Effect of fixture boundary conditions for low-velocity impact: A focus on composites with different matrix and fibers

Abstract

It has been noted that the matrix may have a significant effect on the impact resistance of composite material. Replacing a brittle polymer with a more “flexible” one can improve the impact resistance of composite. However, composites with soft polymer as matrix may challenge the standard experimental methods for tests, such as the low-velocity impact. Due to the extremely large elastic deformation, a standard fixture can hardly grip the sample due to severe slip of the sample at the clamping region. To address this issue, a new fixture was designed and implemented for testing highly deformable composite laminates subjected to low-velocity impacts that can adequately clamp the sample with a set of ‘bolt teeth’. The new fixture, however, provides a different boundary condition. Therefore, an investigation on the effect of the fixture on the low-velocity impact of “soft” composite was performed. This work can help to understand the influence of different boundary conditions on the mechanical performance during the low-velocity impact tests. Thus, the current work was performed with epoxy-based composites, which can fit both standard and designed fixtures. The analysis was carried out on experimental results with different types of fibers (glass/aramid) as well as different energy levels for the two fixtures. Through analysis of the experimental data, it was found that a smaller permanent deformation, as well as a higher peak force, were obtained from specimens tested with the standard fixture, indicating a stiffer boundary condition, compared with the designed fixture for soft composites.