Dulieu-Barton, Janice M.

Longana, Marco

Pierron, Fabrice

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                          Longana, M., Dulieu-Barton, J. M., & Pierron, F. (2015). Identification of thestrain rate dependence of the elastic properties of CFRP using digital imagecorrelation. Abstract from CompTest 2015, Madrid, Spain.Early version, also known as pre-printLink to publication record in Explore Bristol ResearchPDF-documentUniversity of Bristol - Explore Bristol ResearchGeneral rightsThis document is made available in accordance with publisher policies. Please cite only the publishedversion using the reference above. Full terms of use are available:http://www.bristol.ac.uk/pure/about/ebr-terms.htmlTake down policyExplore Bristol Research is a digital archive and the intention is that deposited content should not beremoved. However, if you believe that this version of the work breaches copyright law please contactopen-access@bristol.ac.uk and include the following information in your message:• Your contact details• Bibliographic details for the item, including a URL• An outline of the nature of the complaintOn receipt of your message the Open Access Team will immediately investigate your claim, make aninitial judgement of the validity of the claim and, where appropriate, withdraw the item in questionfrom public view.7th International Conference on Composites Testing and Model Identification C. González, C. López, J. LLorca (Editors) IMDEA, 2015 IDENTIFICATION OF THE STRAIN RATE DEPENDENCE OF THE ELASTIC PROPERTIES OF CFRP USING DIGITAL IMAGE CORRELATION  Marco L. Longana1, Janice M. Dulieu-Barton2 and Fabrice Pierron2  1ACCIS (Advanced Composites Centre for Innovation & Science) University of Bristol, Queen's Building, University Walk, BS8 1TR, Bristol, UK Email: m.l.longana@bristol.ac.uk, web page: http://www.bristol.ac.uk/composites/   1Faculty of Engineering and the Environment, Engineering Sciences University of Southampton, Highfield, Southampton, SO17 1BJ Email: janice@soton.ac.uk, web page: http://www.soton.ac.uk    Keywords: Strain rate, elastic properties, Digital Image Correlation (DIC)   ABSTRACT  A methodology for the full-field study of the strain rate dependent constitutive behaviour of FRP materials with the aid of Digital Image Correlation has been devised, applied and validated. In this work, a high-speed servo-hydraulic tensile test machine is used to impart an intermediate strain rate loading. A methodology that identifies the Young’s moduli, E11 and E22, and the Poisson’s ratio at strain rates up to 100 s-1 using high-speed imaging and full-field strain measurement techniques has been presented in [1]. An example of the evolution of the strain and strain rate maps, obtained from a unidirectional lay-up of glass reinforced epoxy specimen at nominal strain rate of 80 s-1, for the identification of E11 and ν12 is shown in Figure 1. It is clear from the strain rate plots that there is a region where a constant strain rate can be obtained from which the elastic properties can be derived. However, an additional specimen configuration is required to determine the shear modulus, G12.   Figure 1: Strain and strain rate maps for material characterization  There are various techniques available to identify the shear modulus (G12) at quasi-static strain rates, such as rail shear test, Iosipescu double V-notched beam test and the thin tube subject to torsion. However these specimens would prove extremely difficult to set up in a high speed servo-hydraulic test machine, as to minimise inertial effects the actuator has to accelerate to a ‘constant’ velocity prior to clamping the specimen. Therefore, to obtain G12 the off-axis tensile test on specimens manufactured from unidirectional material is used [2], as this allows the use of the same specimen geometry and experimental set-up as used in [1]. The specimens incorporate oblique end-tab to mitigate the effect of stress concentration in the proximity of the end-tabs [3].  Furthermore, the specimen geometry enables a large area to be imaged to perform DIC with sufficient images to characterise the material. Figure 2 shows the test specimen geometry and nomenclature.  Marco L. Longana, Janice M. Barton and Fabrice Pierron  Figure 2: Specimen geometry and nomenclature  The methodology used here to achieve a precise material characterisation involves initial tensile tests on specimens with 0o fibre orientation to identify E11 and ν12 and 90o fibre orientation to identify E22, as well as an off-axis test with square end-tabs to estimate G12. The preliminary results are used to define the end-tab and the optimal off-axis angle to identify G12. The benefits of oblique end-tabs, i.e. parallel displacement contours and reduction of stress concentration at the specimen ends, are shown in Figure 3.   Figure 3: Displacement and strain maps for square and oblique end-tabs, FE and experimental results  This methodology has been used to characterise a CFRP material, MTM58FRB/HS(24K)-450-38%RW, and to inform a model of the stiffness-strain rate dependency, as shown in Figure 4.   Figure 4: Normalised moduli as function of the strain rates  REFERENCES   [1] M.L. Longana, J.M. Dulieu-Barton and F. Pierron, Identification of constitutive properties of composite materials under high strain rate loading using optical strain measurement techniques, Proceedings of the 15th European Conference on Composite Materials (ECCM), 24-28 June 2012, Venice, Italy. [2] C.C. Chamis and J.H. Sinclair. Ten-deg off-axis test for shear properties in fiber composites, Experimental Mechanics, 17(9):339–346, 1977. [3] C.T. Sun and I. Chung. An oblique end-tab design for testing off-axis composite specimens, Composites, 24(8):619–623, 1993. 

Identification of the strain rate dependence of the elastic properties of CFRP using digital image correlation

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Identification of the strain rate dependence of the elastic properties of CFRP using digital image correlation

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