Limit Stress Research Articles

Investigating the Dynamic Behavior and Tensile Properties of Coal Gangue Shotcrete Under Impact Loading Conditions SHPB Device

Shotcrete is the primary support material for coal mine tunnel linings and is often subjected to dynamic loads such as blasting and impact. To promote the resource utilization of coal gangue (CG), this study incorporated it into shotcrete and investigated the dynamic mechanical properties of coal gangue shotcrete (CGSC) at different coal gangue aggregate (CGA) replacement ratios. Impact tensile splitting tests were conducted using a split Hopkinson pressure bar (SHPB) device, and the specimen failure process was recorded with a high-speed camera. The results showed that the dynamic tensile splitting strength (DSTS) and energy absorption of CGSC exhibit a significant strain rate effect, with the strain rate sensitivity of DSTS decreasing as the CGA replacement ratio increases. As the strain rate increases, the elastic limit stress of the specimens rises, and the failure mode tends to become more fragmented. Based on energy theory, this paper establishes a dynamic tensile splitting strength model for CGSC, providing theoretical support for its application in engineering.

Lower Maximal Skin Wettedness in Both Warm-Humid and Hot-Dry Environments with Advanced Age (PSU HEAT Project).

Maximum skin wettedness (ωmax) is the proportion of the body covered in sweat at the upper limit of compensable heat stress. It has yet to be determined how ωmax changes with aging. We examined variability in ωmax at the upper limit of compensable heat stress in warm-humid (WH) and hot-dry environments (HD) in young (Y, 18-29 yrs), middle-aged (MA, 40-60 yrs) and older (O, 65-89 yrs) adults during minimal activity (MinAct; ~1.8 METS) and in O subjects at rest. ωmax was calculated using partitional calorimetry for 27 Y (13F), 27 MA (16F), and 32 O (18F) at the previously determined upper limits of compensable heat stress in WH and HD environments. In WH environments, ωmax was greater in Y (0.69 ± 0.12) and MA (0.64 ± 0.20) compared to O (0.47 ± 0.14; both P<0.05), but not different between Y and MA (P=0.85). In HD environments, ωmax was greater in Y (0.52 ± 0.05) compared to O adults (0.40 ± 0.07; P<0.05), but not different between MA (0.48 ± 0.10) and Y or O (both P≥0.15). In O participants at rest, ωmax was lower than MinAct in WH (P<0.001) but not HD environments. These findings indicate that (1) ωmax is lower with advanced age across environments and (2) is lower at rest than during light activity in O in humid conditions. ωmax established herein for unacclimated adults during activities of daily living and older adults at rest may be used to model heat stress responses for these populations and environments.

Title: Systematic insights into cell density-dependent transcriptional responses upon medium replacements.

Understanding the molecular mechanisms governing transfection efficiency and particle secretion in high cell density cultures is critical to overcome the cell density effect upon transient gene expression. The effect of different conditioned media in HEK293 transcriptome at low and high cell density is explored. A systematic pair-wise comparative study was performed to shed light on the effect on previous phenotypical characteristics of different media conditions: fresh, exhausted and media depleted from extracellular vesicles (EVs) as well as associated proteins and RNAs. The obtained results suggest that restorative effects observed in transfection efficiency when employing EV-depleted media may arise predominantly from physicochemical alterations rather than cellular processes. A significant downregulation of genes associated with nucleocytoplasmic transport for the conditions involving the use of exhausted or EV-depleted media was observed. Moreover, upregulation of histone-related genes in EV-depleted media suggest a role for histone signaling in response to cellular stress or growth limitations, thereby highlighting the potential of manipulating histone levels as a promising strategy to enhance transient transfection. It was also corroborated that the accumulation of extracellular matrix proteins upon cell growth may inhibit transfection by an already-known competitive effect between cell membrane-bound and free proteoglycans. Proteomic characterization of EV-depleted media further unveiled enrichment of pathways associated with infection response and double-strand DNA breaks, suggesting that HEK293 cells undergo an induced infection-like state that disrupts cellular processes. Importantly, the study reveals that EV-depleted media stimulates virion release pathways underscoring the complex interplay between extracellular vesicles and viral budding.

