Issue 39

S. Seitl et alii, Frattura ed Integrità Strutturale, 39 (2017) 118-128; DOI: 10.3221/IGF-ESIS.39.13 119 the pulling forces and the hazard of a local fracture originated at these holes. The modified compact tension test (MCT [4, 5, 9, 10, 21, 23) is a quite new test configuration on notched specimens to obtain fracture mechanics parameters of materials in laboratory conditions, note that test is derived from classic CT test. A detailed research program/campaign has to be done before the configuration starts to be used as a standard. The several authors used cohesive crack model and prepared MCT model in software ATENA [10] or in software ABAQUS [5]. Pilot experimental measurement and comparison of selected configurations with three point bending specimen is introduced in contributions [4, 9]. The main advantage of MCT test is a round shape of the specimen that makes it appropriate for testing cement based composites. Due to its shape, it is easy to prepare specimen both ways: by cutting them of the drilled core in case of constructions which are already being used [6-8, 15,] as well as in forms from the fresh concrete mixture [24]. The geometry of the specimen is shown in Fig. 1. Figure 1 : Modified compact tension test: a) schema of the test and b) a photo from the test. The aim of the paper is to provide calibration curves according to four different fracture mechanics parameters and to compare selected case with the values obtained from 3D model with the results from 2D model, which have already been published in [21]. The first considered parameter is stress intensity factor K I [MPa·m 1/2 ], see e.g. [1, 3, 11]. The value of stress intensity factor for each normalized crack length a/W is obtained by linear extrapolation from values in particular nodes behind the crack tip up to 3 mm distance. Values in a number of first nodes had to be neglected due to big mistake caused by stress singularity near to the crack tip. Values of T -stress [MPa] defined e.g. were obtained by different method. Both parameters were normalized as dimensionless biaxiality factors B 1 [-] and B 2 [-] by (1) using the Eqs. (2) and (3), see [11, 13]: , 0 Wt P K  (1) , 0 1 K K B I  (2) , 2 I K a T B   (3) where P is loading force in [N], t is thickness of the specimen in [mm], W stands for the position of loading force in [mm] and a is the crack length in [mm]. a) b) 1.35W x y z

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