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排序方式: 共有694条查询结果,搜索用时 15 毫秒
91.
A new approach based on the concepts of the discrete element method, is presented for impact resistance analysis of composites. The method is capable of analysing the progressive fracturing and fragmentation behaviour, as well as potential post-cracking interactions caused by the newly created crack sides and segments. The imminence of a material crack is monitored by an anisotropic Hoffman model. To avoid the mesh dependency of the results, a bilinear local softening model, based on modes I and II, is also adopted in this study to account for release of energy and redistribution of forces that caused the formation of a crack. A special re-meshing method has been developed to geometrically model an individual crack by splitting the element, separating the failed node, creating new nodes and dividing the neighbouring elements to preserve the compatibility conditions. Numerical simulations have been performed to assess the performance of the proposed algorithm. The method has proved to be an efficient approach for impact analysis of composites undergoing progressive delamination and cracking. 相似文献
92.
《低温学》2018
Second-generation high-temperature superconducting (2G HTS) tape is used in magnets and cables because of its outstanding electromagnetic characteristics. However, with the development of winding technology, thinner tapes are required in the construction of magnets. The effect of using thinner substrates on the resulting mechanical and electrical properties of 2G HTS tapes must thus be urgently understood. The interfacial adhesive strength is an important index used to characterize the mechanical strength of 2G HTS tape. Previous experimental studies have shown that thermal stress is one of the major factors in the delamination of the component tape used for magnet winding or cable assembly. In this study, the effect of substrate thickness on the interfacial adhesive strength of 2G HTS tape was investigated using peel test modeling. The thermal residual stresses accumulated during tape synthesis and caused by altered temperature during tape preparation and application at 77 K were also considered. To address the geometrical, physical, and boundary nonlinear problem, the finite element method was used. The simulation results indicate that interfacial stress caused by thermal shrinkage may separate the tape near the superconductor layer at the outer edge; however, no significant effect was observed for the central part. When the thermal residual stress was considered, the peel strength was reduced by approximately 20%. The substrate thickness also played an important role in the magnitude of thermal residual stress, which resulted in an increase of the peel strength with decreasing substrate thickness. 相似文献
93.
C.M. Cepeda-Jimnez M. Pozuelo O.A. Ruano F. Carreo 《Materials Science and Engineering: A》2008,490(1-2):319-327
The microstructure and mechanical properties, with emphasis in the impact fracture toughness behaviour, of two multilayer laminate materials have been investigated. The multilayer materials are constituted by alternated sheets of pure aluminium (Al 1200 or Al 1050) and high strength Al 7075 alloy. Stacked layers of these alloys have been successfully joined using two processing routes with different total hot rolling strains. Both laminates have been tested at room temperature under impact Charpy tests, three-point bend tests and shear tests on the interfaces. Both laminates exhibited more than eight times improvement in impact fracture toughness over the monolithic Al 7075-T6. The toughness increase in the higher rolling strained laminate is almost entirely due to crack blunting mechanism, while in the lower strained laminate, crack deflection by delamination and crack renucleation processes were active. 相似文献
94.
Various cutting techniques are available to drill holes, but drilling is the most common way in secondary machining of composite materials owing to the need for structure joining. Twist drills are widely used in the industry to produce holes rapidly and economically. Since the twist drill has a chisel edge, increasing the length of a chisel edge will result in an increase in the thrust force generated. Whereas, a saw drill has no chisel edge; it utilizes the peripheral distribution of the thrust force for drilling. As a result, the saw drill can achieve better a machining quality in drilling composite laminates than twist drill. The deviation of cutting edge that occurs in saw drill would result in an increase of thrust force during drilling, causing delamination damage when drilling composite materials in particular. A comprehensive model concerning delamination induced by the thrust force of a deviation saw drill during drilling composite materials has been established in the present study. For a deviation saw drill, the critical thrust force that triggers delamination increases with increasing β. A lower feed rate has to be used with an increasing deviation saw drill in order to prevent delamination damage. The results agree with real industrial experience. A guide for avoiding the drill deviation during drill regrinding or drill wear has been proved analytically by the proposed model, especially when the deviation ratio (β) affects the critical thrust force. This approach can be extended to examine similar deviation effects of various drills. 相似文献
95.
有机印制板上倒装芯片的可靠性研究 总被引:2,自引:0,他引:2
对一种有机印制板上倒装芯片(Flipchip)进行温度循环试验,测出其失效分布曲线,然后通过扫描声显微镜、红外显微镜和剖面等失效分析手段,发现失效模式主要是合金焊点中的断裂以及下部填充料(Underfil)中的损伤如分层(Delamination)和内部裂缝(Crack)。详细地阐述了倒装芯片中的下部填充料损伤在温度循环试验条件下的产生、发展及它们对合金焊点可靠性的影响。 相似文献
96.
1IntroductionAloy2090isoneoftherelativelyweldevelopedhighstrength,heatresistantseriesamongcommercialAlLialloys.Theavail... 相似文献
97.
98.
采用扫描电镜及电子探针对55 t钢锭成材148 mm厚2.25Cr-1Mo-0.25V钢板尾部分层缺陷进行观察分析,结果表明:分层缺陷是由于模铸保护渣卷入钢液造成的。为减少钢板尾部分层缺陷,对冶炼工艺进行优化,精炼过程中采用碳粉、电石及1.2~2.0 kg/t钢Al线复合脱氧工艺,真空后软吹12~14 min,采用高粘度、低熔点、高熔速及膨胀系数较大的模铸保护渣。优化工艺后,钢板尾部分层缺陷出现概率分别为11.3%、9.6%、6.9%,分层缺陷导致钢板废品率由原8.1%降至1.7%。 相似文献
99.
《Measurement》2014
In this paper, two silicon nitride layers with thickness, 0.2 and 0.4 μm, are coated onto single crystal silicon (SCS) in order to achieve Si3N4/Si cantilever microbeams. The effect of LPCVD silicon nitride surface coatings on fatigue properties of SCS cantilever microbeams is investigated. Fatigue testing is conducted at both 40 Hz and 100 Hz. Typical S–N (strain amplitude–fatigue cycle) curves of the beams are achieved and correlated fatigue failure modes are investigated. It is found that thinner Si3N4 coating of 0.2 μm results in better fatigue lives of Si3N4/Si beams than thicker Si3N4 coating of 0.4 μm. Both thinner and thicker coated beams have major fatigue crack planes along {1 1 1} planes; however, thicker coated beams possess specific failure mode of delamination, which is not found in thinner coated beams. Delamination reduces the reinforcing effect of thicker Si3N4 coating and leads to its shorter fatigue life. For thicker coated beams, fatigue life at 100 Hz is longer than that at 40 Hz. The mechanism for delamination and the effect of cyclic frequency is investigated, and factors for better fatigue life are proposed. 相似文献
100.