IDAC Materials Properties Guide.

Introduction

This document describes how the material properties are defined. Please keep an eye out for product and documentation updates on our website.

Multilinear Isotropic Hardening (ML)

Multilinear isotropic hardening data is in the form of a graph of Stress vs. Plastic Strain, starting from the yield stress. From this, the stress-strain behaviour of the material after its yield point can be found.

The data is input as true stress vs. logarithmic true plastic strain, to account for changes in cross-sectional area of the component during. This is different to the traditional engineering stress vs. engineering strain that is commonly found.

This material model is often used in large strain analyses. Do not use this model for cyclic or highly non-proportional load histories in small-strain analyses.

All the data is taken from test specimens under longitudinal, tensile stresses only, except for ceramics, where compressive tests were performed. The actual stress-strain behaviour of a component may vary from this data due to different geometries of material and the particular treatment of the material. The data becomes less accurate after the point of necking, due to the inconsistent behaviour of most metals under necking, and so analyses of very large strains past this point may be less geniuine.

Uniaxial Test (UT)
Uniaxial test data is in the form of a graph of Stress vs. Strain. From this, the stress-strain behaviour of elastomers, undergoing hyperelasticity, can be found. Hyperelasticity can be used to analyze elastomers that undergo large strains and displacements, with small volume changes (nearly incompressible materials). This data can be used as data input to a material curve fit, to calculate hyperelasticity coefficients.

Temperature-dependent Young’s Modulus (YM)
Temperature-dependent Young’s Modulus data is in the form of Young’s Modulus vs. Temperature. From this, the behaviour of the Young’s Modulus with varying temperature can be found.

Temperature-dependent Poisson’s Ratio (PR)
Temperature-dependent Poisson’s Ratio data is in the form of Poisson’s Ratio vs. Temperature. From this, the behaviour of the Poisson’s Ratio with varying temperature can be found.

Temperature-dependent Thermal Expansion (TE)
Temperature-dependent Thermal Expansion data is in the form of Thermal Expansion vs. Temperature. From this, the behaviour of the thermal expansion coefficient with varying temperature can be found.

Temperature-dependent Thermal Conductivity (TC)
Temperature-dependent thermal conductivity data is in the form of Thermal Conductivity vs. Temperature. From this, the behaviour of the thermal conductivity with varying temperature can be found.

Alternating Stress (AS)
Alternating stress data is in the form of a graph of Cyclic Stress vs. Cycles to Failure (an SN curve). From this, the fatigue life of the material can be found, i.e. the number of cycles which the material can undergo before it will fail due to fatigue.
Some materials have more than one curve, which corresponds to different r-ratios. The r-ratio is defined as the ratio of the second loading to the first: r = L 2 / L 1. Typical experimental r-ratios are -1 (fully reversed), 0 (zero-based), and 0.1 (to ensure that a tensile stress always exists in the part).

For example:

Cyclic Stress = 600 MPa, r = 0
Cyclic Stress = 500 MPa, r = -1

 

The relevant r-ratio must be chosen, depending on the particular load case in the analysis.

All the data is taken from test specimens under longitudinal stresses only. The actual fatigue life of a component may vary from this data due to different geometries of material, the particular treatment of the material, and the statistical nature of fatigue life analysis.

For further information contact Simon Smith on Tel: +44(870) 160 5900 or email: ssmith@idac.co.uk