• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.4
• /
• pp.1033-1040
• /
• 1995

To simulate strength reliability and durability of ceramic parts under gas turbine application environments, particle impact damage behaviors in silicon carbide oxidized at 1673 K and 1523 K for 200 hours in atmosphere were investigated. The long-term oxidation produced a slight increase in the static fracture strength. Particle impact caused a spalling of oxide layer. The patterns of spalling and damage induced were dependent upon the property and impact velocity of the particle. Especially, the difference in spalling behaviors induced could be explained by introducing the formation mechanism of lateral crack and elastic-plastic deformation behavior at impact sit. At the low impact velocity regions, the oxidized SiC showed a little increase in the residual strength due to the cushion effect of oxide layer, as compared with the as-received SiC without oxide layer.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2003.10a
• /
• pp.64-69
• /
• 2003

This paper describes a study on the tearing damage of the ship's bottom plating during a grounding. It has been known widely that difference scaling laws are applied for bodies undergoing simultaneously plastic flow and crack propagation in the deformation of the plate tearing. Especially, the basic scaling law is not followed for the fracture. In this study plate cutting experiments for the geometrically similar models have been performed in order to verify the problem. From the experimental results, it has been observed that the cutting forces and energy for the larger models are significantly lower than those of the smaller models the damage become large. A simplified analytical method for the estimation of tearing is proposed based on the experiments and it has been observed that the results of the present formula are correlated very well with the experiments

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2002.10a
• /
• pp.118-121
• /
• 2002

Polyvinylidene di-fluoride (PVDF) film sensor appeared to be practically useful for the structural health monitoring of composite materials and structures. PVDF film sensors were either attached to or embedded in the graphite/epoxy composite (CFRP) samples to detect the fatigue damage at the bondline of single-lap joints or the tensile failure of unidirectional laminates. PVDF sensors were sensitive enough to detect and determine the crack front in linear location since composites usually produce very energetic acoustic emission (AE). PVDF sensors are extremely cost-effective, as flexible as other plastic films, in low profile as thin as a few tens of microns, and have relatively wide-band response, all of which characteristics are readily utilized for the structural health monitoring of composite structures. Signals due to fatigue damage showed a characteristics of mode II (shear) type failure whereas those from fiber breakage at DEN notches showed that of mode I (tensile) type fracture.

• International Journal of Highway Engineering
• /
• v.16 no.4
• /
• pp.11-19
• /
• 2014

PURPOSES: This study is to suggest the improvement for bus rapid transit system in Seoul METHODS: The maintenance cost for bus lane damages and plastic deformations are increased by bus passing speed, heavy bus weight, and climate change (localized torrential downpour, subtropical climate) and the accident risk has been increased. RESULTS: Recent analysis of pavement damage indicates that bus lane damage caused by heavy weight is overwhelming and it is urgent to prepare countermeasures. CONCLUSIONS : Pavement data of bus rapid transit system, bus transit numbers and pavement damage elements were analyzed. By analyzing pavement maintenance, design and construction, the countermeasures for the improvement of bus lane pavement and effective maintenance were suggested.

• International Journal of Aeronautical and Space Sciences
• /
• v.14 no.4
• /
• pp.350-355
• /
• 2013

Electrical resistance change measurements were performed, to detect fatigue damage of a quasi-isotropic CFRP and cross-ply CFRP laminates. A four-probe method was used to measure the exact electrical resistance change. A three-probe method was used to measure the electrical contact resistance change, during long cyclic loading. The specimen side surface was observed using a video-microscope to detect damage. The measured electrical resistance changes were compared with the observed damage. The results of this study show that the electrical resistance increase of the quasi-isotropic laminate was caused by a delamination crack between ${\pm}45^{\circ}$ plies. Matrix cracking caused a small electrical resistance increase of the cross-ply laminate, but the decreased electrical resistance caused by the shear-plastic deformation impedes matrix-cracking detection.

