Decrease In Maximum Load Research Articles

Study of Mechanical Properties of Membrane-Electrode Assemblies for Proton Exchange Membrane Fuel Cells By the Small-Punch Technique

Mechanical properties of membrane-electrode assemblies (MEAs) for proton exchange membrane fuel cells (PEMFCs) have been studied with the small-punch technique. MEAs were operated according to a non-accelerated aging protocol, with changes in humidification and cell temperature. After operation, degradation of the MEA is reflected by a decrease in power density, increase in the internal resistance, and decrease in open circuit voltage. Small disks (8 mm diam.) were taken from different locations of the degraded MEA to test the mechanical properties by small-punch. The results show an increase in plastic deflection and a decrease in maximum load of degraded MEAs, that result in lower apparent Young modulus. The degradation is larger in the area close to oxygen outlet. SEM microscopy shows that degradation affects majorly to the fibers of the carbon cloth gas diffusion layer (GDL). Combined small-punch and SEM correlate the change in mechanical properties on aged MEA with carbon fibers degradation. Such GDL degradation must also be principal responsible for the increase in the internal resistance.

Environmental effects on mode II fracture toughness of unidirectional E-glass/vinyl ester laminated composites

Abstract In this article, mode II fracture toughness ( G IIc {G}_{\text{IIc}} ) of unidirectional E-glass/vinyl ester composites subjected to sulfuric acid aging is studied at two different temperatures (25 and 90°C). Specimens were manufactured using the hand lay-up method with the [ 0 ] 20 {{[}0]}_{20} stacking sequence. To study the effects of environmental conditions, samples were exposed to 30 wt% sulfuric acid at room temperature (25°C) for 0, 1, 2, 4, and 8 weeks. Some samples were also placed in the same solution but at 90°C and for 3, 6, 9, and 12 days to determine the interlaminar fracture toughness at different aging conditions. Fracture tests were conducted using end notched flexure (ENF) specimens according to ASTM D7905. The results obtained at 25°C showed that mode II fracture toughness increases for the first 2 weeks of aging and then it decreases for the last 8 weeks. It was also found that the flexural modulus changes with the same trend. Based on the results of the specimens aged at 90°C, a sharp drop in fracture toughness and flexural modulus with a significant decrease in maximum load have been observed due to the aging. Finite element simulations were performed using the cohesive zone model (CZM) to predict the global response of the tested beams.

Effect of Seawater Ageing on Fracture Toughness of Stitched Glass Fiber/Epoxy Laminates for Marine Applications

Composite materials are used in various industries such as marine, aircraft, automotive, etc. In marine applications, composites are exposed to seawater, which can affect their mechanical properties due to moisture absorption. This work focuses on the durability of composite materials under the short-term effect of seawater ageing. The specimens were prepared from glass fiber/epoxy using a hand lap-up method and stitched in the z-direction with Kevlar fiber. The specimens were submerged in seawater for 24 and 35 days. A significant decrease in maximum load was found as specimen immersion time in seawater increased. The seawater ageing also affected fracture toughness with a reduction of 30% for 24 days immersion and 55% for 35 days. The ageing also caused the swelling of composites due to moisture absorption, which increased the weight of the specimens. Compared to the dry specimens, the weight of the specimen for 24 days increases to 5.2% and 7.89% for 35 days’ seawater ageing. The analysis also showed that due to seawater ageing, the de-bonding rate increased as the number of days increased.

Volumetric MicroCT Intensity Histograms of Fatty Infiltration Correlate with the Mechanical Strength of Rotator Cuff Repairs: An Ex Vivo Rabbit Model.

