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11.
WADOOD Y. HAMAD 《Cellulose (London, England)》1997,4(1):51-56
Wood-pulp fibres are recognized as concentrically-layered, laminated composite tubes of structural reinforcing material, the
cellulose microfibrils, embedded in a cementing matrix of hemicellulose and lignin. When the single fibres are subjected to
cyclic mechanical action, their morphological behaviour is characterized by the fatigue growth of micro-voids and surface
damage which individually and collectively give rise to stress concentrations, and eventually crack development. The progressive
damage phenomena, evinced by the surface imaging and optical sectioning techniques through utilizing confocal laser scanning
microscopy, are understood to be consequences of the cumulative material micromechanical degradation and subsequent microstructural
breakdown of the cellulose microfibrillar framework. This structural breakdown is believed to effect the fibrillation and
flexibilization of the fibres
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
Hong-yu Li Zhi-qiang Chen Hai-qiao Wang Bo Meng Xiao-yu Li 《高分子科学》2007,(2):217-220
Ordered macroporous titania photonic crystals (PCs) and photonic balls were fabricated by functional modified polymer colloidal crystals. The TiO2 PCs and balls formed through this method exhibit no cracks and lacunae in large areas on their surface and their inner structures. 相似文献
13.
Fatigue damage behavior of a surface-mount electronic package under different cyclic applied loads 下载免费PDF全文
This paper studies and compares the effects of pull-pull and 3-point bending cyclic loadings on the mechanical fa- tigue damage behaviors of a solder joint in a surface-mount electronic package. The comparisons are based on experimental investigations using scanning electron microscopy (SEM) in-situ technology and nonlinear finite element modeling, respec- tively. The compared results indicate that there are different threshold levels of plastic strain for the initial damage of solder joints under two cyclic applied loads; meanwhile, fatigue crack initiation occurs at different locations, and the accumulation of equivalent plastic strain determines the trend and direction of fatigue crack propagation. In addition, simulation results of the fatigue damage process of solder joints considering a constitutive model of damage initiation criteria for ductile materials and damage evolution based on accumulating inelastic hysteresis energy are identical to the experimental results. The actual fatigue life of the solder joint is almost the same and demonstrates that the FE modeling used in this study can provide an accurate prediction of solder joint fatigue failure. 相似文献
14.
Dr. Ning Chen Dr. Yanglin Shen Dr. Ting Xu Dr. Wangqiang Shen Prof. Xing Lu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(65):16212-16218
Surface cracks could improve the optical and photoelectronic properties of crystalline materials as they increase specific surface area, but the controlled self-assembly of fullerene (C60) molecules into micro-/nanostructures with surface cracks is still challenging. Herein, we report the morphology engineering of novel C60 microstructures bearing surface cracks for the first time, selecting phenetole and propan-1-ol (NPA) as good and poor solvents, respectively. Our systematic investigations reveal that phenetole molecules initially participate in the formation of the ends of the C60 microstructures, and then NPA molecules are involved in the gradual growth of the sidewalls of the microstructures. Therefore, the surface cracks of C60 microstructures can be finely regulated by adjusting the addition of NPA and the crystallization time. Interestingly, the cracked C60 microstructures show superior photoluminescence properties relative to the smooth microstructures due to the increased specific surface area. In addition, C60 microstructures with wide cracks show preferential recognition of silica particles over C60 particles owing to electrostatic interactions between the negatively charged C60 microstructures and the positively charged silica microparticles. These C60 crystals with surface cracks have potential applications from optoelectronics to biology. 相似文献
15.
A. C. Lowe 《Molecular Crystals and Liquid Crystals》2013,570(1):295-308
An optimized configuration of the nematic guest-host effect is described in which a 90° twist cell is used. In order to assess the suitability of nematic guest-host systems for use in integrated displays in which a significant dc voltage may appear across the liquid crystal, several dye/host systems were tested with up to 1.5V dc superimposed on the normal 5V r.m.s. drive signal. Degradation was monitored by measurement of tilt, clearing point and absorbance. One system tested showed no significant degradation after 9 × 103 hr. Excellent correlation was observed between stability of a dye/host system in a driven display and the reversibility of the reduction of the dye in acetonitrile solution at a platinum electrode. 相似文献
16.
17.
论文针对中密度聚乙烯材料(MDPE),采用平板试样进行了I型疲劳裂纹扩展和单次过载下裂纹扩展试验.发现与金属材料类似,单次拉伸过载对聚乙烯(PE)的疲劳裂纹扩展有明显的迟滞作用,降低了裂纹扩展速率.试验还通过变载荷刻线法获取疲劳裂纹扩展前缘的实际形貌和变化规律,对常规变载荷刻线方法进行了调整和验证,其修正方法对高分子材料的疲劳裂纹扩展前缘刻线具有较好的效果.通过观察发现含楔形塑性区的裂尖钝化是裂纹迟滞的主要原因.过载引入的塑性区内残余应力对裂纹迟滞也起了重要作用.论文利用Dugdale模型计算了塑性区尺寸,使用基于残余应力的Wheeler模型对过载迟滞进行了很好的拟合. 相似文献
18.
Víctor Leiva 《商业与工业应用随机模型》2019,35(1):133-137
Sam C. Saunders, the son of Elizabeth Cundiff and Winston E. Saunders, was born in Richland, OR, on February 24, 1931. The family moved to La Grande, OR, in 1944, where Sam completed high school and two years at Eastern Oregon College. He then received the BSc degree in Mathematics from the University of Oregon, Eugene, OR, in 1952, and he attended the University of Washington, Seattle, WA, receiving a PhD degree under Z. W. Birnbaum. After graduating, he accepted employment at the Boeing Company in its Mathematical Services Unit and, in 1972, a position as a Full Professor at Washington State University, Pullman, WA, from which he retired in 1996. 相似文献
19.
Mahdi Azarnoosh Ali Motie Nasrabadi Mohammad Reza Mohammadi Mohammad Firoozabadi 《Complexity》2012,17(6):7-16
This study investigates the behavioral indices of attention. A simple repetitive attentive task that resulted in mental fatigue was used consecutively in four trials. In the first step, reaction time and error responses were recorded to evaluate differences among trials. During the task, subjects showed different responses to stimulations. In the second part, to recognize the strategies, multiple clustering methods such as k‐means and fuzzy c‐means were performed in which behavioral indices and nonlinear features were used. In the last section, mental behavior was identified as a result of the chaotic properties of variations in reaction time. Therefore, the Lyapunov exponent of reaction times was evaluated. Results revealed that behavioral indices could distinguish attention from the occurrence of mental fatigue in trials. In addition, the three strategies used by subjects during the test protocol were assessed. Finally, variation of indices extracted from nonlinear analysis, that is, decrease in degree of chaotic behavior determined the transition from attention to mental fatigue. © 2012 Wiley Periodicals, Inc. Complexity, 2012 相似文献
20.
In this contribution, an electron acceptor attached diarylethene derivative was synthesized and fully characterized. The photochromic behavior was investigated in THF. Under exposure of UV and visible light cycles, the solution color can be switched between colorless and yellow smoothly. Fatigue resistance measurements could be repeated 50 times with an acceptable degradation. Due to the electron acceptor attached to the framework of diarylethene, the photo- and thermal-stability were enhanced both. A full-photo mode switch can be established based on the well-defined states by external excitation. The molecular structures of ring-open and ring-closed form were optimized by Dmol3. The distance between photocyclizing atoms in aptiparallel conformation meets the requirement for photochromic reaction. And the calculated absorption wavelengths were also in agreement with the experimental values. 相似文献