Fractography

About: Fractography is a research topic. Over the lifetime, 5043 publications have been published within this topic receiving 86068 citations.

The application of fractal and quantum geometry to brittle fracture

Abstract: This paper examines three apparently disparate views of fracture in brittle materials with the purpose of showing the interrelationship of the fracture process at different length scales. Quantitative fractographic analysis of brittle fracture surfaces shows that there are characteristic markings on the surfaces that are self-similar and scale invariant, implying that fractal analysis is a reasonable approach to analyzing these surfaces. The fractal dimension is directly proportional to the fracture energy, γ, during fracture for many brittle materials, i.e., γ= 1 2 Ea 0 D ∗ where E is the elastic modulus, a0 a structural parameter and D* is the fractal dimensional increment. Analysis of previous results of molecular dynamics modeling shows that the fractal nature of the fracture surface is consistent with the predicted surface produced during simulated fracture. The fractal dimensional increment, D*, of the simulated fracture surface in a silica glass and silicon single crystal over a single order of magnitude matched well with those values measured on fracture surfaces of beams fractured in flexure for the same materials at length scales 1000–100 000 times larger. Finally, a ring contraction mechanism, modeled using semi-empirical quantum mechanical molecular orbital methods, is shown to be a likely step in the fracture of silica tetrahedra along the crack front. The geometry of the structure formed at the atomic scale from these ring contractions can be related to a0 and leads to the basis for propagation into a fractal structure. Thus, we have identified a reasonable atomic level foundation for the structural parameter, a0. Based on a comparison of atomic and molecular modeling with macroscopically measured values of D* and a0, we suggest that the fracture process is a percolation of a series of ring contractions along the crack front, which result in the observed fracture surfaces for several brittle materials.

Intergranular fracture in 13 wt% chromium martensitic stainless steel

Abstract: Fracture of 13 wt% chromium steel blades has been observed to occur in the intergranular mode in certain service failures An attempt has been made in this study to identify the conditions in respect of material, loading and environment which may lead to intergranular fracture Three different materials were subjected to varying heat treatments selected on the basis of fracture characteristics of as-received materials It has been concluded that grain-boundary segregations of impurities and carbide precipitation, intergranular network of delta ferrite at prior austenitic grain boundaries, and a sufficient concentration of NaCl in conjunction with cyclic stress, promote intergranular fracture in a 13 wt% chromium steel