Performance analyses of laminates subjected to low velocity impact based on non-contact measurement displacement

In order to obtain the performances of composite laminates under low-velocity impact through the displacement of impacted point, the displacement and velocity for the back of impacted point were measured by high-speed laser displacement sensors during drop weight impact test of laminates firstly. Then, based on spring-mass impacted model, the impacted contact load was calculated by the displacement of impacted point, and the parameters of spring-mass model were calibrated with non-destructive impact test. After that, the contact load during the impact process with damage happening was simulated, the time of delamination initiated was judged by the testing velocity response of impacted point, and the delamination threshold load was obtained by simulated results. Finally, the reduction for flexural rigidity of laminate was conducted according to the result of non-destructive test, the contact load and energy absorption curves after impact damage initiated were calculated using spring-mass model, the real-time depth of indentation was calculated by the displacements of impactor and back of impacted point. The results show that when the structure is impacted and delamination initiates, violent vibration for the velocity of impacted point appears due to the sudden reduction of laminate rigidity. This phenomenon can be used as the recognition characteristic for the delamination damage of structure initiating. The calculated results for contact load and energy absorption curves after the impact damage initiated coincide with the measured results of tests. The varying tendency for the real-time depth of indentation with the impact energy obtained by calculation is in accords with the varying tendency for the depth of indentation measured after impact. These results indicate that the proposed method based on non-contact measurement technology can be applied to analyze the impact performances of laminates under the condition that contact load can not be measured directly.