基于熔融沉积法的快速成形柔性丝材技术研究

目的研究柔性材料的熔融沉积(Fused Deposition Modeling,FDM)快速成形工艺。方法通过理论推导和实验研究的方法,针对柔性材料的FDM技术做了初步的探讨。结果柔性材料FDM工艺,相对于硬质材料来说,其进丝量需要更加精准的控制,进丝齿轮旋转角速度和打印速度、打印层厚呈正比关系,其比例系数取决于喷嘴直径、齿轮外径以及所使用丝材直径;同时,打印温度、打印层厚,尤其是首层打印间隙等工艺参数对于柔性打印制件的表观质量有更加重要的影响,这主要是因为熔融态柔性材料粘性较大所导致。结论现有硬质材料的FDM机器,需要作出适当的调整,才能更好地适应柔性材料打印。     

羟基磷灰石的表面改性及其对聚乳酸基多孔支架性能的影响

分别采用柠檬酸和硬脂酸对纳米羟基磷灰石（n-HA）进行表面处理,并利用TGA、FTIR、XPS等研究了不同改性剂的改性效果,发现柠檬酸和硬脂酸能够成功接枝在n-HA表面,但硬脂酸的接枝率更高。将柠檬酸改性的n-HA与聚乳酸（PLA）共混制备复合材料,通过SEM观察发现,制备的n-HA/PLA复合材料在n-HA粉体添加量不超过20wt%时,经处理后的n-HA粉体在基体中分散均匀,两相界面处结合紧密。同时研究了n-HA/PLA复合材料制备多孔骨支架的3D打印成型工艺,并测试了其力学性能,结果表明,采用熔融沉积3D打印技术制备的支架有良好的压缩模量,但达到10%形变时所承受的压缩强度与PLA相比仍然有一定差距。     

气压驱动石蜡熔融沉积成型工艺研究及优化

熔融沉积成型(FDM)工艺因其加工时间短,精度高,可打印材料广的特点广泛应用于3d打印行业。本文提出以固体石蜡作为原材料代替线材进行熔融沉积成型打印,探究以YH-W205铸造蜡为材料的气压驱动式石蜡熔融沉积特点及气压,喷嘴直径,基板距离喷嘴距离和平台移动速度的变化对石蜡沉积精度的影响。实验以石蜡为材料,设计实验方案并进行试验。结果表明,通过优化石蜡打印系统运动参数,能够得到质量较好的单层石蜡线,验证石蜡熔融沉积工艺在三维成型及模具打印方面应用的可行性,为后续成型高质量石蜡模具的打印制造提供了必要的基础。     

熔融沉积纤维增强复合材料的研究进展

熔融沉积增材制造属于热塑性聚合物材料3D打印成型技术之一,具有原料广泛、制造成本低、个性化可定制等特点.随着制备工艺和技术的优化,近年来成型质量不断提高.同时,这种基于分层打印、逐层堆积的材料成型方式导致其力学强度偏低.发展适用于熔融沉积技术的纤维增强热塑性聚合物复合材料,利用纤维具有高比强度、高比模量的特性,可显著提高熔融沉积热塑性聚合物成型件的抗拉强度和拉伸模量等力学性能.然而,在熔融沉积纤维增强复合材料成型过程中,伴随着材料的流动与纤维取向、丝/层间结合、热量传导和残余应力等一系列复杂现象,明晰上述现象及其内在的关联性,是促进该技术应用和发展的关键.因此,近年来国内外研究者们主要从选择合适的纤维和优化制备工艺等方面不断尝试,并取得了丰硕的成果.用于熔融沉积纤维增强复合材料的纤维主要以短纤维和连续纤维两大类材料为主.短纤维复合材料发展较早、制备工艺相对简单;连续纤维复合材料成型件的力学性能相对较高.近年来,国内外研究者基于纤维增强复合材料的制备工艺、材料性能、成型机理等关键要素,聚焦于纤维含量、沉积角度、打印速度、喷嘴温度、层厚和化学助剂添加等工艺参数变化对成型件力学性能影响的相关研究,拟充分发挥纤维增强材料的技术优势,为制备较高力学性能和较好质量打印成型件提供可能.本文主要介绍了近年来国内外研究者在熔融沉积纤维增强复合材料方面的研究进展.从熔融沉积增材制造成型原理、纤维增强复合材料技术研究现状出发,介绍了短纤维和连续纤维增强复合材料的力学性能,以及工艺参数对增强复合材料力学性能的影响.最后,归纳了该技术仍存在的亟待解决的基础科学问题和关键技术问题,以及未来可能的研究方向.     

