Wedge Splitting Test Specimens Research Articles

Effect of alkali-silica reaction on the fracture properties of confined concrete

Alkali-silica reaction (ASR), which was recently discovered in nuclear power plant structures commonly without shear reinforcement, has previously been shown to induce anisotropic expansion in confined concrete. The fracture properties (strength, stiffness, and specific fracture energy) of ASR-induced anisotropically-damaged concrete specimens were quantified by varying both the damage level and relative direction of the ASR-induced cracking orientation against the loading direction corresponding to the fracture propagation. The effect of different orientations (0, 45, and 90° relative to the notch of the specimen) of expected ASR-induced cracks on the fracture properties was investigated using a wedge-splitting test (WST). Specimens without ASR expansion generally showed the highest fracture properties; however, the specific fracture energy was highest for ASR-affected specimens in which the expected orientation of ASR-induced cracks was perpendicular to the WST specimen notch. Specimens in which the ASR-induced cracks were parallel to the notch exhibited the lowest strength and fracture energy.

Fracture mechanics analysis of generalized compact tension specimen geometry using the mechanics of net-section

Fracture mechanics analysis of a generalized compact tension specimen, on the basis of the mechanics of deformation of the net-section, is shown to provide a simple and a broadly useful expression for stress intensity factor calculations. A single analytical expression is found to be sufficient for the characterization of crack behavior in compact tension, extended compact tension and wedge splitting test specimens without any restriction on the specimen length (or height) and width. The analysis is enabled by the concept of the change in net-section energy, which is determined by summing the changes in strain energies of the net-section of the generalized specimen for tension and bending deformation modes, which result from the introduction of the crack. This is equivalent in concept to the increase in strain energy upon the introduction of the crack, as in the Griffith’s fracture theory. The square-root of the change in net-section strain energy parameter multiplied by the elastic modulus provides an expression that is equivalent to the conventional stress intensity factor expression. The application of the net-section based expression to the standard compact tension, the extended compact tension and the wedge-splitting test specimens shows very good agreements with the crack behaviors as expressed by the stress intensity factor expressions for the respective geometries. The proposed method enables easy analytical determination of stress intensity factors for any asymmetrically-loaded mode-I crack problem.

Study on fracture characteristics of reinforced concrete wedge splitting tests

To study the influence on fracture properties of reinforced concrete wedge splitting test specimens by the addition of reinforcement, and the restriction of steel bars on crack propagation, 7 groups reinforced concrete specimens of different reinforcement position and 1 group plain concrete specimens with the same size factors were designed and constructed for the tests. Based on the double-K fracture criterion and tests, fracture toughness calculation model which was suitable for reinforced concrete wedge splitting tensile specimens has been obtained. The results show that: the value of initial craking load Pini and unstable fracture load Pun decreases gradually with the distance of reinforcement away from specimens

Study on the Constitutive Behavior and Damage Evolution in the FPZ of WST Specimens Using the Vic-2D and Strain Gauges

The Vic-2D is an innovate system that uses a non-invasive method called Digital Image Correlation (DIC) technique, which provides a contour map of strains of an entire specimen surface subject to mechanical tests, based on gray value digitalized images. The paper presents the results of experimental investigations of the constitutive behavior and damage evolution in the fracture process zone (FPZ) of concrete using the Vic-2D, in comparison with the traditional strain gauge method. The model tests were performed with notched concrete specimens via the Wedge Splitting Test (WST) method. During the tests, stress-strain curves and evolution of the damage variable were determined and analyzed at multiple levels. The results provide the achievements obtained and some limitations with both two methods.

Multi-parameter crack tip stress state description for estimation of fracture process zone extent in silicate composite WST specimens

For wedge splitting test specimens, the stress and displacement fields both in the vicinity and also in larger distance from the crack tip are investigated by means of numerical methods. Several variants of boundary conditions were modeled. The stress intensity factor K, T-stress and even higher-order terms of William series were determined and subsequently utilized for analytical approximation of the stress field. A good fit between the analytical and numerical solution in dependence on the distance from the crack tip was shown, compared and discussed. Presented approach is considered as suitable for estimation of the fracture process zone extent in silicate composite materials.

Experimental Study of the Influence of the Initial Notch Length in Cubical Concrete Wedge-Splitting Test Specimens

The wedge-splitting test (WST) is a frequently used test configuration for performing stable crack fracture experiments on concrete specimens, thus allowing to determine the fracture process and crack propagation in the heterogeneous material. However, there are no standard rules regarding the wedge-splitting specimens geometry, groove dimensions or notch length. This paper concentrates on the influence of the initial notch length in geometrically identical, cubical specimens, cast from vibrated concrete. The experimental results of nine WSTs under monotonic loading, including Fsp-CMOD curves - splitting force versus crack mouth opening displacement - and fracture energy Gf, are presented. An important effect of the starting notch length on the fracture properties is observed.

Two-parameter fracture mechanical analysis of a near-crack-tip stress field in wedge splitting test specimens

The stress intensity factor and the T-stress for the near-crack-tip field for wedge splitting test (WST) specimens with several variants of boundary conditions are computed using finite element software. The WST is a convenient alternative to classical fracture tests (bending, tensile) for the quasi-brittle fracture of building materials. The WST specimen is investigated within the framework of two-parameter fracture mechanics; near-crack-tip stress field parameters are determined and compared with those of the compact tension specimen due to its shape similarity to the WST. The sensitivity of the values of these parameters to the boundary conditions is also shown.

Experimental Investigation on Relative Crack Length For Fracture Toughness of Concrete

The wedge splitting test specimens with three series of different relative crack length were used to study the influences of relative crack length on the fracture toughness of common concrete. The suitable formulation for fracture toughness of concrete with different relative crack length was gotten on comparing between fracture toughness test results and computation results of the model developed from Hu formula.

Determining double-K fracture parameters of concrete for compact tension and wedge splitting tests using weight function

The paper presents use of universal form of weight functions for determining the double-K fracture parameters KICini and KICun on compact test and wedge splitting test specimens. The proposed method enables to obtain a closed form expression of cohesion toughness of concrete specimens. A comparison with existing analytical method shows that the weight function method for determination of double-K fracture parameters yields results without any appreciable error. Significant influence of initial notch to depth (a0/D) ratio on the double-K fracture parameters is not also observed. Finally, a possible definition of brittleness of concrete using double-K fracture parameters is proposed.