Influence Of Ply Angle On Mechanical Properties Of Hybrid Fiber Composites For Helmet Shells

Pilot helmet is a complex integrated display helmet that integrates communication,target targeting,information display and other functions.Helmet shell is the carrier of multi-functional helmet.It absorbs external impact force through its deformation to ensure the safety of human body.Therefore,it has high requirements on the dimension accuracy,material used,thickness tolerance and mechanical properties of helmet body.Because of the existence of curved surface,the orientation and arrangement of warp and weft yarns will change,which will affect the forming quality of helmet.In this paper,the effects of warp orientation Angle on the mechanical properties of helmet composite materials are studied.Firstly,the helmet model is digitized.Helmet shell surface is non-developable surface.In order to develop it with high precision,a shear opening should be added to the surface.In this paper,five shear opening schemes are designed.According to the principle that the geodesic parallel relation between the remaining warp yarns and the first warp yarns should be maximized,the optimal cutting scheme is selected.In this scheme,four sets of threshold values are set according to the normal vector of the triangular mesh divided on the model,and the warp orientation Angle in the same area under different thresholds is calculated.The maximum threshold value when the orientation Angle is stable is taken as the critical value to slice the surface.According to the results,ten areas were selected to calculate the warp orientation Angle,and the results were 2.10°,3.23°,5.03°,12.22°,32.23°,43.30°,45.14°,74.82°,79.97°and84.66°.Secondly according to the calculation results,two groups of composite laminates for helmet shell with unidirectional orientation of carbon fiber fabric 0°,3°,5°,12°,32°,43°,45°,75°,80°and 85°were prepared by using aramid weft biaxial fabric and carbon fiber satin fabric with surface densities of 280g/m~2and 300g/m~2,and carries on the tensile,compression,bending performance testing.The experimental results show that the tensile strength and modulus of the samples decrease first and then increase with the increase of the lamination Angle.The tensile load-displacement curves of the 20 samples all show the same change law.They rise linearly in the early stage of loading,arc-rise in the middle and late stage of loading,and drop linearly after reaching the maximum load.The samples show brittle failure.The tensile failure forms of the samples are mainly matrix cracking,fiber fracture and fiber extraction,and the fracture direction is consistent with the orientation of the meridional fiber.The bending strength and modulus of the samples decrease first and then increase with the increase of the lamination Angle.In the early stage of loading,the load-displacement curve rises linearly,while in the middle and late stage of loading,the curve rises in an arc or sawtooth shape to reach the maximum load,and the curve drops in a straight line.The samples show the characteristics of brittle material.The bending failure forms of the samples are mainly matrix cracking,fiber fracture and lamination.The compression strength and modulus of the samples decrease first and then increae with the increase of the lamination Angle.When the lay-up Angle is 0°,3°,5°and 12°,the load-displacement curves of the samples increase linearly,and drop linearly after reaching the maximum load.When the lay-up Angle is 32°,43°,45°,75°,80°and 85°,the samples increase linearly at the initial stage of loading,increase in an arc in the middle and later stage of loading,and drop in a straight line after reaching the maximum load.The compression failure forms of the samples were mainly matrix cracking,fiber fracture,matrix and fiber desiccation,and delamination.