金屬損傷失效的模擬

1.  總體介紹

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.

金屬材料的損傷演化需要具備下面三種條件：

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.（金屬的斷裂包括延性損傷和剪切損傷）

Damage initiation criteria for the necking instability of sheet metal（金屬薄板的頸縮不穩定性）. 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.

損傷起始：

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.（可以同時指定多種損傷起始準則） 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.（如果不指定損傷演化階段，材料響應將不受任何損傷起始的影響，而相應的損傷輸出只是為了輸出查看）

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

損傷演化：

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.（總體損傷變量捕獲所有激活失效機制的聯合效應，它的計算時根據單個損傷變量）

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.（單元完全失效刪除前，其熱屬性不受影響，但是單元失效刪除后，其熱屬性也刪除）

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).（薄板金屬的頸縮不穩定性模擬使用FLD, FLSD, MSFLD, and M-K準則，所以二維單元是適用于平面應力單元）

2.    損傷起始準則介紹

Damage initiation for ductile metals（損傷起始準則）

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). （顯示分析中幾種準則可以分別于其他塑性準則聯合使用）

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、長大和合并而導致的韌性斷裂） and shear fracture due to shear band localization（由于剪切帶局部化而導致的剪切斷裂）. 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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------具體每個損傷起始準則的解釋及具體設置在此不再贅述（見幫助文檔）------

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).

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:

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.  損傷演化準則介紹

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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------具體每個損傷演化準則的解釋及具體設置在此不再贅述（見幫助文檔）------

最大剛度退化的設置（僅支持inp修改）：

*SECTION COOLS, MAX DEGRADATION=

單元是否移除設置（僅支持inp修改）：

*SECTION COOLS, ELEMENT DELETION=

收斂性困難的解決辦法：

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:

例子：

a) 附上幫助文檔的一個例子---薄壁鋁擠壓損傷（軸向壓潰）：

axialcrushing_alextrusion.txt

直接將txt后綴改為inp即可

b) 附上自己做的一個例子---小球有角度沖擊靶材：

cae.rar

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