Abstract

AbstractThe 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 (> 102 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° 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°, 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.

Highlights

  • The widespread use of polymer-matrix composites for primary load-bearing structures often requires design consideration for dynamic loading (e.g.: blast, crash, foreign object strike, etc.)

  • Literature suggests that that stiffness and strength of polymer matrix materials exhibit a moderate sensitivity to strain rate [1, 2]; the number of studies attempting to measure high-strain-rate interlaminar properties are scarce and inconsistent [2]

  • For low wave speed materials, such as polymer matrix composites in the interlaminar planes, it is generally accepted that Kolsky bar apparatus is not able to provide a true measurement of the initial stiffness [5,6,7,8]

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Summary

Introduction

The widespread use of polymer-matrix composites for primary load-bearing structures often requires design consideration for dynamic loading (e.g.: blast, crash, foreign object strike, etc.) Under these conditions significant interlaminar stresses can be generated over a wide range of strain rates. Literature suggests that that stiffness and strength of polymer matrix materials exhibit a moderate sensitivity to strain rate [1, 2]; the number of studies attempting to measure high-strain-rate interlaminar properties are scarce and inconsistent [2]. Part of this is a result of limited test development for interlaminar characterisation. Inertia is thought to be the largest contributor to the high amounts of scatter in reported measurements of stiffness and strength in the literature as documented in the review by Van Blitterswyk et al [2]

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