ORCID Profile
0000-0003-2813-4994
Current Organisations
University of Southampton
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MatchID NV
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Publisher: Springer Science and Business Media LLC
Date: 06-02-2019
Publisher: Springer Science and Business Media LLC
Date: 06-05-2019
Publisher: Springer Science and Business Media LLC
Date: 11-09-2018
Publisher: Springer Science and Business Media LLC
Date: 24-08-2018
Publisher: Springer Science and Business Media LLC
Date: 05-08-2020
DOI: 10.1007/S40870-020-00258-4
Abstract: 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.
Publisher: Elsevier BV
Date: 09-2018
Publisher: EDP Sciences
Date: 2018
DOI: 10.1051/EPJCONF/201818302041
Abstract: 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 G 12 and E 22 .
Publisher: EDP Sciences
Date: 2018
DOI: 10.1051/EPJCONF/201818302051
Abstract: The behavior and failure mechanisms of materials often change at high strain rates ( 100 1/s) when compared with their quasi-static response. These differences are critical when designing structures or components that will be subjected to impact or blast loads. The recent progress in ultra-high speed imaging and full-field measurement techniques provides a unique opportunity to improve the quality of high strain rate test data. The objective of the current work is to design and validate an experimental technique to identify the elastoplastic material properties of metals. The methodology uses an ultra-high speed camera and the grid method to obtain time-resolved full-field deformation data as impact induced stress waves propagate in a s le. The virtual fields method is then used to inversely identify the plastic properties of the specimen. The results for five aluminum 6082-T6 impacted at 50 m/s are presented.
Publisher: EDP Sciences
Date: 2018
DOI: 10.1051/EPJCONF/201818302042
Abstract: 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 d en 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.
Publisher: Wiley
Date: 06-10-2020
DOI: 10.1111/STR.12369
Publisher: EDP Sciences
Date: 2018
DOI: 10.1051/EPJCONF/201818304014
Abstract: Bone cement is widely used for the fixation of orthopaedic implants. It is a multi-component material that consists of a PMMA base with a small proportion of (usually ceramic) radiopacifier to enable the cement to be observed by X-ray. Bone cement is formed through an exothermic reaction in which a powder of pre-polymerised beads of PMMA reacts with MMA monomer. The resulting polymer microstructure consists of PMMA beads in a matrix of newly formed PMMA containing radiopacifier particles. In service, bone cement can experience deformation over a range of strain rates, from the lower end in normal gait to 100s of s -1 in the case of falls or impacts. In the current study, it is hypothesised that the response of homogeneous (clear) PMMA to high strain rates will be different to that of bone cement due to the microstructural differences. There have been very few studies on this topic in the past, mostly because of the difficulty involved in adapting the Hopkinson bar protocol to this material, particularly for dynamic tension. The objective of this paper is to present new results on the stiffness and d ing of bone cement at strain rates in the range of 100 s -1 , and to compare the data with that obtained on clear PMMA. The technique employed here to measure the mechanical properties of both commercial grade PMMA and bone cement is a new image-based DMTA method recently proposed by Seghir and Pierron (Seghir, Pierron, Exp. Mech., 2018). This allows for the measurement of the complex modulus over a range of temperatures and strain rates (100s of s -1 ). The method relies on imaging the deformation of the specimen bearing a printed grid using a Shimadzu HPV-X camera at up to 5 million frames per second. This allows for the time-resolved displacements to be measured, leading to fields of strain and acceleration, the latter being used to derive stress information to build up stress-strain curves. The methodology is described in more details in www.photodyn.org .
Publisher: Wiley
Date: 24-02-2021
DOI: 10.1111/STR.12375
Publisher: Wiley
Date: 22-02-2021
DOI: 10.1111/STR.12374
Publisher: Emerald
Date: 04-03-2019
Abstract: Micro-focus X-ray computed tomography (CT) can be used to quantitatively evaluate the packing density, pore connectivity and provide the basis for specimen derived simulations of gas permeability of sand mould. This non-destructive experiment or following simulations can be done on any section of any size sand mould just before casting to validate the required properties. This paper aims to describe the challenges of this method and use it to simulate the gas permeability of 3D printed sand moulds for a range of controlling parameters. The permeability simulations are compared against experimental results using traditional measurement techniques. It suggests that a minimum volume of only 700 × 700 × 700 µm 3 is required to obtain, a reliable and most representative than the value obtained by the traditional measurement technique, the simulated permeability of a specimen. X-ray tomography images were used to reconstruct 3D models to simulate them for gas permeability of the 3D printed sand mould specimens, and the results were compared with the experimental result of the same. The influence of printing parameters, especially the re-coater speed, on the pore connectivity of the 3D printed sand mould and related permeability has been identified. Characterisation of these sand moulds using X-ray CT and its suitability, compared to the traditional means, are also studied. While density and 3PB strength are a measure of the quality of the moulds, the pore connectivity from the tomographic images precisely relates to the permeability. The main conclusions of the present study are provided below. A minimum required s le size of 700 × 700 × 700 µm 3 is required to provide representative permeability results. This was obtained from sand specimens with an average sand grain size of 140 µm, using the tomographic volume images to define a 3D mesh to run permeability calculations. Z-direction permeability is always lower than that in the X-/Y-directions due to the lower values of X-(120/140 µm) and Y-(101.6 µm) resolutions of the furan droplets. The anisotropic permeability of the 3D printed sand mould is mainly due to, the only adjustable, X-directional resolution of the furan droplets the Y-directional resolution is a fixed distance, 102.6 µm, between the printhead nozzles and the Z-directional one is usually, 280 µm, twice the size of an average sand grain.A non-destructive and most representative permeability value can be obtained, using the computer simulation, on the reconstructed 3D X-ray tomography images obtained on a specific location of a 3D printed sand mould. This saves time and effort on printing a separate specimen for the traditional test which may not be the most representative to the printed mould. The experimental result is compared with the computer simulated results.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Fabrice Pierron.