Mechanisms for fatigue crack growth in meso/micro and nano specimens - crack initiation and short crack growth under geometrical and mechanical constraints

细观/微米和纳米样品中疲劳裂纹扩展的机制 - 几何和机械约束下的裂纹萌生和短裂纹扩展

• 批准号: 521371248
• 负责人: Professor Dr. Christian Motz
• 金额: --
• 依托单位: Lehrstuhl für Materialphysik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/521371248?language=en
• 关键词: Mechanisms; fatigue; crack; growth; meso

Wider research context / theoretical framework: Fracture mechanical concepts are known since many decades and become more and more important in many fields of applications to optimise the efficiency of materials in parts and components, which is essential for e.g. lightweight constructions to save resources and energy. Size effects are an intrinsic and commonly known problem in fracture mechanics even at the macroscopic scale which leads to size requirements even for the samples defined in the according test-standards. The situation becomes even more complicated when complex specimen geometries are used e.g. for testing of MEMS and/or comparably large plastic and process zones are present in front of the crack tip which is typically the case in small-scale fracture testing. In addition, a complex microstructure, found e.g. in multilayers, can strongly influence crack initiation and propagation through mechanical and microstructural constraints. These effects and challenges have not been addressed in past in detail and will be the focus of the current proposal. Hypotheses/research questions /objectives: How must specimen size, boundary conditions (constraints), material behaviour and inhomogeneities be considered regarding the applicability of the fracture mechanical concepts for small-scale specimens and are there necessary pre-sets for testing of micron-sized specimens (e.g. fatigue pre-cracks)? Approach/methods: To analyse short crack growth under mechanical constraints we will not only vary the specimen size, but also design tailored multilayer structures with varying grain sizes via electrodeposition. We propose a scale-bridging investigation. Meso to micron-sized samples are tested at the Saarland University, Montanuniversität Leoben provides testing of nano and micro samples. We will vary the sample size, the layer system and the grain size regarding quasi-static and LCF physically short cracks. Combining our experience in micro and nano-mechanics we will achieve a characterization of the crack via the displacements and strain fields in the plastic zone. Level of originality / innovation: Up to now, work has mostly focussed on understanding the origin of static size effects, but there is no detailed study of size dependent evolution of cyclic plasticity and fracture. Furthermore, knowledge of the underlying mechanisms arising from microstructural and mechanical constraints is crucially missing. The aim of this project is to gain an improved understanding of the driving force of physically short cracks, both quasi-statically and in the low cycle fatigue regime (LCF), under geometrical, microstructural and mechanical boundary conditions and constraints to develop a comprehensive model of fatigue and fracture in inhomogeneous materials in micron-sized dimensions.

更广泛的研究背景/理论框架：断裂力学概念几十年来一直为人所知，在优化零部件材料效率的许多应用领域变得越来越重要，这对于轻量化结构节省资源和能源至关重要。尺寸效应是断裂力学中一个固有的、众所周知的问题，即使是在宏观尺度上，也会导致对试验标准中定义的样品的尺寸要求。当使用复杂的试样几何形状时，情况变得更加复杂，例如用于MEMS测试和/或在裂纹尖端前存在相当大的塑性和工艺区域，这是小规模断裂测试的典型情况。此外，复杂的微观结构，例如在多层材料中，可以通过力学和微观结构约束强烈地影响裂纹的萌生和扩展。这些影响和挑战在过去没有得到详细的解决，将是当前提案的重点。假设/研究问题/目标：如何考虑试样尺寸、边界条件（约束）、材料行为和非均质性对小规模试样断裂力学概念的适用性，以及是否有必要的预先设定来测试微米尺寸的试样（例如疲劳预裂纹）？途径/方法：为了分析在力学约束下的短裂纹扩展，我们不仅要改变试样尺寸，还要通过电沉积设计不同晶粒尺寸的定制多层结构。我们建议进行规模桥接调查。中至微米尺寸的样品在萨尔大学进行测试，Montanuniversität Leoben提供纳米和微观样品的测试。我们将改变准静态和LCF物理短裂纹的样本量、层系和晶粒尺寸。结合我们在微观和纳米力学方面的经验，我们将通过塑性区的位移和应变场来实现裂纹的表征。独创性/创新水平：到目前为止，工作主要集中在了解静态尺寸效应的起源，但没有详细研究尺寸依赖于循环塑性和断裂的演化。此外，由于微观结构和机械约束而产生的潜在机制的知识是至关重要的缺失。该项目的目的是为了更好地理解在几何、微观结构和力学边界条件和约束下，准静态和低周疲劳状态（LCF）下物理短裂纹的驱动力，以建立微米尺寸非均匀材料的疲劳和断裂综合模型。