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It is well known that the compressive strength of composite laminates decreases after impact load, even if the impact damage is barely visible in appearance. This compression after impact (CAI) strength is one of the most important design criteria for composite structures. Currently, in order to reduce time-consuming model tests and simultaneously ensure structural reliability, analytical or numerical methods are required which are capable of reproducing the actual failure behavior of composite structures (failure mode and load). In this study, impact damage and CAI strength were continuously evaluated by means of numerical progressive failure analysis using dynamic explicit FEA. Since impact and subsequent CAI are dynamic and a static loading processes, respectively, analyses for removing the dynamic effect in the CAI process were performed in the following three steps: 1) impact, 2) relaxation of vibration and 3) CAI. In these analyses, the LaRC failure criteria which take into account fiber-kinking failure mode were employed as stress-based damage initiation criteria, and damage evolution for each lamina was simulated through energy-based damage mechanics. The damage initiation criteria and evolution law were implemented in analyses using the user-subroutine VUMAT of Abaqus/Explicit. In addition, delamination was represented by cohesive elements in stress-based damage initiation criteria and energy-based damage mechanics. As a result of comparison with tests, both of the projected delamination areas caused by impact loading and CAI strength were satisfactorily predicted within an accuracy of ± 15 %. In the CAI simulation, fiber-kinking damage propagated in the direction of width at the maximum applied load, but delamination did not start to propagate. The fiber kinking failure mode was caused by bending due to local buckling at impact area where delamination existed. Accordingly, both of the in-plane fiber kinking damage (which is critical failure mode in CAI) and the delamination (which strongly affects local buckling and subsequent in-plane fiber kinking) are quite important for the accurate prediction of CAI strength.

A high power single-mode fiber laser has received a lot of attention in various materials processing fields. In order to carry out processing under proper conditions with single-mode fiber laser, the dynamic flows of fluids inside the materials should be precisely understood. We carried out the numerical analysis of materials processing using a 5-kW single-mode fiber laser. The dynamic flows of the copper fluid during the bead-on-plate tests are calculated and the results agree well with the experimental results. The processing with the different scan speed and spot size, and at the output power of 10 kW are numerically calculated as well. The proper processing conditions with less spatters and dross for each materials can be determined by the dynamic analysis.

Strength of compression after impact is one of the most important design criteria for structures using laminated fiber-reinforced plastics. Effects of face-on impact damage on compressive strength have been widely studied over the past decades. However, knowledge about effects of edge-on impact damage is limited compared to that of face-on impact. Therefore, in this study, edge-on impact tests and compression after edge-on impact (CAEI) tests were conducted. In addition, intralaminar fracture toughness (energy) of compressive failure of fiber (0°) and matrix (90°) was obtained by single edge notched compression tests and VCCT analysis, since intralaminar failure properties seem to be essential from our previous work. The obtained toughness was used in progressive damage analysis (PDA) of CAEI failure. In the PDA, CAEI failure was simulated under several modelling assumption of impact damage, including delamination and intralaminar pre-crack. As a result, CAEI strength was predicted with relatively small error when intralaminar pre-crack was included as impact damage. Although modelling assumption of impact damage, such as information about crack length or cracking ply, has to be validated based on experimental observation as future task, utility to predict CAEI strength by modelling impact damage as pre-crack was shown.

Compressive strength reduction of composite structures due to notches or impact damage is an important factor for aircraft structure design. Compressive strength reduction is caused by stress concentration around notches such as skin manholes or impact damage due to tool falling during manufacturing. In particular, the compressive strength reduction due to the edge-on impact is large, so it is one of the most important issues for strength design of the aircraft. In this study, in order to evaluate the effect of stacking sequence on compressive strength after edge-on impact, edge-on impact survey test and compression after edgeon impact test using CFRP laminates with different stacking sequence were conducted. As a result, in the Soft laminate, including many ±45°plies, cracks due to edge-on impact spreading in the laminate thickness direction could be observed, and detectability of the damage was better than that of other specimens. And the residual strength after edge-on impact was improved in Hard3 laminate which retained laminate stiffness along the loading direction while suppressing the edge-on impact energy that necessary to apply the dent depth equivalent to the barely visible impact damage (BVID). These results show the possibility of improving the compressive residual strength by the optimization of stacking sequence.

