Research On The Comfort And Multifunctional Integrated Design Of Pilot Helmet Cushioning Pa

Helmet Mounted Display System（HMDS）is an important equipment for pilots to perceive information,interact with the outside world and safety protection.Its performance directly affects the pilot’s combat capability and combat efficiency.However,the existing HMDS have many problems in terms of pressure and thermal comfort.In addition,with the development trend of electromagnetic and information warfare,electromagnetic shielding protection and intelligent monitoring have become essential functions of HMDS.Based on this,a theoretical model of a pilot’s helmet system under overload conditions and the ontological equations were developed,the ideal modulus of elasticity and energy absorption values of the cushioning material were calculated,and a composite warp-knitted spacer fabric/polyurethane foam cushioning liner for pilots’helmets with better pressure cushioning and higher thermal comfort was developed.On the basis of the theoretical analysis,the properties of the selected warp-knitted spacer fabric and the polyurethane foam used in current helmets were characterized and compared,and the compression energy absorption,dynamic impact and thermal and humidity comfort of the warp-knitted spacer fabric as a helmet cushioning liner were investigated and the accuracy of the theoretical model was verified.The finite element models of the pressure distribution of the spacer fabric and the helmet system were developed and samples were made to test the pressure and thermal comfort performance of the improved liner,the experimental results were in good agreement with the simulation results.The experimental results also showed that the spacer fabric/polyurethane sponge composites using partition design can reduce the local maximum stress value of the head from 23 k Pa to 11 k Pa,reductions of more than 50%.The subjective evaluation of comfort during 4 h wearing at room temperature 20℃has increased from sultry feeling to good comfort.Therefore,the gradient structure design of composites can effectively improve the wearing comfort of pilot helmets.A new method of sequentially coating cetyl mercaptan and thermoplastic polyurethane composite coatings on the surface of silver-plated spacer fabrics to improve its electrical resistance stability and anti-perspiration corrosion resistance is proposed.The electromagnetic shielding efficiency of the prepared composite fabric soft liner in the X-band reaches 57.74 d B,the air permeability of the spacer fabric is2436.1 mm/s,and the corrosion inhibition efficiency reaches 86.60%.The prepared composite fabric can effectively prevent the corrosion of human sweat and improve its electromagnetic shield stability.The composite-coated polypyrrole conductive spacer fabric was prepared by in-situ polymerization and dip-spin coating of polymer,and it was combined with copper foil electrode to prepare a piezoresistive sensor.The test results showed that the sensor has a range of 0-10 k Pa,a sensitivity of 94.71 k Pa-1,a response and recovery time of 0.6 s/0.5 s and good repeatability and stability over 500compression cycles at a pyrrole concentration of 0.3 mol/L and an aggregation time of60 min.In order to further improve monitoring of high stress under high overload,a wide-range pressure sensor was prepared by dipping coating carbon nanotubes with different concentrations using polyurethane sponge as the base material.The test results show that the conductive sponge composite has the best performance when the CNT concentration is 4%,with a stress detection range of 0-172.6 k Pa,a sensitivity of 62.73k Pa^-1 and recovery time of 0.6 s/0.5 s and good repeatability and stability over 2000compression cycles.The prepared pressure sensors were then integrated with the cushioning liner using a thermoforming and sewing process to produce a smart pressure monitoring liner with a wide range and high accuracy.Last,the single-mode fiber grating sensor was encapsulated by polymethyl methacrylate（PMMA）to prepare a fiber grating temperature sensor.The prepared sensor has a sensitivity of 10.1 pm/°C,a thermal response time of less than 10 s,good linearity and repeatability,as well as excellent anti-vibration and anti-electromagnetic interference capabilities,which makes it has broad application potential in temperature monitoring of smart wearables in electromagnetic combat environment.