• Korean Journal of Materials Research
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• v.9 no.10
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• pp.970-977
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• 1999

Effect of Mo interlayer on the relaxation of residual stress in AlN/Cu pint bonded by active-metal brazing method was investigated. The stress analyses by finite-element-method, the measurement of pint strength and the observation of fracture surface were carried out and their results were compared with each other. From the results of stress analysis it is confirmed that a Mo interlayer led to a shift of maximum stress concentration site from AlN/insert-metal interface$\rightarro$ insert-metal/Mo$\rightarro$Mo interlayer. Additionally, with increase of the Mo interlayer thickness the stress concentration with tensile component was separately built both at the interface of Cu/Mo and AlN/Mo. whereby the residual stress in the free surface of AlN close to the bonded interface was drastically reduced. The AlN/Mo/Cu pints with Mo interlayer thickness of above 400$\mu\textrm{m}$ showed the strengths higher than 200 MPa. upto max. 275 MPa, while the AlN/Cu pint only max. 52 MPa.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.447-450
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• 2001

Abstract-Si direct bonding(SDB) technology is very attractive for both Si-on-insulator(SOI) electric devices and MEMS applications because of its stress free structure and stability. This paper presents on pre-bonding according to HF pre-treatment conditions in Si wafer direct bonding. The characteristics of bonded sample were measured under different bonding conditions of HF concentration, and applied pressure. The bonding strength was evaluated by tensile strength method. The bonded interface and the void were analyzed by using SEM and IR camera, respectively. Components existed in the interlayer were analysed by using FT-lR. The bond strength depends on the HF pre-treatment condition before pre-bonding (Min : 2.4kgf/cm$^2$∼Max : 14.9kgf/cm$^2$).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.370-373
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• 1999

Si direct bonding (SDB) technology is very attractive for both Si-on-insulator(SOI) electric devices and MEMS applications because of its stress free structure and stability. This paper presents on- pre treatment conditions in Si wafer direct bonding, The paper resents on pre-bonding according to HF pre-treatment conditions in Si wafer direct bonding. The characteristics of bonded sample were measured under different bonding conditions of HF concentration, applied pressure and annealing temperature(200~ 100$0^{\circ}C$) after pre-bonding. The bonding strength was evaluated by tensile strength method. The bonded interface and the void were analyzed by using SEM and IR camera, respectively, Components existed in the interlayer were analyzed by using FT-IR. The bond strength depends on the HF pre-treatment condition before pre-bonding(Min 2.4kgf/$\textrm{cm}^2$~ Max : 14.kgf/$\textrm{cm}^2$)

• Journal of Industrial Technology
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• v.18
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• pp.203-208
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• 1998

Fatigue tests were performed to examine the 4 parameter method for specimens prepared by various heat treatment which resulted in different mechanical properties. Obtained main results are as follows. (1) Samples treated by austempering did not show the expected improvement of fatigue limit although hardness and strength increased. This is attributed to the fact that defect sensitivities of materials increase as increasing of hardness and tensile strength, it is also shown that the graphites acting as stress concentration place become larger by austempering heat treatment than by normal annealing. (2) It is very reasonable to predict the fatigue limit of ductile irons with 4 parameter method based on ${\sigma}_{TS}$, $H_v$, ${\Delta}K_{th}$ and ${\sqrt{area}}_{max}$. (3) The half-austempering treatment appeared to be more useful than the full-austempering method to improve the fatigue limit in the spheroidal graphite cast iron with multi defective material.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1436-1438
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• 2003

In this paper thermal and mechanical properties of elastic epoxy for applying high voltage products were investigated. Glass transition temperature(Tg) of elastic epoxies can't find form room temperature to $200^{\circ}$ by DSC. It occurred weight reduce on $285^{\circ}$ and $451^{\circ}$ by thermo-gravimeter. The first temperature was effected on addictives and the other was epoxy's character. Max, tensile strain showed $28.3kgf/cm^2$ at 20% of mechanical stress in addictives 35phr. SEM micrograph of the fracture surface observed in void and tearing of elastic epoxy at addictives 35phr. The other side, SEM micrograph of rigid epoxy showed the trace which broke.

