金属损伤失效的模拟
1. 总体介绍
Abaqus/Standard and Abaqus/Explicit offer a general capability for predicting the onset of failure and a capability for modeling progressive damage and failure of ductile metals.
金属材料的损伤演化需要具备下面三种条件:
1 the undamaged elastic-plastic response of the material
2 a damage initiation criterion
3 a damage evolution response, including a choice of element removal
Damage initiation criteria for the fracture of metals, including ductile and shear criteria.(金属的断裂包括延性损伤和剪切损伤)
Damage initiation criteria for the necking instability of sheet metal(金属薄板的颈缩不稳定性). These include forming limit diagrams (FLD, FLSD, and MSFLD) intended to assess the formability of sheet metal and the Marciniak-Kuczynski (M-K) criterion (available only in Abaqus/Explicit) to numerically predict necking instability in sheet metal taking into account the deformation history.
损伤起始:
Each damage initiation criterion has an associated output variable to indicate whether the criterion has been met during the analysis. A value of 1.0 or higher indicates that the initiation criterion has been met.
More than one damage initiation criterion can be specified for a given material.(可以同时指定多种损伤起始准则) If multiple damage initiation criteria are specified for the same material, they are treated independently. Once a particular initiation criterion is satisfied, the material stiffness is degraded according to the specified damage evolution law for that criterion; in the absence of a damage evolution law, however, the material stiffness is not degraded.
A failure mechanism for which no damage evolution response is specified is said to be inactive. Abaqus will evaluate the initiation criterion for an inactive mechanism for output purposes only, but the mechanism will have no effect on the material response.(如果不指定损伤演化阶段,材料响应将不受任何损伤起始的影响,而相应的损伤输出只是为了输出查看)
Use the following option to define each damage initiation criterion (repeat as needed to define multiple criteria):
*DAMAGE INITIATION, CRITERION=criterion 1
*DAMAGE INITIATION, CRITERION=criterion 2
*DAMAGE INITIATION, CRITERION=criterion 3
Property module: material editor: MechanicalDamage for Ductile Metalscriterion
损伤演化:
For damage in ductile metals, Abaqus assumes that the degradation of the stiffness associated with each active failure mechanism can be modeled using a scalar damage variable, (), where represents the set of active mechanisms. At any given time during the analysis the stress tensor in the material is given by the scalar damage equation
where D is the overall damage variable and is the effective (or undamaged) stress tensor computed in the current increment. are the stresses that would exist in the material in the absence of damage. The material has lost its load-carrying capacity when . By default, an element is removed from the mesh if all of the section points at any one integration location have lost their load-carrying capacity.
The overall damage variable, D, captures the combined effect of all active mechanisms and is computed in terms of the individual damage variables, , according to a user-specified rule.(总体损伤变量捕获所有激活失效机制的联合效应,它的计算时根据单个损伤变量)
Use the following option immediately after the corresponding *DAMAGE INITIATION option to specify the damage evolution behavior:
*DAMAGE EVOLUTION
Property module: material editor: MechanicalDamage for Ductile Metalscriterion: SuboptionsDamage Evolution
For coupled temperature-displacement elements the thermal properties of the material are not affected by the progressive damage of the material stiffness until the condition for element deletion is reached; at this point the thermal contribution of the element is also removed.(单元完全失效删除前,其热属性不受影响,但是单元失效删除后,其热属性也删除)
The damage initiation criteria for sheet metal necking instability (FLD, FLSD, MSFLD, and M-K) are available only for elements that include mechanical behavior and use a plane stress formulation (i.e., plane stress, shell, continuum shell, and membrane elements).(薄板金属的颈缩不稳定性模拟使用FLD, FLSD, MSFLD, and M-K准则,所以二维单元是适用于平面应力单元)
2. 损伤起始准则介绍
Damage initiation for ductile metals(损伤起始准则)
includes ductile, shear, forming limit diagram (FLD), forming limit stress diagram (FLSD) and Müschenborn-Sonne forming limit diagram (MSFLD) criteria for damage initiation;
includes in Abaqus/Explicit the Marciniak-Kuczynski (M-K) and Johnson-Cook criteria for damage initiation;
can be used in Abaqus/Explicit in conjunction with Mises and Johnson-Cook plasticity (ductile, shear, FLD, FLSD, MSFLD, Johnson-Cook, and MK criteria)
and in conjunction with Hill and Drucker-Prager plasticity (ductile, shear, FLD, FLSD, MSFLD, and Johnson-Cook criteria). (显示分析中几种准则可以分别于其他塑性准则联合使用)
Two main mechanisms can cause the fracture of a ductile metal: ductile fracture due to the nucleation, growth, and coalescence of voids;(由于孔洞的形核、长大和合并而导致的韧性断裂) and shear fracture due to shear band localization(由于剪切带局部化而导致的剪切断裂). Based on phenomenological observations, these two mechanisms call for different forms of the criteria for the onset of damage (Hooputra et al., 2004).
