IMPACT BEHAVIOR OF POLYVINYL ALCOHOL FIBER REINFORCED CEMENTITIOUS COMPOSITES BEAMS

The paper presents results of an investigation conducted to study the impact resistance of polyvinyl alcohol fiber reinforced cementitious composite (PVA-FRCC) beams containing silica fume and fly ash. PVA-FRCC beam specimens of size 100 × 100 × 400 mm were tested under impact loading. The specimen incorporated four different volume fractions i.e. 0, 0.5%, 1.0% and 2.0% of corrugated PVA fibers. Silica fume and fly ash were added for the specimens containing PVA fibers volume fraction of 2.0%. The drop-weight type impact tests were conducted on the test specimens and the number of blows of the hammer required to induce first visible crack and ultimate failure of the specimen were recorded. The results are presented in terms of number of blows required, impact ductility as well as impact energy at first crack and ultimate failure. It has been observed that specimen containing 2.0% PVA fibers gave the best performance under impact loading, and that impact resistance was improved after silica fume and fly ash were added.     

玄武岩纤维高延性水泥基复合材料的动态力学性能

利用玄武岩纤维和水泥基材料，通过一定配比融合制成了在静态拉伸试验中呈现多缝开裂、应变硬化、极限拉伸应变0.5%以上的玄武岩纤维高延性水泥基复合材料(basalt fiber engineered cementitious composites, BF-ECCs)。用分离式霍普金森压杆(split Hopkinson pressure bar, SHPB)装置对不同玄武岩纤维掺量的水泥基复合材料进行动态压缩和动态劈裂试验。结果表明:(1)在压、拉两种应力状态下,玄武岩纤维对水泥基复合材料的静态强度、动态强度均有增强，且高应变率下玄武岩纤维对抗压强度动态增幅较小，对劈裂强度动态增幅较大；(2) BF-ECC的抗压强度和劈裂强度均随应变率升高而显著提高，两者均可以采用动态增强因子(dynamic increase factor, DIF)反映动态强度的增幅，但劈裂强度的应变率敏感性强于抗压强度；(3)依据试验得到的普通水泥混凝土速率敏感性的CEB-FIP方程(2010)不适用于BF-ECCs。     

PP/CF增强珊瑚砂水泥基复合材料冲击压缩力学性能研究

在人工海水制备珊瑚砂水泥基复合材料中混杂加入碳纤维和聚丙烯纤维,得到4种不同纤维掺量的碳-聚丙烯混杂纤维增强珊瑚砂水泥基复合材料。采用直径100 mm的分离式Hopkinson压杆,对材料进行5种应变率下的冲击压缩试验,采用LS-DYNA进行相应的冲击压缩数值模拟。结果表明:(1) 试验应变率临界值为200 s?1,当试验应变率大于200 s?1时,混杂碳纤维和聚丙烯纤维所形成的纤维网络对试块的增韧效果加强;(2) 碳-聚丙烯混杂纤维增强珊瑚砂水泥基复合材料峰值应力具有明显的应变率效应,且动态增强因子对应变率的敏感程度较高;(3) 使用珊瑚砂细骨料导致试块内微裂纹和微空洞等缺陷较多,在珊瑚砂水泥基复合材料内混杂掺加碳纤维和聚丙烯纤维后,试块冲击抗压强度的提升有限,但珊瑚砂水泥基复合材料的抗冲击韧性显著提升;(4) 通过试验数据和参数调试确定了HJC模型的参数,试块峰值应力的模拟结果与试验结果的误差在5.97 %以内。     

Multiscale modeling of strain-hardening cementitious composites

This research involves the multiscale characterization of strain-hardening cementitious composites under tensile loading. The sensitivity of cracking behavior to fiber dispersion is studied using a special form of lattice model, in which each fiber is explicitly represented. It is shown that the nonlocal modeling of fiber bridging forces is essential for obtaining realistic patterns of crack development and strain-hardening behavior. Crack count and crack size are simulated for progressively larger levels of tensile strain. The influence of fiber dispersion is clearly evident: regions with significantly fewer fibers act as defects, reducing strength and strain capacity of the material.     