Transcriptomic Response of Rhizobium leguminosarum to Acidic Stress and Nutrient Limitation Is Versatile and Substantially Influenced by Extrachromosomal Gene Pool.

Multipartite genomes are thought to confer evolutionary advantages to bacteria by providing greater metabolic flexibility in fluctuating environments and enabling rapid adaptation to new ecological niches and stress conditions. This genome architecture is commonly found in plant symbionts, including nitrogen-fixing rhizobia, such as Rhizobium leguminosarum bv. trifolii TA1 (RtTA1), whose genome comprises a chromosome and four extrachromosomal replicons (ECRs). In this study, the transcriptomic responses of RtTA1 to partial nutrient limitation and low acidic pH were analyzed using high-throughput RNA sequencing. RtTA1 growth under these conditions resulted in the differential expression of 1035 to 1700 genes (DEGs), which were assigned to functional categories primarily related to amino acid and carbohydrate metabolism, ribosome and cell envelope biogenesis, signal transduction, and transcription. These results highlight the complexity of the bacterial response to stress. Notably, the distribution of DEGs among the replicons indicated that ECRs played a significant role in the stress response. The transcriptomic data align with the Rhizobium pangenome analysis, which revealed an over-representation of functional categories related to transport, metabolism, and regulatory functions on ECRs. These findings confirm that ECRs contribute substantially to the ability of rhizobia to adapt to challenging environmental conditions.

Symptom perception and coping in patients with primary biliary cholangitis: a qualitative study in the context of SOMA.LIV

Patients with primary biliary cholangitis (PBC) suffer from a variety of physical complaints such as fatigue, itching or joint pain. Since little is known about the experience of symptoms and the corresponding coping strategies in this patient group, a qualitative study was conducted in which 15 patients with PBC were interviewed. The patients reported being burdened by numerous physical complaints, some of which require extensive coping and adaptation processes. By means of thematic analysis, two overarching themes could be generated from the data material: "Accepting limitations and shifting boundaries" describes the patients' challenge of redefining their own stress limits and adapting demands and expectations to their own capabilities. "Maintaining normality and reorienting" describes the tension between the desire to maintain normality and the challenge of integrating the symptoms as perceptible signs of their illness into their own self-image. The results illustrate the central role of physical symptoms in the everyday lives of many patients with PBC, the complexity of the experience of symptoms and the challenges of dealing with these symptoms. They also emphasize the supportive and mediating function of healthcare practitioners in individual symptom management.

Guidance for structural integrity assessment of smooth pipe elbows containing defects using R6

Recently, guidance for fracture assessment of defective elbows using the R6 failure assessment diagram (FAD) method has been included in R6 Revision 4 Amendment 13 (2023). This paper provides an overview of the new guidance and supporting validation. The guidance is validated using 75 cases of 3-D finite element (FE) elastic-plastic J results of smooth pipe elbows of various geometries with axial/circumferential internal/external semi-elliptical/extended/fully-circumferential surface cracks under internal pressure, in-plane/out-of-plane bending moment, torsion and various load combinations, by comparing the FE-based Option 3 failure assessment curves (FAC) with the R6 Option 2 FAC. The results show that, for 74 out of 75 cases, the FE-based Option 3 data points are above the R6 Option 2 FAC with reasonable conservatism when the guidance for evaluating the elbow stress intensity factor and limit load is followed. In other words, following the new guidance can lead to reasonably conservative assessment results.

