Researches on fatigue crack-initiation processes in metals by using atomic-force microscopy (AFM) were reviewed. For fatigue of a low-carbon steel and α-brass in air, morphologies and sizes of slip-bands and crack initiation processes were discussed, and it was found that the depth of an intrusion drastically increased with its outgrowth to a crack. With coalescence of cracks, the width of cracks increased rapidly. Transgranular cracks were initiated when their accumulated sliding distances, those were evaluated from measured intrusion depth as a function of intrusion angle relative to the stress-axis, reached a critical value. The critical value was independent of stress amplitude, mean stress, and grain-size. Change of surface roughness during fatigue process was also presented. In corrosion fatigue crack initiation study of a stainless steel and a high-strength aluminum alloy, even for a crack whose optical micrographs showed that it was initiated from corrosion pit, a micro-crack was sometimes found from AFM images before pit formation. On the other hand, for a crack whose optical micrographs showed that it was initiated from grain-boundary without corrosion pit, AFM image sometimes indicated that there was a small pit at the crack initiation site. These results showed that AFM is a very useful and powerful tool for elucidating micro-mechanisms of fatigue crack initiation process.
The asymptotic homogenization method within the framework of the updated Lagrangian formulation is employed to derive a nonlocal constitutive equation for finitely deformed rate-independent materials with a periodic microstructure. Higher-order asymptotic terms naturally introduce strain gradient terms into constitutive equations for macroscopically homogeneous materials. Macroscopic properties, which are the ensemble average of their counterparts over a microscopic unit cell, are discussed. The variational principle of macroscopically homogeneous materials is then established and the complete boundary value problem is formulated.
A material model for whisker-reinforced metal-matrix composites is constructed that consists of three kinds of essential elements: elastic medium, equivalent slip system, and fiber-bundle. The heterogeneity of material constituents in position is averaged, while the orientation distribution of whiskers and slip systems is considered in the structure of the material model. Crystal and interface sliding criteria are addressed. Based on the stress-strain response of the model material, an elasto-plastic constitutive relation is derived to discuss the initial and deformation induced anisotropy as well as other fundamental features. Predictions of the present theory for unidirectional-fiber-reinforced aluminum matrix composites are favorably compared with FEM results.
The fundamental equations estimating the compressive load-carrying capacity of reinforced concrete columns with tie and/or spiral reinforcements are used all over the world, based upon the ultimate limit state design, but the common equations include both the elastic term and the plastic one; so, there is no unification concept of the ultimate limit state. In recent years, the high-strength type reinforcement (SBPD type) has been used frequently in the RC column and beam in Japan. Now, the common equations can not apply to the case of the high-strength primary reinforcement of the RC column. This paper describes the improvement of the concrete's sharing capacity, the application range of the common equations and the generalized practical equation for the ultimate limit state load-carrying capacity considering the buckling effect of the primary rebars.
The rotating-bending fatigue tests on a TiNi shape-memory alloy wire were carried out in air and in water and low-cycle fatigue was investigated. The fatigue life in water shortened with increasing temperature but did not depend on frequency. The temperature of the wire in air increased with increasing frequency and the fatigue life shortened. The fatigue equation was proposed to describe the fatigue life depending on strain amplitude, temperature and frequency. The fatigue life was estimated well by the proposed equation. The shape memory processing temperature did not affect the fatigue life.
The fracture of many materials causes electronic excitation near fracture surfaces. This electronic excitation was reported to be observed as the electron emission from fractured metal surfaces and as the increase in electrical conduction in fractured semiconductors. However, the mechanism of electronic excitation near fracture surfaces has been hardly studied to date. In the present paper, we give theoretical consideration to fracture-induced electronic excitation in metals and semiconductors in terms of thermal excitation near fracture surfaces. It is shown that the reported electron emission from fractured metal surfaces corresponds to thermoelectronic emission at about 1000K. It is estimated that the reported increase in electrical conduction in fractured semiconductors also corresponds to thermal excitation of carriers at about 1000K. Excited states near fracture surfaces are discussed on the basis of the present estimations.
