Stress analysis and design philosophies

Closed form solutions. Structural adhesive joints are generally designed to be loaded in shear so that treatments of joint analyses are confined essentially to the transfer of load by shear, with some consideration of the transverse normal stresses induced by eccentricities in the load path. In the simplest case the adhesive and the adherends are assumed to behave elastically. The most refined analyses attempt to model the situation when the adhesive yields so that the adhesive and, eventually, the adherends behave plastically as the imposed load is raised. Closed-form analyses are difficult to apply to other than simple geometrical configurations, while a major difficulty with the elasto-plastic model is how to characterise the adhesive. 

The empirical approach to the design of simple overlap joints was to construct a correlation diagram (Fig. 4.3) between failure load 

P = applied loeul/unit width of joint h = adherend thickness 2a = overlap length 

Ga = shear modulus of adhesive E = Young s modulus of adherend t =thickness of adhesive 

This expression correctly shows that the overlap length should depend upon the modulus of the adhesive. 

---