Issue 48

O. A. Mocian et alii, Frattura ed Integrità Strutturale, 48 (2019) 230-241; DOI: 10.3221/IGF-ESIS.48.24 240 preferable? It looks like each normalized parameter gives specific information on the sandwich response and therefore the obtained information from all of them must be corroborated. At lower impact speeds composite facesheets do better than the aluminum ones; more rigid the facesheet and core (type C and PUR) are, the outcome is that the composite panel is surpassing the aluminum one in terms of SEA, but not so evidently for NAE and CFE. At the highest impact speed of 4 m/s the parameter SEA is about the same for both types of facesheets, NAE increases using aluminum facesheets and CFE decreases. (4) For composite facesheets panels the damaged area of the top facesheet is reduced if the facesheet is stiffer – type C versus type A, and by using the more rigid core – PUR versus PS. On the bottom facesheet, in the cases without perforation at 3 and 3.5 m/s, an important decrease of the damaged surface is produces by using PUR foam core instead of PS foam core (more than 3 times for type C facesheet at 3 m/s). At 4 m/s perforation of bottom facesheet is almost produced even for type C facesheet and the surface of the damaged area is greater for PS foam core than for PUR foam core, actually about the same regardless the type of the composite facesheet for each foam core type. A CKNOWLEDGEMENTS iss Oana Alexandra Mocian acknowledges the PhD student scholarship given by the Ministry of National Education from Romania through the contract no. 06.40/2014 which made possible the present researches. All the authors acknowledge that this work was supported by a grant from the Romanian National Authority for Scientific Research and Innovation, CCCDI-UEFISCDI, project number 11/2015. R EFERENCES [1] Gilioli, A., Sbarufatti, C., Manes, A., Giglio, M. (2014). Compression after impact test (CAI) on NOMEX™ honeycomb sandwich panels with thin aluminum skins, Compos. Part B-Eng., 67, pp. 313-325. DOI: 10.1016/j.compositesb.2014.07.015. [2] Zhang, Y., Zong, Z., Liu, Q., Ma, J., Wu, Y., Li, Q. (2017). Static and dynamic crushing response of CFRP sandwich panels filled with different reinforced materials, Mater. Design, 117, pp. 396-408, DOI: 10.1016/j.matdes.2017.01.010. [3] Tan, C.Y., Akil, H.M. (2012). Impact response of fiber metal laminate sandwich composite structure with polypropylene honeycomb core, Compos. Part B-Eng., 43, pp. 1433-1438, DOI: 10.1016/j.compositesb.2011.08.036. [4] Wang, H., Ramakrishnan, K.R., Shankar, K. (2016). Experimental study of the medium velocity impact response of sandwich panels with different cores, Mater. Design, 99, pp. 68-82, DOI: 10.1016/j.matdes.2016.03.048. [5] Wei, K., Peng, Y., Qu, Z., He, R., Cheng, X. (2017). High temperature mechanical behaviors of lightweight ceramic corrugated core sandwich panels, Compos. Struct., 176, pp. 379-386, DOI: 10.1016/j.compstruct.2017.05.053. [6] Jing, L., Xi, C., Wang, Z., Zhao, L. (2013). Energy absorption and failure mechanism of metallic cylindrical sandwich shells under impact loading, Mater. Design, 52, pp. 470-480, DOI: 10.1016/j.matdes.2013.05.090. [7] Zhang, S., Dulieu-Barton, J.M., Thomsen, O.T. (2015). The effect of temperature on the failure modes of polymer foam cored sandwich structures, Compos. Struct., 121, pp. 104-113, DOI: 10.1016/j.compstruct.2014.10.032. [8] McShane, G.J., Radford, D.D., Deshpande, V.S., Fleck, N.A. (2006). The response of clamped sandwich plates with lattice cores subjected to shock loading, Eur. J. Mech. A-Solids, 25, pp. 215-229, DOI: 10.1016/j.euromechsol.2005.08.001. [9] Jover, N., Shafiq, B., Vaidya, U. (2014). Ballistic impact analysis of balsa core sandwich composites, Compos. Part B- Eng., 67, pp. 160-169, DOI: 10.1016/j.compositesb.2014.07.002. [10] Birman, V., Kardomateas, G.A. (2018). Review of current trends in research and applications of sandwich structures, Compos. Part B-Eng., 142, pp. 221-240, DOI: 10.1016/j.compositesb.2018.01.027. [11] Chai, G.B., Zhu, S. (2011). A review of low-velocity impact on sandwich structures, P. I. Mech. Eng. L-J. Mat., 225(4), pp. 207-230, DOI: 10.1177/1464420711409985. [12] Pathipaka, R.K., Namala, K.K., Sunkara, N., Bandaru, C.R. (2018). Damage characterization of sandwich composites subjected to impact loading, J. Sandw. Struct. Mater., DOI: 10.1177/1099636218792717. [13] Siivola, J.T., Minakuchi, S., Mizutani, T., Takeda, N. (2016). Evaluation of damage detectability in practical sandwich structure application conditions using distributed fiber optic sensor, Struct. Health Monit., 15, pp. 3-20, DOI: 10.1177/1475921715620002. [14] Akatay, A., Bora, M.O., Coban, O., Fidan, S., Tuna, V. (2015). The influence of low velocity repeated impacts on residual compressive properties of honeycomb sandwich structures, Compos. Struct., 125, pp. 425-433, M