Sound Insulation Of Lightweight-layered Glass Fiber Felt And Corresponding Composite Structure

Glass fibers have excellent acoustic property,and they are mainly used as absorption material in the field of aerospace.For traditional methods,lightweight structure will cause uneven distribution of glass fibers leading to reduce the acoustic properties.The prupose of the research is to obtain lightweight and uniform glass fiber felts by new method.The acoustic characteristics of fibrous material depends on the morphology of fiber,diameter,strength,mechanical properties,component of fiber,density,stacking way,pore structure and way of winding each other.In this research,glass fiber felt is used for C919 aircraft.The aim is to expore the effect of new process on glass fiber felt structure and analysis the forming mechanism of layered interface;to research the effect of structure parameters on sound insulaton and analyze the influence of the interface on characteristic impedance;to explore vibration modal of glass fiber felt composite structure and analysis sound insulation performance at different acoustic frequencies.In this paper,lightweight-layered glass fiber felts are fabricated by centrifugal-spinneret-blow process.Swing cylinders are used for structure design to obtain uniform,layer and excellent acoustic glass fiber felt.At the same time,acoustic composite structure composed of lightweight-layered glass fiber felt,honeycomb structure,membrane and carbon fiber board are also explored.Acoustic properties of lightweight-layered glass fiber felts and the corresponding composite structure are characterized by B&K impedance tube.Microstructure of lightweight-layered glass fiber felts are observed and characterized using scanning electron microscopy and optical microscope.Tensile strength and airflow resistance are measured by a universal material testing machine and a compressed-air apparatus,respectively.The trajectories and distribution of glass fibers are simulated by MATLAB software.Analysis was made from perspectives of theory and experiment for forming theory and acoustic properties,providing abundant support for the development and design of lightweight-layered glass fiber felts.The main conclusions and innovative results of this dissertation are drawn as follows:(1)Proposed the centrifugation forming mechanism of glass fiber felt,glass fibers are guided by swing cylinders to obtain lightweight,uniform and layered glass fiber felts.Results show that,the variation coefficient(CV)of glass fiber felt by unusing and using swing cylinder are 9.6% and 5.5%,respectively,evenness of glass fiber felt is increased by 42.7%,and microstructure of glass fiber felt is micro-layer.MATLAB soft is used to simulate fiber movement and way of accumulation,under the guidance of swing cylinders,the trajectories of glass fibers are sine or cosine curve;the best way of accumulation is the phase difference of the swing cylinders being ?/2+2k?.(2)Established a mathematical physical model of glass fiber felt to deduce the formula of air flow resistance.Results show that,air flow resistance of glass fiber felt is proportional to the density of glass fiber felt however inverse to glass fiber density,resin density and fiber diameter.It is significant for fiber diameter variation to affect air flow resistance.The smaller the fiber diameters are,the greater the air flow resistance is.Glass fiber felts with smaller fiber diameters yielded more fiber per unit weight,which resulted in higher total fiber surface area and finer pore size which led to increase the air flow resistance.(3)Established interface layer model,the difference between macro interface model and micro interface model is density gradient.Results show that,the mismatch of characteristic impedance lead to increase the sound reflection and improve the sound insulation performance,the improvement of sound insulation loss was 5 dB.Increasing distance between the interface layers can improve the sound insulation performance,however the greater the distance is,the more the number of peaks and troughs in acoustic curve are.(4)Proposed membrane-glass fiber felt-carbon fiber board composite structure and glass fiber filled honeycomb composite structure,the type of glass fiber felts affect vibration mode of composite structure.The results showed that,resonant frequency amplitude of membrane-glass fiber felt-carbon fiber board composite structure reduces by the decrease of fiber diameter,however,the first resonant frequency amplitude of the honeycomb composite structure is weakened and the second resonant frequency amplitude of honeycomb composite structure is strengthened.Fine glass fiber making glass fiber felt has excellent flexible leading to reduce the vibration,sound insulation of composite structure is improved by reduce the resonance mode at low frequencies.