Low-Cycle Fatigue Behavior of Copper Zinc Aluminum Shape Memory Alloys

Abstract

Fatigue and vibration failures continue to plague civil engineering structures. Transmission lines and supporting towers are exposed to wind and develop sustained motions. These sustained motions cause costly damage to conductors and other mechanical and structural subsystems. Wind induced vibrations of tower members have caused the fatigue failure of connecting members [1]. Many structural components in engineered structures are subjected to static and dynamic loading. Static loads, in the form of dead loads, are relatively harmless to a structure as they are anticipated and can be taken into consideration in the design. Dynamic loads, in the form of wind induced vibrations or in the form of earthquakes, are the more critical type of loads experienced by structures. The variability of naturally occurring dynamic loads is critical because their severity is unpredictable. In the construction industry, steel is the material of choice in building structures such as transmission towers. These structures have stood and continue to stand and serve their function rather well. However, over time, with continued exposure to dynamic loading (particularly wind), fatigue sets in and a member of the structure fails. Failure of the single member eventually leads to the failure of the entire structure. Fatigue failures of structures are expensive and dangerous. In terms of service life, steel subjected to cyclic loading fails in fatigue after a certain number of cycles. Shape Memory Alloys (SMA) have been reported to have a very high damping capacity and favorable fatigue properties. Recent studies have examined the possibility of using SMA for seismic energy dissipation. In civil engineering applications passive damping devices are more commonly found when compared to active devices. Employing SMA in structures could possibly reduce fatigue and vibration related problems in structures thereby increasing the service life of these structures. In order to use Copper Zinc Aluminum (CuZnAl) SMA in structural applications, a thorough study of its fatigue properties is required. In this study the low-cycle fatigue (LCF) behavior of CuZnAl in the austenitic phase at room temperature and CuZnAl in the martensitic phase at room temperature are examined.