Fatigue Crack Growth Behavior in Dissimilar Metal Weldment of Stainless Steel and Carbon Steel
Constant amplitude fatigue crack growth (FCG) tests were performed on dissimilar metal welded plates of Type 316L Stainless Steel (SS) and IS 2062 Grade A Carbon steel (CS). The plates were welded by TIG welding using SS E309 as electrode. FCG tests were carried on the Side Edge Notch Tension (SENT) specimens of 5 mm thickness, with crack initiator (notch) at base metal region (BM), weld metal region (WM) and heat affected zones (HAZ). The tests were performed at a test frequency of 10 Hz and at load ratios (R) of 0.1 & 0.6. FCG rate was found to increase with stress ratio for weld metals and base metals, where as in case of HAZ, FCG rates were almost equal at high ΔK. FCG rate of HAZ of stainless steel was found to be lowest at low and high ΔK. At intermediate ΔK, WM showed the lowest FCG rate. CS showed higher crack growth rate at all ΔK. However, the scatter band of data was found to be narrow. Fracture toughness (Kc) was found to vary in different locations of weldments. Kc was found lowest for the weldment and highest for HAZ of stainless steel. A novel method of characterizing the FCG behavior using an Infrared thermography (IRT) camera was attempted. By monitoring the temperature rise at the fast moving crack tip region, the amount of plastic deformation was estimated. Keywords—Dissimilar metal weld, Fatigue Crack Growth,
The temperature wave method of determining fracture toughness values due to crack propagation
A method is presented of determining fracture toughness by measurement of the amount of heat emitted at the tip of a propagating crack. Two thermojunctions placed adjacent to the crack were used to monitor the temperature wave produced at fracture. An electromagnetic fluxmeter was used to integrate the thermojunction output with respect to time and was calibrated to give a direct reading in terms of strain energy release rate G. The temperature wave method is independent of initial crack length and fracture surface area and can be readily used for specimens having complex sections. Values obtained by this method compare favourably with toughness values determined by a linear elastic fracture mechanics analysis. Results of static and dynamic three-point bending tests on specimens at different temperatures within the range −40 to 60° C are reported.
A new technique for viewing deformation zones at crack tips
A new technique has been developed to examine and view the deformation zone that occurs at a crack tip during loading.The technique, referred to as the “image-distortion technique”, is based on the optical distortion that results on a highly polished surface ahead of a crack when it is strained. The “image distortion” is a direct result of the thickness change occurring at the crack tip. While the technique was developed using monotonic loading, it is believed that it also will be applicable to cyclic-loading crack-tip studies. Additional studies are underway that will yield strain fields at the crack tip from the observed images of the deformation zones.