Showing papers on "Hydrostatic stress published in 2022"

Investigation into multiaxial mechanical behaviors of Kelvin and Octet-B polymeric closed-cell foams

Abstract: As a class of effective lightweight energy absorption materials, periodic closed-cell foams have been widely applied in engineering, in which the Kelvin and Octet-B foams have demonstrated great value in the research of multiaxial mechanical characteristics. For this reason, this study aims to develop a series of realistic finite element analysis (FEA) models for investigating their uniaxial, compression-shear, and arbitrary triaxial compression performance. Under uniaxial loading conditions, the mechanical responses and deformation modes of the two foams are compared and analyzed with different densities. The influence of different loading angles is also considered under compressive-shear loading. The deformation pattern of foams subject to equal biaxial and hydrostatic loading are compared with uniaxial compression. Based on sufficient simulation data, the initial yield surfaces of the two foams are plotted in the von Mises and mean stress plane, and fitted by three theoretical yield criteria characterized in terms of quadratic functions. It is found that the Miller criterion can better describe the initial yield surface shape of Kelvin foams than the yield models of Deshpande–Fleck and Zhang et al.; while the above yielding models are all of high fitting accuracy for the Octet-B foam. Further, the ability to resist initial yield of the Kelvin foam has proven superior to Octet-B foams by calculating the curve integration. The study is anticipated to provide new insights into novel design and extensive applications of periodic closed-cell foam materials in practice.

Bioprinting-Associated Shear Stress and Hydrostatic Pressure Affect the Angiogenic Potential of Human Umbilical Vein Endothelial Cells

Abstract: Bioprinting-associated shear stress and hydrostatic pressure can negatively affect the functionality of dispensed cells. We hypothesized that these mechanical stimuli can potentially affect the angiogenic potential of human umbilical vein endothelial cells (HUVECs). A numerical simulation model was used to calculate the shear stress during microvalve-based droplet ejection. The impact of different levels of applied pressure and the resulting shear stress levels on the angiogenic potential of HUVECs was investigated after up to 14 days of cultivation. In vitro results showed that bioprinting-associated stress not only has short-term but also long-term effects. The short-term viability results indicate a 20% loss in post-printing cell viability in samples printed under the harshest conditions compared to those with the lowest shear stress level. Further, it was revealed that even in two-dimensional culture, HUVECs were able to form a capillary-like network organization regardless of bioprinting pressure. In three-dimensional culture experiments; however, the HUVECs printed at 3 bar were not able to form tubular structures due to their exposure to high shear stress levels. In conclusion, this study provides new insights into how the bioprinting process should be conducted to control printing-associated shear stress and hydrostatic pressure to preserve the functionality and angiogenetic potential of HUVEC.

Hydrostatic pressure dependence in tensile and compressive behavior of an acrylonitrile–butadiene–styrene copolymer

Abstract: The strain-rate dependence of a commercial grade ABS copolymer has been analyzed in both compression and tension. By measuring in two loading geometries, the hydrostatic pressure-dependence on the material's deformation behavior can be established. An alternative method to determine pressure-dependence, based on the difference in strain-rate dependence for various loading geometries, has been presented. It was shown to be an effective technique, both for thermorheologically simple materials such as ABS, as well as thermorheologically complex materials, for example, PMMA. A yield criterion, based on an Eyring-type pressure-modified rate equation, has been compared to finite element simulations using the Eindhoven Glassy Polymer (EGP) constitutive model. Although both methods give quantitatively similar results for the yield stress prediction, only the fully 3D EGP model is able to represent the large-strain deformation behavior.

Effect of Residual Stress on Hydrogen Diffusion in Thick Butt-Welded High-Strength Steel Plates

Abstract: Thick high-strength steel plates are increasingly being used for ship structures. Moreover, hydrogen enters the process of manufacturing and service, and large residual tensile stress occurs near the weld. Such stress can facilitate the diffusion and accumulation of hydrogen in the material, leading to hydrogen embrittlement fracture of the shell. Therefore, residual-stress-induced diffusion and accumulation of hydrogen in the stress concentration region of thick butt-welded high-strength steel plate structures need to be studied. In this study, manual metal arc welding was realized by numerical simulation of residual stress in a thick butt-welded high-strength steel plate model using the thermoelastic–plastic theory and a double ellipsoidal heat source model. To analyze residual stress, a set of numerical simulation methods was obtained through comparative analysis of the test results of relevant literature. Residual and hydrostatic stress distributions were determined based on these methods. Then, hydrogen diffusion parameters in each region of the model were obtained through experimental tests. Finally, the results of the residual stress field were used as the predefined field of hydrogen diffusion to conduct a numerical simulation analysis. The distribution of hydrogen diffusion under the influence of residual stress was obtained based on the theory of stress-induced hydrogen diffusion. The weak area of the welding joint was found to be near the weld toe, which exhibited high hydrostatic stress and hydrogen concentration. Further, the maximum hydrogen concentration value of the vertical weld path was approximately 6.1 ppm, and the maximum value of the path parallel to the weld centerline and 31 mm away from the weld centerline was approximately 6.22 ppm. Finally, the hydrostatic tensile stress in the vertical weld path was maximized (~345 MPa), degrading the material properties and causing hydrogen-related cracking. Hence, a reliable method for the analysis of hydrogen diffusion according to residual stress in thick high-strength steel plates was obtained. This work could provide a research basis for controlling and eliminating the adverse effects of hydrogen on the mechanical properties of ship structures and ensuring the safe service of marine equipment.

