Showing papers on "von Mises yield criterion published in 2014"

TSV stress-aware full-chip mechanical reliability analysis and optimization for 3D IC

Abstract: Three-dimensional integrated circuit (3D IC) with through-silicon-via (TSV) is believed to offer new levels of efficiency, power, performance, and form-factor advantages over the conventional 2D IC. However, 3D IC involves disruptive manufacturing technologies compared to conventional 2D IC. TSVs cause significant thermomechanical stress that may seriously affect performance, leakage, and reliability of circuits. In this paper, we discuss an efficient and accurate full-chip thermomechanical stress and reliability analysis tool as well as a design optimization methodology to alleviate mechanical reliability issues in 3D ICs. First, we analyze detailed thermomechanical stress induced by TSVs in conjunction with various associated structures such as landing pad and dielectric liner. Then, we explore and validate the linear superposition principle of stress tensors and demonstrate the accuracy of this method against detailed finite element analysis (FEA) simulations. Next, we apply this linear superposition method to full-chip stress simulation and a reliability metric named the von Mises yield criterion. Finally, we propose a design optimization methodology to mitigate the mechanical reliability problems in 3D ICs.

Fatigue constrained topology optimization

Abstract: We present a contribution to a relatively unexplored application of topology optimization: structural topology optimization with fatigue constraints. A probability based high-cycle fatigue analysis is combined with principal stress calculations in order to find the topology with minimum mass that can withstand prescribed variable-amplitude loading conditions for a specific life time. This allows us to generate optimal conceptual designs of structural components where fatigue life is the dimensioning factor. We describe the fatigue analysis and present ideas that make it possible to separate the fatigue analysis from the topology optimization. The number of constraints is kept low as they are applied to stress clusters, which are created such that they give adequate representations of the local stresses. Optimized designs constrained by fatigue and static stresses are shown and a comparison is also made between stress constraints based on the von Mises criterion and the highest tensile principal stresses. The paper is written with focus on structural parts in the avionic industry, but the method applies to any load carrying structure, made of linear elastic isotropic material, subjected to repeated loading conditions.

Effects of different restraints on the weld-induced residual deformations and stresses in a steel plate

Abstract: Effects of three different plate boundary constraints on the residual stress field and deformation are investigated numerically during butt-joint welding. For the numerical solution of the heat transfer equations, the finite element method is used to predict the temperature profile as well as residual stress field due to three different plate boundary conditions. The distortion of the welded plate is modeled as a nonlinear problem in geometry and material, adopting a finite element solution based upon the thermo–elastic–plastic large deflection theory. High-strength shipbuilding steel AH36 with temperature-depending material properties and nonlinear stress–strain material properties (bilinear isotropic hardening option uses the von Mises yield criteria) are assumed for the numerical analysis. For verifying the results, the temperature profile is compared with the result obtained in a previous research. In the mechanical analysis, three different boundary conditions are applied. Effects of plate thickness, plate width, and mesh model on the residual stress with boundary constraint are studied.

Failure analysis of laminated glass panels subjected to blast loads

Abstract: This paper presents a rigorous and a reliable analytical procedure using finite element (FE) techniques to study the blast response of laminated glass (LG) panel and predict the failure of its components. The 1st principal stress (σ11) is used as the failure criterion for glass and the von mises stress (σv) is used for the interlayer and sealant joints. The results from the FE analysis for mid-span deflection, energy absorption and the stresses at critical locations of glass, interlayer and structural sealant are presented in the paper. These results compared well with those obtained from a free field blast test reported in the literature. The tensile strength (T) of the glass has a significant influence on the behaviour of the LG panel and should be treated carefully in the analysis. The glass panes absorb about 80% of the blast energy for the treated blast load and this should be minimised in the design.

Effect of Exponentially-Varying Properties on Displacements and Stresses in Pressurized Functionally Graded Thick Spherical Shells with Using Iterative Technique

Abstract: A semi-analytical iterative method as one of the newest analytical methods is used for the elastic analysis of thick-walled spherical pressure vessels made of functionally graded materials subjected to internal pressure. This method is accurate, fast and has a reasonable order of convergence. It is assumed that material properties except Poisson’s ratio are graded through the thickness direction of the sphere according to an exponential distribution. For different values of inhomogeneity constant, distributions of radial displacement, radial stress, circumferential stress, and von Mises equivalent stress, as a function of radial direction, are obtained. A numerical solution, using finite element method (FEM), is also presented. Good agreement was found between the semi-analytical results and those obtained through FEM. © 2014 IAU, Arak Branch. All rights reserved.

