Ply orientations

The influence of the orientation of the laminae on the stiffness of the composite is illustrated in Figure 15.15b, where generic stress-strain curves for unidirectional cross-ply random laminates are shown. In the design of laminates it is necessary to define not only the orientation of the plies but also the stacking sequence, i.e., the order in which the plies are placed through the thickness. Figure 15.16 shows examples of symmetrical and non-symmetrical laminates. The most standard ply orientations are 0°,... 

Fiber-reinforced composites are also highly anisotropic when fibers are aligned. In addition, they are nonhomogeneous and usually laminated with individual plies oriented in several different directions. Because of these difficulties, once again the isotropic failure criteria are of little use. However, reasonably successful failure criteria for individual plies have been developed (9-11) and applied to the failure of laminates by laminated plate theory ( , 12). 

Another transducer resonance system is the Fokker Stack Tester, developed to examine ply orientation and stacking sequence in the different layers of CFRP composites. This computer-controlled system displays the signal output in a graphical format. It consists of passing a probe into a rivet or fastener hole and scanning the material surface by a focused laser beam. The intensity of the reflected light is correlated to the orientation of each ply and can provide information on the ply number, the thickness of each ply, and fiber orientation. 

Trakas and Kortschot [76] used carbon fibre epoxy (AS4/3501-6) specimens modified with Teflon edge delaminations in a study comparing unidirectional and 0°/90° and 90°/90° interfaces under mode 1, mode 11 and mode HI loading. Delamination resistance decreased for all modes when going from unidirectional to cross-ply and 90°/90°. The tests were complemented with scanning electron microscopy of the fracture surfaces, but they did not yield a direct quantitative correlation with the measured values of Gc- It was noted that Gc could be used as a material property for design as long as the layup (ply orientation) and mode of fracmre corresponded to those in the intended use. 

Andersons J, Konig M. Dependence of liactute toughness of composite laminates on interface ply orientations and delamination growth direction. Compos Sci Technol 2004 64 2139—52. http //dx.doi.org/10.1016fj.compscitech.2004.03.007. 

Figure 2.5 Laser-based technique to check ply orientation in reinforced plastics laminates (By permission S Hill, Rapid nondestructive testing of carbon fibre reinforced plastics. Materials World, August 1996, Institute of Materials, London)...

The transverse contraction of these laminates is completely different under uniaxial applied strain. The 90° laminate contracts very Uttle (Vjj 0.02), whereas the contraction of the 45° laminate is very large (Vjj 0.773). This difference in the Poisson s ratio causes additional stresses in orthotropic laminates, where the constituent plies have different ply orientations. The contraction of an angle-ply laminate, for example with 90° plies, is hindered by the small Poisson s ratio of the 90° plies. This leads to transverse stresses in other plies. Near free edges and around unloaded holes, the transverse stresses are equilibrated by interlaminar stresses. For... 

Ply orientations in a laminate are taken with reference to a particular loading direction, usually taken to be the direction of the maximum applied load, which, more often than not, coincides with the fibre direction to sustain the maximum load, and this is defined as the 0° direction. It is usual to choose balanced, symmetric laminates in design. A balanced laminate is one in which there are equal numbers of-1-0 and - 0 plies a symmetric laminate is one in which the plies are symmetric in terms of geometry and properties with respect to the laminate mid-plane. Hence, a laminate with a stacking sequence 0/90/-I-45/-45/-45/-I-45/90/0, which is written (0/90/ 45), is both balanced and symmetric. Balanced, symmetric laminates have a simplicity of response. In contrast, an unbalanced, asymmetric laminate will, in general, shear, bend, and twist under a simple axial loading. 

Wang Y Chen X, Young B, Kinloch B, Wells B. A numerical study of ply orientation on ballistic impact resistance of multi-ply fabric panels. Compos B Eng 2015 68 259-65. 

The shear-out failure mode shall if possible be avoided by selecting an appropriate ply-orientation and by using a minimum value of the e/d ratio. 

Having established the failure envelope for a single ply (lamina), the failure envelope for a multi ply laminate can be readily obtained. Figure 4.14 shows how the failure envelope for a four ply laminate, with plies orientated at 0°, 90°, -45° and +45° respectively, can be constructed. 

Sensitivity analyses predict the performance of laminates and structural elements within a specified tolerance set for a design variable such as ply orientation or fibre fraction. Sensitivity analyses are very important since the designer should always check the effect of manufacturing tolerances on the performance of the structure. Computer codes are extremely useful on account of the extensive calculations related to these analyses, in practice, all the computer codes identified above should provide the possibility to specify a tolerance for each important design variable. 

The results of laminate material tests are presented in Table 4. Mechanical properties of A300 WR were not tested as it had the same materials, ply orientations, and number of plies as the A300 HL laminate. The fibre volume fraction presented in Table 4 was... 

A shorthand code for ply orientations has been adapted for use in layouts and studies. Appendix F summarizes the format conventionally used for the ply layup of reinforced composites. 

Appendix F Composite Ply Orientation—Symmetry and Balance Appendix G Important Information Regarding Processing of Plastics G. 1 Plastics and Rubber Fabrication Processes G.2 Guidelines on Part Design for Plastics Processing Methods G.3 Approximate Part Size Ranges for Principal Processes G.4 Plastics Available for Processes... 

Composite Ply Orientation-Symmetry and Balance. Examples of Typical Callouts ... 

In this case, an aluminum-carbon fiber reinforced polymer (CFRP) adhesively bonded SLJ was investigated [46]. Woven CFRP adherent having 0° ply orientation was bonded with an aluminum adherend by epoxy structural adhesive DP 760. 

From the micro-mechanical point of view, the process modeling strategies must consider simultaneous interplay of the following intrinsic factors initial and boimdary conditions in terms of pressure and temperature, fiber content and stacking, sequence of layers (ie ply-to-ply orientation), thermal shrinkage, chemical shrinkage, time-temperature-degree of ciu-e dependent resin properties, and... 

Non-woven materials can avoid these stresses. In one non-woven material type, short, randomly oriented fibers are treated with the resin system In a second type, linear strands of fiberglass are layed down in a balanced, cross-plied orientation which resists subsequent stresses. 

These values are for individual lamina or for a unidirectional composite, and they represent the theoretical maximum (for that fiber volume) for longitudinal in-plane properties. Transverse, shear, and compression properties will show maximums at different fiber volumes and for different fibers, depending on how the matrix and fiber interact. These properties are not reflected in strand data. These values may also be used to calculate the properties of a laminate that has fibers oriented in several directions. Using the techniques shown in Sec. 4.5.1, the methods of description for ply orientation must be introduced. 

The laminates consist of alternate layers aluminium (0.2-0.5 mm thick], which has been anodised and then primed with Cytec-Fiberite s BR-127 corrosion-inhibiting primer, bonded together with fibre-rich, epoxy-based adhesive-prepregs (about 0.125 mm thick]. The reinforcing fibre is usually unidirectional in nature, although woven fabric is occasionally used. Generally two or three sheets of adhesive separate each sheet of aluminium this can be in the 0° direction or laid up in a cross-plied orientation. 

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