Investigation On Fabrication And Mechanical Behaviour Of Self-reinforced PP Structures

Fibre reinforced composites are getting extreme popularity for lightweight applications because of their high strength to weight ratio and stiffness especially in automotive industry.One of the main issues with these traditional fibre reinforced composites is their lower strain to failure and relatively higher brittleness(compared with thermoplastic composites)that sometimes can cause catastrophic failures because of sharp crack propagation along the fibre matrix interface or through the relatively brittle epoxy matrix.In case of self-reinforced polymer composites(SRCs),the fibres and matrix belong to the same family of polymers that can ensure 100% recyclability as well as viscoelastic behaviour as compared with fibre reinforced epoxy matrix composites.At first,the self-reinforced Polypropylene(SrPP)structures were fabricated by an ex-situ consolidation fabrication process that can be potentially applied for mass production.Instead of conventional stamping process that involves complex formability phenomenon;corrugated cores were fabricated from the pre-consolidated SrPP sheets using a designed mould and then the cores were joined with face sheets by same family of polymer adhesives to achieve maximum recyclability.Based on the melting point and thermo-mechanical properties at elevated temperature of constitute material,and global mechanical strength of fabricated structures,an optimal bending temperature was found to maintain the proper fibre content of corrugated SrPP sheets.The interface between core and face sheet was enhanced through phenomenon of mechanical lock by creating various abrasion levels.Then,structures with different core strut thickness were fabricated and out of plane quasi static and dynamic compression tests were performed at various impact velocities.The collapse behaviour & dynamic strengthening effect was investigated theoretically and experimentally.The structures with stubby core collapse under the phenomenon of plastic hinge failure while the cores with slender struts collapse because of buckling of struts,even though the induced stress was lower than the compressive failure stress of parent material.The topology of core plays an important role in compressive energy absorption capacity of sandwich structures under dynamic loading.Next,SrPP sandwich beams(SrPPSBs)with non-symmetric mass distribution between core and face sheet were fabricated and three-point bending tests were performed on the SrPPSBs to investigate the effects of mass distribution on the flexural properties and energy absorption capacity.As the deflection of sandwich beams is a very complex phenomenon due to large number of material and geometrical parameters,a finite element model was developed to predict the deflection behaviour and energy absorption capacity,and the FEA results show good agreement with experimental data.It was observed that the beams with higher mass distribution in core than face sheet exhibit higher energy absorption capacity.In order to reduce the overall weight of the vehicles while keeping the strength up to the safety level,an integrated optimization study is required based on material and structural parameters.In the last chapter,an FEA based study was conducted to optimize the effect of core corrugation angle of sandwiched structures on out of plane compressive strength and flexural strength of SrPP sandwiched beams.The finite element study was preferred in order to avoid the experimental cost.It was observed that the beams with 60 degree corrugation angle exhibited maximum energy absorption capacity and peak load.During out of plane compressive tests,the structural panels with 45 degree corrugation angle exhibited maximum modulus and peak load,while 60 degree corrugated structural panels shows maximum energy absorption capacity.