Longitudinal Critically Refracted Research Articles

Evaluate welding residual of 6082-T6 aluminum alloy welded plate by using ultrasonic method

The residual stress beneath the surface is crucial to the safety of the structures. Neutron Diffraction and Hole-drilling are the two methods being used to measure the inner residual stress. Longitudinal Critically Refracted (LCR) wave transmission that is propagated parallel to surface also can be used for measuring residual stress, but measurements are within an effective depth and need to be further studied. In this paper, the parameters of K are separately tested in WZ, HAZ and BM zone. The welding process of 6082-T6 aluminum alloy welded joints is simulated in SYSWELD, the finite element model has been verified by the X-ray diffraction method. The residual stress value calculated by SYSWELD and the values obtained from the ultrasonic measurement show a good agreement. It is demonstrated that the residual stress of 6082-T6 aluminum alloy welded plate can be evaluated by using the ultrasonic method.

Non-linear property analysis of deformed metallic components using a longitudinal critically refracted wave

In order to apply the ultrasonic non-linear coefficient for non-destructive detection in actual engineering applications, the non-linear property of deformed metallic components is studied using a longitudinal critically refracted (LCR) wave. Firstly, dog-bone components are loaded in two different modes, which ensures that components with different stress states and the corresponding macroscopic deformation of components are measured. Then, online and offline non-linear ultrasonic experiments are conducted on pre-stress components and the relative non-linear coefficient is calculated. Experimental results indicate that the relative non-linear coefficient and the deformation state monotonically increase with stress levels and they have similar variation trends in both online and offline measurements. Furthermore, Pearson correlation coefficients between the relative non-linear coefficient and the macroscopic deformation are 0.988 and 0.9876 for two types of experiment, which indicates that they have a strong correlation relationship. The power-exponent function is applied to establish this dependence relationship. The index coefficients are 1.276 and 0.7305, respectively, and the difference may be due to the microstructure disparity caused by the different loading modes. Therefore, the interrelationship between the relative non-linear coefficient and the macroscopic deformation of metallic components can be applied to predict the variation of the relative non-linear coefficient from the macroscopic point, which is very convenient for damage detection in actual engineering applications.

Influence factors analysis and accuracy improvement for stress measurement using ultrasonic longitudinal critically refracted (LCR) wave

Generally, material stress measurement using ultrasonic longitudinal critically refracted (LCR) wave is inevitably influenced by ambient temperature and coupling condition, which limits its industrial application. In this article, the sensitivity of stress measurement accuracy to temperature variation and coupling condition is discussed analytically and numerically. Based on this, the ultrasonic signal-detecting mode is improved by one-transmitter-two-receiver signal-detecting configuration. Meanwhile, a novel coupling condition is also created by directly filling with couplant between the ultrasonic probe and the measured surface. The testing results showed that the temperature sensitivity could be reduced to 0.81 ns/°C compared with −16.82 ns/°C of the traditional one-transmitter-one-receiver signal detecting configuration, and less distortion and attenuation of the detecting LCR wave signals could also be obtained. Further, a pre-stretched aluminum alloy with uniaxial stress was employed to verify the feasibility of the developed method and probe. The stress measurement accuracy could achieve 20 MPa compared with the simulation results.

Ameliorated longitudinal critically refracted—Attenuation velocity method for welding residual stress measurement

This work aims at quantitative analysing the effect of different microstructures on the velocity at stress-free and stress coefficient (K) of longitudinal critical refraction (LCR) wave in measuring welding residual stress process, ameliorating the traditional LCR wave method for improving its’ effectiveness and accuracy. The longitudinal critically refracted wave attenuation velocity (LCR-AV) method was proposed in the evaluation of residual stresses in A7N01 welded joints. The same initial status base materials samples are used to produce different levels of grain size and precipitation by heat treatment technology, obtained the velocity at stress-free and attenuation of LCR wave. As expected, the voltage amplitude changes linearly with velocity and stress coefficient, and the precipitation effect can be ignored. The LCR-AV method based on the liner relationship between velocity, attenuation and grain size are efficient to decrease the errors resulting from the different microstructure (base metals, heat-affected zones, and welded zones). Differ with the traditional LCR waves method, the LCR-AV method also measures the voltage amplitude, and the measured results of LCR-AV method compared with those obtained by the hole-drilling reference method shows more sufficient measurement reliability and precision. It shows that LCR-AV method is a valuable quantitative technology to estimate the residual stress of welded joints.

