Research On The Mechanical Performance Of Fiber Reinforced Composite Variable Angle Laminates

The composite laminates can be obtained by using the straight-line placement of thefiber. The method is simple, however, it immensely limits the flexibility of the design andalso makes the directional characteristics of composite materials not be fully utilized. But,with the development of the fiber placement, the existing automated fiber placementdevices have been able to achieve the variable angle placement of fiber tow, making theangle in continuous change within the same layer. Compared with the traditional fixedangle placement, it can increase the flexibility of the design and more adequately takeadvantage of the directional characteristics of the composite materials, making possibleto improve the performance of the components or reduce component weight. Compositelaminates are widely used in the practical engineering applications, therefore, it isnecessary to put the variable angle into the lamina and study their associated mechanicalproperties.The angle variation law of the reference fiber path is given and the curve function ofthe reference fiber path is derived on the basis of it. Then, the definition method of thevariable angle fiber laminates is confirmed. Taking into account the effect of the coursewidth, the calculation method of fiber angle for arbitrary point on the course is provided.The shifted method and parallel method are discussed and the reasons causing gaps,overlaps or folds are analyzed. Comparing their advantages and disadvantages, theconstruction method is determined in this paper. Base on the nomenclature of thestraight-line fiber laminate, the notation of the variable angle fiber laminate is given. Themethod which can generate the analysis model of the laminate with variable angle isprovided by applying discrete elements and the corresponding MATLAB code isimplemented.According to the classical laminate theory, the relationship of stress, strain andvariable angle of the simple ply with variable angle is given and the constitutive equationof the variable angle fiber laminate is obtained. Depending on the given theory, twospecifies angle variation of the laminates is given and the finite element models oflaminates with/without overlaps are created. The in-plane static response is studied underthe compression load, the results of the deformation, stress and section force are obtained,and the influence of the variable angle on the got results is analyzed.Laminate under compression load can occur buckling, affecting the overall safety ofthe structure. Considering the geometric nonlinear effect in this paper, the bucklinganalyses of the variable angle fiber laminates with/without a hole are implemented by finite element method and the buckling load, load displacement curve and load deflectioncurve are gained. At the same time, the influence of different initial geometricimperfections on the above results is considered. Similarly, in order to know variableangle effect on the obtained results, the straight-line fiber laminates are also carried onthe corresponding analyses.