Shear joints typically perform much better in applications requiring a water-tight or hermetic seal. The design of shear joints virtually eliminate the possibility of weld discontinuity or voids that could lead to leaks at the seal. The corner at the interface on the inner piece (see figure) effectively acts as an energy director to initially focus the weld energy. The amount of allowable interface changes with the diameter or width of the joint. Consult the table for guidance on the allowable interference for your design. The outer piece must be fixtured to prevent outward deflection during welding, which could lead to hoop stresses and stress cracking over time. Shear joints require more energy to weld than do energy director joints. Be sure not to exceed the limits of the ultrasonic welder. Often the speed with which the parts are pressed together during welding must be reduced to allow adequate time for melting to occur at the joint interface.
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