Hirohisa Kimachi

R-curve behavior in fracture of notched porous ceramics

Abstract Notched specimens of porous silicon carbide (SiC) with porosity 37% were fractured under four-point bending. A single edge notch with six depths ranging from 0.1 to 2.8 mm was introduced to the specimen with a height of 7 mm. The fracture of specimens with a notch depth of 0.1 mm did not start from the notch, but from the intrinsic defect. The size of the non-damaging notch is about 0.1–0.2 mm and roughly equal to the size of SiC particles. When the notch depth was larger than 0.4 mm, the fracture started from the notch for all specimens. The record of the strain gage glued on the compression surface of the specimen as a function of the load showed nonlinearity before reaching the maximum load. The critical stress intensity factor was nearly constant for crack initiation from the notch. The resistance curve was constructed by estimating the crack length from the compliance change of the specimen, and was used for determining the maximum load point in bending tests. Fractographic observations showed the fracture path along the binder phase between silicon particles.

103 The Study on Independent Detection Triply Degenerate Raman Line of Si by Raman Microspectroscopy

1. 緒言 近年,ナノテクノロジーは急速に発達しており,半導体デ バイス等では,構造制御と微細化された材料開発が求められ ている.近年の半導体デバイスの高速化,省電力化に必要不 可欠な材料の代表例として,Si がある.この特性は,ひずみ 量と相関関係があるため,両者の関係を明らかにする必要が ある.サブミクロン空間分解能を備えたひずみ測定法の 1 つ として,顕微ラマン分光法が挙げられる.しかし,従来型の 後方散乱顕微ラマン分光装置を用いた Si のひずみ測定では, Si のラマンスペクトルの三重縮退を解くことができないた め,単軸あるいは等二軸応力状態を仮定した応力測定を行っ ている. そこで本研究では,従来にない斜め入射型偏光顕微ラマン 分光装置を提案することで,Si の三重縮退を解いた応力/ひ ずみ測定の可能性を検討した.そこで(001),(011)配向に対 する Si の偏光ラマン散乱強度の理論展開を行った.さらに, 斜め入射型偏光顕微ラマン分光装置を用いて偏光測定を行 い,理論と実験を比較することで,三重縮退したピークを独 立ピークとして検出する偏光条件を検討した. 2. Si の理論ラマン散乱強度 入射光および散乱光の偏光条件に対するラマン散乱強度 I は,次式で表される. ( ) 3 0 ∑ = ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ = i d i t t i t e T R T e I I π π (1)

Changes of internal stress and microstructure in spontaneous tin whisker growth

Tin thin films with various thicknesses were electrodeposited on Cu substrate with and without Ni undercoat. The changes of the internal stresses in tin films were measured by the X-ray diffractions. For the case of 2.2 μm thick film without Ni undercoat, the initial internal stress was tension and then gradually changed into compression. After 20 h, the internal compressive stress became around −30 MPa and was remained constant afterward. Filament-type whiskers were formed on the surface after the stress changed into compression. For the case of 2.2 μm thick film with Ni undercoat, the stress maintained in tension and no whisker was observed. For the cases of thicker films with and without Ni undercoat, the stress was compression around −30 MPa just after deposition, and remained constant. Nodule-type and Mount-type whiskers were formed on the surface, but no Filament-type whiskers were observed. The compressive stress applied by bending on 2.2 μm thick film with Ni undercoat resulted in the formation of Mount-type whiskers. The postbake process induced the tensile stresses in 2.2 and 16.5 μm thick films. Whisker formation was prevented in thin film and only Mount-type whiskers were formed in thicker films.

Elastic-Plastic Finite Element Analysis of Plastic Zone in Cracked FRP under Mode I Loading.

An elastic-plastic stress analysis was conducted for inhomogeneous fiber-reinforced plastic (FRP)containing a mode I matrix crack by means of the finite element method.The inhomogeneous FRP was modeled as a two-dimensional laminated structure composed of elastic-perfectly plastic matrix, orthotropic elastic fiber and homogeneous FRP.The extent and the shape o the yielding zone around the crack tip for the inhomogeneous FRP were compared to those for the unreinforced matrix material.Under the same value of the matrix stress intensity factor, KIm, the length of the plastic zone ahead of the crack tip, ωχ/dm, for the inhomogeneous FRP was nearly equal to that for the unreinforced matrix material in the range of KIml0.7σY(πdm)1/2, where σYis the yield stress of the matrix material and dm is the height of the matrix phase in the inhomogeneous FRP.In the range of KIm>0.7σY(πdm)1/2, ωχ/dm for the inhomogeneous FRP was larger than that for the unreinforced matrix material.The plastic zone height, ωy/dm, is nearly identical between inhomogeneous FRP and unreinforced matrix material. A simple method is proposed to estimate the height and the length of the plastic zone in the inhomogeneous FRP from the elastic stress distrigution in the inhomogeneous FRP.

Meso-Mechanical Analysis of Elastic Stress Distribution in Cracked FRP under Mode II Loading by Boundary Element Method.

The boundary element method was used to determine the elastic stress distribution near the tip of a delamination crack in fiber-reinforced plastics (FRP). FRP composites were modeled by a two-dimensional laminated structure composed of an isotropic matrix and orthotropic fiber. A mode II crack was induced in the matrix parallel to the fiber direction. The stress intensity factor. K11, and the energy release rate, G11, under mode II in-plane shear loading were calculated for the above inhomogeneous model, and compared with those for a homogeneous model. For long cracks, the energy release rate for the inhomogeneous model was equal to that obtained for the homogeneous model. For short cracks, the energy release rate was larger for the inhomogeneous model than for the homogeneous model. The characteristics of the elastic stress distribution ahead of the tip of a mode II crack in the matrix were compared with those of the elastic stress distribution for a mode I crack.