• 소성∙가공
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• 제26권3호
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• pp.156-161
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• 2017

In this study, the reason of die fracture occurring in hot forging of an aluminum fixed scroll was studied, based on experiments and finite element predictions. The material is assumed to be rigid-viscoplastic, and the die is rigid for the finite element predictions. The stress in the tension at the wrap root is known to cause brittle fracture, and the increase in the tensile stress is owing to the unbalanced filling of material into the die cavities between both sides of the warp. Based on the empirical and numerical achievements, the effects of geometrical parameters of the material on the die fracture were examined to find practical measures for elongated die life. It has been shown from the parametric study that the material with the optimized trapezoidal cross-section, which can be easily made during cutting or the optimized cylindrical billet with its eccentric placement in the die cavity, can considerably reduce the magnitude of the tensile stress around the die corner fractured, indicating that economical manufacturing with reduced number of stages and elongated die life can be realized at once using the optimized practical initial material.

• 한국철도학회논문집
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• 제15권3호
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• pp.266-271
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• 2012

본 연구는 빠르게 대중화 되어가는 철도의 주행안전성과 승차감 개선을 목적으로 수행하였다. 가스압접을 실시하는 장대레일의 강도 안전성을 확보하기 위하여 인장시험과 회전굽힘시험을 실시했다. 실험을 통하여 가스 압접부의 인장강도를 결정하는 요소는 가해진 압력보다 업셋길이의 변화에 기인하며, 업셋길이가 늘어남에 따라서 취성파괴에서 연성파괴가 발생하는 것을 관찰했다. 파단면의 조직검사를 통해 그 면에 존재하는 취성파면의 유무에 따라서 강도 안전성을 용이하게 평가할 수 있었다. 회전굽힘시험 결과 업셋길이 25mm에서 373MPa의 우수한 피로한도가 나타났으며, 무한수명을 얻을 수 있었다.

• Journal of Welding and Joining
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• 제32권6호
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• pp.56-63
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• 2014

To develop and understand dissimilar metals joining of Stainless steel and Copper, ultra-high speed laser lap welding was studied using single mode fiber laser in this study. SUS304 and Cu have large differences in materials properties, and Cu and Fe have no intermetallic compounds by typical binary phase of Cu and Fe system. In this study, ultra-high speed lap welds of SUS304 and Cu dissimilar metals using single-mode fiber laser was generated, and weldability of the weld fusion zone was evaluated using a tensile shear test. To understand the phenomenon of tensile shear load, weld fusion zone of interface weld area and fracture parts after tensile shear test were observed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analysis system. And it was confirmed that Cu was easily melting and penetrating in the grain boundaries of SUS304 because of low melting temperature. And high thermal conductivity of copper occurred dissipate heat energy rapidly. These properties cause the solidification cracking in weld zone.

• 한국분말재료학회지
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• 제18권6호
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• pp.482-487
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• 2011

Alloy 617, Ni-22Cr-12Co-9Mo base oxide dispersion strengthened alloy was fabricated by using mechanical alloying, hot isostatic pressing and hot rolling. Uniaxial tensile tests were performed at room temperature and at $700^{\circ}C$. Compared with the conventional Alloy 617, ODS alloy showed much higher yield strength and tensile strength, but lower elongation. Fracture surfaces of the tensile tested specimens were investigated in order to find out the mechanism of fracture mode at each test temperature. Grain adjustment during tensile deformation was analyzed by electron backscattered diffraction mapping, inverse pole figures and TEM observation.

• 소성∙가공
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• 제25권6호
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• pp.402-408
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• 2016

A manufacturing technology of carbon fiber composites with thermoplastic polymer pellets and continuous woven fiber was investigated using a compression molding process. To secure the impregnation of resin into the porosity of fabric the composite specimens were prepared with general injection-molding grade polypropylene pellets and low viscosity polycarbonate pellets. Tensile tests of polypropylene and polycarbonate composites were performed. Polycarbonate composites showed higher fracture strength than that of polypropylene composites because of the difference of matrix properties. However, the increase rate of strength was lower than that of polypropylene composites due to the difference of coherence between matrix and reinforcement. To investigate the effect of carbon fiber volume fraction on the fracture strength variation polypropylene composites with different volume fraction were compression molded and tensile tests were performed together. It was shown that the fracture strength of the polypropylene composites increased by 3.2, 5.4 and 6.9 times with the increase of carbon fabric volume fraction of 0.256, 0.367, and 0.480, respectively.

• 한국기계기술학회지
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• 제13권2호
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• pp.93-100
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• 2011

This study deals with the high frequency induction hardening (HF at $850^{\circ}C$, 120kHz & 50kW condition) SM45C steel. (1) The HF specimen, which was tempered at $150^{\circ}C$, did not show any tempering effect. A brittle fracture occurred at rounded area of the tensile specimen. AE (acoustic emission) amplitude distribution showed between 45dB and 60dB. (2) A slip and fracture occurred at the hole area of the HF specimen which was tempered at $300^{\circ}C$. As they pass the yield point, the AE energy is increased intermittently and AE amplitude distribution exists between 70dB and 85dB. In addition, after imposing the maximum tensile load, AE signals showed high amplitude and energy distribution. The AE amplitude showed between 45dB and 70dB. (3) A brittle fracture occurred at HF specimen which was tempered at $450^{\circ}C$ as if it is torn in the direction of $45^{\circ}$ on parallel area over the both sides of the tensile specimen, which lead to several peak appeared in AE energy. It was found that the AE amplitude was relatively low and the AE energy was high.

