Elastic Coefficients Research Articles

Effect of repeated temperature cycles on thermal expansion coefficient and elastic moduli of high porosity chalks

This paper describes the impact of repeated temperature cycles on elastic mechanical parameters of chalk. The experiments were performed at both hydrostatic and deviatoric stress geometries at an axial stress 70% of stress at failure. Thus, shear failure tests are reported. Geomechanical stability during cooling was evaluated at constant axial stress, while the side stress was reduced to counteract thermal contraction at uniaxial strain conditions. The study was motivated by the fact that chalk reservoirs are exposed to cooling due to intermittent water injection during hydrocarbon extraction and are future prospects for CO2 storage. Detrimental effects on rock-mechanical stiffness and strengths were anticipated because temperature cycles are known to degrade calcite cemented sedimentary rocks and marble. This study documents how temperature cycles influence elasticity and thermal expansion coefficient of two chalks with different degree of calcite cementation. The more indurated and less porous Kansas chalk, and the less indurated and more porous Belgian Mons chalk.Following temperature cycling, elastic bulk modulus measured under hydrostatic conditions decreased for the softer Mons chalk, while no significant effect was found for the stiffer Kansas chalk. For both chalks, Young´s modulus measured under deviatoric stress, showed no effect of temperature cycling. At hydrostatic stresses, the thermal expansion coefficient of the Kansas chalk was found to decrease with increasing number of temperature cycles, while a less clear, but similar trend was seen for the Mons chalk samples. The thermal-elastic coupling coefficient, needed to evaluate effective stresses during cooling, was measured before and after the repeated temperature changes.

Synthesis of lignin-based elastomers via ARGET ATRP: Exceptional mechanical strength, adhesion, and self-repair properties.

In this study, ARGET ATRP method was employed to graft two functional monomers from lignin, resulting in the synthesis of a series of Lignin-graft-poly(lauryl methacrylate-co-cyclohexyl methacrylate) (Lignin-g-P(LMA-co-CMA)) copolymers with varying feed ratios and lignin content. The results demonstrate that by varying the feed ratios of the two monomers, the glass transition temperature of lignin-based elastomers can be finely tuned. Importantly, the introduction of lignin and CMA imparts outstanding mechanical properties to the lignin-based elastomers, with a maximum tensile strength reaching 20.13 MPa. The elastic recovery rate of the lignin-based elastomers was exceptional, with the elastic recovery coefficient (ER) of Lignin0.52-PLMA500 exceeding 90 %. Adhesion tests on various substrates revealed the remarkable adhesion properties of these copolymers. In particular, Lignin0.52-PLMA500 exhibited strong adhesion on both iron plate and glass substrate, with adhesion strengths of 2.23 MPa and 2.33 MPa, respectively. Notably, Lignin0.52-PLMA500 demonstrated significant self-healing ability after damage. Furthermore, the lignin-based elastomer exhibited exceptional ultraviolet absorption performance. In conclusion, the incorporation of lignin opens up a novel pathway for the development of high-strength and tough lignin-based elastomers. However，more effort still needs to be paid for increasing the adhesive properties aiming to explore more potential application field.

Yielding onset in FGM thick-walled spherical shells under thermo-mechanical loading

Based on von Mises yield criterion, a thermoelasto-plastic analysis of a thick-walled spherical shell composed of functionally graded material (FGM) subjected to internal pressure and thermal gradient is conducted in order to accurately predict the onset radius of yielding within the vessel wall. The modulus of elasticity, thermal conductivity and thermal expansion coefficients, and yield stress of FGM are assumed to follow power-law functions in radius according to Erdogan’s model. The equilibrium differential equation of the shell under thermo-mechanical loading in steady-state conduction heat transfer are derived analytically and then solved to determine through-thickness variations of the radial and circumferential stresses and radial displacement in elastic and perfectly plastic zones in the vessel wall. The presented approach leads to the definition of new formulation to predict the onset radius of yielding. Moreover, a neural network (NN) solution to reliable quantify the influence of all uncertain input parameters with respect to uncertain output parameter is utilized. The numerical results showed that for various FGM parameters and specific thermal gradient, the plastic zone can commence from inside radius, outside radius, simultaneously in both radii, or may be launched in the intermediate radius of the spherical shell wall.

