【作者】 何芳；

【导师】 王玉林；

【作者基本信息】 天津大学 ， 材料学， 2006， 博士

【摘要】 三维编织复合材料具有很高的弯曲强度和冲击韧性、极高的疲劳强度和抗损伤性能及优异的可设计性和成型加工性,极适于制备骨科内固定装置,是一种很有发展潜力的新型生物材料。超高分子量聚乙烯纤维作为新型的高性能有机纤维的代表,良好的生物相容性和优异的化学稳定性使其在生物复合材料领域崭露头角。因此制备三维编织超高分子量聚乙烯纤维复合材料,并将其应用于骨科内固定生物医用领域具有重要的理论与现实意义。本文采用树脂传递模塑(RTM)成型工艺制备了三维编织超高分子量聚乙烯(UHMWPE)纤维增强环氧树脂(ER)复合材料(UH3D/ER)及三维编织UH/CF/ER混杂复合材料,并系统地研究其力学性能、吸湿行为、摩擦磨损性能以及低周疲劳性能,同时对混杂效应系数、吸湿行为以及摩擦系数进行了预测。研究结果表明,在纤维总体积含量一定的情况下,随着碳纤维(CF)含量的提高,三维编织UH/CF/ER混杂复合材料的弯曲及纵向压缩性能提高,而纵向剪切强度及冲击性能降低,且弯曲强度表现出负的混杂效应,横向剪切强度及冲击性能表现正的混杂效应,而弯曲模量、纵向剪切强度及纵向压缩强度与混合定律符合较好;三维编织UH/CF/ER混杂复合材料的破坏机理与UHMWPE纤维和CF自身性能及二者的混杂比密切相关;三维编织UH/CF/ER混杂复合材料的混杂效应系数与纤维分散度、纤维分布方式及相对含量、加载方式等因素有关。由本文建立的混杂效应系数估算方法获得的混杂复合材料的横、纵剪切强度与实验值符合较好。在75%相对湿度下,CF几乎不吸湿,UHMWPE纤维的平衡吸湿率仅为0.35%,而芳纶纤维(KF)的吸湿率已超过5%,并有继续增大的趋势;与纯环氧树脂相比,UH3D/ER和UHL/ER复合材料在37℃蒸馏水中的吸湿速率及吸湿率较高。纤维表面处理可有效降低UH3D/ER复合材料的吸湿速率及吸湿率。三维编织UH/CF/ER混杂复合材料在37℃蒸馏水中的吸湿动力学曲线介于UH3D/ER和CF3D/ER复合材料之间。UH3D/ER、CF3D/ER复合材料及三维编织UH/CF/ER混杂复合材料的吸湿动力学曲线表现出相似的双阶段特征,即第一阶段为典型的Fick扩散,第二阶段的吸湿率与时间的平方根依然呈线性关系,但不可用Fick定律加以描述;采用双阶段数学模型对UH3D/ER及三维编织UH/CF/ER混杂复合材料的吸湿行为进行预测,发现与实验数据符合较好;在0.42 m/s和100 N条件下,随着纤维体积含量的增加,UH3D/ER复合材料的摩擦系数及比磨损率降低。UH3D/ER复合材料主要发生粘着磨损,并伴有一定的磨粒磨损;在0.42 m/s和100 N条件下,CF3D/ER、KF3D/ER及UH3D/ER复合材料的摩擦系数依次降低,CF3D/ER复合材料的比磨损率最低,KF3D/ER及UH3D/ER复合材料的比磨损率略高,且二者相差不大。KF3D/ER及UH3D/ER复合材料主要发生粘着磨损,并伴有一定的磨粒磨损,而CF3D/ER复合材料则以磨粒磨损为主;在总纤维体积含量一定的情况下,碳纤维的含量增加,三维编织UH/CF/ER混杂复合材料的摩擦系数增大,而比磨损率降低。三维编织UH/CF/ER混杂复合材料的磨损机理与UHMWPE纤维及CF的体积比密切相关,当CF含量较高时以磨粒磨损为主,而当UHMWPE纤维含量较高时,则以粘着磨损为主;采用混合载荷分布模式对UH3D/ER复合材料的摩擦系数进行预测发现,摩擦系数计算值与实验值符合较好,而该模式并不适用于三维编织UH/CF/ER混杂复合材料。在相同试验条件下,CF3D/ER复合材料疲劳性能优于UH3D/ER和KF3D/ER复合材料。相同体积含量的UH3D/ER和UHL/ER复合材料的剩余弯曲强度比相差不大,而UHL/ER复合材料的剩余弯曲模量比明显高于UH3D/ER复合材料;三维编织复合材料的疲劳损伤主要有以下几种形式:(a)纤维束/基体界面裂纹扩展;(b)纤维/基体界面脱粘;(c)基体断裂;(d)纤维断裂等。其中纤维束/基体界面的裂纹扩展是三维编织复合材料弯曲疲劳损伤的主要形式之一,这也是与单向纤维复合材料较为明显的区别;吸湿使UH3D/ER复合材料的疲劳性能下降;UH3D/ER复合材料在0.4倍静强度(σo)弯曲载荷下的疲劳寿命为5×106次,在0.5σo弯曲载荷下的弯曲疲劳寿命为8×104次。本文采用RTM工艺制备了UH3D/ER及三维编织UH/CF/ER混杂复合材料。系统地阐述了复合材料在弯曲、剪切及冲击载荷下的破坏机制,验证了长期处于湿热环境中的复合材料吸湿双阶段模型,研究了UH3D/ER及三维编织UH/CF/ER混杂复合材料磨损机理和弯曲疲劳损伤机理,并成功预测了UH3D/ER复合材料的摩擦系数及疲劳寿命。这无疑对缩短三维编织及混杂复合材料研究周期、降低成本具有重要意义。更多还原

