Fatigue Testing and Analysis

Fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. Continued cycling of high-stress concentrations may eventually cause a crack which propagates and results in leakages.

Charge

IEPE

Voltage

Strain / Stress

Force

Full Bridge

Half Bridge

Quarter Bridge

Video

High-speed video

Main Features

INSTANT RESULTS: Temporary fatigue results are available online including additional math channels.
PREPROCESSING: Direct pre-processing or local extreme detection, cycle counting methods with algorithm settings, rainflow filtering, discretization, visualization, and analysis.
STANDARD COUNTING ALGORITHMS: Solution supports standard counting algorithms like rainflow counting algorithm (ASTM) and Markov counting.
POST PROCESSING MADE EASY: Easy analysis of large data sets is possible directly within our Dewesoft X data acquisition but we offer data export to many different standard file-formats including universal file format, excel, Matlab, FlexPro, Diadem, CSV, and many others.
VISUALIZATION: The solution comes bundled with several data visualization options including range diagram, mean diagram, from/to matrix.
LIFETIME FREE SOFTWARE UPGRADES AND SUPPORT: Our data acquisition systems come bundled with award-winning Dewesoft X data acquisition software. The software package is always evolving and new features are being added. We offer lifetime FREE software upgrades and technical support to all our users.

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Preprocessing of Time Domain Signal

Turning points filter - detects turning points (local extremes) in the signal. The filter is applied to the input signal by default and cannot be disabled since the Fatigue Analysis Module requires a sequence of turning points as its input (instead of a full load signal).
Rainflow filter (hysteresis filter) - removes small oscillations from the signal. All turning points that correspond to the cycles with the ranges below the given threshold are removed. Higher the threshold, more turning points are filtered out, and vice versa. The rainflow filtering can significantly reduce the number of turning points, which can be of importance for both testing and numerical simulation. Threshold parameter of value T corresponds to the T% of the absolute load signal range.
Discretization filter - divides the range of a load signal into N equidistant bins and assigns each turning point to its closest bin. Load signals are typically very stochastic, therefore, discretization is often applied to make them flatter and less stochastic. The number of bins is adjusted with the Class count parameter.

Fatigue Rainflow Counting Procedure

Rainflow counting is generally accepted as being the best cycle counting method up to date and has become the industrial de facto standard.

The idea behind the method is to detect the hysteresis loops in the load signal. We'll refer to the hysteresis loops as the closed cycles. Parts of the signal that do not correspond to the closed cycles are the so-called open cycles or residuals.

Different rainflow counting standards, such as ASTM, DIN and AFNOR, differ with respect to the treatment of the residuals. In order to be as general as possible the Fatigue Analysis Module supports both residual and non-residual mode.

Fatigue Markov Counting Method

Markov counting is one of the most straightforward cycle counting methods. It operates on consecutive pairs of turning points and calculates absolute ranges between them.

Data Visualization

In order to graphically represent the results the fatigue analysis module uses the most common visualization techniques used in fatigue analysis:

Range histograms - 2-D graph representing the range distribution of a load signal (range, number of cycles). A typical range histogram use-case would be to obtain the range histogram of a signal, rotate it over diagonal (swap the X-axis and Y-axis), overlay a corresponding S-N curve on top and check whether it stays well below the curve.
From/to matrices - 3-D graph representing the cycle distribution of a load signal (from, to, number of cycles)
Range/mean matrices - 3-D graph representing the cycle distribution of a load signal (cycle range, cycle mean, number of cycles)
Peak/valley channel
RF filter channel
Discretization channel
Rainflow counting
Markov counting

Classes parameter specifies the number of classes the range is divided into. When the auto checkbox is ticked the Dewesodt X software automatically calculates Min range and Max range from the input signal.

Calculate Large Data Sets Easily

When analyzing extremely large data files with the Fatigue Analysis Module the operating system can run out of memory. In order to be as robust as possible and avoid such scenarios, the module supports a special Hard drive mode.

In the hard drive mode all the intermediate data is stored on the hard drive instead of in the RAM, thus substantially decreasing the memory consumption.

Additional Fatigue Test and Analysis Resources

FAQ

What is fatigue?

Fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic or repeated loading.

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What is load?

The load is defined as any physical quantity that reflects the excitation or the behavior of a system or component over time.

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What is a half-cycle and what a full-cycle?

A half-cycle is a pair of two consecutive extrema in the load signal, going from a minimum to a maximum or vice versa. A full-cycle is a cycle consisting of two consecutive half-cycles.

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What is the durability?

Durability is the capacity of an item to survive its intended use for a suitable long period of time. Good durability leads to good quality, company profitability and customer satisfaction.

What is the SN curve?

S-N curves represent statistical models that characterize the material performance. S-N curve is defined as a graph of the cyclic stress against the logarithmic scale of cycles to failure.

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