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排序方式: 共有614条查询结果,搜索用时 15 毫秒
1.
Youngjean Jung Panayiotis Papadopoulos R. O. Ritchie 《International journal for numerical methods in engineering》2004,60(2):429-460
This work concerns the micromechanical constitutive modelling, algorithmic implementation and numerical simulation of polycrystalline superelastic alloys under multiaxial loading. The model is formulated in finite deformations and incorporates the effect of texture. The numerical implementation is based on the constrained minimization of the Helmholtz free energy with dissipation. Simulations are conducted for thin tubes of Nitinol under tension–torsion, as well as for a simplified model of a biomedical stent. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
2.
What has become known as Community Operational Research has been around in the UK for many years. The election of Jonathan Rosenhead as President of the UK OR Society in 1986–87 was the catalyst for bringing together and expanding activities which had been carried out largely by individuals working in isolation on a voluntary basis. The following five years have seen the establishment of the Community OR Unit at Northern College, the Centre for Community OR at Hull University and the Community OR Network, which supports the activities of volunteer OR workers across the UK. This paper reviews the range and types of work which have been undertaken by various practitioners. An assessment of the success of community OR is made and a number of issues which have arisen are discussed. Finally, given the diverse nature of community OR, its practice and practitioners, there is some discussion about the future of the area. 相似文献
3.
M. Ritchie P. D. Lee A. Mitchell S. L. Cockcroft T. Wang 《Metallurgical and Materials Transactions A》2003,34(3):863-877
An energy dispersive X-ray (EDX) detector mounted on a laboratory scale electron beam furnace (30 kW) was employed to assess
the potential use of X-rays as a means of on-line composition monitoring during electron beam (E B) melting of alloys. The
design and construction of the collimation and protection systems used for the EDX are described in Part I. In Part II, a
mathematical simulation of the heat, mass, and momentum transfer was performed for comparison to the EDX and vapor deposition
results. The predicted flow patterns and evaporation rates are used to explain the differences between the two experimental
methods. For the EDX spectra measured, the X-rays generated were from the center of the hearth where fluid flow rising from
the bulk of the pool is sufficient to maintain the bulk composition despite the high evaporative flux from the surface. The
flow moves radially outward from the center of the pool, with the volatile species being depleted. The vapor deposition technique
measures the entire region, giving an average surface composition, and it therefore differs from the EDX results, which gave
a near bulk composition. This combined study using in-situ EDX measurements and numerical simulations both provided an insight into the phenomena controlling the evaporation in an
EB-heated system and demonstrated the viability of using EDX to measure the bulk composition during EB melting processes. 相似文献
4.
5.
6.
K. T. Venkateswara Rao W. O. Soboyejo R. O. Ritchie 《Metallurgical and Materials Transactions A》1992,23(8):2249-2257
A study has been made of the role of ductile-phase toughening on the ambient temperature fracture toughness and fatigue-crack
propagation behavior of a molybdenum disilicide intermetallicmatrix composite reinforced with 20 vol pct niobium spheres.
Using disk-shaped compact DC(T) samples, only moderate improvements (∼24 pct) in fracture toughnessK
lcvalues were found for the composite compared to the unreinforced MoSi2 matrix material. Moreover, (cyclic) fatigue- crack propagation was seen at stress intensities as low as 75 to 90 pct ofK
Ic, with growth rates displaying a high dependency (∼14) on the applied stress-intensity range. The lack of significant toughening
due to the incorporation of ductile Nb particles is associated with an absence of crack/particle interactions. This is attributed
to the formation of a weak reaction-layer interface and elastic mismatch stresses at the crack tip between the Nb and MoSi2, both factors which favor interfacial debonding; moreover, the spherical morphology of Nb phase stabilizes cracking around
the particle. Results suggest that increasing the aspect ratio of the distributed Nb rein- forcement phase with attendant
interfacial debonding and eliminating possible Nb-phase em- brittlement due to interstitial impurity contamination are critical
factors for the successful development of tougher Nb/MoSi2 structural composites.
Formerly with McDonnell
Formerly with McDonnell 相似文献
7.
8.
Ingram S.G. Linfield E.H. Brown K.M. Jones G.A.C. Ritchie D.A. Kelly M.J. 《Electron Devices, IEEE Transactions on》1995,42(6):1065-1069
A vertical hot electron transistor incorporating a two-dimensional electron gas (2DEG) base has been fabricated in the GaAs-AlGaAs materials system. The difficulties caused by the need to form selective ohmic contacts to the different conducting layers have been overcome using a combination of in situ focused ion beam (FIB) isolation and molecular beam epitaxial (MBE) regrowth. This has allowed a high yield of working devices to be achieved with a typical common emitter current gain of hFE=6 at low temperatures 相似文献
9.
When fibrillation occurs during peeling, the normal stress in the adhesive may gradually reduce to zero at the peel front. The shear stress also reduces to zero. Classical beam-spring (or beam-on-elastic-foundation) models do not yield solutions that have these properties. With the use of a beam-on-foundation model combined with a cohesive zone in the neighborhood of the peel front, these properties can be satisfied. In order to obtain analytical solutions, peel tests are considered in which the backing has a small slope and is linearly elastic in the adhered region, and the traction law is assumed to be piecewise linear. Cases are considered with only normal stresses in the adhesive (mode I), only shear stresses (mode II), and both stresses coupled (mixed-mode behavior). Analytical solutions are obtained for displacements of the backing, forces in the backing, and stresses between the adhesive and the backing. 相似文献
10.
The morphology and composition of the oxide film formed under various oxidation conditions on a 1.2% aluminum-magnesium alloy have been studied using electron microscopy and diffraction. Below 350° C the oxide film formed is highly protective and amorphous, while above this temperature the oxide becomes nonprotective. Initially, at temperatures above 350°C, the oxide film consists of only alumina, then with increasing time it contains first MgO, then MgO together with MgAl2O4, and finally it is entirely converted to MgAl2O4. 相似文献