Types Of Mechanical Loading Research Articles

DOWNHILL RUNNING INDUCES SITE-SPECIFIC ARTICULAR CARTILAGE ALTERATIONS

The mechanical performance of articular cartilage and its optimization for load-bearing function is determined by the biochemical assembly of the extracellular matrix (ECM) [Mow, 1992]. Both magnitude and type of mechanical loading have the potential to alter ECM protein synthesis of collagen II and cartilage oligomeric matrix protein (COMP), two major network stabilizing proteins, in a sitespecific manner [Kiviranta, 1988, Skioldebrand, 2010]. Downhill running as a natural form of eccentric exercise [Butterfield, 2005] has been shown to induce higher knee joint loadings compared to level running [Kuster, 1995]. However, its influence on articular cartilage assembly and mechanical properties has not yet been studied. In the present study we examined the effect of different running modes (downhill vs. level) on site-specific cartilage adaptation.

An Investigation on Buckling Behaviour of Functionally Graded Plates Using Finite Strip Method

Semi-analytical finite strip method (FSM) for analyzing the buckling behavior of some functionally graded plates is presented in this paper. The plates are assumed to be under three types of mechanical loadings, namely; uniaxial compression, biaxial compression, and biaxial compression and tension. The material properties are assumed to vary in the thickness direction according to the power-law variation in terms of volume fractions of the constituents. Thus, the material properties are estimated from the both Voigt rule of mixtures (VRM) and Mori-Tanaka homogenization method (MTM). Numerical results for a variety of functionally graded plates with different aspect ratio are given and compared.

MODELING OF CONDUCTIVE HEAT TRANSFER IN LOW-DENSITY PVC FOAMS UNDER MECHANICAL LOAD

Due to their excellent thermal insulation properties, low-density polyvinyl chloride (PVC) foams find applications in a wide variety of technological fields. They are notably used as thermal insulation in fuel tanks of Ariane rockets at very low temperatures. For this application, a relatively high mechanical strength is also required since the foams undergo significant mechanical loads during the flight. As a consequence, the mechanical strain undergone by the foams may affect their thermal behavior and vice versa, leading to a coupling between the mechanical and thermal properties. That is the reason why, in order to improve the modeling of the mechanical and thermal behaviors and to better understand their mutual influences, an original thermal model has been developed that is based on a shell mesh of the porous structures of PVC foams obtained by X-ray tomography. This permits the quick computation of the temperature field prevailing in the solid and fluid phases constituting the material and of the equivalent thermal transfer properties. The temperature field and thermal properties could then be used as entrance data of a mechanical finite-element computation. The effective thermal conductivities computed for non-deformed structures were compared with various correlations in the literature. Thereafter, the numerical model was applied to deformed structures obtained from mechanical finite-element computations modeling various mechanical loads. The analysis of the results highlights the major modifications of the thermal properties brought by different types of mechanical loads.

Cyclic mechanical load causes global translational arrest in articular chondrocytes: a process which is partially dependent upon PKR phosphorylation

The cellular mechanisms by which articular cartilage responds to load are poorly understood, but such responses may involve regulation at the level of protein translation rather than synthesis of mRNA. We investigated the role of translational control in cyclically (0.5 Hz, 0.1 Hz and 0.05 Hz) and statically loaded porcine articular cartilage explants. Messenger RNA was extracted for real time polymerase chain reaction (RT-PCR) and newly synthesised proteins were measured by their incorporation of radiolabelled 35S[methionine/cysteine] or 35SO4. Some medium from loaded and unloaded explants was immunoblotted for type II collagen, CTGF and TIMP3. The pathways that control protein translation were investigated by immunoblotting explant lysates for PKR, PERK (PKR like endoplasmic reticulum kinase), eIF2a (eukaryotic initiation factor 2a), eEFs (eukaryotic elongation factors), and AMP-dependent kinase. Explants were also loaded in the presence of inhibitors of PKR, the fibroblast growth factor (FGF) receptor and PI3 kinase. Cyclic loading caused complete global translational arrest as evidenced by a total suppression of new protein synthesis whilst maintaining mRNA levels. Translational arrest did not occur following static loading and was partly dependent upon the load frequency. There was a rebound increase in protein synthesis when labelling was performed after load had been withdrawn. Phosphorylation of PKR occurred in explants following cyclic load and inhibition of PKR modestly reversed suppression of newly synthesised proteins suggesting that PKR, at least in part, was responsible for loading induced translational arrest. These results show that translational control provides a rapid and potentially important mechanism for controlling the synthetic responses of articular chondrocytes in response to different types of mechanical load.

