Magnitude Of External Load Research Articles

Assessment of the Influence of Protective Polymer Coating on Panda Fiber Performance Based on the Results of Multivariant Numerical Simulation.

This article considers the deformation behavior of Panda optical fiber using different models of material behavior for the tasks of predicting residual stresses after drawing when cooling from 2000 °C to room temperature (23 °C) and indenting the fiber into an aluminum half-space at different parameters. These studies were conducted for single- and double-layer protective coatings (PCs), at different values of external load and thickness of single-layer PC. This paper determined the fields of residual stresses in the fiber formed during the drawing process. They are taken into account in modeling the fiber performance in the further process of this research. This article investigated two variants of PC behavior. The influence of behavior models and the number of covering layers on the deformation of the "fiber-half-space" system was analyzed. This paper establishes qualitative and quantitative regularities of the influence of the external load magnitude and relaxation properties of PCs on the deformation and optical characteristics of Panda optical fiber.

A Note on Korn’s Inequality in an N-Dimensional Context and a Global Existence Result for a Non-Linear Plate Model

In the first part of this article, we present a new proof for Korn’s inequality in an n-dimensional context. The results are based on standard tools of real and functional analysis. For the final result, the standard Poincaré inequality plays a fundamental role. In the second text part, we develop a global existence result for a non-linear model of plates. We address a rather general type of boundary conditions and the novelty here is the more relaxed restrictions concerning the external load magnitude.

Cohesive Model Application in the Assessment of Plastic Zone Magnitude for One Particular Case of Crack Loading

The answer of the thin, infinite, central cracked plate, subjected to in-plane loading, is investigated. The plate is made from a ductile metallic material. The two pairs of the concentrate forces, F, act on the crack surface in the direction perpendicular to it. The other edges of the plate, at infinity, are free of loading. The forces, F, open the crack and they are monotonously increased. The small plastic zones around crack tips will appear. It is assumed an isotropic and non-linear strain hardening of a plate material which can be good described by the Ramberg-Osgood´s equation. The investigations were carried out for the several different values of the strain hardening exponent n which is changed among the discrete values n = 2, 3, 4, 5, 7, 10, 15, 25, 50 and 1000. One well-known cohesive model (Dugdale´s model) was applied in the crack tip plasticity investigating. It was assumed that the cohesive stresses within the plastic zone are changed according to non-linear law. Also, a new algorithm was established which enables direct calculation of plastic zone magnitude depending on the magnitude of external loads. The contemporary mathematical tools, like the software package Wolfram Mathematica, were used. The solutions are presented through the special, Gamma and the Hypergeometric functions.

External loading of common training drills: Ranking drills to design progressive return-to-run programs

Return-to-run protocols following lower extremity injuries commonly include a gradual training and loading progression to allow positive adaptation of musculoskeletal tissue. Before full return to running, training drills designed to provide a low to high external loading progression (i.e., vertical forces) may therefore minimize the risks of re-injury. However, the magnitude of external loading among various training drills has not yet been quantified. ObjectivesThe purpose of this study was to quantify peak vertical forces of multiple common training drills and rank each of them in order from lowest to highest peak vertical force. Design/Participants: 11 experienced runners completed five trials of 46 training drills while in-shoe vertical reaction force (vRF) was measured with wireless force insoles. Main outcome measuresAverage peak vRF was calculated for each drill across all participants. Drills were also grouped by vRF into four categories intended for use by clinicians as stages of rehabilitation. Results46 training drills were ranked in order from least to greatest vRF. The drill with the highest average peak vRF was “Ladder Single Leg Hop Forward”, at 2.80 BW. The drill with the lowest average peak vRF was “Squat Mini Jump”, at 1.02 BW. ConclusionsThese data provide valuable information for clinicians, coaches and pelvic floor practitioners when programming rehabilitation and return-to-run training progressions for runners coming back from lower extremity or pelvic injuries.

