模拟压力容器接管高应变梯度场的一种新型特殊紧凑拉伸（SCT）试样

本文提出一种新型特殊紧凑拉伸(SCT)试样,以模拟压力容器局部高应变梯度接管区。该区主要特征为:高峰值应变,大应变梯度及该局部高应变区受周围弹性区的强烈约束。特殊紧凑拉伸试样是在普通紧凑拉伸试样的基础上,在其中央部位两侧削薄其厚度,并在端部留下筋条;同时在试样中部钻中心孔。故其设计与试验计算较为方便。试验结果表明:对此弯曲型试样所需载荷很低,例如对一个厚12.5mm,宽50mm,长60mm的SCT试样,只需加载4.5kN(千牛顿)即0.45吨即可获得高达8067με(微应变)的峰值应变,并成功地再现了局部高应变梯度区各主要特征,较宽板试验更符合工程结构的实际情况,且可节省材料、劳力、工时,不需特殊的大型试验机,节省经费。将试验结果与压力容器接管实际试验数据对比,表明它成功地提供了一种对研究接管等几何不连续部位的断裂与疲劳及其可靠性评定的有用的工程工具。     

高应变区裂纹尖端张开位移COD表达式

根据工程构件常呈现局部高应变梯度的特征而不是全面屈服状态的事实,本文提出了高应变区中LiCOD表达式。将其与从Dugdale-Muskhelivili模型导得的低应力范围内的COD表达式相结合,即可得到全部应力应变范围内的COD表达式。作者设计了两种SCT试样,试验结果表明:在很大的应力应变范围内,该表达式计算值与试验数据相符。试验还证明:SCT试样成功地再现了实际工程构件(如压力容器接管)高应变梯度区的特征,且不再出现宽板标定曲线的COD冻结等奇异现象,从而证明该表达式可以应用于工程结构。     

高应变区SCT试样闭合效应研究

本文对两组材料为CF6钢，不同孔径的SCT试样进行了疲劳裂纹扩展的闭合效应测定，试验采用裂纹嘴张开位移和裂纹尖端附近张开位移曲线两种测量方法来测量裂纹闭合效应参数Uop,Ucl，通过对同组两试样的比较，得出了SCT试样高应变塑性区疲劳裂纹闭合效应参数。     

SCT试样高应变区疲劳裂纹扩展规律研究

本文研究了SCT试样高应变区的疲劳裂纹闭合效应和疲劳裂纹扩展速率。结果表明:高应变塑性区的存在对疲劳裂纹扩展有较大延缓作用,疲劳裂纹扩展速率可用经U修整后的δ和Paris公式表示,结果与标准试样的结果较为吻合。     

X70管线钢管环焊接头在低约束条件下的断裂韧性

针对基于应变设计的X70管线钢管,采用单边缺口拉伸试验对该钢钢管环焊缝金属及热影响区的裂纹尖端张开位移进行研究,获得了裂纹延性扩展过程的断裂阻力曲线,并对热影响区试样的试验结果进行了有效性验证。结果表明:热影响区试样的裂纹尖端距熔合线的距离在0.5mm以内,焊缝金属和热影响区试样的断裂阻力曲线分别为δ=1.395 78(Δa)0.783 35,δ=1.553 38(Δa)0.821 75;采用单边缺口拉伸试验能准确测出管线钢环焊接头在低约束条件下的断裂韧性;试验结果可以为管线基于应变设计和工程临界评价提供依据。     

