GH4169合金高温力学行为本构建模及参数识别

针对涡轮盘用GH4169合金开展了高温下单调拉伸、对称循环及非对称循环的实验工作,结果表明,该材料具有比较明显的循环软化和平均应力松弛特性.采用带Ohno/Wang修正的Chaboche粘塑性理论本构方程,对其表现出的复杂力学现象进行本构建模,介绍了Levenberg-Marquadt非线性优化算法,结合材料实验数据并通过该算法识别了本构方程参数,将本构方程通过用户子程序嵌入到有限元软件ABAQUS中,对GH4169合金的上述实验现象进行了数值模拟,计算曲线与实验曲线取得了较好的一致性.     

Fatigue and ratcheting assessment of AISI H11 at 500°C using constitutive theory coupled with damage rule

Hot extrusion is one of the most commonly used manufacturing methods for metal plastic deformation, and the consumption of extrusion tooling is considerably high due to its fatigue damage under cyclic serving condition. Hot‐work tool steel AISI H11 is one of these typical materials employed in extrusion tooling. This work is dedicated to calculating the stress/strain state of AISI H11 and predicting its lifetime at high temperature 500°C by building a unified constitutive model coupled with Lemaitre's damage law. Tensile tests and strain/stress reversed cycling tests have been conducted at 500°C to investigate mechanical properties and damage evolution. A unified constitutive model with Armstrong‐Fredrick/Ohno‐Wang kinematic hardening rule and a new proposed isotropic hardening rule is built; Lemaitre's damage law is employed as well. Parameters are determined based on tests and are temperature dependent. Finite element simulation of the deformation behaviour and fatigue lifetime is implemented into commercial software ABAQUS Standard v6.14‐2 with user material subroutine to validate the proposed method. The comparison shows good agreement with experimental results, and this part of work is essential and crucial to subsequent structure analysis.     

Implicit integration and consistent tangent modulus of a time‐dependent non‐unified constitutive model

This paper describes the implicit integration and consistent tangent modulus of an inelastic constitutive model with transient and steady strain rates, both of which are time‐ and temperature‐dependent; the transient rate is influenced by the evolution of back stress decomposed into parts, while the steady rate depends only on applied stress and temperature. Such a non‐unified model is useful for high‐temperature structural analysis and is practical owing to the ease in determining material constants. The implicit integration is shown to result in two scalar‐valued coupled equations, and the consistent tangent modulus is derived in a quite versatile form by introducing a set of fourth‐rank constitutive parameters into the discretized evolution rule of back stress. The constitutive model is, then, implemented in a finite element program and applied to a lead‐free solder joint analysis. It is demonstrated that the implicit integration is very accurate if the multilinear kinematic hardening model of Ohno and Wang is employed, and that the consistent tangent modulus certainly affords quadratic convergence to the Newton–Raphson iteration in solving nodal force equilibrium equations. Copyright © 2003 John Wiley & Sons, Ltd.     

Correlation between crack length and load drop for low-cycle fatigue crack growth in Ti-6242

For low-cycle fatigue tests with smooth bars the number of cycles to initiation is commonly defined from a measured relative drop in maximum load. This criterion cannot be directly related to the crack length, which is the actual measure of interest. In order to establish a relation between load drop and crack length for the high strength titanium alloy Ti-6242, this investigation compares data from controlled low-cycle fatigue crack growth tests and numerical simulations of these tests. To achieve sufficient accuracy in this relation, focus is given to modelling of mean stress relaxation. Three constitutive models, the Chaboche, the Ohno–Wang and the Chaboche with threshold, are evaluated with respect to experiments. Furthermore, a straightforward method with cycle-scaling of the material parameters are used to efficiently reduce calculation cost. It is shown that it is possible to determine the relationship between load drop and crack length from numerical simulations, provided that care is taken to relevant aspects of the materials stress–strain response. These results are also used to numerically evaluate the effect on load drop of the extensometer position relative to the crack.     

