规定非比例伸长应力σpε和规定残余伸长应力σrε

规定非比例伸长应力和规定残余伸长应力都属规定微量塑性伸长应力.所谓非比例伸长是指外力与伸 长不呈比例关系的伸长;而残余伸长则是指外力卸除后,弹性变形回复,试样标距部分的残余伸长.因此,两 者的区别在于所采用的试验方法不同.前者是在受力状态下测定的,后者是在试样卸除外力后测定的. 严格来说,材料的残余伸长不完全等于非比例伸长,因而规定残余伸长应力与规定非比例伸长应力是不 等的,这是由于材料的滞弹性(应变落后于应力)所致. 必须指出的是,滞弹性很大的金属材料是极少数(如GCr15,1Cr18Ni9Ti等),多数材料的滞弹性很小, 甚至可忽略不计.于是可认为规定残余伸长应力与规定非比例伸长应力相等,即σr0. 01=σp0.01=σr 0.05=σp0.05, σr0.2=σp0.2.在试验工作中,当有关材料技术标准对上述指标未作明确规定时,可任意选择一种试验方法进行 试验.     

金属圆棒拉伸试样σ_(p0.2)值在WAW-Y500试验机上的简易测量法

论述了在 WAW- Y50 0试验机上通过绘制力 -夹头位移曲线来测量金属圆棒拉伸试样的规定非比例伸长应力 σp0 .2 值的方法及其可行性。通过分析得出 ,采用该方法在生产检验上测量金属圆棒拉伸试样的规定非比例伸长应力 σp0 .2 时 ,试样可采用的最短平行长度为 50 mm。     

引伸计误差对Rp0.2测量结果的影响

就引伸计标距误差和引伸计系统误差对RP0.2测量结果的影响进行了分析。对几种材料的试验误差分析表明,应变误差造成的RP0.2的测量误差依赖于材料自身的特性。对于普通材料,其应变误差对拉伸性能RP0.2造成的误差可以假设小于1%;但是对于某些合金材料,引伸计误差对拉伸性能RP0.2造成的误差大于1%,在测量这些材料时需要采用比规定级别更高的引伸计。     

规定非比例伸长应力σ_(pe)和规定残余伸长应力σ_(re)

规定非比例伸长应力和规定残余伸长应力都属规定微量塑性伸长应力。所谓非比例伸长是指外力与伸长不呈比例关系的伸长 ;而残余伸长则是指外力卸除后 ,弹性变形回复 ,试样标距部分的残余伸长。因此 ,两者的区别在于所采用的试验方法不同。前者是在受力状态下测定的 ,后者是在试样卸除外力后测定的。严格来说 ,材料的残余伸长不完全等于非比例伸长 ,因而规定残余伸长应力与规定非比例伸长应力是不等的 ,这是由于材料的滞弹性 (应变落后于应力 )所致。必须指出的是 ,滞弹性很大的金属材料是极少数 (如 GCr1 5,1 Cr1 8Ni9Ti等 ) ,多数材料的滞…     

金属材料规定非比例延伸强度Rp0.2测量结果的不确定度评定

根据JJFl059—1999《测量不确定度评定与表示》的要求,系统地对GB／T228—2002《金属材料室温拉伸试验方法》中规定非比例延伸强度Rp0．2测量结果的不确定度进行了评定。针对金属材料力学性能检测领域的测量结果不确定度特点,选用了性能相对均匀的不锈钢板为试验材料,分析了试验过程中方法、设备、量具、人员和环境等不同因素对测试结果的影响程度。结果表明,试验条件下的非比例延伸强度Rp0．2测量结果的相对不确定度为2．55％。     

基于实模态的非比例阻尼体系复模态叠加法

为提高非比例阻尼体系强迫振动时复模态叠加法的计算效率,基于模态摄动法基本原理,提出一种利用无阻尼体系实模态的复模态叠加法.该方法由模态摄动法将非比例阻尼体系的复模态表示为实模态线性组合,在此基础上,建立了强迫振动复模态叠加法的实模态的线性组合解.以一个带附加阻尼的强非比例阻尼三层框架结构为例进行地震反应分析,计算结果表...     

改进的Berman-Baruch法在非比例阻尼有限元模型修正中的应用

该文首先利用识别后的复模态计算出结构的正交模态,然后在Berman-Baruch优化矩阵型法(BB法)基础上提出并推导了改进的Berman-Baruch法(IBB法)。该方法定义了合理的优化目标函数,克服了BB法需要质量归一化模态振型的约束,修正后的模型可保持明确的物理意义和带状特性。该文通过一6个自由度的非比例阻尼质量弹簧阻尼(MSD)系统和实验室下的一6个自由度的框架结构模型修正的计算和比较,验证了IBB 法的有效性和实用性。     

Tangential stress analysis of myocardial wall by finite element method

The stress and strain of heart are two important and effective parameters to describe the deformation of the myocardial wall to analysis the dynamic function of the heart, but which are difficult to be ascertained. In this paper, a novel method is presented to built the triangular surface model and calculate the tangential stress and strain of myocardial wall ,which can be further used to reflect the Left Ventricle Twisting(LVT)-a sensitive index to assess the systolic and diastolic function of heart. Firstly, Point Distribution Model (PDM) is used to obtain the feature points of the left ventricular (LV) surface in SPECT images. Secondly, the surface model of LV is constructed by triangular mesh, and then the subdivision strategy is introduced to refine the model. Thirdly, plane projection and FEM are applied to calculate the tangential stress and strain. Finally, the distribution of tangential modulus of elasticity is discussed. The stimulation results show the proposed method can be used to compute the tangential stress and strain of myocardial wall effectively and the computing result is consistent with the results mentioned in the literatures.     

