• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.2
• /
• pp.125-135
• /
• 2012

The FE model for shot peening often assume that shots impact vertically on the engineering parts to generate compressive residual stresses. However, the shots obliquely impact on the surface in actual peening. In this work, we propose a 3D finite element (FE) model for evaluation of residual stress under angled shot peening. Using the FE model for angled multi-impact, we examine the effects of factors such as impact angle, impact pattern and the number of shots. Plastic deformation of shot is also considered. To validate the model, we then compare the FE solution with experimental result by X-ray diffraction (XRD). The proposed model will be a base of 3D multi-impact FE model with diverse impact angles.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.27 no.8
• /
• pp.1398-1408
• /
• 2003

Tensile and LCF(low cycle fatigue) tests were carried out in air at wide temperature range 20$^{\circ}C$-750$^{\circ}C$ and strain rates of 1${\times}$10$\^$-4//s-1${\times}$10$\^$-2/ to ascertain the influence of strain rate on tensile and LCF properties of prior cold worked 316L stainless steel, especially focused on the DSA(dynamic strain aging) regime. Dynamic strain aging induced the change of tensile properties such as strength and ductility in the temperature region 250$^{\circ}C$-600$^{\circ}C$ and this temperature region well coincided with the negative strain rate sensitivity regime. Cyclic stress response at all test conditions was characterized by the initial hardening during a few cycles, followed by gradual softening until final failure. Temperature and strain rate dependence on cyclic softening behavior appears to result from the change of the cyclic plastic deformation mechanism and DSA effect. The DSA regimes between tensile and LCF loading conditions in terms of the negative strain rate sensitivity were well consistent with each other. The drastic reduction in fatigue resistance at elevated temperature was observed, and it was attributed to the effects of oxidation, creep and dynamic strain aging or interactions among them. Especially, in the DSA regime, dynamic strain aging accelerated the reduction of fatigue resistance by enhancing crack initiation and propagation.

• Journal of Surface Science and Engineering
• /
• v.38 no.6
• /
• pp.207-211
• /
• 2005

In this work a multi-layered nanostructured TiAIN/CrN superlattice coatings was synthesized using closed-field unbalanced magnetron sputtering method and the relationships between their superlattice period (1), micro-structure, hardness and elastic modulus were investigated. In addition, wear test at $500^{\circ}C$ and oxidation resistance test at $900^{\circ}C$ were performed to investigate high temperature properties of these thin films. The coatings were characterized in terms of microstructure and mechanical properties by transmission electron microscopy (TEM) and nano-indentation test. Results from TEM analysis showed that superlattice periods was inversely proportional to the jig rotation speed. The maximum hardness and elastic modulus of 37 GPa and 375 GPa were observed at superalttice period of 6.1 nm and 4.4 nm, respectively. An higher value of microhardness from TiAIN/CrN thin films than either TiAIN (30 GPa) or CrN (26 GPa) was noted while the elastic modulus was approximately an average of TiAIN and CrN films. These enhancement effects in superlattice films could be attributed to the resistance to dislocation glide across interface between the CrN and TiAIN layers. Much improved plastic deformation resistance ($H^3/E^2$) of 0.36 from TiAIN/CrN coatings was observed, compared with 0.15 and 0.16 from TiAIN and CrN, respectively. Also the wear resistance at $500^{\circ}C$ was largely increased than those of single TiAIN and CrN coatings and TiAIN/CrN coatings showed much reduced weight gain after exposure at $900^{\circ}C$ for 20 hours.

• Journal of Surface Science and Engineering
• /
• v.47 no.1
• /
• pp.13-19
• /
• 2014

The various surface treated conditions of Fe-3.0%Ni-0.7%Cr-1.4%Mn-X steel such as as-received, ion nitriding, DLC coated, DLC coated after nitriding for 3 hrs and 6 hrs were investigated to evaluate the beneficial effect for plastic mold steel. Micro Vickers hardness tester was used to estimate nitriding depth from the hardness profile and to measure hardness on the surface. Elastic modulus and residual stress were measured by a nanoindentator. Scratch test and SP (small ball punch test) were utilized to assess the adhesive strength of DLC coating. The depth of nitriding layer was measured as $50{\mu}m$ for the condition of 3 hrs nitriding and $90{\mu}m$ for that of 6 hrs nitriding. Hardness, elastic modulus, residual stress of DLC coating were 20.37 GPa, 162.78 GPa and -1456 MPa respectively. Residual stress on the surface of DLC coating after nitriding could increase to -3914 MPa by introducing nitriding before DLC coating. During the 'Ball-On-Disc' test ${\gamma}^{\prime}$ particles pulled out from the surface of nitrized layer tend to enhance abrasive wear mode since the fraction of ${\gamma}^{\prime}$ (Fe4N) in ion-nitrized layer is known to increases with nitriding time. Thus the specific wear rate of the nitriding layer increased. Comparing with nitriding the specific wear rate in work piece disc as well as ball decreased prominently in DLC coating due to the remarkable reduction in friction coefficient.

• Composites Research
• /
• v.17 no.5
• /
• pp.85-95
• /
• 2004

Other than in the fields of rolling stock and marine, in England, UK, Phenolic Composites (herein after, PCs) have been significantly utilized to fire protecting panels in construction, in particular, in architectures. In general, indeed, so-called "Plastic" or "Synthesized Resins" have been applied successfully in our societies all over the world, however, once, when ignited from somewhat reason, they burn much easily generating large amount of "SMOKE" from their nature of petroleum-borne materials as a matter of fact, people have forgotten about it. "SMOKE" caused many fire accidents horror tragedies as everyday people know today. The experts in this field such as PC engineers, researchers and others can take their responsibilities to explain it, persuade it and realize "Safer Environment for People" with well-experienced and technology innovated PCs. In this paper, the co-authors, collaborating UK and Japan, are making efforts to report how the PCs work good jobs to our societies showing some successful track records in construction or architecture fields in UK. How about on this matter in Japan\ulcorner "SMOKE fire" is always waiting fur us. We should stop smoking and SMOKE fire, in our public places.We should stop smoking and SMOKE fire, in our public places.

