Low Mechanical Load Research Articles

Vascular occlusion for optimising the functional improvement in patients with knee osteoarthritis: a randomised controlled trial.

Knee osteoarthritis (KOA) is a leading cause of global disability with conventional exercise yielding only modest improvements. Here we aimed to investigate the benefits of integrating blood flow restriction (BFR) into traditional exercise programmes to enhance treatment outcomes. The Vascular Occlusion for optimizing the Functional Improvement in patients with Knee Osteoarthritis randomised controlled trial enrolled 120 patients with KOA at Ghent University Hospital, randomly assigning them to either a traditional exercise programme or a BFR-enhanced programme over 24 sessions in 12 weeks. Assessments were conducted at baseline, 6 weeks, 12 weeks and 3 months postintervention using linear mixed models with Dunn-Sidak corrections for multiple comparisons. Primary outcome was the Knee injury and Osteoarthritis Outcome Score (KOOS) questionnaire at 3 months follow-up with knee strength, Pain Catastrophizing Scale questionnaire and functional tests as secondary outcomes. Analysis followed an intention-to-treat approach (NCT04996680). The BFR group showed greater improvements in KOOS pain subscale (effect size (ES)=0.58; p=0.0009), quadriceps strength (ES=0.81; p<0.0001) and functional tests compared with the control group at 12 weeks. At 3 months follow-up, the BFR group continued to exhibit superior improvements in KOOS pain (ES=0.55; p=0.0008), symptoms (ES=0.59; p=0.0004) and quality of life (QoL) (ES=0.66; p=0.0001) with sustained benefits in secondary outcomes. Drop-out rates were similar in both groups. Incorporating BFR into traditional exercise programmes significantly enhances short-term and long-term outcomes for patients with KOA demonstrating persistent improvements in pain, symptoms, QoL and functional measures compared with conventional exercise alone. These findings suggest that BFR can provide the metabolic stimulus needed to achieve muscle strength and functional gains with lower mechanical loads. Reduced pain and increased strength support a more active lifestyle, potentially maintaining muscle mass, functionality and QoL even beyond the supervised intervention period. NCT04996680.

Prototype development of a multi-user augmented reality framework for collaborative medical visualization in shared environments

Abstract This study developed and evaluated a prototype for augmented reality (AR) interaction among multiple users sharing a three-dimensional hologram within a shared physical space. A systems requirements analysis was conducted to determine necessary interactions, followed by an iterative implementation plan with testing at each step. The application for the HoloLens 2 (HL2) headset was developed using Unity for 3D design, C# for programming, and Photon for multiplayer capabilities. The prototype was evaluated in a user study utilizing custom and NASA TLX questionnaires, comparing participants' self-reported task success with recorded data to assess the accuracy of selfassessments. The prototype effectively facilitated multi-user interactions within a shared environment, achieving acceptable synchronization for two users. Most participants successfully completed tasks, with TLX scores indicating low cognitive and mechanical load during AR task execution. This study demonstrates AR's viability for displaying and manipulating complex three-dimensional structures within a collaborative medical context among multiple individuals in the same physical space.

Blood flow restriction training (BFRT) in patients before and after total knee arthroplasty

In healthy individuals, blood flow restriction training (BFRT) has shown positive effects on muscle mass, strength, fatigue resistance, as well as tendon and bone metabolism. BFRT reduces blood flow in the extremities using inflatable cuffs, creating local muscular hypoxia, which produces an anabolic metabolic environment. This promotes significant muscular and cardiovascular adaptations even at low mechanical training loads. BFRT also shows promising initial results in pre- and postoperative applications for knee endoprostheses (KTEP). Both preoperative and postoperative BFRT can improve muscle strength and joint function, accelerate recovery, and alleviate pain. Although the method is generally safe, potential risks such as discomfort and rare side effects must be considered. Clear application protocols are still lacking, necessitating further research and individualized programs to achieve optimal training effects. BFRT thus offers an innovative way to effectively rehabilitate patients despite their low load tolerance.

