Dynamic Cyclic Loading Research Articles

Proton Exchange Membrane Fuel Cell Stack Durability Prediction Using Arrhenius-Based Accelerated Degradation Model

To expand the applications of proton exchange membrane fuel cell (PEMFC) stacks, it is essential to address the issue of their short lifetime. Various studies are being conducted to improve this limitation, and efficient methods for verifying durability in a short period of time are required. This study presents a novel dynamic load cycling protocol designed to emulate the real-world driving conditions of commercial vehicles. This protocol was employed as an accelerated degradation test for PEMFC stacks under two elevated temperatures (65 and 80 °C), each conducted for 1000 h. A bi-exponential model, incorporating Arrhenius principles, was fitted to the degradation data. During this process, a mixed effects modeling approach was employed to distinguish between fixed and random effects within the model parameters. The activation energy was consistent across all cells and was thus designated as a fixed effect. Activation energy, which predominantly affects the long-term durability of PEMFC stacks, was estimated as 0.808 eV. By applying this estimated value to the Arrhenius equation, we calculated the acceleration factors for the degradation of fuel cell performance. Specifically, the rate of voltage degradation was found to be approximately 1.516 times faster at 65 °C and 4.923 times faster at 80 °C, compared to the standard operating temperature of 60 °C. Additionally, Monte Carlo simulations were conducted to predict the failure-time distribution under normal use conditions, estimating a median lifetime of 3884 h, which corresponds to 155,360 km of driving. This methodology offers a reliable and time-efficient framework for assessing PEMFC durability, with significant implications for reducing testing costs and accelerating the development of hydrogen fuel cell technology.

Raman Spectroscopy for Diagnostic Analysis of Fuel Cell Catalyst Coated Membranes

Raman spectroscopy is a useful analytical tool for characterising the carbon chemistry of proton exchange membrane fuel cell (PEMFC) catalyst coated membranes (CCMs) and understanding changes in the carbon matrix due to corrosion and degradation processes. However, interpretation of the data is highly sensitive to the sampling and spectral analysis methods employed. Here we critically assess the use of Raman spectroscopy for diagnostic analysis of uncycled PEMFC CCMs and equivalent CCMs subjected to dynamic load cycling (DLC). We first consider different approaches to quantitative analysis of Raman spectra and show that a two peak spectral fitting model which only considers the characteristic D1 and G peaks in the Raman spectrum provides an inferior fit compared to a four peak fitting model that includes the minority D3 and D4 peaks associated with amorphous carbon and disordered graphitic domains. We furthermore demonstrate that in specific cases these two models can generate opposing trends. We then compare quantitative Raman metrics generated from spectral maps at different locations of CCMs subjected to different durations of cycling. A large degree of scatter in the data precluded conclusive correlation between Raman data and duration of cycling, highlighting the importance of sufficiently large sample sizes when performing quantitative analysis. However, a difference in behaviour between cathode and anode was observed, characterised most prominently by a higher degree of scatter in the Raman metrics associated with disordered and amorphous carbon, potentially pointing to contrasting ageing phenomena resulting from the different conditions at the cathode and anode. We also demonstrate that spectral differences across the cycled anode appear to be highly spatially heterogeneous, indicating that the associated chemical changes are localised on the <100 μm scale.

Deformation theory and energy mechanism of cyclic dynamic mechanical damage for granite in the diversion tunnel under cyclic loading-unloading.

The diversion tunnel is frequently subjected to cyclic dynamic loads during blasting and mechanical excavation. To explore the theory and mechanism of cyclic dynamic mechanical damage for granite in a diversion tunnel under cyclic loading-unloading, the incremental cyclic loading-unloading test and numerical simulation were conducted on granite samples from the diversion tunnel. According to the mechanical and deformation characteristics of rock samples in the process of cyclic loading-unloading, the stress-strain normalization theory evolution model based on viscoelastoplasticity was established, and the cyclic dynamic damage evolution mechanism of rock samples was revealed. The evolution characteristics of stress-strain curves of rock samples under cyclic loading-unloading were effectively described, and the loading-unloading two-stage constitutive equation of rock samples under cyclic loading-unloading was established. The energy and damage evolution mechanism of the final full stress-strain curve and the influence mechanism of shrinkage and expansion of rock particles on the mechanical properties of granite were discussed.

