Preparation And Properties Of Titanium/Carbon Fiber/PMR Polyimide Laminates

Fibre metal laminates(FMLs)are super hybrid materials composed by thin metal layers and fibre reinforced polymer layers.They possess unique characteristics such as manufacturing flexibility,impact behavior,corrosion resistance,fire resistance,elevated damage tolerance and superior fatigue properties.Therefore,FMLs have been selected as promising materials in the manufacture of the fuselage and wing skin,especially for the crucial structure such as leading edge which requires excellent fatigue property and impact resistance.However,with the development of the aerospace industry,aircrafts are being designed to fly faster and to last longer than ever before.It is necessary to develop novel FMLs which possess high temperature resistance and long-term properties.In this thesis,PMR polyimide was selected as the polymer matrix to manufacture novel FMLs(Ti/CF/PMR Polyimide laminates)to improve the high temperature properties.Meanwhile,mechanical properties and durable resistance of Ti/CF/PMR Polyimide laminates were investigated to analyze the failure mechanism and the long-term characteristics.Moreover,shot peening forming technique was utilized to form Ti/CF/PMR Polyimide laminates.Then,the shot peening parameters were optimized and the deformation mechanism was revealed.Firstly,the preparation process of Ti/CF/PMR Polyimide laminates was investigated,including preparation of CF/PMR Polyimide prepreg and surface treatment of the titanium.The optimized parameters to prepare the prepreg were determined as follows:Yarn width 3.7 mm,Arrangement of tension 4-7 N,Configuration speed 22 m/min.Prepreg prepared using these parameters possessed excellent surface quality and about 50%fibre volume content.The result of titanium surface treatment indicated that the interface properties between titanium and polyimide were improved after surface treatment.The single-lap shear strengths increased by 15%,30%and 41%after surface treatment with sandblasting,CAA anodization and NaTESi anodization respectively.The fracture work of single-lap shear improved 53%,168%and 182%while the mode I toughness improved 67%,73%and 87%respectively.The overall properties of Ti/CF/PMR Polyimide laminates were also investigated in this work.The relationship between properties and configuration of Ti/CF/PMR Polyimide laminates was verified by using experimental research and theoretical analysis.Meanwhile,the mechanical response and the failure mechanism of Ti/CF/PMR Polyimide laminates during the loading process were studied.Moreover,the effects of temperature variation on the mechanical characteristics of Ti/CF/PMR Polyimide laminates were also discussed.The results showed that Ti/CF/PMR Polyimide laminates possessed outstanding temperature resistance.Mechanical properties of Ti/CF/PMR Polyimide laminates decreased with the test temperature increased.However,mechanical performances of Ti/CF/PMR Polyimide laminates were still good when tested at 300?.The conservation rates of tensile,flexure and interlaminar shear strength at 300?were approximately 50%,55%and 54%,respectively.Additionally,it was found that the mechanical properties of Ti/CF/PMR Polyimide laminates stayed unchanged after thermal cycling ranged from-65 ??135 ? because the interface between the titanium and CFRP was continuous and intact.Hygrothermal aging treatments were performed on Ti/CF/PMR Polyimide laminates.It was found that the ILSS of Ti/CF/PMR Polyimide laminates showed only?10%decrease while the flexure strength showed-11%decrease after hygrothermal aging for 1000 h at 85?/95%RH condition.Moisture absorption characteristics of Ti/CF/PMR Polyimide laminates were analyzed after hygrothermal aging.Temperature influenced the diffusion rate of the moisture while the relative humidity determined the saturated moisture absorption rate.The saturated moisture absorption rate of the prepreg layers was determined by Me =5.11 ×10-5×(RH)2-15 while the moisture diffusion coefficient in Ti/CF/PMR Polyimide laminates was DYZ= 9.2×10-3 × e(-1532.22/T)mm2/s.Moreover,the relationship between moisture absorptionrate and time was expressed as(?).Shot peening forming characteristics of Ti/CF/PMR Polyimide laminates was experimental investigated.The result proved that shot peening forming technique was suitable to form Ti/CF/PMR Polyimide laminates.Preferably forming results could be achieved by using AZB 425 type ceramic shots.Additionally,surface coverage increased with the extension of the exposure time,resulting in the increment of the arc height of the samples.The surface roughness of the sample was also increased with the extension of the exposure time before it became stable.Effects of Almen intensity on the final arc height were also investigated.It was found that the final are height of the FML strip increased linearly with the augment of the applied Almen intensity.Moreover,it was more difficult to generate the bending deformation in Ti/CF/PMR Polyimide laminates made with unidirectional lay-up,as Ti/CF/PMR Polyimide laminates with different lay-ups showed diverse forming characteristics following the experimental results.Finally,an improvement in tensile properties of the FMLs was confirmed after the shot peening treatment.