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I. Watanabe 《International Journal of Mechanical Sciences》2010,52(2):343-355
We introduce a method of predicting the macroscopic yield strength of polycrystalline metals subjected to plastic forming, which hinges on the reliability of the micro-macro decoupling scheme for solving the corresponding two-scale boundary value problem. A polycrystalline aggregate composed of several crystal grains is adopted as a periodic microstructure, namely unit cell, and is regarded as a numerical specimen for numerical material tests (NMTs) based on the homogenization theory. The NMTs are conducted to identify the material parameters of the assumed approximate macroscopic constitutive model and followed by the de-coupled macro-scale analysis to simulate the macro-scale forming process. We then conduct the de-coupled micro-scale analysis by applying the resulting macroscopic deformation histories to the microstructures associated with the macroscopic points of interest in order to obtain the numerical specimens after plastic forming. Finally, the NMTs are conducted on the prepared specimens to evaluate the macroscopic post-forming yield strengths. We validate the proposed method by taking the three-step forming process as an example of macroscopic plastic forming. The validation of the method is made in comparison with the results with those obtained by the equivalent two-scale analysis with the coupling scheme. To demonstrate the capability and promise of the proposed method for practical applications, we also present an numerical example of the rolling process that causes the texture development in crystal grains. 相似文献
63.
《Drying Technology》2013,31(1-2):387-396
Abstract: In order to design, manufacture, and commission a commercial dryer to dry individually quick frozen (IQF) wild blueberries (Vaccinium angustifolium), The Nova Scotian Fruit Company completed a series of experiments to characterize the effect of air velocity, air temperature, and packed bed depth on drying. Based on previous experience with forced air packed bed drying systems at air temperatures up to 65°C, the experiments focused on measuring the effect of air temperature and velocity during the first few hours of drying. The data collected suggest that drying occurs solely in the falling rate period. These data were used to successfully design, build, and commission a commercial dryer with a tenfold increase in production capacity over previous equipment. 相似文献
64.
The microstructure of a Ti–48Al alloy cooled after a solution treatment in the -field is influenced by the cooling rate. In order to characterize the lamellar structure and to know the values of 2-volume fraction, width of 2-lamellae, and interlamellar spacing, we developed a method of measurement based on an observation of laths in the scanning electron microscope. The study revealed the heterogeneous distribution of the lamellar structure in a commercial purity Ti–48Al alloy cooled from the -field at a rate of 35°C/min. The evolution of 2-volume fraction with the cooling rate showed that the microhardness is determined by the quantity of 2-phase. The values of yield stress also increased and were all the less scattered as the structure became more perfectly lamellar. Yield stress and interlamellar spacing are linked by a Hall–Petch relation. 相似文献
65.
The unidirectional rolled Mg-Zn-Gd sheet usually exhibited non-basal texture with two peaks whose tilting angle were about 42° from normal direction to transverse direction (TD), which would cause the mechanical anisotropy. In this study, multi-cross rolling followed by annealing was used to tailor the texture and mechanical anisotropy for Mg-Zn-Gd alloy. With increasing annealing temperature, the rolled basal texture with two peaks gradually transformed into the circle texture with multi-peaks. In order to figure out different texture components evolution during annealing, the basal texture, R-texture and T-texture component were defined and studied. The results showed that the change of R-texture and T-texture component was asynchronous with increasing annealing temperature from 250 to 400 °C. The tilting angle of R-texture component increased slightly, while the tilting angle of T-texture component increased obviously, and this phenomenon was attributed to the preferential nucleation at grain nucleation stage rather than preferential grain growth. The yield strength along TD was more sensitive to annealing temperature compared with that along rolling direction (RD), resulting in different descending slopes and yield strength anisotropy with increasing annealing temperature. Annealing at 300 °C was the best annealing temperature due to low yield strength anisotropy, moderate strength and good elongation among these annealing temperatures. The Schmid factor for basal slip indicated that the activity of basal slip along RD increased slightly, while that along TD increased obviously with increasing annealing temperature from 250 to 400 °C, which should be caused by the asynchronous change of R-texture component and T-texture component, consequently resulting in the transformation from isotropic yield strength to anisotropic yield strength. 相似文献
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Sheng-Mao Yang S. S. Malhi Jian-Rong Song You-Cai Xiong Wei-Yun Yue Li Li Lu Jian-Guo Wang Tian-Wen Guo 《Nutrient Cycling in Agroecosystems》2006,76(1):81-94
Application of chemical fertilizers and farmyard manure affects crop productivity and improves nutrient cycling within soil–plant systems, but the magnitude varies with soil-climatic conditions. A long-term (1982–2004) field experiment was conducted to investigate the effects of nitrogen (N), phosphorus (P), and potassium (K) fertilizers and farmyard swine manure (M) on seed and straw yield, protein concentration, and N uptake in the seed and straw of 19-year winter wheat (Triticum aestivum L.) and four-year oilseed (three-year canola, Brassica napus L. in 1987, 2000 and 2003; one-year flax, Linum usitatisimum L. in 1991), accumulation of nitrate-N (NO3-N) in the soil profile (0–210 cm), and N balance sheet on a Huangmian soil (calcaric cambisols, FAO) near Tianshui, Gansu, China. The two main plot treatments were without and with farmyard swine manure (M); sub-plot treatments were control (Ck), N, NP, and NPK.␣The average seed yield decreased in the order MNPK ≥ MNP > MN ≥ NPK ≥ NP > M > N > Ck. The average effect of manure and fertilizers on seed yield was in the order M > N > P > K. The seed yield increase was 20.5% for M, 17.8% for N, 14.2% for P, and 2.9 % for K treatment. Seed yield response to fertilizers was much greater for N and P than for K, and it was much greater for no manure than for manure treatment. The response of straw yield to fertilization treatments was usually similar to that of seed yield. The N fertilizer and manure significantly increased protein concentration and N uptake plant. From the standpoint of increasing crop yield and seed quality, MNPK was the best fertilization strategy. Annual applications of N fertilizer and manure for 23 successive years had a marked effect on NO3-N accumulation in the 0–210 cm soil profile. Accumulation of NO3-N in the deeper soil layers with application of N fertilizer and manure is regarded as a potential danger, because of pollution of the soil environment and of groundwater. Application of N fertilizer in combination with P and/or K fertilizers reduced residual soil NO3-N significantly compared with N fertilizer alone in both no manure and manure plots. The findings suggest that integrated and balanced application of N, P, and K fertilizers and␣manure at proper rates is important for protecting soil and groundwater from potential NO3-N pollution and for maintaining high crop productivity in the rainfed region of Northwestern China. 相似文献
68.
通过对高密度聚乙烯(HDPE)和无规共聚聚丙烯(PPR)进行不同拉伸速率的全切痕拉伸测试,考察了两种材料在近似于平面应变条件的拉伸断裂性能。对其全切痕拉伸过程应力-位移曲线、位移-屈服应力曲线分析:HDPE和PPR的屈服应力均随着拉伸速率的增加而增大;在较高拉伸速率时,HDPE全切痕拉伸断裂可认为是由常临界位移控制的银纹断裂,PPR的全切痕拉伸断裂过程几乎无恒定的常拉伸位移。通过显微镜显示的断裂形貌观察揭示了沿拉伸方向上HDPE有微纤空穴产生;在全切痕拉伸断裂过程中,PPR的银纹化易于发生在非晶区的片晶间,银纹微纤可产生在任意方向上。 相似文献
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