Strain rate influence on fracture development in experimental ductile multilayers

The far-field strain rate is a crucial parameter that controls the transition between brittle and ductile deformation. We have used analogue experiments to study the strain rate influence on the development of brittle fractures in a ductile composite material. Plasticine multilayer models were deformed under coaxial boundary conditions at three different strain rates to analyse the transition from non-localised deformation to the development of a brittle fracture network that accommodates part of the deformation. The results show that tension cracks and voids are the first macroscopic structures that nucleate after an early stage of ductile deformation. Coalescence and collapse of these structures lead to the development of brittle shear fractures. The evolution of fracture orientations, lengths and displacements was systematically analysed. The ratio of the accumulated fracture displacement vs. fracture length (dmax/L) depends not only on the total deformation, but also on the strain rate at which the system is deformed. The accumulated displacement with respect to fracture length increases with strain rate.

Research highlights► Strain rate influences the degree of fracture development in ductile materials. ► Shear fractures in these models nucleate mainly by void and tension crack collapse. ► The ratio of fracture displacement vs. length depends on the applied strain rate.