PSI - Issue 14

Arun Kumar Singh et al. / Procedia Structural Integrity 14 (2019) 720–728 Arun Kumar Singh et al./ Structural Integrity Procedia 00 (2018) 000–000

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1. Introduction In the present high end technological applications, polymeric composites have been playing a very significant role due to their excellent specific stiffness/strength and ease of manufacturing aspects. Further the hybridization of composite structures is finding one of the efficient methods to improve the desired properties of composite. Apart from these twin advantages, there is also a possibility to obtain unique property which is not a distinct possibility with single polymeric fibres. Hybrid composites can be divided into many types, such as interply hybrid, intraply hybrid, hybrid of cloths, hybrid of short cut fibre etc. (Hancox (1981)).The performance of the hybrid composites depends upon the properties of composite materials, type of fibre and matrix, orientation of fibre in matrix and also strongly on the processing parameters of moulding of composite laminate (Wang (2004)). In recent time, UHMWPE based composites are very extensively used in the structural applications susceptible to high velocity impact loading. The composite materials subjected to impact loading may suffer from damage in terms of cracks and delamination. Infact, failure in the form of delamination is one of the major modes of failure in such type of composites (Bolotin(2001)). In any fiber reinforced composite, fibers are the main load bearing members and the matrix acts as a load transfer media and provide protection to the fibers (Mallick (2010)). The overall mechanical characteristics of any composite is the combined mechanical properties of fiber, matrix, adhesion between the fiber and matrix, the fiber volume fraction etc. (Shubhra et al. (2011) and Miao et al.(2013)).UHMWPE fibers/fabrics in comparison with other high strength fiber/fabric like carbon, glass, aramid etc. has been found to have high impact resistance, toughness, and tensile strength with the additional properties of light weightiness (Sui et al. (2009) and Marissen (2011)). But the adhesion of UHMWPE fibers to the matrix has been found little weaker due to the non-polar nature of UHMWPE with low surface energy (Oosterom et al. (2006)). Damage in the form of delamination due to impact loading is one of the main failure modes of such type of composite structures (Kim et al. (2003)). The delamination phenomenon in composite structures is typically studied by fracture mechanics. Fracture toughness is measured as a material property and is equivalent to the critical strain energy release rate at the crack tip. The critical energy release rate occurs immediately before crack growth. Fracture can be separated into three modes: mode I; opening mode, mode II; shearing mode and mode III; scissoring mode. The total strain energy release rate is the summation of all three modes. Plane strain fracture toughness (K Ic ) is one of the important parameter for characterizing composite materials and normally known as the resistance to the crack extension in mode-I tensile loading. The quantitative measurement of resistance to crack propagation at the onset (2% or less) is evaluated by K Ic . When the plastic zone size at the end of the crack tip is negligible as compared to the specimen size, then the materials exhibits linear elasticity prior to failure. In such conditions, K Ic is an appropriate fracture resistance/toughness parameter (Xianet al. 2012). (Pei(2008)) found that with increase in the number of layers, the fracture toughness of the composite showed increasing trends. (Pinto et al. (2016)) found 28% more fracture toughness of woven fabrics as compared to the unidirectional fabric. (Ravandi et al. (2016)) compared the K IC values for unidirectional glass fibre composite with unidirectional flax fibre and reported higher value of K IC for unidirectional glass fibre composite. However, the author reported that three times higher value of K IC for woven flax fibre than the unidirectional flax fibre. (Bahramian et al. (2015)) investigated the fracture behaviour of UHMWPE composite and evaluated the fracture toughness of composite fabricated with different type of surface treatment to enhance the K IC values. (Steven et al. (2016) investigated the fracture toughness of woven fabric made of E glass and found the dependency of periodic weave structure of woven fabric composites in fracture behaviour. A study on effect of fabrication process variable of compression moulded UHMWPE composite has been carried out by (Porras et al. (2012)). It has been observed from literatures that unidirectional as well as woven fabric composites have been well characterized and have been widely studied with respect to fracture properties. However, a gap has been observed in respect of fracture behaviour of hybrid of woven and unidirectional composite. In the present paper, the first set of work describe an investigation on the optimization of the compression moulding of p-aramid based UHMWPE hybrid composites based on Box-Behnken design of experiments and surface response methodology. The second set of work describes the interlaminar fracture toughness and crack propagation behaviour in hybrid composites. The outcomes of the presentwork will serve for understanding the fracture behaviour of hybrid composites.