三点弯曲下钢纤维高强混凝土的断裂性能

通过50个尺寸为100 mm×100 mm×515 mm的钢纤维高强混凝土切口梁三点弯曲试验,研究钢纤维体积率对高强混凝土有效裂缝长度、断裂韧度和临界裂缝张开位移的影响.结果表明:随着钢纤维体积率的增加,钢纤维高强混凝土断裂韧度增益比基本呈线性增加,临界裂缝尖端和临界裂缝嘴张开位移分别呈指数型增加.有效裂缝长度趋于稳定值,基本不受钢纤维体积率变化的影响.在分析试验结果的基础上,建立了钢纤维高强混凝土有效裂缝长度、断裂韧度和临界裂缝张开位移的计算公式.     

钢纤维高强混凝土断裂韧度及影响因素

通过钢纤维高强混凝土切口梁三点弯曲试验,探讨了相对切口深度（a0/h）、粗骨料最大粒径（dmax）、水灰比（W/C）和钢纤维体积率（ρf）等因素对钢纤维高强混凝土断裂韧度（KfIC）和断裂韧度增益比（KfIC/KIC）的影响。结果表明：ρf一定时,KfIC随a0/h的增加逐渐减小,随dmax的增加呈增大趋势,随W/C的减小逐渐增加;a0/h一定时,KfIC随ρf的增加逐渐增大;钢纤维能够显著提高高强混凝土断裂韧度,KfIC/KIC大于1;影响因素不同,KfIC/KIC变化趋势不同。在分析试验结果的基础上,建立了钢纤维高强混凝土断裂韧度计算模式。     

钢纤维高强混凝土的抗剪强度

通过68个100mm×100mm×400mm,102个150mm×150mm×150mm高强混凝土和钢纤维高强混凝土试件的直接双面剪切实验、立方体抗压实验和劈裂抗拉实验,分析了钢纤维体积率、钢纤维类型对剪压强度比及剪拉强度比的影响,探讨了高强混凝土及钢纤维高强混凝土抗剪强度与抗压强度、劈拉强度的关系。研究表明:随钢纤维体积率的增大,剪压强度比呈上升趋势,剪拉强度比呈下降趋势。随抗压强度的提高,钢纤维高强混凝土抗剪强度的提高幅度大于高强混凝土的。通过对实验结果的统计分析,提出钢纤维高强混凝土抗剪强度与抗压强度、劈拉强度的关系式,得到不同类型钢纤维对高强混凝土抗剪强度和初裂抗剪强度的增强系数,建议了钢纤维高强混凝土抗剪强度的计算公式,供设计与施工参考。     

钢纤维对超高性能注浆纤维水泥基材料力学性能的影响研究

为研究钢纤维添加对超高性能水泥基材料(UHP-SIFCC)力学性能的影响,制备了UHP-SIFCC试验材料,测试了抗压强度、抗弯强度和弯曲韧性,分析钢纤维添加对抗压强度、抗弯强度和弯曲韧性的影响规律。研究结果表明:(1)UHP-SIFCC的抗压强度随钢纤维体积率和等效直径的增大而增大;(2)UHP-SIFCC的抗弯强度随钢纤维体积率和等效直径的增大而增大;(3)UHP-SIFCC的弯曲韧性随钢纤维体积率和等效直径的增大而增大。     

微细钢纤维对高弹性模量混凝土力学性能的影响

基于修正的Furnas堆积模型和骨料紧密堆积试验设计了一种高弹性模量混凝土,并利用微细钢纤维改善高弹性模量混凝土的韧性,研究了钢纤维体积掺量对骨料紧密堆积状态下混凝土流动性能、强度、弹性模量及弯曲韧性的影响规律。结果表明:采用紧密堆积骨料和适量微细钢纤维可以构筑高弹性模量韧性混凝土,其静弹性模量和动弹性模量最高分别可达50.15 GPa和53.23 GPa,断裂能可达5 680.45 N/m,残余弯曲韧度比从0增加到0.43;高弹性模量混凝土的流动性能随着钢纤维掺量的增加而降低,抗折强度、弹性模量及弯曲韧性则均随着钢纤维掺量的增加而增加,混凝土的抗压强度随着钢纤维掺量增加先增加后降低。在骨料紧密堆积状态下,综合考虑流动性能、力学性能和工程经济性,高弹性模量混凝土中微细钢纤维的合理掺量为0.4%(体积分数)。     

