Many commercial optical glasses exhibit thermorheologically simple behavior, which allows the application of the time-temperature superposition principle within the temperature range from the glass transition temperature (Tg) to the deformation point (At). However, the molding temperature is set above At in cases involving significant deformation during glass molding press, such as with large-aperture concave meniscus lenses. Additionally, stress relaxation is observed in optical glasses even at temperatures below Tg. Nevertheless, the applicability of the time-temperature superposition principle to optical glasses within the temperature range below Tg and above At has not been thoroughly investigated. Therefore, in this study, uniaxial compression creep tests were conducted over a wide temperature range from approximately Tg - 20 °C to At + 50 °C using three types of commercial optical glasses to evaluate their thermo-viscoelastic properties. The results revealed that when the creep functions at each test temperature were shifted along a logarithmic time axis, they formed a smooth single curve (master curve), indicating the applicability of the time-temperature superposition principle. Moreover, while the shift factors for all glasses exhibited Arrhenius behavior within the temperature range of Tg to At, in two types of glasses, they exhibited a curved change below Tg and above At. Therefore, applying the Williams–Landel–Ferry (WLF) equation to approximate these shift factors revealed that they could be well approximated across the entire test temperature range. However, when applying the WLF equation to optical glass, limiting the temperature to a range higher than Tg - 30 °C was necessary. To express the shift factor over a wide temperature range of several hundred degree Celsius, from room temperature to molding temperature, it was practical to use the multi-linear Narayanaswamy equation, in which the apparent activation energies vary near At.

The purpose of this study is to create micro-texture on the surface of various mold materials by ultrasonic-assisted grinding. The effects of materials properties (hardness and fracture toughness) on micro-periodic structure were investigated by performing ultrasonic-assisted grinding, in which ultrasonic vibration is assisted in the axial direction of the grinding wheel in surface plunge grinding. The results showed that periodic structures can be formed without plastic flow on the surface after machining only in the case of cemented carbide with high hardness and low toughness. Furthermore, by modeling the abrasive grain shape and arrangement of the general purpose diamond grinding wheel without special treatment used in the experiments, we attempted to simulate the grinding groove shape formed by a multi-grain grinding wheel when ultrasonic vibration is assisted. The periodic structure formed on the cemented carbide surface was compared with the simulation results, which were in good agreement in terms of the period of the sinusoidal wave and the width of the grinding groove, confirming the validity of this simulation method. From the above, basic knowledge about the machining mechanism of grinding groove in ultrasonic-assisted grinding was obtained.

Carbon fiber reinforced plastics (CFRP) have high specific strength and specific stiffness and are used in various fields such as aircraft, space structures, automobiles, and other transportation equipment. Since the internal structure of CFRP is very complex, it is very difficult to define failure criteria when external loads are applied. Various methods have been proposed to evaluate the interfacial shear strength between carbon fiber and resin matrix, such as microbond test, rupture test, and pull-out test, but currently no effective method has been proposed to evaluate the tensile strength of the CF/resin interface. In this study, we applied the pulsed laser spallation method, which has been confirmed to be effective for evaluating the adhesion strength of thin films and coating films on substrates, to the evaluation of CFRP. A finite element method based on the Laplace transform was used for the numerical analysis of the unsteady elastodynamic problem. The macroscopic stresses generated by ultrasonic waves excited by pulsed laser irradiation were calculated by inverse analysis using a transfer function with the displacement history of the back surface of the CFRP specimen as supplementary information. Microscopic stresses at the fiber/resin interface were evaluated by the homogenization method, taking into account the effects of fiber arrangement, distance between fibers, and molding residual stress in unidirectionally reinforced CFRP laminates. As a result, this series of investigations revealed that the vertical interfacial stress is dominant with respect to the strength of the fiber/resin interface with the strength of about 54MPa.

In this study, finite element analyses are conducted for the glass molding press of a large-diameter concave meniscus lens. As press molding may commence in a non-uniform temperature field, thermal-structure two-way coupling simulations are applied to the molding process to understand the sequential changes in the lens shape and temperature distribution. Three types of glass preform, namely, ball model, approximate curvature model, and near net model, are prepared to investigate the effects of preform shape on formability and internal stress. Preforms with a small clearance (shape difference) from the mold shape require less time for complete transfer; however, high internal stresses occur during cooling. The internal stress generated during cooling is thermal stress, caused by the internal temperature difference; it can be reduced by expanding the contact regions between the lens surfaces and molds. Moreover, to improve formability and reduce internal stress when forming using an approximate curvature model, the preform shape and heat input temperature conditions to the upper and lower molds are optimized. In both cases, although the internal stress is slightly higher during the molding process, the entire lens surface is in contact with the mold during cooling, thus resulting in a significant decrease in internal stress.

