Ultrasonic Stress Measurement Research Articles

Bolt axial stress measurement method based on ultrasound multi-feature fusion

ABSTRACT There exist issues of ill-adaptability and low-accuracy in ultrasonic bolt stress measurement based on acoustic elasticity and scattering attenuation. Therefore, a bolt axial stress measurement method based on ultrasound multi-feature fusion is proposed in this paper. Firstly, ultrasound characteristic parameters based on the theory of acoustic elasticity are extracted, including the difference of time-of-flight (TOF) and the longitudinal wave attenuation coefficient in polycrystalline materials within the Rayleigh scattering range. Then, following the dimension reduction principle, the difference of TOF, attenuation coefficient, and clamping length are chosen as the input feature vectors for the fusion model. Subsequently, the SVR model is employed to establish a multi-feature fusion model for bolt axial stress measurement. Calibration and measurement experiments are conducted using the constructed experimental platform. Comparative analysis between the traditional measurement methods and the proposed method reveals that the SVR model can adapt to measurements of bolts with different lengths, overcoming the limitations of traditional methods. Furthermore, the measurement results of different fusion algorithms show that SVR yields significantly lower average relative errors in the measurement of the three bolts (3.35%, 4.44%, and 4.48%) compared to BP and RBF algorithms. This indicates higher measurement accuracy and immunity to low-stress effects.

A refined energy ratio method based on ultrasonic echoes for measuring short bolt axial stress

Ultrasonic stress measurement methods play an important role in measuring bolt axial stresses. Traditional Time of Flight (TOF) approaches have accuracy limits when applied to short-bolt stress measurement. This paper proposes a Refined Ultrasonic Echo-based Energy Ratio (RUEER) method for bolt stress measurement that considers internal nonlinear scattering attenuation effects, transmission-reflection effects at the interface area, and energy loss in the transition region. The ultrasonic wave inside the stressed bolt is decomposed into different components to better evaluate the energy attenuation of ultrasonic echoes. The proposed method is verified with stress measurement experiments. Results show that the average error of the proposed RUEER method is less than 2.5% for different bolts and clamping lengths. Through comparative testing, the accuracy of the proposed method demonstrates improved performance over the TOF and Energy Attenuation Method (EAM). Additionally, the RUEER method is more robust to variations in equipment performance than the TOF method.

Ultrasonic measurement of contact stress at metal-to-metal interface based on a real rough profile through modeling and experiment

Metal-to-metal seals are widely used in tubing and casing connections in oil and gas wells; therefore, the integrity of sealing is crucial. As the quality of seals is directly influenced by the metal-to-metal contact stress, this study investigates the measurement and evaluation of contact stress at rough interfaces numerically and experimentally using an ultrasonic quantitative method. A two-dimensional ultrasonic propagation model of the rough contact interface is developed based on an actual rough profile. The reflection coefficient decreases gradually as the normal deformation and contact rate increase, and a relationship between the reflection coefficient and the contact rate is established. The reflection coefficient reduces exponentially to approximately zero when the contact rate is less than 0.5. Combined with the contact mechanics theory, for an elastic contact, an empirical fitting formula for the interface reflection coefficient, contact stress, root mean square deviation (Rq), and mean width of the profile elements (RSm) is established. Note that at the same contact rate, the reflection coefficient decreases as the interface lubricant parameter ρc2 increases. Therefore, ρc2 is introduced to optimize the empirical fitting formula. Accuracy of the empirical fitting formula is verified using experimental results, that is, through the ultrasonic measurement of the contact stress at the loaded metal-to-metal interface. Thus, this study serves as a reference for measuring and quantifying the metal-to-metal contact stress.

Preliminary study on modeling blood flow velocity profile for ultrasonic measurement of wall shear stress

The wall shear stress (WSS) contains useful information for the diagnosis of vascular diseases. To improve the accuracy of WSS measurements by ultrasound, some studies have attempted to correct the underestimation of the WSS by approximating a blood flow velocity profile measured by ultrasound to a velocity distribution model such as laminar flow. In this study, a blood flow velocity profile measured by ultrasound was modeled by the Womersley flow model, in order to correct underestimation of WSS in cases of measurements of vessels with complex geometries such as stenotic vessels. The simulation results showed that the rms error of the estimated WSSs was 45.8% from the stenotic vessel with a stenotic ratio of 40% when the spatial gradient was estimated by fitting a linear model to the measured flow profile. Such an error was improved from 45.8% to 25.3% by fitting a Womersley flow model to the measured blood velocity profile.