朱-王-唐非线性粘弹性本构模型在有限元分析中的实现及其应用

LS-DYNA可以满足用户对某些材料本构关系子程序开发的要求.本文首先编制了各向同性线弹性材料本构模型子程序,计算单轴拉伸作用,得到材料子程序开发的可行性;另外主要编制了飞机风挡材料采用的具有应变率效应的非线性粘弹性朱-王-唐本构模型,结果能很好地对朱-王-唐模型进行描述,特别是应变率对该模型的影响.并用于真实风挡的计算,得到的数值结果与试验值比较吻合.     

隔振橡胶本构建模研究

提出适合描述隔振橡胶在宽频振动时力学行为的本构模型。本构模型包含超弹性和粘弹性两个部分，超弹性部分表征橡胶材料的静态特性；非线性粘弹性部分描述橡胶材料在振动、冲击载荷下的动态响应。基于该本构模型，对橡胶材料在宽应变率范围内进行试验，九个材料参数通过高、低应变率下的试验数据拟合确定。模型预测结果与试验结果是相当吻合的。     

循环稳定材料的棘轮行为:I.实验和本构模型

在实验分析结果的基础上,对循环稳定材料的室温单轴和非比例多轴循环棘轮行为进行了本构描述,建立了一个简单而合理的、便于工程应用的粘塑性循环棘轮本构模型。给出了模型参数的确定方法,并根据实验获得的单拉应力-非弹性应变关系曲线确定了针对U71Mn 轨道钢材料的参数值。在此基础上,通过对该材料棘轮行为的本构模拟检验了发展模型的预言能力。结果表明,模型具有很好的预测效果,模拟结果与对应的实验结果符合得很好。     

A finite element algorithm to study creep cracks based on the creep hardening surface

This work addresses finite element (FE) modelling of creep cracks under reversed and cyclic loads in steels. A constitutive model based on the creep hardening surface developed by Murakami and Ohno has been selected for this purpose. This model is particularly accurate for describing creep under reversed and cyclic loads and requires no additional material constants. An FE algorithm for this model has been derived and implemented into a research code FVP. The algorithm is verified by comparing the numerical predictions with closed form solutions for simple geometries and loading configurations. FE predictions are compared with experimental data for a stationary crack in a compact tension specimen. The stress and strain fields in the vicinity of a crack under a sustained load are compared with those for the intermediate unloading case. Several integral fracture parameters are investigated as to their appropriateness for describing creep cracks under reversed and cyclic loads.     

Three-dimensional, finite deformation, viscoplastic constitutive models for polymeric materials

A general methodology for developing three-dimensional. finite deformation, viscoplastic constitutive models for polymeric materials is presented. The development begins with the presentation of a one-dimensional spring and dashpot construction which exhibits behavior typical of polymeric materials, namely strain-rate dependence, stress relaxation, and creep. The one-dimensional construction serves as a starting point for the development of a three-dimensional, finite deformation, viscoplastic constitutive model which also exhibits typical polymeric behavior. Furthermore, the three-dimensional constitutive model may be easily generalized to incorporate an arbitrary number of inelastic processes, representing (inelastic) microstructural deformation mechanisms operating on different time scales. Strain-rate dependence, stress relaxation, and creep phenomena are discussed in detail for a simple version of the constitutive model. Test data for a particular polymer is used to validate the simple model. It is concluded that the methodology provides a flexible approach to modeling polymeric materials over a wide range of loading conditions.     

Computer Simulation of Normal and Oblique Impacts of Yawed Projectiles on Ceramic Targets

The investigation of a three-dimensional problem of normal and oblique interaction of yawed projectiles with ceramic plates in the velocity range up to 4000 m/s was carried out by the finite-element method. The paper presents an advanced constitutive model of AD995 Alumina. The model of a damaged medium is used; it is characterized by a possibility of crack initiation and propagation under impact loading. A kinetic fracture model of active type developed earlier for the simulation of fracture in various materials is used for numerical modeling of failure of ceramics at high velocity impact. Temperature effects are taken into account in the constitutive model.     

