Mineo Mizuno

Monotonic tension, fatigue and creep behavior of SiC-fiber-reinforced SiC-matrix composites: a review

The monotonic tension, fatigue and creep behaviour of SiC-fiber-reinforced SiC-matrix composites (SiC/SiC) has been reviewed. Although the short-term properties of SiC/SiC at high temperatures are very desirable, fatigue and creep resistance at high temperatures in argon was much lower than at room temperature. Enhanced SiC/SiC exhibits excellent fatigue and creep properties in air, but the mechanisms are not well understood. The present Hi-Nicalon/SiC has similar properties to enhanced SiC/SiC, but at higher cost. Improvement of Hi-Nicalon/SiC therefore seems necessary for the development of a high-performance SiC/SiC material.

Creep and fatigue behavior of SiC fiber reinforced SiC composite at high temperatures

Abstract Tensile creep and tension-tension fatigue of SiC fiber reinforced SiC composite were investigated in argon at 1000 and 1300°C. Time-dependent (creep) strains under cyclic loading are much larger than those under constant load. However, the minimum creep strain rates under cyclic loading are similar to those under constant load at 1000°C and lower than those under constant load at 1300°C. All the data of the minimum creep strain rates versus time to rupture under both cyclic loading and constant load fall on the same line, i.e., the relations fit Monkman—Grant relationship. This means that creep controls the rupture life under cyclic loadings at high temperatures. At high stresses, the creep crack propagation paths are similar to fatigue crack propagation. However, at low stresses, more 0° fibers were broken in the way of flush with the matrix under creep load than that under fatigue load.

Tensile creep behavior of a SiC-fiber/SiC composite at elevated temperatures

Abstract The tensile creep behavior of a SiC-fiber-reinforced SiC composite has been investigated in argon at temperatures of 1000–1300°C. The apparent stress exponents for creep of the composite and the apparent activation energies for creep increase with decrease in stress. The threshold stress approach can be used to treat the data. Creep of the CVI–SiC matrix controls the creep of the composite. The relationship between creep rate and the time to rupture can be described by the Monkman–Grant equation which provides a method of life prediction. The Larson–Miller parameter can also be used for creep-life prediction of the composite when the appropriate constant is selected.

Fatigue Behavior of HDPE Composite Reinforced with Silane Modified TiO2

The composite of high density polyethylene reinforced with silane-modified TiO 2 particles (silane-TiO 2 /HDPE) is a potential bone substitute biomaterial. The structure, bioactivity and mechanical properties of silane-TiO 2 /HDPE are analogous to those of natural bone, correspondingly. In order to investigate the effect of silane connection and saline solution on fatigue behaviors, flexural fatigue tests with this composite were carried out in both air and saline solution. Saline solution was found to have different effect on fatigue life. In saline solution, the fatigue life could be improved at stress levels lower than 30 MPa, while the fatigue life could be reduced at stress levels higher than 30 MPa. After analyzing the fracture morphologies, different failure mechanisms were proposed, and the important role of silane connection in the composite during the fatigue process was discussed. Silane connection cannot only support the loading stress but also hinder the failure process under loading effectively. For dry specimens, no interfacial failure between the filler and matrix was found. For wet specimens, it is inferred that the synergetic effect of saline solution and high concentrated stress at high stress level could easily destroy the silane connection, which accelerated the fracture process, whereas the synergetic effect of saline solution and silane connection at low stress level could promote the formation of more microcracks on sample surface, which hindered the final fracture.

In situ observation of cyclic fatigue crack propagation of SiC-fiber/SiC composite at room temperature

Abstract In situ observation of cyclic fatigue crack propagation of SiC-fiber reinforced SiC composite at room temperature has been carried out by laser microscopy. Both smooth (unnotched) and notched specimens are used for tension-tension cyclic fatigue tests. Cracks initiate at the comers of large pores during loading in smooth specimens. In notched specimens cracks are formed at the interfaces between fibers and matrix that are connected to the notch. The balance between the fiber bridging in the wake of propagating crack tip and the breakage of bridged fibers by the degradation of interfaces maintains a steady cyclic crack propagation. Crack propagation rate gradually decreases with time after the maximum load being applied.

