在役设备材料断裂力学参数测定方法综述--小冲杆实验力学研究进展之二

20多年以来, 用小型试件的小冲杆实验技术来测量在役设备材料的各种力学参数已经取得了很大进展. 小冲杆实验的试样虽然还没有标准, 但一般均采用直径为3～10mm,厚度为0.1～0.5mm的圆片试样.这个方法已经用来确定材料的弹性模量、屈服强度、塑性性能、抗拉强度、断裂形态转变温度、断裂韧性、蠕变性能以及表示塑性硬化和韧性损伤的微观力学参数和黏塑性性能等各种力学性能.该方法兼具取样方便和几乎无损的优点,非常适用于那些无法取出传统试样或取样不经济的场合,因此引起科技界和工业界的关注.本文综述了小冲杆试验的测量技术及从测量数据来确定材料断裂形态转变温度、断裂韧性和主曲线的移动温度的各种计算方法研究进展.     

在役设备材料弹塑性力学参数测定方法综述--小冲杆实验力学研究进展之一

20多年以来,采用小型试件的小冲杆试验技术来测量在役设备材料的各种力学参数已经取得了很大进展,这个方法已经用来确定材料的弹性模量、屈服强度、塑性性能、抗拉强度、韧一脆转变温度、断裂韧度、蠕变性能和黏塑性性能等各种力学性能。由于从小冲杆试验的测量结果来确定材料的力学性能是一个反问题,因此,与此有关的反问题分析方法也得到了相应的发展。本文系统综述小冲杆试验的测量技术及从测量数据来确定材料弹塑性参数的各种经验方法和计算方法,例如有限元分析和参数法、反向有限元法、有限元和反方法、反向识别和人工神经网络、有限元优化和试验变形形状以及杂交反方法等。     

含裂纹结构时间相关的疲劳断裂理论与剩余寿命评价技术

高温结构的疲劳失效是与时间相关的, 建立这一失效机制下的断裂理论和寿命评价技术, 进而控制结构失效是人们多年来努力的目标. 从裂纹扩展控制参量、裂纹扩展规律和寿命评价技术、材料老化与环境因素影响和结构完整性评定工程方法等几个方面, 对近年来这一领域的研究进展进行了总结, 并对今后该领域的发展方向进行了预测.      

高强度钢船体焊接结构的安全评定

基于欧洲共同体提出的结构完整性评定方法SINTAP,对含缺陷的高强钢船体焊接接头进行安全评定.根据拉伸试验和断裂韧度试验的结果,建立了高强度钢船体焊接结构的二级失效评定曲线.评定结果表明,评定点在曲线范围内,说明该结构是安全的,取代了将焊接接头近似看作均匀材料进行评定的方法,提高了评定精度.     

小冲杆试验确定材料拉伸断后伸长率的研究

小冲杆试验技术可以近似无损地测试材料的力学性能.本文对几十种材料进行了小冲杆试验研究,对小冲杆试样的抽向挠度δ与拉伸断后伸长率A进行了经验关联.研究表明,对于试验中涉及的几十种材料,二者之间没有统一的线性相关公式,但可以按材料的杭拉强度和屈强比将材料分类,然后分别对δ和A进行线性关联.对于抗拉强度小于600MPa的材料...     

利用红外热像技术快速预测材料的S-N曲线

研究材料疲劳一般采用试验的方法,但试验周期长, 所需试验试件和费用多,一直以来都是材料疲劳试验难以克服的困难,人们一直在探寻能快速得到材料疲劳性能的方法.本文在前人研究的基础上,采用红外热像技术,确定了材料的疲劳极限,并在"同种试件疲劳破坏消耗的塑性功不变"的假设下,通过建立塑性温升、热耗散、塑性功之间的关系给出了试件疲劳寿命的计算公式.由此经过简单的试验,理论上用一根试件,试验几个小时就可以快速确定材料的疲劳寿命,给出材料的S-N曲线.     

