Lanwer Jan-Paul, Höper Svenja, Gietz Lena, Kowalsky Ursula, Empelmann Martin, Dinkler Dieter
iBMB (Institute of Building Materials, Concrete Construction and Fire Safety), Division of Concrete Construction, Faculty of Architecture, Civil Engineering and Environmental Science, Technische Universität Braunschweig, 38106 Braunschweig, Germany.
ISD (Institute of Structural Analysis), Faculty of Architecture, Civil Engineering and Environmental Science, Technische Universität Braunschweig, 38106 Braunschweig, Germany.
Materials (Basel). 2021 Dec 24;15(1):120. doi: 10.3390/ma15010120.
The objective of the contribution is to understand the fatigue bond behaviour of brass-coated high-strength micro steel fibres embedded in ultra-high performance concrete (UHPC). The study contains experimental pullout tests with variating parameters like load amplitude, fibre orientation, and fibre-embedded length. The test results show that fibres are generally pulled out of the concrete under monotonic loading and rupture partly under cyclic tensile loading. The maximum tensile stress per fibre is approximately 1176 N/mm, which is approximately one third of the fibre tensile strength (3576 N/mm). The load-displacement curves under monotonic loading were transformed into a bond stress-slip relationship, which includes the effect of fibre orientation. The highest bond stress occurs for an orientation of 30° by approximately 10 N/mm. Under cyclic loading, no rupture occurs for fibres with an orientation of 90° within 100,000 load changes. Established S/N-curves of 30°- and 45°-inclined fibres do not show fatigue resistance of more than 1,000,000 load cycles for each tested load amplitude. For the simulation of fibre pullout tests with three-dimensional FEM, a model was developed that describes the local debonding between micro steel fibre and the UHPC-matrix and captures the elastic and inelastic stress-deformation behaviour of the interface using plasticity theory and a damage formulation. The model for the bond zone includes transverse pressure-independent composite mechanisms, such as adhesion and micro-interlocking and transverse pressure-induced static and sliding friction. This allows one to represent the interaction of the coupled structures with the bond zone. The progressive cracking in the contact zone and associated effects on the fibre load-bearing capacity are the decisive factors concerning the failure of the bond zone. With the developed model, it is possible to make detailed statements regarding the stress-deformation state along the fibre length. The fatigue process of the fibre-matrix bond with respect to cyclic loading is presented and analysed in the paper.
本文的目的是了解埋入超高性能混凝土（UHPC）中的镀黄铜高强度微钢纤维的疲劳粘结性能。该研究包含了不同参数（如荷载幅值、纤维取向和纤维埋入长度）的试验拉拔试验。试验结果表明，在单调加载下纤维通常从混凝土中拔出，而在循环拉伸加载下部分纤维会断裂。每根纤维的最大拉应力约为1176 N/mm，约为纤维抗拉强度（3576 N/mm）的三分之一。将单调加载下的荷载-位移曲线转换为粘结应力-滑移关系，其中考虑了纤维取向的影响。纤维取向为30°时粘结应力最高，约为10 N/mm。在循环加载下，纤维取向为90°时，在100,000次荷载循环内不会发生断裂。对于30°和45°倾斜纤维建立的S/N曲线表明，对于每个测试的荷载幅值，其疲劳寿命不超过1,000,000次荷载循环。为了用三维有限元法模拟纤维拉拔试验，开发了一个模型，该模型描述了微钢纤维与UHPC基体之间的局部脱粘，并使用塑性理论和损伤公式来捕捉界面的弹性和非弹性应力-变形行为。粘结区模型包括与横向压力无关的复合机制，如粘结和微联锁以及横向压力引起的静摩擦和滑动摩擦。这使得能够表示耦合结构与粘结区之间的相互作用。接触区的渐进开裂及其对纤维承载能力的相关影响是粘结区破坏的决定性因素。利用所开发的模型，可以对沿纤维长度的应力-变形状态做出详细说明。本文介绍并分析了纤维-基体粘结在循环加载下的疲劳过程。