Investigating the Effects of Transcutaneous Electrical Nerve Stimulation on Lumbar Fascia Tissue and Lumbar Curvature in Healthy People

Introduction: Transcutaneous electrical nerve stimulation (TENS) is commonly used for pain management. Recent studies have shown that TENS can improve the condition of low back pain by influencing the elastic coefficient of the lumbar fascia and the balance status; however, the effect of TENS on the lumbar fascia of healthy people has not been investigated. Accordingly, this study examines the effect of TENS on the lumbar fascia of healthy people. Materials and Methods: A total of 60 healthy participants in two groups, underwent 10 sessions of conventional TENS intervention. The first group (intervention group) received TENS with an intensity at the tolerance level, and the second group (control group) received sham TENS. Ultrasonography and a spinal mouse device were assessed lumbar fascia thickness and lumbar curvature before and after the TENS. Results: Significant changes were observed after TENS in the intervention group in reducing the lumbar fascia thickness (P=0.006) and increasing the lumbar curvature (P=0.000). Between- group changes after the intervention sessions indicated a significant difference between the lumbar fascia thickness and curvature (P≤0.003). Conclusion: TENS in healthy people can lead to a decrease in the thickness of the lumbar fascia and improve lumbar curvature. Also, a strong correlation was found between lumbar fascia thickness reduction and increased lumbar curvature.

Quantification of streamflow response to climate change and human activities within upstream mountainous areas of the Daqing River Basin, Northern China

The Daqinghe River Basin is located in the North China Plain. In recent years, however, climate warming, drying, and intense human activities have led to declining ecosystem functions and shrinking wetlands in the region. Understanding streamflow changes in the upstream mountainous areas of the Daqinghe River Basin in this changing environment and identifying the driving factors can provide a scientific basis for water resources management and optimization in these areas. This study focuses on the Beihedian River watershed, the Xidayang Reservoir watershed, and the Wangkuai Reservoir watershed in the upstream mountainous areas of the Daqinghe River. It is based on hydro-meteorological data collected between 1963 and 2019. The methods used in the study include the linear tendency estimation method, the non-parametric Mann-Kendall trend test, the elasticity coefficient method, and hydrological simulation methods. The results of this study suggest that the streamflow, precipitation, and potential evapotranspiration (PET) in the three watersheds showed an overall decreasing trend. The minimum precipitation decrease rate ranged from −1.09 to −0.55 mm/a, and the minimum streamflow decreasing rate at the Beihedian Hydrological Station was −1.32 mm/a, with a minimum range of 0–176.03 mm. Change-point analysis revealed that the streamflow in the Beihedian River and Xidayang Reservoir watersheds experienced a significant change point around 1999, with a significant level of α=0.05. As for the Wangkuai Reservoir watershed, a significant change point was observed around 1980, which is likely attributable to land system reforms and protective forest projects. The attribution analysis which combined both climate change and human activities using the elasticity coefficient method and hydrological simulation methods indicated that climate change contributed an average of 32.93%, 34.50%, and 35.12% to the reduction in streamflow in the three watersheds, respectively. Human activities accounted for an average contribution of 67.07%, 65.50%, and 64.88%, respectively. Water conservancy projects, afforestation, and other human activities were identified as the primary factors contributing to streamflow decreases.

