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Ultrasonic Techniques for Stress Measurement and Material Studies
Published in Don E. Bray, Roderic K. Stanley, Nondestructive Evaluation, 2018
Don E. Bray, Roderic K. Stanley
The basis of the ultrasonic stress measurement technique is the stress induced anisotropic behavior of solids. This is caused by non-linearities in the strain-displacement and constitutive relations of the material. The acoustoelastic effect refers to the changes in the speed of clastic wave propagation in a body that is simultaneously undergoing static elastic deformation. In this section, which is based on the work of Egle and Pray,89 techniques and results of the measurement of the acoustoelastic and third order elastic constants are presented for pearlitic steel.
Non/Loosely Contacting NDE Techniques
Published in J. David, N. Cheeke, Fundamentals and Applications of Ultrasonic Waves, 2017
Bulk shear waves generated by EMAT have been used extensively in stress analysis, for example, in railway wheels and nuclear power pressure tubes. This technique uses the acoustoelastic effect, which describes the effect of stress on the propagation velocities of acoustic waves. EMATs can be used to measure the acoustic birefringence to detect this, whereby the difference in time of flight of two orthogonally polarized shear waves is measured. This has been used in railroad wheels by measuring the velocity difference of shear waves polarized in the circumferential and radial directions. Another application to detect defects in railroad wheels uses emission of linearly polarized shear waves from the back of the rim into the wheel. If there are cracks present, then the shear wave will be partially converted into Rayleigh waves and the shear wave echo from the back wall will be reduced. The depth of the crack can be estimated by displacing the transducer. A laboratory test example is shown in Figure 20.7.
Quantification of delamination in a composite floor using a novel damage index
Published in Nondestructive Testing and Evaluation, 2018
Nadom Khalifa Mutlib, Shahrizan Baharom
RMSD-DI depends on the comparison of the specific signal energy or amplitude with that of the reference signal (before loading) and is assumed to increase with progressive loads until failure. However, this increase does not always occur in structures where conflicting factors exist leading to inconsistent results. These conflicting factors can be found in steel decking that supports a concrete slab and resists the bending load. The first factor is the acoustoelastic effect, which significantly affects the transmission of the ultrasonic waves under high stress [30]. The second factor is the loss of energy leaked to the concrete layer; this loss decreases in the delaminated area via the lack of contact between steel and concrete. One more factor is the transition from compressive stress to tensile stress during loading in the same area where the wave is propagated. Compressive stress and tensile stress affect wave transmission differently. All these factors produce contradicting results that would lead to energy fluctuation of the received waves during loading and consequently to inconsistent results of RMSD-DI. To overcome this drawback, an alternative DI is required. The proposed DI should be more sensitive to the change in wave energy during progressive loading.
Experimental and numerical looseness detection and assessment in flanged joints using vibro-acoustic modulation method
Published in Mechanics Based Design of Structures and Machines, 2022
Seyed Majid Yadavar Nikravesh, Masoud Goudarzi
Another point to bear in mind is that increasing the applied torque does not always decrease the modulation index value. As shown in Figures 17 and 18, excessive applied torque has had a negative effect leading to an increase in the modulation index value. In fact, when excessive torque is imposed on the bolt, the stress field is formed around the bolt which causes nonlinear behavior of the wave passing through the field due to the acoustoelastic effect. This behavior will be illustrated in the form of wave modulation in Fourier transform.
Grain size effect on Lcr elastic wave for surface stress measurement of carbon steel
Published in Nondestructive Testing and Evaluation, 2018
Bin Liu, Wenbing Miao, Shiyun Dong, Peng He
Acoustoelastic theory was the theoretical basis for surface stress measurement with Lcr wave, it stated clearly that surface stress could be measured on the base of determination of Lcr wave propagation velocity that was a linear function of surface stress. While acoustoelastic effect was insensitive, when variation on stress was 100 MPa, the change on Lcr wave propagation velocity in steel material was about 0.01% [1], so accurate calculation of Lcr wave propagation velocity was difficult by conventional experiment. To solve this problem, other characteristic parameter for surface stress measurement, replacing propagation velocity of Lcr wave, was discussed, and difference in time of flight between Lcr wave, passing through the fixed spacing, was adopted. Based on this, acoustoelastic formula for surface stress measurement was deduced by Husson and Ditri [2,3], and lots of relevant studies had been carried out. At present, some studies on surface residual stress measurement of welded joint had been discussed and relevant results also had been obtained [4–7]. Besides welded joint, studies on surface stress measurement of brush electro-plating nickel coating [8], laser cladding coating [9], carbon steel [10], and aluminium alloy [11,12] with Lcr wave also had been reported. But it should be noted that current studies mainly focused on surface stress measurement by calibration test of Lcr wave acoustoelastic coefficient, and rare reports were found about correction of surface stress measurement affected by microstructure effect of experimental material. However, error in surface stress measurement resulting from microstructure effect, including grain size, element content, texture, etc. [13–16], was important for accuracy of surface stress measurement with Lcr wave, thus separation between microstructure effect and acoustoelastic effect was required and needed. In addition, this study would help application of Lcr wave in field of surface stress measurement.