In situ SEM observation of tensile fracture processes in a rubber-epoxy resin dual-phase system

—The toughening mechanism of CTBN rubber-modified epoxy resins was studied by using a tension stand of a scanning electron microscope. On the basis of the results obtained in the in situ SEM experiments, the toughening mechanism of rubber-toughened epoxy resins is discussed mainly in terms of secondary microcrack initiation and propagation during or before propagation of primary cracks. Based on Yang's assumption (Mater. Chem. Phys. 16, 443 (1987)), several models of secondary microcrack formation and propagation are presented.