Damage assessment and progression in a polyisocyanurate based continuous swirl mat composite

This research conducted in conjunction with Oak Ridge National Laboratories and the Automotive Composite Consortium, ACC, was motivated by the desire to reduce vehicle weight for increased efficiency. At present, there are no databases of failure mechanisms, experimental procedures to study failure, mathematical expressions for empirical or theoretical prediction of properties of a continuous swirl mat composite.CSMC. Therefore, to contribute to the increased utilization of this class of materials the following research was performed. This research enabled the failure mechanism to be formulated, development of a method to quantify failure based on ultrasonic attenuation maps, and the prediction of the fracture toughness parameter Kic.The use of scanning electron microscopy, light microscopy, and real-time tensile loading showed that the CSMC failed in a brittle mode. These techniques also provided imaging information as to how a dominant crack propagates in the presence of a continuously swirled E-glass mat reinforcement and voids. This evaluation enabled a reconstruction of failure in order to demonstrate a possible failure mechanism. The Aforementioned techniques revealed that the dominant crack follows the fiber/matrix interface, but may be influenced by the presence of voids. Voids have the tendency of luring the growing crack away from the interface. A growing crack would, however.return to a fiber/matrix interface until complete failure occurred.Another aspect of this work was the quantification of progressive damage using ultrasound. Comparisons were made between ultrasonic attenuation maps for unloaded and sequentially loaded specimens. The sequential loads were applied at different percentages of the ultimate tensile strength, UTS. This technique provided attenuation maps for a series of specimens with a controlled degree of damage, which showed an increase in attenuation with an increase in percent UTS.Fracture toughness experiments yielded an average K_IC value of 17.1 MPa√m,while the prediction of the fracture toughness parameter, K_IC, was achieved by combining K-solution expressions for in-line and parallel crack configurations while evaluating theneeded stress, σ, using of the "Rule of Mixtures". The average void length was used asthe crack length, which was obtained by light microscopy in conjunction with NIH™software. The predicted K_IC value at 40% glass fiber and void orientations of 45%, 30°and25°was 11.4 MPa√m, 17.0 MPa√m and 18.6 MPa√m, respectively.