基于二次回归正交旋转试验熔融沉积超声振动成型研究

为了研究超声振动对熔融沉积成型(FDM)制品力学性能的影响以及各变量之间的相关关系,在原有熔融沉积成型设备的基础上增加了超声振动系统,采用单因素试验与二次回归正交旋转组合试验相结合,分别以打印外壳厚度、填充密度和超声波功率3个因素为研究对象对FDM成型工艺进行研究.结果表明,超声振动功率对材料的拉伸性能具有很大的影响,...     

填充路径对FDM制造ABS力学性能的影响

熔融沉积成型制造的塑料件力学性能主要受成型工艺参数的影响。因此,研究了制造成型方向相关填充路径、温度热处理条件对熔融沉积成型ABS试件力学性能的影响。结果表明,ABS试件弹性模量、极限拉伸强度、断裂伸长率和失效形式呈现出与成型取向及填充路径相关的各向异性。采用0°填充路径的ABS试件的拉伸力学性能与成型材料一致;采用±45°填充路径的试件极限拉伸强度为成型材料的0.81倍;采用90°填充路径的试件的拉伸力学性能较差,其极限拉伸强度和断裂伸长率仅分别为成型材料的60.8%和42.7%。在160℃填充路径的下,加热1 h可最大程度改善90°填充路径的ABS试件层间粘结质量,其极限拉伸强度和断裂伸长率分别提升了1.48倍和3.56倍,与成型材料力学性能相近。0°和±45°填充路径的ABS试件失效表现为填充丝材的拉伸和相邻丝材分离,90°填充路径的试件由于层间粘结分离而被破坏。因此,建立了等效力学性能模型分析成型丝材力学性能、填充路径和孔隙率对打印试件弹性模量和极限拉伸强度的影响,预测值与实验数据吻合较好。     

聚乳酸／聚（3⁃羟基丁酸⁃co⁃3⁃羟基戊酸酯）共混材料3D打印线材改性研究

采用熔融共混法制备聚乳酸／聚（3?羟基丁酸?co?3?羟基戊酸酯）（PLA/PHBV）,以及分别添加苯乙烯?甲基丙烯酸缩水甘油酯共聚物（ADR）、柠檬酸三丁酯（TBC）的共混物PLA/PHBV/ADR和PLA/PHBV/TBC,通过注塑和熔融沉积成型（FDM）技术制备了标准测试样条,研究了添加ADR和TBC后对PLA/ PHBV共混材料及三维（3D）打印样品热学性能和力学性能的影响。结果表明,PHBV结晶度均降低,加入ADR的注塑样品断裂伸长率最大提高到32 %,加入TBC的注塑样品拉伸强度和冲击强度提高,断裂伸长率提高到2.8 %;加入ADR的3D打印制品拉伸强度降低,断裂伸长率提高,添加TBC的3D打印制品相容性得到了明显的提升,通过扫描电子显微镜（SEM）观察无明显的颗粒相,拉伸强度在改性前后无明显变化。     

聚苯酯／石墨／聚甲醛复合材料的力学性能

用转矩流变仪共混-模压成型方法制备了聚苯酯/石墨/聚甲醛复合材料，并对其力学性能（拉伸强度，弯曲强度，冲击强度和压缩强度）进行了研究。结果表明，聚苯酯的加入，使聚苯酯/石墨/聚甲醛复合材料的压缩强度提高，拉伸强度，弯曲强度和冲击强度有所降低，但并不防碍其作为结构零件使用；当聚苯酯含量为20%左右时，复合材料具有较为理想的综合力学性能。     

填充模式对熔融沉积PLA力学性能、成型时间及材料消耗的影响

研究了熔融沉积成型工艺中填充模式对聚乳酸(PLA)打印试件力学性能、成型时间及材料消耗的影响。研究发现同心圆型相比于直线型、线形、蜂窝型、阿基米德和弦型填充图案在相同的填充密度下,具有更高的力学强度,较少的成型时间及材料消耗;随着试件填充密度的提高,试件拉伸、弯曲、冲击强度均有显著提升,但同时也会使成型时间及材料消耗显著增加。     

