor of the proper planetary gearbox condition is connected with perturbation of arm rotation, where an arm rotation gives rise to a specific vibration signal whose properties are depicted by a short-time Fourier transform (STFT) and Wigner-Ville distribution presented as a time-frequency map. The paper gives evidence that there are two dominant low-frequency causes that influence vibration signal modulation, i.e. the varying load, which comes from the nature of the bucket wheel digging process, and the arm/carrier rotation. These two causes determine the condition of the planetary gearboxes considered.

Developing a Magnetic Resonance Imaging measurement of the forces within 3D granular materials under external loads

Science.gov (United States)

Elrington, Stefan; Bertrand, Thibault; Frey, Merideth; Shattuck, Mark; O'Hern, Corey; Barrett, Sean

2014-03-01

Granular materials are comprised of an ensemble of discrete macroscopic grains that interact with each other via highly dissipative forces. These materials are ubiquitous in our everyday life ranging in scale from the granular media that forms the Earth's crust to that used in agricultural and pharmaceutical industries. Granular materials exhibit complex behaviors that are poorly understood and cannot be easily described by statistical mechanics. Under external loads individual grains are jammed into place by a network of force chains. These networks have been imaged in quasi two-dimensional and on the outer surface of three-dimensional granular materials. Our goal is to use magnetic resonance imaging (MRI) to detect contact forces deep within three-dimensional granular materials, using hydrogen-1 relaxation times as a reporter for changes in local stress and strain. To this end, we use a novel pulse sequence to narrow the line width of hydrogen-1 in rubber. Here we present our progress to date, and prospects for future improvements.

Technology of Rock Destruction by Combined Explosion-Mechanical Load

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Oleg M. Terentiev

2017-10-01

Full Text Available Background. Rock drilling is characterized by an energy capacity of more than 120 kWh/m3. This is due to the fact that about 90 % of the energy is expended on the “preparation” of rocks for destruction. This study proposes to combine explosive and mechanical loads to reduce specific energy consumption of rock destruction. Objective. The aim of the paper is energy effective technology development for rock destruction by combined explosive-mechanical loads. Methods. Analytical studies; regression analysis; math modeling; experimental research; technical and economic analysis. Results. Specific energy decreasing for explosive-mechanical rock drilling by 4–16 % was experimentally proved. Conclusions. As a result of the implementation of explosive-mechanical rock drilling on the created full-sized experimental device, the efficiency coefficient increased from 77 to 80 %.

Comparison of athlete-coach perceptions of internal and external load markers for elite junior tennis training.

Science.gov (United States)

Murphy, Alistair P; Duffield, Rob; Kellett, Aaron; Reid, Machar

2014-09-01

To investigate the discrepancy between coach and athlete perceptions of internal load and notational analysis of external load in elite junior tennis. Fourteen elite junior tennis players and 6 international coaches were recruited. Ratings of perceived exertion (RPEs) were recorded for individual drills and whole sessions, along with a rating of mental exertion, coach rating of intended session exertion, and athlete heart rate (HR). Furthermore, total stroke count and unforced-error count were notated using video coding after each session, alongside coach and athlete estimations of shots and errors made. Finally, regression analyses explained the variance in the criterion variables of athlete and coach RPE. Repeated-measures analyses of variance and interclass correlation coefficients revealed that coaches significantly (P coach and athlete. However, athlete drill RPE (P = .14; r = .71) and mental exertion (P = .44; r = .68) were comparable and substantially correlated. No significant differences in estimated stroke count were evident between athlete and coach (P = .21), athlete notational analysis (P = .06), or coach notational analysis (P = .49). Coaches estimated significantly greater unforced errors than either athletes or notational analysis (P coach RPE was explained by intended session exertion and coach drill RPE, while drill RPE and peak HR explained 45.3% of the variance in athlete session RPE. Coaches misinterpreted session RPE but not drill RPE, while inaccurately monitoring error counts. Improved understanding of external- and internal-load monitoring may help coach-athlete relationships in individual sports like tennis avoid maladaptive training.

Features wear nodes mechanization wing aircraft operating under dynamic loads

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А.М. Хімко

2009-03-01

Full Text Available  The conducted researches of titanic alloy ВТ-22 at dynamic loading with cycled sliding and dynamic loading in conditions of rolling with slipping. It is established that roller jamming in the carriage increases wear of rod of mechanization of a wing to twenty times. The optimum covering for strengthening wearied sites and restoration of working surfaces of wing’s mechanization rod is defined.

Stress and reliability analyses of multilayered composite cylinder under thermal and mechanical loads

Science.gov (United States)

Wang, Xiaohua

The coupling resulting from the mutual influence of material thermal and mechanical parameters is examined in the thermal stress analysis of a multilayered isotropic composite cylinder subjected to sudden axisymmetric external and internal temperature. The method of complex frequency response functions together with the Fourier transform technique is utilized. Because the coupling parameters for some composite materials, such as carbon-carbon, are very small, the effect of coupling is neglected in the orthotropic thermal stress analysis. The stress distributions in multilayered orthotropic cylinders subjected to sudden axisymmetric temperature loading combined with dynamic pressure as well as asymmetric temperature loading are also obtained. The method of Fourier series together with the Laplace transform is utilized in solving the heat conduction equation and thermal stress analysis. For brittle materials, like carbon-carbon composites, the strength variability is represented by two or three parameter Weibull distributions. The 'weakest link' principle which takes into account both the carbon-carbon composite cylinders. The complex frequency response analysis is performed on a multilayered orthotropic cylinder under asymmetrical thermal load. Both deterministic and random thermal stress and reliability analyses can be based on the results of this frequency response analysis. The stress and displacement distributions and reliability of rocket motors under static or dynamic line loads are analyzed by an elasticity approach. Rocket motors are modeled as long hollow multilayered cylinders with an air core, a thick isotropic propellant inner layer and a thin orthotropic kevlar-epoxy case. The case is treated as a single orthotropic layer or a ten layered orthotropic structure. Five material properties and the load are treated as random variable with normal distributions when the reliability of the rocket motor is analyzed by the first-order, second-moment method (FOSM).

External load application in gait and posture reeducation after diffuse axonal injury of the corpus callosum. A case report

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Magdalena Zawadka

2018-06-01

Full Text Available Traumatic brain injury caused car accidents is the one of the most common causes of diffuse axonal injury typically located at the grey-white matter junction, in the corpus callosum. A 58-year-old female patient Caucasian race was admitted to the Orthopedic and Rehabilitation Unit with head injury, broken right ulnar bone, numerous broken ribs and broken right iliac crest. Neurological examination resulted in right-sided hemiparesis. There were also coordination and balance disorders while sitting and standing. The patient was unable to walk. After physiotherapy treatment included external load application (ankle weights and rucksack with weights in gait and posture reeducation, patient has improved balance, locomotion and body posture. However, application of external loads during walk and posture reeducation needs to be further investigated with greater number of participants and control group.

Molecular mechanics of silk nanostructures under varied mechanical loading.

Science.gov (United States)

Bratzel, Graham; Buehler, Markus J

2012-06-01

Spider dragline silk is a self-assembling tunable protein composite fiber that rivals many engineering fibers in tensile strength, extensibility, and toughness, making it one of the most versatile biocompatible materials and most inviting for synthetic mimicry. While experimental studies have shown that the peptide sequence and molecular structure of silk have a direct influence on the stiffness, toughness, and failure strength of silk, few molecular-level analyses of the nanostructure of silk assemblies, in particular, under variations of genetic sequences have been reported. In this study, atomistic-level structures of wildtype as well as modified MaSp1 protein from the Nephila clavipes spider dragline silk sequences, obtained using an in silico approach based on replica exchange molecular dynamics and explicit water molecular dynamics, are subjected to simulated nanomechanical testing using different force-control loading conditions including stretch, pull-out, and peel. The authors have explored the effects of the poly-alanine length of the N. clavipes MaSp1 peptide sequence and identify differences in nanomechanical loading conditions on the behavior of a unit cell of 15 strands with 840-990 total residues used to represent a cross-linking β-sheet crystal node in the network within a fibril of the dragline silk thread. The specific loading condition used, representing concepts derived from the protein network connectivity at larger scales, have a significant effect on the mechanical behavior. Our analysis incorporates stretching, pull-out, and peel testing to connect biochemical features to mechanical behavior. The method used in this study could find broad applications in de novo design of silk-like tunable materials for an array of applications. Copyright © 2011 Wiley Periodicals, Inc.

Forecasting of resonances vibration equipment with elastic waves coolant and with the external periodic loads on NPP with WWER

International Nuclear Information System (INIS)

Proskuryakov, K.N.; Zaporozhets, M.V.; Fedorov, A.I.

2015-01-01

Forecasting are carried out for external loads in relation to the main circulation circuit - dynamic loads caused by the rotation of the MCP, dynamic loads caused by the earthquake, dynamic loads caused by damage to the MCP in the earthquake. A comparison of the response spectrum of one of the variants of the base of the NPP, with the frequency vibration of the primary circuit equipment for NPP with WWER-1000 and self-frequency of elastic waves in the fluid. Analysis of the comparison results shows that the frequency of vibration of the main equipment of the reactor plant and elastic waves are in the frequency band in the spectrum response corresponding to the maximum amplitude of the seismic action [ru

LOADING OF MECHANICAL TRANSMISSION OF TROLLEYBUS TRACTION DRIVING GEAR

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A. I. Safonov

2009-01-01

Full Text Available The paper analyzes factors that determine dynamic loads of mechanical transmission of trolleybus traction driving gear. The paper proposes a methodology for determination of calculative moments of loading transmission elements. Results of the research are analyzed and recommendations on  dynamic reduction of trolleybus transmission are given in the paper. 

Full-scale testing of leakage of blast waves inside a partially vented room exposed to external air blast loading

Science.gov (United States)

Codina, R.; Ambrosini, D.

2018-03-01

For the last few decades, the effects of blast loading on structures have been studied by many researchers around the world. Explosions can be caused by events such as industrial accidents, military conflicts or terrorist attacks. Urban centers have been prone to various threats including car bombs, suicide attacks, and improvised explosive devices. Partially vented constructions subjected to external blast loading represent an important topic in protective engineering. The assessment of blast survivability inside structures and the development of design provisions with respect to internal elements require the study of the propagation and leakage of blast waves inside buildings. In this paper, full-scale tests are performed to study the effects of the leakage of blast waves inside a partially vented room that is subjected to different external blast loadings. The results obtained may be useful for proving the validity of different methods of calculation, both empirical and numerical. Moreover, the experimental results are compared with those computed using the empirical curves of the US Defense report/manual UFC 3-340. Finally, results of the dynamic response of the front masonry wall are presented in terms of accelerations and an iso-damage diagram.

The analogy method for the description of external characteristic of inner combustion engines

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A. Stonys

2004-10-01

Full Text Available The original data for the evaluation of vehicle motion dynamics is external characteristic of its engine, which consists of three parameters: torque, power and specific fuel consumption. It is very important to have the dependences of these characteristics on revs for various engine load cases, creating a vehicle model under real motion conditions. Load cases are defined by a load coefficient. Car-makers usually don’t declare full engine external characteristics, which overtake all load coefficient variation interval. The purpose of this article is to research, how to get full description of engine torque function without its full data. The analogy method, which is used in polymers and composites mechanics, was employed for the description of a torque function. The method is based on the creation of summarized characteristic, making horizontal and vertical shifts of torque dependences. From the curve it is possible to get a proper characteristic at a chosen load coefficient.

Individualized Internal and External Training Load Relationships in Elite Wheelchair Rugby Players.

Science.gov (United States)

Paulson, Thomas A W; Mason, Barry; Rhodes, James; Goosey-Tolfrey, Victoria L

2015-01-01

The quantification and longitudinal monitoring of athlete training load (TL) provides a scientific explanation for changes in performance and helps manage injury/illness risk. Therefore, accurate and reliable monitoring tools are essential for the optimization of athletic performance. The aim of the present study was to establish the relationship between measures of internal [heart rate (HR) and session RPE (sRPE)] and external TL specific to wheelchair rugby (WR). Fourteen international WR athletes (age = 29 ± 7 years; body mass = 58.9 ± 10.9 kg) were monitored during 18 training sessions over a 3 month period during the competitive phase of the season. Activity profiles were collected during each training session using a radio-frequency based indoor tracking system (ITS). External TL was quantified by total distance (m) covered as well as time spent and distance covered in a range of classification-specific arbitrary speed zones. Banister's TRIMP, Edwards's summated HR zone (SHRZ), and Lucia's TRIMP methods were used to quantify physiological internal TL. sRPE was calculated as the product of session duration multiplied by perceived exertion using the Borg CR10 scale. Relationships between external and internal TL were examined using correlation coefficients and the 90% confidence intervals (90% CI). sRPE (r = 0.59) and all HR-based (r > 0.80) methods showed large and very large relationships with the total distance covered during training sessions, respectively. Large and very large correlations (r = 0.56 - 0.82) were also observed between all measures of internal TL and times spent and distances covered in low and moderate intensity speed zones. HR-based methods showed very large relationships with time (r = 0.71-0.75) and distance (r = 0.70-0.73) in the very high speed zone and a large relationship with the number of high intensity activities (HIA) performed (r = 0.56-0.62). Weaker relationships (r = 0.32-0.35) were observed between sRPE and all measures of

Individualised internal and external training load relationships in elite wheelchair rugby players

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Thomas Andrew William Paulson

2015-12-01

Full Text Available Aim: The quantification and longitudinal monitoring of athlete training load (TL provides a scientific explanation for changes in performance and helps manage injury/illness risk. The aim of the present study was to establish the relationship between measures of internal (heart rate (HR and session RPE (sRPE and external TL specific to wheelchair rugby (WR. Methods: Fourteen international WR athletes (age = 29 ± 7 yrs; body mass = 58.9 ± 10.9 kg were monitored during 18 training sessions over a 3 month period. Activity profiles were collected during each training session using a radio-frequency based indoor tracking system. External TL was quantified by total distance (m covered as well as time spent and distance covered in a range of classification-specific arbitrary speed zones. Banister’s TRIMP, Edwards’s summated HR zone (SHRZ and Lucia’s TRIMP methods were used to quantify physiological internal TL. sRPE was calculated as the product of session duration multiplied by perceived exertion using the Borg CR10 scale. Relationships between external and internal TL were examined using correlation coefficients and the 90% confidence intervals (90% CI. Results: sRPE (r=0.59 and all HR-based (r >0.80 methods showed large and very large relationships with the total distance covered during training sessions, respectively. Large and very large correlations (r =0.56-0.82 were also observed between all measures of internal TL and times spent and distances covered in low and moderate intensity speed zones. HR-based methods showed very large relationships with time (r=0.71-0.75 and distance (r=0.70-0.73 in the very high speed zone and a large relationship with the number of high intensity activities performed (r=0.56-0.62. Weaker relationships (r=0.32–0.35 were observed between sRPE and all measures of high intensity activity. A large variation of individual correlation co-efficient was observed between sRPE and all external TL measures

Device for mechanized loading of coal into the sump of a skip shaft

Energy Technology Data Exchange (ETDEWEB)

Orlik, M A

1982-01-01

In order to mechanize the process of loading coal and cleaning the sump, the efficiency experts of the mine ''Promyshlennaya'' of the production association ''Vorkutaugol'' have designed a special mechanical loading device which consists of pipes-sleeves, working mechanism-worm and electric drive. The worm lifter is suspended on the beam with clamps and an intermediate floor. Because of the use of mechanical loader, manual operations have been reduced to the minimum (the coal is thrown towards the loading hole manually). Economic effect is R 3100 per year.

Differentiation of mesenchymal stem cells for cartilage tissue engineering: Individual and synergetic effects of three-dimensional environment and mechanical loading.

Science.gov (United States)

Panadero, J A; Lanceros-Mendez, S; Ribelles, J L Gomez

2016-03-01

Chondrogenesis of dedifferentiated chondrocytes and mesenchymal stem cells is influenced not only by soluble molecules like growth factors, but also by the cell environment itself. The latter is achieved through both mechanical cues - which act as stimulation factor and influences nutrient transport - and adhesion to extracellular matrix cues - which determine cell shape. Although the effects of soluble molecules and cell environment have been intensively addressed, few observations and conclusions about the interaction between the two have been achieved. In this work, we review the state of the art on the single effects between mechanical and biochemical cues, as well as on the combination of the two. Furthermore, we provide a discussion on the techniques currently used to determine the mechanical properties of materials and tissues generated in vitro, their limitations and the future research needs to properly address the identified problems. The importance of biomechanical cues in chondrogenesis is well known. This paper reviews the existing literature on the effect of mechanical stimulation on chondrogenic differentiation of mesenchymal stem cells in order to regenerate hyaline cartilage. Contradictory results found with respect to the effect of different modes of external loading can be explained by the different properties of the scaffolding system that holds the cells, which determine cell adhesion and morphology and spatial distribution of cells, as well as the stress transmission to the cells. Thus, this review seeks to provide an insight into the interplay between external loading program and scaffold properties during chondrogenic differentiation. The review of the literature reveals an important gap in the knowledge in this field and encourages new experimental studies. The main issue is that in each of the few cases in which the interplay is investigated, just two groups of scaffolds are compared, leaving intermediate adhesion conditions out of study

Study on Mechanical Properties of Barite Concrete under Impact Load

Science.gov (United States)

Chen, Z. F.; Cheng, K.; Wu, D.; Gan, Y. C.; Tao, Q. W.

2018-03-01

In order to research the mechanical properties of Barite concrete under impact load, a group of concrete compression tests was carried out under the impact load by using the drop test machine. A high-speed camera was used to record the failure process of the specimen during the impact process. The test results show that:with the increase of drop height, the loading rate, the peak load, the strain under peak load, the strain rate and the dynamic increase factor (DIF) all increase gradually. The ultimate tensile strain is close to each other, and the time of impact force decreases significantly, showing significant strain rate effect.

Mechanical Loading Attenuates Radiation-Induced Bone Loss in Bone Marrow Transplanted Mice

Science.gov (United States)

Govey, Peter M.; Zhang, Yue; Donahue, Henry J.

2016-01-01

Exposure of bone to ionizing radiation, as occurs during radiotherapy for some localized malignancies and blood or bone marrow cancers, as well as during space travel, incites dose-dependent bone morbidity and increased fracture risk. Rapid trabecular and endosteal bone loss reflects acutely increased osteoclastic resorption as well as decreased bone formation due to depletion of osteoprogenitors. Because of this dysregulation of bone turnover, bone’s capacity to respond to a mechanical loading stimulus in the aftermath of irradiation is unknown. We employed a mouse model of total body irradiation and bone marrow transplantation simulating treatment of hematologic cancers, hypothesizing that compression loading would attenuate bone loss. Furthermore, we hypothesized that loading would upregulate donor cell presence in loaded tibias due to increased engraftment and proliferation. We lethally irradiated 16 female C57Bl/6J mice at age 16 wks with 10.75 Gy, then IV-injected 20 million GFP(+) total bone marrow cells. That same day, we initiated 3 wks compression loading (1200 cycles 5x/wk, 10 N) in the right tibia of 10 of these mice while 6 mice were irradiated, non-mechanically-loaded controls. As anticipated, before-and-after microCT scans demonstrated loss of trabecular bone (-48.2% Tb.BV/TV) and cortical thickness (-8.3%) at 3 wks following irradiation. However, loaded bones lost 31% less Tb.BV/TV and 8% less cortical thickness (both pbones also had significant increases in trabecular thickness and tissue mineral densities from baseline. Mechanical loading did not affect donor cell engraftment. Importantly, these results demonstrate that both cortical and trabecular bone exposed to high-dose therapeutic radiation remain capable of an anabolic response to mechanical loading. These findings inform our management of bone health in cases of radiation exposure. PMID:27936104

Microcracking in composite laminates under thermal and mechanical loading. Thesis

Science.gov (United States)

Maddocks, Jason R.

1995-01-01

Composites used in space structures are exposed to both extremes in temperature and applied mechanical loads. Cracks in the matrix form, changing the laminate thermoelastic properties. The goal of the present investigation is to develop a predictive methodology to quantify microcracking in general composite laminates under both thermal and mechanical loading. This objective is successfully met through a combination of analytical modeling and experimental investigation. In the analysis, the stress and displacement distributions in the vicinity of a crack are determined using a shear lag model. These are incorporated into an energy based cracking criterion to determine the favorability of crack formation. A progressive damage algorithm allows the inclusion of material softening effects and temperature-dependent material properties. The analysis is implemented by a computer code which gives predicted crack density and degraded laminate properties as functions of any thermomechanical load history. Extensive experimentation provides verification of the analysis. AS4/3501-6 graphite/epoxy laminates are manufactured with three different layups to investigate ply thickness and orientation effects. Thermal specimens are cooled to progressively lower temperatures down to -184 C. After conditioning the specimens to each temperature, cracks are counted on their edges using optical microscopy and in their interiors by sanding to incremental depths. Tensile coupons are loaded monotonically to progressively higher loads until failure. Cracks are counted on the coupon edges after each loading. A data fit to all available results provides input parameters for the analysis and shows them to be material properties, independent of geometry and loading. Correlation between experiment and analysis is generally very good under both thermal and mechanical loading, showing the methodology to be a powerful, unified tool. Delayed crack initiation observed in a few cases is attributed to a

Rat disc torsional mechanics: effect of lumbar and caudal levels and axial compression load.

Science.gov (United States)

Espinoza Orías, Alejandro A; Malhotra, Neil R; Elliott, Dawn M

2009-03-01

Rat models with altered loading are used to study disc degeneration and mechano-transduction. Given the prominent role of mechanics in disc function and degeneration, it is critical to measure mechanical behavior to evaluate changes after model interventions. Axial compression mechanics of the rat disc are representative of the human disc when normalized by geometry, and differences between the lumbar and caudal disc have been quantified in axial compression. No study has quantified rat disc torsional mechanics. Compare the torsional mechanical behavior of rat lumbar and caudal discs, determine the contribution of combined axial load on torsional mechanics, and compare the torsional properties of rat discs to human lumbar discs. Cadaveric biomechanical study. Cyclic torsion without compressive load followed by cyclic torsion with a fixed compressive load was applied to rat lumbar and caudal disc levels. The apparent torsional modulus was higher in the lumbar region than in the caudal region: 0.081+/-0.026 (MPa/degrees, mean+/-SD) for lumbar axially loaded; 0.066+/-0.028 for caudal axially loaded; 0.091+/-0.033 for lumbar in pure torsion; and 0.056+/-0.035 for caudal in pure torsion. These values were similar to human disc properties reported in the literature ranging from 0.024 to 0.21 MPa/degrees. Use of the caudal disc as a model may be appropriate if the mechanical focus is within the linear region of the loading regime. These results provide support for use of this animal model in basic science studies with respect to torsional mechanics.

Mitigation of mechanical loads of NREL 5MW wind turbine tower

International Nuclear Information System (INIS)

Nam, Yoonsu; Im, Chang Hee

2012-01-01

As the size of a wind turbine increases, the mechanical structure has to have an increasing mechanical stiffness that is sufficient to withstand mechanical fatigue loads over a lifespan of more than 20 years. However, this leads to a heavier mechanical design, which means a high material cost during wind turbine manufacturing. Therefore, lightweight design of a wind turbine is an important design constraint. Usually, a lightweight mechanical structure has low damping. Therefore, if it is subjected to a disturbance, it will oscillate continuously. This study deals with the active damping control of a wind turbine tower. An algorithm that mitigates the mechanical loads of a wind turbine tower is introduced. The effectiveness of this algorithm is verified through a numerical simulation using GH Bladed, which is a commercial aero elastic code for wind turbines

Theoretical study of the electromechanical efficiency of a loaded tubular dielectric elastomer actuator

DEFF Research Database (Denmark)

Rechenbach, Björn; Willatzen, Morten; Lassen, Benny

2016-01-01

The electromechanical efficiency of a loaded tubular dielectric elastomer actuator (DEA) is investigated theoretically. In previous studies, the external system, on which the DEA performs mechanical work, is implemented implicitly by prescribing the stroke of the DEA in a closed operation cycle....... Here, a more generic approach, modelling the external system by a frequency-dependent mechanical impedance which exerts a certain force on the DEA depending on its deformation, is chosen. It admits studying the dependence of the electromechanical efficiency of the DEA on the external system. A closed...... operation cycle is realized by exciting the DEA electrically by a sinusoidal voltage around a bias voltage. A detailed parametric study shows that the electromechanical efficiency is highly dependent on the frequency, amplitude, and bias of the excitation voltage and the mechanical impedance of the external...

Rambling and trembling in response to body loading.

Science.gov (United States)

Tahayor, Behdad; Riley, Zachary A; Mahmoudian, Armaghan; Koceja, David M; Hong, Siang Lee

2012-04-01

Various studies have suggested that postural sway is controlled by at least two subsystems. Rambling-Trembling analysis is a widely accepted methodology to dissociate the signals generated by these two hypothetical subsystems. The core assumption of this method is based on the equilibrium point hypothesis which suggests that the central nervous system preserves upright standing by transiently shifting the center of pressure (COP) from one equilibrium point to another. The trajectory generated by this shifting is referred to as rambling and its difference from the original COP signal is referred to as trembling. In this study we showed that these two components of COP are differentially affected when standing with external loads. Using Detrended Fluctuation analysis, we compared the pattern of these two signals in different configurations of body loading. Our findings suggest that by applying an external load, the dynamics of the trembling component is altered independently of the area of postural sway and also independently of the rambling component. The dynamics of rambling changed only during the backloading condition in which the postural sway area also substantially increased. It can be suggested that during loaded standing, the trembling mechanism (which is suggested to be activated by peripheral mechanisms and reflexes) is altered without affecting the central influence on the shifts of the equilibrium point.

Effects of mechanical repetitive load on bone quality around implants in rat maxillae.

Directory of Open Access Journals (Sweden)

Yusuke Uto

Full Text Available Greater understanding and acceptance of the new concept "bone quality", which was proposed by the National Institutes of Health and is based on bone cells and collagen fibers, are required. The novel protein Semaphorin3A (Sema3A is associated with osteoprotection by regulating bone cells. The aims of this study were to investigate the effects of mechanical loads on Sema3A production and bone quality based on bone cells and collagen fibers around implants in rat maxillae. Grade IV-titanium threaded implants were placed at 4 weeks post-extraction in maxillary first molars. Implants received mechanical loads (10 N, 3 Hz for 1800 cycles, 2 days/week for 5 weeks from 3 weeks post-implant placement to minimize the effects of wound healing processes by implant placement. Bone structures, bone mineral density (BMD, Sema3A production and bone quality based on bone cells and collagen fibers were analyzed using microcomputed tomography, histomorphometry, immunohistomorphometry, polarized light microscopy and birefringence measurement system inside of the first and second thread (designated as thread A and B, respectively, as mechanical stresses are concentrated and differently distributed on the first two threads from the implant neck. Mechanical load significantly increased BMD, but not bone volume around implants. Inside thread B, but not thread A, mechanical load significantly accelerated Sema3A production with increased number of osteoblasts and osteocytes, and enhanced production of both type I and III collagen. Moreover, mechanical load also significantly induced preferential alignment of collagen fibers in the lower flank of thread B. These data demonstrate that mechanical load has different effects on Sema3A production and bone quality based on bone cells and collagen fibers between the inside threads of A and B. Mechanical load-induced Sema3A production may be differentially regulated by the type of bone structure or distinct stress distribution

Development of a load cell for mechanical testing in hydrogen

International Nuclear Information System (INIS)

McCabe, L.P.

1982-01-01

Mechanical testing in hydrogen environments is performed on materials to determine hydrogen compatibility. Many tests are performed on small test samples in pressure vessels where monitoring of actual sample load is difficult. A method was developed to monitor small samples by placing inside the vessel a miniature load cell which is capable of measuring loads of less than 100 lbs. The load cell monitors load by means of a Wheatstone Bridge circuit composed of four strain gages. Two of the gages are mounted on a stainless steel stub which becomes part of the vessel load string; the others are wired outside the pressure vessel. Previously, load cells have been short-lived because of hydrogen diffusion into the epoxy-phenolic adhesive used to attach the strain gages to the stub. The use of a flame-sprayed ceramic, however, rather than an organic epoxy to mount the strain gages appears to produce a load cell resistant to the hydrogen test environment

Effects of Zoledronate and Mechanical Loading during Simulated Weightlessness on Bone Structure and Mechanical Properties

Science.gov (United States)

Scott, R. T.; Nalavadi, M. O.; Shirazi-Fard, Y.; Castillo, A. B.; Alwood, J. S.

2016-01-01

Space flight modulates bone remodeling to favor bone resorption. Current countermeasures include an anti-resorptive drug class, bisphosphonates (BP), and high-force loading regimens. Does the combination of anti-resorptives and high-force exercise during weightlessness have negative effects on the mechanical and structural properties of bone? In this study, we implemented an integrated model to mimic mechanical strain of exercise via cyclical loading (CL) in mice treated with the BP Zoledronate (ZOL) combined with hindlimb unloading (HU). Our working hypothesis is that CL combined with ZOL in the HU model induces additive structural and mechanical changes. Thirty-two C57BL6 mice (male,16 weeks old, n8group) were exposed to 3 weeks of either HU or normal ambulation (NA). Cohorts of mice received one subcutaneous injection of ZOL (45gkg), or saline vehicle, prior to experiment. The right tibia was axially loaded in vivo, 60xday to 9N in compression, repeated 3xweek during HU. During the application of compression, secant stiffness (SEC), a linear estimate of slope of the force displacement curve from rest (0.5N) to max load (9.0N), was calculated for each cycle once per week. Ex vivo CT was conducted on all subjects. For ex vivo mechanical properties, non-CL left femurs underwent 3-point bending. In the proximal tibial metaphysis, HU decreased, CL increased, and ZOL increased the cancellous bone volume to total volume ratio by -26, +21, and +33, respectively. Similar trends held for trabecular thickness and number. Ex vivo left femur mechanical properties revealed HU decreased stiffness (-37),and ZOL mitigated the HU stiffness losses (+78). Data on the ex vivo Ultimate Force followed similar trends. After 3 weeks, HU decreased in vivo SEC (-16). The combination of CL+HU appeared additive in bone structure and mechanical properties. However, when HU + CL + ZOL were combined, ZOL had no additional effect (p0.05) on in vivo SEC. Structural data followed this trend with

Relative importance of expertise, lifting height and weight lifted on posture and lumbar external loading during a transfer task in manual material handling.

Science.gov (United States)

Plamondon, André; Larivière, Christian; Delisle, Alain; Denis, Denys; Gagnon, Denis

2012-01-01

The objective of this study was to measure the effect size of three important factors in manual material handling, namely expertise, lifting height and weight lifted. The effect of expertise was evaluated by contrasting 15 expert and 15 novice handlers, the effect of the weight lifted with a 15-kg box and a 23-kg box and the effect of lifting height with two different box heights: ground level and a 32 cm height. The task consisted of transferring a series of boxes from a conveyor to a hand trolley. Lifting height and weight lifted had more effect size than expertise on external back loading variables (moments) while expertise had low impact. On the other hand, expertise showed a significant effect of posture variables on the lumbar spine and knees. All three factors are important, but for a reduction of external back loading, the focus should be on the lifting height and weight lifted. The objective was to measure the effect size of three important factors in a transfer of boxes from a conveyor to a hand trolley. Lifting height and weight lifted had more effect size than expertise on external back loading variables but expertise was a major determinant in back posture.

Design and implementation of an external quality assessment program for HIV viral load measurements using dried blood spots.

Science.gov (United States)

Prach, Lisa M; Puren, Adrian; Lippman, Sheri A; Carmona, Sergio; Stephenson, Sophie; Cutler, Ewalde; Barnhart, Scott; Liegler, Teri

2015-03-01

An external quality assurance program was developed for HIV-1 RNA viral load measurements taken from dried blood spots using a reference panel and field-collected specimens. The program demonstrated that accurate and reproducible quantitation can be obtained from field-collected specimens. Residual proviral DNA may confound interpretation in virologically suppressed subjects. Copyright © 2015, American Society for Microbiology. All Rights Reserved.

Nonlinear Analysis of the Space Shuttle Superlightweight External Fuel Tank

Science.gov (United States)

Nemeth, Michael P.; Britt, Vicki O.; Collins, Timothy J.; Starnes, James H., Jr.

1996-01-01

Results of buckling and nonlinear analyses of the Space Shuttle external tank superlightweight liquid-oxygen (LO2) tank are presented. Modeling details and results are presented for two prelaunch loading conditions and for two full-scale structural tests that were conducted on the original external tank. The results illustrate three distinctly different types of nonlinear response for thin-walled shells subjected to combined mechanical and thermal loads. The nonlinear response phenomena consist of bifurcation-type buckling, short-wavelength nonlinear bending, and nonlinear collapse associated with a limit point. For each case, the results show that accurate predictions of non- linear behavior generally require a large-scale, high-fidelity finite-element model. Results are also presented that show that a fluid-filled launch-vehicle shell can be highly sensitive to initial geometric imperfections. In addition, results presented for two full-scale structural tests of the original standard-weight external tank suggest that the finite-element modeling approach used in the present study is sufficient for representing the nonlinear behavior of the superlightweight LO2 tank.

Dynamical mechanisms for sensitive response of aperiodic firing cells to external stimulation

International Nuclear Information System (INIS)

Xie Yong; Xu Jianxue; Hu Sanjue; Kang Yanmei; Yang Hongjun; Duan Yubin

2004-01-01

An interesting phenomenon that aperiodic firing neurons have a higher sensitivity to drugs than periodic firing neurons have been reported for the chronically compressed dorsal root ganglion neurons in rats. In this study, the dynamical mechanisms for such a phenomenon are uncovered from the viewpoint of dynamical systems theory. We use the Rose-Hindmarsh neuron model to illustrate our opinions. Periodic orbit theory is introduced to characterize the dynamical behavior of aperiodic firing neurons. It is considered that bifurcations, crises and sensitive dependence of chaotic motions on control parameters can be the underlying mechanisms. And then, a similar analysis is applied to the modified Chay model describing the firing behavior of pancreatic beta cells. The same dynamical mechanisms can be obtained underlying that aperiodic firing cells are more sensitive to external stimulation than periodic firing ones. As a result, we conjecture that sensitive response of aperiodic firing cells to external stimulation is a universal property of excitable cells

Mechanical properties of stanene under uniaxial and biaxial loading: A molecular dynamics study

Energy Technology Data Exchange (ETDEWEB)

Mojumder, Satyajit [Department of Mechanical Engineering, Bangladesh University of Engineering and Technology, Dhaka 1000 (Bangladesh); Amin, Abdullah Al [Department of Mechanical and Aerospace Engineering, Case western Reverse University, Cleveland, Ohio 44106 (United States); Islam, Md Mahbubul, E-mail: mmi122@psu.edu [Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States)

2015-09-28

Stanene, a graphene like two dimensional honeycomb structure of tin has attractive features in electronics application. In this study, we performed molecular dynamics simulations using modified embedded atom method potential to investigate mechanical properties of stanene. We studied the effect of temperature and strain rate on mechanical properties of α-stanene for both uniaxial and biaxial loading conditions. Our study suggests that with the increasing temperature, both the fracture strength and strain of the stanene decrease. Uniaxial loading in zigzag direction shows higher fracture strength and strain compared to the armchair direction, while no noticeable variation in the mechanical properties is observed for biaxial loading. We also found at a higher loading rate, material exhibits higher fracture strength and strain. These results will aid further investigation of stanene as a potential nano-electronics substitute.

Thermal loads and their effect on integrity of mechanical systems and components

International Nuclear Information System (INIS)

Koenig, G.; Schoeckle, F.

2010-01-01

The initial step to establish a required quality status of systems and components is performed during the state of design. Main goal of the design is to consider every possible damage mechanism of the future operation (by specification of loads, medium and environment and the selection of the materials). The knowledge during the state of design determines the reliability of the component. Regarding the thermal loads, especially, only global parameters are specified usually (transients of flow and temperature connected to specified operation). These global transients are analyzed according to the standards. In operation, the safety (integrity) resp. remaining life of a component is determined by the real operation history. As experience showed, failures, defects and not specified (new) loads were discovered during operation, e.g. stratification effects in feedwater pipes and in surge lines or thermal effects in the region of valves due to switching or internal leakage. Standard surveillance in operation is performed using plant transducers that can only monitor global loads. However, problems usually are of local nature. Thermal loads like - turbulent temperatures due to mixing of media with different temperatures - temperature differences across shells or in regions of nozzles/thermal sleeves - temperature differences in piping cross sections (local and global stratification effects) - temperature differences along sections of piping systems have to be monitored by use of local instrumentation. During analysis, both the local loads and construction details have to be considered, in detail, using appropriate calculation / analysis tools. The complexity of the loads requires a comprehensive procedure: - determine the types of loads resulting from measured temperature transients - perform sensitivity studies to identify the load type that results in relevant stresses - evaluate the stresses of the significant loads - assess these stresses according to component

The Effect of Mechanical Load on the Thermal Conductivity of Building Materials

Directory of Open Access Journals (Sweden)

J. Toman

2000-01-01

Full Text Available The effect of mechanical load on the thermal conductivity of building materials in the design of envelope parts of building structures is studied. A typical building material is chosen in the practical investigation of this effect, namely the cement mortar. It is concluded that in the range of hygroscopic moisture content, lower levels of mechanical load, typically up to 90 % of compressive strength (CS, are not dangerous from the point of view of worsening the designed thermal properties, but in the overhygroscopic region, the load as low as 57 % of CS may be dangerous. The higher levels of loading are found to be always significant because they lead to marked increase of thermal conductivity which is always a negative information for a building designer.

Electric reaction arising in bone subjected to mechanical loadings

Science.gov (United States)

Murasawa, Go; Cho, Hideo; Ogawa, Kazuma

2006-03-01

The aim of present study is the investigation of the electric reaction arising in bone subjected to mechanical loadings. Firstly, specimen was fabricated from femur of cow, and ultrasonic propagation in bone was measured by ultrasonic technique. Secondary, 4-point bending test was conducted up to fracture, and electric reaction arising in bone was measured during loading. Thirdly, cyclic 4-point bending test was conducted to investigate the effect of applied displacement speed on electric reaction.

Mechanical Behavior of Steel Fiber-Reinforced Concrete Beams Bonded with External Carbon Fiber Sheets.

Science.gov (United States)

Gribniak, Viktor; Tamulenas, Vytautas; Ng, Pui-Lam; Arnautov, Aleksandr K; Gudonis, Eugenijus; Misiunaite, Ieva

2017-06-17

This study investigates the mechanical behavior of steel fiber-reinforced concrete (SFRC) beams internally reinforced with steel bars and externally bonded with carbon fiber-reinforced polymer (CFRP) sheets fixed by adhesive and hybrid jointing techniques. In particular, attention is paid to the load resistance and failure modes of composite beams. The steel fibers were used to avoiding the rip-off failure of the concrete cover. The CFRP sheets were fixed to the concrete surface by epoxy adhesive as well as combined with various configurations of small-diameter steel pins for mechanical fastening to form a hybrid connection. Such hybrid jointing techniques were found to be particularly advantageous in avoiding brittle debonding failure, by promoting progressive failure within the hybrid joints. The use of CFRP sheets was also effective in suppressing the localization of the discrete cracks. The development of the crack pattern was monitored using the digital image correlation method. As revealed from the image analyses, with an appropriate layout of the steel pins, brittle failure of the concrete-carbon fiber interface could be effectively prevented. Inverse analysis of the moment-curvature diagrams was conducted, and it was found that a simplified tension-stiffening model with a constant residual stress level at 90% of the strength of the SFRC is adequate for numerically simulating the deformation behavior of beams up to the debonding of the CFRP sheets.

Analyzing the effects of mechanical and osmotic loading on glycosaminoglycan synthesis rate in cartilaginous tissues.

Science.gov (United States)

Gao, Xin; Zhu, Qiaoqiao; Gu, Weiyong

2015-02-26

The glycosaminoglycan (GAG) plays an important role in cartilaginous tissues to support and transmit mechanical loads. Many extracellular biophysical stimuli could affect GAG synthesis by cells. It has been hypothesized that the change of cell volume is a primary mechanism for cells to perceive the stimuli. Experimental studies have shown that the maximum synthesis rate of GAG is achieved at an optimal cell volume, larger or smaller than this level the GAG synthesis rate decreases. Based on the hypothesis and experimental findings in the literature, we proposed a mathematical model to quantitatively describe the cell volume dependent GAG synthesis rate in the cartilaginous tissues. Using this model, we investigated the effects of osmotic loading and mechanical loading on GAG synthesis rate. It is found our proposed mathematical model is able to well describe the change of GAG synthesis rate in isolated cells or in cartilage with variations of the osmotic loading or mechanical loading. This model is important for evaluating the GAG synthesis activity within cartilaginous tissues as well as understanding the role of mechanical loading in tissue growth or degeneration. It is also important for designing a bioreactor system with proper extracellular environment or mechanical loading for growing tissue at the maximum synthesis rate of the extracellular matrix. Copyright © 2015 Elsevier Ltd. All rights reserved.

10 CFR Appendix Z to Subpart B of... - Uniform Test Method for Measuring the Energy Consumption of External Power Supplies

Science.gov (United States)

2010-01-01

... operation when the external power supply is connected to the main electricity supply and the output is (or “all outputs are” for a multiple-voltage external power supply) connected to a load (or “loads” for a... any mechanical, optical, or electronic switches that automatically disconnect mains power from the...

Features of structural response of mechanically loaded crystallites to irradiation

Energy Technology Data Exchange (ETDEWEB)

Korchuganov, Aleksandr V., E-mail: avkor@ispms.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); National Research Tomsk State University, Tomsk, 634050 (Russian Federation)

2015-10-27

A molecular dynamics method is employed to investigate the origin and evolution of plastic deformation in elastically deformed iron and vanadium crystallites due to atomic displacement cascades. Elastic stress states of crystallites result from different degrees of specimen deformation. Crystallites are deformed under constant-volume conditions. Atomic displacement cascades with the primary knock-on atom energy up to 50 keV are generated in loaded specimens. It is shown that irradiation may cause not only the Frenkel pair formation but also large-scale structural rearrangements outside the irradiated area, which prove to be similar to rearrangements proceeding by the twinning mechanism in mechanically loaded specimens.

Dynamic Response and Failure Mechanism of Brittle Rocks Under Combined Compression-Shear Loading Experiments

Science.gov (United States)

Xu, Yuan; Dai, Feng

2018-03-01

A novel method is developed for characterizing the mechanical response and failure mechanism of brittle rocks under dynamic compression-shear loading: an inclined cylinder specimen using a modified split Hopkinson pressure bar (SHPB) system. With the specimen axis inclining to the loading direction of SHPB, a shear component can be introduced into the specimen. Both static and dynamic experiments are conducted on sandstone specimens. Given carefully pulse shaping, the dynamic equilibrium of the inclined specimens can be satisfied, and thus the quasi-static data reduction is employed. The normal and shear stress-strain relationships of specimens are subsequently established. The progressive failure process of the specimen illustrated via high-speed photographs manifests a mixed failure mode accommodating both the shear-dominated failure and the localized tensile damage. The elastic and shear moduli exhibit certain loading-path dependence under quasi-static loading but loading-path insensitivity under high loading rates. Loading rate dependence is evidently demonstrated through the failure characteristics involving fragmentation, compression and shear strength and failure surfaces based on Drucker-Prager criterion. Our proposed method is convenient and reliable to study the dynamic response and failure mechanism of rocks under combined compression-shear loading.

Oscillations of end loaded cantilever beams

International Nuclear Information System (INIS)

Macho-Stadler, E; Elejalde-García, M J; Llanos-Vázquez, R

2015-01-01

This article presents several simple experiments based on changing transverse vibration frequencies in a cantilever beam, when acted on by an external attached mass load at the free end. By using a mechanical wave driver, available in introductory undergraduate laboratories, we provide various experimental results for end loaded cantilever beams that fit reasonably well into a linear equation. The behaviour of the cantilever beam’s weak-damping resonance response is studied for the case of metal resonance strips. As the mass load increases, a more pronounced decrease occurs in the fundamental frequency of beam vibration. It is important to note that cantilever construction is often used in architectural design and engineering construction projects but current analysis also predicts the influence of mass load on the sound generated by musical free reeds with boundary conditions similar to a cantilever beam. (paper)

Oscillations of end loaded cantilever beams

Science.gov (United States)

Macho-Stadler, E.; Elejalde-García, M. J.; Llanos-Vázquez, R.

2015-09-01

This article presents several simple experiments based on changing transverse vibration frequencies in a cantilever beam, when acted on by an external attached mass load at the free end. By using a mechanical wave driver, available in introductory undergraduate laboratories, we provide various experimental results for end loaded cantilever beams that fit reasonably well into a linear equation. The behaviour of the cantilever beam’s weak-damping resonance response is studied for the case of metal resonance strips. As the mass load increases, a more pronounced decrease occurs in the fundamental frequency of beam vibration. It is important to note that cantilever construction is often used in architectural design and engineering construction projects but current analysis also predicts the influence of mass load on the sound generated by musical free reeds with boundary conditions similar to a cantilever beam.