基于毫小薄片试样获取材料应变疲劳性能的测试方法

通过现行试验标准难以获取小尺寸的薄片、零部件、薄壁管、焊缝区材料的低周疲劳性能。提出一种基于漏斗薄片毫小试样的应变疲劳试验方法:结合应变能分离函数假设,给出毫小薄片试样获取材料循环应力应变关系的预测模型;借助循环应力应变关系,采用有限元得到毫小薄片试样跨漏斗名义应变幅与漏斗根部真实应变幅之间以及平均应力幅与漏斗根部真实应力幅之间的转换方程,从而给出了基于漏斗薄片小试样的材料代表性体积单元(Representative-volume-element,RVE)疲劳寿命曲线并给出Manson-Coffin寿命模型参数。针对不同材料的有限元验证表明,基于应变能分离函数的材料循环应力应变关系预测模型对不同几何尺寸自相似试样和不同幂律材料均具有良好普适性。完成了316L不锈钢等直圆棒试样和厚度为0.7 mm毫小薄片试样的应变对称变幅低循环试验和多级等幅低循环试验,结果表明,通过新方法预测的薄片材料循环应力应变关系和等直圆棒试样试验结果一致,通过毫小薄片试样获得的疲劳寿命曲线与等直圆棒试样试验结果亦吻合良好。     

两种工程结构用钢疲劳裂纹扩展速率的试验研究

对工程结构用钢20MnHR、A508-Ⅲ焊缝和热影响区的疲劳裂纹扩展速率进行了试验研究。试验采用CT试样，用七点递增多项式法求(da/dN)i与(△K)i，并分别将焊缝和热影响区同一组多个试样的(△K)i和(da/dN)i数据点合在一起进行整体回归分析。试验中得列了20MnHR疲劳裂纹扩展速率的斜率转折点，分别测出了平面应变区和平面应力区的Paris表达式。试验分析说明，以平面应变性质为基础的Paris表达式应用于实际工程结构较为安全。     

防屈曲装置与试样间摩擦力对薄板拉压疲劳寿命的影响

采用TC4钛合金薄板防屈曲装置，在不同扭矩(1.5～2.5 N·m)和不同应变水平(0.25%～1.0%)下对SAPH440钢薄板试样进行拉压疲劳试验，研究了摩擦力对薄板试样疲劳寿命的影响，验证了防屈曲装置的适用性。结果表明：在以弹性应变为主导的低应变水平(0.25%)下，试样的疲劳寿命随摩擦力的增大而略微降低；在以塑性应变为主导的中高应变水平(0.5%～1.0%)下，试样的疲劳寿命随摩擦力的增大而增大；应变水平为0.25%,0.5%时试样裂纹扩展区中段疲劳辉纹间距均值分别为0.45,0.86μm,随着应变水平继续增大，疲劳辉纹变得不明显，出现了较为明显的二次裂纹。     

基于弹塑性解析方程的薄片试样低周疲劳试验方法

针对薄片漏斗试样,基于能量密度等效和量纲分析,提出了移幅-载荷幅关系(Relation between displacement-amplitude and load-amplitude, RDL)半解析方程;能量密度等效代表性体积单元(Representative volume element, RVE)的循环等效应力幅、等效应变幅(Cyclic equivalent stress-amplitude and strain-amplitude, CESS)解析方程;漏斗根部材料RVE单轴应变幅(Uniaxial strain-amplitude of material RVE at funnel root, US-R)半解析方程;材料与几何普适的薄片试样低周疲劳试验新方法。针对5种几何尺寸和13种预设材料组合的18种试样工况进行有限元分析,及对G115和16Mn进行薄片试样低周疲劳试验,结果表明,CESS解析方程预测的薄片漏斗试样等效应力幅-应变幅曲线与有限元预设曲线密切吻合,且新试验方法得到的G115和16Mn循环等效应力幅-应变幅关系和Manson-Coffin律与标准圆棒试样低周疲劳试验结果密切吻合。     

形变方式对H62黄铜模压形变等效应变分布的影响

采用三维有限元法(FEM)模拟H62黄铜交叉模压形变过程和平行模压形变过程,分析了这两种不同模压形变方式对试样模压形变后等效应变分布的影响,并与试验结果进行了比较。结果表明,随着模压周期的增加,与平行模压形变相比,交叉模压形变方式下试样等效应变累积值会更高,等效应变分布也会更均匀;其模拟结果中等效应变的分布规律与试验材料显微硬度的分布规律相对应。     

