不锈钢材料的应力-应变模型

不锈钢材料与普通碳素钢的力学性能有较大不同,其应力-应变关系呈显著非线性,且各向异性,因此精确描述不锈钢应力-应变关系是不锈钢构件受力及稳定性分析等相关研究工作的基础.本文回顾了国内外关于不锈钢应力-应变本构模型的研究成果,通过介绍、分析和比较研究指出,Quach三段式应力-应变模型采用Ramberg-Osgood三参数表示,可直接应用现行规范进行结构设计,其准确性已得到相关试验和有限元分析证实.因此,Quach模型是目前可供选用的最佳本构模型.     

三轴应力下塑性混凝土应力应变关系试验研究

通过4组塑性混凝土的单轴和常规三轴压缩应力应变全曲线试验,研究了三轴应力下塑性混凝土应力应变关系.结果表明：在围压作用下,塑性混凝土轴向应力应变曲线与单轴压缩下的曲线差别明显,主要表现为直线上升段很短,曲线上升段较长,无明显峰值点,下降段较平缓.利用割线模量表征塑性混凝土三轴应力下应力应变曲线上升段的主要变形特征,分析了影响割线模量的主要因素,建立了割线模量与围压、单轴抗压强度和弹性模量之间的关系式.研究了塑性混凝土三轴应力下峰值应变随围压、单轴应力下抗压强度及峰值应变的变化规律,并建立了相应的关系式.全面分析了塑性混凝土单轴及三轴作用下应力应变曲线特征,通过归一化处理后,拟合出常规三轴应力下塑性混凝土轴向应力应变关系式.     

等p应力路径下粉煤灰应力-应变关系的三轴试验研究

进行了不同超固结比粉煤灰在等p应力路径下的饱和固结三轴剪切试验,讨论了粉煤灰的应力-应变关系,为粉煤灰的工程应用提供了依据。     

混凝土二轴受拉应力-应变关系

在分析混凝土二轴受拉破坏机制的基础上,通过选取合理的损伤变量和自由能势函数,基于不可逆力学原理,建立二轴受拉的损伤本构模型;利用损伤能释放率确定损伤演化规律,导出混凝土二轴受拉应力—应变关系的显式表达式,其参数可通过单轴拉伸试验确定;利用二轴拉伸曲线特征点条件,得到峰值应变的变化规律;与已有试验结果相比较,效果良好。     

桂林粘土应力-应变关系归一化性状研究

本文通过对桂林粘土的固结不排水三轴剪切试验,基于典型的双曲线方程,从理论上推导了为实现应力-应变方程归-化而必须满足的归一化条件,并提出了用主应力差渐近值作为标准归一化因子.同时,运用标准归-化因子,建立了桂林粘土固结不排水条件下应力-应变特性的归一化方程.利用求得的归一化方程对不同围压下的应力-应变关系进行归一化分析...     

工程中典型应力路径下土的应力-应变特性分析

分别采用Mohr-Coulomb模型、修正剑桥模型和UH模型预测正常固结土在常规三轴压缩、三轴伸长和平均主应力p减小的压缩工况中典型路径下土的变形特性。Mohr-Coulomb模型为理想弹-塑性模型,屈服之前为弹性变形,屈服之后为变形无限增大的弹-塑性变形。修正剑桥模型能够较好地模拟压缩路径条件下正常固结土的应力-应变...     

长期轴压下有初应力的CFRP约束混凝土柱应力-应变关系分析

为了研究有初应力的CFRP约束混凝土柱在长期荷载作用下的应力-应变关系,对有不同初应力的12个CFRP 约束混凝土柱进行了三种模式的长期荷载试验,观测了初应力和长期荷载对CFRP约束柱的长期变形、峰值点应力 、应变及应力-应变曲线特征的影响。试验结果表明,在长期荷载作用下,包裹CFRP后的构件比未包裹的长期变 形小,并随初应力水平的提高,构件的长期变形增大;长期荷载对峰值点应力、应变的影响随初应力水平的提高 而增大,在初应力水平较高时有减小的趋势;与短期荷载相比,长期荷载作用后的应力-应变曲线特征没有发生 明显变化。在此基础上,选取ACI 209-92模型和Findley模型分别作为混凝土和CFRP的徐变模型,提出了CFRP约 束混凝土柱长期变形的计算方法,并针对三种加载模式,分别建立了长期荷载下CFRP约束混凝土柱的应力-应变 关系计算模型,结果表明模型的计算曲线与试验曲线吻合较好。     