Design and development of vacuum system for electron beam powder bed fusion process

A vacuum system is one of the crucial components of the Electron Beam-Powder Bed Fusion Process (EB-PBF). It ensures the generation of a high-intensity electron beam. This paper presents a vacuum system design for the EB-PBF process. The work chamber and EB gun chamber have been designed and verified using ANSYS workbench for stress, strain, and deformation limits and found satisfactory. The analytical calculations have been performed for all the pumps, considering the various gas loads during the process. After the design, the vacuum system has been fabricated and tested for its stability, ultimate vacuum, and leak rate. The helium leak test results show that all the joints have a leak rate better than 1 × 10−8 mbar l/s. Further, the analytical results of each pump have been compared with experimental results and found almost in line with the theoretical results. The results show that a pressure lower than 1 × 10−5 mbar and 5 × 10−6 mbar can be achieved in the work chamber and EB gun chamber in less than 23 min and 10 min respectively. The chamber was evacuated multiple times and found that the chamber could still hold pressure better than 1 × 10−2 mbar after 48 h.

Perspectives for using serratiopeptidase in systemic enzyme therapy for low-intensity chronic inflammation and pain syndromes: from mechanisms of action to practical implementation (literature review)

Background. Recent experimental and clinical stu­dies have confirmed the effectiveness and safety of serratiopeptidase (SRP) as a powerful anti-inflammatory agent, highlighting its potential benefits across various fields of medicine. The ­purpose was to analyze current literature on the mechanisms of action of SRP as a means of systemic enzyme therapy for low-intensity chronic inflammation and pain syndromes, its clinical applications, and prospects for implementation in general medical practice. ­Materials and methods. To identify relevant literature sources, a comprehensive search was conducted in electronic databases, inclu­ding PubMed, Scopus, Web of Science, and the Cochrane Library. ­Results. According to modern literature data, SRP demonstrates quite powerful anti-inflammatory, analgesic, reparative, fibrinoly­tic, and mucolytic properties, and exhibits a certain antimicrobial activity, especially against biofilm-forming bacteria. The combination of this enzyme with traditional antibiotics provides a more effective treatment of infectious processes. SRP has significant potential in the treatment of conditions and diseases associated with the development of low-intensity chronic inflammation and pain syndromes (especially in comorbid ones) due to its anti-inflammatory, anti-edematous, antithrombotic, and analgesic properties associated with the inhibition of cyclooxygenase 1 and 2, 5-lipoxygenase activity, myeloperoxidase and elastase, suppression of the formation and/or release of bradykinin, biogenic amines, pro-inflammatory cytokines, cell adhesion molecules, cleavage of bradykinin-related peptides, limitation of oxidative-nitrosative stress. The effectiveness of the enzyme notably increases when it is combined with some prebiotics and/or probiotics. Conclusions. The development of new dosage forms of SRP, along with further preclinical and clinical trials, could lead to new strategies for the prevention and treatment of inflamatory diseases.

Analysis of Wind Turbine Towers subjected to Blast Loading

The research work in this paper mainly focuses on the dynamic simulation of a High strength steel wind turbine tower subjected to blast loading in increasing order, conducted by using ABAQUS. The analysis of the wind turbine tower evaluates the response and performance of the structure when subjected to blast load levels in the form of TNT charges ranging from 500 kgs to 2000 kgs applied at the base and at the top of the tower respectively. The study focuses mainly on the key parameters such as Von Mises stress, displacement, and reaction forces in which the results indicate that the High strength steel wind turbine tower passes the Von Mises stress limit up to a blast load of 1500 kgs at the base but fails under higher loads of 1750 kgs and 2000 kgs respectively where stresses of the wind turbine tower exceeds the tensile strength of the material. Moreover, at the top of the tower, the structure fails at a low charge of 500 kgs demonstrating its vulnerability to the blast load. Displacement of the wind turbine tower surpasses its recommended limit for TNT charges beyond 1500 kgs at the base with a maximum displacement of 129.49 mm at 2000 kgs. The maximum reaction force recorded was 2890 KN at a TNT charge of 1750 kgs. The study concludes by revealing the findings of the limitations of High-strength steel wind turbine towers under extreme blast conditions and throws spotlight on the need for structural reinforcement or alternative designs and hybrid towers for the wind turbine for improved performance and use in high-risk environmental zones.

