Investigation of the 2D assumption in the image-based inertial impact test

The image-based inertial impact (IBII) test has shown promise for measuring properties of composites at strain rates where existing test methods become unreliable due to inertial effects (>10(2) s(-1)). Typically, the IBII tests are performed with a single camera, and therefore, to use surface measurements for material property identification, it is necessary to assume that the test is two-dimensional. In this work, synchronised ultra-high-speed cameras are used to quantify the relevance of this assumption when nonuniform, through-the-thickness loading is applied to interlaminar samples. Initial experiments revealed that an angular misalignment of approximately 1 degrees between the impact faces of the waveguide and projectile created a bending wave that propagated along the sample behind the axial pulse. Even under these conditions, consistent measurements of stiffness were made by assuming a linear distribution of the behaviour through-the-thickness. When the misalignment was reduced to 0.2 degrees, the effects on single-sided measurements were significantly reduced. The two alignment cases were compared to show that three-dimensional loading had a small effect on stiffness identification (approximately 5% bias) relative to failure stress (approximately 30% bias). This study highlights the importance of impact alignment for reliable characterisation of the interlaminar failure stress and was used to establish guidelines for diagnosing loading issues from single-sided measurements.

Automated summary

The study demonstrates that even under nonuniform, through-the-thickness loading, reducing angular misalignment can decrease the impact on single-sided measurements, with a relatively minor effect on stiffness identification compared to failure stress. Three-dimensional loading has a small impact on stiffness identification (approximately 5% bias) relative to failure stress (approximately 30% bias).