熔融沉积打印微纳米生物质填料增强聚乳酸基复合材料的研究进展

熔融沉积成型(Fused deposition modeling,FDM)因其制造成本低廉和工艺简易等特点成为现今增材制造(Additive manufacturing,AM)技术中应用最广泛的一种类型,而聚乳酸(Polylactic acid,PLA)也因其良好的可生物降解性和生物相容性成为FDM线材的主要原料。但是,PLA较差的脆性、韧性及热稳定性等缺点严重限制了其打印产品在市场上的应用。因此,在PLA线材中加入某种或多种填料是解决其自身缺点的重要措施。其中,生物质填料是一种比较理想的选择,在PLA中加入生物质填料不仅可以有效克服基材的性能缺陷,而且产品具有良好的可生物降解性和环境友好性。本文综述了近几年来FDM打印生物质填料增强PLA复合材料的研究进展,阐释不同尺度结构(由微米尺寸到纳米尺寸)的生物质增强填料(如木粉、天然纤维、纳米纤维素)对PLA基复合材料的性能影响,并分析和总结复合材料的性能改善原因及其界面相容机制,最后对FDM打印PLA基复合材料的未来发展进行了展望。     

基于FDM的3D打印PLA层间黏结机制及质量分析

介绍了熔融沉积快速成形(FDM)技术的原理和工艺特点.根据杨氏方程,结合成形工艺过程,分析了熔融沉积快速成形的层间黏结机制.为实现FDM的普通原型向功能原型转变,以Creatbot 3D打印机为成形设备,选用直径为3.0mm的PLA丝材为成形耗材,研究了成形工艺参数对工件层间黏结质量的影响.层间黏结强力随喷头移动速率和层厚的增大而增大.在保证足够强力的前提下,综合考虑工件成形效率和表面质量,合理设置了成形工艺参数.     

利用聚乳酸线材进行盲文增材制造的最优参数研究

目的 为了解决目前3D打印制造盲文存在的成本高、操作复杂的问题,将生物相容性好、可回收利用的聚乳酸线材应用于熔融沉积成型3D打印机来制造盲文,使盲文的增材制造更加简便、成本更低.方法 首先利用三维软件设计盲文文本,根据盲文文本的特点和标准设计相应的参数,如点径、点距、方距、点高、行距等.然后将设计好的3D文本分层,用单螺杆挤出的聚乳酸线材和熔融沉积3D打印机进行打印,在打印的过程中设置不同的打印温度、打印速度和层高.对打印的质量评价采用平滑度、尺寸精度、耐磨性、耐水性等4个参数进行综合评价.结果 采用正交试验法对打印参数层高、打印温度、打印速度进行分析,当打印温度为180℃,打印速度为90 mm/s,打印层高为0.1 mm时,打印盲文的质量优良.结论 按最优参数打印后的盲文安全无毒,经久耐用,可回收及降解,耐摩擦,具有一定的防水性,而且成本低,操作简单,可用于部分盲文制品.     

