• International Journal of Safety
• /
• 제6권2호
• /
• pp.1-7
• /
• 2007

In this study mechanical strength of A53B carbon steel was analyzed using several types of test specimens directly machined from oil recycling pipe experienced a failure due to hydrogen attack in chemical plants. High temperature hydrogen attack (HTHA) is the damage process of grain boundary facets due to a chemical reaction of carbides with hydrogen, thus forming cavities with high pressure methane gas. Driven by the methane gas pressure, the cavities grow on grain boundaries forming intergranular micro cracks. Microscopic optical examination, tensile test, Charpy impact test, hardness measurement, and small punch (SP) test were performed. Carbon content of the hydrogen attacked specimens was dramatically reduced compared with that of standard specification of A53B. Traces of decarburization and micro-cracks were observed by optical and scanning electron microscopy. Charpy impact energy in hydrogen attacked part of the pipe exhibited very low values due to the decarburization and micro fissure formation by HTHA, on the other hand, data tested from the sound part of the pipe showed high and scattered impact energy. Maximum reaction forces and ductility in SP test were decreased at hydrogen attacked part of the pipe compared with sound part of the pipe. Finite element analyses for SP test were performed to estimate tensile properties for untested part of the pipe in tensile test. And fracture toughness was calculated using an equivalent strain concept with SP test and finite element analysis results.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2004년도 춘계 학술발표대회 개요집
• /
• pp.138-140
• /
• 2004

In case of applying offshore standard of some class societies, the required impact test temperature is lower than that of class rule to be applied for general commercial ship. This study is performed to consider whether the impact value to be required at offshore standard of BV can be obtained or not under SAW method, 1 run both side welding, to be mainly used for butt joint of plates at domestic ship builder.

• 오토저널
• /
• 제10권2호
• /
• pp.46-53
• /
• 1988

Effect of Notch Shape and Hardness Ratio on Characteristics of Impact Fracture in Dual Phase Steels. In this study, it is investigated the effect of notch shape and hardness ratio on the characteristics of impact fracture in dual phase steels. The impact test was carried out at the temperature range from -40.deg. C to room temperature with Instrumented Charpy Impact Tester. The main results obtained are as follows; 1, The maximum impact bending strength (.sigma.$_{max}$) increases with the tensile strength. Also, the impact energy depends on .sigma.$_{max}$. 2, In room temperature, the impact energy depends on crack-initiation energy (E$_{i}$) in case of the high hardness ratio (R=3.4), whereas depends on crack-propagation energy (E$_{p}$) in case of the low hardness ratio (R=1.8) and the dependence of crack-initiation energy of the impact characteristics decreases with increasing test temperature. These phenomena are result from the difficulty of cleavage facet formation.ion.ion.

• Journal of Welding and Joining
• /
• 제3권2호
• /
• pp.42-51
• /
• 1985

The dynamic fracture toughness, fracture characteristics, impact tension and tensile properties of Al-Mg-Si T5 alloy and Al-Zn-Mg T6 alloy respectively welded with filler metal of Alcan 4043 were investigated. The dynamic fracture toughness values were obtained rapidly and simply for the specimen of small size by using instrumented Chirpy impact testing machine. the testing temperatures of the specimen were a range of room temperature and-196.deg. C. The results obtained in this experiment are summarized as follows. With decreasing the testing temperatures, dynamic tensile stress and fracture load were increased, on the other hand the deflection and impact value showed decreasing tendency in order of base metal>HAZ>weld. Changes of total absorbed energy were more influenced by the crack propagation energy than the crack initiation energy. At the low temperatures, the unstable rapid fracture representing the crack propagation appeared for the specimens of Charpy press side notched in Al-Zn-Mg alloy, but it was difficult to obtain the unstable rapid fracture in Al-Mg-Si alloy. Because of the development of plastic zone at the notch root, it was difficult to obtain thevalid $K_{1d}$ value in Al-Mg-Si alloy. Therefore the fatigue cracked specimens were effective in both Al-Mg-Si and Al-Zn-Mg alloys. With decreasing the impact testing temperatures, specimens underwent a transition from dimple-type transgranular fracture to lamella surface-type intergranular fracture because of the precipitate at the grain boundaries, impurities and crystal structure of the precipitates.s.

• Journal of Welding and Joining
• /
• 제11권1호
• /
• pp.42-51
• /
• 1993

In this study, investigations were conducted in calculating parameters of elastic-plastic fracture mechanics using single specimen. The validity of these testing methods was judged by the confirmation of multiple specimen method of stop block test. The results were as follows: In order to measure a fracture toughness using the instrumented impact test, two general requirement must be considered; One, setting up proper impact velocity considered the effect of loading and the other, the necessity of low blow test for obtaining true energy by the compliance correction. It was possible to detect a crack initiation point by calculating the compliance changing rate from a load-defection curve. Criterion of a stable crack growth, $T_{mat}$ could be estimated by using key-curve method for a base metal. and combining Kaiser's rebound compliance with Paris-Hutchison's $T_{appl}$ equation for the brittled zone of welding heat affected.at affected.d.