高温结构蠕变裂尖拘束效应

如何对蠕变裂纹扩展寿命进行准确预测和评价是高温结构完整性评定、寿命设计和运行维护中需要解决的核心问题.基于宏观单参数C?的蠕变断裂行为的评价方法,未有效纳入裂尖拘束效应的影响,因而其评价结果过于保守或非保守.目前国内外还未建立起有效纳入裂尖拘束效应的高温结构蠕变寿命评价的理论体系和技术方法,还没有纳入蠕变拘束效应的高温结构完整性评定规范.本文综述了作者近年来在高温蠕变断裂拘束效应方面的研究工作.主要包括:裂尖拘束对材料蠕变裂纹扩展行为的影响及机理;蠕变裂尖场和拘束参数R的定义和影响因素;载荷无关的蠕变拘束参数R? 的提出及其应用基础;承压管道表面裂纹的拘束参数R? 解及纳入裂尖拘束的蠕变寿命评价方法;试样与管道轴向裂纹蠕变裂尖拘束的关联;基于裂尖等效蠕变应变的面内与面外蠕变裂尖拘束的统一表征参数Ac的研究;材料拘束相关的蠕变裂纹扩展速率的建立;宽范围C? 区蠕变裂纹扩展速率及其拘束效应的数值预测;材料拘束对焊接接头蠕变裂纹扩展行为的影响及机理等.这些研究为建立纳入裂尖拘束效应的高温部件的蠕变裂纹扩展寿命评价方法奠定了理论和技术基础.论文对后续拟开展的工作也进行了展望.     

Creep crack-tip constraint effect in high temperature structures

如何对蠕变裂纹扩展寿命进行准确预测和评价是高温结构完整性评定、寿命设计和运行维护中需要解决的核心问题.基于宏观单参数C^*的蠕变断裂行为的评价方法,未有效纳入裂尖拘束效应的影响,因而其评价结果过于保守或非保守.目前国内外还未建立起有效纳入裂尖拘束效应的高温结构蠕变寿命评价的理论体系和技术方法,还没有纳入蠕变拘束效应的高温结构完整性评定规范.本文综述了作者近年来在高温蠕变断裂拘束效应方面的研究工作.主要包括：裂尖拘束对材料蠕变裂纹扩展行为的影响及机理;蠕变裂尖场和拘束参数R的定义和影响因素;载荷无关的蠕变拘束参数R^*的提出及其应用基础;承压管道表面裂纹的拘束参数R^*解及纳入裂尖拘束的蠕变寿命评价方法;试样与管道轴向裂纹蠕变裂尖拘束的关联;基于裂尖等效蠕变应变的面内与面外蠕变裂尖拘束的统一表征参数A_c的研究;材料拘束相关的蠕变裂纹扩展速率的建立;宽范围C^*区蠕变裂纹扩展速率及其拘束效应的数值预测;材料拘束对焊接接头蠕变裂纹扩展行为的影响及机理等.这些研究为建立纳入裂尖拘束效应的高温部件的蠕变裂纹扩展寿命评价方法奠定了理论和技术基础.论文对后续拟开展的工作也进行了展望.     