MECHANICAL BEHAVIOR OF PRESTRESSED VISCOELASTIC ADHESIVE AREAS UNDER COMBINING LOADINGS

Directory of Open Access Journals (Sweden)

Halil Murat Enginsoy

2017-12-01

Full Text Available In this article, mechanical behaviors of adhesive tape VHB 4950 elastomeric material, which is an element of acrylic polymer group and which is in viscoelastic behavior, under different pre-stress conditions and complex forces of different geometric parameters created by combining loadings have been experimentally and numerically investigated. In experimental studies, loading-unloading cyclic tests, one of the different standardized tests for the mechanical characterization of viscoelastic material, have been applied which give the most suitable convergent optimization parameters for the finite element model. Different material models were also investigated by using the data obtained from loading-unloading test results in all numerical models. According to the experimental results, the most suitable material parameters were determined with the Abaqus Parallel Rheological Framework Model (PRF for 4 Yeoh Networks with Bergstrom-Boyce Flow model created in the Mcalibration software for finite element analysis. Subsequently, using these material parameters, finite element analysis was performed as three dimension non-linear viscoelastic with a commercial finite element software Abaqus. The finite element analysis results showed good correlation to the Force (N-Displacement (mm experimental data for maximum load-carrying capacity of structural specimens.

Comparison of the external physical damages between laser-assisted and mechanical immobilized human sperm using scanning electronic microscopy.

Directory of Open Access Journals (Sweden)

David Y L Chan

Full Text Available We aim to visualize the external physical damages and distinct external phenotypic effects between mechanical and laser-assisted immobilized human spermatozoa using scanning electronic microscopy (SEM. Human spermatozoa were immobilized mechanically or with laser assistance for SEM examination and the membrane integrities were checked on both types of immobilized spermatozoa. We found evidence of external damages at SEM level on mechanically kinked sperm, but not on laser-assisted immobilized sperm. Although no external damage was found on laser-assist immobilized sperm, there were two distinct types of morphological changes when spermatozoa were stricken by infra-red laser. Coiled tails were immediately formed when Laser pulse was applied to the sperm end piece area, whereas laser applied to the sperm principal piece area resulted in a sharp bend of sperm tails. Sperm immobilized by laser did not exhibit any morphological change if the laser did not hit within the on-screen central target zone or if the laser hit the sperm mid piece or head. Our modified membrane integrity assay revealed that the external membrane of more than half of the laser-assisted immobilized sperm remained intact. In conclusion, mechanical immobilization produced membrane damages whilst laser-assisted immobilization did not result in any external membrane damages besides morphological changes at SEM level.

Nonlinear Analysis of the Space Shuttle Super-Lightweight External Fuel Tank

Science.gov (United States)

Nemeth, Michael P.; Britt, Vicki O.; Collins, Timothy J.; Starnes, James H., Jr.

1996-01-01

The results of buckling and nonlinear analyses of the Space Shuttle External Tank super-lightweight liquid oxygen (LOX) tank are presented. Modeling details and results are presented for two prelaunch loading conditions and for two full-scale structural tests conducted on the original external tank. These results illustrate three distinctly different types of nonlinear responses for thin-walled shells subjected to combined mechanical and thermal loads. These nonlinear response phenomena consist of bifurcation-type buckling, short-wavelength nonlinear bending, and nonlinear collapse associated with a limit point. For each case, the results show that accurate predictions of nonlinear behavior generally require a large scale high-fidelity finite element model. Results are also presented that show that a fluid filled launch vehicle shell can be highly sensitive to initial geometric imperfections. In addition, results presented for two full scale structural tests of the original standard weight external tank suggest that the finite element modeling approach used in the present study is sufficient for representing the nonlinear behavior of the super lightweight LOX tank.

Mechanics of arterial subfailure with increasing loading rate.

Science.gov (United States)

Stemper, Brian D; Yoganandan, Narayan; Pintar, Frank A

2007-01-01

Arterial subfailure leads to delayed symptomatology and high morbidity and mortality rates, particularly for the thoracic aorta and carotid arteries. Although arterial injuries occur during high-velocity automotive collisions, previous studies of arterial subfailure focused on quasi-static loading. This investigation subjected aortic segments to increasing loading rates to quantify effects on elastic, subfailure, and ultimate vessel mechanics. Sixty-two specimens were axially distracted, and 92% demonstrated subfailure before ultimate failure. With increasing loading rate, stress at initial subfailure and ultimate failure significantly increased, and strain at initial subfailure and ultimate failure significantly decreased. Present results indicate increased susceptibility for arterial subfailure and/or dissection under higher-rate extension. According to the present results, automotive occupants are at greater risk of arterial injury under higher velocity impacts due to greater body segment motions in addition to decreased strain tolerance to subfailure and catastrophic failure.

A High-Order Theory for the Analysis of Circular Cylindrical Composite Sandwich Shells with Transversely Compliant Core Subjected to External Loads

DEFF Research Database (Denmark)

Rahmani, Omid; Khalili, S.M.R.; Thomsen, Ole Thybo

2012-01-01

A new model based on the high order sandwich panel theory is proposed to study the effect of external loads on the free vibration of circular cylindrical composite sandwich shells with transversely compliant core, including also the calculation of the buckling loads. In the present model......, which is based on a 3D elasticity solution for the core material, can be used as a benchmark in future studies of the free vibration and buckling of circular cylindrical composite sandwich shells with a transversely compliant core....

Grips for testing of electrical characteristics of a specimen under a mechanical load

Science.gov (United States)

Briggs, Timothy; Loyola, Bryan

2018-04-24

Various technologies to facilitate coupled electrical and mechanical measurement of conductive materials are disclosed herein. A gripping device simultaneously holds a specimen in place and causes contact to be made between the specimen and a plurality of electrodes connected to an electrical measuring device. An electrical characteristic of the specimen is then measured while a mechanical load is applied to the specimen, and a relationship between the mechanical load and changes in the electrical characteristic can be identified.

Effects of mechanical loading on human mesenchymal stem cells for cartilage tissue engineering.

Science.gov (United States)

Choi, Jane Ru; Yong, Kar Wey; Choi, Jean Yu

2018-03-01

Today, articular cartilage damage is a major health problem, affecting people of all ages. The existing conventional articular cartilage repair techniques, such as autologous chondrocyte implantation (ACI), microfracture, and mosaicplasty, have many shortcomings which negatively affect their clinical outcomes. Therefore, it is essential to develop an alternative and efficient articular repair technique that can address those shortcomings. Cartilage tissue engineering, which aims to create a tissue-engineered cartilage derived from human mesenchymal stem cells (MSCs), shows great promise for improving articular cartilage defect therapy. However, the use of tissue-engineered cartilage for the clinical therapy of articular cartilage defect still remains challenging. Despite the importance of mechanical loading to create a functional cartilage has been well demonstrated, the specific type of mechanical loading and its optimal loading regime is still under investigation. This review summarizes the most recent advances in the effects of mechanical loading on human MSCs. First, the existing conventional articular repair techniques and their shortcomings are highlighted. The important parameters for the evaluation of the tissue-engineered cartilage, including chondrogenic and hypertrophic differentiation of human MSCs are briefly discussed. The influence of mechanical loading on human MSCs is subsequently reviewed and the possible mechanotransduction signaling is highlighted. The development of non-hypertrophic chondrogenesis in response to the changing mechanical microenvironment will aid in the establishment of a tissue-engineered cartilage for efficient articular cartilage repair. © 2017 Wiley Periodicals, Inc.

STRESS LOADING SIMULATION OF HYDRO-MECHANICAL TRANSMISSION OF DUMP TRUCK

Directory of Open Access Journals (Sweden)

S. A. Sidorov

2006-01-01

Full Text Available The Transmission model and software package to investigate stress loading of a hydromechanical transmission of a dump truck have been developed. The given software package allows to model stress loading of transmission gears in taking-off and acceleration modes at various road resistance, positions of an engine control pedal and initial revolutions of an engine crankshaft, various laws of friction clutch switching and some other parameters that permit to reveal a rate of various operational mode influence on stress loading of a dump truck transmission. An equivalence of the developed software is proved by the comparison of the experimentally obtained stress loading process of the hydro-mechanical transmission of a BelAZ- 7555 dump truck with the results of the simulation 

Expression of muscle anabolic and metabolic factors in mechanically loaded MLO-Y4 osteocytes

NARCIS (Netherlands)

Juffer, P.; Jaspers, R.T.; Lips, P.; Bakker, A.D.; Klein-Nulend, J.

2012-01-01

Lack of physical activity results in muscle atrophy and bone loss, which can be counteracted by mechanical loading. Similar molecular signaling pathways are involved in the adaptation of muscle and bone mass to mechanical loading. Whether anabolic and metabolic factors regulating muscle mass, i.e.,

Long-term dynamic loading improves the mechanical properties of chondrogenic mesenchymal stem cell-laden hydrogel

Directory of Open Access Journals (Sweden)

AH Huang

2010-02-01

Full Text Available Mesenchymal stem cells (MSCs are an attractive cell source for cartilage tissue engineering given their ability to undergo chondrogenesis in 3D culture systems. Mechanical forces play an important role in regulating both cartilage development and MSC chondrogenic gene expression, however, mechanical stimulation has yet to enhance the mechanical properties of engineered constructs. In this study, we applied long-term dynamic compression to MSC-seeded constructs and assessed whether varying pre-culture duration, loading regimens and inclusion of TGF-beta3 during loading would influence functional outcomes and these phenotypic transitions. Loading initiated before chondrogenesis decreased functional maturation, although chondrogenic gene expression increased. In contrast, loading initiated after chondrogenesis and matrix elaboration further improved the mechanical properties of MSC-based constructs, but only when TGF-beta3 levels were maintained and under specific loading parameters. Although matrix quantity was not affected by dynamic compression, matrix distribution, assessed histologically and by FT-IRIS analysis, was significantly improved on the micro- (pericellular and macro- (construct expanse scales. Further, whole genome expression profiling revealed marked shifts in the molecular topography with dynamic loading. These results demonstrate, for the first time, that dynamic compressive loading initiated after a sufficient period of chondro-induction and with sustained TGF-beta exposure enhances matrix distribution and the mechanical properties of MSC-seeded constructs.

NASA GSFC Mechanical Engineering Latest Inputs for Verification Standards (GEVS) Updates

Science.gov (United States)

Kaufman, Daniel

2003-01-01

This viewgraph presentation provides information on quality control standards in mechanical engineering. The presentation addresses safety, structural loads, nonmetallic composite structural elements, bonded structural joints, externally induced shock, random vibration, acoustic tests, and mechanical function.

J evaluation by simplified method for cracked pipes under mechanical loading

International Nuclear Information System (INIS)

Lacire, M.H.; Michel, B.; Gilles, P.

2001-01-01

The integrity of structures behaviour is an important subject for the nuclear reactor safety. Most of assessment methods of cracked components are based on the evaluation of the parameter J. However to avoid complex elastic-plastic finite element calculations of J, a simplified method has been jointly developed by CEA, EDF and Framatome. This method, called Js, is based on the reference stress approach and a new KI handbook. To validate this method, a complete set of 2D and 3D elastic-plastic finite element calculations of J have been performed on pipes (more than 300 calculations are available) for different types of part through wall crack (circumferential or longitudinal); mechanical loading (pressure, bending moment, axial load, torsion moment, and combination of these loading); different kind of materials (austenitic or ferritic steel). This paper presents a comparison between the simplified assessment of J and finite element results on these configurations for mechanical loading. Then, validity of the method is discussed and an applicability domain is proposed. (author)

An exploratory study of using external fluid loading on a vibrating tube for measuring suspended sediment concentration in water

International Nuclear Information System (INIS)

Hsu, Y-S; Hwang, Y-F; Huang, J H

2008-01-01

This paper presents an exploratory study of using external fluid loading on a vibrating tube for measuring the suspended sediment concentration (SSC) in bodies of water such as rivers and reservoirs. This new measuring concept provides an opportunity for an automated on-site monitoring of the conditions in a body of water by taking the fluid sample instantaneously in the area surrounding the vibrating tube. The physical properties of the fluid sample are those of the fluid that naturally flows around the tube, and are more representative of those of the water with SSC to be measured. The theoretical analysis presented in this paper shows that the resonance frequencies of an immersed vibrating tube change significantly with mass density variations that normally occur in bodies of water with suspended sediment. These changes are sensitive enough to have a possible 1% resolution of the measured fluid density. The signal processing issues are discussed, and a schematic of a conceptual measuring setup is proposed. Based on the theoretical analyses and other measurement issues presented in the paper, using the loading by external fluid on a vibrating tube is feasible for measuring the SSC in water bodies

Research of thermal dynamic characteristics for variable load single screw refrigeration compressor with different capacity control mechanism

International Nuclear Information System (INIS)

Wang, Zengli; Wang, Zhenbo; Wang, Jun; Jiang, Wenchun; Feng, Quanke

2017-01-01

Highlights: • Theoretical models of SSRC under part-load condition have been established. • The experiment of SSRC performance under part-load condition was conducted. • Thermal dynamic characteristic of SSRC under part-load condition was gained. • Economy and reliability of SSRC under part-load condition was analyzed. - Abstract: In the single screw refrigeration compressor (SSRC), the capacity control mechanism is normally employed to meet the actual required cooling capacity under different load conditions. In this paper, theoretical calculation models describing the working process of the SSRC with the single slide valve capacity control mechanism (SVCCM) and SSRC with the frequency conversion regulating mechanism (FCRM) are established to research the thermal dynamic characteristics for variable load SSRC under part-load conditions. Experimental investigation on a SSRC under part-load conditions is also carried out to verify the theoretical calculation models. By using these validated models, the thermodynamic performances and dynamic characteristics of the SSRC with different capacity control mechanism under part-load conditions have been analyzed and compared. Through the comparison, the economical efficiency and reliability of the SSRC with different capacity control mechanism were obtained. All of these works can provide the basis for the later optimization design for the variable load single screw refrigeration compressor.

Variable load failure mechanism for high-speed load sensing electro-hydrostatic actuator pump of aircraft

Directory of Open Access Journals (Sweden)

Cun SHI

2018-05-01

Full Text Available This paper presents a novel transient lubrication model for the analysis of the variable load failure mechanism of high-speed pump used in Load Sensing Electro-Hydrostatic Actuator (LS-EHA. Focusing on the slipper/swashplate pair partial abrasion, which is considered as the dominant failure mode in the high-speed condition, slipper dynamic models are established. A forth sliding motion of the slipper on the swashplate surface is presented under the fact that the slipper center of mass will rotate around the center of piston ball when the swashplate angle is dynamically adjusted. Besides, extra inertial tilting moments will be produced for the slipper based on the theorem on translation of force, which will increase rapidly when LS-EHA pump operates under high-speed condition. Then, a dynamic lubricating model coupling with fluid film thickness field, temperature field and pressure field is proposed. The deformation effects caused by thermal deflection and hydrostatic pressure are considered. A numerical simulation model is established to validate the effectiveness and accuracy of the proposed model. Finally, based on the load spectrum of aircraft flight profile, the variable load conditions and the oil film characteristics are analyzed, and series of variable load rules of oil film thickness with variable speed/variable pressure/variable displacement are concluded. Keywords: Coupling lubrication model, Electro-Hydrostatic Actuator (EHA, High-speed pump, Partial abrasion, Slipper pair, Variable load

The Role of Adaptation in Body Load-Regulating Mechanisms During Locomotion

Science.gov (United States)

Ruttley, Tara; Holt, Christopher; Mulavara, Ajitkumar; Bloomberg, Jacob

2010-01-01

Body loading is a fundamental parameter that modulates motor output during locomotion, and is especially important for controlling the generation of stepping patterns, dynamic balance, and termination of locomotion. Load receptors that regulate and control posture and stance in locomotion include the Golgi tendon organs and muscle spindles at the hip, knee, and ankle joints, and the Ruffini endings and the Pacinian corpuscles in the soles of the feet. Increased body weight support (BWS) during locomotion results in an immediate reorganization of locomotor control, such as a reduction in stance and double support duration and decreased hip, ankle, and knee angles during the gait cycle. Previous studies on the effect during exposure to increased BWS while walking showed a reduction in lower limb joint angles and gait cycle timing that represents a reorganization of locomotor control. Until now, no studies have investigated how locomotor control responds after a period of exposure to adaptive modification in the body load sensing system. The goal of this research was to determine the adaptive properties of body load-regulating mechanisms in locomotor control during locomotion. We hypothesized that body load-regulating mechanisms contribute to locomotor control, and adaptive changes in these load-regulating mechanisms require reorganization to maintain forward locomotion. Head-torso coordination, lower limb movement patterns, and gait cycle timing were evaluated before and after a 30-minute adaptation session during which subjects walked on a treadmill at 5.4 km/hr with 40% body weight support (BWS). Before and after the adaptation period, head-torso and lower limb 3D kinematic data were obtained while performing a goal directed task during locomotion with 0% BWS using a video-based motion analysis system, and gait cycle timing parameters were collected by foot switches positioned under the heel and toe of the subjects shoes. Subjects showed adaptive modification in

Modeling the impact of scaffold architecture and mechanical loading on collagen turnover in engineered cardiovascular tissues.

Science.gov (United States)

Argento, G; de Jonge, N; Söntjens, S H M; Oomens, C W J; Bouten, C V C; Baaijens, F P T

2015-06-01

The anisotropic collagen architecture of an engineered cardiovascular tissue has a major impact on its in vivo mechanical performance. This evolving collagen architecture is determined by initial scaffold microstructure and mechanical loading. Here, we developed and validated a theoretical and computational microscale model to quantitatively understand the interplay between scaffold architecture and mechanical loading on collagen synthesis and degradation. Using input from experimental studies, we hypothesize that both the microstructure of the scaffold and the loading conditions influence collagen turnover. The evaluation of the mechanical and topological properties of in vitro engineered constructs reveals that the formation of extracellular matrix layers on top of the scaffold surface influences the mechanical anisotropy on the construct. Results show that the microscale model can successfully capture the collagen arrangement between the fibers of an electrospun scaffold under static and cyclic loading conditions. Contact guidance by the scaffold, and not applied load, dominates the collagen architecture. Therefore, when the collagen grows inside the pores of the scaffold, pronounced scaffold anisotropy guarantees the development of a construct that mimics the mechanical anisotropy of the native cardiovascular tissue.

Aging and loading rate effects on the mechanical behavior of equine bone

Science.gov (United States)

Kulin, Robb M.; Jiang, Fengchun; Vecchio, Kenneth S.

2008-06-01

Whether due to a sporting accident, high-speed impact, fall, or other catastrophic event, the majority of clinical bone fractures occur under dynamic loading conditions. However, although extensive research has been performed on the quasi-static fracture and mechanical behavior of bone to date, few high-quality studies on the fracture behavior of bone at high strain rates have been performed. Therefore, many questions remain regarding the material behavior, including not only the loading-rate-dependent response of bone, but also how this response varies with age. In this study, tests were performed on equine femoral bone taken post-mortem from donors 6 months to 28 years of age. Quasi-static and dynamic tests were performed to determine the fracture toughness and compressive mechanical behavior as a function of age at varying loading rates. Fracture paths were then analyzed using scanning confocal and scanning-electron microscopy techniques to assess the role of various microstructural features on toughening mechanisms.

How to correct for long-term externalities of large-scale wind power development by a capacity mechanism?

International Nuclear Information System (INIS)

Cepeda, Mauricio; Finon, Dominique

2013-01-01

This paper deals with the practical problems related to long-term security of supply in electricity markets in the presence of large-scale wind power development. The success of recent renewable promotion schemes adds a new dimension to ensuring long-term security of supply: it necessitates designing second-best policies to prevent large-scale wind power development from distorting long-run equilibrium prices and investments in conventional generation and in particular in peaking units. We rely upon a long-term simulation model which simulates electricity market players' investment decisions in a market regime and incorporates large-scale wind power development in the presence of either subsidized or market driven development scenarios. We test the use of capacity mechanisms to compensate for long-term effects of large-scale wind power development on prices and reliability of supply. The first finding is that capacity mechanisms can help to reduce the social cost of large scale wind power development in terms of decrease of loss of load probability. The second finding is that, in a market-based wind power deployment without subsidy, wind generators are penalised for insufficient contribution to the long term system's reliability. - Highlights: • We model power market players’ investment decisions incorporating wind power. • We examine two market designs: an energy-only market and a capacity mechanism. • We test two types of wind power development paths: subsidised and market-driven. • Capacity mechanisms compensate for the externalities of wind power developments

Mechanics of load-drag-unload contact cleaning of gecko-inspired fibrillar adhesives.

Science.gov (United States)

Abusomwan, Uyiosa A; Sitti, Metin

2014-10-14

Contact self-cleaning of gecko-inspired synthetic adhesives with mushroom-shaped tips has been demonstrated recently using load-drag-unload cleaning procedures similar to that of the natural animal. However, the underlying mechanics of contact cleaning has yet to be fully understood. In this work, we present a detailed experiment of contact self-cleaning that shows that rolling is the dominant mechanism of cleaning for spherical microparticle contaminants, during the load-drag-unload procedure. We also study the effect of dragging rate and normal load on the particle rolling friction. A model of spherical particle rolling on an elastomer fibrillar adhesive interface is developed and agrees well with the experimental results. This study takes us closer to determining design parameters for achieving self-cleaning fibrillar adhesives.

The mechanics of head-supported load carriage by Nepalese porters.

OpenAIRE

Bastien, Guillaume; Willems, Patrick; Schepens, Bénédicte; Heglund, Norman

2016-01-01

In the Everest valley of Nepal, because of the rugged mountain terrain, roads are nothing more than dirt paths and all material must be conveyed on foot. The Nepalese porters routinely carry head-supported loads, which often exceed their body mass, over long distances up and down the steep mountain footpaths. In Africa, women transport their loads economically thanks to an energy-saving gait adaptation. We hypothesized that the Nepalese porters may have developed a corresponding mechanism. To...

Effect of Court Dimensions on Players’ External and Internal Load during Small-Sided Handball Games

Science.gov (United States)

Corvino, Matteo; Tessitore, Antonio; Minganti, Carlo; Sibila, Marko

2014-01-01

The aim of this study was to investigate the effect of three different court dimensions on the internal and external load during small-sided handball games. Six male amateur handball players took part in this study and participated in three different 8-min 3vs3 (plus goalkeepers) small-sided handball games (each repeated twice). The three court dimensions were 12×24m, 30×15m and 32×16m. Through Global Positioning System devices (SPI pro elite 15Hz, GPSports) and video analysis, the following parameters were recorded: cyclic and acyclic movements (distance covered and number of technical actions executed), heart rate, and rating of perceived exertion (RPE). Total distance travelled increased with court dimensions (885.2m ± 66.6m in 24×12m; 980.0m ± 73.4m in 30×15m; 1095.0m ± 112.9m in 32×16m, p 5.2 m·s-1) highlighted substantial differences: playing with the 30×15m court in comparison to the 24×12m, the players covered less distance in the first speed zone (p = 0.012; ES = 0.70) and more distance in the second (p = 0.049; ES = 0.73) and third (p = 0.012; ES = 0.51) speed zones. Statistical differences were also found between the 24×12m and 32×16m courts: the players covered more distance in the second and third speed zones (p = 0.013, ES = 0.76; p = 0.023 ES = 0.69) with the 32×16m court in comparison to the 24×12m. There was no significant effect of court dimensions on the technical parameters (number of team actions, passes, piston movements toward goal and defensive activities), the number of specific handball jumps and changes of direction, and the time spent in the different heart rate zones. Considering the average data of all the experimental conditions together (24×12m, 30×15m, 32×16m), a pronounced statistical difference was highlighted between the values in first two HR zones and the last two (p handball games can be used to manipulate both external and internal loads on the players. Key points To cover the specific game demands, more

Effect of Court Dimensions on Players' External and Internal Load during Small-Sided Handball Games.

Science.gov (United States)

Corvino, Matteo; Tessitore, Antonio; Minganti, Carlo; Sibila, Marko

2014-05-01

The aim of this study was to investigate the effect of three different court dimensions on the internal and external load during small-sided handball games. Six male amateur handball players took part in this study and participated in three different 8-min 3vs3 (plus goalkeepers) small-sided handball games (each repeated twice). The three court dimensions were 12×24m, 30×15m and 32×16m. Through Global Positioning System devices (SPI pro elite 15Hz, GPSports) and video analysis, the following parameters were recorded: cyclic and acyclic movements (distance covered and number of technical actions executed), heart rate, and rating of perceived exertion (RPE). Total distance travelled increased with court dimensions (885.2m ± 66.6m in 24×12m; 980.0m ± 73.4m in 30×15m; 1095.0m ± 112.9m in 32×16m, p 5.2 m·s(-1)) highlighted substantial differences: playing with the 30×15m court in comparison to the 24×12m, the players covered less distance in the first speed zone (p = 0.012; ES = 0.70) and more distance in the second (p = 0.049; ES = 0.73) and third (p = 0.012; ES = 0.51) speed zones. Statistical differences were also found between the 24×12m and 32×16m courts: the players covered more distance in the second and third speed zones (p = 0.013, ES = 0.76; p = 0.023 ES = 0.69) with the 32×16m court in comparison to the 24×12m. There was no significant effect of court dimensions on the technical parameters (number of team actions, passes, piston movements toward goal and defensive activities), the number of specific handball jumps and changes of direction, and the time spent in the different heart rate zones. Considering the average data of all the experimental conditions together (24×12m, 30×15m, 32×16m), a pronounced statistical difference was highlighted between the values in first two HR zones and the last two (p handball games can be used to manipulate both external and internal loads on the players. Key pointsTo cover the specific game demands, more

Femoral loading mechanics in the Virginia opossum, Didelphis virginiana: torsion and mediolateral bending in mammalian locomotion.

Science.gov (United States)

Gosnell, W Casey; Butcher, Michael T; Maie, Takashi; Blob, Richard W

2011-10-15

Studies of limb bone loading in terrestrial mammals have typically found anteroposterior bending to be the primary loading regime, with torsion contributing minimally. However, previous studies have focused on large, cursorial eutherian species in which the limbs are held essentially upright. Recent in vivo strain data from the Virginia opossum (Didelphis virginiana), a marsupial that uses a crouched rather than an upright limb posture, have indicated that its femur experiences appreciable torsion during locomotion as well as strong mediolateral bending. The elevated femoral torsion and strong mediolateral bending observed in D. virginiana might result from external forces such as a medial inclination of the ground reaction force (GRF), internal forces deriving from a crouched limb posture, or a combination of these factors. To evaluate the mechanism underlying the loading regime of opossum femora, we filmed D. virginiana running over a force platform, allowing us to measure the magnitude of the GRF and its three-dimensional orientation relative to the limb, facilitating estimates of limb bone stresses. This three-dimensional analysis also allows evaluations of muscular forces, particularly those of hip adductor muscles, in the appropriate anatomical plane to a greater degree than previous two-dimensional analyses. At peak GRF and stress magnitudes, the GRF is oriented nearly vertically, inducing a strong abductor moment at the hip that is countered by adductor muscles on the medial aspect of the femur that place this surface in compression and induce mediolateral bending, corroborating and explaining loading patterns that were identified in strain analyses. The crouched orientation of the femur during stance in opossums also contributes to levels of femoral torsion as high as those seen in many reptilian taxa. Femoral safety factors were as high as those of non-avian reptiles and greater than those of upright, cursorial mammals, primarily because the load

Mechanical responses of a-axis GaN nanowires under axial loads

Science.gov (United States)

Wang, R. J.; Wang, C. Y.; Feng, Y. T.; Tang, Chun

2018-03-01

Gallium nitride (GaN) nanowires (NWs) hold technological significance as functional components in emergent nano-piezotronics. However, the examination of their mechanical responses, especially the mechanistic understanding of behavior beyond elasticity (at failure) remains limited due to the constraints of in situ experimentation. We therefore performed simulations of the molecular dynamics (MD) of the mechanical behavior of [1\\bar{2}10]-oriented GaN NWs subjected to tension or compression loading until failure. The mechanical properties and critical deformation processes are characterized in relation to NW sizes and loading conditions. Detailed examinations revealed that the failure mechanisms are size-dependent and controlled by the dislocation mobility on shuffle-set pyramidal planes. The size dependence of the elastic behavior is also examined in terms of the surface structure determined modification of Young’s modulus. In addition, a comparison with c-axis NWs is made to show how size-effect trends vary with the growth orientation of NWs.

Statistical evaluation of low cycle loading curves parameters for structural materials by mechanical characteristics

International Nuclear Information System (INIS)

Daunys, Mykolas; Sniuolis, Raimondas

2006-01-01

About 300 welded joint materials that are used in nuclear power energy were tested under monotonous tension and low cycle loading in Kaunas University of Technology together with St. Peterburg Central Research Institute of Structural Materials in 1970-2000. The main mechanical, low cycle loading and fracture characteristics of base metals, weld metals and some heat-affected zones of welded joints metals were determined during these experiments. Analytical dependences of low cycle fatigue parameters on mechanical characteristics of structural materials were proposed on the basis of a large number of experimental data, obtained by the same methods and testing equipment. When these dependences are used, expensive low cycle fatigue tests may be omitted and it is possible to compute low cycle loading curves parameters and lifetime for structural materials according to the main mechanical characteristics given in technical manuals. Dependences of low cycle loading curves parameters on mechanical characteristics for several groups of structural materials used in Russian nuclear power energy are obtained by statistical methods and proposed in this paper

Investigation of efficiency of electric drive control system of excavator traction mechanism based on feedback on load

Science.gov (United States)

Kuznetsov, N. K.; Iov, I. A.; Iov, A. A.

2018-05-01

The article presents the results of a study of the efficiency of the electric drive control system of the traction mechanism of a dragline based on the use of feedback on load in the traction cable. The investigations were carried out using a refined electromechanical model of the traction mechanism, which took into account not only the elastic elements of the gearbox, the backlashes in it and the changes in the kinematic parameters of the mechanism during operation, but also the mechanical characteristics of the electric drive and the features of its control system. By mathematical modeling of the transient processes of the electromechanical system, it is shown that the introduction of feedback on the load in the elastic element allows one to reduce the dynamic loads in the traction mechanism and to limit the elastic oscillations of the actuating mechanism in comparison with the standard control system. Fixed as a general decrease in the dynamic load of the nodes of traction mechanism in the modes of loading and latching of the bucket, and a decrease the operating time of the mechanism at maximum load. At the same time, undesirable phenomena in the operation of the electric drive were also associated with the increase in the recovery time of the steady-state value of the speed of the actuating mechanism under certain operating conditions, which can lead to a decrease in the reliability of the mechanical part and the productivity of the traction mechanism.

Mechanical Characterization of the Human Lumbar Intervertebral Disc Subjected to Impact Loading Conditions

Science.gov (United States)

Jamison, David, IV

Low back pain is a large and costly problem in the United States. Several working populations, such as miners, construction workers, forklift operators, and military personnel, have an increased risk and prevalence of low back pain compared to the general population. This is due to exposure to repeated, transient impact shocks, particularly while operating vehicles or other machinery. These shocks typically do not cause acute injury, but rather lead to pain and injury over time. The major focus in low back pain is often the intervertebral disc, due to its role as the major primary load-bearing component along the spinal column. The formation of a reliable standard for human lumbar disc exposure to repeated transient shock could potentially reduce injury risk for these working populations. The objective of this project, therefore, is to characterize the mechanical response of the lumbar intervertebral disc subjected to sub-traumatic impact loading conditions using both cadaveric and computational models, and to investigate the possible implications of this type of loading environment for low back pain. Axial, compressive impact loading events on Naval high speed boats were simulated in the laboratory and applied to human cadaveric specimen. Disc stiffness was higher and hysteresis was lower than quasi-static loading conditions. This indicates a shift in mechanical response when the disc is under impact loads and this behavior could be contributing to long-term back pain. Interstitial fluid loss and disc height changes were shown to affect disc impact mechanics in a creep study. Neutral zone increased, while energy dissipation and low-strain region stiffness decreased. This suggests that the disc has greater clinical instability during impact loading with progressive creep and fluid loss, indicating that time of day should be considered for working populations subjected to impact loads. A finite element model was developed and validated against cadaver specimen

Development of a mechanical testing and loading system for trabecular bone studies for long term culture

Directory of Open Access Journals (Sweden)

DB Jones

2003-03-01

Full Text Available A highly accurate (�3% mechanical loading and measurement system combined with a trabecular bone diffusion culture-loading chamber has been developed, which provides the ability to study trabecular bone (and possibly cartilage under controlled culture and loading conditions over long periods of time. The loading device has been designed to work in two main modes, either to apply a specific compressive strain to a trabecular bone cylinder or to apply a specific force and measure the resulting deformation. Presently, precisely machined bone cylinders can be loaded at frequencies between 0.1 Hz to 50 Hz and amplitudes over 7,000�e. The system allows accurate measurement of many mechanical properties of the tissue in real time, including visco-elastic properties. This paper describes the technical components, reproducibility, precision, and the calibration procedures of the loading system. Data on long term culture and mechanical responses to different loading patterns will be published separately.

The seating mechanics of head-neck modular tapers in vitro: Load-displacement measurements, moisture, and rate effects.

Science.gov (United States)

Ouellette, Eric S; Shenoy, Aarti A; Gilbert, Jeremy L

2018-04-01

The mechanically assisted crevice corrosion performance of head-neck modular tapers is a significant concern in orthopedic biomaterials. Fretting crevice corrosion processes in modular tapers are thought to be influenced by a wide array of factors including seating mechanics of the junction, hence there is a need for in vitro test methods that can assess their performance. This study presented a test method to directly measure the load-displacement seating mechanics of modular tapers and used this method to compare the seating mechanics for different tapers, moisture, seating loads and seating rates. Seating mechanics were explored whereby the instantaneous load-displacement behavior of the head seating onto the neck is captured and used to define the mechanics of seating. Two distinct taper design/material combinations were assembled wet or dry using axially applied loads (500, 1,000, 2,000, and 4,000 N) at two loading rates of 100 and 10 4  N/s (n = 5 for each condition) using a servohydraulic test frame. The results showed that pull-off strength scaled with seating load and ranged between 43% and 68% of seating load depending on sample and wetness. Tapers seated wet had higher pull-off strengths (2,200 ± 300 N) than those seated dry (1,800 ± 200 N, p mechanics (load-displacement plots) varied due to sample type and due to wetness with differences in seating energy, seating stiffness, and seating displacement. These results show the detailed mechanics of seating during assembly and provide significant insight into the complex interplay of factors associated with even "ideal" seating (axial, quasistatic) loading. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1164-1172, 2018. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

Microscale failure mechanisms leading to internal short circuit in Li-ion batteries under complex loading scenarios

NARCIS (Netherlands)

Sahraei, E.; Bosco, E.; Dixon, B.; Lai, B.

2016-01-01

One of the least understood mechanisms of Li-ion batteries is the development of internal short circuits under mechanical loads. In this study, a micro mechanical model is developed and subjected to various loading scenarios to understand the sequence of failure in the multi-layer, multi-material

Mechanism of remote controlled after-loading radiotherapy unit

International Nuclear Information System (INIS)

Morimoto, Masaki

1980-01-01

Employing a small amount of Radium-226 or Cesium-137 source was to be used hitherto for the treatment of carcinoma of the uterine cervix in used After-loading techniques. It involved, however, radiation risk to the staff and patient. The long treatment time are also a pain (strain) on the patient. In recent years, we have developed a remote control after-loading unit, which was named as RALSTRON, which was complete eliminated the disadvantage of conventional radium therapy. This unit also has disadvantage, however, that the design for the remote after-loader for intracavitary applicators present considerable difficulties, because many sources of different active lengths and loading patterns are required. A solution to this problem was carried out by using small point source, placed in Tandem applicator, of high activity and moving them back slowly during the treatment. Recently, this unit was installed many hospitals about 80 units in Japan, and are used. In this paper are given about a mechanism and safety deviced of this unit. (author)

Combined loading effects on the fracture mechanics behavior of line pipes

Energy Technology Data Exchange (ETDEWEB)

Bravo, R.E.; Cravero, S.; Ernst, H.A. [Tenaris Group, Campana (Argentina). SIDERCA R and D Center

2009-12-19

For certain applications, pipelines may be submitted to biaxial loading situations. In these cases, it is not clear the influence of the biaxial loading on the fracture mechanics behavior of cracked pipelines. For further understanding of biaxial loading effects, this work presents a numerical simulation of ductile tearing in a circumferentially surface cracked pipe under biaxial loading using the computational cell methodology. The model was adjusted with experimental results obtained in laboratory using single edge cracked under tension (SENT) specimens. These specimens appear as the better alternative to conventional fracture specimens to characterize fracture toughness of cracked pipes. The negligible effect of biaxial loadings on resistance curves was demonstrated. To guarantee the similarities of stress and strains fields between SENT specimens and cracked pipes subjected to biaxial loading, a constraint study using the J-Q methodology and the h parameter was used. The constraint study gives information about the characteristics of the crack-tip conditions. (author)

Ankle Joint Contact Loads and Displacement With Progressive Syndesmotic Injury.

Science.gov (United States)

Hunt, Kenneth J; Goeb, Yannick; Behn, Anthony W; Criswell, Braden; Chou, Loretta

2015-09-01

Ligamentous injuries to the distal tibiofibular syndesmosis are predictive of long-term ankle dysfunction. Mild and moderate syndesmotic injuries are difficult to stratify, and the impact of syndesmosis injury on the magnitude and distribution of forces within the ankle joint during athletic activities is unknown. Eight below-knee cadaveric specimens were tested in the intact state and after sequential sectioning of the following ligaments: anterior-inferior tibiofibular, anterior deltoid (1 cm), interosseous/transverse (IOL/TL), posterior-inferior tibiofibular, and whole deltoid. In each condition, specimens were loaded in axial compression to 700 N and then externally rotated to 20 N·m torque. During axial loading and external rotation, both the fibula and the talus rotated significantly after each ligament sectioning as compared to the intact condition. After IOL/TL release, a significant increase in posterior translation of the fibula was observed, although no syndesmotic widening was observed. Mean tibiotalar contact pressure increased significantly after IOL/TL release, and the center of pressure shifted posterolaterally, relative to more stable conditions, after IOL/TL release. There were significant increases in mean contact pressure and peak pressure along with a reduction in contact area with axial loading and external rotation as compared to axial loading alone for all 5 conditions. Significant increases in tibiotalar contact pressures occur when external rotation stresses are added to axial loading. Moderate and severe injuries are associated with a significant increase in mean contact pressure combined with a shift in the center of pressure and rotation of the fibula and talus. Considerable changes in ankle joint kinematics and contact mechanics may explain why moderate syndesmosis injuries take longer to heal and are more likely to develop long-term dysfunction and, potentially, ankle arthritis. © The Author(s) 2015.

Mechanical loading prevents the stimulating effect of IL-1{beta} on osteocyte-modulated osteoclastogenesis

Energy Technology Data Exchange (ETDEWEB)

Kulkarni, Rishikesh N.; Bakker, Astrid D.; Everts, Vincent [Department of Oral Cell Biology, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University Amsterdam, Research Institute MOVE, Amsterdam (Netherlands); Klein-Nulend, Jenneke, E-mail: j.kleinnulend@acta.nl [Department of Oral Cell Biology, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University Amsterdam, Research Institute MOVE, Amsterdam (Netherlands)

2012-03-30

Highlights: Black-Right-Pointing-Pointer Osteocyte incubation with IL-1{beta} stimulated osteocyte-modulated osteoclastogenesis. Black-Right-Pointing-Pointer Conditioned medium from IL-1{beta}-treated osteocytes increased osteoclastogenesis. Black-Right-Pointing-Pointer IL-1{beta} upregulated RANKL and downregulated OPG gene expression by osteocytes. Black-Right-Pointing-Pointer CYR61 is upregulated in mechanically stimulated osteocytes. Black-Right-Pointing-Pointer Mechanical loading of osteocytes may abolish IL-1{beta}-induced osteoclastogenesis. -- Abstract: Inflammatory diseases such as rheumatoid arthritis are often accompanied by higher plasma and synovial fluid levels of interleukin-1{beta} (IL-1{beta}), and by increased bone resorption. Since osteocytes are known to regulate bone resorption in response to changes in mechanical stimuli, we investigated whether IL-1{beta} affects osteocyte-modulated osteoclastogenesis in the presence or absence of mechanical loading of osteocytes. MLO-Y4 osteocytes were pre-incubated with IL-1{beta} (0.1-1 ng/ml) for 24 h. Cells were either or not subjected to mechanical loading by 1 h pulsating fluid flow (PFF; 0.7 {+-} 0.3 Pa, 5 Hz) in the presence of IL-1{beta} (0.1-1 ng/ml). Conditioned medium was collected after 1 h PFF or static cultures. Subsequently mouse bone marrow cells were seeded on top of the IL-1{beta}-treated osteocytes to determine osteoclastogenesis. Conditioned medium from mechanically loaded or static IL-1{beta}-treated osteocytes was added to co-cultures of untreated osteocytes and mouse bone marrow cells. Gene expression of cysteine-rich protein 61 (CYR61/CCN1), receptor activator of nuclear factor kappa-B ligand (RANKL), and osteoprotegerin (OPG) by osteocytes was determined immediately after PFF. Incubation of osteocytes with IL-1{beta}, as well as conditioned medium from static IL-1{beta}-treated osteocytes increased the formation of osteoclasts. However, conditioned medium from mechanically loaded IL

Mechanical loading prevents the stimulating effect of IL-1β on osteocyte-modulated osteoclastogenesis

International Nuclear Information System (INIS)

Kulkarni, Rishikesh N.; Bakker, Astrid D.; Everts, Vincent; Klein-Nulend, Jenneke

2012-01-01

Highlights: ► Osteocyte incubation with IL-1β stimulated osteocyte-modulated osteoclastogenesis. ► Conditioned medium from IL-1β-treated osteocytes increased osteoclastogenesis. ► IL-1β upregulated RANKL and downregulated OPG gene expression by osteocytes. ► CYR61 is upregulated in mechanically stimulated osteocytes. ► Mechanical loading of osteocytes may abolish IL-1β-induced osteoclastogenesis. -- Abstract: Inflammatory diseases such as rheumatoid arthritis are often accompanied by higher plasma and synovial fluid levels of interleukin-1β (IL-1β), and by increased bone resorption. Since osteocytes are known to regulate bone resorption in response to changes in mechanical stimuli, we investigated whether IL-1β affects osteocyte-modulated osteoclastogenesis in the presence or absence of mechanical loading of osteocytes. MLO-Y4 osteocytes were pre-incubated with IL-1β (0.1–1 ng/ml) for 24 h. Cells were either or not subjected to mechanical loading by 1 h pulsating fluid flow (PFF; 0.7 ± 0.3 Pa, 5 Hz) in the presence of IL-1β (0.1–1 ng/ml). Conditioned medium was collected after 1 h PFF or static cultures. Subsequently mouse bone marrow cells were seeded on top of the IL-1β-treated osteocytes to determine osteoclastogenesis. Conditioned medium from mechanically loaded or static IL-1β-treated osteocytes was added to co-cultures of untreated osteocytes and mouse bone marrow cells. Gene expression of cysteine-rich protein 61 (CYR61/CCN1), receptor activator of nuclear factor kappa-B ligand (RANKL), and osteoprotegerin (OPG) by osteocytes was determined immediately after PFF. Incubation of osteocytes with IL-1β, as well as conditioned medium from static IL-1β-treated osteocytes increased the formation of osteoclasts. However, conditioned medium from mechanically loaded IL-1β-treated osteocytes prevented osteoclast formation. Incubation with IL-1β upregulated RANKL and downregulated OPG gene expression by static osteocytes. PFF upregulated

Numerical and experimental characterization of ceramic pebble beds under cycling mechanical loading

Energy Technology Data Exchange (ETDEWEB)

Pupeschi, S., E-mail: pupeschi.simone@hotmail.it [Institute for Applied Materials, Karlsruhe Institute of Technology (KIT) (Germany); Knitter, R.; Kamlah, M. [Institute for Applied Materials, Karlsruhe Institute of Technology (KIT) (Germany); Gan, Y. [School of Civil Engineering, The University of Sydney, Sydney, NSW, 2006 (Australia)

2016-11-15

Highlights: • The effect of cyclic loading on the mechanical response of pebble beds was assessed. • Numerical simulations were performed with KIT-DEM code. • The numerical simulations were compared with the experimental outcomes. • A good qualitative agreement between experimental and simulation results was found. • The pebble size distribution affects the mechanical response of the assemblies. - Abstract: All solid breeder concepts considered to be tested in ITER (International Thermonuclear Experimental Reactor), make use of lithium-based ceramics in the form of pebble-packed beds as tritium breeder. A thorough understanding of the thermal and mechanical properties of the ceramic pebble beds under fusion relevant conditions is essential for the design of the breeder blanket modules of future fusion reactors. In this study, the effect of cyclic loading on the mechanical behaviour of pebble bed assemblies was investigated using a Discrete Element Method (DEM) code. The numerical simulations were compared with the experimental outcomes. The results of numerical simulations show that the pebble size distribution affects noticeably the stress-strain behaviour of the assemblies. A good qualitative agreement between experimental and simulation results was found in terms of difference between residual strains of consecutive cycles. An increase of the oedometric modulus with the compressive load was observed for all investigated compositions in both experimental and DEM simulations. The numerical results show an increase of the oedometric modulus (E) with progressive compaction of the assemblies due to the cycling loading, while no significant influence of the pebbles size distribution was observed.

