Laminate damage tolerance

One of the most important properties which control the damage tolerance under impact loading and the CAI is the failure strain of the matrix resin (see Fig. 8.8). The matrix failure strain influences the critical transverse strain level at which transverse cracks initiate in shear mode under impact loading, and the resistance to further delamination in predominantly opening mode under subsequent compressive loading (Hirschbuehler, 1987 Evans and Masters, 1987 Masters, 1987a, b Recker et al., 1990). The CAI of near quasi-isotropic composite laminates which are reinforced with AS-4 carbon fibers of volume fractions in the range of 65-69% has... 

Composites with stitched reinforcements have been the subject of extensive study under impact conditions in recent years because the damage resistance and damage tolerance of laminate composites are of major concern in a service environment (Liu, 1990 Farley et al., 1992 Farley, 1992 Farley and Dickinson, 1992 Portanova et al., 1992 Caneva ct al, 1993 Kang and Lee, 1994 Adanur et al., 1995 Wu and... 

Williams, J.G. and Rhodes, M.D. (1982). Effect of resin on impact damage tolerance of graphite/epoxy laminates. In Composite Materials Testing and Design (6th Conf.) ASTM STP 787 (l.M. Daniel ed.). ASTM, Philadelphia, PA. pp 450 80. 

There is also scope for the development of new techniques such as chemical vapour infiltration (CVI) (Caputo and Lackey, 1984 Caputo et al., 1985), normal chemical reaction bonding processes, laminar sialon composites, etc. More recently, laminated composites in non-oxide and sialons have demonstrated very promising results for strengthening (Goto and Kato, 1998) and even achieved a non-brittle failure behaviour accompanied by high damage tolerance (Yu and Krstic, 2003 Yu et al., 2005). 

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. 

The use of a simple, analytical approach to damage tolerance enables the selection of optimum (fuUy uncoupled) stacking sequences for which effective stress levels may exceed 400 MPa, see Figure 4.13. The approach assumes that laminates are locally... 

Baker N, Butler R, York CB. Damage tolerance of fully orthotropic laminates in compression. Compos Sci Technol 2012 72 1083-9. 

Rhead AT, Butier R, Baker N. Analysis and compression testing of laminates optimised for damage tolerance. Appl Compos Mater 2011 18(1) 85—100. 

Most of the criteria discussed so far focus on predicting some form of failure onset, typically first-ply failure. As referred to above, this does not necessarily coincide with final failure or collapse of a laminate. There may be significant additional load carrying capability, which can be very important for damage tolerance considerations. 

The use of fillers tends, with few exceptions, to reduce the damage tolerance, tensile and flexural strength of laminates. The effect on the interlaminar shear strength of glass fabric/epoxy laminates depends on the filler and is shown in Fig. 1.10. Note that glass beads and quartz had no adverse effect whereas the extremely thin-walled hollow glass microspheres were damaging [23]. Thicker walled spheres would have improved the performance. 

Q Yang, Damage Tolerance of Filled Glass-epoxy Laminates, PhD Thesis, Kingston University, 1995. 

S. Madjidi, W S Arnold and IM Marshall, Damage tolerance of CSM laminates subject to low velocity oblique impacts . Compos Struct 1996 34 101-116. 

The absorber materials are in most cases very tough polymer composites. These may consist of aramid fibres in a tough matrix such as heavily plasticised and toughened polymer resin or neoprene. Polyethylene fibre composites are also widely used, although typically these consist of pressure-consoUdated laminates rather than using resin infiltration. Most systems have a covering of fibre composite or fabric to provide impact resistance and to enhance the damage tolerance of the... 

T. Radsick, B. Saruhan, and H. Schneider, Damage tolerant oxide/oxide fiber laminates composites, Journal of the European Ceramic Society 20, 545 550 (2000). 

Kimpara I, Saito H (2007) Part II Post-impact fatigue behavior of woven and knitted fabric CERP laminates for marine use. Long-term durability and damage tolerance of innovative marine composites (NICOP), Technical Reports and Data Base for Office of Naval Research Project, Feb 2007... 

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