• Computational Structural Engineering
• /
• v.9 no.3
• /
• pp.199-207
• /
• 1996

When an initially straight thin cylinder is bent, there is a tendency for the cross section to flatten. This phenomenon was investigated by L.G. Brazier in 1927 and is called "Brazier Effect" or "Brazier Theory". The main characteristic is the reduction of carrying capacity due to the decrease of bending stiffness by shortening of thickness with the increase of external load. And the relationship of curvature-bending moment becomes a soft spring type as shown in Fig.2. In this paper, the Brazier theory on plate type structures is investigated from the following view points : (1) What is the Brazier effect? (2) the reason of the occurrence of the Brazier effect in plate type structures by using beam model and (3) factors which cause the brazier effect.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.25 no.4
• /
• pp.293-300
• /
• 2012

In this study, the delamination analysis has been implemented to investigate the initiation and propagation of crack in composite laminates composed of orthotropic materials. A simple modeling was achieved by moving nodal technique without re-meshing work when crack propagation occurred. This paper aims at achieving two specific objectives. The first is to suggest a very simple modeling scheme compared with those applied to conventional h-FEM based models. To verify the performance of the proposed model, analysis of double cantilever beams with composite materials was implemented and then the results were compared with reference values in literatures. The second one is to investigate the behavior of interior delamination problems using the proposed model. To complete these objectives, the full-discrete-layer model based on Lobatto shape functions was considered and energy release rates were calculated using three-dimensional VCCT(virtual crack closure technique) based on linear elastic fracture mechanics.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.20 no.6
• /
• pp.545-554
• /
• 2000

Compton X-ray backscatter technique has been used to quantitatively assess the impact damage in quasi-isotropic laminated composites and to obtain a cross-sectional profile of impact-damaged laminated composites from the density variation of the cross section. An adaptive filter is applied to the Compton backscattering data for the reconstruction and noise reduction from many sources including quantum noise, especially when the SNR(signal-to-noise ratio) of the image is relatively low. A nonlinear reconstruction model is also proposed to overcome distortion of the Compton backscatter image due to attenuation effects, beam hardening, and irregular distributions of the fibers and the matrix in composites. Delaminations masked or distorted by the first few delaminations near the front surface are detected and characterized both in width and location, by application of an error minimization algorithm.

• Composites Research
• /
• v.13 no.1
• /
• pp.89-97
• /
• 2000

Fatigue damage detection and vibration sensing for a laminated composites and impact location detection for a steel beam have been carried out using optical fiber sensor. Intensity based optical fiber sensor is constructed by placing two cleaved fiber end in a hollow glass tube, and multiple reflection within the cavity is considered. Fatigue signals are measured by embedded optical fiber, surface mounted optical fiber sensor and strain gage simultaneously. For vibration sensing, optical fiber sensor is mounted on the carbon fiber composite beam and its response to free vibration and forced vibration is investigated. In impact location detection, two optical fiber sensors are used and the information obtained from two sensors is arrival time delay of vibration caused by impact. Impact location can be calculated from this time delay. The obtained results show that the intensity based optical fiber sensor provide reliable data during long-term fatigue loading, unlike strain gage which deteriorate during the early part of the fatigue test. Optical fiber sensor signals coincide with gap sensor in vibration sensing. The precise locations of impact can be detected within 4.1% error limit.

• Journal of the Korean Wood Science and Technology
• /
• v.42 no.5
• /
• pp.571-578
• /
• 2014

As a way of developing wooden joint development, a glass fiber reinforced wood plate was manufactured to replace a steel plate. Also, the fracture toughness was evaluated. Through application to a cantilever-type specimen made of a column and a beam, the moment resistance performance was evaluated. For the fracture toughness specimen of the wood plate, 12 types were manufactured by varying the combination of a main member (veneer and plywood) and reinforcement (glass fiber sheet and glass fiber cloth). The results of the fracture toughness test indicated that the 5% yield load of the specimen using plywood was 18% higher than that of the specimen using veneer, and that the specimen reinforced by inserting glass fiber sheets between testing materials (Type-3-PS) had the highest average 5% yield load 4841 N. Thus, a moment resistance strength test was performed by applying Type-3-PS to a column-beam joint. The results of the test indicated that compared to the specimen using a steel plate and a drift pin (Type-A), the maximum moment ratio of the specimen using a glass fiber reinforced wood plate (Type-3-PS) and a drift pin (Type-B) was 0.79; and that a rupture occurred in the wood plate due to high stiffness of the drift pin. The maximum moment ratio of the specimen using a glass fiber reinforced wood plate (Type-3-PS) and a glass fiber reinforced wooden laminated pin (Type-C) was 0.67, which showed low performance. However, unlike Type-A, a ductile fracture occurred on Type-C, and the load gradually decreased even after the maximum moment.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.32 no.7
• /
• pp.43-50
• /
• 2004