Stimulated Raman scattering gives back reflection sensitivity to a high power fiber laser. Therefor SRS suppression is necessary in order to realize stable laser processing by a high power fiber laser. A 5-kW single-mode ytterbium doped fiber laser with a 20-m long delivery fiber has been realized. The fiber laser is an all-fiber single-stage Fabry-Perot system in a co-pumping configuration. The optical to optical efficiency was 80% at the output power of 5.0 kW. And the M-squared figure of 1.3 was obtained. The Stokes light by SRS is suppressed to 45 dB below the laser output by using fibers with the effective mode area of 600 μm2 . While SRS was well suppressed, four wave mixing was observed with the frequency shift of ~6 THz. Four wave mixing between the fundamental mode and the secondary modes is believed to take place. Four wave mixing is believed not to give back reflection sensitivity to the fiber laser. The 5-kW single-mode fiber laser was applied to laser processing. Bead-on-plate tests were carried out with a galvanometer scanner. The laser ran without stopping nor damaging the laser system even during processing highly reflective material. This implies that our SRS suppressed single-mode fiber laser can be used practically in most of processing systems.

We optimized the structural parameters of large-mode-area all-solid photonic bandgap fibers for high-power laser applications with numerical simulations. We obtained an effective mode area of greater than 1000 μm 2 in bending condition while maintaining single-mode operation and realizing compact packaging for both 7- and 19-cell core fibers. We also found out that a core diameter of larger than 115 μm could be achieved for the 19-cell core fibers.

A 3 kW single stage all-fiber Yb-doped single-mode fiber laser with bi-directional pumping configuration has been demonstrated. Our newly developed high-power LD modules are employed for a high available pump power of 4.9 kW. The length of the delivery fiber is 20 m which is long enough to be used in most of laser processing machines. An output power of 3 kW was achieved at a pump power of 4.23 kW. The slope efficiency was 70%. SRS was able to be suppressed at the same output power by increasing ratio of backward pump power. The SRS level was improved by 5dB when 57% backward pump ratio was adopted compared with the case of 50%. SRS was 35dB below the laser power at the output power of 3 kW even with a 20-m delivery fiber. The M-squared factor was 1.3. Single-mode beam quality was obtained. To evaluate practical utility of the 3 kW single-mode fiber laser, a Bead-on-Plate (BoP) test onto a pure copper plate was executed. The BoP test onto a copper plate was made without stopping or damaging the laser system. That indicates our high power single-mode fiber lasers can be used practically in processing of materials with high reflectivity and high thermal conductivity.

Various toughened-material systems to reinforce interlaminar strength of CFRP have been proposed on the basis of the results of coupon tests. In this paper, an applicability of toughened-material systems to structural model such as curved beam subject to static bending was examined. Two kinds of CFRP with different toughened-material system were selected, and both microscopic observation and numerical FEM simulation using VCCT were performed for test results. A difference between coupon and structural model tests was found for the case of the curved beam with artificial anomaly, and the cause was considered due to the difference of delamination pass between coupon and curved beam tests. From a view point of numerical simulation for predicting the strength behavior of the curved beam, an adoption of different fracture toughness from that by coupon test was necessary.

A 2 kw single-mode fiber laser with a 20-m long delivery fiber and high back reflection resistance has been demonstrated. An Yb-doped fiber with large core size and differential modal gain is used to realize high SRS suppression and single-mode operation simultaneously. The 20 m-long delivery fiber gives flexibility to the design of processing systems. An output power of 2 kW is achieved at a pump power of 2.86 kW. The slope efficiency is 70%. The power of the Stokes light is less than -50 dB below the laser power at the output power of 2 kW even with a 20-m delivery fiber. Nearly diffraction-limited beam quality is also confirmed (M2 = 1.2). An output power of 3 kW is believed to be achieved by increasing pumping power. The back reflection resistance properties of the fabricated singlemode fiber laser is evaluated numerically by the SRS gain calculated from measured laser output spectra and fiber characteristics. The acceptable power of the back reflection light into the fiber core is estimated to be 500 W which is high enough for processing of highly reflective materials. The output power fluctuation caused by SRS and back reflection in materials processing will be well suppressed. Our high power single-mode fiber lasers can provide high quality and stable processing of highly reflective materials.

