A new method for limit point determination in composite materials containing defects using image correlation

Abstract A new method is proposed to determine the onset of material failure in composite materials containing defects tested in tension. The new method is proposed since the load versus axial deformation plot from a tension test cannot be always used to identify the onset of material failure in a composite materials containing defects. Digital image correlation (DIC) methods can provide very accurate d4eformation and strain measurements. In this paper, a new DIC based method is proposed that can identify the onset of damage and thus the limit point in composite materials containing defects. In this method (1) surface topography is extracted from the three dimensional DIC data using two cameras; (2) the changes in the surface are monitored during the tension tests; (3) The onset of interlaminar damage is identified by comparing the surface height difference in the test specimen at different time steps; (4) the first derivative of the surface height difference is used to determine the onset of internal instabilities in the material and are correlated to interlaminar damage. Compared to existing standard methods that rely on the load-deformation response to determine the onset of damage, the proposed procedure more accurately defines the onset of interlaminar damage and thus the definition of the boundary of safe operation of the composite material system prior to damage onset.