Epoxy adhesives test rate effects

Table 14.3 contains data that compares the results of plasma treatment and sodium etching for four fluo-ropolymers. Peel strengths of untreated and treated samples were measured by bonding them into T-peel specimen using the flexibilized epoxy adhesive Scotch-Weld 3553 (available from 3M Corp.). The laminates were cured for several hours at 70°C and peel tested at 12.5 cm/min pull rate. Polytetrafluoroethylene does not accept plasma treatment as well as PEA and FEP, as indicated by its relatively low peel strength. Sodium etching is the only effective method of modifying the surface of PTFE. 

A comparison of experimentally determined failure times for different stress levels and those predicted by the above equation for epoxy-aluminum lap shear joints aged at 60°C and 95 percent RH is presented in Table 15.3. These results indicate that the reaction rate method is satisfactory for predicting the effects of temperature and stress on the lifetime of adhesive bonds, provided that failure is cohesive within the adhesive. This, of course, should be validated by prototype testing. 

Goglio et al. (2008) have tested a bi-component epoxy under tension and compression, to assess the effect of the strain rate on the strength of this adhesive. Also, in this work both the Hopkinson bar and a hydraulic test machine have been employed, depending on the desired strain rate (from 10 to 3 x 10 s ). 

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