214 Simulation of Adhesive Layer in a Honeycomb Core Sandwich for Progressive Failure Analysis Rahul V R 1 , K.C. Goplakrishnan 2 and R Ramesh Kumar 3 1 Assistant Professor, Department of Mechanical Engineering, Trinity College of Engineering Thiruvananthapuram, Kerala, India 2 Associate Professor, Department of Mechanical Engineering, College of Engineering Trivanadrum, Kerala, India 3 Professor &Nodal Research Officer, Department of Mechanical Engineering, Sree Chitra Thirunal College of Engineering Thiruvananthapuram, Kerala, India International Journal of Research in Mechanical Engineering Volume 4, Issue 3, May-June, 2016, pp. 214-219 ISSN Online: 2347-5188 Print: 2347-8772, DOA: 27052016 © IASTER 2016, www.iaster.com ABSTRACT Flat-wise tensile (FWT) strength is one of the important design parameters to qualify honeycomb core sandwich structures. In the present study, 3-D finite element model consists of honeycomb core of 0.05mm foil thickness, 0.2 mm thickness of adhesive fillets that covers 30% of the skin area and cohesive zone element at bond interface of unit cell sandwich plate is considered to obtain flat-wise tensile strength. Required input data of mode I and Mode II delamination fracture toughness values and interfacial bond strength are used to predict initiation and progressive failure at bond interface and comparison of FWT strength by test and analysis shows a good agreement. In the case of CZM approach, prediction based on progressive failure is higher by 1.25 times when compared load at initiation of debond. Present study is useful in the design of adhesively bonded sandwich structures. Present study is a useful tool to carry out structural analysis of sandwich products to ensure the health of the bonded structure. Keywords: Bond Strength, Cohesive Zone Model (CZM), Flat - Wise Tension (FWT) Test, Honeycomb Core, Lap Shear Strength. 1. INTRODUCTION Adhesively bonded stringer stiffened shell type and composite or metallic skin honeycomb core sandwich structures are widely used in aerospace applications. When the nature of loads is predominant in compression, the conventional bolted joint can be eliminated to a large extent to save mass. In the case of honeycomb core sandwich structure, adhesive film is introduced between skin and core to form an integral piece following a curing process. Usually, flat-wise tensile coupons of standard configuration are made along with product at the time of realisation to simulate the process undergone. Based on the FWT strength value tested at frequent interval of time structural margin is over a period of usage can be assessed. Most of the earlier analytical studies were based on the assumption of a perfect bond between the skin and honeycomb core and no adhesive layer was considered [1-5]. Recently, cohesive zone model analysis of sandwich panel reported in literature, honeycomb core was considered as an equivalent brick element and no effect of filleting was incorporated (Fig. 1) [3]. Even realised sandwich products after