掺机制砂的高延性水泥基复合材料的制备

采用机制砂,经过人工破碎、筛分,研究不同的砂灰比对高延性水泥基复合材料性能的影响。结果表明,砂灰比(0.35~0.50):1时,水泥基材极限挠度超过17 mm、极限抗弯承载力接近8MPa;通过扫描电镜观察发现试件破坏断面处以纤维被拔出方式为主,以纤维拉断方式为辅,水泥基材呈现出明显的应变硬化行为和多缝开裂特征。     

钢-PVA混杂纤维增强工程水泥基复合材料弯曲性能研究

为了弥补现有钢-聚乙烯醇(PVA)混杂纤维增强工程水泥基复合材料造价过高、工程应用面狭窄的缺陷,本文通过使用廉价的国产PVA纤维部分替代日产PVA纤维制备出一种新型的多元混杂纤维增强工程水泥基复合材料(MFECC)。研究MFECC材料薄板试件的弯曲性能和破坏形态,对试件的弯曲韧性和性价比进行评价,并通过SPSS软件的多元非线性回归法建立极限弯曲性能预测模型。结果表明,引入国产PVA纤维后MFECC薄板的应变硬化力学行为和多缝开裂现象相较于仅掺日产PVA纤维时有所降低,但仍具有较高的强度与延性。当钢纤维、日产PVA纤维和国产PVA纤维体积掺量分别为0.2%、0%和2.0%时,MFECC的极限拉伸应变为4.4%,抗压强度为46.39 MPa,极限抗弯挠度可达12.697 mm,性价比最高。建立的MFECC薄板试件的极限弯曲性能预测模型对试验值的拟合度良好。     

纳米粒子和石英砂对PVA纤维水泥基复合材料单轴拉伸性能的影响

为研究纳米粒子种类和掺量以及石英砂粒径对聚乙烯醇纤维(PVA纤维)水泥基复合材料单轴拉伸性能的影响,通过单轴拉伸试验测得了试件的极限拉应变和极限拉应力,并得到了试件应力-应变关系曲线.PVA纤维的体积掺量为0.9％,选择纳米SiO2质量掺量和石英砂粒径各四种.结果 表明,纳米SiO2的掺加对PVA纤维水泥基复合材料抗拉伸性能有一定的提高,随着纳米SiO2掺量从0％增大到2.5％,试件极限拉应变和极限拉应力整体上呈逐渐增大趋势.相对于纳米CaCO3,纳米SiO2对PVA纤维水泥基复合材料抗拉伸性能的增强效果更明显.石英砂的粒径对PVA纤维水泥基复合材料抗拉性能影响较大,石英砂的粒径越小,PVA纤维水泥基复合材料的极限拉应变和极限拉应力越低.     

超高韧性水泥基复合材料弯曲韧性研究

为研究超高韧性水泥基复合材料(UHTCC)的弯曲韧性,开展了薄板试件四点弯曲加载试验,结合对试件弯拉荷载和跨中挠度的分析,探究了纤维体积掺量、粉煤灰掺量、水胶比三因素对UHTCC弯曲韧性的影响规律,分析了韧性指数IU与极限跨中挠度的变化规律.结果 表明,纤维掺量越大,材料弯曲韧性越好;粉煤灰掺量在F/C为1.2时各阶段韧性指数最大,表明粉煤灰掺量对UHTCC弯曲韧性的影响存在一个最佳值;水胶比为0.24、0.28时韧性指数未达到I50,且水胶比为0.26时峰值荷载对应的韧性指数IU最大,表明过大或过小水胶比都会降低UHTCC持续耗能的能力;在不同因素影响下,峰值荷载所对应的韧性指数IU与极限跨中挠度具有良好的相关性,且峰值荷载处于应变硬化阶段末期,几乎包括荷载-挠度曲线的全部,使用IU能够较好地反映UHTCC的能量吸收能力.     

