Ply stacking sequence

In the case of the fibrous laminate not much work has been done, but it has been observed that a significant loss of stiffness in boron—aluminum laminate occurs when cycled in tension—tension (43,44). Also, in a manner similar to that in the laminated PMCs, the ply stacking sequence affects the fatigue behavior. For example, 90° surface pHes in a 90°/0° sequence develop damage more rapidly than 0° pHes. In the case of laminates made out of metallic sheets, eg, stainless steel and aluminum, further enhanced resistance against fatigue crack propagation than either one of the components in isolation has been observed (45). 

Bartholomew P. Ply stacking sequences for laminated plates having in-plane and bending orthotropy. Fibre Sci Technol 1977 10(4) 239—53. 

In addition, lamination can result in up to 18 elastic coefficients and increased deformational complexities, but the additional coefficients can all be derived from the four primary coefficients using the concept of rotation and ply-stacking sequence. These complications are the result of geometric variables. If the laminate is properly constructed, the in-plane stretching or stiffness properties can still be specified by four elastic coefficients. We shall consider laminates of this nature. 

Smith RA, Clarke B, Ultrasonic C-scan determination of ply-stacking sequence in carbon fiber composites. Insight, 36(10), 741-747, 1994. 

Impact performance was measured on layered structures which were prepared by stacking pre-impregnated plies of carbon and HP-PE fibre woven fabric (Satin weave 8 H) together and curing them for 2 hours under combined vacuum- and pressure conditions in a hot press at 110°C. After curing samples were postcured for 12 hours at 110 C. All laminates were 4 plies thick (nominal thickness 1,5 mm) and within these 4 plies stacking sequences and HP-PE/carbon ratios were varied. The total volume fraction of fibre in the laminate was 70%. Plane samples of 60 mm x 60 mm were cut from these laminates with a bandsaw. 

Example 3.16 A unidirectional carbon hbre/PEEK laminate has the stacking sequence [O/SSa/—352]t- If it has an in-plane stress of = 100 MN/m applied, calculate the strains and curvatures in the global directions. The properties of the individual plies are... 

Solution This stacking sequence is similar to that in Example 3.11 except that in this case the laminate is not symmetrical. As shown in Fig. 3.27, the centre line of the laminate is in the middle of one of the plies and... 

The example considered to illustrate the strength-analysis procedure is a three-layered laminate with a [4-15°/-15°/+15°] stacking sequence [4-10]. The laminae are the same E-glass-epoxy as in the cross-ply laminate example with thickness. 005 in (.1270 mm), so that the total laminate thickness is. 015 in (.381 mm). In laminate coordinates, the transformed reduced stiffnesses are... 

Suppose we replace the 90° layers with a laminae in an attempt to increase the axial stiffness and to increase the first-ply failure load as in Figure 7-61. The load-deflection curve slope after first-ply failure also increases when a laminae replace the 90° layers. However, the energy absorption decreases with such a stacking sequence change. The associated fatigue lives are not known unless both laminates are made and subjected to fatigue loading. 

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°,... 

With the initial aim of evaluating the applicability of the ISO 15024 standard for fracture toughness testing for non-unidirectional composite laminates, ESIS TC4 has conducted a number of round robin studies on cross-ply laminates with different stacking sequences. We report here the results of two test laboratories from the 3 round robin activity in which double cantilever beam (DCB) specimens made from unidirectional (0°/0°-interface) composite laminates were compared to DCB-specimens with 0°/90°- and 90790° interfaces. In the analysis, correlation with observations from the delamination growth (e.g., deviation from the mid-plane) and post-test (e.g., fracture surface) inspection was attempted. The results are compared with some results in the literature. 

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. 

The use of Eqn (4.12) in laminate design is illustrated for two different stacking sequences in Figure 4.12 where it can be seen that the four 45° surface plies in the [(45/—45/45/—45)2/(90/0/90/0)2ls laminate provide enhanced damage tolerance. This is due to the combined effect of delayed buckling (Figure 4.12(a)) and reduced All for the surface plies of this laminated. In the case of the [45/0/ 45/90]4s laminate, the near-surface presence of the 0° ply has the opposite effect. 

Some special classes of laminates are worth mentioning at this point. Symmetric laminates were already defined earlier. For symmetric laminates, the B matrix is zero (Bij = Q). Balanced laminates are laminates in which for every +6 ply (6 0 or 90) there is another —6 ply somewhere in the stacking sequence. For... 

It should be noted that the above equation, which is based on the assumption of a homogeneous plate, is independent of the stacking sequence. Rearranging the plies in a laminate in any order will give the same answer. This means that interlaminar stresses, which for some stacking sequences can be very important, are neglected. 

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