等规聚丙烯微注塑制品的形态结构和力学性能

选用等规聚丙烯材料,基于正交表L_(25)(5~6)进行微注塑成型实验,制备厚度为0.5 mm的微注塑拉伸试样。采用偏光显微镜和广角X射线衍射仪对其形态结构进行表征,并分析工艺参数对微制品形态结构的影响规律和影响度。对微制品试样进行拉伸实验,分析工艺参数对其屈服应力、弹性模量和断裂伸长率的影响规律和重要度。结果表明,注射速度对微试样的形态结构和力学性能的影响最大;皮层厚度和皮层取向度随着注射速度的增大而减小;屈服应力随注射速度、熔体温度的增大而减小;熔体温度对弹性模量和断裂伸长率的影响较大,且弹性模量随着熔体温度的升高而减小,断裂伸长率随着熔体温度的升高而增大。     

等规聚丙烯微注塑制品的力学性能

采用等规聚丙烯材料,选取弹性模量和屈服强度作为微制品力学性能的指标,基于正交实验设计进行微注塑成型实验以成型微拉伸试样,采用直观分析、信噪比分析及方差分析对微试样的拉伸实验结果进行分析,研究工艺参数对厚度1.0 mm,0.5 mm和0.2 mm的微注塑制品力学性能的影响规律及重要性,并分析尺度效应对微制品力学性能的影响。实验结果表明,不同尺度下,各个工艺参数对微制品力学性能的影响规律和重要性均不同,且随着尺寸的减小,微注塑制品的拉伸屈服强度增大,弹性模量增大。     

聚氨酯基体配比对芳纶增强聚氨酯复合材料 力学性能的影响

以甲、乙双组分聚氨酯为基体,芳纶为增强体,制备了不同基体配比的芳纶增强聚氨酯复合材料,并采用拉伸试验、弯曲试验、冲击试验等方法对其力学性能进行了分析。结果表明:随着聚氨酯中乙组份比例的增大,芳纶增强聚氨酯复合材料的拉伸断裂强度、拉伸弹性模量、弯曲强度和弯曲弹性模量也随之增大,断裂伸长率则随之减小,冲击韧度先增大后减小,当甲、乙组比例为10∶4时,冲击韧度最大。     

聚醋酸乙烯酯/二氧化钛杂化纳米纤维毡的形貌及力学性能

采用溶胶-凝胶法结合静电纺丝技术制备了聚醋酸乙烯酯(PVAc)/氧化钛(TiO2)杂化纳米纤维.通过使用扫描电子显微镜(SEM)和单纤维拉伸仪对不同条件下制备的杂化纳米纤维表面形貌和力学性能进行了表征和测试,探讨了有机无机杂化纳米纤维力学性能的影响因素.研究发现,随着TiO2溶胶含量的增加,纳米纤维表面珠状物减少,纳米纤维膜的断裂强度增大而断裂伸长率减小;随着滚筒转速的加快,纳米纤维毡的纤维取向有所改善,纳米纤维毡的断裂强度和断裂伸长率都有所增大;随着环境湿度的增加,纳米纤维毡的纤维之间粘结点增多,纳米纤维的断裂伸长率增大,断裂强度先增大后减小.     

经二氧化碳激光加热拉伸后聚酯长丝的力学性能和微观结构

用CO2激光对聚酯预取向丝(POY)进行加热拉伸,研究了拉伸倍数和激光器电流对聚对苯二甲酸乙二醇酯(PET)长丝的力学性能、分子构成和结晶度的影响。研究发现,PET长丝的断裂强度和结晶度随拉伸倍数和激光器电流的增大而增大,而断裂伸长率随之明显下降。当拉伸倍数为2.4,激光器电流为5 mA时,断裂强度由原来的2.445 cN/dtex增大到4.319 cN/dtex,结晶度由原来的26.45%增加到40.00%,断裂伸长率由原来的121.9%降至9.0%。傅里叶红外光谱分析结果表明,PET长丝的分子构成在激光加热拉伸前后没有明显变化。     