材料组分对UHTCC力学性能的影响研究

通过立方体抗压试验和薄板四点弯曲试验,研究了水胶比、粉煤灰掺量、石英砂粒径对超高韧性水泥基复合材料(UHTCC)力学性能的影响,并结合扫描电子显微镜(SEM)分析了UHTCC薄板试件断面的微观结构.试验结果表明,UHTCC薄板最大跨中挠度可达46.3 mm,最大极限抗弯强度可达9.6 MPa,均出现了应变硬化与多缝开裂现象.随着水胶比的增大,UHTCC抗压强度降低,四点弯曲强度降低,但水胶比过低或过高都不利于提高材料的延性.大掺量的粉煤灰会显著降低UHTCC抗压强度和四点弯曲的初裂强度,但能极大的提高材料的延性.粒径小的石英砂能改善UHTCC材料的弯曲强度和延性.SEM微观结构表明,纤维与基体之间通过桥联作用抑制微裂缝的发展,水胶比过低,断面纤维易被拉断,水胶比过高,断面纤维大量拔出,两者都不利于提高UHTCC的延性.     

循环拉伸下形状记忆合金纤维增强ECC的闭缝性能研究

将不同掺量和不同直径的形状记忆合金(SMA)纤维埋入工程水泥基复合材料(ECC)制得形状记忆合金纤维增强工程水泥基复合材料(SMAF-ECC),通过单轴循环拉伸试验研究SMA纤维直径和纤维掺量对SMAF-ECC试件拉伸应力-应变关系、残余应变、裂缝宽度和裂缝恢复率的影响。结果表明：打结形SMA纤维的加入提高了ECC的极限应变和极限抗拉强度；提高纤维掺量可有效提高SMAF-ECC试件的应变和裂缝恢复率，试验所得试件的最大应变恢复率和裂缝恢复率分别达到69%和77%;纤维直径在一定范围内增长，可以提高应变和裂缝恢复率，纤维直径过小会导致恢复率减小。研究成果为新型SMAF-ECC试件的推广应用提供了理论依据。     

PVA纤维增强水泥基复合材料高温性能研究

对PVA纤维增强水泥基复合材料的高温性能进行研究,分别测试了该材料在经受不同高温后的质量损失、抗压强度以及弯曲韧性,并对其微观结构变化进行了分析.结果表明,相比于普通水泥基材料,PVA纤维增强水泥基复合材料的抗压强度高,变形能力大,抗折强度高,弯曲韧性优越,其中纤维掺量为2％的试块28 d抗压强度达到45.98 MPa,抗折强度可达到14.10 MPa,最大挠度达到0.68 mm;高温处理后掺有PVA纤维的试块完整性良好,没有出现破坏性断裂,只表现为微小裂纹;随着温度的升高,不同纤维掺量砂浆试块的质量损失增大,抗压强度和抗折强度以一定的速率下降,但在800 ℃高温处理后试块仍具有一定的抗压强度和弯曲韧性,纤维掺量为2％的试块的抗压强度能达到18.9 MPa,最大挠度可保持在0.12 mm;根据微观测试可以看出,随着温度的升高,纤维缓慢熔出使试块内部出现相互交错的孔隙通道可有效防止试块高温爆裂,试块内部结构由致密变为松散蜂窝状.     

钢-PVA混杂纤维水泥基复合材料抗压力学性能及经济性研究

纤维增强延性水泥基材料(ECC)造价昂贵,在实际工程应用中尚未被推广。在传统ECC体系中加入钢纤维,并按照不同体积分数(0%、25%、50%、75%、100%)将国产PVA纤维替代日产PVA纤维,制备极具性价比的钢-PVA混杂纤维增强延性水泥基材料,通过立方体轴心抗压试验研究混杂纤维延性水泥基材料的单轴受压力学性能。结果表明：随着国产PVA纤维的增加,钢-PVA混杂纤维水泥基复合材料的抗压强度先减小后增加,抗压韧性指数先增强后减弱,而峰值应变提升效果较为显著;相较于普通水泥基材料,钢-PVA混杂纤维水泥基复合材料具有更好的完整性和延性;综合材料抗压性能与材料造价,国产PVA纤维替代日产PVA纤维配制钢-PVA混杂纤维水泥基复合材料可以实现功能价值和经济价值的协同最大化。     

