Materials are considered to be isotropic if the properties are not dependent on the direction. The isotropic material properties are listed below. Depending on the element type, analysis type and loads, not all the material properties may be required.
The mass density of a material is its mass per unit volume. Mass density is applicable to all linear elements. This property is required in all linear analyses involving gravity or acceleration loads. This property is also required for natural frequency (modal) and all modal superposition analyses.
The modulus of elasticity is the slope of the stress versus strain curve of a material until the proportionality limit, or yield stress. It is also referred to as the Young's modulus of a material. The modulus of elasticity is applicable to all linear elements and is required for all linear analyses.
Poisson's ratio is found by taking the negative lateral strain and dividing it by the axial strain for an axially loaded member. Typical values for Poisson's ratio range from 0.0 to 0.5. This is applicable for all linear element types except for trusses. This is required for all linear analysis types.
The shear modulus of elasticity is the slope of the shear stress versus shear strain of a material until the proportionality limit. This is also referred to as the modulus of rigidity. This is applicable to all linear element types except trusses and beams. If zero is entered, the software uses the equation to calculate shear modulus of elasticity, where E is the modulus of elasticity and n is the Poisson's ratio.
The yield strength of a material is the point on the stress versus strain curve where the material initially starts to go into plastic strain. After yielding once, the new yield stress depends on the type of hardening and the loading history.
The Yield Strength is used with beam elements in linear stress for code checking as a parameter for the allowable stress. Otherwise, the yield stress has no effect on the results in a linear analysis. That is, plasticity effects are not included.