Study On Physical Aging Behavior Of PEEK

Poly-ether-ether-ketone(PEEK)is a semi-crystalline special engineering plastic.Itshows excellent physical and chemical properties,which has a wide application in aerospace,vehicle,ship,biomedical and other fields.However,the physical aging behavior will compromise the performance during its application process,resulting in material failure or even safety accidents.Physical aging is a common problem of polymer materials.Previous studies mostly focus on the non-crystalline polymers,but little is known about the physical aging behavior of the semi-crystalline polymers because of the complex microstructure.In this paper,systematically research is performed on the experiment and numerical simulation of the physical aging behavior of PEEK,which is helpful to deepen the understanding of the physical aging of semi-crystalline polymer and to guide the anti-aging measures of the products.The specific work is as follows:In this paper,we use yield stress to characterize the physical aging behavior of PEEK,and the physical aging model of the yield stress is obtained through experiment testing and data fitting.Standard tensile specimens of PEEK were prepared by injection molding.The test of physical aging was carried out by high temperature heat treatment,and the yield stress of PEEK after heat treatment was obtained by one way tensile test.Finally,taking 132 ? as the reference temperature,the physical aging model of the yield stress was obtained by data fitting,and the correctness of the model was verified through experiments.In the molding process of PEEK material,when the temperature drops below the glass transition temperature,the physical aging behavior starts.In this paper,the thermal analysis of the injection molding and cooling process of PEEK specimen is carried out by numerical simulation.According to the heat history experienced by the specimen,yield stress of the specimen can be predicted.Moldflow is used to calculate the injection molding process of PEEK.The temperature distribution at the end of the molding is used as the initial temperature field of the cooling process,and then Abaqus is used to calculate the process of cooling to room temperature.Finally,the thermal history of each node is extracted,and then we can predict the yield stress distribution of the specimen by the proposed physical aging model of yield stress and verify the results of the prediction through experiments.PEEK material is a kind of semi-crystalline polymer,so its crystallinity has a certain effect on yield stress and physical aging behavior.In this paper,the relationship between crystallinity and yield stress is obtained by experimental test,and then we get the physical aging model of yield stress of PEEK considering different crystallinity.Through the hightemperature heat treatment of PEEK samples at different temperatures and times,we can get PEEK samples with different crystallinity.Four kinds of PEEK samples with different crystallinity were heat-treated to accelerate the physical aging process,and then we use yield stress to characterize the physical aging behavior of PEEK.Finally,by analyzing and fitting data and taking 145 ? as the reference temperature,we can get the physical aging model of yield stress of PEEK with different crystallinity.