Study On Translayer Fracture In Pultruded Mechanical Of Pultruded FRP Composites

Due to the high specific strength、specific stiffness and designability, fiber reinforced polymer (FRP) was first applied in the aviation industry. As the cost of the fiber production declines dramatically and the quality of product becomes stable gradually, production and application range has shown a positive change. The increase in the amount of composite has also promoted the development of mechanics of composite materials. In order to ensure the using reliability of composite materials, the problem of its damage rule and the strength criterion should be solved, the composite material fracture mechanics has been become one of the most concerned research topic. As we all know, in the aspect of predicting fracture response of homogeneous isotropic materials, the linear elastic fracture mechanics has achieved great success. Because fiber reinforced composites are heterogeneous anisotropic materials, linear elastic fracture mechanics can be applied only in very limited circumstances. The pultruded FRP is laminated structure material composed of monolayer plate and translayer fracture is the main damage form. At present the classical laminated plate theory in macromechanics is mainly adopted to study on strength and damage of the material. With the increase of the thickness of the laminated plates, ignoring the practice of material in the three dimensional stress state and high interlaminar stress will be even more inappropriate.A new nonlinear fracture analysis framework is developed for the mode-I fracture response of thick-section fiber reinforced polymeric (FRP) composites. This framework employs 3D micromechanical constitutive models for the nonlinear material behavior along with cohesive elements for crack growth. Fracture tests on various cracked geometries are used to verify the prediction of the failure loads and the crack growth behavior. A commercially available pultruded E-glass/epoxy thick-section FRP composite material was used to demonstrate the proposed fracture approach along with the nonlinear constitutive modeling. Mode I fracture toughness tests for pultruded composites are also examined using the eccentrically loaded, single-edge-notch tension, ESE(T). Material nonlinearity and crack growth effects were observed during the tests and investigated using the proposed analysis framework. The effect of material orthotropy on the stress intensity factor solutions was addressed using the virtual crack closure technique. The analytic and experimental results support the use of the ESE(T) specimen for the measuring the mode-I fracture toughness The calibrated cohesive models were able to predict the measured crack growth in mode-I for various crack geometries. The experimental and analytical results of this study can form a foundation for using fracture--based methods for the design of structures using these materials. In order to study the tensile softening property of pultruded FRP, a three point fracture test on single notched specimens was taken out along the fiber direction notch. According to the P-δ curve, the fracture energies of tested specimen are calculated to obtain bilinear tensile softening curve.