A reflectometry system having a high spatial resolution and an elongated measurement range is constructed, considering an application to optical subscriber networks, using a technique of synthesis of optical coherence function (SOCF). In this system, parameters have been adjusted so that the measurement range is elongated by successively shifting the 20 m measurement window while keeping a high spatial resolution. Reflectivity distribution around the end of a 5 km test fibre is successfully measured with a spatial resolution of 11 cm and an elongated measurement range of 1 km.

It has been recognized that the threshold stress intensity factor range ΔKth of short crack is dependent on many factors. Fatigue tests were performed on materials containing small defects under a wide range of mean stress for three grades of steels with different hardness.Strong dependencies of ΔKth on material hardness, mean stress and defect size were observed. Major tendencies such that softer material had lower ΔKth and smaller defect had lower ΔKth were obtained, which were quite different from those of long cracks. The causes of these effects were investigated based on the crack closure behavior of short crack. The crack closure measurement on a very shallow crack was done. Test results showed that softer material and shorter crack had lower crack closure stresses. It was shown that the threshold effective stress intensity factor range (ΔKeff)th was a unique value for defects deeper than 0.1mm. The crack closure was the major cause of the abovementioned effects of material hardness and mean stress for defects deeper than 0.1mm. On the contrary, (ΔKeff)th significantly decreased compared with that for long cracks when the defect was shallower than 0.1mm. This is another short crack effect which could not be explained only by the crack closure. It was shown that (ΔKeff)th was no more a unique value when the defect depth was shallower than 0.1mm.

Core size scaling in all-solid photonic bandgap fibers (AS-PBGFs) is discussed. It is shown that the effectively single-mode AS-PBGF with 100-μm core diameter can be achievable with 40-cm bending radius operating in the 3rd PBG.

An effectively single-mode all-solid photonic bandgap fiber with large effective area and low bending loss for compact high-power all-fiber lasers is fully investigated. The pitch dependencies of effective area, bending loss, and effectively single-mode operation are discussed numerically and experimentally. The calculation results indicate that an effectively single-mode all-solid photonic bandgap fiber with an effective area of more than 500 μm(2) and a bending loss of less than 0.1 dB/m at a bending radius of 10 cm can be realized by choosing optimum fiber parameters. In a fabricated effectively single-mode all-solid photonic bandgap fiber with 48.0 μm core, the effective area of 712 μm(2), the effectively single-mode operation, and the bending loss of less than 0.1 dB/m at a bending radius of 10 cm are achieved simultaneously at 1064 nm.

Effectively single-mode all-solid photonic bandgap fiber with an effective area of 830 μm2 and a bending loss of less than 0.1 dB/m at a bending radius of 15-cm has been demonstrated.

A large-mode-area all-solid photonic bandgap fiber with a seven-cell core and five high-index rod rings is investigated. Numerical simulations show that an effective area of more than 500 μm2, a bending loss of less than 0.1 dB/m at a bending radius of 10 cm and effectively single-mode operation can be achieved simultaneously. A core diameter of 44.8 μm and an effective area of 650 μm2 at 1064 nm are achieved in a fabricated fiber. Bending loss at 1064 nm is 0.09 dB/m at a bending radius of 7 cm. Effectively single-mode operation is also realized at a bending radius of 10 cm.

We have designed and fabricated a practically deployable large effective area all-solid photonic bandgap fiber. Effectively single mode operation and 440 um effective area were achieved at a 7.5 cm-bending radius.

We have demonstrated an 1180-nm linearly-polarized single cavity fibre laser with an output power of 10.8 W using an Yb-doped polarization-maintaining solid photonic bandgap fibre. A slope efficiency of 56 % has been achieved.

A linearly-polarized fiber laser operating at 1180 nm was demonstrated using a low-loss ytterbium-doped polarization maintaining solid photonic bandgap fiber. A slope efficiency of 30 % was achieved.

A low loss ytterbium-doped polarization maintaining solid photonic bandgap fiber (SPBGF) is fabricated using a new fabrication method. A high efficient fiber laser operated at the low-gain wavelengths is prospected by the fiber.

Several key technologies;large-area recryatallization technique, viahole-filling, and scaled thin SOI devices, have been prepared for realizing 3D LSI.

We demonstrate suppression of amplified spontaneous emission at 1030 nm in a cladding-pumped ytterbium-doped solid photonic bandgap fiber. This fiber should play an important role for a high power fiber laser lasing around 1180 nm.