Fatty infiltration of the rotator cuff occurs after injury to the tendon and results in a buildup of adipose in the muscle. Fatty infiltration may be a biomarker for predicting future injuries and mechanical properties after tendon repair. As such, quantifying fatty infiltration accurately could be a relevant metric for determining the success of tendon repairs. Currently, fatty infiltration is quantified by an experienced observer using the Goutallier or Fuchs staging system, but because such score-based quantification systems rely on subjective assessments, newer techniques using semiautomated analyses in CT and MRI were developed and have met with varying degrees of success. However, semiautomated analyses of CT and MRI results remain limited in cases where only a few two-dimensional slices of tissue are examined and applied to the three-dimensional (3-D) tissue structure. We propose that it is feasible to assess fatty infiltration within the 3-D volume of muscle and tendon in a semiautomated fashion by selecting anatomic features and examining descriptive metrics of intensity histograms collected from a cylinder placed within the central volume of the muscle and tendon of interest. (1) Do descriptive metrics (mean and SD) of intensity histograms from microCT images correlate with the percentage of fat present in muscle after rotator cuff repair? (2) Do descriptive metrics of intensity histograms correlate with the maximum load during mechanical testing of rotator cuff repairs? We developed a custom semiautomated program to generate intensity histograms based on user-selected anatomic features. MicroCT images were obtained from 12 adult female New Zealand White rabbits (age 8 to 12 months, weight 3.7 kg ± 5 kg) that were randomized to surgical repair or sham repair of an induced infraspinatus defect. Intensity histograms were generated from images of the operative and contralateral intact shoulder in these rabbits which were presented to the user in a random order without identifying information to minimize sources of bias. The mean and SD of the intensity histograms were calculated and compared with the total percentage of the volume threshold as fat. Patterns of fat identified were qualitatively compared with histologic samples to confirm that thresholding was detecting fat. We conducted monotonic tensile strength-to-failure tests of the humeral-infraspinatus bone-tendon-muscle complex, and evaluated associations between histogram mean and SDs and maximum load. The total percentage of fat was negatively correlated with the intensity histogram mean (Pearson correlation coefficient -0.92; p < 0.001) and positively with intensity histogram SD (Pearson correlation coefficient 0.88; p < 0.001), suggesting that the increase in fat leads to a reduction and wider variability in volumetric tissue density. The percentage of fat content was also negatively correlated with the maximum load during mechanical testing (Pearson correlation coefficient -78; p = 0.001), indicating that as the percentage of fat in the volume increases, the mechanical strength of the repair decreases. Furthermore, the intensity histogram mean was positively correlated with maximum load (Pearson correlation coefficient 0.77; p = 0.001) and histogram SD was negatively correlated with maximum load (Pearson correlation coefficient -0.72; p = 0.004). These correlations were strengthened by normalizing maximum load to account for animal size (Pearson correlation coefficient 0.86 and -0.9, respectively), indicating that as histogram mean decreases, the maximum load of the repair decreases and as histogram spread increases, the maximum load decreases. In this ex vivo rabbit model, a semiautomated approach to quantifying fat on microCT images was a noninvasive way of quantifying fatty infiltration associated with the strength of tendon healing. Histogram-derived variables may be useful as surrogate measures of repair strength after rotator cuff repair. The preclinical results presented here provide a foundation for future studies to translate this technique to patient studies and additional imaging modalities. This semiautomated method provides an accessible approach to quantification of fatty infiltration by users of varying experience and can be easily adapted to any intensity-based imaging approach. To translate this approach to clinical practice, this technique should be calibrated for MRI or conventional CT imaging and applied to patient scans. Further investigations are needed to assess the correlation of volumetric intensity histogram descriptive metrics to clinical mechanical outcomes.

Pengaruh Air Laut terhadap Kapasitas Beban pada Balok Beton Bertulang yang Diperkuat GFRP-S dengan Perendaman selama Satu Tahun

The test results on specimens without GFRP-S reinforcement showed that there was a decrease in load capacity for BN0 specimens of 1.383%. Decrease in BN6 test material capacity after soaking sea water for 6 months. Whereas for specimens with reinforcement of GFRP-S shows a decrease in maximum load on BF6 and BF12 specimens against BF0 test objects. The percentage of decrease in loads is 3.898% and 4.285%, respectively. Decreased load capacity of BF12 specimens after 12 months of seawater immersion. This is due to a decrease in the capacity of the bond on the GFRP along with the soaking time, thus accelerating the occurrence of debonding.