METHODOLOGY AND RESULTS OF THE SERIES P-2 GLASS SLABS DURABILITY TEST

The paper presents the results of studies of glass plates of series P-2 for durability, which were made of float glass sheets, the methodology of experimental studies of glass plates for durability, as well as the design of the test facility. The analysis of literature sources on the subject made it possible to study the main factors of application of glass slabs as load-bearing structures. Glass is characterized by high strength, but glass structures are not widely used because of the possibility of their sudden brittle fracture and the lack of reliable calculation methods. The strength and reliability of glass structures depend on the type and strength of glass, manufacturing technology, the magnitude of external load and the duration of its action. Glass structures are characterized by the phenomenon of rheology and sudden brittle fracture, so the study of their durability, at different levels of external static load will ensure their reliable operation for the required time. Durability of a structure is the time from the beginning of static load action, which does not exceed the destructive load, with its further endurance until the destruction of the structure. For experimental studies of the durability of glass slabs, there was a need to create a research technique to ensure the stability of the external static load during the entire experiment with the possibility to record the growth of the deflection of the glass slab, the time and the nature of the failure up to the very moment of their sudden brittle failure. The paper describes the methodology and presents the initial results of the experimental study of glass beam slabs for durability. The slabs were hinged to two supports and operated as a single-span beam under a steady static load. Based on the experimental data obtained on the fracture of glass slabs during the action of a steady static load, we can try to predict their durability.

Modeling irradiation-induced intragranular gas bubble in tungsten under external tensile loading

Microstructure damage created by high-energy particle irradiation has an inevitable effect on the performance of material. Helium (He) as the transmutation element in irradiated solid prefers to occupy the vacancy (V) center to form HeV complex, which in turn induces the formation of He bubble. Herein, the external applied stress driven irradiation-induced He bubble formation and evolution in single-crystalline tungsten (W) has been investigated using the phase-field method. Importantly, the trapping and resolution kinetic behavior between He atom and He bubble is described by the diffusion coefficient in terms of rate theory continuum model, and the effect of external stress on the movements of vacancy, self-interstitial and He atom has been implemented into their diffusivities as well. We first concentrate on the intrinsic lattice distortion (stress) patterns of void and bubble to validate the developed model by comparing the reported numerical results. Then, the accelerated growth velocity of bubble along the loading direction is predicted, which agrees well with the previously observed stress pattern around the void/bubble. The evolution behaviors of the stress-assisted single, bi-dispersed and multiple bubbles vary with the direction and magnitude of external loading, indicating a strong correlation between the size and density of bubble and the loading level. It is found that with the contribution of increasing external stress, more bubbles can be generated at the formation stage and visible bubbles tend to reduce at the coarsening stage due to bubble coalescence.

A non-centrosymmetric square lattice with an axial–bending coupling

Metamaterials can enable the design of exotic properties, including the mechanical coupling of different loading modes. Chirality and non-centrosymmetry are known to play essential roles in the rational design of coupling effects. However, there is no theoretical support for the design of coupling behaviors based on the constitutive behavior of lattice structures. Exploring a planar non-centrosymmetric square lattice, we find a novel coupling effect: a compression-induced bending, which a micropolar continuum model can support. Observing the micropolar constitutive equation of a 2D lattice, we find that non-centrosymmetry is necessary but insufficient for designing an axial–bending coupling. The micropolar homogenization is adopted to calculate the material properties of infinite lattices, revealing that the axial-bending coupling coefficient is dependent on the cell size, which is verified by finite element simulations. The axial–bending coupling size effect of finite lattices shows different deformation patterns depending on the cell size and the magnitude of external loading. The novel coupling effect can expand the design space of metamaterials with potential applications in multidirectional mechanical actuators and mechanical logic gates for biomedical, automobile, and aerospace devices.

