• Journal of the Korean Society for Precision Engineering
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• v.17 no.4
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• pp.106-113
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• 2000

One of the recent changes in machining technology is rapid application of micro- and high precision grinding processes. A fine groove generation is necessary for the fabrication of optics, electronics and semiconductor parts. Slot grinding is very efficient for the generation of micro ordered groove with hard and brittle materials. In the process of slot grinding, chipping at the sharp edges and microcracks of the ground grooves are inevitable defects. Chipping should be reduced for the improvement of surface integrity. Mechanical contact with diamond grits causes microcracks at the grooves. This damage resides subsurface, and can be the cause of failure of the punch die. This paper deals with chipping generation at the sharp edges, surface integrity of side groove and fracture strength is related to the microcracks in the slot grinding.

• Steel and Composite Structures
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• v.37 no.6
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• pp.663-678
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• 2020

This paper proposes a novel topology optimization method generating multiple materials for external linear plane crack structures based on the combination of IsoGeometric Analysis (IGA) and eXtended Finite Element Method (X-FEM). A so-called eXtended IsoGeometric Analysis (X-IGA) is derived for a mechanical description of a strong discontinuity state's continuous boundaries through the inherited special properties of X-FEM. In X-IGA, control points and patches play the same role with nodes and sub-domains in the finite element method. While being similar to X-FEM, enrichment functions are added to finite element approximation without any mesh generation. The geometry of structures based on basic functions of Non-Uniform Rational B-Splines (NURBS) provides accurate and reliable results. Moreover, the basis function to define the geometry becomes a systematic p-refinement to control the field approximation order without altering the geometry or its parameterization. The accuracy of analytical solutions of X-IGA for the crack problem, which is superior to a conventional X-FEM, guarantees the reliability of the optimal multi-material retrofitting against external cracks through using topology optimization. Topology optimization is applied to the minimal compliance design of two-dimensional plane linear cracked structures retrofitted by multiple distinct materials to prevent the propagation of the present crack pattern. The alternating active-phase algorithm with optimality criteria-based algorithms is employed to update design variables of element densities. Numerical results under different lengths, positions, and angles of given cracks verify the proposed method's efficiency and feasibility in using X-IGA compared to a conventional X-FEM.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.4
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• pp.62-67
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• 2024

In this paper, we developed and optimized a chitosan-based polymer microbial bead carrier that is cell-friendly, has a high moisture absorption rate, and effectively provides the conditions for microbial biomineral formation as an optimal microbial carrier that protects microorganisms in concrete, and evaluated the self-healing performance of mortar using it. In order to incorporate circular-shaped microbial endospores, a circular-shaped microbial bead carrier was developed by combining chitosan and alginate polymers, and the amount of calcium carbonate produced could be actively controlled by adjusting the composition of the carrier. The amount of biominerals formed and the size of crystals were maximized in the hydrogel bead carrier containing chitosan, and in the case of mortar cracks using this, it was confirmed that self-healing of cracks with a maximum crack width of 0.3mm was achieved within 96 hours after crack generation.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.3
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• pp.133-140
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• 2018

This paper is concerned with the 2-D micostructure generation for $Ni-A{\ell}_2O_3$ dual-phase composite materials and the numerical analysis of mechanical characteristic of hierarchical models of microstructure which are defined in terms of the scale of microstructure. The microstructures of dual-phase composite materials were generated by applying the mathematical RMDF(random morphology description functions) technique to a 2-D RVE of composite materials. And, the hierarchical models of microstructure were defined by the number of Gaussian points. Meanwhile, the volume fractions of metal and ceramic particles were set by adjusting the level of RMD functions. The microstructures which were generated by RMDF technique are definitely random even though the total number of Gaussian points is the same. The randomly generated microstructures were applied to a 2-D beam model, and the variation of normal and shear stresses to the scale of microstructure was numerically investigated. In addition, through the crack analyses, the influence of RMDF randomness and Gauss point number on the crack-tip stress is investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.6
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• pp.609-617
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• 2011

