Predict the cycles to failure of a given composite material under a prescribed load history.
Accomplish this by damaging the composite material with the minimum cycles to failure and allowing the finite element platform to redistribute loading to the adjacent material. Following this fashion, a composite structure can be analyzed, and the cycles to failure for the structure can be estimated.
Running a Progressive Fatigue Analysis:
Please refer to previous sections of the User's Guide before reading this section. To predict the cycles to failure for a composite structure in a finite element setting, you must first setup a progressive failure analysis using Helius PFA. The steps required to transform the static analysis into a fatigue analysis are minimal.
The current version of Helius PFA with progressive fatigue does not support material definitions within a GUI environment. Therefore the remainder of the discussion will center around directly modifying the input file to define a Helius PFA material for a fatigue analysis. Please refer to the Defining a Helius PFA Material section before continuing.
Specifying a material for a fatigue analysis is a direct extension of specifying a material for a static analysis. The main differences are listed below:
In contrast to traditional analyses, you must specify the temperature of the analysis in absolute temperature units (Kelvin or Rankine) as an initial condition. This requires you to specify a temperature for all nodes in the model prior to applying any load. Refer to the ANSYS documentation for aid in specifying an initial temperature.
During the first cycle of the loading, the material could potentially undergo damage due to the static loads being applied. Therefore, the first step in the analysis should consist of loading the composite structure to the maximum load (over multiple load increments) in the prescribed load history.
After the maximum load has been applied to the structure and the static progressive failure analysis has been carried out, you must add a subsequent step in which the load is held constant. This step should consist of multiple increments and no prescribed thermal or mechanical loadings. Refer to the Specifying a Load History for Progressive Fatigue section for more information.
Executing a progressive fatigue analysis is the same as running a conventional finite element analysis from the command line. Follow the instructions in this document for a detailed description of running an analysis with Helius PFA.