Characterization of external load in different types of exercise in professional soccer

PurposeTo compare the duration of exercise and magnitude of external load per type of exercise (warm-up, small-sided games, position games – movements with/without ball but without the dynamics of a real game, simulations of real games – 11 vs. 11, fitness exercises, large-sided games, technical drills) during different training days in professional soccer players and test the relationships between duration of exercise and the external load.MethodsOverall, 22 professional soccer players (25.1 ± 2.9 years, 181.9 ± 6.3 cm, 73.1 ± 6.3 kg) were daily monitored by a microelectromechanical system. The training duration (minutes) and the external load measures of total distance covered and high-speed running distance were collected for each type of exercise.ResultsRepeated measures ANOVA revealed significant differences in training duration, total distance covered, and high-speed running distance between the exercises (p < 0.001). A greater total distance was covered in simulations of real games (2321 m/session), as well as high-speed running (84.6 m/session). The total distance covered in simulations of real games was greater by 77% than in small-sided games, while that in high-speed running in simulations of real games was greater by 153% than in large-sided games.ConclusionsThe study revealed that simulations of real games and position games were the exercises that occupied the most time in the sessions and that the simulations of real games were the greatest contributor to distance covered and distance covered at high-speed running.

Effects of the type of exercise performed on the vibration delivered during whole-body vibration exercises

While the internal load factors of whole-body vibration training have been widely investigated, the study of external load magnitude has been overlooked. Thus, the aim of the present study was to evaluate differences in whole-body vibration stimulus magnitude between static/dynamic whole-body vibration training at various vibration conditions. Four Pro 5 Plate vibration platforms were exposed to twelve different vibration conditions and a triaxial USB Impact X250-2 accelerometer was used to measure platform acceleration during each condition. Paired samples t-test was calculated to evaluate differences among amplitude, frequency, time of acceleration and time of deceleration of each platform at each vibration condition and during static (squat of 90° knee flexion) or dynamic exercise (from stand to 90° knee flexion squat). Also, the intra-class correlation coefficients were examined in order to assess the inter-instrument reliability. Peak-to-peak amplitude, frequency, time of acceleration and deceleration of the vibration platform were not modified by the type of exercise performed. Moreover, the four platforms tested showed high repeatability values during the execution of free vibration, static or dynamic squat in all vibration conditions. This study confirms that the vibration delivered by the Pro 5 Plate vibration platform is not modified during the realization of static or dynamic exercises.

Identification of Static Loading Conditions Using Piezoelectric Sensor Arrays

To make sure the safety, durability, and serviceability of structures in-service, health monitoring systems (HMS) are widely used in management of civil infrastructures in recent years. Compared with traditional force sensors, lead zirconium titanate (PZT) sensor performs better in smart sensing in HMS with advantages of high sensitivity, self-powering and fast response to highly dynamic load. Here, we propose to utilize PZT sensor arrays to identify the position and magnitude of external loads that are applied on a simply supported beam. An identification method is proposed based on experimental tests and theoretical electromechanical analyses, which is proved effective by comparing the identified parameters with the actually applied loading conditions and signals recorded by commercial force sensors. Experimental observations also reveal that PZT sensors respond faster to loading process than commercial force sensor, which makes it qualified in identification of transient loading such as impact processing in loading history. Results also demonstrate the applicability of the method to identify multiple concentrated load and the average moving speed of the applied load. The current method may provide a useful tool for identifying load conditions on various beam structures.

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

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.

An Influence of the Longitudinal Spring Element on Free Vibrations of the Partially Tensioned Column

In this paper the slender system subjected to Euler's load which is partially tensioned is considered. On one of system's ends the discrete element in a form of translational spring which limits the longitudinal displacement was used. The boundary problem of free vibration of the considered system was formulated on the basis of Hamilton's principle and solved according to the small parameter method due to nonlinearities. In the boundary problem formulation process the Bernoulli-Euler theory was used. The relationships between free vibration frequency and parameters such as external load magnitude, translational spring stiffness used for longitudinal displacement control and external load location were studied.

Effect of variable particle stiffness on force propagation and mechanical response of a composite granular material.

