Study On Mechanical Properties Of Carbon Fiber Reinforced Polymer At Different Temperatures

Carbon Fiber Reinforced Polymer(CFRP)are widely used in wind turbines,automobile manufacturing,aerospace and other fields due to their high specific strength,high specific modulus and good designability.The mechanical properties of a wind turbine blade or a car will be influenced by the defects which is aroused in the process of using.On the other hand,some composite structures such as aircraft wings always work in the environment with different temperatures.Therefore,it is of great significance to study the mechanical properties of CFRP with different working temperatures and defects.The main object of this paper is carbon fiber/epoxy resin composite.And the static and dynamic mechanical properties of this composite material under different temperatures and defects are investigated.With the application of electronic speckle interferometry(ESPI)method,we overcome the limitation of temperature on the ESPI method and complete the measurement of the full-field vibration mode.Compared with the traditional contact measurement method and Laser Doppler method,this method is featured with the advantages of low-cost,high-precision,non-contact and full-field real-time measurement.The resonance frequency and the modal shape of the whole field for the measured object are obtained without any contact.And the phenomenon of modal coupling caused by the temperature change of the material has been discovered.The main research of this paper includes:(1)First,the basic principles of the electronic speckle pattern interference method are introduced,and the basic theories in the vibration test process are reviewed at the same time,including the time average method,the subtraction method and the amplitude fluctuation method.Then introduced the ESPI off-plane and in-plane deformation measurement optical path,and built the ESPI off-plane vibration test system.Finally,the specific experimental test method of vibration measurement is explained in detail.(2)The modal measurement and analysis of CFRP laminates under high temperature have been studied.First,by studying the vibration mode of the cantilever beam aluminum plate,the ESPI vibration test is analyzed from the perspective of the cantilever beam bending vibration theory,ESPI off-plane vibration measurement and finite element simulation.Then an optical system for vibration experiments under high temperature conditions is built,and based on this system,the effect of temperature on the vibration modes of CFRP laminates with different offaxis angles is studied.The thermal expansion coefficient of the material is tested by pasting strain gauges.(3)Based on the built-up ESPI off-plane vibration test system,the modal measurement of defective CFRP laminates at room temperature is carried out.The ESPI experimental system is used to measure the vibration characteristics of rectangular cantilevered CFRP sheet structures with edge cracks.The influence of crack length and crack distribution position on the structural resonance frequency and mode shape is studied.(4)The experimental research on the bending mechanical properties of CFRP under high temperature is carried out.A quasi-static three-point bending test is performed on CFRP laminates with different off-axis angles at different temperatures.The influence of temperature on the bending mechanical properties of CFRP laminates is obtained,and the influence of offaxis angle on the bending process and ultimate load-bearing capacity of CFRP materials is discussed.Among them,the focus is on the changes in the elastic modulus,failure mode,and ultimate bearing capacity of 0 degree off-axis CFRP beams at different temperatures.