Long overlap shear testing

Work of some value for stress analysis was done in the early years. This was the so-called long overlap shear testing. It was recognized early on that increasing the overlap in lap shear specimens did not result in a proportionate increase in strength. A length of lap is quickly reached where no further load increase is possible. 

The key to the success of these designs was the acknowledgement that the adhesives shear stresses were, and should be, highly nonuniform. There are enormous differences between the way adhesives behave, under what appear to be the same external loads, in short-overlap test coupons and long-overlap structural joints, as explained in Fig. 44.16. 

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