Determining material properties

Uniform material law estimation of fatigue properties

For steel alloys and for aluminum and titanium alloys, extensive statistical studies have been conducted that show a correlation between the ultimate tensile strength and the fatigue properties, σʹf, εʹf, b, and c. In Specialist Durability, when you create durability material properties, the uniform material law (UML) relations can estimate the fatigue properties based on a statistical study of Bäumel Jr. and Seeger.

UML for steel

The UML estimation of these properties requires input of the elastic modulus (E) and tensile strength (Smax) of the material in MPa, and whether the material is a steel alloy or an aluminum or titanium alloy.

For steel alloys, the compressive strength Smin = 3Smax and the values are estimated based on fully reversed (R = -1) data.

An intermediate parameter, ψ, is defined based on the ratio of the tensile strength to the modulus of elasticity (Young's modulus), as

ψ = 1	for	and
	for

The following values are assigned to the material properties:

Manson-Coffin-Morrow parameters (steel alloy)
σʹf	1.5 Smax
εʹf	0.59 ψ
b	-0.087
c	-0.58

Ramberg-Osgood parameters (steel alloy)
Kʹ	1.65 Smax
nʹ	0.15

Additionally, the strain value at the endurance limit, εE, is determined by

Endurance limit (steel alloy)
εE

The stress at the endurance, σE, is found from the strain at the endurance limit and the Ramberg-Osgood relation for the cyclic stress-strain curve, and the number of cycles to failure at the endurance limit is calculated by the strain-life equation.

UML for aluminum and titanium alloys

For aluminum and titanium alloys, the following relations are used.

Manson-Coffin-Morrow parameters (aluminum or titanium alloy)
σʹf	1.67 Smax
εʹf	0.35
b	-0.095
c	-0.69

Ramberg-Osgood parameters (aluminum or titanium alloy)
Kʹ	1.61 · Smax
nʹ	0.11

Endurance limit (aluminum or titanium alloy)
εE

And again, stress at the endurance, σE, is found from the strain at the endurance limit and the Ramberg-Osgood relation for the cyclic stress-strain curve, and the number of cycles to failure at the endurance limit is calculated by the strain-life equation.

UML for grey cast

Similar examinations have been conducted on grey cast materials.

Manson-Coffin-Morrow parameters (grey cast)
σʹf
εʹf
b	-0.103
c	-0.515

Ramberg-Osgood parameters (grey cast)
Kʹ
nʹ	0.2

Endurance limit (grey cast)
σE	0.26 Smax

Learn more

Local stress-strain behavior

Constant amplitude life curves

Endurance limit and static failure

Mean stress and damage parameters

Axial versus torsion tests

Notch analysis

The strain-life analysis in Specialist Durability

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Determining material properties, Simcenter 3D 2021.1 Series

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