The force propagation and mechanical response are important for understanding the elasticity and deformation of a composite granular packings. In this paper, a 2D composite granular layers composed of particles with variable stiffness is proposed, and the effect of stiffness ratio between component particles on mechanical response is mainly considered. The results show that the decrease of stiffness ratio broadens the linear range of mechanical response and enhances the elasticity of the response in a composite granular system, showing a role similar with the friction in a monodisperse granular packings. Furthermore, a phase diagram for the crossover between a single-peaked and a double-peaked response is proposed, in which the critical stiffness ratio corresponding to the occurrence of the crossover decreases with the magnitude of external loading and increases with the friction. Finally, the microscopic mechanism of the crossover of the response is further discussed based on changes in contact network and force network.

Comparative Study of the Adhesive Component of Friction in Hip Endoprostheses

Kinematic unit friction pairs of human hip endoprosthesis and rabbit hips with induced osteoarthrosis were studied under conditions of either dry or biological medium friction. Deterioration of tribologic characteristics in destructive dystrophic lesions of joints is the key component of joint kinematic properties decompensation. Experimental animal model of osteoarthrosis showed negative influence of dystrophic changes upon the hip joint adhesive characteristics. Study of the adhesive component of friction coefficient in different tribologic pairs of endoprostheses detected that friction characteristics of the studied tribologic pairs depended upon the magnitude of external load and strength of the kinematic unit.

Comparative Study of the Adhesive Component of Friction in Hip Endoprostheses

Kinematic unit friction pairs of human hip endoprosthesis and rabbit hips with induced osteoarthrosis were studied under conditions of either dry or biological medium friction. Deterioration of tribologic characteristics in destructive dystrophic lesions of joints is the key component of joint kinematic properties decompensation. Experimental animal model of osteoarthrosis showed negative influence of dystrophic changes upon the hip joint adhesive characteristics. Study of the adhesive component of friction coefficient in different tribologic pairs of endoprostheses detected that friction characteristics of the studied tribologic pairs depended upon the magnitude of external load and strength of the kinematic unit.

Time-Temperature Superposition in Linear and Non-linear Domain

Long-term behavior of polymers and their composites is related mainly to their time-dependent mechanical properties, i.e. material functions or master curves, usually obtained by time-temperature superposition (tTS) principle. The “weakest” point utilizing tTS lies in “manual or hand” shifting procedure, which can lead to over- or under-estimated life span of polymeric materials. This problem was solved by using closed form mathematical solution called Closed-Form-Shifting (CFS) algorithm which completely removes issues of “manual or hand” shifting procedure. However, it is important to acknowledge that tTS is well established only within the realm of linear viscoelastic theory. Results have shown that utilizing tTS in non-linear domain, where time-dependent properties become dependent on magnitude of external load, my lead to construction of misleading master curves, i.e. overestimated long-term behavior of polymers that could consequently cause premature failure of polymeric products.

Variation of hydraulic gradient in nonlinear finite strain consolidation

In the research field of ground water, hydraulic gradient is studied for decades. In the consolidation field, hydraulic gradient is yet to be investigated as an important hydraulic variable. So, the variation of hydraulic gradient in nonlinear finite strain consolidation was focused on in this work. Based on lab tests, the nonlinear compressibility and nonlinear permeability of Ningbo soft clay were obtained. Then, a strongly nonlinear governing equation was derived and it was solved with the finite element method. Afterwards, the numerical analysis was performed and it was verified with the existing experiment for Hong Kong marine clay. It can be found that the variation of hydraulic gradient is closely related to the magnitude of external load and the depth in soils. It is interesting that the absolute value of hydraulic gradient (AVHG) increases rapidly first and then decreases gradually after reaching the maximum at different depths of soils. Furthermore, the changing curves of AVHG can be roughly divided into five phases. This five-phase model can be employed to study the migration of pore water during consolidation.

