I am trying to prestress the PZT stack for my ultrasonic horn assembly. The picture shows a sectional view of the horn cut along the symmetry plane. PZT stacks are gonna be prestressed by a bolt and nut. Bolt is connected to a connecting body which is turn is connected to ultrasonic horn. My interest about adding a prestress is to use it to run the prestress modal analysis to have stiffening effect. I would like to add prestress of 100 MPa on the stack Here are the few things that I have tried but nothing seems to work right. I tried adding thermal preload using Global Temperature Load after changing the material property for the bolt to add CTE and then successively removed the CTE for the other members to mimic the preload in bolt due to shrinkage and hence prestress in stack. When running the static analysis using Global Temperature load (GTL), I constrained the entire circumferential surface for the connecting body. This was the only constraint I used. I could not use the contact elements as prestress modal analysis does not allow using them. So I ran this setup without contact elements. I adjusted GTL till I got a stress of 100 MPa in my stacks. Then I used these results for my prestress modal analysis to run unconstrained with rigid mode search modal analysis but to find that the modal frequency did not changed much. Rather it decreased by 2 units. I expect frequency to go up by atleast 50-60 Hz due to stiffening of stack. I am not sure now if I should trust prestress modal analysis in Pro/MECHANICA or I am doing something wrong. Anyone ran with these issues in Pro/M Can someone please suggest me how would one go about prestressing stack to use the results in prestress modal analysis? Does it matter with Pro/M if you will use a constraint to run a static analysis and then do not use that same constraint for prestress modal analysis? Thanks in advance. This thread is inactive and closed by the PTC Community Management Team. If you would like to provide a reply and re-open this thread, please notify the moderator and reference the thread. You may also use "Start a topic" button to ask a new question. Please be sure to include what version of the PTC product you are using so another community member knowledgeable about your version may be able to assist.