Fatigue-thermal damage characteristics of red sandstone with a hole under high-temperature cyclic loading coupling and microstructural degradation

In underground coal gasification (UCG) projects, deeply buried subterranean projects are significantly influenced by high temperatures, alongside disruptive loads such as excavation, blasting, and drilling. Therefore, it is essential to study the fatigue behaviors of rocks under the coupled effects of thermal elevation and cyclic loads. This study performed uniaxial compression and cyclic loading-unloading tests on red sandstone specimens with cavities. The high-temperature fatigue behaviors of specimens were explored from various aspects, encompassing stress, deformation, energy, damage, and the microstructural variations of the specimens after high-temperature procedures were assessed by utilizing scanning electron microscopy (SEM). At temperatures below 600 °C, SEM images indicate a contraction of microcracks in the specimens, whereas temperatures above this threshold lead to their expansion. Notably, the total, elastic, and dissipated energy density of the specimens exhibit a curve of second degree with the upper limit stress. Additionally, elastic and dissipated energy densities linearly correlate with input energy density. Furthermore, the coupled damage and axial strain of the specimens positively correlate with the temperature. The damage mode of thermal fatigue is attributed to the accumulation and penetration of transgranular fractures within the red sandstone.

Thermodynamic behavior of high-power inductively coupled plasma quartz tube wall

High-power inductively coupled plasmas are commonly used in planetary entry simulations and are increasingly being used in electric propulsion applications. However, during the operation of the system, the walls of the quartz tube will crack and melt. Its thermodynamic behavior is key to ensuring the safe and reliable operation of the system, which is directly related to the distribution of thermal energy within the discharge volume. In this paper, the temperature and stress distribution of the quartz tube wall of an inductively coupled plasma generator at 27 kW–85 kW are described. A numerical simulation model was established to depict the interaction between the plasma and the quartz tube wall. In the field of experimental research, the temperature of the outer wall of the quartz tube was obtained by using a thermal imager, and a non-uniform B-spline difference method was proposed to fit the outer wall temperature of the quartz tube to eliminate the influence of the induction coil. It is found that the numerical simulation and experimental results show that the temperature is stable region, temperature rise area, temperature drop zone, and the high temperature region of the quartz tube wall is located in the coil area, and the high stress area is also located in this region. On this basis, the outer wall temperature and thermal stress of quartz tubes under different heat fluxes are studied. When the heat flux exceeds 18.6 kW/m2, the stresses in the coil area and downstream of the coil exceed the limit stress. Mechanical failures may occur in areas where the ultimate stresses are exceeded, and these results can provide theoretical data for the optimal design of high-power inductively coupled plasma generators.

Influence of light intensity on the responses of seedlings of neotropical tree species to nitrogen source

Light intensity plays a crucial role in N uptake and assimilation in plants, but its interaction with different N sources is overlooked. Considering the high energy required for N assimilation, it is hypothesised that low light is critical for the seedling development with both N sources, but with increased light intensity, growing with nitrate (NO3-) becomes favourable in relation to ammonium (NH4+). Seedlings of Cecropia pachystachya (pioneer), Guarea kunthiana (shade-tolerant, understory) and Cariniana estrellensis (shade-tolerant, canopy) were grown in hydroponic medium with NO3- or NH4+ as the sole N source and subjected to low (LL) or high light (HL) for 60 days. All three species showed a decrease in growth when cultivated with NH4+, compared to NO3-, under HL, but not under LL. The decrease in biomass reached 54% in C. pachystachya, 36% in G. kunthiana and 26% in C. estrellensis. Growth reduction was associated with stomatal limitation of photosynthesis and reduced leaf area in C. pachystachya, and with non-stomatal limitation of photosynthesis and oxidative stress in G. kunthiana. Cation uptake was negatively affected by NH4+ in all species. Cariniana estrellensis showed no photosynthetic limitation and showed a higher tolerance to NH4+ under HL in terms of nutrient content. In conclusion, neither N source significantly favors seedling development under LL, while NH4+ is considerably more unfavorable for seedling development than NO3- under HL.