Effect of constraint on fracture behavior of welded 17mn4 and aisi304 steels

In this study, 17Mn4 (P295GH) pressure vessels steel and AISI304 stainless steel were welded with ER309L austenitic consumable. In experimental part of the study, tensile tests were conducted on welded plates and variation of hardness values along specimen was measured. J-integral fracture toughness values were investigated for different crack locations. In order to determine the regions where plastic deformation did not take place due to constraint, uni-axial tensile test was performed on welded tensile specimen after attaching strain gauges. In numerical part of the study, finite element (FE) analyses were conducted by fixing 2-D models precracked on different locations by using ANSYS software. In these models, stress triaxiality and plastic deformation characteristics around crack tip were determined for each crack locations after stress — strain analyses. The limitation on the extension of plastic deformation at diffusion line causes extra increase in stress triaxiality at crack tip.     

Observation of notch effect in Al6061-T6 specimens under tensile loading using digital image correlation and finite element method

The fracture of ductile materials such as Al6061-T6 usually starts from void nucleation. In this study, we investigated strengthening effect and stress triaxiality behavior in notched Al alloy specimens. Various specimens, one un-notched and two with different U-types of notch, one with large diameter (L-notched) and another with small diameter (S-notched), having the same width were selected. The distribution of strain in the full-field was examined using the digital image correlation (DIC) method. Under the tensile test, S-notched specimens showed a more pronounced strengthening effect than the L-notched specimens. The results of DIC confirmed that the notch tip of the S-notched specimen experienced high strain, while the L-notched specimen experienced high strain at the center. The maximum stress triaxiality moved rapidly from the notch tip to the center with the increase in notch radius over 10 mm. The results of the stress triaxiality analysis by finite element method were in good agreement with the above DIC measurement results and predicted the void generation and fracture sites in L-notched and S-notched specimens.     

超声疲劳试样动态应变测量及应力检定方法

超声疲劳试验技术是实现超高周疲劳测试的有效手段。然而,目前超声疲劳测试缺少应力检定方法,难以保证测试结果的可靠性与准确性。本文首先给出了超声疲劳测试中不同形状试样的设计方法和应力分布理论公式;然后,利用高速动态应变仪和高速相机对不同形状超声疲劳试样的动态应变进行测量,并将测试值和理论值进行了对比分析,证明了超声疲劳试样应变测量的可行性与准确性。在此基础上,提出了基于应变测量结果的超声疲劳试验检定方法,利用测得的应变值对应力值进行校核或修约,有效保证了超声疲劳测试的可靠性和准确性。     

磁场处理降低残余应力过程中应力应变的测量

在前期研究强脉冲磁场处理与低频交变磁场处理降低残余应力，并取得显著效果的基础上，进一步在磁场处理低碳钢制作的试样（包括单向拉伸试样和无应力试样）时，对应力应变过程进行测量。结果表明，单向拉伸试样经过低频交变磁场处理后，材料内部残余应力在下降的趋势，而且处理过程中具有磁振动现象。无应力试样与单向拉伸试验在磁场中，随场强的增加，试样中的应变逐渐由正值变为负值。克应力试验在不同频率的交变磁场中的应变各不     

一种铁素体钢热变形流变应力行为

利用Gleeble热力模拟试验机在温度为1 123～1 473 K和应变速率为0.001～0.1 s-1的条件下对试验钢进行了热压缩变形试验,测定了其真应力-应变曲线,试验结果表明:试验钢在热压缩变形过程中发生了明显的动态再结晶,流变应力随变形温度的降低和应变速率的提高而增大。通过线性回归分析确定了试验钢的流变应力本构方程。     

Measurements of the diameters of the great arteries and semi-lunar valves of chick and mouse embryos

