All issues
Volume 64, Issue 6
Displaying 1-9 of 9 articles from this issue
- |<
- <
- 1
- >
- >|
-
Yasuhide Shindo, Hiroyuki Kudo, Katsumi Horiguchi, Susumu Kumagai2000 Volume 64 Issue 6 Pages 423-428
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSExperiments and analysis on woven glass-epoxy laminate end notched flexure (ENF) specimens are presented. The ENF tests were performed at room temperature (R.T.), liquid nitrogen temperature (77 K) and liquid helium temperature (4 K) to evaluate the effect of temperature and geometrical variations on the Mode II interlaminar fracture toughness. In order to verify the failure mechanisms, fracture surface examinations were performed on a scanning electron microscope. A finite element model was used to perform the delamination crack analysis. The results of the finite element analysis are utilized to supplement the experimental data.View full abstractDownload PDF (1002K) -
Yoshinori Ito, Nobuhiro Tsuji, Yoshihiro Saito, Hiroshi Utsunomiya, Te ...2000 Volume 64 Issue 6 Pages 429-437
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSUltra-fine grained 1100 commercial purity aluminum sheet was produced by six cycles of an accumulative roll-bonding process (with an equivalent strain of 4.8) at 473 K. The ultra-fine grains in the as-ARB processed sheet had pancake-like morphology 690 nm in diameter and 270 nm in thickness. TEM/Kikuchi-line analysis clarified that the ultra-fine grains are not subgrains but polycrystals having large misorientations with respect to each other. Changes in microstructure and mechanical properties of the ultra-fine grained aluminum by annealing were investigated. As-ARB processed sample showed tensile strength of 275 MPa which is 3.3 times higher than that of starting material, while elongation was limited to 9%. The grain size increased with increasing annealing temperature. The pancake-like ultra-fine grains changed into equiaxed shape firstly, and then rapidly grew. Strength continuously decreased with increasing grain size, but elongation did not recover until the grain size became about 1 μm. Especially, the ultra-fine grained material showed very small uniform elongation. As a result, only limited grain sizes provided both high strength and enough ductility. It was clarified that proof stress increases while strain-hardening exponent decreases with decreasing grain size.View full abstractDownload PDF (1691K) -
Atsuo Gyobu, Yoshio Kawamura, Toshio Saburi, Makoto Asai2000 Volume 64 Issue 6 Pages 438-443
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe martensitic transformation and associated two-way shape memory effect of sputter-deposited Ti-rich Ti-Ni alloy films were investigated.
For investigation of aging (without constraint) on the martensitic transformation behavior, the deposited amorphous films were crystallized and concurrently aged by holding at various temperatures between 693 and 1123 K.
The specimens were analyzed with differential scanning calorimetry (DSC) and the following was found: The martensitic transformation behavior changes depending on crystallization temperatures and composition. The B2 ⇔ R transformation temperatures of the thin films crystallized at temperatures between 693 and 773 K were the lowest at Ti-48.5 at%Ni.
Then, for investigating the aging effect on the spontaneous shape change associated with the transformations, the amorphous films were crystallized by holding at various temperatures between 693 and 743 K followed by aging under constraint (circular shapes) at several different temperatures between 693 and 763 K. On these specimens, observation of spontaneous shape change during cooling and heating was made. The obtained results are the following: The specimens aged under constraint show the two-way shape memory in association with the B2 ⇒ R ⇒ B19′ and the reverse transformations. While the hysteresis of the B2 ⇔ R transformation is less than 2 K, that of the R ⇒ B19′ is about 60 K. Aging at 743 K under constraint gives the largest spontaneous shape change both for B2 ⇒ R and B2 ⇒ R ⇒ B19′ transformations.View full abstractDownload PDF (743K) -
Young Jo Park, Manabu Enoki, Tadatomo Suga, Teruo Kishi2000 Volume 64 Issue 6 Pages 444-450
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSBonded area is largely affected by the surface morphology and mechanical properties of materials, because the room temperature bonding process is carried out under a low temperature and pressure for a short time. Accordingly, interfacial defects cause unavoidable problems in many cases. For an application of this technology, it is important to elucidate the effect of interfacial defects on fracture behavior. Fracture mechanism and criterion for the growth of interfacial defects were investigated using the Al/Sapphire joint known for easy control of bondability. The results clearly showed that the growth of an interfacial defect was the dominant factor for the crack propagation. A critical stress intensity factor for the growth of interfacial defects was estimated by the analysis of FEM calculation and experimental observation.View full abstractDownload PDF (684K) -
Koji Tanoue, Shohei Iwao2000 Volume 64 Issue 6 Pages 451-459
