Measurement of local mechanical properties in pipeline steel welds USING INSTRUMENTED INDENTATION AND DIGITAL IMAGE CORRELATION

摘要

The mechanical properties of welded structures, such as hardness, tensile strength, and toughness are usually measured for qualification acceptance. However, multi-pass welding of pipeline steel creates heterogeneity in the weld region and heat-affected zone (HAZ), which leads to variation in the mechanical properties. Therefore, it is useful to establish new methods to identify the mechanical properties for different weld regions. Indentation experiments have typically been the main method for measuring hardness and elastic properties of each region (1; 2; 3), however strength values and hardness are not always correlated. The focus of this work is to establish methods to test tensile strength heterogeneity through the weld metal (WM) and HAZ of welded HSLA pipeline steels. Recently, The Welding Institute (TWI) in the UK has suggested a project proposal which aims to validate and standardize an indentation method as a new tool to characterize the local mechanical properties of weld zones (4). Testing using an instrumented indentation technique with a flat tip indenter has been proposed by Leroux (5; 6) to measure the yield strength for a wide range of engineering materials. However, the new indentation based approach has not been widely accepted, or validated in peer-reviewed literature. The validation of the indentation technique to measure local mechanical properties would reduce cost and time for assessment of welded structures, especially for microscopic HAZ. Meanwhile, digital image correlation (DIC) has been used increasingly to measure the local strain distribution in weld joints during loading (7; 8).