Experimental Study on the Tensile Properties of Rock-Mortar Interface under Different Strain Rates

Nan Wu,Zhilei He,Zhende Zhu

doi:10.1155/2018/5241848

Abstract

In this paper, an experimental study was carried out on a rock-mortar interface specimen under three different strain rates (10−6, 10−5, and 10−4 s−1) 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.

Highlights

With the natural fracture surface of rocks, each specimen section has its own independent characteristics. e shape of fractures and the area of fracture surfaces lead to the difference of bonding area between rock and mortar directly
This does not affect the applicability of the fictitious crack model (FCM) model
The fictitious crack model (FCM) is a model that describes the constitutive relation from the macrodescription of the phenomenon. e model assumes that all tensile stresses on the bonded surface are consistent, and the tension is equivalent to the force on the projected area. is accords with the application foundation of FCM theory

Summary

Research Article

Experimental Study on the Tensile Properties of Rock-Mortar Interface under Different Strain Rates. E goal of this paper is to research the rock-mortar interface constitutive relation under different strain rate (10−6, 10−5, and 10−4 s−1) using the MTS322 electro-hydraulic servo loading system. Rough 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. Is occurs because, due to different physical parameters, such as the elastic modulus and Poisson’s ratio of the rock and mortar, and owing to the existence of large number of microcracks around the interface, when the peak strength is reached one or several microcracks develop quickly, and making the displacement increase suddenly, which leads to a sudden drop of the pull on the extensometer Severe fluctuations and nonstop fluctuation of the stress may occur at the beginning of the peak, as shown at point 1 in Figure 4(b). is occurs because, due to different physical parameters, such as the elastic modulus and Poisson’s ratio of the rock and mortar, and owing to the existence of large number of microcracks around the interface, when the peak strength is reached one or several microcracks develop quickly, and making the displacement increase suddenly, which leads to a sudden drop of the pull on the extensometer

Sample label

Specimen Extensometer Steel plate

The new function fitting curve