The effects of various experimental conditions on the preferred orientations of titanium nitride (TiN) thin films were investigated. These films were formed on Si (100) wafers and sapphire (0001) substrates by ion beam assisted deposition (IBAD) with various N/Ti transport ratios, N ion incidence angles, film thicknesses and substrate temperatures. The acceleration voltage of the incident ions was 1kV. The preferred orientation of the TiN films changed from (111) to (100) as the N/Ti transport ratios and ion incidence angles increased. This phenomenon is caused by the selective damage to crystal growth due to the energy of the bombarding particles. It was also found that an increase in film thickness changed the preferred orientation of the TiN (100) film to a (100) plus (110) orientation. Furthermore, this orientation reverted to (100) with the heating of the substrate during film preparation. It is concluded that these phenomena were caused by the process of minimizing the overall energy. Thus, the heating of the substrate was useful for synthesizing thick TiN (100) films in this preparation method. Transmission electron microscopy (TEM) observation of TiN (100) films suggested that these films had good crystallinity.
Granite is a brittle material and contains numerous small defects which are preferentially oriented along three mutually perpendicular quarry planes. These defects affect the physical properties of the granite, such as p-wave velocity, tensile strength, and compressive strength. In the present paper, we are reporting mechanical anisotropy of Nangsan and Hamyeol granite produced in Korea. P-wave velocity and Brazilian tensile strength were measured in diametric direction at a 100 interval. A uniaxial compressive test was carried out with measuring two diametric strains of quarry planes which are parallel to load. The result shows a strong correlation between crack density and other mechanical properties.
In this paper, the M-N-φ relationship of a beam section and the calculation of deformation for the externally prestressed tendon with large eccentricities are studied. A general method for analyzing the stress increment of external tendon and beam flexural behavior is presented. In this method, the action of external tendon is expressed as the equivalent loads applying at the deviators and anchorage ends. The beam not including external tendon is subjected to bending moment and axial force caused by both applied loads and equivalent loads. By comparing the different positions of deviators and anchorage ends before and after loading, the force of external tendon is obtained, the deformation compatibility of the external tendon is met, and the loss of tendon's eccentricity can be considered automatically. The calculation results conform well to the experimental results in reference .
A method to simulate the forging process and corresponding strain-induced austenitic-martensite phase transformation is formulated in the Eulerian description and its feasibility is examined. The method uses finite volume meshes for tracking material deformation and an automatically refined facet surface to accurately trace the free surface of the deforming material. By means of this finite volume method, an approach has been developed in the framework of metallo-thermo-mechanics to simulate metallic structure, temperature and stress/strain in the forging process associated with phase transformation. The incremental expression on the formulation of the kinetics equation is derived from Tsuta and Cortes' model. A mixture rule is adopted to evaluate the aggregate flow stress of the austenite-martensite affected by the respective flow stresses and phase transformation. This approach has been implemented in the commercial computer program MSC. SuperForge. This is the first report in which the fundamental framework is stated and the applicability of the developed method is confirmed using experimental results of the forging of a cylindrical billet. Some practical forging applications are demonstrated in the second report.
In Part I, based on the framework of metallo-thermo-mechanics, a finite volume method formulated in the Eulerian description has been set up to simulate the forging process and corresponding strain-induced austeniticmartensite phase transformation. The approach has been developed and implemented in the commercial computer program MSC. SuperForge. In this paper, numerical simulations for SUS304 stainless steel on backward and forward extrusions are carried out in order to verify the method proposed in Part I. Furthermore, the effects of strain rate on the austenitic-martensite phase transformation and the aggregate flow stress are studied.
The effects of interface control and matrix microstructure on the interlaminar shear strength and mode II interlaminar fracture toughness of 5H satin woven C/C composites were investigated by coating bismaleimide-triazine co-polymer (BT-resin) on the surface of carbon fiber and changing the heat-treatment temperature. Three point short beam flexure tests were carried out for the shear strength. End notched flexure specimens were used for the mode II interlaminar fracture toughness tests. Both the interlaminar strength and toughness decreased by coating BT-resin and increasing HTT from 1600°C to 2500°C. However the influence of the BT-resin coating was much larger for the mode II interlaminar fracture toughness than that for the interlaminar shear strength. This difference of the effect of interface control was discussed on the basis of microscopic observation.
