CHARACTERIZATION AND PROMOTION OF DILATATION BANDS IN TOUGHENABLE THERMOSETTING RESINS

Formation of dilatation bands has been found in a series of moderately crosslinked thermosets with molecular weights between crosslinks, Mc, ranging from 560 to 1000 g/mole. These dilatation bands, although the y do not show distinct craze fibrils inside the hand, do behave mechan ically like the well-known crazing phenomenon observed in polystyrene. Although the cause for the formation of dilatation bands is still lar gely unknown, the occurrence of the craze-like fracture phenomenon (di latation bands) is found to be strongly influenced by the stress state the matrix experiences, by the type of loading applied to the specime n, and by the type/size of toughener particles incorporated in the mat rix. The tendency for dilatation band formation in engineering thermos ets can be greatly enhanced by the use of craze-prone toughener partic les, such as nylon particles. The toughening effect via these newly ob served dilatation bands is found to be quite impressive, and in some c ases, can approach that via the shear-handing process. The potential s ignificance of the present finding for a better design of toughened th ermosets for structural applications is discussed. (C) 1995 John Wiley & Sons, Inc.