纤维/金属网增强层板低速冲击损伤机理和演化

本文首先通过落锤低速冲击实验测试了纯玻璃纤维增强环氧树脂复合材料和304不锈钢丝网(SSWM)/玻璃纤维混杂复合材料的力学性能,探究了SSWM嵌入数量对混杂复合材料抗冲击性能的影响．随后采用Abaqus有限元软件建立了混杂复合材料的低速冲击模型,分别采用三维Hashin失效准则和Jason-Cook破坏准则模拟了纤维/基体和SSWM的损伤;建立了基于表面接触的内聚力模型来模拟界面分层;编写了VUMAT用户子程序定义混杂复合材料层合板的渐进失效过程．结果表明：相较于纯玻璃纤维增强环氧树脂层合板,SSWM/玻璃纤维混杂增强环氧树脂层合板的抗冲击性能更优,其中铺层形式为铺层III的混杂复合材料抗冲击性能最佳．通过对比发现有限元仿真结果与实验结果吻合良好,表明建立的模型适用于SSWM/玻璃纤维混杂增强环氧树脂复合材料低速冲击损伤的评估．通过分析仿真结果发现混杂复合材料的低速冲击损伤主要是冲击区域的纤维断裂、基体破坏和层间分层;SSWM通过吸收和传递冲击能量从而提升了混杂复合材料的抗冲击性能．     

玻璃纤维增强MC尼龙复合材料的摩擦磨损性能研究

通过碱催化阴离子聚合反应制备玻璃纤维增强单体浇铸尼龙复合材料(GFMCPA),在MM-200型摩擦磨损试验机上研究了在干摩擦和水润滑条件下,不同玻璃纤维含量对尼龙复合材料摩擦磨损特性的影响,并借助扫描电子显微镜观察其磨损表面形貌.结果表明:玻璃纤维含量对尼龙复合材料的摩擦性能具有显著影响;玻璃纤维质量分数达到30%后复合材料具有较好的耐磨性;在水润滑条件下,复合材料的摩擦系数和磨损量较干摩擦时大幅度降低;玻璃纤维含量低的尼龙复合材料的磨损机制主要为粘着磨损和磨粒磨损;玻璃纤维含量高的尼龙复合材料的粘着磨损减少,磨损机制主要表现为磨粒磨损和疲劳磨损.     

稀土处理玻璃纤维填充聚四氟乙烯复合材料在油润滑下的摩擦学性能

分别用偶联剂、稀土以及偶联剂 -稀土混合物处理玻璃纤维表面 ,以改善玻璃纤维与聚四氟乙烯之间的界面结合力 ,考察了玻璃纤维填充聚四氟乙烯复合材料在油润滑下的摩擦学性能 .结果表明 :在油润滑条件下 ,表面处理玻璃纤维填充聚四氟乙烯复合材料的摩擦系数比未经处理玻璃纤维填充聚四氟乙烯复合材料的低 ,耐磨性亦较优 ;而稀土处理玻璃纤维填充聚四氟乙烯复合材料具有最低的摩擦系数及最高的耐磨性和极限 pv值 ;未经处理玻璃纤维填充聚四氟乙烯复合材料的磨损形式主要为粘着转移 ,偶联剂处理玻璃纤维填充聚四氟乙烯复合材料和偶联剂与稀土处理玻璃纤维填充聚四氟乙烯复合材料均以磨粒磨损为主 ,而稀土处理玻璃纤维填充聚四氟乙烯复合材料的磨损机理主要为粘着磨损和轻微磨粒磨损     

Sm2O3增强聚四氟乙烯／混杂纤维复合材料的摩擦磨损性能研究

采用冷压烧结方法制备Sm2O3增强聚四氟乙烯／混杂纤维复合材料，用AG-1型电子万能试验机和MM-200型摩擦磨损试验机分别评价了Sm2O3增强聚四氟乙烯／混杂纤维复合材料的力学性能和摩擦磨损性能，采用扫描电子显微镜观察其磨损表面形貌．结果表明：添加少量Sm2O3可以提高炭纤维和玻璃纤维混杂填充PTFE复合材料的力学性能和摩擦磨损性能，尤其对改善减摩效果尤为显著；加入1％Sm2O3可以使PTFE／15％CF／10％GF复合材料的拉伸强度、弯曲强度和硬度分别提高9．0％、5．1％和49．1％，摩擦系数降低22％，磨痕宽度降低5．4％，得到性能较为优良的耐磨材料．这是由于Sm2O3起到了润滑及阻止纤维和基体磨损作用的缘故．     

Al2O3纤维及炭纤维增强ZL109混杂复合材料磨粒磨损行为

利用挤压铸造法制备了Al2O3纤维及炭纤维增强ZL109混杂复合材料(Al2O3 Cf／ZL109)，考察了该混杂复合材料的磨粒磨损行为．结果表明：就砂纸粒度对复合材料抗磨粒磨损性能的影响而言，存在砂纸粒度的临界区域；Al2O3纤维有利于提高混杂复合材料的抗磨粒磨损性能，而炭纤维不利于提高复合材料的抗磨粒磨损性能，其中(12％Al2O3f 4％Cf)／ZL109混杂复合材料的抗磨粒磨损性能最佳．     

