Plied lay-ups

Lee and Springer [19] and modified by Li and Loos [22,23] to include unidirectional and cross-ply lay-ups will be used to demonstrate the effects of various geometric, material, and processing parameters on the degree of intimate contact. 

A comparison between the times required for consolidation of unidirectional and cross-ply lay-ups can be observed in Figure 7.18. The consolidation times required for the cross-ply lay-up are almost an order of magnitude higher than that required for the unidirectional lay-... 

Figure 7.18 Consolidation time (tc) versus consolidation pressure for T300/P1700 and APC-2 Batch II prepregs. (a) Unidirectional lay-up. (b) Cross-ply lay-up...

Repeated unstable delamination growth (stick-slip) in most specimens with symmetric [0°/90°]6s cross-ply lay-up, occurring throughout the test. 

Deviation from the mid-plane during delamination propagation in the cross-ply lay-up, specifically jumping from one adjacent unidirectional layer to that on the other side (symmetric) at regular delamination length intervals, resulting in a saw-tooth -type of fracture surface (Fig. 1). 

The different bending stiffness of the unidirectional, symmetric, non-symmetric lay-up is shown by independent three-point bending E-modulus measurements to decrease in that order from about 145 GPa to 73 GPa and 62 GPa. The same trend, with somewhat larger values i > seen in the back-calculated E-moduli (Tables 2-4). This is also apparent from the larger displacements (at similar delamination lengths) of the cross-ply lay-ups compared with th- unidirectional material. 

Fig. 7 shows that the values from the second laboratory tend to be lower than those from the first for both types of cross-ply lay-up, while those for the unidirectional lay-up agree fairly well. The scatter still seen in the R-curves for the cross-ply laminates with a single fracture surface topography (Fig. 7) can probably, at least in part, be attributed to different amounts of fibre-bridging (compare Fig. 1). Another factor is micro-cracking in front of the delamination that may make accurate determination of the delamination length difficult. This would also offer an explanation for the steep rise seen in the R-curves of those specimens for which the delamination does not deviate into the unidirectional plies. This is discussed in detail in [6]. Small (local and short-term) deviations of the delamination into the unidirectional plies not recognised in the visual inspection of the fracture surfaces might also contribute to the scatter by temporarily reducing Gic. Finally, the oscillating interlaminar - intralaminar type of delamination propagation could also account for some of the observed scatter. The analysi > presented in [4] concludes that the intralaminar G is considerably smaller than the...

The trends seen in the present analysis seem to support the conclusion that, if the type of fracture is considered, a meaninghil relative ranking of cross-ply lay-ups (symmetric or non-symmetric) with respect to a unidirectional lay-up of the same material can be achieved. The load-displacement plots and R-curves show that cross-ply materials will )deld a larger scatter but, if effects from changing fracture surfaces are recognised and those specimens are... 

Blackman, B.R.K., Brunner, A.J., (1998) Mode I Fracture Toughness Testing of Fibre-Reinforced Polymer Composites Unidirectional versus Cross-ply Lay-up , Proceedings 12" European Conference on Fracture ECF-12 Vol. Ill, Fracture from Defects, EMAS Publishing, pp. 1471-1476. 

Based on these properties, the level of residual stress in the 90° layer for the different cross-ply lay up used in this study as calculated with the classical lamination theory (CLT) range from 0 to 43.5 MPa as shown in Table 2. 

Melt Infiltrated In-Situ BN SiC/SiC composite (MI SiC/SiC) is the material that was documented in the past work (5). The MI SiC/SiC system has a stochiometric SiC (Sylramic ) fiber in a multiphase matrix of SiC deposited by chemical vapor deposition followed by slurry casting of SiC particulates with a final melt infiltration of Si, The specific MI SiC/SiC tested had 36% volume fraction fibers using a 5 HS weave at 20 EPI with a cross ply lay-up. A cross section of the material is shown in Figure 1. 

Figure 1. Test sample design fca- tensile shear testing according to EN 314-1 (2005) [1] for a 7 ply lay-up.

Figure a illustrates the ply lay-up descriptions. Each ply is shown by a number representing the direction of the fibers in degrees, with respect to a reference (x) axis. Zero degree fibers of both tape and fabric are normally aligned with the largest axial load. 

Abraham T, Banik K and Karger-Kocsis J (2007) AU-PP composites (PURE ) with unidirectional and cross-ply lay-ups djuiamic mechanical thermal analysis. Express Polym Lett 1 519-526. 

The hot compaction technique was very successfully applied to create self-reinforced polymer composites from numerous polymers, as reported in a series of publications from Hine, Ward and others at the University of Leeds and this clearly demonstrated that self-reinforced polymer composites could be produced without the addition of any extra matrix materials. However, Hine et al. also showed that the incorporation of interleaved isotropic polymer films during fabric ply lay-up may provide improvements in interfacial properties, compared to the interfacial properties of composites formed exclusively from hot compacted fibres [96, 146, 147]. hi the case of PE-based composites, a LDPE film was used as an interleaf film, whereas in the case of PP-based composites, the PP interleaf film was of the same grade as the PP used to create the oriented PP tapes. A more recent publication described the S3mergistic effect of combining interleaved films that also... 

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