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Diploma thesis abstract

Laser-ultrasonic diagnostics of subsurface residual stress in metal
Diploma work Of the 6-th year student A .S . P o d o lsk y

An investigation of residual stresses in metal after different surface treatment (shot peening, vibrotreatment and annealing) was presented in the work. Th Laser u ltr a so n ic t e c h n iq u e b a se d o n th e a c o u sto e l a stic e f f e c t a n d u sin g w id e b a n d a c o u stic p u l s e s w a s u s e d . T h e p u l s e s w e r e g e n e r a t e d u s i n g t he r m o o p t i c a l e x c i t a t i o n t e c h n i q u e . Stress in-depth distribution is evaluated from reflectivity of the wide-band ultrasonic p u l s e s . A n e f f e c t i v e p r o c e d u r e o f l o w - f r e q u e n c y s i gn a l p r o c e s s i n g w a s d e v e l o p e d . T h e in-depth distribution of residual stresses in the steel treated by shot-peening technique was evaluated. The result is in good agreement with control data received from a d e str u c tiv e m e th o d . By the example of vibrotreated surface was shown that surface roughness acts considerably on the ability of the method's performance capabilities. The experimental setup for calibration of some modifications of the method was created. It is useful for measuring of slow changes of acoustic impedance and while using surface acoustic waves. Measurements of dependence of ultrasound velocity on tensile stress in several metals was performed. Part of them can be used while calibration of the system for residual stress measurement.