【作者】 赵燕茹；

【导师】 邢永明；

【作者基本信息】 内蒙古工业大学 ， 固体力学， 2008， 博士

【摘要】 纤维增强复合材料中的应力是通过纤维和基体之间的界面进行传递的,界面区域的力学性能及界面的应力传递过程,对整个复合材料的宏观力学性能都会产生重要影响。因此,纤维增强复合材料的界面问题是工程中十分关注的问题。本论文以纤维混凝土复合材料为研究对象,通过对其界面力学行为进行细观层次的研究,分析了纤维对基体增强、增韧、阻裂机理,研究界面附近的应力、应变规律,为纤维混凝土界面力学模型建立提供有价值的实验数据。采用三维数字光弹性实验应力分析方法,对直线形及异形端钩钢纤维与树脂基界面残余应力分布进行了测试。实验结果表明:在单纤维与基体界面的埋入端及埋入末端附近出现界面残余剪应力的极值,纤维增强复合材料中界面残余应力传递主要集中在纤维的埋入端及埋入末端附近。对在拉拔荷载和热残余应力联合作用下直线形单丝钢纤维拔出树脂基复合材料界面剪应力进行了研究。实验结果表明:力、热荷载作用下纤维界面剪应力呈抛物线分布,单丝埋入端附近是应力的主要传递区域,最先达到危险应力,出现界面脱粘破坏,然后剪应力沿纤维埋入长度由纤维埋入端附近向埋入末端逐渐传递。研究了在拉拔荷载和热残余应力共同作用下,异形钢纤维拔出树脂基复合材料界面剪应力传递行为。实验结果表明:纤维埋入端附近是主要的应力传递区域,最先达到危险应力而出现界面脱粘破坏。在界面脱粘之前,剪应力峰值随荷载增加由纤维埋入端附近沿纤维向内部传递,在异形纤维弯折段受到阻碍而传递停滞。随荷载增加界面开始脱粘时,剪应力可以传递到异形纤维弯折段。采用数字图像相关方法和单纤维拉拔试验相结合的实验方法,直接测量了直线形和异形钢纤维从混凝土基体中拉拔过程中全场及界面应变分布及演化规律。实验结果表明:微细观上的应变局部化导致纤维界面剪切破坏的局部化现象,这种界面脱粘破坏逐次发生、发展和转移的应变局部化现象在时间和空间上是呈明显的相互间隔特征。采用MARC有限元计算程序,模拟光弹实验条件下,直线形和端钩形纤维界面残余剪应力及热、力载荷共同作用下纤维界面剪应力沿纤维长度分布,与实验结果进行了对比,并探讨了纤维长度、直径对界面剪应力的影响。分析结果表明:改变增强纤维长度和直径对界面残余剪应力影响不大;拉拔荷载和热残余应力联合作用下,改变增强纤维长度,对界面剪应力影响不大,但纤维直径的变化会影响到界面起始脱粘开裂的位置。改变增强纤维长度,对端钩形纤维直线段界面剪应力影响不大,但会减缓弯折段应力集中程度;改变端钩形纤维直径,对界面剪应力影响较大,端钩形纤维直径越小,纤维界面剪应力越大。更多还原

【Abstract】 The stress in fiber reinforced composites is transferred through the interface of the fiber and the matrix, so the mechanical properties of the interfacial region and the stress transfer behavior of the interface play an important role in the macroscopic mechanical properties of the whole composites. As a result, the interface of fiber reinforced composites has always been a critical part in engineering. This paper, focused on fiber-concrete composites, makes some experimental studies on the interfacial stress behaviors, analyzes the mechanism of the fiber reinforcement, toughness, and failure-resistance, and discusses the characteristics and patterns of the stress and strain near the interface, and therefore to provide some valuable experimental data for the setup of interfacial mechanical model of fiber-concrete composites.First, three-dimensional digital photo-elasticity method is used to test the interfacial residual stress distribution between the linear and specially designed hooked fiber and the resin matrix. The results show that the value of the interfacial residual shear stress reaches its peaks near the fiber’s embedded ends in the interface of the single fiber and the matrix, and the interfacial residual stress transfer is also concentrated around the two ends of the fiber.Second, the three-dimensional interfacial shear stress near a straight fiber under the combined actions of pullout loading and thermal residual stress is studied. The interfacial shear stress has a parabolic distribution, and the transferring area mainly focuses on the region of the embedded end of the fiber where the stress reaches its critical point, causing the debonding of the interface, and then the shear stress transfers along the imbedded fiber length to the other end.In addition, the interfacial sheer stress transfer behavior near a specially designed hooked fiber under the combined actions of pullout loading and thermal residual stress is measured. The stress transfer mainly focuses on the region of the embedded end of the fiber where the stress reaches its critical point, causing the debonding of the interface. Before the debonding, as the pullout loading increases, the peak value of the shear stress transfers along the fiber from the imbedded top to the interior of the matrix, and then stops at the hooked part of the fiber. When the interface begins to debond as the load increases, the shear stress can be transferred to the fiber’s hooked part.A direct measurement of both the whole field and the interfacial strain distributions and patterns is performed when the straight and specially designed hooked fibers are being pulled out from the concrete matrix using the digital image correlation method and the single fiber pullout experiment. The microscopic strain localization can result in the localization of the interfacial shear failure which includes the initiation, development and propagation of the interfacial debonding. This localization shows an apparent characteristic of time and spatial intervals.Finally, MARC finite element software is used to simulate the photo-elasticity experiment of the interfacial residual shear stress in the straight fiber and the specially designed hooked fiber composites, and the photo-elasticity experiment of the interfacial shear stress distributions along the fiber length under the combined actions of pullout loading and thermal residual stress. The simulation results are compared with the experiment results. The influence of the fiber’s length and diameter on the interfacial shear stress is discussed. The change of the reinforced fiber’s length and diameter does not influence the interfacial residual shear stress significantly. Under the combined actions of pullout loading and thermal residual stress, changing the fiber’s length does not influence the interfacial shear stress much, but the change of its diameter leads to the change of the initial position of interfacial debonding and cracking. In addition, changing the fiber’s length does not significantly influence the interfacial shear stress of the straight part of the hooked fiber, but it can reduce the stress concentrations at the hooked part; on the other hand, the change of the fiber’s diameter has a significant influence on the interfacial shear stress—the smaller the diameter, the larger the interfacial shear stress.更多还原