Masaki Kaji

Microhardness anisotropy and the indentation size effect on the basal plane of single crystal hematite

Abstract The Knoop microhardness anisotropy of single crystal hematite, Fe 2 O 3 , was investigated on the basal plane (0001) at indentation test loads from 50 to 1000 g. Microhardness maxima were observed for low indentation test loads when the long axis of the Knoop indenter was parallel to the 11 0>. Microhardness minima occurred for the 1 0> orientations. The microhardness anisotropy at low indentation test loads is associated with slip dominance on the primary slip system of the corundum structure, the {0001} 2 0>. An energy balance was applied to the indentation size effect (ISE) and also to address the microhardness anisotropy. The load independent, orientation independent, Knoop microhardness for the basal plane is 5.35 GPa. The ISE was further investigated by lubrication of the specimen test surface just prior to the Knoop microindentation process. Results from the lubricated microhardness tests are compared with the standard dry Knoop microhardness test results and reveal a significant reduction in the ISE. This indicates that friction between the test specimen and the indenter facets is a major contribution to the ISE.

Study of mount technology on alumina multilayer substrate for automatic transmission ECU

Reliability of electronic components assembly mounting technologies used on multilayer alumina substrates has been investigated for Electronic Control Units (ECUs), specifically for use in harsh locations, such as under the hood or directly attached to the transmissions of automobiles. The technology mainly consists of lead-free solder and bare chip assembly. Reliability evaluation tests have been performed in a practical, severe environment, similar to under the hood of automobiles. The experiments mainly consist of thermal cycling and corrosion tests. Computer simulation techniques have also been conducted in order to obtain accurate prediction of product lifetime. The estimated lifetimes of the lead- free solders agree fairly well with the experimental results. Through these studies, ECUs with higher reliability have been applied to automatic transmissions of commercial passenger vehicles.

Reliability Evaluation of Structural Ceramics Under Multiaxial Stress State

Strength and fatigue lifetime of structural ceramics under multiaxial stress state have been estimated and compared with experimental data. Biaxial strength tests were done by an anticlastic bending test method at room temperature. Biaxial fatigue tests were done by anticlastic bending and also ring-on-ring test method at 1200°C in air. Fracture probability and lifetime were predicted on the basis of a Weibull multiaxial distribution function and subcritical crack growth, using the results of stress analyses by the finite element method. Modified maximum hoop stress theory including an empirical parameter, T, was applied to the equivalent normal stress in the multiaxial distribution function. The empirical parameter T represents a shear stress sensitivity to mixed-mode fracture due to a grain interlocking effect. It has been confirmed that the predicted fracture probability and the fatigue lifetime agrees well with the experimental data if grain interlocking effects are taking into account.Copyright

Evaluation and Simulation of Thermal Shock Behavior by Liquid Solder Quenching

Thermal shock test was studied using liquid solder as the cooling medium to obtain a constant heat transfer coefficient. Tested materials were a silicon nitride, a silicon carbide and an alumina. In the case of silicon nitride, no sudden degradation of the strength was observed. This phenomenon is caused by the statistical deviation of the strength. We have proposed to use the Weibull plot method to determine △ Tc. Applying this method to the experimental results, we have shown that the average △ Tc can be well defined, and this method can be consistently applied to many different ceramics. Considering the effective volume of specimen and the temperature dependence of the material properties, the critical temperature difference was calculated. The calculated value and the experimental data agree very well. We have shown that the judgment of materials by only △ Tc may lead us wrong conclusion.

Evaluation of Fast Fracture Strength of Ceramic Components Under Multiaxial Stress States

Several fracture criteria were studied under multiaxial stress states by Matsuo’s multiaxial fracture probability distribution function including effects of both volume and surface cracks. Tested material was a pressureless-sintered silicon nitride. Tensile (compressive)-torsional tests revealed that experimental data were satisfactorily described by Shitty’s empirical criterion for C=1.46. Good agreements for a spin and a thermal shock tests were obtained applying the Weibull parameters and the Shetty’s parameter.Copyright

Fracture Toughness of Structural Ceramics Under Biaxial Stress State by Anticlastic Bending Test

Mixed-mode fracture of structural ceramics under biaxial stress state was investigated by an anticlastic bending test using the controlled surface flaw technique. The stress state of the anticlastic bending specimen is biaxial. This test enables the study of fractures under pure mode I, pure mode II, or any combination of mode I and mode II loading.To discuss the experimental results, a parameter ‘T’ was introduced to the modified maximum hoop stress criterion. This parameter represents frictional effects of crack interfaces on the mixed-mode fracture and can be obtained experimentally. Relative magnitudes of mode I and mode II stress intensity factors and the directions of non-coplanar crack extension angles were predicted using the parameter ‘T’. Reasonable agreement with the experimental results was obtained.Copyright

Reliability analysis of a ceramic turbine wheel

Failure probability of a ceramic rotor was calculated with Shettys fracture criterion. Shettys parameter was obtained by a multi-axial stress test. Fracture strength of material was evaluated taking surface conditions into account. Stress distribution used for the fracture evaluation is also carefully estimated by a finite element method. Good agreement was obtained in a comparison of the results of cold spin test with the calculation.

Reduction of EMI for ECU with Alumina Multilayer Substrates

Several techniques have been studied for reduction of radiation noise from an ECU (electronic control unit) made of alumina multilayer substrates. Some of them were proven to be effective for the RFI (radio frequency interference) reduction through the development of the ECU. The effective methods were separating the analog and digital power planes, increasing the analog ground area, and using common mode chokes. To reduce the electromagnetic radiation, we have also proposed another technique of a multilayer substrate with the power/ground planes of lossy structure, for dispersing the high frequency electromagnetic radiation energy into the multilayer substrate. Power/ground plane structures in the substrate were evaluated using test modules. We have confirmed that the noise level was fairly reduced by these techniques, in the wide range of frequency, comparing with the conventional design.