The general principles of carbon fiber laminate ply design
The fiber laminate design method mainly refers to how to determine the layer ratio and the number of layers of each paving corner ply after the laying angle combination in the carbon fiber laminate has been roughly selected. The value should be obtained according to the load condition of the structural parts and the required design accuracy. According to different design requirements, such as design according to rigidity, design according to strength, design according to damage tolerance, or according to some special requirements, such as zero thermal expansion coefficient, negative Poisson's ratio, etc., the laminate can be designed, or it may meet multiple requirements at the same time. Multi-objective design required by the design.
In most cases, carbon fiber laminates mainly bear plane loads. In order to maximize the high performance of the fiber axis, the 0° layer should be used to bear the axial load; the ±45° layer is used to bear the shear load, that is, the shear load is broken down into tensile and compressive components to arrange the fiber bearing; 90° Laminates are used to withstand lateral loads to avoid direct loading of the resin and control the Poisson's ratio of the laminate. According to the needs, determine which types of laying angles should be arranged in the laminate.
In order to improve the buckling resistance of carbon fiber components, for components subject to axial compression, such as carbon fiber ribs and beams, flanges of ribs, and carbon fiber skins that need to withstand axial compression, in addition to laying a larger proportion of 0° layup, It is also necessary to arrange a certain number of taxi 45° layers to improve the compressive stability of the structure. For members subject to shear load, such as webs, the main arrangement is ±45° layers, but a small amount of 90° layers should also be arranged to increase the critical load of shear instability.
For components that may suffer low-energy impact perpendicular to the plane of the carbon fiber laminate, laying a ±45° layer or adding a layer of glass cloth on the outermost layer of the laminate can improve the impact resistance, which is also beneficial to anti-peeling, and can also improve Manufacturability.
The plies of the same laying angle should be distributed as evenly as possible along the direction of the laminate, and should not be too concentrated. If more than 4 plies, delamination will easily occur between the plies of the two paving directions. The in-plane rigidity of the laminate is only related to the ratio of the number of layers and the laying angle 0, and has nothing to do with the laying order. But when the performance of the laminated structure is also related to the bending stiffness (such as laminated structural beams), the bending stiffness is related to the laying order.
To sum up, it is generally recommended that carbon fiber components should contain four kinds of plies at the same time. Generally, 6% to 10% of 90° plies must be included in the 0°, ±45° laminate to form an orthotropic board. Except for special needs, balanced and symmetrical laminates should be used to avoid warping due to coupling effects during curing or after loading. If it needs to be designed as a quasi-isotropic board, laminates composed of 0°, 30°, 60°, and 90° layers can also be used.