• Computers and Concrete
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• 제16권4호
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• pp.605-623
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• 2015

A coupled experimental and numerical study of shear fracture in the edge-notched beam specimens of quasi-brittle materials (concrete-like materials) are carried out using four point bending flexural tests. The crack initiation, propagation and breaking process of beam specimens are experimentally studied by producing the double inclined edge notches with different ligament angles in beams under four point bending. The effects of ligament angles on the shear fracturing path in the bridge areas of the double edge-notched beam specimens are studied. Moreover, the influence of the inclined edge notches on the shear-fracture behavior of double edge-notched beam specimens which represents a practical crack orientation is investigated. The same specimens are numerically simulated by an indirect boundary element method known as displacement discontinuity method. These numerical results are compared with the performed experimental results proving the accuracy and validity of the proposed study.

• 대한치과교정학회지
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• 제28권4호
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• pp.659-668
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• 1998

본 연구는 브라켓 간접부착술식시 레진 베이스의 두께에 따른 전단결합강도와 파절양상을 비교함으로써 레진 베이스 두께 증가시 전단결합강도의 저하여부를 평가하기 위하여 시행되었다. 소의 하악 절치를 포매하여 만든 레진블럭에 micromanipulator를 사용하여 치면과 브라켓 기저면 사이의 광중합형 접착제가 0.0, 0.5, 1.0, 1.5, 2.0 mm두께가 되도록 각각 브라켓을 부착한 다음 만능물성시험기를 이용하여 치면으로부터 하중 위치까지의 거리를 일정하게 유지하면서 레진 베이스의 두께를 증가시킨 경우와 레진 베이스 두께의 증가와 함께 치면으로부터 하중 위치까지의 거리를 증가시킨 경우로 나누어 전단결합강도를 측정하고 파절양상을 관찰하여 다음과 같은 결과를 얻었다. 1. 치면으로부터 하중 위치까지의 거리를 일정하게 유지한 경우 레진 베이스 두께의 증가와 함께 브라켓 기저부로부터 하중 위치까지의 거리가 감소함에 따라 전단결합강도가 유의하게 증가하였다. 2. 레진 베이스 두께의 증가와 함께 치면으로부터 하중 위치까지의 거리를 증가시킨 경우 전단결합강도가 감소하는 것으로 나타났으나 그 유의차는 미미하였다. 3. 접착제 잔류지수를 이용하여 레진 베이스의 두께에 따른 파절양상을 비교 관찰한 결과 유의한 차이를 보이지 않았다. 이상의 실험결과를 볼 때 브라켓 부착시 레진 베이스의 두께에 따른 전단결합강도는 브라켓 기저부로부터 하중 위치까지의 거리가 증가함에 따라 감소하는 반면 레진 베이스 두께의 영향은 크게 받지 않는 것으로 나타났다.

• Structural Engineering and Mechanics
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• 제60권6호
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• pp.939-952
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• 2016

A compression to tensile load transforming (CTT) device was developed to determine indirect tensile strength of concrete material. Before CTT test, Particle flow code was used for the determination of the standard dimension of physical samples. Four numerical models with different dimensions were made and were subjected to tensile loading. The geometry of the model with ideal failure pattern was selected for physical sample preparation. A concrete slab with dimensions of $15{\times}19{\times}6cm$ and a hole at its center was prepared and subjected to tensile loading using this special loading device. The ratio of hole diameter to sample width was 0.5. The samples were made from a mixture of water, fine sand and cement with a ratio of 1-0.5-1, respectively. A 30-ton hydraulic jack with a load cell applied compressive loading to CTT with the compressive pressure rate of 0.02 MPa per second. The compressive loading was converted to tensile stress on the sample because of the overall test design. A numerical modeling was also done to analyze the effect of the hole diameter on stress concentrations of the hole side along its horizontal axis to provide a suitable criterion for determining the real tensile strength of concrete. Concurrent with indirect tensile test, the Brazilian test was performed to compare the results from two methods and also to perform numerical calibration. The numerical modeling shows that the models have tensile failure in the sides of the hole along the horizontal axis before any failure under shear loading. Also the stress concentration at the edge of the hole was 1.4 times more than the applied stress registered by the machine. Experimental Results showed that, the indirect tensile strength was clearly lower than the Brazilian test strength.

