注射成型热塑性聚氨酯制件的取向形态演变和力学性能

通过光学双折射、小角X射线散射(SAXS)和广角X射线散射(WAXS)等研究热塑性聚氨酯(TPU)在注射成型过程中熔体流动场对其取向形态演变、残余应力和力学性能的影响.双折射结果表明,沿熔体流动路径上制件残余应力降低.由 SAXS和 WAXS结果可知,TPU分子链中的硬段沿熔体流动方向取向,而团聚成的硬域垂直于熔体流动方向取向.TPU拉伸性能沿熔体流动方向和垂直于熔体流动方向呈现出明显的差异性,制件中间区域的拉伸强度最高,这是因为硬段和硬域在制件中间区域取向度最大,硬段和硬域的取向有助于提升拉伸强度.     

二次注射成型光学制件厚度截面的残余应力分析EI北大核心CSCD

采用光弹法定量对比分析一次注射成型与二次注射成型光学制件在厚度截面上的残余应力。结果表明,一次注射成型和二次注射成型光学制件的截面残余应力分布均为双抛物线状,但后者的应力水平大于前者。同时,二次注射成型的PC/PC和PMMA/PMMA在界面处两侧的低应力层和零应力层消失,相反地,两层的界面处存在高应力峰。另外,与PMMA或PMMA/PMMA的双抛物线应力分布截然不同,PC/PMMA和PMMA/PC复合制件的PMMA层的残余应力表现为沿PMMA外侧面向界面方向逐渐增大的趋势。此外,PC和PMMA的注射顺序对二次注射成型复合制件的残余应力具有显著影响,主要体现在界面处和整个PC层。PC/PMMA的界面处应力明显高于PMMA/PC,且前者PC层靠近界面处仍存在低应力层和零应力层,而后者不存在此两种应力层。     

聚碳酸酯光学制品注塑成型的残余应力EI北大核心CSCD

采用单一变量实验考察了不同注射工艺参数对光学制品双折射的分布规律,通过应力-光弹定律计算了对称轴上残余应力值。用Moldflow软件对制品成型过程中型腔内流场进行模拟,分析了厚度方向应力的变化。结果表明,沿熔体流动方向上,制品残余应力是逐渐减小的,浇口附近有应力集中;在合理工艺范围内,适当提高成型温度和模具温度,延长保压时间和冷却时间有助于减小制品的残余应力,保压压力和注塑速度应适中才能改善制品的成型质量。     

注塑压缩成型工艺对聚甲基丙烯酸甲酯-聚碳酸酯复合平板残余应力的影响EI北大核心CSCD

基于光弹法研究了聚碳酸酯(PC)、聚甲基丙烯酸甲酯(PMMA)两种材料的二次注射压缩成型中不同工艺参数,包括保压压力、保压时间、熔体温度、模具温度及压缩距离等对PMMA-PC复合平板制件残余应力的影响。结果表明,随保压压力的增大、保压时间的延长,残余应力呈现先减小后增大趋势;增加熔体温度和压缩距离会降低复合平板内的残余应力。模具温度的升高会使复合平板的残余应力逐渐增大,原因在于模内不对称冷却加剧了复合平板内部的残余热应力,当模具温度为70～80℃时,复合平板内残余应力较小且分布均匀。所研究的工艺参数中,模具温度和熔体温度对复合平板的残余应力影响最为显著。     

注射成型聚苯乙烯的取向和残余应力

设计带压力传感器和热电偶的矩形模具,进行聚苯乙烯不同工艺条件注射成型实验,通过测试双折射３个热直方向的分量,分析工艺条件对制品性能的影响。最后讨论注射成型制品中的取向分布和残余应力。     

注射成型工艺参数对聚碳酸酯残余应力的影响

采用正交实验法考察了不同注射成型工艺参数对聚碳酸酯(PC)残余应力的影响,结果表明:熔体温度对残余应力影响最大,冷却时间和模具温度次之,注射压力影响最小。熔体温度升高,分子链快速松弛,残余应力减小。同时试样浇口附近处的残余应力较大且分布集中,沿熔体流动方向,残余应力逐渐减小。对于不同成型工艺,残余应力的分布趋势基本相同。     

基于熔融沉积成型的聚乳酸/热塑性聚氨酯的制备与表征EI北大核心CSCD

通过熔融共混法制备了不同质量比的聚乳酸(PLA)/热塑性聚氨酯(TPU)共混物。采用旋转流变仪、扫描电镜、电子万能试验机及差示扫描量热仪等研究了共混物的动态流变行为、微观形貌、力学性能和热性能,并通过线材机牵引成直径为1.75 mm左右的线材进行熔融沉积成型(FDM)。结果表明,加入TPU后能提高材料的储能模量,使熔体弹性增强,利于熔融铺丝。TPU能改善材料的冲击韧性,且随着TPU含量的增加而增大。另外,PLA/TPU熔融共混后体系的结晶能力下降,对熔融沉积成型收缩翘曲具有抑制作用。当TPU质量分数为10%时,线材的熔融沉积成型效果最好。     

