Formation of three dimensional crack patterns

三维裂纹图案的形成

• 批准号: 213158658
• 负责人: Dr.-Ing. Martin Hofmann
• 金额: --
• 依托单位: Lehrstuhl für Werkstofftechnologie (LWT)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2012
• 资助国家: 德国
• 起止时间: 2011-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/213158658?language=en
• 关键词: Formation; three; dimensional; crack; patterns

The aim of the project is a detailed understanding for the mechanisms of the formation of three dimensional (3D) crack patterns as a result of inhomogeneous shrinkage processes. During the 1st phase the method of fracture mechanical 3D bifurcation analysis based on a series expansion of the crack contour itself was developed successfully. This method now shall also be applied to cases with transient thermal shock loads at ceramics. Thereby both, the penetration depth of the cracks at overload cases and the residual strength can be predicted computationally. In addition, the impact on the crack propagation by internal stresses that develop during the thermal sputtering of insulation layers shall be examined. The drying procedure of ceramic precursor material in small tubes leads to star-shaped crack patterns. The mentioned bifurcation analysis shall be applied to investigate this phenomenon as well.For the first time, 3D crack patterns with curved crack surfaces were computed in the last period of the project. This calculation verified successfully that hexagonal cross sections in the columnar structures of basalt are energetically preferred during the process of development. In this simulation it is assumed that the crack front propagates in a direction at which the released energy is at a maximum. Now, the unexplained phenomenon of the oscillating crack surfaces of basalt columns shall be investigated using the same approach.In the experimental part of the project imaging techniques with significantly higher resolution shall be developed in order to improve the imaging of thermal shock cracks in ceramics. That way, cracks with small openings will become detectable. This methodical improvement aims at a quality of the measurement of crack spacings and crack depths that suffices for a verification of the expected results of the simulation. In order to map the cracks more clearly the techniques of computer laminography, serial sectioning technique with dye penetrant testing and tomographic microscopy are compared. Furthermore, instead of the formerly used ceramics with their tiny crack openings, now more suitable ceramics like for example porcelain or pottery shall be subjected to thermal shocks.Moreover, the software that processes the 3D images obtained by X-ray analyses techniques will be enhanced to detect the cracks more robust. For this purpose, the evaluation of each tomographic slice will incorporate the information in the adjacent tomographic slices. A software solution that tracks the column transitions occurring during the development of crack patterns is planned by which the transitions between several column arrangements are identified and their frequencies are quantified . In so doing, the analyses of experimentally obtained 3D images of crack patterns in ceramic systems and in dried starch-water-suspensions will contribute to the general understanding of the development of 3D crack patterns.

该项目的目的是详细了解由于不均匀收缩过程而形成三维（3D）裂纹图案的机制。在第一阶段，成功地开发了基于裂纹轮廓级数展开的断裂力学三维分叉分析方法。这种方法现在也适用于陶瓷上有瞬时热冲击载荷的情况。因此，在超载情况下的裂纹的穿透深度和剩余强度可以通过计算来预测。此外，应检查绝缘层热溅射过程中产生的内应力对裂纹扩展的影响。陶瓷前体材料在小管中的干燥过程导致星形裂纹图案。在此基础上，本文首次采用分叉分析的方法，计算了具有弯曲裂纹面的三维裂纹形态。这一计算成功地证实了玄武岩柱状结构中的六边形截面在发育过程中是能量优先选择的。在该模拟中，假设裂纹前沿在释放能量最大的方向上传播。现在，玄武岩柱的振荡裂纹表面的原因不明的现象应使用相同的方法进行调查。在该项目的实验部分，应开发具有显着更高的分辨率的成像技术，以改善陶瓷中的热冲击裂纹的成像。这样，具有小开口的裂缝将变得可检测。这种方法上的改进旨在裂纹间距和裂纹深度的测量质量，足以验证模拟的预期结果。为了更清楚地绘制裂纹，比较了计算机层片照相技术、连续切片染色渗透检测技术和层析显微镜技术。此外，取代了以前使用的具有微小裂纹开口的陶瓷，现在更合适的陶瓷（例如瓷器或陶器）将经受热冲击。此外，处理通过X射线分析技术获得的3D图像的软件将得到增强，以更可靠地检测裂纹。为此，每个断层摄影切片的评估将结合相邻断层摄影切片中的信息。一个软件解决方案，跟踪裂纹图案的发展过程中发生的列过渡计划，几个列的安排之间的过渡被确定，其频率被量化。在这样做时，实验获得的3D图像的裂纹图案在陶瓷系统和干燥的淀粉-水-悬浮液的分析将有助于3D裂纹图案的发展的一般理解。