Abstract
Ultrasonic evaluation for residual stress measurement has been an effective method owing to its easy implementation, low cost and intrinsically being nondestructive. The velocity variations of acoustic waves in materials can be related to the stress state in the deformed medium by the acoustoelastic effects. In this study, a laser/EMAT ultrasonic method is proposed to evaluate the surface/subsurface longitudinal residual stress distribution generated by gas metal arc welding (GMAW). The velocity variation ΔV/V of Rayleigh wave, which is a surface wave, will be experimentally measured. Q-Switched Nd:YAG laser is used to generate a broadband ultrasonic wave. An electromagnetic acoustic transducer (EMAT) is attached to the welding plate for Rayleigh wave pick up. As the ultrasound receiver, the EMAT is used to measure time of flight (ToF) of the Rayleigh waves traveling along a specific path parallel to the direction of the welding seam. ToF measurements are obtained by changing Rayleigh wave path to welding zone center distance from 0 to 45 mm. A 3D thermomechanical-coupled finite element model is then developed to validate the capability of the proposed technique for welding-induced residual stress evaluation. The distributions of the normalized velocity variations from ToF experiments are compared with the distribution of the normalized longitudinal residual stresses from finite element analysis (FEA). It has been shown that there is a good correlation between these two distributions. The proposed technique provides a potential nondestructive avenue for surface/subsurface residual stress evaluation for welding parts.
Highlights
Residual stress generated from various manufacturing processes would influence the mechanical reliability, fatigue life, and chemical corrosion resistance of engineering structures [1,2,3]
For a typical welding process, the sharp temperature change would directly result in the nonuniform material volume change due to the large temperature gradient in the welding zone
To the best knowledge of the authors, the utilization of the laser/electromagnetic acoustic transducer (EMAT) for weldinginduced surface/subsurface residual stress evaluation based on the Rayleigh wave, time of flight (ToF) measurement has never been done before
Summary
Residual stress generated from various manufacturing processes would influence the mechanical reliability, fatigue life, and chemical corrosion resistance of engineering structures [1,2,3]. There have been reported studies where the Rayleigh waves were used for surface residual stress evaluation with traditional ultrasonic-based residual stress measurement method [20,21]. A laser/EMAT ultrasonic technique (LEU) without direct contact with the measurement structure is introduced. To the best knowledge of the authors, the utilization of the laser/EMAT for weldinginduced surface/subsurface residual stress evaluation based on the Rayleigh wave, time of flight (ToF) measurement has never been done before. Compared to the technique by Wang and Feng [24], using traditional ultrasonic detection system, EMAT is used in this study, which does not require any contact with the inspected sample This method does not require a complicated wave signal processing, which could significantly improve the measurement reliability. Results show that the numerical predictions using FEA correlates well with experimental results
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