Noriyuki Miyazaki

Solid Particle Erosion of Fiber Reinforced Plastics

Solid particle erosion tests were carried out to study the effect of matrix materials, reinforcement fibers, interface strength between matrix material and fibers, im pact angle, and particle velocity on the solid particle erosion behavior of fiber reinforced plastics. In the present study, special attention was focused on the effect of the interface strength between matrix material and fibers, which has not been investigated in a lot of previous works related with the erosion of composite materials. FRPs with treated or un treated fiber surfaces were used as test materials to study the effect of interface strength be tween matrix material and fibers. It is found from the erosion tests that the erosion rate is larger in a FRP than in a neat resin, and that the erosion rate of a FRP decreases with the increase of the interface strength between matrix material and fibers.

Solid particle erosion of thermoplastic resins reinforced by short fibers

Experiments were carried out to study the effects of matrix materials, reinforcement fibers, impact angle and particle velocity on the solid particle erosion behavior of thermoplastic resins reinforced by short fibers. All of the previous research on the erosion of fiber-reinforced plastics deals with steady state erosion, and no work has been done on the initial process of erosion. So special attention was focussed on an incubation period of erosion. Two types of fiber-reinforced plastics were used for erosion tests. One was a new type of thermoplastic polyimide (New-TPI) resin reinforced by short glass or carbon fibers. The other was polyetheretherketone (PEEK) reinforced by short glass or carbon fibers. The fiber-reinforced plastics with different fiber contents were utilized as test materials to examine the effect of fiber content. Initial and eroded surfaces of test specimens were observed with a scanned electron microscope and an optical microscope. The results of the experiments show that the mass of an incubation period is strongly dependent on initial surface roughness. The erosion rate at a steady state depends on the matrix material and on the volume content of fibers, regardless of fiber type.

Stress intensity factor analysis of interface crack using boundary element method—Application of contour-integral method

A new method is presented for stress intensity factor analyses of two-dimensional crack problems including bimaterial interface crack problems. The M1-integral method, an extended version of the J-integral method, is applied to bimaterial interface crack problems, using the results obtained from the boundary element method. The accuracy of the results of internal points is improved using adaptive automatic integration for a singular boundary integral. The value of the J-integral or the M1-integral is also obtained by this automatic integration. The J-integral method is applied to a center-cracked homogeneous plate under tension. Furthermore, a bimaterial plate with an edge interface crack and a bimaterial plate with a center slant interface crack subjected to tension are analyzed. The proposed method gives accurate stress intensity factors not only for a crack in a homogeneous material but also for an interface crack between dissimilar materials.

Mixed mode fracture criterion of interface crack between dissimilar materials

Abstract This study presents an application of fracture mechanics to the interface crack between dissimilar materials. In this study, a concept of the stress intensity factors of an interface crack is discussed, and various types of specimens are tested experimentally for investigating the mixed mode fracture toughness criterion of an interface crack. The fracture toughness based on the stress intensity factors of an interface crack is decided by the fracture test and the boundary element analysis using the contour integral method. The mixed mode fracture toughness criterion is successfully characterized by the stress intensity factors of an interface crack.

Thermal stress analysis of silicon bulk single crystal during Czochralski growth

Abstract The thermal stress analysis of a silicon bulk single crystal with a diameter of 6 or 8 inches is performed in the cases of the [001] and [111] pulling directions by using a three-dimensional finite element program developed for calculating thermal stress in a bulk single crystal during the Czochralski growth. Elastic anisotropy and temperature dependence of material properties are taken into account in this program. The temperature distribution and shape of a silicon bulk single crystal which are required for the thermal stress analysis are obtained from a computer program for a transient heat conduction analysis which is specialized for the Czochralski growth. The stress components obtained from the thermal stress analysis are converted into the parameters related with dislocation density. The time variations of these parameters are shown in this paper. The relation between these parameters and the shape of the crystal-melt interface is discussed.