To determine the optimal molding conditions for thermal imprinting, it is necessary to understand the thermo-viscoelastic properties of polymer obtained by compression tests. This is because contact resistance acts at polymer/mold interface in compression tests, and this contact resistance may affect the thermo-viscoelastic properties. Furthermore, this contact resistance may depend on the specimen thickness. In this study, static compressive creep tests were performed on polycarbonate specimens (3 mm in diameter) with different thicknesses ranging from 0.5 to 5 mm to investigate the effect of contact resistance on thermo-viscoelastic properties. The results showed that specimen thickness had little effect on the shift factor. In contrast, the creep function was affected, and the stress relaxation time was slower with thinner specimen thickness. By clarifying the relationship between the shift amount on the logarithmic time axis of the creep function and the thickness of the specimen, it was possible to predict the creep function of a thin plate specimen from that of a bulk specimen.

In this study, unidirectional compression creep tests were performed on seven types of commercial optical glasses with different chemical compositions to investigate the effect of chemical composition or network structure on stress relaxation behavior. As a result of comparing stress relaxation rates obtained by dividing the shear relaxation modulus by the shear instantaneous modulus, they showed almost the same shape on the logarithmic time axis. In other words, it was clarified that the chemical composition has almost no effect on the stress relaxation behavior, at least in the glasses used in this study. On the other hand, it was confirmed that the difference in chemical composition affects the relaxation time, and the relaxation time of the chain structure glass tends to be delayed compared to that of the three-dimensional network structure glass. Furthermore, the activation energy of viscous flow obtained by approximating the shift factor also tended to be slightly lower in the chain structure glass.

In this study, the parallel plate test which is a kind of viscosity measurement technique was carried out to estimate the shift factor for optical glass. This method can reduce the measurement time in comparison to conventional creep test. First, deformation rates were calculated from histories of the displacement, which were then substituted in Gent’s equation for deriving the viscosities. The estimated viscosities indicated the temperature dependency in the viscoelastic range. Moreover, the shift factors obtained from parallel plate tests agreed well with those from static compression creep tests. Therefore, it was confirmed that the parallel plate test is an effective method for the derivation of shift factor for optical glass. In addition, the shift factors were almost same for measurement loads between 196 to 980 N.

Increasing the pulse current frequency from 0.5 kHz to 5 kHz suppressed the cracking of the Ni-W film. In addition, the film thickness increased from 15 µm to 20 µm. However, the W content of the Ni-W film was around 20 at% and was not affected by the frequency of the pulse current. In the resin mold, the Ni-W film was peeled off. However, Ni type was able to deposit Ni-W film of 78 µm thickness. However, pinholes occurred at the apex of the eye structure of the moth of the Ni-W mold. As a cause of the occurrence of pinholes, it is considered that the hydrogen generated during plating remains in the concave portion of the moth eye structure on the Ni master disk, so it is necessary to prevent hydrogen from remaining in the concave portion.

Acoustic emission (AE) signals from non-charged and cathodic hydrogen charged A7075-T651 and A6061-T6 samples under tension–tension cyclic loading conditions at various stress intensity factor ranges were monitored. Although the AE event counts per cyclic load (AE count rates) were proportional to the crack growth rates in all kind of the sample, the rates were less than unity.Many cracked inclusions were observed on the crack surfaces and were identified as AE sources. Large inclusions in both Al alloys were prone to be fractured. The AE count rate in the A7075 sample was 10 times higher than that in A6061. However, no significant difference in the AE count rates and fatigue crack growth between the non-charged and charged samples were observed.

In the present paper, the interface fracture toughness between a Ti coating film and Al-alloy substrate is evaluated using a laser spallation method and a boundary element method. The fracture toughness can be estimated using inverse analyses by the boundary element method using a transfer function computed from the history of the displacement of the specimen. In the present study, an alternative boundary element program is developed for unsteady state vibration of an axi-symmetric solid body. The mode I interface fracture toughness between the Ti coating film and Al-alloy substrate is confirmed to be about 0.66 MPam1/2 from the present investigation.

The integrity of flange joints is critical in all pipe systems. To test this integrity, an ultrasonic method characterizing the condition of the flange joint would be a vital tool. In this study, we analyzed the contact conditions on a metal/gasket/metal connection. The instantaneous frequency profile, i.e., the phase change of the wave with time for longitudinal waves transmitted in an Al alloy/gasket/Al alloy system, was evaluated under various contact pressures. The instantaneous frequency (IF) was calculated with a complex continuous wavelet transform with a modified Morlet function as a mother wavelet. The maximum IF of the waves monotonically increased with contact pressure, showing similar properties as the amplitude of the waves. A one-dimensional numerical calculation with a finite difference time domain method with a spring condition for expressing various contact conditions or contact stiffness revealed that a large phase delay of the transmission wave was generated at a low contact stiffness interface, and the amount of delay was correlated with the contact stiffness. On the other hand, the delay in the reflected wave was very small.

