JOURNAL OF MATERIALS SCIENCE 37 (2 0 0 2 ) 2659 – 2667 Characterization of microstructures and toughening behavior of fiber-containing toughened nylon 6,6 S. C. WONG ∗, § , G. X. SUI ‡ , C. Y. YUE ‡ Schools of ∗ Materials Engineering and ‡ Mechanical and Production Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Republic of Singapore E-mail: asscwong@ntu.edu.sg Y.-W. MAI Center for Advanced Materials Technology (CAMT), School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, Sydney, NSW 2006, Australia, MEEM, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, People’s Republic of China The toughening behavior of short glass fiber reinforced toughened polymers was studied using fracture mechanics and microscopic techniques. The essential work of fracture (EWF) analysis shows that the inclusion of short glass fibers not only provided a stiffening effect but also a toughening influence. It was observed that rubber-related toughening and fiber-related toughening were competitive in nature for the reinforced, toughened nylon 6,6. When the matrix stress was substantially reduced by the presence of short fibers via the load-shedding mechanism, rubber toughening was severely curtailed. At higher fiber volume fractions, fiber pull-out work contributed significantly to the enhancement of the specific essential fracture work. Fiber-end plasticity was evident under microscopic examination. C  2002 Kluwer Academic Publishers 1. Introduction Toughening of engineering polymers using second elas- tomeric phase has found wide-ranging applications in the automotive and packaging industries. The attempt to elucidate the toughening mechanisms has also ac- complished considerable success [1–3]. In recent years, there has been an increased interest in introducing high modulus glass fibers [4–9] and glass beads [10–12] into toughened matrices. One clear advantage of such a design scheme is the cost-effective fabrication; and the primary motivation is to reinforce the toughened matrix, which often suffers from reduction in tensile strength and modulus caused by the compliant rubber particles. The ideal scenario appears to be one that can accomplish concomitantly toughening as derived from the matrix and strengthening as derived from the rein- forcement. This scenario often does not hold because of the complexity in interaction between the impact modifiers and the reinforcement. Some success in ob- taining high strength and high toughness blends with glass fiber reinforcements was, nevertheless, reported [7, 8, 13]. The toughness in this case was defined as the work dissipated per unit area of crack growth. The theories of rubber toughening were well stud- ied and reviewed by Bucknall in Chapter 22 of Ref. [3]. It arises when matrix plasticity was promoted by § Author to whom all correspondence should be addressed. internal cavitation of rubber particles or by adhesive failure at the particle-matrix boundary. It is noteworthy that for rubber particles that do not serve the purpose of enhancing matrix deformation, which absorbs the predominant amount of energy, there is no reason for rubber toughening. In such cases, the compliant rubber particles only serve to weaken the matrix material and lead to lower toughness. Recent attention has been given to characterizing mechanical and fracture properties of fiber-reinforced toughened polymers using fracture mechanics [4–9, 14, 15]. However, toughening mechanisms of fiber- reinforced toughened plastics are not very well un- derstood particularly with regard to the independent roles of second phases and their interactions [3, 13, 16]. One would conjecture that the mechanisms of frac- ture in connection with fiber-reinforced single poly- mers [14] could be applied to reinforced, toughened polymers. This approach ignores the distinctive role of the second-phase rubber particles and assumes the rubber-toughened matrix to possess certain effective properties in the presence of glass fibers. The actual fracture events as to whether there is a need for both fibers and rubbery phase to be present for toughening re- main unclear. It is understood that the presence of fibers reduces the stress borne by the matrix material, being 0022–2461 C  2002 Kluwer Academic Publishers 2659