Metastable state preceding shear zone instability: Implications for earthquake-accelerated landslides and dynamic triggering

Understanding the dynamic response of granular shear zones under cyclic loading is fundamental to elucidating the mechanisms triggering earthquake-induced landslides, with implications for broader fields such as seismology and granular physics. Existing prediction methods struggle to accurately predict many experimental and in situ landslide observations due to inadequate consideration of the underlying physical mechanisms. The mechanisms that influence landslide dynamic triggering, a transition from static (or extremely slow creeping) to rapid runout, remain elusive. Herein, we focus on the inherent physics of granular shear zones under dynamic loading using ring shear experiments. Except for coseismic slip caused by the dynamic load, varying magnitudes of postseismic creep with increasing cycles of dynamic loading are observed, highlighting the effects of coseismic weakening (shear zone fatigue) and subsequent postseismic healing. A metastable state, characterized by a significant increase in postseismic creep, typically precedes shear zone instability. The metastable state may arise as weakened shear resistance approaches the applied shear stress, demonstrating a phase transition from a solid-like state to a fluid state (plastic granular flow). The metastable state may potentially indicate the shear zone's stress state and serve as a precursor to impending instability. Furthermore, the proposed mechanisms offer a compelling explanation for the widespread postseismic landslide movement following earthquakes. Incorporating these mechanisms into the Newmark method has the potential to improve the prediction of earthquake-induced landslide displacement and enhance our understanding of dynamic triggering.

Degradation-considering adaptive equivalent consumption minimization strategy for fuel cell electric vehicles

In order to improve the economy and durability of fuel cell vehicle, a degradation-considering adaptive equivalent consumption minimization strategy (D-ECMS) was proposed for fuel cell/lithium battery hybrid power system. Aiming at enhancing the adaptability of the equivalent consumption minimum strategy, four different vehicle speed conditions were considered including low speed, medium speed, high speed, and ultra-high speed. Particle swarm optimization (PSO) algorithm was used to optimize the penalty factor under different vehicle speed conditions, and BP neural network was used to identify real-time conditions to form an adaptive equivalent consumption minimum strategy (A-ECMS). The voltage decay model of the fuel cell was established according to the voltage decay rate of the fuel cell under the three adverse conditions of idle speed, high power and dynamic load cycle. The voltage decay of the fuel cell was transformed to hydrogen consumption in the cost function of the A-ECMS strategy to obtain the D-ECMS considering durability degradation. The simulation and the hardware-in-the-loop (HIL) test based on the dSPACE real-time platform was carried out. The results show that: compared with A-ECMS, the hydrogen consumption of the D-ECMS increased by 5.2%, 9.7%, 10.2%, and 0.2% respectively under WLTC, NEDC, UDDS, and HWFET cycles. However, D-ECMS can reduce the voltage decay by 38.3%, 59.7%, 35.2%, and 26% under the above four test conditions, and their total comprehensive cost loss is reduced by 8.7%, 6.7%, 9.6%, and 6.3% respectively. As result, the D-ECMS can reduces the voltage attenuation of fuel cells and improve the durability of fuel cells significantly with a small hydrogen consumption increase,which can reduce the operating cost of fuel cells finally. Furthermore, the average error between the results of HIL test and offline simulation results is less than 5%, which validates the adaptability and real-time application feasibility of D-ECMS.

Fatigue fracture behaviors and damage evolution of coal samples treated with drying–wetting cycles investigated by acoustic emission and nuclear magnetic resonance

