Thermographic Evaluation of SS 304 Material During Monotonic Loading

Abstract

Infrared thermographic technique was employed for evaluating the temperature response in a Stainless steel grade 304 material subjected to different loading conditions such as monotonic tensile and compressive loading. In-situ temperature measurements were made from surface of the material by an infrared thermographic camera (JADE LWIR, Cedip Infrared Systems) while the material is being loaded. Cylindrical low cycle fatigue (LCF) samples were used in this study for monotonic tensile loading. Similarly, samples of aspect ratio 1.5 were used for analyzing monotonic compressive loading. As a material is subjected to tensile elastic loading, it undergoes cooling and when subjected to compressive loading, it undergoes heating. This phenomenon is called thermo-elastic effect. Based on our experimental observations, in case of monotonic tensile loading, the temperature of the material decreases till the material yields due to thermo-elastic effect and increases as the material plastically deforms, due to conversion of mechanical work done on the specimen into heat. But for the case of compressive loading, the temperature increases when the material is stressed in both cases of elastic as well as the elasto-plastic segment. This paper discusses the slope of the temperature response with respect to strain induced in the material and the effect of loading rate on the temperature measurements for the monotonic tensile and compressive loading. Comparison between the thermo-elastic slopes revealed that the thermo-elastic slope for the tensile loading is steeper than the slope from the compressive loading due to surface area contraction during the tensile loading and vice-versa. Experiments conducted at various loading rates ranging from 0.75 to 10 mm/min reveals that as the loading rate increases, temperature of the material increases.