Evaluation of Sub-Surface Residual Stress by Ultrasonic Method and Finite-Element Analysis of Welding Process in a Monel Pressure Vessel

Abstract Welding of nickel-based alloys is increasingly used in the industry to manufacture various important structures in the marine industries, chemical processing, etc. This study investigates evaluation of sub-surface residual stresses, which are produced by the welding process in a pressure vessel made from Monel 400 alloy. The residual stresses are experimentally measured by ultrasonic method in which longitudinal critically refracted (LCR) waves are propagated inside the specimen to evaluate the effect of stress on the wave velocity. Any difference in the wave velocity could be transformed to the material stress by using acoustoelasticity relations. A nondestructive hydro-test process is used to measure the acoustoelastic constant, which is an important material property needed to be embedded in the acoustoelasticity relations. By using a different frequency range than the ultrasonic transducers, the LCR wave penetrates in different depths of the specimen to measure the sub-surface stresses. The welding processes are also numerically analyzed by a 3D thermo-mechanical finite-element (FE) model, which is validated by hole-drilling stress-measurement method. The residual stresses calculated by FE simulation are then compared with those obtained from the ultrasonic stress measurement and an acceptable agreement is achieved. It is demonstrated that the sub-surface residual stresses of the Monel pressure vessel could be accurately evaluated by combination of the FE simulation and stress measurement implemented by the LCR waves.

Residual Stress Measurement and Calibration for A7N01 Aluminum Alloy Welded Joints by Using Longitudinal Critically Refracted (LCR) Wave Transmission Method

Residual stress measurement and control are highly important for the safety of structures of high-speed trains, which is critical for the structure design. The longitudinal critically refracted wave technology is the most widely used method in measuring residual stress with ultrasonic method, but its accuracy is strongly related to the test parameters, namely the flight time at the free-stress condition (t 0), stress coefficient (K), and initial stress (σ0) of the measured materials. The difference of microstructure in the weld zone, heat affected zone, and base metal (BM) results in the divergence of experimental parameters. However, the majority of researchers use the BM parameters to determine the residual stress in other zones and ignore the initial stress (σ0) in calibration samples. Therefore, the measured residual stress in different zones is often high in errors and may result in the miscalculation of the safe design of important structures. A serious problem in the ultrasonic estimation of residual stresses requires separation between the microstructure and the acoustoelastic effects. In this paper, the effects of initial stress and microstructure on stress coefficient K and flight time t 0 at free-stress conditions have been studied. The residual stress with or without different corrections was investigated. The results indicated that the residual stresses obtained with correction are more accurate for structure design.

Comparison Between Using Longitudinal and Shear Waves in Ultrasonic Stress Measurement to Investigate the Effect of Post-Weld Heat-Treatment on Welding Residual Stresses

ABSTARCTFusion welding is a joining process widely used in the industry. However, undesired residual stresses are produced once the welding process is completed. Post-weld heat-treatment (PWHT) is extensively employed in order to relieve the welding residual stresses. In this study, effect of PWHT time and temperature on the residual stresses of a ferritic stainless steel is investigated. Residual stress distributions in eight welded specimens were measured by using an ultrasonic method. Ultrasonic stress measurement is a nondestructive method based on acoustoelasticity law, which correlates mechanical stresses with velocity of an ultrasonic wave propagating within the subject material. The ultrasonic wave employed could be longitudinal or shear wave produced by the longitudinal (normal) or transverse (shear) transducers, respectively. Ultrasonic stress measurements based on longitudinal waves use longitudinal critically refracted (LCR) waves in this direction, while shear wave methods use an ultrasonic birefringence phenomenon. The results show that the effect of PWHT can be successfully inferred by both longitudinal and shear wave methods, but the former is found to be more sensitive to stress variation. Furthermore, the distribution of subsurface residual stresses is found to be more distinguishable when the LCR method is employed.

Sub-surface stress measurement of cross welds in a dissimilar welded pressure vessel

Manufacturing process of pressure vessels used in high-temperature applications normally needs employing dissimilar metal welds (DMWs) between austenitic and ferritic steel. However, high amount of thermal stresses at the welds are induced due to differences in coefficient of thermal expansion between the types of steel. This study investigates the evaluation of welding residual stresses in a pressure vessel manufactured by DMW of 316 L stainless steel shell to A106 carbon steel caps as well as similar welding of stainless steel shells. By using longitudinal critically refracted (LCR) ultrasonic waves, the residual stresses are experimentally measured. The ultrasonic method is based on acoustoelasticity law by which the ultrasonic wave velocity could be connected to the material stress. By changing the frequency in which the ultrasonic transducers are working, the LCR waves are able to penetrate in various depths of the material in order to measure the sub-surface residual stresses. Hence, four main aspects are considered in this study: (I) stress evaluation of the DMW; (II) sub-surface stress measurement; (III) stress evaluation of longitudinal weld and (IV) stress measurement in cross weld. It is demonstrated that the residual stresses of the DMW pressure vessel could be comprehensively evaluated by using the LCR method.

