• Journal of the Korean Institute of Gas
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• v.25 no.6
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• pp.53-65
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• 2021

While the hydrogen refueling station is rapidly expanded and installed, the safety inspection of the hydrogen pressure vessel in the station should be very important. Of these, according to ASME, hydrogen embrittlement tests must be performed for hydrogen vessel that store hydrogen above a certain pressure. The main test method for hydrogen embrittlement inspection is to carry out fracture tests and fatigue fracture tests in a high pressure hydrogen atmosphere, which allows the durability limit of the pressure vessel to be measured and the endurable limit to be determined in the hydrogen atmosphere. In detail, the critical crack depth can be calculated by the stress intensity factor(K), and the service life can be determined by da/dN (fatigue growth rate). API579-1/ ASME FFS-1 part 9 exemplifies the calculation method according to the mode of crack-like flaws, but for various shapes such as plates and cylinders, there are about 55 modes according to the shape and location of the crack. Due to the fairly complex formula, it is not easily accessible. In this study, we will show you how to calculate fracture mechanics numerically via Excel and VBA. In addition, this was applied to analyze the effects of the thickness and inner diameter of the pressure vessel on the service life.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.2
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• pp.416-427
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• 1998

Unidirectional commingled-yarn-based carbon fiber(CF)/polyamide(PA) 6 composite was fabricated under molding pressures of 0.4, 0.6 and 1.0 MPa to study its flexural deformation and fracture behavior. Fiber/matrix interfacial bonding area became larger with an increase of molding pressure from 0.4 to 0.6 MPa. For molding pressures .geq. 0.6 MPa, good flexural performance of similar magnitudes was attained. For the fracture test, four kinds of notch direction were adopted : edgewise notches parallel (L) and transverse (T) to the major direction of fiber bundles, and flatwise notches parallel(ZL) and perpendicular(ZT) to this direction. Nominal bend strength for L and ZL specimens exhibited high sensitivity to notching. ZL specimens revealed the lowest values of the critical stress intensity factor $K_c$ which was slightly superior to those of unfilled PA6 matrix. Enlargement of the compression area for T specimens was analyzed by means of the rigidity reduction resulting from the fracture occurrence.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1421-1428
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• 1992

It has been increasingly recognized that the safety analysis considering fracture mechanics is required of the pressure vessels made of 2 1/4 Cr-1Mo steel for safe operation due to temper-embrittlement during long term service. In this study, the fracture toughnesses of degraded and recovered 2 1/4 Cr-1Mo steels have been studied with J$_{IC}$ test specimens at room temperature and the results will be compared with the data obtained from the Charpy impact test. The fracture toughness data from above experiments will be applied to life prediction based on the surface crack growth for degraded and recovered Cr-Mo pressure vessels.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.338-343
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• 2008

Fracture characteristics of plates and dome shapes for machinable glass ceramics using compressed shock wave. Machinable glass ceramics have been considered as a promising candidate material for the dome port cover of air breathing engine. This part of the air breathing engine has an important role separating solid and liquid fuel, and needs the frangible characteristics whereby the fracture of a part should not affect the internal components of combustion. The objective of this study are to evaluate the fracture pressure and phenomena of separated membrane using a shock tunnel. The experimental apparatus consists of driver, a driven section and a dump tank. The used material is machinable glass ceramic from Corning company. Specimens are used 3, 4.5 and 6mm thickness with plates and dome shapes. It is expected that the results obtained from this study can be used in the basic data for the dome port cover design of an air breathing engine.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.808-813
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• 2005

Structural integrity assessment of defected pipe is important in fitness for service evaluation and proper engineering assessment is needed to determine whether pipelines are still fit for service. This paper present a failure prediction of gas pipes made of APIl X65 steel with gouge using stress-modified true fracture strain, which is regarded as a criterion of ductile fracture. For this purpose, API X65 pipes with gouge are simulated using elastic-plastic FE analyses with the proposed ductile failure criterion and the resulting burst pressures are compared with experimental data. Agreements are quite good, which gives confidence in the use of the proposed criteria to defect assessment fer gas pipelines. Then, further extensive finite element analyses are performed to obtain the burst pressure solution of pipes with gouge as a function of defect depth, length and pipeline geometry.

