In order to make clear the effect of air on the Mode II fatigue crack growth mechanism and threshold, the Mode II fatigue crack growth test was carried out in a vacuum. Fibrous pattern on the Mode II fatigue fracture surface of the specimen tested in a vacuum was clearer than that tested in air. The side view of the Mode II fatigue crack of the specimen tested in a vacuum was thinner than that tested in air due to the lack of oxidation in a vacuum. The layer with the microstructural change was observed in the vicinity of the Mode II fatigue crack as well as that in air. The Vickers hardness of the layer of the specimen tested in a vacuum was 770 (HV = 630 in air). These values were much higher than that of the original matrix (HV = 190). The layer consisted of very fine grains (∼130nm in a vacuum, ∼100nm in air). The Mode II threshold stress intensity factor ranges, ΔKIIth = 10.2MPa√m (Longitudinal) and 12.5MPa√m (Transverse) in a vacuum were higher than that in air ΔKIIth = 9.4MPa√m (Longitudinal) and 10.8MPa√m (Transverse). Both in a vacuum and air, the values of ΔKIIth for crack growth perpendicular to the rolling direction were higher than the values of ΔKIIth for crack growth parallel to the rolling direction.
Effects of hydrogen charge and frequency on fatigue behaviour were studied in bearing steel (JIS-SUJ2) tempered at 823K. The crack growth rate of the hydrogen-charged specimen was faster than that of the uncharged specimen. The morphology of the crack observed on the surface of the hydrogen-charged specimen was thinner than that of the uncharged specimen. It is presumed that the slip deformation at the crack tip was restricted and localized by hydrogen. The definite dependency on test frequency in the crack growth rate was observed in the hydrogen-charged specimens. The lower the test frequency, the faster the crack growth rate in the test of the hydrogen-charged specimens at the frequency of 0.5∼15Hz. However, there was no clear difference in the fracture surface morphology between the uncharged specimens and the hydrogen-charged specimens at the frequency of 0.5∼15Hz. The transgranular fracture caused by fatigue was dominant and the intergranular fracture caused by so-called delayed fracture was little in all of the specimens. Therefore, it is presumed that the increase in the crack growth rate in the hydrogen-charged specimens at lower frequency was caused by enhancement of the fatigue mechanism related to hydrogen motion coupled with slip behaviour. Thus, it is presumed that the dependency on test frequency in the crack growth rate in the hydrogen-charged specimens was caused by the synergetic effect of the enhancement of hydrogen diffusion motion to the slip bands at the crack tip with time and easiness of slip motion by hydrogen.
The internal friction behavior by hydrogen in the 329J4L super duplex stainless weld metal was examined. Two internal friction peaks at low temperature in the weld metal were observed after hydrogen charging. These peaks appear to be caused by stress-induced diffusion of hydrogen in sigma and austenite. These peaks gradually increased with hydrogen charging time and were unique to duplex stainless steel. A sharp peak of significant strength occurred at 245K for a frequency of 1.5Hz in as-welded condition. The activation energy of this peak after 7.2ks charging is approximately 38.7kJ/mol which compares favorably with the hydrogen diffusion energy for austenitic stainless steel. This peak is associated with the stress-induced motion of hydrogen in an interstitial-substitutional pair. On the other hand, the sigma (s) phase precipitation suppressed this peak and showed slightly broader peak, providing a strong indication of hydrogen trapping into the sigma phase. After peak separating calculation using theoretical internal friction curve, two peaks were observed after hydrogen charging. One of the peaks observed at 245K exhibited an activation energy of 38.7kJ/mol. A broad peak at 225K is interpreted as a stress-induced motion of hydrogen in tetragonal sigma phase. The activation energy of peak by hydrogen in sigma phase was estimated to 36.7kJ/mol. Consequently, a broad peak by hydrogen in sigma phase was observed at 225K in the hydrogenated weld metal precipitating sigma phase. It is apparent from these results that hydrogen can easily diffuse in the sigma phase as compared to austenite.
In order to reduce the environmental pollutions and develop a new type construction material with super lightweight and high strength, we did some fundamental studies on the mechanical behaviors. The three kinds of experimental samples were made of fly-ash and full hard polyurethane, whose special mix-ratio and producing methods are described in this investigation. The static mechanical characteristics were discovered in the three kinds of material tests, namely the compression test, the bend test, and the cleavage test. The mechanical behaviors of this new material are also compared with that of concrete in the investigation. The main results obtained in the study are : 1) the new material can be made of fly-ash and full hard urethane, 2) stress-strain relations are discovered in the tests, and 3) the new material can be used not only as reinforcement of steel structural system for seismic design, but also as expansion device for high-way bridge, due to its large capacities of transformation, remarkable lightweight and high strength.
Morphology and mechanical properties of atomic-cluster-assembled structures, which are generated from nano-size cluster of metallic atoms, are studied by using molecular dynamics with many-body interatomic potential. Generation of the structures is carried out by configuring copper clusters (made up of 683 atoms) in regular array with initial approaching velocities. It is confirmed that one-dimensional, two-dimensional, and three-dimensional structures can be designed and fabricated from clusters. Shape of the structures is largely dependent on initial velocities, that is, initial kinetic energy attributed to clusters. In two-dimensional model with low approaching velocity, some structures have voids and show large surface ratio. Subsequently, tensile test is conducted on the structures. By chucking two end regions and pulling them in opposite direction, tensile straining of the structures is carried out. Strain energy calculated from stress-strain curve over testing process can be used as an effective evaluation value for distinguishing ductile structures from brittle structures. On the other hand, tensile strength (maximum stress) does not have marked variation as to the shape of structures. It is found that, in two-dimensional structures, existence of voids enhances the brittleness. It is because, when the structure has void inside, stacking faults appear and disappear more easily than when the structure gets rid of void by clusters being packed closely. Strain rate, as another factor which may alter the mechanical properties, is diminished from that of principal result to smaller value, corresponding to tensile velocity from 100m/s to 5m/s. Though the tensile strength and strain energy are influenced slightly by strain rate, they are always low for the structure with voids.
