CAEfatigue

The Industry Leader in Vibration Based Fatigue

CAEfatigue is a powerful tool to conduct a durability analysis on a structure whether it is in the time or fervency domain.

It also has the capability to:

Perform a durability analysis on spot and seam welds
Time to PSD conversions
Advanced response and collision detection analysis
Surrogates analysis

These capabilities are discussed in more detail below.

GUI (CFG)

The user interface is laid out in a way that will make it easy and intuitive to use for both the experienced everyday user as well as the novice that uses the software for the first time. This is done in 2 ways

A step by step wizard is available to help the user to generate the input file that is required for the fatigue solver. The user will have access to a wide range of parameters that can be changed or used as-is.
There are a lot of tutorials and examples available including more than a 100 hours of video material that can be accessed directly from the GUI to get you started with the operation of the GUI and the software itself. There are tutorials and examples available for the beginner as well as the advanced user.

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Time based fatigue (CFT)

Although CAEfatigue is well known for its fatigue solution in the frequency domain, it has an equally strong and competitive solution available in the time domain.

This solution can be used with the conventual stress and strain results that are scaled over time using measured data. It can also be used with modal stresses and strains that are scaled with modal coordinates/participation factors that are obtained from a model transient analysis.

This time-based fatigue solver makes uses of algorithms that will deliver superior speed and accuracy. The time-based fatigue solver can also be coupled with the vibration base solver allowing customers to have the best of both worlds.

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Frequency based fatigue (CFV)

Solving fatigue on a vibrating structure using PSD inputs

There are currently 2 modules available:

CFV-BASE: This module provides random response and fatigue result outputs for a structure undergoing loading input from a single random PSD. Additional loading from deterministic inputs and mean offsets can also be added.

Results output

The following outputs can be provided:

Mean stress
RMS stress or strain,
Mean stress plus RMS stress or strain
Moments
Zero crossings
Peaks per second
Irregularity factor.
Damage
Life
Margin of safety

Supported loading Inputs

The following loading inputs are supported:

Optistruct
Nastran
Ansys
Abaqus

Typical PSD's

Typical PSD inputs include the following:

Simultaneous wide band and narrow
Wide band random and swept sine
Wide band random and deterministic
Wide band and swept narrow band
Swept narrow band
Swept sine wave.

CFV-MULTI: This module supports the same inputs/outputs as CFV-BASE and additionally supports multiple random input PSD's (including cross PSD's) with mean offsets. The module offers random response, S-N or E-N fatigue results that are generated from multiple correlated load inputs.

CFV-MULTI coupled with CAEfatigue RANDOM provides a powerful toolset to help the user understand output results for displacement, velocity, acceleration, force, stress, strain and fatigue life.

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Welded Joints (CFJ)

It is now possible to perform a full spot and seam weld fatigue analysis in the frequency domain using CAEfatigue. This will give the automotive industry the ability to perform a complete vehicle analysis including the seam and spot welds as part of the analysis.

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Time to PSD (CFC)

Performing infield measurements to see how a structure behaves in operation is a relatively common occurrence these days. The downside of this is that you sit with hours and hours of data. It is often not feasible to use the time-based data as it is simply too much data to process in a fatigue analysis. The best option, in this case, is to convert the time domain data into a representative PSD that can be used to perform the fatigue analysis in the frequency domain.

This approach, however, comes with its own set of challenges and the following set of questions should be awnsered:

Do I use all the recorded data or just the recorded events that cause the most damage?
How do I identify these events that cause the most amount of damage
What window length (buffer size) should I select
How much overlap should I allow between data sections?

The CFC module helps the user to automatically identify events that do not contribute to the damage and convert the damage contributing time data to a representative PSD. This is a vital step to ensure that you get accurate and believable fatigue results from the analysis.

The CFC module also helps the user to convent multiple input data into a PSD matrix (including the cross-correlation PSD's) that can be used as-is in the frequency-based solver. This saves the user a huge amount of time and effort, as it can be difficult to keep track of all the different PSD's as well as constructing the PSD matrix correctly.

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Random response (CFR)

In some industries its is not only required to perform a durability analysis of a system but also to check for possible collusion between components when subjected to a sever base shake excitation. CAEfatige has advanced frequency-domain methods that can be used to conduct a durability analysis and see how the structure responds in the frequency domain.

The CFR module can provide a wide range of outputs that can help to detect collision between components, these outputs include:

Displacement, velocity and acceleration
Force RMS levels
PSD plots for absolute and relative responses.
Residual sum of the squares (RSS) calculation to take into account off-axis responses.

The post-processor allows the user to obtain the relative response of a node and compare it to the actual distance of any other nearby node. This allows the user to assess the probability of components colliding with each other.

CFR coupled with CFV can also be used to predict the response of a structure under complex loading conditions. This is often the case in many engineering applications.

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Surrogate PSD (CFS)

Using the correct input loads are very important in a durability analysis as both the S-N and ε-N fatigue formulations are very sensitive to it. Ideally, the load inputs must be as close to the loading that the structure/component will see under operating conditions.

The load inputs to be used can be obtained from various sources but the most accurate loading that is representative of the structure is obtained through infield measurements and prototype testing. This is a commonly adopted approach in industry. This approach, however, does not allow for test acceleration which is required in some cases to test if a component or system will meet the number of cycles to failure requirement it was designed for.

In the case where accelerated testing is required, laboratory-based simulations are carried out. These simulations often require simplified load inputs that can be simulated one after another. How can this be achieved?

Currently, there are 2 approaches commonly used in industry:

Enveloping: This approach uses an enveloping procedure to combine multiple loads into a single smoothed load profile. This approach requires no knowledge of the structure/component being tested and thus there are no assurances that the enveloped loads will cause the same fatigue damage or distribution as the measured loads.
Fatigue Damage Spectrum (FDS): This approach creates a simplified loading which does the same damage on a hypothetical 1 degree of freedom (DOF) system (where the resonance is moved through the loading). This approach also does not require any knowledge of the structure/component being tested.

The CFS module provides an approach where the properties of the system are taken into account. This approach is a variation of the FDS approach. This module allows the user to transform a complicated multi-input and multi-event time history loading into a simplified load. This load is referred to as a surrogate load that will provide the same fatigue damage as for a system with a complex test time history.

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