碳纤维增强复合材料微观烧蚀行为数值模拟

碳纤维增强复合材料已广泛应用于烧蚀热防护系统中,其微观结构直接影响材料的烧蚀行为,因此材料微观烧蚀机制分析对材料设计和制备具有重要意义.本文采用有限体积法并引入固体相体积分数与界面重构技术,建立了碳纤维增强复合材料微观烧蚀数值模型.利用该微观烧蚀数值模型对碳基体包裹单根碳纤维进行烧蚀模拟,将数值模拟的烧蚀形貌与解析解结果进行对比,验证了数值求解方法的正确性.对单向碳纤维增强复合材料在不同碳纤维倾斜角下的微观烧蚀行为进行了模拟分析,得到了碳纤维倾斜角对微观烧蚀行为的影响规律.研究发现:对于碳纤维的抗氧化性能比基体强的情况,当氧扩散速率远远大于碳氧反应速率时,碳纤维将出现"笋尖"状的烧蚀形貌;当碳氧反应速率远远大于氧扩散速率时,纤维和基体将以相同速率烧蚀.当碳纤维的抗氧化性能比基体强时,纤维倾斜角会对材料微观烧蚀行为产生较大影响;相反,则影响不显著.      

压入实验界面端奇异性研究

纤维压入实验是复合材料界面剪切强度细观实验方法之一,其试件通常由复合材料中切割下来制备而成,从中选取单根纤维,进行压入试验,所以被选中的纤维可看成是被纤维和纯基本材料构成的横观各向同性复合材料所包裹。本文以此为依据,建立了横观各向同性复合材料基体包裹各向同性纤维的轴对称模型,采用逐次渐近等求解方法,得到了求解该模型界面端应力奇异性指数的特征方程,并计算了碳纤维／环氧树脂、碳纤维／铝和碳纤维／Al2O3压入试件界面端奇异性随碳纤维体积百分含量的变化情况。     

碳纤维毡增强铝基复合材料的摩擦磨损性能研究

采用压挤渗透工艺制备了新型碳纤维毡增强铝基复合材料,在MG－2000型高速高温摩擦磨损试验机上考察了其摩擦磨损性质,结果表明：碳纤维毡增强铝基复合材料的摩擦磨损特性明显估于基体合金;复合材料经历由稳定磨损向严重磨损的转化;在稳定磨损阶段,复合材料的磨损表面存在由金属氧化物和碳膜共同构成的复合固体润滑膜,从而有效地改善复合材料的摩擦磨损性能。     

偶件表面粗糙度对碳纤维增强尼龙复合材料摩擦学性能的影响

在栓-盘摩擦磨损试验机上考察了干摩擦条件下偶件表面粗糙度对碳纤维增强尼龙（PA1010）复合材料摩擦学性能的影响,采用不迩显微镜观察分析了偶件表面转移膜的形貌。结果表明,碳纤维能够明显提高PA1010的耐磨性能,当碳纤维增强相的质量分数为10%和20%时,增强PA1010复合材料的磨损率比非增强PA1010的降低3～6倍。这是由于碳纤维起到了承载作用并具有较强的抗犁削能力所致,磨损表面形貌光学显微分析表明：磨损前后偶件表面形貌发生了明显的变化;当偶件表面粗糙度Ra处于0.11～0.13um范围内时,复合材料的摩损率最低;随Ra值的增大或减小微切削和转移膜疲劳脱落加剧致使复合材料的磨损率快速增大。     

炭纤维增强环氧树脂复合材料/N80钢摩擦学性能研究

利用MG-200型摩擦磨损试验机研究了炭纤维增强环氧树脂复合材料/N80钢的摩擦学性能,考察了介质温度对摩擦学性能的影响;用扫描电子显微镜分析了磨损表面形貌.结果表明:在干摩擦条件下,炭纤维增强环氧树脂复合材料与N80钢对摩时的摩擦系数较低,炭纤维增强环氧树脂复合材料的磨损主要表现为树脂基体脱落碳化和炭纤维的折断剥落,偶件钢环则呈现明显的磨粒磨损特征;在油井产出液润滑下炭纤维增强环氧树脂复合材料的磨损率较低,摩擦系数和磨损率随着润滑介质温度的升高而增大,偶件钢环则呈现明显的磨粒磨损和腐蚀磨损特征.     

