Fatigue Testing of a Unidirectional Carbon Fiber Reinforced Polymer : Investigation of damage development using Digital Image Correlation

University essay from KTH/Lättkonstruktioner

Author: Lars Johan Wenner Berg; [2020]

Keywords: ;

Abstract: Carbon Fibre Reinforced Plastic (CFRP) is a material with high specific propertiesand good fatigue and vibration dampening characteristics, and can potentiallybe used instead of steel and aluminium in heavy duty vehicles. This work focuseson testing methodology and the fatigue properties of a unidirectional (UD)material in the 0° and 90°orientation, reproducing and validating the method developedby Wanner[1]. While conducting a fatigue test of a CFRP composite intension-tension fatigue, in-situ strain measurements were performed to examinethe gradual elongation of the specimen (as this relates to stiffness loss, i.e. fatiguedamage). An imaging methodology capturing the specimen at peak loading hasbeen developed, including a trigger mechanism that activates the camera at the desiredtime and cycle count, as well as a method of extracting the photograph ofthe specimen at maximum displacement, allowing for peak-to-peak comparison.A method improving specimen production output and consistency has been developed.SN-curves have been produced for both 0° and 90° fibre orientations.Micrography of sectioned specimen has been conducted. The study finds the fatiguelimit of the 0° specimen to be as high as 80% of the material tensile failurestrength, while results from the 90° study indicate a lower but inconclusivevalue. An attempt at qualitatively determining the factors causing the material behaviourhas been made and is deliberated upon.

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