Image-Based Inertial Impact Test for Composite Interlaminar Tensile Properties

Abstract

In this work an image-based inertial impact test is proposed to measure the interlaminar tensile stiffness and strength of fibre-reinforced polymer composite materials at high strain rates. The principle is to combine ultra-high-speed imaging and full-field measurements to capture the dynamic kinematic fields and exploit the inertial effects generated under high strain rate loading. The kinematic fields are processed using the virtual fields method to reconstruct stress averages from maps of acceleration. In this way, the specimen acts like a dynamic load cell, with no gripping or external force measurement required. Stress averages are combined with strain measurements to construct stress-strain curves and identify the interlaminar stiffness and tensile strength. Special optimised virtual fields are also implemented to identify interlaminar stiffness parameters from complete maps of strain and acceleration. Interlaminar stiffness and tensile strength are successfully identified at average, peak strain rates on the order 3500 s −1 and 5000 s −1 , respectively. Results show an increase in stiffness between 30 and 35%, and an increase in strength of 125% compared to quasi-static values. Keywords High strain rate • Interlaminar tension • Fibre-reinforced polymer composites • Dynamic test methods • Ultrahigh speed imaging • Virtual Fields Method

Generalized Stress–Strain Curves for IBII Tests on Isotropic and Orthotropic Materials

“…The principle was first published in 2014 [9] on an elastically isotropic material. It was then refined and extended to several classes of materials under the name 'Image-Based Inertial Impact' (IBII) test [18][19][20][21]. This test consists of an edge-on impact of a thin rectangular test specimen with all other edges free from any constraints.…”

“…This sends a compression wave into the specimen which reflects off the free edge as a tensile wave. The pulse length can be designed either to load and unload the specimen in compression [9,18] or to develop enough tension after wave reflection so that tensile fracture occurs [19][20][21].…”

“…with orthotropy axes aligned with the specimen axes), this is also possible. However, when a unidirectional composite is tested in the 90 • orientation, Poisson's effect can be neglected because of the high stiffness at 0 • [19,21]. The advantage of this second approach is that it leads naturally to spatially resolved properties, and provides an easy way to plot 2D curves from which the departure from possible linearity / elasticity is easily appraised.…”

The Image-Based Inertial Release (IBIR) Test: A New High Strain Rate Test for Stiffness Strain-Rate Sensitivity Identification

“…For use of the VFM in inertial tests the reader is referred to refs. [7][8][9][10][11]. Here, the VFM relating to inertial testing will be briefly revisited for completeness.…”

“…Subsequently, this idea was further developed as the so-called 'image-based inertial impact' (IBII) test and has been successfully applied to a variety of materials in refs. [9][10][11].…”