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91.
A three-dimensional FE analysis of large deformations for impact loadings using tetrahedral elements
A three-dimensional dynamic program for the anaysis of large deformations in contact-penetration problems is developed using
the finite element Lagrangian method with explicit time integration. By incorporating a tetrahedral element, which allows
a single-point integration without a special hourglass control scheme, this program can be more effective to the present problem.
The position code algorithm is used to search contact surface. Eroding surfaces are also considered. The defense node algorithm
was slightly modified for the calculation of contact forces. A study of obliquity effects on metallic plate perforation and
ricochet processes in thin plates impacted by a sphere was conducted. It is well simulated that on separation of two parts
of the sphere, the portion still within the crater tends to perforate, while the portion in contact with the plate surface
ricochets. This deformation pattern is observed in experiments, especially at high obliquities. A long rod that impacts an
oblique steel plate at high impact velocity was also simulated in order to study the dynamics of the rod caused by the three
dimensional asymmetric contact. The agreement between simulated and experimental results is quite good. Fracture phenomena
occuring at high obliquity deserves further investigations.
Received: 20 February 2002 / Accepted: 20 September 2002 相似文献
92.
To determine three‐dimensional fiber orientation states in injection‐molded short‐fiber composites, a confocal laser scanning microscope (CLSM) is used. Since the CLSM optically sections the specimen, more than two images of the cross sections on and below the surface of the composite can be obtained. Three‐dimensional fiber orientation states can be determined by using geometric parameters of fiber images obtained from two parallel cross sections. For experiments, carbon‐fiber‐reinforced polystyrene is examined by the CLSM and geometric parameters of fibers on each cross‐sectional plane are measured by an image analysis. In order to describe fiber orientation states compactly, orientation tensors are determined at different positions of the prepared specimen. Three‐dimensional orientation states are obtained without any difficulty by determining the out‐of‐plane angles utilizing fiber images on two parallel planes acquired by the CLSM. Orientation states are different at different positions and show the shell–core structure along the thickness of the specimen. Fiber orientation tensors are predicted by a numerical analysis and the numerically predicted orientation states show good agreement with measured ones. However, some differences are found at the end of cavity. They may result from the fountain flow effects, which are not considered in the numerical analysis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 500–509, 2003 相似文献
93.
Dong-Soo Yoon Jae Sung Roh Sung-Man Lee Hong Koo Baik 《Journal of Electronic Materials》2003,32(8):890-898
The effect of a thin RuOx layer formed on the Ru/TiN/doped poly-Si/Si stack structure was compared with that on the RuOx/TiN/doped poly-Si/Si stack structure over the post-deposition annealing temperature ranges of 450–600°C. The Ru/TiN/poly-Si/Si
contact system exhibited linear behavior at forward bias with a small increase in the total resistance up to 600°C. The RuOx/TiN/poly-Si/Si contact system exhibited nonlinear characteristics under forward bias at 450°C, which is attributed to no
formation of a thin RuOx layer at the RuOx surface and porous-amorphous microstructure. In the former case, the addition of oxygen at the surface layer of the Ru film
by pre-annealing leads to the formation of a thin RuOx layer and chemically strong Ru-O bonds. This results from the retardation of oxygen diffusion caused by the discontinuity
of diffusion paths. In particular, the RuOx layer in a nonstoichiometric state is changed to the RuO2-crystalline phase in a stoichiometric state after post-deposition annealing; this phase can act as an oxygen-capture layer.
Therefore, it appears that the electrical properties of the Ru/TiN/poly-Si/Si contact system are better than those of the
RuOx/TiN/poly-Si/Si contact system. 相似文献
94.
As packet cellular networks are expected to support multimedia services, the authors incorporate the multimedia QoS requirements into the design of a new scheduling algorithm. The proposed wireless-adaptive fair scheduling tries to allocate time slots for each user with fair share by considering the varying channel condition while reflecting the stream requirements and achieving high throughput. 相似文献
95.
