一种新的动态回弹模量有限元实现方法

A FEM-based method to implement the model of dynamic resilient modulus

美国在2004年通过NCHRP 1-37A项目提出了用于路基土评估的新的动态回弹模量模型。该模型由于考虑了体应力和偏应力的影响,已得到广泛应用。然而,目前对于该模型的有限元实现均采用基于等效动三轴试验的等效切线模量进行材料点的局部迭代。为克服该实现方法在复杂应力状态下因模型简化带来的偏差,基于广义虎克定律推导了该回弹模量模型的精确一致切线刚度矩阵。通过编写的ABAQUS用户自定义材料子程序(UMAT)对轴压和围压加载情形进行有限元模拟,发现新推导的有限元实现方法较现有基于等效三轴试验的简化方法具有更高的计算效率和精度。最后对典型沥青路面结构的分析表明,为提高复杂应力状态下路基响应计算精度,在路面结构分析中采用基于当前应力状态的一致切线刚度矩阵代替等效切线刚度矩阵是十分必要的。

A new model of dynamic resilient modulus was proposed to evaluate the subgrade soil by NCHRP 1-37 A project in USA in 2004. The model is widely applied in engineering analysis since it considers the influence of volume stress and deviatoric stress. In the finite element analysis, however, the model is usually implemented using the equivalent tangent stiffness matrix determined from an equivalent dynamic triaxial test through local iteration at material points. In order to eliminate the error caused by the simplified method under complex stress state,the accurate consistent tangent stiffness matrix of dynamic resilient modulus is derived based on the general Hooke law. The model is implemented into ABAQUS by compiling the user material subroutine（UMAT）; the finite element simulation is carried out for the cases of axial pressure and confining pressure; the simulated results demonstrate that the new method has a higher precision and efficiency compared to the existing simplified method based on an equivalent triaxial test. Finally,an analysis of typical asphalt pavement structure shows that, in order to improve the accuracy of the response of subgrade under complex stress state, it is necessary to use the consistent tangent stiffness matrix instead of the equivalent stress tangent stiffness matrix in pavement structure analysis.