Selim Yalvac

Transverse Cracking and Stiffness Reduction in Cross Ply Laminates of Different Matrix Toughness

Cross ply laminates of (02,902)s configuration having AS4 graphite fibers in three epoxy resins of different toughness: 3501-6, Tactix® 556 and Tactix® 695, have been tested to determine their transverse cracking behavior and the associated mechanical response under longitudinal tensile loading. The test data are analyzed using Talrejas con tinuum damage model [1-3]. The material constants needed in the model to predict the in- plane stiffness changes are determined. The measured Poissons ratio, which shows signifi cant change, is compared with the prediction of the model. The constants for the three materials are found to increase with the increase in their fracture toughness.

Transverse Ply Cracking in Toughened and Untoughened Graphite/Epoxy and Graphite/Polycyanate Crossply Laminates

Transverse ply cracking of five toughened and untoughened graphite/epoxy and graphite/polycyanate laminates was studied using crossply laminates. Two different theoretical approaches, variational mechanics and resistance curves based on shearlag approximation, were used to analyze the data. Resistance of the laminates to transverse ply cracking was determined. Both theories show the same ranking of the laminates with respect to their resistance to microcracking. These results were compared with the critical strain energy release rate data obtained on the resins and the laminates.

Development and application of an impact fatigue test

Abstract Multiplicity of impacts experienced by a material prior to its failure is reflected in the term “impact fatigue”. In order to overcome difficulties of the existing impact testing methodology, it is suggested here that the test specimen should be rigidly attached to the support so that the global flat shape of a specimen does not change during repeated impacts. In the course of this work low-energy impact fatigue performance of four thermoplastic materials was compared. Using the insight gained with the thermoplastics, the investigation was extended to study the role of a particulate reinforcement on the impact tolerance of thermoset composites. Syntactic composites of various compositions were used as the model system. Results of this work point to the possibility of improving damage tolerance through the introduction of a particulate reinforcement.