• 대한기계학회논문집A
• /
• 제21권1호
• /
• pp.93-103
• /
• 1997

Charpy V-notch impact tests were performed on the full-, half-and third-size specimens from two ferritic SA 508 Cl. 3 steels for nuclear pressure vessel. New normalization factors were proposed to predict the upper shelf energy(USE) and the ductile-brittle transition temperature(DBTT) of full-size specimens from the measured data on sub-size specimens. The factors for the USE and the DBTT are $(Bb^2/Kt); and; (Bb/R)^1/2/, $ respectively, where B the width, b the ligament size, $K_{t}$ the elastic stress concentration factor, and R the notch root radius. These correlations successfully estimated the USE and DBTT of the full-size specimens based on sub-size specimen data. In addition, the size effects were studied to develop the correlations among absorbed energy, lateral expansion(LE) and displacement. It was also found that the LE was able to be estimated from the displacement obtained by the instrumented impact test, and that the displacement would be used as a criterion for the toughness of the steels corresponding to change in their yield strength.h.

• 한국재료학회지
• /
• 제28권9호
• /
• pp.522-527
• /
• 2018

This study investigates the effects of isothermal holding temperature and time on the microstructure, hardness and Charpy impact properties of medium-carbon bainitic steel specimens. Medium-carbon steel specimens with different bainitic microstructures are fabricated by varying the isothermal conditions and their microstructures are characterized using OM, SEM and EBSD analysis. Hardness and Charpy impact tests are also performed to examine the correlation of microstructure and mechanical properties. The microstructural analysis results reveal that granular bainite, bainitic ferrite, lath martensite and retained austenite form differently in the specimens. The volume fraction of granular bainite and bainitic ferrite increases as the isothermal holding temperature increases, which decreases the hardness of specimens isothermally heat-treated at $300^{\circ}C$ or higher. The specimens isothermally heat-treated at $250^{\circ}C$ exhibit the highest hardness due to the formation of lath martensite, irrespective of isothermal holding time. The Charpy impact test results indicate that increasing isothermal holding time improves the impact toughness because of the increase in volume fraction of granular bainite and bainitic ferrite, which have a relatively soft microstructure compared to lath martensite for specimens isothermally heat-treated at $250^{\circ}C$ and $300^{\circ}C$.

• 한국산업융합학회 논문집
• /
• 제26권2_2호
• /
• pp.333-340
• /
• 2023

Environmental regulations are being strengthened worldwide to solve global warming. For this reason, interest in eco-friendly gas fuels such as LNG and hydrogen is continuously increasing. However, when adopting eco-friendly gas fuel, liquefying at a cryogenic temperature is essential to ensure economic feasibility in storage and transportation. Although austenitic stainless steel is typically applied to store cryogenic liquefied gas, structural steel can experience sudden heat shrinkage in the case of leakage in the loading and unloading process of LNG. In severe cases, the phase of the steel may change, so care is required. This study conducted Charpy impact tests on steel material in nine different temperature ranges, from room to cryogenic temperatures, to analyze the effects of cryogenic liquefied gas leaks. As a result of the study, it was not easy to find variations in ductile to brittle transition temperature (DBTT) due to the leakage of cryogenic liquefied gas. Still, the overall impact toughness tended to decrease, and these results were verified through fracture surface analysis. In summary, brittle fracture of the steel plate may occur when a secondary load is applied to steel for hull structural use exposed to a cryogenic environment of -40 ℃ or lower. Therefore, it needs to be considered in the ship design and operating conditions.

• Composites Research
• /
• 제32권6호
• /
• pp.360-367
• /
• 2019

자전거 프레임 및 산업 부품과 같은 다양한 산업 분야에 PETG 열가소성 복합 재료를 적용하려면 제조 된 복합 재료의 내충격성, 내구성, 기계적 특성 및 3D 분석을 안정성 검증이 필수적이다. 본 연구에서는 비정질 수지인 PETG 수지의 기계적 특성, 내구성 및 내충격성을 향상시키기 위해 다양한 질량분율의 POE(폴리올레핀 엘라스토머)를 보강하여 화합물 및 사출 성형 공정을 수행 하였다. POE질량분율에 따른 PETG 열가소성 복합재의 열적 및 기계적 특성 및 샤르피 충격 강도 등에 대한 분석을 수행 하였다. 열적 및 기계적 특성 분석 결과, POE 소재가 첨가 된 PETG 열가소성 복합재의 경우 열적 및 기계적 특성이 감소하는 경향이 있지만 내충격성이 우수한 경향을 나타내었고, POE첨가에 따른 3D 전산해석 결과, 파손여부 없이 우수한 안정성을 나타내었다.

• 대한치과기공학회지
• /
• 제21권1호
• /
• pp.55-65
• /
• 1999

So far, I Conducted an examination with focus on the type, characteristic, and test methods of impact test. which is a type of mechanical that evaluate materials. As mentioned previously, in testing soldering strength of soldering is the load when the object under experiment is broken down with the result of flexibility test or peel test. In this method, a hevay load is necessary until alloy of parent metal is bended, if the alloy of the parent metal has a large mechanical quality(peel strength or resisting power). Once the alloy of the parent metal is bended, however, it tends to come into pieces abruply form the part where soldered. Therefore, a metal has a high breakdown value if the degree of strength of its parent metal is high even if the result of measurement indicates otherwise. Thus, the result of the test did not correspond to the clinical result. Therefore, this study concludes as the following from a test of strength of soldering by mean of conducting an impact test, which is a type of mechanical evaluation methods : 1. Among various impact tests, a charpy thpe is more appropriate than the izod type in testing strength of soldering. 2. As far as test piece is concerned, to use subsized impact test piece is appropriate in the impact test in that it does not have notch. 3. In the matter of analysis, it is appropriate to measure absorbing energy which results from rupture of test piece.