Elastic-plastic Material Properties Research Articles

Determination of constitutive properties of thin metallic films on substrates by spherical indentation using neural networks

The indentation test has been developed into a popular method for investigating mechanical properties of thin films. However, there exist only some empirical or semi-analytical methods for determining the hardness and Young’s modulus of a film from pyramidal indentation of the film on a substrate, where the deformation of film and substrate is subjected to be elastic–plastic. The aim of the present paper is to show how constitutive properties and material parameters may be determined by using a depth-load trajectory which is related to a fictitious bulk film material. This bulk film material is supposed to possess the same mechanical properties as the real film. It is assumed that the film and the substrate exhibit elastic–plastic material properties with nonlinear isotropic and kinematic hardening. The determination of the depth-load trajectory of the bulk film is a so-called inverse problem. This problem is solved in the present paper using both the depth-load trajectory of the pure substrate and the depth-load trajectory of the film deposited on this substrate. For this, use is made of the method of neural networks. Having established the bulk film depth-load trajectory, the set of material parameters entering in the constitutive laws may be determined by using e.g. the method proposed by Huber and Tsakmakis (Huber, N., Tsakmakis, Ch., 1999. Determination of constitutive properties from spherical indentation data using neural networks. Part II: plasticity with nonlinear isotropic and kinematic hardening. J. Mech. Phys. Solids 47, 1589–1607).

Reliability model for Al wire bonds subjected to heel crack failures

In power electronic packages wire bonding is used for the electrical contact of the chips and for interconnections on the module substrate. Limiting factors for the reliability are solder fatigue and wire bond failures. In this work we investigate the material fatigue of aluminum bonding wires stressed by cyclic lateral bonding area displacement. Bond wire heel crack failures observed by experiments are found to be strongly dependent on the loop geometry. Based on a finite element model that accounts for elastic-plastic material properties, a life-time model for the Al wire (Coffin-Manson representation) is derived from the experiments.

An Inverse Analysis Approach to Identify the Elastic-Plastic Material Properties of Al-Based Functionally Graded Materials

An Inverse Analysis Approach to Identify the Elastic-Plastic Material Properties of Al-Based Functionally Graded Materials

A computational method to predict elastic-plastic fracture

This paper presents a computational method for predicting specimen fracture behavior requiring only material stress-strain data. The specimen behavior is simulated numerically using the finite element technique. Nonlinear behavior of the finite element model is caused by boundary changes, elastic-plastic material properties, and an updated Dugdale-type cohesive stress zone. This fracture predictive method relies on a 5% offset criterion to determine crack initiation. Crack growth predictions are based on critical crack tip opening displacement (CTOD) which is computed during the fracture simulation process. Several validation examples under Mode I fracture condition are discussed. For both brittle and ductile fracture cases, the calculated maximum loads were within 6% of experimental values.

Toughness of an interface along a thin ductile layer joining elastic solids

Abstract The contribution of plastic deformation to the effective work of fracture is computed for a crack lying along one of the interfaces of a thin ductile layer joining two elastic solids. A model is proposed for the joint whose major parameters are the layer thickness, the elastic-plastic properties of material in the layer, and the work of separation and peak separation stress of the local interface fracture process. A symmetric mode I loading of the joint is considered under conditions where the thickness of the layer and the extent of the plastic zone are small compared with the crack length. The crack growth resistance behaviour is computed, with special emphasis on the steady-state work of fracture. The role of the layer thickness in the development of the plasticity contribution to toughness is detailed. Plastic dissipation is fully realized for layers above a certain thickness, characteristic of a plastic zone dimension, and is negligible when the layer is thin relative to this dimension. Othe...

Analyses of circumferential and axial flaws of a pressure vessel under PTS loads and failure estimate on the basis of irradiated RCT test specimens

Initiation and slow propagation of cracks in a pressure vessel loaded by severe PTS-transients were studied. J values were calculated using linear-elastic and elastic-plastic material properties. The calculated J values were compared with the J–R curves of the irradiated Round compact tension (RCT)-test specimens at upper shelf temperature. Cladding and weld seam residual stresses were taken into account in the calculations. For short three-dimensional surface cracks, the influence of cladding depends upon the shape of the crack. In the case of a deep three-dimensional crack, very high J values exist in the cladding and at the cladding/base metal interface. For shallow surface cracks, the influence of cladding is not so significant at this interface. The effect of cladding and its residual stresses was also studied in the laboratory using small cladded compact tension (CT) specimens. The first specimens were made of carbon steel and cladded in two layers. Finite element calculations were performed in order to study the J-integral distribution in these CT specimens. Exact fatigue crack profile and cladding residual stresses were taken into account in these calculations. The shape of the calculated J-integral distribution resembled the observed profile of the crack propagation front.