A shear modified enhanced Gurson constitutive relation and implications for localization

Abstract: The most widely used phenomenological constitutive relation to model ductile failure of structural metals at room temperature is based on the work of Gurson (1977) and has the advantage of having both a micromechanics basis and sufficient simplicity to enable complex engineering calculations to be carried out. The predictions of this framework have been most successful in circumstances where the stress triaxiality, the ratio of mean normal stress to Mises effective stress, is relatively large. For stress states with smaller values of stress triaxiality, the predictive capability has typically been much reduced. We present a shear modified enhanced Gurson constitutive relation that combines the shear modification of Nahshon and Hutchinson (2008) with the second porosity concept of Gologanu et al. (1994). This maintains both the connection with micromechanics and the computational simplicity. The predictive capability of the framework is illustrated by the good agreement with cell model calculations for localization of deformation over a wide range of stress states. Strain localization analyses with an initial porosity imperfection predict that for axisymmetric stress states with a superposed hydrostatic tension, the minimum critical strain for the onset of localization follows the onset of coalescence, as defined within the context of the constitutive model here, if the value of the stress triaxiality is sufficiently small. For an imposed shear stress state with a superposed hydrostatic tension, the minimum critical strain for the onset of localization is predicted to precede the onset of coalescence. A strong sensitivity of the critical strain for localization of deformation to the strain or stress range over which void nucleation occurs is also predicted, with void nucleation and localization of deformation essentially coinciding for sufficiently abrupt nucleation.

Stress Distribution Pattern in Mini Dental Implant-Assisted RPD with Different Clasp Designs: 3D Finite Element Analysis

Abstract: Introduction The removable partial denture (RPD) components, especially the retentive arm, play a major role in the loading characteristic on supporting structures. Objective To evaluate and compare the effect of different clasp designs on the stress distribution pattern, maximum von Mises stress, and average hydrostatic pressure on abutment teeth, as well as edentulous ridges, mini dental implants (MDIs), and peri-implant bone between the conventional removable partial denture (CRPD) and mini dental implant-assisted distal extension removable partial denture (IARPD) using a three-dimensional finite element analysis (3D FEA). Materials and Methods 3D FEA models of mandibular arches, with and without bilateral MDI at the second molar areas, and Kennedy class I RPD frameworks, with RPA, RPI, Akers, and no clasp component, were generated. A total of 200 N vertical load was bilaterally applied on both sides of distal extension areas, and the stress was analyzed by 3D FEA. Results The stress concentration of IARPD with RPI clasp design was located more lingually on abutment teeth, MDI, and peri-implant bone, while the other designs were observed distally on the supporting structures. The maximum von Mises stress on the abutment root surface was decreased when the RPDs were assisted with MDIs. The CRPD and IARPD with the Akers clasp design showed the highest von Mises stress followed by the designs with RPA and RPI clasp, respectively. The average hydrostatic pressure in each group was in approximation. Conclusion The placement of MDIs on distal extension ridges helps to reduce the stress concentration on denture supporting structures. The maximum von Mises stress is affected by the different designs of clasp components. The CRPD and the IARPD with RPI clasp provide the least stress on supporting structures.

Mechanochemical Ionization: Differentiating Pressure-, Shear-, and Temperature-Induced Reactions in a Model Phosphate

Abstract: Abstract Using density-functional theory-based molecular dynamics simulations, we study stress and temperature-induced chemical reactions in bulk systems containing triphosphoric acid and zinc phosphate molecules. The nature of the products depends sensitively on the imposed conditions, e.g., isotropic and even more so shear stress create (zwitter-) ionic products. Free ions also emerge from thermal cycles, but the reactions are endothermic rather than exothermic as for stress-induced transitions and zinc atoms remain four-coordinated. Hydrostatic stresses required for reactions to occur lie well below those typical for tribological micro-contacts of stiff solids and are further reduced by shear. Before zinc atoms change their coordination under stress, proton mobility increases, i.e., hydrogen atoms start to change the oxygen atom they are bonded to within 10 ps time scales. The hydrostatic stress for this to occur is reduced with increasing shear. Our finding suggests that materials for which number, nature, and mobility of ions are stress sensitive cannot have a well-defined position in the triboelectric series, since local contact stresses generally depend on the stiffness of the counter body. Moreover, our simulations do not support the idea that chemical reactions in a tribo-contact are commonly those that would be obtained through heating alone. Graphical Abstract