聚乙烯醇纤维混凝土动态断裂过程试验研究

为探究纤维体积掺量对聚乙烯醇纤维增强水泥基复合材料(PVA-ECC)断裂过程的影响,基于50 mm的分离式霍普金森压杆(SHPB)装置对不同纤维体积掺量(0%、0.75%、1.50%、2.25%、3.00%)的PVA-ECC中心切槽半圆盘弯曲(NSCB)试件进行冲击试验,同时结合超高速数字图像(DIC)相关试验系统对PVA-ECC材料的动态断裂过程进行试验研究,得到了预制裂纹尖端张开位移的变化规律以及各组试件的临界裂缝尖端张开位移(CTOD_C)。结果表明,当不添加PVA纤维或添加较少(小于1.50%)时,裂尖宏观裂纹基本出现在裂尖荷载的峰值时刻处,而随着PVA纤维掺量的增加,裂尖宏观裂纹的出现显著早于裂尖荷载的峰值时刻,并且纤维体积掺量越大,裂尖宏观裂纹出现得越早,裂纹扩展至完全断裂的时间也显著增加。添加聚乙烯醇纤维可以显著提高混凝土试件的CTOD_C值,提高试件的阻裂能力,相同冲击荷载下,体积掺量为2.25%的聚乙烯醇纤维试件具有较大的CTOD_C值。     

粉煤灰掺量对PVA纤维水泥基复合材料力学性能影响研究

通过对8组PVA-ECC试件进行抗压强度和抗折强度试验、四点弯曲试验以及直接拉伸试验,探讨粉煤灰掺量对PVA纤维水泥基复合材料力学性能的影响.结果表明:抗压强度与抗折强度均随粉煤灰掺量的增加而降低,四点弯曲试验中试件挠度可达26.5 mm,直接拉伸试验中试件最大极限拉应变为1.6％,是传统混凝土材料的100多倍.     

Effect of multiple loading sequence on time-dependent stress rupture of fiber-reinforced ceramic-matrix composites

In this paper, the effect of multiple loading sequence on time-dependent stress rupture of fiber-reinforced ceramic-matrix composites (CMCs) at intermediate temperatures in oxidative environment is investigated. Considering multiple damage mechanisms, a micromechanical constitutive model for time-dependent stress rupture is developed to determine damage evolution of matrix crack spacing, interface debonding and oxidation length, and fiber failure probability under single and multiple loading sequences. The relationships between multiple loading sequence, composite strain evolution, time, matrix cracking, interface debonding and oxidation, and fiber fracture are established. The effects of fiber volume, matrix crack spacing, interface shear stress in the slip and oxidation region, and environment temperature on the stress/time-dependent strain, interface debonding and oxidation fraction, and fiber broken fraction of SiC/SiC composite are analyzed. The experimental stress rupture of SiC/SiC composite under single and multiple loading sequences at 950°C in air atmosphere is predicted. Compared with single loading stress, multiple loading sequence affects the interface debonding and oxidation fraction in the debonding region, leading to the higher fiber broken fraction and shorter stress-rupture lifetime.     

Compressive fatigue damage and failure mechanism of fiber reinforced cementitious material with high ductility

The fiber reinforced cementitious material with high ductility has potential use in particular environments and structures that undergo repeated or fatigue loads. In this study, a series of monotonic and fatigue tests were performed to investigate the compressive fatigue behavior of this material. It is found that the fatigue life of this material is higher than that of plain concrete and steel fiber reinforced concrete under the same stress level. In addition, the failure deformation of fiber reinforced cementitious material with high ductility under fatigue load was larger than the monotonic envelope, while the envelope coincides with the monotonic loading curve for concrete or fiber reinforced concrete. The failure surface and damage process were investigated and a new failure mode of polyvinyl alcohol fiber with crushed end was discovered. The fatigue failure surface could be divided into three regions, including fatigue source region, transition region and crack extension region.     

