Fracture Failure of 304 Stainless Steel Connectors on the Isolating Switches
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CASE HISTORY—PEER-REVIEWED
Fracture Failure of 304 Stainless Steel Connectors on the Isolating Switches Xiaofeng Wu • Junbo Shi • Ning Ding • Weimin Guo • Na Xu Qishan Zang • Chi-Man Lawrence Wu
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Submitted: 16 November 2014 / in revised form: 18 January 2015 Ó ASM International 2015
Abstract The failure mechanism of the connectors assembled on the isolating switches was analyzed. Under SEM examination, the fracture surface showed obvious crack propagation traces. Beach marks with a reverse bending pattern were found on the fracture surface. Fatigue striations, which were the micro-evidence of fatigue, were observed clearly on the propagation zone. Both the metallurgical examinations and XRD analysis showed that the material of the connector only contained the austenite phase. The collected evidence suggests that that failure of the connectors was induced by fatigue. The vibration of the specimen during transport was the most probable source of the alternating stress. The stretching assembly stress of the connector could increase the fatigue stress ratios of the specimen. Defects existing in the material might destroy the continuity of the material substrate and reduce the fatigue performance of the material. Keywords Fatigue 304 Stainless steel Fracture Connector Reverse bending pattern
X. Wu J. Shi N. Ding (&) W. Guo N. Xu Q. Zang C.-M. L. Wu (&) Research Center of Failure Analysis and Engineering Safety Assessment, Shandong Academy of Sciences, Jinan, People’s Republic of China e-mail: [email protected] C.-M. L. Wu e-mail: [email protected] N. Ding C.-M. L. Wu Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR, People’s Republic of China
Introduction Connectors, which are used to join different components to into a whole, are important components in mechanical equipment. Connectors may be subjected to many kinds of loads, such as bending, torsional, and tensile loads. These types of loads may give rise to the failure of connectors. One of the most common failure mechanisms for connectors is fatigue. Fatigue cracks usually initiate from the location where stress concentration occurs due to microcracks, defects, and discontinuities in materials [1, 2]. Fatigue failure may occur on a component even at fairly low stress levels and give rise to unexpected serious damage. The action of repeated loads is one of the most important variables for components which failed due to fatigue. Sometimes the repeated loads may be unperceived. During the last several decades, a number of fatigue failures of components subjected to repeated loads were recorded, especially for connectors [3–6]. Study on the prevention of fatigue is an important topic for connectors and has drawn much attention [7–9]. However, fatigue failures of connectors are far from being eradicated completely and need to be considered. In this paper, fracture failure of a batch of 304 stainless steel connectors, which were assembled on isolating switches, was investigated using variou
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