Research On Mechanical Properties Of Fiber Reinforced Laminated Composite Sheets And Semi-analytical Modeling

With the development of the aviation,aerospace,oceaneering and the civilian fields,the performance requirements for materials have been higher and higher.Recently,the Ti-Al3Ti metal-intermetallic laminated(MIL)composite has drawn extensive attention as a lightweight structural material.However,Al3Ti exhibits poor room temperature plasticity and low high temperature strength,which limites its practical engineering applications.Besides,for the elasto-plastic contact issue of inhomogeneous materials like Ti-Al3Ti laminated composite,most of the current simulation researches are based on finit element method(FEM).The FEM model is relatively more complicated and its computational efficiency is lower.Therefore,a numerical model with high efficiency and accuracy is needed to carry out the extensive mechanical simulation parametric studies.The aim of the present work is to improve the overall mechanical properties of intermetallic compounds by introducing metal layer and ceramic fiber reinforcements,and meanwhile by means of experiments and new proposed simulation model,to investigate the microstructure morphology,mechanical behavior,fiber strengthening and material failure mechanisms of the novel continuous-ceramic-fiber-reinforced metal-intermetallic-laminated(CCFR-MIL)composite.The overall research scheme is shown below:Ti foils,Al foils and SiC fibers are used to fabricate Ti-(SiCf/Al3Ti)CCFR-MIL composite through vacuum hot pressing.In addition,the microstructure morphology,sintering reaction products,the ratio,crystal structure,element type and distribution for each phase of Ti-(SiCf/Al3Ti)laminated composite are studied via scanning electron miscroscopy(SEM),X-ray diffraction(XRD)and energy dispersion spectrum(EDS).The mechanical properties of Ti-(SiCf/Al3Ti)laminated composite are investigated by microhardness,nanoindentation,tensile tests,"plane-plane" and"sphere-plane" contact compression tests.The failure behavior is studied via observation on fracture surface.Aiming to solve the elasto-plastic point-contact issue for inhomogeneous materials,a high-efficiency semi-analytical numerical equivalent inclusion method elasto-plastic point-contact model is built based on the theories of equivalent inclusion method,elasto-plastic contact mechanics and iteration numerical algorithm.The high accuracy and efficiency of the new simulation model is validated by FEM and experiments.And then,the new model is utilized to conduct extensive mechanical simulation parametric studies.In light of those studies,the relationship among microstructure,plastic deformation,Mises stress distribution,microscopic strengthening and failure mechanisms of CCFR-MIL composite are established.The detailed work are shown below:Firstly,Ti-(SiCf/Al3Ti)laminated composite is prepared by vacuum hot pressing at 660?,which is comprised of alternating Ti layers and SiCf/Al3Ti fiber-reinforced-intermetallic compound layers(SiC fiber as reinforcement).Al3Ti is the solely newly-formed Ti-Al intermetallic compound in the as-fabricated composite.Additionally,together with the so-called centerline,SiC fibers distributed along the center section of Al3Ti layer and are bonded with A13Ti by metallurgical interaction and mechanical j oint.There exist a trace amount of TiC and TiSi2 formed at the SiCf/Al3Ti interfacial zone.Besides,the layers are straight and compactly bonded with uniform thickness.Secondly,Ti-(SiCf/Al3Ti)laminated composites exhibit superior strength and ductility than those of Ti-Al3Ti laminated composites without fiber reinforcement.The failure of the Ti-(SiCf/Al3Ti)laminated composite contained the following process:(1)the formation and propagation of brittle cracks in Al3Ti layer;(2)the cracks deflection and bifurcation ascribed to the arresting of Ti layer and SiC fiber,causing the delamination and fiber-debonding;(3)the pullout and fracture of SiC fibers,fragmentation of Al3Ti,delamination of Ti-Al3Ti interface and the buckling or fracture of Ti.Moreover,Ti layers show typical microvoid coalescence fracture mode and Al3Ti layers exhibit brittle failure,including intergranular and transgranular fracture.Furthermore,the debonding,pullout and fracture of SiC fibers are observed obviously.All the above failure behaviors of the composite can increase the resistance to crack propagation,lengthen the path of crack growth and dissipate or absorb extra fracture energy.As a result,the mechanical properties of Ti-(SiCf/Al3Ti)laminated composite are improved effectively.Thirdly,aiming to solve the elasto-plastic point-contact issue for inhomogeneous materials,the first high-efficiency semi-analytical numerical equivalent inclusion method elasto-plastic point-contact model is built.The consistency equation of inhomogeneous inclusion is derived.The calculation methods for plastic strain increment,residual stresses,and surface residual diaplacements are introduced,and the corresponding algorithm is established.Parallel computing is involved in the model by dividing a large-scale computation into small pieces to be performed on multiple processers in order to boost the computational efficiency.The high-efficiency elastic contact model lays the foundation for further in-depth work.The advantages in precision and efficiency of the new semi-analytical model are verified by comparison with the finite element model as well as the macroscopic indentation tests.Lastly,the new model is utilized to conduct parametric studies for Ti-(SiCf/Al3Ti)laminated composite.The parameters of load,Ti layer volume fraction,hole-defect position,SiC fiber row quantity,the fiber diameter and interval in one row are studied to investigate their influence on plastic deformation,Mises stress distribution,microscopic strengthening and failure mechanisms.Those studies indicate that the SiC fiber rows exert an effective role in bearing the load and dispersing the stress more evenly,especially when the load rises to a high level,by which way the strength and toughness of Ti-(SiCf/Al3Ti)laminated composite are enhanced.And the failure behavior would first occur in the brittle intermetallic layer Al3Ti.The main innovation points are listed below:(1)An innovative fiber reinforced laminated composite Ti-(SiCf/Al3Ti)is designed and fabricated,which possesses high strength and good plasticity;(2)A high-efficiency semi-analytical contact mechanical model is built,which coupling inhomogeneous and elasto-plastic responses for fiber reinforced laminated composites;(3)The optimal microstructural parameters of Ti-(SiCf/Al3Ti)fiber reinforced laminated composite sheet was proposed.