Scientists Have Created a Breakthrough Method for Non-Contact Detection of Defects on Volumetric Surfaces

11:17, September 2, 2021

An article describing the method was published by one of the world's leading scientific journals

Scientists at the University of Helsinki and Ural Federal University (UrFU, Ekaterinburg) have developed a breakthrough method to detect and visualize defects on the surface and inside various objects using lasers.

The fundamental difference of the development is that the use of this method allows, first, to detect damage not only to flat, but also to any volumetric (for example, spherical) surfaces. At the same time, it is possible to carry out the operations in a non-contact manner, thoroughly and with a minimum of interference.

Previously, these tasks have posed a significant difficulty: alternative technologies either apply only to flat surfaces, or due to signal distortions due to the curvature of the object geometry do not guarantee the reliability of the final data.

In addition, the new method eliminates the need to use additional equipment - sensors that are installed on the examined object. Moreover, the processing and interpretation of the information obtained becomes less time-consuming.   

An article describing the technique and the results of its experimental testing was published in Scientific Reports, one of the world's leading scientific journals.

"Using a powerful laser, acoustic waves are generated in the upper part of the object under study. As the waves spread, another laser picks them up. For a successful scan, the detection laser must bounce off the surface of the sample and return to where it originated. The main difficulty was aligning the detection laser, since the sample is curved and the laser beam must be strictly perpendicular to its surface. We solved this problem: in our method, acoustic waves generated at the top of the object are picked up by the detection laser at another point - in the middle, at the "equator" of the object. This distribution of the generation and detection points prevents the formation of interference and ensures high accuracy of the images, which are transmitted to the computer,” Daniel Veira Canle, postgraduate student at the University of Helsinki Department of Physics, describes the essence of the method.

Veira Kenle and Gritsevich were responsible for developing the mathematical model in the research.

"Under laboratory conditions, the sample rotated around the laser source. Another solution is possible when, on the contrary, the laser source will rotate around the object. In both cases, the acoustic waves gradually reproduce a picture of the physical state of the object; gradually a complete and detailed acoustic map is formed. Blackouts indicate the location and size of the damage. To test the effectiveness of the developed method, we scanned four hemispherical stainless steel shells. The acoustic map consisted of 200 signals superimposed on each other. By visualizing the scanning results, we obtained a 3D model of the sample and thus detected defects up to 2 mm in size," says Maria Gritsevich, senior researcher at Ural Federal University, associate professor at the University of Helsinki.

The practical application areas of the developed method are numerous. It can be used in the manufacture and operation of any product, the condition monitoring of which is preferable or possible to carry out contact-free. The developers themselves propose to use the technology they created for orthopedic implants.

"Our non-contact method eliminates the need for prior surgery and therefore reduces the risk of infection. At the same time, our method gives a clear indication of how firmly the prosthesis is attached to the bone, whether there are unwanted voids in the cement that holds the prosthesis in place. This information will be useful for deciding whether surgical intervention is necessary," Daniel Veira Kenle notes.

"We consider that the space industry could also benefit from our method. For example, when solving the problem of remote express-checking the condition of spacecraft fuel tanks," adds Maria Gritsevich.