AutoFEM Fatigue Analysis

The AutoFEM Fatigue Analysis module is used in conjunction with AutoFEM Static Analysis and allows one to evaluate the strength of a structure, which is subjected to cyclic loading. This type of loading is usual in mechanical and structural engineering. The problem is that,when the load is constant, the strength of the structure load may prove to be sufficient. But if this load alternates frequently fatigue of the material occurs and the structure can be damaged or even crushed despite static analysis shows acceptable safety factor.  The AutoFEM Fatigue Analysis module allows you to calculate the safety factor depending on the number of loading cycles and on the law of variation of the load's amplitude .

First, it is necessary to solve static study assuming that the loads are constant. Then the user can define cyclic loading parameters in dedicated dialog box of Fatigue Analysis Study. These parameters determine the type of loading (variation law) and number of cycles.

Before running Fatigue Analysis an S-N Curve for the material of the design should be determined. The special S-N Curve Editor is used for this purpose.

A total of 10 results is available in the Fatigue Analysis. They can be divided into four groups.
The group "Damage" includes the following results:
•    damage by principal stresses;
•    damage by equivalent stresses;
•    damage by stress intensity;
The result is displayed in percentage and indicates the damage rate of the structure under the influence of cyclic stresses with the specified number and nature of loading cycles.
The group "Total Life" includes the following results:
•    total life by principal stresses;
•    total life by equivalent stresses;
•    total life by stress intensity.
The result shows the minimum number of cycles Nmin, at which fatigue failure occurs.
The group "Factor of safety" includes results:
•    factor of safety by the maximum principal stresses.
•    factor of safety by equivalent stresses;
•    factor of safety by stress intensity;

The group "Biaxiality". Biaxiality is the ratio of the smaller alternating principal stress (other than zero) to a larger alternating principal stress. The result characterizes inequality of amplitudes of principal stresses at the point and describes the spatial distribution of "unevenness" of the principal stresses in the volume of the body at every point. The value of biaxiality equal to 1 corresponds to the case of state of homogeneous stress at the point.

Note that AutoFEM Fatigue Analysis module is also available in AutoFEM Analysis Lite.