An experimental study is performed to investigate the tensile failure and fracture behavior of polymer foam containing discontinuities. PVC corecell foam, series A800 and A1200 is used for the investigation. Unnotched dog-bone specimen and specimens with center hole and edge cracks are tested under uniaxial tensile loading. Series of experiments are conducted at different defect size to width ratios, and the effect of the defect size on the net-section tensile strength of the foam is investigated. A fracture study is also conducted, and the effect of density and loading rate on the fracture behavior of foam is investigated. A minimal notch-strengthening effect is observed in specimens with center hole, and a notch-weakening effect is observed in specimen with edge notches. Furthermore, the fracture toughness increases with the increase in the foam density and decreases with the increase in loading rate. 1. Introduction Polymer foams are widely used in lightweight structures, such as core material for sandwich structures, due to their superior blast mitigation and impact resisting behavior. Currently, sandwich structures are among the lightweight structures widely used in aerospace, navy, and other related industries. Polymer foams have shown promising results as a core material for sandwich structures due to their high energy absorption capabilities, especially in the case of impact loading [1, 2]. There are well documented studies on the compressive properties and energy absorbing behavior of these materials [3]. It is shown that the structural response of a polymer foam strongly depends on the foam density, cell microstructure, and solid polymer properties [3]. Recent developments in the manufacturing processes of polymer foams contribute to the expansion of these materials in structural applications. Some of the applications involve cutout and holes. It is well understood that, in the case of a structure with a fully dense material, the presence of cracks, notches, and holes results in a stress concentration that leads to fracture. To understand these phenomena, the fracture behavior of polymers has been studied by different researcher including the early work of McIntyre and Anderton [4] and others [5–7]. McIntyre and Anderton [4] investigated the fracture toughness of a rigid polyurethane foam over a range of densities and found that the fracture toughness increases with density. The fatigue crack growth in the polyurethane foam has been investigated by Noble and Lilley [8]. The fracture process occurring in rigid, closed-cell polyurethane foam has
References
[1]
M. E. Kabir, M. C. Saha, and S. Jeelani, “Tensile and fracture behavior of polymer foams,” Materials Science and Engineering A, vol. 429, no. 1-2, pp. 225–235, 2006.
[2]
E. Wang, N. Gardner, and A. Shukla, “The blast resistance of sandwich composites with stepwise graded cores,” International Journal of Solids and Structures, vol. 46, no. 18-19, pp. 3492–3502, 2009.
[3]
L. J. Gibson and M. F. Ashby, Cellular Solids: Structure and Properties, Cambridge University, Oxford, UK, 2nd edition, 1997.
[4]
A. McIntyre and G. E. Anderton, “Fracture properties of a rigid polyurethane foam over a range of densities,” Polymer, vol. 20, no. 2, pp. 247–253, 1979.
[5]
C. W. Fowlkes, “Fracture toughness tests of a rigid polyurethane foam,” International Journal of Fracture, vol. 10, no. 1, pp. 99–108, 1974.
[6]
M. E. Kabir, M. C. Saha, and S. Jeelani, “Tensile and fracture behavior of polymer foams,” Materials Science and Engineering A, vol. 429, no. 1-2, pp. 225–235, 2006.
[7]
M. A. El-Hadek and H. V. Tippur, “Dynamic fracture behavior of syntactic epoxy foams: optical measurements using coherent gradient sensing,” Optics and Lasers in Engineering, vol. 40, no. 4, pp. 353–369, 2003.
[8]
F. W. Noble and J. Lilley, “Fatigue crack growth in polyurethane foam,” Journal of Materials Science, vol. 16, no. 7, pp. 1801–1808, 1981.
[9]
T. Cotgreave and J. B. Shortall, “The fracture toughness of reinforced polyurethane foam,” Journal of Materials Science, vol. 13, no. 4, pp. 722–730, 1978.
[10]
T. C. Cotgreave and J. B. Shortall, “The mechanism of reinforcement of polyurethane foam by high-modulus chopped fibres,” Journal of Materials Science, vol. 12, no. 4, pp. 708–717, 1977.
[11]
H. Fusheng and Z. Zhengang, “The mechanical behavior of foamed aluminum,” Journal of Materials Science, vol. 34, no. 2, pp. 291–299, 1999.
[12]
E. Amsterdam, P. R. Onck, and J. T. M. de Hosson, “Fracture and microstructure of open cell aluminum foam,” Journal of Materials Science, vol. 40, no. 22, pp. 5813–5819, 2005.