Constructing pumped-storage power stations using underground reservoirs in mines offers a promising method for large-scale energy storage. Watertight coal pillars have the potential to destabilize under the mine-shock cyclic dynamic loading and the drying–wetting cycles (DWCs). Understanding the fatigue damage mechanism and failure precursors in watertight coal pillars under cyclic dynamic loading disturbances in overburdened rock strata has become challenging. This study investigated the fatigue fracture behavior and precursor information of coal samples under acoustic emission (AE) monitoring over 1–7 DWC times. We analyzed the effects of DWC and fatigue cycles on the dynamic parameters and AE response, investigated crack spatial extension behaviors and the tensile-shear cracking evolution law, and analyzed the fatigue damage evolution law and failure precursor with energy and b-value. The results demonstrated that fatigue loading produced a strengthening effect on the DWC coal samples, and DWC promoted plastic softening damage to the specimens and increased the percentage of the elastic phase. The average dynamic fatigue strength and life of the specimens decreased exponentially under 7 DWC times. The average dynamic axial stiffness decreased by 15.67 %, the axial deformation increased by 6.1 × 10−4 in a single cycle, and the dynamic elasticity modulus of the fatigue damage instant decreased by 8.86 %. The greater the number of DWC, the smaller the b-value and the larger the fluctuation amplitude at fatigue failure of the specimen. A large short-term increase or decrease in the b-value can be regarded as a precursor to fatigue failure. This study provides a reference for the stability monitoring and forewarning of underground pumped-storage facilities.

Investigation of 3D Printed Self-Sensing UHPC Composites Using Graphite and Hybrid Carbon Microfibers.

This paper explores the development of 3D-printed self-sensing Ultra-High Performance Concrete (UHPC) by incorporating graphite (G) powder, milled carbon microfiber (MCMF), and chopped carbon microfiber (CCMF) as additives into the UHPC matrix to enhance piezoresistive properties while maintaining workability for 3D printing. Percolation curves were established to identify optimal filler inclusion levels, and a series of compressive tests, including quasi-static cyclic, dynamic cyclic, and monotonic compressive loading, were conducted to evaluate the piezoresistive and mechanical performance of 29 different mix designs. It was found that incorporating G powder improved the conductivity of the UHPC but decreased compressive strength for both mold-cast and 3D-printed specimens. However, incorporating either MCMF or CCMF into the UHPC resulted in the maximum 9.8% and 19.2% increase in compressive strength and Young's modulus, respectively, compared to the plain UHPC. The hybrid combination of MCMF and CCMF showed particularly effective in enhancing sensing performance, achieving strain linearity over 600 με. The best-preforming specimens (3G250M250CCMF) were fabricated using 3 wt% of G, 0.25 wt% of MCMF, and 0.25 wt% of CCMF, yielding a maximum strain gauge factor of 540, a resolution of 68 με, and an accuracy of 4.5 με under axial compression. The 3D-printed version of the best-performing specimens exhibited slightly diminished piezoresistive and mechanical behaviors compared to their mold-cast counterparts, yielding a maximum strain gauge factor of 410, a resolution of 99 με, and an accuracy of 8.6 με.

Estimating Lifetime and Degradation Analysis of PEMFC Under Harsh Load Conditions for Eco-Friendly Off-Road Heavy Equipment

The durability and lifetime are key parameters for commercial usage of Polymer Electrolyte Membrane Fuel Cell(PEMFC) in mobility industry. Off-road heavy equipment, such as excavator, loader, and dozer etcs, have severe amount of carbon emission because of its high energy density. According to California government, the air pollution contribution of off-road heavy equipment is higher than that of on-road vehicles since 2020. Therefore, it is necessary to change its power source to eco-friendly power system, such as battery or hydrogen fuel cell. However, its highly dynamic load cycles and harsh operating conditions could accelerate the degradation of Membrane-Electrode Assembly(MEA), reducing the lifetime of PEMFC and increasing the net-cost. In this work, we developed durability test protocols and model to estimate lifetime for PEMFC considering real experimental data obtained from field test results of Bobcat’s 3.8 tons compact track loader. The exact load conditions to PEMFC were obtained considering its complex movements. The 2000 hours of durability test of PEMFC single cell was conducted using newly developed protocols. The electrochemical analysis data was obtained in every 200 hours in order to analyze the degradation of MEA. The electrochemical surface area(ECSA) was decreased around 70 % with exponential decay behavior. From the electrochemical impedance spectroscopy, it was found that the Ohmic, charge and mass transport resistance were increased. According to the electrochemical analysis data, the degradation of catalyst layer was severe, which is the critical parameter for performance degradation. Using the TEM analysis, the catalyst degradation was confirmed directly.

