Experimental Studies on Micro-fracture Mechanics of High-Temperature Polymer Matrix Composites

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The pupose of the present investigation is to study experimentally the micro-fracture process and mechanism of high-temperarture polymer matrix composite laminates under quasi-static monotonic and repeated fatigue loadings. Three diffirent types of microscopes with displacement-rate-controlled loading devices were used for in-situ microscopic observations of damage initiation and growth. Cross-ply laminates were chosen as basic laminate configurations for high-performance carbon fiber reinforced high-temperature epoxy composites. The damage evolution includes the following three stages : (1)Transverse crack initiation in transverse layrs, (2)Multiple transverse crack formation, and (3)Initiation and growth of delamination from tips of transverse cracks. Based on the above quantitative experimental results, some new theoretical models were proposed to predict the damage evolution.1. The tested CFRP materials include (1)a conventional 180ﾟC-cured TGDDM/DDS system (T300/3601), (2)an impro … More ved toughened system(T800H/3631), (3)an interlaminar-toughened system with interlaminar resin film layrs(T800H/3631-FM300), and(4)a new interlaminar-toughened system with nylon-particle-dispersed interlaminar layrs(T800H/3900-2). The laminate configurations were[0/90_n/0](n=4,8,12).2. In-situ microscopic observations were successfully conducted by a combination of an optical microscope(OM), a scanning electron microscope (SEM), and a scanning acoustic microscope (SAM) with each loading stage. The microscopic deformation and failure processes such as, (1)transverse crack initiation in transverse layrs, (2)multiple transverse crack formation, and(3)initiation and growth of delamination from tips of transverse cracks, were observed at 20ﾟC and 80ﾟC to study the temperatue effects.3. A new evolution law for transverse crack development was proposed based on the statistical strength distribution of 90ﾟlayrs. A new evolution law for delamination from tips of transverse cracks was also proposed based on the energy balance concept. Both theoretical preditions were found to be sufficiently valid to explain the quantitative experimental results. An interaction between transverse cracks and delaminations was also considered for better prediction. These theories were also extended for fatigue-loaded specimens. Less