In the present study, numerical simulations of press molding for a glass aspherical lens using finite element analysis were carried out. Thermo-viscoelastic properties of the glass were estimated by unidirectional compression creep tests based on traditional thermo-viscoelastic theory. Numerical simulations were performed using general purpose finite element code (ANSYS). In order to predict the adaptive molding conditions for complete transcription, relation between molding temperature and pressure was investigated. The effect of molding condition for residual stress and shape error was investigated by the present numerical simulation. Moreover, the die shape was corrected in consideration of the lens shape error estimated by numerical simulations. It was confirmed that the lens shape error against the designed profile was reduced to 1 μm or less.

This study aims to evaluate strength of a diamond-like carbon (DLC) film on a metal for glass press molding at high temperature. Static and cyclic indentation tests at high temperature up to 300℃ with AE monitoring technique were performed. AE monitoring reveled crack generation load or cyclic number during the indentation tests. The static strength of the films at each temperature was determined from maximum stress in the film in the radial direction induced by sink-in deformation due to static indentation. The maximum stress at each temperature was estimated with indentation loads at first AE generation and FEM analysis. Thermal stress in DLC film was at each temperature also calculated. The film strength estimated by taking the thermal stresses into account was decreased with an increase of temperature. In cyclic indentation test, AE due to cracks in film was detected after 1.0×10⁴ cycles at the load where no crack generated under one loading cycle. The cyclic number to crack initiation for the sample in 300℃ was 1/50 smaller than that in room temperature.

In this study, a dynamic mechanical analysis (DMA) using a thermomechanical analyzer was applied to determine the thermo-viscoelastic properties (shift factors and a master curve) of a borosilicate glass (IWAKI_TE-32) under various frequencies and temperatures. It was confirmed that the storage elastic moduli decreased with increasing temperature in 575℃ to 770℃ and decreasing frequency in 0.001 Hz to 0.1 Hz. The shift factors and master curve in the glass sample were derived using datasets of the storage elastic moduli. The shift factors for the glass obtained by DMA test agreed well with those by a static creep test. However, the master curve of relaxation modulus estimated by each test was different. That is, stress relaxation behavior of glass indicates nonlinearity, and it was suggested that the master curves of relaxation moduli are different depending on measurement methods.

In this study, to investigate the influence of the measuring frequency on thermo-viscoelastic properties of polymers, dynamic mechanical analyses (DMA, 0.01-0.1 Hz and 0.5-10 Hz) and immersion ultrasonic testing (1-5 MHz) were carried out. In the ultrasonic testing, loss tangent (tan δ) was derived from the phase velocity and attenuation coefficient. The frequency dispersion curves of tan δ measured at several temperatures were incorporated in a single curve (the master curve) by shifting datasets parallel to the logarithmic frequency axis. That is, it was able to estimate the thermo-viscoelastic properties of a soft epoxy resin by applying the time-temperature superposition principle. As a result of comparing both master curves of tan δ obtained by the ultrasonic testing and DMA testing, they were identical qualitatively, but the difference appeared in the viscosity behavior.

We confirmed that increasing the total metal concentration is effective for the planarization of Ni-W films and Ni-W nanopatterns formed with a uniform height and a 480nm pitch. At the same time, the W content in Ni-W films decreased. We investigated the relationship between the planarization of Ni-W films and the W content in Ni-W films, and confirmed that increasing the total metal concentration is effective for the inhibition of hydrogen generation. We pointed to the inhibition of hydrogen gas generation as a cause of the planarization of Ni-W films, and the reduction in the hydrogen generation amount necessary for the deposition of Was a cause of the reduction in the W content in Ni-W films. In order to obtain a flat plating film with a high W content, it is necessary to generate an adequate amount of hydrogen on the surface of the cathode and to remove hydrogen gas from the cathode surface immediately.

In the present paper, an interfacial strength of composite plate is evaluated by using laser ultrasonic waves and wave propation analysis. The specimens is composed of Al-alloy substrate and resin coating _lm containing carbon nanotube as reinforce material. The laser spallation technique of various laser irradiation has been used to induce delamination between the substrate and the coating _lm. The interfacial stress is estimated by inverse analysis using the displacement velocity of specimen back surface and the impulse response calculated by boundary element method. The interfacial strength between Al-alloy substrate and resin coating has been con_rmed to be 40.9MPa. The obtained value is compared with result from stud pull test and the validity has been confirmed.

Since nanopatterns are used for various purposes including solar cells, super-hydrophilicity, and biosensors, it is necessary to miniaturize the patterns on glass devices from micro-to nano-order. We have studied glass imprinting as an excellent microfabrication technology for glass devices. Uniformity of the nanopattern height is required for a mold, since a nodular structure on the Ni-W surface is recognized as a problem in Ni-W nanopattern formation. We confirmed that the Ni-W plating bath increasing metal ion concentration is effective for inhibition of the nodular structure on the Ni-W film, and succeeded in Ni-W nano pattern formation with uniform height. However, the W content rate of plated Ni-W film was reduced in exchange for enhancing the flatness of the Ni-W film. It is necessary to examine the Ni-W plating condition for obtaining planarization of the Ni-W surface and a high content rate of W in the Ni-W film.

