• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.4
• /
• pp.596-601
• /
• 2002

Rotary bending fatigue tests were carried out to investigate the fatigue characteristics of high performance ductile cast iron experienced super rapid induction treatment. The influence of super rapid induction treatment on fatigue limit was experimentally examined with the special focus on the variation of surface microstructure and the fatigue crack initiation and propagation through fractography. Main results obtained are as follows. By super rapid induction treatment in FCD500, the martensite structure obtained through conventional heat treatment was confirmed on the specimen surface. The fatigue crack initiation in the hardened surface layer was restricted by the martensite structure and compressive residual stress. Thus, it could be interpreted that the initiation stress would be increased by improved structure in the surface. The fatigue crack propagation in the hardened layer was retarded by the presence of the globular shape martensite around the graphite nodule and compressive residual stress and the crack propagation behavior has zigzag pattern in the hardened surface layer.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 1994.04c
• /
• pp.6-6
• /
• 1994

Har dmaterials such as cemented carbides with or without coated layer, cermets, ceramics and diamond or c-BN high pressure sintered compact are used for cutting tools, wear -resistant parts, rock drilling bits and/or high pressure vessels. These hardmaterials contain not only hard phase, but also second consituent as the element for forming ductile phase and/or sintering aid, and the mechanical properties of each material depend on (1) the amount of the second constituent as well as (2) the grain size of the hard phase. The hardness of each material mainly depends on these two factors. The fracture strength, however, largely depends on other microstructur a1 factors as well as the above two factors. For all hardmaterials, the fracture strength is consider ably affected by (3) the size of microstructur a1 defect which acts as the fracture source. In cemented carbides, the following factors which are generated mainly due to the addition of the second constituent are also important; (4) the variation of the carbon content in the normal phase region free from V-phase and graphite phase, (5) the precipitation of $Co_3$ during heating at about $800^{\circ}C$,(6) the domain size of binder phase, and (7) the formation of ${\beta}$-free layer or Co-rich layer near the surface of sintered compacts. For cemented carbides coated with thin hard substance, the important factors are as follows; (8) the kind of coated substance, (9) the formation of ${\eta}$-phase layer at the interface between coated layer and substrate, (10) the type of residual stress (tension or compression) in the coated layer which depends on the kind of coating method (CVD or PVD), and (11) the properties of the substrate, and (12) the combination, coherency and periodicity of multi-layers. In the lecture, the details of these factors and their effect on the strength will be explained.

• Korean Journal of Metals and Materials
• /
• v.48 no.12
• /
• pp.1047-1055
• /
• 2010

The objective of this study is to investigate the ballistic properties of Zr-based amorphous alloy surface composites fabricated by high-energy electron-beam irradiation. The mixture of Zr-based amorphous powders and $LiF+MgF_2$ flux powders was deposited on a pure Ti substrate, and then an electron beam irradiated this powder mixture to fabricate a one-layer surface composite. A four-layer surface composite, in which the composite layer thickness was larger than 3 mm, was also fabricated by irradiating the deposited powder mixture by an electron beam three times on the one-layer surface composite. The microstructural analysis results indicated that a small amount of fine crystalline particles were homogeneously distributed in the amorphous matrix of the surface composite layer. According to the ballistic impact test results, the surface composite layers effectively blocked a fast traveling projectile, while many cracks were formed at the composite layers, and thus the surface composite plates were not perforated. The surface composite layer containing ductile ${\beta}$ dendritic phases showed a better ballistic performance than the one without dendrites because dendritic phases hindered the propagation of shear bands or cracks.

• Steel and Composite Structures
• /
• v.27 no.1
• /
• pp.95-108
• /
• 2018

A new composite reinforced method, namely self-compacting concrete filled circular CFRP-steel jacketing, was proposed in this paper. Experimental tests on eight RC square short columns reinforced with the new composite reinforced method and four RC square short columns reinforced with CFS jackets were conducted to investigate their eccentrically compressive behaviour. Nine reinforced columns were subjected to eccentrically compressive loading, while three reinforced columns were subjected to axial compressive loading as reference. The parameters investigated herein were the eccentricity of the compressive loading and the layer of CFRP. Subsequently, the failure mode, ultimate load, deformation and strain of these reinforced columns were discussed. Their failure modes included the excessive bending deformation, serious buckling of steel jackets, crush of concrete and fracture of CFRP. Moreover, these reinforced columns exhibited a ductile failure globally. Both the eccentricity of the compressive loading and the layer of CFRP had a significant effect on the eccentrically compressive behaviour of reinforced columns. Finally, formulae for the evaluation of the ultimate load of reinforced columns were proposed. The theoretical formulae based on the ultimate equilibrium theory provided an effective, acceptable and safe method for designers to calculate the ultimate load of reinforced columns under eccentrically compressive loading.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1997.10a
• /
• pp.907-910
• /
• 1997

With increasing the needs for micro and precision parts, micro machining technology has been studied to fabricate a small part with high density such as electronics, optics, communications, and medicine industry more than before. But there are many problems to be solved requiring a high-level technology. So this research presents the new method to fabricate a small part through applying chemical mechanical micro machining (C3M) for the Al wafer. Al(thickness I ,u m) was sputtered on the Si substrate. Al is widely used as a lightweight material. However form defect such as burr has a bad effect on products. To improve machinability of ductile material, oxide layer was formed on the surface of AI wafcr before grooving by chemical reaction with HN03(10wt%). And then workpieces were machined to compare conventional micro-machining process with newly suggested method at different machining condition such as load and feed rate. To evaluate whether or not the machinability was improved by the effect of chemical condition, such as the size, the width of grooves 'and burr generation were measured. Finally, it is confirmed that C3M is one of the feasible tools for micro machining with the aid of effect of the chemical reaction.

