Quantitative Prediction of Ductile Fracture Surface Roughness

该项目的目的是阐明韧性断裂表面粗糙度的定量测量与材料抗韧性裂纹扩展之间的关系。大量的实验工作表明，脆性断口表面具有一定的结垢特性。这种结垢特性在多大程度上表征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韧性断裂，这种断裂是由微尺度空洞的成核、生长和聚并引起的。在各种材料微观结构和加载条件下，将使用一个框架进行韧性断裂表面粗糙度的计算，该框架已经给出了各种情况下整体韧性断裂行为的定量预测。拟议的研究将包括基于机理的理论预测，以及使用各种定量表征断裂表面粗糙度的实验测量结果的比较。将解决各种基本问题，包括：断裂表面粗糙度如何取决于材料特性（例如屈服强度）、模式（拉伸、剪切或某些组合）和加载速率？断裂粗糙度的定量测量是如何随材料微观结构的关键特征而变化的（例如，微孔洞成核颗粒的空间分布），这种变化是否与材料的裂纹扩展阻力相关？材料的微观结构是否可以设计成理想的断裂表面粗糙度？是否可以用断口表面粗糙度的定量表征来确定断口的起源？计算出的裂缝表面将在网络上提供，以便其他研究人员可以访问，以便使用随后可能开发的分析工具来量化和表征裂缝表面。如果成功，所提出的工作结果可以作为一系列其他努力的起点，例如，在制造过程中控制表面特性和控制表面的摩擦特性，随后会发生滑动。虽然物理机制与金属断裂有很大的不同，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，地壳断裂表面会发生随后的滑动。

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.