Effects of Exercise on Bone Mass in Young Women with Anorexia Nervosa

The response of bone to exercise in women with anorexia nervosa (AN) is unclear. We investigated the associations between bone mineral density (BMD) and exercise performed while ill and while recovered in women with a history of AN. A cross-sectional study was conducted with 141 women with AN (85 ill; 56 recovered), aged 17-40 yr. BMD at the lumbar spine (LS), femoral neck (FN), and total body (TB) was measured by dual-energy x-ray absorptiometry. Life History Calendar and Minnesota Leisure Time Physical Activity interviews were used to collect lifetime illness and exercise histories (amount and bone loading type). Average hours per week of each of moderate (MOD) and high (HI) bone loading exercise were determined for three illness phases: "before ill," "while ill," and "while recovered." Participants were categorized into four exercise groups for each phase: MOD-ONLY, HI-ONLY, BOTH, and NEITHER (reference group). Weight-adjusted BMD z-scores were compared in the exercise groups by multivariable linear regression, adjusting for illness duration and severity, and exercise during the other illness phases. In ill participants, MOD-ONLY "while ill" had lower BMD at LS (β = -0.69, 95% confidence interval (CI) = -1.02 to -0.05) and TB (β = -0.73, 95% CI = -1.31 to -0.15) than the NEITHER group. In recovered participants, HI-ONLY "while recovered" had higher BMD at FN (β = 0.95, 95% CI = 0.15-1.75) and TB (β = 0.79, 95% CI = 0.07-1.51) than the NEITHER group. The effect of exercise on bone in AN patients is dependent on both the type of mechanical loading and the phase of illness during which it was performed. Excessive moderate loading exercise while ill may put patients at higher risk of low bone mass, but high bone loading activities may provoke bone accrual during recovery.

Polyethylene Foams Produced under a Temperature Gradient with Expancel and Blends Thereof

Thermoplastic polymer foams can be produced using expandable beads like Expancel microbeads. In this work, density graded polyethylene foams were produced by imposing a temperature gradient using compression moulding. This was done by controlling independently the top and bottom plates of the mould at different temperatures. Foaming was done by using different grades of Expancel and blends of them to produce a complex cellular morphology. In this work, a complete morphology in terms of cell size and cell density will be presented in relation with density profile across the foam thickness. The foam behaviour under different types of mechanical loadings will also be discussed.

Failure prediction analysis of an ACCC conductor subjected to thermal and mechanical stresses

In this work, the Aluminum Conductor Composite Core? (ACCC) was numerically investigated to evaluate stress distributions when subjected to thermal and mechanical loads. The thermal analysis was conducted to simulate the cooling cycle of the rod from 250°C to room temperature. Three types of mechanical loads were considered, namely axial tension, small bending, and large bending conditions. This was done to predict potential mechanical failure modes, which could reduce the short term performance of the conductors. It has been shown that the magnitudes of the residual thermal stresses in the composite core are low and insufficient to create internal mechanical damage during manufacturing. As expected, the axial tension analysis indicated that under extreme axial tensile loads the ACCC rod will fail catastrophically. The most important results were obtained through the bending analysis, especially under large displacement conditions. Under these conditions the ACCC rod will develop mechanical compressive damage in its carbon fiber/epoxy section if the rods are bent around relatively small mandrels either during transportation or installation.

Mechanical buckling of cylindrical shells with varying material properties

The analytical solutions of the first-order shear deformation theory are developed to study the buckling behaviour of functionally graded (FG) cylindrical shells under three types of mechanical loads. The Poisson's ratios of the FG cylindrical shells are assumed to be constant, while the Young's moduli vary continuously throughout the thickness direction according to the volume fraction of constituents given by power-law or exponential function. The stability equations are employed to obtain the closed-form solutions for critical buckling loads of each loading case. The dependence of the critical buckling loads on the variations of the material properties with a power-law or exponential function is studied. It is observed that these effects change appreciably the critical buckling loads. Results for critical loads are tabulated for thin and moderately thick shells. Although the critical buckling load of FG cylindrical shells decreases as the circumferential wave numbers increase, it rises for axially compressed long shells as the longitudinal wave numbers increase.

