PSI - Issue 14

Shashidhar Naik H. G. et al. / Procedia Structural Integrity 14 (2019) 900–906 Shashidhar Naik H. G. et.al./ Structural Integrity Procedia 00 (2018) 000–000

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1. Introduction A hybrid laminate structure consisting of GFRP and metal plies is being developed for various applications in aerospace industry. This hybrid composite is observed to improve the impact resistance, as well as the load bearing capabilities. The metal layer placed on the surfaces also prevent the structure from hazardous environmental impacts. The combination stands a chance to employ the advantageous properties of both the materials, whereas the weaknesses are eliminated. Like the FRP composites, damages are inevitable in these hybrid composites. A detailed damage study and delamination growth in specific is carried out. Degradation of stiffness of the structure depends on the geometric characteristics of delamination and its behaviour, nature of loading and material characteristics. Fracture in structural components was initially studied and presented by Rybicki and Kanninen, considering the crack tip forces and relative displacement of the cracks, to calculate SERR [Kanninen, (1973)]. This was further extended to 3D cases and numerical equations were developed [Shivkumar et. al., (1998)]. An overview of the history, approach and applications of VCCT was provided by Krueger [Krueger, (2004)]. Fatigue crack growth in GLARE, between the aluminium and glass fiber adhesive layers, was studied to determine the relationship between delamination growth rate and the calculated energy release rate [Alderliesten et. al., (2006)]. A new approach to numerically investigate the lap shear fracture of a hybrid laminate made of CFRP and aluminium was developed, and was further validated by corresponding experiments [Naghipour et. al., (2012)]. The concept of VCCT was later applied to study delamination growth in Carbon Fiber Composite Laminate, when subjected to spectrum fatigue loads [Raju, (2014)]. A modified cohesive zone model (CZM) was developed in GLARE Fiber-Metal Laminate (FML) specimens containing splice and doubler characteristics under high-cycle fatigue load, to simulate damage initiation and evolution, and thus compute cohesive stiffness degradation under mixed-mode loading [Ahmed et. al., (2016)]. The present study deals with the detailed study of the behaviour of a hybrid composite of GFRP and aluminium under the presence of circular delamination, subject to compressive loads in terms of initial displacement. The values of Critical Energy Release rates in the three modes of fracture; G IC, G IIC and G IIIC , are determined. It is assumed that these values are material specific, and do not dependent on the lay-up sequence and dimensional properties of the specimen. Total Energy Release rate, G T , corresponding to the Critical Energy Release rate, G C , is considered the driving factor for the growth of delamination. 2. Formulation of the problem A hybrid composition of GFRP and aluminium (GLARE 2B-3/ 2– 0.4) was considered for analysis. A square plate specimen 200 mm x 200 mm in dimension was modelled in ABAQUS standard platform with total thickness of 1.7 mm. The specimen comprised of alternate layers of unidirectional S2-glass (FM94 glass/epoxy) of thickness 0.125 mm and aluminium alloy (2024-T3) of thickness 0.4 mm. A schematic representation of the specimen is shown in Figure 1. A 3D finite element model was simulated, and a central circular delamination was introduced between the interfaces of GFRP – Aluminium. The material properties were obtained from existing literature [Alderliesten et. al., (2006)]. The geometric properties of the plate are as given in Table 1.

Table 1. Geometrical Properties of the plate

Dimensional Properties

Dimensions of plate: 200 mm x 200 mm Thickness of plate: 1.7 mm Layer Thickness: Aluminium - 0.4 mm GFRP plies - 0.125 mm