• Proceedings of the KIEE Conference
• /
• 1999.07g
• /
• pp.3301-3303
• /
• 1999

A new method of measuring residual stresses in micromachined films using beam or ring structures is proposed. Using the proposed method, more exact value of residual stress can be obtained without any ambiguities in conventional buckling method. Theoretical modeling with respect to this method is described, and experiment is performed. The structure and fabrication process in this paper are simple and widely used in surface micromachining. Therefore, it is possible to obtain a synchronous measurement. A synchronous and reason -able estimation of residual stresses in micromachined films enables us to obtain the prediction of more exact performance in micromachined devices.

• Journal of Surface Science and Engineering
• /
• v.37 no.4
• /
• pp.226-233
• /
• 2004

The residual stresses on the surfaces of low carbon 12Cr steels used as a nuclear steam turbine blade material have been studied by controlling the flame hardening surface treatments. The temperature cycles on the surfaces of 12Cr steel were controlled precisely as a function of both the surface temperature and cooling rate. The final residual stress state generated by flame hardening was dominated by two opposite competitive contributions; one is tensile stress due to phase transformation and the other is compressive stress due to thermal contraction on cooling. The optimum processing temperatures required for the desirable residual stress and hardness were in the range of $850^{\circ}C$ to $960^{\circ}C$ on the basis of the specification of GE power engineering. It was also observed that the high residual tensile stress generated by flame hardening induced the cracks on the surfaces, especially across the prior austenite grain boundaries, and the material failure virtually, which might limit practical use of the surface engineered parts by flame hardening.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.2 s.173
• /
• pp.279-289
• /
• 2000

Residual stress induced in U-bending and tube-to-tubesheet joint processes of PWR's row-1 heat exchanger tube was measured by X-ray method and Hole-Drilling Method(HDM). Compressive residual stresses(-) at the extrados surface were induced in U-bending, and its maximum value reached -319 MPa in axial direction at the position of $\psi$ = $0^{\circ}$. Tensile residual stresses(+) of $\sigma_{zz}$ = 45 MPa and $\sigma_{\theta\theta}$ = 25 MPa were introduced in the intrados surface at the position of $\psi$ = $0^{\circ}$. Maximum tensile residual stress of 170 MPa was measured at the flank side at the position of $\psi$ = $90^{\circ}$, i.e., at apex region. It was observed that higher stress gradient was generated at the irregular transition regions (ITR). The trend of residual stress induced by U bending process of the tubes was found to be related with the change of ovality. The residual stress induced by the explosive joint method was found to be lower than that by the mechanical roll method. The gradient of residual stress along the expanded tube was highest at the transition region (TR), and the residual stress in circumferential direction was found to be higher than the residual stress in axial direction.

• Korean Journal of Materials Research
• /
• v.25 no.12
• /
• pp.690-693
• /
• 2015

Fatigue crack growth experiments were carried out on a 304 L stainless steel compact-tension(CT) specimen under load control mode. Neutron diffraction was employed to quantitatively measure the residual strains/stresses and the evolution of stress fields in the vicinity of a propagating fatigue-crack tip. Three principal stress components (i.e. crack growth, crack opening, and through-thickness direction stresses) were examined in-situ under loading as a function of distance from the crack tip along the crack-propagation path. The stress/strain fields, measured both at the mid-thickness and near the surface of the CT specimen, were compared. The results show that much higher compressive residual stress fields developed in front of the crack tip near the surface than developed at the mid-thickness area. The change of the stresses ahead of the crack tip under loading is more significant at the mid-thickness area than it is near the surface.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 1998.10a
• /
• pp.121-124
• /
• 1998

It is well known that during the oxygen cutting residual thermal stresses are produced in weldment. Surface compressive residual stress is one of reasons for improvement on fatigue durability. To reduce the residual stress and improve the fatigue strength applied the impact loading in oxygen cutting frame. After applying the impact loading, redistribution of residual stress was measured by cutting method and tested fatigue tests.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.22 no.2
• /
• pp.268-277
• /
• 1998

The numerical procedure for calculating non-uniform residual stress fields by using relieved strain data from incremental hole drilling method is presented. Finite element calculations are described to evaluate the relieved coefficients required for the determination of residual stresses. From the results of simulations it is found that this numerical method is well adopted to measuring non-uniform residual stress in the hole depth range of 0.8 times of the hole diameter from the surface. In order to examine the practicability of this method, the hole drilling procedure for the four point bending test is performed. This method is applied to the measurement of residual stresses in the cold-rolled steel pipe. It is shown that the magnitude of residual stress in the pipe is not negligible when compared with yield stress and the residual stress should be duly considered in designing structures with this pipes.

