respected ndt experts, thank you very much for your response. many people have advised me to refer "Engineering Applications of Ultrasonic Time-of-Flight Diffraction" - by J. P. Charlesworth and J. A. G. Temple.
Unfortunately , it wont be possible for me to buy such an expensive book.(it is $90).so i request those people from india who have this book, to please lend me this book for a couple of days . i will pay all the courier expenses. i will return the book within two days...u can trust me..please please help me out..