一种天然气和石油管道屈服强度的检测方法

按照SY/T 5992—2012设计的钢管静水压爆破试验设备仅限于计算钢管内的压力值,不能自动获得钢管的屈服强度及斜率。依据AS/NZS 2885.5:2012的检测方法,借助钢管静水压爆破试验设备,对试验采集到的原始数据采用Excel软件绘制成压力-进水量曲线和钢管的应力-应变曲线并进行分析,用Excel软件实现了爆破点的1/2斜率屈服强度和实际斜率的计算,结合绘图软件实现了各屈服强度的定量化求取。结果表明:用以上方法所求取的管通的各种屈服强度与实际拉伸试验得到的数据基本一致。该方法可以为按照SY/T 5992—2012设计的钢管静水压爆破试验设备扩展出屈服强度计算能力。     

几个强度理论的屈服实验研究

根据多种塑性金属的二向和三向拉伸与压缩组合主应力屈服强度实验数据,对Tresca强度理论、Mises强度理论、Mohr-Coulomb强度准则、Beltrami最大能量理论、极限应变能强度理论等几个强度理论计算的相对误差进行了比较分析。结果表明极限应变能强度理论计算的误差在10%以内,为最小。Tresca强度理论、Mises强度理论和Mohr-Coulomb强度准则计算的误差分别为-36%、-27%、-23%,计算结果比试验结果偏保守。Tresca强度理论和Mises强度理论都不适用于拉伸屈服强度和压缩屈服强度相等的材料,该材料的理论剪切屈服强度为拉伸屈服强度的倍。极限应变能强度理论可用于二向和三向拉伸与压缩组合主应力强度计算,在全拉伸和全压缩主应力状态下与Rankine强度理论一致,具有工程应用前景和价值。     

轴压作用下CFRP加固圆钢管混凝土短柱的承载力分析

对碳纤维增强复合材料（CFRP）加固圆钢管混凝土（C-CFST）短柱的轴向承载力进行了理论研究。基于连续介质力学,考虑钢管与混凝土处于三向应力状态,CFRP处于环向受拉的应力状态,建立了CFRP-圆钢管混凝土（C-CFRP-CFST）短柱的理论分析模型。通过理论推导,得到了轴压作用下C-CFRP-CFST短柱的屈服承载力及极限承载力的理论计算公式,并将理论解与已有试验值做比对,证明了理论公式预测的精度。最后采用提出的理论公式对C-CFRP-CFST短柱的轴向承载性能进行了参数分析。研究表明:提高钢管屈服强度及混凝土立方抗压强度或减小钢管径厚比D_s/t_s,都会提高C-CFRP-CFST短柱的极限承载力及屈服承载力;增加CFRP层数和CFRP环向抗拉强度也会提高极限承载力,但CFRP层数对屈服承载力影响较小,CFRP的抗拉强度对屈服承载力没有影响。     

单轴拉伸局部屈服状态下的应力方程理论推导与分析

为了进一步研究屈服状态对小孔周围应力的影响,无限大平板在单轴拉伸下,小圆孔垂直方向上产生局部Tresca条件屈服状态下,对屈服圈外的应力方程进行理论推导,并就残余应力小孔应变法测量标准GB/T 31310—2014所推荐应变花尺寸的适用性进行了讨论分析。计算结果表明,GB/T 31310—2014推荐的应变花适用于残余应力水平低于0.971倍屈服强度的残余应力场测试。     

钢管静水压爆破试验中屈服强度的测定

依据AS 2885.5:2002标准的要求进行钢管静水压爆破试验,通过对试验的压力-进水量曲线进行分析,表明钢管静水压爆破试验屈服强度的测定可以在应用数学统计方法和数值计算软件的基础上,使得屈服点的求取定量化.采用Matlab软件进行曲线拟合和函数微分,定量求取了爆破试验的屈服强度.     

强度理论与实验现象

用四大经典理论、莫尔强度理论和质点平衡强度理论的准则和强度条件,对单向拉压、二向拉压、纯扭转等已被认定的实验现象进行对比,对低、中碳钢重新做了纯扭转求最大屈服剪应力实验。发现质点平衡强度理论的符合率较高,13个实验中的有12个符合。尤其是拉伸一剪切使剪切破坏试验变得容易,压缩一剪切使剪切破坏试验变得困难的实验现象与质点平衡强度理论完全符合;莫尔强度理论也只有当拉伸和压缩极限强度不同时才能符合;其他强度理论都与此实验不符合。特别是当三向等应力拉伸（或压缩）时第三强度理论出现相当应力为零;三向等应力拉伸（或压缩）时第四强度理论出现相当应力也为零;即无论多么大的应力都不会使材料破坏的结论,这与实践完全不符。而质点平衡理论得出与第三、第四强度理论不同的结论,并且接近其实验结果。     

