• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.4
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• pp.405-413
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• 2015

In the US, the number of cases of subterranean water contamination from tritium leaking through a damaged buried nuclear power plant pipe continues to increase, and the degradation of the buried metal piping is emerging as a major issue. A pipe blocked from corrosion and/or degradation can lead to loss of cooling capacity in safety-related piping resulting in critical issues related to the safety and integrity of nuclear power plant operation. The ASME Boiler and Pressure Vessel Codes Committee (BPVC) has recently approved Code Case N-755 that describes the requirements for the use of polyethylene (PE) pipe for the construction of Section III, Division 1 Class 3 buried piping systems for service water applications in nuclear power plants. This paper contains tensile and slow crack growth (SCG) test results for high-density polyethylene (HDPE) pipe welds under the environmental conditions of a nuclear power plant. Based on these tests, the fracture surface of the PENT specimen was analyzed, and the fracture mechanisms of each fracture area were determined. Finally, by using 3D finite element analysis, limit loads of HDPE related to premature failure were verified.

• Elastomers and Composites
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• v.44 no.4
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• pp.401-407
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• 2009

Commercial grades of solution styrene-butadiene rubbers extended with high aromatic oils having high polycyclic aromatic compounds (PCA) and low PCA oils were used to study the effect of the processing oil particularly on the crack propagation resistance and frictional wear resistance of the vulcanizates. The aromatic oil based vulcanizates exhibited superior fracture behavior over the low PCA oil extended vulcanizates based on tensile and trouser tear tests. Compounds with aromatic oil showed superior crack propagation resistance compared with those containing low PCA oil, especially at the lower ranges of tearing energy. In terms of frictional wear resistance, the aromatic oil extended compounds showed superior performance particularly in the lower frictional work ($W_f$) range but in the higher $W_f$ range the low PCA oil extended vulcanizates performed better.

• Structural Engineering and Mechanics
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• v.66 no.3
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• pp.343-351
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• 2018

Brazilian disc test is one of the most widely used experiments in the literature of geo-mechanics. In this work, the pre-holed concrete Brazilian disc specimens are numerically modelled by a two-dimensional discrete element approach. The cracks initiations, propagations and coalescences in the numerically simulated Brazilian discs (each containing a single cylindrical hole and or multiple holes) are studied. The pre-holed Brazilian discs are numerically tested under Brazilian test conditions. The single-holed Brazilian discs with different ratios of the diameter of the holes to that of the disc radius are modelled first. The breakage load in the ring type disc specimens containing an internal hole with varying diameters is measured and the crack propagation mechanism around the wall of the ring is investigated. The crack propagation and coalescence mechanisms are also studied for the case of multi-holes' concrete Brazilian discs. The numerical and experimental results show that the breaking mechanism of the pre-holed disc specimens is mainly due to the initiation of the radially induced tensile cracks which are growth from the surface of the central hole. Radially cracks propagated toward the direction of diametrical loading. It has been observed that for the case of disc specimens with multiple holes under diametrical compressive loading, the breaking process of the modelled specimens may occur due to the simultaneous cracks propagation and cracks coalescence phenomena. These results also show that as the hole diameter and the number of the holes increases both the failure stress and the crack initiation stress decreases. The experimental results already exist in the literature are quit agree with the proposed numerical simulation results which validates this simulation procedure.

• Journal of Ocean Engineering and Technology
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• v.15 no.3
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• pp.75-80
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• 2001

The elastic plastic fracture toughness of this material is evaluated by the an unloading compliance method according to the ASTM E813-97 and E1152-97 method on the smooth and side groove 1CT specimens. The effect of smooth and side groove is studied on the material tearing modulus and characterizes the crack tip field under the plane stress and strain. SG-365 steel is observed that J-R curve and Tmat value decrease as 0%, 20%, 30%, and 40%. The 40% side grooved specimen is very useful in estimation of the $J_IC$. Because it is much easier than the smooth specimen to the onset of the ductile tearing by the R curve method. Besides. it improves the accuracy of toughness values, decreases the scattering the them and tunneling and shear lip by the side groove. Applicability of tearing modulus($T_J$ proposed by paris et al as instability panameter for this material is investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.7 s.166
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• pp.1112-1119
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• 1999

Fracture resistance(J-R) curves, which are used for the elastic-plastic fracture mechanics analyses, are known to be dependent on the cyclic loading history. The objective of this paper is to study the effect of reverse cyclic loading on J-R curves in CT specimens. The effect of two parameters was observed on the J-R curves during the reverse cyclic loading. One was the minimum-to-maximum load ratio(R) and the other was the incremental plastic displacement(${\delta}_{cycle}/{\delta}_i$), which is related to the amount of crack growth that occurs in a cycle. Fracture resistance test on CT specimens with varying load ratio and incremental plastic displacement were performed. For the SA 516 Gr. 70 steel, the results showed that the J-R curves were decreased with decreasing the load ratio and the incremental plastic displacement. When the load ratio was set to -1, the results of the J-R curves and the $J_i$ value were about $40{\sim}50$ percent of those for the monotonic loading condition. Also on condition that the incremental plastic displacement reached 1/40, the J-R curves and the $J_i$ value were about $50{\sim}60$ percent of those for the incremental plastic displacement of 1/10.

