Inversion of three-stage stress-strain relation for stainless steel in tension and compression

Presented in this paper is a new stress-strain relation for stainless steel alloys that provides the stress as an explicit function of the strain. The relation is an approximate inversion of a recently proposed three-stage stress-strain relation based on a modified Ramberg-Osgood equation. The three-stage relation is a much more accurate formulation than the previous two-stage formulations and is applicable to both tensile as well as compressive stresses. The new relation is derived by making a rational function assumption on the fractional deviation of the actual stress-strain curve from an idealized linear elastic behaviour. The new expression is valid over the full range of the stress well beyond the elastic region. The validity of the inverted expression is tested over a wide range of material parameters. These tests demonstrate that, the new expression results in stress-strain curves which are both qualitatively and quantitatively in excellent agreement with the fully iterated numerical solution of the full-range stress-strain relation with a maximum error below 4%.     

Development of moment-rotation model equations for flush end-plate connections

This paper presents the development of Ramberg-Osgood and Three-Parameter Power model prediction equations for the moment-rotation (M-θ) behavior of flush end-plate connections with one row of bolts below tension and compression flanges. A finite element model (FEM) of the connection region along with the connected beam and column is developed for load deformation analyses, which included material, geometric, and contact nonlinearities. The FEM model was verified with test results conducted and reported for flush end-plate connections in the literature during the 1980s. A matrix of test cases was obtained by varying the geometric variables of flush end-plate connections within their practical ranges. The connection M-θ data for these test cases were obtained by FEM analyses, which were then curve fitted to Ramberg-Osgood and Three-Parameter Power model equations to obtain parameters defining these equations. Finally, prediction equations were developed for parameters of the model equations as functions of geometric variables of the flush end-plate connections.     

金属玻璃基复合材料的微结构效应

基于自由体积理论和Ramberg-Osgood模型,并利用ABAQUS软件,建立颗粒随机分布代表性体积单元模型,模拟了Ti_(64.5)Zr_(14.5)V_(18.5)Cu_(2.5)颗粒增韧Ti基金属玻璃基复合材料在单轴拉伸状态下的微结构效应,讨论了颗粒的体积分数、团聚数目、长径比、定位取向和界面对金属玻璃韧性的影响。结果表明:提高颗粒体积分数能显著提高复合材料的塑性,但部分牺牲了复合材料的强度;增大颗粒长径比能够增强复合材料的塑性和屈服强度;使颗粒的取向与荷载方向成90°或0°,不仅增强了复合材料的塑性,而且与其他排布相比也增强了复合材料的强度;减少团聚数目至2个以下,能明显减少金属玻璃基复合材料的塑性和强度的损失,使团聚中颗粒与荷载成90°,却能改善复合材料的塑性和强度;在颗粒增韧金属玻璃基复合材料中加入零厚度界面,能观察到在主剪切带上颗粒和基体在界面处脱粘,得到与实验现象更加吻合的结果。通过上述的研究能够很好地理解复合材料的微结构效应,并有利于材料的设计。     

FRP拉挤复合材料本构关系模型研究

为了更加精确的描述厚型拉挤复合材料的力学性能和力学响应特征,文中以厚型E玻璃纤维/环氧树脂拉挤型复合材料系统为例,运用三维细观力学模型描述材料的非线性本构关系。模型从纤维和基质成分的角度对由粗纱层和玻纤双轴布构成的层合材料进行材料响应描述,最终建立了相应的有限元模型并通过试验进行校准。试验和数值分析结果表明:三维细观力学模型能够准确的描述E玻璃纤维/环氧拉挤型复合材料的力学响应,其精确度可以通过横向试样拉伸试验结果进行校准提高。     

评价饱和砂土液化过程中小应变到大应变的本构模型(英文)

在RambergOsgood模型的基础上,建立了一个实用的能描述饱和砂土从液化前小应变到初始液化后大应变范围的非线性本构模型。该模型主要有三个特点:①采用作者曾提出的移动相态转换线(MPTL)和移动临界状态线(MCSL)概念来较为合理地描述变形过程中的有效应力路径和临界状态;②采用一个应力软化模型来描述剪胀和定义超静孔压变化引起的骨架曲线的软化与硬化;③基于笔者等提出的液化后大变形理论来描述初始液化后产生的大剪切变形。文中通过对室内循环剪切试验结果的模拟,验证了模型的预测能力。该模型适用于水平饱和砂土地基的有效应力地震反应分析。     

