Abstract
This paper presents the results of an experimental investigation of fatigue response of stainless steel SS 304 L(N) and SS 316 L(N) using cyclic ball indentation test method. A Tungsten Carbide (WC) spherical ball of 1.57 mm diameter is used for applying compression-compression fatigue cycling on the test specimen having a nominal thickness of 5 mm; the displacement response is monitored as a function of every cycle of loading. The study focused on cases where the stainless steel specimens were welded by two different welding processes – Activated flux TIG welding and conventional multi-pass TIG welding. Fatigue response was monitored at locations of weld zone, heat affected zone (HAZ) and base metal to identify the effect of microstructure variation on fatigue response. It is observed that there is a steady increase in depth of penetration of the spherical indenter due to fatigue cycling; however, after a number of cycles, there is a sudden increase in depth of penetration which indicates the failure of the material beneath the indenter. The specimens after cyclic ball indentation were examined using a scanning electron microscope and one could observe the presence of secondary cracking in the penetrated region of the specimen.
Highlights
Life prediction of safety-critical components and structures is an important task where the accuracy of predictions, reliability and confidence level are critical parameters
Structural stainless steel SS 304 L(N) and SS 316 L(N) in base metal form, as well as in welded form are considered for this study
The indentation depth is less for Multi-Pass TiG (MP-TIG) weld region of SS 304 L(N), which has a finer grain microstructure
Summary
Life prediction of safety-critical components and structures is an important task where the accuracy of predictions, reliability and confidence level are critical parameters. As the volume of material available for testing from working components is limited, recourse is taken to evaluate with reasonable level of confidence the mechanical behaviour of materials using small specimen test methods. The following mechanical properties are widely estimated using small specimen test methods: tensile properties [1,2,3,4], impact [5,6], fracture toughness properties [7,8] and in a few cases fatigue properties are evaluated through sub-size hourglass specimens [9]. Experimental techniques available to evaluate the fatigue properties through in-situ test methods are limited
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