Re: preload vs. torque, Though I haven’t done it, it seems that would be possible to confirm this relationship fairly easily. Bolt mfgrs are fairly consistant in wishing their fasteners be tightened to a measurable “stretch” generally 70-80% of yield strength of fastener to achieve proper clamp & turningbolt/stud into a tension spring. With a low “scatter” lube such as the ARP lube it should be easy to determine the amount of torque it takes to achieve .00xx” stretch speced for each fastener. Inconsistancys could be due to “scatter”, inaccurate torque wrenches & other friction anomolies not resolved or evened out at interface of bolt & nut threads by multiple staged torque pulls to final torque figure that achieves “stretch” sought.

WSH

Torquing to a strain value is the most effective and practical way to achieve uniform fastener preload, since it takes some of the friction variable out of the process. And there are many tools available for easily doing this, including angle measuring torque wrenches with solid state electronics.

Axial preload variation is not the only concern with regards to fastener installations. Fatigue life is affected by the total combined loads on the fastener. The torsional stress produced in the fastener body by torquing adds to the installed preload stresses the fastener will see.