Local Stress Measurement in Thin Aluminum Plates based on Zero-Group-Velocity Lamb mode

The stress state is critical to the reliability of structures, but existing ultrasonic methods are challenging to measure local stress. In this paper, zero-group-velocity (ZGV) Lamb mode was proposed to measure the local stress field in thin aluminum plates. The Lamb wave’s dispersive characteristics under initial stress were analyzed based on the Floquet-Bloch theory with Murnaghan hyperelastic material model. The obtained dispersion curves show that higher-order Lamb wave modes near the cut-off frequencies are sensitive to applied stress across the plate, indicating that the S1-ZGV mode has a rather high sensitivity to stress. Similar to conventional ultrasonic stress measurement, it is found that the frequency of the S1-ZGV mode changes near-linearly with the amplitude of applied stress. Numerical experiments were conducted to illustrate the feasibility of local stress measurement in a thin aluminum plate based on the S1-ZGV mode. Single and multiple localized stress fields were evaluated with the S1-ZGV method, and reconstructed results matched well with actual stress fields, proving that the ZGV Lamb wave method is a sensitive stress measurement technique in thin plates.

Ultrasonic and FEM residual stress measurement in dissimilar St37–St52 welding

Numerous industries, like the military, the oil and gas industry, etc., rely heavily on dissimilar welding. The welding process leaves the structure with a variety of defects, such as residual stress, that degrade its performance and static and fatigue properties. Consequently, weld residual stress must be accurately measured. In this study, ultrasonic and finite element techniques are developed to assess the residual stress in dissimilar St37/St52 welding. In addition, hole-drilling technique is employed to confirm FEM and ultrasonic data. Probe fixture is designed and built for ultrasonic stress measurement, and the acoustoelastic coefficient is measured in St37 and St52. In welding finite element analysis, the Goldak model is used as the heat source, the Brekstad model is employed as the heat loss, and the Dflux subroutine is developed to apply the heat source to the weld line using the sedimentary method. The FEM and ultrasonic data are in good correlation with the hole drilling results (maximum error of 9%). The findings indicate that there is a high degree of concordance between the data gathered by FEM and ultrasonic technique (with error less than 1.75% at the weld zone).

Methodology for Mapping the Residual Stress Field in Serviced Rails Using LCR Waves.

Non-destructive stress measurement by ultrasonic testing is based on calculating the acoustoelastic modulus obtained from the relationship between material stress and sound wave velocity. A critically refracted longitudinal (LCR) wave, which is a bulk longitudinal wave penetrating below and parallel to the surface below an effective depth, is most suitable for ultrasonic stress measurement tests because it exhibits a relatively large change in travel time in response to a change in stress. In particular, the residual stress distribution through the thickness of the subject can be calculated if transducers of different frequencies are applied because of the characteristic of propagation to different depths of penetration depending on the frequency. The main purpose of this study was to visualize the internal or residual stress distribution through the thickness of rails using LCR waves. To this end, LCR probes with different center frequencies were designed and manufactured, and the residual stress values ​​of an unused railroad rail and two used railroad rails operated under different conditions were calculated. This was done using the ultrasonic signals received from each probe, of which the distributions were mapped. Through these mapping results, different residual stress values could be calculated according to the depth. The differences in residual stress generation and distribution according to the conditions surrounding the contact between train wheels and rails, and their characteristics, were visualized and analyzed. As a result, it could be concluded that the non-destructive evaluation technique using LCR waves could detect differences in the residual stress of a rail, and thus can be used to measure the residual stress of the rail accurately.