高温结构蠕变裂尖拘束效应

如何对蠕变裂纹扩展寿命进行准确预测和评价是高温结构完整性评定、寿命设计和运行维护中需要解决的核心问题.基于宏观单参数C~*的蠕变断裂行为的评价方法,未有效纳入裂尖拘束效应的影响,因而其评价结果过于保守或非保守.目前国内外还未建立起有效纳入裂尖拘束效应的高温结构蠕变寿命评价的理论体系和技术方法,还没有纳入蠕变拘束效应的高温结构完整性评定规范.本文综述了作者近年来在高温蠕变断裂拘束效应方面的研究工作.主要包括:裂尖拘束对材料蠕变裂纹扩展行为的影响及机理;蠕变裂尖场和拘束参数R的定义和影响因素;载荷无关的蠕变拘束参数R~*的提出及其应用基础;承压管道表面裂纹的拘束参数R~*解及纳入裂尖拘束的蠕变寿命评价方法;试样与管道轴向裂纹蠕变裂尖拘束的关联;基于裂尖等效蠕变应变的面内与面外蠕变裂尖拘束的统一表征参数A_c的研究;材料拘束相关的蠕变裂纹扩展速率的建立;宽范围C~*区蠕变裂纹扩展速率及其拘束效应的数值预测;材料拘束对焊接接头蠕变裂纹扩展行为的影响及机理等.这些研究为建立纳入裂尖拘束效应的高温部件的蠕变裂纹扩展寿命评价方法奠定了理论和技术基础.论文对后续拟开展的工作也进行了展望.     

基于BP神经网络与小冲杆试验确定在役管道钢弹塑性性能方法研究

为了能够在不停输油气工况下获得在役管道材料的弹塑性力学性能,提出了一种人工智能BP (backpropagation)神经网络、小冲杆试验与有限元模拟相结合,通过确定材料真应力-应变曲线从而获得材料弹塑性力学性能的方法.首先,通过系统改变Hollomon公式中的参数K, n值,获得457组具有不同弹塑性力学性能的假想材料本构关系,其次,将得到的本构关系代入经试验验证的含有Gurson-Tvergaard-Needleman(GTN)损伤参数的小冲杆试验二维轴对称有限元模型,通过有限元计算得到了与真应力-应变曲线一一对应的457条不同假想材料的载荷-位移曲线,最终将两组数据作为数据库输入BP神经网络进行训练,建立了同种材料小冲杆试验载荷-位移曲线与真应力-应变曲线之间的关联关系.通过此关联关系,可利用试验得到的小冲杆载荷-位移曲线获取在役管道钢的真应力-应变曲线,从而确定其弹塑性力学性能.通过对比BP神经网络得到的X80管道钢真应力-应变曲线与单轴拉伸试验的结果以及引用现有文献中不同材料的试验数据对此关系进行验证,证明了该方法的准确性与广泛适用性.     

A Procedure to Measure Biaxial Near Yield Residual Stresses Using the Deep Hole Drilling Technique

Deep Hole Drilling (DHD) is a mechanical strain relief technique used to measure residual stresses within engineering components. Such techniques measure strains or displacements when part of the component is machined away and typically assume elastic unloading. However, in components containing high levels of residual stress, elastic–plastic unloading can occur which may introduce substantial error. For the case of the DHD technique, a modification to the technique referred to here as the incremental or iDHD technique has been developed to allow such high levels of residual stress to be measured. Previous work has demonstrated the accuracy of the iDHD technique, although only for axisymmetric residual stress distributions. In the present investigation, the application of the iDHD technique has been extended to the general case of biaxial residual stress fields. Finite element simulations are first carried out to demonstrate the ability of the iDHD technique to measure biaxial residual stress. Experimental measurements were then made on shrink fit components and ring welded components containing biaxial residual stress to investigate the performance of the technique in practice. Good agreements between iDHD measurements, neutron diffraction measurements and FE predictions of the residual stresses were obtained, demonstrating the generally improved accuracy of the iDHD technique compared to the standard DHD approach.     

Calibration of the X-Ray Diffraction Technique for Stress Quantification in Metallic (Steel) Structures

The X-Ray Diffraction technique has been widely applied for decades in many industrial sectors for the quantification of residual stresses in metallic parts. The present paper describes the laboratory calibration of this technique with the aim of adapting it to the quantification of global stresses (non residual) in metallic structures, in service for civil engineering and building. A small structure specifically built for this research has been repeatedly loaded at laboratory. In each load level the global stresses in a bar of the structure have been quantified by means of X-Ray Diffraction technique. The experimental procedure allows one to discern the residual stresses and the structural (mechanical) stresses in service. The correlation between the stresses deduced experimentally and the applied stresses is excellent. As conclusion, it can be stated that the X-Ray Diffraction technique as a non-destructive technique, has been calibrated to be used for stress deduction in metallic elements in service.     