• Steel and Composite Structures
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• v.30 no.1
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• pp.1-12
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• 2019

In this research, an efficient mixed mode I/II fracture criterion is developed for fracture investigation of orthotropic materials wherein crack is placed along the fibers. This criterion is developed based on extension of well-known Maximum Tensile Stress (MTS) criterion in conjunction with a novel material model titled as Equivalent Reinforced Isotropic Model (ERIM). In this model, orthotropic material is replaced with an isotropic matrix reinforced with fibers. A comparison between available experimental observations and theoretical estimation implies on capability of developed criterion for predicting both crack propagation direction and fracture instance, wherein the achieved fracture limit curves are also compatible with fracture mechanism of orthotic materials. It is also shown that unlike isotropic materials, fracture toughness of orthotic materials in mode $I(K)_{IC}{\mid})$ cannot be introduced as the maximum load bearing capacity and thus new fracture mechanics property, named here as maximum orthotropic fracture toughness in mode $I(K_{IC}{\mid}^{ortho}_{max})$ is defined. Optimum angle between crack and fiber direction for maximum load bearing in orthotropic materials is also defined.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.12
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• pp.8-15
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• 2021

Cold forging is a method in which molding is performed at room temperature. It has a high material recovery rate and dimensional precision and produces excellent surface quality, and it is mainly used for the production of bolted or housing products. The lifespan of cold forging molds is generally determined by the wear of the mold, plastic deformation of the mold, and fatigue strength. Cold forging molds are frequently damaged due to fatigue destruction rather than wear and plastic deformation in a high-temperature environment as it is molded at room temperature without preheating the raw material and mold. Based on the results analyzed through FEM, an effective mold structure design method was proposed by analyzing the changes in tensile and compressive stresses on molds according to the number of molds and reinforcement rings and comparing the product geometry and mold stress using three existing mold models.

• Journal of the Korea Concrete Institute
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• v.21 no.1
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• pp.47-53
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• 2009

12 concrete blocks, on which hybrid fibrous sheets (carbon fiber and glass fiber) had been bonded, were subjected to tensile load in order to estimate properties of the bonded interface. the sheet length was varied by 100mm, 200mm and 400mm. It was found that more than 150mm bond length is required to achieve the maximum bearing capacity of the interface. In this study, maximum bond stress $\tau_{F,max}$, ultimate slip $S_{FU}$ of the interface were estimated $\tau_{F,max}$=3.0MPa and $S_{FU}$= 0.175mm, respectively.

• Computers and Concrete
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• v.14 no.1
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• pp.91-107
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• 2014

Using the principle of damage mechanics, zero-thickness pore pressure cohesive elements (PPCE) are used to simulate the casing-cement interface (CCI) and cement-rock interface (CRI). The traction-separation law describes the emergence and propagation of the PPCE. Mohr-coulomb criteria determines the elastic and plastic condition of cement sheath and rock. The finite element model (FEM) of delamination fractures emergence and propagation along the casing-cement-rock (CCR) interfaces during hydraulic fracturing is established, and the emergence and propagation of fractures along the wellbore axial and circumferential direction are simulated. Regadless of the perforation angle (the angle between the perforation and the max. horizontal principle stress), mirco-annulus will be produced alonge the wellbore circumferential direction when the cementation strength of the CCI and the CRI is less than the rock tensile strength; the delamination fractures are hard to propagate along the horizontal wellbore axial direction; emergence and propagation of delamination fractures are most likely produced on the shallow formation when the in-situ stresses are lower; the failure mode of cement sheath in the deep well is mainly interfaces seperation and body damange caused by cement expansion and contraction, or pressure testing and well shut-in operations.

• Proceedings of the KIEE Conference
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• 1999.07g
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• pp.3313-3315
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• 1999

Si direct bonding(SDB) technology is very attractive for both Si-on-insulator(SOI) electric devices and MEMS applications because of its stress free structure and stability. This paper presents on pre-bonding according to HF pre-treatment conditions in Si wafer direct bonding. The characteristics of bonded sample were measured under different bonding conditions of HF concentration, and applied pressure. The bonding strength was evaluated by tensile strength method. The bonded interface and the void were analyzed by using SEM and IR camera respectively. A bond characteristic on the interface was analyzed by using IT- IR. Si-F bonds on Si surface after HF pre-treatment are replaced by Si-OH during a DI water rinse. Consequently, hydrophobic wafer was bonded by hydrogen bonding of Si $OH{\cdots}(HOH{\cdots}HOH{\cdots}HOH){\cdots}OH-Si$. The bond strength depends on the HF pre-treatment condition before pre- bonding (Min:$2.4kgf/crn^2{\sim}Max:14.9kgf/crn^2$)