• Design & Manufacturing
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• v.16 no.2
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• pp.1-6
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• 2022

As environmental regulations are strengthened, automobile manufacturers continuously research lightweight structures based on carbon fiber reinforced plastic (CFRP). However, it is difficult to see the effect of strength reinforcement when using a single CFRP material. To improve this, a hybrid laminate in which CFRP is mixed with the existing body structural steel was proposed. In this paper, CFRP patch reinforcement is applied to each compression/tensile action surface of a 22MnB5 metal sheet, and it was evaluated through a 3-point bending experiment. Progressive failure was observed in similar deflection on bending deformation to each one-sided reinforced specimen. After progressive failure, the tensile reinforced specimen was confirmed to separate the damaged CFRP patch and 22MnB5 sheet from the center of the flexure. The compression reinforced specimen didn't separate that CFRP patch and 22MnB5, and the strength reinforcement behavior was confirmed. In the compression reinforced specimen, damaged CFRP patches were observed at the center of flexure during bending deformation. As a result of checking the specimen of the compression reinforcement specimen with an optical microscope, It is confirmed that the damaged CFRP patch and the reinforced CFRP patch overlapped, resulting in a concentrated load. Through the experimental results, the 22MnB5 strength reinforcement characteristics according to the reinforcement position of the CFRP patch were confirmed.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.6
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• pp.459-467
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• 2016

Using a line scan camera and a Galvano mirror, we constructed a high-speed line-scanning microscope that can generate 2D images ($8000{\times}8000pixels$) without any moving parts. The line scanner consists of a Galvano mirror and a cylindrical lens, which creates a line focus that sweeps over the sample. The measured resolutions in the x (perpendicular to line focus) and y (parallel to line focus) directions are both $2{\mu}m$, with a 2X scan lens and a 3X relay lens. This optical system is useful for measuring defects, such as spalling, chipping, delamination, etc., on the surface of carbon fiber reinforced plastic (CFRP) holes after machining in conjunction with adjustments in the angle of LED lighting. Defects on the inner wall of holes are measured by line confocal laser scanning. This confocal method will be useful for analyzing defects after CFRP machining and for fast 3D image reconstruction.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.3
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• pp.24-29
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• 2017

In this study, a seat cross member was fabricated by optimizing the resin transfer molding processing of CFRP (Carbon Fiber Reinforced Plastics) materials. This seat cross member is used in automotive underbody parts and provides side impact support. The seat cross was manufactured via vacuum resin transfer molding. The process included 1min of resin injection, 8 mins of heating, and 1 min of cooling, for a total molding time of 10mins. Tensile test results showed an average breaking load of 21.50kN, a tensile strength of 404 MPa, and an elastic modulus of 46.2 GPa. As a result, the CFRP seat cross provides the same strength as a similar steel part, but weighs 42% less.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.1
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• pp.17-22
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• 2011

Ultimate goals in vehicle design can be summarized as environment-friendliness and safety. Along with these requirements, the importance of natural environment conservation has been focused lately. Therefore, reduced emission from vehicle and improved efficiency has become the top priority projects throughout the world. CFRP(Carbon Fiber Reinforced Plastics) of the advanced composite materials as structure materials for vehicles, has a widely application in lightweight structural materials of air planes, ships and automobiles because of high strength and stiffness. This study is to investigate the energy absorption characteristics of CFRP hat-shaped section members under the axial impact collapse test. The CFRP hat-shaped section members which manufactured from unidirectional prepreg sheets were made of 8plies. The axial impact collapse tests were carried out for each section members. The collapse mode and energy absorption characteristics were analyzed for CFRP hat-shaped section member according to the interface numbers(2, 3, 4, 6 and 7).

• Journal of the Korean Society for Precision Engineering
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• v.34 no.4
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• pp.243-246
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• 2017

In this study, flexible fixtures and end effectors are conceptually designed for the holding of thin-walled carbon-fiber reinforced-plastic (CFRP) workpieces in machining processes. Firstly, the fixture scenarios and system requirements for the conceptual designs of flexible-fixture and core units are proposed, including the propounding of the workpiece-holding mechanism and the core-unit requirements. A ball-joint pneumatic system is determined as a locking mechanism of the flexible-fixture system for the machining of thin-walled components. Secondly, conceptual designs of the core units are suggested with the driven requirements from the fixture scenarios. A self-tilting mechanism and an end-effector return mechanism are also proposed. Finally, the prototypes of the core units are manufactured, and the workpiece-holding capacity of each prototype is measured.