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------具体每个损伤起始准则的解释及具体设置在此不再赘述(见帮助文档)------
Initial conditions
Optionally, you can specify the initial work hardened state of the material by providing the initial equivalent plastic strain values (see “Defining initial values of state variables for plastic hardening” in “Initial conditions in Abaqus/Standard and Abaqus/Explicit,” Section 34.2.1) and, if residual stresses are also present, the initial stress values (see “Defining initial stresses” in “Initial conditions in Abaqus/Standard and Abaqus/Explicit,” Section 34.2.1). Abaqus uses this information to initialize the values of the ductile and shear damage initiation criteria, and , assuming constant values of stress triaxiality and shear shear ratio (linear stress path).
Input File Usage: |
Use the following options to specify that material hardening and residual stresses have occurred prior to the current analysis: |
*INITIAL CONDITIONS, TYPE=HARDENING *INITIAL CONDITIONS, TYPE=STRESS |
Abaqus/CAE Usage: |
Use the following options to specify that material hardening and residual stresses have occurred prior to the current analysis: |
Load module: Create Predefined Field: Step: Initial, choose Mechanical for the Category and Hardening and Stress for the Types for Selected Step |
Output
In addition to the standard output identifiers available in Abaqus (“Output variables,” Section 4.2), the following variables have special meaning when a damage initiation criterion is specified:
ERPRATIO |
Ratio of principal strain rates, , used for the MSFLD damage initiation criterion. |
SHRRATIO |
Shear stress ratio, , used for the evaluation of the shear damage initiation criterion. |
TRIAX |
Stress triaxiality, (available in Abaqus/Standard only in conjunction with damage initiation). |
DMICRT |
All damage initiation criteria components listed below. |
DUCTCRT |
Ductile damage initiation criterion, . |
JCCRT |
Johnson-Cook damage initiation criterion (available only in Abaqus/Explicit). |
SHRCRT |
Shear damage initiation criterion, . |
FLDCRT |
Maximum value of the FLD damage initiation criterion, , during the analysis. |
FLSDCRT |
Maximum value of the FLSD damage initiation criterion, , during the analysis. |
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MSFLDCRT |
Maximum value of the MSFLD damage initiation criterion, , during the analysis. |
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MKCRT |
Marciniak-Kuczynski damage initiation criterion (available only in Abaqus/Explicit), . |
A value of 1 or greater for output variables associated with a damage initiation criterion indicates that the criterion has been met. Abaqus will limit the maximum value of the output variable to 1 if a damage evolution law has been prescribed for that criterion (see “Damage evolution and element removal for ductile metals,” Section 24.2.3). However, if no damage evolution is specified, the criterion for damage initiation will continue to be computed beyond the point of damage initiation; in this case the output variable can take values greater than 1, indicating by how much the initiation criterion has been exceeded.
3. 损伤演化准则介绍
uses mesh-independent measures (either plastic displacement or physical energy dissipation) to drive the evolution of damage after damage initiation;
takes into account the combined effect of different damage mechanisms acting simultaneously on the same material and includes options to specify how each mechanism contributes to the overall material degradation; and offers options for what occurs upon failure, including the removal of elements from the mesh.
Figure 24.2.3–1 illustrates the characteristic stress-strain behavior of a material undergoing damage. In the context of an elastic-plastic material with isotropic hardening, the damage manifests itself in two forms: softening of the yield stress and degradation of the elasticity. The solid curve in the figure represents the damaged stress-strain response, while the dashed curve is the response in the absence of damage. As discussed later, the damaged response depends on the element dimensions such that mesh dependency of the results is minimized.
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------具体每个损伤演化准则的解释及具体设置在此不再赘述(见帮助文档)------
最大刚度退化的设置(仅支持inp修改):
*SECTION COOLS, MAX DEGRADATION= |
单元是否移除设置(仅支持inp修改):
*SECTION COOLS, ELEMENT DELETION=
收敛性困难的解决办法:
Viscous regularization in Abaqus/Standard
Unsymmetric equation solver
Output
In addition to the standard output identifiers available in Abaqus (“Abaqus/Standard output variable identifiers,” Section 4.2.1, and “Abaqus/Explicit output variable identifiers,” Section 4.2.2), 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. |
例子:
a) 附上帮助文档的一个例子---薄壁铝挤压损伤(轴向压溃):
直接将txt后缀改为inp即可
b) 附上自己做的一个例子---小球有角度冲击靶材:
ABAQUS断裂模拟收徒 ,快速学会各种ABAQUS断裂模拟方法 **/人(将有机会享有各种插件以及程序,价值**、专门定制视频、全程亲自教学、各种模型调试及解答问题等等,倾囊相教)