This paper proposes models to describe a non-linear unloading-reloading stress-strain response and closure of a cyclic stress-strain hysteresis loop based on the Yoshida-Uemori (Y-U) model. The ...average stress-strain slope given by the non-linear model is consistent with the Y-U model of Young's modulus degradation. The closure of a cyclic stress-strain curve is described by automatically changing one of the Y-U material parameters. An advantage of the above approaches is that no additional parameters are needed for modeling.
•The draw-bent sheet hardness at the surface is larger than that at the mid-plane.•The martensitic transformation differs between draw-bending and uniaxial tension.•The flow stress in a reverse ...deformation is remarkably the Bauschinger effect.•The martensitic transformation is given as a unique function of the effective stress.
Deformation-induced martensitic transformation and workhardening behavior in draw bending process was investigated, on a Type 304 stainless steel sheet, in comparison with that in uniaxial tension experiments. The Vickers hardness of the draw-bent sheet at the surface is much larger than that at the mid-plane, and it becomes remarkably larger with increasing blank holder force. The significant increase of hardness in the deformed sheet is due to α′-martensitic transformation. The volume fraction of α′-martensite in the draw-bent sheet is smaller than that in the uniaxially pulled sheet with the same plastic strain. In uniaxial tension the sheet is plastically deformed in one direction monotonically, but in contrast, in draw-bending tension-to-compression (i.e., bending-to-unbending) deformation takes place when the sheet is drawn over the die-corner. The difference in the evolution of the martensite between draw-bending and uniaxial tension is explained from such a difference in deformation mode. Under cyclic deformation, in the reverse deformation, the martensitic transformation stagnates in a certain extent of plastic strain because of the Bauschinger effect. Including such a case of stress reversal, the evolution of the martensitic transformation is given as a unique function of the effective stress, rather than the effective plastic strain. Thus the behavior of the martensitic transformation of the material during plastic deformation would be understood from the stress-induced phase transformation mechanism.
This paper presents a framework of constitutive modeling of large-strain cyclic plasticity which describes both the deformation- and texture-induced anisotropies of materials. In this model, the ...transient Bauschinger effect is described accurately by a new equation of the backstress evolution, and the strain-range and mean-strain dependencies of cyclic strain hardening are expressed by a model of workhardening stagnation. For the description of texture-induced anisotropy, any of widely accepted yield criteria of orthotropic anisotropy is easily incorporated into this model. This paper demonstrates the advantage of the present model in the springback analysis over other classical models by comparing the FE simulations of draw bending with the corresponding experimental results.
This paper deals with bending and springback phenomena of a stainless-steel clad aluminum sheet in V-shaped air bending. The aim of this study is to investigate the bending characteristics such as ...sheet thickness change and the bending angles of the sheet before/after springback. The first part of this paper is on the experimental observations. V-bending experiments were performed for both the cases of Al
in/SS
out (i.e., aluminum layer is located inside the bent clad) and SS
in/Al
out (i.e., stainless-steel layer is located inside the bent clad). From these results, it was found that the sheet-set condition (either Al
in/SS
out or SS
in/Al
out) has a great influence on the bending phenomena. In the second part, the accurate prediction of springback by FE analysis, especially the role of elasto-plasticity models, is discussed. When using Yoshida–Uemori kinematic hardening model (F. Yoshida, T. Uemori, Int. J. Plasticity 18, 2002; Int. J. Mech. Sci., 45, 2003), which well describes the Bauschinger effect of materials, the springback of the clad sheet is accurately calculated, whereas the classical isotropic hardening model underestimates the springback.
Context. The near-Earth asteroid 3200 Phaethon (1983 TB) is an attractive object not only from a scientific viewpoint but also because of JAXA’s DESTINY+ target. The rotational lightcurve and spin ...properties were investigated based on the data obtained in the ground-based observation campaign of Phaethon. Aims. We aim to refine the lightcurves and shape model of Phaethon using all available lightcurve datasets obtained via optical observation, as well as our time-series observation data from the 2017 apparition. Methods. Using eight 12-m telescopes and an optical imager, we acquired the optical lightcurves and derived the spin parameters of Phaethon. We applied the lightcurve inversion method and SAGE algorithm to deduce the convex and non-convex shape model and pole orientations. Results. We analysed the optical lightcurve of Phaethon and derived a synodic and a sidereal rotational periods of 3.6039 h, with an axis ratio of a∕b = 1.07. The ecliptic longitude (λp) and latitude (βp) of the pole orientation were determined as (308°, −52°) and (322°, −40°) via two independent methods. A non-convex model from the SAGE method, which exhibits a concavity feature, is also presented.