Non-intrusive ultrasonic measurement of tie-bar stress for molding equipment

For molding equipment, the accurate measurement of tie-bar stress helps improve product quality and prolong the lifespan of the machine. In our previous work, the mathematical model between the ultrasonic time difference (UTD) and the tie-bar stress was established, and this model was shown to have high accuracy with the maximum of difference square being only 1.5678 (MPa)2. Nevertheless, when calculating the UTD using the cross-correlation function (CCF) method, it is necessary to manually divide the position of the echoes. This makes it impossible to automate the stress measurement and it is ineffective when dealing with massive data. In this paper, a non-intrusive ultrasonic measurement method for tie-bar stress based on the minimum entropy blind deconvolution is firstly proposed. The results of simulation and verification experiments show that the proposed method has high precision, and the maximum relative error is only 2.44%. Hence this method has been successfully applied in the tie-bar stress measurement in molding equipment. Compared with the CCF method, accuracy is improved and the maximum relative error is reduced from 3.67% to 1.68% when the clamping force is small. In summary, the proposed method is comparable to the CCF method in terms of accuracy, and has a higher resolution during echos disturbance. Moreover, this approach does not require human intervention and is helpful to realize the automation of the tie-bar stress measurement for the molding equipment.

Collaborative detection and on-line monitoring of pipeline stress in oil and gas stations

The types of pipeline used in oil and gas stations is diverse, and it is difficult to comprehensively and accurately measure pipeline stress using a single detection method. Non-contact pipeline magnetic detection (NPMD), metal magnetic memory, ultrasonic stress measurement (USM) and ultrasonic thickness measurement (UTM)constitute a collaborative detection strategy for station pipelines. The pipeline magnetic abnormal evaluation parameter N is derived according to the sensor arrangement in NPMD devices. The magnetic field distribution based on different extraction heights is determined by the magnetic charge model and the experimental results, and a feature parameter E is constructed that can characterize the degree of stress concentration. The pipeline stress concentration points can be quickly determined in accordance with N and E. Reference stress values can be measured using USM and UTM. Monitoring is implemented at the stress concentration points, and the true stress values at the stress concentration points of the pipeline are established by combining the stress detection results. The collaborative detection method is applied to an oil and gas station, and two stress concentrations of 186.7 and 211.6 MPa are identified, respectively. The stress at the excavation pit is confirmed to be 196 MPa based on the monitoring data. Based on collaborative detection and on-line monitoring, fast and efficient collaborative detection and real-time mastering of station pipeline stress are achieved.

Correction of coupling error in contact-type ultrasonic evaluation of bolt axial stress

The stress monitoring of bolted connections is crucial in the evaluation of mechanical systems’ structural health, and the ultrasonic method using TOF (Time of Flight) is considered promising in this application. However, the discrete nature of couplant layer characteristics can deteriorate the robustness of the ultrasonic method significantly. Here, for the purpose of deducting the coupling error, a compensating method of TOF is proposed. In this method, the components of the waves backscattering from bolt bearing surface within the temporal signal are filtered and utilized. The analytical coupling error correction model is established and the influences of the installation eccentricity upon the model are analyzed. Meanwhile, the proposed method is further verified by a finite element simulation and the results are consistent with the analytical derivations. Ultimately, the proposed method is experimentally validated and the scattering components are extracted from the pulse echo signal by using the synchrosqueezed wavelet transform. The results imply that, after being compensated by the proposed method, the stress measurement error decreased from 5% to 1%. This research provides a novel perspective in reducing the coupling error in a concise manner and is potential in improving the practicality of the ultrasonic bolt axial stress measurement methods.

Reliability verification of stress data from extracted specimens using LCR wave stress data from full-section rail specimens