A 3D moisture-stress FEM analysis for time dependent problems in timber structures

This paper presents a 3D moisture-stress numerical analysis for timber structures under variable humidity and load conditions. An orthotropic viscoelastic-mechanosorptive material model is specialized on the basis of previous models. Both the constitutive model and the equations needed to describe the moisture flow across the structure are implemented into user subroutines of the Abaqus finite element code and a coupled moisture-stress analysis is performed for several types of mechanical loads and moisture changes. The presented computational approach is validated by analyzing some wood tests described in the literature and comparing the computational results with the reported experimental data.

Thermomechanical instability of functionally graded truncated conical shells with temperature-dependent material

The thermomechanical instability of truncated conical shells made of functionally graded material under different uniform temperature rises is studied in this paper. It is assumed that the shell is a mixture of metal and ceramic, where its properties change as functions of the shell thickness. The mechanical properties of metal and ceramic are assumed to be temperature dependent. The governing equations are based on the first-order theory of shells and the Sanders non-linear kinematics equations. The results are obtained under different thermal conditions for three types of mechanical loading, namely hydrostatic pressure, axial compressive loading, and their combination. The results are validated with the known data in the literature.

Bone mineral density in female high school athletes: Interactions of menstrual function and type of mechanical loading

During adolescence, skeletal integrity of girls is largely dependent on menstrual function and impact exercise, yet currently there is limited research regarding the interaction between menstrual status and type of mechanical loading associated with various high school sports. Our purpose was to examine associations of menstrual status, type of mechanical loading, and bone mineral density (BMD) in female high school athletes participating in high/odd impact or repetitive/non-impact sport. Participants were 161 female high school athletes (15.7±1.3 years; 165.3±6.9 cm; 59.4±8.7 kg) representing high/odd impact (n=93, including soccer, softball, volleyball, tennis, lacrosse, and track sprinters and jumpers), or repetitive/non-impact sports (n=68, including swimmers, cross-country and track distance runners who participated in events ≥800 m). Areal BMD was measured by DXA at the spine (L1–L4), proximal femur, and total body. Menstrual status was determined by self-report. Athletes with primary, secondary or oligomenorrhea were combined into a single group (oligo/amenorrheic) and compared to eumenorrheic athletes. Analysis of covariance (ANCOVA) with Bonferroni post hoc comparisons adjusted for age, BMI, and gynecological age were used to compare BMD of athletes in combined mechanical loading and menstrual status groups. We found significantly greater total hip (p=0.04) and trochanter (p=0.02) BMD (g cm−2) among eumenorrheic high/odd impact compared to eumenorrheic repetitive/non-impact athletes, and greater spine (p=0.01) and trochanter (p=0.04) BMD among high/odd impact eumenorrheic athletes compared to repetitive/non-impact oligo/amenorrheic athletes. Chi-squared analysis of BMD Z-scores adjusted for gynecological age showed a significantly greater percentage of repetitive/non-impact athletes (33.9%) compared to high/odd impact athletes (11.8%) with low spine BMD for their age (BMD Z-score ≤−1 SD) (p=0.001), indicating that a high percentage of female high school athletes participating in repetitive loading sports, and especially those with oligo/amenorrhea, may not be accruing bone at the expected rate. Female adolescent athletes should be evaluated periodically and advised of the possible negative effects of oligo/amenorrhea on bone health.

Thermomechanical Stability of Imperfect Functionally Graded Plates Based on the Third Order Theory

Mechanical and thermal buckling analysis of rectangular functionally graded plates with initial geometric imperfections is presented in this paper. It is assumed that the nonhomogeneous mechanical properties vary linearly through the thickness of the plate. The plate is assumed to be under three types of mechanical loadings, namely, uniaxial compression, biaxial compression, and biaxial compression and tension; and two types of thermal loadings, namely, the uniform temperature rise and nonlinear temperature gradient through the thickness. The equilibrium, stability, and compatibility equations are derived using the third-order shear deformation plate theory. Resulting equations are employed to obtain the closed-form solution for the critical buckling load for each loading case. The results are compared with the known data in the literature.