Development of a dynamic cumulative damage model and its application to underground hydropower caverns under multiple blasting

Underground infrastructures are crucial for resource extraction, energy storage, and space utilisation. The geomaterials that make up these structures, such as rock and concrete, are subjected to multiaxial stress conditions and are frequently exposed to dynamic and extreme loadings caused by both natural disasters and human activities. These stresses are particularly significant during the construction phase, which involves operations such as drilling and blasting excavation, as well as during the operational phase, which may include events like explosions. For instance, while drilling and blasting induce rock breakage within the excavated profile as designed, they inevitably lead to the formation of a damage zone in the surrounding rock mass. Moreover, the cumulative effects of sequential excavations and multiple blasts can cause significantly greater damage, thereby threatening the stability of tunnel structures during the operation phase. This paper highlights the importance of thoroughly analysing these phenomena during both static and dynamic loadings to ensure the stability of underground infrastructures. To address these challenges, a rate-dependent damage constitutive model is proposed for geomaterials to assess the impacts of blasting loads and the cumulative damage resulting from repeated blasts. The model is conceptualised using the strength envelope of loading-unloading curves to represent the progressive accumulation of damage under repeated impacts. Through theoretical derivation, a dynamic cumulative damage model is developed, based on a modified Mohr-Coulomb strain-softening model incorporating rate-dependent parameters, and is validated against dynamic experimental data. The model captures the transition between static strain-softening and dynamic cumulative damage, triggered by a critical strain-rate threshold. The applicability of the model is demonstrated through simulations of tunnel excavation, emphasising the impact of blasting loads and the accumulation of damage zones. To assess its practical feasibility, the developed model is applied to simulate different excavation scenarios for an underground hydropower cavern. Damage in the surrounding rock mainly results from static unloading and/or dynamic disturbances. Blasting construction, in particular, causes significant damage in tunnel intersection zones and the connecting areas of two benches, leading to increased displacement and higher damage levels compared to static excavation. To mitigate excessive damage while maintaining the construction timeframe, it is recommended to consider alternating cycles of dynamic loading and static excavation unloading continuously, which helps understand damage formation in critical zones without significantly delaying project completion.

Anisotropy and lateral compressive strength of large-size cement-stabilized macadam for bulging deformation resistance: A numerical analysis

Large-size cement-stabilized macadam (LCSM) base effectively hinders bulging deformation in asphalt pavements. Under vibratory compaction, the embedded skeleton structure and anisotropy of large-size aggregates (LSA) impact the mechanical properties of LCSM mixes. To reveal the mesostructure and anisotropy of LSA and determine the optimal volume percentage of LSA in LCSM mixes against bulging deformation, this study first characterized the bulging deformation resistance of LCSM mixes using lateral compressive strength (LCS). Next, the evolution of coordination number (CN) and distributions of contact force and contact normal for LSAs at different volume percentages under dynamic cyclic loading were investigated using the discrete element method (DEM). In particular, the induced anisotropic behavior was explored. Then, indoor tests and numerical simulations were conducted to assess the mixes’ LCS and vertical compressive strength (VCS); additionally, the compressive damage characteristics were analyzed. The results indicate that increasing the volume percentage of LSA and dynamic cyclic loading enhanced the CN, strong contact force, and contact normal density. LSAs at varying volume percentages exhibited pronounced anisotropic characteristics before and after loading, and the anisotropy factor of the LSA dropped after loading at a volume percentage of 65 %. Furthermore, the mixes’ VCS values exceeded LCS ones at the same LSA volume percentage, and there was a consistent relationship between the LSA anisotropy and the VCS/LCS ratio, suggesting that the optimal LSA volume percentage in LCSM mixes ranged from 60 % to 65 %. Finally, as the LSA volume increased, the skeleton effect became more pronounced than the interface attenuation effect, leading to higher VCS and LCS values in the mixes, thus improving their resistance to bulging deformation.

