焊接结构内部孔洞演化特征及其多尺度损伤表征

为了研究结构失效过程中焊接细节处的宏细观损伤演化过程,以含细观孔洞的焊接构件为对象进行拉伸试验,综合采用X-CT(X射线计算机断层扫描)和电测技术分别同步记录拉伸过程中构件内部细观结构和宏观力学性能的演化过程。试验结果发现随着构件变形的增加,其宏观性能变化表现为弹性模量的线性减小,同时其内部结构演化表现为新孔洞的萌生和原有孔洞的增长,孔洞总体积随塑性变形呈线性增加趋势,构件在不同的变形阶段,孔洞的体积与数量之间的关系都呈现出分形特征,分形维数随塑性变形的增加呈平缓增加趋势。根据构件宏观力学性能与其内部孔洞总体积之间的关系,并结合分形特征的意义,提出一种多尺度损伤表征方法,并用基于Lemaitre理论的损伤量化方法对其进行验证。结果表明新的损伤表征方法不但具有更加明确的物理意义,同时还可以很好地描述细观孔洞萌生、增长直到构件断裂的损伤跨尺度演化导致失效的过程。

EVOLUTION CHARACTERISTICS OF VOIDS WITHIN WELDED STRUCTURE AND ITS MULTI-SCALE MODELING

To explore the behavior of defects from meso- to macro-scale on the toe of a welded structure. A welded specimen with meso-voids on the toe of the weld was taken as experimental objects. During the quasi-static loading and unloading testing, X-CT (Micro focus X-ray Computed Tomography System) was employed to record the tomograms of defects, and the macro-scale response of the specimen was measured synchronously when the specimen was loaded up to failure. The experimental results show that the specimen’s modulus decreases linearly with the deformation on the same time of meso-voids initiation and growth keep happening, and the total volume of meso-voids tends to increase linearly with the plastic deformation. The volume-amount of voids shows typical fractal patterns in different stages of plastic deformation, and the fractal dimension is slowly increasing along with plastic strains of the specimen. According to the relation between macro-scale property and total volume of meso-voids, and combining the significance of fractal behavior, a new multi-scale damage characteristic method is proposed, which was verified by Lemaitre’s damage theories. The results show that the new method for the damage modeling has an explicit physical meaning, and that it can well describe the trans-scale damage evolution process of meso-voids initiation, growth, and the failure development of specimen.