Enumeration and gentle sorting of immune cells on chip, key to next generation advanced therapies in outpatient setting

BackgroundA thorough understanding of immune-oncology and molecular medicine has been vital in the development of cell therapeutics. At the basis of this translational research and its future implementation into a medicinal product, lies the availability of pure and viable cell populations. Currently, FACS and magnetic bead isolation are successfully used but suffer to fulfill all requirements. FACS is costly and difficult to upscale due to the limitation of shear stress, especially fragile, cells can handle. Therefore, magnetic bead isolation is often used as it is gentler, but it lacks the multiparametric aspect to isolate more complex cellular profiles. AimsWe aim to develop a versatile technology able of multi marker detection and isolation of complex cell types with high purity, viability and throughput. MethodsWe have developed a gentle sorting mechanism based on a jet flow created by micro vapor bubbles, enabling a closed microfluidic cell isolation platform capable of multiparametric sorting with high viability, purity and throughput. In this work we compared the purity, recovery and viability of sorted CD4+ CD14- cells to magnetic isolation, most often used for other cell manufacturing approaches. Futhermore, we cultured the sorted cells of both isolation strategies and compared their growth curve and expression of activation-induced IL2 and IFN-γ. ResultsWe demonstrate that this tool can achieve a pure population of CD4+ CD14- cells with high viability after sorting without compromising the recovery. On top of the viability also the growth and activation potential of sorted cells is unhampered by comparison to the benchmark gentle magnetic isolation. ConclusionsOur technology allows for the development of a compact system which sets it apart from other efforts intended to create automated cell therapeutic solutions.

Energy-Preserving Perturbation Method for Thermally Induced Dynamics in Aerospace Tensegrity Structures

Tensegrity structures are emerging as pivotal components in the assembly of ultralarge modular spacecraft in orbit, primarily due to their exceptional volume-to-mass ratio and robust controllability. During on-orbit operations, given the low damping and high flexibility of tensegrity, its vibration-induced deformations affect the magnitude of the heat flux, presenting a typical force–shape coupling problem. This paper introduces an energy-preserving matrix perturbation solution designed to efficiently and accurately address the thermally induced vibration challenges in tensegrity. This method effectively mitigates the energy dissipation and numerical instability issues. Furthermore, the analysis incorporates the impact of the axial component of heat flux on structural vibration, uncovering the influence mechanism of this often-overlooked slow variable on the dynamic behavior of tensegrity. The proposed method demonstrates a deviation of less than 1% between the thermal response and the results obtained from finite element analysis, while achieving a 70% reduction in computation time. The varying axial thermal load leads to a rapid decrease in system frequency, resulting in divergent thermal vibrations. Additionally, the significant dynamic stress can potentially surpass the structural stress limits. These findings underscore the critical importance of considering such effects in the design and calculation of tensegrity structures for aerospace applications.