工程水泥基复合材料动态力学性能及抗爆抗冲击能力研究进展

工程水泥基复合材料(ECC)是一种基于微观力学设计的新型纤维增强水泥基材料,它通过连续稳态开裂过程表现出超高延性和韧性,从而克服了普通水泥基材料抗拉能力弱、易开裂的缺点。本文综述了ECC设计机理、动态力学性能及其在抗爆抗冲击方面的研究现状,分析了材料组分设计、高应变率和高温环境对ECC性能的影响,对ECC材料在抗爆抗冲击领域的进一步研究和发展提出了建议。     

金属基聚合物复合材料短纤维桥接界面强化机理

针对金属基聚合物复合材料易诱发界面剥离损伤失效的共性问题,研究了通过多层复合组装注射成型,在聚合物复合层与粘接层界面形成短纤维桥接,实现复合界面强化。基于内聚力剥离损伤模型,构建了短纤维桥接强化界面剥离裂纹扩展断裂失效过程的模拟仿真技术,模拟建立了界面剥离裂纹快速失稳扩展断裂损伤失效临界载荷—桥接纤维特性—界面剥离断裂韧性（损伤启裂应力T₀和临界应变能释放率G_c）的协同关联理论,诠释了短纤维桥接界面强化机理,提出了预防短纤维桥接强化界面诱发剥离裂纹快速失稳扩展失效的设计准则。结果表明,当桥接纤维密度为20根/mm²,可使其临界载荷增加55.9 %,临界载荷受控于桥接纤维密度、初始预裂纹面积、损伤启裂应力和临界应变能释放率,且与桥接纤维密度、损伤启裂应力和临界应变能释放率呈正关联关系,而与初始预裂纹面积呈负关联关系。     

A theory for the flexural strength of steel fiber reinforced concrete

A theory is presented to predict the flexural tensile strength of concrete reinforced with short, discontinuous steel fibers randomly oriented and uniformly dispersed in a cement-based matrix. The theory is based on a dual criterion of crack control and composite mechanics. The first crack in the fibrous composite occurs due to bond slip. The fracture process consists of progressive debonding of fibers during which slow crack propagation occurs. Final failure occurs due to unstable crack propagation when fibers pull out and the interfacial shear stress reaches the ultimate bond strength. The theory is supported by test data on fiber reinforced concrete, mortar and paste.     

NR/SBR并用胶撕裂性能和动态切割性能的研究

分析天然橡胶(NR)/丁苯橡胶(SBR)并用比对胶料撕裂强度(裤形试样)和动态切割性能的影响。结果表明,随着SBR用量增大,试样的撕裂过程由多节撕裂过渡到平稳撕裂,撕裂强度峰值下降,谷值上升。NR为连续相时,胶料易产生长距离撕裂且舌端不容易断裂,动态切割量大;SBR为连续相时,胶料割口扩展速度低且舌端容易断裂,动态切割量小。撕裂强度谷值高的胶料动态切割量小。     

Fatigue behavior of neat and long glass fiber (LGF) reinforced blends of nylon 66 and isotactic PP