纯钼薄板各向异性拉压不对称性本构建模研究

目的 对纯钼薄板的各向异性、拉压不对称性以及本构关系进行研究.方法 对纯钼薄板进行不同方向的单拉实验、中心带孔试样单拉实验,和纯钼薄板V形弯曲实验,同时结合有限元模拟反推材料力学性能以及对CPB06屈服准则及Swift强化模型进行参数标定,并进行模型可靠性验证.结果 纯钼薄板具有一定的面内各向异性、拉压不对称性以及显著...     

Large-Deformation Constitutive Theories for Structural Composites: Rate-Dependent Concepts and Effect of Microstructure

Abstract:  Polymer-based composite materials are widely used in applications subjected to a variety of loading types, including shock and impact loading in the range of hundreds of strain per second. The behaviour of composite laminates loaded at those rates is typically nonlinear and may involve rather large strains to failure. In the present study, the large-deformation characteristics and constitutive representations of structural composites were investigated as functions of strain rate and temperature. A plain-weave vinyl ester composite material was selected for the study. Tensile tests of off-axis coupon specimens were conducted over several orders of strain rates and limited change of temperatures. A three-parameter constitutive model was proposed to model the large-deformation stress–strain relationship. The constitutive model was then used to predict the material response at different strain rates. The model predictions were verified by a different set of tests. The basic concepts and methodologies involved in reducing such data to constitutive equations that can be used in commercial computational codes to enable structural analysis in the presence of large-strain progressive damage under dynamic loading is discussed.     

Determination of Constitutive Model Parameters and 3-D Finite Element Formulation for Powder Compaction

ABSTRACT

The knowledge of stress-strain distribution of particulate materials during compression is crucial to the powder processing industries. The finite element technology holds the potential to accurately describe the powder's stress-strain (pressure-density) response during compression. At present, most of the FEMs are two-dimensional or axisymmetric. which can not precisely model the compaction process. In this project, a 3-D finite element formulation for powder compression is presented. The material parameters (for an elastoplastic model and an elasto-viscoplastic model) for three selected materials have been measured. The flexible boundary cubical triaxial tester was used to determine the constitutive model parameters. The constitutive models were verified using data from cubical triaxial tests.     

Three-scale modeling and numerical simulations of fabric materials

Based on the underlying structure of fabric materials, a three-scale model is developed to describe the mechanical behavior of fabric materials. The current model assumes that fabric materials take on an overall behavior of anisotropic membranes, thus the membrane-scale is taken as the macroscopic scale of the model. Since fabric materials exist only as thin structures and there is no corresponding bulk material having a similar constitutive property, the direct approach of the mechanics of surfaces is employed. Following the membrane-scale, a yarn-scale is introduced, in which yarns and their weaving structure are accounted for explicitly. Yarns are modeled as an extensible elasticae. A unit cell consisting of two overlapping yarns is used to formulate the weaving patterns and the interaction between the yarns, which governs the nonlinear constitutive behavior of fabric materials. The third scale, named fibril-scale, accounts for the fibrils constituting a yarn and incorporates their mechanical properties. Via a coupling (handshake) process between these three scales a couple model is introduced. The overall behavior and performance of various fabric products becomes predictable by the knowledge of the material properties of a single fibril and the weaving structure of the fabrics. In addition, potential damage during deformation is also captured in the current model through breakage of fibrils in the fibril-scale.     

Simulation of penetration into porous geologic media

We present a computational study on the penetration of steel projectiles into porous geologic materials. The purpose of the study is to extend the range of applicability of a recently developed constitutive model to simulations involving projectile penetration into geologic media. The constitutive model is nonlinear, thermodynamically consistent, and properly invariant under superposed rigid body motions. The equations are valid for large deformations and they are hyperelastic in the sense that the stress tensor is related to a derivative of the Helmholtz free energy. The model uses the mathematical structure of plasticity theory to capture the basic features of the mechanical response of geological materials including the effects of bulking, yielding, damage, porous compaction and loading rate on the material response. The new constitutive model has been successfully used to simulate static laboratory tests under a wide range of triaxial loading conditions, and dynamic spherical wave propagation tests in both dry and saturated geologic media.     