弹塑性海床上的管土相互作用分析

海底管线的在位稳定性问题是海底管线设计中的关键问题之一,为对海底管线的设计提供理论依据,采用大型通用有限元软件ABAQUS对管土系统进行分析。土体的本构模型采用动态的Ramberg-Osgood弹塑性模型,通过改变管道的水下重、环境载荷等参数进行计算。计算结果表明,由于土体侧向隆起而形成的楔形与试验结果相比吻合,管道的水下重、环境载荷对管道的稳定性都有一定程度的影响,并得到了管道侧向失稳的判别准则。     

Mechanical properties of roller bent wide flange sections — Part 2: Prediction model

This paper provides a series of simple equations that allow the structural engineer to predict the mechanical properties across the section of roller bent wide flange steel members: proportional limit, yield stress, ultimate tensile stress, strain at ultimate tensile stress and strain at rupture. The equations are based on experimental results from tensile tests performed on coupons taken from roller bent wide flange sections which are presented in a companion paper. The newly obtained mechanical properties yield seven different full stress-strain curves for nine specific locations on the steel cross-section. The stress-strain models for the material of the flanges are defined by non-linear curves. The stress-strain characteristics in the web allow the material to be represented by bi-linear stress-strain curves. Comparison between predicted adjustments in mechanical properties due to roller bending and measured properties gives good agreement. The obtained stress-strain curves are suitable for implementation in finite element models for the analysis of arch structures employing beam, shell or solid elements.     

An explicit stress formulation for stainless steel applicable in tension and compression

In this paper an explicit stress formulation for stainless steel is presented. The formulation is applied to both tension and compression and it is an approximation to the closed form inversion of an existing two-stage stress-strain relation which is based on a modified Ramberg-Osgood equation. The validity of the explicit expression is tested over a wide range of material parameters. The tests demonstrate that the explicit formula is in excellent agreement with the fully iterated numerical solution of the full-range stress-strain relation. By incorporating an existing expression for deformation capacity, the proposed explicit formula is also used to obtain an explicit formulation for the computation of local buckling stress and compression resistance in terms of cross sectional slenderness.     

Explicit full-range stress-strain relations for stainless steel at high temperatures

This paper presents a new explicit stress-strain relation for stainless steel at high temperatures. The relation is an approximation of the closed form inversion of an existing two-stage stress-strain relation based on a modified Ramberg-Osgood equation with corresponding temperature-dependent parameters. This new expression for the stress σ, as an explicit function of the total strain ?, is obtained by making a modified power law assumption on the fractional deviation of the actual stress-strain curve from an idealized linear elastic behaviour. The validity of the inverted expression is tested over a wide range of material parameters and a wide range of temperatures. The tests show that the new expression results in stress-strain curves which are both qualitatively and quantitatively consistent with the fully iterated numerical solution of the full-range stress-strain relation for normal as well as high temperatures.     

The influence of the nitrogen/nickel‐ratio on the cyclic behavior of austenitic high strength steels with twinning‐induced plasticity and transformation‐induced plasticity effects

Austenitic high nitrogen (AHNS) and austenitic high interstitial steels (AHIS) are of interest for mechanical engineering applications because of their unique combination of mechanical (strength, ductility), chemical (corrosion resistance) and physical (non‐ferromagnetic) properties. But despite their high strength values e. g. after cold deformation up to 2 GPa in combination with an elongation to fracture of 30 %, which is based on twinning‐induced plasticity (TWIP) mechanisms and transformation‐induced plasticity (TRIP) mechanisms, the fatigue limit remains relatively small. While for chromium‐nickel steels the fatigue limit rises with about 0.5‐times the elastic limit it does not at all for austenitic high‐nitrogen steels or only to a much smaller extent for nickel‐free austenitic high‐interstitial steels. The reasons are still not fully understood but this behavior can roughly be related to the tendency for planar or wavy slip. Now the latter is hindered by nitrogen and promoted by nickel. This contribution shows the fatigue behavior of chromium‐manganese‐carbon‐nitrogen (CrMnCn) steels with carbon+nitrogen‐contents up to 1.07 wt.%. Beside the governing influence of these interstitials on fatigue this study displays, how the nitrogen/nickel‐ratio might be another important parameter for the fatigue behavior of such steels.