A novel method of long-term aging prediction for proton exchange membrane fuel cell under the dynamic load cycling condition

Estimating the remaining useful life (RUL) of proton exchange membrane fuel cell (PEMFC) is beneficial for deploying control strategies. Long-term aging prediction forms the foundation for RUL estimation, but currently long-term aging prediction and RUL estimation for dynamic load cycling conditions have not been achieved, and uncertainty during the prediction and estimation processes has not been considered. Therefore, in this study, a novel hybrid prediction framework based on Bayesian gated recurrent unit, model uncertainty and state estimation (MUSE), and convolutional neural network-long short-term memory (CNN-LSTM) is proposed. First, MUSE is used to simultaneously quantify the state of health (SOH) and predict aging trend to generate a guiding sequence Next, based on the sequence and historical experimental data, CNN-LSTM is trained and multi-step prediction is performed. Subsequently, Bayesian gated recurrent unit is employed to fuse the MUSE-based prediction sequence with the CNN-LSTM-based prediction, and confidence interval is provided. This results in a novel model and data-driven long-term aging prediction structure. Finally, SOH during the prediction stage is evaluated by MUSE and RUL is estimated. The proposed method is validated using experimental data under a dynamic load cycling condition, demonstrating accurate long-term aging prediction and RUL estimation while considering uncertainty.

Experimental study on degradation of proton exchange membrane fuel cells for eco-friendly heavy equipment

Proton Exchange Membrane Fuel Cells(PEMFC) are considered the main power source for eco-friendly mobility. The degradation of PEMFCs in eco-friendly heavy equipment is analyzed. The target heavy equipment is 4.5 tons track loader of Doosan Bobcat. The complex movement of heavy equipment causes extreme dynamic load cycling in the powertrain. An electrochemical analysis of its Membrane Electrode Assembly(MEA) is conducted to clarify its degradation feature in this work. Dynamic load cycles are obtained from field tests using earth-moving machinery. A 2000 h durability test for a PEMFC single cell is conducted using the obtained dynamic load cycles. According to polarization curve analysis, the maximum power decreases from 19.95 to 13.82 W. This is mainly caused by the degradation of the catalytic activity of the Pt catalyst layer, as confirmed by cyclic voltammetry(CV). The electrochemical surface area(ECSA) decreases by 70 %.

Three-dimensional finite element analysis of the impact of access cavity preparation on first molar fracture resistance: A scoping review.

Access cavity preparation represents the initial step in root canal treatment. Minimally invasive approaches have gained increasing attention and involve advancements in the traditional access cavity preparation. Simultaneously, the development of three-dimensional finite element analysis (3D-FEA) has provided a theoretical foundation for evaluating the merits and drawbacks of various access cavity preparations. Studies using static loading 3D-FEA have suggested that conservative access cavity preparation reduces the concentration of stress in the cervical region, thereby strengthening fracture resistance. However, the lack of support from clinical data raises concerns about the validity of this suggestion. Conversely, studies involving cyclic loading 3D-FEA and dynamic loading 3D-FEA have challenged the prevailing perspectives by taking into account additional factors such as filling materials, thus providing a more comprehensive understanding of the impact of access cavity preparation on fracture resistance. Existing research lacks a comprehensive comparison of the different 3D-FEA methods, and this review fills this gap by providing a systematic assessment of different 3D-FEA methods and their applications in access cavity preparation.

Biomechanical comparison of using traditional and 3D-printed titanium alloy anatomical assembly thin anterior plating under three patellar fracture conditions

ABSTRACT This study attempted to understand the biomechanics of using 3D-printed anatomical assembly thin bone plate (AATBP) and anterior star-shaped plating (ASP) under different patellar fractures. The transverse (C1), transverse plus second fragment (C2) and complex (C3) patella fractures were defined for performing the dynamic cyclic load test and finite element (FE) analysis. The AATBP was fixed onto the patella after adjusting the total fixation height using a ratchet mechanism and providing holding power hooks. The ASP contoured the plate/distal legs based on the patella surface curvature and generated an additional drill guide to avoid screw interference. The average ASP fixation fracture gaps were significantly larger than the AATBP fixation. FE analysis showed that the AATBP biomechanical performance was better than the ASP fixation for different patella fractures. The 3D-printed AATBP can be used effectively for different patella fractures without screw interference and demonstrated greater stability for comminuted patellar fractures.

