Toughened structural adhesives, failure

The simple lap joint may not perform well in load bearing structures when, for various reasons, toughened adhesives may not be used. This is because even modest distortion can cause brittle failure in a conventional structural adhesive and the joint will collapse catastrophically at apparently low load levels. 

Plate 1 The internal structure of a typical toughened adhesive is revealed by the electron microscope. The rounded zones are the rubbery domains which give adhesives of this type their characteristic resistance to brittle failure. Each domain is approximately one micron in diameter. 

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