Magnetic Thermocouple Lab Report

Generally, most of the material experiencing cyclic loading tend to form cracks and over time, increased growth is noticed. The strength of the material decreases when a crack is formed and its intended function can no longer be expected as per design. Furthermore, the in-crease of the crack size affects the residual strength by gradually compromising its effectiveness. Eventually, failure occurs when the remaining strength becomes too low for it to be used to get the desired and intended func-tion [1]. Therefore, it is important to predict the lifespan of the material and the rate of decline as it is being employed for its intended design.
Literature review [2-4] suggests innovative techniques for assessment of various aspects of fatigue
A magnetic thermocouple was employed to record the surface temperature evolution of the spec-imen around the crack growth during the FCG test. The magnetic thermocouple was used to mitigate the delam-ination of the thermocouples from the specimen surface during the test. The second thermocouple was placed near the specimen to record the ambient temperature to ensure that any temperature changes that occur on the specimen surface is not affected by ambient tempera-ture. A high-speed, high-resolution infrared (IR) thermal imager is used to calibrate the thermocouples at the be-ginning of the test, and to capture the thermal image of the crack growth as shown in Fig.2. The temperature was measured at the crack tip. Due to the material’s response to the unexpected movement, dislocations and defects go along with the surface intrusion and extrusion, the surface temperature increases rapidly at the beginning of the test. A typical entropy accumulation was plotted as a function, noting the number of cycles for the low car-bon steel specimen during the entire FCG test under CAL and VAL conditions. Examination of Fig. 3 reveals that the temperature evolution under-went three distinct phases. During the first stage, surface temperature increases rapidly at the beginning of the FCG test. Then, during the second stage, the temperature levels off and becomes steady until it begins to rise ab-ruptly, shortly before failure occurs in the third stage. A variation of temperature evolution under VAL condition, two-step of low-high (L-H) and high-low (H-L) sequence loading during the entire FCG test is shown in Fig.