Kolvin Itamar, Cohen Gil, Fineberg Jay
The Racah Institute of Physics, the Hebrew University of Jerusalem, Jerusalem 9190401, Israel.
Nat Mater. 2018 Feb;17(2):140-144. doi: 10.1038/nmat5008. Epub 2017 Oct 16.
Cracks develop intricate patterns on the surfaces that they create. As faceted fracture surfaces are commonly formed by slow tensile cracks in both crystalline and amorphous materials, facet formation and structure cannot reflect microscopic order. Although fracture mechanics predict that slow crack fronts should be straight and form mirror-like surfaces, facet-forming fronts propagate simultaneously within different planes separated by steps. Here we show that these steps are topological defects of crack fronts and that crack front separation into disconnected overlapping segments provides the condition for step stability. Real-time imaging of propagating crack fronts combined with surface measurements shows that crack dynamics are governed by localized steps that drift at a constant angle to the local front propagation direction while their increased dissipation couples to long-ranged elasticity to determine front shapes. We study how three-dimensional topology couples to two-dimensional fracture dynamics to provide a fundamental picture of how patterned surfaces are generated.
裂纹在其形成的表面上呈现出复杂的图案。由于多面断裂表面通常由晶体和非晶材料中的缓慢拉伸裂纹形成，所以小面的形成和结构无法反映微观有序性。尽管断裂力学预测缓慢的裂纹前沿应该是直的，并形成镜面状表面，但形成小面的前沿在由台阶分隔的不同平面内同时传播。在这里，我们表明这些台阶是裂纹前沿的拓扑缺陷，并且裂纹前沿分离成不连续的重叠段为台阶稳定性提供了条件。对传播裂纹前沿的实时成像与表面测量相结合表明，裂纹动力学受局部台阶控制，这些台阶以与局部前沿传播方向成恒定角度漂移，同时它们增加的耗散与长程弹性耦合以确定前沿形状。我们研究三维拓扑如何与二维断裂动力学耦合，以提供关于图案化表面如何产生的基本图景。