• Geomechanics and Engineering
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• v.37 no.2
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• pp.179-187
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• 2024

In this paper, a unified time-dependent constitutive model of Darcy flow and non-Darcy flow is proposed. The influencing factors of flow velocity are discussed, which demonstrates that permeability coefficient is the most significant factor. Based on this, the dynamic evolution characteristics of water inrush during tunneling through fault fracture zone is analyzed under the constant permeability coefficient condition (CPCC). It indicates that the curves of flow velocity and hydrostatic pressure can be divided into typical three stages: approximate high-velocity zone inside the fault fracture zone, velocity-rising zone near the tunnel excavation face and attenuation-low velocity zone in the tunnel. Furthermore, given the variation of permeability coefficient of the fault fracture zone with depth and time, the dynamic evolution of water flow in the fault fracture zone under the variable permeability coefficient condition (VPCC) is also studied. The results show that the time-related factor (α) affects the dynamic evolution distribution of flow velocity with time, the depth-related factor (A) is the key factor to the dynamic evolution of hydrostatic pressure.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.112-118
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• 1990

Catastrophic fracture cannot be avoided after cracks(initiated from pre-existing defects) propagate rapidly with speeds comparable to a sound wave velocity of the materials. Preventing catastropic failure, crack arrest fracture toughness defined from dynamic(or kinetic) fracture mechanics point of view has been introduced in determining accurate and/or proper crack arrest fracture toughness of a material. For the past decades, many studies have been carried out to render proper theoretical and experimental backgrounds on the use of the static plain strain crack arrest fracture toughness, $K_{1a}$ (which seems to be a material property). $K_{1a}$ has been used to predict the performance of thick walled structures and has been considered as a measure of the ability of a material to stop a fast running crack. Determination of such a material property is of prime importance to the nuclear reactor pressure vessel and bridge materials industries. However, standards procedures for measuring toughness associated with fast running cracks are yet to exist. This study intends to give insight on the determination of the crack arrest fracture toughness of materials such as polymethylmethacrylate(PMMA), SM45C-steel, and A1 7075-T6. The effects of crack jump lengths and fast crack initiation stress intensity factor on the determination of $K_{1a}$ have been experimentally observed.erved.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.191-191
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• 2003

It is well-known that the mechanical behavior of fiber-reinforced composites under hydrostatic pressure environment is different from that of atmospheric pressure environment. It is also known that the mechanical behavior of fiber-reinforced composites is affected by strain rate. In this work, we investigated the effect of strain rate on the compressional elastic modulus and fracture stress of fiber-reinforced composites under hydrostatic pressure environment. The material used in the compressional test was unidirectional carbon/epoxy composites and the hydrostatic pressures applied was 250 MPa. Compressional tests were performed applying various strain rates of 0.05 %/sec, 0.25 %/sec, 0.45 %/sec, and 0.75 %/sec. The results showed that the elastic modulus increased with increasing strain rate while the fracture stress was little affected by the strain rate.

• Transactions of Materials Processing
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• v.16 no.5 s.95
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• pp.360-363
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• 2007

Microstructure and microhardness of metallic powders of pure copper were studied after high pressure torsion(HPT) processing with 10 turns of die rotation and high pressure of 6 GPa. The grain size of copper decreases drastically after HPT and reaches nanometer size ranges. During HPT, the hardness of consolidates of copper powders increases with increasing the temperature of HPT processing. Examinations of the fracture surfaces indicated evidence of ductile fracture. The results proved that HPT of copper powders has a beneficial effect for homogeneous deformation with reducing grain size.

• Nuclear Engineering and Technology
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• v.33 no.5
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• pp.498-513
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• 2001

Performed here is a comparative assessment study for the generation of the pressure- temperature (P/T) limit curve of the reactor vessel. Using the cooling or heating rate and vessel material properties, the stress distribution is obtained to calculate stress intensity factors, which are compared with the material fracture toughness to determine the relations between operating pressure and temperature during cool-down and heat-up. P/T limit curves are generated with respect to crack direction, clad thickness, toughness curve, cooling or heating rate and neutron fluence, and their results are compared.