• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.40 no.12
• /
• pp.1021-1026
• /
• 2016

In this study, crack resistance is evaluated by the crack tip opening angle (CTOA) using a wedge splitting test (WST) on a viscoelastic particulate reinforced composite based on an HTPB binder. Generally, CTOA, as a function of crack extension, is used in order to determinate fracture resistance and has a steady state relative angle. Digital image correlation (DIC) is used to measure the crack tip opening displacement (CTOD) and crack extension for the critical crack tip opening angle (CTOAc). In these results, the CTOAc value of a particulate reinforced composite tends to approach a constant angle after a small amount of crack extension. The CTOAc value increases with decreasing temperature, from $50^{\circ}C$ to $-40^{\circ}C$. These CTOAc values may be used to measure fracture mechanics parameters for particulate reinforced composite.

• Journal of Ocean Engineering and Technology
• /
• v.21 no.6
• /
• pp.7-15
• /
• 2007

A mechanical model was developed to predict the behavior of point-loaded RC slender beams (a/d > 2.5) without stirrups. It is commonly accepted by most researchers that a diagonal tension crack plays a predominant role in the failure mode of these beams, but the failure mechanism of these members is still debatable. In this paper, it was assumed that diagonal tension failure was triggered by the concrete cover splitting due to the dowel action at the initial location of diagonal tension cracks, which propagate from flexural cracks. When concrete cover splitting occurred, the shape of a diagonal tension crack was simultaneously developed, which can be determined from the principal tensile stress trajectory. This fictitious crack rotates onto the crack tip with load increase. During the rotation, all forces acting on the crack (i.e, dowel force of longitudinal bars, vertical component of concrete tensile force, shear force by aggregate interlock, shear force in compression zone) were calculated by considering the kinematical conditions such as crack width or sliding. These forces except for the shear force in the compression zone were uncoupled with respect to crack width and sliding by the proposed constitutive relations for friction along the crack. Uncoupling the shear forces along the crack was aimed at distinguishing each force from the total shear force and clarifying the failure mechanism of RC slender beams without stirrups. In addition, a proposed method deriving the dowel force of longitudinal bars made it possible to predict the secondary shear failure. The proposed model can be used to predict not only the entire behavior of point-loaded RC slender shear beams, but also the ultimate shear strength. The experiments used to validate the proposed model are reported in a companion paper.

• Computers and Concrete
• /
• v.33 no.3
• /
• pp.265-273
• /
• 2024

Predicting fracture properties requires an understanding of structural failure behaviour in relation to specimen type, dimension, and notch length. Facture properties are evaluated using various testing methods, wedge splitting test being one of them. The wedge splitting test was numerically modelled three dimensionally using the finite element method on self compacting concrete specimens with varied specimen and notch depths in the current work. The load - Crack mouth opening displacement curves and the angle of rotation with respect to notch opening till failure are used to assess the fracture properties. Furthermore, based on the simulation results, failure curve was built to forecast the fracture behaviour of self-compacting concrete. The fracture failure curve revealed that the failure was quasi-brittle in character, conforming to non-linear elastic properties for all specimen depth and notch depth combinations.

• Computers and Concrete
• /
• v.3 no.2_3
• /
• pp.91-102
• /
• 2006

To place concrete overlays has become a standard application in the strengthening and rehabilitation of concrete structures such as bridges, tunnels, parking decks and industrial buildings. In general, connectors are used to ensure a monolithic behavior of the two concrete layers. Within the framework of the development of a new connector wedge splitting tests and shear tests were performed, in addition nonlinear finite element analyses were applied to investigate the load transfer behavior of the connectors for different prototypes. The numerical simulation results were compared to experimental data. The computed load-displacement curve demonstrates good correspondence with the curves obtained in the experiments, and the experimental crack patterns are reasonably simulated by the computed crack propagation. Both numerical and experimental investigations on the wedge splitting test and on the shear test served as basis for the development of new type of connectors.

• Journal of the Korea Concrete Institute
• /
• v.26 no.4
• /
• pp.475-482
• /
• 2014

This paper presents the experimental results concentrically reinforced concrete tension members and compares cracking behavior of amorphous steel fiber and normal steel fiber reinforced concrete members. Two kind of steel fibers were included as a major experimental parameter together with the six cover thickness to bar diameter ratio ($c/d_b$). The presence of amorphous steel fibers effectively controlled the splitting cracks initation and propagation. In the amorphous steel fiber reinforced specimens, no splitting cracks were observed that becomes higher with cover thickness to bar diameter ratio is 2.0. Crack spacing of the each specimens reinforced with amorphous steel fibers and normal steel fibers becomes larger with the increase in cover thickness, and also measured maximum and average crack spacing are significantly smaller than current design code provision. Based on the measured crack spacings, a relationships for predicting the crack spacing is proposed using the measured average crack spacing in amorphous steel fiber reinforced concrete tension members.

