اندازه گيري تحليلي تنش هاي پس ماند در جوش به كمك روش موج طولي شكست يافته بحراني

چكيده انگليسي :

95 Analytical Measurement of Welding Residual Stress Using Critically Refracted Longitudinal Lcr Wave Technique Masoud Naghdi Email masoud naghdi@me iut ac ir Date of submission September 18 2013 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor Hamidreza Mirdamadi Email hmirdamadi@cc iut ac irAbstractResidual stresses occur in many manufactured structures and components Large numbers of investigationshave been carried out to study this phenomenon and its effect on the mechanical characteristics of thesecomponents Over the years different methods have been developed to measure residual stress for differenttypes of components in order to obtain reliable assessment Nondestructive measurement of residual stress isimportant to optimize the structures design and control their mechanical strength Unfortunately there is noreliable method that nondestructively gives complete satisfaction in the in situ stress monitoring of thewelded structures Material geometry surface quality cost and accuracy of the measurement are some of theparameters that must be taken into account in choosing a proper method Therefore the development ofseveral methods like X ray diffraction incremental hole drilling and the ultrasonic waves are inevitable Stress measurement by ultrasonic waves is a nondestructive easy to use and reasonably inexpensive methodrecently used in some industrial applications Ultrasonic is one of the most economical measurement methodswhich can be used in the industrial environment This method is very quick in comparison with the othernondestructive techniques such as X ray and neutron diffraction that are very expensive and must to do inadvanced laboratories by professional users Recently the critically refracted longitudinal wave technique hasbecome a widely used to measure residual stresses in literature In this project after studing the theories methodology of residual stress measurement using critically refracted longitudinal wave method will bestablished with measuring butt weldments Taguchi approach is used as statistical design of experiment DOE technique for optimizing the four pulsed welding parameters in terms of minimizing the longitudinalresidual stresses in austenitic stainless steel 304 These parameters are pulse current bachground current on time and pulse frequency with three levels for using a L9 orthogonal array of taguchi design Afterwelding and measuring stresses with critically refracted longitudinal wave technique the peak stresses werereported in centerline of weldments These peak tensile stresses had a direct relationship with heat input ofwelding arc So that is observed that heat input is the master criterion in analyzing the residual stresses Analysis of variance ANOVA is performed on measured data and S N signal to noise ratios The optimumcondition providing the lowest residual stress and heat input This condition were found the lowest level ofpulse current background current and on time and the highest level of pulse frequency As a result ofTaguchi analysis in this thesis the background current was the most influencing parameter on residual stressand pulse current has the next most significant effect The on time is in the third stage and pulse frequencyis the last one The average of these percentage contributions of background current pulse current ontime and pulse frequency in 1 5 and 3 milimetre depth of surface are 51 7 29 17 7 and 1 6 respectively Consequently the Taguchi method was found to be promising technique to obtain the optimumconditions for such studies Keywords Residual stress critically refracted longitudinal wave technique Analysis of variance Design of experiment pulsed current gas tungsten arc welding PCGTAW austeniticstainless steel

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اندازه گيري تحليلي تنش هاي پس ماند در جوش به كمك روش موج طولي شكست يافته بحراني

تحليل واريانس , طراحي آزمايش , جوش پالسي قوسي تنگستن با گاز محافظ خنثي , فولاد زنگ نزن آستنيتي