Papers by Keyword: Bimaterial

Abstract: The aim of this study is to identify simultaneously the thermal conductivity tensor and the volume heat coefficient of a bimaterial (checkerboard) whose heat conduction obeys Fourier's law. This approach is validated by numerical simulation. The simulated temperature fields are obtained by the direct resolution heat conduction solved numerically by the finite element method formulation. To identify parameters, an inverse method is developed by using the finite element temperature approach (FEU-T) model fitting method based on the Levemberg-Marquardt algorithm. We validated the numerical procedure by using noiseless temperature fields at different time and space steps. The influence of the noise on the temperature fields is also studied and shows the efficiency of the inverse method. The results show that this procedure is not very sensitive to the number of elements (or space steps) and the number of time steps.

Abstract: This Based on the elastic theory of a crack perpendicular to and terminating at bimaterial interface, a generalized expression of the stress intensity factor is provided for a crack in single material and a crack perpendicular to bimaterial interface, finite element methods are used to calculate the stress intensity factors. The influences of the material combination and crack length on the the stress intensity factors were investigated. Results show that when the crack terminates at bimaterial interface, singular order of K_Iis different from that of single material, and the values of K_I increase with increasing E₁/E₂ and μ₁/μ₂.

Abstract: Delaminations in structures may significantly reduce the stiffness and strength of the structure and may affect their vibration characteristics. In the present study, an analytical solution is developed to study the vibration of delaminated bimaterial beams fully or partially supported by elastic foundation. The free mode and constrained mode assumptions in delamination vibration are adopted. This is the first study on the vibration of delaminated bimaterial beam on elastic foundation. Results show that the effect of delamination on reducing natural frequency is aggravated by an increasing stiffness of elastic foundation. An empirical estimation of such effects is provided for engineers. The effects of elastic foundation on the variation of natural frequency against axial stiffness ratio and bending stiffness ratio of beams are thoroughly investigated. The analytical results of this study can serve as the benchmark for FEM and other numerical solutions.

Abstract: The presented work is dedicated to studying the forgeability of bimaterial cladded workpiece. Hot upsetting tests of cylindrical low carbon steel (C15) billets weld cladded (MIG) by stainless steel (SS316L) are experimentally and numerically studied. Upsetting tests with different upsetting ratios are performed in different tribology conditions at 1050°C which is within the better forgeability temperature range of both substrate and cladding materials[ ]. Slab model and finite-element simulation are conducted to parametrically study the potential forgeability of the bimaterial cladded workpiece. The viscoplastic law is adopted to model the friction at the die/billet interface. The friction condition at the die/billet interface has a great impact on the final material distribution, forging effort and cracking occurrence. With Latham and Cockcroft Criterion, the possibility and potential position of cracks could be predicted.

Abstract: In this work we studied the fabrication of a monolithic bimaterial micro-cantilever resonant IR sensor with on-chip drive circuits. The effects of high temperature process and stress induced performance degradation were investigated. The post-CMOS MEMS (micro electro mechanical system) fabrication process of this IR sensor is the focus of this paper, starting from theoretical analysis and simulation, and then moving to experimental verification. The capacitive cantilever structure was fabricated by surface micromachining method, and drive circuits were prepared by standard CMOS process. While the stress introduced by MEMS films, such as the tensile silicon nitride which works as a contact etch stopper layer for MOSFETs and releasing stop layer for the MEMS structure, increases the electron mobility of NMOS, PMOS hole mobility decreases. Moreover, the NMOS threshold voltage (Vth) shifts, and transconductance (Gm) degrades. An additional step of selective removing silicon nitride capping layer and polysilicon layer upon IC area were inserted into the standard CMOS process to lower the stress in MOSFET channel regions. Selective removing silicon nitride and polysilicon before annealing can void 77% Vth shift and 86% Gm loss.

Abstract: We present a method for computing the stress intensity factors in bimaterials based on the goal oriented finite element error estimate. The goal oriented analysis focuses on computing the bounds on the local quantities of interest, e.g. local stresses, local displacements, stress intensity factors etc, of a structure, and with the bounds obtained on the coarse finite element mesh we can obtain the quantities of interest with nearly the same accuracy as that obtained on the fine finite element mesh. In this paper the stress intensity factors in bimaterials are first formulated as explicit computable linear function of the displacements by means of the two-points extrapolation method. Then the goal oriented finite element method is used to compute the lower and upper bounds on the stress intensity factors, and the average of the bounds is considered as a prediction of the stress intensity factor. At last, the stress intensity factors, 0 K and r K , in bimaterials are computed with the proposed method to show its efficiency.

Abstract: The finite element alternating method based on the superposition principle has been known as an effective method to obtain the stress intensity factors for general multiple collinear or curvilinear cracks in an isotropic plate. In this paper the method is extended further to solve two-dimensional cracks embedded in a bimaterial plate. The main advantage of this method is that it is not necessary to make crack meshes considering the stress singularity at the crack tip. The solution of the developed code is obtained from an iteration procedure, which alternates independently between the finite element method solution for an uncracked body and the analytical solution for cracks in an infinite body. In order to check the validity of the method, several crack problems of a bimaterial body are solved and compared with the results obtained from the finite element analysis.

Abstract: This paper deals with a Mode III interfacial edge crack in a magnetoelectroelastic bimaterial subjected to line singularities such as an out-of-plane line force, a line electric charge, a line magnetic charge and a straight screw dislocation. The surfaces (including crack surfaces) of the bimateral are assumed to be electrically open and magnetically closed. The closed-form analytical solution to the problem is obtained by employing the complex variable approach in conjunction with the conformal mapping technique. The intensity factors of stress, electric displacement and magnetic induction are given explicitly. The obtained results can be used as the Green's function to solve more complicated problems.

Abstract: Initiation and propagation of interfacial crack along bimaterial interface are considered in this study. A series of interfacial crack initiation and propagation experiments are conducted using the biaxial loading device for various mixed modes. Normal crack opening displacement (NCOD) is measured near crack front by a crack opening interferometry and used for extracting fracture parameters. From mixed mode interfacial crack initiation experiments, large increase in toughness with shear components is observed. Initial velocity of crack propagation is very dependent upon the mode-mixes. It increased with positive mode-mix due to the increase of stress singularities ahead of crack front and decreased with negative mode-mix resulting from the increase of the degree of compressive stress behind the crack front. Crack propagation was less accelerated with positive mode-mix than the negative mode-mix.