• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.15 no.5 s.98
• /
• pp.620-628
• /
• 2005

In this paper, we studied about the dynamic behavior of a cracked rotating cantilever beam. The influences of a rotating angular velocity, the crack depth and the crack position on the dynamic behavior of a cracked cantilever beam have been studied by the numerical method. The equation of motion is derived by using the Lagrange's equation. The cracked cantilever beam is modeled by the Euler-Bernoulli beam theory. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations. The lateral tip-displacement and the axial tip-deflection of a rotating cantilever beam is more sensitive to the rotating angular velocity than the depth and position of crack. Totally, as the crack depth is increased, the natural frequency of a rotating cantilever beam is decreased in the first and second mode of vibration. When the crack depth is constant, the natural frequencies of a rotating cantilever beam are proportional to the rotating angular velocity in the each direction.

• Structural Engineering and Mechanics
• /
• v.76 no.4
• /
• pp.541-550
• /
• 2020

As a new type of concrete material, basic magnesium sulfate cement concrete (BMSC) has the advantages, such as early strength, high strength, good toughness and crack resistance. However, it is unclear about the degradation of the mechanical properties of BMSC columns, which is exposed to the natural environment for several years. In order to apply this new concrete to practical engineering, six large-eccentricity compressive columns of BMSC were studied. The mechanical properties such as the crack propagation, failure morphology, lateral displacement and bearing capacity of BMSC column were studied. The results show that the degradation rate of ultimate load of BMSC column is from 6% to 7%. The degradation rate of the stiffness of the column is from 6% to 13%. With the increase of compressive strength of BMSC, the axial displacement and lateral displacement are gradually reduced. The calculation model of bearing capacity of the BMSC column under the large eccentric compression is proposed. This paper provides a reference for the application of BMSC columns in the civil engineering.

• 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.

• Tribology and Lubricants
• /
• v.10 no.3
• /
• pp.62-70
• /
• 1994

An analytical model of the stress field caused by sliding indentation of brittle materials is developed. The complete stress field is treated as the superposition of applied normal and tangential forces with a sliding blister approximation of the localized inelastic deformation occuring just underneath the indenter. It is shown that lateral cracking is produced by the sliding blister stress field and that median cracking is caused by the applied contact forces. The model is combined with an experimental volume change measurements to show that the relative magnitude of tensile stresses governing lateral crack and median crack growth varies with the magnitude of the applied load. This prediction is consistent with the different regimes of experimentally observed cracking in soda-lime glass.

• Tribology and Lubricants
• /
• v.24 no.6
• /
• pp.332-337
• /
• 2008

This paper presents the surface defect analysis based on the experimental investigation of scribed glasses. The scribing process by a diamond wheel cutter is widely used as a reliable and inexpensive method for sizing of glass sheets. The wheel cutter generates a small median crack on the glass surface, which is then propagated through the glass thickness for complete separation. The surface contour patterns in which are formed during a scribing process are strongly related to wheel cutter parameters such as wheel tip surface finish, tip angle and wheel diameter, and cutting process parameters such as scribing pressure, speed and tooling technique. The scribed surface of a glass sheet provides normal Wallner lines, which represent regular median cracks and crack propagation in glass thickness, and abnormal surface roughness patterns. In this experimental study, normal and abnormal surface topographic patterns are classified based on the surface defect profiles of scribed glass sheets. A normal surface of a scribed glass sheet shows regular Wallner lines with deep median cracks. But some specimens of scribed glass sheets show that abnormal surface profiles of glass sheets in two pieces are represented by a chipping, irregular surface cracks in depth, edge cracks, and combined crack defects. These surface crack patterns are strongly related to easy breakage of the scribed glass imposed by external forces. Thus the scribed glass with abnormal crack patterns should be removed during a quality control process based on the surface defect classification method as demonstrated in this study.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2000.04a
• /
• pp.20-25
• /
• 2000

