多尺度纤维增强水泥基复合材料力学性能试验

基于水泥基材料多尺度的结构特征及破坏过程,设计了一种由钢纤维、聚乙烯醇（PVA）纤维以及碳酸钙晶须构成的多尺度纤维增强水泥基复合材料（MSFRCC）,研究了其抗压强度、抗弯强度、弯曲韧性、多缝开裂形态以及断裂过程等基本力学性能。结果表明：基体材料的强度和韧性均得到了显著提高;MSFRCC在弯曲荷载作用下表现出了硬化行为和多缝开裂模式。扫描电子显微镜和断裂试验结果证实了多尺度纤维在水泥基复合材料破坏过程中发挥了多尺度阻裂作用。研究认为：通过对纤维进行多尺度组合设计,可以显著改善水泥基复合材料的韧性,廉价的碳酸钙晶须可以适量取代钢纤维和PVA纤维。     

聚丙烯纤维化学接枝改性增强水泥基复合材料的界面结合

以过氧化苯甲酰(BPO)为引发剂,采用二步化学接枝法对聚丙烯纤维进行接枝丙烯酸改性,利用正交分析法研究了引发温度、BPO浓度、接枝温度、接枝时间及丙烯酸(AA)浓度对纤维接枝率的影响,并评价了改性前后纤维与水泥基体的界面结合性能.结果表明:上述因素对纤维接枝率的影响大小为引发温度＞ BPO浓度＞接枝时间＞接枝温度＞AA浓度,最佳反应条件为引发温度90℃,BPO 4.50×10-2 mol/L,接枝时间60 min,接枝温度75℃,AA 1.4 mol/L,此时纤维接枝率达13.12％;经化学接枝改性后,聚丙烯纤维表面亲水性和粗糙度增大,与水泥基体的界面结合得到增强,纤维掺量为0.05％(体积分数)时,聚丙烯纤维增强水泥砂浆的抗开裂性能比增大了26.6％,抗塑性收缩开裂性能显著增强.     

聚丙烯纤维化学接枝改性增强水泥基复合材料的界面结合

以过氧化苯甲酰(BPO)为引发剂, 采用二步化学接枝法对聚丙烯纤维进行接枝丙烯酸改性, 利用正交分析法研究了引发温度、BPO浓度、接枝温度、接枝时间及丙烯酸(AA)浓度对纤维接枝率的影响, 并评价了改性前后纤维与水泥基体的界面结合性能。结果表明: 上述因素对纤维接枝率的影响大小为引发温度>BPO浓度>接枝时间>接枝温度>AA浓度, 最佳反应条件为引发温度90℃, BPO 4.50×10^-2mol/L, 接枝时间60 min, 接枝温度75℃, AA 1.4 mol/L, 此时纤维接枝率达13.12%; 经化学接枝改性后, 聚丙烯纤维表面亲水性和粗糙度增大, 与水泥基体的界面结合得到增强, 纤维掺量为0.05%(体积分数)时, 聚丙烯纤维增强水泥砂浆的抗开裂性能比增大了26.6%, 抗塑性收缩开裂性能显著增强。     

聚丙烯纤维增强水泥复合材料抗冲蚀性能及冲蚀机制

针对内蒙古中西部地区风沙环境特征,利用模拟风沙环境侵蚀试验系统,研究了不同聚丙烯(PP)纤维掺量的PP纤维/水泥复合材料在风沙环境中的抗冲蚀性能,并利用SEM观测冲蚀后微观形貌,探究其冲蚀机制.结果 表明:不同PP纤维掺量的PP纤维/水泥复合材料冲蚀率大小为:普通水泥砂浆＞PP纤维质量比为1.5％的PP纤维/水泥复合材...     

预测聚合物基复合材料导热系数方法研究进展

用聚合物与高导热填料共混制得导热聚合物基复合材料应用在防腐和节能要求较高的换热场合,符合换热设备新材料的要求;而复合材料的等效导热系数预测比较复杂,本文总结了预测聚合物基复合材料等效导热系数的各种方法,包括傅里叶定律法、最小热阻力法、热阻网络法、逾渗理论方法和均匀化方法,归纳了这些模型和方法的特点,对应用这些模型和方法提出了参考性的建议.     

