Calibration and Evaluation of Nonlinear Ultrasonic Transmission Measurements of Thin‐Bonded Interfaces

Abstract

Interfaces in bonded structures influence the mechanical behavior of components significantly, and often limit their load capacity. This requires nondestructive testing techniques allowing one to investigate the interaction forces in adhesive joints and to evaluate the quality of bonds. To this end the nonlinear stress-strain relationships of adhesives and adhesive interfaces, which cause a nonlinear modulation of ultrasonic waves in reflection as well as in transmission, may be exploited. Bonded interfaces which are much thinner than the ultrasonic wavelength can be approximately described only by the binding forces, without explicitly taking into account the material properties of the adhesive layers. These may be measured by the amplitudes and phases of ultrasonic waves transmitted through the interface. Measurements are presented on aluminum plates joined together by thin epoxy adhesive layers. A threshold behavior of the harmonics generated in the adhesive layer has been observed. Their amplitudes depend on the excitation following the power series expansion of a quasi-static interaction force curve, and their phases vary little for low-amplitude excitation. Exceeding the threshold causes a change in the response of the interface. The input and output ultrasonic amplitudes in the interface are calibrated interferometrically to obtain the absolute interaction force. The ultrasonic transmission data are related to destructive tensile tests of the adhesive bonds. IntroductionThe interfaces in bonded structures influence the mechanical behavior of components significantly. Therefore, an important task in nondestructive testing (NDT) is the investigation of the interaction forces in adhesive joints and the development of techniques to evaluate the bond quality. The load capacity of such joints is often limited by regions of weak bonding. As in all materials, the 403 Adhesion -Current Research and Application. Wulff Possart

The Ultrasonic Polar Scan for Composite Characterization and Damage Assessment: Past, Present and Future

“…However, it is well-known from literature that nonlinear wave phenomena show an increased sensitivity to early stage damage features as well as to certain classes of contact defects [42][43][44][45]. For this reason, the present authors are currently upgrading the U(B)PS methodology towards the nonlinear regime.…”

Measurement of material nonlinearity using surface acoustic wave parametric interaction and laser ultrasonics

“…5 The higher harmonic generation method measures the harmonic content of a single ultrasonic wave. 6 The technique has been applied to various materials including composites [7][8][9] and to measure fatigue. 10,11 More recent methods include nonlinear time reversal 12-14 and nonlinear reverberation.…”

Nonlinear ultrasonic testing of carbon fibre reinforced plastics in the very high cycle fatigue regime

“…The two remarkable peaks in the distortion factor with subsequent decrease may be caused by a larger delamination which acts as a source of non-classical nonlinearity when it starts to open. Partially open delaminations are known to be strong sources of nonlinearity in composite materials [6,7,8]. With increasing deterioration of the sample the delaminations open completely and become strong classical reflectors for ultrasound exhibiting low nonlinearity.…”