CAEFATIGUE (CF) IS AVAILABLE IN THREE DIFFERENT PACKAGES
CAEfatigue is a random response and vibration fatigue solver for the frequency domain plus a fatigue solver for the time domain. It works with mixed random and deterministic loadings or standard time domain based loadings to provide fatigue life and damage predictions, as well as several forms of response statistics. It is exceptionally fast, easy-to-use and capable of handling very large models.
The software is sold in 3 different package configurations.
The TIME and FREQUENCY package noted below plus the capability to do so much more.
Advanced Random Analysis Output
For many automotive and aerospace systems it is required to calculate both durability and to rule out the possibility of collision of individual components during severe base shake vibration conditions. Advanced frequency domain methods now exist to enable the durability assessment and response to be assessed in the same analysis. With the advanced random analysis output it is possible to output displacement and/or velocity and/or acceleration and/or force RMS levels and Power Spectral Density (PSD) plots for both absolute and relative responses. In addition, a residual sum of the squares (RSS) is calculated to take into account any off axis response. New post processing options allow the relative response from any node to be compared against the actual distance to all nearby nodes in order to check for the probability of collisions (i.e. RATTLE) between adjacent parts. The response maximum is determined using either a ratio of the RMS (e.g. 3.0*rms) from a corresponding level of probability on a Gaussian or Rayleigh distribution, or by using a method which takes into account the number of cycles of response. Advanced Random Analysis output is an excellent addition to predict structural response under complicated loading conditions found in many engineering applications throughout a wide variety of industries.
Calculation of SURROGATE Loading
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 applied one at a time (e.g. X, then Y, then Z), which 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. Surrogate Loading provides a NEW approach, which is a variation of the FDS approach but using the actual system properties. The Surrogate Loading tool provides a way to transform a complicated multi-channel, multi-event time history loading into a simplified “SURROGATE LOAD” that will provide a very similar stress and damage output for the system as the complex test time history did.
Calculations at Welds in the Frequency and Time Domains
CAEfatigue has created an industry first! We now provide the ability to conduct a full Spot Weld, Seam Weld and User Defined weld analysis in the Frequency Domain along with the more traditional methods used in the Time Domain. This capability will allow a full automotive vehicle analysis, that includes spot and seam welds, to be conducted with CF in either the Frequency domain or Time domain.
The TIME package noted below plus the capability to do so much more.
Base Shake PSD Analysis plus Mean Loads plus Deterministic Loads
CAEfatigue 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 CF 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.
Multi Input PSD Analysis for Multi-Channel, Multi-Event Loading
CAEfatigue offers all the input / output options mentioned for Base Shake loading 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 and/or E-N fatigue results generated from the multiple simultaneous correlated load inputs, with any number of DOF’s, inputs, events and frequencies. Coupled with advanced random analysis, CF becomes a powerful tool for understanding output results for displacement, velocity, acceleration, force, stress, strain and fatigue (damage / life).
Conditioning and Conversion of Time Signals to PSDs
For those who only have multi-channel, multi-event time histories, CAEfatigue offers a separate toolset called TIME2PSD. Historical loads conditioning procedures involve a series of user options that are hard for a typical engineer or designer to implement. Some of these have now been automated in the CF TIME2PSD approach. Window length (FFT buffer size), window overlap, and initial deletion of non-relevant parts of the signal can all be done automatically. The toolset provides a way to correctly eliminate sections of the time history that do not contribute to the damage. Conditioning is vital to ensure the damage from the time history is correctly transferred to the Power Spectral Density (PSD). The toolset also converts multi-input time histories to a PSD matrix that organizes, labels and tracks the PSDs to correctly account for cross correlation effects. An option also exists to switch on or off, the correlation terms to evaluate the influence on damage. The connections with solver subcase ID’s are automatically dealt with so the user does not have to take extra time managing the data.
Time Domain Fatigue Analysis
CAEfatigue is designed to provide basic fatigue analysis tools for the linear static superposition approach, the modal participation factor approach and the direct stress recovery method. This TIME package is intended to provide a vast improvement in the analysis process for conventional static superposition analysis, modal participation factor (dynamic transient) analysis and direct stress recovery analysis. The TIME package uses state of the art software development tools and algorithms to deliver a fatigue solver with superior speed and accuracy. Coupling time domain tools with frequency domain tools provides Customers with a complete time and frequency domain analysis package that surpasses the performance and accuracy needs of our users.
Load Scheduler Toolset
CAEfatigue provide a Load Scheduler toolset that allows the User to create unique time based loading profiles from a simple deterministic time signal channel to complicated multi-event, multi-channel loading sequences. Existing RPC, CSV, DAC files can be manipulated / augmented and exported as unique loading event sets.
BUT WAIT! We have a great interface and training library
Response analysis, fatigue analysis and the use of a graphical interface have traditionally suffered from a lack of democratisation; that is to say, only expert users have been fully capably of using the technology. CAEfatigue aims to change this.
First, a Control File text based interface is provided for the advanced Users to help rapidly create an input control file that is needed to run an analysis. Many variables are either used in default mode or are automatically calculated based on an understanding of the system being analysed.
Second, a Process Flow graphical based interface is provided to help novice users quickly gain an understanding of the technology without the need to understand the structured format of the control file interface. The interface is simple and intuitive to use.
Lastly, a comprehensive Technology Transfer package is included within HELP menu of the software, which is directly accessible from within the software GUI. More than 100 hours of video training material from beginner level to advanced level are included along with more than 100 relevant Test Problems to aid the User in understanding the technology. We aim to provide the simplicity desired by the engineer and designer along with the functionality and visual graphics found in many of the post processing packages available today.