If crack size is in the order of several grain diameters or smaller, the stress intensity factor (SIF), which brings about change in crack growth behavior, is affected by various factors caused by the grain. For example, kinks and bifurcations of cracks at grain boundary triple points vary the SIF when the crack runs along grain boundaries. The elastic anisotropy of crystals and inhomogeneous stress distribution at the microstructural level in a polycrystalline body also bring about changes in the SIF. In this paper, such influences of the crystal grain on the SIF are reviewed. Firstly, the SIF of kinked or branched cracks is outlined. Secondly, the SIF of cracks in an anisotropic body as well as inhomogeneous polycrystalline body is summarized. In particular, statistical changes in SIF are shown as a function of crack size. Finally, based on the results obtained, statistical changes in the SIF and their influence on the growth of the microstructurally-small-crack are discussed.

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Rubber tiles are commonly used in playgrounds as protective surfacing to reduce the incidence of head injuries in children caused by falling from equipment. This study developed a rubber tile model consisting of a surface layer of solid and a base layer of plate-cell and used it to investigate head injury protective performance. An explicit finite element method based on the experimental data was used to simulate head impact on the rubber tile. The peak acceleration and head injury criterion (HIC) were employed to assess the shock-absorbing capability of the tile. The results showed that compared to the peak acceleration, use of the HIC index provided a more conservative assessment of the shock absorption ability, and ultimately the protection against head injuries. This study supports the feasibility of using rubber tile with plate-cell construction to improve shock-absorbing capability. The plate-cell structure provided an excellent cushioning effect via a lower axial shear stiffness of the surface layer and lower transverse shearing stiffness of the core. The core's dimensions were an important parameter in determining the shearing stiffness. The analysis suggested that the cushioning effect would significantly reduce the peak force on the head from a fall and delay the occurrence of the peak value during impact, resulting in a marked reduction in the peak acceleration and HIC values of the head. Two plate-cell constructions with honeycomb and box-like cores were proposed and validated in this study. The better protective ability of the honeycomb core was attributed to its lower transverse shearing stiffness.

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In this paper, a spark plasma sintering (SPS) method was employed to solidify single-walled carbon nanotubes (SWCNTs) only, and the effect of processing conditions on the mechanical properties of the SWCNT solids were examined using a small punch (SP) testing method. The sintering temperatures used was in the range of 600∼1400°C, and the sintering pressures used was 40 MPa and 120 MPa. It was demonstrated that the SPS method allowed SWCNTs to be solidified, without any additives. The experimental results showed that the purification of raw soot was critically importance. The SWCNT solids prepared from purified raw soot showed significant non-linear deformation response, producing quasi-ductile fracture behavior. In contrast, raw soot produced brittle solids. The Young's modulus, fracture strength and work of fracture increased with the increasing sintering temperature and pressure. The Raman and SEM analyses showed that the amount of the graphite-like materials were observed to increase with the increasing temperature and pressure, which indicate that the structure of the SWCNTs was changed partially into the graphite-like materials. The formation of graphite-like materials increased tendency of brittle fracture in the SWCNT solids. TEM observations revealed that the fracture surfaces of the SWCNT solids were characterized by pull out of SWCNT bundles. This observation suggests that it may be possible to improve the mechanical properties of SWCNT solids by increasing the cohesion between SWCNTs.

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In this paper, the control of dynamic deformation of a piezoelastic beam subjected to dynamic changes in a mechanical environment by using a closed-loop control system is studied. The analytical model is a symmetric cross-ply laminated beam composed of fiber-reinforced laminae and two piezoelectric layers. The beam is simply-supported at both edges and is subjected to mechanical disturbance. To suppress the dynamic deformation due to the disturbance, the beam is subjected to a closed-loop control procedure in which one of the piezoelectric layers serves as a sensor to detect the deformation due to the disturbance and the other acts as an actuator to suppress it. The analytical solution of the dynamic deflection is formulated based on the classical laminate theory. Using numerical examples, the suppression of the deflection due to mechanical disturbance by a series of electric voltage pulses is examined. The effects of the parameters of the control procedure, such as the gain, sensing time, and duration and frequency of pulses, on the suppression of the deflection are investigated, and the appropriate values are obtained for them.

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Oil jet peening is a new surface modification process developed for the introduction of compressive residual stresses. This paper describes the effect of oil jet peening on the fatigue performance of aluminum alloy, AA 6063-T6. Specimens were peened at an oil injection pressure of 40 MPa with various nozzle-traveling velocities. Each impact of oil droplet generates an indentation on the surface of specimen. The surface roughness increases with decreasing nozzle-traveling velocity. The maximum compressive residual stress developed is about 75% of yield strength. Fatigue life depends on the compressive residual stress as well as surface roughness of oil jet peened specimens. Fracture mechanism of unpeened and oil jet peened specimens were studied using optical and scanning electron microscopes.