Stress, strain and elastic modulus behaviour of SiC/SiC composites during creep and cyclic fatigue

Abstract Creep and fatigue tests of Hi-NicalonTM/SiC (SiC matrix contains glass-forming, boron-based particulates), Standard SiC/SiC (SiC matrix is pure SiC) and Enhanced SiC/SiC (SiC matrix contains glass-forming, boron-based particulates) were carried out in air at 1300°C. The stress–strain hysteresis loops during fatigue and creep were studied. The change of Young’s modulus during creep and fatigue was analysed and compared among the three kinds of materials. Creep strain rates of Hi-NicalonTM/SiC in air were similar to those of Enhanced SiC/SiC, but much lower than those of Standard SiC/SiC. Consequently, the time to rupture at a given stress in Hi-NicalonTM/SiC was similar to that in Enhanced SiC/SiC, but much longer than in Standard SiC/SiC. Fatigue resistance of Hi-NicalonTM/SiC was similar to that of Enhanced SiC/SiC, but much better than Standard SiC/SiC.

Static and cyclic fatigue in SiC whisker-reinforced silicon nitride composite

Abstract Static and cyclic fatigue tests of 20 vol% SiC whisker-reinforced Si3N4 matrix composite processed by gas pressure sintering were carried out at room temperature (RT), 1000°C and 1200°C by four-point bending tests. Cyclic fatigue lives were equal to static ones at both RT and 1000°C, but higher than static ones at 1200°C. Crack propagation was a mixture of intergranular and transgranular modes at RT and 1000°C. However, fracture at 1200°C was characterized by a process of nucleation, growth and interlinkage of cavities in front of a major crack. The enhanced bridging stress under cyclic loading retards the cavity growth and therefore leads to longer fatigue life than under static loading.

A Simulated Synovial Fluid for Wear Characterization of Artificial Hip Joints by a Hip Joint Simulator

The calf serum solution was defined as the international standard lubricant for wear characterization of artificial hip joints. It is, however, known that its composition varies according to age, manufacturing processes or production areas of bovine cattle, and that the difference in composition has large effect on the wear characterization. It was difficult to compare the results obtained by different laboratories. Therefore, it is desirable to develop an artificial lubricant whose composition can be always set to a specified value as an alternative to bovine serum. In the present study, the effect of each major constituent in bovine serum on wear property was studied by hip simulator. As a result, transparent and stable lubricant solutions were prepared. It showed quite similar wear property to bovine serum by controlling the composition. These results serve as a guide to propose the new lubricant suitable for the wear characterization of hip joint.

Effect of Indenter Materials on Indentation Fracture of Alumina Ceramics

The present study describes the effect of indenter materials on Hertzian cracking behavior of alumina ceramics in sphere indentation. Numerical analysis (FEM) was carried out to investigate the influence of the frictional resistance at the interface due to the elastic mismatch between the indenter and the flat specimen on the stress distribution near the contact area. Two kinds of alumina ceramics with different mechanical properties were used for the flat specimen. Materials of the sphere indenter were cemented carbide, silicon nitride, alumina and hardened steel. The indenter was penetrated into the specimen with an electro-mechanical testing apparatus at a constant cross-head-speed in air. The indentation fracture was monitored with the acoustic emission signal. The numerical analysis revealed that the frictional resistance had influenced on the stress distribution. The experimental data showed that the ring crack radius, the crack pass below the contact zone and the indentation strength were different depending on the indenter material. From the comparison between the numerical analysis and the experimental data, it was found that the minimum value of the ring crack radius of the low density alumina flat specimen corresponds to the position of the maximum tensile stress.

Compression Tests of SiC‐Continuous Fiber Ceraric Matrix Composites

Conventional compression test fixtures used for monolithic ceramics and polymer matrix composites were applied to compression tests of continuous SiC-fiber reinforced ceramic matrix composites (CFR-CMC). Effects of fixture structure, tab and specimen configurations were investigated. In compression tests using gripping supports, compression failure occurred in a gage section, and the direct compression, without any gripping parts and reduced gage parts, lead to edge failure. The failure mechanisms were due to the fixture and specimen configurations. Modified IITRI fixture and controlled face supported fixture using a specimen with a reduced gage section are recommended for compression test for CFR-CMC.