Material property definition

@MATERIAL_PROPERTY_DEFINITION {
@MATERIAL_PROPERTY_NAME {MatPropName} {
@MATERIAL_PROPERTY_TYPE {MatType}
@MATERIAL_DENSITY {ρ}
@STIFFNESS_PROPERTIES {
@YOUNG'S_MODULUS {E1, E2, E3}
@POISSON'S_RATIO {ν12, ν13, ν23}
@SHEAR_MODULUS {G12, G13, G23}
}
@VISCOSITY_PROPERTIES {
@BRANCH_PROPERTIES {
@RELAXATION_TIME {τ}
@DAMPING_COEFFICIENT {μ}
@BULK_VISCOSITY {ξ}
@SHEAR_VISCOSITY {η}
}
}
@STRENGTH_PROPERTIES {
@FAILURE_CRITERION_TYPE {FacType}
@ALLOWABLE_TENSILE_STRESS {σ1aT, σ2aT, σ3aT}
@ALLOWABLE_COMPRESSIVE_STRESS {σ1aC, σ2aC, σ3aC}
@ALLOWABLE_SHEAR_STRESS {τ12a, τ13a, τ23a}
}
@COMMENTS {CommentText}
}
}

Introduction

Figure 1. Orthotropic, transversely isotropic and isotropic materials.

The mass, stiffness, viscous, and strength properties of materials are defined in this section. Three data sections are used to define all the properties.

  1. The first section defines the stiffness characteristics of the material. Young's moduli, Poisson's ratios, and shear moduli are defined. Materials to be defined are assumed to be linear elastic materials and are further subdivided into three distinct types: isotropic, orthotropic, and transversely isotropic.
  2. Optionally, the first section defines the viscous characteristics of the material. Bulk, axial, and shear viscosities are defined.
  3. The last section defines the strength characteristics of the material. Allowable tensile, compressive, and shear stresses are defined together with a failure criterion.

Material properties are used for the characterization of lay-ups, which characterize the physical properties of plates and shells in NormalBuilder, and the physical properties of beams SectionBuilder.

In each case, a material basis, E = (e1, e2, e3), is defined that reflects the possible existence of various planes of symmetry and/or orthotropy, as illustrated in fig. 1.

Notes

  1. Material mass properties are defined by a single parameter, the material density, ρ.
  2. It is possible to attach comments to the definition of the object; these comments have no effect on its definition.

Stiffness properties

Material stiffness properties involve Young's moduli, shear moduli, and Poisson's ratios. The flag MatType can take one the following three values.

Viscosity properties

Material viscosity properties involve time constants, bulk, shear, and axial viscosity coefficients. Viscoelasticity of the material is modeled based on a generalized Maxwell model. Each branch of the model is associated with a relaxation time, τ. The stiffness properties of each branch are defined in two mutually exclusive manners.

  1. If the damping coefficient, μ, is defined, the stiffness matrix of the branch is D = μC, where C is the material stiffness matrix.
  2. If no damping coefficient is defined, the bulk and shear moduli of the material must be defined for the branch. An isotropic viscous material has identical properties in all directions. For these materials, the following two stiffness properties are required.
    1. Bulk modulus: κ.
    2. Shear modulus: G.

Failure criterion

To predict strength, a failure criterion is selected by means of parameter FacType, which can take the following values.

Allowable stresses

The failure criteria depend on a number of material strength parameters. In general, up to nine different parameters can be defined.

  1. ALLOWABLE_TENSILE_STRESS: σ1aT, σ2aT, and σ3aT, along unit vectors e1, e2 and e3, respectively.
  2. ALLOWABLE_COMPRESSIVE_STRESS: σ1aC, σ2aC, and σ3aC, along unit vectors e1, e2 and e3, respectively.
  3. ALLOWABLE_SHEAR_STRESS: τ12a, τ13a, and τ23a.

For different types of materials, the required number of strength properties is different.

  1. If MatType = ORTHOTROPIC, all nine strength properties are required.
    • Tension strength: σ1aT, σ2aT, and σ3aT.
    • Compression strength: σ1aC, σ2aC, and σ3aC.
    • Shear strength: τ12a, τ13a, and τ23a.
  2. If MatType = TRANSVERSELY_ISOTROPIC, σ3aT = σ2aT, σ3aC = σ2aC, and τ13a = τ12a: in view of the isotropy in the (e2, e3) plane, the subscripts (.)2 and (.)3 can be interchanged. Furthermore, the isotropy of plane (e2, e3) implies τ23a = σ2aT/√3. The following five properties are required.
    • Tension strength: σ1aT and σ2aT.
    • Compression strength: σ1aC and σ2aC.
    • Shear strength: τ12a.
  3. If MatType = ISOTROPIC, σ1aT = σ2aT = σ3aT = σa, σ1aC = σ2aC = σ3aC = σa and τ12a = τ13a = τ23a = σa/ √ 3. A single property is required,
    • Tension strength: σa.