超早强混杂纤维混凝土断裂性能的研究

本文全面分析和研究了超早强混杂纤维混凝土的断裂性能,实验采用不同的钢纤维体积率,对混凝土试件进行三点弯曲实验,量化各纤维体积率对断裂韧性韧性的影响效果,寻求通过优化配合比设计,有效的提高混杂纤维混凝土阻裂增韧机制。结果表明,随着钢纤维用量的增加,超早强混杂纤维混凝土的断裂性能及其增益比增加较为显著,同时改变了混凝土随龄期增加而韧性降低的现象。纤维混杂掺入超早强普通混凝土中,能够起到较好的改善基体的耗能能力、增强韧性的作用,并且在这过程中,增强韧性的作用是钢纤维起主导作用。     

钢纤维对机制砂混凝土韧性的影响

以机制砂混凝土为研究对象,以混凝土的韧性特征为研究指标,以钢纤维为研究因素,系统研究了钢纤维类型、长径比、掺量对机制砂混凝土韧性指数、等效弯折强度、抗折初裂强度及弯曲韧性比的影响规律。结果表明:切断型钢纤维能够有效改善机制砂混凝土的弯曲韧性;长径比为65的钢纤维具有较大优势;机制砂混凝土的弯曲韧性随着钢纤维体积掺量的增加,整体韧性提高,在掺量1%时,机制砂混凝土弯曲韧性的增长比最大。     

钢纤维混凝土的轴心抗拉韧性

钢纤维混凝土与素混凝土相比,其最大的优点是韧性有极大地提高,因此,钢纤维混凝土可用于抗震、抗爆和抗冲击等特殊混凝土工程的特殊部位。本研究表明,在所用的试验条件下,当钢纤维的体积掺量为1％和2％时,钢纤维混凝土的轴拉韧度值是素混凝土的2至7倍,并且,韧性的改善程度与素混凝土基体的强度有关,强度越低,钢纤维的增韧效果越好。基体强度S_m与钢纤维指数V_fl/d两参数对轴拉韧性的影响有交互作用。     

层布式钢纤维混凝土力学行为及破坏特性研究

通过力学性能试验,研究了钢纤维体积掺量和长径比对层布式钢纤维混凝土力学性能影响,对比了层布式钢纤维混凝土与素混凝土和钢纤维混凝土的力学性能,结果表明层布式钢纤维混凝土改善了混凝土的力学性能,提高了混凝土的延性和弯曲韧性。     

平直型钢纤维掺量与长径比对超高性能混凝土性能的影响

为研究平直型钢纤维体积掺量及长径比对超高性能混凝土(U HPC)施工及力学性能的影响,选用四种镀铜平直型钢纤维,设计并制备了12组不同钢纤维体积掺量(0 ～4％,长径比均为65)及长径比(65、80、90、100,对应钢纤维体积掺量均为2.5％)的UHPC试件.通过扩展度、抗压强度和四点弯曲试验,得到了各组UHPC的扩展度、抗压强度、抗折强度及弯曲应力-挠度曲线;基于UHPC弯曲应力-挠度曲线,并结合CECS13:2009计算了UHPC的弯曲韧性指数.结果 表明:随着钢纤维体积掺量的增加,UHPC的扩展度呈下降趋势,UHPC抗压、抗折强度、弯曲韧性指数基本呈增加趋势,对应最佳钢纤维体积掺量分别为4％(平均值174.4 MPa)、3.5％(平均值46.18 MPa)和4％;随着钢纤维长径比的增大(钢纤维体积掺杂量2.5％不变),UHPC扩展度呈下降趋势,抗压、抗折强度平均值及弯曲韧性指数呈增加趋势;其中,抗压、抗折强度最大值分别为173.53 MPa和44.9 MPa.     