在复杂应力状态下厚壁圆筒的极限分析

应用双剪统一强度理论,考虑材料的拉压异性和同性,推导了在内压力和轴力联合作用下的厚壁圆筒的塑性极限载荷计算公式,并且绘制了其极限载荷线图。在这些计算公式中,当其系数取不同的值时,就能得到按Tresca屈服准则、线性逼近的Mises屈服准则和双剪应力屈服准则的计算结果。应用其极限载荷线图,根据其承受的载荷大小,就能判断厚壁圆筒是否达到了屈服极限状态。绘制了在不同屈服准则下的极限载荷线图,以便对其差异进行比较。     

基于边界效应理论确定热轧碳素钢的韧度与强度

该文研究确定热轧碳素钢的材料韧度与强度特性,提出一种确定热轧碳素钢材料的断裂韧度与屈服强度的模型及方法。建立了等效裂缝长度、名义应力等具体设计参数的计算表达式。通过相同尺寸而不同初始缝高比的单边拉伸Q235B热轧碳素钢板的系列试验,证明所提模型及方法的合理性与适用性。所提模型及方法只需由小尺寸单边裂缝钢板的拉伸试验测得的屈服荷载,即可同时确定出热轧碳素钢平面应力条件下的断裂韧度K_C及屈服强度σ_Y。采用该文所提方法确定热轧碳素钢的材料特性,试验试样不需要满足现行国内外规范对试验试样尺寸、型式,加载条件等的严格规定,试样不需要预制疲劳裂纹。     

正方形断面钢管混凝土短柱轴心受压极限承载力的研究

本文根据钢管混凝土柱轴压实验及有限元分析的结果，首次提出正方形断面钢管混凝土短柱轴心受压极限承载力计算模型．该模型将钢管视为平面应力状态，将核心的混凝土划分为双轴受压区与三轴受压区，利用Ｍｉｓｅｓ屈服曲面以及复杂应力状态混凝土的强度理论，可将钢管混凝土柱的承载力表示为钢管模向应力的函数．根据塑性理论中的下限定理，即可确定钢管混凝土柱的极限承载力。     

疲劳过程中45钢力学性能变化规律的研究

针对疲劳强度设计的理论和方法所应用的均是材料在未受载下的力学性能,对45钢材料在三级应力水平下进行了旋转弯曲疲劳试验,并对疲劳试验后的试样进行了拉伸试验,研究了屈服极限σs 、强度极限σb和截面收缩率ψ的变化规律.研究结果表明,45钢的力学性能在疲劳过程中的变化规律很明显.在疲劳过程中,材料的屈服极限和塑性变形能力均呈逐渐下降的趋势,强度呈逐渐上升的趋势.在不同的载荷作用下,应力水平越高,材料的屈服极限和截面收缩率值越大,强度极限值越小.     

The mechanical behaviour of polystyrene under pressure

Tensile deformation of polystyrene carried out under pressure up to 4 kbar has shown that the pressure-transmitting fluid (silicon oil) acts as a stress crazing and cracking agent. Unsealed specimens showed a brittle-to-ductile transition at 2.95 kbar, while specimens sealed with Teflon tape and rubber showed the same transition at only 0.35 kbar. Analysis of the stress-strain curves for the sealed specimens indicated that the pressure dependency of the craze initiation stress differs from that of shear band initiation stress. The brittle-to-ductile transition occurs when the initiation stresses of both processes become equal. The principal stress for craze initiation showed almost no pressure dependency, suggesting that crazes initiate when the principal stress level of the tensile specimen reaches a critical value irrespective of the applied hydrostatic pressure. Similarly, no pressure dependency was observed for the principal ductile fracture stress. The pressure dependency of yield stress agreed well with a non-linear pressure dependent von Mises yield criterion.     

Numerical implementation of a J_2- and J_3-dependent plasticity model based on a spectral decomposition of the stress deviator

A new plasticity model with a yield criterion that depends on the second and third invariants of the stress deviator is proposed. The model is intended to bridge the gap between von Mises’ and Tresca’s yield criteria. An associative flow rule is employed. The proposed model contains one new non-dimensional key material parameter, that quantifies the relative difference in yield strength between uniaxial tension and pure shear. The yield surface is smooth and convex. Material strain hardening can be ascertained by a standard uniaxial tensile test, whereas the new material parameter can be determined by a test in pure shear. A fully implicit backward Euler method is developed and presented for the integration of stresses with a tangent operator consistent with the stress updating scheme. The stress updating method utilizes a spectral decomposition of the deviatoric stress tensor, which leads to a stable and robust updating scheme for a yield surface that exhibits strong and rapidly changing curvature in the synoptic plane. The proposed constitutive theory is implemented in a finite element program, and the influence of the new material parameter is demonstrated in two numerical examples.     

