Thermal Cycling and Environmental Effect on Tensile Impact Behavior of Adhesive Single Lap Joints for Fiber Metal Lamina
This experimental study investigates the effects of sea water and thermal cycling conditions on strength of adhesive lap joints made for fiber metal laminate (FML) and 430 stainless steel adherends subjected to standard tensile impact loading condition. T
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Thermal Cycling and Environmental Effect on Tensile Impact Behavior of Adhesive Single Lap Joints for Fiber Metal Laminate N. Mehrsefat, S.M.R. Khalili, and M. Sharafi Abstract This experimental study investigates the effects of sea water and thermal cycling conditions on strength of adhesive lap joints made for fiber metal laminate (FML) and 430 stainless steel adherends subjected to standard tensile impact loading condition. The FMLs (three and five layers) were fabricated using 430 stainless steel sheets and fiberglass prepreg layers. The joints are kept in the sea water taken for 30 days in the laboratory. Some of the specimens are then thermally cycled in an oven (5 and 10 cycles, 40/100 C, dwell time 20 min) and also the others are kept in liquid N2 (5 and 10 cycles, 40/ 100 C, dwell time 10 min), and afterwards tested. Experimental results shown that the absorbed energy by adhesive lap joint specimens that are subjected to sea water is reduced. The adhesive joint strength is improved at high thermal cycling, but decreased at cryogenic temperatures with respect to sea water without thermal cycling. Keywords FML • Adhesive joint • Sea water • Impact tensile test • Thermal cycling • Cryogenic temperature
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Introduction
There are two main types of joints: mechanical joints and adhesively bonded joints. Adhesive joining is among the most important joining techniques used for bonding composite structures. Joint design technology has become a main factor in structural integrity to design of composite sub-structures in various engineering disciplines such as aerospace structures, marine engineering, automotive structural parts and also civil structures for strengthening. However, the mechanical performance of adhesively bonded joints is strongly affected by the environment of the joint because the epoxy adhesive properties of adhesively bonded joints can be weakened by temperature or humidity [1, 2]. When moisture is absorbed into the epoxy adhesive layer, it can reduce the glass transition temperature of the adhesive and can generate stress in the adhesive layer due to volume expansion of the epoxy [3]. Kootsookos and Mouritz have investigated the effect of seawater immersion on the durability of glass- and carbon-fibre reinforced polymer composites experimentally [4]. da Silva and Adams used a mixed adhesive joint instead of a joint with a high-temperature adhesive alone which provided a joint that was strong from low to high temperatures [5]. In many real life cases, for instance in applications related to transportation systems, bonded joints may undergo impact loads that, conceptually, can be of two different types. The first type belong to the occasional heavy impacts that cause irreversible damage (i.e. automotive crash), the main issue in this case is the absorption of the kinetic energy obtained through plastic deformation. Of the second type are the frequent low-energy impacts, that the structural members and the joints must withstand without serious damage; in this case the issue is high elastic
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