Masanori Takuma

Estimation of Cutting Tool Life by Processing Tool Image Data with Neural Network

Summary In the manufacturing Systems such as FMS, one of the most important issues is to estimate the rest of cutting tool life under a given cutting conditions as accurately as possible. In this paper, a system based on neural network is proposed to estimate the life and wear type of cutting tools from their image data and cutting conditions. The input of the system is (1) the states of a cutting tool, crater wear and flank wear, obtained as image data, and (2) the cutting conditions. The validity of the system was confirmed by the examinations under various cutting conditions in turning.

Acoustic Emission Measurement by Fiber Bragg Grating Glued to Cylindrical Sensor Holder

Fiber Bragg grating (FBG) is an optical fiber sensor and is suitable for acoustic emission (AE) measurements of structures such as chemical plants that require water resistance, explosion proofing, and so forth, However, directionality has been a problem in conventional usage which glues the grating range of an FBG to the inspection surface. This study proposes a cylinder-FBG (C-FBG) sensor with the FBG glued to a cylindrical sensor holder. Effectiveness of the sensor was evaluated by characterizing directionality and frequency sensitivity of the sensor and by comparing the detected AE signals in a 3-point bending test of a carbon fiber reinforced plastic (CFRP) laminate against a conventional wide-band piezoelectric AE sensor. The features of the detected signals were similar to the signals detected by the wide-band AE sensor. These results show that it is possible to produce a wide-band cylindrical sensor without the directionality limitations of the conventional usage of FBG.

Molecular Dynamics Study on Deformation Mechanism of Grain Boundaries in Magnesium Crystal: Based on Coincidence Site Lattice Theory

As for magnesium (Mg) alloys, it has been noted that they are inferior to plastic deformation, but improvement in the mechanical properties by further refinement of grain size has been recently suggested. It means the importance of atomistic view of polycrystalline interface of Mg crystal. In this study, to discuss the deformation mechanism of polycrystalline Mg, atomistic grain boundary (GB) models by using coincidence site lattice (CSL) theory are constructed and are simulated for their relaxed and deformatted structures. First, GB structures in which the axis of rotation is in direction are relaxed at 10 Kelvin, and the GB energies are evaluated. Then, the deformation mechanism of each GB model under uniaxial tensile loading is observed by using the molecular dynamics (MD) method. The present MD simulations are based on embedded atom method (EAM) potential for Mg crystal. As a result, we were able to observe atomistically a variety of GB structures and to recognize significant difference in deformation mechanism between low-angle GBs and high-angle GBs. A close scrutiny is made on phenomena of dislocation emission processes peculiar to each atomistic local structure in high-angle GBs.

In situ micro-mechanical testing of grain boundaries combined with environmental TEM

In order to evaluate the effect of gaseous environment on grain boundary fracture, a novel micro-mechanical experimental method was proposed. A micro-cantilever containing a single grain boundary was fabricated from a bulk poly-crystalline intermetallic compound (Ni 3 Al). The micro-cantilever was then loaded by using a nano-indenting specimen holder operated in a special high-voltage transmission electron microscope (HVTEM) equipped with an environmental cell (EC). It was shown that, among two specimen types (V-notched and unnotched), grain boundary cracking was only observed in a V-notched specimen loaded in a gas environment containing hydrogen (H 2 ).

Molecular dynamics study on nano-sized wiredrawing: possible atomistic process and application to pearlitic steel wire

The process of nano-sized wiredrawing is investigated by using molecular dynamics (MD) simulation in this study. The authors have constructed novel computation models of wiredrawing, in which a single wire of just a several nanometers in diameter is smoothly drawn through a perfectly rigid die together with lubrication mechanism and is forced to be shaped into thinner one. Interatomic potentials used in MD simulation is a conventional pairwise type useable for iron-carbon binary system (for pearlitic steel). For MD model of pearlite steel wire, it is recognized that ferrite-cementite interface effectively offers high-speed diffusion path for carbon atoms from cementite side to ferrite side (elementary mechanism of cementite decomposition). As conclusion, we showed by using atomistic simulation that nano-sized wiredrawing process is theoretically quite possible.