Investigation was carried out on the influence of mechanical properties on the intensity of axial residual stress after cold drawing of metallic bars. Yield stress, Young's modulus, and work-hardening ratio were chosen as indications of mechanical properties, and quantitative influence was examined numerically on an ordinary cold drawing. After examining the quantitative influence of mechanical properties on the axial residual stress after drawing, further numerical experiments were carried out on the skin-pass effect in reducing the intensity of axial residual stress distribution, which the authors presented a result in the previous study by using S45C steel bars. In order to clarify the validity of the numerical analysis, various materials of different mechanical properties were selected, and cold drawing experiments were carried out in a laboratory to check the validity of the numerical results. The materials selected were (1) high-carbon steel, (2) medium carbon steel, (3) copper, and (4) aluminum. The residual stress was measured by Sachs method, and good agreement was obtained between the calculated and measured results in any case. It was found that the axial residual stress distribution is most sensitive to the work-hardening ratio, and an optimum skin-pass drawing condition was presented by quantitatively examining the effect of skin-pass in reducing the axial residual distribution.
This paper describes the effective utilization of industrial wastes such as ferric oxide powder and aluminum sludge for soil stabilization. Mixing these industrial wastes with hydrated lime to form some new type of stabilizers will be useful for both strength improvements of soils and environmental protection. The primary objective of this study is to investigate the effect of wastes on the strength development of stabilized soils. To perceive the strength development mechanisms of stabilized soils, X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods were employed in order to evaluate the formation of chemical reaction products and microstructural changes occurred in the stabilized soils. The industrial wastes contained in stabilized soil improve the mechanical properties of soils by chemical reactions between the reacting elements of industrial wastes and clay minerals in the soil. In particular, adding aluminum sludge into ferrum lime lead to a marked improvement in the early strength or flexural strength of stabilized soils.
The present study investigates the behavior of residual stress and thermal stress in thin copper films with X-rays. The copper films were deposited on a glass substrate by radio frequency (RF) sputtering. In-situ thermal stress measurement was also made on copper films during heat cycles. The residual stress of as-deposited state was tensile regardless of the conditions of film preparation. Early in the cooling stage, thermal stress behaves in an elastic manner so as to reduce the tensile stress until it stabilizes close to zero. In the cooling stage, little increase in the thermal stress was observed above 100°C and the hysteresis of thermal cycle was very small.
Epoxy resin and its particulate filled composites are being used widely in many fields of industry. High quality as well as reliability are especially necessary for electric and electronic products such as heavy generators and IC packages. For quality assurance, therefore, it is important to detect or evaluate the quality of these materials without causing destroying them. The purpose of this study is to establish a non-destructive evaluation method for the quality of cast epoxy resin and its particulate filled composites. This paper describes the results of an investigation made to clarify the relation among structure, physical and mechanical properties and ultrasonic characteristics of these materials by using an ultrasonic pulse reflection technique.
The fundamental characteristics of AE signals, such as the attenuation, frequency dependency of AE signals in CFRP composites, were investigated. The fracture process of the s.f.c. (single fiber composite) was examined. As a result, the frequencies of AE signals were almost unchanged, while AE amplitudes attenuated greatly with the increment of propagation distance. This proves that the frequency analysis is an effective way in processing AE signals of CFRP composites. Using the frequency analysis, the relationships between the micro failure modes and the frequencies at the peaks of the power spectrum distribution were established. In the fracture process of the s.f.c., the sources of AE signals were the failure modes at the fiber breakages. Using the time-frequency method of the short-time Fourier transform to process AE signals in CFRP composites, the micro failure modes at a fiber breakage and the microfracture mechanism, such as the sequence of failure modes and their interaction, were made clearer. It was shown that two processing methods of AE signals, the frequency analysis and the short-time Fourier transform, were powerful to identify the micro failure modes and elucidate the microfracture mechanisms in CFRP composites.