Mechanical loading of the gymnast’s motor system during swings on rings

Directory of Open Access Journals (Sweden)

R Serafin

2008-12-01

Full Text Available The aim of this work was to identify the mechanical loading of the gymnast’s motor system during forward and backward swings on gymnastic rings. A junior gymnast of the First Class, aged 14, with body mass 53.1 kg and body length 1.61 m, participated in the study. He executed a series of ten cyclic swing movements on rings with his maximum amplitude. Kinematic variables of the gymnast’s centre of mass (COM as well as reaction forces in the cables were measured and synchronized using the SIMI MOTION movement analysis system. Two separate phases of mechanical loading of the motor system have been identified: resistance phase and non resistance phase. In the non resistance phase the gymnast attains similar values of the COM’s momentum but different angular displacements. In the resistance phase the forces acting on the motor system have their maximum. They amount to 5.5 BW for the forward swing and 6.5 BW for the backward swing movement. The maximum rate of change of the force for forward and backward swing is 42.6 BWs-1 and 67.4 BWs-1, respectively. These two variables differentiate the mechanical loading of the gymnast’s motor system between forward and backward swings. The reaction force produced by the gymnast is significantly greater during the execution of forward swings. It seems probable that horizontal displacements of COM may be the factor responsible for reduction of the mechanical loading experienced by the gymnast.

Effect of kenaf short fiber loading on mechanical properties of biocomposites

Science.gov (United States)

Andilolo, J.; Nikmatin, S.; Nugroho, N.; Alatas, H.; Wismogroho, A. S.

2017-05-01

The research of biocomposite product with kenaf (Hibiscus cannabinus) short fiber as a filler and Acrylonitrile Butadiene Styrene (ABS) as the matrix had been done to understand the mechanical properties of this material. Kenaf short fiber was obtained from mechanical sieving after doing the mechanical milling. TAPPI method has been done to determine the chemical properties. In order to form a granular biocomposite a single screw extruder was performed with a variation of particle loading 10 and 15%. The original of acrylonitrile butadiene styrene (ABS) has been used as matrix. The fabrication of speciment had been done by molding injection process. Mechanical properties test was done by ASTM standarization. The results showed the density of the fibers of 1.008 g/cm3 with a fiber length of 897.07 µm and a diameter of 66.38 µm. Tensile strength of kenaf short fiber loading 10 and 15% was 23.522 ± 8.36 MPa and 20.739 ± 6.79 MPa, respectively. The tensile properties showed a decreasing trend as the fiber loading was increased. The values of impact strength were 68.657 ± 4.89 kJ m-2 and 82.090 ± 5.56 kJ m-2, respectively and the hardness values were 96.60 ± 6.03 HR and 105.20 ± 13.17 HR, respectively. Kenaf fiber can be a good reinforcement candidate for high performance polymer bio-composites.

Dynamic mechanical behaviour of nanoparticle loaded biodegradable PVA films for vaginal drug delivery.

Science.gov (United States)

Traore, Yannick L; Fumakia, Miral; Gu, Jijin; Ho, Emmanuel A

2018-03-01

In this study, we investigated the viscoelastic and mechanical behaviour of polyvinyl alcohol films formulated along with carrageenan, plasticizing agents (polyethylene glycol and glycerol), and when loaded with nanoparticles as a model for potential applications as microbicides. The storage modulus, loss modulus and glass transition temperature were determined using a dynamic mechanical analyzer. Films fabricated from 2% to 5% polyvinyl alcohol containing 3 mg or 5 mg of fluorescently labeled nanoparticles were evaluated. The storage modulus and loss modulus values of blank films were shown to be higher than the nanoparticle-loaded films. Glass transition temperature determined using the storage modulus, and loss modulus was between 40-50℃ and 35-40℃, respectively. The tensile properties evaluated showed that 2% polyvinyl alcohol films were more elastic but less resistant to breaking compared to 5% polyvinyl alcohol films (2% films break around 1 N load and 5% films break around 7 N load). To our knowledge, this is the first study to evaluate the influence of nanoparticle and film composition on the physico-mechanical properties of polymeric films for vaginal drug delivery.

Mechanical Behavior of Shale Rock under Uniaxial Cyclic Loading and Unloading Condition

Directory of Open Access Journals (Sweden)

Baoyun Zhao

2018-01-01

Full Text Available In order to investigate the mechanical behavior of shale rock under cyclic loading and unloading condition, two kinds of incremental cyclic loading tests were conducted. Based on the result of the short-term uniaxial incremental cyclic loading test, the permanent residual strain, modulus, and damage evolution were analyzed firstly. Results showed that the relationship between the residual strains and the cycle number can be expressed by an exponential function. The deformation modulus E50 and elastic modulus ES first increased and then decreased with the peak stress under the loading condition, and both of them increased approximately linearly with the peak stress under the unloading condition. On the basis of the energy dissipation, the damage variables showed an exponential increasing with the strain at peak stress. The creep behavior of the shale rock was also analyzed. Results showed that there are obvious instantaneous strain, decay creep, and steady creep under each stress level and the specimen appears the accelerated creep stage under the 4th stress of 51.16 MPa. Based on the characteristics of the Burgers creep model, a viscoelastic-plastic creep model was proposed through viscoplastic mechanics, which agrees very well with the experimental results and can better describe the creep behavior of shale rock better than the Burgers creep model. Results can provide some mechanics reference evidence for shale gas development.

Identifying interactive effects of task demands in lifting on estimates of in vivo low back joint loads.

Science.gov (United States)

Gooyers, Chad E; Beach, Tyson A C; Frost, David M; Howarth, Samuel J; Callaghan, Jack P

2018-02-01

This investigation examined interactions between the magnitude of external load, movement speed and (a)symmetry of load placement on estimates of in vivo joint loading in the lumbar spine during simulated occupational lifting. Thirty-two participants with manual materials handling experience were included in the study. Three-dimensional motion data, ground reaction forces, and activation of six bilateral trunk muscle groups were captured while participants performed lifts with two loads at two movement speeds and using two load locations. L4-L5 joint compression and shear force-time histories were estimated using an EMG-assisted musculoskeletal model of the lumbar spine. Results from this investigation provide strong evidence that known mechanical low back injury risk factors should not be viewed in isolation. Rather, injury prevention efforts need to consider the complex interactions that exist between external task demands and their combined influence on internal joint loading. Copyright © 2017 Elsevier Ltd. All rights reserved.

Validation of an instrumented dummy to assess mechanical aspects of discomfort during load carriage.

Directory of Open Access Journals (Sweden)

Patrick D Wettenschwiler

Full Text Available Due to the increasing load in backpacks and other load carriage systems over the last decades, load carriage system designs have to be adapted accordingly to minimize discomfort and to reduce the risk of injury. As subject studies are labor-intensive and include further challenges such as intra-subject and inter-subject variability, we aimed to validate an instrumented dummy as an objective laboratory tool to assess the mechanical aspects of discomfort. The validation of the instrumented dummy was conducted by comparison with a recent subject study. The mechanical parameters that characterize the static and dynamic interaction between backpack and body during different backpack settings were compared. The second aim was to investigate whether high predictive power (coefficient of determination R2>0.5 in assessing the discomfort of load carriage systems could be reached using the instrumented dummy. Measurements were conducted under static conditions, simulating upright standing, and dynamic conditions, simulating level walking. Twelve different configurations of a typical load carriage system, a commercially available backpack with a hip belt, were assessed. The mechanical parameters were measured in the shoulder and the hip region of the dummy and consisted of average pressure, peak pressure, strap force and relative motion between the system and the body. The twelve configurations consisted of three different weights (15kg, 20kg, and 25kg, combined with four different hip belt tensions (30N, 60N, 90N, and 120N. Through the significant (p<0.05 correlation of the mechanical parameters measured on the dummy with the corresponding values of the subject study, the dummy was validated for all static measurements and for dynamic measurements in the hip region to accurately simulate the interaction between the human body and the load carriage system. Multiple linear regressions with the mechanical parameters measured on the dummy as independent

Ad-hoc Network of Smart Sensors for Mechanical Load Measurement

Directory of Open Access Journals (Sweden)

Manuel A. Vieira

2016-07-01

Full Text Available Strain gauges load cells are transducers devices capable of converting changes in applied mechanical load into an electrical analog signal. Those devices have a large spectrum of applications ranging from domestic to industrial or even medical appliances just to name a few. In this work, they are used in the electronic instrumentation of a force platform that will be used to carry out the analysis and characterization of human biomechanical walking. In this platform, four load cells are installed, each one capable of measuring forces along two different axis. A total of eight strain-gauges per load cell are employed. Hence, analog signal transmission, besides requiring a large number of connection wires, is prone to interference and noise. Moreover, with this solution, scalability requires severe changes in the connection topology. In order to circumvent those problems, an alternative in-situ signal conditioning and digital data transmission system was devised. This approach, as far as investigated, presents an innovative solution to signal conditioning and data transmission for load-cells. In particular, the presented solution allows the creation of an ad-hoc network of load cells, using the I²C protocol with a master interface that allows the users to interact and change the parameters of each load cell. This instrumentation structure has been successfully tested and the obtained results are documented in this article.

Stresses from pressure, radial, and moment loads in cylinder-to-cylinder vessel by a finite plate method

International Nuclear Information System (INIS)

Brown, S.J.; Fox, M.E.

1977-08-01

A structural problem that has received continued interest and development over the last several decades is the determination of stresses in two normally intersecting cylindrical shells subjected to internal pressure and external loading. In nuclear pressure vessels the external loading of the vessel through the attachment is encountered in thermal interaction, seismic loading and various postulated rupture or failure mechanisms. A simple technique, the Finite Plate Method, (FPM) is presented to analyze stresses in cylinder-to-cylinder junctures. The approach uses shallow shell formulations and a three term series expansion plate formulation, which limits the range of applicability. It is felt that the value of the method is its accuracy, economy, and ease in modeling a structure which falls within the range of applicability. Another appealing feature of the method is that its simplistic approach of superposition of results permits an easy extension to include additional loads not treated. For those mechanical loadings not developed, it is felt that their effect can either be accounted for by the mechanisms discussed or by simple calculations. Generally, the stresses resulting from torsional or transverse shear are small compared to the loads discussed, however, these shear effects may be included. Finally, in the instance of thermal stress within the cylinder-to-cylinder structure, it has been shown in an unpublished study by Brown that the FPM yields very good results for the range of curvatures discussed

Properties and Semicrystalline Structure Evolution of Polypropylene/Montmorillonite Nanocomposites under Mechanical Load

DEFF Research Database (Denmark)

Stribeck, Norbert; Zeinolebadi, Ahmad; Ganjaee Sari, Morteza

2012-01-01

Small-angle X-ray scattering (SAXS) monitors tensile and load-cycling tests of metallocene isotactic polypropylene (PP), a blend of PP and montmorillonite (MMT), and two block copolymer compatibilized PP/MMT nanocomposites. Mechanical properties of the materials are similar, but the semicrystalline......%. Other results concern the evolution of Strobl’s block structure and void formation during tensile loading....

Thin circular cylinder under axisymmetrical thermal and mechanical loading

International Nuclear Information System (INIS)

Arnaudeau, F.; Zarka, J.; Gerij, J.

1977-01-01

To assess structural integrity of components subjected to cyclic thermal loadings one must look at thermal ratchetting as a possible failure mode. Considering a thin circular cylinder subjected to constant internal pressure and cyclically varying thermal gradient through the thickness Bree, J. Strain Analysis 2 (1967) No.3, obtained a diagram that serves as a foundation for many design rules (e.g.: ASME code). The upper part of the french LMFBR main vessel is subjected to an axisymmetrical axial thermal loading and an axial load (own weight). Operation of the reactor leads to cyclic variations of the axial thermal loading. The question that arises is whether or not the Bree diagram is realistic for such loading conditions. A special purpose computer code (Ratch) was developed to analyse a thin circular cylinder subjected to axisymmetrical mechanical and thermal loadings. The Mendelson's approach of this problem is followed. Classical Kirchoff-Love hypothesis of thin shells is used and a state of plane stress is assumed. Space integrations are performed by Gaussian quadrature in the axial direction and by Simpson's one third rule throughout the thickness. Thermoelastic-plastic constitutive equations are solved with an implicit scheme (Nguyen). Thermovisco-plastic constitutive equations are solved with an explicit time integration scheme (Treanor's algorithm especially fitted). A Bree type diagram is obtained for an axial step of temperature which varies cyclically and a sustained constant axial load. The material behavior is assumed perfectly plastic and creep effect is not considered. Results show that the domain where no ratchetting occurs is reduced when compared with the domain predicted by the Bree diagram

Mechanical and thermo-mechanical response of a lead-core bearing device subjected to different loading conditions

Directory of Open Access Journals (Sweden)

Zhelyazov Todor

2018-01-01

Full Text Available The contribution is focused on the numerical modelling, simulation and analysis of a lead-core bearing device for passive seismic isolation. An accurate finite element model of a lead-core bearing device is presented. The model is designed to analyse both mechanical and thermo-mechanical responses of the seismic isolator to different loading conditions. Specifically, the mechanical behaviour in a typical identification test is simulated. The response of the lead-core bearing device to circular sinusoidal paths is analysed. The obtained shear displacement – shear force relationship is compared to experimental data found in literature sources. The hypothesis that heating of the lead-core during cyclic loading affects the degrading phenomena in the bearing device is taken into account. Constitutive laws are defined for each material: lead, rubber and steel. Both predefined constitutive laws (in the used general–purpose finite element code and semi-analytical procedures aimed at a more accurate modelling of the constitutive relations are tested. The results obtained by finite element analysis are to be further used to calibrate a macroscopic model of the lead-core bearing device seen as a single-degree-of-freedom mechanical system.

The mechanical design and fabrication of a ridge-loaded waveguide for an RFQ

International Nuclear Information System (INIS)

Valdiviez, R.; Roybal, P.; Clark, B.; Martinez, F.; Casillas, D.; Gonzales, G.; Tafoya, J.

1998-01-01

A Radio Frequency Quadrupole (RFQ) accelerator with an RF power input of 2 MW and an H + beam output current of 100 mAmps at 6.7 MeV, continuous duty factor utilizes twelve nearly identical ridge-loaded waveguides. The ridge-loaded, vacuum waveguides couple the RF power to the RFQ accelerating cavity. The mechanical design and fabrication of the ridge-loaded waveguides are the topics of this paper

The Effects of Load Carriage and Muscle Fatigue on Lower-Extremity Joint Mechanics

Science.gov (United States)

Wang, He; Frame, Jeff; Ozimek, Elicia; Leib, Daniel; Dugan, Eric L.

2013-01-01

Military personnel are commonly afflicted by lower-extremity overuse injuries. Load carriage and muscular fatigue are major stressors during military basic training. Purpose: To examine effects of load carriage and muscular fatigue on lower-extremity joint mechanics during walking. Method: Eighteen men performed the following tasks: unloaded…

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.

Elastic-plastic Fracture Mechanics Assessment of nozzle corners submitted to thermal shock loading

International Nuclear Information System (INIS)

Chapuliot, S.; Marie, S.

2016-01-01

This paper focuses on the development of a simplified analytical scheme for the elastic-plastic Fracture Mechanics Assessment of large nozzle corners. Within that frame, following the specific numerical effort performed for the definition of a Stress Intensity Factor compendium, complementary elastic-plastic developments are proposed here for the consideration of the thermal shock loading in the elastic-plastic domain: this type of loading is a major loading for massive structures such as nozzle corners of large components. Thus, an important numerical was performed in order to extend the applicability domain of existing analytical schemes to those complex geometries. The final formulation is a simple one, applicable to a large variety of materials and geometrical configurations as long as the structure is large and the defect remains small in comparison to the internal radius of the nozzle. - Highlights: • Fracture Mechanics Assessment of large nozzle corners. • Elastic-plastic Stress Intensity Factor determination under thermal shock loading. • Semi-analytical schemes for J calculation.

High temperature fatigue behaviour of TZM molybdenum alloy under mechanical and thermomechanical cyclic loads

International Nuclear Information System (INIS)

Shi, H.J.; Niu, L.S.; Korn, C.; Pluvinage, G.

2000-01-01

High temperature isothermal mechanical fatigue and in-phase thermomechanical fatigue (TMF) tests in load control were carried out on a molybdenum-based alloy, one of the best known of the refractory alloys, TZM. The stress-strain response and the cyclic life of the material were measured during the tests. The fatigue lives obtained in the in-phase TMF tests are lower than those obtained in the isothermal mechanical tests at the same load amplitude. It appears that an additional damage is produced by the reaction of mechanical stress cycles and temperature cycles in TMF situation. Ratcheting phenomenon occurred during the tests with an increasing creep rate and it was dependent on temperature and load amplitude. A model of lifetime prediction, based on the Woehler-Miner law, was discussed. Damage coefficients that are functions of the maximum temperature and the variation of temperature are introduced in the model so as to evaluate TMF lives in load control. With this method the lifetime prediction gives results corresponding well to experimental data

Mechanical properties of the human spinal cord under the compressive loading.

Science.gov (United States)

Karimi, Alireza; Shojaei, Ahmad; Tehrani, Pedram

2017-12-01

The spinal cord as the most complex and critical part of the human body is responsible for the transmission of both motor and sensory impulses between the body and the brain. Due to its pivotal role any types of physical injury in that disrupts its function following by shortfalls, including the minor motor and sensory malfunctions as well as complicate quadriplegia and lifelong ventilator dependency. In order to shed light on the injuries to the spinal cord, the application of the computational models to simulate the trauma impact loading to that are deemed required. Nonetheless, it has not been fulfilled since there is a paucity of knowledge about the mechanical properties of the spinal cord, especially the cervical one, under the compressive loading on the grounds of the difficulty in obtaining this tissue from the human body. This study was aimed at experimentally measuring the mechanical properties of the human cervical spinal cord of 24 isolated fresh samples under the unconfined compressive loading at a relatively low strain rate. The stress-strain data revealed the elastic modulus and maximum/failure stress of 40.12±6.90 and 62.26±5.02kPa, respectively. Owing to the nonlinear response of the spinal cord, the Yeoh, Ogden, and Mooney-Rivlin hyperelastic material models have also been employed. The results may have implications not only for understanding the linear elastic and nonlinear hyperelastic mechanical properties of the cervical spinal cord under the compressive loading, but also for providing a raw data for investigating the injury as a result of the trauma thru the numerical simulations. Copyright © 2017 Elsevier B.V. All rights reserved.

Intelligent Control of Diesel Generators Using Gain-Scheduling Based on Online External-Load Estimation

DEFF Research Database (Denmark)

Mai, Christian; Jepsen, Kasper Lund; Yang, Zhenyu

2014-01-01

The development of an intelligent control solution for a wide range of diesel generators is discussed. Compared with most existing solutions, the advantages of the proposed solution lie in two folds: (i) The proposed control has the plug-and-play capability which is reflected by an automatic...... recognition procedure when it is plugged into a specific diesel generator, such that some extensive manual-tuning of the installed controller can be significantly reduced; (ii) The proposed control has an real-time adaptability by using the online external load estimation, such that the integrated system can...... keep a consistent performance for a wide range of operating conditions. Technically, a general nonlinear dynamic model is firstly developed based on fundamental principles of diesel generators. Then, the system parameters of this model can be identified experimentally or partially retrieved from...

Compressive damage mechanism of GFRP composites under off-axis loading: Experimental and numerical investigations

DEFF Research Database (Denmark)

Zhou, H.W.; Li, H.Y.; Gui, L.L.

2013-01-01

the angle between the fiber direction and the loading vector goes from 0° to 45° (by 2.3–2.6 times), and then slightly increases (when the angle approaches 80–90°). At the low angles between the fiber and the loading vector, fiber buckling and kinking are the main mechanisms of fiber failure....... With increasing the angle between the fiber and applied loading, failure of glass fibers is mainly controlled by shear cracking. For the computational analysis of the damage mechanisms, 3D multifiber unit cell models of GFRP composites and X-FEM approach to the fracture modeling were used. The computational...

Progressive damage analysis of carbon/epoxy laminates under couple laser and mechanical loading

Directory of Open Access Journals (Sweden)

Wanlei Liu

Full Text Available A multiscale model based bridge theory is proposed for the progressive damage analysis of carbon/epoxy laminates under couple laser and mechanical loading. The ablation model is adopted to calculate ablation temperature changing and ablation surface degradation. The polynomial strengthening model of matrix is used to improve bridging model for reducing parameter input. Stiffness degradation methods of bridging model are also improved in order to analyze the stress redistribution more accurately when the damage occurs. Thermal-mechanical analyses of the composite plate are performed using the ABAQUS/Explicit program with the developed model implemented in the VUMAT. The simulation results show that this model can be used to proclaim the mesoscale damage mechanism of composite laminates under coupled loading. Keywords: Laser irradiation, Multiscale analysis, Bridge model, Thermal-mechanical

Hypoxic ischemia encephalopathy leading to external hydrocephalus and the cerebral atrophy: mechanism and differential diagnosis

International Nuclear Information System (INIS)

Huang Zhenglin; Mo Xiaorong

2002-01-01

Objective: It is a study of the mechanism and differential diagnosis of the infant external hydrocephalus and cerebral atrophy. Methods: In total 84 cases of neonatal hypoxic ischemia encephalopathy followed by infant external hydrocephalus were investigated, among which 26 patients gradually were found having developed cerebral atrophy in follow up. Results: Characteristic dilation of the frontal-parietal subarachnoid space and the adjacent cistern was noted on the CT images of the external hydrocephalus. CT revealed the enlarged ventricle besides the dilated subarachnoid space in the cases of cerebral atrophy, while these two entities were indistinguishable on CT in the early stage. Conclusion: Clinical manifestations make a major differential diagnosis of the external hydrocephalus and cerebral atrophy: tic and mild delayed development of locomotion over major presentation of external hydrocephalus, while cerebral atrophy is featured by remarkable dysnoesia and severe delayed development of locomotion. In addition, hemiplegia and increased muscular tension are presented in a few cases of cerebral atrophy

Direct Time Domain Numerical Analysis of Transient Behavior of a VLFS during Unsteady External Loads in Wave Condition

Directory of Open Access Journals (Sweden)

Yong Cheng

2014-01-01

Full Text Available The transient response of the VLFS subjected to arbitrary external load is systematically investigated by a direct time domain modal expansion method, in which the BEM solutions based on time domain Kelvin sources are used for hydrodynamic forces. In the analysis, the time domain free-surface Green functions with sufficient accuracy are rapidly evaluated in finite water depth by the interpolation-tabulation method, and the boundary integral equation with a quarter VLFS model is established taking advantage of symmetry of flow field and structure. The validity of the present method is verified by comparing with the time histories of vertical displacements of the VLFS during a mass drop and airplane landing and takeoff in still water conditions, respectively. Then the developed numerical scheme is used in wave conditions to study the combined action taking into account the mass drop/airplane landing/takeoff loads as well as incident wave action. It is found that the elevation of structural waves due to mass drop load can be significantly changed near the impact region, while the vertical motion of runway in wave conditions is dominant as compared with that only generated by airplane.

The effect og aging and mechanical loading on the metabolism og articular cartilage

DEFF Research Database (Denmark)

Jørgensen, Adam El Mongy; Kjær, Michael; Heinemeier, Katja Maria

2017-01-01

Objective. The morphology of articular cartilage (AC) enables painless movement. Aging and mechanical loading are believed to influence development of osteoarthritis (OA), yet the connection remains unclear. Methods. This narrative review describes the current knowledge regarding this area......, with the literature search made on PubMed using appropriate keywords regarding AC, age, and mechanical loading. Results. Following skeletal maturation, chondrocyte numbers decline while increasing senescence occurs. Lower cartilage turnover causes diminished maintenance capacity, which produces accumulation...... collagen network damage and proteoglycan loss, leading to irreversible cartilage destruction because of lack of regenerative capacity. Catabolic pathways involve inflammation and the transcription factor nuclear factor-κB. Thus, age seems to be a predisposing factor for OA, with mechanical overload being...

The Effect of Aging and Mechanical Loading on the Metabolism of Articular Cartilage

DEFF Research Database (Denmark)

Jørgensen, Adam El Mongy; Kjaer, Michael; Heinemeier, Katja Maria

2017-01-01

Objective. The morphology of articular cartilage (AC) enables painless movement. Aging and mechanical loading are believed to influence development of osteoarthritis (OA), yet the connection remains unclear. Methods. This narrative review describes the current knowledge regarding this area......, with the literature search made on PubMed using appropriate keywords regarding AC, age, and mechanical loading. Results. Following skeletal maturation, chondrocyte numbers decline while increasing senescence occurs. Lower cartilage turnover causes diminished maintenance capacity, which produces accumulation...... collagen network damage and proteoglycan loss, leading to irreversible cartilage destruction because of lack of regenerative capacity. Catabolic pathways involve inflammation and the transcription factor nuclear factor-κB. Thus, age seems to be a predisposing factor for OA, with mechanical overload being...

DACS II - A distributed thermal/mechanical loads data acquisition and control system

Science.gov (United States)

Zamanzadeh, Behzad; Trover, William F.; Anderson, Karl F.

1987-01-01

A distributed data acquisition and control system has been developed for the NASA Flight Loads Research Facility. The DACS II system is composed of seven computer systems and four array processors configured as a main computer system, three satellite computer systems, and 13 analog input/output systems interconnected through three independent data networks. Up to three independent heating and loading tests can be run concurrently on different test articles or the entire system can be used on a single large test such as a full scale hypersonic aircraft. Thermal tests can include up to 512 independent adaptive closed loop control channels. The control system can apply up to 20 MW of heating to a test specimen while simultaneously applying independent mechanical loads. Each thermal control loop is capable of heating a structure at rates of up to 150 F per second over a temperature range of -300 to +2500 F. Up to 64 independent mechanical load profiles can be commanded along with thermal control. Up to 1280 analog inputs monitor temperature, load, displacement and strain on the test specimens with real time data displayed on up to 15 terminals as color plots and tabular data displays. System setup and operation is accomplished with interactive menu-driver displays with extensive facilities to assist the users in all phases of system operation.

Mechanical load on the low back and shoulders during pushing and pulling of two-wheeled waste containers compared with lifting and carrying of bags and bins.

Science.gov (United States)

Schibye, B; Søgaard, K; Martinsen, D; Klausen, K

2001-08-01

Compare the mechanical load on the low back and shoulders during pushing and pulling a two-wheeled container with the load during lifting and carrying the same amount of waste. Only little is known about risk factors and mechanical loads during push/pull operations. A complete 2(3) factor push/pull experiment. A two-wheeled container with 25 or 50 kg was pushed in front of and pulled behind the body by seven waste collectors. Further, the same subjects lifted and carried a paper bag and a dustbin both loaded with 7 and 25 kg. All operations were video recorded and the push/pull force was measured by means of a three-dimensional force transducer. Peak Motus and Watbak software were used for digitising and calculation of torque at L4/L5 and the shoulder joints and compression and shear forces at L4/L5. During pushing and pulling the compression at L4/L5 is from 605 to 1445 N. The extension torque at L4/L5 produced by the push/pull force is counteracted by the forward leaning of the upper body. The shear force is below 202 N in all situations. The torque at the shoulders is between 1 and 38 Nm. In the present experiments the torques at the low back and the shoulders are low during pushing and pulling. No relation exists between the size of the external force and the torque at the low back and the shoulder. Pushing and pulling are common in many workplaces and have often replaced lifting and carrying situations. This has emphasised the need for more knowledge of the internal mechanical load on the body during these activities.

The mechanical stability of retained austenite in low-alloyed TRIP steel under shear loading

Energy Technology Data Exchange (ETDEWEB)

Blondé, R., E-mail: r.j.p.blonde@tudelft.nl [Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands); Materials Innovation Institute, Mekelweg 2, 2628 CD Delft (Netherlands); Jimenez-Melero, E., E-mail: enrique.jimenez-melero@manchester.ac.uk [Dalton Cumbrian Facility, The University of Manchester, Westlakes Science and Technology Park, Moor Row, Cumbria CA24 3HA (United Kingdom); Zhao, L., E-mail: lie.zhao@tudelft.nl [Materials Innovation Institute, Mekelweg 2, 2628 CD Delft (Netherlands); Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft (Netherlands); Schell, N., E-mail: norbert.schell@hzg.de [Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Max Planck Strasse 1, 21502 Geesthacht (Germany); Brück, E., E-mail: e.h.bruck@tudelft.nl [Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands); Zwaag, S. van der, E-mail: s.vanderzwaag@tudelft.nl [Novel Aerospace Materials Group, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft (Netherlands); Dijk, N.H. van, E-mail: n.h.vandijk@tudelft.nl [Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands)

2014-01-31

The microstructure evolution during shear loading of a low-alloyed TRIP steel with different amounts of the metastable austenite phase and its equivalent DP grade has been studied by in-situ high-energy X-ray diffraction. A detailed powder diffraction analysis has been performed to probe the austenite-to-martensite transformation by characterizing simultaneously the evolution of the austenite phase fraction and its carbon concentration, the load partitioning between the austenite and the ferritic matrix and the texture evolution of the constituent phases. Our results show that for shear deformation the TRIP effect extends over a significantly wider deformation range than for simple uniaxial loading. A clear increase in average carbon content during the mechanically-induced transformation indicates that austenite grains with a low carbon concentration are least stable during shear loading. The observed texture evolution indicates that under shear loading the orientation dependence of the austenite stability is relatively weak, while it has previously been found that under tensile load the {110}〈001〉 component transforms preferentially. The mechanical stability of retained austenite in TRIP steel is found to be a complex interplay between the interstitial carbon concentration in the austenite, the grain orientation and the load partitioning.

The EPR-a comprehensive design concept against external events

International Nuclear Information System (INIS)

Stoll, U.; Waas, U.

2006-01-01

The main objective of design provisions against external hazards is to ensure that the safety functions required to bring the plant to safe shutdown are not inadmissibly affected by any external hazards that might be postulated for the intended site of the plant. In the design of the European Pressurized Water Reactor (EPR) particular attention was paid to external hazards such as earthquake, airplane crash, and explosion pressure wave. The standard EPR covers a large range of possible site conditions, the design earthquake enveloping safe shutdown earthquakes (SSE) to be expected for potential sites. The loads for the design basis airplane crash and - if required - for the design extension airplane crash as well as for external Explosion Pressure Wave are defined depending on site specific requirements. Protection against other external load cases such as extreme winds and external flooding is also included in the standard design

Effect of Cytokines on Osteoclast Formation and Bone Resorption during Mechanical Force Loading of the Periodontal Membrane

Directory of Open Access Journals (Sweden)

Hideki Kitaura

2014-01-01

Full Text Available Mechanical force loading exerts important effects on the skeleton by controlling bone mass and strength. Several in vivo experimental models evaluating the effects of mechanical loading on bone metabolism have been reported. Orthodontic tooth movement is a useful model for understanding the mechanism of bone remodeling induced by mechanical loading. In a mouse model of orthodontic tooth movement, TNF-α was expressed and osteoclasts appeared on the compressed side of the periodontal ligament. In TNF-receptor-deficient mice, there was less tooth movement and osteoclast numbers were lower than in wild-type mice. These results suggest that osteoclast formation and bone resorption caused by loading forces on the periodontal ligament depend on TNF-α. Several cytokines are expressed in the periodontal ligament during orthodontic tooth movement. Studies have found that inflammatory cytokines such as IL-12 and IFN-γ strongly inhibit osteoclast formation and tooth movement. Blocking macrophage colony-stimulating factor by using anti-c-Fms antibody also inhibited osteoclast formation and tooth movement. In this review we describe and discuss the effect of cytokines in the periodontal ligament on osteoclast formation and bone resorption during mechanical force loading.

Antimicrobial, Mechanical and Thermal Studies of Silver Particle-Loaded Polyurethane

Directory of Open Access Journals (Sweden)

Deepen Paul

2013-12-01

Full Text Available Silver-particle-incorporated polyurethane films were evaluated for antimicrobial activity towards two different bacteria: Escherichia coli (E. coli and Staphylococcus aureus (S. aureus. Distributed silver particles sourced from silver nitrate, silver lactate and preformed silver nanoparticles were mixed with polyurethane (PU and variously characterized by field emission scanning electron microscopy (FESEM, fourier transform infra-red (FTIR spectroscopy, X-ray diffraction (XRD and contact angle measurement. Antibacterial activity against E.coli was confirmed for films loaded with 10% (w/w AgNO3, 1% and 10% (w/w Ag lactate and preformed Ag nanoparticles. All were active against S. aureus, but Ag nanoparticles loaded with PU had a minor effect. The apparent antibacterial performance of Ag lactate-loaded PU is better than other Ag ion-loaded films, revealed from the zone of inhibition study. The better performance of silver lactate-loaded PU was the likely result of a porous PU structure. FESEM and FTIR indicated direct interaction of silver with the PU backbone, and XRD patterns confirmed that face-centred cubic-type silver, representative of Ag metal, was present. Young’s modulus, tensile strength and the hardness of silver containing PU films were not adversely affected and possibly marginally increased with silver incorporation. Dynamic mechanical analysis (DMA indicated greater thermal stability.

Load monitoring of aerospace structures utilizing micro-electro-mechanical systems for static and quasi-static loading conditions

International Nuclear Information System (INIS)

Martinez, M; Rocha, B; Li, M; Shi, G; Beltempo, A; Rutledge, R; Yanishevsky, M

2012-01-01

The National Research Council Canada (NRC) has worked on the development of structural health monitoring (SHM) test platforms for assessing the performance of sensor systems for load monitoring applications. The first SHM platform consists of a 5.5 m cantilever aluminum beam that provides an optimal scenario for evaluating the ability of a load monitoring system to measure bending, torsion and shear loads. The second SHM platform contains an added level of structural complexity, by consisting of aluminum skins with bonded/riveted stringers, typical of an aircraft lower wing structure. These two load monitoring platforms are well characterized and documented, providing loading conditions similar to those encountered during service. In this study, a micro-electro-mechanical system (MEMS) for acquiring data from triads of gyroscopes, accelerometers and magnetometers is described. The system was used to compute changes in angles at discrete stations along the platforms. The angles obtained from the MEMS were used to compute a second, third or fourth order degree polynomial surface from which displacements at every point could be computed. The use of a new Kalman filter was evaluated for angle estimation, from which displacements in the structure were computed. The outputs of the newly developed algorithms were then compared to the displacements obtained from the linear variable displacement transducers connected to the platforms. The displacement curves were subsequently post-processed either analytically, or with the help of a finite element model of the structure, to estimate strains and loads. The estimated strains were compared with baseline strain gauge instrumentation installed on the platforms. This new approach for load monitoring was able to provide accurate estimates of applied strains and shear loads. (paper)

Internal and External Triggering Mechanism of "Smart" Nanoparticle-Based DDSs in Targeted Tumor Therapy.

Science.gov (United States)

Qiana, Xian-Ling; Li, Jun; Wei, Ran; Lin, Hui; Xiong, Li-Xia

2018-05-09

Anticancer chemotherapeutics have a lot of problems via conventional drug delivery systems (DDSs), including non-specificity, burst release, severe side-effects, and damage to normal cells. Owing to its potential to circumventing these problems, nanotechnology has gained increasing attention in targeted tumor therapy. Chemotherapeutic drugs or genes encapsulated in nanoparticles could be used to target therapies to the tumor site in three ways: "passive", "active", and "smart" targeting. To summarize the mechanisms of various internal and external "smart" stimulating factors on the basis of findings from in vivo and in vitro studies. A thorough search of PubMed was conducted in order to identify the majority of trials, studies and novel articles related to the subject. Activated by internal triggering factors (pH, redox, enzyme, hypoxia, etc.) or external triggering factors (temperature, light of different wavelengths, ultrasound, magnetic fields, etc.), "smart" DDSs exhibit targeted delivery to the tumor site, and controlled release of chemotherapeutic drugs or genes. In this review article, we summarize and classify the internal and external triggering mechanism of "smart" nanoparticle-based DDSs in targeted tumor therapy, and the most recent research advances are illustrated for better understanding. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Silver nanoparticles-loaded activated carbon fibers using chitosan as binding agent: Preparation, mechanism, and their antibacterial activity

Energy Technology Data Exchange (ETDEWEB)

Tang, Chengli, E-mail: tcl-lily@mail.zjxu.edu.cn [College of Mechanical and Electrical Engineering, Jiaxing University, Jiaxing 314001 (China); Hu, Dongmei [College of Mechanical Science and Engineering, Jilin University, Changchun 130022 (China); Cao, Qianqian [College of Mechanical and Electrical Engineering, Jiaxing University, Jiaxing 314001 (China); Yan, Wei [Department of Environmental Science and Engineering, Xi’an Jiaotong University, Xi’an 710049 (China); Xing, Bo [College of Mechanical and Electrical Engineering, Jiaxing University, Jiaxing 314001 (China)

2017-02-01

Highlights: • Chitosan was firstly introduced as binding agent for AgNPs loading on ACF surface. • Molecular dynamics simulation was used to explore the AgNPs loading mechanism. • Loading mechanism was proposed based on the experimental and simulation results. • Antibacterial AgNPs-loaded ACF showed use potential for water disinfection. - Abstract: The effective and strong adherence of silver nanoparticles (AgNPs) to the substrate surface is pivotal to the practical application of those AgNPs-modified materials. In this work, AgNPs were synthesized through a green and facile hydrothermal method. Chitosan was introduced as the binding agent for the effective loading of AgNPs on activated carbon fibers (ACF) surface to fabricate the antibacterial material. Apart from conventional instrumental characterizations, i. e., scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), zeta potential and Brunauer-Emmett-Teller (BET) surface area measurement, molecular dynamics simulation method was also applied to explore the loading mechanism of AgNPs on the ACF surface. The AgNPs-loaded ACF material showed outstanding antibacterial activity for S. aureus and E. coli. The combination of experimental and theoretical calculation results proved chitosan to be a promising binding agent for the fabrication of AgNPs-loaded ACF material with excellent antibacterial activity.

micro-mechanical experimental investigation and modelling of strain and damage of argillaceous rocks under combined hydric and mechanical loads

International Nuclear Information System (INIS)

Wang, L.

2012-01-01

The hydro-mechanical behavior of argillaceous rocks, which are possible host rocks for underground radioactive nuclear waste storage, is investigated by means of micro-mechanical experimental investigations and modellings. Strain fields at the micrometric scale of the composite structure of this rock, are measured by the combination of environmental scanning electron microscopy, in situ testing and digital image correlation technique. The evolution of argillaceous rocks under pure hydric loading is first investigated. The strain field is strongly heterogeneous and manifests anisotropy. The observed nonlinear deformation at high relative humidity (RH) is related not only to damage, but also to the nonlinear swelling of the clay mineral itself, controlled by different local mechanisms depending on RH. Irreversible deformations are observed during hydric cycles, as well as a network of microcracks located in the bulk of the clay matrix and/or at the inclusion-matrix interface. Second, the local deformation field of the material under combined hydric and mechanical loadings is quantified. Three types of deformation bands are evidenced under mechanical loading, either normal to stress direction (compaction), parallel (microcracking) or inclined (shear). Moreover, they are strongly controlled by the water content of the material: shear bands are in particular prone to appear at high RH states. In view of understanding the mechanical interactions a local scale, the material is modeled as a composite made of non-swelling elastic inclusions embedded in an elastic swelling clay matrix. The internal stress field induced by swelling strain incompatibilities between inclusions and matrix, as well as the overall deformation, is numerically computed at equilibrium but also during the transient stage associated with a moisture gradient. An analytical micro-mechanical model based on Eshelby's solution is proposed. In addition, 2D finite element computations are performed. Results

Inner-Learning Mechanism Based Control Scheme for Manipulator with Multitasking and Changing Load

Directory of Open Access Journals (Sweden)

Fangzheng Xue

2014-05-01

Full Text Available With the rapid development of robot technology and its application, manipulators may face complex tasks and dynamic environments in the coming future, which leads to two challenges of control: multitasking and changing load. In this paper, a novel multicontroller strategy is presented to meet such challenges. The presented controller is composed of three parts: subcontrollers, inner-learning mechanism, and switching rules. Each subcontroller is designed with self-learning skills to fit the changing load under a special task. When a new task comes, switching rule reselects the most suitable subcontroller as the working controller to handle current task instead of the older one. Inner-learning mechanism makes the subcontrollers learn from the working controller when load changes so that the switching action causes smaller tracking error than the traditional switch controller. The results of the simulation experiments on two-degree manipulator show the proposed method effect.

Mechanical behavior of ultrafine-grained materials under combined static and dynamic loadings

Directory of Open Access Journals (Sweden)

Guo Y.Z.

2015-01-01

Full Text Available Ultrafine-grained (UFG materials have extensive prospects for engineering application due to their excellent mechanical properties. However, the grain size decrease reduces their strain hardening ability and makes UFG materials more susceptible to deformation instability such as shear localization. In most cases, critical shear strain is taken as the criterion for formation of shear localization under impact loading or adiabatic shear band (ASB. Recently, some researchers found that the formation of ASB was determined only by the dynamic loading process and had nothing to do with its static loading history. They proposed for coarse-grained metals a dynamic stored energy-based criterion for ASB and verified it by some experiments. In this study, we will focus on the shear localization behavior of UFG metals such as UFG titanium and magnesium alloy AZ31. Quasi-static loading and dynamic loading will be applied on the same specimen alternately. The shear localization behavior will be analyzed and the criterion of its formation will be evaluated.

Behavior of duplex stainless steel casting defects under mechanical loadings

International Nuclear Information System (INIS)

Jayet-Gendrot, S.; Gilles, P.

2000-01-01

Several components in the primary circuit of pressurized water reactors are made of cast duplex stainless steels. This material contains small casting defects, mainly shrinkage cavities, due to the manufacturing process. In safety analyses, the structural integrity of the components is studied under the most severe assumptions: presence of a large defect, accidental loadings and end-of-life material properties accounting for its thermal aging embrittlement at the service temperature. The casting defects are idealized as semi-circular surface cracks or notches that have envelope dimensions. In order to assess the real severity of the casting defects under mechanical loadings, an experimental program was carried out. It consisted of testing, under both cyclic and monotonic solicitations, three-point bend specimens containing either a natural defect (in the form of a localized cluster of cavities) or a machined notch having the dimensions of the cluster's envelope. The results show that shrinkage cavities are far less harmful than envelope notches thanks to the metal bridges between cavities. Under fatigue loadings, the generalized initiation of a cluster of cavities (defined when the cluster becomes a crack of the same global size) is reached for a number of cycles that is much higher than the one leading to the initiation of a notch. In the case of monotonic loadings, specimens with casting defects offer a very high resistance to ductile tearing. The tests are analyzed in order to develop a method that takes into account the behavior of casting defects in a more realistic fashion than by an envelope crack. Various approaches are investigated, including the search of equivalent defects or of criteria based on continuum mechanics concepts, and compared with literature data. This study shows the conservatism of current safety analyses in modeling casting defects by envelope semi-elliptical cracks and contributes to the development of alternative approaches. (orig.)

Microscale experimental investigation of deformation and damage of argillaceous rocks under cyclic hydric and mechanical loads

International Nuclear Information System (INIS)

Wang, Linlin; Yang, Diansen; Heripre, Eva; Chanchole, Serge; Bornert, Michel; Pouya, Ahmad; Halphen, Bernard

2012-01-01

Document available in abstract form only. Argillaceous rocks are possible host rocks for underground nuclear waste repositories. They exhibit complex coupled thermo-hydro-chemo-mechanical behavior, the description of which would strongly benefit from an improved experimental insight on their deformation and damage mechanisms at microscale. We present some recent observations of the evolution of these rocks at the scale of their composite microstructure, essentially made of a clay matrix with embedded carbonates and quartz particles with sizes ranging from a few to several tens of micrometers, when they are subjected to cyclic variations of relative humidity and mechanical loading. They are based on the combination of high definition and high resolution imaging in an environmental scanning electron microscope (ESEM), in situ hydro-mechanical loading of the samples, and digital image correlation techniques. Samples, several millimeters in diameter, are held at a constant temperature of 2 deg. Celsius while the vapor pressure in the ESEM chamber is varied from a few to several hundreds of Pascals, generating a relative humidity ranging from about 10% up to 90%. Results show a strongly heterogeneous deformation field at microscale, which is the result of complex hydro-mechanical interactions. In particular, it can be shown that local swelling incompatibilities can generate irreversible deformations in the clay matrix, even if the overall hydric deformations seem reversible. In addition, local damage can be generated, in the form of a network of microcracks, located in the bulk of the clay matrix and/or at the interface between clay and other mineral particles. The morphology of this network, described in terms of crack length, orientation and preferred location, has been observed to be dependent on the speed of the variation of the relative humidity, and is different in a saturation or desaturation process. Besides studying the deformation and damage under hydric

Free vibration analysis of magneto-electro-elastic microbeams subjected to magneto-electric loads

Science.gov (United States)

Vaezi, Mohamad; Shirbani, Meisam Moory; Hajnayeb, Ali

2016-01-01

Different types of actuating and sensing mechanisms are used in new micro and nanoscale devices. Therefore, a new challenge is modeling electromechanical systems that use these mechanisms. In this paper, free vibration of a magnetoelectroelastic (MEE) microbeam is investigated in order to obtain its natural frequencies and buckling loads. The beam is simply supported at both ends. External electric and magnetic potentials are applied to the beam. By using the Hamilton's principle, the governing equations and boundary conditions are derived based on the Euler-Bernoulli beam theory. The equations are solved, analytically to obtain the natural frequencies of the MEE microbeam. Furthermore, the effects of external electric and magnetic potentials on the buckling of the beam are analyzed and the critical values of the potentials are obtained. Finally, a numerical study is conducted. It is found that the natural frequency can be tuned directly by changing the magnetic and electric potentials. Additionally, a closed form solution for the normalized natural frequency is derived, and buckling loads are calculated in a numerical example.

