How does Workbench handle multiple loadcase in the calculations in the Fatigue Tool. In particular, when I insert a solution combination into the problem, how is each load case handled fatigue-wise? I.e., how is the load set for each used, particularly when the loading type(reversed, zero-based etc.) is different in each load environment. What if one load is present all the time, like gravity?

At the present time (Release 9.0), the fatigue tool calculations in each Environment are independent and are based upon the specifications of that environment. Under the details of the Fatigue tool there are currently 3 options that need to be set; the type of loading (Zero based, Full reversed, ratio, Non Proportional and history), the fatigue analysis theory type (Goodman, Soderberg, etc) and the stress component to use for the fatigue analysis. Note that non proportional is only available for solution combination type of environment. The analyst should choose the type of fatigue calculation that is appropriate to that loading and review the results after solution.

The Solution Combinations type of environment calculates fatigue in a similar manner. What is different is that the loads are defined in other environments. The results from the contributing environments are combined and the fatigue calculations that are performed based upon the loading combination and are independent of any fatigue tool calculations of the contibuting environments. So, if you have one environment with a vertical load and one environment with a lateral load, the solution combination would be the sum of these to loads. And the fatigue calculations would be based upon the load combination. The one exception is for the solution combination with proportional loading in the fatigue tool. In this case, only two environments are permitted in the combination and the fatigue calculations will alternate between the two environments.

As for loads that areconstant for all environments, such as earth gravity, the constant load contribution to the fatigue calculation is dependent upon the type of loading. For Zero based, Full reversed and ratio, the presence of the load in any environment will be combined with all other loads in the other environments. If gravity is present in two environments, then the effect of gravity would be doubled. For these cases, gravity should only be present in one of the environments. For proportional loading, since the fatigue calculation is based upon alternating between environments, both environments would need to have gravity present for the solution to be correct. What this means is that the analyst will need to base the choice of loading environments upon the fatigue loading type that is to be performed, at least for Solution Combinations. For basic environments, the fatigue calculations will be based on the loadings in the environment.

Finally, multiple load cases only have meaning for NonProportional and History Data. Again, non proportional has meaning for two and only two load cases. History Data likely has meaning only for single environments since all loadings in the environment will be scaled by the values in the load history file. This would include Solution Combination environments.

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