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*Stress/Strain

Purpose

To define generalised stress-strain curves for non-linear materials.

Theory

Refer to Non-Linear Elastic materials for further information on this feature.

Note that this keyword has effectively been superseded by the new non-linear material definition keywords which explicitly distinguish between bending, axial and torsional stiffness. Refer to *MOMENT-CURVATURE, *FORCE-STRAIN and *TORQUE-TWIST for further information.

Keyword Format

A block of lines that defines a stress-strain curve, repeated as often as necessary. The block begins with a line defining the curve name. It is followed by as many lines as necessary to define each point on the curve.

Line defining the curve name:

CURVE=Curve Name

Line defining a point on a curve:

Generalised Stress, Generalised Strain

Each curve must have at least two points defined. This type of stress-strain curve may not be associated with non-linear beam elements which are defined using the rigid riser format for geometric properties specification.

Table Input

Notes

(a)This table is used to define generalised stress-strain curves that define EIyy, EIzz, GJ or EA for a particular set of elements. Generalised stress-strain curves may be assigned to element sets using the Flexible Riser Format.

(b)If the non-linear material curve defines a bending stiffness, then the generalised stress inputs are bending moments and the generalised strains are the corresponding curvature values. If the curve is defining torsional stiffness, then the generalised stress inputs are torsional moments and the generalised strain inputs are the corresponding torsional strains with units [Radian]/[Length]. If the curve is defining axial stiffness, then the generalised stress inputs are axial forces and the generalised strains are the corresponding axial strains.

(c)Use as many lines as you need to completely define a particular stress-strain curve. Simply leave Column 1 blank for second and subsequent lines. For subsequent stress-strain curves, put the curve name in Column 1 and specify the stress-strain data in the same way.

(d)The points defining the non-linear stress-strain curve may be specified in any order. Flexcom subsequently sorts the data pairs into ascending order of strain.

(e)If the strain in an element lies between the stress-strain data points you specify, Flexcom uses linear interpolation to determine the relevant stiffness for the element.

(f)If the strain in the element lies outside the specified range of the stress-strain curve, then Flexcom simply extrapolates from the first or last section of the curve as appropriate.

(g)If none of the specified strain terms have a negative value, the curve is assumed to be symmetrical about the origin (i.e. the behaviour of the element is the same for both positive and negative strains).