Revealing low temperature-mechanical coupling failure mechanisms in CFRP laminates with in-situ observations

The number of layers and ply orientations determined the service performance of carbon fiber-reinforced polymer (CFRP) materials. Under low-temperature service conditions, the unclear weakening mechanism of mechanical properties of CFRP aggravates the failure risks of aerospace structures. In present work, the unclear correlation between layers with alternating orientations and the tensile-failure mechanisms of CFRP, the low temperature-mechanical coupling micromechanical behavior, and the failure mechanism of CFRP was experimentally revealed by using a horizontal testing instrument integrated with a low-temperature loading module and real-time optical imaging function. Based on various temperatures in a range from −40 °C to room temperature (RT) and two strain rates, the gradually decreasing trends of tensile strength, Young's modulus, and elongation after fracture with decreasing temperature are obtained. Three failure modes including fiber brittle fracture, fiber pull-out, and interface debonding are proposed to reveal the low temperature-mechanical coupling failure mechanism. Low-temperature asynchronous shrinkage of carbon fiber and epoxy resin promoted the transition from fiber brittle fracture to delamination at the interface. The proposed instrument could establish the approximatively actual service conditions involving low temperature and mechanical load.

Single-cell RNA sequencing reveals the impact of mechanical loading on knee tibial cartilage in osteoarthritis

Articular cartilage degeneration is one of the major pathogenic alterations observed in knee osteoarthritis (KOA). Mechanical stress has been verified to contribute to KOA development. To gain insight into the pathogenic mechanism of KOA development, we investigated chondrocyte subsets under different mechanical loading conditions via single-cell RNA sequencing (scRNA-seq). Articular cartilage tissues from both high mechanical loading (named the OATL group) and low mechanical loading (named the OATN group) surfaces were obtained from the proximal tibia of KOA patients, and scRNA-seq was conducted. Chondrocyte subtypes, including a new subset, HTC-C (hypertrophic chondrocytes-C), and their functions, development and interactions among cell subsets were identified. Immunohistochemical staining was also conducted to verify the existence and location of each chondrocyte subset. Furthermore, differentially expressed genes (DEGs) and their functions between regions with high and low mechanical loading were identified. Based on Gene Ontology terms for the DEGs in each cell type, the characteristic of cartilage degeneration in the OATL region was clarified. Mitochondrial dysfunction may be involved in the KOA process in the OATN region.

Effects of low-load blood flow restriction on the venous system in comparison to traditional low-load and high-load exercises.

Purpose: Blood-Flow-Restriction (BFR) training provides the ability to achieve hypertrophy effects even though only light mechanical loads are applied. However, its impact on venous pressures and function are still unknown. Therefore, the present study investigates the influence of BFR-training on intravascular venous pressure and venous function in comparison to control exercises with low or high mechanical loads. Methods: In a randomized cross-over design, ten healthy men (27.6 ± 6.4 years) underwent three trials of unilateral knee-extensor exercise with three different training protocols, low-load- (LL-RT, 30% of the individual 1-repetition-maximum, 1RM), low-load BFR- (LL-BFR-RT, 30% 1RM, 50% limb occlusion pressure, LOP) and high-load resistance exercise (HL-RT, 75% 1RM). Exercise protocols contain about four sets of knee extension exercise (Range-of-Motion: 0-0-95°), separated by 60s of rest. Each set was performed until volitional muscle failure. For analysis of changes in intravascular venous pressures and venous function, a venous catheter was placed at the exercising leg before each trial. Whereas venous pressures were recorded throughout the exercise trials, phlebodynamometric investigations were performed before and after each trial. Furthermore, subjective pain perception during and after exercise was accessed by visual analogue scale. One-way ANOVA was used to assess mean differences between training protocols, while two-way repeated-measures ANOVA (rANOVA; time x condition) was performed to compare changes in measures over time among conditions. Data were given as means ± standard deviation (SD). Results: In comparison to the exercise trials without venous occlusion, total workload was significantly lower in the LL-BFR-RT (LL-RT: 1745 ± 604kg vs LL-BFR-RT: 1274 ± 237kg vs HL-RT: 1847 ± 367kg, p = 0.004) without indicating statistical differences in venous pressures during the exercise sets (interaction: p = 0.140) or pain perception (interaction: p = 0.574). Similarly, phlebodynamometric assessment of venous function (e.g. refill-time of the venous system pre-vs. post exercise trials-LL-RT: 29.7 ± 11.0s vs 25.5 ± 9.6s, LL-BFR-RT: 26.6 ± 13.0s vs 27.3 ± 13.8s, HL-RT: 25.9 ± 10.9s vs 23.1 ± 8.2s) revealed no time (p = 0.156), condition effect (p = 0.802) or their interactions (p = 0.382). Conclusion: The present study is the first one describing the acute effects of LL-BFR-RT to muscle failure on venous pressures and function in comparison to a LL- and HL-RT in the lower limbs. In contrast to the existing literature, LL-BFR-RT does not elevate the venous pressures during exercise higher than a comparative exercise without BFR and does not show any adverse effects on venous function after the exercise.