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。     

聚酯型热塑性聚氨酯弹性体的合成及对聚氯乙烯的增韧EI北大核心CSCD

以二苯基甲烷二异氰酸酯(MDI)、聚ε-己内酯多元醇(PCL)及1,4-丁二醇(1,4-BDO)为原料,成功设计合成了聚酯型热塑性聚氨酯弹性体(TPU)。合成条件:异氰酸酯指数R=0.98,温度60~70℃,反应时间1 h。通过元素分析、红外光谱、核磁共振、差示扫描量热分析、凝胶色谱等测试,确定了TPU中的硬段含量及化学结构。通过与聚氯乙烯(PVC)进行共混,评价了合成TPU对PVC的增韧效果,经力学性能测试、差示扫描量热分析以及扫描电子显微镜观察研究了共混材料的结构与性能,揭示增韧机理。结果表明,合成TPU与PVC之间具有良好的相容性,对PVC有良好的增韧作用,当m(PVC)∶m(TPU)=170∶30时,力学性能优于市售TPU牌号。合成的TPU随硬段比例增加,PVC/TPU共混物材料拉伸强度变化不大,断裂伸长率下降,而冲击强度大幅提高,实现了对PVC的增韧。     

二氧化碳诱导热塑性聚氨酯结晶增强其拉伸性能EI北大核心CSCD

通过高压傅里叶变换红外光谱方法研究了CO_2对热塑性聚氨酯(TPU)氢键结构的作用,结合广角X射线衍射和扫描电镜的方法,研究了CO_2低温退火对TPU结晶性能及拉伸强度的影响。结果表明,CO_2可以与TPU产生Lewis酸碱作用,并且能降低TPU的氢键化程度;CO_2可以诱导TPU的结晶,使其结晶度增大,从而增强其拉伸强度;CO_2退火后出现微发泡,比未发泡的TPU样品拉伸强度更高。     

Effect of extrusion process melt temperature on polyurethane catheter surfaces

Determination of optimum process melt temperature of medical-grade polyurethane (PU) is an indispensable challenge witnessed during the catheter manufacturing process. This resin does not contain a uniform crystal structure but exists in an amorphous state. The lower shore hardness PU material, used in catheter manufacture, has just a “melt temperature range” instead of a definite melt temperature. This temperature plays a significant role in shaping the catheter surfaces, which directly interact with human tissues and cause health-care-associated issues. The objective of this work is to evaluate the effects of variations in the melt temperature during the extrusion process of medical catheters on their outer surfaces. Medical PU, Pellethane, was used for this study and 12 Fr (4.0?mm) catheters were manufactured with optimal validated parameters, excluding melt temperature. The manufactured catheters were examined under Optical Microscopy and Atomic Force Microscopy (AFM) for surface topography studies. Wettability studies were carried out using a Goniometer for evaluating the water contact angles. The effects of melt temperature on the surface roughness (R_a) and wettability of the catheter surfaces were analyzed through analysis of variance (ANOVA). The conclusion was that the process melt temperature variations have a significant effect on catheter R_a and its wettability characteristics.     

Effect of gate size on the melt filling behavior and residual stress of injection molded parts

This paper studies the effects of gate size on the cavity filling pattern and residual stress of injection molded parts. A total of three rectangular gates with different sizes were used. Experiments were carried out by using a dynamic visualization system. A flow visualization mold was specially designed and made for this study. A high-speed video camera was used to record the mold filling phenomena of cavities with different gate size and different processing parameters. In addition, a Stress Viewer was used to characterize the residual stress of molded samples. It was found that the undersized gate has many adverse effects on the filling behavior and residual stress of molded parts. With a larger gate, the cavity will be filled faster and residual stress of parts may be smaller. The result of the study also indicates that nozzle temperature and injection rate can significantly affect the above two aspects.     

纳米SiO_2功能化改性石墨烯/热塑性聚氨酯复合材料的制备与性能

采用Hummers法制备了氧化石墨烯(Graphene Oxide,GO),再与经硅烷偶联剂(APTES)偶联改性纳米SiO_2所得的产物(nano SiO_2—NH_2)混合,制备了石墨烯片(Graphene Sheets,GS)接枝纳米SiO_2杂化材料(nano SiO_2-g-GS)。以nano SiO_2-g-GS为填料,热塑性聚氨酯(TPU)为基体,通过熔融共混法制备共混型nano SiO_2-g-GS/TPU复合材料,并对填料和复合材料进行测试和表征。拉伸测试显示nano SiO_2-g-GS的加入对基体TPU有一定的补强作用,使复合材料定伸应力(300%、500%和1 000%)增大。DSC测试显示,与纯TPU相比,nano SiO_2-g-GS/TPU复合材料的结晶温度有大幅升高,填料含量为1wt%时,TPU的结晶温度升高了44℃。形状记忆测试结果显示,随nano SiO_2-g-GS含量增加,nano SiO_2-g-GS/TPU复合材料的形状回复率(Rr)逐渐降低,但形状固定率(Rf)逐渐升高。当nano SiO_2-g-GS质量分数为1wt%时,nano SiO_2-g-GS/TPU复合材料性能最佳。     