【Abstract】 3-D braided composites have high flexural strength and impact toughness and fatigue life and damage tolerance, and they are promising biomedical materials for high-load applications. As a new polymer fiber with high performance, UHMWPE fiber which exhibits very low friction coefficient, high wear resistance and high impact strength is widely used in biomedical applications. So study on the 3-D braided composites using as biomedical materials is of academic and practical significance.3-D braided UHMWPE fiber reinforced epoxy resin composites (UH3D/ER) were prepared by resin transfer molding (RTM) process. At the same time, carbon fiber and UHMWPE fiber were used to produce the 3-D braided hybrid composites (3-D UH/CF/ER) in order to improve weak compressive and creep properties of the UH3D/ER composites, and their mechanical, moisture absorption, friction and wear and fatigue properties were studies in this paper.The results show that, with the increase of the CF/UHMWPE fiber hybrid ratio, the flexural and longitudinal compressive performance of the 3-D UH/CF/ER composites improves, and their longitudinal shear strength and impact toughness decrease. The fracture mechanism of the 3-D UH/CF/ER hybrid composites is determined by the properties of the two fibers and their hybrid ratio. The fiber dispersion, distributing mode, hybrid ratio and load model have obvious effects on the hybrid effect coefficient of the 3-D UH/CF/ER hybrid composites, and the computation values of the transverse and longitudinal shear strength of the hybrid composites through hybrid effect coefficient have good coherence with the experimental values.Under the relative humidity of 75%,the moisture absorption rate of CF and UHMWPE fiber is about zero and 0.35%, respectively, while that of KF exceeds 5%. Compared with epoxy resin, the moisture absorption velocity and rate of the UH3D/ER and UHL/ER composites in 37℃distilled water are higher. Fiber surface treatment can effectively reduce the moisture absorption velocity and rate of the UH3D/ER composites. The moisture absorption dynamics curves of the 3-D UH/CF/ER hybrid composites in 37℃distilled water distribute between those of the UH3D/ER and CF3D/ER composites, and all of these curves show similar two-stage characteristics, viz. the first stage is typical Fick’s diffusion, and the moisture absorption rate and the square root of time still satisfy linear relation in the second stage, while the curves in this stage can not be described with Fick’s law. The two-stage mathematics model is successfully used to forecast the moisture absorption behaviors of the UH3D/ER and 3-D UH/CF/ER hybrid composites in this paper.At the sliding velocity of 0.42 m/s and the normal load of 100 N, the friction coefficient and wear rate of the UH3D/ER composites decrease with the improvement of fiber volume fraction, and adhesive wear and light abrasive wear occur in thissituation. The friction coefficient of the CF3D/ER composites is higher than that of the UH3D/ER and KF3D/ER composites, while the wear rate of the CF3D/ER composites is lowest among the three materials. Similar to the UH3D/ER composites, adhesion wear occurs on the surface of the KF3D/ER composites, while abrasive wear appears on the CF3D/ER composites surface. With the same total fiber volume fraction, the friction coefficient of the 3-D UH/CF/ER hybrid composites increases and their wear rate decreases with the increase of the CF/UHMWPE fiber hybrid ration. The wear mechanism of the hybrid composites intensively depends on the CF/UHMWPE fiber hybrid ration. Abrasive wear is dominant when the hybrid ratio is high, and contrarily adhesion wear is leading. The mixture load distributing mode is used to forecast the friction coefficient of the UH3D/ER composites, and the result shows that the computation value equals to the experimental one whenθ=0.74 (p<0.05), while this mode is not fit for the 3-D UH/CF/ER hybrid composites.Under the same experimental condition (0.4σo, 105 times), the fatigue performance of the CF3D/ER composites is better than that of the UH3D/ER and KF3D/ER composites. The flexural fatigue damage forms of 3-D braided composites mainly are these types as follows: (a) crack extension in the fiber bundles/resin matrix interface, (b) fiber/matrix interface fracture, (c) resin matrix rupture, (d) fiber fracture and so on. Among these damage forms, the crack extension in the fiber bundles/resin matrix interface is the uppermost, and this is obvious difference between the 3-D and unidirectional composites. Moisture absorption will lead to the decrease of the fatigue tolerance of the UH3D/ER composites. The fatigue life of the UH3D/ER composites under the flexural load of 0.4σo is 5×106 times, and it reduces to 8×104 times under 0.5σo.The hybrid effect coefficient the 3-D UH/CF/ER hybrid composites and friction coefficient and fatigue life of the UH3D/ER composites were successively forecasted in this paper. This is significant to reduce study period and cost of the 3-D braided and hybrid composites.更多还原