Investigation of X70 line pipe steel fracture during single edge-notched tensile testing using acoustic emission monitoring

This paper presents an investigation of the fracture behavior of X70 pipeline steel using the acoustic emission (AE) monitoring technique. The AE monitoring technique is widely used in mechanical and materials research for detection of plastic deformation, fracture initiation and crack growth. However, quantitative dependences of the AE parameters (such as signal amplitude and frequency) on the fracture parameters of X70 pipeline steel (such as ductile and brittle fracture initiation and propagation) have not been studied in depth and are therefore not completely understood. In this paper, we report an investigation of the effect of loading conditions on the fracture behavior of X70 pipeline steel using AE monitoring and single-edge notch tensile (SENT) testing. The fracture development was observed using a high speed video camera. The AE was recorded and analyzed using the hardware and software produced by Physical Acoustics Corporation (USA). The variations in AE parameters with loading conditions were analyzed using the 'Average Hit' features and Wave Form and Power Spectrum methodologies and correlated with the load-displacement/load-time curves obtained during SENT testing. The strain rate, temperature, and features of the sample notch, that was used to simulate a crack, were shown to affect the fracture mode and the relative magnitude of mode-dependent AE signatures.