水灰比对PVA纤维增强水泥基复合材料性能和显微结构的影响

对3种不同水灰比(0.2,0.4,0.65)形成的聚乙烯醇(PVA)纤维增强水泥基材料,通过三点弯曲试验,结合表观裂缝形状和裂缝处PVA纤维形态,研究了水灰比对材料弯曲性能的影响;通过对断裂面处纤维表面、纤维嵌入端和纤维拉断或拔出端的SEM影像分析,从微观层面研究了水灰比对PVA纤维-基体界面显微结构的影响。弯曲试验结果表明:随着水灰比增加,跨中部位裂缝数量明显增加,裂缝处拔出的纤维数量增多而拉断的数量减少,材料的弯曲韧度和开裂强度到弯曲强度的增强幅度提高。界面显微结构表明:随着水灰比增加,基体结构由致密变疏松,界面粘结力减弱,桥接裂缝的PVA纤维状态由瞬间猝断转变为滑动拔出且表面有轻微刮削,纤维对材料增强增韧的效率显著提高。     

偶联剂改性玄武岩纤维增强水泥基复合材料力学性能

为改善玄武岩纤维(BF)与水泥基材料的界面结合作用,分别采用质量分数为0.4%、0.8%和1.2%的γ-氨丙基三乙氧基硅烷(CG550)、γ-甲基丙烯酰氧丙基三甲氧基硅烷(CG570)和乙烯基三乙氧基硅烷(Z6518)的三种硅烷偶联剂对玄武岩纤维进行表面处理,研究改性后纤维及其增强混凝土的力学性能影响规律。实验结果表明,随着CG550溶液浓度增加,改性玄武岩纤维及其水泥基复合材料力学性能整体呈上升趋势,当CG550溶液浓度为1.2%时,纤维及其增强水泥基材料有最佳的力学性能;随着CG570溶液浓度增加,改性后玄武岩纤维的断裂强度先升高后降低,断裂伸长率基本不变,纤维断裂强度最高提升5.8%,其水泥基复合材料的力学性能随溶液浓度增加呈上升趋势,抗折强度最高提升24.4%,抗压强度最高提升7.3%;随着Z6518溶液浓度上升,改性后玄武岩纤维的断裂强度逐渐降低,但断裂伸长率逐渐增高,表现出较好的延性;其水泥基复合材料力学性能随浓度变化无明显改善。综合考虑实验结果,三种硅烷偶联剂对纤维的改性效果好坏依次为CG570、CG550、Z6518。     

PVA纤维增强水泥基复合材料热处理后的力学性能

为了促进聚乙烯醇(PVA)纤维增强水泥基复合材料(PVA-ECC)在热环境工程领域中的应用,通过狗骨试件拉伸试验,研究了高粉煤灰掺量的PVA-ECC热处理后的力学性能变化;采用单纤维抗拉试验、单纤维拔出试验以及单裂缝拉伸试验研究了PVA-ECC性能提升的机制。结果表明:在不高于200℃的热处理后,PVA-ECC仍能实现多裂缝开裂,相比20℃,50、100、200℃热处理后的PVA-ECC复合材料的拉伸力学性能提高,其幅度为100℃> 50℃> 200℃;纤维强度不是PVA-ECC抗拉性能变化的控制因素,适当的温度处理提高了纤维与基体的化学黏结力和摩擦力,从而提高了纤维的桥接作用和裂缝的余能,进而提高了PVA-ECC的抗拉性能和摩擦耗能能力。PVA-ECC性能变化的机制分析为PVA-ECC工程设计提供了良好的理论基础。      

