【作者】 孙卓；

【导师】 葛增杰；

【作者基本信息】 大连理工大学 ， 工程力学， 2006， 硕士

【摘要】 本论文基于冻土断裂力学,有限元分析的基本理论,针对典型的实验室模型——冻土三点弯曲模型和冻土四点弯曲模型进行了数值模拟计算,主要对冻土的Ⅰ型裂纹的应力强度因子（K_Ⅰ）和Ⅱ型裂纹的应力强度因子（K_Ⅱ）进行数值计算。并且在分析实验室模型的基础上,对实际的工程问题——桩基础冻拔稳定性评价分析,进行了数值模拟计算。 在二维模型中,分别建立了冻土三点弯曲试样和四点弯曲试样的有限元分析模型。对于三点弯曲试样,考虑其对称性,建立了对称的二分之一裂纹模型。针对不同的试样尺寸以及不同的试样温度,分别进行数值计算,得到各自的应力强度因子（K_Ⅰ）与不同参数直接的关系。结果与文献中的结论相一致。对于四点弯曲试样,采用了完整的裂纹模型进行数值计算。同样分别计算了不同尺寸以及不同温度的试样,得到了各自的应力强度因子（K_Ⅱ）与不同的参数直接的关系。结果与已有文献中的结果一致。 在三维模型中,选取已有的测定冻土三点弯曲试样Ⅰ型断裂韧度K_IC的尺寸数据,建立对称的四分之一模型,对试样的临界应力强度因子,即断裂韧度(K_IC进行数值模拟计算,并将得到的有限元分析结果与实测的冻土试样的理论断裂韧度相比较。通过这一测试实例,验证了有限元数值模拟方法在求解冻土断裂韧度方面的有效性。 文中对实际的工程问题,通过分析系统的受力情况,将桩基础的冻拔问题转化成为冻土层的（Ⅰ+Ⅱ）复合型的断裂力学问题。以简化的冻土断裂力学模型为依据,建立完整的裂纹模型进行数值计算,与利用理论公式计算分析得到的结果进行了比较。说明了在解决冻土断裂力学的问题中采用有限元数值模拟技术是可行的、有效的,计算结果为建立冻土广义强度理论的进一步研究提供了理论依据。并将对桩基稳定性评价的断裂力学方法与传统的方法进行比较,说明断裂力学方法是传统方法的补充和发展。更多还原

【Abstract】 Based on the theory of fracture mechanics of frozen soil and finite element method (FEM), this paper presents a numerical calculation of typical experimental models, three-point bending sample of frozen soil and four-point bending sample of frozen soil, with emphasis on calculation of the stress intensity factor of spreading-open type crack (K_I) and the stress intensity factor of sliding-open type crack (K_II). And a numerical simulation is developed to solve the frost uplift problem of pile foundation.A two dimensional finite element analysis of three-point bending sample of frozen soil and four-point bending sample of frozen soil, based on FEM has been carried out to study the fracture toughness. According to the symmetry, a one-half finite element modeling of three-point bending sample is built to get the stress intensity factor of spreading-open type crack (K_I) of different sample dimension and temperature. The results are consistent with conclusion of the literatures. In this paper, a full model is established to calculate the stress intensity factor of sliding-open type crack (K_II). And the results of different sample dimension and temperature are also consistent with conclusion of the literatures.A three dimensional finite element model is established to simulate the three-point bending sample. According to the symmetry, the fracture toughness of frozen soil was calculated by a quarter models. The results of frozen soil samples with different dimension, which obtained from numerical simulation, were agreement with those of practical samples, indicating that FEM is effectual in calculating fracture toughness of frozen soil.In this paper, based on its loading condition, the frost uplift problem of pile foundation can be transferred to (I +II) tipping-open type crack model. The evaluation of this problem is realized with a full model. Drawing a comparison of the results with those derivative results, we can find that FEM numerical simulation technique is feasible and effectual. By comparing the classic method with the fracture mechanics method in evaluation of the frost uplift problem of pile foundation, a conclusion is reached that the fracture mechanics method is supplement and development of the classic method.更多还原