聚四氟乙烯短纤维的热及化学稳定性研究

通过表观形态观测,得出聚四氟乙烯(PTFE)短纤维的直径服从高斯分布。针对细度差异性较大的PTFE短纤维,提出一种基于线密度差异性的单根纤维追踪测量法,用于测试酸碱处理前后纤维的力学性能。结果表明,经常温酸碱处理后,纤维断裂强度基本无变化,而初始模量减小,断裂伸长率增大;高温酸碱处理后的纤维断裂强度略有增大而断裂伸长率减小;经干热空气和沸水处理后,纤维的断裂强度基本无变化,而断裂伸长率由于解取向略有降低。此外,热失重分析表明PTFE短纤维具有优异的耐高温性能。     

应力三轴度和应变率对6063铝合金力学性能的影响及材料表征

对6063铝合金试样在不同应力三轴度和不同应变率下进行拉伸试验,得到了该合金在这两种情况下的力学性能.研究结果表明:随着应力三轴度的减小,材料的等效弹性模量、等效屈服应力减小,但等效断裂应变增大;随着应变率逐渐增大,材料的屈服强度和断裂强度略有增大;断裂应变明显减小;抗拉强度基本不变.Johnson-cook本构模型及其断裂应变模型可以用来描述6063铝合金在不同三轴应力度和不同应变率下的本构及失效关系.通过材料表征,得出了Johnson-cook本构模型及其断裂应变模型中各个参数,为有限元(ABAQUS)模拟提供帮助.     

微注塑拉伸试样设计及流动特性分析

微拉伸试样的设计,是成功测试微尺度下力学性能的关键。文中设计了不同厚度微拉伸试样及相应的微注塑模具,分析了模具设计及尺度效应对微拉伸试样充填行为的影响,并研究了工艺参数对不同厚度微试样(0.1mm、0.2mm、0.5mm、1mm)充填行为的影响。短射实验表明,随着微试样厚度减小,在微试样有效拉伸长度内,熔体流动前沿呈现为一维平板流动;4个厚度下,0.5mm厚的熔体流动性明显优于其它3个尺寸。工艺影响实验表明,随注射速度、模具温度、熔体温度工艺参数的增加,熔体流动性增强。     

齿科隐形正畸矫治器用膜片的力学性能研究

本文通过测试不同厚度的PETG/PC/TPU齿科隐形正畸矫治器用膜片的力学性能,得到相应的拉伸弹性模量、屈服应力、屈服拉伸应变以及直角撕裂强度,为选择厚度适宜的齿科隐形正畸矫治器用膜片制作无托槽隐形矫治器提供指导。结果显示,弹性模量随膜片厚度增加而逐渐增大（膜片的厚度从0.3mm增至0.7mm,弹性模量从622.4MPa增至1027.6MPa）,PETG/PC/TPU膜片厚度从0.3mm增至0.7mm,直角撕裂强度均>280kN/m。综合分析不同厚度膜片的拉伸弹性模量、屈服应力以及屈服拉伸应变,当PETG/PC/TPU膜片厚度为0.5mm时,矫治器的矫治效果较优异。     

微注塑成型工艺对聚丙烯制品形态结构的影响

文中基于一组薄壁微制品的微注塑成型实验,研究熔体温度和注射速度对厚度为1.0 mm和500μm微制品形态结构的影响。实验结果表明,这两种微制品都呈现出一种相似的皮芯结构,但不同于传统注塑制品4层或5层结构,微制品只有冷冻层、剪切层和芯层3层结构。随着注射速度的提高,在厚度方向上剪切层比例增大,当注射速度超过一定值后,呈现无芯层结构;随着熔体温度的提高,500μm微制品形态变化不大,1.0mm微制品芯层小幅增厚。     

Effects of gate design and cavity thickness on filling,morphology and mechanical properties of microinjection mouldings

Miniaturized parts weighing up to tens of milligrams represent a large category of microinjection moulded products. Both miniaturization and extreme processing under microinjection moulding cause material to experience high shear rates and high cooling rates, and to have different morphology and final properties from conventional injection moulding. It also makes mould design quite challenging. This study investigates micro gate design (opening and thickness) and cavity thickness (100–500 μm) on filling, morphology and mechanical properties of Poly(ether-block-amide) miniaturized dumbbell parts. It is found that a reduction of gate size has two conflicting effects: increased shear heating increases flow length; increased cooling rate reduces flow length. Filling increases significantly with an increase of cavity thickness. In addition, skin ratio reduces from ∼70% to ∼10%, when part thickness increases from 100 μm to 500 μm. Such oriented skin layer determines molecular orientation and broadly influences Young’s modulus, elongation and yield stress. Natural aging at room temperature induces an increase of modulus and yield stress, and a decrease of strain at break. Mechanical properties of microinjection mouldings are significantly different from conventional injection mouldings and measurement at the microscale is required for successful miniaturized product design.     

