As the external force is increased the force acting on the bolt is proportionally increased. At the same time the clamp force acting on the joint is decreased. If the external force continues to increase then either:

1) The proportion of the external force acting on the bolt together with the bolt's preload, results in the yield of the bolt material being exceeded with the imminent likelyhood of bolt failure. Even if failure does not immediately occur when the external force is removed, the preload will be reduced. The joint diagram showing an external force causing the bolt to yield is illustrated below.

2) The clamp force acting on the joint will continue to decrease until it becomes zero. Any further increase in the applied force will result in a gap forming between the plates comprising the joint and the bolt sustaining all of the additional force. This is illustrated in the joint diagram below.

If a gap does form between the plates comprising the joint then the bolt or bolts are almost always subjected to non-linear loadings from bending and shear forces acting. This usually quickly leads to bolt failure. Hence it is normal to set a design criteria that the applied forces must not under any circumstances result in a gap forming within the joint.