Novel Concept to Detect an Optimum Thixoforming Condition of Al-Al3Ni Functionally Graded Material by Wavelet Analysis for Online Operation

A novel technique to characterize the transition phenomenon from solid to melt of Al-Al3Ni functionally graded material (FGM) through a wavelet analysis for the development of a thixoforming system is investigated. Identification of an optimum semi-solid condition for thixoforming is necessary not only for the construction of a system but also the fabrication of a near-net-shape product with fine microstructure. An online wavelet analysis system using Haar’s wavelet function, which is applied for its simplicity compared with Daubechies’ wavelet function, is developed to find the optimum operating condition. A thixoforming system, which is constructed adapting a threshold value as an index, monitors successfully a discontinuity of deformation of Al-Al3Ni FGM with the temperature rise. Thus, the timing of an operation is not at pre-fixed temperature but at the time when the index related to a wavelet function is satisfied. The concept is confirmed to be suitable from the micro-structural observation of the Al-Al3Ni FGM product, because the product under the optimum condition is found to have refined Al3Ni grains, which change from coarse grains and are expected to improve the mechanical properties

Influence of Fracture Zone on Final Slope Displace-ment : Insights from Long-Term Monitoring in the Une Mine

The final slope of Une mine experienced sudden increases in displacement in specific sections during the typhoons of 2007 and 2011, as observed through long-term monitoring since the excavation from the top. The rise in groundwater due to increased rainfall was identified as a significant factor leading to measures specifically targeting rainfall. Notably, despite previous instances of heavy rainfall, sudden displacements occurred without clear triggers, emphasizing the need for a comprehensive understanding of the behavior of the rock slope. Future maintenance efforts rely on elucidating these mechanisms, often solely attributed to rainfall. To analyze factors beyond rainfall affecting the final slope's displacement, this study introduces the concept of "unit rainfall displacement," representing displacement per unit rainfall. The unit rainfall displacement is defined as the annual final slope displacement divided by the cumulative effective annual rainfall. The cumulative effective annual rainfall is determined by cumulating rainfall for events with 100 mm or more rainfall for a year, based on previous studies indicating that the final slope exhibits behavior in such conditions. Focusing on the W4, a key fracture zone of Mt.Buko, this study explores the relationship between unit rainfall displacement and the exposure status of W4 on the final slope. ’ and the exposure status of W4 on the final slope. As a result, this study revealed an overview of W4's impact on the variations in unit rainfall displacement, providing insight into the rock slope displacement attributed to W4

Evaluation of the rheological behavior of a semi-solid Al–SiC composite using a parallel-plate drop-forge viscometer

This paper presents of studies performed to assess the effect of rheological behavior on the near-net shape forming of an Al–20 vol% SiC composite of Duralcan F3A.20S and of the mother aluminum alloy A356 for comparison. Isothermal experiments were conducted using results of a parallel-plate drop-forge viscometer in a temperature range from 849 K (576 ℃) to 862 K (590 ℃). Each experiment indicated that the viscosity decreased in the early increasing shear rate stage and　subsequently increased with decreasing shear rate. The overall relationship between the viscosity, μ [Pa・s], and the shear rate, γ [s_-1], can be described by a power-law model of μ = 3.2×10^7μ^1.5 for Duralcan and μ = 1.6×10^7μ^1.5 for A356. The power-law　index was the same for both materials, whereas the power-law constant of Duralcan was two times greater than that of the A356 mother alloy because of the distribution of 20 vol% SiC particles. The decrease in the viscosity that accompanied an increase in　the shear rate depended on both the temperature and the applied force. The viscosities of 32 kPa・s for both Duralcan and A356 at the maximum effective duration of deformation, which obtained from the plot as a function of the viscosity, appeared to be the points at which the dominant factor governing the visco-plastic flow process transitions from plastic forming to casting. The viscosity must also represent optimum semi-solid forming conditions, as indicated by the achievement of both a moderate working time and an adequate deformation. The optimum operating temperature for both materials can be ranged from 855 K (582 ℃) to 857 K (584 ℃), which is just above the melting point

Effect of the near-net shape forming on silicon morphology in an Al–Si functionally graded material generated by the centrifugal method

A work toward practical usage of hypereutectic Al–25 mass% Si alloy, which exhibits superior properties, as a functionally graded material (FGM) was done. The Al–Si FGM, which is based on the concept of overcoming the limitations imposed by the presence of a hard silicon phase in an aluminum matrix, was generated by a vacuum centrifugal method as a thick-walled tube. Grain coarsening, which is the primary disadvantage of the centrifugal method, was observed. The fraction of silicon phase in the tube unexpectedly varied from greater than 60 mass% at the outer surface to 15 mass% at the inner surface because of the greater density of molten silicon compared to that of the eutectic melt. Thus, the outer region of the tube was lighter than the inner region after solidification. FGM billets for near-net shape forming were machined from the thick-walled tube and were formed into an Al–Si FGM cup using a backward extruding. The products of the FGM cup were successfully manufactured in the temperature range from 853 K (580 ℃) to 863 K (590 ℃) through visco-plastic deformation. The fraction of silicon phase in the FGM cup varied from greater than 70 mass% Si at the formed cup bottom region to less than 15 mass% Si at the cup wall region. Coarse silicon particles were refined irrespective of the pre-existence of elongated spindle-shaped particles under some experimental conditions. The optimum operating conditions were inferred to be high-speed operation at approximately 853 K (580 ℃), which was just above the melting point of the eutectic Al–Si alloy

Extension of Improved Particle and Energy Confinement Regime in the Core of LHD Plasma

Recent two major topics of Large Helical Device (LHD) towards fusion relevant conditions, high-density operation and high-ion-temperature operation, are reported. Super dense core plasma was obtained by the combination of repetitive hydrogen ice pellet injection and high power neutral beam injection (NBI) heating. A very peaked density profile with the highest central density of 1.1 × 1021 m-3 was produced showing that the particle transport was suppressed very well in the plasma core. The spatial density profile varies as the position of magnetic axis (Rax), and the steepest profile is obtained at Rax = 3.95 m. The highest central ion temperature of 5.6 keV was obtained in hydrogen plasma at electron density of 1.6 × 1019 m-3 by NBI, where a peaked ion-temperature profile with internal ion energy transport barrier was observed. The profile of electron temperature did not change much and was broad even when the ion temperature had a peaked profile. The central ion temperature is higher than the electron temperature, which is a new operation regime of LHD. High central ion temperature accompanied strong toroidal rotation and an extreme hollow profile of carbon ions (impurity hole). These steep temperature profiles were obtained so far at around Rax = 3.6 m. The compatibility between particle and energy confinement is a new issue of LHD to explore a new operation regime for attractive fusion reactor