As we know, considering the viscoelasticity of materials, composite bolted joints are easier to relax than metal bolted joints, and damping can also reflect the viscoelastic properties of materials. So how do we compare composite bolted joints and metal materials by damping? What are the loosening properties of bolted joints?

Use of a digital torque tester will allow you to apply a specific torque to both joints. There will be an almost instantaneous relaxation of the joint that can be measured immediately. A gradual relaxation will then occur over time.

I would suggest using large sample sets where you apply a torque to 100 joints (50 composite, 50 metal) and measure the relaxation after 30 seconds.

Create another sample set of 50/50 using new bolts, torque to the same value and measure after 15 minutes.

Repeat this test using fresh bolts each time while increasing the test time to build up your data set and perform statistical analysis of the samples

Strain gauges could also be implemented to measure the clamping forces which would decrease over time.

Sorry,Trevor,

I am not asking how to compare the relaxtion of composite and mental bolt joints by experiment,but by theory.

I have got the result that composite bolt joints are easier to relax than mental bolt joint by experiment! and what i want to know is why the phenomenon will take place?

Thank you!