Monitoring of fracture of welded joints in hazardous facilities by acoustic emission under static and cyclic loadings

Abstract

Background/Objectives: Acoustic emission under static and fatigue failure of steel welded joints 9MnSi5 in a zone of thermal influence is investigated at temperatures of 296 K and 233 K. Methods/Statistical Analysis: Flat samples with a welded seam, weakened by a notch in the Zone of Thermal Influence (ZTI), were made for static and cyclic tests of steel 9MnSi5 monoaxial stretching. Type of welded connection: end-to-end, double-sided with full pen of chamfers (C255 type). Stress risers in tension were manufactured by a sparkerrosion wire-cutting machine Sodick AG400L LN2W with high precision of positioning and repeatability of the shape of notches. All static and dynamic tests were carried out by servohydraulic machine Instron 8802. Findings: The received results show that origin and development of fatigue cracks are significantly easier at positive temperatures, than at negative. This fact testifies that origin of fatigue cracks on real objects, most likely, happens during the summer period, and their sudden development (break down) - in winter. That means that the low temperature of operation is not the defining factor for catastrophic failure. This fact should be born in mind in the analysis of AE registered by monitoring systems during the summer and winter period in case of controlling objects working in the conditions of cyclic loadings. Applications/Improvements: It is shown that at all types of tests; the range of AE-signals is shifted towards lower frequencies as the moment of failure approaches. Criteria parameters based on the signal wave form and its power spectral density are suggested with the aim of using them in automatic monitoring systems.