应变硬化水泥基复合材料损伤失效机理研究

发布时间：2018-01-06 05:00

本文关键词：应变硬化水泥基复合材料损伤失效机理研究　出处：《青岛理工大学》2014年博士论文　论文类型：学位论文

【摘要】：应变硬化水泥基复合材料(Strain Hardening Cement—based Composite,简称SHCC)在拉伸荷载作用下具有应变硬化特性和多缝开裂特性,其极限拉伸应变可达到4%以上。因此SHCC在控制结构裂缝以及提高结构抗震性能等方面有广阔的应用前景。目前,SHCC的设计理论、基本力学性能、耐久性能等方面的成果较多。但大多数研究是针对未收损伤构件进行的,这与实际工程有一定的差别。所以,本文针对上述问题研究SHCC的开裂损伤机理以及开裂后的耐久性,主要结论如下： (1)采用数字图像处理的方法研究了拉伸荷载作用下SHCC试件成型面和底面的裂缝开展过程,并用数理统计和概率的方法对其进行分析。发现试件底面的裂缝密度低于试件成型面,其平均裂缝宽度大于成型面,裂缝密度、平均裂缝宽度等裂缝宽度统计参数均与拉伸应变呈三次多项式关系,并且通过分析发现拉伸荷载作用下SHCC的裂缝宽度分布可以用Gamma分布进行描述。在此基础上进行毛细吸水试验和氯离子侵蚀试验,研究不同拉伸应变下SHCC的耐久性,同时研究了硅烷浸渍防水处理对开裂SHCC的防护效果。发现随着拉伸应变的增加,SHCC试件的吸水速度增快,吸水量增大,毛细吸收系数随拉伸应变线性增加,氯离子侵入深度和侵入量增大。而硅烷防水处理可以有效地延缓开裂SHCC中水分和氯离子的侵入。最后基于上述研究结果给出了裂缝特征与SHCC渗透性的关系,用于开裂SHCC的耐久性评价。 (2)应用中子成像技术,突破SHCC的非透明局限,实现了对SHCC材料在未开裂以及多缝开裂情况下水分侵入过程的可视化成像追踪和定量计算。研究发现：SHCC在无裂缝时,水分侵入量很少；但当多缝开裂且裂缝宽度较大时,水分迅速沿裂缝侵入试件内部,并为裂缝两侧基体提供水源,甚至通过纤维与水泥基体之间的微孔道大量渗透而侵入整个开裂区域。但采用内掺硅烷乳液方法制备的整体防水SHCC在开裂后表现出良好的耐久性。 (3)从引起干缩的本质原因——湿度扩散着手,针对应变硬化水泥基材料湿度扩散和干燥收缩提出了一种湿度扩散系数和干缩应力的反演分析方法。在迭代计算过程中引入了遗传算法进行优化。由反演分析法计算得到的SHCC及其基体的失水曲线和收缩曲线与试验曲线基本吻合。表明文中采用的反演算法反演值可信度较好,计算精度较高。同时也表明反演算法具有良好的适应性,可达到多参数反演分析的目的。从试验结果来看：随着环境湿度的减小,SHCC及其基体的失水率和干缩率均增大；所有试件前期失水速度和干缩速度快,后期逐渐减小；SHCC的气态水湿度扩散系数D,小于其基体的D,。随着干燥龄期的增长,试件内部靠近试件表面处由于湿度梯度的作用逐步受拉,甚至达到其抗拉强度,从而引起开裂；当干缩应力达到材料的抗拉强度时,由于该种材料特有的应变硬化特性,其应力并没有软化降低,而是保持该抗拉强度值；随着干燥龄期的增长,试件的干燥前锋逐步向试件内部推进；当试件某位置达到其抗拉强度时,其内部的应力先由抗拉逐步降低并逐步过渡到受压,呈梯度分布。非常直观的呈现了SHCC在干燥收缩过程中的损伤全过程。 (4)通过快速冻融试验,研究了不同冻融循环次数下SHCC的相对动弹性模量变化、质量损失率、SHCC棱柱体弯曲韧性、毛细吸水特性、抗氯离子侵蚀性能、碳化性能以及SHCC与钢筋的粘结滑移性能。SHCC经300次冻融循环后相对动弹性模量损失仅4%,质量损失不到2%。纤维的掺入有效的提高了SHCC的抗冻性。随着冻融循环次数的增加,由于PVA纤维与基体界面之间粘结强度的降低,PVA纤维在拉伸作用下的拔出数量增多,而拔断数量减少,从而使得SHCC棱柱体试件的弯曲抗拉强度有一定幅度的下降,但试件跨中挠度增大。冻融前后SHCC试件的毛细吸水试验、抗氯离子侵蚀试验以及碳化试验均表明,冻融作用对其耐久性能影响不大。随着冻融循环次数的增加,钢筋与普通混凝土极限粘结强度近似线性降低。试件发生劈裂破坏。而SHCC粘结试件随着冻融循环次数的增加,钢筋与SHCC极限粘结强度逐渐下降,但降低幅度不大。试件发生拔出破坏。
[Abstract]:Strain hardening cementitious composites (Strain Hardening Cement based Composite, referred to as SHCC) under tensile load with strain hardening characteristics and multiple cracking behaviors, the ultimate tensile strain can reach above 4%. Therefore SHCC has a wide application prospect in the control of structural cracks and improve the seismic performance of the structure. At present, design theory SHCC, basic mechanical properties, durability and other aspects of the results more. But most of the studies for uncollected component damage, which have some differences with the actual project. Therefore, the durability of the cracking mechanism for the problem of SHCC and after cracking, the main conclusions are as follows:
(1) studied under tensile loads SHCC specimen surface and the bottom surface of the cracking process using digital image processing method, and carries on the analysis using the method of mathematical statistics and probability. The specimen found the bottom surface of the crack density is lower than the specimen surface, the average crack width is greater than the molding surface, crack density. The average crack width and crack width statistical parameter showed three polynomial relationship with the tensile strain and crack width under tensile loads SHCC distribution can be described by the Gamma distribution through the analysis. On the basis of experiment of capillary water absorption test and chloride ion erosion, the durability of different tensile strain SHCC, were also studied. Silane waterproofing treatment has protective effect on the cracking of SHCC. It is found that with the increase of tensile strain, SHCC test the water absorption speed increased, the water absorption increased, with capillary absorption coefficient Stretch strain increases linearly, the chloride penetration depth and penetration increases. While the water repellent treatment can effectively delay the intrusion of moisture and chloride cracking in SHCC. Finally, the research results are given based on the fracture characteristics and SHCC permeability relationship for durability evaluation of cracking SHCC.
