熔融沉积快速成形工艺材料粘结质量分析

在FDM 工艺中,粘结强度直接决定零件的机械性能和使用效果. 文中在理论分析的基础上,结合较系统的工艺试验,初步探索几种聚合物材料在不同工艺条件下的粘结质量问题,总结出不同材料在FDM 工艺中的最佳喷嘴温度范围、成形室温度范围和合理的层厚. 实验结果对于FDM 工艺中不同成形材料工艺参数的优化控制提供了重要的依据.     

FDM薄板振动特性的理论与实验研究

熔融沉积成型(FDM)是一种能够直接打印出具有复杂几何形状零件的快速成型技术.然而,FDM在振动性能方面很难与传统加工方式相媲美,需要对其进行更为实际的振动特性分析,为此首次提出FDM 3D打印薄板的振动特性理论建模方法.以悬臂边界条件下FDM薄板为研究对象,基于经典层合板理论,采用双向梁函数组合法表示振型函数,并通过Ritz法求解获得了复合薄板的固有特性;搭建了FDM 3D打印薄板的固有特性测试实验台,以获得薄板的模态振型和固有频率;计算与实验结果验证了理论计算方法的正确性和可靠性.     

增材制造中耦合零件表面粗糙度及支撑面积的建造方向优化

以熔融沉积(fused deposition modeling, FDM)技术为基础,研究了建造方向对于零件表面粗糙度以及支撑的影响.通过实验测试新型聚乳酸(polylactic acid, PLA)材料零件不同建造方向下的表面粗糙度,结合理论及经验公式,建立符合实际情况的粗糙度综合预测模型.对于复杂多面体零件,通过选择功能性表面,建立建造方向集合,在有限的方向集合内选择最优建造方向,从而整体提升零件表面粗糙度.提出了基于光固化立体造型术(stereolithography, STL)文件格式的支撑面积数学模型,以支撑面积最小为优化目标,使用遗传算法(genetic algorithm, GA)进行单目标优化,搜寻最优建造方向.针对不同建造方向下,表面粗糙度和支撑面积的耦合问题,建立多目标优化模型,使用遗传算法全局搜寻最优建造方向.     

利用模型分解的曲面分层五轴挤出打印装置及工艺

针对传统平面熔融沉积成型(FDM)只能在平面内排布丝材,导致零件力学性能差、表面粗糙度高、浪费材料等问题,研究了曲面分层五轴挤出打印装置及工艺。首先,以球面并联机器人作为双轴转动成型平台,结合经典的并联臂型三维挤出打印机,搭建曲面分层五轴挤出打印设备;然后,以底层曲面为基准,将零件的三维模型分解为按照打印顺序排列的曲面,每层曲面再分解为按宽度铺满曲面的丝材路径;之后,按照坐标变换公式和位姿反解公式在下位机控制软件Marlin固件中编写轨迹规划函数,解释并执行零件路径规划文件进行曲面分层五轴三维打印。通过对零件进行力学试验,相同零件的五轴挤出打印比三轴挤出打印,最大破坏力由(189.37±8.7) N提高到了(445.54±52.57) N,材料消耗减少了46%。因此,低成本、高精度的五轴三维打印设备能够打印高强度、高刚度、无支撑、表面粗糙度低的零件,在曲面结构打印、无支撑结构打印以及复合材料连续打印等方面有重要的应用前景。     

功能梯度材料零件层片路径扫描算法

提出了一种用于加工功能梯度材料零件的路径扫描算法.首先将功能梯度材料零件进行分层处理,把每一层片内连续分布的材料离散为若干个材料均匀分布的子区域,再对每个子区域分别加工从而实现一定精度要求下功能梯度材料零件的加工制造.给出了路径规划实例,验证了路径扫描算法的正确性.     

