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Fatigue Material

Author:

Patxi Uriz

Contact Information:

Exponent - Failure Analysis Associates

149 Commonwealth Drive Menlo Park, CA 94025

patxi@exponent.com

The fatigue material uses a modified rainflow cycle counting algorithm to accumulate damage in a material using Miner's Rule. Element stress/strain relationships become zero when fatigue life is exhausted.

uniaxialMaterial Fatigue $matTag $tag <-E0 $E0> <-m $m>
<-min $min> <-max $max>

This material model accounts for the effects of low cycle fatigue. A modified rainflow cycle counter has been implemented to track strain amplitudes. This cycle counter is used in concert with a linear strain accumulation model (i.e. Miner's Rule), based on Coffin-Manson log-log relationships describing low cycle fatigue failure. This material "wraps" around another material and does not influence the stress-strain (or force-deformation) relationship of the parent material.

Once the Fatigue material model reaches a damage level of 1.0, the force (or stress) of the parent material becomes zero (1.0x10-8 times the call to the material). If failure is triggered in compression, the material stress is dropped at the next zero-force crossing (i.e. compression force never "drops" to zero).

The Fatigue material assumes that each point is the last point of the history, and tracks damage with this assumption. If failure is not triggered, this pseudo-peak is discarded.

The material also has the ability to trigger failure based on a maximum or minimum strain (i.e. not related to fatigue). The default for these values is set to very large numbers.

The default values are calibrated parameters from low cycle fatigue tests of European steel sections Ballio and Castiglioni (1995), for more information about how material was calibrated, the user is directed to Uriz (2005).

$matTag

unique material object integer tag

$tag

Unique material object integer tag for the material that is being "wrapped"

$E0

Value of strain at which one cycle will cause failure (default 0.191)

$m

Slope of Coffin-Manson curve in log-log space (default -0.458)

$min

Global minimum value for strain or deformation (default -1e16)

$max

Global maximum value for strain or deformation (default 1e16)

Example Command:

Example command: uniaxialMaterial Fatigue 2 1 -E0 0.191 -m -0.458

where 2 is the Fatigue material tag, and 1 is the material that is being wrapped, the -E0 and -m values I have listed here are the default values.

Valid recorder objects for the material are 'stress','tangent', 'strain', 'stressStrain', and 'damage'. The stress, strain, and tangent recorder options must be available in the material that you are wrapping.

In This Section

FatigueMaterialExample.tcl

References

See Also

-- Contributed Uniaxial Materials

BARSLIP Material

Bond_SP01 - - Strain Penetration Model for Fully Anchored Steel Reinforcing Bars

Concrete04 Material -- Popovics Concrete Material

Limit State Material

PINCHING4 Material

PyTzQz Uniaxial Materials

Reinforcing Steel Material