• Journal of the Semiconductor & Display Technology
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• v.14 no.1
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• pp.19-25
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• 2015

Strengthened glass is widely used in the display industry for the smart phone and the tablet PC's, the market of which shows steady growth. The strengthened glass is prone to the fracture due to the machined surface defects such as crack and notch. The surface defects are caused mostly by the vibrations of the laser cutter. In this study, the vibrations of the laser cutter were investigated through the frequency response experiment and the computer simulation. The main reasons of the structural vibrations were analyzed, and further the design alterations were deduced and applied to the machine to check the effects of those alterations and to eventually improve the structural stability. The result shows that simple design modifications without major structural change can substantially suppress the vibrations, and improve the quality of the machined surface.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.6
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• pp.1836-1842
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• 1996

In this paper, static and fatigue bending strengths of CFRP(carbon fiber reinforced plastic laminates having impact damage(FOD) are evaluated. Composite laminates used for this experiment are CF/EPOXY and CF/PEEK orthotropy laminated plates, which have two-interfaces[${0^0}_4{90^0}_4}$]$_sym$. A steel ball launched by the air gun colides against CFRP laminates to generate impact damages. The damage growth during bending fatigue test is observed by the scanning acoustic microscope(SAM). When the impacted side is compressed, the residual fatigue bending strength of CF/PEEK specimen P is greater that that of CF/EPOXY SPECIMEN B. On the other hand, when the impacted side is in tension, the residual fatigue bending strength of CF/PEEK speicemen P is smaller than that of CF/EPOXY specimen B. In the case of impacted-side compression, fracture is proposed from the transverse crack generated near impact point. On the other hand, fracture is developed toward the impact point from the edge of interface-b delamination in the case of impacted-side tension.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.79-86
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• 1990

A method to determine directly $J_{IC}$ from load-displacement curve without measuring crack growth amount is studied. A method to use key curve in determination of $J_{IC}$ is also considered. The values of $J_{IC}$ obtained from the above methods are compared with that obtained from the ASTM standard test method (E813). By performing experiments using both compact-tension specimen and three-point-bending specimen of a structural alloy steel SCM4, it is shown that the methods proposed here may be used in determination of $J_{IC}$.

• Journal of the Korean Ceramic Society
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• v.25 no.3
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• pp.201-206
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• 1988

To investigate the effects of Mo addition on the microstructures and mechanical properties of Al_2O_3$ ceramics, two kinds of Mo particles with average sizes of 2-${\mu}{\textrm}{m}$ and 6-${\mu}{\textrm}{m}$ were used as additives. It was shown that Mo particles inhibited the grain growth of Al_2O_3$, and the smaller Mo particles were more effective. In case of 2-${\mu}{\textrm}{m}$ Mo dispersion, the bending strength and the fracture toughness were increased. Dispersion of 6-${\mu}{\textrm}{m}$ MO did not increase the strength but improved the fracture toughness a little. The toughening mechanisms of Al_2O_3$-Mo composites are thought to be the crack deflection and microcracking mechanisms.

• Journal of the Korean Ceramic Society
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• v.25 no.6
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• pp.704-712
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• 1988

In order to investigate the effect of the second phase on Al2O3 matrix, SiC whisker was dispersed in Al2O3 matrix as a second phase over the content range of 5vol% to 20vol%. To this mixture, Y2O3 or TiO2 powder was added as a sintering additive before isostatically pressing and pressureless sintering at 1800-190$0^{\circ}C$ for 90min in N2 atmosphere. With increasing SiC whisker content, relative densities of composites were decreased and the grain growth of Al2O3 was restricted. When Y2O3 was added as a sintering aid the sintering temperature was 180$0^{\circ}C$, the maximum values of flexural strength, hardness and fracture toughness were 537MPa, 12.1GPa, 3.7MPa.m1/2, respectively. However, when the sintering temperature was elevated to 190$0^{\circ}C$, maximum values of flexural strength, hardness and fracture toughness were 453MPa, 17.5GPa, 4.9MPa.m1/2, respectively. Improved mechanical properties are assumed to be attributed to the crack deflection by the second phase SiC whisker and whisker pullout mechanism.