航站楼内多目标路径规划方法设计与实现

针对航站楼多楼层的室内导航和多目标的路径优化问题,提出一种基于改进遗传算法的航站楼内交通换乘导航路径规划方法:依据航站楼内的空间特征和环境变化建立以路径为权值和以人流密度为权值的双路网,并权衡路径的距离成本、客流拥挤度和时间成本3种因素,建立了航站楼内的多目标路径优化模型.最后使用融合广度优先搜索策略(Breadth First Search,BFS)的遗传算法在本文构建的多层路网中实现航站楼内多目标路径优化,生成考虑路径距离、拥挤度、时间成本的单目标最优路径和多目标优化路径.研究结果表明,使用融合BFS的遗传算法在本文构建的多层路网中可实现航站楼内多目标路径优化,生成考虑路径距离、拥挤度、时间成本的单目标最优路径和多目标优化路径.     

应用DOE方法分析和优化3D打印零件的翘曲变形量

以聚乳酸材料的FDM(fused deposition manufacturing)成型零件的翘曲变形分析为例,对3D打印零件变形进行了理论模型的建立和研究,初步分析了堆积层数、堆积层厚度等参数对零件发生变形的影响,筛选出3D打印零件发生变形的重要因子.应用试验设计(DOE)方法对这些重要因子进行试验分析,确认了3D打印零件发生翘曲变形的关键因子,借助响应优化模型和线性回归方法进而优化打印的工艺参数,这样可以减少3D打印零件的变形程度和3D打印的试验成本和时间.     

基于改进遗传算法的多车间计划与调度

生产计划与调度是企业生产和管理的核心内容,传统的单车间调度优化不能满足多车间调度优化的要求.针对这情况,提出一种基于改进遗传算法的层次化多车间计划和调度优化方案,其中生产计划层负责零件的分发,车间调度层负责零件加工路线的规划.以一个三制造车间的调度优化为例,验证多车间调度模型的有效性.结果表明所提出的方案在将加工零件合理地分配到适当的车间同时,实现了零件加工路径的规划,从而为解决分布式多车间调度优化问题提供一种有效而又实用的方法.     

基于主应力σ2σ3为参数的岩石破坏强度准则

本文提出了一种基于中间主应力和最小主应力乘积(σ₂σ₃)为参数的显式岩石破坏强度准则.该准则通过骨架曲线和分支曲线两部分来描述岩石的强度规律.骨架曲线即三轴压缩实验的结果,分支曲线即最小主应力固定的实验结果.通过研究岩石真三轴压缩实验结果发现岩石的破坏强度与中间主应力和最小主应力乘积的平方根■之间存在着较强的相关性,并且平面内骨架曲线和分支曲线在交点处的斜率相等.推导出了在最大主应力和中间主应力平面内,骨架曲线的斜率在交点处是分支曲线斜率的2倍.对于同一种岩石,在最大和中间主应力平面内随着中间主应力和最小主应力的差值达到某个值,所有分支曲线其斜率逐渐衰减为0,岩石的破坏强度达到最大值.基于以上特征,得到骨架及分支曲线的函数形式.本文提出的岩石强度准则经过实验数据的检验,并与其他准则的计算结果进行对比.结果表明本文提出的岩石强度准则可以较好地拟合岩石材料在三轴受压条件下的破坏强度.此外,该强度准则可以用较少的数据拟合出相对比较稳定精确的结果,显示了该准则的稳定性与合理性.     

FDM工艺过程中丝材的粘结机理与热学分析

分析了熔融堆积成形(FDM)工艺中挤出丝材的温度随时间、路径的变化规律,通过对丝材物理模型的合理假设,建立了挤出丝材温度场的数学模型,并根据Stratasys商用机FDM2000所使用的ABS-P400丝材的热学参数,结合聚合物的粘结机理,验证了模型的合理性.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Design and analysis of generic LBS application developing platform

Location based services is promising due to its novel working style and contents.A software platform is proposed to provide application programs of typical location based services and support new applications developing efficiently. The analysis shows that this scheme is easy implemented, low cost and adapt to all kinds of mobile nework system.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that