Calculating method of the fatigue life for the main supporting bearing of mixing drum in concrete mixing truck when considering drum’s vibration

It has been observed that there are many studies focusing on the vibration properties of bearings caused by manufacturing errors, assembly related errors, out-of-balance rotor rotation, cage instability, etc. But there are fewer research studies on the effect of rotor’s vibration on double-row rolling element bearings’ mechanical properties. In this paper, a calculating method has been established for bearing’s roller load and fatigue life when considering rotor’s vibration. And this model is applied to study the main supporting bearing of the mixing drum of a certain type of concrete mixing truck with the consideration of the mixing drum’s vibration. The effects of rotating speed, inclination angle, concrete liquid level, and rolling wheels’ supporting position on the roller load and bearing’s fatigue life are studied with a specific example with and without considering the mixing drum’s vibration. Results show that with the increase in the rotating speed, the bearing roller’s maximum load decreases, while the fatigue life of main supporting bearing increases. With the decrease of the concrete liquid level, there is increase in the inclination angle and the movement of rolling wheel from left to right, and the bearing roller’s maximum load increases, while the fatigue life of main supporting bearing decreases. The changes of the mixing drum’s inclination angle have tremendous effect on bearing’s fatigue life, while the change in the rolling wheel’s supporting position has little influence on the fatigue life of the main supporting bearing. When considering the mixing drum’s vibration, the roller’s maximum load is larger than that without considering mixing drum’s vibration, while the fatigue life of the main supporting bearing is shorter than that without considering mixing drum’s vibration.

PD48-04 EFFECTS OF COLLAGENASE TREATMENT ON BIOMECHANICAL PROPERTIES OF PEYRONIE'S PLAQUES

You have accessJournal of UrologySexual Function/Dysfunction/Andrology: Peyronie's Disease1 Apr 2015PD48-04 EFFECTS OF COLLAGENASE TREATMENT ON BIOMECHANICAL PROPERTIES OF PEYRONIE'S PLAQUES Thomas Schmid, Vincent Wang, Elizabeth Shewman, Michael McLane, James Tursi, and Laurence Levine Thomas SchmidThomas Schmid More articles by this author , Vincent WangVincent Wang More articles by this author , Elizabeth ShewmanElizabeth Shewman More articles by this author , Michael McLaneMichael McLane More articles by this author , James TursiJames Tursi More articles by this author , and Laurence LevineLaurence Levine More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2015.02.2761AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES The purpose of this study was to measure the biomechanical properties of tissues recovered from surgical correction of patients with Peyronie's Disease (PD) and determine if these properties change after enzymatic treatment with a purified bacterial collagenase (AA4500). METHODS Tissue specimens were collected from PD patients after surgery with patients' consent and institutional approval. Specimens were stored frozen in saline. Strips of tunica albuginea from PD plaques were isolated from two orthogonal directions, parallel to (longitudinal strips), and perpendicular to (circumferential strips) the long axis of the penis, and used for tensile testing. Tensile tests were performed on 2 × 12 mm tissue strips. Specimens with mineral foci were detected by x-ray, and excluded from the study. RESULTS The data revealed substantial variation in the biomechanical parameters of different donor tissues. Less variation was evident in adjacent tissue strips taken from the same orientation (longitudinal or circumferential) compared to strips from different PD donors. The circumferential strips supported a higher maximal load and work to maximum load than similar sized longitudinal strips. The strain (amount tissue stretched) was greater for longitudinal than circumferential sections. Additional tissues were injected with clinical concentrations of collagenase AA4500. Strips treated with the collagenase showed a dramatic decrease in maximum load, stiffness, work to maximum load, and maximum stress (see figure). CONCLUSIONS Large variations in tensile properties across multiple PD donor tissues could be minimized by comparing adjacent longitudinal versus circumferential strips from single donors. The injection of collagenase AA4500 into PD plaque tissues caused a dramatic reduction in tensile properties. These experiments are a proof-of-concept that treatment of PD plaques with collagenase in vitro reduces tissue biomechanical properties. Such in vitro testing may help optimize injection protocols for the therapeutic use of AA4500 collagenase in PD patients. © 2015 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 193Issue 4SApril 2015Page: e967 Advertisement Copyright & Permissions© 2015 by American Urological Association Education and Research, Inc.MetricsAuthor Information Thomas Schmid More articles by this author Vincent Wang More articles by this author Elizabeth Shewman More articles by this author Michael McLane More articles by this author James Tursi More articles by this author Laurence Levine More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Monitoring Fatigue Cracking in Interconnects in a Ball Grid Array by Measuring Electrical Resistance