There is a trend towards the progressive use of higher operating temperatures and stresses to achieve improved efficiencies in power-generation equipment. It is important to perform the crack assessment under hightemperature and high-pressure conditions. The C(t)-integral is a key parameter in crack assessment for transient creep states. The estimation of the C(t)-integral is complex when considering the mechanical and thermal loads simultaneously. In this paper, we study estimation of C(t)-integral under combined mechanical and thermal load depending on loading conditions.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.4
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• pp.1-8
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• 2020

Mechanical components that support structures in aerospace and power generation industries require high-strength materials. Particularly, in the aerospace industry, aluminum alloys, titanium alloys, and composite materials are increasingly used due to their high maneuverability and durability to withstand low temperature extreme environments; however, ultra-high-strength steel is still used in key components under heavy loads such as landing gears. In this paper, the fault cause analysis and troubleshooting of aircraft parts made of ultra-high-strength steel (300M) broken during normal operation are described. To identify the cause of the defect, a temporary inspection of the same aircraft was performed, and material testing, non-destructive inspection, microstructure examination, and fracture area inspection of the damaged parts were performed. Fracture analysis results showed that a crack in the shape of a branch developed from the tool mark in the direction of the intergranular strain. Based on the results, the cause of fracture was confirmed to be stress corrosion.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1108-1109
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• 2008

To survive in outdoor environments, photovoltaic modules rely on packaging materials to provide requisite durability. We analyzed the properties of encapsulant materials that are important for photovoltaic module packaging. Recently, the thickness of solar cell gets thinner to reduce the quantity of silicon. And the reduced thickness make it easy to be broken while PV module fabrication process. Solar cell's micro cracks are increasing the breakage risk over the whole value chain from the wafer to the finished module, because the wafer or cell is exposed to tensile stress during handling and processing. This phenomenon might make PV module's maximum power and durability down. So, when using thin solar cell for PV module fabrication, it is needed to optimize the material and fabrication condition which is quite different from normal thick solar cell process. Normally, gel-content of EVA sheet should be higher than 80% so PV module has long term durability. But high gel-content characteristic might cause micro-crack on solar cell. In this experiment, we fabricated several specimen by varying curing temperature and time condition. And from the gel-content measurement, we figure the best fabrication condition. Also we examine the crack generation phenomenon during experiment.

• Composites Research
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• v.24 no.3
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• pp.25-30
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• 2011

The studies on the non-destructive testing methods of the composite materials are very important for improving their reliability and safety. AE(Acoustic Emission) can evaluate the defects by detecting the emitting strain energy when elastic waves are generated by the generation and growth of a crack, plastic deformation, fiber breakage, matrix cleavage or delamination. In this paper, the AE signals of the filament wound composite cylinder and sandwich cylinder during the pressure test were measured and analyzed. The signal characteristics of PVDF sensors were measured, and an AE signal analyzer which had the band-pass filter and L-C resonance filter were designed and fabricated. Also, the crack detection capability of the fabricated AE signal analyzer wes evaluated during the pressure tests of the filament wound composite cylinder and the sandwich cylinder.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.9-9
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• 2008

Recently, the thickness of solar cell gets thinner to reduce the quantity of silicon. And the reduced thickness make it easy to be broken while PV module fabrication process. This phenomenon might make PV module's maximum power and durability down. So, when using thin solar cell for PV module fabrication, it is needed to optimize the material and fabrication condition which is quite different from normal thick solar cell process. Normally, gel-content of EVA sheet should be higher than 80% so PV module has long term durability. But high gel-content characteristic might cause micro-crack on solar cell. In this experiment, we fabricated several specimen by varying curing temperature and time condition. And from the gel-content measurement, we figure the best fabrication condition. Also we examine the crack generation phenomenon during experiment.

• Journal of Industrial Technology
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• v.22 no.A
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• pp.3-8
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• 2002

In this study, extremely low cycle fatigue tests were carried out under push-pull loading conditions using graphite cast iron (GCD). In order to clarify the fatigue fracture mechanism of GCD in an extremely low cycle fatigue regime successive observations of internal fatigue damage were performed. The results obtained are as follows. (1) The process of extremely low cycle fatigue can be classified into three stages which are composed of the generation, growth and coalescence of microvoids inside materials. (2) In an extremely low cycle fatigue regime, microvoids originate from debonding of graphite-matrix interface.