Combined shear/tension testing of fibre composites at high strain rates using an image-based inertial impact test

J. dynamic behavior mater.

2019

This article presents a particular use of the Virtual Fields Method to exploit the results of Image-Based Inertial Impact (IBII) tests. This test consists on an edge-on impact of a free-standing thin flat rectangular coupon. The specimen response is recorded using an ultra-high speed camera filming the deformation of a grid pattern printed at its surface. From these images, displacement fields are derived, from which strain and acceleration can be obtained. The Virtual Fields Method makes use of the acceleration fields to derive stress information. Until now, a very simple 'stress-gauge' approach was used that could only provide relevant stress-strain information if the test was predominantly uniaxial. The alternative was to use the full inverse approach with the Virtual Fields Method but this would not allow the same degree of data understanding as the 'stressgauge' approach. This article proposes an extension to this 'stress-gauge' approach for fully multiaxial tests. The equations are first derived and then validated using simulated and experimental IBII test data on isotropic and orthotropic materials.

Section: Validation On Experimental Datamentioning

confidence: 99%

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

J. dynamic behavior mater.

2019

“…The design process could be optimised using a parametric sweep of a suitable finite element model. A basic example of extending the IBIR test would be to use an off-axis unidirectional carbon fibre composite sample along with the analysis procedures described in [18,42] to obtain the in-plane transverse and shear modulus in the same test. It could even be extended to the full set of orthotropic stiffness components using a short open-hole off-axis specimen as in [40].…”

Section: Test Designmentioning

confidence: 99%

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

2020

Exp Mech

A key limitation of current moderate and high strain rate test methods is the need for external force measurement. For high loading rate hydraulic machines, ringing in the load cell corrupts the force measurement. Similarly, the analysis of split-Hopkinson bar tests requires the assumption that the specimen is in a state of quasi-static equilibrium. Recently, image-based inertial test methods have shown that external force measurement is not required if full-field measurements are available and inertial effects are significant enough. In this case the load information is provided by the acceleration fields which are derived from full-field displacement measurements. This article describes a new image-based inertial test method that can be used for simultaneous quasi-static and high strain rate stiffness identification on the same test sample. An experimental validation of the new test method is provided using PMMA samples. A major advantage of this new test method is that it utilises a standard tensile test machine and the only specialist equipment that is required is an ultra-high speed camera. Keywords High strain rate • Full-field measurements • Virtual fields method • Grid method • Polymers 493 Experimental Mechanics (2020) 0:-6 508

“…Several recent studies have considered ultra-high-speed imaging and full-field measurements as an alternative way of characterising high-strain-rate material properties [20][21][22][23][24][25][26][27][28][29][30][31]. The virtual fields method (VFM) enables the inertial effects to be exploited with the specimen acting as a dynamic load cell, thus alleviating the requirement for external force measurement.…”

Section: Introductionmentioning

confidence: 99%

“…This concept of using full-field measurements and the VFM for high-strain-rate stiffness identification was first validated by Moulart et al [32] and Pierron and Forquin [20]. Follow on studies have resulted in the formalisation of the image-based inertial impact (IBII) test, which has been successfully demonstrated to measure high-strain-rate inplane [21,22,24,25] and interlaminar [26] properties of composites, and ceramics [27].…”

Section: Introductionmentioning

confidence: 99%

“…With the goal of complete interlaminar characterization, it is now desired to expand the test to develop a configuration that can be used to identify shear properties. Preliminary work [24] has demonstrated that the in-plane shear modulus and elastic modulus can be simultaneously identified using an edge-on impact configuration with fibres cut off-axis to the loading direction. While it would be ideal to extend the same concept for testing interlaminar specimens, this is challenging to do given the restriction on specimen length (limited by laminate thickness).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Image-Based Inertial Impact (IBII) Tests for Measuring the Interlaminar Shear Moduli of Composites

Blitterswyk

J. dynamic behavior mater.

2020

The image-based inertial impact test has previously shown that inertial effects generated with high-strain-rate loading can be used to measure the dynamic constitutive properties of composites at strain rates on the order of $$1600\,{\rm s}^{-1}$$ 1600 s - 1 . This work represents an important next step in exploring the potential of this concept with two tests presented where loading heterogeneity is exploited to measure the interlaminar shear modulus and stress–strain behaviour at high strain rates. The first test configuration used a short-beam with asymmetric loading to activate the shear behaviour. The virtual fields method was used to directly identify the interlaminar shear modulus from heterogeneous full-field maps of strain and acceleration. Simulated experiments were used to optimise the test configuration, select optimal smoothing parameters, and quantify uncertainty from grid rotation on the shear modulus identifications. The test was validated experimentally with three different virtual fields identifying an average shear modulus ranging from 5.7 to 5.9 GPa measured at $$1600\,{\rm s}^{-1}$$ 1600 s - 1 , representing a 16–19% increase compared to quasi-static measurements. The shear modulus could also be identified from shear introduced into specimens tested in the standard, end-on interlaminar IBII configuration from slight in-plane misalignments of the impactor. The identified value of 5.6 GPa validates measurements from the first configuration and also demonstrates the capability to identify multiple interlaminar stiffness parameters from a single test.