Fabrication And Bending Properties Of Honeycomb Core Composite Sandwich Structures With Interfacial Toughening

As a kind of composite sandwich structures,honeycomb core sandwich structure has become one of most common structure in the application of sandwich structure,due to their mature preparation technology and excellent energy absorption capacity.However,panels and cores of honeycomb core sandwiches often have large structural and performance differences,local interface cracking and large area debonding failure tend to occur duo to local contact,impact or over load in a complex service environment,which seriously affects the safety of the structure.In this paper,dynamic mechanical response of short aramid fiber toughened sandwich structure was studied,and a method of strengthening carbon fiber/aluminum honeycomb sandwich with carbon fiber belt was put forward.The related work in this thesis are as follows:1.Investigation on manufacturing of carbon fiber prepreg with short aramid fiber veil toughenedThe need of carbon fiber prepreg is with the wide application of carbon fiber composites.At present,the laminates and sandwich structures prepared by common prepreg have poor impact resistance and are prone to delamination and debonding.In order to improve the interfacial toughness of the composites,a short aramid fiber veil with low surface density,good toughness and high strength was used to toughened carbon fiber prepreg in this paper.On the basis of the preparation of low-density short aramid fiber veil by dry and wet methods,the production processes of toughened carbon fiber prepreg prepared by solution method and hot-melt adhesive film method were studied and designed respectively.Finally,the carbon fiber prepreg with short aramid fiber toughening was prepared successfully,which can meet the requirements of insulation,light weight,no limitation of bubble discharge and high material utilization.This prepreg was applied to the preparation of carbon fiber/aluminum honeycomb sandwich structure in this paper.2.Experimental study on the dependence of short aramid fiber veil toughened carbon fiber/aluminum honeycomb sandwich on loading rateThe strengthening and toughening effects of short aramid fiber toughened prepreg was studied by comparing the mechanical properties of sandwiches with and without toughened prepreg under three-point bending condition.At the same time,the effects of the two sandwich structures on the loading rate were studied.The result of three-point bending testwas indicated to be independent of the loading rates for the toughened sandwich beam under three-point bending condition while the mechanical properties of untoughened sandwich obviously dependent on the loading rate.Under different loading rates,the average peak load and average energy absorption performance of the toughened sandwich structures were obviously better than those of the untoughened structures.3.Mechanical properties and toughening mechanism of carbon fiber/aluminum honeycomb sandwich with fiber belt tougheningA method of strengthening carbon fiber/aluminum honeycomb sandwich with fiber belt was put forward based on the toughening method of aramid fiber veil,which aim to further improve the interfacial toughness and overall performance of sandwich.During the sandwich fabrication process,carbon fiber prepreg belts were inserted aluminum honeycomb core in turn,and the corrugated structures were formed in the core.To improve the interfacial bonding properties,the core structures were changed and the contact area between face sheet and core was increased.The mechanical properties and failure modes of fiber belt toughened sandwich structures were studied by three-point bending test.The result of three-point bending test indicated that the fiber belt can improve the local stiffness of the sandwich structure,which effectively avoid face wrinkling,indentation,local instability failure,and significantly improve the ultimate bearing capacity and energy absorption performance of the structure.Moreover,the failure modes and failure interfaces of sandwich structures were observed.It is found that the fiber has a blocking effect on crack propagation,which revealed the toughening mechanism of fiber belt toughening carbon fiber/aluminum honeycomb sandwich.