权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Effect of Crack-Parallel Stresses on Fracture of Concrete and Other Quasibrittle Materials

裂纹平行应力对混凝土和其他准脆性材料断裂的影响

基本信息

批准号：
2029641
负责人：
Zdenek Bazant
金额：
$ 60万
依托单位：
Northwestern University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2020
资助国家：
美国
起止时间：
2020-08-15 至 2024-07-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=2029641&HistoricalAwards=false
关键词：
Effect Crack Parallel Stresses Fracture

项目摘要

This research will address prediction and control of fracture in concrete, with implications in other heterogenous materials such as rocks, fiber composites, ceramics, sea ice, rigid foams, shale, various bio-, biomimetic and printed architectured materials. Concrete fracture is a serious safety concern generally, and particularly during earthquakes. Fracture is always accompanied by cracking which, in the long term, leads to environmental degradation as well. Realistic fracture predictions based on standardized laboratory tests and computer simulations is therefore critical to strong and durable civil infrastructure. Recent research reveals that crack tips in quasibrittle materials are surrounded by a wide zone of visually undetectable microcracking damage, which controls crack growth yet is very sensitive to stresses that are parallel to the cracks. The effects of these crack-parallel stresses are currently unknown. This research will devise a new type of laboratory test, which can measure the changes of energy required for fracture growth at various crack-parallel stress levels. Testing will be conducted to better understand the effect of crack-parallel stresses on normal and high-strength concretes as well as fiber-reinforced concretes, and the results will be used to formulate a new mathematical model for quasibrittle fracture. The crack-parallel stress effects have gone unnoticed because they do not appear in the currently standardized fracture tests and are not thermodynamic variables in existing linear elastic fracture mechanics and cohesive crack models. The key idea of this research is a modification of the notched three-point bend test with four crucial features: 1) plastic support pads at notch mouth introduce constant notch-parallel compression; 2) the end supports installed with gaps engage only when the pads are yielding; 3) the test setup switches from one statically determinate configuration to another, allowing unambiguous interpretation; and 4) the size effect method, most effective for fracture energy testing, is made possible. A finite element crack band model with a tensorial damage softening law will be developed and calibrated by optimal fitting of the test results. Finally, a multiscale model that incorporates mesoscale mechanisms of frictional slip, microcrack opening, interlock and splitting causing the crack-parallel stress effects will be devised. The results are expected to transform fracture mechanics of quasibrittle materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

这项研究将解决混凝土断裂的预测和控制问题，并涉及其他非均质材料，如岩石，纤维复合材料，陶瓷，海冰，硬质泡沫，页岩，各种生物，仿生和印刷建筑材料。混凝土断裂通常是一个严重的安全问题，特别是在地震期间。断裂总是伴随着开裂，从长远来看，这也会导致环境退化。因此，基于标准化实验室测试和计算机模拟的现实断裂预测对于坚固耐用的民用基础设施至关重要。最近的研究表明，在准脆性材料的裂纹尖端是由一个很宽的区域的视觉不可检测的微裂纹损伤，控制裂纹的扩展，但非常敏感的应力是平行的裂纹包围。这些平行裂纹应力的影响目前尚不清楚。这项研究将设计一种新型的实验室测试，它可以测量在不同的裂纹平行应力水平下的断裂扩展所需的能量的变化。将进行测试，以更好地了解正常和高强度混凝土以及纤维增强混凝土的裂纹平行应力的影响，其结果将被用来制定一个新的准脆性断裂的数学模型。平行裂纹应力效应没有被注意到，因为它们没有出现在目前标准化的断裂试验中，也不是现有线弹性断裂力学和内聚裂纹模型中的热力学变量。本研究的核心思想是对缺口三点弯曲试验的改进，它具有四个关键特征：1）缺口口处的塑料支撑垫引入恒定的缺口平行压缩; 2）安装有间隙的端部支撑仅在垫屈服时接合; 3）试验装置从一种静定构型切换到另一种静定构型，允许明确的解释;（4）使断裂能测试最有效的尺寸效应方法成为可能。将建立一个具有张量损伤软化规律的有限元裂纹带模型，并通过试验结果的最佳拟合进行标定。最后，一个多尺度模型，结合细观机制的摩擦滑动，微裂纹的开放，联锁和分裂造成的裂纹平行应力效应将被设计。该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。