Abaqus/CAE User's Manual 
12.8.5 Defining field variables at a material point
（在一个材料点定义场变量）
In Abaqus/Standard you can introduce dependence on solution variables with user subroutine USDFLD. This subroutine allows you to define field variables at a material point as functions of time, of any of the available material point quantities listed in “Abaqus/Standard output variable identifiers,” Section 4.2.1 of the Abaqus Analysis User's Manual, and of material directions. Material properties defined as functions of these field variables may, thus, be dependent on the solution.
User subroutine USDFLD is called at each point for which the material definition includes a reference to the user subroutine.
（在ABAQUS里面，你能够用子程序USDFLD来求解变量。USDFLD允许你将一个材料点上的
场变量定义为时间函数，能够使用到的材料点在用户使用手册4.2.1节中“abaqus输出变量的标识码”中被提及到。材料的特性被定义作为场变量的函数，因此依赖于求解方法。）
（在每个被定义材料性能的点USDFLD能够被调用）
To include a reference to user subroutine USDFLD in a material definition:
1. From the menu bar in the Edit Material dialog box, select GeneralUser Defined Field.
(For information on displaying the Edit Material dialog box, see “Creating or editing a material,” Section 12.7.1.)
2. 调用子程序的例子Click OK to close the Edit Material dialog box. Alternatively, you can select another material behavior to define from the menus in the Edit Material dialog box (see “Browsing and modifying material behaviors,” Section 12.7.2, for more information).
 
Abaqus/CAE User's Manual 
 （子程序USDFLD在材料中的定义过程可参考下面：
1. 在编辑材料的对话框中，选择General- User Defined Field
2. 点击OK关闭编辑材料的对话框，或者在编辑对话框中选择另外的一个材料特性。）
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Abaqus User Subroutines Reference Manual 
1.1.49 USDFLD
User subroutine to redefine field variables at a material point.
（在一个材料点上使用USDFLD重新定义场变量）
Product: Abaqus/Standard 
References（参考）
∙ “Obtaining material point information in an Abaqus/Standard analysis,” Section 2.1.6
∙ “Material data definition,” Section 20.1.2 of the Abaqus Analysis User's Manual
∙ *USER DEFINED FIELD
∙ “Damage and failure of a laminated composite plate,” Section 1.1.14 of the Abaqus Example Problems Manual
∙ “USDFLD,” Section 4.1.24 of the Abaqus Verification Manual
Overview（概述）
User subroutine USDFLD:
∙ allows you to define field variables at a material point as functions of time or of any of the
available material point quantities listed in the Output Variable Identifiers table (“Abaqus/Standard output variable identifiers,” Section 4.2.1 of the Abaqus Analysis User's Manual) except the user-defined output variables UVARM and UVARMn;
∙ can be used to introduce solution-dependent material properties since such properties can easily be defined as functions of field variables;
∙ will be called at all material points of elements for which the material definition includes user-defined field variables;
∙ must call utility routine GETVRM to access material point data;
∙ can use and update state variables; and
∙ can be used in conjunction with user subroutine UFIELD to prescribe predefined field variables.
（子程序USDFLD：
1. 允许你在一个材料点定义场变量作为时间函数，在输出变量的标示符中列出了所有材料点的变量，除了用户定义的输出变量和uvarm uvarm。
2. 能够用来介绍材料的性能，并且这种性能能够被定义为场变量的函数。
3. 在各元素的材料点中，用户定义的场变量能够被调用。
4. 必须调用使用程序GETVRM来接入材料点数据
5. 可以和UFIELD一起使用来描述预定义的场变量）
Explicit solution dependence(明确解的关系)
Since this routine provides access to material point quantities only at the start of the increment, the solution dependence introduced in this way is explicit: the material properties for a given increment are not influenced by the results obtained during the increment. Hence, the accuracy of the results depends on the size of the time increment. T
herefore, you can control the time increment in this routine by means of the variable PNEWDT.
（由于程序提供的接入点只是在增量的开始，解之间的相互关系应该被明确：在增量的过程中，材料的性能不应该被得到的结果所影响。因此，结果的准确性依赖于时间增量的大小。因此，你能通过PENWDT来控制程序中的时间增量。）
Defining field variables(定义场变量)
Before user subroutine USDFLD is called, the values of the field variables at the material point are calculated by interpolation from the values defined at the nodes. Any changes to the field variables in the user subroutine are local to the material point: the nodal field variables retain the values defined as initial conditions, predefined field variables, or in user subroutine UFIELD. The values of the field variables defined in this routine are used to calculate values of material properties that are defined to depend on field variables and are passed into other user subroutines that are called at the material point, such as the followin
g:
（在子程序USDFLD被调用之前，通过节点中定义的数值采用差值法计算出材料点的场变量。子程序中场变量的任意改动都是在材料点上的改动：节点场变量保持着数值被定义为初始状态（预定义场变量），或者使用子程序UFIELD,程序中场变量的值被用来计算材料的性能，材料的特性被定义依赖于场变量，并且在其他子程序中被调用。例如下面的程序:）

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