Investigation the effect of clamping stress on ultrasonic velocity in cylinder head bolt of diesel engine

Clamp load is the most important characteristics of a bolted joint that should be estimated with precise method. This paper investigate the effect of clamping stress on ultrasonic velocity in cylinder head bolt of diesel engine using pulse-echo method. So in assembly process, clamping force, fasting torque and ultrasonic result are measured simultaneously. To investigate effect of new and used bolt and also effect of thread coating, various conditions are tested. Results showed that at first stage of assembly, minor plastic deformation in blot thread can decrease clamping force. In addition in used bolt the plastic deformation of thread is not significant, but increasing of friction coefficient role play in clamping force. Although using zinc phosphate can decrease of friction coefficient and increase preload, but also using torque-angle procedure can control effect of this term. Effect of blot assembly stress on ultrasonic velocity is approximately linear elastic depending on clamping force and friction coefficient. Finally relation of ultrasonic velocity and blot stresses in a real assembly process is derived in whole elastic region of high tension bolt that can estimate clamping force in various size blot with less than 10% error