使用横梁位移测定铍材的断后伸长率

GB/T 228.1-2010规定了使用直接法和移位法测定金属材料的断后伸长率。但铍材拉伸试样的横截面积和断后伸长率较小,若使用直接法测定,其断后伸长率随断口所在位置及试样断裂部分拼接状态的变化而变化,不具备唯一性;若使用移位法测定,虽弥补了直接法的不足,但操作较为麻烦。笔者介绍了利用横梁位移计算铍材拉伸试样断后伸长率的方法,可弥补上述两种方法的不足。通过试验及数据统计分析,证明此种方法可以准确快速地测定铍材试样的断后伸长率。     

Practical Case Application for Stress Model Validation and Enhancement by Means of Metrological Tools

Models consider ideal and simplified situations that will never be met in the real case. The process of comparing model predictions and experimental observation is in the basis of scientific research. This comparison is however complicated because of the uncertainties of the model input data and the difficulty to control the accuracy of the tests and to obtain a significant statistical sampling. Moreover, there isn't yet a consensus on a validation parameter. This paper presents a three‐step validation procedure that allows quantifying the application limits of a two‐dimensional stress model in a three‐dimensional situation. A global uncertainty model is calculated comprising the uncertainty of the model and also the uncertainty coming from the experimental results. The E_N number, a statistical magnitude for interlaboratory comparisons, is used to analyse the compatibility between the experimental and theoretical results. Finally, a bootstrapping method is proposed to calculate the coverage interval of the sampling and determine if new experiments should be carried out. Numerical results of this new validation procedure are provided for the case under study. It is also demonstrated that the computed uncertainty budget can be a useful tool to enhance the two‐dimensional model by enlarging its uncertainty limits.     

氮化层弹性模量及残留内应力的测定

为了计算钢铁材料氮化层的弹性模量,提出了组合樑物理模型,采用等强樑的试样,测定氮化层弹性模量及残留内应力.试验结果表明:氮化层的弹性模量比母材高出约29.2%.X射线应力常数比母材提高44.4%.     

三种方法测定金属薄板塑性应变比值的结果比较

分别采用半自动、全自动以及光学非接触式引伸计三种不同的方法,测定了四种不同厚度规格的DC03冷轧薄板的塑性应变比(r)值,将三种方法测定得到的试验结果进行比较,发现存在较大差异,进而分析了造成差异的原因.结果表明:半自动法测定的r值与光学非接触式引伸计法测定的r值较接近,试验结果具有较高的可靠性和重现性;而全自动法测定...     

Numerical Study on the Effects of Equi-biaxial Residual Stress on Mechanical Properties of Nickel Film by Means of Nanoindentation

In this paper,mechanical properties of Nickel film under residual stress have been systematically examined by finite element method in nanoindentation.It was found that load-displacement curves shifted under elastic residual stress and residual stress exceeded the yield stress for fixed indentation depth.Indentation profiles changed monotonously with compressive and tensile stresses at peak force which determinates contact area observed directly by finite element modeling (FEM).The elastic residual stress h...     

Measuring mechanical properties of plasma-sprayed alumina coatings by nanoindentation technique

AISI 1020 steel substrate is coated with alumina as feedstock material using plasma spraying process in order to correlate the microstructural features with mechanical properties of coating. The present work focuses on the effects of microstructural inhomogeneity on mechanical properties of alumina coating through nanoindentation technique. Young’s modulus and hardness of the alumina coating are analytically evaluated. Indentation stress–strain curves are generated from the experimentally obtained load–displacement curves to characterise the mechanical properties of the coating. The results have shown large variation in hardness and Young’s modulus of alumina due to microstructural inhomogeneity of the coating.     

基于比容测量对材料三维残余应力及其分布的测试分析

目的 判断比容差法是否可应用于材料内部残余应力分布状态的定量研究,旨在提供一种新的残余应力的测试方法。方法 通过对材料非切应变时的弹性力学进行讨论,推导体积应变,得出残余应力的计算公式。应用比容差法对一种工业纯铝的残余应力状态进行定量测量与表征,并进行钻孔法的定量验证。在此基础上,应用比容差法对纯铝镦粗变形后的三维平均残余应力的分布进行了测量研究。结果 比容差法对纯铝镦粗变形后的体积变化测量,可精确、定量表征材料的残余应力状态,与钻孔法实验结果相比,两者的误差在20%以内;镦粗变形后,残余压应力在坯料中心处取得最大值,且对称于中心沿高度方向逐渐减小,呈对称递减分布。结论 比容差法可用于材料三维残余应力分布的研究,为残余应力分布规律,提供了一种新的有效且精确的测试方法,具有实际应用的价值。