In displacement controlled mechanical fatigue of ball grid solder interconnect arrays, decrease in maximum load monitors total increase in crack area in an array while electrical resistance monitors only the area of large cracks that lead to electrical failure. Small cracks with good electrical contact between the crack surfaces have only minor effect on the resistance of the array. In this mechanical fatigue research of ball grid arrays, the fatigue damage was continually followed by simultaneously measuring maximum load and electrical resistance. Experimental details, results, and analysis of the results are given including a Paris relation fit to the data.

Physicochemical and morphological properties of poly(acrylamide) and methylcellulose hydrogels: Effects of monomer, crosslinker and polysaccharide compositions

AbstractThis article describes the physicochemical (mechanical and swelling) and morphological characterization of poly(acrylamide) and methylcellulose (PAAm‐MC) hydrogels synthesized with different formulations by the free radical polymerization method. The structure‐property relationship of the PAAm‐MC hydrogels is very important for application of these materials in different fields. Results showed that the properties of the PAAm‐MC hydrogels can be controlled by varying the acrylamide (AAm) and N′,N‐methylene‐bis‐acrylamide (MBAAm) concentrations and methylcellulose (MC) content. Increase of AAm and MBAAm concentrations causes a pronounced decrease in swelling degree (SD) values and porosity, and an increase in mechanical properties. Increasing the MC concentration caused an increase in SD values and porosity, but decrease in maximum load and modulus of elasticity because of the increase in the hydrogel hydrophilicity due to incorporation of hydroxyl groups from MC chains. PAAm‐MC hydrogels are excellent candidates for several applications, such as matrices for cell transplantation, controlled release (agrochemicals and drugs), tissue repair and regeneration. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

A biomechanical modeling of injury, repair, and rehabilitation of ulnar collateral ligament injuries of the thumb

Purpose The use of early active motion protocols after repair of the thumb ulnar collateral ligament (UCL) theoretically could avoid the complications of postoperative immobilization and improve ligament healing. The goals of this study were as follows: (1) to develop an accurate model of acute UCL rupture, (2) to determine the strain pattern in the UCL during constrained active thumb motion in intact and repaired thumbs, and (3) to determine the load to failure and strain of the UCL during rupture in forced abduction. Methods Sixteen fresh-frozen adult cadaver thumbs were mounted in a testing apparatus designed for testing the strain in the UCL during constrained active motion and abduction load to failure. Strain data for the UCL during motion were measured. Specimens were tested to failure using an MTS machine. Dynamic strain data were acquired throughout the loading cycle. Repair of the torn ligament was performed with a suture anchor technique. Strain and load-to-failure measurements then were repeated in the repaired specimens. Differences in the strain values and failure forces between the intact and repaired specimens then were compared. Results A reliable model of a UCL rupture was created. Strains in the UCL were similar during active motion in both intact and repaired specimens. A significant decrease in maximum load to failure was noted in repaired specimens but failure reliably occurred at strains 3 times greater than expected with active motion. Conclusions A controlled active motion therapy protocol after suture anchor repair of a ruptured UCL of the thumb is safe from a biomechanical point of view.

