Puncture properties of aluminum foil over a wide range of deformation rates

The puncture properties of 40-µm 8006 aluminum alloy foil at a wide range of velocities were evaluated. First, to perform the impact puncture test, which has not been reported so far, a load cell for impact puncture testing, which combines a needle and a stress sensing part, was investigated using finite element analysis (FEA), and it was shown that the load could be measured under several m/s. A falling-weight impact puncture test apparatus was then developed. Next, puncture tests were carried out over a wide range of displacement rates (1.0 × 10^–5–1.3 × 10⁰ m/s). The resulting trend of the displacement rate dependence of the material strength obtained from the load-displacement relationship was in qualitative agreement with the strain rate dependence of the material strength obtained from uniaxial tensile tests. However, when the displacement rate increased above 1 m/s, the trend of load increase in the early stages of deformation changed. Observation with a high-speed camera and the results of FEA showed that the deformation in the puncture test direction propagated from the contact area between the needle and the specimen towards the specimen anchorage area. This deformation wave is reflected back to the contact area in the opposite phase when it reaches the specimen anchor, causing deformation that entrains the tip of the needle, thus increasing the load. Based on the above results, the thrusting properties of the film were evaluated over a wide range of speeds, from quasi-static to impact velocity, and the mechanism of the thrusting deformation was clarified.