Ceramics are harder than metals and polymers and have excellent wear resistance, high mechanical strength, and high chemical stability. In addition, these properties can be arbitrarily controlled depending on the compositions and microstructures of the materials. Therefore, ceramics are widely used in orthopedic surgery as artificial joints and bones. Such ceramics for biomedical applications are called bioceramics. In the application of bioceramics, the mechanical property is one of the most important material characteristics. For example, alumina (Al2O3) or zirconia (ZrO2) ceramics are often used for the sliding parts of artificial joints that require excellent wear resistance and appropriate mechanical strength. Bioceramics used in orthopedics can be divided into three types, bioinert, bioactive, and bioabsorbable ceramics, depending on the biological response when implanted into a bone defect. In this review paper, firstly, we describe the mechanical properties of Al2O3 and ZrO2 ceramics as typical bioinert ceramics, then the mechanical properties of Na2OCaO-SiO2-P2O5 glass, hydroxyapatite/beta-type tricalcium phosphate biphase ceramics and glass-ceramic containing fluorapatite and wollastonite as typical bioactive ceramics were reviewed. The mechanical properties of calcium phosphate cements and calcium phosphate-polymer composites including recently developed soft ones were also introduced.
An axial thermo-mechanical fatigue testing method was developed to evaluate the mechanical properties of thermoplastic resin under the actual conditions of use. The suitable shape and dimensions of the plate type specimen for the axial cyclic fatigue test were determined with numerical analysis and tensile testing. In addition, a heating and cooling method for the resin specimens at a thermal cycle rate of 1 K/s was established. The axial thermo-mechanical fatigue test and isothermal fatigue test of glass fiber reinforced polyphenylene sulfide was available with the plate type specimen that has 4 mm width at the center gauge part. In-phase type and out-of-phase type thermo-mechanical fatigue tests were conducted in the temperature range of 253 K (-20°C) to 393 K (120°C) under mechanical strain control conditions. Mean stress at the in-phase type test was lower than that at the out-of-phase type thermo-mechanical fatigue test.
Wendong TANG and Hidekazu NISHIMURA To quantitatively evaluate the mechanical behavior related in damage of RC member by roadmap model, the static cyclic loading experiments were applied to the model beams. The load displacement relationships were obtained. The natural frequency taken for represent condition of soundness using the Impact Vibration Test (IVT), which measured the RC beam in each loading stage. Focusing on the natural frequency changes between the condition of soundness and the damages in each stage of loading, it confirmed that the decrease of bending stiffness can be reflected more accurately in higher-mode vibration. Furthermore, to examine the measured results of IVT, the eigenvalue analyses were conducted, where local reduction of bending stiffness to the beam can be taken into account rationally. In this way, a higher accuracy of analyses was achieved. Based on those results, the adequacy of natural damage estimation using natural frequency in RC member by roadmap model was verified.
Kaoru UESUGI, Kenya SATO and Kazuaki NAGAYAMA Cells are affected by various mechanical stimulations and change their mechanical and physiological properties. Recently, we found that mechanical stress possibly inhibits the ultraviolet (UV)-induced DNA damage of cells. Thus, in this study, the morphological change and the UV damage of nuclear DNA of cultured cells exposed to hydrostatic pressure were evaluated. First, a hydrostatic pressure-imposing experimental setup was constructed and morphological change of rat smooth muscle cell’s (A7r5) nucleus was evaluated. The results showed that the shape of the nucleus of cells exposed to hydrostatic pressure came close circle and the projected area and the volume decreased. The height of the nucleus did not change significantly. Then, the UV damage of nuclear DNA of A7r5 cells exposed to hydrostatic pressure was evaluated. An evaluation of breakage of DNA with γ-H2AX shown that the UV damage of cells exposed to hydrostatic pressure was inhibited. An evaluation using nuclear staining was shown that the UV damage of cells exposed to hydrostatic pressure was more decreased than that of cells unexposed, simultaneously with intranuclear DNA aggregations. These results mean that the DNA aggregation that occurred by a decrease of nuclear shape may work as a physical barrier against UV irradiation.
Gas turbines of power generation systems used in high-temperature environments are expected to improve their thermal efficiency by increasing the turbine inlet temperature. In such environments, thermal barrier coating of turbine blades has become an indispensable material technology. In this study, the elastic moduli of the thermal barrier coatings were measured at high temperatures up to 1000 ℃. Experiments and finite element analysis were performed using a rectangular section bar with a metal substrate coated with two layers, that is, a metallic bond coat and a ceramic top coat. The elastic modulus of each layer is calculated from the natural frequency of the specimen by applying the multilayer beam theory for the flexural free vibration. The elastic moduli of the substrate, the bond coat and the top coat in the cooling down process after heating at 1000 ℃ increased as the temperature decreased.
Aging road bridges have become a problem in Japan, and regular inspections are carried out once every five years by proximity visual inspection. However, the shortage of inspection technicians and budget is a problem, and there is a need for inspection technology that is efficient and can perform diagnosis equivalent to proximity visual inspection. In this study, we focused on the image processing technology of the 3D data generation software SfM, generated a 3D model from the crack image of the concrete member taken by UAV, and compared the actual crack width with the crack width obtained from the 3D model. As a result of the verification, it was suggested that by using UAV and SfM, the crack width of 0.2 mm or more can be judged with relatively high accuracy by photographing the area around the actual crack from a short distance.
A rapid heating test was performed using an electric furnace to evaluate the exothermic behavior of riser sleeve materials for casting in accordance with the real casting process. Rapid heating was performed by quickly inserting the riser sleeve sample into a muffle furnace at holding temperatures of 200, 400, 600, 800, and 1000 oC. The sizes of the samples were 10 mm × 10 mm × 18 mm, 20 mm × 20 mm × 18 mm and 30 mm × 30 mm × 18 mm. At a furnace temperature of 1000 oC, when the temperature of the sample was 350 oC, the resin in the sample oxidized. When the temperature of the sample was 900 oC, aluminum oxidized. Moreover, when the temperature was over 900 oC, thermite reaction occurred. The chain exothermic reaction occurred when the temperature of the riser sleeve sample reached over 1372 oC. and the efficient exothermic reaction occurred in the riser sleeve sample for casting.