表面处理玄武岩纤维增强水泥基复合材料力学性能

为提高玄武岩纤维(BF)与水泥基体的界面结合力和桥接作用,分别采用HCl溶液(0~2.0mol/L)和NaOH溶液(0~2.0mol/L)对BF表面进行刻蚀糙化处理,研究纤维表面处理对BF增强水泥基复合材料的力学性能影响规律。结果表明:随着HCl溶液浓度增加,BF/水泥复合材料抗折强度与弯曲强度均先增加后降低,挠度呈现缓慢增加趋势,而抗压强度变化幅度较小;当HCl溶液浓度为1mol/L时,BF/水泥复合材料的强度与韧性最佳;碱处理BF后,BF/水泥复合材料的力学性能随NaOH浓度增加而显著降低,且复合材料韧性无明显改善;BF经HCl溶液腐蚀后的质量保留率变化规律与NaOH溶液腐蚀后的变化规律接近,而经HCl溶液腐蚀后BF强度保留率大于NaOH溶液腐蚀后的BF强度保留率。     

Rate-dependent tensile behavior of high performance fiber reinforced cementitious composites

High Performance Fiber Reinforced Cementitious Composites (HPFRCC) show strain hardening behavior accompanied with multiple micro-cracks under static tension. The high ductility and load carrying capacity resulting from their strain hardening behavior is expected to increase the resisting capacity of structures subjected to extreme loading situations, e.g., earthquake, impact or blast. However, the promise of HPFRCCs for dynamic loading applications stems from their observed good response under static loading. In fact, very little research has been conducted to investigate if their good static response translates into improved dynamic response and damage tolerance. This experimental study investigates the tensile behavior of HPFRCC using High strength steel fibers (High strength hooked fiber and twisted fiber) under various strain rates ranging from static to seismic rates. The test results indicate that the tensile behavior of HPFRCC using twisted fiber shows rate sensitivity while that using hooked fiber shows no rate sensitivity. The results also show that rate sensitivity in twisted fibers is dependent upon both fiber volume fraction and matrix strength, which influences the interface bond properties.     

A study on the effects of high temperature on mechanical properties of fiber reinforced cementitious composites

The flexural strength and ductility properties of cementitious composites (mortar) under high temperature may be significantly improved by incorporating different types of fibers. In this study, four different types of fibers are added to cement mortars with the aim to investigate their mechanical contributions to mortars under high temperature, comparatively. Polypropylene (PP), carbon (CF), glass (GF) and polyvinyl alcohol (PVA) fibers are chosen for research. These fibers are added into mortars in five different ratios (0.0%, 0.5%, 1.0%, 1.50% and 2.0%) by volume. The mortars are subjected to the following temperatures: 21 °C (normal conditions), 100 °C (oven dry), 450 °C and 650 °C. The mechanical properties investigated are flexural strength, deflection and compressive strength of the cement mortars. In addition, thin sections of mortars are investigated to obtain changes in mortar because of high temperature. It is concluded that all fiber types contribute to the flexural strengths of mortars under high temperature. However, this contribution decreases with an increase in temperature. The samples with PVA show the best flexural performance (75–150%) under high temperature. CF which does not melt under high temperature also gives high flexural strength (11–85%). The compressive strengths of the mortars reduce under high temperature or with fiber addition. The highest increase in flexural strength and the lowest decrease in compressive strength is at 0.5–1.5% for CF if all temperature conditions are taken into consideration. The optimum fiber addition ratios of the samples containing PP and GF are 0.5% by volume. And for PVA, it is between 0.5% and 1.5% by volume.     

Enhancing fiber/matrix bonding in polypropylene fiber reinforced cementitious composites by microbially induced calcite precipitation pre-treatment

In fiber reinforced cementitious composites (FRCC), bonding between the fibers and matrix governs many important properties, including strengths, fracture energy, ductility, and energy absorption capacities. This study explores the application of a microbiological process of microbially induced calcite precipitation (MICP) to pre-treating surface of polypropylene (PP) fibers for enhancing the interfacial boning strength. This technique utilizes MICP process to produce calcium carbonate that binds onto the fiber surface, leading to increased interfacial bond area and strength. Laboratory tests indicate that MICP modification could increase the post-cracking resistance and energy absorption capacity of the FRCC beam specimens by 58% and 69.3%, respectively. Microstructure analysis reveals that PP fibers after MICP treatment were coated with a layer of CaCO₃ with thickness around 20–50 μm depending on the degree of deposition. Results acknowledged a significant role of MICP pre-treatment in enhancing the fiber-matrix bonding properties of FRCC and the corresponding mechanical performance.     

