Issue 48

T. Febra et alii, Frattura ed Integrità Strutturale, 48 (2019) 242-248; DOI: 10.3221/IGF-ESIS.48.25 247 Fig. 8 compares the results of the recovered energy obtained for the multi-impacts and the single impact tests. The results indicate that for low energy the effect of the insert fibre and of the previous impact is quite reduced. However, for impact energies above 6J, previous impacts significantly reduce the recovered energy and the impact energy for which the perforation was achieved. The BGFn mat insert promotes a slightly improved impact response for both series of tests. C ONCLUSIONS he present work studied the effect of the fiber type on the impact response of insert injection overmolding talc filled PP composites subjected to single impact and the multi-impacts tests, for which successive impacts with increasing energy were applied. The main conclusions that can be drawn were as follows: - For single impact tests, the highest impact energy required to achieve impactor perforation is obtained with Kevlar insert while the highest percentage of energy recovered is achieved with biaxial glass fiber netting. The maximum impact stiffness was obtained with Kevlar insert, with both glass fibre inserts achieving similar results. The maximum post-impact load was also obtained with Kevlar insert, while the minimum for the multiaxial glass fibre mesh; - For the multi-impact tests, the recovered energy and the dynamic stiffness show the same tendencies of the single impact tests. However, a significant difference was observed on the dynamic stiffness values for the multi-impacted specimens which decrease significantly after the peaking for an intermediate impact energy; - The comparison of the recovered energy obtained for the multi-impact and single impact tests show that for low energy the effect of the insert fibre and of the previous impact is quite reduced, while for impact energies above 6J previous impacts reduce significantly the recovered energy and the impact energy for which the perforation was achieved. A CKNOWLEDGMENTS he authors would like to acknowledge GECO-Moldes, Leiria, Portugal, for the supply of the samples and the sponsoring of this research by FEDER funds through the program COMPETE – Programa Operacional Factores de Competitividade – and by national funds through FCT – Fundação para a Ciência e a Tecnologia –, under the project UID/EMS/00285/2013. R EFERENCES [1] Carella, A.R., Alonso, C., Merino, J.C., Pastor, J.M. (2002). Sequential injection of thermo-plastic polymers. Analysis of processing parameters for optimal bonding conditions, Polym Eng Sci, 42, pp. 2172–2181. [2] Schellekens, M., Twene, D., Vander Waals, A. (2011). Block copolymers for waterborne coatings—a novel eco- friendly approach for improved coating adhesion to untreated polypropylene based plastics. Prog Org Coat, 72, pp. 138–143. DOI: 10.1016/j.porgcoat.2011.03.007 [3] Dondero, M., Pastor, J.M., Carella, J.M., Perez, C.J. (2009). Adhesion control for injection overmolding of polypropylene with elastomeric ethylene copolymers. Polym Eng Sci, 49, pp. 1 886–1893. [4] Nguyen, S., Perez, C.J., Desimone, M., Pastor, J.M., (2013). Overmolding of elastomeric propylene copolymers on polypropylene. Effects of block and random microstructures. International Journal of Adhesion & Adhesives, 46, pp 44–55. DOI: 10.1016/j.ijadhadh.2013.05.016 [5] Huang, D.Y., Chen, R.S. (1999). Bonding strength at solid-melt interface for polystyrene in a sequential two-staged injection molding process, Polym Eng Sci, 39, pp. 2159–2171. [6] Weng, D., Andries, J., Morin, P., Saunders, K., Politis, J. (2000). Fundamentals and material development for thermoplastic elastomer(TPE) overmolding. J Injection Molding Technol, 4, pp.22–28. [7] Richardson, M.O.W., Wisheart, M.J. (1996). Review of low-velocity impact properties of composite materials. Compos Part A-Appl S, 27, pp. 1123-1131. DOI: 10.1016/1359-835X(96)00074-7. [8] Lankford, J. (1997). Shear versus Dilatational Damage Mechanisms in the Compressive Failure of Fibre Reinforced Composites. Compos Part A-Appl S, 28, pp. 215-222. DOI: 10.1016/S1359-835X(96)00110-8. [9] Lee, S.H., Yerramalli, C.S., Waas, A.M. (2000). Compressive Splitting Response of Glass–fiber Reinforced Unidirectional Composites. Compos Sci Technol, 60, pp. 2957-2966. DOI: 10.1016/S0266-3538(00)00159-7. T T