The technology of internal stress control in critical elements of metal structures

Short summary A Ukrainian university offers a technology for measuring internal stress in critical elements of metal structures under load using the holographic interferometry method. The technology makes it possible to record the stress changes with an accuracy of 1-3% of Young's modulus of the metal and monitor the working condition of the critical elements. They are looking for partners to finalize the technology for various metals and alloys and to produce compact sensors based on the technology.

Full description Metal elements play a significant role in the creation of structures that are used under various types of stress. Examples of such structures can be elements of bridges, airplanes, pipes, nuclear power plants or space vehicles, and much more. The specificity of the operation of such metal elements places high demands on their reliability of functioning in real conditions. Under the influence of various types of stress in metals and alloys, a bunch of defects appears, which eventually leads to the failure of the metal elements of structures. Constant monitoring of the state of such elements is of critical importance for the reliable operation of the structures. The proposed technology is based on the use of recording changes in metal lattice constant by the method of probe holes and three-exposure holographic interferometry. During the first exposure, a hologram of the surface area of the critical metal element of the structure is recorded before drilling the hole, the second surface with the hole before the occurrence of loads, and the third exposure is recorded with a selected frequency during the operation of the metal element of the structure. Thanks to the use of specially prepared thermoplastic materials, the sensitivity of measuring changes of stress is up to 1-3% of Young's modulus of the metal of the structural element being monitored. The proposed method of determining the final stress using a test hole with holographic interferometry is illustrated in Fig. 1. Here (1) is a metal sample, (2) is a block of piezo quartz, (3) is an alternating voltage generator, (4) is a receiver of ultrasonic signals, (5) is a two-beam oscilloscope, (6) is a drilling device, (7) – laser, (8) – optical unit for splitting the laser beam and forming the path of secondary optical rays, (9) – video camera, (10) – a computer with a program for deciphering interferograms, which determines the height of the parapet at the edge of the drilled hole (Fig. 2). The university is looking for partners for researching to finalize the technology for various metals and alloys via a research and development cooperation agreement and investors to organize the introduction of the technology into production in the form of the output of compact sensors of final stress via an investment agreement.

Advantages and innovations

• minimum dimensions of the hole: depth up to 0.4 mm, diameter up to 1 mm;
• the sensitivity of measuring the ultimate stress at the level of 1
• 3% of Young's modulus of the metal;
• the ability to perform measurements within a few seconds in a time interval;
• the possibility of choosing the time interval between measurements. For example, to measure several times a day, once a week, or once a month, etc.

Contact / source: NEXT EEN Widgets (europa.eu)