Double cantilever beam fracture toughness measurement method for glass

A simple method of measuring Mode I fracture toughness, K_IC, of glass using the double cantilever beam (DCB) geometry is presented. An inert atmosphere is created at the crack tip to prevent subcritical crack growth and enable “pinning” the crack while the specimen is loaded to failure. This was achieved experimentally using liquid toluene or a glovebox with dry argon. K_IC values measured by this method showed good agreement with published literature values for selected glasses. Applicability of the analytical stress intensity factor solution based on crack length, crack front curvature, and the height of the crack guiding groove are confirmed through experimental data and finite element analysis. The experimentally observed crack front curvature, which leads near the edges for small groove heights and leads in the center for larger groove heights, is predicted from the geometry of the DCB specimen for a linear elastic solid through finite element modeling.     

聚氯乙烯增韧改性研究进展

介绍了目前国内外PVC增韧改性的研究现状、增韧改性剂的种类和增韧机理以及PVC增韧研究的发展方向。     

陶瓷基复合材料的强韧化研究进展

增韧补强对于脆性陶瓷材料来说是一个永恒的课题,材料科学工作者对此开展了富有成效的研究,并取得了巨大的成功。本文综述了陶瓷基复合材料的相变增韧、纤维增韧、颗粒增韧、自增韧补强的方法、增韧效果及相关的增韧机理。     

球罐用B610CF钢板冲击与断裂性能试验研究

针对宝山钢铁股份有限公司开发的B610CF钢板及其焊接接头的冲击及断裂性能进行了系统的试验研究.结果表明:钢板调质状态和调质+消除应力热处理状态在- 20℃时都具有较高的冲击性能,钢板和焊接接头在- 20℃时都有着良好的断裂韧度,该钢用于- 20℃以上工况的球罐是完全可行的,所用焊接材料与母材匹配且焊接工艺合理.     

Comparison of Methods to Determine the Fracture Toughness of Three Glass-Ceramics at Elevated Temperatures

Two standardized methods for measuring k _Ic in ceramics are compared for use at high temperatures (precracked beam and surface crack in flexure). Results from a third technique involving the measurement of cracks around Vickers indentations are also presented. Three dental glass-ceramics, differing primarily in microstructure, were used as model materials in this study. They emphasized the importance of microstructure in determining high-temperature k _Ic values and the challenges in measuring them. The measured fracture toughnesses decreased with temperature and increased with imbedded grain size for all three methods.     

Improvements in microstructural and mechanical properties of ZrO2 ceramics after addition of BaO

The effects of the addition of BaO on the sinterability, phase balance, microstructure, and mechanical properties of 8 mol% yttria-stabilized cubic zirconia (8YSZ) were investigated using scanning electron microscopy, X-ray diffraction (XRD) analyses, and micro-hardness testing. The 8YSZ powder was doped with 0–15 wt% BaO using a colloidal process. The undoped and BaO-doped 8YSZ specimens were sintered at 1550 °C for 1 h. The XRD analyses results showed that the specimens doped with up to 1 wt% BaO did not exhibit BaO-related peaks, indicating that BaO was completely solubilized in the 8YSZ matrix. However, when more than 1 wt% BaO was added, BaZrO₃-related peaks appeared, suggesting that the overdoped BaO did not dissolve in the 8YSZ matrix but formed a secondary phase of BaZrO₃ at high temperatures. Grain size measurements showed that the grain size of 8YSZ decreased with an increase in the amount of BaO added. The decrease in the grain size was owing to the fact that the grains of BaZrO₃, which precipitated at the grain boundaries and grain junctions of 8YSZ, increased the grain boundary cohesive resistance because of the pinning effect. This resulted in a decrease in the grain boundary mobility, and an increase in the grain boundary energy. Furthermore, while the addition of BaO to 8YSZ caused a slight decrease in the hardness of 8YSZ, the fracture toughness of 8YSZ increased from 1.64 MPa m^1/2 to 2.08 MPa m^1/2, owing to the resulting decrease in the grain size.     

