Hiroyasu Araki

Fatigue crack propagation of Sic whisker reinforced 6061 aluminum alloy composite

Abstract The fatigue strength and fatigue crack propagation (FCP) behavior of SiC whisker reinforced 6061-T6 aluminum-matrix composite fabricated by the high pressure infiltration method were studied. In addition to tensile strength, fatigue strength was increased by whisker reinforceb ment. However, because of the highly aligned whiskers to the L direction caused by the extrusion process they showed strong orientation dependence. The L orientation showed higher strengths than the T orientation. The FCP resistance in T-L or T-T oriented composites was lower than that in unreinforced 6061-T6 alloy, while in L-T oriented composites, deflected FCP occurred and great increases in the FCP resistance resulted by whisker reinforcement when comparison was made by the mode I stress intensity factor. Fractographic investigation was also made to clarify the fatigue mechanism of this composite.

Evaluation of Fracture Toughness Distribution in Ceramic-Metal Functionally Graded Materials

This paper deals with evaluation of fracture toughness in functionally graded materials (FGMs) consisting of partially stabilized zirconia (PSZ) and austenitic stainless steel SUS 304. FGMs and non-graded composites (non-FGMs) with fine and coarse microstructures are fabricated by powder metallurgy using PSZ and two kinds of SUS 304 powders. The fracture toughness is determined by conventional tests for several non-FGMs with each material composition and by a method utilizing stable crack growth for FGMs. Based on the experimental results, fracture mechanism, influences of microstructure on fracture toughness, and difference in fracture toughness between the FGMs and non-FGMs has been discussed.

Mechanical Properties of Carbon Nanofiber Reinforced Polylactic Acid

Carbon nanofiller reinforced PLA was fabricated, and the mechanical properties and heat resistivity were measured. Vapor grown carbon fiber (VGCF) produced by Showa Denko K.K. was used for reinforcement, which has 150 nm in diameter and 10 μm in length. No surface treatment of VGCF was conducted. VGCF and PLA were compounded by using a twin screw extrusion machine and then pelletized. The weight fraction of VGCF ranged from 1wt% to 10wt%. Three point bending specimens were fabricated by using injection molding. At first, three point bending tests were carried out at room temperature. The bending stiffness increased from 3GPa to as high as 5GPa, but the bending strength slightly decreased. SEM observation of the fracture surfaces indicated pull-out of VGCFs over the fracture surfaces. These results imply that adhesion between VGCF and matrix was imperfect. Then, the heat deflection temperatures and glass transition temperatures of the specimens were measured. The addition of VGCF did not increase the glass transition temperature but slightly increased the heat deflection temperature.

Effect of Material Composition on Mechanical Properties of Ceramics-Metal Composite Materials

This paper deals with fabrication and strength evaluation of biocompatible composites consisting of partially stabilized zirconia (PSZ) and pure titanium (Ti). The biocompatible composites of PSZ-Ti were fabricated by a hot pressing method of powder metallurgy. A volume ratio of PSZ and Ti was changed. Four-point bending tests and Vickers hardness tests of the PSZ-Ti composite were performed to determine the Youngs modulus, bending strength, Vickers hardness and fracture toughness. These properties were characterized as a function of Ti volume fraction. The Youngs modulus and Vickers hardness were higher than the prediction of the rule of mixture. The bending strength and fracture toughness were decreased with increasing Ti content. To discuss these results from a viewpoint of reaction products, the components of raw powders and sintered composites were investigated by X-ray diffraction analysis. It is concluded that oxide of titanium and other reaction products were created after sintering and they affected the mechanical performances of the composites.

FATIGUE BEHAVIOR OF SiC/Al COMPOSITE MATERIALS

ABSTRACT Fatigue strength and fatigue crack propagation behavior of SiC whisker (SiCw) or particulate (SiCp) reinforced 6061-T6 aluminum matrix composite fabricated by the high pressure infiltration method were studied. A comparison was made with the properties of unreinforced 6061-T6.

Fatigue of Metal Free Reed due to Self-Excited Oscillation

Metal free reeds are used for musical instruments like harmonica. Free reeds are small, thin cantilevers, and oscillate by blowing air. It is reported that free reeds break due to fatigue during play. In order to elongate the life of free reeds, the fatigue properties should be investigated and a motion analysis method should be developed. The experimental and analytical research on metal free reed, however, has been rarely reported. In this study, two types of fatigue testing machines were developed to obtain basic fatigue characteristics. The fatigue testing machines are designed for bending fatigue of actual free reeds whose thickness is less than 400 μm. An S-N diagram is successfully obtained up to 107 cycles by using the developed fatigue testing machines. The fracture surfaces of fatigued specimens are in good agreement with those of free reeds failed in use. Then, an analytical method for the self-excited oscillation of free reeds was developed based on a mass-damper-spring model. The proposed method can take account for the shape of free reed. The self-excited oscillation of free reeds with different shape are analyzed and in good agreement with experimental results.

Deformation Behavior of Shape-Control Plate Using NiTi Shape Memory Alloy Wire

This study deals with deformation behavior of a shape-control plate which consists of an aluminum alloy plate and a pre-strained NiTi shape memory alloy (SMA) wire. The shape-control plate exhibits reciprocating bending deformation by heating and cooling. Deformation behavior of the plate is examined by electric heating and natural cooling of the SMA wire. Experimental results exhibit that the bending deformation of the plate is considerably stable over more than two thousand heating-cooling cycles and can be well controlled by electric current. Furthermore, the deformation behavior of the plate is analyzed by a simple beam theory for the aluminum alloy plate and Brinson’s one-dimensional constitutive model for the SMA wire taking account of not only martensitic transformation but also rhombohedral-phase transformation. Numerical results describe well the deformation behavior of the shape-control plate observed in the experiments.