For the simultaneous measurement of strain and damage signal a fiber Bragg grating sensor system with a dual demodulator was proposed. The dual demodulator is composed of a demodulator using a tunable Fabry-Perot filter measuring the low-frequency signal with large magnitude such as strain and the other using a passive Mach-Zehnder interferometer detecting the high-frequency signal with small amplitude such as impact or damage signal. Using the proposed fiber Bragg grating sensor system, both the strain and damage signals of a cross-ply laminated composite beam under tensile loading were simultaneously measured. The strain and damage signals detected by single fiber Bragg grating sensor showed that sudden strain shifts were accompanied with vibration at a maximum frequency of several hundreds of kilohertz at the instant of matrix crack propagation in the 90 degree layer in composite beam.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2004.04a
• /
• pp.95-102
• /
• 2004

For the simultaneous measurement of strain and damage signal, a fiber Bragg grating sensor system with a dual demodulator was proposed. One demodulator using a tunable Fabry-Perot filter can measure low-frequency signal such as strain and the other demodulator using a passive Mach-Zehnder interferometer can detect high-frequency signal such as damage signal or impact signal. Using a proposed fiber Bragg grating sensor system, both the strain and damage signal of a cross-ply laminated composite beam under tensile loading were simultaneously measured. Analysis of the strain and damage signals detected by single fiber Bragg grating sensor showed that sudden strain shifts were induced due to transverse crack propagation in the 90 degree layer of composite beam and vibration with a maximum frequency of several hundreds of kilohertz was generated.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.18 no.7
• /
• pp.97-103
• /
• 2019

Mn+1AXn (MAX) phases are a family of nano-laminated compounds that possess unique combination of typical ceramic properties and typical metallic properties. As a member of MAX-phase, $Ti_2AlN$ bulk materials are attractive for some high temperature applications. In this study, $Ti_2AlN$ bulk with high density were synthesized by spark plasma sintering method. X-ray diffraction, micro-hardness, electrical and thermal conductivity were measured to compare the effect of material properties both $Ti_2AlN$ bulk samples and a conventional Ti-6Al-4V alloy. A femto-second laser conditions were conducted at a repetition rate of 6 kHz and laser intensity of 50 %, 70% and 90 %, respectively, laser confocal microscope were used to evaluate the width and depth of ablation. Consequently, the laser ablation result of the $Ti_2AlN$ sample than that of the Ti-6Al-4V alloys show a considerably good ablation characteristics due to its higher thermal conductivity regardless of to high densification and high hardness.

• Radiation Oncology Journal
• /
• v.17 no.3
• /
• pp.256-260
• /
• 1999

Purpose : An investigation has been carried out on the factors which affect the response reading of thermoluminescent dosimeters (TLD-100) loaded with thin material in high energy Photon. The aim of the study was to assess the energy response of TLD-100 to the therapeutic ranges of photon beam. Materials and Methods : In this technique, TLD-100 (abbreviated as TLD) chips and three different thin material (Tin, Gold, and Tissue equivalent plastic plate) which mounted on the TLD chip were used in the clinical photon beam. The thickness of each metal plates was 0.1 mm and TE plastic plate was 1 mm thick. These compared with the photon energy dependence of the sensitivities of TLD (normal chip), TLD loaded with Tin or Gold plate, for the photon energy range 6 MV to 15 MV, which was of interest in radiotherapy. Results : The enhancement of surface dose in the TLD with metal plate was clearly detected. The TLD chips with a Gold plate was found to larger response by a factor of 1.83 in 10 MV photon beam with respect to normal chip. The sensitivity of TLD loaded with Tin was less than that for normal TLD and TLD loaded with Gold. The relative sensitivity of TLD loaded with metal has little energy dependence. Conclusion : The good stability and linearity with respect to monitor units of TLD loaded with metal were demonstrated by relative measurements in high energy Photon ($6\~15$ MV) beams. The TLD laminated with metals embedded system in solid water phantom is a suitable detector for relative dose measurements in a small beam size and surface dose.

• Structural Engineering and Mechanics
• /
• v.73 no.3
• /
• pp.353-365
• /
• 2020

In the previous studies, the authors proposed the use of laminated veneer lumber - carbon fiber reinforced polymer (LVL-CFRP) composite beams for structural application. Bond strength of the LVL-to-CFRP interface and flexural strengthening schemes to increase the bending capacity subjected to positive and negative moment were discussed in the previous works. In this article, theoretical models are proposed to predict the moment capacity when the LVL-CFRP beams are subjected to negative moment. Two common failure modes - CFRP fracture and debonding of CFRP are considered. The non-linear model proposed for positive moment is modified for negative moment to determine the section moment capacity. For the debonding based failure, previously developed bond strength model for CFRP-to-LVL interface is implemented. The theoretical models are validated against the experimental results and then use to determine the moment-rotation behaviour and rotational rigidity to compare the efficacy of various strengthening techniques. It is found that combined use of bi- and uni-directional CFRP U-wrap at the joint performs well in terms of both moment capacity and rotational rigidity.