孔洞缺陷对气缸盖材料性能影响的映射分析模型

针对某收获机柴油机气缸盖在使用中易发生渗漏失效的问题，使用WCB铸钢为试验材料，加工出2组不同高度的拉伸试件。根据射线探伤照片，得到了其中心疏松缩孔缺陷的分布场。将试件毛坯中的无缺陷区域加工为基体试件进行试验，得到了与ASTM标准值吻合度较高的拉伸特性值。基于探伤照片中的灰度分布，计算出相应部位的孔隙率场分布，通过插值法将分布场映射至有限元模型的相应节点处，最终得到能够表征孔洞实际形貌的有限元重构模型。通过与试验数据的对比，表明使用映射重构法能够较好地模拟试件的弹塑性行为，并能较为准确地预测断裂位置，解释了由于孔洞演化造成的宏观断裂现象。

Mapping Analysis Model for Void Defect Impact on Cylinder Head Material Performance

According to the problem of leakage exists in the cylinder head used in the harvester diesel, ASTM A216 WCB cast steel with centerline porosity defect was used as test material and two teams of specimens which had different heights were machined. Non-linear elastic and plastic behaviors depended on porosity were mathematically described by relevant equation sets. From the radiographic inspection, centerline porosity distributions inside the specimens were obtained. Taking the no-defect part of the cast blank as matrix specimen, the sound tensile properties were obtained by tests, which had good correspondence with ASTM E8 tensile standard data. Based on the gray density distribution of radiograph, the void fraction field was calculated and mapped to the relevant nodes of the mid-sections of the finite element models by using interpolation method and relevant computer language code. Then the finite element models could generate the actual void morphologies. ABAQUS input parameters were confirmed by trial simulations to the matrix specimen and comparison with test results. Fine agreements of the result curves between simulations and tests could be observed, and predicted positions of the tensile fracture were turned to be in accordance with the tests. Chord modulus was used to obtain the equivalent elastic stiffness because of the non-linear features. It was turned out that elongation was the most influenced term on the defect cast steel, compared with elastic stiffness and yield stress. Additional visual explanations on the tensile fracture caused by void propagation were also given by the result contours at different mechanical stages, including distributions of Mises stress and plastic strain. By comparing with the test results, the established models could precisely simulate the elastoplastic behaviors of the specimens and predict the accurate locations of the fractures. The proposed method could provide an alternative way for the study of materials containing casting defects.