尼龙线材FDM成型质量优化研究

为提高尼龙线材熔融沉积(FDM)成型精度和拉伸性能，基于试验法和灰色关联模型研究确定了尼龙线材的FDM成型精度和拉伸性能的影响因素并进行了优化分析。以打印速度、层厚、喷嘴温度、热床温度与填充密度为因素变量，以Z向成型精度、拉伸强度等成型质量为优化目标，进行了正交试验，并基于灰色关联分析和熵权法进行了成型质量与其因素变量间的灰色关联综合评价。结果表明，各影响因素对成型精度的灰色关联度大小依次为层厚>填充密度>喷嘴温度>热床温度>打印速度，对拉伸性能的灰色关联度大小依次为填充密度>喷嘴温度>热床温度>层厚>打印速度，各因素对成型质量综合影响程度大小依次为：层厚、填充密度、喷嘴温度、热床温度和打印速度，最优工艺参数组合为打印速度60 mm/s,层厚0.15 mm,喷嘴温度250℃,热床温度100℃,填充密度100%。研究结果为提高尼龙线材的FDM成型质量提供了数据支持。     

阻燃增强PBT/AS合金的性能研究

通过双螺杆挤出机制备了一系列阻燃增强聚对苯二甲酸丁二醇酯(PBT)/苯乙烯-丙烯腈共聚物(AS)合金,研究了PBT与AS配比对合金的力学性能、阻燃性能和成型收缩率的影响,并用差示扫描量热(DSC)和热失重(TG)对材料的熔融行为、结晶行为和热稳定性能进行了分析。结果表明,PBT/AS配比对阻燃增强PBT/AS合金的拉伸强度、弯曲强度和阻燃性能影响较小,但AS用量的增加会明显降低材料的缺口冲击强度、热变形温度和纵向收缩率;DSC和TG测试表明,PBT/AS配比对阻燃增强PBT/AS合金的熔融温度、结晶温度、结晶速度和结晶度均无影响,材料的熔融焓、结晶焓和热稳定性随AS用量增加逐渐下降。     

PA12试件多射流熔融成型工艺研究

采用多射流熔融增材制造技术制备了PA12试件,研究了PA12试件不同的构建取向对其成型精度和力学性能以及致密度的影响规律。结果表明,当位置尺寸为宽度方向时,尺寸精度总是呈正偏差,并且在不同得成型角度下,无明显变化规律,与宽度方向相比,厚度方向与长度方向尺寸精度随成型角度增加,变化规律较为明显;试件的力学性能与延伸率受成型角度影响规律相似,当成型角度从0 °增加到45 °时,试件拉伸强度与延伸率逐渐降低,在成型角度大于45 °后,拉伸强度与延伸率显著提升;致密度变化趋势与力学性能保持一致;综合分析可得,当成型角度为45 °时,试件的尺寸精度达到最佳水平;最佳力学性能成型角度为0 °,此时PA12试件的平均拉伸强度为50.95 N/mm²,平均延伸率为37.02 %;致密度最高成型角度为0 °,平均致密度可达到99.311 %。     

熔融沉积成型与注塑成型聚乳酸产品力学性能对比

通过挤出成型制备聚乳酸(PLA)线材,采用熔融沉积方法制备标准拉伸试样,对比熔融沉积成型(FDM)与注塑成型对PLA产品力学性能的影响。研究结果表明:PLA打印产品的拉伸强度较注塑成型下降了31.9%,然而其断裂伸长率相对提升了186%;3D打印产品结构对产品力学性能有一定影响,沉积丝的拉伸应变主要是由产品内部结构的弯曲变形引起的;打印线材的形状对拉伸形变和弯曲形变几乎没影响。     

3D打印工艺参数对PLA试件拉伸强度的影响

为了提高熔融沉积成型工艺打印件的力学性能以及减少打印时间成本,利用3ds Max三维建模软件,设计出打印力学试件的三维模型,结合单因素和正交试验分析,研究了填充角度、打印速度、打印温度、填充密度以及分层厚度对聚乳酸(PLA)试件拉伸强度的影响,并对试件拉伸强度进行测试。结果表明,各参数对3D打印PLA试件的影响大小为:填充密度分层厚度填充角度打印温度打印速度,且当打印分层厚度为0.3 mm,打印速度为80 mm/s,打印温度为210℃,填充密度为40%,填充角度为45°,试件具有最优的拉伸强度。     