Baeyens Y. Georgiou G. Weiner J.S. Leven A. Houtsma V. Paschke P. Lee Q. Kopf R.F. Yang Yang Chua L. Chen C. Liu C.T. Young-Kai Chen 《Solid-State Circuits, IEEE Journal of》2002,37(9):1152-1159
The combination of device speed (f/sub T/, f/sub max/ > 150 GHz) and breakdown voltage (V/sub bceo/ > 8 V) makes the double heterojunction bipolar InP-based transistor (D-HBT) an attractive technology to implement the most demanding analog functions of 40-Gb/s transceivers. This is illustrated by the performance of a number of analog circuits realized in an InP D-HBT technology with an 1.2- or 1.6-/spl mu/m-wide emitter finger: a low phase noise push-push voltage-controlled oscillator with -7-dBm output power at 146 GHz, a 40-GHz bandwidth and low-jitter 40-Gb/s limiting amplifier, a lumped 40-Gb/s limiting driver amplifier with 4.5-V/sub pp/ differential output swing, a distributed 40-Gb/s driver amplifier with 6-V/sub pp/ differential output swing, and a number of distributed preamplifiers with up to 1.3-THz gain-bandwidth product. 相似文献
96.
K. P. Lee S. J. Pearton M. E. Overberg C. R. Abernathy R. G. Wilson S. N. G. Chu N. Theodoropolou A. F. Hebard J. M. Zavada 《Journal of Electronic Materials》2002,31(5):411-415
In p-GaN implanted with Mn (3×1016 cm−2 at 250 keV), the material after annealing shows ferromagnetic properties below 250 K. Cross-sectional transmission electron
microscopy (TEM) revealed the presence of platelet structures with hexagonal symmetry. These regions are most likely GaxMn1−xN, which produce the ferromagnetic contribution to the magnetization. In p-GaN implanted with Fe, the material after annealing
showed ferromagnetic properties at temperatures that were dependent on the Fe dose, but were below 200 K in all cases. In
these samples, TEM and diffraction analysis did not reveal any secondary phase formation. The results for the Fe implantation
are similar to those reported for Fe doping during epitaxial growth of GaN. 相似文献
97.
Chel-Jong Choi Tae-Yeon Seong Key-Min Lee Joo-Hyoung Lee Young-Jin Park Hi-Deok Lee 《Electron Device Letters, IEEE》2002,23(4):188-190
The leakage mechanism in p+/n shallow junctions fabricated using Co silicidation and shallow trench isolation processes has been investigated using transmission electron microscopy (TEM) combined with selective chemical etching. TEM and TSUPREM-4 simulation results show that dopant profiles bend upward near the edge of the active region. The formation of the abnormal profile is attributed to transient enhanced diffusion induced by source/drain implantation. Based on the TEM and simulation results, it is suggested that the shallower junctions formed near the active edge can serve as a source for leakage current in the silicided p+ /n shallow junctions 相似文献
98.
Ki Yong Lee Souhwan Jung 《Electronics letters》1998,34(16):1567-1568
The authors investigate the problem of nonlinear adaptive equalisation in the presence of intersymbol interference, additive white Gaussian noise and co-channel interference. An extended radial basis function (RBF) network is proposed, in which regression weights are used in the output layer and the hidden unit is defined to have the Gaussian formula with the Mahalanobis distance. It is shown by simulation that the proposed structure gives reduced computational complexity without performance degradation, compared to that of the conventional RBF equaliser 相似文献
99.
Robust backward adaptive formant prediction for speech coder 总被引:1,自引:0,他引:1
To improve the error performance of speech coders, an adaptation method for the backward adapted formant predictor is proposed. The filtered residual signal is used instead of the reconstructed output signal as the input to an adaptation of the formant predictor. The performance of the filtered-residual driven adaption method in the noise free channel is as good as that of conventional output driven adaptation. Moreover, the new adaptation method maintains the same robustness to channel errors as residual driven adaptation 相似文献
100.