Quantitative Analysis of Big End Journal Form and Bolt Installation using Ultrasonic Time of Flight Measurements

Connecting rod bolts have the effect of compressing the bearing cap when preload is applied, placing the journal into an out of form state when exacting levels of torque are not exercised. In this paper, this effect has been highlighted by means of practical measurements and then simulated with FEA models. A further study into ultrasonic velocity through torque to yield fasteners has highlighted as torque is increased, there is a coherent decrease in sound wave velocity. Testing also highlighted a change in Young’s modulus during the elastic region, throwing animosity to the conventional linearity of Hooke’s law. Based on current literature, a relationship linking increased hardness to a reduction in ultrasonic velocity resulted in further testing that indicated as fasteners yield, the material locally strain hardens, causing a decrease in sound velocity in the heavily yielded region. It is then regarded that high frequency ultrasonic testing can identify localised micro structural changes due to strain hardening, giving a variation in Young’s modulus during the elastic region when compared to the linearity of the conventional bulk tensile test that cannot identify such details