Drop-weight impact performance of flexible laminated films

Low velocity impact tests have been performed on flexible laminated films with different layups employing a novel small-scale instrumented drop-weight testing approach. Thermoplastic polyurethane (TPU) and Polyimide (PI) layers were bonded together using an optically clear adhesive (OCA) to produce six types of flexible laminated film. An impact performance coefficient (K_t) has been defined to evaluate the impact resistance of the different films, which considers in one relationship the effect of absorbed energy, peak load and impact duration. Following testing, a lamination based on a TPU/TPU/PI (TTP) flexible film was identified as giving a superior impact performance. Finite element analyses of the load-time and energy-time curves showed good agreement with the experimental results. It has been shown that as the TPU content increases, K_t initially increases and then decreases. The modelling, as well as the experiments, show a maximum value of K_t was obtained when the TPU volume fraction was approximately 60%. This quantitative design guideline for TPU content and configuration is novel and provides valuable insights for developing impact-resistant protective films. The proposed methodology, combining small-scale drop-weight testing with finite element modelling, represents a new approach for assessing and optimizing flexible laminated films.