[13]
B. John, C. P. R. Nair, K. A. Devi, and K. N. Ninan, “Effect of low-density filler on mechanical properties of syntactic foams of cyanate ester,” Journal of Materials Science, vol. 42, no. 14, pp. 5398–5405, 2007.
[14]
E. Woldesenbet, N. Gupta, and A. Jadhav, “Effects of density and strain rate on properties of syntactic foams,” Journal of Materials Science, vol. 40, no. 15, pp. 4009–4017, 2005.
[15]
L. Liu and F. H. Samuel, “Effect of inclusions on the tensile properties of Al-7% Si-0.35% Mg (A356.2) aluminium casting alloy,” Journal of Materials Science, vol. 33, no. 9, pp. 2269–2281, 1998.
[16]
L. Marsavina, E. Linul, T. Voiconi, and T. Sadowski, “A comparison between dynamic and static fracture toughness of polyurethane foams,” Polymer Testing, vol. 32, pp. 673–680, 2013.
[17]
V. Rizov, “Characterization of low-velocity impact fracture behavior of rigid foam by single edge notched bend specimens,” Solids and Structures, vol. 2, no. 1, pp. 1–8, 2013.
[18]
E. W. Andrews and L. J. Gibson, “The influence of cracks, notches and holes on the tensile strength of cellular solids,” Acta Materialia, vol. 49, no. 15, pp. 2975–2979, 2001.
[19]
E. W. Andrews and L. J. Gibson, “The influence of crack-like defects on the tensile strength of an open-cell aluminum foam,” Scripta Materialia, vol. 44, no. 7, pp. 1005–1010, 2001.
[20]
A. Paul, T. Seshacharyulu, and U. Ramamurty, “Tensile strength of a closed-cell Al foam in the presence of notches and holes,” Scripta Materialia, vol. 40, no. 7, pp. 809–814, 1999.
[21]
N. A. Fleck, O. B. Olurin, C. Chen, and M. F. Ashby, “The effect of hole size upon the strength of metallic and polymeric foams,” Journal of the Mechanics and Physics of Solids, vol. 49, no. 9, pp. 2015–2030, 2001.
[22]
K. R. Mangipudi and P. R. Onck, “Notch sensitivity of ductile metallic foams: a computational study,” Acta Materialia, vol. 59, no. 19, pp. 7356–7367, 2011.
[23]
J. W. Dally and R. J. Sanford, “Strain-gage methods for measuring the opening-mode stress-intensity factor, KI,” Experimental Mechanics, vol. 27, no. 4, pp. 381–388, 1987.
[24]
J. R. Berger and J. W. Dally, “An overdeterministic approach for measuring KI using strain gages,” Experimental Mechanics, vol. 28, no. 2, pp. 142–145, 1988.
[25]
T. L. Anderson, Fracture Mechanics: Fundamentals and Applications, Taylor and Francis Group, 3rd edition, 2005.
[26]
L. Rubio, J. Fernández-Sáez, and C. Navarro, “Determination of dynamic fracture-initiation toughness using three-point bending tests in a modified hopkinson pressure bar,” Experimental Mechanics, vol. 43, no. 4, pp. 379–386, 2003.
[27]
A. Kidane and A. Shukla, “Quasi-static and dynamic fracture initiation toughness of Ti/TiB layered functionally graded material under thermo-mechanical loading,” Engineering Fracture Mechanics, vol. 77, no. 3, pp. 479–491, 2010.
[28]
L. Wang, K. Labibes, Z. Azari, and G. Pluvinage, “Generalization of split Hopkinson bar technique to use viscoelastic bars,” International Journal of Impact Engineering, vol. 15, no. 5, pp. 669–686, 1994.
[29]
H. Zhao, G. Gary, and J. R. Klepaczko, “On the use of a viscoelastic split Hopkinson pressure bar,” International Journal of Impact Engineering, vol. 19, no. 4, pp. 319–330, 1997.
[30]
A. Sharma and A. Shukla, “Mechanical characterization of soft materials using high speed photography and split hopkinson pressure bar technique,” Journal of Materials Science, vol. 37, no. 5, pp. 1005–1017, 2002.
[31]
D. T. Casem, W. Fourney, and P. Chang, “Wave separation in viscoelastic pressure bars using single-point measurements of strain and velocity,” Polymer Testing, vol. 22, no. 2, pp. 155–164, 2003.