Effect of bond thickness on the fracture toughness of adhesive joints

The effect of bond thickness on the fracture toughness of adhesive joints was investigated from a microstructural perspective, using compact tension (CT) adhesive-joint specimens with different bond thicknesses. The adhesive material was a rubber-modified epoxy resin with 12.5 wt% carboxy-terminated butadiene acrylonitrile (CTBN) elastomer. The shapes of the rubber particles dispersed in adhesive layers of damaged and undamaged specimens were observed with an optical microscope. The damage was distributed along the interfaces between the adhesive layer and the two adherends. The results show that the primary causes of variations in the fracture toughness of at adhesive joint with the bond thickness are not only a damage zone around a crack tip hut also the combination of a damage zone around a crack tip and additional damage zones along the interfaces.

Effect of Interfacial Strength on Erosion Behavior of FRPs

Experiments were carried out to study the effect of interfacial strength between a matrix material and fibers on the solid particle erosion behavior of FRPs. The FRPs used were epoxy resins unidirectionally reinforced by carbon fibers. Although more than ten papers have been published concerning the erosion behaviors of FRPs, it has not been clarified how the interfacial strength between a matrix material and fibers affects the erosion behavior of FRPs. In the present erosion experiments, FRPs with treated fibers or untreated fibers were used as test materials to examine the effect of interfacial strength between a matrix material and fibers on the erosion rate. According to the tensile tests, the FRPs with treated fibers show higher interfacial strength between a matrix material and fibers than the FRPs with untreated fibers. The results of the erosion tests show that the FRPs with treated fibers have higher erosion resistance than the FRPs with untreated fibers due to higher interfacial strength between a matrix material and fibers.

Failure of a Ductile Adhesive Layer Constrained by Hard Adherends

The evaluation of a fracture from a thin layer constrained by a hard material is important in relation to the structural integrity of adhesive joints and composite materials. It has been reported that the fracture toughness of a crack in a ductile adhesive joint depends on the bond thickness, but the mechanism has not yet been elucidated clearly. In this study, the J-integral and the near-tip stress of a crack in an adhesive joint are investigated. It is determined that a decrease of the bond thickness increases the stress ahead of a crack tip, which results in the decrease of fracture toughness.

Development of finite element computer program for dislocation density analysis of bulk semiconductor single crystals during Czochralski growth

A finite element computer program was developed for continuous simulation of the dislocation density in a bulk single crystal during Czochralski (CZ) growth process. In this computer program, the shape of crystal-melt interface and the temperature in a crystal at an arbitrary time were determined by linear interpolation of the discrete results which were obtained by a heat conduction analysis of a CZ single crystal growth system. A dislocation kinetic model called the Haasen-Sumino model was used as the constitutive equation of a single crystal. Dislocation density analyses were performed using this computer program for 8 in. diameter Si, InP and GaAs bulk single crystals. The present analyses indicate W-type dislocation density distributions across the diameter in InP and GaAs single crystals which can be observed in the actual CZ growth of InP and GaAs.

Damage zone around crack tip and fracture toughness of rubber-modified epoxy resin under mixed-mode conditions

Abstract Damage zones that form around crack tips before the onset of fracture provide significant data for evaluating the fracture behavior of polymeric materials. The size of the damage zone correlates closely with the fracture toughness of the resin. In this study, we investigate the relationship between the fracture toughness and damage zone size around crack tips of a rubber-modified epoxy resin under mixed-mode conditions. The fracture toughness, G C , based on the energy release rate, is measured using an end-notched circle type (ENC) specimen. The deformation of rubber particles in the damage zones is also observed using an optical microscope. The results show that the fracture toughness, G C , of the rubber-modified epoxy resin is closely related to the area of the damage zone. In the specimen with a loading angle of 30°, the rubber particles were deformed ellipsoidally due to the difference between the first and second principal stresses.