等通道转角挤压加工中挤压温度对聚丙烯结构和性能的影响

在45℃至105℃挤压温度范围内对等规聚丙烯（iPP）进行等通道转角挤压，研究了挤压温度对iPP结构和性能的影响。结果表明：经过等通道转角挤压加工后，iPP晶粒明显细化并获得剪切取向变形，挤压温度的升高有利于iPP晶相取向的形成和结晶度增大。等通道转角挤压使iPP的透明性提高，65℃挤压后iPP透光率增幅最大，提高了21．3％；随着挤压温度的升高，iPP冲击强度和拉伸强度逐渐增加，105℃挤压后其冲击强度、拉伸强度分别比ECAE前提高了127％、38％。ECAE挤压后jPP表现出韧性延性拉伸断裂特征，断裂伸长率的增幅随挤压温度的升高而降低，45℃挤压后其增幅最大，达到1090％。     

等通道转角挤压加工中聚合物剪切塑性变形行为分析

结合挤压负荷-行程曲线,采用视塑性试验方法研究了聚丙烯在等通道转角挤压过程中的剪切塑性变形行为,并分析了屈服负荷随挤压工艺条件和聚合物种类而发生变化的情况.结果表明:剪切塑性变形发生在模具通道的相交面处;塑性变形响应由模具通道的内角处开始,向模具外角处扩展,形成完整剪切变形带后发生塑性屈服;聚丙烯的剪切屈服负荷随着挤压温度的升高而明显降低,而挤压速度对其影响不显著;不同聚合物抵抗剪切变形的能力也不同,其剪切屈服负荷因聚合物种类而异.     

聚丙烯等通道转角挤压加工中挤压载荷变化规律的实验研究

对聚丙烯(PP)进行等通道转角挤压(ECAE)加工,利用电子万能试验机获得:PP在不同挤压工艺参数下的挤压载荷一行程曲线,根据其宏观剪切变形情况,分析了在ECAE加工过程中挤压载荷的变化规律;并分析了挤压工艺参数对PP屈服载荷的影响.结果表明:在ECAE加工中挤压载荷分为压缩弹性变形引起的载荷增加,形成塑性剪切带引起的载荷快速增加,持续的剪切塑性变形引起的载荷基本稳定3个阶段;在挤压工艺参数中挤压温度对挤压载荷-行程曲线影响显著,在同一挤压速度下,屈服载荷随着挤压温度的升高而显著降低.     

β成核剂对PPR管材专用树脂性能的影响

制备了β晶型无规共聚聚丙烯(PPR)管材专用树脂,并研究了5种不同β成核剂对β晶型PPR性能的影响。结果表明:β晶型PPR的性能与β成核剂的种类和加入量相关。当β成核剂E的质量分数为0.20%时,β晶型PPR的β晶含量达80%以上,简支梁缺口冲击强度达100 k J/m2。β成核剂C对β晶型PPR负荷变形温度影响最大,能使其升至76℃左右。分别加入β成核剂A,B,C,D,则β晶型PPR断裂伸长率均增加20%。综合考虑,加入β成核剂E能满足β晶型PPR对抗冲击性能和耐热性能的要求。     

PPR管材性能影响因素分析

采用凝胶渗透色谱(GPC)、13C-NMR、差示扫描量热法(DSC)等分析技术对无规共聚聚丙烯(PPR)管材的结构和性能进行研究。对PPR管材结构性能影响因素分析结果表明,熔体流动速率和熔点对PPR生产具有决定性的影响。     

热处理对PPR/纳米TiO2复合材料力学性能的影响

制备了无规共聚聚丙烯(PPR)/纳米TiO₂复合材料,并研究了热处理对复合材料力学性能和断口形貌的影响。结果表明：使用4%(w)经硅铝复合包膜改性后的纳米TiO₂可大幅提高PPR的力学性能,复合材料的拉伸强度由未改性的24.0 MPa提高到36.5 MPa,断裂伸长率由未改性的45%提高到90%;热处理可消除复合材料内部热应力,促进结晶的完善,有效改善PPR/纳米TiO₂复合材料的拉伸性能及弯曲性能,热处理最佳温度为120℃,最佳时间为40 min,在此条件下,复合材料的拉伸强度及弯曲强度增幅分别达33.8%,35.9%。     

