Study On The Manufacture And Mechanical Properties Of Z-pinned Polybenzoxazine Composites

In this paper, Z-pin technology is used to reinforce the interfacial performance ofpolybenzoxazine composites, which offers polybenzoxazine matrix composite a breakthrough in theapplication on the primary components of aircrafts. Meanwhile, by studying on the law of influenceZ-pin’s insertion pattern has on the in-plane properties of laminate, a new method was obtained tolowering the damage of Z-pin insertion, which can ensure the safty of Z-pin technology and promotethe widely ultilization of Z-pin reinforced composite.In order to get the polybenzoxazine resin matrix Z-pin reinforced by glass fiber, the properpultrusion parameters were determined with reference to analysis of viscosity-temperature and curingcharacteristics of the resin. The temperatures of resin bath, mould and curing oven should berespectively set at70℃,140℃and200℃, and3mm Z-pin could be pultruded per minutes. Moreover,in order to get rid of the pores in Z-pins, an open heating system was equipped to volatilize theresidual solvent out of resin. Several solutions were discussed for the Z-pin insertion angle offset,including developing automation equipments for Z-pin insertion, restraining interlayer slide ofprepreg and controlling the insertion depth. And the maximum insertion depth of different matrixresin Z-pins was investigated in prepreg with and without being heated.To explore the influence that Z-pins have on the interlaminar mechanical performance anddamage mechanism of Z-pin reinforced polybenzoxazine laminates, a great amount of groups ofspecimens were prepared for interlaminar shear test and double catilever beam (DCB) test. Resultsshowed that he reinforcement of Z-pins modified the interlaminate shear strength by delaying thecrack propagation under the interfacial shear condition. Compared to the control group, the interlayershear strength was increased by15.1%. Z-pin’s bridging effect endowed the laminate a strongcapacity of delamination resistance, which give a significant rise to the mode I interlaminar fracturetoughness (GI C). With the reinforcement of Φ0.5mm Z-pins with0.785%volume rate, the increase ofGI Cwas up to219%.The tensile and compressive experiments were conducted to research the foundermentalmechanical behavior of Z-pin reinforced polybenzoxazine laminate. According to the results, theinsertion of Z-pins would lead to a degradation of in-plane tensile property of lamenatedpolybenzoxazine composites. In contrast to unpinned laminate, the presence of Z-pins decreased thetensile strength by23.4%. In the meanwhile, the tensie strength would be severely corrupted if Z-pin did not penetrate through the laminate. Under the compressive condition, the presence of Z-pin causedstress concentration in the insertion region, on the other hand, it resist interlayer delamination usuallyoccurred during the buckling. Summarily, Z-pin insertion had not obvious effect on the compressivestrength and module of polybenzoxazine laminate.The quantitative relation of and the in-plane tensile and compressive strength with the insertionpattern were concluded to search the solution for the in-pane properties degradation of Z-pinnedcomposites, through the experimental study on the influence that the insertion pattern had on thein-plane properties of Z-pinned laminates with the same volume rate of Z-pin. The degradation ofZ-pinned laminate in-plane strength was modified by changing the insertion pattern of Z-pins. Thefinite element model was built to evaluate the strain concentration in the Z-pin insertion region, whichresulted in the final tesile failure. Based on the research results the in-plane tensile strength ofZ-pinned polybenzoxazine laminate was increased by12.8%.