Righting response of artificially inclined maritime pine (Pinus pinaster) saplings to wind loading

To determine if trees respond to dynamic and static loading in the same manner, 2-year-old maritime pine (Pinus pinaster Ait.) trees were subjected to different types of mechanical loading in the field. One block of trees (the control) were kept in pots and planted in the field at an angle of 0 or 45 degrees to the vertical. A similar block of leaning potted trees was planted nearby and subjected to frequent, unilateral wind loading for a period of 1 s every 2 min. Half the leaning trees were oriented toward the direction of wind loading and half were oriented along the axis of wind loading. The stem profile was measured three times during the growing season to quantify the rate of stem straightening. Compression wood formation and stem shape were measured in all plants. No differences in mean height or diameter were observed between blocks and all leaning trees straightened, but not at the same rate. Although no difference in the rate of apical straightening occurred between control and wind-treated trees, the righting response of the basal part of the stem of leaning trees subjected to wind was four times greater than that of leaning trees without wind. No differences in the righting response were observed between leaning trees growing toward and trees growing away from the source of wind. No significant differences in compression wood formation were found between control trees and wind-treated trees, indicating that other factors must determine the reorientation rate of leaning trees. Results are discussed with reference to the quality of compression wood in conifers and the mechanotransductive pathway in plants.

Buckling of thick functionally graded plates under mechanical and thermal loads

Buckling analysis of rectangular thick functionally graded plates under mechanical and thermal loads is presented in this paper. It is assumed that the non-homogeneous mechanical properties vary linearly through the thickness of the plate. The plate is assumed to be under three types of mechanical loadings, namely; uniaxial compression, biaxial compression, and biaxial compression and tension and two types of thermal loadings, namely; uniform temperature rise and non-linear temperature rise through the thickness. The equilibrium and stability equations are derived using the third order shear deformation plate theory. Resulting equations are employed to obtain the closed-form solution for the critical buckling load for each loading case. The results are verified with the known data in the literature.

Bone Mineral Density and Degenerative Changes of the Lumbar Spine in Former Elite Athletes

The aim of this study was to assess bone mineral density (BMD) and degenerative changes in the lumbar spine in male former elite athletes participating in different track and field disciplines and to determine the influence of body composition and degenerative changes on BMD. One hundred and fifty-nine former male elite athletes (40 throwers, 97 jumpers, 22 endurance athletes) were studied. Anthropometric (age, body mass index [BMI]) and sport-specific data (personal best, intensity, duration, and time since termination of competitive sports career as well as current sporting activity) were collected. Degenerative changes of the lumbar spine in lateral view were evaluated by using the Kellgren and Lawrence Score. Bone mineral density of the lumbar spine was measured in an anterior-posterior view with dual energy X-ray absorptiometry (DEXA, T-score). Throwers had a higher body mass index than jumpers and endurance athletes. Throwers and jumpers had higher BMD (T-LWS) than endurance athletes. Bivariate analysis revealed a negative correlation of BMD (T-score) with age and a positive correlation with BMD and Kellgren score (p<0.05). Even after multiple adjustment for confounders lumbar spine BMD is significantly higher in throwers, pole vaulters, and long- and triple jumpers than in marathon athletes. Different types of mechanical loading caused by sporting activities seem to influence the BMD of the lumbar spine, even if different body constitutions (i.e. BMI) and age, training history, and degenerative changes in the lumbar spine of former throwers, jumpers, and endurance athletes are taken into consideration.

INFLUENCE OF TYPE OF MECHANICAL LOADING, MENSTRUAL STATUS, AND TRAINING SEASON ON BONE DENSITY IN YOUNG WOMEN ATHLETES

Bone mineral density (BMD) variables were compared in 2 groups of women Division I collegiate athletes—gymnasts (GYM) and cross-country runners (CC)—during the preseason and during the competitive season. An osteogenic advantage may exist in women athletes involved in impact loading (gymnastics) over those women in active loading sports like long-distance running. The effects of menstrual status and the time of the training season on BMD also were examined. Dietary intake, menstrual status, BMD, and serum estradiol levels were measured during the preseason and during the competitive season in 26 women athletes (18–22 years of age). GYM had significantly higher BMD (p < 0.05) at all sites for both the pre- and posttests compared to CC. Neither group experienced a significant change (p ≤ 0.05) in BMD between trials for any site; however, CC showed slight decreases at all BMD sites from baseline to the posttest. GYM had a higher prevalence of self-reported menstrual cycle disturbances than CC. No significant difference (p ≤ 0.05) in BMD was found between the eumenorrheic and menstrual dysfunction groups (oligo/amenorrheic). In conclusion, the gymnasts had significantly higher (p < 0.05) BMD than the runners, suggesting BMD is influenced by the type of mechanical loading. Menstrual status did not significantly affect BMD in these women athletes. Cross-country runners were determined to be at greater risk than the gymnasts for low bone mass; thus, it is recommended that these athletes include more high-impact activities in their training regimen to optimize their bone health.