PPH/PPR/PPB共混体系力学性能的研究

研究了均聚聚丙烯(PPH)、无规共聚聚丙烯(PPR)、嵌段共聚聚丙烯(PPB)3种聚丙烯(PP)共混体季的力学性能，探讨了各组分对材料性能的影响。结果表明：PPH能使材料具有较高的刚性，PPB则能提高材料的韧性，PPH／PPR／PPB体系的冲击强度随PPB用量的增加而增加。     

β成核剂对PPR结晶行为的影响

采用差示扫描量热仪(DSC)、X射线衍射仪(XRD)、偏光显微镜(PLM)研究了β成核剂对无规共聚聚丙烯(PPR)结晶行为及晶体结构的影响.结果表明:PPR中加入β成核剂后,PPR的晶体形态由α晶型向β晶型转变;当加入质量分数0.05％β成核剂时,β晶相对含量在60％以上,和纯PPR相比,PPR中β晶相对含量显著增加,...     

PPR/甘蔗渣复合材料的力学性能

利用硅烷处理的甘蔗渣纤维填充无规共聚聚丙烯制备了复合材料,研究其力学性能与相态结构。结果表明:在甘蔗渣用量为10～15份时,用硅烷KH570处理的甘蔗渣制备的复合材料较直接填充物的拉伸强度与冲击强度各提高30％以上;试样结晶更完善,纤维在树脂中分布更均匀。     

PP及PP/HDPE复合材料的等通道转角挤压加工

研究了聚丙烯(PP)和PP／高密度聚乙烯(HDPE)复合材料在等通道转角挤压(ECAE)加工中的宏观形变情况。结果表明,PP长方形网格线形变成平行四边形,其形变角约40°,A路径的二次ECAE加工使试样的塑性形变加大,平行四边形的形变角减小到33°,C路径的二次ECAE加工使平行四边形形变恢复为与PP试样未ECAE加工前的长方形,表明采用不同的ECAE加工路径可获得不同形变结构的试样;最佳的ECAE挤出速率为3 mm／min,且挤出速率须保持恒定;PP／HDPE复合材料的ECAE加工性能除与复合材料的摩擦系数有关外,还与复合物的结构有关, 当HDPE用量在10％时,ECAE加工较容易,但当用量大于10％时,在挤出过程中容易发生开裂和破碎现象;PP／ HDPE复合材料的最佳ECAE加工挤出速率为2 mm／min,可挤性能最好的是PP／HDPE质量比为90／10的复合材料。     

The effect of microstructure on the toughness of polypropylene random copolymer

ABSTRACT

This article mainly explores the mechanism and deformation of polypropylene random copolymer at different temperatures and the role of microstructure in the toughening process. Firstly, the conventional differential scanning calorimetry, wide-angle X-ray diffraction, and scanning electron microscopy were employed to study different structures of crystalline and amorphous regions. Furthermore, the dynamic thermomechanical analysis was used to study the changes in the molecular mobility in samples. Secondly, the toughness and fracture morphology of the material was analyzed by notched Izod impact test and scanning electron microscopy. Thirdly, samples were stretched and combined 2D-WAXD to analyses the changes in its crystal regions. The thickness and distribution of the lamellae, as well as stress transmitters, work synergistically during polypropylene random copolymer deformation. The yield is due to the spherulite deformation and a small part of lamellae rotation and reorientation when the temperature is 25 C. When near the glass transition temperature, a large number of lamellae are crushed and oriented to form a large number of microfibers at the yield point.