XFEM simulation of stable crack growth using J – R curve under finite strain plasticity

Abstract: In the present work, extended finite element method (XFEM) has been extended to simulate stable crack growth problems using J–R criterion under finite strain plasticity. In XFEM, a physical representation of crack is not required, and a crack is completely modeled by enrichment functions. The modeling of large deformation is performed using updated Lagrangian approach. The nonlinear equations obtained as a result of large deformation are solved by Newton–Raphson iterative method. Von-Mises yield criterion is used with isotropic hardening to model the finite strain plasticity. The elastic-predictor and plastic-corrector algorithm is employed for stress computation. Three problems i.e. crack growth in compact tension specimen; crack growth in triple point bend specimen and crack growth in bi-metallic triple point bend specimen are solved using J–R curve under plane stress condition to demonstrate the capability of XFEM in crack growth problems.

A rate dependent tension?torsion constitutive model for superelastic nitinol under non-proportional loading; a?departure from von Mises equivalency

Abstract: In this work, a modified 3D model is presented to capture the multi-axial behavior of superelastic shape memory alloys (SMAs) under quasi-static isothermal or dynamic loading conditions. General experimental based equivalent stress and strain terms are introduced and improved flow rule and transformation surfaces are presented. The 3D constitutive equations are found for both isothermal and dynamic loading states. An extended experimental study is conducted on NiTi thin walled tubes to investigate the performance of the model. The proposed approach is shown to be able to capture the SMA response better than the original model in tension‐torsion loading conditions.

The equivalent strain in high pressure torsion

Abstract: The results of experiments carried out by means of high pressure torsion (HPT) are frequently described in terms of the Eichinger “equivalent” strain. When employed in conjunction with equivalent stresses derived using von Mises in conjunction with the Fields and Backofen analysis, the values of the work done/unit volume associated with the Eichinger-based flow curves are shown to be only a small fraction of the actual work done. By contrast, the values of the work done/unit volume that correspond to the shear stress/shear strain as well as the von Mises flow curves are in full agreement with the torque/twist work done/unit volume. When the principle of work conjugacy is employed, the Eichinger strain-based work done values are necessarily in agreement with the shear stress/shear strain and torque/twist results, but then the “equivalent” stresses are unrealistically high. It is concluded that only the von Mises equivalent stresses and strains should be employed in the description of HPT results and that the Eichinger “equivalent” strain should not be used for this purpose.

New approach to evaluate non‐proportionality in multiaxial loading conditions

Abstract: The shear stress amplitude is one of the most important parameters in the formulation of many multiaxial fatigue models proposed in literature. The shear stress amplitude is usually evaluated by the longest projection or the minimum circumscribed circle approach in a shear stress space. Further, the von Mises and Tresca stress spaces are the most used ones under multiaxial loading conditions, where the damage ratio between axial and shear damages is a constant value: 0.577 for von Mises and 0.5 for Tresca. However, the damage scale in each stress space's axes may vary significantly depending on materials' type. Therefore, evaluating proportional and non-proportional damages using conventional stress spaces (von Mises or Tresca) may lead to erroneous interpretations. In this work, systematic fatigue experiments under proportional and non-proportional loading conditions are presented for three structural steels: Ck45, AISI303 and the 42CrMo4. To quantify the relative damage between proportional and non-proportional loading paths, a material's non-proportional sensitivity parameter (Y parameter), determined based on materials experimental tests, is proposed. From this research, it can be drawn that the appropriate axial/shear damage relation should be used to estimate multiaxial fatigue life.

A model study for cyclic thermal loading and thermal performance of a thermoelectric generator

Abstract: SUMMARY Thermal cyclic loading influences the life cycle of the thermoelectric device pins because of the thermal stress developed in the pins. Although thermal efficiency improves for different geometric configurations of the device pins, development of thermal stresses limit the selection of pin geometry in practical applications, particularly under cyclic thermal loading. Consequently, in the present study, thermal stress analysis of thermoelectric pins under cyclic thermal loading is carried out. The influence of thermoelectric pin geometry on the stress levels is examined when the device is subjected to the thermal cyclic loading. The predictions of thermal stress distribution are validated with the data presented in the open literature. It is found that pin geometric configuration has a significant effect on the stress levels developed in the pin when subjected to cyclic thermal loading. The pin configuration RA = 1 (parallel pins) results in the minimum value of the maximum von Mises stress in the pins as compared to that corresponding to other configurations. Copyright © 2014 John Wiley & Sons, Ltd.

Gurson's Criterion and Its Derivation Revisited

Abstract: This paper revisits Gurson’s [1,2] classical limit-analysis of a hollow sphere made of some ideal-plastic von Mises material and subjected to conditions of homogeneous boundary strain rate (Mandel [3], Hill [4]). Special emphasis is placed on successive approximations of the overall dissipation, based on a Taylor expansion of one term appearing in the integral defining it. Gurson considered only the approximation based on the first-order expansion, leading to his well-known homogenized criterion; higher-order approximations are considered here. The most important result is that the correction brought by the second-order approximation to the first-order one is significant for the porosity rate, if not for the overall yield criterion. This bears notable consequences upon the prediction of ductile damage under certain conditions.