CFRP-混凝土界面4ENF断裂试验研究

Fracture tests on CFRP-4ENF interfaces

为了研究CFRP-混凝土的Ⅱ型和混合型断裂能量释放率(energy release rate,ERR),进行了铝板调整CFRP-混凝土4ENF断裂试验,根据Timoshenko梁(TB)模型、双参数弹性基础上的4点受弯端部切口试件(four-point bending end-notched flexure specimen,4ENF)柔度模型和多亚层柔性节点模型的J积分方法求得了ERR.试验结果表明:在相同的黏接条件下,Ⅱ型或混合型断裂破坏方式有3种:(a)剥离发生在胶层-混凝土界面和界面混凝土上;(b)剥离始于胶层-混凝土界面或界面混凝土且混凝土梁发生破坏;(c)剥离发生在界面混凝土上且混凝土梁发生破坏.Ⅱ型或复合层刚度大于混凝土刚度的混合型断裂试件,可以获得较高的ERR.若复合层刚度小于混凝土层刚度,裂缝始于胶层-混凝土界面,发展到一定长度后沿界面混凝土发展,并导致混凝土发生斜拉破坏,ERR很低.通过试验表明,本4ENF可以有效地对Ⅱ型和混合型CFRP-混凝土界面断裂进行研究.

Interface fracture tests using aluminum beam-contoured CFRP-concrete four-point bend end-notched flexure （4ENF） specimens （4ENF） were performed to determine the energy release rates （ERR） of mode Ⅱ and mixed mode fracture. By using the Timoshenko beam model, the double-parameter 4ENF model on elastic foundation, and the J-integration of multi-layer flexible model, the corresponding ERRs were obtained. The test results show that under the same bonding condition, the fracture patterns of the mode Ⅱ and mixed mode of the CFRP-concrete interface are as follows： （1） The crack occurs on the CFRP-concrete interface and in the concrete near the interface; （2） The crack occurs on the CFRP-concrete interface and in the concrete near the interface, and the concrete beam breaks; （3） The crack occurs in the concrete near the interface, and the concrete beam breaks. When the bending stiffness of the aluminum-FRP compound layer is larger than that of concrete, the specimens for the mixed mode fracture yield a higher ERR, representing the real ERR measurement of CFRP-concrete interface. When the bending stiffness of the compound layer is smaller than that of concrete, the specimens produce cracks at the concrete near the interface or within the concrete beam, thus measuring the ERR of the concrete, rather than that of CFRP-eoncrete interface. As demonstrated in this study, the 4ENF specimens, if used properly, can be used effectively to characterize mode-Ⅱ and mixed mode fracture of CFRP-concrete bonded interface.