Function
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Specify a plastic material model for material nonlinear analysis.
Plastic Material Models
Tresca & Von Mises
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Appropriate for ductile metals, which exhibit Plastic Incompressibility.
Mohr-Coulomb, Drucker-Prager -
Appropriate for brittle materials such as concrete, rock and soils, which exhibit the behavior of volumetric plastic straining
Masonry
- Appropriate for brittle materials such as concrete, rock and soils, which exhibit the behavior of volumetric plastic straining.
Masonry material model is applicable to plate, 4-node solid, 6-node solid, and 8-node solid elements.
Call
From the main menu, select [Properties] tab > [Material Properties] group > [Plastic Material]
Input
Plastic Material dialog box
Add/Modify Plastic Material dialog box
Name
Name of plastic model
Model
Type of plastic model
Tresca : This yield criterion is suitable for ductile materials such as metals, which exhibit Plastic Incompressibility.
Von Mises : This yield criterion is based on distortional strain energy and is the most widely used yield criterion for metallic materials.
Mohr-Coulomb : This yield criterion is a generalization of the Coulomb's friction rule and is suitable for materials such as concrete, rock and soils, which exhibit volumetric plastic deformations.
Drucker-Prager : This criterion is a smooth approximation of the Mohr- Coulomb criterion and is an expansion of the von Mises criterion. This Drucker-Prager criterion is suitable for materials such as concrete, rock and soils, which exhibit volumetric plastic deformations.
For additional details on the above 4 plastic models, refer to "Material Nonlinear Analysis" in the analysis manual.
Masonry : This model is suitable for the elastic analysis finding the crack positions using masonry materials such as bricks, mortar joints, etc.
Orthotropic material properties are assumed for modeling a masonry structure. So it is important to define the Material Coordinate System properly.
When Global Coord is selected for the Material Coordinate System, the Global Y axis corresponds to the gravitational direction of the model, and the Global X axis corresponds to the horizontal direction of the model. However, if the Element Local Coord is selected as the Material Coordinate System, the local y axis of the element should correspond to the gravitational direction of the model, and the local x axis of the element should correspond to the horizontal direction of the model.
Therefore, for masonry models where the local axes of elements are not oriented in the same direction, it is better to select Global Coord as the material coordinate system and model the masonry structure on the global X-Y plane. When the masonry model is not on the global X-Y plane, select Element Local Coord as the Material Coordinate System and set the local y axis of the elements in the gravitational direction
Concrete-Damage : The model is a continuum, plasticity-based, damage model for concrete. It assumes that the main two failure mechanisms are tensile cracking and compressive crushing of the concrete material.
Stress resultant beam model
• Stress resultant beam model is introduced to apply beam elements in the material nonlinear analysis. Thus, not only plate elements but also beam elements can be used for the analysis in which both geometric nonlinear effect and material nonlinear effect need to be taken into account. This feature would be useful for the nonlinear stability analysis of U-frame steel bridges which are often simulated using both beam elements and plate elements to represent cross beams and main girders, respectively
• The von-Mises yield criterion is used as the basis of the model.
• The stress-strain curve is linear elastic/perfectly plastic (i.e. zero hardening).
• Plastic axial force and plastic bending moment about major axis and minor axis are only calculated.
• The coupled effect between axial force and moment is not considered.
• Non-composite steel section is only supported. (Channel, I-Section, T-Section, Box, Pipe, Rectangle, Round section only.)
Plastic Data
When Tresca, von Mises are selected
Initial Uniaxial Yield Stress : The yield stress obtained from uniaxial tension test.
When Mohr-Coulomb, Drucker-Prager are selected, specify Initial Cohesion and Initial Friction Angle.
Initial Cohesion
When the normal stress is '0', the yield stress due to shear stress alone is equal.
Initial Friction Angle
For plastic material models such as Mohr-Coulomb or Drucker-Prager, the input for the initial friction angle is allowed within the range of "0 < Initial Friction Angle < 90". If a value outside this range is entered, the initial friction angle will automatically be initialized to the default value of 30.
Hardening
As a material yields, hardening defines the change of yield surface with plastic straining, which is classified into the following three types.
Isotropic : Isotropic hardening
Kinematic : Kinematic hardening
Mixed : Mixed type hardening
For additional details on the above 3 hardening criteria, refer to "Material Nonlinear Analysis" in analysis manual.
Back Stress Coefficient : Represents the extent of Hardening
'1' for Isotropic Hardening
'0' for Kinematic Hardening
between '0~1' for Mixed Hardening
Total increment of Plastic can be expressed by Isotropic Hardening and Kinemetic Hardening as follows:
In this case, M here referred to as Back Stress Coefficient ranges between 0 and 1.
Hardening Coefficient
Tangent stiffness of material after yielding. Generally, after the primary yield, the slope of the initial tangent decreases or reaches a constant value.
For a plastic material (in the case of von Mises), the hardening coefficient cannot exceed the elastic modulus of the material.
When Masonry is selected
Brick Material
Young's Modulus
Poisson's Ratio
Tensile Strength, ft
Stiffness Reduction Factor
Bed Joint Material
Young's Modulus
Poisson's Ratio
Tensile Strength, ft
Stiffness Reduction Factor
Head Joint Material
Young's Modulus
Poisson's Ratio
Tensile Strength, ft
Stiffness Reduction Factor
Geometry
Brick Length, L
Brick Height, H
Thickness of Bed, Tb
Thickness of Head, Th