The in-situ formed rubber phase in polypropylene random copolymer plays a significant role in the toughening process. When the temperature is 25 C the yield is due to the spherulite deformation and a small part of lamellae rotation and reorientation. While a large number of lamellae are crushed and oriented to form a large number of microfibers at the yield point when the temperature is 0 C.     

On the effect of pulsed laser ablation on shear strength and mode I fracture toughness of Al/epoxy adhesive joints

The present work describes an experimental study about the shear strength and the mode I fracture toughness of adhesive joints with substrates pre-treated by pulsed laser ablation. An ytterbium-doped pulsed fiber laser was employed to perform laser irradiation on AA6082-T4 alloy. Morphological and chemical modifications were evaluated by means of surface profilometry, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Thick adherend shear tests were carried out in order to assess the shear strength while the mode I fracture toughness was determined using the double cantilever beam. For comparison, control samples were prepared using classical surface degreasing. The results indicated that laser ablation has a favorable effect on the mechanical behavior of epoxy bonded joints; however, while a + 20% increase was recorded for shear strength, a remarkable threefold enhancement of fracture toughness was observed with respect to control samples. XPS analyses of treated substrates and SEM observations of the fracture surfaces indicated that laser pre-treatment promoted chemical and morphological modifications able to sustain energy dissipation through mechanical interlocking. As a result cohesive failure within the adhesive bond-line was enabled under predominant peel loading.     

Iosipescu shear deformation and fracture in model thermoplastic polyolefins

Shear deformation and fracture behaviors in polypropylene (PP)‐based model thermoplastic polyolefins (TPOs) were investigated with the Iosipescu shear test. The shear deformation process was monitored in situ via video camera to obtain experimental shear stress–strain curves of model TPOs. Shear fracture mechanisms were studied with optical microscopy and scanning electron microscopy. Macroscopically, the cracks in neat PP propagated along the maximum shear plane, which indicated that mode‐II shear failure existed in neat PP. Microscopically, it was shown that shear fracture initiated in the form of partial, discontinuous inclined microcracks that later coalesced and formed the final continuous crack. The incorporation of rubber in PP could transform the shear fracture process into a stretching process in the shear damage zone. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3201–3214, 2001     

Effect of pressurization on the fracture toughness of borosilicate glasses

In this study, hot-compression is applied to two multicomponent borosilicate glasses, Borofloat33 (Boro33) and N-BK7, using molecular dynamics simulations. The effects of pressure on elastic properties, surface energy, and fracture toughness ( are investigated. It is found that the impact on is mainly dominated by the change of Young's modulus under pressure, which is proportional to the relative change in density. Between the two glasses under investigation, can be improved more effectively by the hot-compression process for Boro33, due to its higher concentration of 3-coordinated boron (B³), which facilitates densification via B³ to B⁴ conversion under compression.     

生物降解材料聚（DL）-乳酸剪切变形强韧化研究

研究了等通道转角挤压技术对生物降解材料聚（DL）-乳酸（PDLLA）的增强、增韧。探讨了挤压温度、挤压次数对PDLLA性能的影响。实验表明，随挤压次数增加，材料强韧性提高；挤压温度对材料性能影响明显。经过2次挤压后，PDLLA的弯曲强度由83．3MPa增加到178．7MPa；原始试样弯曲断口呈脆性断裂，强韧化挤压后，断口呈典型韧性断裂特征，强韧性明显提高。扫描电镜观察表明，断口有大量纤维尾端，呈明显纤维化。广角X射线衍射和差示扫描量热分析表明，随挤压次数增加，PDLLA玻璃化转变温度提高，结构更趋稳定。     

Impact fracture behavior of molecularly orientated polycarbonate sheets

The impact fracture behavior of molecularly orientated polycarbonate (PC) sheets was investigated. The molecular orientation was achieved via a newly developed equal channel angular extrusion (ECAE) process. Improvement in impact fracture propagation resistance was observed in the ECAE processed PC sheets. The improved impact resistance was found to be directly related to the changes in molecular orientation because of ECAE. The unique characteristics of the ECAE process for polymer extrusion are described. The potential benefits of ECAE in enhancing physical and mechanical properties of the extruded PC sheets are discussed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2060–2066, 2001     