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIt is investigated how the grain boundary cavitation caused by different grain morphologies has an effect on creep at high temperatures after changing the morphology of secondary recrystallized grains grown in powder metallurgy tungsten fine wires. The morphology of secondary recrystallized grains and the number of cavities grown on grain boundaries can be quantitatively related to each other by using f1 as a grain morphology index. The apparent activation energy for steady state creep Ha obtained in the region of the power-law creep increases with increasing temperature and decreases drastically with an increase in f1, namely an increasing number of grain boundary cavities. It is concluded that the former increase in Ha results from a decrease in threshold stress due to a decreasing number of bubbles existing inside a grain with increasing temperature, and that the latter decrease in Ha results from the growth of cavities controlled by the coupled mechanisms of grain boundary diffusion and dislocation glide based on the Peierls mechanism.View full abstractDownload PDF (944K) -
Masao Hayakawa, Toru Hara, Saburo Matsuoka, Kaneaki Tsuzaki2000 Volume 64 Issue 6 Pages 460-466
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSMicrostructures of JIS-SCM440 steel tempered at 723 K were observed by atomic force microscopy (AFM). Two kinds of specimen surface were prepared by electrically polishing and by chemically etching. The quality of AFM images was much better on the electropolished surface because the high vertical resolution of AFM could be fully utilized. Since the electropolishing rate depends on the crystal phase and the surface orientation, prior austenite grains, packets, blocks and small precipitates were clearly distinguished on the electropolished surface, and the average block width was determined to be 0.6 μm. The density of the heterogeneously precipitated carbides along prior austenite grain boundaries was not uniform, suggesting that the nucleation of the carbides depends on the grain boundary characteristics. The apparent size of the carbides observed by AFM was larger than the actual size observed by TEM due to the effect of the tip curvature.View full abstractDownload PDF (1237K) -
Kimitsugu Soki, Hisami Yumoto, Kazuo Akashi, Shigeru Ito, Tsutomu Seki2000 Volume 64 Issue 6 Pages 467-473
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn this study, a Nb film for use as a hydrogen permeable membrane was prepared at 0.4∼5.3 Pa of Ar, using a PVD method such as arc-ion plating (AIP). Peculiar Nb droplets (0.1∼10 μm) were observed on the membrane. The disconnection of the droplets from the membrane occurred on a flat surface of Al2O3 substrate, which caused the formation of pinholes. However, a membrane without pinholes was successfully prepared on a rough surface of Al2O3 by increasing the film thickness to 2 μm.
Columnar Nb crystals grew on the flat substrate and the surface of the film also became flat. Corn-shaped crystals grew on the rough substrate so that the surface of the film was also rough. Since the adhesion of the droplets flying on the rough surface was high, a membrane without pinholes was obtained on the rough substrate.
A geometrical growth model was used to explain the growth of the hemispherical droplets into rugby-ball-shaped crystals by Nb deposition.View full abstractDownload PDF (1487K) -
Hisatoshi Hirai, Tatsuo Tabaru, Hidetoshi Ueno, Akira Kitahara, Shuji ...2000 Volume 64 Issue 6 Pages 474-480
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn order to examine the possibility of niobium solid solution/niobium silicides in-situ composites as future high temperature structural materials, directionally solidified Nb-xMo-22Ti-18Si(x=0, 10, 20 and 30) alloys were prepared by the floating zone melting technique. A part of each specimen was annealed at 1870 K in a vacuum for 100 h and examined by optical and scanning electron microscopy. Vickers hardness was measured at room temperature. The high temperature compression strength of annealed specimens was measured at 1470 and 1690 K in a vacuum at an initial strain rate of 1×10−4 s−1.
By adding molybdenum, the microstructure became finer and the silicide changed from (Nb, Ti)3Si to (Nb, Mo, Ti)5Si3. The Vickers hardness of annealed specimens increased almost linearly with increasing molybdenum content, from 510 to 880. At 1470 K, a specimen with x=0 displayed high yield stress, but it fractured at a small plastic strain. As for specimens with x=10, 20 and 30, yield stress, maximum stress and compressive ductility increased with increasing molybdenum content. At 1690 K, specimens with x=0 and 10 had the higher maximum stress than the others, but they showed a sharp decrease in stress after reaching the maximum stress because of easy cracking. On the other hand, specimens with x=20 and 30 showed lower yield stress and maximum stress than those with x=0 and 10. They showed small stress drop after reaching the maximum stress, however, and almost constant flow stress of 330 MPa(x=20) and 400 MPa(x=30) for large strain range without any apparent cracking.View full abstractDownload PDF (927K) -
Hajime Matsumoto, Eiichi Sukedai, Hatsujiro Hashimoto2000 Volume 64 Issue 6 Pages 481-482
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSFormation of athermal ω-phase crystals (ωath) in Ti-10, 15 and 20(mass%)Mo alloys cooled to 131 K was investigated using a TEM in-situ dark field imaging technique. The formation of ωath in Ti-15Mo and Ti-20Mo alloys was confirmed. The volume-fraction of ωath in the Ti-15Mo alloy was larger than that in the Ti-20Mo alloy. This result is the same trend as the increment of electrical resistivity in the negative temperature dependence region in a Ti-15Mo alloy is larger than that in a Ti-20Mo alloy. It seems that in the Ti-10Mo alloy, the formation of ωath was not observed.View full abstractDownload PDF (321K)
- |<
- <
- 1
- >
- >|