The design of models for cryogenic wind tunnels. [mechanical properties and loads

Science.gov (United States)

Gillespie, V. P.

1977-01-01

Factors to be considered in the design and fabrication of models for cryogenic wind tunnels include high model loads imposed by the high operating pressures, the mechanical and thermodynamic properties of materials in low temperature environments, and the combination of aerodynamic loads with the thermal environment. Candidate materials are being investigated to establish criteria for cryogenic wind tunnel models and their installation. Data acquired from these tests will be provided to users of the National Transonic Facility.

Meso-Scale Finite Element Analysis of Mechanical Behavior of 3D Braided Composites Subjected to Biaxial Tension Loadings

Science.gov (United States)

Zhang, Chao; Curiel-Sosa, Jose L.; Bui, Tinh Quoc

2018-04-01

In many engineering applications, 3D braided composites are designed for primary loading-bearing structures, and they are frequently subjected to multi-axial loading conditions during service. In this paper, a unit-cell based finite element model is developed for assessment of mechanical behavior of 3D braided composites under different biaxial tension loadings. To predict the damage initiation and evolution of braiding yarns and matrix in the unit-cell, we thus propose an anisotropic damage model based on Murakami damage theory in conjunction with Hashin failure criteria and maximum stress criteria. To attain exact stress ratio, force loading mode of periodic boundary conditions which never been attempted before is first executed to the unit-cell model to apply the biaxial tension loadings. The biaxial mechanical behaviors, such as the stress distribution, tensile modulus and tensile strength are analyzed and discussed. The damage development of 3D braided composites under typical biaxial tension loadings is simulated and the damage mechanisms are revealed in the simulation process. The present study generally provides a new reference to the meso-scale finite element analysis (FEA) of multi-axial mechanical behavior of other textile composites.

Study of Acoustic Emission and Mechanical Characteristics of Coal Samples under Different Loading Rates

Directory of Open Access Journals (Sweden)

Huamin Li

2015-01-01

Full Text Available To study the effect of loading rate on mechanical properties and acoustic emission characteristics of coal samples, collected from Sanjiaohe Colliery, the uniaxial compression tests are carried out under various levels of loading rates, including 0.001 mm/s, 0.002 mm/s, and 0.005 mm/s, respectively, using AE-win E1.86 acoustic emission instrument and RMT-150C rock mechanics test system. The results indicate that the loading rate has a strong impact on peak stress and peak strain of coal samples, but the effect of loading rate on elasticity modulus of coal samples is relatively small. When the loading rate increases from 0.001 mm/s to 0.002 mm/s, the peak stress increases from 22.67 MPa to 24.99 MPa, the incremental percentage is 10.23%, and under the same condition the peak strain increases from 0.006191 to 0.007411 and the incremental percentage is 19.71%. Similarly, when the loading rate increases from 0.002 mm/s to 0.005 mm/s, the peak stress increases from 24.99 MPa to 28.01 MPa, the incremental percentage is 12.08%, the peak strain increases from 0.007411 to 0.008203, and the incremental percentage is 10.69%. The relationship between acoustic emission and loading rate presents a positive correlation, and the negative correlation relation has been determined between acoustic emission cumulative counts and loading rate during the rupture process of coal samples.

Inverse load calculation procedure for offshore wind turbines and application to a 5-MW wind turbine support structure: Inverse load calculation procedure for offshore wind turbines

Energy Technology Data Exchange (ETDEWEB)

Pahn, T. [Pahn Ingenieure, Am Seegraben 17b 03051 Cottbus Germany; Rolfes, R. [Institut f?r Statik und Dynamik, Leibniz Universit?t Hannover, Appelstra?e 9A 30167 Hannover Germany; Jonkman, J. [National Renewable Energy Laboratory, 15013 Denver West Parkway Golden Colorado 80401 USA

2017-02-20

A significant number of wind turbines installed today have reached their designed service life of 20 years, and the number will rise continuously. Most of these turbines promise a more economical performance if they operate for more than 20 years. To assess a continued operation, we have to analyze the load-bearing capacity of the support structure with respect to site-specific conditions. Such an analysis requires the comparison of the loads used for the design of the support structure with the actual loads experienced. This publication presents the application of a so-called inverse load calculation to a 5-MW wind turbine support structure. The inverse load calculation determines external loads derived from a mechanical description of the support structure and from measured structural responses. Using numerical simulations with the software fast, we investigated the influence of wind-turbine-specific effects such as the wind turbine control or the dynamic interaction between the loads and the support structure to the presented inverse load calculation procedure. fast is used to study the inverse calculation of simultaneously acting wind and wave loads, which has not been carried out until now. Furthermore, the application of the inverse load calculation procedure to a real 5-MW wind turbine support structure is demonstrated. In terms of this practical application, setting up the mechanical system for the support structure using measurement data is discussed. The paper presents results for defined load cases and assesses the accuracy of the inversely derived dynamic loads for both the simulations and the practical application.

New Cooperative Mechanisms of Low Energy Nuclear Reactions Using Superlow Energy External Fields

OpenAIRE

Gareev, F. A.; Zhidkova, I. E.

2005-01-01

We proposed a new mechanism of LENR: cooperative processes in whole system - nuclei+atoms+condensed matter can occur at smaller threshold then corresponding ones on free constituents. The cooperative processes can be induced and enhanced by low energy external fields. The excess heat is the emission of internal energy and transmutations at LENR are the result of redistribution inner energy of whole system.

Hypothesis: spring-loaded boomerang mechanism of influenza hemagglutinin-mediated membrane fusion.

Science.gov (United States)

Tamm, Lukas K

2003-07-11

Substantial progress has been made in recent years to augment the current understanding of structures and interactions that promote viral membrane fusion. This progress is reviewed with a particular emphasis on recently determined structures of viral fusion domains and their interactions with lipid membranes. The results from the different structural and thermodynamic experimental approaches are synthesized into a new proposed mechanism, termed the "spring-loaded boomerang" mechanism of membrane fusion, which is presented here as a hypothesis.

Macrocrack propagation in concrete specimens under sustained loading: Study of the physical mechanisms

Energy Technology Data Exchange (ETDEWEB)

Rossi, Pierre, E-mail: pierre.rossi@lcpc.fr; Boulay, Claude; Tailhan, Jean-Louis; Martin, Eric; Desnoyers, Dominic

2014-09-15

This study presents a series of 4-point bending tests performed to describe the delayed behavior of unreinforced pre-cracked beams under low, moderate and high sustained loading levels. The deflection creep rate, the failure time and the load level were assessed. A linear relation, in a semi-log scale, was found for the deflection creep rate at high load levels. In addition, a linear relation, in a log–log scale, between the secondary deflection creep rate and failure time was observed. Besides, it was shown that the secondary creep deflection rate increases with the sustained loading level and the macrocrack propagation rate when macrocrack propagation occurs during the sustained loading. Physical mechanisms are proposed to explain these results and may be summarized as follows: the delayed behavior of an unreinforced cracked concrete specimen under sustained loading is mainly due to the cracking evolution, thus the creation of microcracks and/or the propagation of a macrocrack.

Macrocrack propagation in concrete specimens under sustained loading: Study of the physical mechanisms

International Nuclear Information System (INIS)

Rossi, Pierre; Boulay, Claude; Tailhan, Jean-Louis; Martin, Eric; Desnoyers, Dominic

2014-01-01

This study presents a series of 4-point bending tests performed to describe the delayed behavior of unreinforced pre-cracked beams under low, moderate and high sustained loading levels. The deflection creep rate, the failure time and the load level were assessed. A linear relation, in a semi-log scale, was found for the deflection creep rate at high load levels. In addition, a linear relation, in a log–log scale, between the secondary deflection creep rate and failure time was observed. Besides, it was shown that the secondary creep deflection rate increases with the sustained loading level and the macrocrack propagation rate when macrocrack propagation occurs during the sustained loading. Physical mechanisms are proposed to explain these results and may be summarized as follows: the delayed behavior of an unreinforced cracked concrete specimen under sustained loading is mainly due to the cracking evolution, thus the creation of microcracks and/or the propagation of a macrocrack

Predicting the conditions under which vibroacoustic resonances with external periodic loads occur in the primary coolant circuits of VVER-based NPPs

Science.gov (United States)

Proskuryakov, K. N.; Fedorov, A. I.; Zaporozhets, M. V.

2015-08-01

The accident at the Japanese Fukushima Daiichi nuclear power plant (NPP) caused by an earthquake showed the need of taking further efforts aimed at improving the design and engineering solutions for ensuring seismic resistance of NPPs with due regard to mutual influence of the dynamic processes occurring in the NPP building structures and process systems. Resonance interaction between the vibrations of NPP equipment and coolant pressure pulsations leads to an abnormal growth of dynamic stresses in structural materials, accelerated exhaustion of equipment service life, and increased number of sudden equipment failures. The article presents the results from a combined calculation-theoretical and experimental substantiation of mutual amplification of two kinds of external periodic loads caused by rotation of the reactor coolant pump (RCP) rotor and an earthquake. The data of vibration measurements at an NPP are presented, which confirm the predicted multiple amplification of vibrations in the steam generator and RCP at a certain combination of coolant thermal-hydraulic parameters. It is shown that the vibration frequencies of the main equipment may fall in the frequency band corresponding to the maximal values in the envelope response spectra constructed on the basis of floor accelerograms. The article presents the results from prediction of conditions under which vibroacoustic resonances with external periodic loads take place, which confirm the occurrence of additional earthquake-induced multiple growth of pressure pulsation intensity in the steam generator at the 8.3 Hz frequency and additional multiple growth of vibrations of the RCP and the steam generator cold header at the 16.6 Hz frequency. It is shown that at the elastic wave frequency equal to 8.3 Hz in the coolant, resonance occurs with the frequency of forced vibrations caused by the rotation of the RCP rotor. A conclusion is drawn about the possibility of exceeding the design level of equipment vibrations

Rationales for capacity remuneration mechanisms: Security of supply externalities and asymmetric investment incentives

International Nuclear Information System (INIS)

Keppler, Jan Horst

2017-01-01

Economics so far provides little conceptual guidance on capacity remuneration mechanisms (CRM) in deregulated electricity markets. Ubiquitous in real-world electricity markets, CRMs are introduced country by country in an ad hoc manner, lacking the theoretical legitimacy and the conceptual coherence enabling comparability and coordination. They are eyed with suspicion by a profession wedded to a theoretical benchmark model that argues that competitive energy-only markets with VOLL pricing provide adequate levels of capacity. While the benchmark model is a consistent starting point for discussions about electricity market design, it ignores the two market failures that make CRMs the practically appropriate and theoretically justified policy response to capacity issues. First, energy-only markets fail to internalize security-of-supply externalities as involuntary curbs on demand under scarcity pricing generate social costs beyond the private non-consumption of electricity. Second, when demand is inelastic and the potential capacity additions are discretely sized, investors face asymmetric incentives and will underinvest at the margin rather than overinvest. After presenting the key features of the theoretical benchmark model, this paper conceptualizes security of supply externalities and asymmetric investment incentives and concludes with some consideration regarding design of CRMs. - Highlights: • Capacity remuneration mechanisms are ubiquitous in real-world electricity markets. • Theory claims that energy-only markets can provide optimal capacity on their own. • However theory fails to account for two types of market failures. • Involuntary demand curbs under VOLL-pricing create security-of-supply externalities. • With inelastic demand, discretely sized capacity options lead to underinvestment.

Management mechanisms for development of personnel professional competencies at a loading and haulage company

Science.gov (United States)

Shishkina, S. V.; Pristupa, Yu D.; Pavlova, L. D.; Fryanov, V. N.

2018-05-01

The necessity for development a management mechanism for development of personnel professional competencies at a loading and haulage company in order to ensuring the compliance of competencies with labor functions, regulated by the current professional standards, is substantiated. A functional diagram of the organizational and technical system of the loading and haulage company was developed, that includes the interaction mechanism between the personnel and the objects of the main production. The problem of algorithm development to assess the correspondence of communicative competencies and labor functions of loading and haulage companies, ensuring the achievement of the management goal with a minimum risk of an emergency situation or an accident, was set and solved. The idea of management problem solving consists in the operational development and implementation of anticipatory measures at each deviation in personnel actions from normative or target indicators. The dependence of the risk of imbalance of communicative competences and labor functions in a given period of time is established. The effectiveness of the developed and implemented mechanism is confirmed by the positive dynamics of the test results.

Intercellular communication via gap junctions affected by mechanical load in the bovine annulus fibrosus.

Science.gov (United States)

Desrochers, Jane; Duncan, Neil A

2014-01-01

Cells in the intervertebral disc, as in other connective tissues including tendon, ligament and bone, form interconnected cellular networks that are linked via functional gap junctions. These cellular networks may be necessary to affect a coordinated response to mechanical and environmental stimuli. Using confocal microscopy with fluorescence recovery after photobleaching methods, we explored the in situ strain environment of the outer annulus of an intact bovine disc and the effect of high-level flexion on gap junction signalling. The in situ strain environment in the extracellular matrix of the outer annulus under high flexion load was observed to be non-uniform with the extensive cellular processes remaining crimped sometimes at flexion angles greater than 25°. A significant transient disruption of intercellular communication via functional gap junctions was measured after 10 and 20 min under high flexion load. This study illustrates that in healthy annulus fibrosus tissue, high mechanical loads can impede the functioning of the gap junctions. Future studies will explore more complex loading conditions to determine whether losses in intercellular communication can be permanent and whether gap junctions in aged and degenerated tissues become more susceptible to load. The current research suggests that cellular structures such as gap junctions and intercellular networks, as well as other cell-cell and cell-matrix interconnections, need to be considered in computational models in order to fully understand how macroscale mechanical signals are transmitted across scales to the microscale and ultimately into a cellular biosynthetic response in collagenous tissues.

Soil mechanical stresses in high wheel load agricultural field traffic: a case study

DEFF Research Database (Denmark)

Lamandé, Mathieu; Schjønning, Per

2017-01-01

highly skewed. Across tyres, the maximum stress in the contact area correlated linearly with, but was much higher than, the mean ground pressure. For each of the three soil depths, the maximum stresses under the tyres were significantly correlated with the wheel load, but not with other loading......Subsoil compaction is a serious long-term threat to soil functions. Only a few studies have quantified the mechanical stresses reaching deep subsoil layers for modern high wheel load machinery. In the present study we measured the vertical stresses in the tyre–soil contact area and at 0.3, 0...

Is the internal connection more efficient than external connection in mechanical, biological, and esthetical point of views? A systematic review.

Science.gov (United States)

Goiato, Marcelo Coelho; Pellizzer, Eduardo Piza; da Silva, Emily Vivianne Freitas; Bonatto, Liliane da Rocha; dos Santos, Daniela Micheline

2015-09-01

This systematic review aimed to evaluate if the internal connection is more efficient than the external connection and its associated influencing factors. A specific question was formulated according to the Population, Intervention, Control, and Outcome (PICO): Is internal connection more efficient than external connection in mechanical, biological, and esthetical point of views? An electronic search of the MEDLINE and the Web of Knowledge databases was performed for relevant studies published in English up to November 2013 by two independent reviewers. The keywords used in the search included a combination of "dental implant" and "internal connection" or "Morse connection" or "external connection." Selected studies were randomized clinical trials, prospective or retrospective studies, and in vitro studies with a clear aim of investigating the internal and/or external implant connection use. From an initial screening yield of 674 articles, 64 potentially relevant articles were selected after an evaluation of their titles and abstracts. Full texts of these articles were obtained with 29 articles fulfilling the inclusion criteria. Morse taper connection has the best sealing ability. Concerning crestal bone loss, internal connections presented better results than external connections. The limitation of the present study was the absence of randomized clinical trials that investigated if the internal connection was more efficient than the external connection. The external and internal connections have different mechanical, biological, and esthetical characteristics. Besides all systems that show proper success rates and effectiveness, crestal bone level maintenance is more important around internal connections than external connections. The Morse taper connection seems to be more efficient concerning biological aspects, allowing lower bacterial leakage and bone loss in single implants, including aesthetic regions. Additionally, this connection type can be successfully

Increased expression of matrix extracellular phosphoglycoprotein (MEPE in cortical bone of the rat tibia after mechanical loading: identification by oligonucleotide microarray.

Directory of Open Access Journals (Sweden)

Christianne M A Reijnders

Full Text Available Skeletal integrity in humans and animals is maintained by daily mechanical loading. It has been widely accepted that osteocytes function as mechanosensors. Many biochemical signaling molecules are involved in the response of osteocytes to mechanical stimulation. The aim of this study was to identify genes involved in the translation of mechanical stimuli into bone formation. The four-point bending model was used to induce a single period of mechanical loading on the right tibia, while the contra lateral left tibia served as control. Six hours after loading, the effects of mechanical loading on gene-expression were determined with microarray analysis. Protein expression of differentially regulated genes was evaluated with immunohistochemistry. Nine genes were found to exhibit a significant differential gene expression in LOAD compared to control. MEPE, Garnl1, V2R2B, and QFG-TN1 olfactory receptor were up-regulated, and creatine kinase (muscle form, fibrinogen-B beta-polypeptide, monoamine oxidase A, troponin-C and kinesin light chain-C were down-regulated. Validation with real-time RT-PCR analysis confirmed the up-regulation of MEPE and the down-regulation of creatine kinase (muscle form and troponin-C in the loaded tibia. Immunohistochemistry showed that the increase of MEPE protein expression was already detectable six hours after mechanical loading. In conclusion, these genes probably play a role during translation of mechanical stimuli six hours after mechanical loading. The modulation of MEPE expression may indicate a connection between bone mineralization and bone formation after mechanical stimulation.

The effects of mechanical loading on tendons--an in vivo and in vitro model study.

Directory of Open Access Journals (Sweden)

Jianying Zhang

Full Text Available Mechanical loading constantly acts on tendons, and a better understanding of its effects on the tendons is essential to gain more insights into tendon patho-physiology. This study aims to investigate tendon mechanobiological responses through the use of mouse treadmill running as an in vivo model and mechanical stretching of tendon cells as an in vitro model. In the in vivo study, mice underwent moderate treadmill running (MTR and intensive treadmill running (ITR regimens. Treadmill running elevated the expression of mechanical growth factors (MGF and enhanced the proliferative potential of tendon stem cells (TSCs in both patellar and Achilles tendons. In both tendons, MTR upregulated tenocyte-related genes: collagen type I (Coll. I ∼10 fold and tenomodulin (∼3-4 fold, but did not affect non-tenocyte-related genes: LPL (adipocyte, Sox9 (chondrocyte, Runx2 and Osterix (both osteocyte. However, ITR upregulated both tenocyte (Coll. I ∼7-11 fold; tenomodulin ∼4-5 fold and non-tenocyte-related genes (∼3-8 fold. In the in vitro study, TSCs and tenocytes were stretched to 4% and 8% using a custom made mechanical loading system. Low mechanical stretching (4% of TSCs from both patellar and Achilles tendons increased the expression of only the tenocyte-related genes (Coll. I ∼5-6 fold; tenomodulin ∼6-13 fold, but high mechanical stretching (8% increased the expression of both tenocyte (Coll. I ∼28-50 fold; tenomodulin ∼14-48 fold and non-tenocyte-related genes (2-5-fold. However, in tenocytes, non-tenocyte related gene expression was not altered by the application of either low or high mechanical stretching. These findings indicate that appropriate mechanical loading could be beneficial to tendons because of their potential to induce anabolic changes in tendon cells. However, while excessive mechanical loading caused anabolic changes in tendons, it also induced differentiation of TSCs into non-tenocytes, which may lead to the development

Assessing Cognitive Load Theory to Improve Student Learning for Mechanical Engineers

Science.gov (United States)

Impelluso, Thomas J.

2009-01-01

A computer programming class for students of mechanical engineering was redesigned and assessed: Cognitive Load Theory was used to redesign the content; online technologies were used to redesign the delivery. Student learning improved and the dropout rate was reduced. This article reports on both attitudinal and objective assessment: comparing…

Cooperative Enhancement Mechanisms of Low Energy Nuclear Reactions Using Superlow Energy External Fields

OpenAIRE

Gareev, F. A.; Zhidkova, I. E.

2006-01-01

We proposed a new mechanism of LENR: cooperative processes in whole system - nuclei+atoms+condensed matter can occur at smaller threshold energies then corresponding ones on free constituents. The cooperative processes can be induced and enhanced by low energy external fields. The excess heat is the emission of internal energy and transmutations at LENR are the result of redistribution inner energy of whole system.

External exposure dose of car mechanics during the maintenance of the cars from the risk cautionary area

International Nuclear Information System (INIS)

Kawakami, Hiroto; Yamada, Norikazu; Sasaki, Satoru; Kawasaki, Satoru

2011-12-01

At the request of the Local Nuclear Emergency Response Headquarters, JNES has estimated the effective external exposure dose of car mechanics during the maintenance of the cars from the risk cautionary area. JNES investigated the contamination of the cars from the risk cautionary area and of the average cars at Fukushima city cooperated by the Japan Automobile Dealers Association. Data of screed cars by the Local Nuclear Emergency Response Headquarters is also considered in. Effective external exposure dose of car mechanics treating the cars screened with the emergency situation screening level is estimated to be less than 1 mSv/y under the conservative conditions. This result shows that particular health concern isn't necessary for them. (author)

Trunk and hip biomechanics influence anterior cruciate loading mechanisms in physically active participants.

Science.gov (United States)

Frank, Barnett; Bell, David R; Norcross, Marc F; Blackburn, J Troy; Goerger, Benjamin M; Padua, Darin A

2013-11-01

Excessive trunk motion and deficits in neuromuscular control (NMC) of the lumbopelvic hip complex are risk factors for anterior cruciate ligament (ACL) injury. However, the relationship between trunk motion, NMC of the lumbopelvic hip complex, and triplanar knee loads during a sidestep cutting task has not been examined. To determine if there is an association between multiplanar trunk motion, NMC of the lumbopelvic hip complex, and triplanar knee loads with ACL injury during a sidestep cutting task. Descriptive laboratory study. The hip and knee biomechanics and trunk motion of 30 participants (15 male, 15 female) were analyzed during a sidestep cutting task using an optoelectric camera system interfaced to a force plate. Trunk and lower extremity biomechanics were calculated from the kinematic and ground-reaction force data during the first 50% of the stance time during the cutting task. Pearson product moment correlation coefficients were calculated between trunk and lower extremity biomechanics. Multiple linear regression analyses were carried out to determine the amount of variance in triplanar knee loading explained by trunk motion and hip moments. A greater internal knee varus moment (mean, 0.11 ± 0.12 N·m/kg*m) was associated with less transverse-plane trunk rotation away from the stance limb (mean, 20.25° ± 4.42°; r = -0.46, P = .011) and a greater internal hip adduction moment (mean, 0.33 ± 0.25 N·m/kg*m; r = 0.83, P < .05). A greater internal knee external rotation moment (mean, 0.11 ± 0.08 N·m/kg*m) was associated with a greater forward trunk flexion (mean, 7.62° ± 5.28°; r = 0.42, P = .020) and a greater hip internal rotation moment (mean, 0.15 ± 0.16 N·m/kg*m; r = 0.59, P = .001). Trunk rotation and hip adduction moment explained 81% (P < .05) of the variance in knee varus moment. Trunk flexion and hip internal rotation moment explained 48% (P < .05) of the variance in knee external rotation moment. Limited trunk rotation displacement

Effect of mechanical pre-loadings on corrosion resistance of chromium-electroplated steel rods in marine environment

Science.gov (United States)

Shubina Helbert, Varvara; Dhondt, Matthieu; Homette, Remi; Arbab Chirani, Shabnam; Calloch, Sylvain

2018-03-01

Providing high hardness, low friction coefficient, as well as, relatively good corrosion resistance, chromium-plated coatings (∼20 μm) are widely used for steel cylinder rods in marine environment. However, the standardized corrosion test method (ISO 9227, NSS) used to evaluate efficiency of this type of coatings does not take into account in-service mechanical loadings on cylinder rods. Nevertheless, the uniform initial network of microcracks in chromium coating is changing under mechanical loadings. Propagation of these microcracks explains premature corrosion of the steel substrate. The aim of the study was to evaluate relationship between mechanical loadings, propagation of microcracks network and corrosion resistance of chromium coatings. After monotonic pre-loading tests, it was demonstrated by microscopic observations that the microcracks propagation started at stress levels higher than the substrate yield stress (520 MPa). The microcracks become effective, i.e. they have instantly undergone through the whole coating thickness to reach the steel substrate. The density of effective microcracks increases with the total macroscopic level, i.e. the intercrack distance goes from 60 ± 5 μm at 1% of total strain to approximately 27 ± 2 μm at 10%. Electrochemical measurements have shown that the higher the plastic strain level applied during mechanical loading, the more the corrosion potential of the sample decreased until reaching the steel substrate value of approximately ‑0.65 V/SCE after 2 h of immersion. The polarization curves have also highligthed an increase in the corrosion current density with the strain level. Therefore, electrochemical measurements could be used to realize quick and comprehensive assesment of the effect of monotonic pre-loadings on corrosion properties of the chromium coating.

Prediction of contact mechanics in metal-on-metal Total Hip Replacement for parametrically comprehensive designs and loads.

Science.gov (United States)

Donaldson, Finn E; Nyman, Edward; Coburn, James C

2015-07-16

Manufacturers and investigators of Total Hip Replacement (THR) bearings require tools to predict the contact mechanics resulting from diverse design and loading parameters. This study provides contact mechanics solutions for metal-on-metal (MoM) bearings that encompass the current design space and could aid pre-clinical design optimization and evaluation. Stochastic finite element (FE) simulation was used to calculate the head-on-cup contact mechanics for five thousand combinations of design and loading parameters. FE results were used to train a Random Forest (RF) surrogate model to rapidly predict the contact patch dimensions, contact area, pressures and plastic deformations for arbitrary designs and loading. In addition to widely observed polar and edge contact, FE results included ring-polar, asymmetric-polar, and transitional categories which have previously received limited attention. Combinations of design and load parameters associated with each contact category were identified. Polar contact pressures were predicted in the range of 0-200 MPa with no permanent deformation. Edge loading (with subluxation) was associated with pressures greater than 500 MPa and induced permanent deformation in 83% of cases. Transitional-edge contact (with little subluxation) was associated with intermediate pressures and permanent deformation in most cases, indicating that, even with ideal anatomical alignment, bearings may face extreme wear challenges. Surrogate models were able to accurately predict contact mechanics 18,000 times faster than FE analyses. The developed surrogate models enable rapid prediction of MoM bearing contact mechanics across the most comprehensive range of loading and designs to date, and may be useful to those performing bearing design optimization or evaluation. Published by Elsevier Ltd.

Load speed regulation in compliant mechanical transmission systems using feedback and feedforward control actions.

Science.gov (United States)

Raul, P R; Dwivedula, R V; Pagilla, P R

2016-07-01

The problem of controlling the load speed of a mechanical transmission system consisting of a belt-pulley and gear-pair is considered. The system is modeled as two inertia (motor and load) connected by a compliant transmission. If the transmission is assumed to be rigid, then using either the motor or load speed feedback provides the same result. However, with transmission compliance, due to belts or long shafts, the stability characteristics and performance of the closed-loop system are quite different when either motor or load speed feedback is employed. We investigate motor and load speed feedback schemes by utilizing the singular perturbation method. We propose and discuss a control scheme that utilizes both motor and load speed feedback, and design an adaptive feedforward action to reject load torque disturbances. The control algorithms are implemented on an experimental platform that is typically used in roll-to-roll manufacturing and results are shown and discussed. Copyright © 2016 ISA. Published by Elsevier Ltd. All rights reserved.

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.

Grid Faults Impact on the Mechanical Loads of Active Stall Wind Turbine

DEFF Research Database (Denmark)

Iov, Florin; Cutululis, Nicolaos A.; Hansen, Anca D.

2008-01-01

Emphasis in this paper is on the fault ride-through operation impact on the wind turbines structural loads. Grid faults are typically simulated in power system simulation tools using simplified drive train mechanical model, approach which doesn't allow a thorough investigation of structural loads...... as the electrical design of the wind turbine response during grid faults. The two-step simulation procedure is assessed by means of a simulation example. The effect of a grid fault on the structural part of a typical fixed speed wind turbine, equipped with an induction generator, is assessed....

Fuel assemblies mechanical behaviour improvements based on design changes and loading patterns computational analyses

International Nuclear Information System (INIS)

Marin, J.; Aullo, M.; Gutierrez, E.

2001-01-01

In the past few years, incomplete RCCA insertion events (IRI) have been taking place at some nuclear plants. Large guide thimble distortion caused by high compressive loads together with the irradiation induced material creep and growth, is considered as the primary cause of those events. This disturbing phenomenon is worsened when some fuel assemblies are deformed to the extent that they push the neighbouring fuel assemblies and the distortion is transmitted along the core. In order to better understand this mechanism, ENUSA has developed a methodology based on finite element core simulation to enable assessments on the propensity of a given core loading pattern to propagate the distortion along the core. At the same time, the core loading pattern could be decided interacting with nuclear design to obtain the optimum response under both, nuclear and mechanical point of views, with the objective of progressively attenuating the core distortion. (author)

Patterning of alloy precipitation through external pressure

Science.gov (United States)

Franklin, Jack A.

Due to the nature of their microstructure, alloyed components have the benefit of meeting specific design goals across a wide range of electrical, thermal, and mechanical properties. In general by selecting the correct alloy system and applying a proper heat treatment it is possible to create a metallic sample whose properties achieve a unique set of design requirements. This dissertation presents an innovative processing technique intended to control both the location of formation and the growth rates of precipitates within metallic alloys in order to create multiple patterned areas of unique microstructure within a single sample. Specific experimental results for the Al-Cu alloy system will be shown. The control over precipitation is achieved by altering the conventional heat treatment process with an external surface load applied to selected locations during the quench and anneal. It is shown that the applied pressures affect both the rate and directionality of the atomic diffusion in regions close to the loaded surfaces. The control over growth rates is achieved by altering the enthalpic energy required for successful diffusion between lattice sites. Changes in the local chemical free energy required to direct the diffusion of atoms are established by introducing a non-uniform elastic strain energy field within the samples created by the patterned surface pressures. Either diffusion rates or atomic mobility can be selected as the dominating control process by varying the quench rate; with slower quenches having greater control over the mobility of the alloying elements. Results have shown control of Al2Cu precipitation over 100 microns on mechanically polished surfaces. Further experimental considerations presented will address consistency across sample ensembles. This includes repeatable pressure loading conditions and the chemical interaction between any furnace environments and both the alloy sample and metallic pressure loading devices.

Crack nucleation in solid materials under external load - simulations with the Discrete Element Method

Directory of Open Access Journals (Sweden)

Klejment Piotr

2018-01-01

Full Text Available Numerical analysis of cracking processes require an appropriate numerical technique. Classical engineering approach to the problem has its roots in the continuum mechanics and is based mainly on the Finite Element Method. This technique allows simulations of both elastic and large deformation processes, so it is very popular in the engineering applications. However, a final effect of cracking - fragmentation of an object at hand can hardly be described by this approach in a numerically efficient way since it requires a solution of a problem of nontrivial evolving in time boundary conditions. We focused our attention on the Discrete Element Method (DEM, which by definition implies “molecular” construction of the matter. The basic idea behind DEM is to represent an investigated body as an assemblage of discrete particles interacting with each other. Breaking interaction bonds between particles induced by external forces imeditelly implies creation/evolution of boundary conditions. In this study we used the DEM approach to simulate cracking process in the three dimensional solid material under external tension. The used numerical model, although higly simplified, can be used to describe behaviour of such materials like thin films, biological tissues, metal coatings, to name a few.

Comprehensive Understanding of Ductility Loss Mechanisms in Various Steels with External and Internal Hydrogen

Science.gov (United States)

Takakuwa, Osamu; Yamabe, Junichiro; Matsunaga, Hisao; Furuya, Yoshiyuki; Matsuoka, Saburo

2017-11-01

Hydrogen-induced ductility loss and related fracture morphologies are comprehensively discussed in consideration of the hydrogen distribution in a specimen with external and internal hydrogen by using 300-series austenitic stainless steels (Types 304, 316, 316L), high-strength austenitic stainless steels (HP160, XM-19), precipitation-hardened iron-based super alloy (A286), low-alloy Cr-Mo steel (JIS-SCM435), and low-carbon steel (JIS-SM490B). External hydrogen is realized by a non-charged specimen tested in high-pressure gaseous hydrogen, and internal hydrogen is realized by a hydrogen-charged specimen tested in air or inert gas. Fracture morphologies obtained by slow-strain-rate tensile tests (SSRT) of the materials with external or internal hydrogen could be comprehensively categorized into five types: hydrogen-induced successive crack growth, ordinary void formation, small-sized void formation related to the void sheet, large-sized void formation, and facet formation. The mechanisms of hydrogen embrittlement are broadly classified into hydrogen-enhanced decohesion (HEDE) and hydrogen-enhanced localized plasticity (HELP). In the HEDE model, hydrogen weakens interatomic bonds, whereas in the HELP model, hydrogen enhances localized slip deformations. Although various fracture morphologies are produced by external or internal hydrogen, these morphologies can be explained by the HELP model rather than by the HEDE model.

Mean load effect on fatigue of welded joints using structural stress and fracture mechanics approach

International Nuclear Information System (INIS)

Kim, Jong Sung; Kim, Cheol; Jin, Tae Eun; Dong, P.

2006-01-01

In order to ensure the structural integrity of nuclear welded structures during design life, the fatigue life has to be evaluated by fatigue analysis procedures presented in technical codes such as ASME B and PV Code Section III. However, existing fatigue analysis procedures do not explicitly consider the presence of welded joints. A new fatigue analysis procedure based on a structural stress/fracture mechanics approach has been recently developed in order to reduce conservatism by erasing uncertainty in the analysis procedure. A recent review of fatigue crack growth data under various mean loading conditions using the structural stress/fracture mechanics approach, does not consider the mean loading effect, revealed some significant discrepancies in fatigue crack growth curves according to the mean loading conditions. In this paper, we propose the use of the stress intensity factor range ΔK characterized with loading ratio R effects in terms of the structural stress. We demonstrate the effectiveness in characterizing fatigue crack growth and S-N behavior using the well-known data. It was identified that the S-N data under high mean loading could be consolidated in a master S-N curve for welded joints

A Universal Educational and Research Stand to Simulate Electrical Drive Loading

Directory of Open Access Journals (Sweden)

V. S. Grishin

2016-01-01

Full Text Available Universal educational and research stand was developed for analyzing an electrical drive’s behavior with different load disturbance effects. Major components of the stand are two electrical drives with rigidly coupled shafts. As a result, first electrical drive (loader has a capability to imitate effects of different loading types to another one (trial drive.Control software for the stand is developed. It allows us to combine a variety of loading types and change parameters of current loading such as joint moment, damping, additional inertia, and external torque. Also there is a capability to imitate effects of elasticity and backlash of mechanical transmissions. The paper considers the main challenge of creating the given system, i.e. discretization with a variable step. Some methods to decrease its negative effects on system stability are suggested.The given system allows to change loading parameters more rapidly and in a wider range as compared to a system with real mechanical outfit.These stands are currently used for laboratory classes within the course “Electrical robotic drives” at SM7 department in Bauman Moscow State Technical University. Also the system of interdepended stands for semi-realistic simulation of manipulation systems is under development.

Continuum damage mechanics analysis of crack tip zone

International Nuclear Information System (INIS)

Yinchu, L.; Jianping, Z.

1989-01-01

The crack tip field and its intensity factor play an important role in fracture mechanics. Generally, the damage such as microcracks, microvoids etc. will initiate and grow in materials as the cracked body is subjected to external loadings, especially in the crack tip zone. The damage evolution will load to the crack tip damage field and the change of the stress, strain and displacement fields of cracks tip zone. In this paper, on the basis of continuum damage mechanics, the authors have derived the equations which the crack tip field and its intensity factor must satisfy in a loading process, calculated the angle distribution curves of stress, strain and displacement fields in a crack tip zone and have compared them with the corresponding curves of HRR field and linear elastic field in undamaged materials. The equations of crack tip field intensity factors have been solved and its solutions give the variation of the field intensity factors with the loading parameter

Performance Targets and External Benchmarking

DEFF Research Database (Denmark)

Friis, Ivar; Hansen, Allan; Vámosi, Tamás S.

Research on relative performance measures, transfer pricing, beyond budgeting initiatives, target costing, piece rates systems and value based management has for decades underlined the importance of external benchmarking in performance management. Research conceptualises external benchmarking...... as a market mechanism that can be brought inside the firm to provide incentives for continuous improvement and the development of competitive advances. However, whereas extant research primarily has focused on the importance and effects of using external benchmarks, less attention has been directed towards...... the conditions upon which the market mechanism is performing within organizations. This paper aims to contribute to research by providing more insight to the conditions for the use of external benchmarking as an element in performance management in organizations. Our study explores a particular type of external...

Mechanical properties of two-way different configurations of prestressed concrete members subjected to axial loading

Energy Technology Data Exchange (ETDEWEB)

Zhang, Chaobi; Chen, Jian Yun; Xu, Qiang; Li, Jing [School of Civil and Hydraulic Engineering, Dalian University of Technology, Dalian (China)

2015-08-15

In order to analyze the mechanical properties of two-way different configurations of prestressed concrete members subjected to axial loading, a finite element model based on the nuclear power plant containments is demonstrated. This model takes into account the influences of different principal stress directions, the uniaxial or biaxial loading, and biaxial loading ratio. The displacement-controlled load is applied to obtain the stress-strain response. The simulated results indicate that the differences of principal stress axes have great effects on the stress-strain response under uniaxial loading. When the specimens are subjected to biaxial loading, the change trend of stress with the increase of loading ratio is obviously different along different layout directions. In addition, correlation experiments and finite element analyses were conducted to verify the validity and reliability of the analysis in this study.

Mechanical Behaviour of Bolted Joints Under Impact Rates of Loading

Science.gov (United States)

2012-01-01

M. (1995). Bearing Strength of Autoclave and oven cured kevlar / epoxy laminates under static and dynamic loading. Compostes, 451-456. Kretsis, G...Joints in Glass Fibre/ Epoxy Laminates. Composites, Volume 16. No 2. Kolsky, H. (1949). An Investigation of the Mechanical Properties of Materials at...elongating the pulse width. The responses are read by the strain gages bonded on the incident and transmission bar with Vishay AE-10 epoxy . The gages

Analysis of external events - Nuclear Power Plant Dukovany

International Nuclear Information System (INIS)

Hladky, Milan

2000-01-01

PSA of external events at level 1 covers internal events, floods, fires, other external events are not included yet. Shutdown PSA takes into account internal events, floods, fires, heavy load drop, other external events are not included yet. Final safety analysis report was conducted after 10 years of operation for all Dukovany operational units. Probabilistic approach was used for analysis of aircraft drop and external man-induced events. The risk caused by man-induced events was found to be negligible and was accepted by State Office for Nuclear Safety (SONS)

Load rate dependence of the mechanical properties of thermal barrier coating systems

Energy Technology Data Exchange (ETDEWEB)

Zotov, Nikolay; Eggeler, Gunther [Institut fuer Werkstoffe, Ruhr Universitaet Bochum, 44780 Bochum (Germany); Bartsch, Marion [Institut fuer Werkstoff-Forschung, DLR Koeln, 51147 Koeln (Germany)

2009-07-01

Thermal barrier coatings (TBC), composed of yttrium-stabilized zirconia (YSZ) ceramic top coat (TC) and intermetallic NiCoCrAlY bond coat (BC) are commonly used as protective coatings of Ni-based high temperature gas engine components. Nanoindentation techniques are increasingly applied for determining the TBC mechanical properties on a nanometre scale. However, little is known about the load-rate dependence of the mechanical properties, which is important for better understanding of cyclic thermal fatigue experiments. Nanoindentations with different load rates omega were performed on polished cross-sections of TBC, deposited by EB-PVD on IN625 substrates (S), using a XP Nanoindenter (MTS) equipped with Berkovich diamond tip. The Young's modulus (E) of the TC is independent of omega, while E for the BC and the S decreases with omega. The hardness (H) of the TC and the BC increases, while H for the S decreases with omega. From the dependence of H on omega, creep power-law exponents c = 0.24(11) and c = 0.023(6) for the TC and the BC were determined. For all TBC components, a decrease with omega of the power-law exponents n and m, describing the loading and unloading nanoindentation curves, is observed.

Match-play activity profile in professional soccer players during official games and the relationship between external and internal load.

Science.gov (United States)

Suarez-Arrones, L; Torreño, N; Requena, B; Sáez De Villarreal, E; Casamichana, D; Barbero-Alvarez, J C; Munguía-Izquierdo, D

2015-12-01

The aim was to quantify for the first time the physical and physiological profile of professional soccer players in official games using GPS and heart rate (HR) response. Thirty professional soccer players were investigated during a half in competitive club level matches (N.=348) using GPS devices. The relative total distance was 118.9±10.7 m∙min(-1) and player's Work-To-Rest Ratio was 2.1:1. Defenders covered the lowest total distance, while Second-Strikers (2(nd)S) and Wide-Midfielders (W-MD) traveled the greatest total distance. Defenders presented the lowest Work-To-Rest Ratio values. Playing position also impacted on all sprinting performance results, except in average sprint distance and time of sprint. The number of sprints and repeated-sprint sequences recorded by the W-MD and Strikers (S) were significantly greater than any other group. The average HR recorded was 87.1%HRmax and the relationship between the external and internal load value (Effindex) was 1.4 with significant differences in both between playing positions. W-MD recorded a significantly smaller average HR than any other group and Centre-Backs showed a significantly smaller Effindex value than any other group. Conversely, W-MD showed a significantly greater Effindex value than any other group, except the 2(nd)S. This study has verified a number of statistically significant differences between the different playing positions. Coaches should be focused on the specific physical and physiological requirements of the playing positions to optimize the training prescription in soccer. The relationships between external and internal load measures among position-specific indicates that players with less overall running performance during match-play were the worst in Effindex.

Effects of mechanical and thermal load cycling on micro tensile bond strength of clearfil SE bond to superficial dentin

Directory of Open Access Journals (Sweden)

Ali Reza Daneshkazemi

2013-01-01

Full Text Available Background: Certain studies have been conducted on the effects of mechanical and thermal load cycling on the microtensile bond strength (microTBS of composites to dentin, but the results were different. The authors therefore decided to evaluate these effects on the bonding of Clearfil SE bond to superficial dentin. Materials and Methods: Flat dentinal surface of 42 molar teeth were bonded to Filtek-Z250 resin composite by Clearfil SE bond. The teeth were randomly divided into 7 groups and exposed to different mechanical and thermal load cycling. Thermocycling was at 5-55°C and mechanical load cycling was created with a force of 125 N and 0.5 Hz. Then, the teeth were sectioned and shaped to hour glass form and subjected to microTBS testing at a speed of 0.5 mm/min. The results were statistically analyzed by computer with three-way analysis of variance and T-test at P < 0.05 significant. To evaluate the location and mode of failure, the specimens were observed under the stereomicroscope. Then, one of the specimens in each group was evaluated under Scanning Electron Microscopy (SEM for mode of failure. Results: All of the study groups had a significantly lower microTBS as compared to the control group ( P < 0.001. There was no statistically significant difference between mechanical cycling with 50K (kilo = 1000 cycles, and 50K mechanical cycles plus 1K thermal cycles. Most of the fractures in the control group were of adhesive type and this type of fracture increased after exposure to mechanical and thermal load cycling. Conclusion: Thermal and mechanical load cycling had significant negative effects on microTBS and the significant effects of mechanical load cycling started to be significant at 100K cycles.

Fluid load support and contact mechanics of hemiarthroplasty in the natural hip joint.