The bonding quality of an adhesive component was estimated using the frequency of zero-group-velocity (ZGV) Lamb waves, which can be generated and detected with a laser ultrasonic technique. Two distinct peaks corresponding to ZGV Lamb waves in the amplitude spectrum were obtained for well- and weak-bonded adhesive plate samples. The frequency difference between the measured low frequency mode and the calculated frequency, which can be obtained by assuming a continuous stress and strain at a bonding interface, linearly increased with shear strength, as obtained by the shear-tensile test. The frequency of ZGV Lamb waves was also calculated with reduced shear modulus of the bonding layer to express a weak bonding, and the change in the calculated frequency in low frequency ZGV Lamb waves showed a similar tendency to that in measured one.

This study aims to evaluate adhesion quality of oxide scale on low carbon steel plate at high temperature. The scratch test, indentation test and pull-out test are generally adopted to evaluate the adhesion quality of thin films. However, these methods requires contact between a probe and a specimen, and are not allowed to perform at high temperature. Since a laser spallation technique is a non-contact measuring method which produces tensile stress acting on an interface by ultrasonic wave, the method enables us to evaluate the adhesion quality at high temperature. In this study, adhesion quality of the oxide scale on low carbon steel was attempted to evaluate at room temperature and up to 200 °C with the laser spallation technique. The exfoliation which was induced by laser spallation technique can be identified by change in correlation coefficient for a series of the waveform obtained at each energy of incident YAG laser. Tensile stress acting on interface was estimated from stress distribution of the wave propagating through the interface calculated with a numerical simulation. As a result, it was confirmed that the adhesion quality of the oxide scale increased with testing temperature. It may be because the residual stress which acts on an oxide scale/substrate interface decreased with temperature.

In the present study the effect of carbon nanofiber interlayers on the fatigue crack propagation of woven fabric CFRP laminates made by VaRTM is investigated. Double cantilever beam (DCB) tests are carried out to determine the mode I static fracture toughness and mode I fatigue crack propagation curve. The experimental results clearly show that the interlaminar fracture toughness and the fatigue crack growth resistance can be substantially improved by the addition of CNF interlayers to the CFRP laminates. In more details, as far as the mode I fatigue crack tests are concerned, thanks to the addition of MWNT-7 interlayers the number of cycles to failure becomes 1.5 or more times greater than that of base laminates. Furthermore, it is found that the fatigue fracture toughness G(Imax) (the upper limit of the energy release rate in a fatigue test) is increased by about 300%. (C) 2014 Elsevier Ltd. All rights reserved.

In this work, manufacturing techniques and mode-I interlaminar mechanical properties of fibre metal laminates (FML) based on aluminium alloy 2017 and glass fibre reinforced plastic (GFRP) were investigated. Various toughening techniques including patterned surface manufacturing and acid etching on Al, and addition of carbon nanofibres between Al and the GFRP were employed to improve the interlaminar fracture toughness of the Al/GFRP laminates. The double cantilever beam (DCB) tests indicated that the combination of these toughening techniques can significantly enhance the mode-I fracture toughness and resistance of the Al/GFRP laminates. Crack propagation path and fractured surface were observed by confocal laser scanning microscopy to interpret the improvement mechanism of interlaminar mechanical properties.

Corrosion on piping under thermal insulation is localized corrosion and a problem for plants which are located near the sea shore. Thermal insulation offers a corrosive environment where chloride ions allow concentration and humidity is high by penetrating rain water or splashes from the sea containing chloride ions to the insulation. A visual inspection can detect the corrosion after removing the insulator. However, removing and restoring the insulation needs enormous time and troubles. Therefore, a method for identifying the corrosion without removing the insulation is required. An acoustic emission（AE） method can detect elastic waves emitted by fractures of corrosion product（rust）. In this study, AE monitoring was applied to evaluate the corrosion volume on a steel plate in high humidity with MgCl2 solution. AE activity increased with time from several days later after providing MgCl2 solution and then decreased. AE activity became high again after providing MgCl2 solution. While AE activity was high, the thickness of the plate on the corrosion drastically changed. When the thickness did not change, externally low AE activity was detected. The relation between corrosion volume and cumulative AE count from the corrosion showed different linear relation in the early and following stages.

We proposed a simple method to fabricate a Ni-W electroformed mold for glass micro-press molding. For example, borosilicate glass (D263) was molded using the Ni-W electroformed mold. A Ni-W electroformed mold with a fine line was fabricated by photolithography and electroforming technology. Additionally, the Ni-W electroformed mold did not require a release layer. As the result of molding D263 at 883 K, the minimum pitch of the glass pattern was the same as that of the Ni-W electroformed mold. We argue that the crystallization of amorphous Ni-W occurred with the activation energy derived from the heating of micro-press molding. The heating temperature was 833 K. Additionally, the release characteristics of a Ni-W film were improved by increasing the percentage of W. In terms of the thermochemical stability and high content rate of W, we indicated that Ni-W electroformed molds can be used repeatedly for glass micro-press molding. © 2013 The Japan Society of Applied Physics.