Self-sustained chaotic movement of electrothermal responsive liquid crystal elastomer pendulum

Self-sustained movement has the ability to absorb energy from the external environment to maintain its own movement. In the present work, a self-sustained chaotic simple pendulum system featuring an electrothermal responsive liquid crystal elastomers fiber and a mass ball is proposed and examined. The power-on state is achieved in the system through the infusion of liquid metal into this fiber. Which enables the fiber to shrink, feeding energy into the system to compensate for the energy dissipation resulting from damping, thus allowing the system to maintain its self-sustained movement. On the basis of the existing dynamic liquid crystal elastomer model, the dynamic governing equations are established, and the movement behavior of the system under electrothermal stimulation is theoretically explored. Numerical findings suggest that the simple pendulum system presents three different movement patterns, namely stationary pattern, self-sustained oscillatory pattern, and self-sustained chaotic pattern. Moreover, five system parameters of elastic coefficient, viscosity coefficient, gravitational acceleration, shrinkage coefficient and electrothermal strength are examined. The present work can contribute to a better understanding of self-sustained chaotic systems driven by electrothermal responsive materials and offer guidance for further exploration of applications such as chaos machine, and mind-brain chaos analysis.

Analysis of the Impacts of Coal Mining on Baseflow Changes Under the Budyko Framework: A Case Study of Northern Shaanxi, China

Coal mining alters the regional and local hydrogeological conditions and subsurface parameters, significantly impacting the hydrological cycle. Baseflow is particularly sensitive to changes in subsurface parameters and hydrogeological conditions. Therefore, studying the impact of coal mining on baseflow is crucial for understanding its effects on the water cycle. In this paper, 9 segmentation methods are used to separate the baseflow, after the applicability analysis, the Chapman-Maxwell and Boughton-Chapman separation methods were used. The Mann-Kendall and Pettitt tests are employed to determine the mutation years of baseflow. Finally, within the Budyko framework, the elasticity coefficient is calculated to estimate the changes in baseflow attributed to variations in precipitation, potential evapotranspiration, and underlying surface index. The results indicate that: (1) Based on the comparison of results and error analysis, we conclude that the Chapman-Maxwell separation method and the Boughton-Chapman separation method are the most suitable for the typical basins in the Shaanxi mining area. (2) During the study period, baseflow experienced a mutation in the late 1990s and showed an overall declining trend. (3) There is spatial heterogeneity in the influence of coal mining activities on baseflow, which has a negative impact. The change of base flow after mutation is -2.86×108 m3.

Technical and Economic Efficiency of Production Factors in Javanese Tobacco Farming: A Case Study of Belun Village, East Java

This study analyzes the technical and economic efficiency of production factors in tobacco farming in Belun Village, Temayang Subdistrict, Bojonegoro District, East Java. Using stochastic frontier software 4.1, the analysis was conducted with a sample of 87 Javanese tobacco farmers. The production inputs evaluated include land area, seeds, urea fertilizer, NPK fertilizer, NPK Phonska Plus fertilizer, labor, pesticides, and production output. The results indicate that the gamma elasticity coefficient for technical efficiency is 0.949, with all variables being statistically significant at the 1% level (t-table 2.64), except for pesticide input, which is significant at the 5% level (t-table 1.99). In the economic efficiency analysis, seedlings were identified as the inefficient input with an efficiency estimate (EE) of > 1 (52.4), while other inputs showed EE < 1. The study concludes that 94.9% of the inefficiency stems from production factors, while 5.1% is attributed to external factors. Moreover, the inputs used in Javanese tobacco farming are neither technically nor economically efficient. To achieve full technical efficiency, farmers should reduce inputs such as land area, NPK fertilizer, and NPK Phonska Plus fertilizer, while increasing the use of seeds, pesticides, urea fertilizer, and labor.

Giant piezoelectricity in antiferromagnetic CrS2 and CrSe2 monolayers

Abstract Two-dimensional (2D) materials, particularly transition metal dichalcogenides (TMDs), have garnered significant attention in the nanoscale piezoelectric field due to their high crystallinity and ability to withstand large strains. Through density-functional theory calculations, we have discovered that monolayer H-phase CrS2 and CrSe2 exhibit antiferromagnetic semiconducting properties, in contrast to the previously held belief that they were nonmagnetic (NM) semiconductors. While the piezoelectric coefficients of NM CrS2 and CrSe2 are comparable to those of MoS2, their antiferromagnetic ground states demonstrate significantly enhanced piezoelectric coefficients ( d 11 ) of 27.66 pm V−1 and 52.36 pm V−1, respectively. These values exceed that of MoS2 by an order of magnitude, marking the highest recorded for TMD materials and the highest in 2D magnetic materials to date. The greatly enhanced piezoelectric responses in the antiferromagnetic states of CrS2 and CrSe2 compared to their NM states arise from three primary factors. Firstly, the displacement of the Wannier center under strain is more pronounced in the antiferromagnetic state, leading to a greater change in dipole moment (enhanced clamped-ion contribution). Secondly, there is a heightened polarization change due to internal atomic distortions (internal-strain term) in response to macroscopic strain in the antiferromagnetic state. Thirdly, the material undergoes a softening of the elastic coefficient in its antiferromagnetic state. These findings open new avenues for designing high-performance piezoelectric and magnetic multifunctional materials.

