Comparative analysis of failure of Al/GFRP laminates after tensile strength test
Monika Ostapiuk, Barbara Surowska
Quarterly No. 4, 2015 pages 259-265
DOI:
keywords: fibre metal laminates, tensile strength, fractography, failure
abstract Fibre-metal laminates are modern composite materials that are replacing certain metal elements in aircraft structures. Such hybrid materials have synergic properties determined by their component properties and configuration. This article presents studies of GLARE laminates consisting of aluminium and glass-epoxy composite sheets manufactured using the autoclave method. 2024T3 aluminium alloy sheets were subjected to chromic acid anodising (CAA) and sulphuric acid anodising (SAA). Three different lay-up configurations of the composite layers were used in the structure of 2/1 laminates: [0°], [0/90°] and [±45°]. Tensile strength studies were conducted using a strength testing machine (MTS 322) in accordance with the ASTM standard for composite materials. Microstructural and fractographic observations were conducted using an optical microscope and a scanning electron microscope (Zeiss Ultra Plus, NovaNanoSEM 450). The tensile strength test did not result in cracking of the metal plies; it was the composite that underwent degradation. After the test, the samples were found to have undergone deformation and delamination as a result of the tension; the laminates with an SAA layer were more greatly affected. The plastic range properties are determined by the fibre configuration. The metal/composite adhesion force was higher than the cohesive force in the composite for all the configurations. The degradation mechanism of the laminate structure during uniaxial tensile strength tests does not depend on the type of anodised layer. The configuration of the fibrous composite layers affects the propagation of cracks in the composite area. Transverse cracking of the fibres, cracking of the anodised layer and decohesion of the matrix with tearing-out of fibres were observed in all the cases. The surface morphology of the fracture caused by the decohesion of the composite in an FML is of the same nature as the fracture in the composite material.