The usual methods are not suitable for the testing of the products with the boundary perpendicular to the free surface. The diesel motor piston with the niresist insert under the first ring after the operation of roughing and discovery of the insert can be used an example of this task. In such cases the control must be performed from the surface to the depth (1-15)10^-2 m. One of the prospective version of such joints testing is the testing by the head acoustic wave.

The method of testing

In the case of testing of the adhesion joint the use of transverse head wave is the most interesting. Since the head wave is the result of the interaction between the normal and tangential displacements in the wave, the solution for it will be obtained by summing up the solutions for the components. Moreover, the head wave is non-uniform and in each propagation point re-emits the side transverse waves. During the wave propagation near the surface, at the distance of approximately the diffraction component waves have preferential significance while the components determined by the geometrical optics laws tend to zero. At the depths of (6-8) the geometrical components become determinant.

More dipper, to the depths of the order of (10-12)the adhesion joint is controlled by the walking away side wave as well as the surface portion at the distance of (0-1)from the surface.

Experimental results

In order to check the efficiency of the proposed mechanism of the testing the experimental investigations have been performed. The

investigations were carried out on the joint of aluminum with the carbon steel. The sloped transducers with the Plexiglas prism with angle 63° were made. It was ascertained that with the frequency filling of the impulse of 3 MHz, the system has approximately uniform sensitivity (within the range of 1 dB) to the depths 1.8.10^-2 m which corresponds to approximately 17. The sensitivity has been approximately 1 dB per 1.5mm², which is quite sufficient for the practical use.

Conclusions

The important advantage of the proposed method is the fact that the probing signal can be formed on the short area of the surface, less than 1.10^-2 m. On the basis of the proposed model, the devices for automatic control of the diesel engine pistons after the roughing were made. To increase the sensitivity, the mirror-shadow method was used. The metallographic investigations have shown the complete coincidence of the presence of defects with the places revealed according to this method.