Some experiments for press molding of glass spherical lens and its numerical simulation were carried out using finite element method. The optimal molding condition of slow cooling time that gives appropriate transcription profile was examined experimentally. Moreover, in order to investigate the temperature and internal stress distributions, numerical simulation was carried out using general purpose finite element code. As a result of comparing experiments with numerical simulations, it was confirmed that the relationship between amount of shrink of spherical lens and slow cooling time estimated by FE simulation approximately agreed with experimental value. Furthermore, it was found out that the optimal slow cooling time was 300-600 s by FE analyses. © 2013 The Japan Society of Mechanical Engineers.

In the present paper, the interfacial adhesion strength between Ti coating film and Al-alloy substrate is evaluated by using laser ultrasonic waves and boundary element method. The adhesion strength can be estimated by inverse analyses using transfer function from the history of displacement of the specimen and boundary element analysis for unsteady 3-dimensional vibration. In the present study, an alternative boundary element program has been made for the axisymmetric solid body. Using data processing by Weibull distribution, the interfacial strength between Ti coating film and Al-alloy substrate could be confirmed to be 59.2MPa from the present investigation.

In the present study, the impact damage of CNF/CFRP hybrid laminates and influence of carbon nanofiber (CNF) interlayer on impact damages were investigated by the drop weight impact tests. Vapor grown carbon fiber (VGCF) has been employed for the toughener of the interlayer on the CFRP laminate. Drop weight impact tests were carried out using "Dynatup" impact test equipment. Damaged area occurring in the interlayer of the CFRP laminate was observed by ultrasonic flaw detection system. The damage properties of the CNF/CFRP hybrid laminates were considered from the viewpoint of the relation between damaged area and impact energy. Moreover, by compression after impact (CAI) tests, the relation between residual compression strength, impact energy and damaged area was investigated. It was confirmed that the damaged area could be reduced, and CAI strength became higher by inserting CNF interlayer. Moreover, the optimal additive amount of VGCF for the interlayer was about 20 g/m².

We proposed an electroformed mold for thermal imprint of borosilicate glass in this paper. The mold was made of Ni-W electrodeposition film that was superior to heat-resistance and removing glass. The resist pattern for electroforming was fabricated with SU8-10. Ni-W solution for electroforming was developed by mixing nickel sulfamate, tungsten sodium and citric acid. The minimum pitch and the height of the pattern on Ni-W electroformed mold were about 40 urn and 3.8 um, respectively. The thermal imprint for borosilicate glass carried out with Ni-W electroformed mold. The shape of the Ni-W electroformed mold was printed on the borosilicate glass by thermal imprint. The borosilicate glass was removed from the Ni-W electroformed mold easily. © 2013 The Japan Society of Mechanical Engineers.

Thermal imprinting of glass-optical devices and its numerical simulation using the finite element method were investigated. The constitutive equation of the glass material was estimated using compression creep tests based on conventional thermoviscoelastic theory. The relaxation modulus of 0263 glass was approximated by the generalized Maxwell model. For glass thermal imprinting, a glassy carbon die was used on which line and space or microlens array patterns were machined with a focused ion beam (FIB). The optimum molding-temperature condition that gives precise transcription profile was investigated in detail. Finite element analyses were performed to simulate the experimental glass thermal imprinting. In comparing experimental and numerical. results, the transcription heights of groove or microlens obtained by experimental tests approximately agreed with numerical values. Finite element analyses using thermoviscoelastic property of glass are reliable in estimating suitable conditions for glass thermal imprinting. (C) 2012 Elsevier B.V. All rights reserved.

In the present paper, the influence of carbon nanofiber on interlaminar fracture toughness of CFRP investigated using MMB(Mixed Mode Bending) tests. Vapor grown carbon fiber VGCF and VGCF-S, and multi-walled carbon nanotube MWNT-7 has been employed for the toughener of the interlayer on the CFRP laminates. In order to evaluate the fracture toughness and mixed mode ratio of it, double cantilever beam (DCB) tests, end notched fracture (ENF) tests and mixed mode bending (MMB) tests have been carried out. Boundary element analysis was applied to the CFRP model to compute the interlaminar fracture toughness, where extrapolation method was used to determine the fracture toughness and mixed mode ratio. The interlaminar fracture toughness and mixed mode ratio can be extrapolated by stress distribution in the vicinity of the crack tip of the CFRP laminate. It was found that the interlaminar fracture toughness of the CFRP laminates was improved inserting the interlayer made by carbon nanofiber especially in the region where shear mode deformation is dominant.