Non-destructive stress measurement using ultrasonic techniques is based on calculation of the acoustoelastic coefficient obtained from the relationship between material stress and sound wave velocity. Longitudinal critically refracted (LCR) waves are the most suitable for ultrasonic stress measurement testing. This is because these waves exhibit a relatively large change in flight time in relation to a change in stress. In general, to calculate the acoustoelastic coefficient, tensile tests are performed with specimens extracted from the test objects to be inspected, and the difference in the speed of ultrasonic waves is measured in relation to the stress applied. However, train rails are usually subjected to compressive loads and no research has been conducted to confirm whether the results obtained using this method match the coefficients obtained from test objects in full cross-section. Therefore, results from compression tests on full cross-section specimens are needed as reference data to determine the reliability of the results obtained using extracted specimens. In this study, experiments were conducted to compare the result from applying compressive loads to full cross-section specimens to the experimental result obtained from specimens extracted from each rail section. For this purpose, ultrasonic probes capable of generating LCR waves were designed and manufactured to apply the technique to measure the applied stress. Based on the results obtained using this probe, the acoustoelastic coefficient values obtained from each specimen were compared. Then, the feasibility of calculating the internal stresses in railway rails using the acoustoelastic constants obtained from the extracted specimens was determined, and the reliability of the method was verified. It was concluded that there was no significant difference in the acoustoelastic coefficients calculated using the data from extracted specimens and those using full cross-section specimens.

Ultrasonic measurement of tie-bar stress for die-casting machine

Ultrasonic measurement of tie-bar stress for die-casting machine

1Pb5-1 Evaluation of Accuracy of Ultrasonic Measurement of Wall Shear Stress at Stenosis by Computational Fluid Dynamics

1Pb5-1 Evaluation of Accuracy of Ultrasonic Measurement of Wall Shear Stress at Stenosis by Computational Fluid Dynamics

Experimental Measurement of Residual Stress Distribution in Rail Specimens Using Ultrasonic LCR Waves

Longitudinal critically refracted (LCR) waves are considered bulk longitudinal waves and penetrate into an effective depth beneath the surface parallel to the material surface. Such LCR waves can be employed to measure residual stresses because the acoustoelastic effect is the basis for ultrasonic residual stress measurements. This effect is described by the relationship between change of wave travel time and stress applied when such waves propagate in a stressed medium. In this paper, stresses applied in a rail were evaluated by using a developed LCR probe. With this transducer, it was verified how the difference in the arrival times of the LCR waves showed a trend as the tensile stresses increased. The acoustoelastic coefficients were calculated using the relationship between the stresses and the travel times, and the residual stresses of the used rails were measured using these coefficients. In addition, the difference in residual stress distribution according to the characteristics of the wheel-rail contact surface was analyzed from the obtained residual stress value. It was concluded that this non-destructive evaluation technique using LCR waves could be employed for accurate stress measurement of rails because differences in stress applied to the rail can be detected.

Denoising of LCR Wave Signal of Residual Stress for Rail Surface Based on Lifting Scheme Wavelet Packet Transform

According to the acousto elastic effect, the residual stress on the surface of the rail can be evaluated by measuring the change in the propagation velocity of ultrasonic waves, such as longitudinal critically refracted (LCR) waves on the surface of the rail. The LCR wave signal is often polluted by a variety of noise sources, coupled with the influence of the poor surface condition of the inspected component, which greatly reduces the detectability and online measurement ability of the LCR wave signal. This paper proposes the application of the lifting scheme wavelet packet transform (LSWPT) denoising method to solve the noise suppression problem of LCR wave signal. The traditional wavelet transform (WT), wavelet packet transform (WPT), as well as the lifting scheme wavelet transform (LSWT) and lifting scheme wavelet packet transform are compared and analyzed in the soft thresholding and hard thresholding processing of denoising ability and efficiency of the noisy LCR wave signal. The experimental results show that the LSWPT method has the characteristics of fast calculation speed and a good denoising effect, and it is an efficient method of denoising signals for on-line ultrasonic measurement of residual stress on the rail surface.

Ultrasonic Measurement Method of Bolt Axial Stress Based on Time Difference Compensation of Coupling Layer Thickness Change

The accurate measurement of the axial stress of the core engine rotor bolts is of great significance for improving the assembly quality and safety of aeroengines. To solve the problem that the thickness change of the coupling layer affects the measurement accuracy in ultrasonic measurement of axial stress, a measurement method based on time difference compensation of the thickness change of the coupling layer is proposed in this article. Based on the principle that different loads applied to the ultrasonic transducer will cause the thickness of the coupling layer to change, which leads to changes in the amplitude and propagation time of the ultrasonic echo signal, the principle of time difference compensation for changes in the thickness of the coupling layer is proposed. Based on this principle, the propagation time difference caused by the thickness change of the coupling layer is compensated, thereby improving the measurement accuracy of the propagation time difference caused by the stress and reducing the measurement error of the axial stress. The experimental results show that the average errors of the axial stress measurement model based on the time difference compensation of the thickness change of the coupling layer and the conventional axial stress measurement model are 1.048 and 1.723 MPa, respectively. Therefore, the time difference compensation for the thickness change of the coupling layer can effectively reduce the measurement error of the axial stress. This study provides a promising method for the accurate measurement of the axial stress of aeroengine bolts.

