Impact Delamination and Fracture in Aluminum/Acrylic Sandwich ...

ConclusionsFrom this study one can conclude that• impact damage in acrylic is very sensitive to impactheight (hence impact velocity) and temperature;• though providing certain shielding for impact, aluminumface sheets can not prevent delamination and fracturefrom happening;• delamination occurs before cracking if aluminum shieldis on top of acrylic whereas cracking precededdelamination if acrylic is struck first;• simple theory of stress wave propagation can be used toexplain the formation of radial and ring cracks.AcknowledgmentsThis study was supported by NASA Faculty Award forResearch (FAR) under Grant No. NAG3-2259 and byPSC-CUNY under Grants 69394-00 29 and 61429-00 01.Dr. Kenneth J. Bowles is the Technical Monitor of the NASAgrant. Part of the equipment used in this investigation wasacquired through Army Research Office Grant No. DAAD19-99-1-0366.References1. J. R. Vinson, Behavior of Sandwich Structures ofIsotropic and Composite Materials, TechnomicPublishing Co., Lancaster, PA, 1999.2. S. A. Ambartsumyan, Theory of Anisotropic Plates:Strength, Stability, vibration, Technomic Publishing Co.,Stamford, CT, 1970.3. A. Leissa, Vibration of Plates, Reprinted Edition,Acoustical Society of America, 1993.4. Y.-Y. Yu, Vibrations of Elastic Plates, Springer-Verlag,New York, 1996.5. N. Jones, Structural Impact, Cambridge UniversityPress, Cambridge, UK, 1989.6. S. Abrate, Impact on Composite Structures, CambridgeUniversity Press, Cambridge, UK, 1998.7. C. Hiel, D. Dittman, and O. Ishai, “Composite sandwichconstruction with syntactic foam core: A practicalassessment of post-impact damage and residualstrength,” Composites, Vol. 24, No. 5, pp. 447-450,1993.8. T. Gottesman, S. Grishovich, E. Drukker, N. Sela, and J.Log, “Residual strength of impacted composite: analysisand tests,” J. Composites Technology and Research,Vol. 16, No. 3, pp. 244-255, 1994.9. A. Vlot, “Impact Properties of fiber metal laminates,”Composite Engineering, Vol. 3, No. 10, pp. 911-927,1993.10. A. N. Nayfeh, Wave Propagation in Layered AnisotropicMedia with Applications to Composites, ElsevierScience, Amsterdam, The Nethelands, 1995.11. W. D. Callister, Jr., Materils Science and Engineering:An Introduction, 5th Ed., Wiley, New York, 2000.1.25” 1.5”Figure 1. Damage patterns of cast acrylic impacted by aweight dropped from different heights at roomtemperature.Load (N)1400900400-100LoadEnergy1.25 inch drop1.5 inch drop0 2 4 6 8 10 12Time (ms)Figure 2. Time histories of loading and energy of a purecast acrylic plate impacted at room temperatureby a weight dropped from different heights.1” 2” 3”Figure 3. Damage patterns of cast acrylic with aluminumshielding on top impacted by a weight droppedfrom different heights at room temperature.2.52.01.51.00.50.0Energy (J)517

Load (N)40003000200010000-1000EnergyLoad1 inch drop2 inch drop3 inch drop0 5 10 15 20Time (ms)Figure 4. Time histories of loading and energy of a castacrylic plate with aluminum shielding on topimpacted at room temperature by a weightdropped from different heights.2520151050Energy (J)180°F 205°FFigure 7. Damage patterns of cast acrylic at varioustemperatures impacted by a weight dropped from5”.Load (N)240019001400900400-100LoadEnergy180 F205 F0 5 10 15 20Time (ms)1086420Energy (J)Figure 8. Time histories of loading and energy of a purecast acrylic specimen impacted at varioustemperatures by a weight dropped from 5”.3001” 3” 5”Figure 5. Damage patterns of cast acrylic with aluminumsupport from bottom impacted by a weightdropped from different heights at roomtemperature.Load (N)500040003000200010000-1000LoadE n e yEnergy1 inch drop3 inch drop5 inch drop0 5 10 15 20Time (ms)50403020100Energy (J)Crack length (mm)2502001501005000 25 50 75 100 125 150 175 200 225 250Temperature (F)Figure 9. Temperature effect on total crack length in a purecast acrylic specimen impacted by a weightdropped from 5”.Figure 6. Time histories of loading and energy of a castacrylic plate with aluminum support from bottomimpacted at room temperature by a weightdropped from different heights.518