Mechanical loading and autophagy: A study on the BoNT-A injection-induced condylar cartilage degeneration

Botulinum toxin A (BoNT-A) has emerged as a treatment option for temporomandibular disorder (TMD). By injecting BoNT-A into the masseter muscle, it is possible to reduce mechanical loading on the temporomandibular joint (TMJ). However, numerous prior studies have indicated excessive reduction in mechanical loading can have detrimental effects on TMJ cartilage. This study proposes that autophagy, a process influenced by mechanical loading, could play a role in BoNT-A-induced mandibular condyle cartilage degeneration. To explore this hypothesis, we employed both BoNT-A injection and an excessive biting model to induce variations in mechanical loading on the condyle cartilage of C57BL/6 mice, thereby simulating an increase and decrease in mechanical loading, respectively. Results showed a significant reduction in cartilage thickness and downregulation of Runt-related transcription factor 2 (Runx2) expression in chondrocytes following BoNT-A injection. In vitro experiments demonstrated that the reduction of Runx2 expression in chondrocytes is associated with autophagy, possibly dependent on decreased YAP expression induced by low mechanical loading. This study reveals the potential involvement of the YAP/LC3/Runx2 signaling pathway in BoNT-A mediated mandibular condylar cartilage degeneration.

Influence of cyclic water content changes during long-term storage on the mechanical stability of wood pellets

In the case of wood pellets, a water content >10 wt.-% should not be exceeded, as they begin to break even under low mechanical loads. However, during storage, they are exposed to different environmental conditions, including rising and falling humidity. In this study, by humidifying and re-drying wood pellets, it was found that their loss of stability at high humidity is reversible and they can recover to a high degree at subsequent low humidity. However, exceeding the saturation vapor pressure and a pellet water content >12 wt.-% leads to much greater swelling and loss of stability. In this case, pellets recover significantly less during subsequent drying. Long-term tests with multiple cycles of humidification <12 wt.-% have shown that pellets with high density and stability in their original state suffer a significant loss of stability within the first 10 cycles, while pellets with high porosity didn't change during long-term storage.

Blood flow restriction training in the pre- and postoperative phases of joint surgery

AbstractOrthopedic patients are frequently affected by temporary phases of immobility during the course of traumatic/degenerative joint diseases and particularly after joint surgery. These phases are usually accompanied by a significant loss of muscle mass and strength. However, since the patients’ load capacity is usually reduced, physicians and physiotherapists are often faced with the dilemma of not being able to offer an adequate therapeutic strategy for muscle preservation or early muscle building, since the high mechanical loads required for this in the training process are usually not feasible or even contraindicated for a certain period of time. In recent years, a training technique originating from sports science, called blood flow restriction (BFR) training, has increasingly been used in preoperative therapy or for rehabilitation. As the BFR method uses special blood pressure cuffs to occlude venous outflow from the exercising limb during exclusively low mechanical load strength training, the significant effects of muscle hypertrophy demonstrated by this method are of greatest interest to rehabilitation research. This article focuses on the training technique, the underlying mechanisms and potential risks, as well as integration of the technique into the clinical rehabilitation process based on existing data. Furthermore, this article provides the basis for a future consensus paper to validate the usability and effectiveness of BFR training in the conservative and rehabilitative therapeutic phases of joint surgery.