Investigation of Clamping Effect on the Welding Residual Stress and Deformation of Monel Plates by Using the Ultrasonic Stress Measurement and Finite Element Method

Welding of nickel-based alloys is increasingly used in the industry to manufacture many important components of the marine industries, chemical processing, etc. In this study, a 3D thermomechanical finite element (FE) analysis is employed to evaluate residual stresses and deformations caused by the tungsten inert gas (TIG) welding of Monel 400 (Nickel-Copper alloy) plates. The FE results related to the residual stresses and deformations have been verified by using the hole-drilling stress measurement and common dimensional measurement tools, respectively. Residual stresses analyzed by the FE simulation are then compared with those obtained from ultrasonic stress measurement. The ultrasonic stress measurement is based on acoustoelasticity law, which presents the relation between the acoustic waves and the stress of material. The ultrasonic stress measurement is carried out by using longitudinal critically refracted (LCR) waves which are longitudinal ultrasonic waves propagated parallel to the surface inside the tested material. Two welded plates are experimentally prepared (with and without using clamp) to investigate the clamping effect on the welding residual stress and deformations. By utilizing the FE analysis along with the LCR method, the distribution of longitudinal residual stress could be achieved. It has been concluded that the applied methodologies are enough accurate to distinguish the clamping effect on the welding residual stresses and deformations of Monel plates.

Ultrasonic stress evaluation through thickness of a stainless steel pressure vessel

This paper investigates ultrasonic method in stress measurement through thickness of a pressure vessel. Longitudinal critically refracted (LCR) waves are employed to measure the welding residual stresses in a vessel constructed from austenitic stainless steel 304L. The acoustoelastic constant is measured through a hydro test to keep the pressure vessel intact. Hoop and axial residual stresses are evaluated by using different frequency range of ultrasonic transducers. The welding processes of vessel shell and caps are simulated by a 3D finite element (FE) model which is validated by hole-drilling method. The residual stresses calculated by FE simulation are then compared with those obtained from the ultrasonic measurement while a good agreement is observed. It is demonstrated that the residual stresses through thickness of the stainless steel pressure vessel can be evaluated by combining FE and LCR method (known as FELCR method).

Taguchi optimization and ultrasonic measurement of residual stresses in the friction stir welding

The main goal of this study is optimization of residual stresses produced by friction stir welding (FSW) of 5086 aluminum plates. Taguchi method is employed as statistical design of experiment (DOE) to optimize welding parameters including feed rate, rotational speed, pin diameter and shoulder diameter. The optimization process depends on effect of the welding parameters on longitudinal residual stress, which is measured by employing ultrasonic technique. The ultrasonic measurement method is based on acoustoelasticity law, which describes the relation between acoustic waves and internal stresses of the material. In this study, the ultrasonic stress measurement is fulfilled by using longitudinal critically refracted (LCR) waves which are longitudinal ultrasonic waves propagated parallel to the surface within an effective depth. The ultrasonic stress measurement results are also verified by employing the hole-drilling standard technique. By using statistical analysis of variance (ANOVA), it has been concluded that the most significant effect on the longitudinal residual stress peak is related to the feed rate while the pin and shoulder diameter have no dominant effect. The rotational speed variation leads to changing the welding heat input which affects on the residual stress considerably.

Comparison between Contact and Immersion Method in Ultrasonic Stress Measurement of Welded Stainless Steel Plates

Abstract This study presents a comparison between contact and immersion ultrasonic method to measure welding residual stress of austenitic stainless steel plates (AISI 304L). Longitudinal critically refracted (LCR) waves are employed to measure the residual stresses. By using contact and immersion transducers, a 3D distribution of longitudinal residual stress for the entire of the welded plate is presented. A finite-element model of welding process, which is validated by the hole-drilling method, is used to verify the ultrasonic results. The results show no considerable differences between using contact or immersion transducers in ultrasonic stress measurement of stainless steel plates; however, some practical considerations are mentioned.

