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CAEfatigue

The Industry Leader in Vibration Based Fatigue
Link to CAEfatigue Supplier Website

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 two 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 accesses 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 level as well as the advanced level user.
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 is scaled over time using measured data. It can also be used with modal stresses and strains that is scaled with modal coordinates/participation factors that is 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.
Frequency based fatigue

Solving fatigue an a vibrating structure using single and multiple PSD inputs

The CFV-BASE module is designed to provide the user with both the random response results and the fatigue results from a structure undergoing loading input from a single random PSD with or without additional loading from deterministic inputs and mean offsets. Response outputs includes mean stress, RMS stress or strain, mean stress plus RMS stress or strain, moments, zero crossings, peaks per second and irregularity factor.  Fatigue results including damage, life and margin of safety from a single random input.

The loading inputs needed for CFV can come from Optistruct, Nastran, Ansys or Abaqus generated from (virtually) any size model.  Examples of inputs are simultaneous wide band and narrow band inputs, wide band random and swept sine inputs, wide band random and deterministic inputs, wide band and swept narrow band inputs, swept narrow band or swept sine wave.

The CFV-MULTI module offers all the input / output options from CFV-BASE plus the ability to use multiple random input PSDs (and cross PSDs) with mean offsets i.e., data from a test rig with multiple events and multiple channels per event plus a mean offset.  This module offers random response and S-N or E-N fatigue results generated from the multiple simultaneous correlated load inputs, with any number of DOFs, inputs, events and frequencies.  Coupled with CAEfatigue RANDOM, CFV-MULTI becomes a powerful tool for understanding output results for displacement, velocity, acceleration, force, stress, strain and fatigue (damage / life).

Welded Joints
 
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 to ability to perform a complete vehicle analysis including the seam and spot welds as part of the analysis.
Time to PSD
 
Performing infield measurements to see how a structure behaves in operation is a relatively common occurrence these days. The down side 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 to much data to proses 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 op challenges that included:
  • Do I use all the recorded data or just the recorded events that causes the most damage?
  • How do I identify these events that causes the most amount of damage
  • What window length (buffer size) should I select
  • How much overlap should I allow between data sections?
The CFC tool available in CAE fatigue helps the user to automatically identify event that does not contributor to the damage and convert the damage contributing time data to a representative PSD. This is a vital step to to ensure that you get accurate and believable fatigue results from the analysis.  
 
The CFC tool 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 time and effort, as it can often be difficult to keep track of all the different PSD's and ensuring that the PSD matrix is constructed correctly.
Random response
 
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  vibration 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 response.
 
The post-processor allows the user to obtain the rlatative response of a node and compare it to the actual distance of any other nearby node. This allows the user to asses 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.
Surrogate PSD
 
The specification of loads for durability is a very important topic. Ideally, any loads used in an analysis or in a laboratory based test procedure, should be as close as possible to the Customers use of the product. In practice, the nearest scenario that can be achieved is to measure multi events and multi input loads (with correlation) from prototype vehicles (test tracks) and then replay these in the laboratory or analysis environment. For analysis, this is feasible and is a commonly adopted method although it does not easily deal with the topic of test acceleration. For laboratory based simulation, especially of parts or subsystems, there is a need (usually because of available test equipment) to simplify the loads down to single input load one at a time (e.g, X, then Y, then Z), which this poses significant challenges. Two common approaches are currently used. First, an enveloping procedure can be applied to the loads where the multiple loads are combined into a single smoothed profile. A classical application of this procedure involves no knowledge of the structural system so there is no assurance that the enveloped loads will cause the same damage values or distribution. Second, is to use the concept of a Fatigue Damage Spectrum (FDS) where a simplified loading is created which does the same damage on a hypothetical 1 DOF system (where the resonance is moved through the loading). Again, this takes no account of the actual structural system or systems. The CFS* module provides a NEW approach, which is a variation of the FDS approach but using the actual system properties. The CFS tool provides a way to transform a complicated multi-input and multi-event time history loading into a simplified “SURROGATE LOAD” that will provide the SAME damage output for the system as the complex test time history.

*CFS is currently under development and is scheduled to be released in Q2 2019 or sooner.

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