• Composites Research
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• v.28 no.1
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• pp.6-14
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• 2015

Polymerization shrinkage stress analysis of dimethacrylate-based composite (Clearfil AP-X, Kuraray) and silorane-based composite (Filtek P90, 3M ESPE) used for dental composite restorations was performed using strain-gage measurement and FEM analysis. A theoretical equation based on Young's modulus and polymerization shrinkage of the composite resin was proposed to predict the polymerization shrinkage stress. Experimental results showed that the maximum shrinkage stress of Clearfil AP-X was about 2.8 times higher than Filtek P90. FEM analysis agreed with such experimental stress behaviours and showed that the maximum Von-Mises stress appeared near the margin of the filled resin adhered with PMMA ring. The stress concentration at the interface on the specimen surface was higher than that in the interior. The maximum error of shrinkage stress by the theoretical equation was reasonable within 5% in comparison to FEM results under plane stress.

• Korean Journal of Materials Research
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• v.8 no.1
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• pp.80-84
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• 1998

본 연구에서는 석영을 기판으로 사용하여 텅스텐 실리사이드 게이트를 고온에서 결정화시키고, 이\ulcorner 발생되는 crack 에 대한 생성원인을 조사하였다. 증착된 텅스텐실리사이드의 실리콘 조성과 실리콘 완층충의 두께가 증가함에 따라 열응력이 감소하는 경향이 관찰되었으며, 과잉의 실리콘 조성을 가진 실리사이드를 열처리한 경우에는 crack에 대한 저항이 증가함을 알 수 있었다. 그러나 실리콘 완충층을 사용한 경우는 두께가 증가함에 따라 열응력이 감소하는 경향이 있으나, crack이 보다 쉽게 발생되는 결과를 얻었다. 이는 실리사이드 반응에 의하여 거칠어진 계면에 응력이 집중되어 crack생성을 쉽게하는 것으로 여겨진다. 결과적으로 석영과 텅스텐실리사이드의 열\ulcorner창계수차이에 의하여 생성되는 열응력이 crack생성의 주원인으로 작용하고, 실리콘 완층층을 사용한 구조하에서는 계면에서 일어나는 실리사이드반응이 crack생성에 큰 영향을 미치는 것으로 생각된다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.1
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• pp.34-42
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• 1986

An interface of a circular arc formed by two isotropic, homogeneous elastic materials is investigated. It is shown that L integral satisfies the conservation law for the interface if it is perfectly bonded, in frictionless contact or separated such as in a crack with the origin of the coordinate system being located at the center of the circular arc. The property of path independence of the L integral is applied to an interfacial crack problem, to obtain the stress intensity factors, where the interfacial crack is located along the arc of the circular inclusion embedded in infinite matrix. It is assumed here that the contact zone exist as in the model proposed by Comninou, thus removing the overlapping of the materials along the interface. Another example is shown for case of a circular interfacial crack in the matrix of finite size, where the stress intensity factors are determined by computing a value of the L integral numerically along the path far from the crack tip.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2007.04a
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• pp.107-108
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• 2007

박막형태의 소재는 일반적으로 광 전자 및 소재가 공 관련 산업에서 특수한 기능이 요구되는 부품 제조에 광범위하게 응용되고 있다. 이러한 박막 소재는 물성 면에서 벌크물질일 때의 물성과 매우 다를 수 있는 것으로알려져 있다. 박막에 스트레인이 존재하면 전자의 이동도나 밴드갭 에너지를 변화시켜 줄 수 있으며, 계면의 전위는 소자를 열화 시키는 역할을 하기도 한다. 이러한 이유로 박막 성장 시 실시간으로 스트레인을 관찰하고 이 결과를 실제 제조공정에 피드백 하여, 소자의 신뢰성을 확보하는 노력이 행해지고 있다. 구리박막의 실시간 응력거동은 F.Spaepen에 의해 보고된 초기 압축응력, 인장응력, 2차적으로 나타나는 점진성의 압축응력의 독특한 3단계 응력거동으로 나타나는 것으로 알려져 있으며, 본 실험에서는 박막증착도중 단시간 증착을 중단한 이후 재 증착을 하여 응력거동을 관찰함으로써 독특한 3단계 응력거동의 메커니즘을 알고자 하였다.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.781-788
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• 2009

Mechanical properties of steel-concrete interface were evaluated on the basis of experimental observations. The properties included bond strength, unbounded and bonded friction angles, residual level of friction angle, mode I fracture energy, mode II bonded fracture energy and unbonded slip-friction energy under different levels of normal stress, and shape parameters to define geometrical shape of failure envelope. For this purpose, a typical type of constitutive model of describing steel-concrete interface behavior was presented based on a hyperbolic three-parameter Mohr-Coulomb type failure criterion. The constitutive model depicts the strong dependency of interface behavior on bonding condition of interface, bonded or unbounded. Values of the interface parameters were determined through interpretation of experimental results, geometry of failure envelope and sensitivity analysis. Nonlinear finite element analysis that incorporates steel-concrete interface as well as material nonlinearities of concrete and steel were performed to predict the experimental results.

