김경종
4.9 KiB
Input File Usage:
Use the following option to delete failed elements from the mesh (default):
*SECTION CONTROLS, ELEMENT DELETION=YES
Use the following option to keep failed elements in the mesh computations:
*SECTION CONTROLS, ELEMENT DELETION=NO
Difficulties associated with element removal in Abaqus/Standard
When elements are removed from the model, their nodes remain in the model even if they are not attached to any active elements. When the solution progresses, these nodes might undergo non-physical displacements in Abaqus/Standard. In addition, applying a point load to a node that is not attached to an active element will cause convergence difficulties since there is no stiffness to resist the load. It is the responsibility of the user to prevent such situations.
Elements
Damage evolution for ductile materials can be defined for any element that can be used with the damage initiation criteria for a low-cycle fatigue analysis in Abaqus/Standard (“Damage initiation for ductile materials in low-cycle fatigue,” Section 24.4.2).
Output
In addition to the standard output identifiers available in Abaqus/Standard (“Abaqus/Standard output variable identifiers,” Section 4.2.1), the following variables have special meaning when damage evolution is specified:
STATUS
Status of element (the status of an element is 1.0 if the element is active, 0.0 if the element is not).
SDEG
Overall scalar stiffness degradation, D.
25. Hydrodynamic Properties
Overview 25.1
Equations of state 25.2
25.1 Overview
• “Hydrodynamic behavior: overview,” Section 25.1.1
25.1.1 HYDRODYNAMIC BEHAVIOR: OVERVIEW
The material library in Abaqus/Explicit includes several equation of state models to describe the hydrodynamic behavior of materials. An equation of state is a constitutive equation that defines the pressure as a function of the density and the internal energy (“Equation of state,” Section 25.2.1). The following equations of state are supported in Abaqus/Explicit:
• Mie-Grüneisen equation of state: The Mie-Grüneisen equation of state (“Mie-Grüneisen equations of state” in “Equation of state,” Section 25.2.1) is used to model materials at high pressure. It is linear in energy and assumes a linear relationship between the shock velocity and the particle velocity.
• Tabulated equation of state: The tabulated equation of state (“Tabulated equation of state” in “Equation of state,” Section 25.2.1) is used to model the hydrodynamic response of materials that exhibit sharp transitions in the pressure-density relationship, such as those induced by phase transformations. It is linear in energy.
• P – α equation of state: The equation of state (“P – α equation of state” in “Equation of state,” Section 25.2.1) is designed for modeling the compaction of ductile porous materials. The constitutive model captures the irreversible compaction behavior at low stresses and predicts the correct thermodynamic behavior at high pressures for the fully compacted solid material. It is used in combination with either the Mie-Grüneisen equation of state or the tabulated equation of state to describe the solid phase.
• JWL high explosive equation of state: The Jones-Wilkins-Lee (or JWL) equation of state (“JWL high explosive equation of state” in “Equation of state,” Section 25.2.1) models the pressure generated by the release of chemical energy in an explosive. This model is implemented in a form referred to as a programmed burn, which means that the reaction and initiation of the explosive is not determined by shock in the material. Instead, the initiation time is determined by a geometric construction using the detonation wave speed and the distance of the material point from the detonation points.
• Ideal gas equation of state: The ideal gas equation of state (“Ideal gas equation of state” in “Equation of state,” Section 25.2.1) is an idealization to real gas behavior and can be used to model any gases approximately under appropriate conditions (e.g., low pressure and high temperature).
Deviatoric behavior
The material modeled by an equation of state may have no deviatoric strength or may have either isotropic elastic or viscous (both Newtonian and non-Newtonian) deviatoric behavior (“Deviatoric behavior” in “Equation of state,” Section 25.2.1). The elastic model can be used by itself or in conjunction with the Mises, the Johnson-Cook, or the extended Drucker-Prager plasticity models to model hydrodynamic materials with elastic-plastic deviatoric behavior.
Thermal strain
Thermal expansion cannot be introduced for any of the equation of state models.
25.2 Equations of state
• “Equation of state,” Section 25.2.1