Solving for maximum pressure

[roldy]

I have a pressure vessel under some unknown internal pressure. The factor of safety is set at 2 and a yield strength for aluminum as 95 MPa. How do I go about solving for the maximum pressure the vessel can withstand? What I have been doing was going into Preprocessor/Material Props/Failure Criteria to Add/Edit. Then for stress in tension I set x, y, and z = to 47.5 MPa (half of the yield strength). I should note that the vessel is axisymmetric about the y-axis. Does Ansys perform an iterative procedure given some initial pressure value. In other word, does Ansys allow the setting of an initial pressure value and then it increases the pressure incrementally until the failure criteria is met? What is the correct way of doing this?

 

[Navin A S]

A:First, you should note that the maximum pressure is related to the factor of safety and yield strength by the following equation:$P_{max} = \frac{F}{2} \cdot \sigma_y$Where $F$ is the factor of safety and $\sigma_y$ is the yield strength. So in your case, you can solve for the maximum pressure as follows:$P_{max} = \frac{2}{2} \cdot 95 MPa = 95 MPa$Now, regarding the use of Ansys, you are correct that it does perform an iterative procedure for determining the maximum pressure. Ansys will start with some initial pressure value (which you can specify) and then increase the pressure incrementally until it reaches the failure criteria. To do this, you will need to set up a static structural analysis in Ansys and define the material properties, boundary conditions, and load cases. Then, you can define the failure criteria and run the analysis. Ansys will then calculate the maximum pressure that the vessel can withstand and report the results.