• Computers and Concrete
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• 제20권1호
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• pp.57-63
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• 2017

A coupled experimental-numerical study on shear fracture in concrete specimens with different geometries is carried out. The crack initiation, propagation and final breakage of concrete specimens are experimentally studied under compression loading. The load-strain and the strength of the specimens are experimentally measured, indicating decreasing effects of the shear behavior on the failure load of the specimen. The effects of specimen geometries on the shear fracturing path in the concrete specimens are also investigate. Numerical models using an indirect boundary element method are made to evaluate the crack propagation paths of concrete specimens. These numerical results are compared with the performed experiments and are validated experimentally.

• 한국도로학회논문집
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• 제13권4호
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• pp.61-70
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• 2011

본 연구에서는 아스팔트 콘크리트의 전단 물성을 고려한 영구변형 예측 모델을 개발하였다. 아스팔트 콘크리트의 전단 물성과 영구변형과의 상관성을 고찰하기 위해서 세 가지 종류의 아스팔트 콘크리트에 대해서 반복재하삼축압축(RLTC) 시험 및 삼축압축강도 시험과 간접인장강도 시험을 다양한 하중과 온도 조건에서 시행하였다. 주어진 아스팔트 콘크리트에 대하여 온도가 증가함에 따라 점착력은 감소하였으나 온도가 $40^{\circ}C$ 이상인 경우 마찰각은 온도 변화에 민감하지 않은 거동을 나타내었다. 축차응력, 구속압, 온도 및 하중 주파수가 영구변형에 미치는 영향이 크다는 것을 관측할 수 있었다. 이러한 실내 시험 결과로 부터 아스팔트 콘크리트의 전단물성과 하중재하시간에 기초한 영구변형 모델을 개발하였다. 또한 일반적인 포장 단면에서 실시한 포장가속시험 결과를 이용해서 영구변형 모델을 보정하였다. 본 연구에서 제안한 영구변형 모델을 이용하여 다양한 온도와 하중조건에서 아스팔트 콘크리트의 영구변형을 예측할 수 있었다.

• Computers and Concrete
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• 제17권5호
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• pp.639-653
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• 2016

The present article discusses the effect of the ratio of bridge surface to total shear surface, number of bridge areas and normal stress on the failure behavior of the planar non-persistent open joints. Totally, 38 models were prepared using plaster and dimensions of $15cm{\times}15cm{\times}15cm$. The bridge area occupied $45cm^2$, $90cm^2$ and $135cm^2$ out of the shear surface. The number of rock bridges increase in fixed area. Two similar samples were prepared on every variation in the rock bridges and tested for direct shear strength under two high and low normal loads. The results indicated that the failure pattern and the failure mechanism is mostly influenced by the ratio of bridge surface to total shear surface and normal stress so that the tensile failure mode change to shear failure mode by increasing in the value of introduced parameters. Furthermore, the shear strength and shear stiffness are closely related to the ratio of bridge surface to total shear surface, number of bridge areas and normal stress.

• Structural Engineering and Mechanics
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• 제86권5호
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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.

• Restorative Dentistry and Endodontics
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• 제39권1호
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• pp.12-16
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• 2014

Objectives: Extensively destroyed teeth are commonly restored with composite resin before cavity preparation for indirect restorations. The longevity of the restoration can be related to the proper bonding of the resin cement to the composite. This study aimed to evaluate the microshear bond strength of two self-adhesive resin cements to composite resin. Material and Methods: Composite discs were subject to one of six different surface pretreatments: none (control), 35% phosphoric acid etching for 30 seconds (PA), application of silane (silane), PA + silane, PA + adhesive, or PA + silane + adhesive (n = 6). A silicone mold containing a cylindrical orifice ($1mm^2$ diameter) was placed over the composite resin. RelyX Unicem (3M ESPE) or BisCem (Bisco Inc.) self-adhesive resin cement was inserted into the orifices and light-cured. Self-adhesive cement cylinders were submitted to shear loading. Data were analyzed by two-way ANOVA and Tukey's test (p < 0.05). Results: Independent of the cement used, the PA + Silane + Adhesive group showed higher microshear bond strength than those of the PA and PA + Silane groups. There was no difference among the other treatments. Unicem presented higher bond strength than BisCem for all experimental conditions. Conclusions: Pretreatments of the composite resin surface might have an effect on the bond strength of self-adhesive resin cements to this substrate.