Ultrasonic Measurement of Axial Stress Using High-Frequency Cylindrical Guided Wave

A new stress measurement method using single source high-frequency cylindrical guided waves is put forward to promote the efficiency and precision of the contact-type ultrasonic testing technique. The propagation patterns and acousto-elasticity of cylindrical guided waves, traveling in a loaded steel rod, are analyzed under the theoretical framework of the Pochhammer-Chree equation and nonlinear acoustics. According to the theoretical derivations, the ratio of the maximum group velocities of different modes is selected as the measurement criterion of stress. Then, a stress calibration/measurement experiment is conducted to prove the validity of the method. A single-source ultrasonic transducer driven with an impulsive excitation is introduced in the experiment and the generated multimode guided waves in the received signals are analyzed. It is observed from experimental results that the group speed ratio of two different modes is linearly proportional to the axial stress and the evaluation errors of the proposed method is less than 6%.

Evaluation of Total Compressive Stress in Steel W-Flange Members Using Ultrasonic Shear Waves

AbstractThis research investigates the potential for ultrasonic stress measurement (USM) to be used to evaluate the total stress in wide-flange steel sections (W-section) for a postevent condition ...

Subsurface Stress Measurement in GIS Epoxy Composite by Using LCR Waves

Internal stress in basin insulators of gas-insulated metal-enclosed switchgear (GIS) can lead to cracks, which affects the safe operation of these apparatuses. In this research, we proposed a subsurface internal stress measurement method for GIS epoxy composites. This method is based on an ultrasonic longitudinal critically refracted (LCR) wave technique. In this study, some epoxy composite specimens were synthesized with similar materials and manufacturing processes to those of 252 kV GIS basin insulators. An ultrasonic stress measurement system that utilized the LCR wave technique was set-up to investigate the relationship between stress and LCR wave propagation time, as well as to measure the compressive stress of the epoxy specimen within 0–50 MPa. The results show that LCR wave propagation time linearly decreased when stress increased in the subsurface zone and the acoustoelastic coefficient was −4.95. We found the relative errors of stress measurements to be less than 13%.

Ultrasonic Measurement of Stress in SLM 316L Stainless Steel Forming Parts Manufactured Using Different Scanning Strategies.

Selective Laser Melting (SLM) technology is a new kind of additive manufacturing technology developed in in the last decade. Measurement and control of stress in metal forming layer is the basic problem of SLM forming parts. Critical Refraction Longitudinal (LCR) wave method was used to measure stress. The acoustic-elastic formulas for measuring stresses in SLM 316L stainless steel forming parts manufactured using meander, stripe, and chess board scanning strategies, respectively, were established based on static load tensile test. The experimental results show that the acoustic time difference of LCR wave in SLM specimen manufactured with 316L stainless steel increases linearly with the increase of stress when the tensile stress is less than critical stress (372 MPa, 465 MPa, and 494 MPa). Due to the inhomogeneous deformation of the anisotropic SLM forming layer and the dimple-micropore aggregation fracture mechanism, the acousto-elastic curve fluctuates up and down along the irregular curve when the tensile stress is larger than critical stress. The results of corroboration experiments show that nondestructive measurement of stress in SLM forming specimen can be realized by using LCR wave method. The scanning strategy can significantly affect the tensile strength and yield strength of SLM forming specimen. The stresses were all in tension stress state at the edge of the specimens, whatever scanning strategy was used. Sub-area scanning and scanning sequence of alternate and intersect were adopted, which can effectively reduce the stress in the SLM forming specimen. The overall stress values of SLM forming specimen manufactured using chess board scanning strategy were smaller than that using meander and stripe strategies. The distribution of stress were more uniform.