Residual Stress Determination Using Hole Drilling and 3D Image Correlation

In recent years, the hole drilling method for determining residual stresses has been implemented with optical methods such as holographic interferometry and ESPI to overcome certain limitations of the strain rosette version of hole drilling. Although offering advantages, the interferometric methods require vibration isolation, a significant drawback to their use outside of the laboratory. In this study, a 3D image correlation approach was used to measure micron-sized surface displacements caused by the localized stress relief associated with hole drilling. Residual stresses were then found from the displacements using non-dimensional relations previously derived by finite element analysis. A major advantage of image correlation is that it does not require interferometric vibration isolation. Experiments were performed to check the ability of this new approach for uniaxial and equi-biaxial states of stress. Stresses determined by the approach were in good agreement with computed values and those determined by hole drilling using holographic interferometry.     

疲劳损伤临界值分析

通过对疲劳过程和疲劳失效的临界状态的分析，提出疲劳失效判据应与损伤程度和应力水平两个因素有关，并在试验的基础上建立了一个剩余强度退化的对数模型。根据疲劳过程中材料强度退化的事实及其规律。分析了损伤临界值与循环应力水平之间的关系，给出了一般应力水平下疲劳损伤临界值的范围，对于随机疲劳问题，给出了损伤临界值的分布规律。     

大理岩动态拉伸强度及弹性模量的SHPB实验研究

提出了获取脆性材料动态拉伸强度及弹性模量的实验步骤及相关记录数据的分析方法。利用直径为100mm的分离式Hopkinson压杆径向冲击巴西圆盘和平台巴西圆盘试样,测试了大理岩在高应变率加载下的动态力学性能。应力波加载下动态劈裂拉伸圆盘在试样中心产生了约45/s的拉伸应变率。分析了实验的有效性并考虑了试样两个端面应力波波形差异的影响以提高实验结果的精度。结果表明准静态下的公式可适用于动态劈裂拉伸实验;大理岩的动态拉伸强度及弹性模量比静态时有明显的增加。     

Determination of critical molecular weight for entangled macromolecules using the tensile strength data

The multivariable power dependence of polymer properties on molecular characteristics (Dobkowski, 1981) has been applied to molecular weight dependence of tensile strength, and the known equation of Flory (1945) has been extended taking polydispersity of polymers into account. Constant parameters of the relevant regression equations have been calculated using experimental data on tensile strength and molecular weight averagesM _n andM _w of polystyrene (PS) and polycarbonate (PC). Then, the critical molecular weight for entanglementsM _c has been obtained from the following relationship:A=K M _cwhereA and are parameters of the extended Flory equation for the tensile strength, and the constantK = 2 is assumed for linear polymers. It has been found thatM _c of injection and compression moulded PS is equal to 34000 and 37350g/mole, respectively, whileM _c of injection moulded PC equals to 5000 g/mole. The values ofM _c calculated from the polymer tensile strength are consistent with published data obtained by other methods and with the computer modeling calculations. Branched polymers have only qualitatively been discussed. Dimensionless equations have been proposed for tensile strength characteristics for polymer materials.The described procedure can be suggested as applicable to various polymers for the determination of theirM _c values. However, more experimental data on another polymer materials will be necessary to support hitherto obtained results.The essential part of a lecture presented during the NATO Advanced Study Institute Rheological Fundamentals of Polymer Processing, Alvor, Portugal, 26 September–7 October 1994     

复合材料层合板的低速冲击损伤及其剩余压缩强度研究

本文采用理论和实验方法研究了复合材料层合板的低速冲地及其剩余压缩强度。文中利用有限元方法和能量转换原理计算了层合板受到低速冲击的受载最危险状态，以及此时的应力分布；并用Ｔｓａｉ－Ｗｕ张量准则判断损伤情况，对产生损伤的单元进行相应的刚度折减，且作重复计算直至不产生新的损伤为止；最后，对受冲击的层合板还进行剩余压缩强度计算。在实验中，采用激光全息无损检测法测量了层合板的冲击损伤，并对受冲击的层合板进行     

弹塑性随机振动系统中恢复力数学模型的若干形式

本文基于弹塑性随机振动系统恢复力数学模型的统一形式，提出了能考虑刚度下降段和系统在滞变过程中强度退化的四种恢复力数学模型，为适应系统在多次强随机干扰下的反应分析需要，根据试验结果，提出了经受过强随机干扰的有损伤系统的恢复力模型，并建立了相应的数学表达式，最后针对钢筋砼框架结构在主余震作用下的弹塑性地震反应分析给出了具体算例。     

T300/648迭层板接头挤压疲劳损伤参数的选择与测定

本文对碳纤维增强复合材料迭层板(C.F.R.P)接头在不同环境条件下的挤压疲劳损伤扩展进行了实验研究.并根据“剩余强度,剩余刚度”理论和“疲劳模量”概念,讨论了接头的刚度下降和强度变化.由此提出了“损伤参数”D的定义和测量方法;并对损伤试件,进行了X射线检测分析,验证了累积损伤的扩展.     

岩石节理粗糙面的分形几何特性与剪切强度关系的实验研究

自然形成的岩石节理面的表面形状具有分形特性，利用分形理论来描述岩石节理的粗糙特性，并确立与岩石节理面的剪切力学特性间的关系对于指导岩体工程设计，和管理具有重要一研究利用开发设计的三维激光测距仪在精确测定岩石节理面的表面形状４ 基础上，依据变量图法建立了 岩石节理面的     

线性强化材料厚壁圆筒的统一极限分析

运用统一强度理论对承受内压的拉压屈服强度不同的线性强化材料的厚壁圆筒进行了极限载荷分析，得到了适用于多种材料的厚壁圆筒极限载荷的统一解析式．     

Investigation of shrinkage-induced stresses in stereolithography photo-curable resins

An experimental study has been undertaken to investigate the shrinkage characteristics of acrylic-based and epoxy-based stereolithography (SL) photopolymer resin systems after they have been laser cured and post-cured under ultraviolet (UV), and thermal exposure. The induced residual stresses and strains were determined by the shadow moiré and the hole-drilling strain-gage methods. Out-of-plane displacements (warpage) of acrylic-based post-cured resin plates were recorded by means of the shadow moiré method and correlated to the shrinkage strains by theoretical analysis. The induced residual stresses in the epoxy-based cylindrical resin specimens were determined from strains of three-element strain-gage rosettes of the blind-hole drilling method. Results are presented for the shrinkage stresses and strains for both material systems as a function of the post-curing process (UV, thermal). It was found that the shrinkage strains in the acrylic-based photopolymer resin were of considerable magnitude, while thermal post-curing resulted in higher shrinkage stresses for both material systems. The values of the shrinkage stresses compare well with those of the existing literature.