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，成功开发了基于裂纹轮廓本身的级数扩展的断裂力学 3D 分叉分析方法。该方法现在也适用于陶瓷瞬态热冲击载荷的情况。因此，可以通过计算来预测过载情况下裂纹的渗透深度和残余强度。此外，还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。小管中陶瓷前驱体材料的干燥过程会导致星形裂纹图案。上述分叉分析也适用于研究这种现象。在项目的最后阶段，首次计算了具有弯曲裂纹表面的 3D 裂纹模式。该计算成功验证了玄武岩柱状结构在发展过程中大力优先采用六边形截面。在此模拟中，假设裂纹前沿沿释放能量最大的方向扩展。现在，玄武岩柱振荡裂纹表面的无法解释现象将使用相同的方法进行研究。在该项目的实验部分，将开发具有更高分辨率的成像技术，以改善陶瓷热冲击裂纹的成像。这样，带有小开口的裂缝就可以被检测到。这种有条理的改进旨在提高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图，对计算机层析成像技术、染料渗透检测的连续切片技术和断层扫描显微镜进行了比较。此外，现在将使用更合适的陶瓷（例如瓷器或陶器）来承受热冲击，而不是以前使用的具有微小裂纹开口的陶瓷。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便更牢固地检测裂纹。为此，每个断层摄影切片的评估将合并相邻断层摄影切片中的信息。规划了一种软件解决方案，用于跟踪裂纹模式形成过程中发生的柱过渡，通过该解决方案可以识别多个柱排列之间的过渡并量化它们的频率。在此过程中，对通过实验获得的陶瓷系统和干燥淀粉水悬浮液中裂纹图案的 3D 图像进行分析将有助于对 3D 裂纹图案发展的总体理解。