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11.
Donghyon Kim Jung-ok Beak Youngson Choe Wonho Kim 《Korean Journal of Chemical Engineering》2005,22(5):755-761
The cure kinetics of blends of epoxy resin (4,4’-tetraglycidyl diaminodiphenyl methane; TGDDM)/curing agent (diaminodiphenyl
sulfone; DDS) with ATPEI (amine terminated poly-etherimide) -CTBN (carboxyl terminated poly (butadiene-co-acrylonitrile))
block copolymer (AB type) were studied using differential scanning calorimetry under isothermal conditions to determine the
reaction kinetic parameters such as activation energy and reaction constants. Final cure conversion decreased with increasing
amount of AB in the blends. A diffusion controlled reaction was observed as the cure conversion increased, and the curing
reaction was successfully analyzed by incorporating the diffusion control term in the rate equation for the epoxy/DDS/AB blends.
The fracture toughness was improved to about 350% compared to that of the unmodified resin at 30% of AB block copolymer. This
is attributed to the formation of co-continuous morphology between the epoxy phase and AB block copolymer phase. By increasing
the amount of AB, the modulus of the cured blends decreased, which was due to the presence of CTBN rubbery phases. 相似文献
12.
13.
Hwan-Cheol Kim In-Jin Shon J.E. Garay Z.A. Munir 《International Journal of Refractory Metals and Hard Materials》2004,22(6):257-264
The rapid sintering of nano-structured WC hard materials in a short time is introduced with a focus on the manufacturing potential of this spark plasma sintering process. The advantage of this process allows very quick densification to near theoretical density and prohibition of grain growth in nano-structured materials. A dense pure WC hard material with a relative density of up to 97.6% was produced with simultaneous application of 60 MPa pressure and electric current of 2800 A within 2 min. A larger current caused a higher rate of temperature increase and therefore a higher densification rate of the WC powder. The finer the initial WC powder size the higher is the density and the better are the mechanical properties. The fracture toughness and hardness values obtained were 6.6 MPa m1/2 and 2480 kg/mm2, respectively under 60 MPa pressure and 2800 A using 0.4 μm WC powder. 相似文献
14.
15.
颗粒增强铝基复合材料断裂韧度研究 总被引:5,自引:2,他引:5
采用搅熔复合法制备颗粒增强铝基复合材料.对复合材料断裂韧度进行了测试。系统研究了影响该材料断裂韧度的各种影响因素:结果表明:在增强相加入量相同时.采用Sic颗粒复合材料的断裂韧度比Al2O3的影响显著,而增强颗粒质量分数越高.则复合材料的断裂韧度越低.增强颗粒尺寸越小,复合材料断裂韧度值越大。热处理状态对断裂韧度也有较大影响,人工时效比自然时效状态下的断裂韧度高。 相似文献
16.
Bioinspired Nacre‐Like Ceramic with Nickel Inclusions Fabricated by Electroless Plating and Spark Plasma Sintering 下载免费PDF全文
Zhe Xu Jiacheng Huang Cheng Zhang Soheil Daryadel Ali Behroozfar Brandon McWilliams Benjamin Boesl Arvind Agarwal Majid Minary‐Jolandan 《Advanced Engineering Materials》2018,20(5)
17.
本文通过有缺口和无缺口冲击试验、断裂韧性测试以及结合扫描电镜分析断面形貌,研究了酞侧基聚芳醚砜/聚苯硫醚共混物的断裂行为,讨论了聚苯硫醚增韧聚芳醚砜的机理。结果表明,共混物冲击强度的改善主要是由于其裂纹引发能的提高;共混物断裂韧性提高的原因是由于外加应力场在PPS微纤附近产生应力集中,促使基体和微纤都发生塑性形变,从而吸收更多的能量所致。 相似文献
18.
