Observation of the Propagation of Plastic Strain in HSLA 80 Steel

We observed using the in-plane moire method the propagation of plastic strain in a uniform tension specimen made of HSLA 80 steel loaded quasi-statically. The steel shows a localized, heterogeneous type of transition from elastic to plastic deformation. Plastic strain generally initiates at one end of the specimen and gradually propagates toward the other end. The magnitude of plastic strain, once initiated and propagation begun, is about seven times the elastic strain. An interface band of the order of a few millimeters separates the elastic and plastic zones. Since it is a nonuniform deformation, local strain measurement methods such as strain gage, clip gage, etc. are not suitable to characterize the mechanical properties of this material.