Impact dynamic behavior of soft composites at low temperatures

Dynamic testing soft composite, matrix, and other hyper-viscoelastic materials at high velocities replicating impacts is difficult to perform, either due to the lack of equipment such as a split Hopkinson pressure bar setup, or more commonly, the challenges related to sensors and monitoring the dynamic response. For certain soft composites and hydrogel matrices with low moduli on the order of 215,000 Pa, sensing would require a highly sensitive load cell that would also need to survive >1,000 s^-1 without failure and/or without digital image correlation allowed as paint or other speckles may not adhere to the specimen surface. Our current research addresses this issue by examining the temperature effects on the material response. By exploring the interaction between temperature and viscoelasticity, we have validated a theoretical framework for performing up to two decades of strain rate testing (100 – 10,000 s^-1) without altering the impact velocity (7 m/s), and using only a 14 °C temperature change. The implications of this research should allow us to examine strain rate effects for certain soft polymer composites at loading rates exceeding the capabilities of our instruments without any new equipment or sensors.