Evolution of Permeability and Sensitivity Analysis of Gas-Bearing Coal under Cyclic Dynamic Loading

It is imperative to conduct experimental studies on the seepage behavior of gas-bearing coal under cyclic dynamic loading conditions. This paper focuses on the evolution of coal permeability under the combined effects of dynamic loading, static loading, and gas adsorption. The principal conclusions are as follows: (1) As the frequency and amplitude of dynamic loading increase, the development of pore and fissure structures within the coal body becomes increasingly pronounced during dynamic loading cycles, resulting in a gradual rise in permeability. Notably, as the coal approaches its yielding stage, the permeability can increase by up to 47%. (2) The permeability curve is divided into four regions: the compaction reduction zone, the oscillation zone, the gradual recovery zone, and the abrupt failure increase zone. Ultimately, in the failure phase, the permeability surges dramatically, potentially reaching four to five times the initial permeability. (3) When the static loading stage and dynamic load are constant, the rate of change in coal permeability decreases with increasing adsorption amounts. When the adsorption amount is constant, the rate of change in permeability of the coal under dynamic loading increases with the increase in the static loading stress stage, with the maximum increase reaching 75.2%. It can be concluded from the rate of change in permeability and the dynamic loading sensitivity coefficient that the permeability of coal is highly sensitive to cyclic dynamic loading, with increased sensitivity associated with larger static loading stages and decreased sensitivity with greater adsorption amounts.

A robust low-friction triple network hydrogel based on multiple synergistic enhancement mechanisms

Hydrogels exhibit promising applications, particularly due to their high water content and excellent biocompatibility. Despite notable progress in hydrogel technology, the concurrent enhancement of water content, mechanical strength, and low friction poses substantial challenges to practical utilization. In this study, employing molecular and network design guided based on multiple synergistic enhancement mechanisms, we have developed a robust polyvinyl alcohol (PVA)–polyacrylic acid (PAA)–polyacrylamide (PAAm) three-network (TN) hydrogel exhibiting high water content, enhanced strength, low friction, and fatigue resistance. The hydrogel manifests a water content of 63.7%, compression strength of 6.3 MPa, compression modulus of 2.68 MPa, tensile strength reaching 7.3 MPa, and a tensile modulus of 10.27 MPa. Remarkably, even after one million cycles of dynamic loading, the hydrogel exhibits no signs of fatigue failure, with a minimal strain difference of only 1.15%. Furthermore, it boasts a low sliding coefficient of friction (COF) of 0.043 and excellent biocompatibility. This advancement extends the applications of hydrogels in emerging fields within biomedicine and soft bio-devices, including load-bearing artificial tissues, artificial blood vessels, tissue scaffolds, robust hydrogel coatings for medical devices, and joint parts of soft robots.

Aging Effects Observed in Automotive Fuel Cell Stacks by Applying a New Realistic Test Protocol and Humidity Control

ABSTRACTTraditional automotive proton exchange membrane fuel cell (PEMFC) endurance testing relies on the fuel cell (FC) dynamic load cycle (FC‐DLC) protocol, which inadequately reflects real‐world driving conditions. To address this limitation the “Investigations on degradation mechanisms and Definition of protocols for PEM Fuel cells Accelerated Stress Testing” (ID‐FAST) consortium defined the new representative “ID‐FAST driving load cycle,” a novel approach capturing the load distribution, transitions, temperature variations, and humidity fluctuations experienced by FCs in real‐world operation. We demonstrate the ID‐FAST driving cycle itself and the integration into a realistic durability test program for FC test benches and present the resulting test data. Furthermore, we showcase its implementation within an accelerated stress testing (AST) protocol, highlighting its potential to significantly reduce testing time by accelerating degradation. Additionally, a novel method for highly dynamic humidity adjustment within test benches is introduced. By overcoming limitations of existing methods and incorporating the ID‐FAST driving cycle, this work paves the way for a new era of efficient and realistic FC endurance testing, ultimately contributing to the development of more robust and durable automotive FC stacks.

Mechanical properties of 3D-printed resin denture teeth: An in vitro study.

