# Material Properties in Simulation

 Elastic Modulus Elastic Modulus in the global X, Y, and Z directions. For a linear elastic material, the elastic modulus in a certain direction is defined as the stress value in that direction that causes a unit strain in the same direction. Also, it is equal to the ratio between the stress and the associated strain in that direction. Elastic Moduli are used in static, nonlinear, frequency, dynamic, and buckling analyses. The modulus of elasticity was first introduced by Young and is often called Young’s Modulus. Shear Modulus The shear modulus, also called modulus of rigidity, is the ratio between the shearing stress in a plane divided by the associated shearing strain. Shear Moduli are used in static, nonlinear, frequency, dynamic and buckling analyses. Poisson’s Ratio Extension of the material in the longitudinal direction is accompanied by contractions in the lateral directions. If a body is subjected to a tensile stress in the X-direction, then Poisson’s Ratio is defined as the ratio of lateral contraction in the Y-direction divided by the longitudinal strain in the X-direction. Poisson’s ratios are dimensionless quantities. For isotropic materials, the Poisson’s ratios in all planes are equal. Poisson ratios are used in static, nonlinear, frequency, dynamic and buckling analyses. Coefficient of Thermal Expansion The Coefficient of Thermal Expansion is defined as the change in length per unit length per one degree change in temperature (change in normal strain per unit temperature).You specify the average coefficient of thermal expansion that is based on the reference temperature ( T0) associated with the stress-free condition: Coefficients of thermal expansion are used in static, frequency, and buckling analyses if thermal loading is used. Frequency analysis uses this property only if you consider the effect of loads on the frequencies (in-plane loading). Thermal Conductivity The Thermal Conductivity indicates the effectiveness of a material in transferring heat energy by conduction. It is defined as the rate of heat transfer through a unit thickness of the material per unit temperature difference. The units of thermal conductivity are Btu/in sec oF in the English system and W/m K in the SI system. Thermal conductivity is used in steady state and transient thermal analyses. Density The Density is mass per unit volume. Density units are lb/in3 in the English system, and kg/m3 in the SI system. Density is used in static, nonlinear, frequency, dynamic, buckling, and thermal analyses. Static and buckling analyses use this property only if you define body forces (gravity and/or centrifugal). Specific Heat The Specific Heat of a material is the quantity of heat needed to raise the temperature of a unit mass of the material by one degree of temperature. The units of specific heat are Btu in/lbf oF in English system and J/kg K in the SI system. This property is used in transient thermal analysis only. Material Damping Ratio The material damping ratio allows the definition of damping as a material property. This property is used in dynamic analysis to calculate equivalent modal damping ratios.