Residual stress distribution on surface-treated Ti-6Al-4V by X-ray diffraction

The x-ray diffraction technique has been used to measure surface residual stress in Ti-6Al-4V samples subjected to shot peening (SP), laser shock peening (LSP) and low plasticity burnishing (LPB). The magnitude, spatial and directional dependence and uniformity of the surface residual stresses have been investigated. The results show that residual stresses due to SP are uniform and independent of direction. LSP has been observed to produce non-uniform residual stress varying from one region to another, and also within a single laser shock. In the case of LPB, residual stresses have uniform spatial distribution but have been observed to be direction-dependent. Various components of the residual stress tensor in the LPB sample have been determined following the Dolle-Hauk method. The results of the residual stress due to three surface treatments are compared, and possible reasons for spatial and directional dependence are discussed.     

Acoustoelastic determination of residual stress with laser doppler velocimetry

The main object of this study is to develop a new technique for stress nondestructive measurement. A noncontact measurement technique of ultrasonic wave velocity is proposed. In the measurement system, a laser Doppler velocimeter, which is noncontact, is used to detect wave motions due to Rayleigh waves instead of a piezoelectric transducer. The noncontact measurement technique is applied to determine the stress-acoustic coefficient of Rayleigh waves for aluminum 5052 and a structural steel, and the results are in good agreement with those obtained using knife-edge piezoelectric transducers. The technique is also used to evaluate residual stress existing in an H-section rolled beam of the structural steel. The distribution of residual stress is reasonable.     

Residual stresses in thick-walled cylinders resulting from mechanically induced overstrain

Autofrettage is a process for inducing elastic response in thick-walled cylinders subjected to internal pressures which otherwise cause plastic strains. To extend the use of autofrettage to higher pressure applications and to elminate many of the problems encountered in the use of the conventional process based on the use of direct internal hydrostatic pressure, a new technique has been developed which utilizes the mechanical advantage of a sliding wedge to produce the desired bore enlargement. Since the use of a sliding wedge or mandrel will induce shearing forces at the mandrel-cylinder interface, the resultant residual-stress distribution will differ from that theoretically predicted as characteristic of the direct hydrostatic process. It is the purpose of this work to determine the residual-stress distribution as a function of magnitude of overstrain and diameter ratio, and how it affects the reyielding characteristics of cylinders autofrettaged by this technique. Residual-stress distributions, determined by the Sachs boring-out technique for diameter ratios ranging from 1.5 to 2.3 and for several different magnitudes of overstrain, are shown. The shearing force associated with this technique induces substantial longitudinal residual stresses. The increase in the magnitude of this longitudinal residual stress with overstrain and the resultant decrease in the tangential residual stress are shown and discussed. Hydrostatic reyielding tests of autofrettaged cylinders are used to substantiate the decrease of tangential residual stress with increased overstrain. The substantially lower optimum overstrain as compared to the direct hydrostatic technique is shown and discussed. For optimum overstrain, the elastic strength of cylinders autofrettaged by swaging is comparable to that characteristic of the conventional process.     

