Reinforcing interlaminar

However, a severe and persistent problem in laminated composites made of anisotropic fiber-reinforced plies is delamination. High interlaminar peel and shear stresses near edges start delamination cracks that grow along the non-reinforced interlaminar planes with little resistance. Delamination substantially reduces the load-bearing capacity and durability of advanced composites and has led to disastrous structural failures. Since the discovery and explanation of the mechanisms of delamination in advanced composites in the early 70s, many researchers have tried to... 

Laminates ate a special form of composite material or reinforced plastic because the continuous reinforcing ply of fibrous material imparts significant strength in the x—j plane. The strength along the axis results from interlaminar bonding of resins. Very few fibers ate oriented in the direction, so it tends to be the weak link in this type of composite. 

Note that no assumptions involve fiber-reinforced composite materials explicitly. Instead, only the restriction to orthotropic materials at various orientations is significant because we treat the macroscopic behavior of an individual orthotropic (easily extended to anisotropic) lamina. Therefore, what follows is essentially a classical plate theory for laminated materials. Actually, interlaminar stresses cannot be entirely disregarded in laminated plates, but this refinement will not be treated in this book other than what was studied in Section 4.6. Transverse shear effects away from the edges will be addressed briefly in Section 6.6. 

Another approach to exploit the properties of nanocarbons consists in integrating them in standard fiber-reinforced polymer composites (FRPC). The rationale behind this route is to form a hierarchical composite, with the nanocarbon playing a role at the nanoscale and the macroscopic fiber providing mainly mechanical reinforcement. This strategy typically aims to give FRPCs added functionality, improve their interlaminar properties and increase the fiber surface area. The first two properties are critical for the transport industry, for example, where the replacement of structural metallic... 

ISO 3597-4 2003 Textile-glass-reinforced plastics - Determination of mechanical properties on rods made of roving-reinforced resin - Part 4 Determination of apparent interlaminar... 

ISO 14130 1997 Fibre-reinforced plastic composites - Determination of apparent interlaminar shear strength by short-beam method ISO 15024 2001 Fibre-reinforced plastic composites - Determination of mode I interlaminar fracture toughness, GIC, for unidirectionally reinforced materials... 

Gilbert, A.H., Goldstein, B. and Marom, G. (1990), A liquid droplet measurement technique as a means of assessing the interlaminar shear strength of fiber reinforced composites. Composites 21. 408-414. 

ASTM D 5528 (1994). Mode I interlaminar fracture toughness of unidirectional fiber-reinforced polymer matrix composites. 

Davies, P. Kausch, H.H., Williams, J.G. and 29 other researchers (1992). Round-robin interlaminar fracture testing of carbon fiber reinforced epoxy and PEEK composites. Composites Sci. Technol. 43, 129-136. 

Fisher, S., Rosensaft, M. and Marom, G. (1986). Dependence of the interlaminar shear strength on the loading span-to-depth ratio in aramid fiber-reinforced beams. Composites Sci. Technol. 25, 69-73. 

Suzuki, Y., Maekawa, Z., Hamada, H., Yokoyama, A. and Sugihara, T. (1993). Influence of silane coupling agents on interlaminar fracture in glass fiber fabric reinforced unsaturated polyester laminates. J. Mater. Sci. 28, 1725-1723. 

This section examines the advantages and disadvantages of using three-dimensional textile preforms, especially through-the-thickness stitches, as the reinforcements for composites. Their major mechanical properties are compared with those of conventional two-dimensional composites, such as strength, stiffness, interlaminar properties, impact resistance and tolerance, etc. Dransfield et al. (1994) have recently given a useful review on the improvement of interlaminar fracture toughness of stitched composites. 

Recently Nishijima et al. investigated the radiation effects of three-dimensional glass-fabric reinforced plastics (3DFRP) mentioned in the preceding section, since the interlaminar shear strength of composites was expected to be greatly enhanced by the presence of Z-axis reinforcement [78]. Two kinds of 3DFRP were newly developed and named as ZI-003 and ZI-005 of which the matrices were epoxy and BT resins, respectively [28]. The compressive tests... 

Bowles KJ, Frimpong S. Voids effects on the interlaminar shear strength of imidirectional graphite-fiber-reinforced composites. J. Comp. Mater. 1992 26 10 1487-509. 

ISO, Standard test method for mode I interlaminar fracture toughness, G/c, of unidirectional fibre-reinforced polymer matrix Composites. ISO 15024 2001. Blackman, B.R.K., H. Hadavinia, A.J. Kinloch, M. Paraschi and J.G, Williams, The calculation of adhesive fracture energies in mode I revisiting the tapered double cantilever beam (TDCB) test. Engineering Fracture Mechanics 2003. 70 p. 233-248. BSI, Determination of the mode I adhesive fracture energy, Gic, of structural adhesives using the double cantilever beam (DCB) and tapered double cantilever beam (TDCB) specimens. 2001. BS 7991. 

ISO 15024. (2001) Standard test method for mode I interlaminar fracture toughness, G/c, of unidirectional fibre-reinforced polymer matrix composites. 

The properties of filled materials are eritieally dependent on the interphase between the filler and the matrix polymer. The type of interphase depends on the character of the interaction which may be either a physical force or a chemical reaction. Both types of interaction contribute to the reinforcement of polymeric materials. Formation of chemical bonds in filled materials generates much of their physical properties. An interfacial bond improves interlaminar adhesion, delamination resistance, fatigue resistance, and corrosion resistance. These properties must be considered in the design of filled materials, composites, and in tailoring the properties of the final product. Other consequences of filler reactivity can be explained based on the properties of monodisperse inorganic materials having small particle sizes. The controlled shape, size and functional group distribution of these materials develop a controlled, ordered structure in the material. The filler surface acts as a template for interface formation which allows the reactivity of the filler surface to come into play. Here are examples ... 

Besides graphite, carbon and glass fibers, organic fibers, e.g., Kevlar, have also been used to reinforce thermosetting resins, e.g., epoxy resin (38). One of the newest developments is fiber-reinforced thermoplastics, e.g., carbon fiber-reinforced polyether ether ketone (PEEK) ( ). These materials are rather tough as demonstrated in the interlaminar toughness values (Table... 

The reinforcing fabrics used were aramid (Kevlar DuPont) and poly(p-pheny-lene-2,6-benzobisoxazole) (PBO) (Zylon Toyobo). The fabrics were first treated with a 1.5% solution of HB PAMAM (AD-102), dried, then interleaved with an epoxy film structural adhesive (epoxy stage B on polyester net), and compression-molded for 90 min at 120 °C. For the aramid-based composite, FM-73 (Cy-tec) was used as the matrix. For the PBO-based composite, AF-191 (3M) was used as the matrix. The laminates were cut into strips and tested for interlaminar shear strength (ASTM D-2344) using a three-point bending instrament. 

The mechanical results of interlaminar shear strength for the two kinds of laminates prepared using hyperbranches impregnated in the reinforced fibers are presented in Table 15.8. The two laminates tested included Kevlar fabric primed with 1.5 wt.% HMW PAMAM (AD-102) and bonded with FM-73, and Zylon fabric primed with 1.5 wt.% HMW PAMAM (AD-102) and bonded with AF-191. 

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