Speaker
Description
Prior information of physical and mechanical properties of materials is very crucial in design and development of a mechanical system. In the normal course, sufficient data is available at around room temperature. However, data of these properties are not easily available at cryogenic temperatures. At the same time, the available data cannot be extrapolated down to cryogenic temperature since the properties suddenly change at low temperatures like ductile to brittle transition for carbon steels, etc. Wide varieties of materials are used for low temperature applications and obtaining information of the low temperature properties becomes a case to case study. Knowledge of fatigue strength is very essential for materials which are subjected to continuous cyclical stresses e.g. springs. Fatigue is a progressive, localised and permanent structural change that occurs in materials subjected to fluctuating stresses and strains that may result in cracks or fracture after sufficient number of stress cycles. Cyclic stresses induce micro cracks within the material which tend to grow with time. These cracks initiate and propagate in regions where strain is very severe. Since most of the engineering materials contain internal defects, fatigue cracks mainly initiate and grow from these structural defects. Inadequate fatigue strengths can lead to premature failure of mechanical components resulting in entire collapse of the system. In view of this critical background, a rotating beam fatigue testing machine for cryogenic temperature zone has been designed and developed. This machine can be used to obtain the data of fatigue properties of any specified material from room temperature down to cryogenic temperature. The cryogenic temperature environment is produced by circulating controlled quantity of liquid nitrogen (LN2) around the test specimen. In this experimental work, fatigue properties of stainless steel (SS304) are determined both at room and cryogenic temperature. The test results are compared and analysed.
Keywords: Liquid nitrogen, Fatigue strength, Stress, Strain, S-N curve, Cryotreatment
| Submitters Country | INDIA |
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