I have modelled a clamp which has been designed to resist bending stresses in a flange joint during installation. The clamp has been assessed in a separate analysis and is structurally ok. The issue I have is that the M39 bolts are failing. I have tried to apply just the pre-load on the clamp but the FOS achieved is only 0.5, which seems strange because I am only loading the bolts to approximately 50% proof load. 

The pipe is HDPE and with custom input material data.

I have added a No Penetration contact with a 0.2 friction factor, between the clamp and pipe and also restrained the ends of the pipeline with a fixed restraint. I have researched extensively and ran multiple analyses and nothing seems to work.

The clamp deforms when the bolts are pre-tensioned, which is exactly what will happen, but I am unsure if this is causing large bending moments in the bolts which will not occur in a real life situation.

I have attached my model for checking if anyone has time to take a look.

Thanks,

Mike