Science.gov (United States)

Pawaskar, Sainath Shrikant; Ingham, Eileen; Fisher, John; Jin, Zhongmin

2011-01-01

The articular cartilage covering the ends of the bones of diarthrodial synovial joints is thought to have evolved so that the loads are transferred under different and complex conditions, with a very high degree of efficiency and without compromising the structural integrity of the tissue for the life of an individual. These loading conditions stem from different activities such as walking, and standing. The integrity of cartilage may however become compromised due to congenital disease, arthritis or trauma. Hemiarthroplasty is a potentially conservative treatment when only the femoral cartilage is affected as in case of femoral neck fractures. In hemiarthroplasty, a metallic femoral prosthesis is used to articulate against the natural acetabular cartilage. It has also been hypothesized that biphasic lubrication is the predominant mechanism protecting the cartilage through a very high fluid load support which lowers friction. This may be altered due to hemiarthroplasty and have a direct effect on the frictional shear stresses and potentially cartilage degradation and wear. This study modelled nine activities of daily living and investigated the contact mechanics of a hip joint with a hemiarthroplasty, focussing particularly on the role of the fluid phase. It was shown that in most of the activities studied the peak contact stresses and peak fluid pressures were in the superior dome or lateral roof of the acetabulum. Total fluid load support was very high (~90%) in most of the activities which would shield the solid phase from being subjected to very high contact stresses. This was dependent not only on the load magnitude but also the direction and hence on the location of the contact area with respect to the cartilage coverage. Lower fluid load support was found when the contact area was nearer the edges where the fluid drained easily. Copyright © 2010 IPEM. Published by Elsevier Ltd. All rights reserved.

A new pressure chamber to study the biosynthetic response of articular cartilage to mechanical loading.

Science.gov (United States)

Steinmeyer, J; Torzilli, P A; Burton-Wurster, N; Lust, G

1993-01-01

A prototype chamber was used to apply a precise cyclic or static load on articular cartilage explants under sterile conditions. A variable pressure, pneumatic controller was constructed to power the chamber's air cylinder, capable of applying, with a porous load platen, loads of up to 10 MPa at cycles ranging from 0 to 10 Hz. Pig articular cartilage explants were maintained successfully in this chamber for 2 days under cyclic mechanical loading of 0.5 Hz, 0.5 MPa. Explants remained sterile, viable and metabolically active. Cartilage responded to this load with a decreased synthesis of fibronectin and a small but statistically significant elevation in proteoglycan content. Similar but less extensive effects on fibronectin synthesis were observed with the small static load (0.016 MPa) inherent in the design of the chamber.

Friction Stir Weld Failure Mechanisms in Aluminum-Armor Structures Under Ballistic Impact Loading Conditions

Science.gov (United States)

2013-01-01

REPORT Friction Stir Weld Failure Mechanisms in Aluminum-Armor Structures Under Ballistic Impact Loading Conditions 14. ABSTRACT 16. SECURITY...properties and of the attendant ballistic-impact failure mechanisms in prototypical friction stir welding (FSW) joints found in armor structures made of high...mechanisms, friction stir welding M. Grujicic, B. Pandurangan, A. Arakere, C-F. Yen, B. A. Cheeseman Clemson University Office of Sponsored Programs 300

Self-healing of mechanically-loaded self consolidating concretes with high volumes of fly ash

Energy Technology Data Exchange (ETDEWEB)

Mustafa Sahmaran; Suleyman B. Keskin; Gozde Ozerkan; Ismail O. Yaman [University of Gaziantep, Gaziantep (Turkey). Department of Civil Engineering

2008-11-15

This article discusses the effects of self-healing on self consolidating concretes incorporating high volumes of fly ash (HVFA-SCC) when subjected to continuous water exposure. For this purpose, self consolidating concretes with fly ash replacement ratios of 0%, 35%, and 55% were prepared having a constant water-cementitious material ratio of 0.35. A uniaxial compression load was applied to generate microcracks in concrete where cylindrical specimens were pre-loaded up to 70% and 90% of the ultimate compressive load determined at 28 days. Later, the extent of damage was determined as percentage of loss in mechanical properties and percentage of increase in permeation properties. After pre-loading, concrete specimens were stored in water for a month and the mechanical and permeation properties are monitored at every two weeks. It was observed that HVFA-SCC mixtures initially lost 27% of their strength when pre-loaded up to 90% of their ultimate strength, and after 30 days of water curing that reduction was only 7%, indicating a substantial healing. On the other hand, for SCC specimens without fly ash that were pre-loaded to the same level, the loss in strength was initially 19%, and after a month of moist curing it was only 13%. Similar observations were also made on the permeation properties with greater effects. As the HVFA-SCCs studied have an important amount of unhydrated fly ash available in their microstructure, these observations are attributed to the self-healing of the pre-existing cracks, mainly by hydration of anhydrous fly ash particles on the crack surfaces.

External And Internal Work Of A T-6 Paraplegic Propelling A Wheelchair And Arm Cranking A Cycle Ergometer: Case Study

Science.gov (United States)

Novak, Charles W.

1982-02-01

In this, the International Year of the Disabled, attention is directed among other areas toward rehabilitation and sports participation of wheelchair users. As an application of movement analysis in medicine and rehabilitation and as an application of sports research using biomechanics, this investigation was performed to compare the results of two methods of gathering data on the stress of wheelchair propelling at equivalent work loads and to account for differences in physiological responses with a mechanical analysis of wheelchair propelling. Physiological data collected were heart rate, systolic blood pressure, and rate-pressure product. A biomechanical cinematography analysis was used to determine external work in wheelchair propelling and to determine the extent to which modifications in segment actionsoccurred during increasing magnitude of work. A cycle ergometer was adjusted to replicate external work loads performed during wheelchair propelling. A t-test of equivalent external work loads indicated that heart rate was not different between the two exercise modes at the .05 level of significance. The t-test did indicate a significant difference in systolic blood pressure and rate-pressure product at the .05 level of significance. The biomechanical analysis of wheelchair propelling established that an increase in external work was accomplished by a decrease in the range of motion and an increase in the speed of movement. During cycle ergometry the range and speed of movement remained the same while resistance was increased. Results of the study established that while heart rate for equivalent external work loads was the same for wheelchair propelling and arm cranking cycle ergometry, systolic blood pressure and rate-pressure product were not the same. The suggestion was that some means of propelling a wheelchair other than that which is con-sidered "standard" might be considered which produces less stressful responses in wheelchair users.

Mechanisms of adaptation to intensive loads of 400 meters’ hurdles runners at stage of initial basic training

Directory of Open Access Journals (Sweden)

A.S. Rovniy

2015-08-01

Full Text Available Purpose: is study of adaptation mechanisms of 400 meter’ hurdles-runners to intensive physical loads. Material: in the research 13 - 400 meters’ hurdles-runners and 13 - 400 meters’ runners participated. Results: it was found that physiological cost of sportsmen’s special workability has fragmentary character. We presented results of physiological and bio-chemical adaptation mechanisms to dozed work. The received results have no confident distinctions and can not objectively characterize mechanisms of sportsmen’s special workability. We did not detect definite differences in indicators of mechanisms, ensuring sportsmen’s special workability under dozed loads. We found, that level of anaerobic glycolysis is an objective criterion of 400 meter’ hurdles-runners’ special workability. It was shown that for determination of functional potentials for such kind of functioning it is necessary to apply special loads. Conclusions: the received results deepen information about mechanisms of adaptation to specific competition functioning. Correct approaches to processing and analysis of the research’s results permit to more specifically determine sportsmen’s functional potentials in different kinds of competition functioning.

Thermal and mechanical cyclic loading of thick spherical vessels made of transversely isotropic materials

International Nuclear Information System (INIS)

Komijani, M.; Mahbadi, H.; Eslami, M.R.

2013-01-01

The aim of this paper is to obtain the dependency of the ratcheting, reversed plasticity, or shakedown behavior of spherical vessels made of some anisotropic materials to the stress category of imposed cyclic loading. The Hill anisotropic yield criterion with the kinematic hardening theories of plasticity based on the Prager and Armstrong–Frederick models are used to predict the yield of the vessel and obtain the plastic strains. An iterative numerical method is used to simulate the cyclic loading behavior of the structure. The effect of mean and amplitude of the mechanical and thermal loads on cyclic behavior and ratcheting rate of the vessel is investigated respectively. The ratcheting rate for the vessels made of transversely isotropic material is evaluated for the various ratios of anisotropy. -- Highlights: ► Cyclic loading analysis of anisotropic spheres is assessed. ► Using the Prager model results in ratcheting. ► Armstrong-Frederick model predicts ratcheting for load controlled cyclic loadings. ► The A-F model predicts ratcheting to a stabilized cycle for thermal loadings

Monitoring Elite Soccer Players' External Loads Using Real-Time Data.

Science.gov (United States)

Barrett, Steve

2017-11-01

To assess the validity of measuring locomotor activities and PlayerLoad using real-time (RT) data collection during soccer training. Twenty-nine English soccer players participated. Each player wore the same MEMS device (Micromechanical Electrical Systems; S5, Optimeye; CatapultSports, Melbourne, Australia) during 21 training sessions (N = 331 data sets) in the 2015-16 and 2016-17 seasons. An RT receiver (TRX; Catapultsports, Melbourne, Australia) was used to collect the locomotor activities and PlayerLoad data in RT and compared with the postevent downloaded (PED) data. PlayerLoad and locomotor activities (total distance covered; total high-speed running distance covered, >5.5#x00A0;m/s; total sprinting distance covered, >7 m/s; maximum velocity) were analyzed. Correlations were near perfect for all variables analyzed (r = .98-1.00), with a varied level of noise between RT and PED also (0.3-9.7% coefficient of variation). Locomotor activities and PlayerLoad can use both RT and PED concurrently to quantify a player's physical output during a training session. Caution should be taken with higher-velocity-based locomotor activities during RT compared to PED.

[Analysis of the results of the HIV-1, HCV and HBV viral load of SEIMC External Quality Control Program. Year 2014].

Science.gov (United States)

Medina González, Rafael; Orta Mira, Nieves; Guna Serrano, María Del Remedio; Latorre Martínez, José-Carlos; Gopegui, Enrique Ruiz de; Rosario Ovies, María; Poveda, Marta; Gimeno Cardona, Concepción

2016-07-01

Human immunodeficiency virus type 1 (HIV-1), hepatitis B virus (HBV) and hepatitis C virus (HCV) viral load determinations are among the most relevant markers for the follow up of patients infected with these viruses. External quality control tools are crucial to ensure the accuracy of results obtained by microbiology laboratories. This article summarizes the results obtained from the 2014 SEIMC (Spanish Society of Infectious Diseases and Clinical Microbiology) External Quality Control Programme for HIV-1, HCV, and HBV viral loads. In the HIV-1 program, a total of 5 standards were sent. One standard consisted in seronegative human plasma, while the remaining 4 contained plasma from 3 different viremic patients, in the range of 2-5 log10 copies/mL; 2 of these standards were identical aiming to determine repeatability. A significant proportion of the laboratories (30.8% on average) obtained values out of the accepted range (mean ± 0.25 log10 copies/mL), depending on the standard and on the method used for quantification. Repeatability was excellent, with up to 95.8% of laboratories reporting results within the limits (Δ quality of the results obtained by a particular laboratory, as well as the importance of the post-analytical phase on the overall quality. Due to the remarkable interlaboratory variability, it is advisable to use the same method and the same laboratory for patient follow up. Copyright © 2016 Elsevier España, S.L.U. All rights reserved.

Protection of nuclear power plants against external events

International Nuclear Information System (INIS)

Suetterlin, L.

1978-01-01

The different aspects for the selection of external events to be accounted for in designing nuclear power plants and in defining load assumptions are illustrated: 1) In case of earthquake the severest possible events according to the state of science and technology are assumed. 2) For events where it is not or only to a certain extent possible to apply this method, e.g. in the load case airplane crash, load assumptions are defined in a combined probabilitic-deterministic way. By the example of plant protection, it is shown that by integrating all measures for protecting against interference of third parties (sabotage) or other external events, optimum protection concepts may be achieved. In all considerations on interference of third parties or other external events, one has to take into account that absolute protection is not possible. Nevertheless, it may be confirmed that nuclear power plants not only have a much higher level of protection than other, non-nuclear plants with equal or even higher potential hazard, but also that they meet the requirement not to increase significantly the current risk of society. (orig./HP) [de

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.

Mechanical effects associated with surface loading of dry rock due to glaciation

International Nuclear Information System (INIS)

Wahi, K.K.; Hunter, R.L.

1985-01-01

Many scenarios of interest for a repository in the Pasco Basin begin with glaciation. Loading and unloading of joints and fractures due to the weight of ice sheets could affect the hydrologic properties of the host rock and surrounding units. Scoping calculations performed using two-dimensional numerical models with simplifying assumptions predict stress changes and uplift or subsidence caused by an advancing glacier. The magnitudes of surface uplift and subsidence predicted by the study agree well with previous independent predictions. Peak stress unloading near the repository horizon is a small fraction of the ambient stress. Any resultant aperture increase is likewise small. Based on the results of this study, mechanical loading caused by a glacier is expected to have a minimal effect on rock permeability, assuming that the excess compressive loads do not crush the rock. 13 refs., 3 figs., 1 tab

Fullerene–epoxy nanocomposites-enhanced mechanical properties at low nanofiller loading

International Nuclear Information System (INIS)

Rafiee, Mohammad A.; Yavari, Fazel; Rafiee, Javad; Koratkar, Nikhil

2011-01-01

In this study, we characterized the mechanical properties of fullerence (C 60 ) epoxy nanocomposites at various weight fractions of fullerene additives in the epoxy matrix. The mechanical properties measured were the Young’s modulus, ultimate tensile strength, fracture toughness, fracture energy, and the material’s resistance to fatigue crack propagation. All of the above properties of the epoxy polymer were significantly enhanced by the fullerene additives at relatively low nanofiller loading fractions (∼0.1 to 1% of the epoxy matrix weight). By contrast, other forms of nanoparticle fillers such as silica, alumina, and titania nanoparticles require up to an order of magnitude higher weight fraction to achieve comparable enhancement in properties.

X-ray endoscopic techniques for external and internal drainage of bile ducts in mechanical jaundice

International Nuclear Information System (INIS)

Kharchenko, V.P.; Sinev, Yu.V.; Solomatin, A.D.

2000-01-01

Generalized information is considered on the application of external-internal X-ray endoscopic drainage of stomach, gallbladder, bile ducts in case of mechanical jaundice caused by both neoplasms and other diseases of pancreatobiliary zone. Indications for drainage are presented as well as contraindications, necessary equipment and instruments, recommendations on procedure realization [ru

Failure mechanisms of closed-cell aluminum foam under monotonic and cyclic loading

International Nuclear Information System (INIS)

Amsterdam, E.; De Hosson, J.Th.M.; Onck, P.R.

2006-01-01

This paper concentrates on the differences in failure mechanisms of Alporas closed-cell aluminum foam under either monotonic or cyclic loading. The emphasis lies on aspects of crack nucleation and crack propagation in relation to the microstructure. The cell wall material consists of Al dendrites and an interdendritic network of Al 4 Ca and Al 22 CaTi 2 precipitates. In situ scanning electron microscopy monotonic tensile tests were performed on small samples to study crack nucleation and propagation. Digital image correlation was employed to map the strain in the cell wall on the characteristic microstructural length scale. Monotonic tensile tests and tension-tension fatigue tests were performed on larger samples to observe the overall fracture behavior and crack path in monotonic and cyclic loading. The crack nucleation and propagation path in both loading conditions are revealed and it can be concluded that during monotonic tension cracks nucleate in and propagate partly through the Al 4 Ca interdendritic network, whereas under cyclic loading cracks nucleate and propagate through the Al dendrites

Design and operations of a load-tolerant external conjugate-T matching system for the A2 ICRH antennas at JET

International Nuclear Information System (INIS)

Monakhov, I.; Graham, M.; Blackman, T.; Dowson, S.; Durodie, F.; Jacquet, P.; Lehmann, J.; Mayoral, M.-L.; Nightingale, M.P.S.; Noble, C.; Sheikh, H.; Vrancken, M.; Walden, A.; Whitehurst, A.; Wooldridge, E.

2013-01-01

A load-tolerant external conjugate-T (ECT) impedance matching system for two A2 ion cyclotron resonance heating (ICRH) antennas was successfully put into operation at JET. The system allows continuous injection of the radio-frequency (RF) power into plasma in the presence of strong antenna loading perturbations caused by edge-localized modes (ELMs). Reliable ECT performance was demonstrated under a variety of antenna loading conditions including H-mode plasmas with radial outer gaps (ROGs) in the range 4–14 cm. The high resilience to ELMs predicted during the circuit simulations was fully confirmed experimentally. Dedicated arc-detection techniques and real-time matching algorithms were developed as a part of the ECT project. The new advanced wave amplitude comparison system has proven highly efficient in detection of arcs both between and during ELMs. The ECT system has allowed the delivery of up to 4 MW of RF power without trips into plasmas with type-I ELMs. Together with the 3 dB system and the ITER-like antenna, the ECT has brought the total RF power coupled to ELMy plasma to over 8 MW, considerably enhancing JET research capabilities. This paper provides an overview of the key design features of the ECT system and summarizes the main experimental results achieved so far. (paper)

Thermo-mechanical modelling of salt caverns due to fluctuating loading conditions.

Science.gov (United States)

Böttcher, N.

2015-12-01

This work summarizes the development and application of a numerical model for the thermo-mechanical behaviour of salt caverns during cyclic gas storage. Artificial salt caverns are used for short term energy storage, such as power-to-gas or compressed air energy storage. Those applications are characterized by highly fluctuating operation pressures due to the unsteady power levels of power plants based on renewable energy. Compression and expansion of the storage gases during loading and unloading stages lead to rapidly changing temperatures in the host rock of the caverns. This affects the material behaviour of the host rock within a zone that extends several meters into the rock mass adjacent to the cavern wall, and induces thermo-mechanical stresses and alters the creep response.The proposed model features the thermodynamic behaviour of the storage medium, conductive heat transport in the host rock, as well as temperature dependent material properties of rock salt using different thermo-viscoplastic material models. The utilized constitutive models are well known and state-of-the-art in various salt mechanics applications. The model has been implemented into the open-source software platform OpenGeoSys. Thermal and mechanical processes are solved using a finite element approach, coupled via a staggered coupling scheme. The simulation results allow the conclusion, that the cavern convergence rate (and thus the efficiency of the cavern) is highly influenced by the loading cycle frequency and the resulting gas temperatures. The model therefore allows to analyse the influence of operation modes on the cavern host rock or on neighbouring facilities.

Mechanical Behavior of Red Sandstone under Incremental Uniaxial Cyclical Compressive and Tensile Loading

Directory of Open Access Journals (Sweden)

Baoyun Zhao

2017-01-01

Full Text Available Uniaxial experiments were carried out on red sandstone specimens to investigate their short-term and creep mechanical behavior under incremental cyclic compressive and tensile loading. First, based on the results of short-term uniaxial incremental cyclic compressive and tensile loading experiments, deformation characteristics and energy dissipation were analyzed. The results show that the stress-strain curve of red sandstone has an obvious memory effect in the compressive and tensile loading stages. The strains at peak stresses and residual strains increase with the cycle number. Energy dissipation, defined as the area of the hysteresis loop in the stress-strain curves, increases nearly in a power function with the cycle number. Creep test of the red sandstone was also conducted. Results show that the creep curve under each compressive or tensile stress level can be divided into decay and steady stages, which cannot be described by the conventional Burgers model. Therefore, an improved Burgers creep model of rock material is constructed through viscoplastic mechanics, which agrees very well with the experimental results and can describe the creep behavior of red sandstone better than the Burgers creep model.

Abnormal liquid loading in gas wells of the Samandepe Gasfield in Turkmenistan and countermeasures

Directory of Open Access Journals (Sweden)

Peijun Zhang

2015-10-01

Full Text Available With complicated formation mechanisms, liquid loading in gas wells during gasfield development may significantly affect the productivity of gas wells and the ultimate recovery rate. Dynamic monitoring data of the Samandepe Gasfield in Turkmenistan shows that liquid loading can be found extensively in gas wells. Their formation mechanisms and negative impacts on gasfield development severely restrict the productivity enhancement of this gasfield. With their origins taken into consideration, liquid loads in gas wells were classified into three types: formation water, condensed liquid, and external liquid. By using the hydrostatic pressure gradient method and through PLT monitoring, properties of liquid loads in the Samandepe Gasfield were determined. In addition, formation mechanisms related to liquid loading in gas wells were obtained through analyses of critical fluid-carrying capacities and by using gas-reservoir production data. The following findings were obtained. Liquid loading was commonly found in this gas well with majority of reservoir formations in lower well intervals flooded. However, the formation mechanisms for these liquid loads are different from those of other gasfields. Due to long-term shut-down of gas wells, killing fluids precipitated and pores in lower reservoir formations were plugged. As a result, natural gas had no access to boreholes, killing fluids were impossibly carried out of the borehole. Instead, the killing fluid was detained at the bottomhole to generate liquid load and eliminate the possibility of formation water coning. Moreover, since the gasfield was dominated by block reservoirs with favorable physical properties and connectivity, impacts of liquid load on gasfield development were insignificant. Thus, to enhance the recovery rate of the Samandepe Gasfield significantly, it is necessary to expand the gasfield development scale and strengthen the development of marginal gas reservoirs.

Dynamics and mechanics of bed-load tracer particles

Directory of Open Access Journals (Sweden)

C. B. Phillips

2014-12-01

Full Text Available Understanding the mechanics of bed load at the flood scale is necessary to link hydrology to landscape evolution. Here we report on observations of the transport of coarse sediment tracer particles in a cobble-bedded alluvial river and a step-pool bedrock tributary, at the individual flood and multi-annual timescales. Tracer particle data for each survey are composed of measured displacement lengths for individual particles, and the number of tagged particles mobilized. For single floods we find that measured tracer particle displacement lengths are exponentially distributed; the number of mobile particles increases linearly with peak flood Shields stress, indicating partial bed load transport for all observed floods; and modal displacement distances scale linearly with excess shear velocity. These findings provide quantitative field support for a recently proposed modeling framework based on momentum conservation at the grain scale. Tracer displacement is weakly negatively correlated with particle size at the individual flood scale; however cumulative travel distance begins to show a stronger inverse relation to grain size when measured over many transport events. The observed spatial sorting of tracers approaches that of the river bed, and is consistent with size-selective deposition models and laboratory experiments. Tracer displacement data for the bedrock and alluvial channels collapse onto a single curve – despite more than an order of magnitude difference in channel slope – when variations of critical Shields stress and flow resistance between the two are accounted for. Results show how bed load dynamics may be predicted from a record of river stage, providing a direct link between climate and sediment transport.

Estimation of the mechanical loading of the shoulder joint in daily conditions

NARCIS (Netherlands)

De Vries, W.H.K.

2015-01-01

The goal of this thesis is to assemble a method to estimate shoulder joint reaction forces, in daily conditions, based on long term collection of ambulatory measurable variables, to obtain the desired long term mechanical load profile of the shoulder. Chapter 2 examines, and discusses one of the

Effect of elastic and plastic tensile mechanical loading on the magnetic properties of NGO electrical steel

Energy Technology Data Exchange (ETDEWEB)

Leuning, N., E-mail: nora.leuning@iem.rwth-aachen.de [Institute of Electrical Machines, RWTH Aachen University, D-52062 Aachen (Germany); Steentjes, S. [Institute of Electrical Machines, RWTH Aachen University, D-52062 Aachen (Germany); Schulte, M.; Bleck, W. [Steel Institute, RWTH Aachen University, D-52072 Aachen (Germany); Hameyer, K. [Institute of Electrical Machines, RWTH Aachen University, D-52062 Aachen (Germany)

2016-11-01

The magnetic properties of non-grain-oriented (NGO) electrical steels are highly susceptible to mechanical stresses, i.e., residual, external or thermal ones. For rotating electrical machines, mechanical stresses are inevitable and originate from different sources, e.g., material processing, machine manufacturing and operating conditions. The efficiency and specific losses are largely altered by different mechanical stress states. In this paper the effect of tensile stresses and plastic deformations on the magnetic properties of a 2.9 wt% Si electrical steel are studied. Particular attention is paid to the effect of magnetic anisotropy, i.e., the influence of the direction of applied mechanical stress with respect to the rolling direction. Due to mechanical stress, the induced anisotropy has to be evaluated as it is related to the stress-dependent magnetostriction constant and the grain alignment. - Highlights: • A detailed look at magnetic anisotropy of FeSi NGO electrical steel. • Study of magnetic behavior under elastic as well as plastic tensile stresses. • Correlation of magnetic behavior with microscopic deformation mechanisms. • Discussion of detrimental and beneficial effects of external stresses. • Loss separation at different polarizations and frequencies under increasing stress.

Effect of elastic and plastic tensile mechanical loading on the magnetic properties of NGO electrical steel

International Nuclear Information System (INIS)

Leuning, N.; Steentjes, S.; Schulte, M.; Bleck, W.; Hameyer, K.

2016-01-01

The magnetic properties of non-grain-oriented (NGO) electrical steels are highly susceptible to mechanical stresses, i.e., residual, external or thermal ones. For rotating electrical machines, mechanical stresses are inevitable and originate from different sources, e.g., material processing, machine manufacturing and operating conditions. The efficiency and specific losses are largely altered by different mechanical stress states. In this paper the effect of tensile stresses and plastic deformations on the magnetic properties of a 2.9 wt% Si electrical steel are studied. Particular attention is paid to the effect of magnetic anisotropy, i.e., the influence of the direction of applied mechanical stress with respect to the rolling direction. Due to mechanical stress, the induced anisotropy has to be evaluated as it is related to the stress-dependent magnetostriction constant and the grain alignment. - Highlights: • A detailed look at magnetic anisotropy of FeSi NGO electrical steel. • Study of magnetic behavior under elastic as well as plastic tensile stresses. • Correlation of magnetic behavior with microscopic deformation mechanisms. • Discussion of detrimental and beneficial effects of external stresses. • Loss separation at different polarizations and frequencies under increasing stress.

Temporal mechanically-induced signaling events in bone and dorsal root ganglion neurons after in vivo bone loading.

Directory of Open Access Journals (Sweden)

Jason A Bleedorn

Full Text Available Mechanical signals play an integral role in the regulation of bone mass and functional adaptation to bone loading. The osteocyte has long been considered the principle mechanosensory cell type in bone, although recent evidence suggests the sensory nervous system may play a role in mechanosensing. The specific signaling pathways responsible for functional adaptation of the skeleton through modeling and remodeling are not clearly defined. In vitro studies suggest involvement of intracellular signaling through mitogen-activated protein kinase (MAPK, phosphatidylinositol 3-kinase (PI3K/protein kinase B (Akt, and mammalian target of rapamycin (mTOR. However, anabolic signaling responses to bone loading using a whole animal in vivo model have not been studied in detail. Therefore, we examined mechanically-induced signaling events at five time points from 0 to 24 hours after loading using the rat in vivo ulna end-loading model. Western blot analysis of bone for MAPK's, PI3K/Akt, and mTOR signaling, and quantitative reverse transcription polymerase chain reaction (qRT-PCR to estimate gene expression of calcitonin gene-related protein alpha (CGRP-α, brain-derived neurotrophic factor (BDNF, nerve growth factor (NGF, c-jun, and c-fos in dorsal root ganglion (DRG of the brachial intumescence were performed. There was a significant increase in signaling through MAPK's including extracellular signal-related kinase (ERK and c-Jun N-terminal kinase (JNK in loaded limbs at 15 minutes after mechanical loading. Ulna loading did not significantly influence expression of the genes of interest in DRG neurons. Bone signaling and DRG gene expression from the loaded and contralateral limbs was correlated (SR>0.40, P<0.05. However, bone signaling did not correlate with expression of the genes of interest in DRG neurons. These results suggest that signaling through the MAPK pathway may be involved in load-induced bone formation in vivo. Further characterization of the

Kenaf/PP and EFB/PP: Effect of fibre loading on the mechanical properties of polypropylene composites

Science.gov (United States)

Anuar, N. I. S.; Zakaria, S.; Harun, J.; Wang, C.

2017-07-01

Kenaf and empty fruit bunch (EFB) fibre which are the important natural fibres in Malaysia were studied as nonwoven polymer composites. The effect of fibre loading on kenaf polypropylene and EFB polypropylene nonwoven composite was studied at different mixture ratio. Kenaf polypropylene nonwoven composite (KPNC) and EFB polypropylene nonwoven composite (EPNC) were prepared by carding and needle-punching techniques, followed by a compression moulding at 6 mm thickness. This study was conducted to identify the optimum fibre loading of nonwoven polypropylene composite and their effect on the mechanical strength. The study was designed at 40%, 50%, 60% and 70% of fibre content in nonwoven mat and composite. The tensile strength, flexural strength and compression strength were tested to evaluate the composite mechanical properties. It was found that the mechanical properties for both kenaf and EFB nonwoven composites were influenced by the fibre content. KPNC showed higher mechanical strength than EPNC. The highest flexural strength was obtained at 60% KPNC and the lowest value was showed by 40% EPNC. The tensile and flexural strength for both KPNC and EPNC decreased after the fibre loading of 60%.

Using the Enhanced Daily Load Stimulus Model to Quantify the Mechanical Load and Bone Mineral Density Changes Experienced by Crew Members on the International Space Station

Science.gov (United States)

Genc, K. O.; Gopalakrishnan, R.; Kuklis, M. M.; Maender, C. C.; Rice, A. J.; Cavanagh, P. R.

2009-01-01

Despite the use of exercise countermeasures during long-duration space missions, bone mineral density (BMD) and predicted bone strength of astronauts continue to show decreases in the lower extremities and spine. This site-specific bone adaptation is most likely caused by the effects of microgravity on the mechanical loading environment of the crew member. There is, therefore, a need to quantify the mechanical loading experienced on Earth and on-orbit to define the effect of a given "dose" of loading on bone homeostasis. Gene et al. recently proposed an enhanced DLS (EDLS) model that, when used with entire days of in-shoe forces, takes into account recently developed theories on the importance of factors such as saturation, recovery, and standing and their effects on the osteogenic response of bone to daily physical activity. This algorithm can also quantify the tinting and type of activity (sit/unload, stand, walk, run or other loaded activity) performed throughout the day. The purpose of the current study was to use in-shoe force measurements from entire typical work days on Earth and on-orbit in order to quantify the type and amount of loading experienced by crew members. The specific aim was to use these measurements as inputs into the EDLS model to determine activity timing/type and the mechanical "dose" imparted on the musculoskeletal system of crew members and relate this dose to changes in bone homeostasis.

Experimental Study on Mechanical and Acoustic Emission Characteristics of Rock-Like Material Under Non-uniformly Distributed Loads

Science.gov (United States)

Wang, Xiao; Wen, Zhijie; Jiang, Yujing; Huang, Hao

2018-03-01

The mechanical and acoustic emission characteristics of rock-like materials under non-uniform loads were investigated by means of a self-developed mining-induced stress testing system and acoustic emission monitoring system. In the experiments, the specimens were divided into three regions and different initial vertical stresses and stress loading rates were used to simulate different mining conditions. The mechanical and acoustic emission characteristics between regions were compared, and the effects of different initial vertical stresses and different stress loading rates were analysed. The results showed that the mechanical properties and acoustic emission characteristics of rock-like materials can be notably localized. When the initial vertical stress and stress loading rate are fixed, the peak strength of region B is approximately two times that of region A, and the maximum acoustic emission hit value of region A is approximately 1-2 times that of region B. The effects of the initial vertical stress and stress loading rate on the peck strain, maximum hit value, and occurrence time of the maximum hit are similar in that when either of the former increase, the latter all decrease. However, peck strength will increase with the increase in loading rate and decrease with the increase in initial vertical stress. The acoustic emission hits can be used to analyse the damage in rock material, but the number of acoustic emission hits cannot be used alone to determine the degree of rock damage directly.

Mechanical analysis of the EC upper launcher with respect to electromagnetic loads

International Nuclear Information System (INIS)

Vaccaro, A.; Kleefeldt, K.; Spaeh, P.; Strauss, D.

2009-01-01

The design of the EC upper launcher for ITER approaches maturity and thus it needs to be qualified with respect to the critical loads. One major source of critical loads are eddy currents, which are induced in the structure during plasma instabilities, of which the most severe conditions may happen during a vertical displacement event (VDE) followed by a fast current quench. High mechanical loads are then acting on the front end of the cantilevered launcher structure as a consequence of the interaction between the static toroidal field and the eddy currents. The EC upper launcher has a length of about 6 m and the nominal gap to the neighbouring components is 20 mm. The targeted limit for the launcher displacements is 10 mm, when accounting for tolerances in manufacturing, positioning and thermal displacement. The conceptual design of the launcher is at risk to miss this requirement, thus different configurations of the main frame are considered and analysed. Especially, the cross-section of the single wall segment has been varied to identify the most efficient strategy for increasing the stiffness of the structure. For this purpose, the mechanical loads from an upward VDE (linear current decay from 15 to 0 MA within 40 ms) are used as input to a finite element analysis with the ANSYS software tool. The displacement at the free plasma facing end of the launcher is calculated and analyzed. Its main component is in toroidal direction and the effort of mitigation is concentrated primarily on the bottom-wall. The approach satisfies the limitations given by the space requests of the mm-wave system which is to be integrated into the port plug.

High Strain Rate Deformation Mechanisms of Body Centered Cubic Material Subjected to Impact Loading

Science.gov (United States)

Visser, William

Low carbon steel is the most common grade of structural steel used; it has carbon content of 0.05% to 0.25% and very low content of alloying elements. It is produced in great quantities and provides material properties that are acceptable for many engineering applications, particularly in the construction industry in which low carbon steel is widely used as the strengthening phase in civil structures. The overall goal of this dissertation was to investigate the deformation response of A572 grade 50 steel when subjected to impact loading. This steel has a 0.23% by weight carbon content and has less than 2% additional alloying elements. The deformation mechanisms of this steel under shock loading conditions include both dislocation motion and twin formation. The goal of this work was achieved by performing experimental, analytical and numerical research in three integrated tasks. The first is to determine the relationship between the evolution of deformation twins and the impact pressure. Secondly, a stress criterion for twin nucleation during high strain rate loading was developed which can account for the strain history or initial dislocation density. Lastly, a method was applied for separating the effects of dislocations and twins generated by shock loading in order to determine their role in controlling the flow stress of the material. In this regard, the contents of this work have been categorically organized. First, the active mechanisms in body centered cubic (BCC) low carbon steel during shock loading have been determined as being a composed of the competing mechanisms of dislocations and deformation twins. This has been determined through a series of shock loading tests of the as-received steel. The shock loading tests were done by plate impact experiments at several impact pressures ranging from 2GPa up to 13GPa using a single stage light gas gun. A relationship between twin volume fraction and impact pressure was determined and an analytical model was

Mechanisms for closing bores and releasably securing articles within the bores under longitudinal load

International Nuclear Information System (INIS)

Klahn, F.C.; Nolan, J.H.; Wills, C.

1979-01-01

This invention relates to mechanisms for closing bores of tubular passages and for releasably securing articles within the bores under longitudinal load. The system includes an axially movable latch, an actuator and locking devices. Embodiments of the invention can be used as closure mechanisms for tubular irradiation surveillance specimen assembly holders used in nuclear reactors. (UK)

Mechanisms for closing bores and releasably securing articles within the bores under longitudinal load

International Nuclear Information System (INIS)

Kalen, D.D.; Mitchem, J.W.

1979-01-01

This invention relates to mechanisms for closing bores of tubular passages and for releasably securing articles within the bores under longitudinal load. The system includes an axially movable actuator and a latch which engages the tubular opening. Embodiments of the invention can be used as closure mechanisms for tubular irradiation surveillance specimen assembly holders used in nuclear reactors. (UK)

Load response of shape-changing microswimmers scales with their swimming efficiency

Science.gov (United States)

Friedrich, Benjamin M.

2018-04-01

External forces acting on a microswimmer can feed back on its self-propulsion mechanism. We discuss this load response for a generic microswimmer that swims by cyclic shape changes. We show that the change in cycle frequency is proportional to the Lighthill efficiency of self-propulsion. As a specific example, we consider Najafi's three-sphere swimmer. The force-velocity relation of a microswimmer implies a correction for a formal superposition principle for active and passive motion.

EVALUATION OF SHEAR STRENGTH FOR UPPER SLABS OF CAISSON FOUNDATION BASED ON LOAD CARRYING MECHANISM

Science.gov (United States)

Hattori, Hisamichi; Tadokoro, Toshiya; Tanimura, Yukihiro; Nishioka, Hidetoshi; Watanabe, Tadatomo; Maruyama, Osamu

In upper slabs of caisson foundation, a seismic desi gn is difficult with an incr ease in earthquake load. So we carried out loading tests and FEM analysis for upper slabs of caisson foundation. As a result, we proposed a new design method which takes into co nsideration the effective width on the pull out side based on crack pattern of test specimens, which is not considered in the existing design method. Moreover, we proposed a rational design method based on load carrying mechanism for upper slabs of caisson foundation.

CISM course on mechanical behaviour of soils under environmentally induced cyclic loads

CERN Document Server

Wood, David; Mechanical Behaviour of Soils Under Environmentally Induced Cyclic Loads

2012-01-01

The book gives a comprehensive description of the mechanical response of soils (granular and cohesive materials) under cyclic loading. It provides the geotechnical engineer with the theoretical and analytical tools necessary for the evaluation of settlements developng with time under cyclic, einvironmentally idncued loads (such as wave motion, wind actions, water table level variation) and their consequences for the serviceability and durability of structures such as the shallow or deep foundations used in offshore engineering, caisson beakwaters, ballast and airport pavements and also to interpret monitoring data, obtained from both natural and artificial slopes and earth embankments, for the purposes of risk assessment and mitigation.

Nonlinear dynamic response of electro-thermo-mechanically loaded piezoelectric cylindrical shell reinforced with BNNTs

International Nuclear Information System (INIS)

Yang, J H; Yang, J; Kitipornchai, S

2012-01-01

This paper presents an investigation on the nonlinear dynamic response of piezoelectric cylindrical shells reinforced with boron nitride nanotubes (BNNTs) under a combined axisymmetric electro-thermo-mechanical loading. By employing the classical Donnell shell theory, the von Kármán–Donnell kinematic relationship, and a piezo-elastic constitutive law including thermal effects, the nonlinear governing equations of motion of the shell are derived through the Reissner variational principle. The finite difference method and a time-integration scheme are used to obtain the nonlinear dynamic response of the BNNT-reinforced piezoelectric shell. A parametric study is conducted, showing the effects of geometrically nonlinear deformation, applied voltage, temperature change, mechanical load, BNNT volume fraction and boundary conditions on the nonlinear dynamic response. (paper)

New cooperative mechanisms of low-energy nuclear reactions using super low-energy external field

International Nuclear Information System (INIS)

Gareev, F.A.; Zhidkova, I.E.

2006-01-01

We propose a new mechanism of LENR: cooperative processes in the whole system, nuclei + atoms + condensed matter, can occur at a smaller threshold energies than the corresponding ones on free constituents. The cooperative processes can be induced and enhanced by low-energy external fields. The excess heat is the emission of internal energy and transmutations at LENR are the result of redistribution of inner energy of the whole system. (author)

New Cooperative Mechanisms of Low-Energy Nuclear Reactions Using Super Low-Energy External Field

Science.gov (United States)

Gareev, F. A.; Zhidkova, I. E.

We propose a new mechanism of LENR: cooperative processes in the whole system, nuclei + atoms + condensed matter, can occur at a smaller threshold energies than the corresponding ones on free constituents. The cooperative processes can be induced and enhanced by low-energy external fields. The excess heat is the emission of internal energy and transmutations at LENR are the result of redistribution of inner energy of the whole system.

Slide release mechanism. [for space shuttle orbiter/external tank connection device

Science.gov (United States)

Bunker, J. W.; Ritchie, R. S. (Inventor)

1985-01-01

A releasable support device is described which is comprised of a hollow body with a sleeve extending transversely there-through for receiving the end of a support shank. A slider-latch, optionally lubricated, extends through side recesses in the sleeve to straddle the shank, respectively, in latched and released positions. The slider-latch is slid from its latched to its unlatched position by a pressure squib whereupon a spring or other pressure means pushes the shank out of the sleeve. At the same time, a follower element is lodged in and closed the hole in the body wall from which the shank was discharged. The mechanism was designed for the shuttle orbiter/external tank connection device.

Bifurcations and chaos of the nonlinear viscoelastic plates subjected to subsonic flow and external loads

International Nuclear Information System (INIS)

An, Fengxian; Chen, Fangqi

2016-01-01

Highlights: • The subharmonic bifurcations and chaotic motions are studied by means of Melnikov method. • The critical conditions for the occurrence of chaotic motions and subharmonic bifurcations are obtained. • The chaotic features on the system parameters are discussed. • The theoretical predictions are confirmed by numerical simulations. - Abstract: The subharmonic bifurcations and chaotic motions of the nonlinear viscoelastic plates subjected to subsonic flow and external loads are studied by means of Melnikov method. The critical conditions for the occurrence of chaotic motions are obtained. The chaotic features on the system parameters are discussed in detail. The conditions for subharmonic bifurcations are also obtained. For the system with no structural damping, chaotic motions can occur through infinite subharmonic bifurcations of odd orders. Furthermore, we confirm our theoretical predictions by numerical simulations. The theoretical results obtained here can help us to eliminate or suppress large nonlinear vibrations and chaotic motions of the nonlinear viscoelastic plates. Based on Melnikov method, complex dynamical behaviors of the nonlinear viscoelastic plates can be controlled by modifying the system parameters.

Simulation based engineering in solid mechanics

CERN Document Server

Rao, J S

2017-01-01

This book begins with a brief historical perspective of the advent of rotating machinery in 20th century Solid Mechanics and the development of the discipline of the Strength of Materials. High Performance Computing (HPC) and Simulation Based Engineering Science (SBES) have gradually replaced the conventional approach in Design bringing science directly into engineering without approximations. A recap of the required mathematical principles is given. The science of deformation, strain and stress at a point under the application of external traction loads is next presented. Only one-dimensional structures classified as Bars (axial loads), Rods (twisting loads) and Beams (bending loads) are considered in this book. The principal stresses and strains and von Mises stress and strain that used in design of structures are next presented. Lagrangian solution was used to derive the governing differential equations consistent with assumed deformation field and solution for deformations, strains and stresses were obtai...

Externally predictive quantitative modeling of supercooled liquid vapor pressure of polychlorinated-naphthalenes through electron-correlation based quantum-mechanical descriptors.

Science.gov (United States)

Vikas; Chayawan

2014-01-01

For predicting physico-chemical properties related to environmental fate of molecules, quantitative structure-property relationships (QSPRs) are valuable tools in environmental chemistry. For developing a QSPR, molecular descriptors computed through quantum-mechanical methods are generally employed. The accuracy of a quantum-mechanical method, however, rests on the amount of electron-correlation estimated by the method. In this work, single-descriptor QSPRs for supercooled liquid vapor pressure of chloronaphthalenes and polychlorinated-naphthalenes are developed using molecular descriptors based on the electron-correlation contribution of the quantum-mechanical descriptor. The quantum-mechanical descriptors for which the electron-correlation contribution is analyzed include total-energy, mean polarizability, dipole moment, frontier orbital (HOMO/LUMO) energy, and density-functional theory (DFT) based descriptors, namely, absolute electronegativity, chemical hardness, and electrophilicity index. A total of 40 single-descriptor QSPRs were developed using molecular descriptors computed with advanced semi-empirical (SE) methods, namely, RM1, PM7, and ab intio methods, namely, Hartree-Fock and DFT. The developed QSPRs are validated using state-of-the-art external validation procedures employing an external prediction set. From the comparison of external predictivity of the models, it is observed that the single-descriptor QSPRs developed using total energy and correlation energy are found to be far more robust and predictive than those developed using commonly employed descriptors such as HOMO/LUMO energy and dipole moment. The work proposes that if real external predictivity of a QSPR model is desired to be explored, particularly, in terms of intra-molecular interactions, correlation-energy serves as a more appropriate descriptor than the polarizability. However, for developing QSPRs, computationally inexpensive advanced SE methods such as PM7 can be more reliable than

Computational modeling of the mechanical modulation of the growth plate by sustained loading

Directory of Open Access Journals (Sweden)

Narváez-Tovar Carlos A

2012-09-01

Full Text Available Abstract This paper presents a computational model that describes the growth of the bone as a function of the proliferation and hypertrophy of chondrocytes in the growth plate. We have included the effects of the mechanical loads on the sizes of the proliferative and hypertrophic areas, the number of proliferative chondrocytes and the final size of the hypertrophic chondrocytes. The validation of the model was performed with experimental data published on other investigations about proximal tibia of rats, subjected to sustained axial stresses of 0.1 MPa, 0.0 MPa, -0.1 MPa and −0.2 MPa. Growth was simulated during 23 days, obtaining numerical errors between 2.77% and 3.73% with respect to experimental growth rates. The results obtained show that the model adequately simulates the behavior of the growth plate and the effect of mechanical loads over its cellular activity.

Study on Mechanical Characteristics of Fully Grouted Rock Bolts for Underground Caverns under Seismic Loads

Directory of Open Access Journals (Sweden)

Guoqing Liu

2017-01-01

Full Text Available This study establishes an analytical model for the interaction between the bolt and surrounding rock based on the bearing mechanism of fully grouted rock bolts. The corresponding controlled differential equation for load transfer is deduced. The stress distributions of the anchorage body are obtained by solving the equations. A dynamic algorithm for the bolt considering shear damage on the anchoring interface is proposed based on the dynamic finite element method. The rationality of the algorithm is verified by a pull-out test and excavation simulation of a rounded tunnel. Then, a case study on the mechanical characteristics of the bolts in underground caverns under seismic loads is conducted. The results indicate that the seismic load may lead to stress originating from the bolts and damage on the anchoring interface. The key positions of the antiseismic support can be determined using the numerical simulation. The calculated results can serve as a reference for the antiseismic optimal design of bolts in underground caverns.