In this study, Epoxy resin that is a typical thermosetting resin was used as a matrix resin, and 3-phase composites (Epoxy reinforced by carbon nanofiber (CNF) and PAN-based carbon fiber (CF)) were manufactured. By evaluating mechanical properties, the thermal characteristic and the electrical characteristic of each composite, the effect of filler addition was investigated in detail. As a result of 3-phase composite was compared with 2-phase composite (Epoxy reinforced by CNF or CF), thermal conductivity was deteriorated. However tensile strength Young's modulus and the electrical conductivity were greatly improved. Moreover, to improve CNF/Epoxy matrix adhesion, the oxidation treatment by heating in the air atmosphere was done to CNF. By the oxidation treatment for CNF, the improvement of the Young's modulus and tensile strength was admitted in only 2-phase composite. On the other hand, thermal conductivity and the volume resistivity were inferior compared with untreated CNF. ©2012 The Japan Society of Mechanical Engineers.

In the present paper, the interfacial adhesion strength between thin film and substrate is evaluated by using laser ultrasonic waves. The laser beam is irradiated on the substrate which has a thin film on the opposite side. The ultrasonic elastic wave is excited by the laser beam, and it propagates in the thickness direction of the substrate. The ultrasonic compressive wave reflects at the opposite surface as a tensile wave, and reaches the interface. Finally, delamination at the interface is caused by the tensite wave. In the present study, the interfacial stress is estimated by inverse analysis using Laplace-transformed boundary element method. The displacement history on the surface of the specimen can be related to the interfacial stress by a transfer function. The transfer function can be obtained numerically by 3-dimensional boundary element analysis. The test specimens made from Al alloy substrate and Ti thin film were used in the present study. It is confirmed that the interfacial strength between thin film and substrate is 68.3MPa from the present investigation.

Glass-like carbon (GC) is expected as a die material for press molding of glass micro optical devices. However, the mechanical and thermal properties are not enough to use as precision mold die. So, GC composites reinforced by vapor grown carbon fiber (GC/VGCF composites) were developed to improve the properties. The GC/VGCF composites achieved high thermal conductivity and bending strength, and the decreased linear expansion coefficient and good mold releasability. However, surface roughness of the GC/VGCF composites after focused ion beam (FIB) etching increased up to 50nm, when VGCF of 28vol% was added. © 2011 The Society of Materials Science, Japan.

In the present paper, some experiments for press molding of lens and its numerical simulations using finite element method were investigated. Thermo-viscoelastic property of the BK-7 glass specimen was estimated using unidirectional compression creep test based on traditional thermo-viscoelastic theory. The adaptive condition of molding temperature which given appropriate transcription profile of the glass was investigated by the experimental tests. Moreover, numerical simulation for press molding of the glass was carried out by finite element method using universal FEM code (ANSYS ver.11.0). As a result of comparing experimental results with numerical ones, it was confirmed that the surface profile of the lens estimated by FEM approximately agreed with experimental value.

Many kinds of optical glass devices are needed in various fields such as optics, biotechnology, medical care and so on. If an optical device such as an aspheric lens does not have a simple shape, and/or its size is micro-/nanometer scale, press molding should be carried out at a higher temperature than the glass transition temperature (T_g) to reduce cost and increase productivity. However, the most suitable conditions for glass molding are generally determined by performing many experiments. Consequently, it is useful to be able to predict the most suitable molding condition by numerical simulation. Press molding experiments and numerical simulation using finite element analysis, in relation to micro press molding of the borosilicate glasses Pyrex and D263, were carried out. Thermo-viscoelastic properties of the glasses were estimated using unidirectional compression creep testing according to traditional thermo-viscoelastic theory. Glass micro press molding was carried out with a glassy carbon die with a line and space pattern machined by a dicing saw. The optimum molding temperatures for accurate transcription of the die profile to the glass were investigated. Numerical simulation of micro press molding of the glass was carried out by the finite element method using universal FEM code (ANSYS ver.11.0). Experimental and numerical simulation results for the cross-section shape and the height of the groove profile were in approximate agreement.

Uniaxial tensile tests of glass specimens were carried out at a range of strain rate and temperatures. The strain rate and temperature dependencies on the tensile strength (breaking stress) of the glass were investigated in detail. The relationship between tensile strength, strain rate and temperature can be expressed using exponential functions given by Norton's law and an Arrhenius type equation. An empirical equation expressing the temperature and strain rate dependencies of tensile strength was obtained from the experimental results. The strength of the glass was discussed from the standpoint of the thermo-viscoelastic properties of the material.