乙烯咔唑接枝聚乙烯的空间电荷特性及力学性能

为了研究聚乙烯材料的空间电荷特性及力学性能,采用熔融法制备乙烯咔唑(VK)接枝聚乙烯(VK-g-LDPE),并通过电声脉冲法、差热扫描量热法和拉伸试验对VK-g-LDPE的空间电荷分布、结晶度和拉伸性能进行了测试。结果表明,随着接枝率的增加,对VK-g-LDPE内部空间电荷的抑制效果呈现先增强后减弱的趋势;当接枝率为12.45%时,对VK-gLDPE材料空间电荷的抑制作用最好,试样的电荷密度最大值仅为0.31 C/m~3,比聚乙烯降低了95.87%;随着接枝率的增加,VK-g-LDPE的结晶度呈下降趋势;随着接枝率的增加,VK-g-LDPE的拉伸强度呈现先增大后降低的趋势,且当接枝率为13.02%时达到最大值14.2 N/mm~2;随着接枝率的增加,VK-g-LDPE的断裂伸长率和弹性模量呈现下降的趋势。     

两次挤出制备尼龙66/纳米SiO2复合材料及其结构与性能

通过双螺杆两次挤出技术制得了尼龙66/SiO2纳米微粒复合材料,发现二次挤出的复合材料的拉伸强度、断裂伸长率、杨氏模量、简支梁缺口冲击强度较纯尼龙66均有很大程度的提高,并通过动态力学热分析研究了复合材料的动态力学性能,复合材料的储能模量及玻璃化转变温度均有不同程度的提高。借助SEM分析了复合材料的拉伸断面形貌,并用DSC研究了复合材料的结晶行为。     

MAH对干法酯化淀粉/PLA复合材料性能的影响

以玉米淀粉和马来酸酐(MAH)为原料,通过干法合成MAH酯化淀粉,通过熔融挤出法制备酯化淀粉/聚乳酸(PLA)复合材料.研究了MAH用量对复合材料结晶度和相容性的影响,同时考察了相容性和结晶度的变化对复合材料热性能、熔融流动性能、力学性能、耐水性能和流变性能的影响.FTIR结果证明通过干法成功合成了MAH酯化淀粉.酯化淀粉的取代度随MAH用量增多逐渐增大,反应效率高达90%.XRD和DSC结果表明:随着MAH用量增多,酯化淀粉/PLA复合材料的结晶度逐渐降低,淀粉和PLA的相容性逐渐提高.结晶度的降低和相容性的提高使复合材料的玻璃化转变温度逐渐降低,熔融流动性提高,耐水性提高.在力学性能和流变性能受相容性和结晶度的共同影响下,酯化淀粉中MAH用量从0增加到1.0wt%时,复合材料拉伸强度、弯曲强度、储能模量和复数黏度都逐渐增大,MAH用量超过1.0wt%后,性能逐渐降低.     

纺丝液合成因素对木材液化物炭纤维原丝性能的影响

利用木材苯酚液化物合成纺丝液, 熔融纺丝制成新的炭纤维原丝, 研究了纺丝液合成因素对原丝性能的影响。试验结果表明: 增加合成纺丝液时液化原料中的苯酚/木材比(液固比), 则原丝的力学性能提高明显, 其中液固比由3增加至4时, 原丝拉伸强度增加了近9倍; 合成剂用量的增加却导致原丝力学性能的降低, 当合成剂用量为6%时, 原丝的拉伸强度和拉伸模量降幅较明显, 而断裂伸长率的最大降幅却出现在合成剂用量为4%时; 原丝的拉伸强度和拉伸模量随合成温度的升高而增加, 但增幅较小, 断裂伸长率随合成温度的升高却呈下降趋势, 且从110℃升高到115℃时断裂伸长率降幅较大; 原丝的力学性能随合成纺丝液升温时间的增加而先升高后降低, 升温时间为40min时制备的炭纤维原丝的力学性能最优。      

