Failure in printed gaskets

When the bead is compressed it deforms as indicated in Fig. 14.8. The rubber is essentially incompressible (Poisson s Ratio 0.5) and it cannot move laterally because one surface is bonded. 

In its deformed shape the points A are under high tensile stress, and thus liable to crack growth, should there be a localized stress concentration, such a small adventitious crack or an imperfection, such as a large additive or dirt particle. Under severe conditions, a crack can initiate spontaneously, once the critical failure stress is reached. 

The presence of such failure cracks is observed in the released gasket at the position indicated in Fig. 14.8(a), at A.  

The new bead formulation, numbered 4068, emerged from increased demands in service, and a critical assessment of the failure mode shown by gaskets. 

Release Plate O all Bead Call Bead Block Gap Cycles 

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