In Situ Fracture Toughness Testing of Core Materials in Sandwich Panels

摘要

The in situ fracture toughness of six core materials was measured using a new test method.The materials tested were seven composite sandwich panels fabricated using vacuum-assisted resin transfer molding (VARTM).The core materials were PVC or balsa of different densities.All of the core materials were tested with E-glass-vinylester face-sheets,while one was tested with carbon-epoxy face-sheets.The fracture tests were conducted using a modified Cracked Sandwich Beam (CSB) test configuration.The cracks in the foam-core panels grew in the sub-interface region and paralleled the interface.The distance from the interface to the location of the sub-interface crack was related to the mismatch in the material properties between the face-sheet and core.The fracture toughness of the PVC core materials ranged from 367 to 1350 J/m~2.The results for the sandwich specimens with PVC cores were compared to the Mode I fracture toughness of the neat PVC foam-core materials and values obtained from in situ testing of foam-cored sandwich panels using the Tilted Sandwich Debond (TSD) specimen with no tilt angle.The in situ fracture toughness of the core materials in a sandwich panel was found to be significantly higher than the Mode I fracture toughness of core material even though the cracks grew completely within the core.The crack growth in the balsa-cored panels was significantly different than that of the cracks in the foam panels.The cracks in the balsa panels grew in one of the three distinct fashions: as an interface crack when bonding between face-sheet and core was weak,or when the bonding was strong,as a through-the-thickness crack,or a sub-interface crack.The fracture toughness of the sandwich specimens with balsa-core materials ranged from 693 to 1008 J/m~2.The results from the balsa-cored panels were compared to results obtained from similar balsa-cored sandwich materials using the Single Cantilever Beam (SCB) specimen.