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In this paper, a method for identification of a crack in a beam is demonstrated by the use of the genetic algorithm (GA) based on changes in natural frequencies. To calculate the natural frequencies of cracked beams, p-FEM code, which is based on a parametric three dimensional finite element, is developed because the accuracy of the forward analysis is important. In the analysis, an edge crack model is considered. To identify the crack location and the depth from frequency measurements, crack parameters of the beam are coded into a fixed-length binary digit string. By using GA, the square sum of residuals between the measured data and the calculated data is minimized in the identification process and thus the crack is identified. To avoid a high calculation cost, a response surface method (RSM) is also adopted in the minimizing process. The combination of GA and RSM have made the identification more effective and robust. The availability of the proposed method is confirmed by the results of numerical simulation.

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Indentation analysis based on the representative strain offers an effective way of obtaining material elastoplastic properties from the reverse analysis of indentation load-displacement curve. In this paper, the formulations of the representative stress and strain are optimized to obtain the best accuracy, while retaining a simple form with only one fitting parameter for determining the yield stress and work hardening exponent. The formulations are valid for a wide parameter space of materials. A simple method of estimating the elastic modulus is also proposed. For ductile materials with relatively small yield strains, the elastic modulus can be estimated from one sharp indentation test, and an explicit analysis may be used to obtain the material plastic properties by using plural sharp indenters.

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This paper reports on the contact mechanism between the crushing tip of a center bevel blade and the dent of a counter plate. Pushing tests of the blade on the counter plate were carried out experimentally and numerically by varying the mechanical flow properties of both the blade tip and the counter plate. A yield line force ratio β was proposed to characterize the contact deformation in terms of blade apex angle. Through this research, it was found that: (1) the crushed tip of a mild blade could be kept in moderate for the mild counter plate; (2) the counter plate's dent depth is linearly related to the β and depends on the combination of the mechanical properties of both the blade and the counter plate; (3) the total clearance of the deformed tools is almost independent from the tools material combination; (4) the profile angle of the blade tip and the crushed tip thickness mainly depend on the blade's properties.

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Present study reports acoustic emission (AE) technique to evaluate corrosion damages of bottom plates (floor conditions) in above-ground tanks. Artificial AE signals were generated by pencil lead breaks at arbitrary locations on the bottom of a tank (300 kL in capacity) to investigate accuracy of AE source location. Attenuation of AE waves was shown to be very small in liquid. AE source location analysis was conducted, using a neural network (NN). Input and output units of the NN were arrival time differences between four AE sensors and coordinate of the AE source location, respectively. Arrival time differences of AE waves were determined by visual observation of the first signal arrivals and threshold crossing times of the AE signal normalized by its peak amplitude. It was concluded that accurate AE source location can be obtained by the decision process resulted from automated readings of threshold crossing time, based on the NN trained method by theoretical calculation.

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Al-Fe alloys with composition 1.0, 2.5, 5.0at.%Fe are fabricated by repeated compaction and backward extrusion in a closed die set using raw materials as elemental powder mixture. This process is done in solid state at room temperature. The produced alloyed preforms are further consolidated by hot forging to achieve high density billet. Alloyed preforms are tested for thermal stability by using differential thermal analysis. Phase changes during heating are investigated by using x-ray diffraction, and confirmed by scanning electron microscope using EDS line scan mode. The alloyed billets are subjected to tensile test.

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The outstanding performance of Al₂O₃-TiC ceramic cutting tools in term of high cutting speed can lead to economies in the metal machining. However, there is limited use of this ceramic because of its expensive price. In this work, the microwave combustion synthesis method was applied to produce Al₂O₃-TiC powder from low cost precursors. The microwave combustion synthesis of Al₂O₃-TiC can be achieved in a very short time. As a consequence, Al₂O₃-TiC cutting tools were produced by pressureless sintering. The performance of microwave combustion synthesized Al₂O₃-TiC cutting tools was investigated and compared to that of commercial insert. The flank wear of Al₂O₃-TiC insert was increased with cutting time and cutting speed. Although the cutting time of microwave combustion synthesized insert was shorter than that of the commercial one, its cutting performance demonstrated that the microwave combustion synthesized Al₂O₃-TiC powder showed some potentials to be developed as a cutting tools insert by proper control of composition and sintering temperature of combusted powders.

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