The Study Of Mechanical Properties Of2d Triaxial Braided Composites

The longitudinal mechanics property and stability of2D triaxial braided composites areenhanced by adding axial yarns in the composite structure. As a new kind of structural material,2Dtriaxial braided composites are expected to be widely used in the future. Due to the lack of knowledgeabout stress state and failure mechanism of the composite, it is necessary to establish a model topredict elastic constants and strength properties of the composite. Analyzing the distribution ofmesoscopic stress and the damage evolution of2D triaxial braided composite is the foundation of itsapplication in engineering project.A geometrical model was proposed for the2D triaxial braided composites with the considerationof the undulation, twist and spatial interlacing of the yarns. Based on the volume-averaged method, ananalytical model was developed for the prediction of engineering constants of2D triaxial braidedcomposites. Furthermore, a finite element model was established for the analysis of the mechanicalproperties by introducing an improved periodical boundary condition and the mesoscopic entitystructure of2D triaxial braided composites. The results of both predicted models show goodagreements with experimental results. The mesoscopic stress distributions of the composite underloads were investigated and the influences of braiding parameters on the elastic constants werediscussed. It shows that axial mechanical properties are reinforced and the stresses arewell-distributed; braid angle and fiber volume fraction have great influence on elastic properties.A progressive damage model was developed and the damage process was analyzed to predict thestrength of the composite. Tsai-Wu failure criteria and Mises failure criteria were adopted to identifythe occurring of damage events of yarns and matrix. A stiffness degradation rule was introduced torepresent the failure of elements. The strength and the stress-strain curve predicted by the progressivedamage model are well agreed with experiment results. The effects of braid angle and fiber volumefraction on strength of the composite were also discussed.