Since you can extract any data anywhere in the mesh from any solution, you can specify margin of safety checks anywhere and StressCheck will automatically identify the points where those margins have been exceeded.
Margin Check Solver
The Margin Check Solver combines a nonlinear load step analysis with the parametric formula to compute margins of safety (MS) at specified locations (regions) in the model. Failure criteria (MS equations) are constructed as formula and associated with a region (area or volume) in the model. The formula is evaluated at each load increment to determine if the failure criteria has been exceeded. Returns a table showing the margins of safety at each load level.
Key Features and Advantages
- Define formulae that represent margin criteria to be checked during the Margin Check solution
- Define named extraction settings that calculate these formulae at any location
- Select the named extraction settings that will be checked as the load increases
The Margin Check Solver is simple to use:
- First, run a linear analysis for a load value that produces little or no plasticity. By running a p-extension, say p=1 to 8, the use can assess the quality of the linear solution.
- Second, setup a Margin Check analysis based on user defined values for load step and limit load. You can choose to stop the analysis upon reaching the first negative margin of safety or you can opt to let the analysis continue up to the limit load.
- Third, select a linear solution as a starting solution and provide a tolerance for convergence. In this case we would want to select p=6 as our starting solution since convergence is verified
- SOLVE! – a summary table is generated that list the names of each of the acceptance criteria along with the calculated margin of safety for the failure load or limit load depending on which option was selected
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“The addition of incremental theory of plasticity in StressCheck has greatly improved our ability to accurately predict the fatigue life of joints with interference fit fasteners and cold worked holes. This ability is especially important, not only in support of maintaining aging aircraft but also in analyzing some of the new cold working techniques that have been introduced in recent years.
Prior to this implementation, analysts often relied on closed-form approximations or simple factors that were often overly conservative and sometimes even unconservative when used in life prediction. Now, not only can we more accurately predict residual stresses in these complex structural joints, but we can also do so in a timely manner given the modeling and analysis efficiency that exists with a p-version FEA code such as StressCheck.”F-15 Structures Manager
The Boeing Company