Beryllium Copper Strip
Performance of Beryllium Copper
(3) Thermal Stability
Beryllium Copper is widely used in electrical components such as connectors, switches and relays. Spring parts in these components need to keep the contact force reliable over a long period of time. In addition, they are often exposed to the effect of heat. The heat may be due to environmental conditions, or self heating by electric current. Loss of contact force may occur due to stress relaxation.
Fig. 4 represents stress relaxation of beryllium copper and phosphor bronze. Stress relaxation is measured on test specimens which are fixed as shown in Fig. 4 and are exposed to the heat under designated conditions of temperatures and periods of time. The permanent set of each test specimen is measured and converted into loss of force value.
Beryllium copper exhibits far less stress relaxation and much better performance in heat resistance than phosphor bronze. Stress relaxation is a kind of creep phenomena. Since it is not practical to monitor the material behavior over a long period of time, we usually estimate the behavior based on the test results for a shorter period of time. Because of the high accuracy the Larson-Miller method is commonly used.
Equation (1) shows the Larson-Miller's experimental formula.
Fig. 5 shows a relationship between remaining stress of Beryllium Copper and Larson-Miller's parameter "P". From this curve, "P" corresponding to given remaining stress is obtained, and we can estimate remaining stress under the combination of temperature and exposure time necessary for the design.
Fig. 4 Stress Relaxation of beryllium copper
in comparison with Phosphor Bronze
Fig. 5 Relationship between Remaining Stress and
Larson-Miller Parameter "P"