Slim 198gold-grain implanter loaded with standard royal marsden 14-grain magazines

International Nuclear Information System (INIS)

Delclos, L.; Moore, E.B.

1979-01-01

We designed a slim gold-grain implanter with adaptable lengths to implant areas accessible only through long, narrow, examining instruments, such as a suspension laryngoscope. The implanter is loaded with the same 14-grain magazine designed for and supplied with the Royal Marsden gun. The simplicity of the loading mechanism with a minimum of moving parts makes the instrument practically trouble free. Although it is designed to be used along narrow examining instruments, it can also be used in any situation in which a permanent implant is required, for instance, prostatic cancer and pelvic recurrences in cancer of the uterine cervix previously treated by external and intracavitary irradiation

Effect of surface loading on the hydro-mechanical response of a tunnel in saturated ground

Directory of Open Access Journals (Sweden)

Simon Heru Prassetyo

2016-09-01

Full Text Available The design of underground spaces in urban areas must account not only for the current overburden load but also for future surface loads, such as from construction of high-rise buildings above underground structures. In saturated ground, the surface load will generate an additional mechanical response through stress changes and ground displacement, as well as a hydraulic response through pore pressure changes. These hydro-mechanical (H-M changes can severely influence tunnel stability. This paper examines the effect of surface loading on the H-M response of a typical horseshoe-shaped tunnel in saturated ground. Two tunnel models were created in the computer code Fast Lagrangian Analysis of Continua (FLAC. One model represented weak and low permeability ground (stiff clay, and the other represented strong and high permeability ground (weathered granite. Each of the models was run under two liner permeabilities: permeable and impermeable. Two main cases were compared. In Case 1, the surface load was applied 10 years after tunnel construction. In Case 2, the surface load was applied after the steady state pore pressure condition was achieved. The simulation results show that tunnels with impermeable liners experienced the most severe influence from the surface loading, with high pore pressures, large inward displacement around the tunnels, and high bending moments in the liner. In addition, the severity of the response increased toward steady state. This induced H-M response was worse for tunnels in clay than for those in granite. Furthermore, the long-term liner stabilities in Case 1 and Case 2 were similar, indicating that the influence of the length of time between when the tunnel was completed and when the surface load was applied was negligible. These findings suggest that under surface loading, in addition to the ground strength, tunnel stability in saturated ground is largely influenced by liner permeability and the long-term H-M response of

Modeling of the mechanical behavior of austenitic stainless steels under pure fatigue and fatigue relaxation loadings

International Nuclear Information System (INIS)

Hajjaji-Rachdi, Fatima

2015-01-01

Austenitic stainless steels are potential candidates for structural components of sodium-cooled fast neutron reactors. Many of these components will be subjected to cyclic loadings including long hold times (1 month) under creep or relaxation at high temperature. These hold times are unattainable experimentally. The aim of the present study is to propose mechanical models which take into account the involved mechanisms and their interactions during such complex loadings. First, an experimental study of the pure fatigue and fatigue-relaxation behavior of 316L(N) at 500 C has been carried out with very long hold times (10 h and 50 h) compared with the ones studied in literature. Tensile tests at 600 C with different applied strain rates have been undertaken in order to study the dynamic strain ageing phenomenon. Before focusing on more complex loadings, the mean field homogenization approach has been used to predict the mechanical behavior of different FCC metals and alloys under low cycle fatigue at room temperature. Both Hill-Hutchinson and Kroener models have been used. Next, a physically-based model based on dislocation densities has been developed and its parameters measured. The model allows predictions in a qualitative agreement with experimental data for tensile loadings. Finally, this model has been enriched to take into account visco-plasticity, dislocation climb and interaction between dislocations and solute atoms, which are influent during creep-fatigue or fatigue relaxation at high temperature. The proposed model uses three adjustable parameters only and allows rather accurate prediction of the behavior of 316L(N) steel under tensile loading and relaxation. (author) [fr

Mechanical Assessment of the Drip Shield Subject to Vibratory Motion and Dynamic and Static Rock Loading

International Nuclear Information System (INIS)

R.C. Quittmeyer

2005-01-01

The purpose of the drip shield (DS) is to divert water that may seep into emplacement drifts from contacting the waste packages, and to protect the waste packages from impact or static loading from rockfall. The objective of this document is to summarize, into one location, the results of a series of supporting engineering calculations that were developed to study the effect of static and dynamic loads on the mechanical performance of the DS. The potential DS loads are a result of: (1) Potential earthquake vibratory ground motion, and resulting interaction of the DS, waste package and pallet, and drift invert; (2) Dynamic impacts of rockfall resulting from emplacement drift damage as a result of earthquake vibratory motion; and (3) Static load of the caved rock rubble that may come to rest on the DS as a result of vibratory motion or from time-dependent yielding of the rock mass surrounding the emplacement drift. The potential mechanical failure mechanisms that may result from these loads include: (1) Overturning and/or separation of the interlocking DS segments; (2) Loss of structural integrity and stability of the DS, including excessive deformation or buckling; and (3) Localized damage to the top and side-wall plates of the DS. The scope of this document is limited to summarizing results presented in the supporting calculations in the areas of analysis of the potential for DS collapse, and determination of the damaged surface area of the DS plates. New calculations are presented to determine whether or not separation of DSs occur under vibratory motion

Dislocation density and mechanical threshold stress in OFHC copper subjected to SHPB loading and plate impact

Energy Technology Data Exchange (ETDEWEB)

Hu, Qiushi [National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang, Sichuan, 621900 (China); Zhao, Feng, E-mail: ifpzfeng@163.com [National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang, Sichuan, 621900 (China); Fu, Hua; Li, Kewu [National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang, Sichuan, 621900 (China); Liu, Fusheng [Key Laboratory of Advanced Technologies of Materials, Southwest Jiaotong University, Chengdu, Sichuan, 610031 (China)

2017-05-17

The dislocation density and mechanical threshold stress (MTS) of oxygen-free high-thermal-conductivity (OFHC) copper loaded at strain rates in the range of 10{sup 2} to 10{sup 6} s{sup −1} were measured. Moderate-strain-rate (10{sup 2} to 10{sup 4} s{sup −1}) experiments were performed using a Split Hopkinson Pressure Bar (SHPB). A steel collar was placed around each specimen to control the maximum loading strain. High-strain-rate (10{sup 5} to 10{sup 6} s{sup −1}) experiments were carried out using a 57-mm-bore single-stage gas gun. The radial release effect was eliminated using the momentum trapping technique. The loaded samples were recovered, and the dislocation characteristics and dislocation density were determined by X-ray diffraction profile analysis. The fraction of the screw dislocation was found to decrease with increasing loading strain and strain rate. The dislocation density was found to lie between 1.8×10{sup 14} and 2.2×10{sup 15} m{sup −2}. Quasi-static reload compression tests were performed on the recovered samples at room temperature. The mechanical threshold stress (or the flow stress at 0 K) was obtained by fitting the reload stress–strain data to the MTS model. The results of analysis of the equivalent strain, mechanical threshold stress, and dislocation density measurements suggest that the relation between the mechanical threshold stress and the dislocation density can be described well by the Taylor relationship.

Modeling the impact of scaffold architecture and mechanical loading on collagen turnover in engineered cardiovascular tissues

NARCIS (Netherlands)

Argento, G.; de Jonge, N.; Söntjens, S.H.M.; Oomens, C.W.J.; Bouten, C.V.C.; Baaijens, F.P.T.

2015-01-01

The anisotropic collagen architecture of an engineered cardiovascular tissue has a major impact on its in vivo mechanical performance. This evolving collagen architecture is determined by initial scaffold microstructure and mechanical loading. Here, we developed and validated a theoretical and

Motor unit recruitment and firing rate in medial gastrocnemius muscles during external perturbations in standing in humans.

Science.gov (United States)

Pollock, C L; Ivanova, T D; Hunt, M A; Garland, S J

2014-10-01

There is limited investigation of the interaction between motor unit recruitment and rate coding for modulating force during standing or responding to external perturbations. Fifty-seven motor units were recorded from the medial gastrocnemius muscle with intramuscular electrodes in response to external perturbations in standing. Anteriorly directed perturbations were generated by applying loads in 0.45-kg increments at the pelvis every 25-40 s until 2.25 kg was maintained. Motor unit firing rate was calculated for the initial recruitment load and all subsequent loads during two epochs: 1) dynamic response to perturbation directly following each load drop and 2) maintenance of steady state between perturbations. Joint kinematics and surface electromyography (EMG) from lower extremities and force platform measurements were assessed. Application of the external loads resulted in a significant forward progression of the anterior-posterior center of pressure (AP COP) that was accompanied by modest changes in joint angles (recruitment, motor unit firing rate immediately after the load drop was significantly lower than during subsequent load drops or during the steady state at the same load. There was a modest increase in motor unit firing rate immediately after the load drop on subsequent load drops associated with regaining balance. There was no effect of maintaining balance with increased load and forward progression of the AP COP on steady-state motor unit firing rate. The medial gastrocnemius utilized primarily motor unit recruitment to achieve the increased levels of activation necessary to maintain standing in the presence of external loads. Copyright © 2014 the American Physiological Society.

INVESTIGATION OF HYDROELASTIC BEHAVIOR OF A PONTOON-TYPE VLFS DURING UNSTEADY EXTERNAL LOADS IN WAVE CONDITION USING A HYBRID FINITE ELEMENT-BOUNDARY ELEMENT (FE-ME METHOD

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Yong Cheng

2017-01-01

Full Text Available The hydroelastic behaviour of a pontoon-type VLFS subjected to unsteady external loads in wave condition is investigated in the context of the time-domain modal expansion theory, in which the boundary element method (BEM based on time domain Kelvin sources is used for hydrodynamic forces and the finite element method (FEM is adopted for solving the deflections of the VLFS. In this analysis, the interpolation-tabulation scheme is applied to assess rapidly and accurately the free-surface Green function in finite water depth, and the boundary integral equation of a quarter VLFS model is further established taking advantage of symmetry of flow field and structure. The VLFS is modelled as an equivalent solid plate based on the Mindlin plate theory. The coupled plate-water model is performed to determine the wave-induced responses and transient behaviour under external loads such as a huge mass impact onto the structure and moving loads of an airplane, respectively. These results are verified with existing numerical results and experimental test. Then, the developed numerical tools are used in the study of the combined action taking into account of the mass drop/airplane landing as well as forward or reverse incident wave action. The deflections of the runway, the time history of vertical positions and the trajectory of the airplane are also presented through a systematic time-domain simulation, which illustrates the usefulness of the presently developed numerical solutions.

Experimental Study On Lateral Load Capacity of Bamboo RC Beam Column Joints Strengthened By Bamboo Mechanical Anchors

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Sri Umniati B.

2017-01-01

Full Text Available In this paper, the prospective of bamboos which available abundantly especially in Indonesia as rebars and mechanical anchors are studied. And also the endurance of the bamboos mechanical anchors to withstand cyclic loading were observed. Nine classes of bamboos bar were evaluated: consist of 3 different anchors (0, 4 and 8 anchors and 3 different compressive strength (19.19 MPa, 29.61 MPa and 37.96 MPa means 3 × 3 parameters. The results show that the lateral load capacity increased significantly with the present of bamboo anchors specimens: 26.04 % for 4 anchors specimens (C2 and 25 % for the 8 anchors specimens (C3 compared to zero anchor specimens (C1. On the other hand, the compressive strength of concrete have no significant effects to the lateral load capacity. Overall it can be concluded that, bamboo can be used as mechanical anchorage to strengthen beam column joint.

The Pneumatic Actuators As Vertical Dynamic Load Simulators On Medium Weighted Wheel Suspension Mechanism

Science.gov (United States)

Ka'ka, Simon; Himran, Syukri; Renreng, Ilyas; Sutresman, Onny

2018-02-01

Almost all of road damage can be caused by dynamic loads of vehicles that fluctuate according to the type of vehicle that passes through. This study aims to calculate the vertical dynamic load of the vehicle actually occurs on road construction by the mechanism of vehicle wheel suspension. Pneumatic cylinders driven by pressurized air directly load the spring and shock absorber installed on the wheels of the vehicle. The load fluctuations of the medium weight categorized vehicles are determined by the regulation of the amount of pressurized air that enters into the pneumatic cylinder chamber, pushing the piston and connecting rods. The displacement that occurs during compression on the spring and shock absorber, is substituted into the equation of vehicle dynamic load while taking into account the spring stiffness constant, and the fluid or damper gas coefficient. The results show that the magnitude of the displacement when the compression force works has significant influences to the amount of vertical dynamic load of the vehicle that overlies the road construction. The presence of dynamic load of vehicles that fluctuates and repeats, also affects on the reduction of road ability to receive the load. Experimental results using pneumatic actuators instead of real dynamic vehicle loads illustrate the characteristics of the relationship between work pressure and dynamic load. If the working pressure of P2 (bar) is greater, the vertical dynamic load Ft (N) that overloads the road structure is also greater. The associate graphs show that the shock absorber has a greater ability to reduce dynamic load vertically that burden the road structure when compared with the ability of screw spring.

Impact of Cyclic Loading on Chloride Diffusivity and Mechanical Performance of RC Beams under Seawater Corrosion

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Sen Pang

2017-01-01

Full Text Available An experimental study was conducted to investigate the impact of cyclic loading on the mechanical performance and chloride diffusivity of RC beams exposed to seawater wet-dry cycles. To induce initial damage to RC beam specimen, cyclic loading controlled by max load and cycles was applied. Then beam specimens underwent 240 wet-dry cycles of seawater. Results show that the chloride content increased as max load and cycle increased. The chloride content at steel surface increased approximatively linearly as average crack width increased. Moreover, the max load had more influence on chloride content at steel surface than cycle. The difference of average chloride diffusion coefficient between tension and compression concrete was little at uncracked position. Average chloride diffusion coefficient increased as crack width increased when crack width was less than 0.11 mm whereas the increasing tendency was weak when crack width exceeded 0.11 mm. The residual yield load and ultimate load of RC beams decreased as max load and cycle increased. Based on univariate analysis of variance, the max load had more adverse effect on yield load and ultimate load than cycle.

Dynamic analysis of elastic rubber tired car wheel breaking under variable normal load

Science.gov (United States)

Fedotov, A. I.; Zedgenizov, V. G.; Ovchinnikova, N. I.

2017-10-01

The purpose of the paper is to analyze the dynamics of the braking of the wheel under normal load variations. The paper uses a mathematical simulation method according to which the calculation model of an object as a mechanical system is associated with a dynamically equivalent schematic structure of the automatic control. Transfer function tool analyzing structural and technical characteristics of an object as well as force disturbances were used. It was proved that the analysis of dynamic characteristics of the wheel subjected to external force disturbances has to take into account amplitude and phase-frequency characteristics. Normal load variations impact car wheel braking subjected to disturbances. The closer slip to the critical point is, the higher the impact is. In the super-critical area, load variations cause fast wheel blocking.

Misfit of Three Different Implant-Abutment Connections Before and After Cyclic Load Application: An In Vitro Study.

Science.gov (United States)

Gehrke, Sergio Alexandre; Delgado-Ruiz, Rafael Arcesio; Prados Frutos, Juan Carlos; Prados-Privado, María; Dedavid, Berenice Anina; Granero Marín, Jose Manuel; Calvo Guirado, José Luiz

This study aimed to evaluate the misfit of three different implant-abutment connections before and after cycling load. One hundred twenty dental implants and correspondent prefabricated titanium abutments were used. Three different implant-abutment connections were evaluated: Morse taper (MT group), external hexagon (EH group), and internal hexagon (IH group). Forty implants and 40 abutments were used per group. The parameters for the mechanical evaluation were set as: 360,000 cycles, load of 150 N, and frequency of 4 Hz. Samples were sectioned in their longitudinal and transversal axes, and the misfit of the implant-abutment connection was evaluated by scanning electron microscopy analysis. One-way analyses of variance, Tukey post hoc analyses (α = .05), and t test (P .05). Transversally, only the MT group showed full fitting after cycling load compared with the other groups (EH and IH) (P abutment connection in internal, external, and Morse taper connections. In the longitudinal direction, the accommodation decreases and/or eliminates the gap observed initially (before load). In the horizontal direction, Morse cone implant-abutment connections experience a complete accommodation with the elimination of the gap.

Androgen receptor disruption increases the osteogenic response to mechanical loading in male mice

NARCIS (Netherlands)

Callewaert, F.; Bakker, A.; Schrooten, J.; Van Meerbeek, B.; Verhoeven, G.; Boonen, S.; Vanderschueren, D.

2010-01-01

In female mice, estrogen receptor-alpha (ERα) mediates the anabolic response of bone to mechanical loading. Whether ERα plays a similar role in the male skeleton and to what extent androgens and androgen receptor (AR) affect this response in males remain unaddressed. Therefore, we studied the

Thin circular cylinder under axisymmetrical thermal and mechanical loading

International Nuclear Information System (INIS)

Arnaudeau, F.; Zarka, J.; Gerij, J.

1977-01-01

A special purpose computer code (Ratch) was developed to analyse a thin circular cylinder subjected to axisymmetrical mechanical and thermal loadings. The Mendelson's approach of this problem is followed. Classical Kirchoff-Love hypothesis of thin shells is used and a state of plane stress is assumed. Space integrations are performed by Gaussian quadrature in the axial direction and by Simpson's one third rule throughout the thickness. Thermoelastic-plastic constitutive equations are solved with an implicit scheme (Nguyen). Thermovisco-plastic constitutive equations are solved with an explicit time integration scheme (Treanor's algorithm especially fitted). A Bree type diagram is obtained for an axial step of temperature which varies cyclically and a sustained constant axial load. The material behavior is assumed perfectly plastic and creep effect is not considered. Results show that the domain where ratchetting occurs is reduced when compared with the domain predicted by the Bree diagram. To investigate the effect of material hardening the authors verify Halphen's Theorem which states that a structure made of material with kinematic hardening behavior and constant properties with temperature will always shake down to a periodic behavior. (Auth.)

Effect of Court Dimensions on Players’ External and Internal Load during Small-Sided Handball Games

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Matteo Corvino

2014-06-01

Full Text Available The aim of this study was to investigate the effect of three different court dimensions on the internal and external load during small-sided handball games. Six male amateur handball players took part in this study and participated in three different 8-min 3vs3 (plus goalkeepers small-sided handball games (each repeated twice. The three court dimensions were 12×24m, 30×15m and 32×16m. Through Global Positioning System devices (SPI pro elite 15Hz, GPSports and video analysis, the following parameters were recorded: cyclic and acyclic movements (distance covered and number of technical actions executed, heart rate, and rating of perceived exertion (RPE. Total distance travelled increased with court dimensions (885.2m ± 66.6m in 24×12m; 980.0m ± 73.4m in 30×15m; 1095.0m ± 112.9m in 32×16m, p 5.2 m·s-1 highlighted substantial differences: playing with the 30×15m court in comparison to the 24×12m, the players covered less distance in the first speed zone (p = 0.012; ES = 0.70 and more distance in the second (p = 0.049; ES = 0.73 and third (p = 0.012; ES = 0.51 speed zones. Statistical differences were also found between the 24×12m and 32×16m courts: the players covered more distance in the second and third speed zones (p = 0.013, ES = 0.76; p = 0.023 ES = 0.69 with the 32×16m court in comparison to the 24×12m. There was no significant effect of court dimensions on the technical parameters (number of team actions, passes, piston movements toward goal and defensive activities, the number of specific handball jumps and changes of direction, and the time spent in the different heart rate zones. Considering the average data of all the experimental conditions together (24×12m, 30×15m, 32×16m, a pronounced statistical difference was highlighted between the values in first two HR zones and the last two (p < 0.05; large ES. The rating of perceived exertion was significantly higher during the drill with the 32×16m court compared with the 24

Presentation of an approach for the analysis of the mechanical response of propellant under a large spectrum of loadings: numerical and mechanical issues

Science.gov (United States)

Fanget, Alain

2009-06-01

Many authors claim that to understand the response of a propellant, specifically under quasi static and dynamic loading, the mesostructural morphology and the mechanical behaviour of each of its components have to be known. However the scale of the mechanical description of the behaviour of a propellant is relative to its heterogeneities and the wavelength of loading. The shorter it is, the more important the topological description of the material is. In our problems, involving the safety of energetic materials, the propellant can be subjected to a large spectrum of loadings. This presentation is divided into five parts. The first part describes the processes used to extract the information about the morphology of the meso-structure of the material and presents some results. The results, the difficulties and the perspectives for this part will be recalled. The second part determines the physical processes involved at this scale from experimental results. Taking into account the knowledge of the morphology, two ways have been chosen to describe the response of the material. One concerns the quasi static loading, the object of the third part, in which we show how we use the mesoscopic scale as a base of development to build constitutive models. The fourth part presents for low but dynamic loading the comparison between numerical analysis and experiments.

Mechanical stability of nanoporous metals with small ligament sizes

International Nuclear Information System (INIS)

Crowson, Douglas A.; Farkas, Diana; Corcoran, Sean G.

2009-01-01

Digital samples of nanoporous gold with small ligament sizes were studied by atomistic simulation using different interatomic potentials that represent varying surface stress values. We predict a surface relaxation driven mechanical instability for these materials. Plastic deformation is induced by the surface stress without external load, related to the combination of the surface stress value and the surface to volume ratio.

Mechanical loading stimulates chondrogenesis via the PKA/CREB-Sox9 and PP2A pathways in chicken micromass cultures.

Science.gov (United States)

Juhász, Tamás; Matta, Csaba; Somogyi, Csilla; Katona, Éva; Takács, Roland; Soha, Rudolf Ferenc; Szabó, István A; Cserháti, Csaba; Sződy, Róbert; Karácsonyi, Zoltán; Bakó, Eva; Gergely, Pál; Zákány, Róza

2014-03-01

Biomechanical stimuli play important roles in the formation of articular cartilage during early foetal life, and optimal mechanical load is a crucial regulatory factor of adult chondrocyte metabolism and function. In this study, we undertook to analyse mechanotransduction pathways during in vitro chondrogenesis. Chondroprogenitor cells isolated from limb buds of 4-day-old chicken embryos were cultivated as high density cell cultures for 6 days. Mechanical stimulation was carried out by a self-designed bioreactor that exerted uniaxial intermittent cyclic load transmitted by the culture medium as hydrostatic pressure and fluid shear to differentiating cells. The loading scheme (0.05 Hz, 600 Pa; for 30 min) was applied on culturing days 2 and 3, when final commitment and differentiation of chondroprogenitor cells occurred in this model. The applied mechanical load significantly augmented cartilage matrix production and elevated mRNA expression of several cartilage matrix constituents, including collagen type II and aggrecan core protein, as well as matrix-producing hyaluronan synthases through enhanced expression, phosphorylation and nuclear signals of the main chondrogenic transcription factor Sox9. Along with increased cAMP levels, a significantly enhanced protein kinase A (PKA) activity was also detected and CREB, the archetypal downstream transcription factor of PKA signalling, exhibited elevated phosphorylation levels and stronger nuclear signals in response to mechanical stimuli. All the above effects were diminished by the PKA-inhibitor H89. Inhibition of the PKA-independent cAMP-mediators Epac1 and Epac2 with HJC0197 resulted in enhanced cartilage formation, which was additive to that of the mechanical stimulation, implying that the chondrogenesis-promoting effect of mechanical load was independent of Epac. At the same time, PP2A activity was reduced following mechanical load and treatments with the PP2A-inhibitor okadaic acid were able to mimic the effects of

Effect of conditioner load on the polishing pad surface during chemical mechanical planarization process

Energy Technology Data Exchange (ETDEWEB)

Shin, Cheol Min; Qin, Hong Yi; Hong, Seok Jun; Jeon, Sang Hyuk; Kulkarni, Atul; Kim, Tae Sun [Sungkyunkwan University, Suwon (Korea, Republic of)

2016-12-15

During the Chemical mechanical planarization (CMP), the pad conditioning process can affect the pad surface characteristics. Among many CMP process parameters, the improper applied load on the conditioner arm may have adverse effects on the polyurethane pad. In this work, we evaluated the pad surface properties under the various conditioner arm applied during pad conditioning process. The conditioning pads were evaluated for surface topography, surface roughness parameters such as Rt and Rvk and Material removal rate (MRR) and within-wafer non-uniformity after wafer polishing. We observed that, the pad asperities were collapsed in the direction of conditioner rotation and blocks the pad pores applied conditioner load. The Rvk value and MRR were founded to be in relation with 4 > 1 > 7 kgF conditioner load. Hence, this study shows that, 4 kgF applied load by conditioner is most suitable for the pad conditioning during CMP.

THE EFFECT OF CORPORATE GOVERNANCE MECHANISM, OWNERSHIP STRUCTURE, AND EXTERNAL AUDITOR TOWARD CORPORATE SOCIAL RESPONSIBILITY DISCLOSURE WITH EARNING MANAGEMENT AS MODERATING VARIABLE

Directory of Open Access Journals (Sweden)

Suwana M.A.J.

2017-08-01

Full Text Available The purpose of this study is to examine the moderating effect of earning management on corporate governance mechanism, ownership structure, and external auditor toward corporate social responsibility disclosure. This study finds that the increase of ownership structure (foreign ownership and institutional ownership will increase corporate social responsibility disclosure. However corporate governance mechanism and external auditor is not affecting corporate social responsibility disclosure. Furthermore, this study provides additional empirical evidence for agency theory especially agency cost, that corporate governance mechanism, ownership structure, and Big Four audit firm do not have an effective role as agency cost to prevent or decrease earning management practice.

The influence of ergonomic devices on mechanical load during patient handling activities in nursing homes.

Science.gov (United States)

Koppelaar, Elin; Knibbe, Hanneke J J; Miedema, Harald S; Burdorf, Alex

2012-07-01

Mechanical load during patient handling activities is an important risk factor for low back pain among nursing personnel. The aims of this study were to describe required and actual use of ergonomic devices during patient handling activities and to assess the influence of these ergonomic devices on mechanical load during patient handling activities. For each patient, based on national guidelines, it was recorded which specific ergonomic devices were required during distinct patient handling activities, defined by transferring a patient, providing personal care, repositioning patients in the bed, and putting on and taking off anti-embolism stockings. During real-time observations over ~60 h among 186 nurses on 735 separate patient handling activities in 17 nursing homes, it was established whether ergonomic devices were actually used. Mechanical load was assessed through observations of frequency and duration of a flexed or rotated trunk >30° and frequency of pushing, pulling, lifting or carrying requiring forces 230 N from start to end of each separate patient handling activity. The number of patients and nurses per ward and the ratio of nurses per patient were used as ward characteristics with potential influence on mechanical load. A mixed-effect model for repeated measurements was used to determine the influence of ergonomic devices and ward characteristics on mechanical load. Use of ergonomic devices was required according to national guidelines in 520 of 735 (71%) separate patient handling activities, and actual use was observed in 357 of 520 (69%) patient handling activities. A favourable ratio of nurses per patient was associated with a decreased duration of time spent in awkward back postures during handling anti-embolism stocking (43%), patient transfers (33%), and personal care of patients (24%) and also frequency of manually lifting patients (33%). Use of lifting devices was associated with a lower frequency of forces exerted (64%), adjustable bed and

Stability of internal response and external load during 4-a-side football game in an indoor environment

Directory of Open Access Journals (Sweden)

Karel Hůlka

2015-03-01

Full Text Available Background: Small-sided games (SSG are spontaneous forms of specific training where exercise intensity can be manipulated mainly by modifying external factors. When using the SSG, there is a risk that the variability of intensity between players and on repetition of SSG may lead to some players training at inappropriate exercise intensities. Objective: The purpose of this study is to determine intra-individual repeatability and inter-individual variability in exercise intensity in small-sided 4on4 football games. Methods: Twenty five highly trained junior football players (age 17.68 ± 1.52 years; BMI 23.8 ± 1.92 kg . m-2 participated in the study. Distance covered (software package Video Manual Motion Tracker 1.0 and heart rate (HR, expressed as a percentage of peak heart rate were measured. All participants completed three measurements of 4-a-side games for three consecutive weeks. Results: The high intraclass correlation coefficient value (Heart rate [HR]: ICC = .88, 95% CI [.65, .94]; Distance covered [DC]: ICC = .76, 95% CI [.66, .96] implies a very high level of intra-individual repeatability. The Pearson's correlation coefficient value (HR: r = .93; DC: r = .85 indicates a high correlation between the results of any measurement. Bland and Altman's 95% limits of agreement were ± 10.32 beats . min-1 and ± 65.46 m of distance covered. Conclusions: The results of this study demonstrated that measured SSG elicit consistent heart rate responses and external load of the players.

Fracture Mechanics Analyses of Subsurface Defects in Reinforced Carbon-Carbon Joggles Subjected to Thermo-Mechanical Loads

Science.gov (United States)

Knight, Norman F., Jr.; Raju, Ivatury S.; Song, Kyongchan

2011-01-01

Coating spallation events have been observed along the slip-side joggle region of the Space Shuttle Orbiter wing-leading-edge panels. One potential contributor to the spallation event is a pressure build up within subsurface voids or defects due to volatiles or water vapor entrapped during fabrication, refurbishment, or normal operational use. The influence of entrapped pressure on the thermo-mechanical fracture-mechanics response of reinforced carbon-carbon with subsurface defects is studied. Plane-strain simulations with embedded subsurface defects are performed to characterize the fracture mechanics response for a given defect length when subjected to combined elevated-temperature and subsurface-defect pressure loadings to simulate the unvented defect condition. Various subsurface defect locations of a fixed-length substrate defect are examined for elevated temperature conditions. Fracture mechanics results suggest that entrapped pressure combined with local elevated temperatures have the potential to cause subsurface defect growth and possibly contribute to further material separation or even spallation. For this anomaly to occur, several unusual circumstances would be required making such an outcome unlikely but plausible.

Loading, electromyograph, and motion during exercise

Science.gov (United States)

Figueroa, Fernando

1993-01-01

A system is being developed to gather kineto-dynamic data for a study to determine the load vectors applied to bone during exercise on equipment similar to that used in space. This information will quantify bone loading for exercise countermeasures development. Decreased muscle loading and external loading of bone during weightlessness results in cancellous bone loss of 1 percent per month in the lower extremities and 2 percent per month in the calcaneous. It is hypothesized that loading bone appropriately during exercise may prevent the bone loss. The system consists of an ergometer instrumented to provide position of the pedal (foot), pedaling forces on the foot (on the sagittal plane), and force on the seat. Accelerometers attached to the limbs will provide acceleration. These data will be used as input to an analytical model of the limb to determine forces on the bones and on groups of muscles. EMG signals from activity in the muscles will also be used in conjunction with the equations of mechanics of motion to be able to discern forces exerted by specific muscles. The tasks to be carried out include: design of various mechanical components to mount transducers, specification of mechanical components, specification of position transducers, development of a scheme to control the data acquisition instruments (TEAC recorder and optical encoder board), development of a dynamic model of the limbs in motion, and development of an overall scheme for data collection analysis and presentation. At the present time, all the hardware components of the system are operational, except for a computer board to gather position data from the pedals and crank. This board, however, may be put to use by anyone with background in computer based instrumentation. The software components are not all done. Software to transfer data recorded from the EMG measurements is operational, software to drive the optical encoder card is mostly done. The equations to model the kinematics and

Contact resistance at ceramic interfaces and its dependence on mechanical load

DEFF Research Database (Denmark)

Koch, Søren; Hendriksen, P.V.

2004-01-01

Low contact resistance between individual components is important for solid oxide fuel cell stacks if high performance is to be achieved. Several mechanisms may result in high contact resistance, e.g., current constriction due to low area of contact and formation of resistive phases between...... the components. In this study, the importance of current constriction due to limited area of contact at an interface is investigated by comparing the characteristics of contacts between LSM pellets with different surface finish. The load behaviour of the contact resistance has been investigated and a power law...... of the contact resistance was calculated using a simple model describing the variation of the contact area with load based on the measured surface roughness. Good agreement between the calculations and the experimentally observed resistances was found. (C) 2004 Elsevier B.V. All rights reserved....

The mechanism for efficacy of eccentric loading in Achilles tendon injury; an in vivo study in humans.

Science.gov (United States)

Rees, J D; Lichtwark, G A; Wolman, R L; Wilson, A M

2008-10-01

Degenerative disorders of tendons present an enormous clinical challenge. They are extremely common, prone to recur and existing medical and surgical treatments are generally unsatisfactory. Recently eccentric, but not concentric, exercises have been shown to be highly effective in managing tendinopathy of the Achilles (and other) tendons. The mechanism for the efficacy of these exercises is unknown although it has been speculated that forces generated during eccentric loading are of a greater magnitude. Our objective was to determine the mechanism for the beneficial effect of eccentric exercise in Achilles tendinopathy. Seven healthy volunteers performed eccentric and concentric loading exercises for the Achilles tendon. Tendon force and length changes were determined using a combination of motion analysis, force plate data and real-time ultrasound. There was no significant difference in peak tendon force or tendon length change when comparing eccentric with concentric exercises. However, high-frequency oscillations in tendon force occurred in all subjects during eccentric exercises but were rare in concentric exercises (P < 0.0001). These oscillations provide a mechanism to explain the therapeutic benefit of eccentric loading in Achilles tendinopathy and parallels recent evidence from bone remodelling, where the frequency of the loading cycles is of more significance than the absolute magnitude of the force.

Distraction and mind-wandering under load.

Science.gov (United States)

Forster, Sophie

2013-01-01

Attention research over the last several decades has provided rich insights into the determinants of distraction, including distractor characteristics, task features, and individual differences. Load Theory represented a particularly important breakthrough, highlighting the critical role of the level and nature of task-load in determining both the efficiency of distractor rejection and the stage of processing at which this occurs. However, until recently studies of distraction were restricted to those measuring rather specific forms of distraction by external stimuli which I argue that, although intended to be irrelevant, were in fact task-relevant. In daily life, attention may be distracted by a wide range of stimuli, which may often be entirely unrelated to any task being performed, and may include not only external stimuli but also internally generated stimuli such as task-unrelated thoughts. This review outlines recent research examining these more general, entirely task-irrelevant, forms of distraction within the framework of Load Theory. I discuss the relation between different forms of distraction, and the universality of load effects across different distractor types and individuals.

Distraction and mind-wandering under load

Directory of Open Access Journals (Sweden)

Sophie eForster

2013-05-01

Full Text Available Attention research over the last several decades has provided rich insights into the determinants of distraction, including distractor characteristics, task features and individual differences. Load Theory represented a particularly important breakthrough, highlighting the critical role of the level and nature of task load in determining both the efficiency of distractor rejection and the stage of processing at which this occurs. However, until recently studies of distraction were restricted to those measuring rather specific forms of distraction by external stimuli which I argue that, although intended to be irrelevant, were in fact task-relevant. In daily life, attention may be distracted by a wide range of stimuli, which may often be entirely unrelated to any task being performed, and may include not only external stimuli but also internally generated stimuli such as task-unrelated thoughts. This review outlines recent research examining these more general, entirely task-irrelevant, forms of distraction within the framework of Load Theory. I discuss the relation between different forms of distraction, and the universality of load effects across different distractor types and individuals.

Flaw behavior in mechanically loaded clad plates

International Nuclear Information System (INIS)

Iskander, S.K.; Robinson, G.C.; Oland, C.B.

1989-01-01

A small crack near the inner surface of clad nuclear reactor pressure vessels is an important consideration in the safety assessment of the structural integrity of the vessel. Four-point bend tests on large plate specimens, conforming to ASTM specification for pressure vessel plates, alloy steels, quenched and tempered, Mn-Mo and Mn-Mo-Ni (A533) grade B six clad and two unclad with stainless steels 308, 309 and 312 weld wires, were performed to determine the effect of cladding upon the propagation of small surface cracks subjected to stress states. Results indicated that the tough surface layer composed of cladding and/or heat-affected zone has enhanced the load-bearing capacity of plates under conditions where unclad plates have ruptured. The results are interpreted in terms of fracture mechanics. The behavior of flaws in clad reactor pressure vessels is examined in the light of the test results. 11 refs., 8 figs., 2 tabs

Numerical modelling of crack initiation and propagation in concrete structure under hydro-mechanical loading

International Nuclear Information System (INIS)

Bian, H.B.; Jia, Y.; Shao, J.F.

2012-01-01

Document available in extended abstract form only. This subject is devoted to numerical analysis of crack initiation and propagation in concrete structures due to hydro-mechanical coupling processes. When the structures subjected to the variation in hydraulic conditions, fractures occur as a consequence of coalescence of diffuse damage. Consequently, the mechanical behaviour of concrete is described by an isotropic damage model. Once the damage reaches a critical value, a macroscopic crack is initiated. In the framework of extended Finite Element Method (XFEM), the propagation of localized crack is studied in this paper. Each crack is then considered as a discontinuity surface of displacement. According to the determination of crack propagation orientations, a tensile stress-based criterion is used. Furthermore, spatial variations of mechanical properties of concrete are also taken into account using the Weibull distribution function. Finally, the proposed model is applied to numerical analysis of a concrete liner in the context of feasibility studies for geological storage of radioactive wastes. The numerical results show that the proposed approach is capable to reproduce correctly the initiation and propagation crack process until the complete failure of concrete structures during hydro-mechanical loading. The concrete is most widely used construction material in many engineering applications. It is generally submitted to various environmental loading: such as the mechanical loading, the variation of relative humidity and the exposure to chemical risk, etc. In order to evaluate the safety and durability of concrete structures, it is necessary to get a good knowledge on the influence of loading path on the concrete behaviour. The objective of this paper is to study numerically the crack propagation in concrete structure under hydro-mechanical loading,.i.e. the mechanical behaviour of concrete subjected to drying process. The drying process leads to desiccation

Robust controller for synchronous generator with local load via VSC

Energy Technology Data Exchange (ETDEWEB)

Cabrera-Vazquez, J. [Universidad de Guadalajara, Centro Universitario de Ciencias Exactas e Ingenierias, Departamento de Electronica, Av. Revolucion No. 1500, Modulo ' ' O' ' , Apdo. Postal 44840, Guadalajara Jalisco (Mexico); Loukianov, Alexander G.; Canedo, Jose M. [Centro de Investigacion y de Estudios Avanzados del IPN, Apdo. Postal 31-438, Plaza La Luna, C. P. 44550, Guadalajara, Jalisco (Mexico); Utkin, Vadim I. [Department of Electrical Engineering, The Ohio-State University, Columbus, OH 43210-1272 (United States)

2007-05-15

The objective of this paper is to design a nonlinear observer-based excitation controller for power system comprising a single synchronous generator connected to an infinite bus with local load. The controller proposed is based on the using first singular perturbation systems concepts and then Sliding Mode Control technique combining with Block Control Principle. To reduce ''chattering'' a nonlinear observer with estimation of the mechanical torque and rotor fluxes is designed. This combined approach enables to compensate the inherent nonlinearities of the generator and to reject external disturbances. (author)

Shear behavior of concrete beams externally prestressed with Parafil ropes

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A.H. Ghallab

2013-03-01

Full Text Available Although extensive work has been carried out investigating the use of external prestressing system for flexural strengthening, a few studies regarding the shear behavior of externally prestressed beams can be found. Five beams, four of them were externally strengthened using Parafil rope, were loaded up to failure to investigate the effect of shear span/depth ratio, external prestressing force and concrete strength on their shear behavior. Test results showed that the shear span to depth ratio has a significant effect on both the shear strength and failure mode of the strengthened beams and the presence of external prestressing force increased the ultimate load of the tested beams by about 75%. Equations proposed by different codes for both the conventional reinforced concrete beams and for ordinary prestressed beams were used to evaluate the obtained experimental results. In general, codes equations showed a high level of conservatism in predicting the shear strength of the beams. Also, using the full strength rather than half of the concrete shear strength in the Egyptian code PC-method improves the accuracy of the calculated ultimate shear strength.

Unified model to predict flexural shear behavior of externally bonded RC beams

International Nuclear Information System (INIS)

Colotti, V.; Spadea, G.; Swamy, R.N.

2006-01-01

Structural strengthening with externally bonded reinforcement is now recognized as a cost-effective, structurally sound and practically efficient method of rehabilitating deteriorating and damaged reinforced concrete beams. There is now an urgent need to develop a sound engineering basis which can predict the failure loads of all such strengthened beams in a reliable and consistent manner. Existing models to predict the behavior at ultimate of strengthened beams suffer from many limitations and weaknesses. This paper presents a unified global model, based on the Strut-and-Tie approach, to predict the failure loads of reinforced concrete beams strengthened for flexure and/or shear. This structural model is based on rational engineering principles, considers all the possible failure modes, and incorporates the load transfer mechanism bond to reflect the debonding phenomena which has a dominant influence on the failure process of plated beams. The model is validated against about 200 strengthened beam test reported in the literature and failing in flexure and/or shear, involving a large number of structural variables and steel, carbon and glass fiber reinforced polymer laminates as reinforcing medium. (author)

Monitoring of Failure Mechanisms in a Composite Bending Actuator during Cyclic Loading by Acoustic Emission

Science.gov (United States)

Woo, Sung-Choong; Goo, Nam Seo

The objective of this work is to investigate the influence of electromechanical cyclic loading on the performance of a bending piezoelectric composite actuator. We have analyzed the fatigue damage mechanisms in terms of the behavior of the AE event rate. It was found that whether the actuators are subjected to purely electric loading or electromechanical loading, the initial fatigue damage of the bending piezoelectric composite actuator was caused by the transgranular fracture in the PZT ceramic layer; the final failure was caused only in the case of PCAWB under electromechanical loading by a local discharge, which critically affected the performance reduction of the actuators. As the number of cycles increased, a large reduction in displacement performance coincided with a high AE event rate, which was identified via microscopic observations.

The Effect of Cyclic Loading on the Mechanical Performance of Surgical Mesh

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Ho Y.C.

2010-06-01

Full Text Available Polymeric meshes in the form of knitted nets are commonly used in the surgical repair of pelvic organ prolapses. Although a number of these prosthetic meshes are commercially available, there is little published data on their mechanical performance, in particular on the change in stiffness under the repeated loading experienced in vivo. In this in vitro study, cyclic tensile loading was applied to rectangular strips of four different commercially available meshes. The applied force and resultant displacement was monitored throughout the tests in order to evaluate the change in stiffness. In addition, each mesh was randomly marked using indelible ink in order to permit the use of threedimensional digital image correlation to evaluate local displacements during the tests. However, the scale and form of the deformation experienced by some of the meshes made correlation difficult so that confirmation of the values of stiffness were only obtained for two meshes. The results demonstrate that all the meshes experience an increase in stiffness during cyclic loading, that in most cases cyclic creep occurs and in some cases large-scale, irreversible reorganisation of the mesh structure occurs after as few as 200 cycles at loads of the order of 10N.

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

Multi-scale mechanics of traumatic brain injury : predicting axonal strains from head loads

NARCIS (Netherlands)

Cloots, R.J.H.; Dommelen, van J.A.W.; Kleiven, S.; Geers, M.G.D.

2013-01-01

The length scales involved in the development of diffuse axonal injury typically range from the head level (i.e., mechanical loading) to the cellular level. The parts of the brain that are vulnerable to this type of injury are mainly the brainstem and the corpus callosum, which are regions with

Mechanical loading of the low back and shoulders during pushing and pulling activities.

NARCIS (Netherlands)

Hoozemans, M.J.M.; Kingma, I.; Dieen, van J.H.; Vries, de W.K.H.; Woude, van der L.H.V.; Veeger, H.E.J.; Frings-Dresen, M.H.W.; Beek, van der A.J.

2004-01-01

The objective of this study was to quantify the mechanical load on the low back and shoulders during pushing and pulling in combination with three task constraints: the use of one or two hands, three cart weights, and two handle heights. The second objective was to explore the relation between the

Mechanical loading of the low back and shoulders during pushing and pulling activities

NARCIS (Netherlands)

Hoozemans, Marco J. M.; Kuijer, P. Paul F. M.; Kingma, Idsart; van Dieën, Jaap H.; de Vries, Wiebe H. K.; van der Woude, Luc H. V.; Veeger, Dirk Jan H. E. J.; van der Beek, Allard J.; Frings-Dresen, Monique H. W.

