PSI - Issue 14

Kishora Shetty et al. / Procedia Structural Integrity 14 (2019) 849–854 Kishora Shetty et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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mainly chemical changes of the matrixmaterials and de-bonding at fibre/matrix interface. The reduced ILSS strength of CFRP due to hygrothermal conditioning shows thatCompositeundergoes changes in materials properties under hot-wet conditions. The material degradation due to moisture absorption in composite includes mainly chemical changes of the matrix materials and de bonding at fibre/matrixinterface. In caseof hygrothermal effects, infused water intomatrixor interface regionof compositewould act as plasticizer, spacing the polymer chains apart. This phenomenonmakes composites softer and thus reduction in mechanical properties since the matrix becomes pliable due to the presence of the plasticizer. These changes affect the overall CFRP performance parameters such as damage growth, strength and stiffness. Moisture absorptionby this CFRP for different hot-wet condition follow Fick’s lawof diffusion. Specimens were observed to gain moisture quickly in the beginning and then tend towards saturation, a typical Fickian behavior observed in fiber/epoxy composite materials. Initial weight gain was more and as the duration of conditioning increases moisture absorption rate comes down and reaches saturation. The basic diffusionmechanisms pertaining topolymers as well as their fibrous composites, exposed to hot and humid conditions followFickian diffusion model for these materials.Moisture absorption in CFRPs is going to cause mechanical property degradations, thermal degradations mainly with reference to the glass transition temperature, which in turn affects the composites’ structural integrity, a crucial issue related to the aerospaceapplications. Moisture may also accumulate in matrix microcrack and minor delaminations between the layers of the composite laminate - Shylaja Srihari et al. (2002). Moisture absorption into composite is a diffusion driven phenomenon and the moisture concentration gradient between the environment and the composite material, causing continuous absorption until saturation limits are reached -Victor Giurgiutiu (2016) and Smith, A.L et al. (1959). Interface between reinforcing fibres andmatrixplays an important role in compositeproperties.Water enters a composite material principally by themechanismof diffusion. Other possible mechanisms are: capillarity along the fibre surface and fibre-matrix interface and also transport throughmicrocracks - Santhosh Mahale et al. (2004). Water entrance into a composite lead to plasticization of the polymer matrix and degradation of the fibre/matrix interface - Ying Wang et al. (2007). All these factors lead to drop in mechanical strength including ILSS. Microscopic observation of failed samples also investigated by Scanning Electron Microscope (SEM) analyses to study the fracture/failure behaviour. Figures 1 to 3 shows SEMMicrographs of specimens tested for ILSS from different aging conditions.

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