12-07-2012, 01:38 PM
Fatigue Analysis Using ANSYS
[attachment=27507]
Introduction
It is estimated that 50-90% of structural failure is due to fatigue, thus there is
a need for quality fatigue design tools. However, at this time a fatigue tool is
not available which provides both flexibility and usefulness comparable to
other types of analysis tools. This is why many designers and analysts use
"in-house" fatigue programs which cost much time and money to develop. It
is hoped that these designers and analysts, given a proper library of fatigue
tools could quickly and accurately conduct a fatigue analysis suited to their
needs.
The focus of fatigue in ANSYS is to provide useful information to the
design engineer when fatigue failure may be a concern. Fatigue results can
have a convergence attached. A stress-life approach has been adopted for
conducting a fatigue analysis. Several options such as accounting for mean
stress and loading conditions are available.
Capabilities
A fatigue analysis can be separated into 3 areas: materials, analysis, and
results evaluation. Each area will be discussed in more detail below:
Materials
A large part of a fatigue analysis is getting an accurate description of the
fatigue material properties. Since fatigue is so empirical, sample fatigue
curves are included only for structural steel and aluminum materials. These
properties are included as a guide only with intent for the user to provide
his/her own fatigue data for more accurate analysis. In the case of
assemblies with different materials, each part will use its own fatigue
material properties just as it uses its own static properties (like modulus of
elasticity).
Stress-life Data Options/Features
• Fatigue material data stored as tabular alternating stress vs. life points.
• The ability to define mean stress dependent or multiple r-ratio curves if
the data is available.
• Options to have log-log, semi-log, or linear interpolation.
• Ability to graphically view the fatigue material data
• The fatigue data is saved in XML format along with the other static
material data.
• Figure 1 is a screen shot showing a user editing fatigue data in ANSYS.
[attachment=27507]
Introduction
It is estimated that 50-90% of structural failure is due to fatigue, thus there is
a need for quality fatigue design tools. However, at this time a fatigue tool is
not available which provides both flexibility and usefulness comparable to
other types of analysis tools. This is why many designers and analysts use
"in-house" fatigue programs which cost much time and money to develop. It
is hoped that these designers and analysts, given a proper library of fatigue
tools could quickly and accurately conduct a fatigue analysis suited to their
needs.
The focus of fatigue in ANSYS is to provide useful information to the
design engineer when fatigue failure may be a concern. Fatigue results can
have a convergence attached. A stress-life approach has been adopted for
conducting a fatigue analysis. Several options such as accounting for mean
stress and loading conditions are available.
Capabilities
A fatigue analysis can be separated into 3 areas: materials, analysis, and
results evaluation. Each area will be discussed in more detail below:
Materials
A large part of a fatigue analysis is getting an accurate description of the
fatigue material properties. Since fatigue is so empirical, sample fatigue
curves are included only for structural steel and aluminum materials. These
properties are included as a guide only with intent for the user to provide
his/her own fatigue data for more accurate analysis. In the case of
assemblies with different materials, each part will use its own fatigue
material properties just as it uses its own static properties (like modulus of
elasticity).
Stress-life Data Options/Features
• Fatigue material data stored as tabular alternating stress vs. life points.
• The ability to define mean stress dependent or multiple r-ratio curves if
the data is available.
• Options to have log-log, semi-log, or linear interpolation.
• Ability to graphically view the fatigue material data
• The fatigue data is saved in XML format along with the other static
material data.
• Figure 1 is a screen shot showing a user editing fatigue data in ANSYS.