2004-01-01

The objective of this study was to quantify the mechanical load on the low back and shoulders during pushing and pulling in combination with three task constraints: the use of one or two hands, three cart weights, and two handle heights. The second objective was to explore the relation between the

THE STRENGTH OF REINFORCED CONCRETE BEAM ELEMENTS UNDER CYCLIC ALTERNATING LOADING AND LOW CYCLE LOAD OF CONSTANT SIGN

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Semina Yuliya Anatol'evna

2015-09-01

Full Text Available The behavior of reinforced concrete elements under some types of cyclic loads is described in the paper. The main aim of the investigations is research of the stress-strain state and strength of the inclined sections of reinforced concrete beam elements in conditions of systemic impact of constructive factors and the factor of external influence. To spotlight the problem of cyclic loadings three series of tests were conducted by the author. Firstly, the analysis of the tests showed that especially cyclic alternating loading reduces the bearing capacity of reinforced concrete beams and their crack resistance by 20 % due to the fatigue of concrete and reinforcement. Thus the change of load sign creates serious changes of stress-strain state of reinforced concrete beam elements. Low cycle loads of constant sign effect the behavior of the constructions not so adversely. Secondly, based on the experimental data mathematical models of elements’ strength were obtained. These models allow evaluating the impact of each factor on the output parameter not only separately, but also in interaction with each other. Furthermore, the material spotlighted by the author describes stress-strain state of the investigated elements, cracking mechanism, changes of deflection values, the influence of mode cyclic loading during the tests. Since the data on the subject are useful and important to building practice, the ultimate aim of the tests will be working out for improvement of nonlinear calculation models of span reinforced concrete constructions taking into account the impact of these loads, and also there will be the development of engineering calculation techniques of their strength, crack resistance and deformability.

Counterrotating-Shoulder Mechanism for Friction Stir Welding

Science.gov (United States)

Nunes, Arthur C., Jr.

2007-01-01

upper and lower bevel gears. The lower bevel gear would be attached to the upper shoulder and would slide and rotate freely over the spindle. The spindle would be fastened by its threaded upper end to an external submechanism that would exert axial tension on the spindle to load the workpiece in compression between the shoulders. By reducing or eliminating (relative to the use of a self reacting tool) the torque that must be reacted externally, the use of the proposed tool would reduce the tendency toward distortion or slippage of the workpiece. To begin a weld, the spindle would be inserted through a hole in the workpiece or run-on tab at the beginning of the seam and fastened to the loading submechanism. Rotation and axial loading would be increased gradually from zero and, after a time to be determined by trial and error, translation along the weld seam would be increased gradually from zero to a steady weld speed. The weld would be ended by running the mechanism off the workpiece or, if the lower shoulder were detachable, by detaching the lower shoulder from the spindle and pulling the pin tool out.

Mechanical behavior of glass/epoxy composite laminate with varying amount of MWCNTs under different loadings

Science.gov (United States)

Singh, K. K.; Rawat, Prashant

2018-05-01

This paper investigates the mechanical response of three phased (glass/MWCNTs/epoxy) composite laminate under three different loadings. Flexural strength, short beam strength and low-velocity impact (LVI) testing are performed to find an optimum doping percentage value for maximum enhancement in mechanical properties. In this work, MWCNTs were used as secondary reinforcement for three-phased composite plate. MWCNT doping was done in a range of 0–4 wt% of the thermosetting matrix system. Symmetrical design eight layered glass/epoxy laminate with zero bending extension coupling laminate was fabricated using a hybrid method i.e. hand lay-up technique followed by vacuum bagging method. Ranging analysis of MWCNT mixing highlighted the enhancement in flexural, short beam strength and improvement in damage tolerance under LVI loading. While at higher doping wt%, agglomeration of MWCNTs are observed. Results of mechanical testing proposed an optimized doping value for maximum strength and damage resistance of the laminate.

External wave-launcher study. Final report

International Nuclear Information System (INIS)

1983-01-01

The rationale for liquid dielectrically-loaded external wave-guide launchers is discussed. The arguments are strongly indicative that a liquid dielectric-filled waveguide system could be a practical technique for launching ICRH power into a fusion reactor. A detailed summary of the work performed in the study is presented

Experimental study of the anisotropic properties of argillite under moisture and mechanical loads

International Nuclear Information System (INIS)

Yang, D.S.; Chanchole, S.; Wang, L.L.; Bornert, M.; Gatmiri, B.

2012-01-01

Document available in extended abstract form only. Due to various factors, such as sedimentation, layered morphology of clay mineral, in-situ stress, etc., the behavior of argillite rocks is often anisotropic. In order to study the anisotropy of the Callovo-Oxfordian (COx) argillite considered as a possible host rock for high-level radioactive nuclear waste repository in France, a series of tests including uniaxial compression and dehydration and hydration at different constant applied stress levels, are carried out using a specific setup combining mechanical and moisture loading devices. During these hydro-mechanical tests, this specific setup can also continuously capture images of the sample surfaces to be subsequently analyzed using Digital Image Correlation techniques (DIC) in order to determine full-field strains. In this study, three sampling directions are used with the angle θ between the bedding plane and the cylindrical sample axis equal to 45 deg., 60 deg. and 90 deg.. To investigate the mechanical anisotropy, uniaxial compressive tests with mechanical loading and unloading cycles are performed on several different samples at the same moisture level. The results show that the mechanical parameters (apparent modulus, failure stress) depend on loading orientation relative to the stratification plane. For a given water content, the failure stress reaches maximum values for θ =90 deg. and minimum values for θ =45 deg.. To study the hydric anisotropy, dehydration and hydration tests under stress-free conditions are performed on two cylindrical samples (θ=90 deg. and θ=60 deg.). Three cycles of hydration and dehydration are carried out by varying the relative humidity between 40% and 95%. The sample weight, the deformation measured by strain gages and the relative humidity are continuously recorded during the test by means of another specific setup described in [Pham et al., 2007]. Fig.1a illustrates the evolution of the strains of the sample EST28030-No

Influence of multiwall carbon nanotube functionality and loading on mechanical properties of PMMA/MWCNT bone cements.

Science.gov (United States)

Ormsby, Ross; McNally, Tony; Mitchell, Christina; Dunne, Nicholas

2010-08-01

Poly (methyl methacrylate) (PMMA) bone cement-multi walled carbon nanotube (MWCNT) nanocomposites with weight loadings ranging from 0.1 to 1.0 wt% were prepared. The MWCNTs investigated were unfunctionalised, carboxyl and amine functionalised MWCNTs. Mechanical properties of the resultant nanocomposite cements were characterised as per international standards for acrylic resin cements. These mechanical properties were influenced by the type and wt% loading of MWCNT used. The morphology and degree of dispersion of the MWCNTs in the PMMA matrix at different length scales were examined using field emission scanning electron microscopy. Improvements in mechanical properties were attributed to the MWCNTs arresting/retarding crack propagation through the cement by providing a bridging effect and hindering crack propagation. MWCNTs agglomerations were evident within the cement microstructure, the degree of these agglomerations was dependent on the weight fraction and functionality of MWCNTs incorporated into the cement.

Functional adaptation to mechanical loading in both cortical and cancellous bone is controlled locally and is confined to the loaded bones.

Science.gov (United States)

Sugiyama, Toshihiro; Price, Joanna S; Lanyon, Lance E

2010-02-01

In order to validate whether bones' functional adaptation to mechanical loading is a local phenomenon, we randomly assigned 21 female C57BL/6 mice at 19 weeks of age to one of three equal numbered groups. All groups were treated with isoflurane anesthesia three times a week for 2 weeks (approximately 7 min/day). During each anaesthetic period, the right tibiae/fibulae in the DYNAMIC+STATIC group were subjected to a peak dynamic load of 11.5 N (40 cycles with 10-s intervals between cycles) superimposed upon a static "pre-load" of 2.0 N. This total load of 13.5 N engendered peak longitudinal strains of approximately 1400 microstrain on the medial surface of the tibia at a middle/proximal site. The right tibiae/fibulae in the STATIC group received the static "pre-load" alone while the NOLOAD group received no artificial loading. After 2 weeks, the animals were sacrificed and both tibiae, fibulae, femora, ulnae and radii analyzed by three-dimensional high-resolution (5 mum) micro-computed tomography (microCT). In the DYNAMIC+STATIC group, the proximal trabecular percent bone volume and cortical bone volume at the proximal and middle levels of the right tibiae as well as the cortical bone volume at the middle level of the right fibulae were markedly greater than the left. In contrast, the left bones in the DYNAMIC+STATIC group showed no differences compared to the left or right bones in the NOLOAD or STATIC group. These microCT data were confirmed by two-dimensional examination of fluorochrome labels in bone sections which showed the predominantly woven nature of the new bone formed in the loaded bones. We conclude that the adaptive response in both cortical and trabecular regions of bones subjected to short periods of dynamic loading, even when this response is sufficiently vigorous to stimulate woven bone formation, is confined to the loaded bones and does not involve changes in other bones that are adjacent, contra-lateral or remote to them. (c) 2009 Elsevier Inc

Mechanism of Fatigue Crack Growth of Bridge Steel Structures

Directory of Open Access Journals (Sweden)

Zhu H.

2016-12-01

Full Text Available This study was carried out on the background of Sutong Bridge project based on fracture mechanics, aiming at analyzing the growth mechanism of fatigue cracks of a bridge under the load of vehicles. Stress intensity factor (SIF can be calculated by various methods. Three steel plates with different kinds of cracks were taken as the samples in this study. With the combination of finite element analysis software ABAQUS and the J integral method, SIF values of the samples were calculated. After that, the extended finite element method in the simulation of fatigue crack growth was introduced, and the simulation of crack growth paths under different external loads was analyzed. At last, we took a partial model from the Sutong Bridge and supposed its two dangerous parts already had fine cracks; then simulative vehicle load was added onto the U-rib to predict crack growth paths using the extended finite element method.

Creatine Loading, Resistance Exercise Performance, and Muscle Mechanics.

Science.gov (United States)

Stevenson, Scott W.; Dudley, Gary A.

2001-01-01

Examined whether creatine (CR) monohydrate loading would alter resistance exercise performance, isometric strength, or in vivo contractile properties of the quadriceps femoris muscle compared with placebo loading in resistance-trained athletes. Overall, CR loading did not provide an ergogenic benefit for the unilateral dynamic knee extension…

Synthetic oligorotaxanes exert high forces when folding under mechanical load

Science.gov (United States)

Sluysmans, Damien; Hubert, Sandrine; Bruns, Carson J.; Zhu, Zhixue; Stoddart, J. Fraser; Duwez, Anne-Sophie

2018-01-01

Folding is a ubiquitous process that nature uses to control the conformations of its molecular machines, allowing them to perform chemical and mechanical tasks. Over the years, chemists have synthesized foldamers that adopt well-defined and stable folded architectures, mimicking the control expressed by natural systems1,2. Mechanically interlocked molecules, such as rotaxanes and catenanes, are prototypical molecular machines that enable the controlled movement and positioning of their component parts3-5. Recently, combining the exquisite complexity of these two classes of molecules, donor-acceptor oligorotaxane foldamers have been synthesized, in which interactions between the mechanically interlocked component parts dictate the single-molecule assembly into a folded secondary structure6-8. Here we report on the mechanochemical properties of these molecules. We use atomic force microscopy-based single-molecule force spectroscopy to mechanically unfold oligorotaxanes, made of oligomeric dumbbells incorporating 1,5-dioxynaphthalene units encircled by cyclobis(paraquat-p-phenylene) rings. Real-time capture of fluctuations between unfolded and folded states reveals that the molecules exert forces of up to 50 pN against a mechanical load of up to 150 pN, and displays transition times of less than 10 μs. While the folding is at least as fast as that observed in proteins, it is remarkably more robust, thanks to the mechanically interlocked structure. Our results show that synthetic oligorotaxanes have the potential to exceed the performance of natural folding proteins.

Biomechanical comparison of supraacetabular external fixation and anterior pelvic bridge plating.

Science.gov (United States)

Çavuşoğlu, Ali Turgay; Erbay, Fatma Kübra; Özsoy, Mehmet Hakan; Demir, Teyfik

2017-10-01

Unstable pelvic ring injuries are complex and risky injuries due to high morbidity and mortality. Although anterior pelvic external fixator is a suitable method for rapid stabilization of an injured pelvic ring, due to some disadvantages such as high complication rate, nerve damage, and difficulties of patient's mobility and comfort, there has recently been increased searching for alternative methods for stabilization of the pelvic ring. Pubic symphysis zone freely moves in pelvic models. This study aims to evaluate the biomechanical stability of anterior pelvic bridge plating and compare it with supraacetabular external fixators in an untreated unstable pelvic fracture model. Samples were loaded statically with 2-mm/min loading rate in single leg standing position. Maximum load was 2.3 kN. When loading the samples, photographs were taken continuously. Stiffness values were calculated from the load displacement curves. Some reference parameters were described and were measured from unloaded and 2.3-kN-loaded photographs of the test. The mean stiffness values were 491.14 ± 52.22, 478.55 ± 41.44, and 470.25 ± 44.51 N/mm for anterior pelvic bridge plating group, supraacetabular external fixator group, and Control group, respectively. According to the measured parameters from photographs, the mean displacement at the pubic symphysis was 4.7 ± 0.32, 15.8 ± 2.01, and 18.2 ± 0.47 mm for anterior pelvic bridge plating, supraacetabular external fixator, and Control group, respectively. The highest displacement in the pubic symphysis was found in Control group, and minimum displacement was observed in anterior pelvic bridge plating group. When the perpendicular distance between the right and left lower end of ischium was examined, it was observed that displacement was minimum in anterior pelvic bridge plating group compared to other two groups, regarding to the high stability of pubic symphysis. In conclusion, this study revealed

Hyaluronan supplementation as a mechanical regulator of cartilage tissue development under joint-kinematic-mimicking loading.

Science.gov (United States)

Wu, Yabin; Stoddart, Martin J; Wuertz-Kozak, Karin; Grad, Sibylle; Alini, Mauro; Ferguson, Stephen J

2017-08-01

Articular cartilage plays an essential role in joint lubrication and impact absorption. Through this, the mechanical signals are coupled to the tissue's physiological response. Healthy synovial fluid has been shown to reduce and homogenize the shear stress acting on the cartilage surfaces due to its unique shear-thinning viscosity. As cartilage tissues are sensitive to mechanical changes in articulation, it was hypothesized that replacing the traditional culture medium with a healthy non-Newtonian lubricant could enhance tissue development in a cartilage engineering model, where joint-kinematic-mimicking mechanical loading is applied. Different amounts of hyaluronic acid were added to the culture medium to replicate the viscosities of synovial fluid at different health states. Hyaluronic acid supplementation, especially at a physiologically healthy concentration (2.0 mg ml -1 ), promoted a better preservation of chondrocyte phenotype. The ratio of collagen II to collagen I mRNA was 4.5 times that of the control group, implying better tissue development (however, with no significant difference of measured collagen II content), with a good retention of collagen II and proteoglycan in the mechanically active region. Simulating synovial fluid properties by hyaluronic acid supplementation created a favourable mechanical environment for mechanically loaded constructs. These findings may help in understanding the influence of joint articulation on tissue homeostasis, and moreover, improve methods for functional cartilage tissue engineering. © 2017 The Author(s).

Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) Pathway Is Induced by Mechanical Load and Reduces the Activity of Hedgehog Signaling in Chondrogenic Micromass Cell Cultures

Science.gov (United States)

Juhász, Tamás; Szentléleky, Eszter; Szűcs Somogyi, Csilla; Takács, Roland; Dobrosi, Nóra; Engler, Máté; Tamás, Andrea; Reglődi, Dóra; Zákány, Róza

2015-01-01

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neurohormone exerting protective function during various stress conditions either in mature or developing tissues. Previously we proved the presence of PACAP signaling elements in chicken limb bud-derived chondrogenic cells in micromass cell cultures. Since no data can be found if PACAP signaling is playing any role during mechanical stress in any tissues, we aimed to investigate its contribution in mechanotransduction during chondrogenesis. Expressions of the mRNAs of PACAP and its major receptor, PAC1 increased, while that of other receptors, VPAC1, VPAC2 decreased upon mechanical stimulus. Mechanical load enhanced the expression of collagen type X, a marker of hypertrophic differentiation of chondrocytes and PACAP addition attenuated this elevation. Moreover, exogenous PACAP also prevented the mechanical load evoked activation of hedgehog signaling: protein levels of Sonic and Indian Hedgehogs and Gli1 transcription factor were lowered while expressions of Gli2 and Gli3 were elevated by PACAP application during mechanical load. Our results suggest that mechanical load activates PACAP signaling and exogenous PACAP acts against the hypertrophy inducing effect of mechanical load. PMID:26230691

Pituitary Adenylate Cyclase Activating Polypeptide (PACAP Pathway Is Induced by Mechanical Load and Reduces the Activity of Hedgehog Signaling in Chondrogenic Micromass Cell Cultures

Directory of Open Access Journals (Sweden)

Tamás Juhász

2015-07-01

Full Text Available Pituitary adenylate cyclase activating polypeptide (PACAP is a neurohormone exerting protective function during various stress conditions either in mature or developing tissues. Previously we proved the presence of PACAP signaling elements in chicken limb bud-derived chondrogenic cells in micromass cell cultures. Since no data can be found if PACAP signaling is playing any role during mechanical stress in any tissues, we aimed to investigate its contribution in mechanotransduction during chondrogenesis. Expressions of the mRNAs of PACAP and its major receptor, PAC1 increased, while that of other receptors, VPAC1, VPAC2 decreased upon mechanical stimulus. Mechanical load enhanced the expression of collagen type X, a marker of hypertrophic differentiation of chondrocytes and PACAP addition attenuated this elevation. Moreover, exogenous PACAP also prevented the mechanical load evoked activation of hedgehog signaling: protein levels of Sonic and Indian Hedgehogs and Gli1 transcription factor were lowered while expressions of Gli2 and Gli3 were elevated by PACAP application during mechanical load. Our results suggest that mechanical load activates PACAP signaling and exogenous PACAP acts against the hypertrophy inducing effect of mechanical load.

Effect of fiber distribution and realignment on the nonlinear and inhomogeneous mechanical properties of human supraspinatus tendon under longitudinal tensile loading.

Science.gov (United States)

Lake, Spencer P; Miller, Kristin S; Elliott, Dawn M; Soslowsky, Louis J

2009-12-01

Tendon exhibits nonlinear stress-strain behavior that may be partly due to movement of collagen fibers through the extracellular matrix. While a few techniques have been developed to evaluate the fiber architecture of other soft tissues, the organizational behavior of tendon under load has not been determined. The supraspinatus tendon (SST) of the rotator cuff is of particular interest for investigation due to its complex mechanical environment and corresponding inhomogeneity. In addition, SST injury occurs frequently with limited success in treatment strategies, illustrating the need for a better understanding of SST properties. Therefore, the objective of this study was to quantitatively evaluate the inhomogeneous tensile mechanical properties, fiber organization, and fiber realignment under load of human SST utilizing a novel polarized light technique. Fiber distributions were found to become more aligned under load, particularly during the low stiffness toe-region, suggesting that fiber realignment may be partly responsible for observed nonlinear behavior. Fiber alignment was found to correlate significantly with mechanical parameters, providing evidence for strong structure-function relationships in tendon. Human SST exhibits complex, inhomogeneous mechanical properties and fiber distributions, perhaps due to its complex loading environment. Surprisingly, histological grade of degeneration did not correlate with mechanical properties.

Mechanics of the Delayed Fracture of Viscoelastic Bodies with Cracks: Theory and Experiment (Review)

Science.gov (United States)

Kaminsky, A. A.

2014-09-01

Theoretical and experimental studies on the deformation and delayed fracture of viscoelastic bodies due to slow subcritical crack growth are reviewed. The focus of this review is on studies of subcritical growth of cracks with well-developed fracture process zones, the conditions that lead to their critical development, and all stages of slow crack growth from initiation to the onset of catastrophic growth. Models, criteria, and methods used to study the delayed fracture of viscoelastic bodies with through and internal cracks are analyzed. Experimental studies of the fracture process zones in polymers using physical and mechanical methods as well as theoretical studies of these zones using fracture mesomechanics models that take into account the structural and rheological features of polymers are reviewed. Particular attention is given to crack growth in anisotropic media, the effect of the aging of viscoelastic materials on their delayed fracture, safe external loads that do not cause cracks to propagate, the mechanism of multiple-flaw fracture of viscoelastic bodies with several cracks and, especially, processes causing cracks to coalesce into a main crack, which may result in a break of the body. Methods and results of solving two- and three-dimensional problems of the mechanics of delayed fracture of aging and non-aging viscoelastic bodies with cracks under constant and variable external loads, wedging, and biaxial loads are given

Nonlinear behaviors of FRP-wrapped tall trees subjected to high wind loads

Science.gov (United States)

Kang, J.; Yi, Z. Z.; Choi, S. G.

2017-12-01

This study investigated the mechanical stability of historical tall trees wrapped with fiber-reinforced polymer (FRP) laminates using finite element (FE) analysis. High wind loads are considered as external loading conditions as they are one of the major threats on the structural stability of tall old trees. There have been several traditional practices to enhance the stability of tall trees exposed to high windstorms such as tree supporters and anchorages. They, however, have been sometimes causing negative effects with their misuses as the application guidelines for those methods were not adequately studied or documented. Furthermore, the oldest known trees in the country should be protected from the damage of external surface as well as ruin of the landscape. The objective of this study was to evaluate the structural effects of FRP wraps applied to tall trees subjected to high wind loads. The anisotropic material properties of wood and FRP laminates were considered in the analysis in addition to geometrically nonlinear behaviors. This study revealed that FRP wrapping for tall trees could effectively reduce the deflections and maximum stresses of trees, which results in the enhanced stability of tall trees. The optimum geometry and thicknesses of FRP wraps proposed in this study would provide fundemental guidelines for designing and constructing the application of innovative FRP wraps on tall trees, which are structurally unstable or should be preserved nationally and historically.

External fixation using locking plate in distal tibial fracture: a finite element analysis.

Science.gov (United States)

Zhang, Jingwei; Ebraheim, Nabil; Li, Ming; He, Xianfeng; Schwind, Joshua; Liu, Jiayong; Zhu, Limei

2015-08-01

External fixation of tibial fractures using a locking plate has been reported with favorable results in some selected patients. However, the stability of external plate fixation in this fracture pattern has not been previously demonstrated. We investigated the stability of external plate fixation with different plate-bone distances. In this study, the computational processing model of external fixation of a distal tibial metaphyseal fracture utilizing the contralateral femoral less invasive stabilization system plate was analyzed. The plate was placed on the anteromedial aspect of tibia with different plate-bone distances: 1, 10, 20, and 30 mm. Under axial load, the stiffness of construct in all groups was higher than intact tibia. Under axial load with an internal rotational force, the stiffness of construct with 1 and 10 mm plate-bone distances was similar to that of an intact tibia and the stiffness of the construct with 20 and 30 mm distances was lower than that of an intact tibia. Under axial load with an external rotational force, the stiffness of the construct in all groups was lower than that of an intact tibia. The maximum plate stresses were concentrated at the two most distal screws and were highest in the construct with the 10 mm plate-bone distance, and least in the construct with a 1 mm plate-bone distance. To guarantee a stable external plate fixation in distal tibial fracture, the plate-bone distance should be less than 30 mm.

The dopamine receptor D4 gene and familial loading interact with perceived parenting in predicting externalizing behavior problems in early adolescence: the TRacking Adolescents' Individual Lives Survey (TRAILS).

Science.gov (United States)

Marsman, Rianne; Oldehinkel, Albertine J; Ormel, Johan; Buitelaar, Jan K

2013-08-30

Although externalizing behavior problems show in general a high stability over time, the course of externalizing behavior problems may vary from individual to individual. Our main goal was to investigate the predictive role of parenting on externalizing behavior problems. In addition, we investigated the potential moderating role of gender and genetic risk (operationalized as familial loading of externalizing behavior problems (FLE), and presence or absence of the dopamine receptor D4 (DRD4) 7-repeat and 4-repeat allele, respectively). Perceived parenting (rejection, emotional warmth, and overprotection) and FLE were assessed in a population-based sample of 1768 10- to 12-year-old adolescents. Externalizing behavior problems were assessed at the same age and 212 years later by parent report (CBCL) and self-report (YSR). DNA was extracted from blood samples. Parental emotional warmth predicted lower, and parental overprotection and rejection predicted higher levels of externalizing behavior problems. Whereas none of the parenting factors interacted with gender and the DRD4 7-repeat allele, we did find interaction effects with FLE and the DRD4 4-repeat allele. That is, the predictive effect of parental rejection was only observed in adolescents from low FLE families and the predictive effect of parental overprotection was stronger in adolescents not carrying the DRD4 4-repeat allele. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

Locomotor loading mechanics in the hindlimbs of tegu lizards (Tupinambis merianae): comparative and evolutionary implications.

Science.gov (United States)

Sheffield, K Megan; Butcher, Michael T; Shugart, S Katherine; Gander, Jennifer C; Blob, Richard W

2011-08-01

Skeletal elements are usually able to withstand several times their usual load before they yield, and this ratio is known as the bone's safety factor. Limited studies on amphibians and non-avian reptiles have shown that they have much higher limb bone safety factors than birds and mammals. It has been hypothesized that this difference is related to the difference in posture between upright birds and mammals and sprawling ectotherms; however, limb bone loading data from a wider range of sprawling species are needed in order to determine whether the higher safety factors seen in amphibians and non-avian reptiles are ancestral or derived conditions. Tegus (family Teiidae) are an ideal lineage with which to expand sampling of limb bone loading mechanics for sprawling taxa, particularly for lizards, because they are from a different clade than previously sampled iguanas and exhibit different foraging and locomotor habits (actively foraging carnivore versus burst-activity herbivore). We evaluated the mechanics of locomotor loading for the femur of the Argentine black and white tegu (Tupinambus merianae) using three-dimensional measurements of the ground reaction force and hindlimb kinematics, in vivo bone strains and femoral mechanical properties. Peak bending stresses experienced by the femur were low (tensile: 10.4 ± 1.1 MPa; compressive: -17.4 ± 0.9 MPa) and comparable to those in other reptiles, with moderate shear stresses and strains also present. Analyses of peak femoral stresses and strains led to estimated safety factor ranges of 8.8-18.6 in bending and 7.8-17.5 in torsion, both substantially higher than typical for birds and mammals but similar to other sprawling tetrapods. These results broaden the range of reptilian and amphibian taxa in which high femoral safety factors have been evaluated and further indicate a trend for the independent evolution of lower limb bone safety factors in endothermic taxa.

A fracture mechanics study of tungsten failure under high heat flux loads

International Nuclear Information System (INIS)

Li, Muyuan

2015-01-01

The performance of fusion devices is highly dependent on plasma-facing components. Tungsten is the most promising candidate material for armors in plasma-facing components in ITER and DEMO. However, the brittleness of tungsten below the ductile-to-brittle transition temperature is very critical to the reliability of plasma-facing components. In this work, thermo-mechanical and fracture behaviors of tungsten are predicted numerically under fusion relevant thermal loadings.

Mechanical loading by fluid shear stress of myotube glycocalyx stimulates growth factor expression and nitric oxide production

NARCIS (Netherlands)

Juffer, P.; Bakker, A.D.; Klein-Nulend, J.; Jaspers, R.T.

2014-01-01

Skeletal muscle fibers have the ability to increase their size in response to a mechanical overload. Finite element modeling data suggest that mechanically loaded muscles in vivo may experience not only tensile strain but also shear stress. However, whether shear stress affects biological pathways

Characteristics of physical loads endured by military officers of mechanized troops during field maneuvres

Directory of Open Access Journals (Sweden)

I.L. Shlyamar

2015-09-01

Full Text Available Purpose: observation over influence of physical loads on military officers in process of acquiring and mastering of military applied skills during field maneuvers. Material: in experiment 120 military officers of 20-25 years old age with equal physical fitness participated. Results: it was determined that in period of field maneuvers the greatest load was endured by military officers in attack exercises and on the march. The least physical loads were in period of organization and fulfillment of combat shooting. It was also established that main part of motor actions was fulfilled in aerobic mode. Military officers’ functioning in field maneuvers was accompanied by heart beats rate of 120-150 b.p.m. and 60-90 b.p.m. during long time. Conclusions: We offered to practice physical training of mechanized units’ military officers in modes, close to field ones.

Investigation of in-plane biaxial low cycle fatigued austenitic stainless steel AISI 321. I. Mechanical testing on the planar biaxial load machine

International Nuclear Information System (INIS)

Taran, Yu.V.; Balagurov, A.M.; Kuznetsov, A.N.; Schreiber, J.; Bomas, H.; Stoeberl, Ch.; Rathjen, P.; Vorster, W.J.J.; Korsunsky, A.M.

2007-01-01

During fatigue loading of structural materials such as stainless steel, changes in the microstructure which affect the mechanical and physical properties occur. Experimental simulation of the loading conditions that induce the changes can be performed by mechanical loading, usually in the form of uniaxial tension-compression cycling. However, real machines and structures are subjected to more complex multiaxial stresses. Fatigue and fracture under multiaxial stresses are one of the most important current topics aimed at ensuring improved reliability of industrial components. The first step towards better understanding of this problem is to subject the materials to biaxial loading. The material examined was low austenitic stainless steel AISI 321 H. A set of the four samples of cruciform geometry was subjected to the biaxial tension-compression fatigue cycling with the frequency of 0.5 Hz at the applied load of 10-17 kN. The samples are intended for the neutron diffraction measurements of the residual stresses and the mechanical characterizations on a dedicated stress-diffractometer

Effects of load on ground reaction force and lower limb kinematics during concentric squats.

Science.gov (United States)

Kellis, Eleftherios; Arambatzi, Fotini; Papadopoulos, Christos

2005-10-01

The purpose of this study was to examine the effects of external load on vertical ground reaction force, and linear and angular kinematics, during squats. Eight males aged 22.1 +/- 0.8 years performed maximal concentric squats using loads ranging from 7 to 70% of one-repetition maximum on a force plate while linear barbell velocity and the angular kinematics of the hip, knee and ankle were recorded. Maximum, average and angle-specific values were recorded. The ground reaction force ranged from 1.67 +/- 0.20 to 3.21 +/- 0.29 times body weight and increased significantly as external load increased (P squat exercises is not achieved at the same position of the lower body as external load is increased. In contrast, joint velocity coordination does not change as load is increased. The force-velocity relationship was linear and independent from the set of data used for its determination.

Mechanical torque measurement in the proximal femur correlates to failure load and bone mineral density ex vivo

Directory of Open Access Journals (Sweden)

Stefan Grote

2013-06-01

Full Text Available Knowledge of local bone quality is essential for surgeons to determine operation techniques. A device for intraoperative measurement of local bone quality has been developed by the AO-Research Foundation (DensiProbe®. We used this device to experimentally measure peak breakaway torque of trabecular bone in the proximal femur and correlated this with local bone mineral density (BMD and failure load. Bone mineral density of 160 cadaver femurs was measured by ex situ dual-energy X-ray absorptiometry. The failure load of all femurs was analyzed by side-impact analysis. Femur fractures were fixed and mechanical peak torque was measured with the DensiProbe® device. Correlation was calculated whereas correlation coefficient and significance was calculated by Fisher’s Z-transformation. Moreover, linear regression analysis was carried out. The unpaired Student’s t-test was used to assess the significance of differences. The Ward triangle region had the lowest BMD with 0.511 g/cm2 (±0.17 g/cm2, followed by the upper neck region with 0.546 g/cm2 (±0.16 g/cm2, trochanteric region with 0.685 g/cm2 (±0.19 g/cm2 and the femoral neck with 0.813 g/cm2 (±0.2 g/cm2. Peak torque of DensiProbe® in the femoral head was 3.48 Nm (±2.34 Nm. Load to failure was 4050.2 N (±1586.7 N. The highest correlation of peak torque measured by Densi Probe® and load to failure was found in the femoral neck (r=0.64, P<0.001. The overall correlation of mechanical peak torque with T-score was r=0.60 (P<0.001. A correlation was found between mechanical peak torque, load to failure of bone and BMD in vitro. Trabecular strength of bone and bone mineral density are different aspects of bone strength, but a correlation was found between them. Mechanical peak torque as measured may contribute additional information about bone strength, especially in the perioperative testing.

Functional and unmodified MWNTs for delivery of the water-insoluble drug Carvedilol - A drug-loading mechanism

International Nuclear Information System (INIS)

Li Yuting; Wang Tianyi; Wang Jing; Jiang Tongying; Cheng Gang; Wang Siling

2011-01-01

The purpose of this study was to develop carboxyl multi-wall carbon nanotubes (MWNTs) and unmodified MWNTs loaded with a poorly water-soluble drug, intended to improve the drug loading capacity, dissolubility and study the drug-loading mechanism. MWNTs were modified with a carboxyl group through the acid treatment. MWNTs as well as the resulting functionalized MWNTs were investigated as scaffold for loading the model drug, Carvedilol (CAR), using three different methods (the fusion method, the incipient wetness impregnation method, and the solvent method). The effects of different pore size, specific surface area and physical state were systematically studied using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transformation infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), nitrogen adsorption, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The functional MWNTs allowed a higher drug loading than the unmodified preparations. The methods used to load the drug had a marked effect on the drug-loading, dissolution, and physical state of the drug as well as its distribution. In addition, the solubility of the drug was increased when carried by both MWNTs and functional MWNTs, and this might help to improve the bioavailability.

Statistical mechanics of microscopically thin thermalized shells

Science.gov (United States)

Kosmrlj, Andrej

Recent explosion in fabrication of microscopically thin free standing structures made from graphene and other two-dimensional materials has led to a renewed interest in the mechanics of such structures in presence of thermal fluctuations. Since late 1980s it has been known that for flat solid sheets thermal fluctuations effectively increase the bending rigidity and reduce the bulk and shear moduli in a scale-dependent fashion. However, much is still unknown about the mechanics of thermalized flat sheets of complex geometries and about the mechanics of thermalized shells with non-zero background curvature. In this talk I will present recent development in the mechanics of thermalized ribbons, spherical shells and cylindrical tubes. Long ribbons are found to behave like hybrids between flat sheets with renormalized elastic constants and semi-flexible polymers, and these results can be used to predict the mechanics of graphene kirigami structures. Contrary to the anticipated behavior for ribbons, the non-zero background curvature of shells leads to remarkable novel phenomena. In shells, thermal fluctuations effectively generate negative surface tension, which can significantly reduce the critical buckling pressure for spherical shells and the critical axial load for cylindrical tubes. For large shells this thermally generated load becomes big enough to spontaneously crush spherical shells and cylindrical tubes even in the absence of external loads. I will comment on the relevance for crushing of microscopic shells (viral capsids, bacteria, microcapsules) due to osmotic shocks and for crushing of nanotubes.

Jump Shrug Height and Landing Forces Across Various Loads.

Science.gov (United States)

Suchomel, Timothy J; Taber, Christopher B; Wright, Glenn A

2016-01-01

The purpose of this study was to examine the effect that load has on the mechanics of the jump shrug. Fifteen track and field and club/intramural athletes (age 21.7 ± 1.3 y, height 180.9 ± 6.6 cm, body mass 84.7 ± 13.2 kg, 1-repetition-maximum (1RM) hang power clean 109.1 ± 17.2 kg) performed repetitions of the jump shrug at 30%, 45%, 65%, and 80% of their 1RM hang power clean. Jump height, peak landing force, and potential energy of the system at jump-shrug apex were compared between loads using a series of 1-way repeated-measures ANOVAs. Statistical differences in jump height (P .05). The greatest magnitudes of jump height, peak landing force, and potential energy of the system at the apex of the jump shrug occurred at 30% 1RM hang power clean and decreased as the external load increased from 45% to 80% 1RM hang power clean. Relationships between peak landing force and potential energy of the system at jump-shrug apex indicate that the landing forces produced during the jump shrug may be due to the landing strategy used by the athletes, especially at lighter loads. Practitioners may prescribe heavier loads during the jump-shrug exercise without viewing landing force as a potential limitation.

Analysis and Behaviour of Sandwich Panels with Profiled Metal Facings under Transverse Load

Directory of Open Access Journals (Sweden)

M. Budescu

2004-01-01

Full Text Available Sandwich panels with thin steel facings and polyurethane core combine the load-carrying capacity of metal facings and protection functions with core properties. The core separates the two facings and keeps them in a stable condition, transmits shear between external layers, provides most of the shear rigidity and occasionally makes of useful contribution to the bending stiffness of the sandwich construction as a whole [1]. An experimental program on sandwich panels has been organized to prove that the mechanical properties of core and interface satisfy the load-carrying requirements for structural sandwich panels. The analysis of sandwich panels with deep profiles facings for cladding elements, respectively the roof constructions, has been carried out according to the European design norms [1], [5].

Data on the no-load performance analysis of a tomato postharvest storage system.

Science.gov (United States)

Ayomide, Orhewere B; Ajayi, Oluseyi O; Banjo, Solomon O; Ajayi, Adesola A

2017-08-01

In this present investigation, an original and detailed empirical data on the transfer of heat in a tomato postharvest storage system was presented. No-load tests were performed for a period of 96 h. The heat distribution at different locations, namely the top, middle and bottom of the system was acquired, at a time interval of 30 min for the test period. The humidity inside the system was taken into consideration. Thus, No-load tests with or without introduction of humidity were carried out and data showing the effect of a rise in humidity level, on temperature distribution were acquired. The temperatures at the external mechanical cooling components were acquired and could be used for showing the performance analysis of the storage system.

Dynamics of a Circular Mindlin Plate under Mechanical Loading and Elevated Temperature

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Warminska Anna

2016-01-01

Full Text Available Dynamics of a nonlinear circular Midlin plate is studied in the paper. The mathematical model represented by partial differential equations includes nonlinear geometrical terms resulted from large displacements. The plate is subjected to mechanical and thermal loadings. The dynamics of a coupled thermo-mechanical problem is reduced from partial to ordinary differential equations. Considering the first mode reduction and uniformly distributed temperature just a single nonlinear differential equation is obtained. The bifurcation analysis shows that elevated temperature shifts the rezonanse curve and new solutions arise. Depending on initial conditions this may lead to buckling phenomenon and then relatively small oscillations around this state, symmetric periodic oscillations of large amplitude, or irregular oscillations.

Internalising externalities of energy use through price mechanism: a developing country perspective

International Nuclear Information System (INIS)

Bhattacharyya, S.C.

1995-01-01

As concern grows about the environmental aspect of energy use, it is increasingly suggested in recent years that energy pricing should take negative externalities of energy use into account. A large body of literature, both theoretical and applied, has grown up over the years proposing a variety of options and methods for internalising environmental costs. However, most of these theories and methods, developed in the industrialised countries, have hitherto neglected two aspects of developing economies: the existence of informal sector in the economy and widespread use of traditional energies. This paper discusses the issues related to internalising environmental costs through price mechanism when these two aspects are included. It also calls for a more careful analysis of energy and environmental policies. (author)

Mechanical and Thermal Properties of Epoxy Composites Containing Zirconia-Impregnated Halloysite Nanotubes with Different Loadings.

Science.gov (United States)

Kim, Suhyun; Kim, Moon Il; Shon, Minyoung; Seo, Bongkuk; Lim, Choongsun

2018-09-01

Epoxy resins are widely used in various industrial fields due to their low cost, good workability, heat resistance, and good mechanical strength. However, they suffer from brittleness, an issue that must be addressed for further applications. To solve this problem, additional fillers are needed to improve the mechanical and thermal properties of the resins; zirconia is one such filler. However, it has been reported that aggregation may occur in the epoxy composites as the amount of zirconia increases, preventing enhancement of the mechanical strength of the epoxy composites. Herein, to reduce the aggregation, zirconia was well dispersed on halloysite nanotubes (HNTs), which have high thermal and mechanical strength, by a conventional wet impregnation method. The HNTs were impregnated with zirconia at different loadings using zirconyl chloride octahydrate as a precursor. The mechanical and thermal strengths of the epoxy composites with these fillers were investigated. The zirconia-impregnated HNTs (Zr/HNT) were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and tunneling electron microscopy (TEM). The hardening conditions of the epoxy composites were analyzed by differential scanning calorimetry (DSC). The thermal strength of the epoxy composites was studied by thermomechanical analysis (TMA) and micro-calorimetry and the mechanical strength of the epoxy composites (flexural strength and tensile strength) was studied by using a universal testing machine (UTM). The mechanical and thermal strengths of the epoxy composites with Zr/HNT were improved compared to those of the epoxy composite with HNT, and also increased as the zirconia loading on HNT increased.

Experimental study of low amplitude, long-duration mechanical loading of reactive materials

International Nuclear Information System (INIS)

Urtiew, P A; Forbes, J W

2000-01-01

Studies of the low amplitude, long-duration mechanical loading of reactive materials rely very heavily on the experimental data in general and in particular on the data obtained from gauges placed within the experimental test sample to measure accurately the local changes of parameters of the investigated material. For a complete description of these changes taking place in a dynamically loaded material one would like to know both the spatial and the temporal resolution of pressure, temperature, volume, wave and mass velocity. However, temperature and volume are not easily attainable. Therefore, most of the in-situ work is limited to measurements of pressure and both wave and mass velocities. Various types of these gauges will be discussed and their records will be illustrated. Some of these gauges have limitations but are better suited for particular applications than others. These aspects will also be discussed. Main limitation of most in-situ gauges is that they are built for one-dimensional application. However, some work is being done to develop two-dimensional gauges. This work will also be briefly discussed. While these experiments are necessary to validate theoretical models of the phenomenon, they can also provide sufficient amount of data to yield complete information on material characteristics such as its equation of state (EOS), its phase change under certain loads and its sensitivity to shock loading. Processing of these data to get important information on the behavior of both reactive and non-reactive materials will also be demonstrated

The Influence of the Loading Rate on the Mechanical Properties of Drawing Steel Sheet

Directory of Open Access Journals (Sweden)

Buršák, M.

2006-01-01

Full Text Available The paper analyzes the influence of the loading rate in the interval from 1 to 1000 mm/min on the mechanical properties of drawing steel sheet H260LAD with the gauge of 1 mm, used for the manufacture of automotive parts, under tension and bending conditions. It describes the aspects of material characteristics under tension and bending conditions, while bending tests were made on notched specimens (a modified impact bending test. The paper presents knowledge that using a modified notch toughness test it is possible to achieve the pressability (formability characteristics corresponding to dynamic strain rates even under the static loading.

Mechanical Behaviour of Stainless Steels under Dynamic Loading: An Investigation with Thermal Methods

Directory of Open Access Journals (Sweden)

Rosa De Finis

2016-11-01

Full Text Available Stainless steels are the most exploited materials due to their high mechanical strength and versatility in producing different alloys. Although there is great interest in these materials, mechanical characterisation, in particular fatigue characterisation, requires the application of several standardised procedures involving expensive and time-consuming experimental campaigns. As a matter of fact, the use of Standard Test Methods does not rely on a physical approach, since they are based on a statistical evaluation of the fatigue limit with a fixed probabilistic confidence. In this regard, Infra-Red thermography, the well-known, non-destructive technique, allows for the development of an approach based on evaluation of dissipative sources. In this work, an approach based on a simple analysis of a single thermographic sequence has been presented, which is capable of providing two indices of the damage processes occurring in material: the phase shift of thermoelastic signal φ and the amplitude of thermal signal at twice the loading frequency, S2. These thermal indices can provide synergetic information about the mechanical (fatigue and fracture behaviour of austenitic AISI 316L and martensitic X4 Cr Ni Mo 16-5-1; since they are related to different thermal effects that produce damage phenomena. In particular, the use of φ and S2 allows for estimation of the fatigue limit of stainless steels at loading ratio R = 0.5 in agreement with the applied Standard methods. Within Fracture Mechanics tests, both indices demonstrate the capacity to localize the plastic zone and determine the position of the crack tip. Finally, it will be shown that the value of the thermoelastic phase signal can be correlated with the mechanical behaviour of the specific material (austenitic or martensitic.

Community Characteristics and Trajectories of Adolescent Internalizing and Externalizing Behaviors: The Cumulative Advantage/Disadvantage and Subjective Appraisals of Social Support as Mechanisms

OpenAIRE

Zhang, Jing

2012-01-01

Studies examining neighborhood effects on adolescent outcomes have indicated that adolescents growing up in low-income neighborhoods are at higher risk of developing internalizing and externalizing behaviors. However, knowledge of the long-term effects of neighborhood disadvantages on internalizing and externalizing behaviors and the involved mechanisms across adolescence is limited. Using family life course theory and the cumulative advantage/disadvantage perspective, this study examined how...

Experimental Investigation on the Fatigue Mechanical Properties of Intermittently Jointed Rock Models Under Cyclic Uniaxial Compression with Different Loading Parameters

Science.gov (United States)

Liu, Yi; Dai, Feng; Dong, Lu; Xu, Nuwen; Feng, Peng

2018-01-01

Intermittently jointed rocks, widely existing in many mining and civil engineering structures, are quite susceptible to cyclic loading. Understanding the fatigue mechanism of jointed rocks is vital to the rational design and the long-term stability analysis of rock structures. In this study, the fatigue mechanical properties of synthetic jointed rock models under different cyclic conditions are systematically investigated in the laboratory, including four loading frequencies, four maximum stresses, and four amplitudes. Our experimental results reveal the influence of the three cyclic loading parameters on the mechanical properties of jointed rock models, regarding the fatigue deformation characteristics, the fatigue energy and damage evolution, and the fatigue failure and progressive failure behavior. Under lower loading frequency or higher maximum stress and amplitude, the jointed specimen is characterized by higher fatigue deformation moduli and higher dissipated hysteresis energy, resulting in higher cumulative damage and lower fatigue life. However, the fatigue failure modes of jointed specimens are independent of cyclic loading parameters; all tested jointed specimens exhibit a prominent tensile splitting failure mode. Three different crack coalescence patterns are classified between two adjacent joints. Furthermore, different from the progressive failure under static monotonic loading, the jointed rock specimens under cyclic compression fail more abruptly without evident preceding signs. The tensile cracks on the front surface of jointed specimens always initiate from the joint tips and then propagate at a certain angle with the joints toward the direction of maximum compression.

