• Structural Engineering and Mechanics
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• v.83 no.4
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• pp.495-513
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• 2022

This paper aims to study the fracture mechanism of rocks under the 'u'shape cutters considering the effects of crack (pre-existing crack) distances, crack spacing and crack inclination angles. The effects of loading rates on the rock fragmentation underneath these cutters have been also studied. For this purpose, nine experimental samples with dimensions of 5 cm×10 cm×10 cm consisting of the non-persistent cracks were prepared. The first three specimens' sets had one non-persistent crack (pre-existing crack) with a length of 2 cm and angularity of 0°, 45°, and 90°. The spacing between the crack and the "u" shape cutter was 2 cm. The second three specimens" set had one non-persistent crack with a length of 2 cm and angularity of 0°, 45°, and 90° but the spacing between pre-existing crack and the "u" shape cutter was 4 cm. The third three specimens'set has two non-persistent cracks with lengths of 2 cm and angularity of 0°, 45° and 90°. The spacing between the upper crack and the "u" shape cutter was 2 cm and the spacing between the lower crack and the upper crack was 2 cm. The samples were tested under a loading rate of 0.005 mm/s. concurrent with the experimental investigation. The numerical simulations were performed on the modeled samples with non-persistent cracks using PFC2D. These models were tested under three different loading rates of 0.005 mm/s, 0.01 mm/sec and 0.02 mm/sec. These results show that the crack number, crack spacing, crack angularity, and loading rate has important effects on the crack growth mechanism in the rocks underneath the "u" shape cutters. In addition, the failure modes and the fracture patterns in the experimental tests and numerical simulations are similar to one another showing the validity and accuracy of the current study.

• Structural Engineering and Mechanics
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• v.81 no.2
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• pp.243-258
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• 2022

In this paper, tensile behavior of joint filling has been investigated under experimental test and numerical simulation (particle flow code). Two concrete slabs containing semi cylinder hole were prepared. These slabs were attached to each other by glue and one cubic specimen with dimension of 19 cm×15 cm×6 cm was prepared. This sample placed in the universal testing machine where the direct tensile stress can be applied to this specimen by implementing a special type of load transferring device which converts the applied compressive load to that of the tensile during the test. In the present work, two different joint filling thickness i.e., 3 mm and 6 mm were prepared and tested in the laboratory to measure their direct tensile strengths. Concurrent with experimental test, numerical simulation was performed to investigate the effect of hole diameter, length of edge notch, filling thickness and filling length on the tensile behavior of joint filling. Model dimension was 19 cm×15 cm. hole diameter was change in four different values of 2.5 cm, 5 cm, 7.5 cm and 10 cm. glue lengths were different based on the hole diameter, i.e., 12.5 cm for hole diameter of 2.5 cm, 10 cm for hole diameter of 5 cm, 7.5 cm for hole diameter of 7.5 cm and 5 cm for hole diameter of 10 cm. length of edge notch were changed in three different value i.e., 10%, 30% and 50% of glue length. Filling thickness were changed in three different value of 3 mm, 6 mm and 9 mm. Tensile strengths of glue and concrete were 2.37 MPa and 6.4 MPa, respectively. The load was applied at a constant rate of 1 kg/s. Results shows that hole diameter, length of edge notch, filling thickness and filling length have important effect on the tensile behavior of joint filling. In fixed glue thinks and fixed joint length, the tensile strength was decreased by increasing the hole diameter. Comparing the results showed that the strength, failure mechanism and fracture patterns obtained numerically and experimentally were similar for both cases.

• Structural Engineering and Mechanics
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• v.86 no.5
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• pp.607-619
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• 2023

This study, it was tried to evaluate the asphalt behavior under tensile loading conditions through indirect Brazilian and direct tensile tests, experimentally and numerically. This paper is important from two points of view. The first one, a new test method was developed for the determination of the direct tensile strength of asphalt and its difference was obtained from the indirect test method. The second one, the effects of particle size and loading rate have been cleared on the tensile fracture mechanism. The experimental direct tensile strength of the asphalt specimens was measured in the laboratory using the compression-to-tensile load converting (CTLC) device. Some special types of asphalt specimens were prepared in the form of slabs with a central hole. The CTLC device is then equipped with this specimen and placed in the universal testing machine. Then, the direct tensile strength of asphalt specimens with different sizes of ingredients can be measured at different loading rates in the laboratory. The particle flow code (PFC) was used to numerically simulate the direct tensile strength test of asphalt samples. This numerical modeling technique is based on the versatile discrete element method (DEM). Three different particle diameters were chosen and were tested under three different loading rates. The results show that when the loading rate was 0.016 mm/sec, two tensile cracks were initiated from the left and right of the hole and propagated perpendicular to the loading axis till coalescence to the model boundary. When the loading rate was 0.032 mm/sec, two tensile cracks were initiated from the left and right of the hole and propagated perpendicular to the loading axis. The branching occurs in these cracks. This shows that the crack propagation is under quasi-static conditions. When the loading rate was 0.064 mm/sec, mixed tensile and shear cracks were initiated below the loading walls and branching occurred in these cracks. This shows that the crack propagation is under dynamic conditions. The loading rate increases and the tensile strength increases. Because all defects mobilized under a low loading rate and this led to decreasing the tensile strength. The experimental results for the direct tensile strengths of asphalt specimens of different ingredients were in good accordance with their corresponding results approximated by DEM software.