Hi,

I am having a hard time applying bolt loads in Abaqus/CAE and I will appreciate if someone could give me some advice on it. 

The bolt model includes the bolt shank, the bolt head, and a nut right under the plates; all modeled using solid elements. The bolt has been divided into to cells at its mid-height. Three load steps are defined; "initial", "bolt load", and the "loading". The bolt load is applied as a force on a surface at mid-height of the bolt in the bolt load step, in the bolt shank direction (z direction), and it has been modified to "Fix at current length" in the "loading" load step. For the "Loading" step a load larger than the pretension load is applied on the top of the bolt to control the bolt behavior. Contact surfaces are defined between the bolt head and the plate underneath, and the nut and the plate above it. 

It is expected that at the end of the "bolt load" step the plates are clamped together by the clamping force which produces deformations in the plate. Applying displacements in the "loading" step the clamping force should reduce gradually to zero and eventually the bolt head should be separated from the plate. 

The model does not work properly. The problems are briefly mentioned below:

1. There is no sign of deformation of the plates and the bolt due to the bolt pretension. Displacements are all zero in z direction both in the plates and the bolt. 

2. Checking the stresses in the bolt shank, the bolt load is only applied to half of it and is zero on the other half. The load is not applied uniformly to the bolt shank.

3. In the "loading" step the analysis gets aborted. 

I suppose the  way that the bolt load is applied is not entirely correct or some other constraints need to be implemented.

I will be very grateful for any suggestions.

With many thanks,

Hossein