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Quantitative analysis of voids in multi-layer bonded structures based on transmitted laser ultrasonic waves

100%

Zhang K. , Li S. , Zhou Z.

tom Vol. 19, no. 1

79--90

A laser ultrasonic method based on transmission has been investigated to characterize voids in the bonded layer and its corresponding quantitative strategy has been proposed to feed back accurate manufacturing information on multi-layer metal bonded structures. Characteristics of laser ultrasonic waves obtained at epicentre in a bonded joint were analyzed and interaction of laser ultrasound with voids in the bonded layer was explained with aids of simulation results and experimental data. The longitudinal wave amplitude gradually increases and then decreases with the increase of distances off epicentre, while the shear wave amplitude shows a monotonic decline with distances off epicentre rising. Moreover, the relative sensitivity has been proposed to quantitatively measure the sizes of voids and its variation is from −2.48 dB to −2.44 dB with defects of 3 mm to 15 mm in diameter. The laser ultrasonic C-scan result based on shear waves with transmission can find the small void with 3 mm size and other natural defects. The proposed quantitative method is effective for measurement of void sizes. As a result, laser ultrasonic C-scans on basis of transmitted shear waves jointed with the proposed quantitative method have great potential for quantitative characterization of voids in bonded structures.

Deformations and decrease of load-carrying capacity of welded structures due to residual welding stresses

84%

Farkas J. , Jarmai K.

tom No. 7

117-126

Residual deflection due to restrained shrinkage of longitudinal welds is calculated in the case of an asymmetric I-section crane runway girder. The residual welding compression stresses decrease the load-carrying capacity of a welded I-section compression strut in a significant measure. The effective width of a welded stiffened plate should be calculated considering residual welding stresses. The fatigue strength of welded joints is influenced by residual welding stresses significantly. These effects are illustrated by numerical examples.