For optimizing the conditions of glass imprinting, many researchers commonly use the trial-and-error method. Therefore, it is advantageous to carry out a preliminary analysis of glass imprinting. The viscoelastic property of glass is necessary for MEMS-ONE in which a viscoelastic model is used. Assuming glass materials to be viscoelastic boies, the relaxation share modulus was measured by the creep test based on traditional thermo-viscoelastic theory. The Williams-Landel-Ferry (WLF) equation is applied using the temperature dependence of liquid viscosity. We compared experimental results with the analytic results of MEMS-ONE simulation under the conditions of fixed pressure (3.56 MPa) and time (10 min). The object of evaluation is the height of the central position prong. The molding temperature can be predicted within 10 degrees C error by the simulation. (C) 2010 The Japan Society of Applied Physics

Glass-like carbon (GC) is expected as a die material for mold-press of optical glass devices. However, the mechanical and thermal properties are not enough to use as mold die. Recently, glass-like carbon/carbon nanotube composite (GC-V) reinforced by vapor grown carbon fiber (VGCF) was developed to improve the properties. In this study, optimum machining conditions on electrical discharge machinability of GC-V were examined to enable wide area machining. The machined surface of GC-V with 5 or 14vol% VGCF was characterized by no crack and smaller roughness than that of the GC when machined in a voltage range of 50∼70V. Also, the machining time of the GC-V was shortened. Furthermore, the surface roughness of GC-V etched by focused ion beam (FIB) was enough to use as glass mold die.

Glass-like carbon is expected as a die material for mold-press of optical glass devices. In this study, optimum machining conditions on electrical discharge machinability of glass-like carbon die were examined in working fluid such as oil or ion-exchanged water. Short machining time was achieved by electrical discharging in ion-exchanged water, as well as good machined surface with small roughness. This was caused by low electric resistivity of the water and a small amount of isolated carbon. Furthermore, the surface roughness of glass-like carbon discharged in ion-exchanged water was smaller than that done in oil. The glass-like carbon was suitably discharged in ion-exchanged water under conditions of voltage of 40V, electrode rotational speed of 1000∼3000rpm, pulse ON time of 5μs and duty factor of 0.3∼0.7. Under these conditions, excess melting of glass-like carbon, local discharging, adhesiveness of isolated carbon on electrode, etc. were suppressed.

In the present paper, some experiments for press molding and numerical simulation about micro press molding of glass devices using finite element method is investigated. Thermo-viscoelastic properties of the glass materials were estimated using unidirectional compression creep test based on traditional thermo viscoelastic theory. In this study, Pyrex and D263 were used as glass materials. Glass micro press molding was carried out with Glass-like Carbon (GC) mold given to Line & Space patterns machined by dicing. The adaptive condition of the molding temperature which given appropriate transcription profile of the glass was investigated. Moreover, numerical simulation for micro press molding of the glass was carried out by finite element method using universal FEM code (ANSYS ver. 11.0). As a result of comparing experimental results with numerical ones, the cross section shape and the height of groove profile obtained by FEM simulation approximately agree with experimental value.

The Mems-ONE is well known software which simulates thermo-viscoelastic properties in the conduct of nanoimprinting. Assuming the glass materials to be viscoelastic body, the relaxation shear modulus was measured by the creep test, Williams-Landel-Ferry (WLF) equation is applied for expressing the temperature dependence of liquid viscosity. We compared experimental with analytic results used by Mems-ONE with the condition of fixed pressure and time. Thermo-viscoelastic properties of the glass materials were estimated using unidirectional compression creep test based on traditional thermo viscoelastic theory. Glass was Borosilicate Glass (D263, Schott). Glass imprinting was carried out on Glassy Carbon (GC) mold with line & spacelO um patterns fabricated by dicing saw. The machining accuracy is most important thing as the evaluation mold. The glass imprinting temperature consulted thermo-viscoelastic properties of the glass materials. The numerical simulation was carried out on the small portion of mold and glass. The constant value of WLF equation fitting in high temperature translates the master curve of D263 with a high degree of accuracy. It caused the accuracy improvement of analysis result. In addition, we confirm that WLF equation intended to resin can use to the glass imprinting. © 2010 The Institute of Electrical Engineers of Japan.

To produce micro glass lens by mold-press, 3D micro lens die was fabricated on glass-like carbon (GC) by focused ion beam (FIB) etching. The dimensional accuracy and surface roughness, as well as transcriptional performance, were investigated. A precise and smooth die was completed by optimizing dwell time, current and step number of 2D bit map data, which agreed well with theoretical estimation. Micro glass lenses with different diameter and gradient angle were mold-pressed using the GC die. The diameter and sag were confirmed to be nearly equivalent to or just smaller than those of GC die.

In the present paper, numerical simulation about press forming process of glass lens using finite element method is investigated. It is well known that constitutive equation (elastic constants) of glass depend on time-history and temperature. Therefore, stress relaxation or creep arise on the glass subjected to applied loading, and these behaviors vary drastically depending on the temperature. In the present study, creep test has been conducted to determine the thermo-viscoelastic properties of glass. The creep function obtained by the experiment has been transformed into relaxation function employing Laplace transform and its inversion. Shift factor which gives the relation between the time and temperature can be determined by creep test under several temterature, too. Using typical glass "TaF-3" which has been used for press forming, some numerical simulation by FEM are demonstrated. Residual stresses and residual deformations under some processing conditions are estimated, and the optimal conditions of forming process for glass lens are discussed in detail.