A neural network constitutive model for hyperelasticity based on molecular dynamics simulations

Numerical analysis of the hyperelastic behavior of polymer materials has drawn significant interest from within the field of mechanical engineering. Currently, hyperelastic models based on the energy density function, such as the Neo-Hookean, Mooney-Rivlin, and Ogden models, are used to investigate the hyperelastic responses of materials. Conventionally, constants relating to materials were determined from experimental data by using global least-squares fitting. However, formulating a constitutive equation to capture the complex behavior of hyperelastic materials was difficult owing to the limitations of the analytical model and experimental data. This study addresses these limitations by using a system of neural networks (NNs) to design a data-driven surrogate model without a specific function formula, and employs molecular dynamics (MD) simulations to calculate the massive amount of combined loading data of hyperelastic materials. Thus, MD simulations were used to propose an NN constitutive model for hyperelasticity to derive the constitutive equation to model the complex hyperelastic response. In addition, the probability distributions of the numerical solutions of hyperelasticity are used to characterize the uncertainty of the MD models. These statistical finite element results not only present numerical results with reliability ranges but also scattered distributions of the solution obtained from the MD-based probability distributions.     

Constitutive modeling of aluminum nitride for large strain,high-strain rate,and high-pressure applications

This paper presents constitutive modeling of aluminum nitride (AlN) for severe loading conditions that produce large strains, high-strain rates, and high pressures. The Johnson–Holmquist constitutive model (JH-2) for brittle materials is used. Constants are obtained for the model using existing test data that include both laboratory and ballistic experiments. Due to the wide range of experimental data the majority of constants are determined explicitly. The process of determining constants is provided in detail. The model and constants are used to perform computations of many of the experiments including those not used to generate the constants. The computational results are used to validate the model, provide insight into the response of AlN, and to demonstrate that one set of constants can provide reasonable results over a broad range of experimental data.     

Theory of creep of cyclically unstable materials

The structural model of the medium is used as a basis for describing determining relations of the theory of creep of cyclically unstable materials. The relations are based on the concept of the memory surface proposed by N. Ohno. In the theory equations this surface is introduced on the macrolevel which greatly simplifies calculation equations. The experimental data are compared with the calculations carried out using the proposed theory.Translated from Problemy Prochnosti, No. 9, pp. 44–47, September, 1993.     

Modelling of the Mechanical Properties of Composite Materials at High Temperatures: Part 1. Matrix and Fibers

This paper is devoted to modelling the thermomechanical behaviour of charring composite materials at high temperatures. A multi-level model with an internal structure of unidirectional composite materials consisting of four structural levels is developed.With the help of this model, structural constitutive relations and expressions connecting elastic modules and strength characteristics of charring matrix and fibres with the properties of their internal phases are derived. Comparison of the model with experimental data for different types of matrices and fibres is conducted. Specific phenomena of the high-temperature behaviour of charring composites at high temperatures are analyzed.     

Higher-order fractional constitutive equations of viscoelastic materials involving three different parameters and their relaxation and creep functions

Two higher-order fractional viscoelastic material models consisting of the fractional Voigt model (FVM) and the fractional Maxwell model (FMM) are considered. Their higher-order fractional constitutive equations are derived due to the models’ constructions. We call them the higher-order fractional constitutive equations because they contain three different fractional parameters and the maximum order of equations is more than one. The relaxation and creep functions of the higher-order fractional constitutive equations are obtained by Laplace transform method. As particular cases, the analytical solutions of standard (integer-order) quadratic constitutive equations are contained. The generalized Mittag–Leffler function and H-Fox function play an important role in the solutions of the higher-order fractional constitutive equations. Finally, experimental data of human cranial bone are used to fit with the models given by this paper. The fitting plots show that the models given in the paper are efficient in describing the property of viscoelastic materials.