Fracture of High-Performance Quasibrittle Materials: Effects of Loading Rate & Fatigue

准脆性材料的断裂力学，包括高 高性能材料如高强度混凝土已经出现， 在过去的几年里，但一个关键方面仍然被忽视- 超前率的影响（超出动态范围），负载循环 和疲劳。 实验和理论，侧重于混凝土， 将进行岩石覆盖。 缺口断裂试验 试样将包括：1）在不同的载荷-挠度曲线 恒定位移速率，2）后加载松弛试验， 峰值软化范围; 3）疲劳试验; 4）切口试验。 部分测试将与 行业，材料服务公司，芝加哥。 理论 公式，以改善近似的顺序，但 减少简单性，将包括：1）R的速率推广- 粘塑性线裂纹模型 和粘塑性的关系， 桥应力与张开位移的关系，用 基于涂抹尖奇异积分微分方程 裂纹叠加：3）非局部有限元模型， 开裂损伤、蠕变和率相关非线性三轴 断裂过程区的本构模型; 随机颗粒模型的推广模拟了 混凝土微观结构 这个问题的解决将为 开发更好的材料的方法;对于他们的更多 有效和更安全的使用;更好和更安全的设计， 特殊或超大型混凝土结构， 现有经验;更可靠的预测长期 混凝土结构的裂缝;以及更现实的预测 岩石边坡、开挖、地下开口的破坏 和钻孔。

Fracture mechanics of quasibrittle materials, which include high performance materials such as high strength concrete, has emerged during the last few years but one key aspect is still ignored- the effects of leading rate (beyond the dynamic range), load cycling and fatigue. Experiments and theory, focused on concretes and also covering rocks will be conducted. The tests of notched fracture specimens will include: 1) load-deflection curves at various constant displacement rates, 2) load relaxation tests in the post- peak softening range, 3) fatigue tests and 4) renotching tests. Part of the testing will be carried out in cooperation with industry, Material Service Corp., Chicago. The theoretical formulations, in the order of improving approximation but decreasing simplicity, will include: 1) Rate generalization of R- curve approach; 2) Cohesive line-crack model with viscoplasticity in the bulk of the specimen and viscoplasticity in the relation of bridging stress to opening displacement, solved by means of a singular integro-differential equation based on smeared-tip superposition of cracks: 3) nonlocal finite element model with cracking damage, creep and rate-dependent nonlinear triaxial constitutive model for the fracture process zone; and 4) generalization of the random particle model simulating the microstructure of concrete. Resolution of this problem will pave the way for development of better materials; for their more effective and safer utilization; for better and safer designs of special or very large concrete structures beyond the range of existing experience; for more reliable predictions of long-time cracking in concrete structures; and for more realistic predictions of the failure of rock slopes, excavations, underground openings and boreholes.