Epoxy laminate

Acoustic Emission to Model the Fatigue Behaviour of Quasi-Isotropic Carbon-Epoxy Laminate Composites. 

Lafarie-Frenot, M.C. and Henaff-Gardin, C., Formation and Growth of 90° Ply Fatigue Cracks in Carbon/Epoxy Laminates , Composites Science and Technology Vol. 40, p. 307-324, 1991... 

Fig. 1 High re.solution X-ray refraction topography of low energy impact (5J) at CFRP epoxy laminate. Image area 2 mm X 4 mm. Horizontal resolution 0.2 mm. The image represents selectively an area of debonded fibers of vertical fiber orientation.

Fig. 9. Pie2oelectric embedded inside a glass—epoxy laminate to form a composite smart stmcture.

The mechanical properties of the laminates are somewhat poorer than observed with phenolic and melamine laminates. Tensile and flexural strength figures are typically about 20% less than for the corresponding P-F and M-F materials and about 60% of values for epoxy laminates. 

Maximum deflection results for a graphite-epoxy laminate for which... 

Example Unsymmetric Cross-Ply Graphite-Epoxy Laminate (After Jones [5-19])... 

Square Graphite-Epoxy Laminates (After Hyer [6-38])... 

See also Albumin Eggplant, citric acid in, 6 632t E-glass-epoxy laminates, 17 843 E-glass fibers, 26 758 Egyptian Giza cotton, 8 2 Egyptian mummies... 

Russell, A.J. and Street, K.N. (1984). Factors affecting the interlaminar fracture energy of graphite/epoxy laminates. In Proc. 4th Intern. Conf. on Composite Materials. (T. Hayashi, K. Kawata and S. Umekawa eds.), Japan Society of Composites Materials, Tokyo, p. 129. 

Bathias, C., Esnault, R. and Bellas, J. (1983). On the increasing fracture toughness at increasing notch length of 0/90 and 0/ 45/0 graphite/epoxy laminates. Composites 14, 365-369. 

Caprino, G. Halpin, J.C. and Nicolais, L. (1980). Fracture toughness of graphite/epoxy laminates. Composites 11, 105-107. 

Ishikawa. T, Fukunaga, H. and Ono, K.I. (1989) Graphite-epoxy laminates with almost null coefficient of thermal expansion under a wide range of temperature. J. Mater. Sci. 24,2011-2017. 

In particular, the techniques based on the termination of certain plies within the laminate has also shown promise. Static tensile tests of [30°/-30°/30°/90°]s carbon-epoxy laminates containing terminals of [90°] layers at the mid-plane show that premature delamination is completely suppressed with a remarkable 20% improvement in tensile strength, compared to those without a ply terminal. Cyclic fatigue on the same laminates confirms similar results in that the laminate without a ply terminal has delamination equivalent to about 40% of the laminate width after 2x10 cycles, whereas the laminates with a ply terminal exhibit no evidence of delamination even after 9x10 cycles. All these observations are in agreement with the substantially lower interlaminar normal and shear stresses for the latter laminates, as calculated from finite element analysis. A combination of the adhesive interleaf and the tapered layer end has also been explored by Llanos and Vizzini, (1992). 

Herszberg, I., Weller, T., Leong, K.H. and Bannister, M.K. (1996). The residual tensile strength of stitched and unstitched carbon/epoxy laminates impacted under tensile load. In Proc. 1st Australasian Congre.ss on Applied Mechanics. Melbourne, pp. 309-314. 

Jordan W.M. and Bradley W.L. (1987). Microniechanisms of fracture in toughened graphite-epoxy laminates. In Toughened Composites (N.J. Johnston ed.), ASTM STP 937, ASTM, Philadelphia, PA, pp. 95-114. 

Masters. J.E. (1987b). Characterisation of impact damage development in graphite/epoxy laminates. In Fractography of Modern Engineering Materials Composites and Metals, ASTM STP 948, ASTM. Philadelphia, PA, pp. 238-258. 

Sun. C.T. and Luo, J. (1988). Failure loads for notched graphite/epoxy laminates with a softening strip. Composites Sci. Techno . 22, 121-133. 

Figures 10 and 11 show a manufacturing application in which a resin s flow properties are measured in-sltu at a particular point in a thick laminate during cure in an autoclave. The sensor was inserted on the tool surface and in the center of a thick 192 TGDDM graphite epoxy laminate. Figure 10 shows the noise free raw data taken by the center sensor during cure in the 8x4 foot production size autoclave. Using the procedures described, the ionic mobility was measured at both the tool surface and the center of the thick laminate. In Figure 11, the sensor values of a show a 10 to 20 minute time lag in the point of maximum flow on the surface versus the laminate s center. Measurements of a versus q, as shown in...

Figure 10. Raw data from the sensor in the middle of a 1 thick 3501-6 graphite epoxy laminate during cure in a production size autoclave.

Figure 10. The EE, AE, and load accompanying the flexural straining of (a) (0)jg and ( b)( 45)jg graphite/epoxy laminates (Thornel 300/NARMCO 5208).

Figure 5.122 Strength chart for a (0, 9) unidirectional carbon-fiber-reinforced epoxy laminate composite. Reprinted, by permission, from N. G. McCrum, C. P. Buckley, and C. B. BucknaU, Principles of Polymer Engineering, 2nd ed., p. 408. Copyright 1997 by Oxford University Press.

For thick epoxy laminates processed in the autoclave, voids once formed and stabilized can only be removed by dissolution or by resin flow. Furthermore, resin gradients are deleterious to structural laminates. These two key phenomena make an understanding of resin transport vital to the development of any processing model. 

Figure 6.11 Resin pressure profiles in the laminate thickness direction (vertical) in a 1.4-in. thick unidirectional graphite-epoxy laminate for one-dimensional flow (edge-dammed) under conditions indicated in the figure...

Browning, C.E., Campbell, F.C., Mallow, A.R., Effect of Precompaction on Carbon/Epoxy Laminate Quality, AIChE Conference on Emerging Materials, August 1987... 

Probably the first major publication of a process model for the autoclave curing process is one by Springer and Loos [14]. Their model is still the basis, in structure if not in detail, for many autoclave cure models. There is little information about results obtained by the use of this model only instructions on how to use it for trial and error cure cycle development. Lee [16], however, used a very similar model, modified to run on a personal computer, to do a parametric study on variables affecting the autoclave cure. A cure model developed by Pursley was used by Kays in parametric studies for thick graphite epoxy laminates [18]. Quantitative data on the reduction in cure cycle time obtained by Kays was not available, but he did achieve about a 25 percent reduction in cycle time for thick laminates based on historical experience. A model developed by Dave et al. [17] was used to do parametric studies and develop general rules for the prevention of voids in composites. Although the value of this sort of information is difficult to assess, especially without production trials, there is a potential impact on rejection rates. 

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