Microstructure Effect on the Lcr Elastic Wave for Welding Residual Stress Measurement

Abstract

The ultrasonic residual stresses measurement is based on the acoustoelastic effect that refers to the change in velocity of the elastic waves when propagating in a stressed media. The experimental method using the longitudinal critically refracted (Lcr) waves requires an acoustoelastic calibration and an accuracy measurement of the time-of-flight on both stressed and unstressed media. The accuracy of this method is strongly related to that of the calibration parameters, namely the time-offlight at free stress condition (t 0 ) and the acoustoelastic coefficient (K). These parameters should be obtained on a free stress sample that has an identical microstructure to that of the stressed media. Our study concerns the ultrasonic evaluation of the welding residual stresses. This assembly process induces three distinct microstructures in the weld seam: the melted zone (MZ), heat affected zone (HAZ) and the parent metal (PM). Previously, the residual stresses evaluation in the steel welded plates, by the use of the Lcr wave method, was only possible in the MZ and in the PM zones. While in the HAZ, the residual stresses were incorrectly evaluated due to its small width impeding the extraction of the calibration sample. In this paper, we propose an original approach to solve this problem, which consists of reproducing the microstructure of this zone using a specific heat treatment. For the experimental part, P355 steel welded plates were used and the three zones were probed. The results compared with those obtained by the hole-drilling reference method show a proven potential of the ultrasonic method using the Lcr waves. The Lcr wave residual stresses measurements were made with sufficient accuracy, such as the variability of repeated measures was estimated on the order of ± 36 MPa.

Using finite element and ultrasonic method to evaluate welding longitudinal residual stress through the thickness in austenitic stainless steel plates

“…It means that, L CR wave can penetrate in the depth of stainless steel and measure the residual stress of the bulk. The potential of the L CR waves to measure the bulk stresses, is also confirmed by the majority of previous studies [1,11,17,18,[21][22][23][24].…”

“…The acoustoelastic constant of HAZ is less than the PM while the MZ constant is the maximum. Similar results were previously reported in the acoustoelastic constant measurement of P335 steel [17]. The stress-free samples are the same as the tensile test specimens which are stress relieved by heat treatment.…”

Sets of Piezoelectric Probeheads for Stress Evaluation with Subsurface Waves

“…Paper [26] discusses the influence of sample bending on TOF measured with a TRR set of probes. Paper [8] presents the experiments with a TRR set for longitudinal subsurface waves having a time resolution of 0.2 ns. However, despite the compensating feature of TRR sets, use of such a high time resolution required the sample to be precisely machined before the measurements.…”

“…For example, [4] describes such measurements in steel wires, [5] in cast steel, [6] in forged steel and [7] presents results of measurements in wood. Also, the dependence of stress induced velocity changes on material structure was investigated [8].…”

Calculation Techniques of two-dimensional residual stress field for mechanical engineering application

“…At present, the research mainly focus on the method of Rayleigh wave [1,2], ultrasonic microscopic [3], laser ultrasonic [4] and critically refracted longitudinal wave [5] and so on, which are used to measure the distribution of residual stress for welding structures and plate structures based on the acoustoelasticity [6]. Moreover, by the means of finite element analysis, the calculation [7] and characterization technique [8] of residual stress are studied theoretically.…”