A Generalized Yield Criterion

A generalized yield criterion is proposed based on the metai plastic deformation mechanics and the fundamental formula in theory of plasticity. Using the generalized yield criterion, the reason is explained that Mises yield criterion and Tresca yield criterion do not completely match with experimental data. It has been shown that the yield criteria of ductile metals depend not only on the quadratic invariant of the deviatoric stress tensor J2, but also on the cubic invariant of the deviatoric stress tensor J3 and the ratio of the yield stress in pure shear to the yield stress in uniaxial tension κ/σs. The reason that Mises yield criterion and Tresca yield criterion are not in good agreement with the experimental data is that the effect of J3 and κ/σs is neglected.     

材料三剪屈服准则研究

在分析Tresca屈服准则和双剪屈服准则的基础上,通过考虑十二面体单元主剪面上所有三个主剪应力的共同作用,提出了材料的三剪屈服准则,并对该准则作了极限线分析、应力莫尔圆分析、中间主应力效应曲线分析和滑移面方向分析。结果表明,新准则与统一屈服准则一样表示的是一个屈服准则系列,其中Tresca屈服准则和vonMise屈服准则是该屈服准则的特例。但与双剪统一屈服准则不同,新屈服准则的极限线和中间主应力效应曲线是非线性的,能够描述材料的非线性屈服特性。另外,也克服了双剪统一屈服准则中存在的在某些特定应力状态下会得出双重滑移面并且滑移面方向会发生变化的问题。     

GM屈服准则求解Ⅰ型裂尖塑性区

用几何中线(GM)屈服准则求解了Ⅰ型裂尖塑性区的形状与尺寸,对比了基于Mises和Tresca准则的求解结果。表明在平面应变条件下,GM准则求解的塑性区面积在Tresca和Mises结果之间,Tresca塑性区面积最大,Mises面积最小,GM塑性区与Mises塑性区非常接近,三者的塑性区均成哑铃状。在平面应力下,GM和Mises塑性区二者仍最接近并为豆芽状,Tresca的塑性区最大。无论平面应力还是平面应变,GM准则计算结果与Mises结果均有最佳接近度。     

Effect of yield surface vertex on failure of ductile materials

This paper is concerned with the lengthening of a solid rod or tubular specimen along the principal axis about which it is being twisted, this aspect of the elastic-plastic deformation of a material being referred to as the Poynting-Swift effect. The Swift effect is the counterpart in the plastic range of deformation to the Poynting effect in the elastic range of deformation. Central to any study of the Swift effect is the problem of identifying an appropriate yield criterion. A generalised isotropic yield criterion is formulated in such a way that it can be applied to materials which satisfy the von Mises yield criterion, or some modified, but continuously difierentiable form of it, and to materials which satisfy a piece-wise continuous yield condition such as the Tresca yield criterion. The choice of the constitutive equation describing the purely elastic deformation behaviour determines the initial yield function. In this context, the constitutive equation of a simple elastic material is only compatible with von Mises yield criterion, a conclusion which applies also to classical infinitesimal theory. An attempt is made to generalise the constitutive equation of a simple elastic material to give a constitutive equation which is compatible with the proposed generalised isotropic yield criterion. This approach introduces an additional term into the constitutive equation which is quadratic in the stress. The two loading coefficients associated with the stress loading function are assumed to be deriveable from the generalised isotropic yield criterion which is now assumed to hold over the entire range of deformation, and in this context is referred to as the stress intensity function. It is a matter of observation that the proposed constitutive equation describes the total, post-yield, elastic-plastic response to simple loading. Consideration is given to the application of the Poynting-Swift effect to the failure of ductile materials using the proposed constitutive equation.     

均布载荷作用下简支圆板塑性极限载荷的解析解

该文建立了受均布载荷作用简支圆板运动许可应变场,并首次以EA(等面积)屈服准则进行了塑性极限分析,获得了极限载荷的解析解。该解为圆板半径a、圆板厚度h以及屈服强度的函数。与Tresca、TSS以及Mises解比较表明,Tresca屈服准则预测极限载荷的下限,TSS屈服准则预测极限载荷的上限,EA和Mises屈服准则预测的极限载荷恰居二者中间,且EA解几乎与Mises解重合。此外,该文还讨论了挠度与相对位置r/a之间的变化关系。