Using ultrasonic waves and finite element method to evaluate through-thickness residual stresses distribution in the friction stir welding of aluminum plates

The main goal of this study is ultrasonic measuring of through-thickness residual stresses in friction stir welding of aluminum plates. A 3D thermo-mechanical finite element analysis is used to evaluate residual stresses caused by friction stir welding of 5086 aluminum plates. The finite element (FE) model has been validated by the hole drilling method. Residual stresses obtained from the FE analysis is then compared with those obtained from ultrasonic stress measurement. The ultrasonic measurement technique is based on acoustoelasticity law which describes the relation between the acoustic waves and the stress of material. The ultrasonic stress measurement is accomplished by using longitudinal critically refracted (LCR) waves which are propagated parallel to the surface within an effective depth. Through-thickness distribution of longitudinal residual stresses is evaluated by employing the LCR waves produced by four different frequencies (1MHz, 2MHz, 4MHz and 5MHz) of ultrasonic transducers. Utilizing the FE analysis along with the LCR method (known as FELCR method), the through-thickness distribution of longitudinal residual stress could be achieved. The comparison between ultrasonic and FE results show an acceptable agreement, hence the FELCR method could be successfully applied on the FSW plates. It has been concluded that the longitudinal residual stresses of aluminum plates joined by friction stir welding can be evaluated by using the FELCR method. The good potential of FELCR as a nondestructive method is also confirmed in through-thickness stress measurement of aluminum plates.

Ultrasonic inspection of a welded stainless steel pipe to evaluate residual stresses through thickness

This study investigates ultrasonic method in axial and hoop stress measurement through thickness of an austenitic stainless steel pipe. Longitudinal critically refracted (LCR) waves are employed to measure the welding residual stresses while outer and inner surfaces of the pipe are inspected by using different frequency range of ultrasonic transducers. The acoustoelastic constant is measured on a plate with the same material and thickness of the investigated pipe to keep the pipe intact. Welding process of the pipe is simulated by a 3D finite element (FE) model which is validated by hole-drilling method performed on 25 points. The residual stresses calculated by FE simulation are then compared with those obtained from the ultrasonic measurement while a good agreement is observed. It is demonstrated that the residual stresses through thickness of the stainless steel pipe can be evaluated by combining FE and LCR method (known as FELCR method).

Comparison between contact and immersion ultrasonic method to evaluate welding residual stresses of dissimilar joints

This paper presents a comparison of contact and immersion waves used to measure residual stresses. The residual stresses are produced due to a dissimilar welding of stainless steel (304) to carbon steel (A106). Longitudinal critically refracted (LCR) wave propagated by 2MHz contact and immersion ultrasonic transducers is employed to measure the residual stresses. A Finite Element (FE) model of welding process, which is validated by hole-drilling method, is used to verify the ultrasonic results while an acceptable agreement is achieved. The best agreement is observed in the parent material while the maximum difference is measured in the heat affected zone (HAZ). The results show no considerable difference between using contact and immersion transducers in ultrasonic stress measurement of dissimilar joints.

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

This paper uses a 3D thermo-mechanical finite element analysis to evaluate welding residual stresses in austenitic stainless steel plates of AISI 304L. The finite element model has been verified by the hole drilling method. The validated finite element (FE) model is then compared with the ultrasonic stress measurement based on acoustoelasticity. This technique uses longitudinal critically refracted (LCR) waves that travel parallel to the surface within an effective depth. The residual stresses through the thickness of plates are evaluated by four different series (1MHz, 2MHz, 4MHz and 5MHz) of transducers. By combining FE and LCR method (known as FELCR method) a 3D distribution of residual stress for the entire of the welded plate is presented. To find the acoustoelastic constant of the heat affected zone (HAZ), a metallographic investigation is done to reproduce HAZ microstructure in a tensile test sample. It has been shown that the residual stresses through the thickness of stainless steel plates can be evaluated by FELCR method.

Goniometer service

This paper presents a comparison of contact and immersion waves used to measure residual stresses. The residual stresses are produced due to a dissimilar welding of stainless steel (304) to carbon steel (A106). Longitudinal critically refracted (LCR) wave propagated by 2 MHz contact and immersion ultrasonic transducers is employed to measure the residual stresses. A Finite Element (FE) model of welding process, which is validated by hole-drilling method, is used to verify the ultrasonic results while an acceptable agreement is achieved. The best agreement is observed in the parent material while the maximum difference is measured in the heat affected zone (HAZ). The results show no considerable difference between using contact and immersion transducers in ultrasonic stress measurement of dissimilar joints.