[Paper Review] Brittle to Quasi-Brittle Transition and Crack Initiation Precursors in Disordered Crystals

Stefanos Papanikolaou, J. Thibault+3 more|arXiv (Cornell University)|Jul 13, 2017

Microstructure and mechanical properties29 references3 citations

TL;DR

This study investigates the transition from brittle to quasi-brittle fracture in disordered crystals using phase-field crystal plasticity simulations, revealing that increasing notch radius shifts crack initiation from notch-driven to bulk disorder-driven. Key findings show detectable stress-drop precursors before crack nucleation above the transition, offering experimental observables for early fracture detection in coarse-grained, disordered metals.

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 bulk-disorder 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.

Motivation & Objective

• To understand how microstructural disorder and notch geometry influence crack initiation in brittle metals.
• To identify the transition point from notch-driven to bulk disorder-driven crack nucleation.
• To quantify detectable precursors preceding crack initiation in the quasi-brittle regime.
• To provide experimentally observable signatures for early fracture detection in disordered metallic materials.

Proposed method

• Employing a phase-field approach coupled with crystal plasticity to simulate fracture in disordered crystalline materials.
• Varying the notch radius and disorder strength to probe the transition between crack initiation mechanisms.
• Simulating mode I fracture loading to analyze damage evolution and stress response.
• Using statistical analysis of stress drops to identify precursors to crack nucleation.
• Performing extensive, realistic simulations across multiple disorder strengths and geometric configurations.
• Validating the transition behavior through damage evolution and stress-drop statistics.

Experimental results

Research questions

• RQ1 How does increasing notch radius shift the dominant crack initiation mechanism from notch-driven to disorder-driven in disordered crystals?
• RQ2 What measurable precursors emerge before crack initiation in the quasi-brittle regime?
• RQ3 How does microstructural disorder influence the onset of the brittle-to-quasi-brittle transition?
• RQ4 Can stress-drop statistics serve as reliable indicators of impending crack nucleation?
• RQ5 What experimental observables can be derived from the simulated precursors for validation?

Key findings

• A dynamic transition from notch-induced to bulk-disorder-driven crack initiation occurs as the notch radius increases.
• Above the transition threshold, detectable stress-drop precursors emerge prior to crack nucleation, quantified via statistical analysis of stress response.
• The magnitude and distribution of stress drops increase with disorder strength, indicating higher fracture susceptibility.
• The transition point is identifiable through distinct changes in damage evolution patterns across different disorder levels.
• The simulated precursors are consistent across multiple realizations and are robust to variations in notch geometry and disorder strength.
• The findings suggest that stress-drop signatures can be experimentally monitored to predict crack initiation in disordered metallic materials.