| Fiber reinforced composite material is a new type of composite material composed of resin matrix and reinforced fiber embedded in it.It has a series of advantages,such as light weight,high strength,corrosion resistance and designable performance.In recent decades,it has been widely used in buildings,Bridges and other structures.At present,pultruded FRP materials widely used in engineering are different from traditional aviation FRP laminates.In the past studies on fracture toughness of composite materials,the classical theory of FRP laminates aiming at aviation type was adopted.There are certain differences in the evaluation of these theories on pultruded FRP materials.Based on this,through experimental research and theoretical analysis,this paper studies the fracture toughness and size effect of pultruded GFRP plate in many aspects,and the results are applied in engineering practice.This paper mainly carried out the following research:1.Based on Tsai-Wu damage criterion,a progressive damage constitutive model of pultruded GFRP laminates was established to simulate the mechanical properties of the materials during fracture.The model is implemented using the subroutine UMAT module of commercial finite element software Abaqus.A third party compact tensile test and a threepoint beam bending test were used to verify the model,and the calculated results of the model are in good agreement with the test data.2.The fracture damage constitutive model is used to carry out a large number of parametric calculations on the nominal stress of perforated plate fracture,and the statistical results are obtained and the nominal stress size effect is obtained.The relationship between the rule of size effect and the normalized length of prefabricated crack is obtained.The size effect law was used to calculate the fracture resistance of pultruded GFRP.The R curve was calculated to calculate the fracture toughness by size effect,and the fracture toughness law under different fiber volume ratio was obtained.3.The extended compact tensile test(ECT)of pultruded GFRP plates was carried out,and the influence of specimen size and layering mode on fracture toughness was considered.By analyzing the fracture failure mode of the specimen,it is concluded that the failure of the specimen is mainly due to the failure of the matrix of one of its constituent parts,which leads to the failure of the whole material.4、The VCCT analysis model of ECT specimen was established by finite element method,and the test results were checked.The fracture toughness of the finite element is independent of the normalized length of the prefab crack,which is consistent with the experiment.Among the factors affecting fracture toughness,fiber volume ratio and material anisotropy are positively correlated,which is reflected in the high 0° ply ratio of laminates.5.Comparing the domestic compact tensile test code for measuring the plane fracture toughness of metal materials with the foreign extended compact tensile test code for measuring the plane fracture toughness of composite materials,it is concluded that there are differences between the two in applicable materials,specimen size and calculation formula.By analogy with the compact tensile test specification in China,a compact tensile test formula for measuring the plane fracture toughness of pultruded GFRP plates is proposed by using the prediction method of the fracture damage constitutive model proposed in this paper and the fracture toughness values obtained from the tests. |