Runoff Change Characteristics and Response to Climate Variability and Human Activities Under a Typical Basin of Natural Tropical Rainforest Converted to Monoculture Rubber Plantations

Climate variability and human activities are major influences on the hydrological cycle. However, the driving characteristics of hydrological cycle changes and the potential impact on runoff in areas where natural forests have been converted to rubber plantations on a long-term scale remain unclear. Based on this, the Mann–Kendall (MK) and Pettitt breakpoint tests and the Double Mass Curve method were employed to identify the variation characteristics and breakpoints of precipitation (P), potential evapotranspiration (ET0), and runoff depth (R) in the Wanquan River Basin (WQRB) during the 1970–2016 period. The changes in runoff attributed to P, ET0, and the catchment characteristics parameter (n) were quantified using the elastic coefficient method based on the Budyko hypothesis. The results revealed that the P and R in the WQRB exhibited statistically insignificant decreasing trends, while ET0 displayed a significant increasing trend (p < 0.05). The breakpoint of runoff changes in the Jiabao and the Jiaji stations occurred in 1991 and 1983, respectively. The runoff changes show a negative correlation with both the n and ET0, while exhibiting a positive correlation with P. Moreover, it is observed that P and ET0 display higher sensitivity towards runoff changes compared to n. The decomposition analysis reveals that in the Dingan River Basin (DARB), human activities account for 53.54% of the runoff changes, while climate variability contributes to 46.46%. In the Main Wanquan River Basin (MWQRB), human activities contribute to 46.11%, whereas climate variability accounts for 53.89%. The research findings suggest that runoff is directly reduced by climate variability (due to decreased P and increased ET0), while human activities indirectly contribute to changes in runoff through n, exacerbating its effects. Rubber forest stands as the prevailing artificial vegetation community within the WQRB. The transformation of natural forests into rubber plantations constitutes the primary catalyst for the alteration of n in the WQRB. The research findings provide important reference for quantifying the driving force of hydrological changes caused by deforestation, which is of great significance for sustainable management of forests and water resources.

Fabrication and characterization of new hot extruded ZK60/CNTs+AgNPs nanocomposites for biomedical applications

Magnesium (Mg), with properties such as biodegradability and having a density and elasticity coefficient close to the bones of the body, has attracted a lot of attention as a serious option for orthopedic applications. However, the low compressive strength of Mg compared to the human bone and its weak antibacterial function limit its applications as a substitute for temporary implants to be used under load-bearing conditions. The aim of this paper is to evaluate the synergistic effect of CNTs + AgNPs nanofillers on the in vitro degradation, mechanical and antibacterial behavior of new ZK60/xCNTs + xAgNPs(x: 0, 0.25, 0.5, 1) composites made using semi powder metallurgy, followed by hot extrusion method. The ZK60/0.5CNTs+0.5 AgNPs (CA2) composite boasts a higher ultimate compressive strength (UCS) of 371 ± 15 MPa compared to 297 ± 6 MPa for ZK60 based alloys. The CA2 composite also exhibits a grain size of 9.8 μm and a microhardness of 81 HV.Also, the antibacterial activity assessment demonstrated that adding CNTs + AgNPs hybrid nanofillers to the Mg matrix could notably prevent growing and penetration of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), which indicates the synergy between antibacterial mechanisms of CNTs and AgNPs. Cytotoxicity studies confirm that composites with low amounts of CNTs + AgNPs did not show cytotoxic behavior against MG63 cells, although higher loading of CNTs + AgNPs caused toxicity. Also, the examination of osteogenic activity is consistent with other results. In general, according to the results, the potential application of CA2 composite for under load bearing implant application and bone infection treatment is proved.