Glass-like carbons (GCs) for press molding die of micro optical glass lens and electroless Ni-P alloy films for injection molding die of micro optical plastic lens were machined by focused ion beam (FIB) and their dimensional accuracy, surface roughness and transcriptional performance were investigated. The GCs completed a fine surface roughness of Ra=1nm after FIB machining, although their FIB etching rate was decreased to a half rate of Si(100) single crystal. On the other hand, amorphous Ni-P alloy films containing phosphorus more than 7wt% possessed higher etching rate than Si(100) crystal, as well as fine surface roughness less than 8nm. Precision GCs and Ni-P alloy films molding dies with 3-D microlens array of 7μm square were fabricated by FIB. Subsequently, transcriptional performance to micro optical lens was evaluated on precision GC dies.

To apply glass-like carbon (GC) to precision die for press-molding of optical glass lens, the wettability between optical glasses and the GC materials was investigated in nitrogen, argon or air atmosphere heated up to 900-1050℃. The GC material calcinated at about 2000℃ (GC20) exhibited larger contact angle than that of the GC materials calcinated at 1300℃ or 3000℃. This was caused by that calcination at 1300℃ or 3000℃ promoted graphite reaction of the GC materials. When the contact angle between the GC20 material and some commercial glasses with different chemical composition was compared, kron (Crown) glass achieved the same large contact angle as flint glass. In the kron glass, lower adhesion or more melted fragment of glass was also observed on the GC20 surface. It was expected that a lack of PbO, Na_2O and K_2O brought on good characteristics of the kron glass.

In this study, unidirectional compression creep tests were performed for various commercial optical glasses to investigate the effects of glass compositions or network structures on stress relaxation behavior. As a result, it was clarified that these two factors have little effect on the stress relaxation behavior and draw a master curve of shear relaxation modulus with almost the same shape in any glass. In addition, we tried to measure the viscosity by the parallel plate test and succeeded in calculating the shift factor from the estimated viscosity. In other words, it has become possible to significantly reduce the measurement time for the shift factor compared to the conventional creep test. Furthermore, the parallel plate tests with an extremely low loads using a thermomechanical analyzer were also performed, and it was clarified that the shift factors are not affected by the measured loads.

We fabricated a Ni-W mold with a moth - eye structure using Ni-W plating with excellent releasability. Since aluminum nano-holes have been studied as a light receiving element utilizing plasmon resonance, we have studied aluminum nanoimprinting using a Ni-W mold. As a result, nanoholes could be formed on the surface of the pure aluminum plate at room temperature. The required pressure was 100 MPa. Compared to thermal nanoimprint for thermoplastic resin, the pressure of aluminum nanoimprint is more than 10 times greater, and it is a task to lower the pressure. In addition, Ni - W molds with large warpage due to thermal nanoimprint embrittles and has a high possibility of cracking. Therefore, we stopped thermal nanoimprint for glass.

To evaluate adhesion quality of diamond-like carbon (DLC) film for the life prediction of the die for glass press molding, laser spallation technique, thermal shock test and indentation test were carried out. Cyclic thermal shock test was useful to evaluate the adhesion quality and surface damage of the DLC film at high temperature, and was possible to estimate the influence of the intermediate layer structure on the adhesion quality. In the indentation test, the adhesion quality of the DLC film at high temperature up to 300℃ was decreased with temperature increasing. The cyclic number to crack initiation for the sample in 300℃ was smaller than that in room temperature.

In the present study, the interfacial adhesion strength between coating film and interface fracture toughness between coating film and substrate were evaluated by laser ultrasonic waves and boundary element method. The adhesion strength can be estimated by inverse analyses using transfer function from the history of displacement of the specimen and boundary element analysis for unsteady 3-dimensional vibration. In the present study, an alternative boundary element program has been made for the axisymmetric solid body. Using data processing by Weibull distribution, the interfacial strength between Ti coating film and Al-alloy substrate could be confirmed to be 59.2MPa from the present investigation.

Some experimental testing and numerical simulations by FEM for thermal imprinting of glass-optical devices were investigated. Thermo-viscoelastic property of the glass material was estimated using compression creep tests. In this study, D263 was used as glass material. Glass thermal imprint tests were carried out with amorphous carbon dies that were given to line & space or micro-lens array pattern machined by focused ion beam (FIB). The optimum condition of imprinting temperature which given appropriate transcription profile of the glass was investigated. Moreover, numerical simulations for thermal imprinting of the glass were carried out by finite element method. Comparing experimental results with numerical ones, the transcription of height of groove or micro-lens obtained by experimental tests approximately agreed with numerical values. In addition, the relationship between tensile strength, temperature and strain rate was obtained by the uniaxial tensile test.