Study On Dynamic Mechanical Properties Of Carbon Fiber Reinforced Polymer

Carbon Fiber Reinforced Polymer(CFRP)have many advantages,such as high specific strength and modulus,stable chemical properties,designable properties and easy integral forming.So the study and application of CFRP are very active all over the world.They have been widely used in aerospace,automobile body,wind turbine fan and concrete structure repair.From the wing structure of aircraft to the blade of generator fan,high frequency vibration will occur due to external excitation such as airflow disturbance,so the dynamic mechanical properties are the key consideration in the design and research.The traditional contact measurement method,on the one hand,will bring additional mass to the object.For the structure with small stiffness and mass,the test results are inaccurate.On the other hand,the measurement will be limited by the working conditions of the sensor.And the common single-point measurement method can't directly obtain the complete vibration modes of materials.It's difficult to find the detailed characteristics of vibration modes by fitting the results of multiple sensors.The electronic speckle pattern interferometry(ESPI)is a kind of optical measurement method,which has the characteristics of high accuracy,non-contact,real time and full-field.It could overcome the limitations and obtain the object resonance frequency and full-field mode shapes directly under non-contact conditions.In this paper,the off-axis tensile properties of CFRP were studied by tensile test.The vibration characteristics of CFRP cantilever beam and cantilever plate were studied by ESPI off-plane vibration test system.The main work includes:(1)The basic principle of ESPI was introduced,including principles of intervention,the generation of laser speckle and the common optical paths in deformation measurement by ESPI.This paper reviewed the basic theory and common methods of vibration measurement by ESPI,such as time average method,the subtraction method,the amplitude fluctuation method,etc.Finally,the ESPI off-plane vibration measurement system and the experimental methods used were introduced in detail.(2)The theoretical analysis of CFRP was carried out based on the theory of composite single-layer plate,and the off-axis tensile test is designed and carried out.The deformation of the specimens were measured by strain gauges and digital image correlation method(DIC),and the stiffness characteristics of the off-axis specimens were obtained by both theoretical and experimental methods.At the same time,the tensile failure modes of off-axis specimens were explained through off-axis tensile failure experiments,combined with tensile failure stress-strain curves and fracture analysis.(3)By using ESPI off-plane vibration measurement system and real-time phase subtraction perturbation method,the dynamic mechanical properties of CFRP materials with different off-axis directions are experimentally studied,and the resonance frequencies and corresponding modes of the samples are obtained,which are compared with the results of ABAQUS finite element numerical simulation.The influence of off-axis direction and lamination number on resonance frequency and mode shape is analyzed.(4)Based on the non-contact characteristics of ESPI,an out-of-plane vibration measurement system under ESPI fluid environment is built.The resonance frequencies and modes of the samples in the fluid are obtained.The effects of fluid loading on the vibration characteristics of the samples are studied,and the effects of the modal modes of the samples and the fluid interface on the fluid loading are analyzed.