Fracture toughness evaluation across length scales in metallic materials and alloys: Methods, measurements, and insights

Fracture in materials is a critical issue across various fields, including engineering, physics, and materials science. Fracture toughness, which quantifies a material’s resistance to crack propagation, can vary significantly with the scale of measurement. Traditional continuum mechanics often fail at small scales because the assumptions of homogeneity and continuity break down. At the nanoscale, fracture behavior differs due to the discrete nature of atoms and pronounced surface effects, leading to size-dependent fracture properties. Since experimental studies at this scale are limited, molecular dynamics (MD) simulations are frequently employed to investigate fracture mechanisms. The challenge of length-scale dependence remains a major obstacle in accurately determining fracture toughness. Metals and their alloys, particularly iron and aluminum are widely used structural materials, and their applications now extend from the continuum scale to micro and nanoscale systems. This review summarizes methods for determining fracture toughness of iron, aluminum, and their alloys across different scales, compares reported values, and discusses the implications of length-scale effects based on available results. The findings underscore the importance of deeper exploration into length-scale influences and fracture mechanisms to refine the determination of fracture toughness. Addressing these challenges will enable more reliable design of advanced materials for multi-scale applications. Future research should integrate experimental, computational, and theoretical approaches to bridge the gap between atomistic and continuum models.