13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- whereas composite, c90, has fibres laid in x direction i.e. perpendicular to the direction of the applied load. Volume fractions of fibre and resin in each composite layer are 0.522 and 0.478 respectively. The coefficients of thermal expansion of the laminate in longitudinal (y) direction, ll α , and in transverse (x) direction, tl α , are found to be 6 19.4 10− × C-1 and 6 19.77 10− × C-1 respectively. Expected dimensions of the laminate were 200 mm (h), 50 mm (w) and 2.346 mm (d). However, minor deviations could not be avoided during fabrication. Important material data are available in Table 1. Property Aluminum 2014T6 alloy, al (Isotropic) E-Glass fibre, f (Amorphous) Epoxy resin, r (Isotropic) Modulus of elasticity, E (MPa) Shear modulus, µ (MPa) 72000.0 27060.0 71000.0 29710.0 3500.0 1250.0 Poisson’s ratio ( )υ , % elongation 0.33, 8.0 0.22, 4.8 0.33, 4.0 Yield strength, Y (MPa) Ultimate tensile strength (MPa) 372.0 415.0 --- 3450.0 --- 60.0 Coeff. of thermal expansion ( )α , C-1 6 23 10− × 6 5.0 10− × 6 57.5 10− × Plane strain fracture toughness ( ) IC K , MPa m 14.0-20.0 4.0-5.0 0.5-0.7 3. Theoretical aspects Stress that develops in un-identical material layers of un-cracked Glare subjected to load differs from the applied stress due to load redistribution caused by elasticity mismatch between the layers. Also, the presence of residual stress, generated in materials during laminate curing due to their varying stiffness and coefficients of thermal expansions, further changes the stress state. The stressstrain constitutive equations and stiffness matrices of the materials in plane stress case (x-y plane) are given as follows:- Table 1. Material properties . 2nd Prepreg 64748 64748 1st Prepreg. View from A c90 Resin, r Fibre, f Aluminum, al 0.573 0.4 c0 Dimensions are in mm Aluminum Aluminum Aluminum 0.0455 0.091 0.091 0.0455 Figure 1. Glare laminate Thickness details:- al t = 0.4 mm rt = 0.0455 mm f t = 0.1 mm 0ct = 0.191 mm 90 ct =0.191 mm h w d z y x al t A
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