AbstractHeavily deformed two‐phase materials, often referred to as in‐situ composites, have been shown to exhibit strengths which approach the theoretical limit. This paper considers the mechanical response of these materials from both a macroscopic and microscopic point of view in terms of the competing processes of continued plastic Bow and fracture. The results from a wide variety of composite systems and experimental techniques are examined to suggest a number of areas requiring further study in the fields of plasticity and fracture of engineering materi