喷嘴行进速度及高度对3D打印混凝土力学性能影响的试验

为研究喷嘴行进速度、喷嘴高度等打印参数对3D打印混凝土力学性能的影响,制备了相同配合比的浇筑试块和不同打印参数组合下的打印试块,通过混凝土立方体抗压试验、棱柱体轴心抗压试验和立方体劈裂抗拉试验,考察了其受力破坏过程和破坏形态,分析了喷嘴行进速度、喷嘴高度对3D打印混凝土力学性能的影响,得到了3D打印混凝土轴心受压应力-应变曲线,建立了3D打印混凝土各强度之间的关系。结果表明：3D打印混凝土立方体抗压强度、轴心抗压强度、劈裂抗拉强度均随喷嘴行进速度的加快、喷嘴高度的升高而降低,且喷嘴高度对强度的不利影响强于喷嘴行进速度;在较优打印参数组合下,打印试块的抗压强度高于浇筑试块,但因打印试块存在层间粘结弱面,其劈裂断面在其层间界面处,致使断面明显平滑,劈裂抗拉强度低于浇筑试块;通过回归分析,建立了3D打印混凝土各强度与打印参数间的函数关系及轴心抗压强度、劈裂抗拉强度与立方体抗压强度之间的换算关系。     

层间温度对H13钢丝材电弧增材制造成形质量的影响

目的 为获得外观形貌好、成形质量优的单道多层成形件，研究最佳的层间温度。方法 在调质处理后的H13钢基板上，根据已确定的工艺参数分别在50、100、150、200 ℃这4种层间温度下沉积20层。通过宏观形貌、微观组织和抗拉强度测试，分析层间温度对单道多层成形件的形貌及成形质量的影响。结果 层间温度为100、150、200 ℃时，成形件顶层平滑，侧面成形较规则。不同层间温度下成形件平均高度的最大值与最小值之差仅为0.55 mm。层间温度为200 ℃时相邻2层沉积层间冷却时间最短，沉积20层总耗时最短，为44.57 min。层间温度大于100 ℃时，抗拉强度大于1 200 MPa。结论 在H13钢基板上进行丝材电弧增材制造时，控制层间温度在150~200 ℃能够得到外观形貌好、成形质量优良的成形件。     

基于熔融沉积3D打印聚乳酸基复合材料的研究进展

目的 半结晶性聚乳酸(PLA)因透明性好、力学性能优异、能生物降解等优点,在加工领域表现出适用范围广等特性,因此对PLA基复合材料在3D打印技术中的研究应用及最新进展状况进行总结,以期提供借鉴与参考。方法 以熔融沉积成型(FDM)、PLA基体为主线,在查阅近年中外文献基础上,分别从PLA结构性能、3D打印成型工艺、PLA基复合材料改性等方面进行了探讨,着重分析工艺参数的技术优化,以及复合材料的结构改性最新研究进展。结果 FDM制备PLA基复合材料的研究取得了丰硕的成果,在3D打印行业中表现优异,潜力巨大,商品化程度越来越高。结论 低廉、高效、可定制的3D打印受到国内外科研工作者广泛关注与青睐,随着新技术的不断探索和突破,以及纳米材质和新型聚合物材料等新型材质应用,使3D打印在成型加工技术上占据绝对优势。     

Preparation and mechanical properties of carbon fiber reinforced hydroxyapatite/polylactide biocomposites

A novel biocomposite of carbon fiber (CF) reinforced hydroxyapatite (HA)/polylactide (PLA) was prepared by hot pressing a prepreg which consisting of PLA, HA and CF. The prepreg was manufactured by solvent impregnation process. Polymer resin PLA dissolved with chloroform was mixed with HA. After reinforcement CF bundle was impregnated in the mixture, the solvent was dried completely and subsequently hot-pressed uniaxially under a pressure of 40 MPa at 170°C for 20 min. A study was carried out to investigate change in mechanical properties of CF/HA/PLA composites before and after degradation in vitro. The composites have excellent mechanical properties. A peak showed in flexural strength, flexural modulus and shear strength aspects, reaching up 430 MPa, 22 GPa, 212 MPa, respectively, as the HA content increased. Degraded in vitro for 3 months, the flexural strength and flexural modulus of the CF/HA/PLA fell 13.2% and 5.4%, respectively, while the shear strength of the CF/HA/PLA composites remains at the 190 MPa level. The SEM photos showed that there were gaps between the PLA matrix and CF after degradation. Water uptake increased to 5%, but the mass loss rate was only 1.6%. The pH values of the PBS dropped less than 0.1. That’s because the alkaline of HA neutralize the acid degrades from PLA, which can prevent the body from the acidity harm.     