The great arteries of embryos are small channels of a complex three-dimensional arrangement. Measurements of their diameters, as required for understanding cardiovascular morphogenesis and the genesis of malformations, cannot be performed in two-dimensional histological sections. We present and evaluate a quick and simple method for performing highly significant and objective measurements of the diameters of blood vessels in vertebrate embryos and used this method for providing statistics of the diameter of the semi-lunar valves and the lumina of the great arteries of early chick and mouse foetus. We employed the high-resolution episcopic microscopy technique for generating volume data and three-dimensional computer models of the arterial trees of 30 chick embryos (Hamburger Hamilton stage 34), 30 mouse embryos of the OF1 strain harvested on 14.5 dpc, 30 embryos of the OF1 strain harvested on 15.5 dpc and 28 mouse embryos of the PARKES strain harvested on 14.5 dpc. The three-dimensional models (voxel size 2 μm × 2 μm × 2 μm and 3 μm × 3 μm × 3 μm) were used for defining virtual resection planes perpendicular to the longitudinal axis of the blood vessels at comparable positions. In these planes, we measured the lumen areas and the lumen perimeters. We also calculated the lumen diameter and the true lumen area from the perimeter and present statistical analysis. Finally, we evaluate and discuss the reliability and reproducibility of our method and present all measurements in a form that minimizes the influence of specimen size variation, specimen processing and data generation methods.     

基于塑性应变能的涡轮盘多轴疲劳寿命预测方法

在分析疲劳裂纹产生机理的基础上,将塑性应变能和临界平面结合起来,同时引入剪应变能比例因子,提出一种新的多轴损伤参量,通过试棒单轴低循环疲劳试验应力应变曲线得到总的塑性应变能,进而得到一种新的多轴疲劳寿命预测模型。通过对比分析,得到了最佳剪应变能比例因子。使用该模型、Chen-Xu-Huang(CXH)模型、Liu-Wang(LW)模型对某型发动机涡轮盘销钉孔低循环疲劳寿命进行预测,并与真盘试验结果进行对比。结果表明,该多轴疲劳寿命预测模型预测误差为20.5%,优于CXH和LW模型。     

多晶铜微小试样的ISDG试验

介绍了新近研制的用于测量微电子机械系统(MicroelectronicMechanicalSystem,MEMS)材料机械性能的单轴拉伸试验系统。拉伸试样的厚度只有200μm,试验段宽度为300μm,用有限元法模拟拉伸试验时试样的应力分布,分析试样几何形状参数对应力分布的影响并优化设计了试样,采用激光干涉应变计法测量试样应变,得到多晶铜试样的应力应变曲线。     

小冲孔试样高温蠕变损伤的有限元分析

基于小冲孔蠕变试验，建立1Cr0．5Mo耐热钢小冲孔蠕变试样的有限元模型。应用改进的K-R蠕变损伤本构方程，分析在550℃、恒载荷条件下的试样中心挠度、应变等随时间的变化规律以及试样蠕变损伤的发展与断裂过程。计算结果表明，整个试样的损伤在中心位置比较严重，且呈现明显的局部化特征；试样的失效首先发生在下表面上，离试样下表面中心约0．8mm，这与试验观察到的试样颈缩部位完全一致。     

Study on true stress correction from tensile tests

Average true flow stress-logarithmic true strain curves can be usually obtained from a tensile test. After the onset of necking, the average true flow stress-logarithmic true strain data from a tensile specimen with round cross section should be modified by using the correction formula proposed by Bridgman. But there have been no firmly established correction formulae applicable to a specimen with rectangular cross section. In this paper, a new easy-to-use formula is presented based on parametric finite element simulations. The new formula requires only incremental plastic strain and hardening exponents of the material, which are simply presented from a tensile test. The newly proposed formula is verified with experimental data for high strength steel DH32 used in the shipbuilding and offshore industry and is proved to be effective during the diffuse necking regime.