The thermal properties of carbon nanotube which possesses very high thermal conductivity comparable with diamond are of great interest in controlling the thermal properties of nanotube devices. Since carbon nanotube practically has defects, i.e., Stone-Wales defect, point defect and so on, the thermal conductivity should be lower than the ideal thermal conductivity. The experimental study of thermal conductivity for nanotube with defects has not been studied yet, because the direct defect observation is usually quite difficult even by using the state-of-the-art microscopies. In this paper, we estimate thermal conductivity of single walled carbon nanotubes with and without Stone-Wales defects using conventional molecular dynamics simulation, and discuss the effect of the defects to the thermal conductivity.
A chlorine adsorption process was proved to be effective to disperse the diamond powder agglomerated in a baking process. The oxidation of no diamond carbon on the diamond surface was suppressed in this process and the agglomerates were broken down into constituent particles by cutting the bonds between the diamond particles. The chlorine adsorption process is also useful as an intermediate step for providing oxygen-containing hydrophilic group on the non-diamond surface layer of baked diamond particles.
In this work, the three-phase composites of CNF/NiTi/UPR, carbon nanofiber (CNF), shape memory alloy particles (NiTi) and unsaturated polyester resin (UPR), are innovated, and their electrical properties are investigated. It is found that the CNF/NiTi/UPR composite materials are of very low electrical percolation threshold due to CNF. Their electrical resistance increases with increasing NiTi particles in spite of being significant percolation threshold. The effect of the filler content on the electrical conductivity is discussed as a function of temperature. Moreover, the three-phase composites express a positive temperature coefficient (PTC), and its intensity increases around the percolation threshold because of the contribution of NiTi particles of 5wt% and 10wt%. The electrical resistance reduces with the increment of thermal cycle number. For the time dependence of electrical property, there exist the characteristics of a dynamic percolation and overcurrent protective effect with current attenuation. It is shown that the relation between current and voltage is linear and the electrical conductivity obeys an Ohmic law for these three-phase composites.
The purpose of this study was to propose a method of determining the aging of wood by measurement of cutting resistance. To clarify the effect of the aging of wood on the cutting resistances, it is necessary to focus on the way the restorators judges the age of wood material by taking into consideration the cutting process and the way of using the chisels (nomi). In this paper, aging is defined as “slow oxidation caused by oxygen in the air”. Base on the temperature-time conversion law, an accelerated aging test was performed by heat treatment at 180°C for 0, 120, 300, 600, 720, 2160, 3600, 5040, 7200minutes respectively to obtain different levels of accelerated aging wood samples. When restorators of Buddhist sculptures restorate ancient statues, they face various qualities of timber, according to the tree species and the age of the material used for the statue. They make decisions by visual inspection. Thus the experience and judgement of the Japanese restorators is one of the key conditions to measure the cutting resistance and types of chip formation. The orthogonal cutting test of cross, radial and tangential section were made to examine the relationships cutting resistances and treatment time of the accelerated aging of wood materials. The results were summarized as follows : 1) The cutting resistances fell with increasing the accelerated aging treatment time. The cutting resistances dropped sharply in the early stages up to 1000 minutes treatment, and then reduced by 80% at 7200minutes treatment. 2) The types of chip formation changed from flow type to powder with increasing the accelerated aging treatment time. 3) The forces in cross sectional cutting with clearance angle 5° were three times in value with clearance angle 1°. The forces in orthogonal cutting test in radial and tangential section were almost same in value at clearance angle 1° and 5°.
The rapid excavation with TBMs is an ultimate dream to tunnelers in the world. In order to establish a useful and practical guide several ideas and concepts have been proposed up to the present. For example, there are the Tarkoy's Total Hardness (1975), Sanio's relation between rolling and penetration forces (1985), the Estimated Rock Strength by Fukui and Okubo et al. (1996), the Specific Energy in Rock Drilling by K. Ryoke et al. (1998), the Torque Variation by T. Aoki (1999), β-value by Hashizume (2000), etc. Considering the papers in the past, the authors propose the concept of the TBM Excavation Index (TEI) so as to generalize the relationship between excavation rate and variation in geological condition. This concept came from the analyses of three TBM applications to sedimentary, metamorphic, and igneous rock formations. The proposed index is based on dividing the total TBM's workload into the primary fragmentation for excavation and the secondary fragmentation for the other activities. And it is calculated with torque, thrust and penetration, excluding any uncertain constants. In conclusion, the standard deviation of 0.2 in the TBM Excavation Index clearly suggests the remarkable variation in geology, and when the standard deviation exceeds 0.2, excessive cutter wear occurs due to hard rock with low brittleness and less cracks and TBM operation is forced to be halted due to the instability of a face and its vicinity.
The oxidation behavior of an aluminum nitride (AlN) thin film, fabricated by reactive DC magnetron sputtering using aluminum metal as a target material was examined. The obtained AlN film was transparent with a flat surface. An annealing test was carried out for the AlN film at 1000°C in air. The oxidation product was identified as γ-Al2O3 by Rutherford backscattering composition and X-ray diffraction analyses. Transmission electron microscopy showed a polycrystalline Al2O3 film with a grain size of several tens of nm. It was confirmed that the interface of AlN film and silicon substrate was protected from oxidation although the Al2O3 layer thickness increased during the oxidation.