42 T.S. Chawla and M.N. Cavalli 6.2 Specimen Preparation The specimens for mixed mode testing (Fig. 6.1) were made in accordance with ASTM D 6671/D 6671M – 06. The lower adherend (parent laminate) represented a fiber glass reinforced polyester composite and the upper adherend (repair laminate) simulated the flat part of a one-sided scarf repair. The lay-up and materials used for the upper and lower adherends are given in Table 6.1. Commercially available resins were used for parent laminate resin infusion as well as for hand layup repairs. The listed number of plies was chosen in order to have specimens with h 5 mm (Fig. 6.1). The lower adherends (parent laminates) were manufactured using vacuum assisted resin transfer/infusion molding (VARTM/VARIM) (Fig. 6.2.) and were cured at room temperature for 24 h. They were further post-cured in an oven at 60 ıC for 24 h and then at 95 ıC for 3 h to ensure that they had the same degree of cure. In order to study the effect of variation in grinding depth on the mixed-mode fracture toughness of the repairs, complete top plies in one set of four parent laminates and partial top plies in the other set of four parent laminates were ground off. The variation in top ply grinding depths is shown in Fig. 6.3. Then the simulated 2h 2L a b L L Delamination Hinge Fig. 6.1 Mixedmode specimen [1] Table 6.1 Specimen Lay-up and post curing details Lay-up Part Details 5 Unidirectional plies (0ı, glass fiber) Repaired Laminate: Curing: 1 Chopped strand mat Hand Lay-up 24 h at room temperature Polyester and Vinyl Ester repair resins Post curing: (Upper adherend) 16 h at 40 ıC Insert (Crack Initiator) Polymer film Thickness 13 m 5 Unidirectional plies (0ı, glass fiber) Parent Laminate: Curing: VARTM 24 h at room temperature Polyester infusion resin Post curing: (Lower adherend) 24 h at 60 ıC 3 h at 95 ıC Fig. 6.2 VARTM set-up (during infusion) Fig. 6.3 Repair surface top ply grinding depth variation. (a) Complete top ply ground off. (b) Partial top ply ground off
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