• Computers and Concrete
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• v.18 no.3
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• pp.337-354
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• 2016

To study the influence on fracture properties of reinforced concrete wedge splitting test specimens by the addition of reinforcement, and the restriction of steel bars on crack propagation, 7 groups reinforced concrete specimens of different reinforcement position and 1 group plain concrete specimens with the same size factors were designed and constructed for the tests. Based on the double-K fracture criterion and tests, fracture toughness calculation model which was suitable for reinforced concrete wedge splitting tensile specimens has been obtained. The results show that: the value of initial craking load Pini and unstable fracture load Pun decreases gradually with the distance of reinforcement away from specimens's top. Compared with plain concrete specimens, addition of steel bar can reduce the value of initial fracture toughness KIini, but significantly increase the value of the critical effective crack length ac and unstable fracture toughness KIun. For tensional concrete member, the effect of anti-cracking by reinforcement was mainly acted after cracking, the best function of preventing fracture initiation was when the steel bar was placed in the middle of the crack, and when the reinforcement was across the crack and located away from crack tip, it plays the best role in inhibiting the extension of crack.

• Computational Structural Engineering
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• v.7 no.4
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• pp.113-118
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• 1994

The purpose of this study is elastic plastic finite element analysis for standard fracture toughness specimens. The principles of elastic-plastic fracture mechanics are shortly summarized and the special requirements for computational tools are derived. Possibilities to model the crack tip singularities are mentioned. The relevant fracture parameters like J-Integral and COD and their correlation are evaluated from elastic plastic finite element calculations of standard fracture toughnes specimens. The size and form of the plastic zone are shown. The comparion between experiment and caculation is discussed as well as the application of the limit load analysis.

• Journal of the Korean Ceramic Society
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• v.43 no.3 s.286
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• pp.152-155
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• 2006

Silicon carbide ceramics seeded with 10-30 wt% SiC whiskers are fabricated by hot pressing and annealing. A quantitative texture analysis including calculation of the Orientation Distribution Function (ODF) is used for obtaining the degrees of preferred orientation of the fabricated samples. The microstructure and crystallographic texture are discussed with respect to the effect of ${\beta}-SiC$ whisker seeds on the resulting fracture toughness values. The SEM microstructures and the texture data reveal a correlation between texture and fracture toughness anisotropy.

• Steel and Composite Structures
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• v.17 no.5
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• pp.549-560
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• 2014

The paper provides the test results and analysis on the behavior of steel 1.7147 at different temperatures. Mechanical uniaxial tests were used to determine mechanical properties, resistance to creep and Charpy impact tests to determine impact energy. Test results are presented in the form of engineering stress-strain diagrams, creep curves as well as numerical data related to impact energy. The results show that the tensile strength has the highest value at room temperature, and the same goes for the yield strength as well as for modulus of elasticity. After room temperature both of mentioned properties decrease with temperature increasing. Some of creep curves were modeled using rheological models and analytical equation. Based on Charpy impact energy an assessment of fracture toughness was made.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.103-111
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• 1990

This paper presents a methodology for predicting stable crack growth and instability of a cracked body under monotonically increasing load. It is based on a model that incremental crack extensions and load increments after fracture initiation occur by turns in sequence and the criterion that the crack grows by an incremebt .delta.a when the opening displacement at the current crack tip increases by a critical value V$_{c}$. It is shown that the value I$_{c}$ = V$_{c}$/ .delta. a is a material constant characterizing ductile crack growth resistance. Along with the fracture initiation toughness value, the constant is used for the calculation of the loads against crack extensions by adding up each increment. The specimen failure is defined to occur when the necessary load increment for crack extension is zero or when the limit load in the current ligament is reached. The predicted failure loads are in good agreement with the avaliable experimental failure loads for the compact and center-cracked tension specimens of 7075-T651, 2024-T351 aluminum alloys and 304 stainless steel.steel.