• Transactions of Materials Processing
• /
• v.16 no.8
• /
• pp.603-613
• /
• 2007

This paper is concerned with joining of thin metal sheets by single stroke clinching process. This method has been used in sheet metal work as it is a simple process and offers the possibility of joining similar-dissimilar thin sheet metals. Clinching generates a joint by overlapping metal sheets deforming plastically by punching and squeezing sequence. AA 5754 aluminum alloy of 0.5 mm thick sheets have been selected as a modal material and the process has been simulated under different process conditions and the results have been analyzed in terms of the quality of clinch joints which are influenced mainly by tool geometries. The rigid-plastic finite element method is applied to analyses in this paper. Analysis is focused mainly on investigation of deformation and material flow patterns influenced by major geometrical parameters such as die diameter, die depth, groove width, and groove corner radius, respectively. To evaluate the quality of clinch joints, four controlling or evaluation parameters have been chosen and they are bottom, neck thickness of bottom and top sheets, and undercut thickness, respectively. It has been concluded from the simulation results that the die geometries such as die depth and diameters are the most decisive process parameters influencing on the quality of clinch joints, and the bottom thickness is the most important evaluation parameter to determine if the quality of clinch joints satisfies the demand for industrial application.

• Journal of Korean Society of Steel Construction
• /
• v.16 no.5 s.72
• /
• pp.555-564
• /
• 2004

Steel materials, which are normally used in bridge structures, are prone to corrosion and have thin plate structures. Steel bridges that have been damaged through increased vehicle load and corrosion are frequently expected to be strengthened. Repair or strengthening methods generally include cutting, bolting, and welding. The basic characteristics of stress and deformation behavior generated by cutting and welding in the course of the repair work, however, are not yet understood. It is difficult to say whether the safety of the structure after welding conforms with existing safety evaluation methods.Therefore, to gain confidence in the material and to guarantee the safety of the structure after welding, the stress generated by heat, through welding and cutting, was generalized. The effect of additional loads with respect to stress generated by heat was also investigated.

• Korean Journal of Materials Research
• /
• v.4 no.3
• /
• pp.349-356
• /
• 1994

For the deformation, life time prediction and improvement of the life time in high temperature materials it's very important to know the mechanism of deformation. For these mechanisms the dislocation loop models of Orlova et al. and Mills et al. are used often now. But they show controversial differencies, even if they have unertaken similar experimental tests with the same alloy of A1-5.5at.% Mg. In this work also the similiar tests of them have done under the same temperature of 573 K ; (1) The specimen was deformed by $\sigma$= 30MPa and $\varepsilon$=0.03. (2) Direct after creep deformation of $\sigma$= 30MPa and $\sigma$= 0.03 the stress reduction tests to 15, 10 and OMPa have been performed. (3) To study the loop models dislocation structure and dislocation density ( p ) have been observed.

• Journal of Surface Science and Engineering
• /
• v.36 no.5
• /
• pp.357-363
• /
• 2003

The aim of this work is the synthesis of a-C:H films from methane gas using surface spark discharge at the atmospheric pressure. Properties of these films have been investigated as functions of energy W delivered per a methane molecule in the discharge. The method enables the coatings to be deposited with high growth rates (up to $100 \mu\textrm{m}$/hour) onto large-area substrates. It is shown that the films consist of spherical granules with diameter of 20∼50 nm formed in the spark channel and then deposited onto the substrate. The best film characteristics such as minimum hydrogen-to-carbon atoms ratio H/C=0.69, maximum hardness $H_{v}$ =3 ㎬, the most dense packing of the granules and highest scratch resistance has been obtained under the condition of highest energy W of 40 eV. The deposited a-C:H coatings were found to be more soft and hydrogenated compared to the diamond-like hydrogenated (a-C:H) films which obtained by traditional plasmaenhanced chemical vapor deposition methods at low pressure (＜10 Torr). Nevertheless, these coatings can be potentially used for scratch protection of soft plastic materials since they are of an order harder than plastics but still transparent (the absorption coefficient is about $10^4$∼$10^{5}$ $m^{-1}$ At the same time the proposed method for fast deposition of a-C:H films makes this process less expensive compared to the conventional techniques. This advantage can widen the application field of. these films substantially.y.

• Korean Chemical Engineering Research
• /
• v.50 no.1
• /
• pp.6-10
• /
• 2012

The main objective of this work was studying the influence of paraffin oil(PO) on the adhesion properties at low temperature in styrene-butadiene-styrene(SBS) copolymer and crumb rubber(CR) modified asphalt. The temperature susceptibility of SBS/CR asphalt and PO/SBS/CR/asphalt blends were measured by penetration and softening point. Adhesion properties at low temperature and dispersion of modifiers in PO/SBS/CR/asphalt blends were evaluated by universal test machine and florescence microscopy, respectively. The adhesion properties of PO/SBS/CR/asphalt blends at low temperature increased in the proportion of SBS contents with both 5 and 10 wt % of paraffin oil. Results showed that the maximum tensile adhesion strength and toughness energy at $-20^{\circ}C$ were obtained when PO and SBS contents were 10 wt % and 6 wt %, respectively. The addition of PO is effective for enhancing the flexibility of SBS/CR/asphalt blends and leads to the increase of toughness at low temperature.