Brittle to quasi-brittle transition and crack initiation precursors in crystals with structural Inhomogeneities

Abstract

Crack initiation emerges due to a combination of elasticity, plasticity, and disorder, and it is heavily dependent on the material's microstructural details. In this paper, we investigate brittle metals with coarse-grained, microstructural disorder that could originate in a material's manufacturing process, such as alloying. As an investigational tool, we consider crack initiation from a surface, ellipsoidal notch: As the radius of curvature at the notch increases, there is a dynamic transition from notch-induced crack initiation to bulkdisorder crack nucleation. We perform extensive and realistic simulations using a phase-field approach coupled to crystal plasticity. Furthermore, the microstructural disorder and notch width are varied in order to study the transition. We identify this transition for various disorder strengths in terms of the damage evolution. Above the transition, we identify detectable precursors to crack initiation that we quantify in terms of the expected stress drops during mode I fracture loading. We discuss ways to observe and analyze this brittle to quasi-brittle transition in experiments.

Direct detection of plasticity onset through total-strain profile evolution

“…Regarding the plasticity model, we consider [36][37][38] the case of tensile loading in the x direction for 2D and 3D specimens which are periodic in all directions and have sample dimensions in (x, y, z) of (512,512,2) and (64,64,64), respectively, where each cell can be interpreted as a representative volume element with dimensions of 2 μm in each direction, promoting the perspective of investigating 1 mm 2 2D or submillimeter 3D samples. We study two different geometries so that the geometry effect on our measures is checked.…”

“…Details of the model's hardening dynamics can be also found in Refs. [38,40]. The utilized model is built upon commonly used modern phenomenological crystal plasticity assumptions, which captures effectively the essential aspects of slip-based macroscale plasticity through a combination of fundamental assumptions and basic constitutive laws that have been confirmed in various metals over the last four decades [39].…”

Early prediction of macrocrack location in concrete, rocks and other granular composite materials

“…As shown recently 16 , damage in the early stages of of the prefailure regime mainly occurs away from the macrocrack path C . Similar stress redistributions around strain concentration sites have been observed to divert damage away from the crack path (viz., the crack tip) into the bulk of the sample 9,41 . Given that C essentially coincides with the energy bottleneck B(F E ) , this may initially seem counterintuitive given the close proximity to fracture of the bonds in B(F E ) .…”

Quantifying the Contribution of Crystallographic Texture and Grain Morphology on the Elastic and Plastic Anisotropy of bcc Steel

“…The employed DAMASK package [38] offers a variety of such physics-based models for bcc materials [69], fcc steels [70] and Tungsten [71]. More advanced modeling approaches that allow to investigate in detail the influence of dislocation movement and interaction with grain boundaries [72] or the role of damage [73][74][75] are additionally available. However, the challenge remains to increase the computational performance of these models drastically before they can be employed to polycrystals that contain a sufficient number of grains to be statistically representative.…”