The formation of residual stresses in laminated thermoplastic composites

The means by which residual stresses are generated in continuous carbon-fibre-reinforced thermoplastic composites are reviewed, with specific attention to the macroscopic stresses which form on a ply-to-ply level. Different means for their estimation are assessed, and approximate stress levels are defined for a variety of materials. The capacity for stress relaxation to occur during processing is examined, and it is shown that little useful stress-relieving ability can be promoted in such systems.     

热塑性聚氨酯/聚乙烯醇共混材料制备及性能

通过溶液共混的办法,制备了热塑性聚氨酯(TPU)/聚乙烯醇(PVA)共混材料。通过FI-IR、DMTA初步考查了两相的相互作用;同时对共混材料的水溶胀性能进行了表征。结果表明, TPU/PVA两相存在氢键作用,具有一定的相容性;共混材料吸水率随着PVA的加入而逐渐增大,两相配比为7:3时,共混材料力学性能最佳。     

Experiments and prediction of in-cavity stress for injection molded part

Prediction of residual stress of the injection molded polymers is one of the most challenging issues in this process. To investigate the development of this residual stress, creep experiments were carried out and creep rule was found. In the light of the experimental results, a creep model for predicting in-cavity stress of the molding was built. The elastic module of material was obtained with Tait equation and its viscous factor obtained with inversion method. In-cavity stress was calculated with the model and finite element method for an injection molded plate made by ABS. The predicted results was verified by the experiments and compared with relaxation model. The results showed that the new model was more accurate than relaxation model. The solution of the problem will effectively prompt the numerical simulation of injection molding, and will be a valuable development for the quality control.     

矫直辊辊型曲线对中厚板残余应力的影响

为深入研究矫直过程中矫直辊辊型曲线对中厚板残余应力的变化规律,分析了新一代矫直机的典型弯辊结构,针对其中一种弯辊结构运用接触有限元软件计算了其弯辊效果,得到了从负弯到正弯等多种矫直辊辊形曲线.建立了矫直辊辊形曲线对残余应力影响的解析模型和流程,运用数值方法求解该模型.研究结果表明:弯辊量对较宽的轧件的残余应力影响不显著,即使弯辊手段用反了,残余压应力仍然可以得到一部分消减;弯辊量对较窄的轧件的残余应力影响很大,如果弯辊手段用反了,残余拉、压应力都得不到有效消减.     

振动时效工艺在消除膨胀波纹管残余应力中的应用

膨胀波纹管体冷压成型后存在较大的残余应力常导致管端面严重变形和尺寸不稳定,已成为制约管体焊接连接质量和效率提高技术瓶颈。探索振动时效法用于消除或减弱波纹管体残余应力的可行性。结合室内试验和现场试验数据,建立振动时效法适用的关键技术、工艺参数、评价方法以及后处理分析手段。采用所建立的评价体系,通过振动时效参数曲线观测和盲孔法残余应力测量,评定了该试验振动过程及振动时效效果有效性,这证明振动时效工艺可显著降低膨胀波纹管残余应力,能够满足膨胀波纹管焊接等工程需要,提高其尺寸稳定性。     

渗碳淬火件残余应力场的有限元模拟

本文对渗碳淬火后的残余应力场的形成机理进行了详细阐述,基于实验得到的不同温度下材料的热传导系数、比热、对流系数以及相变温度、比焓值和热膨胀系数等参数,利用有限元分析软件ANSYS对包涵多个时变参数的渗碳过程进行了数值模拟,得到了渗碳过程中应力场形成的有关数据和渗碳结束后的残余应力场,讨论了渗碳深度等参数对残余应力场的影...     

残余应力和粗糙度对叶片振动疲劳性能的影响

为了研究叶片表面完整性对其振动疲劳性能的影响,本文模拟分析了某型高温合金叶片在振动疲劳实验过程中的动力学应力响应,获得叶片共振时应力幅值随时间的变化规律,分析了残余应力和粗糙度对叶片振动疲劳寿命和疲劳极限的影响规律.结果表明:叶片共振过程中的应力响应幅值先增大后减小呈周期性变化,属于"拍"现象,满足关系σ=1 046sin(242.83t)sin(5 828t);叶片的振动疲劳极限和疲劳寿命均随残余应力和粗糙度的增大而减小,振动疲劳极限和残余应力之间的关系满足σfat=510.9-0.31-70.93σrest;而疲劳极限和粗糙度之间的关系则满足σfat=9.67R2roughness-70.93Rroughness+713.23.