As the degree of integration and speed of VLSI are advanced, the multilayered interconnection techniques become increasingly important. At the moment when the VLSI technology is advanced to 0.5 μm technology represented by 16 MDRAMs, electromigration by the high-current density of Al interconnections and the stress migration by the stress from the interlayer insulating films are important in reliability of Al-interconnections. Although the latter can be rectified by low-temperature formation of the insulating films, the prevention of the former is still in a development stage. Since the spacing between the interconnections and the aspect ratio of the connecting hole increase, good planarization of the interlayer insulating films and buried planarization of the connecting holes are required. These problems can be resolved by directive deposition of the insulation films and selective CVD of W. Further, as the miniaturization and the number of interconnection layers are increased, the crosstalk noise of the device due to the interconnection capacitances becomes significant. It is necessary to reduce the film thickness of the insulating layer and the interconnection so that the interconnection capacitance is reduced. In this paper, first the present status of the fine multilevel interconnections, the problems and solutions are presented. Next, the necessity of reduction of the interconnection capacitance and the prospect of the multilevel interconnection in the future after the 0.5 μm generation are described.

A long-range and high-resolution reflectometry by synthesis of optical coherence function at region beyond the coherence length is proposed. We discuss and simulate the principle of the reflectometry system. In basic experiments, the reflectivity distribution is successfully measured at the region beyond the coherence length with a spatial resolution of 19cm and a measurement range of 1km. We have also proposed two methods to improve dynamic range of the system. In the experiments, dynamic range of 45dB is successfully achieved.

A buried source and drain (BSD) structure, that realizes ultra-shallow junctions, is proposed. Regions for source and drain are etched off. An in-situ highly doped amorphous silicon layer is selectively deposited on the etched region and is crystallized by solid phase epitaxy. Junction depth can be reduced to 10 nm without lowering the dopant concentration, because the doped layer can be used as source and drain. Thus, the sheet-resistance was lowered to 300 /spl Omega// for a junction with the depth of 30 nm. Junction leakage current for the BSD structure was equal to or lower than that fabricated by ion-implantation.

It was found that a high concentration of holes was generated without any post‐annealing by boron ion implantation into silicon in the high‐dose region of more than 1×1016 cm−2. X‐ray photoelectron spectroscopy and Fourier transform infrared absorption spectrum revealed that B12 icosahedra were created just after implantation. The generation of holes can be explained by the model in which B12 icosahedra act as a double acceptor.

The effects of oxygen on the metabolism of lipophilic nitroxide and the membrane structure of microsomes were investigated with an ESR spectrometer equipped with a hand-made gas-permeable sampling tube. The half life of gas change in the membrane was confirmed to be 48 s by the line-width of the ESR signal. The signal intensity of lipophilic nitroxide in microsomal membranes decreased with NADPH under N2 and increased under O2. The change of signal intensity was reversible, suggesting that lipophilic nitroxide can be used as an indicator of the redox state in membranes for in vivo ESR imaging.

A high hole concentration region of about 1×1021 cm-3 was generated without any post-annealing by the implantation of high doses of boron into silicon substrates. X-ray photoelectron spectroscopy (XPS) measurement and Fourier transform IR spectroscopy (FTIR) absorption spectra revealed that B12 icosahedra were created in as-implanted samples. A new model of the generation of holes is proposed in which B12 icosahedron acts as a double acceptor.

Fatigue tests were performed on materials containing small cracks to investigate the effects of material hardness, mean stress, and crack size on the threshold stress intensity factor of small cracks. The crack closure measurement on a very small crack was done. Although most of those effects could be explained by the characteristic behavior of crack closure in small cracks, it was also shown that (ΔKeff)th was also affected by crack size. The combination of (ΔKeff)th and the crack closure behaviors caused the peculiar characteristics of ΔKth in small cracks. At an extremely high R region, an unusual decrease in ΔKth was found to occur. The large reduction occurred under the conjunction of three factors: extremely high stress ratio higher than 0.8, shallow crack less than a few tenths of a millimeter, and hard material whose HV is higher than 300. The near-threshold fatigue crack propagation rate could be uniquely evaluated even in such a short crack regime using the effective stress intensity factor with the following modification {ΔKeff − (ΔKeff)th,a}. This expression could be applicable in the short crack regime. ΔKeff still plays a role as the governing parameter for fatigue crack propagation of short crack as short as 0.04 mm.