Age-related changes in skeletal-muscle myosin heavy-chain composition: effect of mechanical loading.

The purpose of this study was to investigate the effect of compensatory hypertrophy (CH), heavy-resistance exercise training (HRET), and simultaneous CH and HRET on fast-twitch skeletal-muscle myofibrillar-protein synthesis, myosin heavy-chain (MHC) turnover rate, and MHC-isoform composition in young and old rats. In young animals all treatments intensified myofibrillar-protein synthesis, whereas in old animals with CH protein synthesis remained unchanged. The relative content of MHC I and IID in plantaris muscle increases with age, and the relative content of MHC IIB decreases. HRET and simultaneous CH and HRET decreased the proportion of MHC IIB and IIA and increased that of MHC IID in young rat muscle. In old rat muscle, relative content of MHC IID decreased and that of MHC IIB increased. CH decreased relative content of MHC IIB in both age groups and of MHC IIA in old animals. Relative content of MHC IID increased in both groups, and of MHC IIA, in young animals. MHC in plantaris of young rats turned over much faster in all types of mechanical loading but in old rats only during HRET and its combination with CH.

Textural quality assessment for fresh fruits and vegetables.

Academically, quantitative measurement of texture is essential for the study of the chemical and physiological mechanisms of texture. Commercially, quantitative measurement of texture is essential to ensure the quality of produce at packout. The diversity of tissues involved, the variety of attributes required to fully describe textural properties, and the changes in these attributes as the product ripens and senesces contribute to the complexity of texture measurement. Texture is a human assessment of the structural elements of a food. It is generally accepted that texture relates primarily to mechanical properties, so instrumental measurements relate mainly to mechanical properties. Fruits and vegetables exhibit viscoelastic behavior under mechanical loading, which means that the force, distance, and time involved in loading determine the value of any measurement. Because of their viscoelastic character, every effort should be made to hold the speed of the test constant in manual texture measurements and the rate of loading should be specified and controlled in mechanized measurements. There are many types of mechanical loading: puncture, compression, shearing, torsion (twisting), extrusion, crushing, tension, bending, vibration, and impact. The most widely used texture measurement for fruits and vegetables, after manual squeezing of course, is the Magness-Taylor fruit firmness test, which measures the maximum force to puncture the product in a specified way. The Kramer shear or shear-compression test is widely used in the processed foods industry, but is less commonly used by horticulturists. Nondestructive methods are highly desired both for sorting and for postharvest research. Compression tests of excised tissue pieces are frequently used in research. Nondestructive testing using impact, vibrational behavior, light scattering, and optical methods are being investigated but none has been widely accepted to date. Multiple instrumental measurements may be necessary to adequately the diversity of textural attributes sensed by the human consumer.

Fatigue behavior of ferroelectric ceramics under mechanically–electrically coupled cyclic loads

The fatigue behavior of commercial ferroelectric ceramics PZT-5 was studied by carrying out four-point bending experiments for the poled and unpoled samples. Two types of mechanical loads (constant and cyclic) coupled with a cyclic electrical field were applied. It was observed that under the same cyclic electrical field the fatigue life of the PZT ceramics significantly reduced as the applied mechanical loads (either constant or cyclic) became larger. When coupled with the same electric field, the application of constant forces lowered the fatigue life of the poled samples more significantly than that of the unpoled samples, while the application of mechanically cyclic load remarkably decreased the fatigue life of the unpoled samples.

Stress analysis in silicon die under different types of mechanical loading by finite element method (FEM)

Stress analysis is of crucial importance in the design of components and systems in the electronics industry. In this paper, the authors present a new strength criterion combined with finite element analysis (FEA) to predict the failure stress of silicon die. Several different models of pushers were designed to apply load in the vfBGA reliability test until some units failed the electrical test. Meanwhile, finite element analysis was performed in order to find the location of the highest stress and the expected modes of failure. In the simulation, a parametric study of the effect of different types of pushers on the internal stress of the die is carried out and the failure stress can be determined eventually. The potential for chip damage under certain pushers during electrical tests has been assessed and the relationship between the maximum principal stress and the thickness of the silicon die is also explored.