Retained properties of concrete exposed to high temperatures: Size effect

Concrete as a construction material is likely exposed to high temperatures during fire. The retained properties of concrete after such exposures are still of great importance in terms of the serviceability of structures. This paper presents the effects of high temperatures on the physical, mechanical, and microstructural properties of concrete. Specimens with different sizes were exposed to high temperatures ranging from 200 to 1200^°C. The compressive strength, splitting tensile strength, ultrasonic pulse velocity, and rebound numbers of the specimens were determined. The microstructures of the specimens were examined by scanning electron microscope (SEM) analyses. The test results indicated that the retained compressive strength of concrete considerably decreased with increase in temperature. The effect of specimen size on the retained compressive strength was not pronounced. The retained splitting tensile strength of concrete remarkably reduced as the temperature was increased. The specimen size played an important role on the retained splitting tensile strength of concrete up to 400^°C. The test results revealed that ultrasonic pulse velocity (UPV) test can be successfully used in order to check the uniformity of fire‐damaged structures. The rebound numbers decreased with increase in exposure temperature. SEM studies on specimens exposed to 800^°C revealed significant changes in the microstructure of the concrete. Copyright © 2009 John Wiley & Sons, Ltd.     

Localized effects of dynamic melt manipulation on flow induced orientation and mechanical performance of injection molded products

This study investigates the effects that dynamic melt manipulation based injection molding has on the locally induced molecular orientation and tensile strength of injection molded polystyrene. Melt manipulation refers to a process where the polymer melt is manipulated during molding beyond the extent normally encountered in conventional injection molding. The specific melt manipulation process investigated in this article is vibration assisted injection molding, where a conventional injection molding machine is augmented by oscillating the injection screw (in the axial direction) during the injection and packing phases of the molding cycle. The localized final molecular orientation and morphology that results dictates the resultant product response, and typically improved mechanical properties are observed. Specimens with molecular orientation distributed more uniformly along the gage length typically exhibited higher tensile strength than samples with a gradient of orientation along the gage length. Smaller test specimens machined along the gage length of larger molded specimens showed dramatic tensile strength increase in the regions of higher melt manipulation, further supporting the promise of this novel processing methodology. POLYM. ENG. SCI., 47:1912–1919, 2007. © 2007 Society of Plastics Engineers     

Fatigue performance of injection‐molded short e‐glass fiber reinforced polyamide‐6,6. II. Effects of melt temperature and hold pressure

Tensile and fatigue properties of an injection molded short E‐glass fiber reinforced polyamide‐6,6 have been studied as a function of two key injection molding parameters, namely melt temperature and hold pressure. It was observed that tensile and fatigue strengths of specimens normal to the flow direction were lower than that in the flow direction, indicating inherent anisotropy caused by injection molding. Tensile and fatigue strengths of specimens with weld line were significantly lower than that without weld lines. For specimens in the flow direction, normal to the flow direction and with weld line, tensile strength and fatigue strength increased with increasing melt temperature as well as increasing hold pressure. The effect of specimen orientation on the tensile and fatigue strengths is explained in terms of the difference in fiber orientation and skin‐core morphology of the specimens. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers.     

乙烯⁃醋酸乙烯共聚物纳米纤维网状结构黏合材料

通过添加无机盐改善乙烯?醋酸乙烯共聚物(EVA）纳米纤维静电纺丝困难的问题,得到一种网状结构的黏合材料。将其置于两层丙纶熔喷布之间,经热压得到复合材料。探究最佳纺丝参数及热压温度对层间剪切强度的影响,在最适温度下制备复合材料,并测试了其拉伸性能以及空气过滤效率。结果表明,当纺丝液浓度为6 %、三氯甲烷(CHCl₃)与四氢呋喃(THF)的质量比为7∶3,氯化锂(LiCl)添加量为0.2 %（质量分数,下同）时,EVA纳米纤维形态良好;80 ℃下热压时剪切强度最高;经测量复合材料的空气过滤效率能达到98.71 %以上,显著优于4层商用口罩熔喷布的过滤效率;复合材料的与力学性能复合前的熔喷布相比,也有了明显的提高。     