Proximity Effects in Matrix-Inclusion Composites: Elastic Effective Behavior, Phase Moments, and Full-Field Computational Analysis

Abstract: This work focuses on the effects of inclusion proximity on the elastic behavior of dilute matrix-inclusion composites. Rigid or soft monodisperse spherical inclusions are considered with moderate volume fractions. To conduct this study, Representative Volume Elements (RVE) with an effective local minimum distance between inclusions varying between the sphere’s radius and one-tenth of the radius are built. Numerical finite element calculations on the RVE are performed. The obtained homogenized elastic properties, as well as the phase stress moments (first and second), are compared to Mori–Tanaka estimates, which are well established for this kind of composite. The behavior of local fields (stresses) in the microstructure with respect to inclusion proximity is also analyzed. It follows that the effective properties and phase stress moments converge asymptotically to the Mori–Tanaka estimates when the minimal distance between spheres increases. The asymptote seems to be reached around a distance equal to the sphere’s radius. Effective and phase behaviors show a deviation that can achieve and even exceed (for the second moments) ten percent when the inclusions are close. The impact of the inclusions’ proximities is even more important on local stress fields. The maximum stress values (hydrostatic or equivalent) can be more than twice as high locally.

Effect of Compressive Creep and Hydrostatic Pressure on Diffusion in NiCr and NiSi Systems

Abstract: Interdiffusion coefficients were measured in NiSi and NiCr systems from diffusion couples under hydrostatic pressures between 50 and 326 MPa, at 1200 °C. Uniaxial compression creep tests were also carried out on Ni–Cr diffusion couples at 885 °C, 940 °C and 1000 °C with stress values between 0 and 25 MPa, to observe the effect of applied stress on diffusion. A numerical inverse method was elaborated to determine interdiffusion coefficients that takes into account the plastic strain. The comparison of all the diffusion coefficients shows no significant effect of stress for the creep tests and a slight decrease of the interdiffusion coefficients for the hot isostatic pressing (HIP) tests in both systems when the compressive stress increases. This variation is less than twofold, thus the effect is negligible compared to the scatter observed for one diffusion coefficient from different sources of the literature.

Analysis of Hydrogen-Assisted Brittle Fracture Using Phase-Field Damage Modelling Considering Hydrogen Enhanced Decohesion Mechanism

Abstract: This study proposes a hydrogen-assisted fracture analysis methodology considering associated deformation and hydrogen transport inside a phase-field-based formulation. First, the hydrogen transport around a crack tip is calculated, and then the effect of hydrogen enhanced decohesion (HEDE) is modeled by defining the critical energy release rate as a function of hydrogen concentration. The proposed method is based on a coupled hydrogen mechanical damage under phase-field and implemented through a user subroutine in ABAQUS software. The test using compact tension (CT) sample is investigated numerically to study the hydrogen embrittlement on 45CrNiMoVA steel. Experimentally, the microstructural fracture presents a mixed brittle fracture mode, consisting of quasi-cleavage (QC) and intergranular (IG) fracture with hydrogen. This fracture mode is consistent with the suggested HEDE mechanism in the model. The simulation results show that hydrogen accumulates at the crack tip where positive hydrostatic stress is located. Moreover, the model estimates the initial hydrogen concentration through iterations. The simulated load-line displacement curves show good agreement with the experimental plots, demonstrating the predictive capabilities of the presented scheme.

Influence of Plate Thickness on Residual Stress in Single Point Incremental Forming of Hydrostatic Support

Abstract: The residual stress of single-point incremental forming parts is relatively large, which will cause the parts to spring back and deform during operation, which will affect the normal use of the parts. Aiming at this problem, this paper introduces hydrostatic support into the single-point incremental forming technology to reduce the residual stress of the parts. To analyze the influence of the plate thickness on the residual stress of the single point incremental forming of the static pressure support, the finite element model of the single point incremental forming of the static pressure support is established in this paper. The static pressure was taken as 0.06 MPa, and the plate thickness was taken as 1 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3 mm, and 3.5 mm. The residual stress under different plate thicknesses was simulated. The influence law of plate thickness on residual stress with and without hydrostatic support is obtained separately. The research results provide theoretical and technical support for an in-depth analysis of the influence of static pressure support on the microscopic characteristics of single point incremental forming.

Stress and equilibrium

Abstract: Abstract This chapter covers the basics of force and moment equilibrium. The definitions of traction and stress are given, and the special state of plane stress is described. The traction-stress relation is derived, and the equations of force equilibrium and moment balance are developed using differential element constructions. The equations of motion which account for inertia are also discussed. Common states of homogeneous stress—pure tension/compression, pure shear, and hydrostatic pressure—are discussed. The notions of mean normal stress and stress deviator are also introduced.