We detected 51 faint Jovian Trojan asteroids in the L4 Lagrangian swarm in survey observations near opposition and the ecliptic using a wide-field mosaicked CCD camera on the 8.2 m Subaru Telescope. ...We report the Trojan size distributions in this paper. The surveyed sky area was about 3 deg2 and located ~30° in longitude ahead of the L4 point. From trailed-image simulations of hypothetical Trojans, we measured the 90% complete detection limiting magnitudes for our Trojan asteroids on a CCD chip-by-chip basis. The limiting magnitudes varied by 0.4-0.5 mag between chips; therefore, we introduce a new measure of detection limit appropriate for multichip CCD cameras. By statistically comparing the observed number of Trojans with the predictions from theoretical size distributions near the limiting magnitude calculated in this way, we determined a limiting diameter of D ~ 2 km, corresponding to the detection limit of this survey. On the other hand, the detected Trojans covered a size range of 0.7 km < D < 12.3 km (with an assumed albedo of 0.04 for each object, which is the mean value of known Trojans thus far). Hence, we discuss the size distribution of the observed Trojans in the size range of 2 km < D < 10 km. For this entire range, we found the mean slope of the cumulative size distribution, namely, the power-law distribution index, to be 1.9 ± 0.1; this value is consistent with the 2000 estimate by Jewitt and coworkers. However, we noted a slight change in the slope of the cumulative size distribution at D ~ 5 km. Therefore, we obtained separately fitted slopes for the size ranges of 2 km <= D < 5 km and 5 km < D <= 10 km of 1.3 ± 0.1 and 2.4 ± 0.1, respectively. This break in the slope of the size distribution has also been seen in the size distribution of kilometer to subkilometer main-belt asteroids (Yoshida and coworkers), and so we compared the size distributions of the two populations. Based on the surface distribution model of L4 Trojans proposed by Jewitt and coworkers, we estimated the total number of L4 Trojans with D > 1 km. Finally, we discuss, from a cosmogonic viewpoint, a possible relation between Trojans and short-period comets on the basis of their size distribution slopes.
Since February, 2001, we have been conducting a series of survey observations to investigate the physical property of very small Main Belt Asteroids (sub-km MBAs) using the Subaru prime-focus camera ...(Suprime-Cam) attached to the 8.2
m Subaru telescope. We call our surveys “SMBAS: Subaru Main-Belt Asteroids Survey”. This paper presents the results of the second SMBAS (SMBAS-II) which was performed in October 2001. In SMBAS-II,
a
∼
4.0
deg
2
sky area near the opposition and near the ecliptic was surveyed with the
R- and
B-bands. We detected 1838 moving objects up to
R
∼
25
mag
. In SMBAS-II, we could not determine the exact orbits of the objects, because of the short observational arc of only
∼
40
min
. Instead, we statistically estimated the semi-major axis (
a) of each moving object from its apparent sky-motion vector assuming its circular orbit and then, we used the
a's to select MBAs and to estimate their absolute magnitudes (
H). The limiting magnitude of SMBAS-II for MBAs was
R
∼
24.2
mag. It corresponds to
H
∼
20
mag at the outer edge of main belt. Thus, assuming their mean albedos, down to
D
∼
0.3
km of S-type asteroids and 0.6 km of C-type asteroids were detected in SMBAS-II.
We found that the slopes (
b) of the cumulative size distribution (CSD) (i.e.
N
(
>
D
)
∝
D
-
b
,
D: diameter) for sub-km MBAs ranging from 0.6 to 1
km in diameter is
1.29
±
0.02
. Our
b value (1.29) is much shallower than those (
∼
1.8) of the Palomer Leiden Survey (PLS) van Houten, C.J., van Houten, G.I., Herget, P., Gehrels, T., 1970. The Palomar-Leiden survey of faint minor planets. Astr. Astrophys. Suppl. 2, 339–448 and Spacewatch surveys Jedicke, R., Metcalfe, T.S., 1998. The orbital and absolute magnitude distributions of main belt asteroids. Icarus 131, 245–260. for larger asteroids (
D
>
5
km) and almost consistent with that (1.3) of SDSS Ivezić, Ž., Tabachnik, S., Rafikov, R., Lupton, R.H., Quinn, T., Hammergren, M., Eyer, L., Chu, J., Armstrong, J.C., Fan, X., Finlator, K., Geballe, T.R., Gunn, J.E., Hennessy, G.S., Knapp, G.R., Leggett, S.K., Munn, J.A., Pier, J.R., Rockosi, C.M., Schneider, D.P., Strauss, M.A., Yanny, B., Brinkmann, J., Csabai, I., Hindsley, R.B., Kent, S., Lamb, D.Q., Margon, B., McKay, T.A., Smith, J.A., Waddel, P., York, D.G. (for the SDSS Collaboration), 2001. Solar system objects observed in the Sloan Digital Sky Survey commissioning data. Astron. J. 122, 2749–2784 for MBAs with 0.4
km
<
D
<
5
km. This means that the number of sub-km MBAs is much more depleted than the result extrapolated from the size distribution for larger asteroids. This shallow slope of sub-km MBAs has been obtained from our first SMBAS (SMBAS-I) (
b
=
1.19
±
0.02
) which was carried out in February 2001 Yoshida, F., Nakamura, T., Watanabe, J., Kinoshita, D., Yamamoto, N., Fuse, T., 2003. Size and spatial distributions of sub-km main-belt asteroids. Publ. Astron. Soc. Jpn. 55, 701–715.
