The Effect Of Surface Modification Of Carbon Fiber On The Interface, Mechanics And Fatigue Resistance Of Composites

With the wide application of carbon fiber reinforced epoxy composites in various fields of civil,military and industrial fields,people have put forward higher requirements on the interfacial and specific mechanical properties of composites.However,due to the poor interfacial properties between the carbon fiber and resin matrix,it's difficult to meet the needs of people.Therefor,it is very important to improve the interfacial strength and to study the influence of interfacial properties on the mechanical properties and anti-fatigue properties.In this paper,carbon nanotues were deposited by microwave plasma-enhanced chemical vapor deposition method in order to increase the interfacial strength of carbon fiber/epoxy composites.On the other hand,electrophoretic deposition of carbon nanotubes,ar plasma treatment and UV radiation grafting acrylic acid were chose to obtain the same interfacial strength of different composites(Respectively referred to as EPD-CF/EP,Ar-CF/EP,UV-CF/EP),and then study on the strengthening mechanism of interfacial properties of composite on mechanical properties and anti-fatigue properties,providing reference for the design of interface structure.Carbon nanotubes were in situ growth on the surface of carbon fiber by microwave plasma vapor deposition method.When the deposited time reached 15 min,the interfacial shear strength of carbon fiber/epoxy composites increased 153%,reaching to 129.92Mpa.Furthermore,we conducted a study to obtain the same interfacial shear strength of all samples using single-fiber fragmentation test.The results of interlaminar shear strength indicated that the macro interface strength of all samples were similar.That is to say,we have obtained the same interfacial properties using different treating methods.After the material mechanical performance tests,it was found that the mechanical properties of the composites were improved in varying degrees by different fiber modification methods.The UV-CF7/EP has the maximum flexural strength(1082.1 Mpa),leading to an increase of 19.1%compared to that of CF/EP.The flexural modulus and tensile strength for EPD-CF/EP were increased by 16.4%and 25.7%.The residual flexural strength retention ratio were increased by 2.4%(EPD-CF/EP)?6%(Ar-CF3/EP),respectively,after 4,0000 times of cycliy fatigue damage at bending mode.The results of ultrasonic C-scan showed that the virgin carbon fiber composites have the most internal fatigue damage.In order to clarify the reinforce mechanisms of interfacial strength and the influence of different treatment methods on mechanical and anti-fatigue properties,scanning electron microscopy and the force modulation of atomic force microscopy were used to detect the interfacial micro-structure and the thickness of the interface layer.It was found that part of the CNTs were diffused into the resin matrix around the carbon fibers during molding and curing process,which formed a gradient interface layer between the carbon fiber and epoxy resin.Although the composites obtained by the other two treatment methods did not form an interfacial transition layer,whereas,the thickness of the interface layer of the composite material was also increased to a certain extent due to the physicochemical reaction between the fibers and resin at the interface micro area.Although the enhancement mechanism of each fiber surface modification method is different,the overall performance of the composite was improved to a certain extent.