A study on integrity assessment of the resistance spot weld by Infrared Thermography

AbstractIn the automotive industry, the Resistance Spot Welding(RSW) has been applied for many years In order toreduce the vehicle's weight and production costs. Typically, a car body contains about more than 4300 spot welds joining sheets of different thicknesses for making just one car and this trend is expected to be continued. However, There are not manyMethods to inspect the resistance spot weld. Although measurement of Tensile shear strength and nugget diameter is widely used, another method which is more efficient is required for time and cost savings. The scope of the present study was to find out the most effective approach to non-destructive evaluation of resistance spot welding. Three different techniques such as Photo infrared thermography, Ultrasound-infrared thermography and Lock-in methods were used to acquire information for evaluation of weld soundness. Through experiment,we were able to obtain infrared images and then compared the nugget sizewith using the naked eye. Eventually, we concludedThe mean size of the nugget observed by the naked eye showed the difference of about 20% in the mean size of a nugget actually; The mean size of the nugget observed by infrared thermography showed the difference of about 8% in the mean size of a nugget actually

Acoustic emission characteristics of stress corrosion cracks in a type 304 stainless steel tube

Acoustic emission (AE) is one of the promising methods for detecting the formation of stress corrosion cracks (SCCs) in laboratory tests. This method has the advantage of online inspection. Some studies have been conducted to investigate the characteristics of AE parameters during SCC propagation. However, it is difficult to classify the distinct features of SCC behavior. Because the previous studies were performed on slow strain rate test or compact tension specimens, it is difficult to make certain correlations between AE signals and actual SCC behavior in real tube-type specimens. In this study, the specimen was a AISI 304 stainless steel tube widely applied in the nuclear industry, and an accelerated test was conducted at high temperature and pressure with a corrosive environmental condition. The study result indicated that intense AE signals were mainly detected in the elastic deformation region, and a good correlation was observed between AE activity and crack growth. By contrast, the behavior of accumulated counts was divided into four regions. According to the waveform analysis, a specific waveform pattern was observed during SCC development. It is suggested that AE can be used to detect and monitor SCC initiation and propagation in actual tubes

Toward the multiscale nature of stress corrosion cracking

This article reviews the multiscale nature of stress corrosion cracking (SCC) observed by high-resolution characterizations in austenite stainless steels and Ni-base superalloys in light water reactors (including boiling water reactors, pressurized water reactors, and supercritical water reactors) with related opinions. A new statistical summary and comparison of observed degradation phenomena at different length scales is included. The intrinsic causes of this multiscale nature of SCC are discussed based on existing evidence and related opinions, ranging from materials theory to practical processing technologies. Questions of interest are then discussed to improve bottom-up understanding of the intrinsic causes. Last, a multiscale modeling and simulation methodology is proposed as a promising interdisciplinary solution to understand the intrinsic causes of the multiscale nature of SCC in light water reactors, based on a review of related supporting application evidence