4.4.6 Impact Stress

4.4.6 Impact Stress

Impact is dynamic stress at high speed. Impact stress may be applied as compression, tension, shear, cleavage, peel or any combination of these. The toughness of the substrate and the adhesive will be key in resisting impact stress. A strong material under static loading may fail under impact if it is brittle.

The impact resistance of a material or an assembly depends on its ability to move or deform to accommodate the impact internally. In a bonded assembly, the toughness of the substrate and adhesive and how the geometry distributes the impact throughout will determine the assembly’s toughness and resistance to impact.

There are many tests for impact resistance, including drop tests (compression), side-impact (shear) and wedge impact (cleavage). Testing may be done on homogenous cured samples or assemblies, either standard test specimens or end-use assemblies. Results are typically reported in units of work (force x displacement), or joules, required to break the sample bond. The graph in Figure 100 illustrates other useful information such as joint behaviour and force to initiate failure.

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