Finite element formulation and analysis for an arterial wall with residual and active stresses

In this study, for predicting arterial function and pathogenesis from a mechanical viewpoint, we develop a continuum mechanical model of an arterial wall that embodies residual and active stresses following a traditional anisotropic passive constitutive law. The residual and active stresses are incorporated into finite element methods based on a two-field variational principle described in the Lagrangian form. The linearisation of nonlinear weak-form equations derived from this variational principle is then described for developing an original finite element algorithm. Numerical simulations reveal the following: (i) residual stresses lead to a reduction in stress gradient regardless of the magnitude of external load; (ii) active stresses help homogenise stress distribution under physiological external load, but this homogeneity collapses under pathological external load; (iii) when residual and active stresses act together, the effect of the residual stresses is relatively obscured by that of the active stresses. We conclude that residual stresses have minor but persistent mechanical effects on the arterial wall under both physiological and pathological external loads; active stresses play an important role in the physiological functions and pathogenesis of arteries, and the mechanical effect of residual stresses is dependent on the presence/absence of active stresses.

Lower Extremity Biomechanical Changes Associated With Symmetrical Torso Loading During Simulated Marching

The dose-response relationship between biomechanical variables and the magnitude of external loads is unclear. The use of different load distributions (e.g., pack types) may confound results because of changes in torso center of mass. Therefore, we examined the relationship between load magnitude and sagittal plane lower extremity mechanics of Soldiers walking with two symmetrically distributed loads. Fourteen Soldiers marched on a force-sensing treadmill at 1.34 m/s for 10 minutes with no load (BW_00) and while wearing vest-borne loads of 15 kg (BW_15) and 55 kg (BW_55). The effects of the loads on sagittal plane joint angles and moments were compared using 1-way repeated measures analyses of variance. Compared with BW_00, knee extension moment increased with the 15- and the 55-kg loads (both p < 0.003), confirming previously reported load-related biomechanical responses. Knee moment increases during early stance appeared to be the primary means by which the lower extremity counteracted BW_15 during early stance; in contrast, hip extensors and ankle dorsiflexors appeared to be the primary muscular efforts responsible for propulsion during late stance. Findings elucidated the effects of load magnitude on lower extremity mechanics without postural changes that result from pack-related shifts in torso center of mass.

Static prehension of a horizontally oriented object in three dimensions

We studied static prehension of a horizontally oriented object. Specific hypotheses were explored addressing such issues as the sharing patterns of the total moment of force across the digits, presence of mechanically unnecessary digit forces, and trade-off between multi-digit synergies at the two levels of the assumed control hierarchy. Within the assumed hierarchy, at the upper level, the task is shared between the thumb and virtual finger (an imagined finger producing a wrench equal to the sum of the wrenches of individual fingers). At the lower level, action of the virtual finger is shared among the four actual fingers. The subjects held statically a horizontally oriented handle instrumented with six-component force/torque sensors with different loads and torques acting about the long axis of the handle. The thumb acted from above while the four fingers supported the weight of the object. When the external torque was zero, the thumb produced mechanically unnecessary force of about 2.8N, which did not depend on the external load magnitude. When the external torque was not zero, tangential forces produced over 80% of the total moment of force. The normal forces by the middle and ring fingers produced consistent moments against the external torque, while the normal forces of the index and little fingers did not. Force and moment variables at both hierarchical levels were stabilized by covaried across trials adjustments of forces/moments produced by individual digits with the exception of the normal force analyzed at the lower level of the hierarchy. There was a trade-off between synergy indices computed at the two levels of the hierarchy for the three components of the total force vector, but not for the moment of force components. Overall, the results have shown that task mechanics are only one factor that defines forces produced by individual digits. Other factors, such as loading sensory receptors may lead to mechanically unnecessary forces. There seems to be no single rule (for example, ensuring similar safety margin values) that would describe sharing of the normal and tangential forces and be valid across tasks. Fingers that are traditionally viewed as less accurate (e.g., the ring finger) may perform more consistently in certain tasks. The observations of the trade-off between the synergy indices computed at two levels for the force variables but not for the moment of force variables suggest that the degree of redundancy (the number of excessive elemental variables) at the higher level is an important factor.