Characterization of Tensile Damage for a Short Birch Fiber-reinforced Polyethylene Composite with Acoustic Emission

A biocomposite was prepared using paper industry wood fibers (birch) mixed with a thermoplastic matrix of linear low-density polyethylene (LLDPE) at various fiber weights. Monotonie and load-unload tensile tests were performed at room temperature. The acoustic emission (AE) technique was used to characterize microstructural damage events leading to overall failure of the biocomposite. The behavior evolution (stress/strain) of the biocomposite appears to be correlated with the evolution of the AE cumulative energy, exhibiting four phases. The failure mechanisms in the short fiber-reinforced thermoplastic composites were identified using a neural network based on a Kohonen non-supervised self-organizing map (KSOM). Three parameters of the AE burst signals (amplitude, count and duration) were found to be very useful in classifying damage modes. As a result, a new damage mode definition is proposed based on a neural network with three parameters. The participation of each mode in the final failure was evaluated. The results indicated that fiber content plays a primary role in biocomposite failure. This finding has been further supported by scanning electron microscopy (SEM) micrographs of the fractured face.