Stress-strain Dynamics Research Articles

RESIDUAL - STRESS AND TEMPERATURE FIELDS IN SURFACE TESTING: FINITE-ELEMENT ANALYSIS

Numerous advancements have been made to treat part surfacing, however, the presence of surface imperfections resulting from finishing processes has raised concerns about their potential to serve as stress concentrators. To address this concern, the present study utilized the power of the finite element method and cutting-edge software applications. The main aim of the study is to evaluate the stress-strain condition of material surfaces post-finishing, leveraging the comprehensive capabilities offered by these software systems. A significant component of the investigation centered on the influence of non-stationary temperature fields, as monitored by dynamic thermoelements, on the stress-strain dynamics within material surfaces. Visualization techniques were employed to depict the specified field functions, revealing notable variations in temperature distribution. The findings demonstrated that the standard function identified the highest temperature area within the 3-7-4 node segment, while the alternative function pinpointed it within the 4-node segment, indicated by the red area. These outcomes highlight the valuable role of non-stationary temperature fields in balancing the mechanical and physical aspects of the finishing process. This study contributes significant insights into the post-finishing stress-strain state of material surfaces, emphasizing the potential advantages of using modern software systems for in-depth exploration.

Preface

Abstract The 2023 4th International Conference on Material Chemistry and Composite Materials (MCCM 2023) took place during December 22nd to 24th, 2023 in Sanya, China. MCCM exists as an annual international academic conference which tries to meet the needs for various kinds of material chemistry and composite materials. Bearing the principle of “bringing together global wisdom in scientific innovation to promote high-quality development”, MCCM 2023 encouraged the exchange of information on research frontiers in different fields related to material chemistry and composite materials, connected the most advanced academic resources at home and abroad, and turned research results into industrial solutions. It also promoted the development of related disciplines, expanded the international scientific and academic exchange channels, enhanced scientific innovation on a global scale, and contributed to academic cooperation between China and the international community. The Conference was attended by about 100 participants and hosted 6 keynote speeches, many oral and poster presentations, as well as Questions & Answer part. The topics of the 4th MCCM cover various research fields where material chemistry and composite materials are applied, such as Surface Chemistry, New Energy Materials, Nanotechnology and Materials, Physical and Structural Properties of Materials, Multiferroic Materials and Composites, etc. According to all the attendees, the scientific program was excellent with high level of presentations and the scientific environment was fruitful, thus all of them had a great and creative time. In the keynote speech part, Professor Liguang Wang (Zhejiang University, China) shared his research on Understanding the Degradation Mechanisms in High-Energy Density Cathodes via Synchrotron X-Ray Techniques. To advance the development of the next generation of high-energy-density cathode materials, his research endeavors have systematically unraveled the intricacies of performance degradation mechanisms inherent in layered structure cathodes. This exploration leveraged a sophisticated combination of advanced synchrotron X-ray-based characterization techniques across multiple scales. His investigation has been transformative, shedding light on the intrinsic correlation between stress-strain dynamics and mechanical degradation within layered cathode materials. With rounds of dramatic researches sharing and ideas exchanging, the Conference was made filled with academic atmosphere. We would like to thank Beihang University, China for its support. We would also like to acknowledge the members of the Organizing Committee and Technical Program Committee for their preparation and suggestion on the Conference. Our gratitude also goes to the members of Journal of Physics: Conference Series for their support in publishing this paper volume. The Committee of MCCM 2023 List of Committee Member is available in this pdf.

The Stress Strain Analysis of Forward Extrusion Process of Hollow Elements

This paper presents an analysis focused on the stress-strain dynamics within the forward extrusion process for hollow elements. The forward extrusion of hollow elements is characterized by extensive plastic deformation and complex material flow. This process involves splitting the metal continuum, subjecting it to plastic deformation, and merging it into a seamless product with a predetermined cross-sectional shape as it exits the tool. Employing modern numerical finite element methods is essential for designing such processes, as it enables the simulation of metal behavior within the tool. These simulations help predict mechanical parameters within the deformable material continuum, such as stress, strain, temperatures, and strain rates. Additionally, they allow for the optimization of tool designs tailored to the specific product, improving process efficiency and quality. Understanding the stress-strain distribution at individual nodes enables proactive measures to prevent mechanical disruptions within the continuum, ensuring the integrity and quality of the final product—an essential criterion in the forward extrusion process for hollow elements.

