High speed stereo-vision study of laminated glass fragmentation upon impact

The different stages of an impact on laminated glass are difficult to observe and quantify but are essential for numerical model validation. To assess the performance of this composite to low-velocity ( ∼ 10 m/s) high-mass impacts, dynamical impact tests, inspired by ball-drop tests, are performed, equipped with multiple high-speed cameras. From the set of images, a continuous 3D shape reconstruction of the deformed laminated glass over time is performed using Stereo-Digital Image Correlation (S-DIC). Significant brightness and contrast variations captured by two cameras due to large rotations of glass fragments and large strain of the polymer interlayer between fragments render the use of S-DIC difficult as the impactor penetrates deeper into the plate. To circumvent this problem, an axisymmetric regularization is introduced which has the advantage of not requiring prior knowledge of the mechanical behavior for the tested specimen. It is shown that it offers a more extended period of time (as compared to regular S-DIC) over which a trustful analysis can be performed. The time evolution of the fragmented laminated glass and the density of cracks, both available from our analysis, are key ingredients to elaborate quantitative modeling of the dynamic performance of the laminate.