Abstract
In this work, the effects of natural particles on the micro failure mechanisms and static strength of an epoxy are studied using scanning electron microscope (SEM) technique. To this end, bulk specimens and adhesively bonded single lap joints (SLJs) containing different amount of micro cork particles were fabricated and tested. To investigate the toughening mechanisms, the fracture surfaces of the specimens were analyzed using SEM and a magnifying glass. It was shown that the deviation of the crack path and formation of micro-cracks generate multi fracture surfaces which is one of the main sources of energy absorption and resulted in higher fracture energy of the enhanced adhesives. Acting as a crack stopper and consequently stabilizing the crack propagation, prevents developing large and unstable cracks which is another source of energy consumption. However, the micro analysis showed that higher contents of cork lead to agglomeration of the particles which acts as a source of stress concentration, with a higher possibility of delamination between the matrix and the micro corks. Accordingly, there is an optimum amount of cork where the best adhesive fracture toughness is reached. The results showed that the optimum value of micro particles depends on the loading conditions.
Highlights
Applications of adhesives and specially epoxy resins, as an alternative to traditional fasteners, have considerably increased in different industries [1, 2]
The current research deals with the assessment of the micro failure mechanisms of an epoxy enhanced with micro cork particles
According to Fig. (6), cleavage in the fracture surface of the bulk specimens with 1 vol% cork is higher than the adhesive with no-cork or 5 vol% micro particles
Summary
Applications of adhesives and specially epoxy resins, as an alternative to traditional fasteners, have considerably increased in different industries [1, 2]. Epoxies show good mechanical properties, the structure of these thermoset polymers causes insufficient energy absorption with a low resistance to the propagation of cracks [1, 3, 4] For this reason, improving their toughness has been extensively studied in the last decades [5,6,7]. Barbosa et al [8] studied the effect of size and volume fraction of cork particles on the impact toughness of adhesive bonding In their analysis, the cork particles ranging from 38 to 250 μm were considered. Barbosa et al [14] studied the effect of natural cork particles on the stress-strain behavior of an epoxy based adhesive Their results showed that the cork particles cause higher ductility and improve the failure strain of the adhesive. The fracture surfaces of the joints and bulk specimens were analyzed using SEM technique and a magnifying glass
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