The purpose of this study was to compare the wear, fracture strength, and mode of failure of various brands of 3D-printed resin denture teeth with prefabricated acrylic resin. Additionally, the study aimed to analyze the different modes of failure exhibited by these teeth. The study utilized 90 3D-printed and 30 prefabricated, 3D-printed resin teeth from three brands: L = Optiprint Lumina, A = ASIGA DentaTooth, P = Power resins, along with prefabricated acrylic teeth from M = Major Super Lux. Each of the 30 samples per main group was divided into two subgroups: The first subgroup samples (M1, A1, L1, P1) were subjected to thermal cycling and mechanical loading; M2, A2, L2, and P2 were not aged and tested directly. A scan of a prefabricated acrylic tooth was taken using an intraoral scanner, and then the STL file was printed using an Asiga 3Dprinter. The specimens underwent aging to simulate 5 years of clinical use with 10,000 thermal cycles and 1,200,000 dynamic load cycles on a chewing simulator. Surface roughness parameters (Rz, Ra, Rq) were measured using a 3D Optical Profilometer, fracture resistance was assessed using a universal testing machine, and SEM analysis was performed to observe failure modes. Statistical analysis using T-test, one-way analysis, and two-way analysis processed by the Statistical Package for Social Sciences (SPSS) software version 23.0 (SPSS: Inc., Chicago, IL, USA) was done with a level of significance set at <0.05. The results showed that the difference in surface roughness parameters (Rz, Ra, Rq) before and after aging for Group M, Group A, Group L, and Group P was statistically significant (p < 0.05). Two-way ANOVA for wear resistance between aging and groups on dependent variable Rz (p = 0.002), Ra (p = 0.001), Rq (p = 0.001) were significant. Multiple comparisons for surface roughness parameters showed Group A and Group L were lower than Group P and Group M (p < 0.05). For fracture strength, One-way ANOVA showed a significant difference between groups for fracture strength either without or after the aging procedure (p < 0.05). Multiple comparisons for fracture strength without aging showed no significant difference between Group M, Group A, and Group L (p > 0.05). After the aging procedure fracture strength for Group M was higher than Group A, Group L, and Group P (p < 0.05). 3D-printed resin teeth showed a greater and comparable wear resistance to prefabricated acrylic teeth. Fracture strength was comparable between prefabricated acrylic teeth and 3D-printed resin (Asiga and Lumina) before aging, but after aging 3D-printed resin teeth showed less fracture strength.

Mechanical performance of an asphalt stabilized base with natural asphalt, hydrated lime and Portland cement

This study aimed to evaluate the mechanical performance of an asphalt stabilized base with natural asphalt mix (ASB-NA) with added contents of 1.0 %, 2.0 %, and 3.0 % of Hydrated Lime (HL) and Portland Cement (PC). Tests were employed under dry and wet conditions to analyze the response to monotonic loading in compression and indirect traction and evaluate the susceptibility to water. Additional tests were conducted to analyze the resistance to cyclic dynamic loading, employing resilient modulus, permanent deformation, and fatigue resistance testing. The results reported that adding HL and PC in ASB-NA significantly increased the mechanical performance under monotonic and dynamic loading. These increases were evidenced by higher compressive strength, indirect tensile strength, resilient modulus, fatigue resistance and permanent deformation. Regarding water susceptibility (durability), higher resistance values to moisture damage were presented for the samples with 2 % HL and PC contents. This paper presents new materials for pavement asphalt base courses, which would reduce asphalt consumption, save energy, cut costs, and protect the environment.

Kinetic analysis and stability evaluation of femoral neck fracture with internal fixation based on gait rehabilitation training

To explore the biomechanical effects of different internal fixation methods on femoral neck fractures under various postoperative conditions, mechanical analyses were conducted, including static and dynamic assessments. Ultimately, a mechanical stability evaluation system was established to determine the weights of each mechanical index and the evaluation scores for each sample. In static analysis, it was found that the mechanical stability of each model met the fixation requirements post-fracture. During the healing process, the maximum stress on the hollow nail slightly increased, and stress distribution shifted from multi-point to a more uniform single-point distribution, which contributes to fracture healing and reduces the risk of stress concentration. In dynamic analysis, resonance points frequently occurred at low frequencies. With increasing walking speed, the maximum stress increased significantly. At slow speeds, the maximum stress approached the material's yield limit. Under cyclic dynamic loading, the number of cycles barely met the requirements of the healing period, and increasing walking speed may lead to fatigue fractures. The evaluation model established in this study comprehensively considers different mechanical performances in static and dynamic analyses. Based on various mechanical analyses and evaluation systems, the applicability of internal fixation treatment plans can be assessed from multiple dimensions, providing the optimal simulated mechanical solution for each case of femoral neck fracture treatment.