Multiscale Analysis of Residual Stresses with Novel Non-Destructive and Destructive Approaches using Surface Displacement Measurements

工程材料和零件在开发过程中承受严重的机械和热负荷，导致内部残余应力的形成。残余应力(名义上的力除以面积)是由内力引起的，即使在所有外部载荷移除后仍保持不变。尽管残余应力会大大降低使用寿命，但目前还不存在在不破坏零件的情况下确定残余应力的全面而实用的方法。目前的非破坏性技术只允许在零件的表面进行量化。因此，通过对工艺过程中可能产生的残余应力进行彻底估计，可以极大地帮助开发新材料或制造技术。例如，残余应力在附加制造的零件中非常普遍，并且以一种复杂的方式强烈依赖于工艺参数，而这些参数并没有被很好地理解。该奖项支持基于材料力学的逆计算方法的基础研究，以非破坏性和破坏性的方式从力和表面位移的测量值估计残余应力。残余应力分析的进步将促进新材料和制造工艺开发中的机会主义使用和缓解，这将极大地促进汽车、航空航天、国防和核工业的发展。研究小组还将通过参加夏令营项目来促进工程和教育，夏令营项目将吸引女性和代表性不足的高中生参加。为了开发非破坏性方法，将使用数码相机图像跟踪散斑图案，在不同的零件尺寸上经济高效地测量表面位移。使用伴随方程推导出的基于力学的数学算法将被用来从这些测量结果中推断残余应力分布。将对3D打印的橡胶类材料进行验证。为了开发破坏性方法，将从多晶样品中取出非常薄的切片样品，以消除所有残余应力，这意味着薄片将因此而变形。随后的样品加载将被用来使用基于力学的数学模型来确定材料的非均质、各向异性颗粒微结构。对已知的微结构应用反向变形以恢复原始构型，然后可以用来预测给定材料截面中的残余应力。这两种方法背后的基本科学问题是：唯一绘制残余应力图所需的实验数据集和变形模式(即实验)的最小数量是多少？

Engineered materials and parts undergo severe mechanical and thermal loads during their development that result in the formation of internal residual stresses. Residual stresses (nominally force divided by area) are caused by internal forces that remain even after all external loads are removed. Despite the fact that residual stresses can reduce the service life considerably, comprehensive and practical methods to determine them without destroying the parts do not exist. Current non-destructive techniques allow their quantification on the surface of the parts only. Thus, development of new materials or manufacturing techniques can be greatly helped by a thorough estimation of residual stresses that might develop during the processes. For example, residual stresses are extremely prevalent in additively manufactured parts and strongly depend on process parameters in a complex way that are not understood well. This award supports fundamental research in inverse computational methods based on the mechanics of materials to estimate residual stresses in both non-destructive and destructive fashions from the measurement of forces and surface displacements. Advancement in residual stress analysis will promote both opportunistic use and mitigation in the development of new materials and manufacturing processes, which will greatly enhance automotive, aerospace, defense, and nuclear industries. The research team will also promote engineering and education through participation in the summer camp programs that will involve female and underrepresented high school students.For the development of the non-destructive approach, surface displacements will be measured cost-effectively on varying part sizes using digital camera images to trace speckle patterns. Mechanics-based mathematical algorithms derived using adjoint equations will be implemented to infer residual stress distribution from these measurements. Validation on a 3D printed rubber like material will be conducted. For the development of the destructive approach, very thin sectioned samples will be retrieved from the polycrystalline specimens to relieve all residual stresses, with the implication that the thin slices will deform as a result. Subsequent loadings of the samples will be used to determine the heterogeneous, anisotropic granular microstructure of the material using mechanics-based mathematical models. Application of reverse deformation on the now known microstructure to retrieve the original configuration can then be used to predict the residual stresses in the given section of the material. The fundamental scientific issue underlying both approaches is: What are the minimum number of experimental data sets and deformation modes, i.e., experiments, required to uniquely map residual stresses?