氧化铝纤维含量对Al2O3f＋Cf／ZL109混杂复合材料耐磨性能的影响

利用挤压铸造法制备了Al2O3f Cf/ZL09短纤维混杂金属基复合材料，并探讨了炭纤维体积分数为4％时，Al2O3纤维含量变化对该复合材料耐磨性能的影响。结果表明：随着Al2O3体积分数增加，复合材料的摩擦系数逐渐增大，复合材料从轻微磨损到急剧磨损的临界转变载荷大幅度提高，并随Al2O3含量的增加而逐渐增大；在临界载荷以下，影响复合材料磨损率的Al2O3含量临界值为12％，当Al2O3含量低于临界值时复合材料磨损表面无明显剥落，而当Al2O3含量超过临界值后，复合材料磨损表面存在大量的剥落坑，磨损率增大。     

碳纤维增强聚醚砜复合材料的摩擦磨损性能研究

利用销－盘磨擦磨损试验机考察了聚醚砜及其复合材料在干滑动摩擦条件下的摩擦磨损性能。结果表明：碳纤维使聚醚砜的摩擦磨损性能得到明显的改善,春改善程度同碳纤维的长度和体积分数相关;当碳纤维的体积分数约为１５％时,聚醚砜复合材料的摩擦系数及比磨损率最低;添加固体润滑剂可以使复合材料的摩擦磨损性能得到进一步改善;随着温度及外载荷的变化,摩擦系数及比磨损率表现出不同的变化趋势。     

智能结构中光纤智能夹层力学特性的实验研究

根据光纤自诊断系统模块化、集成化要求,制作出光纤智能夹层,它可以铺设于复合材料结构表面或埋入复合材料结构内部。对智能夹层试件的轴向拉伸试验和层间拉伸试验表明,光纤智能夹层的埋入对复合材料结构的强度性能无显著影响,可以埋入复合材料结构内部并实施健康监测。试验还表明,在一定应变范围内,单膜交错光纤中光强—应变之间具有良好的线性关系,可以在埋入复合材料之前进行标定。     

A dynamic meso-scale model of the pullout behavior for non-straight fibers and corresponding DEM3 simulation

Lots of work had been reported in the experimental investigation and modeling of the debonding and pullout behavior for straight crack-bridging fibers in brittle matrix composites, but few of them involving in the dynamic and/or non-straight fiber case. In this paper, a dynamic meso-scale model for non-straight fiber was proposed on the work of Chanvillard. The model was time-dependent and related to the impact loading through the interfacial shearing stress along the embedded part of the steel fiber, and properly setting the thresholds, the dynamic meso-damage model of the fiber's debonding and pullout process was eventually constructed. The model prediction fitted the experimental data of Chanvillard for non-straight steel fiber under static condition quite well and could demonstrate the rate sensitivity of the reinforcing effects of fibers. Then, a 3-D discrete meso-element method (DEM3) was used to simulate the dynamic pullout behavior of such fiber configurations as wiredrawn fibers from cementitious matrix with pores. Comparing to afro-mentioned model, DEM3 was more effective in simulating the complete procedures of matrix dynamic failure and fiber pullout and would be more helpful in the analyses of complicated configurations of fiber.     

Micro-mechanical approximation to the stress field around an inclined fiber of FRCC

Matrix spalling or crushing is one of the important mechanisms of fiber-matrix interaction of fiber reinforced cementitious composites (FRCC). The fiber pullout mechanisms have been extensively studied for an aligned fiber but matrix failure is rarely investigated since it is thought not to be a major affect. However, for an inclined fiber, the matrix failure should not be neglected. Due to the complex process of matrix spalling, experimental investigation and analytical study of this mechanism are rarely found in literature. In this paper, it is assumed that the load transfer is concentrated within the short length of the inclined fiber from the exit point towards anchored end and follows the exponential law. The Mindlin formulation is employed to calculate the 3D stress field. The simulation gives much information about this field. The 3D approximation of the stress state around an inclined fiber helps to qualitatively understand the mechanism of matrix failure. Finally, a spalling criterion is proposed by which matrix spalling occurs only when the stress in a certain volume, rather than the stress at a small point, exceeds the material strength. This implies some local stress redistribution after first yield. The stress redistribution results in more energy input and higher load bearing capacity of the matrix. In accordance with this hypothesis, the evolution of matrix spalling is demonstrated. The accurate prediction of matrix spalling needs the careful determination of the parameters in this model. This is the work of further study.     

纤维增强铸型尼龙在水润滑条件下的摩擦磨损性能研究

考察了玻璃纤维和碳纤维增强MC尼龙在水润滑条件下的摩擦磨损特性,并借助扫描电子显微镜和表面形貌仪分析了磨损机理。结果表明：在水润滑条件下,纤维增强MC尼龙的摩擦系数比干摩擦下的低,耐磨性优于未增强的基体材料;其中碳纤维增强MC尼龙比玻璃纤维增强MC尼龙具有更低的摩擦系数和更高的耐磨性能;碳纤维增强MC尼龙的磨损机理主要是粘着转移,同时伴有犁削作用,而玻璃纤维增强MC尼龙的磨损机理主要是犁削作用。