A. R. Khodabandeh M. Jahazi S. Yue S. T. Aghdashi 《Materials and Manufacturing Processes》2006,21(1):105-110
The influences of various reheating and forging temperatures as well as cooling rates on the microstructure and mechanical properties, particularly impact energy, during the forging of a Nb-V microalloyed steel to be used for automotive safety parts were investigated. Increasing the prior austenite grain size increased the volume percent of acicular ferrite and reduced pearlite content in the microstructure even for very low post-forging cooling rates, resulting in improved toughness and tensile strength values. Increasing the cooling rate enhanced the acicular ferrite content, thereby increasing the impact energy properties. At lower reheating temperatures the yield strength and impact energy levels are determined by the percentage of pearlite present in the microstructure; while as the cooling rate is increased the amount of acicular ferrite and retained austenite are increased, improving the toughness and tensile strength of the forged part. This effect is more pronounced for the parts solutionized at 1250°C and is related to the presence of very fine carbonitride precipitates under these conditions, which contributes to improved yield strength, particularly at higher cooling rates. An optimized forging process was determined and adapted to a 25 MN production forging press to validate the experimental results on semi-industrial production scale. By adequate control of the above parameters, high-strength, high-toughness parts (T.S. = 800 MPa, CVN = 35 J) were forged and optimum mechanical properties were achieved without the need for any additional heat treatment. 相似文献
19.
Four mechanical parameters of physical vapor-deposited (PVD) hard coatings were obtained, which were the residual strain, Young's modulus, film toughness, and interface toughness, concerning titanium aluminum nitride (TiAlN) and titanium nitride (TiN) coatings deposited on WC-Co substrates. The results were quantitatively compared with the author's previous trials for the case of chemical vapor-deposited (CVD) diamond coatings. Due to the significant difference in the mechanical properties between PVD hard coatings and CVD diamond coatings, it was necessary to develop new experimental techniques, which could properly evaluate those parameters for the case of PVD hard coatings. As a conclusion, film toughness of PVD hard coatings was surprisingly brittle. It was an order of magnitude smaller than that of CVD diamond coatings. In contrast, no significant difference was found in interface toughness between these different kinds of coatings. Concerning the residual strain, TiN had far larger level than the other two. These differences in mechanical properties were further discussed in relation to the difference in their wear behavior. 相似文献
20.
In 1976, a pressure vessel of a tank wagon burst during gravity shunting. The pressure vessel was filled with cold fluid carbon dioxide and failed by cleavage fracture explosively. Big parts of the vessel were flung up to 300 m, a building was destroyed, and rails as well as the superstructure of the gravity shunting yard were damaged.The initiation sites of the fracture and the orientations of crack propagation were determined by means of the patterns on the fracture surfaces of the broken parts. The initiation sites were located in the heat-affected zone (HAZ) of welds, close to transitions of cross-sections and the starting and end points, respectively, of the welds. The primary initiation of crack propagation was almost certainly on the left side, close to the weld of the fixed bearing connecting the vessel with the carriage.The results of metallographic investigations indicated the development of cold weld cracks during welding. Mechanical behavior assessments on specimens extracted from the failed vessel indicated sufficient strength and ductility in tensile loading. The values of the notched-bar impact energy or toughness were within the limits according to industry rules and standards, except for one metal sheet of the vessel that was welded to the left fixed bearing.During shunting, two tank wagons were inappropriately braked, and began to roll too quickly. One rail brake used for deceleration of the wagons caused impulsive noises and vibrations, resulting in high impulsive loading of the first wagon. The cold weld cracks in the heat-affected zones near the fixed bearing of the pressure vessel were initiation points for unstable crack growth. As the result of very low notched-bar impact toughness, crack propagation was not arrested and unstable cleavage fracture occurred.Due to a second similar accident, happened one year before, a program was started to assess characteristic values of pressure vessel materials and the influence of weld parameters by the manufacturer, the inspecting authority, and BAM. The scientific findings led to modifications of industry rules and standards with regard to using ISO-V specimens and to higher required values for notched-bar impact energy for fine grain structural steels. 相似文献