混凝土单向受拉损伤的应力应变关系

本文结合几何损伤理与试验研究结果，研究混凝土单向拉伸时的损伤行为，建立了双曲线的损伤演化方程及相应的应力变关系表达式。     

微矿粉高性能混凝土的轴拉应力-应变关系

微矿粉是一种高火山灰活性的微粉 ,由水淬高炉矿渣经磨细而得 ,其在混凝土中的作用原理与硅粉及其他火山灰相似 ,主要是微矿粉的填充效应、对硅酸盐水泥的加速水化作用及与Ｃａ（ＯＨ）２ 的火山灰反应 ,即活性ＳｉＯ２ 和Ａｌ２Ｏ３ 与Ｃａ（ＯＨ）２ 水化生成ＣＳＨ凝胶和水化铝酸钙（Ｃ４ＡＨ１３ ·Ｃ３ＡＨ６）、水化硫铝酸钙（Ｃ２ＡＳ Ｈ８）［１、２］。大量研究结果表明 ,微矿粉能显著改善混凝土的和易性 ,提高混凝土的保水性［３］,提高混凝土的强度 ,尤其是长期强度 ,并通过绝热温升试验证明能大大降低混凝土的水化热 ,减小温差…     

不同应力路径对砂土应力-应变关系影响

<正> 一、前言 目前广泛应用于土坝和地基应力-变形分析中的本构关系数学模型,多建立在常规三轴试验的基础上,并认为模型参数与应力路径无关。实际工程中填方工程和一些地基中的土体常经历等主应力比的应力路径,地基中的固结情况则更符合于K₀固结应力状态。工程中应力条件千差万别,而建立在常规三轴试验基础上的数学模型对工程的适用性如何,即如何验证模型的问题,越来越被重视。国外已有许多人对不同应力路径的应力-应变关系进行了研究,如     

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%.     

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.     

受压不锈钢—碳钢管混凝土短柱的研究

介绍不锈钢-碳钢管混凝土(CFSCT)柱这种新型的组合构件。这种将不锈钢和钢管混凝土(CFST)结构的优点结合在一起的组合件被认为具有更高的抗腐蚀性、承载力和更低的成本。对新提出的组合柱进行了一系列的抗压试验,提出一个关于改进混凝土芯的应力-应变模型,建立一个三维的非线性有限元(FE)模型并验证了试验结果。在荷载-变形响应方面的试验结果与数值结果相当一致。对包括钢管厚度、直径和碳钢管屈服强度在内的参数进行了研究,从而更清晰地认识这种组合柱的性能。     

不锈钢构件截面的残余应力分析

对碳钢结构截面的残余应力的大小及分布的研究已经比较成熟,但是对不锈钢截面的残余应力研究却还很少见。不锈钢与碳钢有着不同的材料应力-应变特性和热性能,它们都影响着残余应力的形成。这意味着已确定的碳钢残余应力模型可能并不适合不锈钢。随着不锈钢的应用日益增多,对其残余应力的研究显得尤为重要。     

不锈钢椭圆中空受压构件的结构响应

冷加工不锈钢椭圆中空截面结合了圆形中空截面和不锈钢的美感以及不同几何形状的横截面相对于两个主轴的结构功效。迄今为止,对这种横截面的构件尚没有结构设计指南,主要是产品相对较新,缺乏基础结构试验数据。对冷加工不锈钢椭圆空心截面受压构件的结构响应进行研究,提出设计建议。为获得结构性能的基础数据,进行一系列试验。首先,通过张拉试验建立基本的材料应力-应变关系。随后,通过短柱试验确定横截面的平均受压响应,通过弯曲试验获得极限承载力以确定不锈钢椭圆中空截面合理的弯曲曲线。对试件进行包括初始缺陷的几何性质测定。对试件的荷载位移响应进行记录并在文中给予介绍。与试验同步,进行了有限元模拟。如果有限元模拟的结果与试验结果不相符,将对个别关键参数进行进一步的研究,包括外形比例、横截面长细比和构件长细比。基于试验与数值分析结果,提出3组不锈钢椭圆中空截面受压限值以及椭圆中空截面柱合理弯曲曲线。     