Mechanical,thermal and morphological properties of durian skin fibre reinforced PLA biocomposites

Durian skin waste generated by durian fruit or Durio zibethinus Murray show potential as a new reinforcement based-natural fibre. Similar to other lignocellulosic fibre, durian skin fibre (DSF) is capable in reinforcing polylactic acid (PLA) through extrusion and injection moulding processes for various applications. In current study, the effects of fibre content and pre-treatment using 4% sodium hydroxide (NaOH) on DSF were investigated on impact and thermal properties of PLA biocomposites. Treated DSF significantly enhanced the properties of PLA biocomposites as compared to untreated biocomposite. PLA can be replaced by 30 wt% DSF for similar impact performance. Thermogravimetry analysis (TGA) demonstrated that pre-treated DSF improved the thermal stability of PLA biocomposite. Differential scanning calorimetry (DSC) showed the presence of pre-treated DSF minimally enhanced the glass transition temperature (T_g), crystallization temperature (T_c) and melting temperature (T_m) relative to untreated DSF which suggests on better reinforcement with NaOH pre-treatment.     

Effect of aluminum trihydroxide on flame retardancy and dynamic mechanical and tensile properties of kenaf/poly(lactic acid) green composites

In this work, the effect of aluminum trihydroxide (ATH) on the flame retardancy and dynamic mechanical and tensile properties of kenaf/poly(lactic acid) green composites was explored. Prior to composite fabrication, poly(lactic acid) (PLA) pellets filled with ATH powder at different loadings (0, 10, 20, 30, and 50?wt.%) were processed by using a twin-screw extrusion technique. The green composites were fabricated using the pellets and chopped kenaf fibers by a compression molding method. The kenaf fibers were used as primary reinforcement, and the contents were fixed to 40?wt.% of the total, and the average fiber length was 3?mm long. It was noticeable that the flame retardancy of kenaf/PLA green composite with ATH was improved by 66%, and the storage modulus and tensile modulus were enhanced by 136 and 59%, respectively, compared with the kenaf/PLA counterpart without ATH. It was concluded that the ATH incorporated into PLA by extrusion technique played a significant role not only as flame-retardant but also as secondary reinforcement of kenaf/PLA green composites.     

碳纤维(CF)表面接枝对聚酰亚胺(PMR-15)基复合材料界面性能的影响

通过冷等离子体连续表面接枝技术对CF进行表面处理,采用XPS对CF表面组成及特征基团变化进行分析。同时测定了CF/PMR-15层间剪切强度、拉伸强度和冲击强度,研究了表面接枝对CF/PMR-15界面强度和韧性的影响。      

Numerical analysis of spontaneously condensing phenomena in nozzle of steam-jet vacuum pump

The primary fluid in a steam-jet vacuum pump is not assumed as a perfect gas as general research in the present study. A mathematic model based on the wet steam model for transonic flow is proposed to investigate the flow behaviours of primary fluid in the nozzle of a steam-jet vacuum pump. The simulation based on a wet steam model was carried out to predict the flow characteristics of primary fluid along the nozzle axis by a commercial computational fluid dynamics (CFD) code (FLUENT6.3). The simulation results showed that there was spontaneous condensation as the supersonic flow passing through the nozzle and the simulation results had a good agreement with the experimental data. It is found from the numerical simulation results that the steam flow characteristics in nozzle are quite different from a wet steam model and a perfect gas assumption: the outlet pressure of the nozzle predicted in the present study is higher than that as the primary fluid assumed as perfect gas, the outlet velocity is about 10% lower than that as the primary fluid assumed as a perfect gas, and the temperature at the outlet of the nozzle is much higher than that as the primary fluid assumed as a perfect gas. The simulation results demonstrate that the thermo-positive process due to steam condensation would hinder the supersonic expanding flow process in nozzle and depress the efficiency of the nozzle which would affect the pumping performance of steam-jet pump.     