The effect of the orientation texture of cross-sectional graphitic layer planes on transverse compressive properties was studied in pitch-based carbon fibers. The finite element analysis indicated that radially oriented fiber could be expected to display higher transverse modulus and lower transverse compressive strength than randomly oriented fiber. The transverse compressive test was carried out by means of direct pressing of single filaments in which each filament's strength and modulus were measured. The cross-sectional orientation texture was identified not only by observation under scanning electron microscope (SEM) but also by torsional modulus measurement. The transverse modules and transverse compressive strength were found to decrease with increasing crystallite size. It was however not possible to find out clear differences between radially and randomly oriented fiber. These transverse properties cannot therefore be attributed to differences in cross-sectional texture. Bonding between crystallites appears to be the dominant factor in determining the transverse modulus, while the strength in the central area of the cross section is expected to determine the transverse compressive strength of the filament.
The electrodeposition method for rehabilitation of cracked reinforced concrete is presented here. Electrodeposition means precipitation of material on the surface of an electrode by electrolysis. The aim of electrodeposition method is to fill the crack in concrete and to coat the concrete surface by electrodeposits of chemical compounds. These layers of inorganic compounds provide a physical barrier and reduce the flux of gas or solution inside the concrete. This is expected to be accomplished by feeding a weak direct current between the reinforced steel in a concrete structure and an electrode located in the external solution. The electrodeposition test was conducted using reinforced concrete beams of 15×15×125cm. Cracked specimens by carbonation were immersed in an electrolyte zinc sulfate solution, and were applied with a constant current for 4 weeks. Visual observation and electrochemical investigations were performed in order to assess the effectiveness of this method in the improvement of concrete properties. The laboratory test results were also verified with the application on reinforced concrete members of real structure. The results indicate that electrodeposits formed on the concrete surface are capable closing the concrete cracks and that the electrodeposition method is effective on the repassivity of the reinforcing steel in concrete.
Au-Sn and Au-Ag bonding processes were developed by applying a micro-bonding process for LSI packages. An Au-plated Cu lead was bonded by a termo-compression bonding method on a Sn- or Ag-plated Cu frame using a bonding tool. The junctions were processed at a high temperature of 150°C for up to 1000h after bonding. Bonding strengths were subsequently evaluated by a 90° peeling test. As a result, Au-Sn bonding strengths were from 3 to 4.5N/mm and slightly dependent on the bonding pressure. For the Au-Ag junctions, on the other hand, these strengths were from 2 to 9N/mm and dependent on the bonding pressure. The Au-Sn and Au-Ag strengths after thermal aging were substantially the same as the initial strengths. With the Au-Sn junction, the bonding layer composed of Au, Sn and Cu, was formed. The thicknesses of the bonding layers which were made at 50MPa and 100MPa were about 2μm and 1μm, respectively. In the Au-Ag junctions, no bonding layer was formed on the interface. The unbonded area was formed at the Au-Ag interface at low pressure bonding. On the other hand, when the bonding was made at a high pressure of 150MPa, the bonding strengths were high because of no unbonded area.
The photo-catalytic mechanism of the TiO2 crystallites was studied for formaldehyde adsorbed in the carbonized TiO2-woody composites. To do so, the effects of the presence of oxygen and/or water were investigated on photo-catalytic activities of the composites. As a result, it became clear that photo-catalysis of the carbonized TiO2-woody composites requires water to decompose formaldehyde into CO2. However, the oxygen is not essential for its decomposition. Based on this requirement, the photo-catalytic mechanism of the TiO2 crystallites was discussed for adsorbed formaldehyde in the carbonized TiO2-woody composites.
It is a worldwide problem to build safer reinforced concrete (under-mentioned RC) structures on reflection of the great Hanshin earthquake disaster in 1995, Japan. The researches on the durability and the earthquake proof have advanced and the various countermeasures for these have been proposed. This paper deals with the specification of deterioration zones and its reliance, by using an external impact-acoustic detector, newly developed, which enables us to examine nondestructively the corrosive state of the inside of a concrete structure, and furthermore the verification with the natural potential method. The main experimental results concerning the building used in common are as follows: (1) The macroscopical corrosive degree of the RC structure can be evaluated by measuring the natural potential by means of the CuCuSO4 half cell and the effectiveness of the corrosion map. (2) “The external impact-acoustic method” can specify precisely the corrosive parts of reinforcement without the least damage on the RC structure, although the judgment of the corrosive grade is difficult; so, this disadvantage must be covered by using the natural potential method at the same time. (3)The relationship between the natural potential method and the external impact-acoustic one is quantitatively analyzed concerning an existing building.