A “WEST” Theory in the East: Decoupling and synergistic evolution of water utilization, economy, and society in China

AbstractTo attain a thorough examination of the dynamic interaction mechanism between China's utilization of water resources and its economic and social development, this paper innovatively introduces a Western theoretical framework within an Eastern context. The aim is to quantify the process of decoupling and synergistic evolution from 2006 to 2020. Decoupling signifies achieving economic growth while reducing resource use or mitigating environmental impacts, whereas synergy denotes enhancing economic efficiency while contributing to environmental protection. This paper employs the Tapio elastic coefficient method to construct a decoupling model. A collaborative model, based on the entropy weight Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) and weighted average methods, also assesses the organization and coordination of subsystems within the complex water‐economic‐social system. The findings reveal a strong decoupling between China's water resource management and economic and social systems, as indicated by a consistently negative decoupling index. Similarly, the economic system exhibits a degree of inefficiency influenced by factors like economic cyclicality and resource allocation. In contrast, the social system experienced a decline, particularly during the pandemic (2019–2020), leading to a social instability. This study provides valuable policy formulation and sustainable development insights, contributing to a comprehensive understanding of the intricate dynamics between water utilization, economy, and society.

Piezoelectricity and flexoelectricity in biological cells: the role of cell structure and organelles.

Living tissues experience various external forces on cells, influencing their behaviour, physiology, shape, gene expression, and destiny through interactions with their environment. Despite much research done in this area, challenges remain in our better understanding of the behaviour of the cell in response to external stimuli, including the arrangement, quantity, and shape of organelles within the cell. This study explores the electromechanical behaviour of biological cells, including organelles like microtubules, mitochondria, nuclei, and cell membranes. A two-dimensional bio-electromechanical model for two distinct cell structures has been developed to analyze the behavior of the biological cell to the external electrical and mechanical responses. The piezoelectric and flexoelectric effects have been included via multiphysics coupling for the biological cell. All the governing equations have been discretized and solved by the finite element method. It is found that the longitudinal stress is absent and only the transverse stress plays a crucial role when the mechanical load is imposed on the top side of the cell through compressive displacement. The impact of flexoelectricity is elucidated by introducing a new parameter called the maximum electric potential ratio ( ). It has been found that depends upon the orientation angle and shape of the microtubules. The magnitude of exhibit huge change when we change the shape and orientation of the organelles, which in some cases (boundary condition (BC)-3) can reach to three times of regular shape organelles. Further, the study reveals that the number of microtubules significantly impacts effective elastic and piezoelectric coefficients, affecting cell behavior based on structure, microtubule orientation, and mechanical stress direction. The insight obtained from the current study can assist in advancements in medical therapies such as tissue engineering and regenerative medicine.

Does public pension promote or inhibit enterprise total factor productivity? Evidence from China

The relationship between pension contribution rates and productivity remains a significant topic of discussion. This study utilizes micro-level data to examine the interaction between statutory pension contribution rates, actual contribution rates, and the total factor productivity (TFP) of enterprises. The findings indicate that the reduction in the Basic Old-age Insurance contribution rate resulted in a 0.985 percentage point decline in actual contribution rates and 4.3 percentage point decline in TFP. Pension insurance contribution collection by tax authorities results in the highest collection intensity and lowest elasticity coefficient, while agency collection exhibits greater variability. Additionally, actual pension contribution rates and TFP exhibit an inverted U-shaped relationship. When the public pension contribution rate is either too high or too low, it may hinder improvements in enterprise production efficiency. Instead, there exists an optimal range of contribution rates where public pensions can foster a positive interaction between R&D investment, capital-skill substitution, and employee incentives. State-owned, labor-intensive, and low-wage firms experience sharper productivity declines beyond a lower optimal contribution rate, indicating that these firms reach peak productivity at lower contribution levels.

