Continuity control method of cutter posture vector for efficient five-axis machining

During five-axis machining of impeller, the excessive local interference avoidance leads to inconsistency of cutter posture, low quality of machined surface and increase of processing time. Therefore, in order to improve the efficiency of five-axis machining of impellers, it is necessary to minimize the cutter posture changes and create a continuous tool path while avoiding interference. By using an MC-space algorithm for interference avoidance, an MB-spline algorithm for continuous control was intended to create a five-axis machining tool path with excellent surface quality and economic feasibility. A five-axis cutting experiment was performed to verify the effectiveness of the continuity control. The result shows that the surface shape with continuous method is greatly improved, and the surface roughness is generally favorable. Consequently, the effectiveness of the suggested method is verified by identifying the improvement of efficiency of five-axis machining of an impeller in aspects of surface quality and machining time.     

B样条小波权函数无网格法及其在杆、板结构中的应用

以三次B样条小波函数作为权函数,设计了一种无网格实用算法.以一维杆和二维板结构为例,分别采用基于Gauss权函数、三次样条权函数与三次B样条小波权函数的无网格算法进行仿真分析.计算结果表明,本文算法得到的位移、应力近似解与精确解在多尺度、稳定性方面具有比其他权函数更好的拟合效果.本文研究拓宽了无网格法在工程结构分析中的...     

A numerical approach to the cooling curves of porous P/M materials for quenching process

The software is developed in FORTRAN to obtain the cooling curves of powder metallurgy (P/M) of porous materials. The software is written in two-dimensional form and in cylindrical coordinates. The thermal conductivity of the porous materials is obtained using empirical correlations given in the literature. The natural convection, nucleate boiling and film boiling processes without and with radiation are considered in the analysis. The heat transfer coefficients on vertical and horizontal surfaces are calculated using the empirical correlations given in the literature. Energy equations are solved using the control volume method, but the effect of pore geometries is not considered in the analysis. Examples of the cooling curves are given for plain carbon steel with the water as the quenchant for 2.5%, 5%, 10%, 15% and 20% porosities. It is shown that the software can be used for different quenchants and the porous materials with different geometries.     

渐进迭代逼近方法在等距曲线逼近中的应用

渐进迭代逼近(PIA)方法在CAD领域有很好的自适应性和收敛稳定性,在曲线或曲面的逼近和拟合问题上具有很好的应用前景.文中将该方法应用于二维自由曲线的等距曲线(也称offset曲线)的逼近,提出基于PIA的等距曲线逼近算法.首先在等距曲线上采样数据点,采用Floater的方法对数据点进行参数化,并以这些采样点作为初始控制顶点,由这些初始控制顶点产生初始逼近曲线;然后考察相同参数值处采样点和逼近点的误差,并运用PIA方法逐步逼近等距曲线.该算法分别考虑了等距曲线的多项式逼近和有理逼近.数值实例结果表明,综合控制顶点数和算法误差这2项因素,文中算法具备较好的优势.     

Evaluation of Putative Allelochemicals in Rice Root Exudates for Their Role in the Suppression of Arrowhead Root Growth

In previous studies, 15 putative allelopathic compounds detected in rice root exudates were quantified by GC/MS/MS. In this study, multiple regression analysis on these compounds determined that five selected phenolics, namely caffeic, p-hydroxybenzoic, vanillic, syringic, and p-coumaric acids, from rice exudates were best correlated with the observed allelopathic effect on arrowhead (Sagittaria montevidensis) root growth. Despite this positive association, determination of the phenolic acid dose-response curve established that the amount quantified in the exudates was much lower than the required threshold concentration for arrowhead inhibition. A similar dose-response curve resulted from a combination of all 15 quantified compounds. Significant differences between the amounts of trans-ferulic acid, abietic acid, and an indole also existed between allelopathic and non-allelopathic rice cultivars. The potential roles of these three compounds in rice allelopathy were examined by chemoassay. Overall, neither the addition of trans-ferulic acid nor 5-hydroxyindole-3-acetic acid to the phenolic mix significantly contributed to phytotoxicity, although at higher concentrations, trans-ferulic acid appeared to act antagonistically to the phytotoxic effects of the phenolic mix. The addition of abietic acid also decreased the inhibitory effect of the phenolic mix. These studies indicate that the compounds quantified are not directly responsible for the observed allelopathic response. It is possible that the amount of phenolic acids may be indirectly related to the chemicals finally responsible for the observed allelopathic effect.     

Mechanical Behavior of Butyl Adhesives

Butyl adhesives are widely used to bond elastomeric membranes. The results of uniaxial tension tests and simple shear tests conducted on bulk samples of butyl adhesives are presented in this paper. Butyl adhesives were found to have a rate-sensitive mechanical response with very low tensile and shear strengths. The stress-strain curves of the adhesive are characterized by an initial elastic response followed by a region of large plastic flow. A three-element viscoelastic model was used to model the stress-strain behavior of the adhesive. The model effectively combines a viscous dashpot and a network spring to capture the plastic flow in the material after the initial yield. The parameters of the model are calibrated to simulate a wide range of mechanical response of the adhesive.     

Dual representation of spatial rational Pythagorean-hodograph curves

In this paper, the dual representation of spatial parametric curves and its properties are studied. In particular, rational curves have a polynomial dual representation, which turns out to be both theoretically and computationally appropriate to tackle the main goal of the paper: spatial rational Pythagorean-hodograph curves (PH curves). The dual representation of a rational PH curve is generated here by a quaternion polynomial which defines the Euler–Rodrigues frame of a curve. Conditions which imply low degree dual form representation are considered in detail. In particular, a linear quaternion polynomial leads to cubic or reparameterized cubic polynomial PH curves. A quadratic quaternion polynomial generates a wider class of rational PH curves, and perhaps the most useful is the ten-parameter family of cubic rational PH curves, determined here in the closed form.     

Electroactive polymer films for stainless steel corrosion protection

Electroactive polymer films of polyaniline, poly-o-toluidine and a composite of both were deposited on stainless steel and their performance as protective coatings against corrosion was evaluated. Open circuit potential and potentiodynamic studies of the polymer-coated stainless steel in a corrosive medium showed a significant shift in the corrosion potential towards more positive values. Mechanical characteristics of the films were evaluated by means of microhardness measurements, revealing nonelastic films in all cases and low hardness values that increased from polyaniline to poly-o-toluidine to the composite. The best results were obtained in the case of the polyaniline-o-toluidine composite.     

测井曲线自动分层的建模与应用

测井曲线分层是物理勘探中的首要工作.论文在分析自然伽玛、自然电位、密度等多条曲线形态特征的基础上,提出了主成分分析、小波变换与综合方差比分析相结合的方法,完成了对多测井曲线的自动分层.针对非地层因素引起的数据干扰问题,加入了程序比较字符串的方式提取公共曲线,并归并薄层界面.实际结果表明,该方法兼顾了分层效率和分层精度的要求,具有较高的应用价值.