The effect of filler addition on the fatigue strength of adhesive joints was in vestigated. Both epoxy resin (Epikote 828) and polyamide (Versamid 125 or 115) were adopted as the adhesive components; the filler added in the adhesive was chrysotile- asbestos. The experimental results showed that the fatigue strength is improved by add ing the filler and depends on adhesive layer thickness as well as adhesive composition. Furthermore, the variation trends in strain range of the adhesive layer during the fatigue process were examined for the specimens with/without filler. For the specimen with the filler the strain range rapidly increases just before the fracture, and a fatigue hardening phenomenon is revealed in the fatigue life over 106 cycles.
SynopsisImpact fatigue behaviors of the steel/CTBN-modified adhesivehteel butt joint were investigated. The adhesive butt joint specimens used in the present work were bonded with epoxy-polyamide and CTBN-modified epoxy-polyamide adhesives. Fatigue tests were also conducted under nonimpact stress conditions to compare with the results from the impact fatigue test. The experiments showed that for the joint specimen from the adhesive modified with the CTBN the fatigue strength becomes higher under both of the stress conditions. In particular, the fatigue strength was improved remarkably under impact stress condition, that is, the distinct stress cycles d6pendence of impact strength was decreased by modifying the adhesive with CTBN. Furthermore, the effect of adhesive thickness on the fatigue strength was also discussed for the adhesive joint modified with CTBN. Under impact stress conditions, the relation between the fatigue strength and the adhesive layer thickness is different from that under the nonimpact one.
This paper describes a method of estimating the fatigue life of adhesively bonded lap joints on the basis of the stress analysis in adhesive layer with finite element method. First, cyclic tensile fatigue tests were conducted for adhesively bonded lap joints with different lap length and adhesive layer thickness. The results were evaluated from the viewpoint of the maximum values of both tensile and shear stress obtained numerically, instead of the apparent stress. Then these standardized fatigue strength were compared with those of adhesively bonded butt joints of a thin wall tube under cyclic tensile and fully reversed torsional load conditions. The results indicate that fatigue strength of lap joints evaluated from the maximum tensile stress of the adhesive layer agrees well with the fatigue strength of adhesively bonded butt joints of thin wall tube under cyclic tensile load condition. It is confirmed that fatigue strength of lap joints can be estimated adequately based on the fatigue strength of the butt joint of thin wall tube and the numerical results for the stress state of adhesive layer.
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