Modifying Microstructure and Improving Mechanical Properties of New Ti-Al-V Titanium Alloys via Fe Addition.

A comprehensive study was carried out to investigate the effects of Fe addition (0-0.9 wt.%) on the microstructure evolution and mechanical properties of Ti-6Al-4V alloys. The results indicate that Fe addition has a significant refinement effect on the microstructure of titanium alloys; specifically, 0.9 wt.% Fe addition can lead to a 47.37% decrease in the width of lamellar α. The modulus also decreases by 18.89% with the increase in the Fe content, being 91.40 GPa in Ti-6Al-4V-0.9Fe. And the microhardness and wear resistance are improved due to Fe addition. In addition, the constitutive equation of the Fe content and the elastic compliance coefficient were calculated, which can better describe the relationship between Fe addition and the elastic-plastic properties of titanium alloys. The slip systems' activity during the deformation process was also discussed using the Schmid factor. It shows that Fe addition is beneficial for the activity of prismatic and pyramidal slip systems, especially in the {101¯0} <112¯0>, {101¯1} <112¯3>, and {112¯2} <112¯3> slip systems.

Cooperation mode selection strategies in platform ecosystems: analyzing brand value, cross-selling, and platform empowerment

Purpose This paper aims to investigate the vertical cooperative relationship between the core enterprise and the manufacturer within the platform ecosystem, specifically analyzing the optimal decision-making processes of both parties under the original equipment manufacturer (OEM) and original brand manufacturer (OBM) modes. Design/methodology/approach This paper uses game theory to analyze the problem, considering factors such as brand value difference, cross-selling and platform empowerment. It constructs the game models for both OEM and OBM modes and discusses the selection strategies for the cooperation mode. Findings The results indicate that the choice of cooperation mode by the manufacturer and the core enterprise depends on the relative size of their brand values. In cases of inconsistent choices, cooperation can be improved by designing a transfer payment contract. When the brand value is constant, the product price is comprehensively affected by cross-selling revenue, price elasticity coefficient, cost coefficient of sales effort and cost coefficient of platform empowerment. The enterprise reduces the price only when the potential revenue brought by increasing product sales exceeds the marginal profit brought by increasing product pricing; otherwise, it raises the sales price. Originality/value The platform ecosystem is emerging as a future direction for business mode development. However, there is a paucity of research on the cooperation modes between manufacturers and core enterprises within the platform ecosystem.

Effective elasto‐(visco)plastic coefficients of a bi‐phasic composite material with scale‐dependent size effects

We employ the theory of asymptotic homogenization (AH) to study the elasto‐plastic behavior of a composite medium comprising two solid phases, separated by a sharp interface and characterized by mechanical properties, such as elastic coefficients and “initial yield stresses” (i.e., a threshold stress above which remodeling is triggered), that may differ up to several orders of magnitude. We speak of “plastic” behavior because we have in mind a material behavior that, to a certain extent, resembles plasticity, although, for biological systems, it embraces a much wider class of inelastic phenomena. In particular, we are interested in studying the influence of gradient effects in the remodeling variable on the homogenized mechanical properties of the composite. The jump of the mechanical properties from one phase to the other makes the composite highly heterogeneous and calls for the determination of effective properties, that is, properties that are associated with a homogenized “version” of the original composite, and that are obtained through a suitable averaging procedure. The determination of the effective properties results convenient, in particular, when it comes to the multiscale description of inelastic processes, such as remodeling in soft or hard tissues, like bones. To accomplish this task with the aid of AH, we assume that the length scale over which the heterogeneities manifest themselves is several orders of magnitude smaller than the characteristic length scale of the composite as a whole. We identify both a fine‐scale problem and a coarse‐scale problem, each of which characterizes the elasto‐plastic dynamics of the composite at the corresponding scale, and we discuss how they are reciprocally coupled through a transfer of information from one scale to the other. In particular, we highlight how the coarse‐scale plastic distortions influence the fine‐scale problem. Moreover, in the limit of negligible hysteresis effects, we individuate two viscoplastic effective coefficients that encode the information of the two‐scale nature of the composite medium in the upscaled equations. Finally, to deal with a case study tractable semi‐analytically, we consider a multilayered composite material with an initial yield stress that is constant in each phase. Such investigation is meant to contribute to the constitution of a robust framework for devising the effective properties of hierarchical biological media.