Low Frequency Cyclic Mechanical Loading of Till Deposits from Northern Germany under Oedometric Conditions

Glacial deposits are of significant importance to geotechnical engineers and geologists in northern Europe, North America, and Northern Asia, as vast areas of these land surfaces were historically covered with ice leading to the formation of a wide variety of till deposits. The use of these areas for various engineering purposes warrants their subjection to mechanical loads (of static and cyclic forms) from manmade structures, as well as natural hazards such as earthquakes. This paper focuses on the experimental investigation of the cyclic mechanical loading behavior of two glacial tills from northern Germany under one-dimensional loading or oedometric conditions, and in different soil wetting conditions. The experimental results show a significant dependence of the cyclic mechanical response of the glacial tills on wetting condition and number of loading cycles. The recorded values of accumulated plastic strains of the glacial tills generally increase with an increase in wetting or moisture content, with the highest measured value for the two tills being around 3.9% after 19 cycles of loading. The findings of the experimental cyclic mechanical tests of the glacial tills are discussed in view of the intrinsic soil behavior and fabric.

In Vitro and In Vivo Evaluation of a Bio-Inspired Adhesive for Bone Fixation.

Compared to metallic hardware, an effective bone adhesive can revolutionize the treatment of clinically challenging situations such as comminuted, articular, and pediatric fractures. The present study aims to develop such a bio-inspired bone adhesive, based upon a modified mineral-organic adhesive with tetracalcium phosphate (TTCP) and phosphoserine (OPS) by incorporating nanoparticles of polydopamine (nPDA). The optimal formulation, which was screened using in vitro instrumental tensile adhesion tests, was found to be 50%molTTCP/50%molOPS-2%wtnPDA with a liquid-to-powder ratio of 0.21 mL/g. This adhesive has a substantially stronger adhesive strength (1.0-1.6 MPa) to bovine cortical bone than the adhesive without nPDA (0.5-0.6 MPa). To simulate a clinical scenario of autograft fixation under low mechanical load, we presented the first in vivo model: a rat fibula glued to the tibia, on which the TTCP/OPS-nPDA adhesive (n = 7) was shown to be effective in stabilizing the graft without displacement (a clinical success rate of 86% and 71% at 5 and 12 weeks, respectively) compared to a sham control (0%). Significant coverage of newly formed bone was particularly observed on the surface of the adhesive, thanks to the osteoinductive property of nPDA. To conclude, the TTCP/OPS-nPDA adhesive fulfilled many clinical requirements for the bone fixation, and potentially could be functionalized via nPDA to offer more biological activities, e.g., anti-infection after antibiotic loading.

Rational construction of multifunctional hydrophilic coatings with sustainable anti-fogging, UV-shielding and anti-freezing abilities

Special wettability endows surface anti-fogging performance on transparent substrates by promoting filmwise condensation via hydrophilic materials or preventing water adhesion via hydrophobic materials. However, the harsh environments associated with low temperature and mechanical loads restrict their anti-fogging persistence. In this work, a hydrophilic coating with long-lasting anti-fogging, anti-freezing, and anti-aging properties was rationally prepared by constructing a double-layer structure. The bottom layer (T coating) adopts a titanium dioxide coating obtained by hydrolysis of tetrabutyl titanate, which can act as a UV absorber and improve the UV-shielding property of the coating. The top layer (ZGS coating) is constructed of a cross-linked network structure with zein, gelatin, glucose and silica for anti-freezing and anti-fogging properties. The resulting coating (ZGST) can maintain excellent anti-fogging performance after placing in a hot fog environment (100℃) for 1 h, 300 cycles abrasion, 70 tape-peeling, 120 min ultrasonication and extended service time (261 days so for). One application of greenhouse films with anti-fogging performance was demonstrated, which can improve the status quo of agricultural film and has important significance for the field of agricultural development. It is anticipated that this work may offer valuable guidance for the preparation of anti-fogging, anti-freezing and UV resistant optical materials, which allows potential applications in vehicles, medical, agricultural or vision systems under extreme environments.