Fracture toughness of random fibrous materials with ultrahigh porosity at elevated temperatures

The fracture toughness of three‐dimensional random fibrous (3D RF) material was investigated from room temperature to 1273 K by virtue of experimental method, theoretical model and Finite Element Method (FEM) in the through‐the‐thickness (TTT) and in‐plane (IP) directions. The experiments showed that the fracture toughness in the TTT and IP directions increases (from 0.0617 to 0.0924 Mpa·m^1/2 and from 0.2958 to 0.3982 Mpa·m^1/2 for the TTT and IP directions, respectively) as the temperature until reaching a transition temperature (1123 K and 1223 K for the TTT and IP directions, respectively), then the fracture toughness decreases from 0.0924 to 0.0393 Mpa·m^1/2 and from 0.3982 to 0.3106 Mpa·m^1/2 for the TTT and IP directions, respectively. The fracture behavior was related to the bulk microstructures, the mechanical properties of fibers and the blunting of crack tip. The crack tip blunting affected the fracture toughness at elevated temperatures which was verified using the theoretical model. A FEM model with a single edge crack where special attention was drawn to the influence of the morphological characteristic was developed to simulate the fracture behavior of 3D RF material. Numerical results from the FEM modeling along with a theoretical model with crack tip blunting mechanism incorporated agreed well with the experimental results.     

Residual stress effect on the fracture toughness of lithium disilicate glass-ceramics

In glass-ceramics (GCs), on cooling from the crystallization temperature, internal residual stresses are generated due to the difference between the thermal expansion coefficient (TEC) of the crystal phase(s) and the residual glass. These stresses could degrade or promote their mechanical properties. In this work, we varied the magnitude of the residual stresses in lithium silicate GCs by designing their microstructures. The level of internal stresses was measured using (Synchrotron) X-ray diffraction. The effects of anisotropy of thermal expansion, crystal shape, and intensity of the residual stresses were analyzed and compared using theoretical models. We extended the Hsueh-Becher model to include the thermal expansion anisotropy of the orthorhombic lithium disilicate (LS2) crystals. We found that the average residual stresses within the LS2 crystals are compressive or null (−100 to ~0) and highly anisotropic. Most importantly, within the limits of this study, we found no evidence for the influence of (compressive or null) residual stresses on the fracture toughness of the studied GCs. Within the crystal size range from 1 to 5 μm, a highly crystallized volume fraction coupled to relatively large crystals (5 μm) of high elastic modulus improved the glass-ceramic fracture toughness. This result can guide the microstructural design of novel tough GCs.     

The impact of densification on indentation fracture toughness measurements

The fracture toughness was measured by the Vickers indentation method and by chevron notch for a series of xCaO-xAl₂O₃-(100 − 2x)SiO₂ glasses. As the silica content was increased, the fixed ξ value Vickers indentation fracture toughness (IFT) values increased, while the chevron notch values decreased. Glasses with higher silica contents deform with more densification and less shear when indented with a Vickers tip, thus resulting in reduced residual stress in the region surrounding the indent. The reduction in residual stress for high silica glasses results in less median/radial crack extension and unreasonably high Vickers IFT values. This indicates that a fixed ξ value of 0.016 is not appropriate for the glasses in this series. By repeating the IFT method with a sharper 110° four-sided pyramidal diamond indenter, it is demonstrated that indentation toughness and chevron notch toughness values now trend in the same direction and are in good agreement with a fixed ξ value of 0.0297. With the sharper indenter tip, the densification component to the deformation is substantially reduced for all glass types such that it no longer has such a prominent influence on the residual stress field. This result suggests that a fixed ξ value IFT method may be appropriate for all glass types if a sharper indenter tip is substituted in the place of the Vickers tip.