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91.
92.
Wrinkling is a well known phenomenon experimented by tension membranes in Civil Engineering applications. This paper will
present an efficient numerical technique for the computational simulation of such wrinkles in a prestressed membrane. In particular,
the relaxed energy approach (Pipkin in IMA J Appl Math 36:85–99, 1986) is particularized for prestressed membranes (Gil in
Textile composites and inflatable structures, CIMNE, 2003) undergoing moderate strains. Wrinkling conditions in terms of the
Euler-Lagrange finite deformation tensor along principal directions will be obtained. This will provide a framework to describe
properly the initial instant when wrinkles start to be encountered in a prestressed Saint Venant–Kirchhoff hyperelastic membrane.
Subsequently, a modified Helmholtz’s free energy functional will be introduced with the purpose of describing the modified
constitutive behaviour of the continuum after the onset of wrinkling. Consistent derivations of the stress tensor as well
as the constitutive tensor will de depicted. The results will be particularized for membranes and cables in a Finite Element
discretization basis. Some numerical examples will prove the accuracy and robustness of the described algorithm. 相似文献
93.
A novel approach to the derivation of Bažant’s size effect law is presented. Contrarily to the original Lagrangian derivation
which hinged on energetic consideration, a Newtonian approach based on local stress intensity factors is presented. Through
this approach, it is shown that Bažant’s size effect law is the first (and dominant) term in a series expansion for the nominal
stress. Furthermore, analytical expressions forB are derived for selected specimen geometries. 相似文献
94.
文章较全面的介绍了如何根据设备、装置、构件所处的工作环境及使用条件进行防腐蚀设计,及其防腐蚀设计的内容和注意事项,选择合适的防腐蚀材料,确保产品的使用寿命 相似文献
95.
96.
N. F. Kuschevskaya A. E. Kushchevskii A. I. Oleshko 《Powder Metallurgy and Metal Ceramics》2006,45(3-4):202-206
The possibility of utilizing nanopowders of iron and Fe-Co-Ni produced bu a thermochemical method in the fabrication of sealing
composition materials is investigated. It is established that such hermetic sealing composition materials function reliably
under extremal conditions and guarantee elevated strength of adhesion to the surface of the metal and high corrosion and temperature
stability.
__________
Translated from Poroshkaya Metallurgiya, Nos. 3–4(448), pp. 112–117, March–April, 2006. 相似文献
97.
Influence of Storage Time and Temperature on Absorption of Flavor Compounds from Solutions by Plastic Packaging Materials 总被引:1,自引:0,他引:1
R. Van Willige D. Schoolmeester A. Van Ooij J. Linssen A. Voragen 《Journal of food science》2002,67(6):2023-2031
ABSTRACT: Linear low-density polyethylene (LLDPE), oriented polypropylene (OPP), polycarbonate (PC), polyethylene terephthalate (PET film and PET bottle), and polyethylene naphthalate (PEN) were stored in a model solution containing 10 flavor compounds at 4, 20, and 40 °C and flavor absorption by the plastic materials was followed in time. The absorption rate and/or total amount absorbed increased considerably with temperature from 4 to 40 °C. Depending on storage temperature, total flavor absorption by the polyolefins (LLDPE and OPP) was 3 to 2400 times higher than by the polyesters (PC, PET, and PEN). Therefore, in the factor of flavor absorption, polyesters are preferred over polyolefins as packaging material. 相似文献
98.
蒸馏与减粘热联合装置的设备腐蚀及防护 总被引:4,自引:2,他引:2
介绍了锦西石化分公司南蒸馏与减粘热联合装置炼制辽河高酸值原油及带炼高硫进口油在 2 0 0~40 0℃范围内对设备、管线和阀门的腐蚀特点、腐蚀机理以及针对高温环烷酸腐蚀所采取的防护措施。通过试验和理论分析 ,提出了应用新材料和新工艺解决减粘后高温渣油系统的腐蚀及低温露点腐蚀的建议 相似文献
99.
Nuclear magnetic resonance (n.m.r.) studies of 19F nuclei in a random copolymer of vinylidene fluoride and trifluoroethylene were performed at 9.14 MHz and 20.0 MHz. The free induction decays (FIDs) were analysed in terms of two T2 components attributed to the amorphous and crystalline portions of the polymer. The changes in crystallinity as well as the effects of the ferroelectric transition were observed during cycles of heating and cooling between 20°C and 140°C. The crystalline component of the FID lengthens by a factor of 2 at 100°C on heating and decreases by this factor at 60°C on cooling, thus exhibiting the thermal hysteresis of this ferroelectric transition. The spin-lattice relaxation was also investigated. From measurements at 9.14 MHz the observed longitudinal relaxation time T1 appears to be dominated by the dynamics of the amorphous phase and exhibits no anomaly through the phase transition. However, from measurements at 20 MHz, well defined minima of T1 were observed, which are associated with the ferroelectric transition (especially after repeated annealing of the samples). Results are discussed in terms of the crystalline phase structure, which appears dynamically disordered above the ferroelectric phase transition. An analogy is considered with the plastic phase transitions encountered in molecular crystals. 相似文献
100.