• Composites Research
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• v.12 no.2
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• pp.10-25
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• 1999

A new evaluation method for the interfacial properties of fibrous composites based on a fragmentation technique is proposed by using the gradual multi-fiber composite, in which the inter-fiber spacing is gradually changed. The results showed that as the inter-fiber distance increased, the aspect ratio of broken fibers decreased while the interfacial shear strength between the fiber and matrix increased. When the reciprocal of the inter-fiber destance was taken for the above relations, both the aspect ratio and interfacial shear strength showed a saturated value. This means that the gradual multi-fiber composite indicates an upper bound in aspect ratio and an upper bound in interfacial shear strength. It was concluded that this fragmentation test could be a new method for composite evaluation, since reducing a difference between these two bounds is effective for composite strengthening. In addition an elastoplastic finite element analysis was carried out to relate the above results with fiber stress a distribution around fiber breaks. It was proved that the bound obtained in the gradual multi-fiber composite test is closely related to stress concentrations caused by a group of multi-fiber breaks.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.2002-2014
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• 1991

A refined two-dimensional analysis method, taking into account the crack opening deformation, is proposed for the evaluation of stress distributions in transverse cracked cross-ply laminates. The interlaminar stresses which play an important role in laminate failure are evaluated using the concept of interface layer. A series expansion of the displacements is employed and the thermal residual stresses and Poisson's effects in the laminated are taken into consideration in the formulation. The stress distributions are compared with finite element results. The proposed method represents well the characteristics of the stress distributions. The through-the-thickness variation of the stress distribution is remarkable near the transverse crack due to the crack opening deformation. The interlaminar stresses have significant values at the transverse crack tip and the proposed analysis can be applied as a basis for the prediction of the induced delamination onset by using appropriate failure criteria.

• Korean Journal of Materials Research
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• v.9 no.10
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• pp.962-969
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• 1999

Elastic and elasto-plastic stress analyses of AlN/Cu and AlN/W pints produced by active-metal brazing method using Ag-Cu-Ti insert-metal were performed with use of Finite-Element-Method(FEM). The results of stress analyses were compared with those from the pint strength tests and the observations of fracture behaviors. It was shown that a remarkably larger maximum principal stress is built in the AlN/Cu pint compared to the A1N/ W joint. Especially, the stress concentration with tensile component was confirmed at the free surface close to the bonded interface of AlN/Cu. The elasto-plastic analysis under consideration of stress relaxation effect of Ag-Cu-Ti insert possessing a so-called 'soft-metal effect' showed that the insert leads to a lowering of maximum principal stress in AlNiCu pint, even though an increase of the insert thickness above 100$\mu\textrm{m}$ could not bring its further decrease. The maximum pint strengths measured by shear test were 52 and 108 MPa for AlNiCu and AlN/W pints. respectively. Typical fractures of AlN/Cu pints occurred in a form of 'dome' which initiated from the free surface of AlN close to the bonded interface and proceeded towards the AlN inside forming a large angle. AlN/W pints were usually fractured at AlN side along the interface of AlN/insert-metal.

• Journal of the Microelectronics and Packaging Society
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• v.12 no.4 s.37
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• pp.351-357
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• 2005

Comparison of shear strength and shear energy of the 48Sn-52In solder bumps reflowed on Cu UBM were made with variations of reflow temperature from $150^{\circ}C$ to $250^{\circ}C$ and reflow time from 1 min to 20 min to establish an evaluation method for the mechanical reliability of solder bumps. Compared to the shear strength, the shear energy of the Sn-52In solder bumps was much more consistent with the solder reaction behavior and the fracture mode at the Sn-52In/Cu interface, indicating that the bump shear energy can be used as an effective tool to evaluate the mechanical integrity of solder/UBM interface.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.1
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• pp.97-103
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• 2000

This paper deals with residual stresses induced at the viscoelastic adhesive layer between the semiconductor chip and the leadframe during adhesion process. The adhesive layer has been assumed to be“thermorheologically simple”. The time-domain boundary element method(BEM) has been employed to investigate the behavior of interface stresses. Numerical results show that very large stress gradients are present at the interface corner and such singularity might lead to local yielding or edge delamination.