Initial Stress Level

Photo ©1998 AMP INC.

Although time and temperature are usually determined by the expected application of a connector, with a suitable choice of contact alloy the loss of contact force over design life can be curtailed. By management of three secondary variables, the loss of contact force over time can be further reduced. The secondary variables are: initial stress level, orientation, and temper.

The rate of stress relaxation is influenced by the initial stress (S i). If the beam is initially deflected such that it is stressed at its yield strength, then rapid loss of contact force may occur. If the stress is only 20% of the yield strength, practically no loss occurs. Initial contact forces are such that applied stresses are commonly 30-90% of the metal's yield strength, and within that range the loss of contact force is almost invariant with S i. That's why stress relaxation testing is usually done with initial stress levels of 75% of the metal's yield strength.