On the Origin of Extrinsic Size Effects on the Fracture Resistance of Thin ETP Copper Sheets

Abstract

Size effects are well known to influence the mechanical behavior of materials and impact the structural integrity and reliability of devices such as thin films, coatings, foils, and sheet metals. There is little literature on extrinsic (specimen size) effects on fracture resistance of thin polycrystalline sheets while keeping the internal parameters constant. Herein, we determine the impact of specimen thickness on the fracture behavior of electrolytic tough pitch (ETP grade) Cu sheets, under two different grain sizes and initial dislocation densities. Elastic–plastic fracture mechanics (EPFM) combined with digital image correlation‐based full‐field strain mapping has been utilized to determine both the fracture resistance and plastic zone evolution as a function of specimen thickness. A smaller is weaker trend has been observed in both conditions. The specimen thickness effect is quantified in terms of a size exponent and is related to the truncation of the process zone ahead of growing crack, leading to reduced fracture resistance. The effect of intrinsic microstructural parameters such as grain size and dislocation density on the strain hardening ability, tensile elongation to fracture, and fracture toughness is also quantified and the plastic strain is found to correlate with fracture toughness.