Interfacial Fracture Strength of Micro-Scale Si/Cu Components with Different Free-Edge Shape

The strength against interfacial fracture initiation from a free-edge of Si/Cu micro-components was evaluated. The micro-scale cantilever specimens containing dissimilar interfaces were fabricated with a focused-ion-beam (FIB) technique, and they were loaded with a quantitative nanoindenter holder operated in a transmission electron microscope (TEM). The specimens were successfully fractured along the Si/Cu interface, and the critical loads at fracture were measured. The critical stress distribution near the free-edge was evaluated with the finite element method (FEM). The near-edge stress distributions of 90°/90°-shaped specimens were scattered while those of 135°/135°-shaped specimens were in good agreement despite the difference in specimen dimensions. Such a difference was discussed in terms of the relation between the magnitude of stress singularity and the microstructures of material.

Molecular Dynamics Study on Lubrication Mechanism in Crystalline Structure between Copper and Sulfur

To clarify the nanosized mechanism of good lubrication in copper disulfide (Cu2S) crystal which is used as a sliding material, atomistic modeling of Cu2S is conducted and molecular dynamics (MD) simulations are performed in this paper. The interatomic interaction between atoms and crystalline structure in the phase of hexagonal crystal of Cu2S are carefully estimated by first-principle calculations. Then, approximating these interactions, we originally construct a conventional interatomic potential function of Cu2S crystal in its hexagonal phase. By using this potential function, we perform MD simulation of Cu2S crystal which is subjected to shear loading parallel to the basal plane. We compare results obtained by different conditions of sliding directions. Unlike ordinary hexagonal metallic crystals, it is found that the easy-glide direction does not always show small shear stress for Cu2S crystal. Besides, it is found that shearing velocity affects largely the magnitude of averaged shear stress. Generally speaking, higher velocity results in higher resistance against shear deformation. As a result, it is understood that Cu2S crystal exhibits somewhat liquid-like (amorphous) behavior in sliding condition and shear resistance increases with increase of sliding speed.

Giga-Cycle Property of a New Age-Hardened Aluminium Alloy Containing Excess Solute Magnesium

The giga-cycle property of a newly developed Al alloy, which contains 0.5wt.% excess Mg solute compared to a standard age-hardened 6061 alloy (6061-T6), was investigated by using smooth specimens subjected to ultrasonic fatigue. The fatigue strength of the new alloy was higher than that of a normal 6061 alloy particularly at relatively low stress amplitude level. Several analyses (surface crack observation, fractography, FIB cross-sectioning, etc.) were also conducted to reveal the micro-mechanism of the observed strength properties. The following results were obtained: i) No fatigue limit was confirmed for both 6061 and new alloy. ii) Total life (Nf) of 6061 and new alloys was determined by a single fatigue crack initiated from a surface PSB crack. iii) Crack initiation resistance defined by N25 (number of cycles to reach ρ = 25 mm-2, where ρ is the PSB crack number density) for new alloy was higher than that of 6061. iv) The higher fatigue strength of new alloy was explained by the effect of excess Mg solute which increased the resistance against the formation of PSB cracks.

Study on Evaluation System of Tool Life for Shearing (Wavelet Transform and Chaos Time Series Analysis of AE Signals)

Shearing is one of the most important working methods in the manufacturing process, because it is repeated many times until the completion of the products. Therefore, it is very serious problem for the quality control of the products and the improvement of the productivity to evaluate the machining conditions. In this study, waveform analysis, wavelet transform analysis and chaos time series analysis were carried out to the detected AE signals during the shearing. And the extraction of the parameters for evaluating the machining conditions and the tool life was examined. As the results, it has been proved that the RA value of the time fluctuation waveform of wavelet coefficient and chaos time series analysis results are effective parameters for evaluating the conditions and the life. And the evaluation system using the RA value was proposed, and the validity of the system was confirmed by comparing the experimental results.

Study on Generation Mechanism of Magneto-mechanical Acoustic Emission (2nd Report, Effect of Texture)

In assuring the safety of a structure, it is important to evaluate the state of structural members non-destructively. Magneto-mechanical acoustic emission (MAE) is one of the non-destructive inspections. In the previous paper, we had studied MAE signals of a pure iron using displacement and shear sensors, for the detection of the longitudinal and shear components of the signals, which were analyzed with wavelet transform. From the analysis, the following things became clear : (1) the low frequency component (150 to 300 kHz) has strong displacement sensor response coincident with the rate of magnetic induction, suggesting magnetization via the discontinuous motion of domain walls. (2) the high frequency component (400 to 800 kHz) has strong shear sensor response and is observed near magnetic saturation, suggesting rotational magnetization effect. In this paper, the character of the detected MAE signals was discussed on the effect of the preferred orientation of the texture when the carbon steel specimens (0.23 wt% Carbon) deform plasticity. As the results, it was became clear that there is a close relation between the character and its preferred orientation