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Experimental Study on the Tensile Properties of Rock-Mortar Interface under Different Strain Rates 时间:2018-09-13 13:11 来源:未知作者:admin 点击: 次 Abstract:In this paper, an experimental study was carried out on a rock-mortar interface specimen under three different strain rates (, , and ) using the MTS322 electrohydraulic servo loading system, and a new constitutive relation function of fictitious crack model (FCM) according to the axial-stress-crack-width curves of the rock-mortar interface is established, because the traditional nonlinear softening function easily distorts, shakes, and so cannot describe the damage-evolution process of the rock-mortar interface accurately. Through the use of a precise servo actuator system and three extensometers measured axial-stress-crack-width curves, it is shown that the rock-mortar interface is very sensitive to the strain rate. The tensile strength increases with strain rate, the crack width decreases at the same time, and the axial-stress-crack-width curves gradually evolve from a concave-downward trend to a linear decreasing trend. At the same time, the new constitutive relation function can reflect the tensile strength, crack width, and the downward trend of the rock-mortar interface more accurately.
1. Introduction
The interface between rock and mortar in the project often becomes the weakest point of the entire project, and thus research in this area is of great significance. Owing to the structural characteristics of rock and concrete itself, which usually act as the compression material in most structures, the compressive strain rate accounts for a large subfield in the study of rock and concrete material properties under different strain rates. However, the different strain rates’ tensile stress in the actions of explosions and earthquakes cannot be avoided. In the Great Hanshin-Awaji earthquake, some special damage in building structures were likely caused by interface tensile stress wave propagation [1].
However, the dynamic tensile has not been widely investigated, and there are few papers describing direct tensile test of the different strain rates in particular [2, 3]. This is because the direct tensile test is difficult, the equipment requires high precision and cannot achieve easily. It is believed that the tensile strength is approximately proportional to the square root of the compressive strength [3]. But a survey of the technical literature indicates wide scatter in tensile strength data. To date, the research on the axial tensile test of rock-mortar interface is very rare [4]. Yan et al. studied the dynamic tensile strength property of the rock interface and its host rocks sampled using split-Hopkinson pressure bar (SHPB) tests [5]. It was reported that the dynamic tensile strengths of the two host rocks, that is, tuff and basalt, have typical loading-rate dependency. However, the dynamic response of the rock interface is much more complicated and varies between those of tuff and basalt when the loading rate is given. Similar works and test results were also reported [6–9].
In order to further study the principle of this phenomenon, Hillerborg found that a large number of microcracks appear in the crack front and the surrounding area before overall instability of the material occurs and that the macrocracks always appear after these microcracks. Based on this, the fictitious crack model (FCM), which applied to describe the nonlinear behavior of brittle materials, was proposed by Hillerborg et al. [10]. Reinhardt et al. presented a nonlinear softening function to describe the constitutive relation [11]. In some experiments, correct results can be obtained by fitting the experimental data with the nonlinear softening function.
The goal of this paper is to research the rock-mortar interface constitutive relation under different strain rate (, , and ) using the MTS322 electro-hydraulic servo loading system. Through use of the direct tensile test method to obtain more accurate and reliable data, we propose a new constitutive relation function for fictitious crack model (FCM) and explore the changing trends of tensile strength, crack width, and downward trend with strain rate.