• Journal of the Korean Ceramic Society
• /
• v.35 no.12
• /
• pp.1343-1350
• /
• 1998

A study is made of mechanical properties of unglazed matrix as a funtion of sintering temperature and crack patterns in layer structur pottery consisting of glaze and substrate and in matrix which is sintered at 120$0^{\circ}C$ and 130$0^{\circ}C$ respectively. The mechanical properties of matrix are increased due to density and vitrification to 130$0^{\circ}C$ The interface of glazed bilayer reveals the reactive intermediate layer. Herzian indentation testing is used to investigate the evolution of damage modes as a function of load. In the materials sintered at 120$0^{\circ}C$ quasi-plastic deformation is developed at the matrix and the cone-like cracks initiate at the glazing top surface and additionally upward-extending transverse cracks initiate at the internal in-just initiate at the glazing top surface which pass through the interface with increasing of indentation load. Finally the dominant damage mode shifts from substrate quasi-plasticity to coating fracture with increasing sintering temperature.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2009.05a
• /
• pp.378-381
• /
• 2009

In this study, the repetitive loading-unloading tensile tests with AZ31B magnesium sheet metal have been conducted under various elevated temperatures to check out how the Young's moduli of the sheets evolve during the plastic deformation. The loading-unloading tests have been carried out at every 1% of strain increment. With the tested results, some damage parameters of magnesium sheets based on the Lemaitre's continuum damage theory could be calculated at room temperature, $100^{\circ}C$, $150^{\circ}C$, $200^{\circ}C$ and $250^{\circ}C$. It has been shown that the critical damage parameters obtained in all temperature conditions are within the range of 0.12 to 0.18.

• Journal of the Korean Ceramic Society
• /
• v.56 no.1
• /
• pp.77-83
• /
• 2019

MgO-C refractories are used in basic furnaces and steel ladles due to their many desirable properties, such as excellent thermal shock resistance via low thermal expansion, and high thermal conductivity. However, the mechanical and thermal properties of the refractory continuously deteriorate by spalling phenomena and pore generation due to the oxidation of graphite, used as a carbon source, indicating that the characteristics and performance of MgO-C refractories need to be improved by using a new material or composition. In this study, the use of a Hertzian indentation test as a method for determining the damage and fracture behavior of an MgO-C refractory is described. The results highlight that Hertzain indentation tests can be one of the important evaluation tools for quasi-plastic damage accumulation of MgO-C refractories during falling process of scrap metal.

• Journal of Welding and Joining
• /
• v.26 no.3
• /
• pp.67-73
• /
• 2008

Fatigue life evaluation of welded structures in a range of high cycles is one of the most difficult problems since extremely small plastic deformation and damage occur during the loading cycles. Moreover, it is very difficult to identify the strong non-linearities of welding, inducing residual stress. In this paper, numerical fatigue test method for welded structures was developed using continuum damage mechanics with inherent strain. Recently, continuum damage mechanics, which can simulate both crack initiation at the micro-scale level and crack propagation at the meso-scale level, has been adopted in the fracture related problem. In order to consider the residual stresses in the welded strictures, damage calculation in conjunction with welding, inducing inherent strain, was proposed. The numerical results obtained from the damage calculation were compared to experimental results.

• Advanced Composite Materials
• /
• v.18 no.2
• /
• pp.121-134
• /
• 2009

The present study investigated, both experimentally and numerically, the improvement of low-velocity impact damage resistance of carbon fiber reinforced plastic (CFRP) laminates due to through-the-thickness stitching. First, we conducted drop-weight impact tests for stitched and unstitched laminates. The results of damage inspection confirmed that stitching did improve the impact damage resistance, and revealed that the improvement effect became greater as the impact energy increased. Moreover, the stitching affected the through-the-thickness damage distribution. Next, we performed FEM analysis and calculated the energy release rate of the delamination crack using the virtual crack closure technique (VCCT). The numerical results revealed that the stitching affected the through-the-thickness damage distribution because the stitch threads had a marked effect on decreasing both the modes I and II energy release rate around the bottom of the laminate. Comparison of the results for models that contained delaminations of various sizes revealed that the energy release rate became lower as delamination size increased; therefore the stitching improved the impact resistance more effectively when the impact energy was higher.