This paper focuses on the study of the fatigue behavior of neat and long glass fiber (LGF) reinforced nylon 66/PP-blends. The fatigue was characterized using Parislaw plots in the stable crack growth acceleration range. The fatigue crack propagation (FCP) is presented as a function of the crack growth per cycle (da/dN), the amplitude of the stress intensity factor ΔK, and of the strain energy release rate ΔG. It was also of interest to compare the order of performance found in fatigue to that in the static fracture test. The fracture surfaces were characterized with SEM to determine the failure mechanisms. Further, thermographic camera recordings were used to study the size of a “heated” area (ΔT = 2°C) that developed around the crack tip during the cyclic loading of LGF-PP with different amounts of maleic anhydride grafted PP (PP-g-MAH). For the neat materials, a different order of performance was detected under static and cyclic loading. This was explained by the different failure mechanisms observed after static and cyclic fracture that were related to different stress states of the specimens during the fracture process. On the other hand, the LGF-blends showed a similar order of performance during the static and the fatigue test. This was explained by the observation that similar fiber related failure mechanisms occurred in the composite, both after failure caused by the static and cyclic loading, respectively. For the LGF-PPs with varying PP-g-MAH content, the order of performance in fatigue did not correspond to the size of the “heated area” around the crack tip. This was caused by a change in the composite failure mechanisms, which contributed differently to the size of the “heated area” and to the fatigue performance.     

FRP筋异强混凝土叠浇梁挠度与延性研究

为提高纤维增强聚合物(FRP)筋异强混凝土叠浇梁的抗弯性能与延性,研究了钢纤维掺量、钢纤维混凝土叠浇层厚度对FRP筋异强混凝土叠浇梁的影响。以钢纤维体积掺量(0%、0.5%、1.0%、1.5%)与钢纤维混凝土叠浇层厚度(0 mm、180 mm、210 mm、300 mm)为变量,对6根FRP筋异强混凝土叠浇梁进行三分点弯曲试验,并对试验梁的破坏过程、破坏形态、裂缝宽度以及跨中挠度进行分析。研究结果表明:钢纤维的掺入改善了FRP筋异强混凝土叠浇梁的受力性能,使其由脆性破坏向延性破坏发展;随着钢纤维掺量、钢纤维混凝土叠浇层厚度的增加,FRP筋异强混凝土叠浇梁的极限承载力提高了9%~33%,抗弯性能提升了4%~21%,延性提升了22%~89%。基于试验与理论分析,建立了钢纤维作用下的FRP筋异强混凝土叠浇梁挠度计算公式与延性评价方法。     

Fracture behavior of sisal fiber–reinforced starch‐based composites

The fracture behavior of biodegradable fiber–reinforced composites as a function of fiber content under different loading conditions was investigated. Composites with different fiber content, ranging from 5 to 20 wt%, were prepared using commercial starch‐based polymer and short sisal fibers. Quasistatic fracture studies as well as instrumented falling weight impact tests were performed on the composites and the plain matrix. Results showed a significant increase in the crack initiation resistance under quasistatic loading. This was caused by the incorporation of sisal fibers to the matrix and the development of failure mechanisms induced by the presence of the fibers. On the other hand, a modest increasing trend of the resistance to crack initiation with fiber loading was detected. An improved fracture behavior was also observed when the impact loading was parallel to the thickness direction. Under these experimental conditions, the composites exhibited higher values of ductility index, energy at initiation and total fracture energy than the plain matrix. Furthermore, an increasing trend of these parameters with fiber content was detected in the biocomposites. Overall, the addition of sisal fibers to the biodegradable matrix appears to be an efficient mean of improving fracture behavior under both quasistatic and impact loading conditions. POLYM. COMPOS. 26:316–323, 2005. © 2005 Society of Plastics Engineers     

分形及分维在单轴向三维编织复合材料拉伸实验中的应用

基于分形几何的计盒维数研究了三维编织复合材料拉伸实验的断裂样照,结果表明,该材料的断裂曲线具有统计自相似性,在不同的尺度范围内具有不同的空间分布格局;而计盒维数定量地表征了其尺度变化规律;准静态和低应变率加载条件下材料的分维数较大,表明其空间占据程度较大,曲线弯曲结构复杂,这是因为低应变率加载时材料内部结构断裂时间不同造成;而高应变率加载时,断裂曲线分维数较小,曲线空间占据小,弯曲结构比较简单,这是由高应变率加载时材料内部结构断裂时间差异缩小造成。