• Proceedings of the KSME Conference
• /
• 2000.11a
• /
• pp.322-327
• /
• 2000

This paper investigates the time-dependent crack growth in X20CrMoV 12 1 steel weld joints. Crack growth test are carried out $545^{\circ}C$ on side-grooved 1/2T CT specimens under static loads. A simulated material is produced for the intercritical HAZ, where fracture normally occurs. Constitutive properties are obtained for the simulated HAZ material as well as for the base metal and weld metal. Finite element analyses of crack growth are performed on the models with and without a HAZ layer, using the experimental crack length-time history. The inclusion of HAZ layer increase the load line velocities significantly. The crack growth rates are correlated reasonably well with $C^*$. The smallest crack size for the validity of $C^*$ is found much smaller than the ASTM crack initiation size for 1T CT specimen of creep ductile materials.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.19 no.6
• /
• pp.90-96
• /
• 2011

In this study, the characteristic of fractured portion and shape on solder joints were investigated according to the thermal shock test for Automotive Application Component using Sn-3.0Ag-0.5Cu solder, which has a outstanding property as Lead-free solder. The value of pull and shear strength was decreased in principle after 432 cycles thermal shock test. In addition, fracture mode was verified by using EDS and SEM to observe fractured shape on the solder joints before and after thermal shock. In before thermal shock test, the fracture mode revealed typically solder layer's fracture mode. In after thermal shock test, we identified multiple fracture mode of the ductile and brittle fracture. Even though same composition of solder was used to experimental for estimating. the fracture mode varied on the fracture portion's height and the directional angles of shear strength. In conclusion, we identified that mechanical strength was affected on the solder layer's fracture mode.

• Journal of Korea Foundry Society
• /
• v.24 no.6
• /
• pp.323-330
• /
• 2004

This study aims to investigate on the effects of the microstructures on the wear characteristics of the different grey cast iron(GC) and spheroidal ductile cast iron(DCI). Wear test using wear tester of pin-on-disc type was carried out under the conditions of load 47.2N , velocity 0.2m/s, distance 4000m. At the GC, Wear rates depend on graphite type and oxide layer formed at wear surface. Weak rosette graphites are easily broken and formed wear debris over 30 ${\mu}m$. This wear debris occurs scuffing at wear surface. As a result of surface deformation, Narrow regions of the matrix between the graphite flakes and the contact surface lead to the failure of the necks. Wear rate for the DCI depended on hardness of matrix more than size of graphite.

• Journal of the Korean institute of surface engineering
• /
• v.29 no.5
• /
• pp.379-385
• /
• 1996

Adhesion of Cu/Cr and Cu/$Cu_xCr_{1-x}$ thin films onto polyimide substrates has been studied. For an adhesion layer, Cr or Cu-Cr alloy films were deposited onto polyimide using DC magnetron sputtering machine. Then Cu was sputter-deposited and finally, Cu was electroplated. Adhesion was evaluated using $90^{\circ}C$ peel test or T-peel test. Plastic deformation of the peeled metal layer was qualitatively measured using XRD technique. It is confirmed that high interfacial fracture energy and large plastic deformation are important to enhance the peel adhesion strength. High peel strength is obtained when the interface is strongly bonded. More ductile film has higher peel strength. In Cu-Cr alloy films, opposite effects of the Cr addition in the alloy film on the peel strength are operative: a beneficial effect of strong interfacial bonding and a negative effect of smaller plastic deformation.

• Journal of Welding and Joining
• /
• v.32 no.4
• /
• pp.46-54
• /
• 2014

In this study, the effect of bonding temperature and bonding pressure on deformation and tensile properties of diffusion bonded joint of STS304 compact heat exchanger was investigated. The diffusion bonds were prepared at 700, 800 and $900^{\circ}C$ for 30, 60 and 90 min in pressure of 3, 5, and 7 MPa under high vacuum condition. The height deformation of joint decreased and the width deformation of joint increased with increasing bonding pressure at $900^{\circ}C$. The ratio of non-bonded layer and void observed in the joint decreased with increasing bonding temperature and bonding pressure. Three types of the fracture surface were observed after tensile test. The non-bonded layer was observed in diffusion bonded joint preformed at $700^{\circ}C$, the non-bonded layer and void were observed at $800^{\circ}C$. On the other hand, the ductile fracture occurred in diffusion bonded joint preformed at $900^{\circ}C$. Tensile load of joint bonded at $800^{\circ}C$ was proportional to length of bonded layer and tensile load of joint bonded at $900^{\circ}C$ was proportional to minimum width of pattern. The tensile strength of joint was same as base metal.