Collapse mechanisms of metal foam matrix composites under static and dynamic loading conditions

Energy Technology Data Exchange (ETDEWEB)

Linul, Emanoil, E-mail: emanoil.linul@upt.ro [Department of Mechanics and Strength of Materials, Politehnica University of Timisoara, 1 Mihai Viteazu Avenue, 300 222 Timisoara (Romania); Marsavina, Liviu [Department of Mechanics and Strength of Materials, Politehnica University of Timisoara, 1 Mihai Viteazu Avenue, 300 222 Timisoara (Romania); Kováčik, Jaroslav [Institute of Materials and Machine Mechanics, Slovak Academy of Sciences, Dúbravská cesta 9, 845 13 Bratislava (Slovakia)

2017-04-06

The collapse mechanisms of metal foam matrix composites under static and dynamic loading conditions were experimentally and analytically investigated. Closed-cell aluminium foam AlSi10 with 325±10 kg/m{sup 3} density was used as core material, while stainless-steel-mesh is the faces materials. Prior to characterizing the composite sandwich structure, the stainless steel mesh face material and closed-cell aluminium foam were characterized by tensile testing and compression testing, respectively. Experimental tests were performed on sandwich beams using both High Speed Camera and Digital Image Correlation system for strain distribution. All experimental tests were performed at room temperature with constant crosshead speed of 1.67×10{sup −4} m/s for static tests and 2 m/s impact loading speed for dynamic tests. Two main deformation behaviours of investigated metal foam matrix composites were observed following post-failure collapse: face failure and core shear. It was showed that the initiation, propagation and interaction of failure modes depend on the type of loading, constituent material properties and geometrical parameters.

Mechanical Properties of a Unidirectional Basalt-Fiber-Reinforced Plastic Under a Loading Simulating Operation Conditions

Science.gov (United States)

Lobanov, D. S.; Slovikov, S. V.

2017-01-01

The results of experimental investigations of unidirectional composites based on basalt fibers and different marks of epoxy resins are presented. Uniaxial tensile tests were carried out using a specimen fixation technique simulating the operation conditions of structures. The mechanical properties of the basalt-fiber-reinforced plastics (BFRPs) were determined. The diagrams of loading and deformation of BFRP specimens were obtain. The formulations of the composites with the highest mechanical properties were revealed.

Mechanical/structural performance test method of a spacer grid

International Nuclear Information System (INIS)

Yoon, Kyung Ho

2000-06-01

The spacer grid is one of the main structural components in the fuel assembly, which supports the fuel rods, guides cooling water, and protects the system from an external impact load, such as earthquakes. In order to develop the spacer grid with the high mechanical performance, the mechanical and structural properties of the spacer grids must be extensively examined while designing it. In this report, the mechanical/structural test methods, i.e. the characteristic test of a spacer grid spring or dimple, static buckling test of a partial or full size spacer grid and dynamic impact test of them are described. The characteristic test of a spacer grid spring or dimple is accomplished with universal tensile test machine, a specimen is fixed with test fixture and then applied compressive load. The characteristic test data is saved at loading and unloading event. The static buckling test of a partial or full size spacer grid is executed with the same universal tensile testing machine, a specimen is fixed between cross-heads and then applied the compressive load. The buckling strength is decided the maximum strength at load vs. displacement curve. The dynamic impact test of a partial or full size spacer grid is performed with pendulum type impact machine and free fall shock test machine, a specimen is fixed with test fixture and then applied the impact load by impact hammer. Specially, the pendulum type impact test machine is also possible under the operating temperature because a furnace is separately attached with test machine

AC loss, interstrand resistance and mechanical properties of prototype EU DEMO TF conductors up to 30 000 load cycles

Science.gov (United States)

Yagotintsev, K.; Nijhuis, A.

2018-07-01

Two prototype Nb3Sn cable-in-conduit conductors conductors were designed and manufactured for the toroidal field (TF) magnet system of the envisaged European DEMO fusion reactor. The AC loss, contact resistance and mechanical properties of two sample conductors were tested in the Twente Cryogenic Cable Press under cyclic load up to 30 000 cycles. Though both conductors were designed to operate at 82 kA in a background magnetic field of 13.6 T, they reflect different approaches with respect to the magnet winding pack assembly. The first approach is based on react and wind technology while the second is the more common wind and react technology. Each conductor was tested first for AC loss in virgin condition without handling. The impact of Lorentz load during magnet operation was simulated using the cable press. In the press each conductor specimen was subjected to transverse cyclic load up to 30 000 cycles in liquid helium bath at 4.2 K. Here a summary of results for AC loss, contact resistance, conductor deformation, mechanical heat production and conductor stiffness evolution during cycling of the load is presented. Both conductors showed similar mechanical behaviour but quite different AC loss. In comparison with previously tested ITER TF conductors, both DEMO TF conductors possess very low contact resistance resulting in high coupling loss. At the same time, load cycling has limited impact on properties of DEMO TF conductors in comparison with ITER TF conductors.

Mechanical Loads Test Report for the U.S. Department of Energy 1.5-Megawatt Wind Turbine

Energy Technology Data Exchange (ETDEWEB)

Santos, Rick [Santos Wind Engineering Technologies, Inc., Portland, ME (United States); van Dam, Jeroen [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

2015-07-16

The objective of the test was to obtain a baseline characterization of the mechanical loads of the DOE 1.5 wind turbine located at NREL. The test was conducted in accordance with the International Electrotechnical Commission (IEC) Technical Specification, IEC 61400-13 Wind Turbine Generator Systems – Part 13: Measurement of mechanical loads; First Edition 2001-06 [1]. The National Wind Technology Center (NWTC) at NREL conducted this test in accordance with its quality system procedures so that the final test report meets the full requirements of its accreditation by the American Association for Laboratory Accreditation (A2LA). NREL’s quality system requires that all applicable requirements specified by A2LA and International Standards Organization/IEC 17025 be met or to note any exceptions in the test report.

External Coulomb-Friction Damping For Hydrostatic Bearings

Science.gov (United States)

Buckmann, Paul S.

1992-01-01

External friction device damps vibrations of shaft and hydrostatic ring bearing in which it turns. Does not rely on wear-prone facing surfaces. Hydrostatic bearing ring clamped in radially flexing support by side plates clamped against radial surfaces by spring-loaded bolts. Plates provide friction against radial motions of shaft.

Role of age and injury mechanism on cervical spine injury tolerance from head contact loading.

Science.gov (United States)

Yoganandan, Narayan; Chirvi, Sajal; Voo, Liming; Pintar, Frank A; Banerjee, Anjishnu

2018-02-17

The objective of this study was to determine the influence of age and injury mechanism on cervical spine tolerance to injury from head contact loading using survival analysis. This study analyzed data from previously conducted experiments using post mortem human subjects (PMHS). Group A tests used the upright intact head-cervical column experimental model. The inferior end of the specimen was fixed, the head was balanced by a mechanical system, and natural lordosis was removed. Specimens were placed on a testing device via a load cell. The piston applied loading at the vertex region. Spinal injuries were identified using medical images. Group B tests used the inverted head-cervical column experimental model. In one study, head-T1 specimens were fixed distally, and C7-T1 joints were oriented anteriorly, preserving lordosis. Torso mass of 16 kg was added to the specimen. In another inverted head-cervical column study, occiput-T2 columns were obtained, an artificial head was attached, T1-T2 was fixed, C4-C5 disc was maintained horizontal in the lordosis posture, and C7-T1 was unconstrained. The specimens were attached to the drop test carriage carrying a torso mass of 15 kg. A load cell at the inferior end measured neck loads in both studies. Axial neck force and age were used as the primary response variable and covariate to derive injury probability curves using survival analysis. Group A tests showed that age is a significant (P < .05) and negative covariate; that is, increasing age resulted in decreasing force for the same risk. Injuries were mainly vertebral body fractures and concentrated at one level, mid-to-lower cervical spine, and were attributed to compression-related mechanisms. However, age was not a significant covariate for the combined data from group B tests. Both group B tests produced many soft tissue injuries, at all levels, from C1 to T1. The injury mechanism was attributed to mainly extension. Multiple and noncontiguous injuries occurred

Numerical Modeling and Mechanical Analysis of Flexible Risers

OpenAIRE

Li, J. Y.; Qiu, Z. X.; Ju, J. S.

2015-01-01

ABAQUS is used to create a detailed finite element model for a 10-layer unbonded flexible riser to simulate the riser’s mechanical behavior under three load conditions: tension force and internal and external pressure. It presents a technique to create detailed finite element model and to analyze flexible risers. In FEM model, all layers are modeled separately with contact interfaces; interaction between steel trips in certain layers has been considered as well. FEM model considering contact ...

Diastereoselective Addition of α-Metalated Sulfoxides to Imines Revisited: Mechanism, Computational Studies, and the Effect of External Chiral Ligands

DEFF Research Database (Denmark)

Pedersen, Brian; Rein, Tobias; Søtofte, Inger

2003-01-01

six-membered "flat chair") was probed by quantum mechanical calculations, which underpinned the idea of using external chiral ligands to enhance the diastereoselectivity of otherwise moderately selective reactions. In this way, the diastereomeric ratio of the product 3a could be raised from (84 : 16...

Antibiotic-loaded acrylic bone cements: An in vitro study on the release mechanism and its efficacy

Energy Technology Data Exchange (ETDEWEB)

Miola, Marta, E-mail: marta.miola@polito.it [Applied Science and Technology Department, Politecnico di Torino (Italy); Bistolfi, Alessandro [Department of Orthopaedics, Traumatology and HM, University of Turin (Italy); AO CTO, M Adelaide Hospital, Turin (Italy); Valsania, Maria Carmen; Bianco, Carlotta [Department of Orthopaedics, Traumatology and HM, University of Turin (Italy); Fucale, Giacomo [Chemical, Clinical and Microbiological Analyses Dept., CTO, Turin (Italy); Verné, Enrica [Applied Science and Technology Department, Politecnico di Torino (Italy)

2013-07-01

An in vitro study was carried out in order to investigate the antibiotic release mechanism and the antibacterial properties of commercially (Palacos® R + G and Palacos® LV + G) and manually (Palacos® R + GM and Palacos® LV + GM) blended gentamicin-loaded bone cements. Samples were characterized by means of scanning electron microscopy (SEM) and compression strength was evaluated. The antibiotic release was investigated by dipping sample in simulated body fluid (SBF) and periodically analyzing the solution by means of high pressure liquid chromatography (HPLC). Different antibacterial tests were performed to investigate the possible influence of blending technique on antibacterial properties. Only some differences were observed between gentamicin manually added and commercial ones, in the release curves, while the antibacterial effect and the mechanical properties seem to not feel the blending technique. Highlights: • The efficacy of commercially and manually mixed antibiotic-loaded cements is studied. • Exhaustive mechanical, drug release and antibacterial studies are carried out. • The blending technique does not affect the antibacterial and mechanical properties. • The blending process influences only the release curve, not the released drug amount.

Antibiotic-loaded acrylic bone cements: An in vitro study on the release mechanism and its efficacy

International Nuclear Information System (INIS)

Miola, Marta; Bistolfi, Alessandro; Valsania, Maria Carmen; Bianco, Carlotta; Fucale, Giacomo; Verné, Enrica

2013-01-01

An in vitro study was carried out in order to investigate the antibiotic release mechanism and the antibacterial properties of commercially (Palacos® R + G and Palacos® LV + G) and manually (Palacos® R + GM and Palacos® LV + GM) blended gentamicin-loaded bone cements. Samples were characterized by means of scanning electron microscopy (SEM) and compression strength was evaluated. The antibiotic release was investigated by dipping sample in simulated body fluid (SBF) and periodically analyzing the solution by means of high pressure liquid chromatography (HPLC). Different antibacterial tests were performed to investigate the possible influence of blending technique on antibacterial properties. Only some differences were observed between gentamicin manually added and commercial ones, in the release curves, while the antibacterial effect and the mechanical properties seem to not feel the blending technique. Highlights: • The efficacy of commercially and manually mixed antibiotic-loaded cements is studied. • Exhaustive mechanical, drug release and antibacterial studies are carried out. • The blending technique does not affect the antibacterial and mechanical properties. • The blending process influences only the release curve, not the released drug amount

A biomechanical comparison of tendon-bone interface motion and cyclic loading between single-row, triple-loaded cuff repairs and double-row, suture-tape cuff repairs using biocomposite anchors.

Science.gov (United States)

Barber, F Alan; Drew, Otis R

2012-09-01

To compare tendon-bone interface motion and cyclic loading in a single-row, triple-loaded anchor repair with a suture-tape, rip-stop, double-row rotator cuff repair. Using 18 human shoulders from 9 matched cadaveric pairs, we created 2 groups of rotator cuff repairs. Group 1 was a double-row, rip-stop, suture-tape construct. Group 2 was a single-row, triple-loaded construct. Before mechanical testing, the supraspinatus footprint was measured with calipers. A superiorly positioned digital camera optically measured the tendon footprint motion during 60° of humeral internal and external rotation. Specimens were secured at a fixed angle not exceeding 45° in reference to the load. After preloading, each sample was cycled between 10 N and 100 N for 200 cycles at 1 Hz, followed by destructive testing at 33 mm/s. A digital camera with tracking software measured the repair displacement at 100 and 200 cycles. Ultimate load and failure mode for each sample were recorded. The exposed anterior footprint border (6.5% ± 6%) and posterior footprint border (0.9% ± 1.7%) in group 1 were statistically less than the exposed anterior footprint border (30.3% ± 17%) and posterior footprint border (29.8% ± 14%) in group 2 (P = .003 and P row rotator cuff repair had greater footprint coverage, less rotational footprint displacement, and a greater mean ultimate failure load than the triple-loaded, single-row repair on mechanical testing. No double-row or single-row constructs showed 5 mm of displacement after the first 100 cycles. The most common failure mode for both constructs was suture tearing through the tendon. Differences in cuff fixation influence rotational tendon movement and may influence postoperative healing. Stronger repair constructs still fail at the suture-tendon interface. Copyright © 2012 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.

Piezosurgery in External Dacryocystorhinostomy.

Science.gov (United States)

Czyz, Craig N; Fowler, Amy M; Dutton, Jonathan J; Cahill, Kenneth V; Foster, Jill A; Hill, Robert H; Everman, Kelly R; Nabavi, Cameron B

Dacryocystorhinostomy (DCR) can be performed via an external or endoscopic approach. The use of ultrasonic or piezosurgery has been well described for endoscopic DCRs but is lacking for external DCRs. This study presents a case series of external DCRs performed using piezosurgery evaluating results and complications. Prospective, consecutive case series of patients undergoing primary external DCR for lacrimal drainage insufficiency. A standard external DCR technique was used using 1 of 2 piezosurgery systems for all bone incision. All patients received silicone intubation to the lacrimal system. Surgical outcome was measured in terms of patient-reported epiphora as follows: 1) complete resolution, 2) improvement >50%, 3) improvement 50% improvement. There were 4 patients (7%) who had <50% improvement. There was 1 (2%) intraoperative complication and 2 (4%) postoperative complications recorded. Piezourgery is a viable modality for performing external DCRs. The lack of surgical complications shows a potential for decreased soft tissues damage. The surgical success rate based on patient-reported epiphora is similar to those published for mechanical external DCRs. This modality may benefit the novice surgeon in the reduction of soft and mucosal tissue damage.

Positional Differences in Elite Basketball: Selecting Appropriate Training - Load Measures.

Science.gov (United States)

Svilar, Luka; Castellano, Julen; Jukic, Igor; Casamichana, David

2018-01-18

The purpose of this paper was to study the structure of interrelationships among external training load measures and how these vary among different positions in elite basketball. Eight external variables of jumping (JUMP), acceleration (ACC), deceleration (DEC) and change of direction (COD), and two internal load variables (RPE and sRPE) were collected from 13 professional players with 300 session records. Three playing positions were considered: guards (n=4), forwards (n=4) and centers (n=5). High and total external variables (hJUMP and tJUMP, hACC and tACC, hDEC and tDEC, hCOD and tCOD) were used for the principal component analysis. Extraction criteria were set at the eigenvalue of greater than one. Varimax rotation mode was used to extract multiple principal components. The analysis showed that all positions had two or three principal components (explaining almost all of the variance), but the configuration of each factor was different: tACC, tDEC, tCOD and hJUMP for centers, hACC, tACC, tCOD and hJUMP for guards, and tACC, hDEC, tDEC, hCOD, and tCOD for forwards are specifically demanded in training sessions and, therefore, these variables must be prioritized in load monitoring. Furthermore, for all playing positions, RPE and sRPE have high correlation with the total amount of ACC, DEC and COD. This would suggest that, although players perform the same training tasks, the demands of each position can vary. A particular combination of external load measures is required to describe training load of each playing position, especially to better understand internal responses among players.

Dynamic simulation of road vehicle door window regulator mechanism of cross arm type

Science.gov (United States)

Miklos, I. Zs; Miklos, C.; Alic, C.

2017-01-01

The paper presents issues related to the dynamic simulation of a motor-drive operating mechanism of cross arm type, for the manipulation of road vehicle door windows, using Autodesk Inventor Professional software. The dynamic simulation of the mechanism involves a 3D modelling, kinematic coupling, drive motion parameters and external loads, as well as the graphically view of the kinematic and kinetostatic results for the various elements and kinematic couplings of the mechanism, under real operating conditions. Also, based on the results, the analysis of the mechanism components has been carried out using the finite element method.

Deformation mechanisms in Ti/TiN multilayer under compressive loading

International Nuclear Information System (INIS)

Yang, Wei; Ayoub, Georges; Salehinia, Iman; Mansoor, Bilal; Zbib, Hussein

2017-01-01

The promising mechanical, physical and chemical properties of nano-scale metal/ceramic multilayers (MCMs) are of high interest for extreme environment applications. Understanding the plastic deformation mechanisms and the variables affecting those properties is therefore essential. The interface characteristics and the plastic deformation mechanisms under compressive loading in a Ti/TiN multilayer with a semi-coherent interface are numerically investigated. The interface structure of the Ti/TiN interface and the interface misfit dislocation were characterized using molecular dynamic simulations combined with atomically informed Frank-Bilby method. Three possible atomic stacking interface structures are identified according to the crystallographic analysis of the interface. Upon relaxation, large interface areas are occupied with the energetically stable configuration. Furthermore, the higher energy stacking are transformed into misfit dislocations or dislocation nodes. The molecular dynamic compressive stress strain response of the Ti/TiN multilayers exhibited three distinctive peaks. The first peak was generated by the dislocation dissociation of perfect dislocation into pairs of partials dislocation around extended nodes region at the interface. Upon further compression the second peak, identified as the first yielding, resulted from the activation of pyramidal slip planes in the Ti layer. Finally, a third peak identified as the second yielding, occurred when dislocation nucleated/transmitted in/into the TiN layer.

Thermal–mechanical stress analysis of pressurized water reactor pressure vessel with/without a preexisting crack under grid load following conditions

Energy Technology Data Exchange (ETDEWEB)

Mohanty, Subhasish, E-mail: smohanty@anl.gov; Soppet, William K.; Majumdar, Saurin; Natesan, Krishnamurti

2016-12-15

Highlights: • Use of intermittent renewable-energy source in power grid is becoming a trend. • Gird load-following can leads to variable power demand from Nuclear power plant. • Reactor components can be stressed differently under gird load-following mode. • Estimation of stress–strain state under grid load-following condition is essential. - Abstract: In this paper, we present thermal–mechanical stress analysis of a pressurized water reactor pressure vessel and its hot-leg and cold-leg nozzles. Results are presented from thermal and thermal–mechanical stress analysis under reactor heat-up, cool-down, and grid load-following conditions. Analysis results are given with and without the presence of preexisting crack in the reactor nozzle (axial crack in hot leg nozzle). From the model results it is found that the stress–strain states are significantly higher in case of presence of crack than without crack. The stress–strain state under grid load following condition are more realistic compared to the stress–strain state estimated assuming simplified transients.

Thermal–mechanical stress analysis of pressurized water reactor pressure vessel with/without a preexisting crack under grid load following conditions

International Nuclear Information System (INIS)

Mohanty, Subhasish; Soppet, William K.; Majumdar, Saurin; Natesan, Krishnamurti

2016-01-01

Highlights: • Use of intermittent renewable-energy source in power grid is becoming a trend. • Gird load-following can leads to variable power demand from Nuclear power plant. • Reactor components can be stressed differently under gird load-following mode. • Estimation of stress–strain state under grid load-following condition is essential. - Abstract: In this paper, we present thermal–mechanical stress analysis of a pressurized water reactor pressure vessel and its hot-leg and cold-leg nozzles. Results are presented from thermal and thermal–mechanical stress analysis under reactor heat-up, cool-down, and grid load-following conditions. Analysis results are given with and without the presence of preexisting crack in the reactor nozzle (axial crack in hot leg nozzle). From the model results it is found that the stress–strain states are significantly higher in case of presence of crack than without crack. The stress–strain state under grid load following condition are more realistic compared to the stress–strain state estimated assuming simplified transients.

The EPR-a comprehensive design concept against external events

International Nuclear Information System (INIS)

Waas, U.; Stoll, U.

2005-01-01

The main objective of design provisions against external hazards is to ensure that the safety functions required to bring the plant to safe shutdown are not inadmissible affected. In the design of the EPR particular attention was paid to the following external hazards: Earthquake, Airplane crash, Explosion pressure wave. The design concept for these events is discussed below. The standard EPR covers a large range of possible site conditions, the design earthquake enveloping safe shutdown earthquakes (SSE) to be expected for potential sites. The Basic Design was developed for the seismic loads given in the European Utility Requirements with a horizontal free field Peak Ground Acceleration (PGA) for all site conditions of 0.25 g. The seismic protection is based on a deterministic design approach, with the intention of ensuring the safety functions in case of SSE. The loads for the design basis airplane crash and - if required - for the design extension airplane crash are defined depending on site specific requirements. For the design basis airplane crash as defined in Finland the safety goals are fulfilled for postulated single failure and preventive maintenance as well as for specific unlikely scenarios with local impacts where one redundant train is assumed to be lost. For the design extension airplane crash no single failure and preventive maintenance are assumed. Reactor building (RB), fuel building (FB), safeguard building (SB) 2 and 3 are protected by design against airplane crash. The common base mat of the RB, FB and SBs ensures global stability. To avoid penetration the wall thickness of the outer building structures of RB, FB and SB2/3 is set at 1.80 m (result of an optimization process). To rule out major induced vibrations due to airplane crash the inner building structures are decoupled from the outer walls. The SB 1 and SB4, the main steam and feedwater valve compartments, the diesel buildings and the service water pump buildings are protected against

Gender dimorphic ACL strain in response to combined dynamic 3D knee joint loading: implications for ACL injury risk.

Science.gov (United States)

Mizuno, Kiyonori; Andrish, Jack T; van den Bogert, Antonie J; McLean, Scott G

2009-12-01

While gender-based differences in knee joint anatomies/laxities are well documented, the potential for them to precipitate gender-dimorphic ACL loading and resultant injury risk has not been considered. To this end, we generated gender-specific models of ACL strain as a function of any six degrees of freedom (6DOF) knee joint load state via a combined cadaveric and analytical approach. Continuously varying joint forces and torques were applied to five male and five female cadaveric specimens and recorded along with synchronous knee flexion and ACL strain data. All data (approximately 10,000 samples) were submitted to specimen-specific regression analyses, affording ACL strain predictions as a function of the combined 6 DOF knee loads. Following individual model verifications, generalized gender-specific models were generated and subjected to 6 DOF external load scenarios consistent with both a clinical examination and a dynamic sports maneuver. The ensuing model-based strain predictions were subsequently examined for gender-based discrepancies. Male and female specimen-specific models predicted ACL strain within 0.51%+/-0.10% and 0.52%+/-0.07% of the measured data respectively, and explained more than 75% of the associated variance in each case. Predicted female ACL strains were also significantly larger than respective male values for both simulated 6 DOF load scenarios. Outcomes suggest that the female ACL will rupture in response to comparatively smaller external load applications. Future work must address the underlying anatomical/laxity contributions to knee joint mechanical and resultant ACL loading, ultimately affording prevention strategies that may cater to individual joint vulnerabilities.

The Effects of Triggering Mechanisms on the Energy Absorption Capability of Circular Jute/Epoxy Composite Tubes under Quasi-Static Axial Loading

Science.gov (United States)

Sivagurunathan, Rubentheran; Lau Tze Way, Saijod; Sivagurunathan, Linkesvaran; Yaakob, Mohd. Yuhazri

2018-01-01

The usage of composite materials have been improving over the years due to its superior mechanical properties such as high tensile strength, high energy absorption capability, and corrosion resistance. In this present study, the energy absorption capability of circular jute/epoxy composite tubes were tested and evaluated. To induce the progressive crushing of the composite tubes, four different types of triggering mechanisms were used which were the non-trigger, single chamfered trigger, double chamfered trigger and tulip trigger. Quasi-static axial loading test was carried out to understand the deformation patterns and the load-displacement characteristics for each composite tube. Besides that, the influence of energy absorption, crush force efficiency, peak load, mean load and load-displacement history were examined and discussed. The primary results displayed a significant influence on the energy absorption capability provided that stable progressive crushing occurred mostly in the triggered tubes compared to the non-triggered tubes. Overall, the tulip trigger configuration attributed the highest energy absorption.

Nondestructive Estimation of Muscle Contributions to STS Training with Different Loadings Based on Wearable Sensor System.

Science.gov (United States)

Liu, Kun; Liu, Yong; Yan, Jianchao; Sun, Zhenyuan

2018-03-25

Partial body weight support or loading sit-to-stand (STS) rehabilitation can be useful for persons with lower limb dysfunction to achieve movement again based on the internal residual muscle force and external assistance. To explicate how the muscles contribute to the kinetics and kinematics of STS performance by non-invasive in vitro detection and to nondestructively estimate the muscle contributions to STS training with different loadings, a wearable sensor system was developed with ground reaction force (GRF) platforms, motion capture inertial sensors and electromyography (EMG) sensors. To estimate the internal moments of hip, knee and ankle joints and quantify the contributions of individual muscle and gravity to STS movement, the inverse dynamics analysis on a simplified STS biomechanical model with external loading is proposed. The functional roles of the lower limb individual muscles (rectus femoris (RF), gluteus maximus (GM), vastus lateralis (VL), tibialis anterior (TA) and gastrocnemius (GAST)) during STS motion and the mechanism of the muscles' synergies to perform STS-specific subtasks were analyzed. The muscle contributions to the biomechanical STS subtasks of vertical propulsion, anteroposterior (AP) braking and propulsion for body balance in the sagittal plane were quantified by experimental studies with EMG, kinematic and kinetic data.

A study of long-term static load on degradation and mechanical integrity of Mg alloys-based biodegradable metals

International Nuclear Information System (INIS)

Koo, Youngmi; Jang, Yongseok; Yun, Yeoheung

2017-01-01

Highlights: • Long-term stress corrosion cracking (SCC) test of Mg alloys was performed. • AZ31B-H24 shows transgranular stress corrosion cracking (TGSCC) and ZE41A-T5 intergranular stress corrosion cracking (IGSCC). • Long-term static loading accelerated crack propagation, leading to the loss of mechanical strength. - Abstract: Predicting degradation behavior of biodegradable metals in vivo is crucial for the clinical success of medical devices. This paper reports on the effect of long-term static stress on degradation of magnesium alloys and further changes in mechanical integrity. AZ31B (H24) and ZE41A (T5) alloys were tested to evaluate stress corrosion cracking (SCC) in a physiological solution for 30 days and 90 days (ASTM G39 testing standard). Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) and micro-computed tomography (micro-CT) were used to characterize surface morphology and micro-structure of degraded alloys. The results show the different mechanisms of stress corrosion cracking for AZ31B (transgranular stress corrosion cracking, TGSCC) and ZE41A (intergranular stress corrosion cracking, IGSCC). AZ31B was more susceptible to stress corrosion cracking under a long term static load than ZE41A. In conclusion, we observed that long-term static loading accelerated crack propagation, leading to the loss of mechanical integrity.

A study of long-term static load on degradation and mechanical integrity of Mg alloys-based biodegradable metals

Energy Technology Data Exchange (ETDEWEB)

Koo, Youngmi; Jang, Yongseok; Yun, Yeoheung, E-mail: yyun@ncat.edu

2017-05-15

Highlights: • Long-term stress corrosion cracking (SCC) test of Mg alloys was performed. • AZ31B-H24 shows transgranular stress corrosion cracking (TGSCC) and ZE41A-T5 intergranular stress corrosion cracking (IGSCC). • Long-term static loading accelerated crack propagation, leading to the loss of mechanical strength. - Abstract: Predicting degradation behavior of biodegradable metals in vivo is crucial for the clinical success of medical devices. This paper reports on the effect of long-term static stress on degradation of magnesium alloys and further changes in mechanical integrity. AZ31B (H24) and ZE41A (T5) alloys were tested to evaluate stress corrosion cracking (SCC) in a physiological solution for 30 days and 90 days (ASTM G39 testing standard). Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) and micro-computed tomography (micro-CT) were used to characterize surface morphology and micro-structure of degraded alloys. The results show the different mechanisms of stress corrosion cracking for AZ31B (transgranular stress corrosion cracking, TGSCC) and ZE41A (intergranular stress corrosion cracking, IGSCC). AZ31B was more susceptible to stress corrosion cracking under a long term static load than ZE41A. In conclusion, we observed that long-term static loading accelerated crack propagation, leading to the loss of mechanical integrity.

Expression of insulin-like growth factor I, insulin-like growth factor binding proteins, and collagen mRNA in mechanically loaded plantaris tendon

DEFF Research Database (Denmark)

Olesen, Jens L; Heinemeier, Katja M; Haddad, Fadia

2006-01-01

Insulin-like growth factor I (IGF-I) is known to exert an anabolic effect on tendon fibroblast production of collagen. IGF-I's regulation is complex and involves six different IGF binding proteins (IGFBPs). Of these, IGFBP-4 and -5 could potentially influence the effect of IGF-I in the tendon...... because they both are produced in fibroblast; however, the response of IGFBP-4 and -5 to mechanical loading and their role in IGF-I regulation in tendinous tissue are unknown. A splice variant of IGF-I, mechano-growth factor (MGF) is upregulated and known to be important for adaptation in loaded muscle....... However, it is not known whether MGF is expressed and upregulated in mechanically loaded tendon. This study examined the effect of mechanical load on tendon collagen mRNA in relation to changes in the IGF-I systems mRNA expression. Data were collected at 2, 4, 8 and 16 days after surgical removal...

Experimental study of reinforced concrete pile caps with external, embedded and partially embedded socket with smooth interface

Directory of Open Access Journals (Sweden)

R. Barros

Full Text Available On Precast concrete structures the column foundation connections can occur through the socket foundation, which can be embedded, partially embedded or external, with socket walls over the pile caps. This paper presents an experimental study about two pile caps reinforced concrete with external, partially embedded and embedded socket submitted to central load, using 1:2 scaled models. In the analyzed models, the smooth interface between the socket walls and column was considered. The results are compared to a reference model that presents monolithic connections between the column and pile cap. It is observed that the ultimate load of pile cap with external sockets has the same magnitude as the reference pile cap, but the ultimate load of models with partially embedded and embedded socket present less magnitude than the reference model.

LOFT facility PSS experiments: analysis of wet well vertical loads resulting from transient initiation

International Nuclear Information System (INIS)

Berta, V.T.

1977-05-01

Fourteen experiments on the Loss-of-Fluid Test (LOFT) facility pressure suppression system (PSS) are analyzed in relation to the vertical load generated on the suppression tank in the first 0.5 sec of the transient. Variations in principle parameters affecting the generation of vertical loads were included in the experiments. The internal and external vent submergences are identified from the analysis as being parameters which are first order in influencing the magnitude of the vertical load. These parameters are geometric in nature and depend only on PSS design. Physical parameters of total energy input and rate of energy input to the dry well, which influence the dry well pressurization, also are identified as being first order in influencing the magnitude of the vertical loads. The vertical load magnitude is a direct function of these geometric and physical parameters. The analysis indicates that a small value in any one of the parameters will cause the vertical load to be small and to have little dependence on the magnitude of the other parameters. In addition, the phenomena of nonuniform nonsynchronized vent inlet pressures, which have origins that are either geometric, physical, or a combination of both, act as a significant vertical load reduction mechanism

Behavior of duplex stainless steel casting defects under mechanical loadings

Energy Technology Data Exchange (ETDEWEB)

Jayet-Gendrot, S [Electricite de France, 77 - Moret-sur-Loing (France). Dept. of Materials Study; Gilles, P; Migne, C [Societe Franco-Americaine de Constructions Atomiques (FRAMATOME), 92 - Paris-La-Defense (France)

1997-04-01

Several components in the primary circuit of pressurized water reactors are made of cast duplex stainless steels. This material contains small casting defects, mainly shrinkage cavities, due to the manufacturing process. In safety analyses, the structural integrity of the components is studied. In order to assess the real severity of the casting defects under mechanical loadings, an experimental program was carried out. It consisted of testing, under both cyclic and monotonic solicitations, three-point bend specimens containing either a natural defect (in the form of a localized cluster of cavities) or a machined notch having the dimensions of the cluster`s envelope. The tests are analyzed in order to develop a method that takes into account the behavior of castings defects in a more realistic fashion than by an envelope crack. Various approaches are investigated, including the search of equivalent defects or of criteria based on continuum mechanics concepts, and compared with literature data. This study shows the conservatism of current safety analyses in modelling casting defects by envelope semi-elliptical cracks and contributes to the development of alternative approaches. (author) 18 refs.

A probabilistic approach for evaluation of load time history of an aircraft impact

International Nuclear Information System (INIS)

Zorn, N.F.; Schueller, G.I.; Riera, J.D.

1981-01-01

In the context of an overall structural realiability study for a containment located in the F.R. Germany the external load case aircraft impact is investigated. Previous investigations have been based on deterministic evaluations of the load time history. However, a close analysis of the input parameters, such as the mass distribution, the stiffness of the aircraft, the impact velocity and the impact angle reveal their random properties. This in turn leads to a stochastic load time history the parameters of which have been determined in this study. In other words, the randomness of the input parameters are introduced in the calculation of the load time history and their influence with regard to the load magnitude and frequency content is determined. The statistical parameters such as the mean values and the standard deviation of the mechanical properties are evaluated directly from the design plans of the manufacturer for the aircraft Phantom F4-F. This includes rupture loads, mass distributions etc.. The probability distributions of the crash velocity and impact angle are based on a thorough statistical evaluation of the crash histories of the airplane under consideration. Reference was made only to crashes which occurred in the F.R. Germany. (orig.)

Detailed mechanical design of the LIPAc beam dump radiological shielding

Energy Technology Data Exchange (ETDEWEB)

Nomen, Oriol, E-mail: onomen@irec.cat [IREC, Barcelona, Catalonia (Spain); CDEI-UPC, Barcelona, Catalonia (Spain); Martínez, José I.; Arranz, Fernando; Iglesias, Daniel; Barrera, Germán; Brañas, Beatriz [CIEMAT, Madrid (Spain); Ogando, Francisco [UNED, Madrid (Spain); Molla, Joaquín [CIEMAT, Madrid (Spain); Sanmartí, Manel [IREC, Barcelona, Catalonia (Spain)

2013-10-15

Highlights: ► Mechanical design of the IFMIF LIPAc beam dump shielding has been performed. ► Lead shutter design performed to shield radiation from beam dump when LIPAc is off. ► External loads, working and dismantling conditions, included as design constraints. -- Abstract: The LIPAc is a 9 MeV, D{sup +} linear prototype accelerator for the validation of the IFMIF accelerator design. The high intensity, 125 mA CW beam is stopped in a copper cone involving a high production of neutrons and gamma radiation and activation of its surface. The beam stopper is surrounded by a shielding to attenuate the resulting radiation so that dose rate values comply with the limits at the different zones of the installation. The shielding includes for that purpose polyethylene rings, water tanks and gray cast iron rings. A lead shutter has also been designed to shield the gamma radiation that comes through the beam tube when the linear accelerator is not in operation, in order to allow access inside the building for maintenance tasks. The present work summarizes the detailed mechanical design of the beam dump shielding and the lead shutter taking into account the design constraints, such as working conditions and other external loads, as well as including provisions for dismantling.

Mechanical properties of HDPE/UHMWPE blends: effect of filler loading and filler treatment.

Science.gov (United States)

Lai, K L K; Roziyanna, A; Ogunniyi, D S; Zainal, Arifin M I; Azlan, Ariffin A

2004-05-01

Various blend ratios of high-density polyethylene (HDPE) and ultra high molecular weight polyethylene (UHMWPE) were prepared with the objective of determining their suitability as biomaterials. In the unfilled state, a blend of 50/50 (HDPE/UHMWPE) ratio by weight was found to yield optimum properties in terms of processability and mechanical properties. Hydroxyapatite (HA) was compounded with the optimum blend ratio. The effects of HA loading, varied from 0 to 50wt% for both filled and unfilled blends were tested for mechanical properties. It was found that the inclusion of HA in the blend led to a remarkable improvement of mechanical properties compared to the unfilled blend. In order to improve the bonding between the polymer blend and the filler, the HA used was chemically treated with a coupling agent known as 3-(trimethoxysiyl) propyl methacrylate and the treated HA was mixed into the blend. The effect of mixing the blend with silane-treated HA also led to an overall improvement of mechanical properties.

Development of a novel sodium fusidate-loaded triple polymer hydrogel wound dressing: Mechanical properties and effects on wound repair.

Science.gov (United States)

Jin, Sung Giu; Kim, Kyeong Soo; Kim, Dong Wuk; Kim, Dong Shik; Seo, Youn Gee; Go, Toe Gyung; Youn, Yu Seok; Kim, Jong Oh; Yong, Chul Soon; Choi, Han-Gon

2016-01-30

To develop a novel sodium fusidate-loaded triple polymer hydrogel dressing (TPHD), numerious polyvinyl alcohol-based (PVA) hydrogel dressings were prepared with various hydrophilic polymers using the freeze-thaw method, and their hydrogel dressing properties were assessed. Among the hydrophilic polymers tested, sodium alginate (SA) improved the swelling capacity the most, and polyvinyl pyrrolidone (PVP) provided the greatest improvement in bioadhesive stength and mechanical properties. Thus, PVA based-TPHDs were prepared using different ratios of PVP:SA. The effect of selected PVP:SA ratios on the swelling capacity, bioadhesive strength, mechanical properties, and drug release, permeation and deposition characteristics of sodium fusidate-loaded PVA-based TPHDs were assessed. As the ratio of PVP:SA increased in PVA-loaded TPHD, the swelling capacity, mechanical properties, drug release, permeation and deposition were improved. The TPHD containing PVA, PVP, SA and sodium fusidate at the weight ratio of 10/6/1/1 showed excellent hydrogel dressing properties, release, permeation and deposition of drug. Within 24h, 71.8 ± 1.3% of drug was released. It permeated 625.1 ± 81.2 μg/cm(2) through the skin and deposited of 313.8 ± 24.1 μg/cm(2) within 24h. The results of in vivo pharmacodynamic studies showed that sodium fusidate-loaded TPHD was more effective in improving the repair process than was a commercial product. Thus, this sodium fusidate-loaded TPHD could be a novel tool in wound care. Copyright © 2015 Elsevier B.V. All rights reserved.

Concentrated loads on concrete

DEFF Research Database (Denmark)

Lorenzen, Karen Grøndahl; Nielsen, Mogens Peter

1997-01-01

This report deals with concentrated loads on concrete.A new upper bound solution in the axisymmetrical case of a point load in the center of the end face of a cylinder is developed.Based on previous work dealing with failure mechanisms and upper bound solutions, new approximate formulas are devel......This report deals with concentrated loads on concrete.A new upper bound solution in the axisymmetrical case of a point load in the center of the end face of a cylinder is developed.Based on previous work dealing with failure mechanisms and upper bound solutions, new approximate formulas...

Leveraging External Sources of Innovation

DEFF Research Database (Denmark)

West, Joel; Bogers, Marcel

2014-01-01

, it suggests a four-phase model in which a linear process—(1) obtaining, (2) integrating, and (3) commercializing external innovations—is combined with (4) interaction between the firm and its collaborators. This model is used to classify papers taken from the top 25 innovation journals, complemented by highly...... cited work beyond those journals. A review of 291 open innovation-related publications from these sources shows that the majority of these articles indeed address elements of this inbound open innovation process model. Specifically, it finds that researchers have front-loaded their examination...... external innovations create value rather than how firms capture value from those innovations. Finally, the interaction phase considers both feedback for the linear process and reciprocal innovation processes such as cocreation, network collaboration, and community innovation. This review and synthesis...

Relationship Between Pretraining Subjective Wellness Measures, Player Load, and Rating-of-Perceived-Exertion Training Load in American College Football.

Science.gov (United States)

Govus, Andrew D; Coutts, Aaron; Duffield, Rob; Murray, Andrew; Fullagar, Hugh

2018-01-01

The relationship between pretraining subjective wellness and external and internal training load in American college football is unclear. To examine the relationship of pretraining subjective wellness (sleep quality, muscle soreness, energy, wellness Z score) with player load and session rating of perceived exertion (s-RPE-TL) in American college football players. Subjective wellness (measured using 5-point, Likert-scale questionnaires), external load (derived from GPS and accelerometry), and s-RPE-TL were collected during 3 typical training sessions per week for the second half of an American college football season (8 wk). The relationship of pretraining subjective wellness with player load and s-RPE training load was analyzed using linear mixed models with a random intercept for athlete and a random slope for training session. Standardized mean differences (SMDs) denote the effect magnitude. A 1-unit increase in wellness Z score and energy was associated with trivial 2.3% (90% confidence interval [CI] 0.5, 4.2; SMD 0.12) and 2.6% (90% CI 0.1, 5.2; SMD 0.13) increases in player load, respectively. A 1-unit increase in muscle soreness (players felt less sore) corresponded to a trivial 4.4% (90% CI -8.4, -0.3; SMD -0.05) decrease in s-RPE training load. Measuring pretraining subjective wellness may provide information about players' capacity to perform in a training session and could be a key determinant of their response to the imposed training demands American college football. Hence, monitoring subjective wellness may aid in the individualization of training prescription in American college football players.

Stress Fractures of Tibia Treated with Ilizarov External Fixator.

Science.gov (United States)

Górski, Radosław; Żarek, Sławomir; Modzelewski, Piotr; Górski, Ryszard; Małdyk, Paweł

2016-08-30

Stress fractures are the result of cyclic loading of the bone, which gradually becomes damaged. Most often they are treated by rest or plaster cast and, in rare cases, by internal fixation. There is little published data on initial reposition followed by stabilization with the Ilizarov apparatus in such fractures. Six patients were treated with an external fixator according to the Ilizarov method for a stress fracture of the tibia between 2007 and 2015. Three patients were initially treated conservatively. Due to increasing tibial deformation, they were qualified for surgical treatment with external stabilization. In the other patients, surgery was the first-line treatment. All patients demonstrated risk factors for a stress fracture. After the surgery, they fully loaded the operated limb. No patient developed malunion, nonunion, infection or venous thrombosis. The average time from the first operation to the removal of the external fixator was 19 weeks. Radiographic and clinical outcomes were satisfactory in all patients. 1. The Ilizarov method allows for successful stabilization of stress fractures of the tibia. 2. It may be a good alternative to internal stabilization, especially in patients with multiple comorbidities which affect bone quality and may impair soft tissue healing.

Influence of a 12.8-km military load carriage activity on lower limb gait mechanics and muscle activity.

Science.gov (United States)

Rice, Hannah; Fallowfield, Joanne; Allsopp, Adrian; Dixon, Sharon

2017-05-01

The high stress fracture occurrence in military populations has been associated with frequent load carriage activities. This study aimed to assess the influence of load carriage and of completing a load carriage training activity on gait characteristics. Thirty-two Royal Marine recruits completed a 12.8-km load carriage activity as part of their military training. Data were collected during walking in military boots, pre and post-activity, with and without the additional load (35.5 kg). Ground contact time, lower limb sagittal plane kinematics and kinetics, and electromyographic variables were obtained for each condition. When carrying load, there was increased ground contact time, increased joint flexion and joint moments, and increased plantar flexor and knee extensor muscle activity. Post-activity, there were no changes to kinematic variables, knee extensor moments were reduced, and there was evidence of plantar flexor muscle fatigue. The observed gait changes may be associated with stress fracture development. Practitioner Summary: This study identified gait changes due to load carriage and after a military load carriage training activity. Such activities are associated with lower limb stress fractures. A pre-post study design was used. Gait mechanics changed to a greater extent when carrying load, than after completion of the activity when assessed without load.