Drop weight tensile impact testing of adhesively bonded carbon/epoxy laminate joints

Crashworthiness of composite structures is a key issue for the design of lightweight vehicles. In particular the joined parts of the structures must be able to absorb a high amount of energy in order to protect the passengers. In this paper the dynamic behavior of adhesively bonded carbon/epoxy laminate joints is investigated. The adherends are made of unidirectional plies, whose orientations are carefully chosen in order to assess the influence of the adherend mechanical properties on the joint behavior. A drop weight machine has been modified in order to impact specimens under tension. Single lap joints are tested under impact tension at velocities from 1 to 4 m/s. Results of the impact tests that are compared to reference quasi-static test results emphasize the rate-sensitivity of the joints. The stiffness, the failure load and the absorbed energy all increase with increasing loading rate. One major result is that the joint behavior is qualitatively the same under quasi-static and impact loading: the failure mode and the joint ranking (based on their strength) remain identical. Therefore the impact design of the adhesive joints could be based on a static design at moderate loading rates.