| Concrete is prone to spalling,brittle fracture,and other damage in practical application,which will greatly reduce the protective effect of buildings.Therefore,this paper introduces the concept of negative Poisson’s ratio(NPR)fiber,and explores whether the mechanical properties of fiber reinforced concrete can be improved by changing the fiber structure.On the one hand,the fiber is used to toughen the concrete to improve its ductility;on the other hand,the negative Poisson’s ratio structure of the fiber is designed to solve the problem that the fiber is easy to pull out and break,to further improve the ductility and mechanical properties of the fiber reinforced concrete.Based on this,this paper carried out the structural design,obtained the auxetic fiber,and tested the static and dynamic mechanical properties of concrete by adding the tensile expansion fiber.The results showed that:Based on the existing negative Poisson’s ratio structure,the fiber diameter ratio is1:3 and the initial wrap angle is 5 °～25 °,the initial wrap angle is 10° The NPR effect is the best,and the maximum NPR is-1.35.The auxetic fiber was mixed into the concrete in two ways: short cut and layer cloth,compared with ordinary concrete,the compressive strength,splitting strength and flexural strength of the auxetic concrete were increased by 11.5% and 18.5%,43.2% and 33.1%,24.9% and 2.4%,respectively.The dynamic load test showed that the compressive impact strength of the auxetic concrete increases by 18.7% and 19.1% respectively,and the impact fracture energy increases by 11.4% and 25.8% respectively;The falling ball impact test showed that the impact damage energy of laminated fiber reinforced concrete was 5 ～ 9 times higher than that of plain concrete.Through the analysis of digital speckle correlation method software,it can be concluded that the laminated auxetic fiber can significantly reduce the transverse expansion of concrete in compression;Under the same bending load,the strain of laminated fiber reinforced concrete was the smallest,and it has good integrity.The results showed that the Poisson’s ratio of the two kinds of auxetic fiber reinforced concrete can be reduced by 13.9% and 22.8% respectively.At the same time,the finite element software ABAQUS was used to simulate the fiber preform and fiber reinforced concrete.Under the same diameter ratio,the error of Poisson’s ratio is only 1.5%.In the three-point bending finite element model of fiber reinforced concrete,the auxetic fiber reinforced concrete showed better ductility,and the displacement nephogram of the model is basically consistent with the deflection value obtained from the test and the displacement size and change of the nephogram obtained by digital speckle correlation method. |