Optimal assist strategy exploration for a direct assist device under stress‒strain dynamics.

The aim of this paper is to introduce a new assist strategy for a direct assist device that can enhance the heart's pumping efficiency and decrease the chances of myocardial injury in contrast to the conventional assist strategy. We established a finite element model of a biventricular heart, divided the ventricles into several regions, and applied pressure to each region separately in order to identify the primary and secondary assist areas. Then combined and tested these areas to obtain the optimal assist strategy. The results indicate that our method exhibits an assist efficiency approximately ten times higher than that of the traditional assist method. Additionally, the stress distribution in the ventricles is more uniform after assistance. In summary, this approach can result in a more homogenous stress distribution within the heart while also minimizing the contact area with it, which can reduce the incidence of allergic reactions and the likelihood of myocardial injury.

A unified model of hysteresis and long-time relaxation in heterogeneous materials

A physical model of stress-strain dynamics and long-time relaxation (slow time) in structured media is proposed. The model is based on the analysis of inter-grain contacts and the resulting surface force potential with a barrier. The result is a unified description of the classical acoustic nonlinearity, stress-strain hysteresis, and logarithmic relaxation law for sound velocity (and, hence, for the frequency of nonlinear resonance in samples of structured materials). Estimates of a characteristic volume of interacting contacts give close values for the variety of consolidated materials. For weak (linear) testing waves, the logarithmic relaxation occurs if a classical quadratic nonlinearity is added to the stress-strain relation.

A unified model of hysteresis and relaxation in geophysical materials

A physical model of stress-strain dynamics and long-time relaxation (slow time) in structured media such as the rock is suggested. It is based on an adhesion mechanism (JKR model) for inter-grain contacts which implies the surface force potential with a barrier. This model results in a unified description of the classical nonlinearity, stress-strain hysteresis, and logarithmic relaxation law for sound velocity and, hence,for the frequency of nonlinear resonance in samples of structured materials. Estimates of a characteristic volume of interacting contacts give close values for a variety of consolidated materials. Propagation of waves in such materials is briefly considered. For a weak (linear) testing wave, the logarithmic relaxation occurs if the classical quadratic nonlinearity is added to the stress-strain relation.

Stress-induced state transitions in flexible liquid-crystal devices

This work studies the stress–strain dynamics for the transient optoelectronic characteristics of flexible liquid-crystal (LC) devices. Due to the fast response of LC directors, the configuration of the LC is assumed to be in quasi-equilibrium during the process of elastic deformations of the flexible structures. The LC medium hence can be treated effectively as a thin-film layer and can approximately follow the strain–stress mechanism in the solids. Relevant theoretical algorithms are studied in this work, and numerical results present the stress-induced state transitions in the π cell.

Ultrafast Kikuchi Diffraction: Nanoscale Stress–Strain Dynamics of Wave-Guiding Structures

Complex structural dynamics at the nanoscale requires sufficiently small probes to be visualized. In conventional imaging using electron microscopy, the dimension of the probe is large enough to cause averaging over the structures present. However, by converging ultrafast electron bunches, it is possible to select a single nanoscale structure and study the dynamics, either in the image or using electron diffraction. Moreover, the span of incident wave vectors in a convergent beam enables sensitivity levels and information contents beyond those of parallel-beam illumination with a single wave vector Bragg diffraction. Here, we report the observation of propagating strain waves using ultrafast Kikuchi diffraction from nanoscale volumes within a wedge-shaped silicon single crystal. It is found that the heterogeneity of the strain in the lateral direction is only 100 nm. The transient elastic wave gives rise to a coherent oscillation with a period of 30 ps and with an envelope that has a width of 140 ps. The origin of this elastic deformation is theoretically examined using finite element analysis; it is identified as propagating shear waves. The wedge-shaped structure, unlike parallel-plate structure, is the key behind the traveling nature of the waves as its angle permits "transverse" propagation; the parallel-plate structure only exhibits the "longitudinal" motion. The studies reported suggest extension to a range of applications for nanostructures of different shapes and for exploring their ultrafast eigen-modes of stress-strain profiles.

