Ramberg-Osgood model

The Ramberg-Osgood equation is the most commonly used cyclic stress-strain relation for fatigue analysis. The total strain is the sum of the elastic (1) and plastic (2) strains, which can be written as:

where

• is the stress amplitude.

• is the strain amplitude.

• νe is Poisson's ratio.

• r is the stress biaxial ratio.

• E is the modulus of elasticity.

• n is the strain hardening coefficient material property.

• H is the cyclic strength coefficient material property.

	Ramberg-Osgood model
Power hardening model
Linear model
Monotonic curve
Cyclic yield
Monotonic yield

Using the Ramberg-Osgood relation, the plastic strain can be very significant even in the monotonic linear region which is assumed for the linear FE analysis. In the preceding figure, for a given stress σa the strain from the Ramberg-Osgood curve can be very different from the εa in the linear relation used for FE analysis. Therefore, taking stress history to convert for strain-based life prediction may lead to a very short fatigue life. It is recommended that you use strain history for durability evaluation if you use strain-based fatigue life criteria. These criteria are:

• Smith-Watson-Topper

• Strain life

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Ramberg-Osgood model, Simcenter 3D 2021.1 Series

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