In order to study the impact fracture behavior of brittle materials, a steel-ball-impact experiment was Performed. Five kinds of materials were used in this study : soda-lime glass plates, glass/epoxy prepreg-one layer-bonded and unbonded glass plates, glass/epoxy prepreg-three layers-bonded and unbonded glass plates. Fracture patterns, the maximum stress and absorbed fracture energy were observed according to various impact velocities 40-120m/s. With increasing impact velocity, ring crack, cone crack, radial crack and lateral crack took place in the interior of glass plates. The generation of such cracks was largely reduced with glass/epoxy prepreg coating. Consequently, it is thought that the characteristics of the dynamic Impact fracture behavior could be evaluated using the absorbed fracture energy and the maximum stress measured at the back surface of glass plates.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.7 no.2
• /
• pp.35-41
• /
• 1988

The optimum test conditions of measuring the crack height were determined for the two-probe ultrasonic diffraction method. The applicability and the accuracy of the two-probe ultrasonic diffraction method on the inclined artificial cracks and the fatigue cracks were evaluated. It us possible to measure the height of the normal and inclined artificial cracks with the maximum error of ${\pm}\;0.5mm$ with the two-probe ultrasonic diffraction method. It was found, however, that the accuracy of this method in meaasuring the height of the fatigue crack depends on the degree of closure of the crack tip. It was desirable to choose a refraction angle as small as possible, but the angle should not be so small that the distortion of the lateral waveform became appreciable.

• The Korean Journal of Ceramics
• /
• v.5 no.2
• /
• pp.119-124
• /
• 1999

Silicon nitride ceramics with highly oriented microstructure were prepared by tape casting a slurry containing 5 wt% of the silicon nitride whiskers. The whiskers were aligned in the casting direction and worked as seeds for the grain growth. The anisotropy was observed from the sintering shrinkage, Vickers indentation crack lengths, and XRD patterns. The cracks were much longer on the surface normal to the aligned grains than on the tape casting surface where the lateral cracks were also observed. The effect of sintering additives and the annealing treatment on the indentation crack length was examined. The sample with higher silica content had longer cracks than the one with lower silica content. The crack length anisotropy increased after annealing at 2123K.

• Advances in materials Research
• /
• v.12 no.4
• /
• pp.273-286
• /
• 2023

The fracture mechanics make it possible to characterize the behavior with cracking of structures using parameters quantifiable in the sense of the engineer, in particular the stress field, the size of the crack, and the resistance to cracking of the material. Any structure contains defects, whether they were introduced during the production of the part (machining or molding defects for example). The aim of this work is to determine numerically by the finite element method the stress concentration factor Kt of a plate subjected to a tensile loading containing a lateral form defect with different sizes: a semicircle of different radii, a notch with different opening angles and a crack of different lengths. The crack propagation is then determined using the extended finite element technique (X-FEM). The modeling was carried out using the ABAQUS calculation code.

• Journal of Ocean Engineering and Technology
• /
• v.12 no.3 s.29
• /
• pp.49-59
• /
• 1998

The damage mechanism of $Cr_2O_3$ plasma coated soda-lime glass and uncoated glass by steel ball particle impact was analyzed in this study. And the shape variation of the cracks was investigated by stereo-microscope according to the impact velocity and steel ball diameter. In order to improve the damage reduction effect by $Cr_2O_3$ coating layer, crack size was measured and surface erosion state was observed for both of two kinds of specimen after impact experiment. And the results were compared with each other. The 4-point bending test was performed according to ASTM D790 testing method to evaluate the effect of coating layer for bending strength variation. As a result, it was found that the crack size of $Cr_2O_3$ coated specimen was smaller than that of uncoated one, because of the impact absorption by interior pores in the coating layer and the load dispersion by the structural characteristic of the coating layer. For the specimens subjected to the steel ball impact, the bending strength of coated specimen was higher than that of uncoated specimen.