ABAQUS [DEFINE : Plasticity in ductile metals]

[Brian Lee]

Figure 8–3 Decomposition of the total strain into elastic and plastic components.

This relationship is written

where

is true plastic strain,

is true total strain,

is true elastic strain,

is true stress, and

is Young's modulus.

Example of converting material test data to ABAQUS input

The stress-strain curve in Figure 8–4 will be used as an example of how to convert the test data defining a material's plastic behavior into the appropriate input format for ABAQUS. The six points shown on the nominal stress-strain curve will be used as the data for the *PLASTIC option.

Figure 8–4 Elastic-plastic material behavior and correspondng ABAQUS input data.

The first step is to use the equations relating the true stress to the nominal stress and strain and the true strain to the nominal strain (shown earlier) to convert the nominal stress and nominal strain to true stress and true strain. Once these values are known, the equation relating the plastic strain to the total and elastic strains (shown earlier) can be used to determine the plastic strains associated with each yield stress value. The converted data are shown in Table 8–1.

Table 8–1 Stress and strain conversions.

Nominal	Nominal	True	True	Plastic
Stress	Strain	Stress	Strain	Strain
200E6	0.00095	200.2E6	0.00095	0.0
240E6	0.025	246E6	0.0247	0.0235
280E6	0.050	294E6	0.0488	0.0474
340E6	0.100	374E6	0.0953	0.0935
380E6	0.150	437E6	0.1398	0.1377
400E6	0.200	480E6	0.1823	0.1800

While there are few differences between the nominal and true values at small strains, there are very significant differences at larger strain values; therefore, it is extremely important to provide the proper stress-strain data to ABAQUS if the strains in the simulation will be large. The format of the input data defining this material behavior is shown in Figure 8–4.