• Composites Research
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• v.26 no.3
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• pp.195-200
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• 2013

This study aims to detecting and analyzing the defects of damaged carbon fiber reinforced composites after impacts, particularly focusing on barely visible impact damages. The impact test was progressed by a drop-weight machine and applied to introduce simulated damages on laminated composites used in aircrafts. Various nondestructive testing (NDT) techniques were applied to identify the defects on the specimens with different levels of impact energies. Based on the measurements data, the levels of the barely visible impacts, and the applicability and effectiveness of the detection methods were discussed. Generally, the results demonstrated that their inner damages contained bigger footprints than those on the surfaces. However, when the damage energy was low, it was found that the inner damage size could be smaller than those appeared on the surfaces.

• Journal of the Korean Society of Safety
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• v.27 no.6
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• pp.20-25
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• 2012

Currently, the most important purpose in designing automobile is environment-friendly and safety performance aspect. CFRP(Carbon Fiber Reinforced Plastics) of the advanced composite materials as structure materials for vehicles, has a wide application in lightweight structural materials of air planes, ships and automobiles because of high strength and stiffness. In this study, experimental investigations are carried out for CFRP single and double hat shaped section member in order to study the effect of various stacking condition. They were cured by heating to the appropriate curing temperature($130^{\circ}C$) by means of a heater at the vacuum bag of the autoclave. The stacking conditions were selected to investigate the effect of the interface numbers. The CFRP single and double hat shaped section members which manufactured from unidirectional prepreg sheets were made of 8ply. The static collapse tests performed and the collapse mode and energy absorption capability were analyzed according to interface number.

• Steel and Composite Structures
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• v.29 no.5
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• pp.635-645
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• 2018

Beam-column joints play a significant role in static and dynamic performances of reinforced concrete frame structures. This study contributes a numerical approach of topologically optimal design of carbon fiber reinforced plastics (CFRP) to retrofit existing beam-column connections with crack patterns. In recent, CFRP is used commonly in the rehabilitation and strengthening of concrete members due to the remarkable properties, such as lightweight, anti-corrosion and simplicity to execute construction. With the target to provide an optimal CFRP configuration to effectively retrofit the beam-column connection under semi-failure situation such as given cracks, extended finite element method (X-FEM) is used by combining with multi-material topology optimization (MTO) as a mechanical description approach for strong discontinuity state to mechanically model cracked structures. The well founded mathematical formulation of topology optimization problem for cracked structures by using multiple materials is described in detail in this study. In addition, moved and regularized Heaviside functions (MRHF), that have the role of a filter in multiple materials case, is also considered. The numerical example results illustrated in two cases of beam-column joints with stationary cracks verify the validity, benefit and supremacy of the proposed method.

• Smart Structures and Systems
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• v.28 no.6
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• pp.737-744
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• 2021

In this study, structural health monitoring (SHM) methods of carbon fiber reinforced plastics (CFRPs) were investigated using electrical resistance. The developed sensing technique monitored electrical resistance in accordance with the impact damage of a CFRP. The changes in electrical resistances with multiple electrode sets enabled SHM without extra sensors so that this technique can be called self-sensing. Moreover, this study proposed electrodes only at peripheral side of a structure to minimize the number of electrodes compared to those in an array which has square number of sensors as the sensing area increases. For the intensive investigation, electromechanical sensitivity in terms of electrode distance was analyzed and optimized under drop weight impact testing. Then, SHM methods with electrodes in an array and electrodes in peripheral edges were comparatively investigated. The developed methods successfully localized impact damages into 2D coordinates. Furthermore, damage severity can be shown with a damage map by calculating electrical resistance change ratio. Therefore, structural health self-sensing system using electrical resistance was successfully developed with the minimum number of electrodes.

• Composites Research
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• v.28 no.5
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• pp.327-332
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• 2015

In this research, a parametric study was carried out to design a metal-carbon fiber reinforced plastics (CFRP) hybrid pantograph for weight reduction of high speed train (KTX). To design a light-weight and high-stiffness pantograph, some parts of the original steel upper arm was replaced by CFRPs with appropriate stacking sequences. For the parametric study, steel was replaced by aluminium considering structure stiffness and weight of hybrid upperarm of a pantograph. Finite element analysis (FEA) was performed for checking the structure stiffness with varying design parameters. Static vertical load stiffness and weight changing ratio were derived from real CX-PG pantograph model analyses. From the FEA results, the geometries of high-stiffness, light-weight pantograph have been suggested.