Elevated temperature material properties of stainless steel alloys

Appropriate assessment of the fire resistance of structures depends largely on the ability to accurately predict the material response at elevated temperature. The material characteristics of stainless steel differ from those of carbon steel due to the high alloy content. These differences have been explored in some detail at room temperature, whilst those at elevated temperature have been less closely scrutinised. This paper presents an overview and reappraisal of previous pertinent research, together with an evaluation of existing elevated temperature stainless steel stress-strain test data and previously proposed material models. On the basis of examination of all available test data, much of which have been recently generated, revised strength and stiffness reduction factors at elevated temperatures for a range of grades of stainless steel have been proposed, including four grades not previously covered by existing structural fire design guidance. A total of eight sets of strength reduction factors are currently provided for different grades of stainless steel in EN 1993-1-2 and the Euro Inox/SCI Design Manual for Structural Stainless Steel, compared to a single set for carbon steel. A number of sets of reduction factors is appropriate for stainless steel since the elevated temperature properties can vary markedly between different grades, but this has to be justified with sufficient test data and balanced against ease of design — it has been proposed herein that the eight sets of reduction factors be rationalised on the basis of grouping grades that exhibit similar elevated temperature properties. In addition to more accurate prediction of discrete features of the elevated temperature material stress-strain response of stainless steel (i.e. strength and stiffness reduction factors), a material model for the continuous prediction of the stress-strain response by means of a modified compound Ramberg-Osgood formulation has also been proposed. The proposed model is less complex than the current provisions of EN 1993-1-2, more accurate when compared to test results, and the model parameters have a clear physical significance.     

火灾下不锈钢梁—柱节点数值分析

评估了EC3中不锈钢梁-柱节点发生或不发生侧向扭转屈曲的设计准则的准确性和安全性。对焊接方式相同的H型钢梁-柱节点进行了大量数值参数研究,以此为基础进行评估。研究中考虑了残余应力、截面高厚比、弯矩图形状和不锈钢等级的影响。提出了火灾下不锈钢梁-柱节点的新设计方程,计算结果与数值分析结果进行对比,结果表明,新设计方程比EC3中设计方程更为安全。此外,对火灾时不锈钢梁在梁端弯矩与横向荷载共同作用下的侧向扭转屈曲进行了研究。     

钢纤维橡胶混凝土的循环受压应力-应变关系

采用等强配合比优化设计来制备橡胶掺量0%～20.0%、钢纤维掺量0%～1.5%的12组钢纤维橡胶混凝土（SFR-RuC）试件,并且通过单轴循环受压应力-应变全曲线试验分析其循环受压力学性能.结果表明：配合比优化设计后,在橡胶掺量为20.0%时可以得到与普通C60混凝土基本等强的SFR-RuC;与普通混凝土、橡胶混凝土及钢纤维混凝土相比,SFR-RuC的循环受压力学性能更优,破坏呈明显延性特征,延性和韧性更高,滞回耗能能力更强,塑性应变累积和刚度退化更缓慢;综合考虑橡胶及钢纤维掺量的影响,在试验数据基础上提出的SFR-RuC单轴循环受压应力-应变关系模型,可以为SFR-RuC结构的设计分析提供一定的理论基础.     

不锈钢螺栓连接节点的破坏研究

尽管不锈钢与碳素钢的机械性能有显著的不同,但是现有规范关于不锈钢连接节点的设计规定都基于碳素钢的设计准则。对于不锈钢螺栓连接节点的设计抗力,EN1993-1-4和SCI/EuroInox(美国《科学引文索引》/欧洲不锈钢协会)的不锈钢设计手册基于EN1993-1-8和EN1993-1-3作了一些小修改。研究了厚板和薄板的不锈钢螺栓连接节点的承载性能。提出了一个奥氏体不锈钢和铁素体不锈钢试件的数值分析模型,并证明其正确性。将该模型用于螺栓节点承载力的参数分析,可研究主要变量对其影响。这些参数包括螺栓边距e2,端距e1和板厚t。结果表明,不锈钢螺栓节点的变形性能与碳钢节点存在某种程度的不同。数值模型中最初出现裂纹的部位与试验中观察到的不锈钢节点和碳素钢节点相符,这种相符性被作为定义一种强度失效准则的基础。以参数分析结果为基础的不锈钢螺栓连接节点承载能力极限状态和正常使用极限状态设计法则比现行的EC3法则更加经济和简捷。