We examined taxonomic distribution of sub-km MBAs. Although we could not exactly distinguish S-type and C-type asteroids only using the
R and
B-magnitude, we divided SMBAS-II MBAs into two groups: S-like asteroids (rocky) and C-like asteroids (carbonaceous). The heliocentric distribution of S-like MBAs was almost flat throughout the entire main belt, while that of C-like MBAs shows an asymmetric distribution, namely, the number of C-like asteroids increases with the heliocentric distance. The number ratio of S- and C-like MBAs with
D
>
0.6 km was 1:1 in the inner belt (2.0
AU
<
a
<
2.6
AU), 1:2.3 in the middle belt (2.6
AU
<
a
<
3.0
AU), and 1:4 in the outer belt (3.0
AU
<
a
<
3.5
AU), respectively. For the entire main belt, the ratio was 1:2.3.
Because of its fast metabolism gadolinium as a commercial drug was not considered to be suitable for neutron capture therapy. We studied additive effect of gadolinium and boron co-administration ...using colony forming assay. As a result, the survival of tumor cells with additional 5ppm of Gd-DTPA decreased to 1/10 compared to the cells with boron only. Using gadolinium to increase the effect of BNCT instead of additional X-ray irradiation might be beneficial, as such combination complies with the short-time irradiation regimen at the accelerator-based neutron source.
•Gd-DTPA is widely clinically used as a contrast medium for MRI.•Shift to an accelerator-based neutron source is advantageous for gadolinium NCT.•Boron–gadolinium NCT effects on tumor cell lines were significant.•Additional administration of Gd-DTPA might enhance the effect of BPA–BNCT.
Abstract The local strength of pathological synchronization in the region of the subthalamic nucleus (STN) is emerging as a possible factor in the motor impairment of Parkinson's Disease (PD). In ...particular, correlations have been repeatedly demonstrated between treatment-induced suppressions of local oscillatory activity in the beta frequency band and improvements in motor performance. However, a mechanistic role for beta activity is brought into question by the difficulty in showing a correlation between such activity at rest and the motor deficit in patients withdrawn from medication. Here we recorded local field potential (LFP) activity from 36 subthalamic regions in 18 patients undergoing functional neurosurgery for the treatment of PD. We recorded directly from the contacts of the deep brain stimulation (DBS) electrodes as they were introduced in successive 2 mm steps, and assessed phase coherence as a measure of spatially extended, rather than local, oscillatory synchronization. We found that phase coherence in the beta frequency band correlated with the severity of Parkinsonian bradykinesia and rigidity, both in the limbs and axial body. Such correlations were frequency and site specific in so far as they were reduced when the lowermost contact of the DBS electrode was above the dorsal STN. Correlations with limb tremor occurred at sub-beta band frequencies and were more lateralized than those between beta activity and limb bradykinesia and rigidity. Phase coherence could account for up to ∼25% of the variance in motor scores between sides and patients. These new data suggest that the strength of spatially extended oscillatory synchronization, as well as the strength of local synchronization, may be worthwhile incorporating into modelling studies designed to inform surgical targeting, post-operative stimulation parameter selection and closed-loop stimulation regimes in PD. In addition, they strengthen the link between pathological synchronization and the different motor features of Parkinsonism.
The deep drawability of tailored blanks (TBs) composed of thick and thin sheets is considerably lower than that of their component sheets, since the plane-strain stretching mode is more likely to ...occur in such TBs as a result of the movement of the weld line at the bottom of the cup during forming. To improve the deep drawability of TBs, a new forming technology using a counterpunch is proposed, where the movement of the weld line during forming is strongly constrained by the counterpunch pressure. From the results of square-cup drawing experiments on several types of TB of mild steel/high-strength steel sheets, it was found that the limiting cup height increases markedly with increasing counterpunch pressure. One good feature of this forming technology is that the action of counterpunch pressure is necessary only on the thicker (or stronger) sheet part, not on the entire cup bottom.
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