Measurement of true stress–strain curves and evolution of plastic zone of low carbon steel under uniaxial tension using digital image correlation

• 3D-DIC is used to determine the true stress–strain curves of low carbon steel.
• The evolution of plastic zone of low carbon steel is studied as well.
• Results verify some plastic theories of ductile material from experimental aspects.
• The proposed method could be used for other ductile materials.

Three-dimensional digital image correlation has been utilized widely in many fields due to its advantages of non-contact, full-field measurement and simplicity. Based on 3D-DIC measurement system and electronic universal testing machine, two uniaxial tension tests for low carbon steel specimen were performed to acquire the true stress–strain curves. An assumption was made that specimen’s cross section keeps as a circle in tension test whose diameter could be determined by calculation of the curvature of surface shape. Therefore, true stress of specific cross section was acquired and hence the true stress–strain curves were obtained. In addition, the evolution of plastic zone of specimen under uniaxial tension was studied as well. And experimental results indicate that at certain time instant of expanding process of plastic zone, region that has already entered the plastic zone and that has not entered such zone yet is keeping in a constant deformed state, while region that is entering the plastic zone provides axial plastic deformation, which is almost equal to crosshead movement of testing machine.