Low Mass-High Velocity and High Mass-Low Velocity Impact Testing on CFRP Specimen Under Equal Impact Energy

In this study, we investigate the low mass (2.48 kg)-high velocity (5m/s) and high mass (12.48kg)-low velocity (2.29m/s) response of the Carbon Fiber Reinforced Polymer (CFRP) specimens from low-velocity impact testing under equal energy. Three different environmental test conditions are employed to study the differences in impact behavior. CFRP samples are subjected to the impact at room temperature (23ºC), low temperature (-70ºC), and low temperature (-70ºC) with 3mm thick ice covering the top facesheet of the target. To create ice facesheet, 3D printed molds are used to hold the composite specimens so that water can be poured over it without significant leakage and kept in the freezer. The objective of including the ice sheet into consideration is to emulate the ship's surface, which would be covered with ice during travel in a low-temperature region. The samples were tested at impacted energies of 31J, and 62J, according to ASTM D7136/D7136M-15.

A relative comparison of the impact response from the CFRP specimens under different conditions is presented in terms of force, energy, and displacement. The greater value of the highest peak force with less test duration is observed for low mass-high velocity (LMHV) condition at both energy levels. The impactor is in contact with the target for a relatively long time when high mass-low velocity (HMLV) is considered. Moreover, LMHV incidents cause more permanent deformation in the samples, along with higher absorbed energy for each energy level. A little higher permanent deformation is found from the samples with ice facesheet due to the additional thickness from ice at -70ºC. However, it does not influence the absorbed energy significantly. Further, damage responses are characterized at different temperatures. Though LMHV shows less peak force at 31J, a higher value of peak force is found at 62J for HMLV cases under 23ºC and -70ºC. Samples with the ice facesheet at -70ºC show a different trend here. Besides, they also represent a variation in the relationship between permanent displacement to peak displacement than the other two conditions. X-ray micro-computed tomography testing is performed to reveal the damages in the composite specimens. A large area of crack propagation with localized physical damage was observed from the samples from LMHV incidents. A great portion of the damage from those samples is Barely Visible Impact Damage (BVID) types. On the other hand, HMLV incidents show a large area of delamination in the samples due to increased contact duration between the indenter and the samples. A relative study on the damage initiation process will also be discussed for three different scenarios. Finally, an analytical model will be demonstrated for low mass and high mass impact to provide a correlation with the experimental outcomes.