由于相互接触的不同结构体或同一结构体的不同部分之间的热膨胀系数不匹配，在加热或冷却时彼此的膨胀或者收缩程度不一致，从而导致热应力的产生。

    热应力问题实际上就是热和应力两个物理场之间的相互作用，故属于耦合场分析问题。与其他耦合场的分析方法类似，ansys提供两种分析热应力的方法：直接法和间接法。

    直接法：直接采用具有温度和位移自由度的耦合单元，同时得到热分析和结构应力分析的结果。

    间接法：先进行热分析，然后将求得的节点温度作为载荷施加到结构应力分析中。

   1 直接法进行热应力分析基本步骤

    直接法热应力分析的基本步骤包括建立有限元模型、施加载荷、求解和后处理。

    1.1 建立有限元模型

        注意：必须定义热——结构耦合单元。

              必须定义材料的导热系数、热膨胀系数和弹性模量。

    1.2  施加载荷

         采用直接法进行热应力分析过程中，不仅可以在模型上施加温度、热流率、对流、热流密度、生热率以及热辐射等6中基本热载荷外，还可以在模型上施加集中力（力矩），压力、位移、角速度等基本结构载荷。

    1.3  结构载荷

         1.3.1  在单个或多个节点上施加集中力（力矩）载荷

                main menu/preprocessor/loads/define loads/apply/structural/force&moment/on nodes

                main menu/solution/define loads/apply/structural/force&moment/on nodes

         1.3.2  在节点上施加集中力（力矩）载荷

                main menu/preprocessor/loads/define loads/apply/structural/force&moment/on nodes compnents

                main menu/solution/define loads/apply/structural/force&moment/on nodes compnents

         1.3.3  在关键点上施加集中力（力矩）载荷

                 main menu/preprocessor/loads/define loads/apply/structural/force&moment/on keypoints

                 main menu/solution/define loads/apply/structural/force&moment/on keypoint

         1.3.4   压力载荷

                 在节点上、节点组、单元、线段上、面上施加压力载荷
           main menu/preprocessor/loads/define loads/apply/structural/pressure/on nodes

                                                                              /on node compnents

                                                                              /on elements

                                                                              /on lines

                                                                              /on areas

           main menu/solution/define loads/apply/structural/pressure/on nodes

                                                                    /on node compnents

                                                                    /on elements

                                                                    /on lines

                                                                    /on areas

          1.3.5  位移载荷

                 在节点上、节点组、关键点、线段上、面上施加位移载荷

                 main menu/preprocessor/loads/define loads/apply/structural/displacement/on node

                                                                               /on node compnents

                                                                               /on keypoints

                                                                               /on line

                                                                               /on areas

                 main menu/solution/define loads/apply/structural/displacement/on node

                                                                               /on node compnents

                                                                               /on keypoints

                                                                               /on line

                                                                               /on areas

           1.3.6  在节点上施加反对称位移载荷

                 main menu/preprocessor/loads/define loads/apply/structural/displacement/antissmm B.C./ on node

   

           1.3.7  整体角速度载荷

                 main menu/preprocessor/loads/define loads/apply/structural/inertia/angular veloctiy/global 

        /on components/by origin  在单元组上施加角载荷

                 main menu/solution/define loads/apply/structural/inertia/angular velocity/global

                                                                                         /on components/by origin  在单元组上施加角载荷

          1.3.8  施加整体角加速度

                 main menu/preprocessor/loads/define loads/apply/structural/inertia/angular accel/global  

     on components/by origin 在单元组上施加角角速度

                  /by axis

                 main menu/solution/loads/define loads/apply/structural/inertia/angular accel/global 

     on components/by origin 在单元组上施加角角速度

                  /by axis

   2 间接法进行热应力分析基本步骤

         2.1  进行热分析   具体的热分析可参阅稳态热分析与瞬态热分析过程

         2.2   重新进入前处理器，转换单元类型

            热分析求解完毕后，应重新进入前处理器，热单元转换成相应的结构单元。

            main menu/preprocessor/element type/switch elem type

         2.3   设置结构分析中的材料属性

               当热单元转换为结构单元后，应设置结构分析中的材料属性，如弹性模量、线膨胀系数、泊松比等。

              main menu/preprocessor/material props/material models

         2.4  读入热分析结果并将其作为结构分析载荷

              main menu/solution/define loads/apply/structural/temperature/from thermal analy

         2.5  指定参考温度

              main menu/preprocessor/loads/define loads/setting/reference temp

              main menu/solution/define loads/setting/reference temp

         2.6  求解及后处理

              参阅热应力直接法求解及后处理过程