A design approach for the mechanical properties of polypropylene discontinuous fiber reinforced cementitious composites by extrusion molding

Polypropylene discontinuous fiber reinforced cementitious composites were prepared by extrusion molding and tested in uniaxial tension to determine the mechanical properties such as ultimate composite strength and strain, and the critical volume fraction for multiple cracking. It was shown that the experimentally determined critical fiber volume fraction reasonably agreed with the theoretical value predicted by a micromechanics model. The extruded fiber composites yielded the ultimate composite strength of 9.0 MPa and composite strain of 0.55% at the fiber volume fraction of 7.4%. Our experimental results suggest that there is an optimal fiber aspect ratio and fiber volume fraction for enhancing the fracture properties.     

长玻璃纤维增强聚丙烯复合材料的研究

选用无碱玻璃纤维 ,采用特殊方法使长纤维与基体聚丙烯树脂有序复合 ,制备了一系列不同纤维长度、含量以及采用不同表面处理的玻纤 /PP复合材料 ,并测定了材料的力学性能 ,通过SEM观察了复合体系的界面 ,从微观上验证了材料力学性能的变化规律。实验表明 ,所采用的复合材料制备方法可使纤维的排布更加有序 ,并可改进材料的力学性能。     

Microstructure variability and macroscopic composite properties of high performance fiber reinforced cementitious composites

High performance fiber reinforced cementitious composites have made major advances in recent years, to the point where they are being adopted in building and bridge constructions. The most significant advantage of HPFRCC over conventional concrete is their high tensile ductility. However, the tensile strain capacity has been observed to vary, most likely as a result of the variability of the microstructure derived from the processing of these materials.This paper describes the composite property variability, as well as the variability of the material microstructure. Scale linkage is discussed. In particular, the tensile stress–strain curves, and the crack pattern on uniaxially loaded specimens are presented. The treatment of random fibers in micromechanical models, and tailoring of matrix flaw size distribution for saturated multiple cracking are examined. It is suggested that robust composite properties can be achieved by deliberate control of microstructure variability. Some open issues concerning the randomness of microstructures and possibly related macroscopic behavior are also identified. Further gains in composite property control may be expected from improvements in characterization and modeling of the microstructure randomness.     

Evaluation of the consistency of fiber reinforced cementitious composites

The rheological properties of fresh concrete, mortar or cement paste are among the most important parameters when cementitious building materials are placed. New material designs, like high or ultrahigh performance concretes, include the addition of a high volume of fibers to the fresh mix influencing its workability properties. However, the analysis of the rheological properties of fiber reinforced cementitious composites is difficult. Conventional methods mostly do not apply, especially when a high fiber content and relatively stiff mixtures are used. For this reason, a new method was developed to evaluate the workability of fiber reinforced composites. This method was applied to carbon and PVA fiber reinforced high performance composites and was used to optimize the rheological properties of these composites for an application in a centrifugation casting process.     

平纹编织碳纤维增强树脂复合材料离散电导率建模方法

编织碳纤维增强树脂复合材料(CFRP)的电阻抗分布具有各向异性、异质性、几何结构复杂等特点。建立电阻抗分布模型是利用电磁涡流无损检测技术获取编织CFRP缺陷及疲劳损伤信息的关键关节。基于电阻抗张量建模理论,采用多层编织结构CFRP二维平面的分块均化电学特性表征方法,建立编织结构CFRP的简化电阻抗分布模型,从而实现编织结构CFRP电磁特性的精确、快速有限元分析。在有限元仿真基础上,通过设计双空气旋转线圈电磁传感器对平纹编织CFRP进行电磁无损检测,选用阻抗的极坐标图描述被测材料沿不同方向的阻抗变化趋势,通过实验验证有限元建模的正确性。最后利用所提出的建模方法模拟了双空气旋转线圈传感器对平纹编织CFRP的结构缺陷及循环载荷疲劳的检测效果。      

高导热炭纤维及其炭基复合材料

主要介绍了国际上近十年来高导热炭纤维（CF）及其炭基复合材料发展的新动向。