Bone Mineral Content Distribution in Response to Long-term Training of Elite Rowers.

Bone response to exercise depends on the type and size of the mechanical stimulus. In rowing, athletes are exposed to low mechanical but large compression loads mainly on the trunk. Thus, this study aimed to investigate the impact of rowing on total and regional bone quality and bone turnover parameters in elite rowing athletes vs. control subjects. Twenty world-class rowers and twenty active, but not athletic, men participated in the study. Bone mineral density (BMD) and body mineral content (BMC) were assessed by dual-energy X-ray absorptiometry (DXA). Bone turnover markers (OPG and RANKL) in serum were assessed by Elisa method. The current research revealed no statistical difference in total bone mineral density (TBMD) and total body mineral content (TBMC) between elite-level rowers and control subjects. Nevertheless, Trunk BMC (p=0.02) and Trunk BMC/TBMC ratio (p=0.01) were significantly higher in rowers than those in the control group. In contrast, in the control group, the Lower limbs BMC/TBMC ratio (p=0.007) was statistically higher. Furthermore, RANKL (p=0.011) and OPG (p=0.03) were statistically significantly higher in rowers, whereas the OPG/RANKL ratio (p=0.012) was statistically higher in the control group. Rowing, as a non-weight-bearing exercise, did not alter total bone density but induced a remarkable redistribution of bone density from the lower limbs to the trunk. In addition, the current evidence suggests that the underlying molecular mechanism is based on turnover of intermediates, rather than solely bone redistribution.

Kinetics and Pore Formation of the Sodium Metal Anode on NASICON‐Type Na3.4Zr2Si2.4P0.6O12 for Sodium Solid‐State Batteries

AbstractIn recent years, many efforts have been made to introduce reversible alkali metal anodes using solid electrolytes in order to increase the energy density of next‐generation batteries. In this respect, Na3.4Zr2Si2.4P0.6O12 is a promising solid electrolyte for solid‐state sodium batteries, due to its high ionic conductivity and apparent stability versus sodium metal. The formation of a kinetically stable interphase in contact with sodium metal is revealed by time‐resolved impedance analysis, in situ X‐ray photoelectron spectroscopy, and transmission electron microscopy. Based on pressure‐ and temperature‐dependent impedance analyses, it is concluded that the Na|Na3.4Zr2Si2.4P0.6O12 interface kinetics is dominated by current constriction rather than by charge transfer. Cross‐sections of the interface after anodic dissolution at various mechanical loads visualize the formed pore structure due to the accumulation of vacancies near the interface. The temporal evolution of the pore morphology after anodic dissolution is monitored by time‐resolved impedance analysis. Equilibration of the interface is observed even under extremely low external mechanical load, which is attributed to fast vacancy diffusion in sodium metal, while equilibration is faster and mainly caused by creep at increased external load. The presented information provides useful insights into a more profound evaluation of the sodium metal anode in solid‐state batteries.

Experimental study of contacting surfaces microgeometry and gas gap impact on thermal contact conductance of metallic joints