Adaptation of the chevron‐notch beam fracture toughness method to specimens harvested from diesel particulate filters

The apparent fracture toughness of a porous cordierite ceramic was estimated using a large specimen whose geometry was inspired by the ASTM‐C1421‐standardized chevron‐notch beam. Using the same combination of experiment and analysis used to develop the standardized chevron‐notch test for small, monolithic ceramic bend bars, an apparent fracture toughness of 0.6 and 0.9 MPa√m were estimated for an unaged and aged cordierite diesel particulate filter structure, respectively. The effectiveness and simplicity of this adapted specimen geometry and test method lends itself to the evaluation of (macroscopic) apparent fracture toughness of an entire porous‐ceramic, diesel particulate filter structure.     

Craze plasticity and toughness of particulate block copolymer blends

Blends of KRO-1 Resin in high molecular weight polystyrene in which the K-Resin appears as dispersed spherical composite particles with the characteristic K-Resin morphology have been modified by incorporating into them additional polybutadiene of a molecular weight of 3 kg/mole (PB3K). It was found that small additions of PB3K into KRO-1 initiate first a morphological transformation resulting in particles with two coexisting morphologies of distorted rods and parallel lamellae. At a ratio of PB3K/KRO-1 of somewhat above 0.33 the transformation is complete and results in composite particles with a very regular concentric spherical shell morphology of PB and PS. The craze initiating effectiveness of composite particles peaks with this morphology, resulting in craze flow stresses as low as 8 MPa and strains to fracture in excess of 0.80 for a PB3K/KRO-1 ratio of 0.5. Larger volume concentrations of PB3K result in reprecipitation of free PB3K inside particles and this gives rise to a rapid degradation of toughness. The very effective craze initiating action of the spherical shell particles cannot be fully accounted for by the best techniques of numerical stress analysis of the elastic and thermal properties of the composite particles utilizing locally multiaxial craze initiation criteria that were developed for surface crazing in homo-PS. It is suspected that the craze initiation condition is locally relaxed around such composite particles by the presence of certain pre-existing ‘catalytic’ interface configurations that makes the nucleation of crazes from such particle interfaces more a heterogeneous nucleation phenomenon than a homogeneous nucleation phenomenon.     

ZTM_(15)/20SiC_p陶瓷材料性能测试方法比较及分析

本文采用不同方法测定了ZTM15 /2 0SiCP 材料的弹性模量、维氏硬度、强度和韧性。结果表明因测试方法的不同 ,同一材料所测得的强度和韧性有较大差异。分别采用三点弯曲和单边切口梁法所测得的ZTM15 /2 0SiCP 材料的强度和韧性值偏大 ,由径向加载法所测得的强度值较小 ,因试样受双向应力 ,纵向最大压力是横向最大拉应力的 3倍 ,该压应力对断裂有很大影响。用压痕法测定材料的韧性时必须考虑残余应力的影响。     

Notch radius effect on fracture toughness of ceramics pertinent to grain size

Unlike fracture toughness, the notch fracture toughness of a ceramic is not a constant; rather, it increases with the notch-root radius ρ in a notched specimen. In this study, by analyzing the fracture measurements of eight different notched ceramics with an average grain size G of 3–40 μm, a simple model describing the relation between the notch fracture toughness and fracture toughness is proposed as a function of the relative notch-root radius ρ/G. The normal distribution is incorporated to consider the inevitable scatter in measurements where fracture mechanisms and errors are present. The results demonstrate that the model can effectively predict the quasi-brittle fracture variation trend for ceramics, including the upper and lower bounds, with 96% reliability, from a normal distribution; thus, it can address virtually all of the experimental data. We also determined that the notch fracture toughness approximates the fracture toughness if ρ ≤ G.