PSI - Issue 14

M.K. Singh et al. / Procedia Structural Integrity 14 (2019) 475–481 M. K. Singh, R. Kitey / Structural Integrity Procedia 00 (2018) 000 – 000

476

monotonic increment in flexural modulus with increase in volume fraction for both spherical and milled fiber composite whereas for same volume fraction, the milled fiber composite showed consistently higher flexural modulus when compared with particle filled case. Also the milled-fiber composites exhibited consistently higher K IC values when compared to the spherical particle cases the K IC increases more rapidly with V f for the milled-fiber case.

Nomenclature B

Beam geometry: thickness

E f K I

Flexural modulus Stress intensity factor

K IC

Mode-I fracture toughness Beam geometry: Span Volume fraction of filler Beam geometry: Width Mid span load

L P

V f W

a δ

Crack length

Mid span deflection Flexural strain Flexural stress Flexural strength

ε f σ f

σ fu

ξ

a/W rat io

Rahul and Kitey (2016) used diglycidyl ether of bisphenol-A (DGEBA) as epoxy resin and methyl tetra hydrophthalic Anhydride (MTHPA) as curing agent (hardener) with various R/H ratio and reported higher fracture toughness values in hardener-rich and resin rich epoxy systems when compared with stoichiometric (100:80 R/H). They suggested the higher fracture toughness due to crazing and (possibly) plastic deformation for both anhydride and resin rich epoxy systems. Fu et. al. (2000) investigated tensile properties of polypropylene (PP) reinforced with short glass fibers (SGF) of diameter 13.8 µm and short carbon fibers (SCF) of diameter 7.5 µm with three different fiber volume fraction. They reported that addition of glass and carbon fibers effectively enhanced the ultimate strength of composite. The effect of mean fiber length on composite s’ strength was found to be significantly large whereas composite s’ modulus was more dependent on fiber volume fraction. Consequently, modulus of both types of composites increased with increase in filler volume fraction. Furthermore, decrease in mean fiber length with increase in fiber volume fraction was also reported which was attributed to higher fiber-fiber interaction for both SGF and SCF case. Nam et. al. (2014) investigated fracture toughness of polyurethane adhesive reinforced with chopped glass fiber of three different lengths (i.e.; 1mm, 3mm, and 7mm) and various volume fractions using double cantilever beam (DCB) test. They used stainless steel and aluminium as DCB materials for conducting tests at - 150 0 C. They observed that an improvement in fracture toughness values for 3 mm long fiber reinforcements over 1 mm fiber. Whereas specimen reinforced with 7 mm long fiber (V f 15%) exhibit lower fracture toughness than composite reinforced with 3 mm long fiber (V f 20%). This was attributed due to locally severely intervened fibers causing increase in the unwetted area. Kitey, and Tippur (2005) investigated the effect of size of spherical fillers on filler-matrix adhesion in dynamic fracture behaviour. They reported that weakly bonded particles have better dynamic fracture properties than strongly bonded particles whereas elastic property does not change with filler size. From the above literature review, it is observed that microstructure of the epoxy system plays a crucial role in improving the fracture toughness of the epoxy system. Furthermore, addition of fillers also improve the fracture toughness of the composites as compared to the neat matrix. Hence, tailoring the shape, size and volume fraction of the fillers greatly enhance the fracture toughness of the composites. The prime objective of this work is to study the effect of the filler size on the quasi-static fracture and flexural behaviour of the milled fiber reinforced epoxy composites.