• Journal of the Korean Ceramic Society
• /
• v.49 no.4
• /
• pp.301-307
• /
• 2012

SiAlON glasses are silicates or alumino-silicates, containing Mg, Ca, Y or rare earth (RE) ions as modifiers, in which nitrogen atoms substitute for oxygen atoms in the glass network. These glasses are found as intergranular films and at triple point junctions in silicon nitride ceramics and these grain boundary phases affect their fracture behaviour. This paper provides an overview of the preparation of M-SiAlON glasses and outlines the effects of composition on properties. As nitrogen substitutes for oxygen in SiAlON glasses, increases are observed in glass transition temperatures, viscosities, elastic moduli and microhardness. These property changes are compared with known effects of grain boundary glass chemistry in silicon nitride ceramics. Oxide sintering additives provide conditions for liquid phase sintering, reacting with surface silica on the $Si_3N_4$ particles and some of the nitride to form SiAlON liquid phases which on cooling remain as intergranular glasses. Thermal expansion mismatch between the grain boundary glass and the silicon nitride causes residual stresses in the material which can be determined from bulk SiAlON glass properties. The tensile residual stresses in the glass phase increase with increasing Y:Al ratio and this correlates with increasing fracture toughness as a result of easier debonding at the glass/${\beta}-Si_3N_4$ interface.

• Journal of the Korean Society for Heat Treatment
• /
• v.13 no.3
• /
• pp.170-176
• /
• 2000

A novel method for improving the adhesion of diamond films on cemented carbide tool inserts has been investigated. This method is based on the formation of a compositionally graded interface by developing a microrough surface structure using a pulsed laser process. Residual stresses of diamond films deposited on laser modified cemented carbides were measured as a function of substrate roughness using micro-Raman spectroscopy. The surface morphology and roughness of diamond films and cemented carbides were also investigated at different laser modification conditions. It was found that the increasing interface roughness reduced the average residual stress of diamond films, resulting in improved adhesion of diamond films on cemented carbides.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.14 no.4
• /
• pp.39-45
• /
• 2010

Thick-walled cylinders, such as a cannon or nuclear reactor, are autofrettaged to induce advantageous residual stresses into pressure vessels and to increase operating pressure and the fatigue lifetimes. As the autofrettage level increases, the magnitude of compressive residual stress at the bore also increases. The purpose of the present paper is to predict the accurate residual stress of SCM440 high strength steel using the Kendall model which was adopted by ASME Code. Hydraulic pressure process was applied in the inner part and thick-walled cylinders were autofrettaged up to 30% overstrain levels. Electro polishing on the surface of autofrettage specimen was performed to get more accurate residual stress. Residual stresses were measured by X-ray diffraction method. The autofrettage surface which was plastically deformed analyzed using a scanning electron microscope(SEM). Although there were some differences in measured residual stress and numerical results, it has a tendency to agree comparatively with each other.

• Journal of the Korean Society for Heat Treatment
• /
• v.7 no.4
• /
• pp.233-243
• /
• 1994

Constitutive relation of thermoelasto-plastic material undergoing phase transformation during quenching process were developed on the basic of continuum thermodynamics. The metallic structure, temperature and residual stresses distributions were numerically calculated by the finite element technique. The metallic structure were defined by transformation from austenite to pearlite and characterized as a fuction of thermal history and mixture rule of phase. On the distribution of thermal stress along the radial direction, axial and tangential stresses are compressive in the surface, and tential in the inner part. Radial stress is tensile in the whole body. The reversion of residual stress takes plase at 11.5~15.5mm from the center.