CERAMIC COATED GAS TURBINE SEALS INELASTIC HIGH-TEMPERATURE THERMOMECHANICAL RESPONSE OF CERAMIC COATED GAS TURBINE SEALS

Abstract Through the use of a constrained Newton-Raphson time stepping finite element scheme, the inelastic thermomechanical response of ceramic coated gas turbine parts is considered. Due to the generality of the solution procedure developed, the combined thermoelastic-plastic-creep properties associated with ceramics is treated. This includes the handling of temperature-dependent elastic-plastic creep and thermal material properties. To illustrate the procedure, the thermomechanical response of ceramic coated outer gas path seals is considered. This includes the evaluation of time-dependent thermal ratcheting and its concomitant residual stress and strain fields.

A Finite Element Model of Orthogonal Metal Cutting

A finite element model of orthogonal metal cutting is described. The paper introduces a new chip separation criterion based on the effective plastic strain in the workpiece. Several cutting parameters that are often neglected in simplified metal-cutting models are included, such as elastic-plastic material properties of both the workpiece and tool, friction along the tool rake face, and geometry of the cutting edge and workpiece. The model predicts chip geometry, residual stresses in the workpiece, and tool stresses and forces, without any reliance on empirical metal cutting data. The paper demonstrates that use of a chip separation criterion based on effective plastic strain is essential in predicting chip geometry and residual stresses with the finite element method.

Dynamic finite element model for laminated structures

A finite element structural model has been developed for the dynamic analysis of laminated, thick plates. The model uses quadrilateral elements to represent the shape of the plate and the elements are stacked in the thickness direction to represent various material layers. This analysis allows for orthotropic, elastic-plastic or elastic-viscoplastic material properties. Non-linear strain displacement relations are used to represent large transverse plate deflections. A finite difference technique is used to perform the numerical time integration. Assumptions are made about the response through the thickness of the plate that allow for the use relatively large time increments in the numerical integration method. These led to a set of element equilibrium equations which help to keep small error from affecting the values of stress that are calculated. The results from the analytical model are compared with experimental results. A good agreement is found between the calculated and measured values of the transverse plate deflections.

配管・レストレント系の動的応答解析 ＰＷＲ‐ＬＯＣＡ条件４ｉｎ．口径管パイプホイップ試験の解析

This paper presents the results of the dynamic response analysis of the pipe-restraints system by the general purpose finite element program ADINA. The analysis was carried out for the pipe whip tests performed under the PWR·LOCA conditions using 4-in. test pipe. In the analysis, the test pipe was modeled by an assemblage of the beam elements with the isotropic elastic-plastic material properties and the restraints were represented by the truss elements with the nonlinear elastic material properties including gap effect.The following results are obtained through the analysis. (1) Pipe can be modeled with the beam elements, when the overhang length is short and, therefore, the flattening of a cross-section of pipe is small. (2) The steady state restraint force can be predicted by modeling the restraints with the truss elements.

Finite element stress formulation for dynamic elastic-plastic analysis

The solution to wave propagation problems in solids with elastic-plastic material properties is obtained by using the finite element method directly in terms of the stresses. A variational principle due to Gurtin is modified by including a plastic strain tensor in the constitutive relationship. The resulting finite element equations, which represent the strain-displacement equations written in terms of the stresses, are simultaneous integral equations in time. With a transformation of variables, a set of simultaneous differential equations is obtained of the form H s ̈ + Qs+ Ve p = q(t) , where H is a symmetric positive-semidefinite matrix, and Q is a symmetric positive-definite matrix. The stresses and the plastic strains are represented by s ̈ and e p , respectively. Finite element equations are developed for an axisymmetric ring element with an arbitrary quadrilateral cross section in which the stresses and the plastic strains vary linearly along the sides of the elements. The equations are numerically integrated with respect to time by Newmark's generalized acceleration method. An iterative procedure is presented, which uses the finite element strain-displacement equations and the plasticity relationships, to determine the state of stress at the end of the time step. Several examples are used to demonstrate the solution technique for elastic and elastic-plastic problems.

An analysis of cold strip rolling

A method of analysis is presented for investigating the mechanics of cold strip rolling. This method takes into account the elastic deformations of the strip and the rolls and the effect of applied strip tensions, as well as the plastic strip deformations. Predictions of load and torque requirements for reducing strip of any material and dimensions are obtainable along with the pressure distributions between the rolls and the strip, the shape and length of the contact arc, and the resulting roll flattening. The only information required for the application of this method is the dimensions and elastic-plastic material properties of the roll and strip. The results of a number of numerical examples are presented and compared with experimental results to indicate limits on the accuracy of the method.