Thermal contact resistance is an important phenomenon in heat transfer and impacts many fields of technology. The interrelated influences of many factors—such as geometry and microgeometry of contacting surfaces, their mechanical and thermal properties, apparent contact pressure, type and properties of interstitial fluid—make prediction of this resistance problematic and necessitate both theoretical and experimental research. The paper reports an experimental study of thermal contact conductance (the reciprocal of thermal contact resistance) of joints created by flat, conforming metallic surfaces in static contact. The measurements were performed for samples made of mild steel and stainless steel with relatively low roughness (σ = 0.5 - 2.14 µm) and large slope of asperities (m = 0.4 – 1.3), resulting in values of σef/mef = 1.25 - 1.96 µm that are distinctly lower than reported in the majority of experimental research on thermal contact conductance. The apparent contact pressure was changed from 1.5 to 11 MPa and for some cases up to 19 MPa. Analysis of the results obtained showed that the correlations available in the literature, for greater values of roughness and smaller asperity slope, mostly overestimated the predicted thermal contact conductance. The elasticity indices values for samples used in this study indicated plastic deformation of asperities, but it was concluded that the smoothest surfaces of both kinds of steel underwent elastic deformation. A new experimental correlation for contact of mild steel surfaces (σ = 0.5 - 2.14 µm, σef/mef = 1.25 - 1.96) was proposed. The results of this study indicate the need for further investigation of thermal contact conductance, especially for this range of surface microgeometry parameters, which is not dealt with in the correlations available in the literature. There is also a need to study the impact of asperity curvature on contact conductance. The results of this study proved the important role that air gaps play in the transfer of heat across a joint. The gap conductance values were predicted correctly for low mechanical loads and rough surfaces.

Real-time sinusoidal parameter estimation for damage growth monitoring during ultrasonic very high cycle fatigue tests

Ultrasonic fatigue tests (UFT) are used to study the fatigue life behavior of metallic components undergoing a very high number of cycles (typically ≥107−109 cycles) under relatively low mechanical loads. By soliciting fatigue specimens at 20 kHz, ultrasonic fatigue machines are indispensable for monitoring damage growth and fatigue failures in a reasonable amount of time. As fatigue damage accumulates in the specimen, the specimen’s free-end exhibits a nonlinear dynamic response. The resulting quasi-stationary, harmonic signals have sinusoidal parameters (frequency and amplitude) which are slowly time-varying with respect to the excitation frequency. The discrete Fourier transform (DFT) is typically used to extract these evolving sinusoidal parameters from a window of finite data of the vibration signal. Alternative spectral estimation methods, specifically line spectra estimators (LSEs), exploit a priori information of the signal via their modeling basis and overcome limitations seen by the DFT. Many LSEs are known to have state-of-the-art results when benchmarked on purely stationary signals with unit amplitudes. However, their performances are unknown in the context of slowly time-varying signals typical of UFT, leading to a widespread use of the DFT. Thus, this paper benchmarks classical and modern LSEs against specific synthetic signals which arise in UFTs. Adequate algorithms are then recommended and made publicly available to process experimental data coming from ultrasonic fatigue tests depending on performance metrics and experimental restraints.

Prospects for the production of weather-resistant rolled steel with increased cold resistance

The main advantages and areas of application of weather-resistant steels are considered. The main features of the chemical composition and oxidation mechanism of the materials under consideration are noted. As a result of comparing the main performance characteristics of weather-resistant steels produced by leading foreign and Russian manufacturers, the relevance and prospects of organizing high-tech production of weather-resistant rolled steel with increased cold resistance are substantiated. Special attention is paid to a comprehensive project for the creation of high-tech production, implemented by PJSC Magnitogorsk Iron and Steel Works together with scientists from FSBEI HE Nosov Magnitogorsk State Technical University. One of the promising materials being developed within the framework of the project is weather-resistant rolled steel, which has a high level of strength, ductility and cold resistance. The proposed combination of properties will ensure high efficiency of the functioning of strategic facilities of the oil and gas and machine-building complexes of Russia, as well as transport and bridge building, subjected to the simultaneous effects of low temperatures and high mechanical loads. At the same time, high resistance to atmospheric corrosion significantly increases the service life of the material, reduces operating costs and expands the scope of metal products, including in climatically cold conditions.P. P. Poletskov, S. V. Denisov, P. A. Stekanov, E. V. Braichev, and P. G. Adishchev,&nbsp;a post-graduate student of the MTa-21-2 group, took part in the work.The work is carried out at the Nosov Magnitogorsk State Technical University with&nbsp;the financial support of the Ministry of Education and Science of Russia as part&nbsp;of the implementation of a comprehensive project to create the high-tech production&nbsp;(agreement with the Ministry of Education and Science of Russia No. 075-11-2021-063&nbsp;dated 06/25/2021).