• Tunnel and Underground Space
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• v.30 no.3
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• pp.256-269
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• 2020

The objective of this study is to evaluate the stress thresholds in crack development and the corrected fracture toughness of KURT granite under dry and saturated conditions. The stress thresholds were identified by calculation of inelastic volumetric strain from an uniaxial compression test. The corrected fracture toughness was estimated by using the Level II method (Chevron Bend specimen), suggested by ISRM (1988), in which non-linear behaviors of rock was taken into account. Average crack initiation stress(σ_ci) and crack damage stress(σ_cd) under a dry condition were 91.1 MPa and 128.7 MPa. While, average crack initiation stress(σ_ci) and crack damage stress(σ_cd) under a saturated condition were 58.2 MPa and 68.2 MPa. The crack initiation stress and crack damage stress of saturated ones decreased 36% and 47% respectively compared to those of dry specimens. A decrease in crack damage stress is relatively larger than that of crack initiation stress under a saturated condition. This indicates that the unstable crack growth can be more easily generated because of the saturation effect of water compared to the dry condition. The average corrected fracture toughness of KURT granite was 0.811 MPa·m^0.5. While, the fracture toughness of saturated KURT granite(K_CB) was 0.620 MPa·m^0.5. The corrected fracture toughness of rock in saturated condition decreases by 23.5% compared to that in dry condition. It is found that the resistance to crack propagation decreases under the saturated geological condition.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.5
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• pp.610-616
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• 2004

The aim of this study was to investigate the hydride embrittlement when the LBB evaluation was carried out for the integrity of PHWR Pressure Tubes. The transverse tensile and CCT toughness tests were performed at three hydrogen concentrations while the test temperatures were changed (RT to 30$0^{\circ}C$). Both the transverse tensile and the fracture toughness tests showed the hydrogen embitterment clearly at RT but this phenomenon was disappeared while the test temperature arrived at 25$0^{\circ}C$. Using the DHC test results, the CCL and LBB time were calculated and compared. The hydride embrittlement at the LBB evaluation made the LBB time short definedly. If the operating temperature, DHCV and LBB deterministic parameters such as A and m were known, LBB time could be estimated without the calculation of CCL.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.9 no.1
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• pp.70-76
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• 2013

Several finite element models for the leak-before-break (LBB) assessment of overlay dissimilar metal weldment were constructed and analyzed to develop a simple finite element modeling method. The J-integral, crack opening displacement (COD) and J-integral distribution along the crack front in thickness direction due to the applied moment were obtained from the analysis results of the constructed finite element models, and studied compared to the previous literatures. It is concluded that the modeling with base material only is simple and produces a slightly conservative results compared to the complex modeling composed with weld metal and base metal in the calculation of J-integrals and COD values which are used for the calculation of fracture toughness and postulated leakage crack length respectively.

• Korean Journal of Metals and Materials
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• v.46 no.12
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• pp.771-779
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• 2008

An effective way of increasing the strength and fracture toughness of reactor pressure vessel steels is to change the material specification from that of Mn-Mo-Ni low alloy steel(SA508 Gr.3) to Ni-Mo-Cr low alloy steel(SA508 Gr.4N). In this study, we evaluate the effects of alloying elements on the microstructural characteristics of Ni-Mo-Cr low alloy steel. The changes in the stable phase of the SA508 Gr.4N low alloy steel with alloying elements were evaluated by means of a thermodynamic calculation conducted with the software ThermoCalc. The changes were then compared with the observed microstructural results. The calculation of Ni-Mo-Cr low alloy steels confirms that the ferrite formation temperature decreases as the Ni content increases because of the austenite stabilization effect. Consequently, in the microscopic observation, the lath martensitic structure becomes finer as the Ni content increases. However, Ni does not affect the carbide phases such as $M_{23}C_6 $ and $M_7C_3$. When the Cr content decreases, the carbide phases become unstable and carbide coarsening can be observed. With an increase in the Mo content, the $M_2C$ phase becomes stable instead of the $M_7C_3$ phase. This behavior is also observed in TEM. From the calculation results and the observation results of the microstructure, the thermodynamic calculation can be used to predict the precipitation behavior.