Study On Tensile Damage Model Of Polypropylene Fiber Concrete

The achievements of concrete constitutive relation model are diversiform, involved in all sorts of classical mechanics. Among them, the damage mechanics have been widely touted for considering the existence of micro cracks, and being able to accurately describe the damage characteristics of concrete. But its application in fiber reinforced concrete is still a relative lack. For fiber reinforced concrete, the short-cut fiber disorderly to random distribution as a medium, and the internal structure is complex. So its mechanics properties research is always used test method in the majority; theoretical research is used more fracture mechanics. A few about damage constitutive research is confined to the macro phenomenological theory, research method is still need to improve.This paper studies the constitutive relationship of polypropylene fiber concrete, which has the strong crack-resistance, by using the mesoscopic random damage theory. Put forward t a kind of polypropylene fiber concrete tensile damage model, based on the existing ordinary concrete stochastic damage constitutive model. We did the concrete uniaxial tension tests to obtain specific parameters of the model. This approach can make the combination of theory and practice, and also can be used to verify the identical degree about theoretical model and experimental data. The test design two concrete strength, with each strength containing five kinds of polypropylene fiber dosage, which are 0 kg/m~3, 0.3 kg/m~3, 0.6 kg/m~3, 0.9 kg/m~3, 1.2 kg/m~3 .This paper mainly gets the following conclusions:(1) By using the series-parallel micro spring model to simulate the mesoscopic damage elements of the concrete, established the tensile condition mesoscopic physics model of polypropylene fiber concrete. Assume the destruction of mesoscopic unit of strain as random variables, to describe the randomness of emergence and development of injuries in polypropylene fiber concrete. And according to the classical theory of damage mechanics, established tensile damage constitutive model with stochastic characteristics. On the basis of mathematical characteristics of peak point on the concrete tensile stress-strain curve, identified the fracture strain random field parameters of mesoscopic unit in the model.(2) Polypropylene fiber c tensile test results show that: Adding polypropylene fiber to concrete increased concrete tensile strength in a certain degree;Polypropylene fiber also has reduced effect to the concrete tensile elastic modulus, when fiber dosage for 0.9 kg/m~3, tensile elastic modulus is larger, and the declined respectively achieved 21.6%, 16.7% for the water-cement ratio of 0.5, 0.4.(3) The parameters identified is correspond with the existing stochastic damage model parameters on magnitude and value interval. Random damage constitutive model curve and polypropylene fiber uniaxial tensile test stress-strain curve anatomists in good condition, this explains the mesoscopic stochastic damage constitutive theory applies to polypropylene fiber concrete materials; and prove that the mesoscopic damage model of ordinary concrete after being modified by model parameters can be applied to fiber reinforced concrete materials. Finally, in order to engineering application, this stochastic damage model is simplified. And a constitutive relationship equation, which is concerned with tensile elastic modulus, stretching peak stress and strain, is obtained.