• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
• /
• pp.659-664
• /
• 2001

Concrete has a different fracture mechanism from the other materials, with the existing of FPZ at the ahead of its cracks, and represents the softening curves at the post-peak load in the load-displacement diagrams. So, it can transmit the stress at the post-peak load. This can not be understood with the traditional concept of strength, but with the theory based energy approach. For the purpose of this study is mainly used RILEM(1990 TC89-FMT) and TPM, and the concrete fracture properties have been evaluated according to the its compressive strength. The evaluated fracture properties is $G_{F}$, $a_{c}$, $K_{IC}$ , CTODc, Q etc.c.c.

• Journal of Korean Neurosurgical Society
• /
• 제57권6호
• /
• pp.484-486
• /
• 2015

Unilateral pedicle stress fracture accompanying spondylolytic spondylolisthesis is rare even in the elderly. Most are associated with major trauma, previous spine surgery, or stress-related activity. Here, the authors describe an unique case of unilateral pedicle fracture associated with spondylolytic spondylolisthesis at the L5 level, which was successfully treated by posterior lumbar interbody fusion with screw fixation at the L5-S1 level. As far as the authors' knowledge, no such case has been previously reported in the literature. The pathophysiological mechanism of this uncommon entity is discussed and a review of relevant literature is included.

• 마이크로전자및패키징학회지
• /
• 제21권2호
• /
• pp.59-64
• /
• 2014

Transfer is the critical issue of producing high-quality and scalable graphene electronic devices. However, conventional transfer processes require the removal of an underlying metal layer by wet etching process, which induces significant economic and environmental problems. We propose the etching-free mechanical releasing of graphene using polymer adhesives. A fracture mechanics approach was introduced to understand the releasing mechanism and ensure highyield process. It is shown that the thickness of adhesive and target substrate affect the transferability of graphene. Based on experimental and fracture mechanics simulation results, we further observed that compliant adhesives can reduce the adhesive stress during the transfer, which also enhances the success probability of graphene transfer.

• 한국정밀공학회지
• /
• 제6권3호
• /
• pp.90-99
• /
• 1989

In this study, J-integral values obtained by various methods, i.e, R-Curve, Unloading Compliance, Strectched Zone Width [SZW], and Acoustic Emission [AE] methods are investigated. Elasto-plastic fracture toughness [$J_IC$] estimations by R-curve method are overestimated than those by SZW method, and those by unloading compliance method is around middle value of them. And the difference between them is little. The $J_IC$ value by AE method was almost agreed with that by SZW, and then proved to be useful. Crack propagation mechanism on fractography is a stable ductile fracture. For the identification of ductile fracture, both fractography analysis and AE method were applied to estimate the characteristics more precisely.

• 대한기계학회논문집A
• /
• 제30권12호
• /
• pp.1573-1580
• /
• 2006

In this study, fatigue tests were carried out under push-pull loading condition using spheroidal graphite cast iron in order to clarify the internal fatigue fracture mechanism in an extremely low cycle fatigue regime. It is found that a successive observation of internal fatigue damage it is found that the fracture processes go through three stages, that is, the generation, growth and coalescence of microvoids originated from debonding of graphite-matrix interface. It is also found that the crack which is initiated from the void propagates by coalescence of neighboring cracks and the fatigue crack growth rate can be expressed in form of the Manson-Coffin rule type. In this paper, quantitative analyses of fatigue properties for realization of simulation about fatigue life evaluation are also presented.

• 소성∙가공
• /
• 제20권4호
• /
• pp.303-308
• /
• 2011

Using a mechano-luminescent(ML) paint, which allows the visualization of fast propagating crack under conventional loading conditions, a catastrophic fracture mechanism associated to crack tip melting and wake bridging in bulk metallic glass, is described in this paper. Fracture occurs in two steps with, first, crack initiation from the mechanically machined sharp notch tip in a rectangular shaped compact tension specimen and melting of its tip due to intense shear deformation within very few deformation bands. Then, the crystalline phase in the glass matrix gradually converts the molten crack into a conventional bridged crack as it propagates.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
• /
• pp.181-184
• /
• 2006

In this investigation, fracture mechanism of the pre-cracked beams strengthened with FRP-Rod and GSP(Glass Fiber-Steel Plate) were experimentally studied by the repeating load test according to the three different loading speeds. In the experiments, it was identified that pre-crack in the damaged beams led the significant fracture type of the strengthened beams and loading speed did not influence the behaviors of the fractures. On the other hand, strengthened beams by GSP have more large increasing effects of the strength comparing to beams strengthened with FRP-Rod, but they have a brittle behaviors in fracture.