Effect of melt vibration on structure and mechanical properties of HDPE/nano-CaCO3 blend

Melt vibration technology was used to prepare injection sample of HDPE/nano-CaCO₃ blend, whose mechanical properties were improved significantly. Compared with conventional injection molding, the enhancements of the tensile strength and impact strength of the sample molded by vibration injection molding were 41.2 and 43.2%, respectively. According to the SEM, WAXD, and DSC measurement, it was found that a much better dispersion of nano-CaCO₃ in sample was achieved by vibration injection molding. Moreover, crystal orientation degree of matrix HDPE increased under the effect of melt vibration. The crystallinity degree of HDPE in vibration sample increased by 5.5% compared with conventional one. The improvement of mechanical properties of HDPE/nano-CaCO₃ blend prepared by low-frequency vibration injection molding attributes to the even distribution of nano-CaCO₃ particles and the orientation of HDPE crystals and increase of crystallinity degree under the influence of melt vibration.     

Study on integrally molded PA6/304 stainless steel by micro-nano pressing technology

With application of micro-nano pressing technology (MNPT) polyamide 6 (PA6) and 304 stainless steel were integrally molded, and the mechanical properties and structure on the interface of plastic and metal were investigated in the study. The micro structures on the stainless steel specimen surface were achieved by physical and/or chemical surface treatment techniques including polishing and etching methods, respectively. The tensile shear strength and work of fracture for the integrally molded specimen were influenced greatly by the surface treatment on stainless steel. The maximal tensile shear strength and the fracture work for the MNPT molded sample reached up to ca. 11?MPa and 17?KJ/m², respectively. In addition, the interface fractography of the MNPT molded specimen was characterized by scanning electron microscope (SEM) and atomic force microscope (AFM). These results indicated PA6 melt flew into the micro and/or nano holes on the chemical etched metal surface during hot press molding to form micro mechanical interlock structure to prepare strong MNPT molded samples.     

Microstructure and tensile properties of injection molded thermoplastic polyurethane with different melt temperatures

The use of injection molding technology to prepare heterogeneous interlayer film of laminated glass holds strong applicable potential. This article aims to investigate the effects of melt temperature and melt flow on the microstructure evolution and tensile properties of thermoplastic polyurethane (TPU) specimens during the injection molding process. The tensile properties of the TPU specimens show dependency on the melt temperature and melt flow direction. The results of birefringence indicate that melt flow and lower melt temperature induce higher stretching deformation of the molecular chain network. Small-angle X-ray scattering analysis approves that besides the melt temperature and flow direction, the testing position on the cross section of the specimen has great influence on the microstructure of the TPU sheet. Further analysis and conclusions can be made using wide-angle X-ray scattering method. The above results demonstrate that both the tensile properties and microstructure of the injection molded TPU specimens tend to be isotropic with the increase of melt temperature. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48891.     

Improving the mechanical properties of polypropylene via melt vibration

The effect of melt vibration on the mechanical properties of polypropylene prepared by low-frequency vibration-assisted injection molding (VAIM) has been investigated. With the application of melt vibration technology, the mechanical properties of polypropylene are improved. The yield strength increases with the increment of the vibration frequency, and a peak stands at a special frequency for VAIM; the elongation at break decreases first and then increases with increasing vibration frequency, and a valley stands at a special frequency. The tensile properties increase sharply at an enlarged vibration pressure amplitude with sharply decreased elongation at break. The Young's modulus and impact strength also increase with the vibration frequency and pressure vibration amplitude. When it is prepared at 59.4 MPa and 0.7 Hz, the maximal yield strength is approximately 40 MPa versus 33.7 MPa for a conventional sample; an 18.7% increase in the tensile strength is produced. Self-reinforcing and self-toughening polypropylene molded parts have been found to be prepared at a high vibration frequency or at a large pressure vibration amplitude. Scanning electron micrographs have shown that, in the vibration field, the enhancement of the mechanical properties is attributable to more pronounced spherulite orientation and increased crystallinity in comparison with conventional injection moldings. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008