PSI - Issue 14

Mohd Tauheed et al. / Procedia Structural Integrity 14 (2019) 354–361 Mohd Tauheed/ Structural Integrity Procedia 00 (2018) 000–000

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1.1. Material Specification and characterization The material considered throughout this study is a unidirectional carbon fiber prepreg from Hindoostan Mills Ltd. was used for the making of composite laminates. Lamination involved packing the layup in a vacuum bag and heat curing using the cycle given by the manufacturer. Considering that the loading is only in one direction, the layup used for the laminate was [0] 10, i.e. 10 layers in 0 ° orientation. The prepreg sheets were orientated and then laid on a flat aluminium plate coated with release agent. Then, a peel fabric was laid and the layup was then sealed in a vacuum bag and vacuumed up to 0.8 bar. Vacuum assisted in the removal of trapped air and applied uniform pressure over the laminate during the curing process. The whole setup was then placed in an oven and a cuing cycle of 45 minutes at 120 ℃ was followed. The cured laminate was then released from aluminium plate. An average laminate thickness of 1.7 mm was achieved. The uniaxial tensile test were performed using Instron universal testing machine (capacity 100 kN) according to the ASTM D3039 standard in the longitudinal direction of the laminate to determine tensile modulus. E 11 and ν 12 were determined by applying DIC technique to the strain field. The fiber volume fraction (V f ) and E 22 were determined using the mechanics of material approach given in Jones (1997). Industrial grade two-part structural toughened epoxy adhesive Araldite 2015 from Huntsman were procured. The rest of the mechanical properties of unidirectional CFRP laminate and the properties of toughened epoxy adhesive were taken from the literature as shown in Table 1. Table 1. Mechanical properties of unidirectional CFRP laminate and properties of Araldite 2015. Values in bold are for composite and adhesive were taken from Campilho et al. (2013) Modulus of elasticity Poisson’s ratio Modulus of rigidity Araldite 2015 E 11 = 102 GPa ν 12 = 0.167 G 12 = 4.3 GPa E = 1.85 � 0.21 GPa E 22 = 4.9 GPa ν 13 = 0.167 G 13 = 4.3 GPa ν = 0.33 E 33 = 4.9 GPa ν 23 = 0.38 G 23 = 3.2 GPa G = 0.56 � 0.21 GPa 2. Double cantilever beam (DCB) test A DCB specimen was used to determine mode I fracture parameters. Composite adhesive joints were made of carbon fiber/epoxy composite adherend and toughened epoxy adhesive (Araldite 2015). Prior to bonding the composite laminates were pre-treated by sanding with 220 grit sandpaper in the direction lateral to the length of the specimen, which was followed by acetone cleaning. Adhesive thickness, � = 0.3 mm was maintained by providing shims or razor blade in between the adherends. ASTM D5528 standard test method was followed in DCB specimen preparation as shown in Fig.1 and determining the critical energy release rate in mode I (G IC ). Here, ‘ a ’ is the initial crack length measured from loading point to the crack tip.

Fig. 1. The geometry of DCB specimen Fig. 2 shows the experimental setup used for testing for DCB specimens under displacement control at 0.5 mm/min using a 10 kN universal testing machine (Shimadzu, AG-Xplus Table-top type). The �� value was calculated by modified beam theory using Eq. 1. To obtain the cohesive parameters the displacement field about the crack tip was captured using a 5MP monochromatic CCD camera (Point Grey GS3-U3-51S5M-C 2/3” Grasshopper USB 3.0) and was analysed using the DIC technique.