Modeling the devolatilization and fragmentation of biomass pellets with the bonded particle method for fluidized bed applications

By extending the bonded particle method, the major structural changes during the devolatilization of a wood pellet in a fluidized bed and the resulting mechanical behavior have been successfully reproduced. A comparison with experiments from the literature showed that the implemented particle-based pyrolysis model enables predicting the entire pellet’s kinetics with a high agreement. The developed shrinkage model for the particles and bonds further allowed to emulate the reported formation of a large-scale pore network inside the pellet. The simulation of a radial compression test with the predicted structure showed good agreement with experimental data and could confirm the importance of the pores for the mechanical behavior. The results demonstrated that the large pores cause the fragmentation of agglomerates already at low mechanical loads which could promote attrition. In general, the results have shown that the developed extension of the bonded particle method allows studying and predicting the behavior of a single pellet during conversion inside a fluidized bed gasification reactor in more detail.

Approach to quantify the resistance of polymeric foams against thermal load under compression

Abstract Nowadays, numerous techniques are used to quantify the resistance of cellular polymers against a thermal load. These techniques differ in significance and reproducibility and are all dependent on foam density, structure (i.e., cell size and -distribution) and sample geometry. Very different behaviors are expected for extrusion- and bead foams, as well as for amorphous and semi-crystalline polymers. Moreover, established tests use temperature ramps which would lead to temperature gradients within the sample and thus to faulty results. In this study, we developed a new approach from an engineering perspective to minimize these influences. In this approach, the resistance against the thermal load is derived from a steady creep test with defined temperature steps under a mechanical load, which is specifically set for each foam sample depending on its static compression behavior at room temperature. The two-stage test therefore combines (i) a standard quasi-static compression test at room temperature and (ii) a creep test with stepwise increased thermal loading. For each foam type, a rather low mechanical load (stress) is determined from the quasi-static compression test at room temperature; low enough to remain below the collapse strength and avoid irreversible deformation (i.e., buckling and/or breaking of the cell walls). This load is then applied in a creep test where the temperature is increased in defined steps from room temperature to a temperature close to T g or T m . The stepwise increase and holding of the temperature for a defined time enables a homogeneous temperature in the test specimen. The approach was applied to (i) polystyrene extrusion and bead foams (i.e., XPS and EPS), which have different foam structure, (ii) amorphous and semi-crystalline bead foams of polystyrene (EPS) and polypropylene (EPP), (iii) bead foams with different densities (30, 60, 120, and 210 kg/m3) and (iv) to a new type of bead foam made of the engineering polymer polybutylene terephthalate (E-PBT). The termination criterion for the test is defined as the temperature at which a relative compression of 10% is reached in the creep test with temperature steps. We suggest calling it the heat stability temperature T HS. For the studied foams, the procedure delivers characteristic T HS values that allow a good comparison between different polymer matrices and densities. The heat stability temperature T HS of amorphous PS foams (i.e., XPS and EPS) was determined to be 98 °C, which is close to the glass transition temperature T g . Using the same approach, values of 99–107 °C were determined for EPP and 186 °C for the semi-crystalline bead foam E-PBT.

Influence of Changes in the Shape of the Anode Channel in Polymer Electrolyte Fuel Cell on the Loss of Its Service Life.

The fuel cell operation is associated with significant current density and durability problems, among other anode collectors. We used a numerical model based on flows with chemical reactions in a porous medium to solve these problems. We tested four variants of the anode channels. In the shape of the anode channel, we introduced changes to improve the current density. We also examined the influence of the channel shape on the stress field and rheological processes in the casing material. We verified the numerical model on the experimental data. Furthermore, we corrected the amount of the hydrogen stream and the produced water in the whole range of the cell’s operation. The test results show that it is possible to increase the current density in all operating fields of the fuel cell while maintaining a low mechanical load on graphite elements and their safe operation time.