# Experimental Analysis on the Impact of Current on the Strength and Lifespan of a Ni-Ti Element
## 1 Introduction  
Starting from the variants studied within the Laboratory of Invention and Technological Transfer of the University of Suceava [1; 2; 3; 4], in which the elastic elements of materials with shape memory were tested in different ways, an application was developed that allows the life of the materials to be monitored and tested, by subjecting them to a significant number of tests (heating--cooling), controlling them with an electric current, and self-heating the nitinol element above the transition temperature, which generates internal forces due to changes in the crystalline structure of the alloy. In this paper, the tested element is in the form of a superelastic nitinol spring, often used in dentistry, with a length of 20 mm and a wire diameter of 0.7 mm.  
Applications based on thermal memory can be free return (medicine, engineering--autonomous heliotrope) [5; 6; 7], with retained return (hydro-pneumatic couplings, electrical connectors, fasteners and space applications) or mechanical work generators [8; 9; 10; 11]. Mechanical work generating applications are mainly used in the construction of actuators (actuators), sensors and heat engines. Depending on how the energy that is transformed into mechanical work is supplied, the actuators can be thermal or electric [12].  
The most well-known examples of the use of thermal actuators with shape memory are: fire protection by detecting a predetermined temperature (by varying resistivity), temperature control in refrigeration systems, thermal protection of water filters, steam control in heating systems, etc. Shape memory electric actuators only have the function of performing mechanical work. In applications, they successfully replace conventional actuators, such as electromagnetic solenoids, electric, pneumatic, or hydraulic servomotorsand motors that are superior in compactness, quieter operation, and simplicity. In addition to robotics, where the most successful applications of electric actuators with shape memory (micromanipulators, submarine robotic crabs) were made, they were also introduced in other fields: the automotive industry, the protection of electrical circuits from overheating, and proportional control [13].  
Electric actuators that use shape memory alloys are real alternatives to conventional actuators [14; 15]. The advantage of these is that they create a good reason to reduce the size, weight and complexity of robotic systems. Additionally, shape memory electric actuators are particularly compact and simple, and the weight-to-force ratio is remarkable. A noteworthy advantage is the silence they show during operation.  
In addition to all these advantages in many applications, there are some disadvantages, including the low efficiency, with the specification that an electric actuator with shape memory is actually a heat engine where the material used converts heat energy into mechanical work by way of the Joule effect. The operating cycle is quite slow and directly dependent on the applied electric current and how it is self-heated to perform useful mechanical work. However, the main parameter that affects the operating cycle is the ambient temperature at which the actuator operates [16].