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排序方式: 共有540条查询结果,搜索用时 31 毫秒
521.
Frans P. van der Meer Carlos G. Dávila 《International Journal of Solids and Structures》2013,50(20-21):3308-3318
This study aims to bridge the gap between classical understanding of transverse cracking in cross-ply laminates and recent computational methods for the modeling of progressive laminate failure. Specifically, the study investigates under what conditions a finite element model with cohesive X-FEM cracks can reproduce the in situ effect for the ply strength. It is shown that it is possible to do so with a single element across the thickness of the ply, provided that the interface stiffness is properly selected. The optimal value for this interface stiffness is derived with an analytical shear lag model. It is also shown that, when the appropriate statistical variation of properties has been applied, models with a single element through the thickness of a ply can predict the density of transverse matrix cracks. 相似文献
522.
523.
524.
为系统研究粉煤灰、吸水保水剂(SAP)对喷射混凝土早龄期开裂损伤的影响,以掺入了粉煤灰、SAP的喷射混凝土为研究对象,对喷射混凝土的早龄期开裂损伤进行平板法试验研究。完成了各种试件的早龄期开裂损伤测试,研究了粉煤灰对喷射混凝土以及SAP对掺入20%粉煤灰喷射混凝土的早龄期开裂损伤的改善作用。试验结果表明,掺粉煤灰等量取代10%、20%水泥后,喷射混凝土的早龄期开裂损伤与基准喷射混凝土相比分别减小约7.2%和26.8%。掺0.25%SAP和0.5%SAP可以使20%粉煤灰掺量喷射混凝土的早龄期开裂损伤与基准喷射混凝土相比分别减小约57.9%和66.50%。因此,掺粉煤灰可有效地降低喷射混凝土早龄期开裂损伤,且在掺加粉煤灰的基础上再掺加适量的SAP效果会更佳。 相似文献
525.
采用DFT和MP2方法对1,1,2,2-四甲基-1,2-二氯二硅烷的催化裂解机理进行了研究. 结果表明, 催化剂三氯化铝先与二硅烷反应, 生成中间产物后再与裂解气三氯甲烷作用并生成产物. 反应分3步进行, 各步活化能分别为: 152.543, 79.322和128.889 kJ•mol-1. 速控步为第一步反应, 3步的焓变分别为: 83.785, -275.771和-120.712 kJ•mol-1, 总焓变为-312.698 kJ•mol-1, 即为放热的. 反应的标准摩尔吉布斯自由能为-306.462 kJ•mol-1, 裂解反应的平衡常数 =4.9295×1053, 在常温常压下反应的理论产率较高, 与实验结果一致. 相似文献
526.
The stiffness reduction in [S, 90
n
]
s
laminates due to transverse cracking in 90-layers is analyzed using the synergistic continuum damage mechanics (SCDM) and a micromechanics approach. The material constants involved in the SCDM model are determined using the stiffness reduction data for a reference cross-ply laminate. The constraint efficiency factor, which depends on the stiffness and geometry of neighboring layers, is assumed to be proportional to the average crack opening displacement (COD). The COD as a function of the constraint effect of adjacent layers and crack spacing is described by a simple power law. The crack closure technique and Monte Carlo simulations are used to model the damage evolution: the 90-layer is divided into a large number of elements and the critical strain energy rate G
c having the Weibull distribution is randomly assigned to each element. The crack density data for a [02/904]
s
cross-ply laminate are used to determine the Weibull parameters. The simulated crack density curves are combined with the CDM stiffness reduction predictions to obtain the stiffness versus strain. The methodology developed is successfully used to predict the stiffness reduction as a function of crack density in [±/904]
s
laminates. 相似文献
527.
A. Guarino A. Garcimartín S. Ciliberto 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(1):13-24
The statistical properties and the localization of fracture precursors on heteregeneous materials is studied by recording
their acoustic emission as a function of the applied load. It's found that the microcrack cluster together as the load increases
and the instantaneous acoustic energy has an invariant power law distribution. The integrated acoustic energy presents a critical
divergency close to the failure load for the sample. These result support the idea that fracture can be viewed as a critical
phenomenon. Finally a measure of the concentration of microcraks, which allows us to predict the failure load, is introduced.
These properties are studied also when a periodic load is applied to the sample. It's found that the Kaiser effect is not
strictly satisfied in heteregeneous materials.
Received: 23 January 1998 / Revised: 20 April 1998 / Accepted: 17 June 1998 相似文献
528.
重油裂解反应器内多相流动分析吴邦贤(中国科学院工程热物理研究所北京100080)关键词重油裂解,多相流,直升反应器通过重油裂解反应生产轻油已成为现代炼油业中的关键转换过程。在重油裂解反应器内同时存在众多的物理,化学,流动过程,其中包括:重油液滴雾化,... 相似文献
529.
The criterion for occurrence of intergranular fatigue cracking in copper has been investigated from the view point of both the grain boundary (GB) character and the cyclic deformation property of constituent grains. The copper bicrystals were prepared to have several orientation relationships close to 3(1 1 1) coherent twin (3 vicinal domain) so as to change the GB character rapidly with increasing deviation angles || from the 3 relation. These bicrystals were shaped to single-edge-notched specimens in which a GB plane was perpendicular to the tensile axis. The fatigue crack propagation tests were carried out in air at room temperature. The specimens having deviation angles || less than 3° involved no intergranular fatigue cracking. When the || values were ranged from 3° to 5°, the ratio of the intergranular cracking increased. In the specimens having the || values more than 9°, the intragranular cracking became predominate again. The increase in the intergranular cracking with increasing deviation angle at the || values less than 5° could be understood in terms of the increasing GB susceptibility to the GB damage due to air environment. On the other hand, the intragranular cracking at the || values more than 9° could be attributed to the formation of the persistent slip bands in the constituent grains and subsequent crack propagation preferentially along them. 相似文献
530.
Jianyu Wang Pusheng Liu Mercedes Boronat Pau Ferri Zhaoguo Xu Peng Liu Baojian Shen Zhendong Wang Jihong Yu 《Angewandte Chemie (International ed. in English)》2020,59(39):17225-17228
Zeolite Y, with a high SiO2/Al2O3 ratio (SAR), plays an important role in fluidized catalytic cracking processes. However, in situ synthesis of zeolite Y with high SARs remains a challenge because of kinetic limitations. Here, zeolite Y with an SAR of 6.35 is synthesized by a hydroxyl radical assisted route. Density‐functional theory (DFT) calculations suggest that hydroxyl radicals preferentially enhanced the formation of Si‐O‐Si bonds, thus leading to an increased SAR. To further increase the SAR, a dealumination process was carried out using citric acid, with a subsequent second‐step hydrothermal crystallization, giving an SAR of up to 7.5 while maintaining good crystallinity and high product yield. The resultant zeolite Y shows good performance in cumene cracking. Introduced here is a new strategy for synthesizing high SAR zeolite Y, which is widely used in commercial applications. 相似文献