Issue 35

T. Holušová et alii, Frattura ed Integrità Strutturale, 35 (2016) 242-249; DOI: 10.3221/IGF-ESIS.35.28 243 or cement based composites [1]. The common fracture-mechanics test methods for concrete in laboratory conditions are three-point bending (3PB) and four-point bending (4PB) tests, which are both performed on concrete beams of specific dimensions [2]. The specimen for the MCT test is similar to specimens used for another standardized fracture-mechanics test, the so-called wedge-splitting test (WST) [3], for which cubic and cylindrical specimens can be used. The MCT specimen is similar to standard compact tension (CT) test specimens, which are used for fracture and fatigue parameters of metallic materials [4]. The fracture mechanics parameters and fatigue behavior of quasi-brittle materials, which is currently research topic, see following references: the experimental [5-8] and numerical [9, 10]. Previous numerical studies of the modified compact tension test were focused on comparing the fracture energy values that are obtained from the 3PB, WST and MCT [11], or on investigating the influence of the location of the steel bars [12]. Also, measurements were obtained during the experimental test by an ARAMIS 3D optical camera system, and the quality of the numerical model was evaluated [13]. The numerical evaluation of the use of this type of configuration to determine the fracture energy of concrete was performed with ABAQUS software [14]. The aim of this contribution is the comparison of two different specimen fixtures and their possible use during experiments from the numerical point of view. The idea of using eye nuts at the ends of the steel bars (see Fig. 3b) is to avoid an undesirable moment (which could arise due to the way the specimen is held in the grips during the test) and render the experimental set-up as close as possible to that employed in the standard CT test. The fracture energy is calculated according to RILEM recommendations [15] from loading curves obtained from numerical simulations performed with ATENA 2D FE software [16]. Finally, the results are compared and discussed. M ODIFIED C OMPACT T ENSION S PECIMENS s mentioned above, the geometry of MCT test specimens is derived from that of the original standard compact tension test specimen. It is well known that concrete-like materials exhibit good behavior in compression and poor behavior in tension. On the other hand, metallic materials are well known for their high quality in tension and somewhat lower in compression performance due to buckling. When combined, these two materials create optimal construction material. The tests mentioned above represent standard tests for determining the fracture mechanics parameters of concrete-like materials. Typically, specimens for 3PB and 4PB tests are block shaped (their length is significantly greater than their other two dimensions). Cubic and cylindrical specimens are typically used for the WST; in this respect it is similar to the MCT test, for which these shapes can also be used. Figure 1 : Visualization of a modified compact tension specimen in 3D format. A A lig B