Abstract
The article presents the issues of the mechanical properties of epoxy adhesives and the adhesive joints strength of steel sheets which were made using the epoxy adhesives. The aim of the paper is to study the mechanical properties of epoxy adhesive of different epoxy resin/curing agent ratios (within and above the recommended stoichiometric ratio) and their effect on mechanical properties of adhesive joints of steel sheets. In experimental tests three types of epoxy adhesives, containing a low molecular weight epoxy resin based on bisphenol A and polyamide curing agent, were used. A single-lap adhesive joint type of stainless-steel sheets was also applied. Two types of strength test were used: the compressive strength tests (DIN EN 196-1) for epoxy adhesive samples and the shear strength tests (DIN EN 1465) for adhesive joints. Both the analysis of the strength results of the samples of epoxy adhesive and adhesive joints as well as the failure analysis was carried out. On the basis of the results of strength tests it can be stated that the greatest deformation occurred for the samples of epoxy adhesive containing the modified epoxy resin (epoxy number—0.40) and the polyamide curing agent, and the smallest for the samples of epoxy adhesive containing the basic epoxy resin (epoxy number—0.49–0.52) and the polyamide curing agent. The epoxy adhesives with a smaller amount of curing agent were characterized by higher strength. This applies to all analyzed epoxy resins. The same dependences were obtained for the strength of adhesive joints of steel sheets made of the analyzed epoxy adhesive.
Highlights
Adhesive joints are classified as non-detachable bonded joints
Regarding the second criterion (C2) and the third criterion (C3) in the case of E53/PAC/ 100:80 and E57/PAC/100:80 epoxy adhesives, which contained the highest amount of curing agent content in the recommended stoichiometric ratios, a higher value of compressive strength was obtained in comparison to these epoxy adhesives, but containing a polyamide curing agent above the recommended stoichiometric ratio (i.e., 100 g curing agent per 100 g epoxy resin)
Referring to the results presented in [33], related to the determination of elongation at break in tensile strength tests for an adhesive composition containing Epidian 5 epoxy resin and polyamide curing agent (PAC trade name), it was noticed that among the adhesive compositions Epidian 5/PAC, the highest elongation was obtained for Epidian 5/PAC/100:80—the lowest amount of curing agent and the lowest for the epoxy adhesive containing the largest amount of curing agent, 100 g per 100 g epoxy resin
Summary
Adhesive joints are classified as non-detachable bonded joints. Adhesives are used to joint elements, but often the use of adhesive is to seal various elements, e.g., threaded joints. Obtaining adhesive joints of adequate strength in given operating conditions requires a series of tests It depends, inter alia, on the properties of the adhesive used to make the joints [1,2,3,4]. Inter alia, on the properties of the adhesive used to make the joints [1,2,3,4] Due to their favorable properties and high processing possibilities, epoxy resins are increasingly being used in various industries and many applications [5,6,7,8,9,10,11]. A large variety of resins and curing agents, as well as the possibility of modifying the properties of epoxy adhesives allow for the selection of the most appropriate composition for the joined material and the operating conditions [9,12,16,17,18]. The use of the appropriate curing agent allows for joining together moist materials or joining at low temperatures [18]
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