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

2018 ◽  
Vol 183 ◽  
pp. 02041 ◽  
Author(s):  
Lloyd Fletcher ◽  
Jared Van-Blitterswyk ◽  
Fabrice Pierron
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
Stress Wave ◽  
Impact Test ◽  
High Strain ◽  
Hopkinson Bar ◽  
Test Method ◽  
Strain Rates ◽  
Fibre Composites ◽  
Split Hopkinson

Testing fibre composites off-axis has been used extensively to explore shear/tension coupling effects. However, off-axis testing at strain rates above 500 s-1 is challenging with a split Hopkinson bar apparatus. This is primarily due to the effects of inertia, which violate the assumption of stress equilibrium necessary to infer stress and strain from point measurements taken on the bars. Therefore, there is a need to develop new high strain rate test methods that do not rely on the assumptions of split Hopkinson bar analysis. Recently, a new image-based inertial impact test has been used to successfully identify the transverse modulus and tensile strength of a unidirectional composite at strain rates on the order of 2000 -1. The image-based inertial impact test method uses a reflected compressive stress wave to generate tensile stress and failure in an impacted specimen. Thus, the purpose of this study is to modify the image-based inertial impact test method to investigate the high strain rate properties of fibre composites using an off-axis configuration. For an off-axis specimen, a combined shear/tension or shear/compression stress state will be obtained. Throughout the propagation of the stress wave, full-field displacement measurements are taken. Strain and acceleration fields are then derived from the displacement fields. The kinematic fields are then processed with the virtual fields method (VFM) to reconstruct stress averages and identify the in-plane stiffness components G12 and E22.

scholarly journals An Image-Based Impact Test for the High Strain Rate Tensile Properties of Brittle Materials

2018 ◽  
Vol 183 ◽  
pp. 02042
Author(s):  
Lloyd Fletcher ◽  
Fabrice Pierron
Keyword(s):  
Tensile Strength ◽  
Elastic Modulus ◽  
High Strain Rate ◽  
Strain Rate ◽  
Stress Wave ◽  
High Strain ◽  
Brittle Materials ◽  
Test Method ◽  
Strain Rates ◽  
High Strain Rates

Testing ceramics at high strain rates presents many experimental diffsiculties due to the brittle nature of the material being tested. When using a split Hopkinson pressure bar (SHPB) for high strain rate testing, adequate time is required for stress wave effects to dampen out. For brittle materials, with small strains to failure, it is difficult to satisfy this constraint. Because of this limitation, there are minimal data (if any) available on the stiffness and tensile strength of ceramics at high strain rates. Recently, a new image-based inertial impact (IBII) test method has shown promise for analysing the high strain rate behaviour of brittle materials. This test method uses a reflected compressive stress wave to generate tensile stress and failure in an impacted specimen. Throughout the propagation of the stress wave, full-field displacement measurements are taken, from which strain and acceleration fields are derived. The acceleration fields are then used to reconstruct stress information and identify the material properties. The aim of this study is to apply the IBII test methodology to analyse the stiffness and strength of ceramics at high strain rates. The results show that it is possible to identify the elastic modulus and tensile strength of tungsten carbide at strain rates on the order of 1000 s-1. For a tungsten carbide with 13% cobalt binder the elastic modulus was identified as 516 GPa and the strength was 1400 MPa. Future applications concern boron carbide and sapphire, for which limited data exist in high rate tension.

High Strain Rate Torsion and Bauschinger Tests on Ti6Al4V

2012 ◽  
Vol 706-709 ◽  
pp. 774-779 ◽  
Author(s):  
Jan Peirs ◽  
Patricia Verleysen ◽  
Kim Verbeken ◽  
Frederik Coghe ◽  
Joris Degrieck
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
High Strain ◽  
Kinematic Hardening ◽  
Hopkinson Bar ◽  
Image Correlation ◽  
Material Behaviour ◽  
Split Hopkinson Bar ◽  
Strain And Strain Rate ◽  
Split Hopkinson

An accurate isotropic and kinematic hardening model and description of the strain rate dependent material behaviour is necessary for simulation of fast forming processes. Consequently, the material model parameter identification requires experiments where large strains, high strain rates and strain path changes can be attained. Usually, quasi-static tension-compression Bauschinger tests are used to assess the materials kinematic hardening. Hereby it’s important to have the same specimen geometry and boundary conditions in the forward and reverse loading step which is not easily achieved in high strain rate testing techniques. In this work, high strain rate split Hopkinson bar torsion experiments on Ti6Al4V are carried out to study the constitutive material behaviour at large plastic strain and strain rate. In torsion experiments, due to the absence of cross sectional area reduction, higher strains than in tensile tests can be obtained. In addition, a modified torsional split Hopkinson bar setup is developed to perform dynamic Bauschinger tests. A shear reversed-shear load is applied instead of the classical tension-compression load cycle. The test results are analysed to find out if the technique can be used for characterisation of the kinematic material behaviour. Digital image correlation and finite element simulations are used to improve the interpretation of the experimental results.

Mechanical Behavior of Rubber at High Strain Rates

2006 ◽  
Vol 79 (3) ◽  
pp. 429-459 ◽  
Author(s):  
C. M. Roland
Keyword(s):  
Hydrostatic Pressure ◽  
Strain Rate ◽  
Mechanical Response ◽  
High Strain ◽  
Glassy State ◽  
Hopkinson Bar ◽  
Strain Rates ◽  
Rate Data ◽  
Split Hopkinson ◽  
Low Strain Rate

Abstract Methods to obtain the mechanical response of rubber at high rates of strain are reviewed. These techniques include the extrapolation of low strain, low strain rate data, the limitations of which are discussed, extrapolations to elevated hydrostatic pressure, and direct determinations using split Hopkinson bar and drop weight testers, as well as miscellaneous methods. Some applications involving rubber at strain rates sufficient to induce a transition to the glassy state are described.

Sign in / Sign up

Export Citation Format

Share Document