INFLUENCE OF SEA BUCKTHORN EXTRACT POWDER ON PHYSICOCHEMICAL, STRUCTURAL AND MECHANICAL PROPERTIES OF MINCED MEAT MINCE

The article examines the effect of sea buckthorn extract powder on the physico-chemical properties of minced meat. One of the key aspects of the study is the active acidity of the minced meat, which directly depends on the concentration of the added sea buckthorn powder. According to the results, an increase in the content of sea buckthorn in minced meat leads to a decrease in the pH value, which can help reduce the shelf life of the product. The optimal dosage was determined by 4-5% of sea buckthorn powder, which provides a balance between improving properties and maintaining organoleptic characteristics.The effect of the powder on the moisture-retaining ability of minced meat was also investigated. It has been shown that an increase in the amount of sea buckthorn powder initially improves moisture binding, but when a certain threshold is exceeded (more than 10%), this property begins to decrease. Thus, it is important to consider the dosage in order not to worsen the quality of the final product.Another important parameter is the shear stress limit. Studies have shown that at the initial stage of adding sea buckthorn, this indicator remains stable, but with prolonged stirring it begins to decrease, which is associated with a change in the structure of the minced meat and a decrease in its plasticity. The optimal mixing time is 3-5 minutes, which ensures the achievement of the required consistency and prevents the destruction of the structural and mechanical characteristics of the product.Thus, the addition of sea buckthorn powder to minced meat has a significant effect on acidity, moisture content and mechanical properties, while it is important to accurately observe the concentration and technological modes to achieve optimal product quality.

Plastic Limit Pressure and Stress Intensity Factor for Cracked Elbow Containing Axial Semi-Elliptical Part-Through Crack

The aim of this study is to provide a solution for the plastic limit pressure and stress intensity factor of the elbows containing a part-through axial semi-elliptical crack by considering various crack sizes. The supporting system and loading conditions of the pipeline are described. The critical part of the observed pipeline was isolated for analysis and subjected to various sizes of semi-elliptical cracks. By performing numerical analysis, results were obtained for crack dimension ratios of c/a, and depth/thickness ratios of a/t. The obtained results include plastic limit pressure and stress intensity factor. The results were analyzed with a symbolic regression algorithm, and closed-form solutions for the limit pressure and stress intensity factor were proposed. To validate pipeline integrity, the Structural Integrity Assessment Procedure (SINTAP) was applied, and the FAD (Failure Assessment Diagram) was generated for cracks below the FAD function. The failure pressure was calculated by determining the points where the loading paths intersect the FAD function.

Effects of simulated precipitation changes on soil respiration:Progress and prospects.

Soil respiration, the main pathway for transferring terrestrial carbon pool to atmospheric carbon pool, is profoundly affected by the intensification in global precipitation variability in the context of climate change. Nowadays, variable controlling methods and field manipulation experiments are two main methods widely used to investigate the effects of simulated precipitation changes on soil respiration. Yet, due to the heterogeneity of soil properties, vegetation types, and the magnitude of precipitation change, there is substantial inconsistency in the conclusions of simulated precipitation change effects on soil respiration. Here, we analyzed data from domestic and foreign literature, and examined the effects of simulated precipitation change on soil respiration. Firstly, we described the response pattern of soil respiration to soil moisture fluctuation and pointed out that the magnitude and direction of the response of soil respiration to simulated precipitation change depended on whether soil moisture was optimally conditioned at different precipitation treatments. Second, we summarized the response patterns of soil respiration to symmetric increase and decrease in precipitation, which mainly included symmetric and asymmetric responses (positive and negative asymmetric). Meanwhile, the adaptation of plants and soil microorganisms to drought stress and soil oxygen limitation, as well as the reduction of organic substrates, were the main mechanisms accounting for the shifts of soil respiration response patterns to simulated precipitation change from symmetric to asymmetric responses. Third, we identified a significant effect of ambient climate on soil respiration in response to precipitation treatments as increasing duration of the experimental treatments. In addition, cumulative or buffering effects of ambient climatic conditions on precipitation treatment could affect the sensitivity of soil respiration along precipitation gradient by altering hydrothermal conditions. Finally, to accurately assess the implications of precipitation changes on soil carbon balance processes, we proposed three aspects of future precipitation effects on soil respiration for attention: 1) focusing on the phenomenon of "threshold effects" in the asymmetric response of soil respiration along precipitation gradients; 2) distinguishing the intrinsic mechanisms of autotrophic and heterotrophic components in soil respiration in response to precipitation changes; and 3) focusing on the impacts of intensified precipitation variability on soil respiration in the context of future climate extremes. In conclusion, with the intensified variability in global precipitation patterns, clarifying the response mechanism of soil respiration to precipitation changes is of great significance for accurately predicting and evaluating the alterations of soil carbon cycle processes and carbon balance in the context of global changes.