喷丸镍基合金材料微区残余应力的切槽法测量研究

本文结合聚焦离子束-电子束(Focused ion beam-electron beam,简称FIB-EB)双束系统和真空镀膜工艺,进行微区散斑的制备工艺研究,并将所发展的微散斑制备工艺应用于喷丸镍基合金材料表面制斑,进而结合切槽法进行残余应力高温释放规律的测量研究。在FIB-EB双束系统下记录切槽前后制斑微区的图像,利用数字图像相关法计算切槽后的位移,结合InglisMuskhelishvili理论公式可计算得到残余应力。文中研究了不同温度及保温时间对残余应力释放的影响规律。结果表明,残余应力随保温时间的增长释放速度逐渐减小,最后残余应力趋于稳定值。同时,温度越高,残余应力释放越彻底,800℃下近乎完全释放。该工艺具有适用性好,效率高等优点,可望在材料微区变形测量中得到进一步应用。     

Modifications to the hole-drilling technique of measuring residual stresses for improved accuracy and reproducibility

The hole-drilling technique is a relatively well established and straightforward semidestructive method for measuring residual stresses in fabricated components. However, a number of factors can have a marked influence on the accuracy of this technique. Some of the factors evaluated in the present work were the method of drilling the hole, the size and shape of the hole, and the equations used to calculate the principal residual stresses from the relaxed-strain measurements. In this investigation, air-abrasive hole drilling using a 0.062-in.-ID stationary nozzle gave the most reproducible and accurate results. Of the three approaches used to calculate the residual stresses, one method proved to be superior, especially in a biaxial-stress field.     

Residual-stress determination through combined use of holographic interferometry and blind-hole drilling

Holographic interferometry is used to determine in-plane radial displacements due to release of residual stresses by hole drilling. A method is derived for relating radial displacements measured in three directions of illumination to the state of residual stress, analogous to relations used in the conventional strain-rosette technique. Residual stress is produced by an interference fit of two circular tubes. Agreement between stress determined holographically with a computed value and with that determined by the conventional technique is good. Advantages of the holographic technique in overcoming various shortcomings of the conventional technique are discussed. A modification of the holographic technique involving data collection in only two directions of illumination is described.     

Stress Monitoring of Post-processed MEMS Silicon Microbridge Structures Using Raman Spectroscopy

Inherent residual stresses during material deposition can have profound effects on the functionality and reliability of fabricated Micro-Electro-Mechanical Systems (MEMS) devices. Residual stress often causes device failure due to curling, buckling, or fracture. Typically, the material properties of thin films used in surface micromachining are not well controlled during deposition. The residual stress; for example, tends to vary significantly for different deposition methods. Currently, few nondestructive techniques are available to measure residual stress in MEMS devices prior to the final release etch. In this research, micro-Raman spectroscopy is used to measure the residual stresses in polysilicon MEMS microbridge devices. This measurement technique was selected since it is nondestructive, fast, and provides the potential for in-situ stress monitoring. Raman spectroscopy residual stress profiles on unreleased and released MEMS microbridge beams are compared to analytical and FEM models to assess the viability of micro-Raman spectroscopy as an in-situ stress measurement technique. Raman spectroscopy was used during post-processing phosphorus ion implants on unreleased MEMS devices to investigate and monitor residual stress levels at key points during the post-processing sequences. As observed through Raman stress profiles and verified using on-chip test structures, the post-processing implants and accompanying anneals resulted in residual stress relaxation of over 90%.     

A New Procedure to Measure Near Yield Residual Stresses Using the Deep Hole Drilling Technique

Mechanical strain relief techniques for estimating the magnitude of residual stress work by measuring strains or displacements when part of the component is machined away. The underlying assumption is that such strain or displacement changes result from elastic unloading. Unfortunately, in components containing high levels of residual stress, elastic-plastic unloading may well occur, particularly when the residual stresses are highly triaxial. This paper examines the performance of one mechanical strain relief technique particularly suitable for large section components, the deep hole drilling (DHD) technique. The magnitude of error is calculated for different magnitudes of residual stress and can be substantial for residual stress states close to yield. A modification to the technique is described to allow large magnitudes of residual stress to be measured correctly. The new technique is validated using the case of a quenched cylinder where use of the standard DHD technique leads to unacceptable error. The measured residual stresses using the new technique are compared with the results obtained using the neutron diffraction technique and are shown to be in excellent agreement.