• Fibers and Polymers
• /
• 제5권4호
• /
• pp.259-263
• /
• 2004

Rubber-modified epoxy resins have been employed as adhesive and matrix materials for glass and corbon-fiber composites. The behavior of fracture around a crack tip for rubber-modified epoxy resin is investigated through the acoustic emission (AE) analysis of compact tension specimens. Damage zone and rubber particles distributed around a crack tip were observed by a polarized optical microscope and an atomic force microscope (AFM). The damage zone in front of pre-crack tip in rubber-modified specimen $(15wt\%\; rubber)$ began to form at about $13\%$ level of the fracture load and grew in size until $57\%$ load level. After that, the crack propagated in a stick-slip manner. Based on time-frequency analysis of AE signals and microscopic observation of damage zone, it was thought that AE signals with frequency bands of 0.15-0.20 MHz and 0.20­0.30 MHz were generated from cavitation in the damage zone and crack propagation, respectively.

• Computers and Concrete
• /
• 제16권6호
• /
• pp.933-961
• /
• 2015

Damage by high-speed impact fracture is a dominant mode of failure in several applications of concrete structures. Numerical modelling can play a crucial role in understanding and predicting complex fracture processes. The commonly used mesh-based Finite Element Method has difficulties in accurately modelling the high deformation and disintegration associated with fracture, as this often distorts the mesh. Even with careful re-meshing FEM often fails to handle extreme deformations and results in poor accuracy. Moreover, simulating the mechanism of fragmentation requires detachment of elements along their boundaries, and this needs a fine mesh to allow the natural propagation of damage/cracks. Smoothed Particle Hydrodynamics (SPH) is an alternative particle based (mesh-less) Lagrangian method that is particularly suitable for analysing fracture because of its capability to model large deformation and to track free surfaces generated due to fracturing. Here we demonstrate the capabilities of SPH for predicting brittle fracture by studying a slender concrete structure (column) under the impact of a high-speed projectile. To explore the effect of the projectile material behaviour on the fracture process, the projectile is assumed to be either perfectly-elastic or elastoplastic in two separate cases. The transient stress field and the resulting evolution of damage under impact are investigated. The nature of the collision and the constitutive behaviour are found to considerably affect the fracture process for the structure including the crack propagation rates, and the size and motion of the fragments. The progress of fracture is tracked by measuring the average damage level of the structure and the extent of energy dissipation, which depend strongly on the type of collision. The effect of fracture property (failure strain) of the concrete due to its various compositions is found to have a profound effect on the damage and fragmentation pattern of the structure.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
• /
• 제30권6호
• /
• pp.530-535
• /
• 2004

Objectives. The purpose of this study was to evaluate mandibular third molars as risk factors for angle fracture in a patient sample with fractured mandible. Materials and methods. The medical records and panoramic radiographs of 107 patients with mandibular fractures were examined. The presence and absence and degree of impaction of the lower third molar were assessed for each patient and related to the occurrence of fracture of the mandibular angle. Data were also collected for age, sex and mechanism of injury. Data were analyzed by a chisquare statistics and Student t test. Result. The incidence of mandibular angle fracture was found to be significantly greater when a lower third molar was present(p <0.05) especially at class III state.(p < 0.05)(by Pell & Gregory system) Of the 78 patients with a lower third molar, 46(58.97%) had angle fractures. Of the 29 without a lower third molar, 24(82.76%) had not angle fractures. Conclusion. The result of this study showed that the mandibular angle that have a lower third molar is more susceptible to fracture when exposed to an impact than an angle without an lower third molar.