Effect of menatetrenone (V.K2) on bone mineral density and bone strength in Ca/Mg deficient rats

Two experiments were carried out using 7-week-old male Wistar rats. Exp. 1: Rats in the intact group were fed with normal diet (0.5% Ca, 0.09% Mg). Ca/Mg deficient rats were fed low Ca (0.01%) diets containing 0.003, 0.015 or 0.09% Mg for 4 weeks. After 4 weeks, the bone mineral density (BMD) and maximum load in the femur were decreased in Ca/Mg deficient rats, but this was not dependent on dietary Mg concentration. The elasticity, stiffness, and Mg concentration in the femur of these rats were also decreased and Ca deposition in the kidney were increased, compared to those of normal rats, which were related to Mg concentration in the diet. From these results, Mg may play an important role in qualitative changes in bone (i.e., reduced stiffness). Exp. 2: We investigated the effects of V.K2 on the changes in BMD and bone strength in femur induced by low Ca/Mg (0.01%/0.003%) diet for 8 weeks. Compared to the intact group, Ca and Mg levels in serum and femur and cortical thickness, cortical area, and maximum load of the femoral midshaft were decreased in the Ca/Mg-deficient group. In these rats, PTH in the serum and renal Ca concentration were increased. In V.K2-treated rats, these changes in the serum Ca, Mg and PTH levels and the renal Ca concentration were improved. V.K2 also improved the decrease in maximum load in spite of no influence on the cortical thickness, cortical area and Mg concentration in the femur. These findings suggest that V.K2 may affect the qualitative change in bone.

The biomechanical integrity of bone in experimental diabetes

Patients with diabetes mellitus incur a higher incidence of fractures compared to healthy individuals. This suggests that the structural integrity of the skeletal system may be compromised. To examine the biomechanical consequences of diabetes, we studied the structural integrity of the femur and tibia of rats with streptozotocin-induced diabetes. The induction of diabetes was confirmed by measuring blood glucose levels (>300 mg/dl). Seven-weeks following the establishment of diabetes, the animals were euthanized and the hind limbs removed. The femur and tibia of each hind limb were excised, and prepared for three point bending test on an Instron Materials Testing System. The results revealed a 37% decrease in maximum load (breaking strength) of the femur of diabetic rats when compared to controls. The diabetic femurs had 25% less deformation at maximum load compared to controls. Similarly, energy absorption capacity to yield point and toughness were reduced by 27 and 34%, respectively, in the diabetic femur. A 38% increase in the bending stiffness was observed in the femurs of diabetic rats. Similar results were obtained with the tibias of both groups. Measurement at the break point revealed that the bones of diabetic rats bore significantly less load, deformation and energy absorption capacity than controls. Overall, our findings warrant the conclusion that the diabetic state is associated with mechanical deterioration of bone, resulting in bones with inferior biomechanical integrity.

EXPERIMENTAL STUDY OF TWO NEW FLEXOR TENDON SUTURE TECHNIQUES FOR POSTOPERATIVE EARLY ACTIVE FLEXION EXERCISES

We used a rabbit model to test the postoperative mechanical strengths of two new tendon suture techniques. These were compared with the conventional modified Kessler and double looped suture techniques. For each technique, maximum load until 3 mm gap, load at 1 mm gap and ultimate load were measured at the time of operation and at weeks 1 and 3 after operation. Maximum load until 3 mm gap and load at 1 mm gap were significantly higher in the new techniques than in the conventional techniques at the time of operation and at 1 week; there was no statistical difference between the four techniques at 3 weeks. No technique resulted in a decrease in maximum load until 3 mm gap, load at 1 mm gap and ultimate load at 1 week. The new techniques reported here have the potential to withstand early active flexion exercises.

Experiments on the Ratchetting Behavior of AISI 316L(N) Austenitic Steel at Room Temperature

Uniaxial tension-compression ratchetting tests were performed on AISI 316 L(N) austenitic stainless steel at room temperature. The mean stresses were low in comparison to the stress amplitudes. Nevertheless, they have been found to be of major importance to strain accumulation. Also, the stress amplitude exerts a distinct but, under the given conditions, smaller influence. No plastic shakedown has been found in the tests with constant mean stress and stress amplitude. Tests with an increase in the maximum load after a number of cycles, due to an increase in mean stress or stress amplitude, show a behavior similar to that in tests performed with the higher load only. Tests with a decrease in maximum load exhibit immediate shakedown, although tests performed with only the lower load showed ratchetting.