PSI - Issue 28

Anurag Singh et al. / Procedia Structural Integrity 28 (2020) 2206–2217 Anurag Singh/ Structural Integrity Procedia 00 (2019) 000 – 000

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retention and less lightning damages. In this article, AVIC composite centre China produced two distinctive composite materials and INEGI, Portugal performed their mechanical characterisation. One of the specimens is carbon fibre reinforced epoxy-based composite, and another is electrically conductive carbon fibre reinforced epoxy composite produced by the Functionalised Interlayer Technology (FIT) (Guo et al. 2014; Guo and Yi 2013; Multifunct. Polym. Compos. 2015; X. S. Yi 2015). Tensile test, flexural test and mode I fracture toughness tests characterises these distinct composite specimens. Control specimens marked as reference specimens (ref specimen) and electrically modified specimens as the electrical conductive specimens (ec specimen). The effect of electrical modification of these composites on the mechanical properties is studied and compared. 2. Materials and Methods 2.1. Materials AVIC composite centre, China developed and manufactured two distinct carbon fibre reinforced epoxy composites by using the functionalised interlayer Technology (FIT). As per the agreement in the Nanopol, an FCT project; INEGI, Portugal, studied the mechanical characterisation of composites mentioned above. Two unique composite specimens, classified as the reference specimen (ref specimen) and the electrical conductive specimens (ec specimen), the FIT modified the latter. As per the FIT, the interweaving of a conductive nylon veil between two adjacent carbon fibre layers is what distinguishes the ec specimens from the ref specimens. Structural composite is composed of T800-grade carbon fibre from Toray, with epoxy resin as a matrix material. Unidirectional (UD) laminated composite with 0° layup configuration is the underlying architecture of these specimens; their dimensions are as per the different test standards mentioned in the next sections. For more details about the manufacturing process, refer to this European patent (X. Yi et al. 2015). 2.2. Digital image correlation (DIC) DIC is a non-contact optical technique which combines image recording and tracing methods for accurate 2D measurements of changes in images. In DIC correlation coefficient is determined from pixel intensity array subsets on multiple corresponding images and extracting the deformation mapping function that relates the images. In this manner, the displacements of individual regions in an image are tracked over the sequence of images, resulting in strain field calculation. An area of interest (AOI) is manually specified and divided into an evenly spaced virtual grid. The displacements are then computed at each point of the virtual grids to obtain full-field deformation. Two images are compared corresponding to the flat surface of a test specimen. The first image corresponds to a reference state, and the rest corresponds to a strained state (under mechanical loading). The surface of the specimen must display a random pattern, a thin spray of black and white paints fulfils this purpose. 2.3. Tensile test Tensile tests on ref and ec specimens use test standard ASTM D3039 (ASTM 2014); dimensions of the specimens tested were 250x25x2.5 mm. According to the test protocol, seven specimens were tested with polymer matrix composite (PMC) tabs to prevent the specimens from slippage and damage. Specimens were mounted in the grips of mechanical testing machine and monotonically loaded in tension while simultaneously recording the load and displacement values. Ultimate tensile strength of the CFRP's is the maximum load experienced by these composites before failure. The tensile test uses DIC as a contactless method to get the strain field directly from the samples; black and white spray paint generates the random speckle pattern on to the samples to get the DIC measurements. Figure 1a) shows the tensile test setup with the DIC system. Figure 1b) showed the tensile test specimen after achieving the ultimate tensile strength.