17.2.2 No compression or no tension

**Products: **ABAQUS/Standard ABAQUS/CAE

**Warning:
**Except when used with truss or beam elements, ABAQUS/Standard does not form an exact material stiffness for this option. Therefore, the convergence can sometimes be slow.

The no compression and no tension elasticity models:

are used to modify the linear elasticity of the material so that compressive stress or tensile stress cannot be generated; and

can be used only in conjunction with an elasticity definition.

Defining the modified elastic behavior

The modified elastic behavior is obtained by first solving for the principal stresses assuming linear elasticity and then setting the appropriate principal stress values to zero. The associated stiffness matrix components will also be set to zero. These models are not history dependent: the directions in which the principal stresses are set to zero are recalculated at every iteration.

Input File Usage: | Use one of the following options: |

*NO COMPRESSION *NO TENSION |

ABAQUS/CAE Usage: | Property module: material editor: No compression or No tension |

The no compression effect for a one-dimensional stress case such as a truss or a layer of a beam in a plane is illustrated in Figure 17.2.2–1. No compression and no tension definitions modify only the elastic response of the material. The overall behavior in a one-dimensional no compression elasticity model where the member is pulled, pushed, and then pulled again is as indicated in Figure 17.2.2–2.

Stability

Using no compression or no tension elasticity can make a model unstable: convergence difficulties may occur. Sometimes these difficulties can be overcome by overlaying each element that uses the no compression (or no tension) model with another element that uses a small value of Young's modulus (small in comparison with the Young's modulus of the element using modified elasticity). This technique creates a small “artificial” stiffness, which can stabilize the model.

Material options

No compression and no tension definitions can be used only in conjunction with an elasticity definition. The models can be used when the material behavior includes plasticity. See “Combining material behaviors,” Section 16.1.3, for more details.