• Structural Engineering and Mechanics
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• 제69권4호
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• pp.467-477
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• 2019

Digital image correlation (DIC) is now a popular and extensively used full-field metrology technique. In general, DIC is performed by using a turnkey solution offered by various manufacturers of DIC. In this paper, a simple and economical set-up for DIC is proposed which uses easily accessible digital single-lens reflex (DSLR) camera rather than industrial couple-charged device (CCD) cameras. The paper gives a description of aspects of carrying a DIC experiment which includes experimental set-up, specimen preparation, image acquisition and analysis. The details provided here will be helpful to carry DIC experiments without specialized DIC testing rig. To validate the responses obtained from proposed DIC set-up, tension and fatigue tests on specimens made of IS 2062 Gr. E300 steel are determined. Tensile parameters for a flat specimen and stress intensity factor for an eccentrically-loaded single edge notch tension specimen are evaluated from results of DIC experiment. Results obtained from proposed DIC experiments are compared with those obtained from conventional methods and are found to be in close agreement. It is also noted that the high resolution of DSLR allows the use of proposed approach for fracture characterization which could not be carried out with a typical turnkey DIC solution employing a camera of 2MP resolution.

• Journal of Advanced Marine Engineering and Technology
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• 제37권8호
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• pp.862-868
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• 2013

직조 형태의 복합재료의 파손 메커니즘은 복합적이다. 지금까지 평직 복합재료를 대상으로 많은 연구가 이루어졌으나, 파괴 저항성 거동은 아직도 표준화 되지 못한 실정이다. 또한 섬유배열방향에 따라 다른 거동을 보인다. 그래서 하중방향에 대한 섬유배열방향에 따른 파괴 저항성 평가가 필요하다. 이에 본 연구에서는 평직 CFRP 복합재료를 대상으로 다양한 섬유배열방향에 따른 파손강도 및 파괴 저항성 평가를 수행하였다.(섬유배열 방향: $0^{\circ}$, $15^{\circ}$, $30^{\circ}$, $45^{\circ}$) CT 시험편을 이용하여 모드 I 조건으로 시험을 수행하였다.

• The Journal of Advanced Prosthodontics
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• 제6권3호
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• pp.151-156
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• 2014

PURPOSE. To investigate the microtensile bond strength between two all-ceramic systems; lithium disilicate glass ceramic and zirconia core ceramics bonded with their corresponding glass veneers. MATERIALS AND METHODS. Blocks of core ceramics (IPS e.max$^{(R)}$ Press and Lava$^{TM}$ Frame) were fabricated and veneered with their corresponding glass veneers. The bilayered blocks were cut into microbars; 8 mm in length and $1mm^2$ in cross-sectional area (n = 30/group). Additionally, monolithic microbars of these two veneers (IPS e.max$^{(R)}$ Ceram and LavaTM Ceram; n = 30/group) were also prepared. The obtained microbars were tested in tension until fracture, and the fracture surfaces of the microbars were examined with fluorescent black light and scanning electron microscope (SEM) to identify the mode of failure. One-way ANOVA and the Dunnett's T3 test were performed to determine significant differences of the mean microtensile bond strength at a significance level of 0.05. RESULTS. The mean microtensile bond strength of IPS e.max$^{(R)}$ Press/IPS e.max$^{(R)}$ Ceram ($43.40{\pm}5.51$ MPa) was significantly greater than that of Lava$^{TM}$ Frame/Lava$^{TM}$ Ceram ($31.71{\pm}7.03$ MPa)(P<.001). Fluorescent black light and SEM analysis showed that most of the tested microbars failed cohesively in the veneer layer. Furthermore, the bond strength of Lava$^{TM}$ Frame/Lava$^{TM}$ Ceram was comparable to the tensile strength of monolithic glass veneer of Lava$^{TM}$ Ceram, while the bond strength of bilayered IPS e.max$^{(R)}$ Press/IPS e.max$^{(R)}$ Ceram was significantly greater than tensile strength of monolithic IPS e.max$^{(R)}$ Ceram. CONCLUSION. Because fracture site occurred mostly in the glass veneer and most failures were away from the interfacial zone, microtensile bond test may not be a suitable test for bonding integrity. Fracture mechanics approach such as fracture toughness of the interface may be more appropriate to represent the bonding quality between two materials.

• 한국해양공학회지
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• 제29권6호
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• pp.445-453
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• 2015

The stress triaxiality and lode angle are known to be most dominant fracture parameters in ductile materials. This paper proposes a three-dimensional failure strain surface for a ductile steel, called a low-temperature high-tensile steel (EH36), using average stress triaxiality and average normalized lode parameter, along with briefly introducing their theoretical background. It is an extension of previous works by Choung et al. (2011; 2012; 2014a; 2014b) and Choung and Nam (2013), in which a two-dimensional failure strain locus was presented. A series of tests for specially designed specimens that were expected to fail in the shear mode, shear-tension mode, and compression mode was conducted to develop a three-dimensional fracture surface covering wide ranges for the two parameters. This paper discusses the test procedures for three different tests in detail. The tensile force versus stroke data are presented as the results of these tests and will be used for the verification of numerical simulations and fracture identifications in Part II.