Quantitative Prediction of Ductile Fracture Surface Roughness

该项目的目的是阐明延性断裂表面粗糙度的定量测量与材料的延性裂纹扩展阻力之间的关系。已有大量的实验工作表明，脆性断裂表面表现出一定的标度特征。这种伸缩特性在多大程度上表征了韧性断裂表面，仍然是一个悬而未决的问题。提出的研究重点是结构金属的延性断裂，这种断裂是通过微尺度空洞的形核、长大和合并而发生的。延性断裂表面粗糙度的计算将在各种材料的微观结构和加载条件下进行，使用的框架已经给出了在各种情况下整体延性断裂行为的定量预测。建议的研究将包括基于机理的理论预测与使用各种断裂表面粗糙度的定量表征的实验测量的比较。将讨论各种基本问题，包括：断裂表面粗糙度如何取决于材料属性(例如屈服强度)以及模式(拉伸、剪切或某种组合)和加载速度？断裂粗糙度的定量测量如何随材料微观结构的关键特征(例如微孔形核颗粒的空间分布)而变化，以及这种变化是否与材料的裂纹扩展阻力相关？材料的微观结构能设计成提供所需的断口表面粗糙度吗？能用断口表面粗糙度的定量表征来确定断口的来源吗？将在网上提供计算的断裂面，以便其他研究人员能够使用随后可能开发的分析工具来量化和表征断裂面。如果成功，拟议工作的结果可以作为一系列其他努力的起点，例如，控制制造过程中的表面特征和控制随后发生滑动的表面的摩擦特性。虽然物理机制与金属断裂有很大不同，但所开发的能力也可以作为预测地壳断裂表面粗糙度的起点，在地震期间地壳中会发生随后的滑动。

The goal of this project is to elucidate the relation between a quantitative measure of ductile fracture surface roughness and a material's resistance to ductile crack growth. There has been a great deal of experimental work that has shown that brittle fracture surfaces exhibit certain scaling characteristics. The extent to which such scaling properties characterize ductile fracture surfaces remains an open question. The focus in the proposed studies is on ductile fracture in structural metals which takes place by the nucleation, growth and coalescence of micro-scale voids. Calculations of ductile fracture surface roughness will be carried out for a variety of material microstructures and loading conditions using a framework that has given quantitative predictions of overall ductile fracture behavior in a variety of circumstances. The proposed study will involve a combination of mechanism based theoretical predictions coupled with a comparison with experimental measurements using various quantitative characterizations of fracture surface roughness. A variety of basic issues will be addressed including: how does the fracture surface roughness depend on material properties (e.g. yield strength) and on the mode (tensile, shear or some combination) and rate of loading? How do quantitative measures of the fracture roughness vary with key features of the material's microstructure (e.g. the spatial distribution of the micro-void nucleating particles) and does any such variation correlate with the material's crack growth resistance? Can the material microstructure be designed to give a desired fracture surface roughness? Can a quantitative characterization of fracture surface roughness be used to identify the fracture origin? The computed fracture surfaces will be made available on the web so that other researchers can have access in order to use analysis tools that may be subsequently developed to quantify and characterize the fracture surfaces. If successful, the results of the proposed work can serve as a starting point for a range of other endeavors including, for example, control of surface characteristics in manufacturing processes and controlling the frictional properties of surfaces along which sliding will subsequently take place. Although the physical mechanism has significant differences from metal fracture, the capabilities developed could also serve as a starting point for predicting the roughness of fracture surfaces in the earth's crust where subsequent sliding occurs during earthquakes.