Experimental study on axial compressive properties of bamboo scrimber after high temperature

This study examines the uniaxial compressive mechanical properties of after high temperature bamboo scrimber, taking into account the combined effects of temperature, constant temperature duration, and moisture content. A series of 46 uniaxial compression tests were conducted on bamboo scrimber under various conditions to investigate the failure modes after high temperatures. The analysis focuses on the changes in compressive elastic modulus and peak stress of bamboo scrimber parallel and perpendicular to the grain, in relation to temperature, constant temperature duration, and moisture content. The findings reveal that below 180℃, diagonal shear failure and Y-type shear failure are the primary failure modes for specimens parallel to the grain, while diagonal shear failure predominates for specimens perpendicular to the grain. Above 180℃, bond failure and eccentric crushing become the main failure modes for specimens parallel and perpendicular to the grain, respectively. The peak compressive stress decreases significantly beyond 180℃, with a slower decrease observed as moisture content increases. Constant temperature duration has a notable impact on peak stress, with longer durations resulting in lower peak stress at the same temperature. Although temperature has a lesser effect on the elastic modulus compared to peak stress, empirical formulas were derived to establish the relationship between compressive elastic modulus and peak stress reduction coefficient with variations in temperature, constant temperature duration, and moisture content based on the experimental data.

Forced vibrations of the shaft line based on the model of a two-stage rod with an elastic connection of sections

The paper considers a method for solving the problem of dynamics of forced vibrations of a wall line based on a model of an equivalent elastic two-stage rod with a pliable connection of sections. The model is represented by a system of partial differential equations. The solution of the equations is obtained by the Fourier method for eigenfunctions orthogonal with weight. It is established that the presence of an elastic element at the junction of the sections does not affect the orthogonality of the eigenfunctions. The influence of the elastic coupling compliance coefficient on the natural frequency spectrum of the shaft line is estimated. The obtained forms of natural vibrations of an equivalent elastic two-stage rod are consistent in appearance with the corresponding forms known in the literature for a discrete model of a similar torsional circuit. A partial solution of the equations is found for the case of the action of the harmonic load on the engine and the averaged torque on the propeller. As an example, the dynamics of forced vibrations of the shaft line of a barge of the Sosnovka type is studied. The results of calculating the natural frequencies of the considered model are compared with the classical discrete mass method. The analysis of the obtained plots of the twisting angles and torques showed that the angles are satisfactorily approximated by the first proper oscillation shape, and for moments, high shapes must be taken into account. The comparison of the simulation results with the data of the torsiogram obtained under production testing conditions indicates the need for further development of the model. Further improvement of the torsional circuit, as well as a more detailed study of the nature of the operating loads, are considered as promising areas of research.

Analysis of bolt load uniformity in raised flange connection

Aiming at the problem of uneven preload of raised flange, a model considering elastic interaction is established to study the uniformity of bolt load under raised flange connection. Firstly, the elastic interaction coefficient method of bolt flange connection structure is extended to multiple times, and the initial preload of all bolts at each tightening step is determined by analytical model; secondly, a three-dimensional finite element model of bolt flange connection structure is established, and the correctness of the finite element model is verified by comparing with the literature test, and the influence of tightening sequence and tightening steps on bolt preload is explored; finally, the results of raised flange under symmetrical tightening conditions with and without considering elastic interaction are compared and analyzed. The results show that when the tightening method is symmetrical tightening and the tightening steps are three steps, the elastic interaction of each bolt is the smallest, and the final preload uniformity is better; on this basis, the results of the model considering elastic interaction further improve the uniformity of the final preload and are closer to the target preload. The problem of bolt preload dispersion caused by elastic interaction is solved, and the research results can provide guidance for the safety and reliability design of bolt flange connection structure.