Crack growth in epoxies

In the study of crack growth in epoxy polymers the double-torsion and compact-tension specimens have been the most widely used. The values of KIc may be obtained from 1,2)... 

The effects of microstructure may be more complex in the initiation of crack growth in epoxies. While M, is apparently the only structural variable to which crack arrest is sensitive in the DGEBA/DDS networks, crack initiation... 

Additional analytic tests show( ) that in fact the embedding dimension is quite small (3-4). Stochastic processes tend to raise the embedding dimension, so that this result supports the notion of chaotic behavior. Furthermore, the embedding dimension indicates the number of variables needed in the equation of motion to describe the phE intensity behavior. Thus, the underlying process of phE during crack growth in epoxy is amendable to a description based on a relatively small number of variables. Although we do not known what these variables are for sure, they more than likely include local microstructure at the crack tip and the velocity vector of each point on the crack front. 

Cracking in bonded or encapsulated bodies will often initiate at a sharp interface comer whenever such comers are present. For example, crack growth in epoxy-bonded, metal-adherend, cylindrical butt joints initiates adhesively (on the interface) along a small segment of the specimen periphery [1-3]. However,... 

Most of the recent advances in the understanding of the fracture behaviour of epoxy polymers has been through the application of fracture mechanics 2) and the present Chapter is therefore concerned with the study of the mechanisms and mechanics of crack growth in crosslinked epoxies using fracture mechanics. 

One of the most curious aspects of crack growth in most epoxies is the apparently unstable manner by which propagation occurs, even over wide ranges of temperature and test rate. This behavior is commonly referred to as stick-slip , and is characterized by the crack growing in a series of discrete, unstable jumps. Even some of the earliest works on epoxy fracture report this mode of crack growth. The suspected origins of stick-slip fracture behavior in epoxies is discussed in a subsequent section. Unhke epoxies, thermoplastic polymers, such as poly(methyl methacrylate) and polystyrene, are characterized by stable, continuous crack growth. This mode of fracture sometimes can be observed in epoxies, in particular, when they are tested at fast rates and/or low temperatures. 

F E Sloan and R J Seymour, The effect of seawater exposure on mode I interlaminar fracture and crack growth in graphite/epoxy , J Compos Mater 1992 26(18) 2655-2673. 

Sirrruk A, Penumadu D, and Weitsman YJ (2010) Fatigue behavior of carbon fiber and vinyl ester sandwich facing material due to sea environment. In Ninth international conference on sandwich structures (ICSS-9). California Institute of technology, Pasadena, 14—16 June 2010 Sloan FE, Seymour RJ (1992) The effect of seawater exposure on mode I interlaminar fracture and crack growth in graphite/epoxy. J Compos Mater 26(18) 2655-2673 Smith LV, Weitsman YJ (1996) The immersed fatigue response of polymer composites. Int J Fract 82(1) 31 2... 

Thermosetting epoxy polymers are widely employed in structural engineering applications and thus a knowledge of the mechanics and mechanisms of the fracture of such materials is of vital importance. The present Chapter discusses the fracture of epoxy polymers, concentrating on the use of a continuum fracture mechanics approach for elucidating the micromechanisms of crack growth and identifying pertinent failure criteria. 

The typical effect of rate on the measured value of K,c and the associated type of crack growth can clearly be seen in Fig. 4 for an epoxy polymer based upon a DGEBA resin and cured with various amounts of TETA. The values of K ci and K ca are those for crack initiation and arrest (Fig. 2b) respectively and the difference between them characterises the amount of crack jumping which has taken place. When the difference... 

Although epoxies dominate the thermoset fracture literature, work has been reported on other systems, e.g., polyester resins, phenol-formaldehyde compounds, peroxide cured polystyrene, and highly crosslinked polyurethanes. In general, these materials exhibit fracture behaviors similar to epoxies, and suggest that thermosets, as a class of materials, display characteristic crack growth properties. 

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