Study On Mechanical Properties And Fiber Distribution Characterization Of Carbon Fiber Reinforced Polyamides Injection Parts

Polyamides is widely used engineering structural plastics,which has good fatigue resistance and wear resistance,but there are some problems in the use process,such as low impact toughness,dimensional accuracy and so on.Carbon fiber reinforced polyamides(CFRPA)has been proved to be one of the effective methods to improve the impact properties of polyamides materials.This method has been widely used in injection moulding of plastic products such as notebook case to improve the impact resistance of these products when they fall.However,the quantitative effect of short carbon fibers on the mechanical properties of polyamides,especially under dynamic impact,is still unclear.In view of this,this paper studies the dynamic and static mechanical properties of CFRPA with different fiber content,and explores the quantitative characterization method and fast prediction method of internal fiber distribution for the complex internal structure of fiber reinforced polyamides.This study has important theoretical guiding significance for the development of fiber reinforced plastics products.The main contents of this paper are as follows:Study on static tensile mechanical properties of CFRPA.The static tension test of CFRPA was carried out,and the stress-strain curves of the samples were obtained.The effects of different fiber content on the tensile properties of the reinforced polyamides were compared and analyzed.The reinforcing efficiency of the fiber filling was studied,and the macro and micro material section morphology characteristics were analyzed.The results show that the tensile strength of polyamides increases firstly and then decreases with the increase of fiber content.The samples with fiber content of 30 wt% show the maximum tensile strength of 178.0 MPa.The excessive fiber content leads to the decrease of interfacial strength of the fibers,thus affecting the tensile strength.The filling of carbon fibers can slow down the breakage of the tensile fracture and pull out of the carbon fibers at break.Polyamides matrix is the main reason to reduce fracture debris.Study on impact mechanical properties of CFRPA plate.The dynamic impact test of CFRPA was carried out.The force-displacement curves of the samples were obtained.The effects of different fiber content on the impact properties of the reinforced polyamides were compared and analyzed.The impact failure modes and impact resistance were studied.The results showed that the impact strength of polyamides materials increased with the increase of fiber content,and the damage area increased sharply with the increase of fiber content.As a result,the failure mode changes from the mode of random rapid expansion of cracks to the mode of near-elliptical centralized failure in the impact center.Quantitative characterization of the distribution of CFRPA fibers.X-ray tomography of CFRPA was carried out,and the image of fiber distribution was obtained.The distribution parameters such as fiber diameter,projection length of flow plane and fiber orientation were quantitatively characterized.The results show that the fiber content changes along the thickness direction,the fiber content in the surface layer is low,and the fiber content in the center layer is high,the difference is about 2%.The statistical fiber diameter is close to the actual carbon fiber length,which is 5.8 um.The fiber orientation is mainly along the flow direction of polyamides,and the maximum deviation angle is about 6.9%.Fast prediction of fiber distribution.The flow forming simulation analysis model of CFRPA sample was established in Molex 3D software to simulate the forming process of the drawing sample.The fiber distribution of each layer of the formed drawing sample was analyzed and compared with that obtained in Chapter IV.The maximum error between the results obtained and the quantitative characterization of fiber orientation was found to be 9.1%.The elastic modulus of the tensile sample is predicted by the results of fiber distribution based on the flow forming simulation.The error is about 10% compared with the elastic modulus measured by experiments.