熔体温度对注塑成型iPP制品结晶形态的影响

注塑成型聚丙烯制品的内部结晶形态对制品的最终性能起着至关重要的作用,而结晶形态的形成对成型条件(尤其是熔体温度)有一定依赖性。文中利用偏光显微镜、小角X射线散射和广角X射线衍射等实验方法,详细研究了熔体温度对注塑成型iPP制品结晶形态的影响。研究结果表明,在实验温度范围内,制品厚度方向形态呈现五层皮芯结构,即冷冻层、过渡层、剪切层、β晶层、α球晶层。随着熔体温度提高,皮层厚度减小;结晶度提高,取向度极大值并无明显变化。     

Effects of recycling on the microstructure and the mechanical properties of isotactic polypropylene

Polypropylene (PP) was injection moulded several times to mimic the effect of recycling procedures. The influence of the recycling was studied by following changes in chemical structure, melt viscosity, crystallisation behaviour, and tensile and fracture properties. The main effect of recycling is the lowering of the melt viscosity, which is attributed to molecular weight decrease. Recycled PP exhibits greater crystallisation rate, higher crystallinity and equilibrium melting temperature than those measured for virgin PP. Elastic modulus and yield stress increase with the number of recycling steps. However, elongation at break and fracture toughness decrease.     

温度对V-5Cr-5Ti合金拉伸性能及组织结构的影响

对真空自耗重熔制备的V-5Cr-5Ti合金进行了室温到1150℃温度范围的拉伸性能测试,获得了不同温度下的拉伸应力应变曲线,用SEM和光学显微镜对断口形貌和金相组织进行了观察,分析了温度对断口形貌和组织的影响。结果表明:V-5Cr-5Ti合金的屈服强度和极限强度总体上随温度升高而降低,但在300℃到700℃之间出现应变失效效应,断裂伸长率随温度升高而降低,断面收缩率随温度升高先增大再而降低,在400℃时断面收缩率最大;温度较低时塑性变形以滑移为主,温度较高时以晶界开裂为主,并伴随有晶界熔化的现象,高温断口表现为韧性断裂为主,具有韧性与脆性共存的现象。     

Production and Anisotropic Tensile Behavior of Resin‐Metal Interpenetrating Phase Composites

Metal‐polymer composites can be used to synthesize material properties. A variety of interpenetrating phase composites have been produced by spontaneously infiltrating porous short‐fiber preforms with unsaturated polyester resin under vacuum conditions. Porous preforms are fabricated by compacting and sintering short 304 stainless steel fibers from cutting stainless steel fiber ropes. Tensile experiments are conducted, and fractographs are examined via scanning electron microscopy. The results reveal that the tensile strength, elongation at maximum stress, and elasticity modulus of the IPCs increase with the increasing fiber fractions and exhibit anisotropy in different directions. The tensile strength and elongation at maximum stress are significantly improved compared with the consistent preforms. A nonlinear elastic behavior and sawtooth‐like fluctuation during yield deformation are noted. Compared with the through‐thickness direction, a higher tensile strength and larger elongation at maximum stress are observed in the in‐plane direction. Finer‐diameter fibers can improve the strength and increase the elongation at maximum stress. The tensile fracture surfaces show a mixture of brittle and plastic fracture characteristics.

     

Relationships between processing conditions and mechanical properties of PA12 tubes. The EWF approach

In polyamide 12 (PA12) tube extrusion, calibration is the key step of the process that affects the subsequent mechanical properties. In previous work it has been shown that according to the calibration conditions, a very oriented skin layer may be created, which has been correlated to an important decrease of elongation at break. In this paper, we present new results showing a good correlation between molecular orientation and fracture toughness, as evaluated by the EWF (Essential Work of Fracture) approach. They concern notched specimens and confirm the results obtained in classical tensile testing. The specific essential work of fracture is very sensitive to the orientation generated in the skin region by appropriate processing conditions: it decreases from the external to the inner regions of the tube, and increases with skin orientation.