PC/CF共混体系的加工流变性能与力学性能

利用微量双螺杆挤出机(Hakke MiniLabⅡ,Rheomex CTW5),通过熔融共混挤出注塑的方法,在聚碳酸酯(PC)中添加炭纤维(CF)进行复合增强。实验对共混物加工过程中的流变行为进行了分析,研究了炭纤维含量对复合材料力学性能的影响,探讨了其黏度与力学性能变化的机理,由扫描电子显微镜观测拉伸及冲击破坏的试样断面形态。结果表明,当CF质量分数为2%时,复合材料非牛顿指数n值最小,假塑性最强,易于加工;同时,复合材料的综合力学性能也最为优异。扫描电镜照片显示,拉伸破坏的主要方式为界面脱胶,而冲击破坏的主要方式为纤维断裂。     

改性椰纤维增强聚乳酸复合材料力学性能

目的添加适量椰纤维(CF)改善聚乳酸(PLA)的力学性能,以适应产品的包装。方法采用熔融共混法制备不同CF含量的CF/PLA复合材料。通过力学性能测试、扫描电子显微镜观察和动态热力学性能测试,探讨添加不同含量的碱洗CF对复合材料力学性能的影响。结果与纯PLA相比,复合材料的拉伸强度降低,冲击强度增大,储能模量增大,玻璃化转变温度降低。当碱洗CF质量分数为3%时,复合材料的冲击强度比纯PLA增加了24%。结论添加CF有利于提高复合材料的力学性能,碱液浸泡更有利于改善CF和PLA基体的界面相容性。     

界面过渡层对SiC/Al双连续相复合材料性能的影响

研究了界面过渡层对SiC/Al双连续相复合材料性能的影响.结果表明,界面过渡层降低了复合材料中的残余应力,改善了界面的结合,提高了复合材料的压缩性能.当界面过渡层中SiC的体积分数接近50%时,复合材料的压缩强度最高,塑性最好,但弹性模量较低.界面过渡层的存在改变了复合材料的弯曲断裂机制.SiC原始泡沫增强的复合材料在断裂时,增强体SiC泡沫先断裂,基体后破坏,断裂表面凹凸不平;含界面过渡层的复合材料断裂时,过渡层的外侧界面先被撕开,内侧界面结合良好,基体与增强体同时断裂,断口平整.     

A finite element model of the fragmentation test for the case of a coated fiber

The fiber/matrix interface in composite materials is generally studied by means of the fragmentation test by using a single filament embedded in a polymeric matrix. The average shear strength, , of the interface is computed from the well-known shear-lag theory. For the case of a fiber coated with a thin layer of an interphase having a low modulus, a finite element analysis model has been developed to describe the profiles of the tensile and shear stresses along a fiber fragment. The introduction of a soft interlayer decreases the stresses at the ends of the fragment, and as the interlayer thickness increases this effect becomes more important. This model shows the limits of the shear-lag theory and could explain experimental results obtained for the case of an elastomer-coated glass fiber in an epoxy matrix.     

Numerical investigation on the natural convection effects in the melting process of PCM in a finned container using lattice Boltzmann method

This work presents a numerical study to investigate the melting process inside a finned rectangular container of phase change material. This issue is interested to know what will happen in the presence of fins, which increase the rate of heat transfer and immerse the solid body through the liquid phase. Momentum exchange between the liquid and solid phases necessitates to consider the immersed boundary condition on the solid–liquid interface. This procedure is done by considering the direct-forcing scheme in the lattice Boltzmann framework. In this regard, velocity and temperature fields are obtained using the multi relaxation time model. To track the solid–liquid interface, a set of Lagrangian points is intended on the boundary of the solid phase. Also, the phase change process is modeled by applying the energy conversion on the finite control volume around these points. Results include melting process for three states: assumption of pure conduction, considering the effects of natural convection around the fixed solid body and natural convection through the free solid phase. Comparing results of melting history and solid–liquid interface position in those states specifies the importance of momentum exchange between solid and liquid phases, in which the forced exerted by the fluid flow accelerates the melting process.