• Journal of the Korea Concrete Institute
• /
• v.14 no.1
• /
• pp.58-66
• /
• 2002

The objective of this study is to examine the fracture characteristics of concrete at early ages such as critical stress intensity factor, critical crack-tip opening displacement, fracture energy, and bilinear softening curve based on the concepts of the effective-elastic crack model and the cohesive crack model. A wedge splitting test for Mode I was performed on cubic wedge specimens with a notch at the edge. By taking various strengths and ages, load-crack mouth opening displacement curves were obtained, and the results were analyzed by linear elastic fracture mechanics and the finite element method. The results from the test and analysis showed that critical stress intensity factor and fracture energy increased, and critical crack-tip opening displacement decreased with concrete ages from 1 day to 28 days. By numerical analysis four parameters of bilinear softening curve from 1 day to 28 days were obtained. The obtained fracture parameters and bilinear softening curves at early ages may be used as a fracture criterion and an input data for finite element analysis of concrete at early ages.

• Smart Structures and Systems
• /
• v.29 no.4
• /
• pp.535-547
• /
• 2022

Failure patterns of rock specimens represent valuable information about the mechanical properties and crack evolution mechanism of rock. Several kinds of research have been conducted regarding the failure mechanism of brittle material, however; the influence of brittleness on the failure mechanism of rock specimens has not been precisely considered. In the present study, experimental and numerical examinations have been made to evaluate the physical and mechanical phenomena associated with rock failure mechanisms through the uniaxial compression test. In the experimental part, Unconfined Compressive Strength (UCS) tests equipped with Acoustic Emission (AE) have been conducted on rock samples with three different brittleness. Then, the numerical models have been calibrated based on experimental test results for further investigation and comparing the micro-cracking process in experimental and numerical models. It can be perceived that the failure mode of specimens with high brittleness is tensile axial splitting, based on the experimental evidence of rock specimens with different brittleness. Also, the crack growth mechanism of the rock specimens with various brittleness using discrete element modeling in the numerical part suggested that the specimens with more brittleness contain more tensile fracture during the loading sequences.

• Steel and Composite Structures
• /
• v.48 no.2
• /
• pp.131-143
• /
• 2023

The CFRP bar was used to achieve more ductile and durable headed-stud shear connectors in composite components. Three series of push-out tests were firstly conducted, including specimens reinforced with pure steel fibers, steel and CFRP bars. The distributed stress was measured by the commercial PPP-BOTDA (Pre-Pump-Pulse Brillouin optical time domain analysis) optical fiber sensor with high spatial resolution. A series of numerical analyses using non-linear FE models were also made to study the shear force transfer mechanism and crack response based on the test results. Test results show that the CFRP bar increases the shear strength and stiffness of the large diameter headed-stud shear connection, and it has equivalent reinforcing effects on the stud shear capacity as the commonly used steel bar. The embedded CFRP bar can also largely improve the shear force transfer mechanism and decrease the tensile stress in the transverse direction. The parametric study shows that low content steel fibers could delay the crack initiation of slab around the large diameter stud, and the CFRP bar with normal elastic modulus and the standard reinforcement ratio has good resistance to splitting crack growth in headed stud shear connectors.

• International Journal of Concrete Structures and Materials
• /
• v.2 no.2
• /
• pp.153-160
• /
• 2008

Fracture of prestressed concrete beams is studied with a novel and robust three-dimensional meshfree method. The meshfree method describes the crack as a set of cohesive crack segments and avoids the representation of the crack surface. It is ideally suited for a large number of cracks. The crack is modeled by splitting particles into two particles on opposite sides of the crack segment and the shape functions of neighboring particles are modified in a way the discontinuous displacement field is captured appropriately. A simple, robust and efficient way to determine, on which side adjacent particles of the corresponding crack segment lies, is proposed. We will show that the method does not show any "mesh" orientation bias and captures complicated failure patterns of experimental data well.

• Advances in concrete construction
• /
• v.16 no.6
• /
• pp.277-290
• /
• 2023

In order to study the mechanical properties of basalt fiber reinforced ultra-fine fly ash concrete (BFUFARC), the effects of ultra-fine fly ash (UFA) content, basalt fiber content, basalt fiber length and water reducing agent content on the compressive strength, splitting tensile strength and flexural strength of the composite material were studied through experimental and theoretical analysis. Also, a scanning electron microscope (SEM) was employed to analyze the mesoscopic structure in the fracture surface of composite material specimens at magnifications of 500 and 3500. Besides, the energy release rate (G_c) and surface free energy (γ_s) of crack tip cracking on BFUFARC in different basalt fiber content were studied from the perspective of fracture mechanics. Further, the cracking resistance, reinforcement, and toughening mechanisms of basalt fibers on concrete substrate were revealed by surface free energy of BFUFARC. The experimental results indicated that basalt fiber content is the main influence factor on the splitting tensile strength of BFUFARC. In case that fiber content increased from 0 to 0.3%, the concrete surface free energy at the tip of single-sided crack showed a trend of increased at first and then decreased. The surface free energy reached at maximum, about 3.59 × 10^-5 MN/m. During the process of increasing fiber content from 0 to 0.1%, G_C-2_γS showed a gradually decreasing trend. As a result, an appropriate amount of basalt fiber can play a preventing cracking role by increasing the concrete surface free energy, further effectively improve the concrete splitting tensile performance.