(2) the application of neutron imaging technology, non transparent to transcend the limitation of SHCC, the calculation of the SHCC material under the condition of multiple cracking of water intrusion process visualization and quantitative imaging tracking without cracking as well. It is found that the SHCC in the absence of cracks, water intrusion is few; but when multiple cracks and crack width is large water, quickly along the crack intrusive specimens, and provide water for cracks on both sides of the matrix, even through micro channels between fiber and cement matrix infiltration and invasion. But the whole cracking area with silane emulsion method for the preparation of waterproof SHCC showed good durability after cracking.
(3) from the nature of the reasons caused by shrinkage, moisture diffusion to the moisture diffusion of strain hardening cementitious materials and drying shrinkage presents a moisture diffusion coefficient and the shrinkage stress inversion method. In the iterative calculation process of the introduction of genetic algorithm optimization. The SHCC matrix and the calculated water loss curve and the shrinkage curve and test curve basically by inverse analysis method. The results show the inversion algorithm of value credibility better, higher calculation precision. At the same time also shows that the algorithm has good adaptability, can achieve the analysis of multi parameter inversion. The test results show: with the decrease of relative humidity, water loss and SHCC matrix and the rate of shrinkage increases; all specimens pre dehydration rate and shrinkage speed, later gradually decreased; the water moisture diffusion coefficient D of gaseous SHCC, less than the matrix D. With the drying up of the age, inside the specimen near the specimen surface due to humidity gradient effect gradually tension, even reaches its tensile strength, causing shrinkage cracking; when the stress reaches the tensile strength of the material, because of the unique strain hardening material, the stress no softening decreased, but maintain the tensile strength; with the drying up of the age, try a drying front gradually to inside the specimen when the specimen in a position of propulsion; reaches its tensile strength, the internal stress of the tensile decreased gradually and gradually transition to the pressure gradient is very intuitive. Presents the whole process of SHCC damage in drying shrinkage process.
(4) by rapid freezing and thawing test, study the different relative dynamic elastic modulus of freeze-thaw cycles under SHCC, the mass loss rate, SHCC prism flexural toughness, capillary water absorption characteristics, chloride penetration, carbonation resistance and SHCC and reinforced the bond slip performance of.SHCC after thawing, the relative loss of dynamic elastic modulus of only 4% and 300 times of freeze, mass loss less than 2%. fiber can effectively improve the frost resistance of SHCC. With the increase of the number of freeze-thaw cycles, due to a decrease in bond strength between PVA fiber and matrix interface, PVA fiber pullout in tension increased, and reduce the number of pull off, bending the tensile strength of SHCC so that the prism specimens dropped to a certain extent, but the specimen deflection increases. After freezing and thawing SHCC capillary water absorption test component, chlorine ion erosion test and carbonation test showed that the effect of freeze-thaw Its durability has little effect. With the increase of freeze-thaw cycles, the ultimate bond strength of ordinary concrete reinforced with a nearly linear decrease. The specimens of splitting failure occurred. While SHCC specimens with the increase in the number of freeze-thaw cycles, the bond strength of steel and the limit of SHCC gradually decreased, but decreased slightly. When the specimens are pulled out destroy.

【学位授予单位】：青岛理工大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU528

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