Engineering of a periodontal ligament construct: cell and fibre alignment induced by shear stress

We report an in vitro technique to establish alignment of collagen fibres and cells within a three-dimensional tissue equivalent that mimics the natural periodontal ligament (PDL) using a novel custom-designed bioreactor. Shear stress was applied to the tissue equivalent prepared with collagen solution and seeded with human PDL cells. Stress-strain dynamics and the alignment of collagen fibres and PDL cells in tissue equivalents were analysed. Shear stress aligned collagen fibres and PDL cells in a direction parallel to the principle strain vector. PDL cells and Collagen fibres aligned in strained tissue equivalents with higher uniformity than in unstrained tissue equivalents. The cell and fibre alignment of the engineered PDL was precisely guided by mechanical shear stress along the direction of principal strain vector using a custom-designed bioreactor, suggesting that the enhanced functional property of engineered PDL constructs could be achieved with this technique.

On the Volterra integral equation relating creep and relaxation

The evolving stress–strain response of a material to an applied deformation is causal. If the current response depends on the earlier history of the stress–strain dynamics of the material (i.e. the material has memory), then Volterra integral equations become the natural framework within which to model the response. For viscoelastic materials, when the response is linear, the dual linear Boltzmann causal integral equations are the appropriate model. The choice of one rather than the other depends on whether the applied deformation is a stress or a strain, and the associated response is, respectively, a creep or a relaxation. The duality between creep and relaxation is known explicitly and is referred to as the ‘interconversion equation’. Rheologically, its importance relates to the fact that it allows the creep to be determined from knowledge of the relaxation and vice versa. Computationally, it has been known for some time that the recovery of the relaxation from the creep is more problematic than the creep from the relaxation. Recent research, using discrete models for the creep and relaxation, has confirmed that this is an essential feature of interconversion. In this paper, the corresponding result is generalized for continuous models of the creep and relaxation.

Measurement of Human Muscle In Vivo Stress–Strain Dynamics Using Velocity Encoded Phase Contrast Magnetic Resonance Imaging: Analysis of Ankle Plantarflexors and Dorsiflexors.

Measurement of Human Muscle In Vivo Stress–Strain Dynamics Using Velocity Encoded Phase Contrast Magnetic Resonance Imaging: Analysis of Ankle Plantarflexors and Dorsiflexors.

Stress induced electrical noise in stainless steel

Stainless steel wires under tensile stress displayed narrow band peaks in the low frequency region of the power spectrum that were ∼104 times the background Johnson noise. The electrical response to stress was analyzed in terms of the root mean squared (rms) voltage (Vrms) of the noise signal over a 13 Hz bandwidth. The information obtained from such measurements is independent of other nondestructive testing methods and is therefore a useful probe of the stress-strain dynamics in metals and alloys. The rms voltage initially increases exponentially with the applied stress but subsequently decreases near the point of failure. This voltage is also approximately proportional to the square root of the sample resistance (Rs1/2). It is proposed that this noise signal is due to the fluctuations in the piezoresistivity as a result of stress induced reorientation of defects, similar to the Zener relaxation of solute atoms in a solid solution.

Characterization and control of chaotic stress oscillations in a model for the Portevin-Le Châtelier effect

The Portevin-Le Chatelier (PLC) effect, otherwise known as serrated yielding, repeated yielding, or jerky flow, has been a subject of investigation for many years. Modeling studies, and experiments have shown that the oscillatory PLC stress-strain dynamics can sometimes be a form of deterministic chaos. In such cases, the spontaneously occurring oscillations are aperiodic and are characterized by at least one positive Lyapunov exponent. However, whether they be chaotic or not, these oscillations are detrimental to the mechanical integrity of the material, so that some means by which they can be suppressed would be a desirable feature. In the work described below, a strategy for suppressing these oscillations is developed and applied to a model for the PLC effect. The strategy is physically realistic in the sense that it is based on the feedback of a control signal, obtained from a measurable quantity, to an accessible (i.e., controllable) parameter. Application is made here to a case for which the oscillations are chaotic, although the approach is applicable to periodic stress oscillations as well.