基于等效纯弯曲梁的混凝土双K断裂参数研究

STUDY OF THE DOUBIE-K FRACTURE PARAMETERS OF CONCRETE BASED ON EQUIVALENT PURE BENDING BEAMS

因四点弯曲梁跨中裂缝截面附近处于纯弯段,故其从理论上更符合Ι型断裂模式。基于此,该文通过开展跨中带缝的四点弯曲梁试验,将荷载作用下的四点弯曲梁纯弯曲段等效为纯弯曲梁,基于线性叠加原理给出了计算混凝土四点弯曲梁双K断裂参数的计算公式,并研究了不同初始缝高比(0.2、0.3、0.4、0.5及0.6)对四点弯曲梁双K断裂参数的影响,结果表明:随着初始缝高比的增大,试件起裂荷载Pini,最大荷载Pmax及相对临界有效裂缝扩展长度(ac-a0)/H均逐渐减小;起裂断裂韧度ini IC K和失稳断裂韧度un IC K基本保持不变。可见,四点弯曲梁可以用于研究混凝土的双K断裂参数。

In a four-point bending(FPB)test,the beam segment near the mid-span cracking section is under pure bending.Therefore,the modeΙfracture model can be better applied in theory.Based on this,FPB tests on notched beams were carried out.The calculation formulae of double-K fracture parameters were established by assuming that the pure bending segment of a FPB specimen under external load is equivalent to a pure bending specimen and by using the linear superposition principle.Moreover,the effect of different initial crack-depth ratios(0.2,0.3,0.4,0.5 and 0.6)on the fracture parameters was evaluated.The results indicate that with the increase of the initial crack-depth ratio,the initial fracture load,Pini,the maximum fracture load,Pmax and the critical relative effective crack propagation length,(ac-a0)/H,decrease gradually while the initial fracture toughness,ini KIC and the unstable fracture toughness,un KIC keep almost constant.Consequently,FPB tests can be applied to determine the double-K fracture parameters of concrete.