Micro‐Mechanical Analysis for Residual Stresses and Shakedown of Cohesionless‐Frictional Particulate Materials Under Moving Surface Loads

AbstractResidual stresses and shakedown have been successfully presented by two‐dimensional numerical experiments based on the discrete element method (DEM), wherein a cohesionless‐frictional material under moving surface loads was replicated through irregular‐shaped particles. With surface loads below the shakedown limit, both permanent deformations and residual stresses cease to accumulate and the numerical structure shakes down after a number of load passes. Corresponding micro‐mechanical analyses indicate that strong forces and normal forces make a dominant contribution to residual stresses. Besides, averaged magnitudes of interparticle forces and corresponding total contact numbers initially change with load passes, and their final variation trends will differ as the structure shakes down or not. Furthermore, polar distributions of interparticle forces and contacts have been presented, and variations of their preferential orientations were emphasised. Lastly, the fabric tensor and anisotropy of resultant forces were studied, presenting the anisotropy weakening of macro‐stress fields, induced by developments of residual stresses.

Investigation of local mechanical behavior during the shear process of rough rock joints using DEM

Rough joints are prevalent in natural rock masses, and their shear mechanical properties are crucial for ensuring the safety and stability of these masses. Existing studies often neglect the contribution of various joint asperities to shear stress resistance. This study addresses this gap by eluci-dating the local shear mechanisms of different asperities in rough joints throughout the shear process. This was achieved through a combination of quantitative and qualitative analyses using the Discrete Element Method (DEM). Initially, Barton's ten standard roughness joint profiles were dig-itized, and rough joints were modeled using the Modified Smooth Joint Model (MSJM). Direct shear tests on joint specimens under constant nor-mal stress were performed using servo-controlled methods. Subsequently, the shear stress behavior was analyzed in relation to the test results. The failure modes of the joint specimens were examined in detail using crack tracking and force chain analysis. The study also explored the relation-ship between the number of cracks and shear stress. Additionally, variations in average stress across ten different segments of joints during shear were monitored using the measuring circle function. The shear resistance contributions of local joint segments were quantitatively assessed using three stress indices: maximum stress, upper limit of maximum stress, and the distribution range of maximum stress. The Joint Roughness Coeffi-cient (JRC) of joints was found to correlate well with these indices. Overall, the progressive failure of local joint segments was analyzed both qual-itatively and quantitatively. The study confirmed that the local shear mechanisms of different joint segments during the shear process are distinct.

Research on the Vibration Fatigue Characteristics of Ancient Building Wood Materials

In this study, we selected ancient building timber as the research object. A series of static load tests were conducted to analyze the different performances of timber under tensile and compressive loads. After that, vibration fatigue tests on ancient timber samples were carried out under different upper limit stress ratios. Finally, a dynamic constitutive model of ancient timber was established based on the Ramberg–Osgood model. The static load test results show that the tensile strength was approximately 80% of the compressive strength. Meanwhile, the samples that failed under compressive pressure had obvious residual strength, and their failure strains were also much larger than those under tensile stress. In the vibration fatigue tests, the stress–strain curves were analyzed and the results showed that the curves displayed a trend moving to sparse from dense during the loading process. Meanwhile, the curves moved right with the increase in the upper limit stress ratios. The relationship between axial strain and the number of cycles appeared to be characterized by a three-stage form, i.e., damage occurrence, damage expansion, and damage penetration, and this relationship was formulated by a nonlinear function model. Finally, a dynamic constitutive model with high accuracy in describing the vibration fatigue characteristics of ancient timber was established by converting constant parameters to the variable parameters of the Ramberg–Osgood model.