Residual stress can significantly affect engineering properties of structural components, notably fatigue life, dimensional stability, corrosion resistance. Such effects usually lead to considerable expenditures in repairs and restoration of details, equipment and structural elements. For that reason, the residual stress analysis is a compulsory stage in the design of structural elements and in the estimation of their reliability under real service condition.

Although certain progress has been achieved in the development of the techniques of residual stress measurement, a considerable effort is still required to develop efficient and cost-effective methods of residual stress analysis.

Ultrasonic Computerized Complex for residual stress measurement

An Ultrasonic Computerized Complex (UCC) for residual stress measurement was developed recently in a joint project between Integrity Testing Laboratory Inc. from Toronto, Canada and the National Academy of Science of Ukraine. The UCC includes a measurement unit with supporting software and a laptop with an advanced database and an Expert System for analysis of the influence of residual stresses on the service life of structural components (Figure). The Complex allows determining uni-, bi-, triaxial applied and residual stresses for a wide range of materials and structures. In addition, the developed Expert System (ES) can be used for calculation of the effect of measured residual stresses on the fatigue life of structural elements, depending on the mechanical properties of the materials used, type of welded element and parameters of cyclic loading.

The supporting software allows controlling the measurement process, to store of the ultrasonic measurement data, calculation and drawing of distribution of residual stresses and the use of the designed method and equipment with standard PC's.

Using the ES, it is possible to assess, through calculations, the influence of the residual stresses and their redistribution under the effect of various improvement treatments and cyclic loading on the service life of structural components without having to perform time- and labor-consuming fatigue tests. The program package enables to calculate the fatigue life of structural components after application of heat-treatment, vibration treatment, overloading, ultrasonic peening and other improvement treatments.

MAIN TECHNICAL PARAMETERS OF MEASUREMENT UNIT

The developed equipment allow one to determine the magnitudes and signs of uni-, bi- and triaxial applied and residual stresses for a wide range of materials as well as stress, strain and force in bolts (pins). Quartz plates measuring from 3´3 mm to 10´10 mm in cross-section are used as acoustic transducers. These gages are attached to the object of investigation by special clamping straps and electromagnets.

The main technical characteristics of the measurement unit:

• stress can be measured in materials with thickness 3 - 150 mm;
• error of stress determination (from external load) 5 - 10 MPa;
• error of residual stress determination 0.1 sy MPa;
• stress, strain and force measurement in bolts (pins) 25 - 1000 mm long;
• independent power supply (accumulator battery 12 V);
• overall dimensions of measurement device 300x200x150 mm;
• weight of unit with transducers 6 kg.

References

• Y. Kudryavtsev, J. Kleiman and O. Gushcha. Advanced Ultrasonic Equipment and Supporting Software for Residual Stress Analysis. Proceedings of the SEM Annual Conference on Theoretical, Experimental and Computational Mechanics. Cincinnati, Ohio, USA, June 7-9, 1999. p. 652-655.
• Y. Kudryavtsev, J. Kleiman and O. Gushcha. Measurement of Residual Stresses in Structural Components by Ultrasonic Method. Short Paper Proceedings of the Third World Congress of Structural and Multidisciplinary Optimization. Buffalo, New York, USA, May 17-21, 1999. Volume 2. p. 611-613.
• Y. Kudryavtsev, J. Kleiman and O. Gushcha. Ultrasonic Measurement of Residual Stresses in Welded Railway Bridge. Structural Materials Technology: An NDT Conference. Atlantic City. NJ. February 28-March 3, 2000. p. 213-218.
• Y. Kudryavtsev, J. Kleiman, V. Trufiakov and P. Mikheev. Expert System for Fatigue Assessment and Optimization of Welded Elements. Short Paper Proceedings of the Third World Congress of Structural and Multidisciplinary Optimization. Buffalo, New York, USA, May 17-21, 1999. Volume 2. p. 469-471.
• Y. Kudryavtsev, J. Kleiman and O. Gushcha. Residual Stress Measurement in Welded Elements by Ultrasonic Method. IX International Congress on Experimental Mechanics. Orlando. Florida. USA, June 5-8, 2000.