Comparative Study between Impact Behaviors of Composites with Aluminum Foam and Honeycomb

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1 Send Orders for Reprints to Current Nanoscience, 2014, 10, Comparative Study between Impact Behaviors of Composites with Aluminum Foam and Honeycomb Y.C. Kim and J.U. Cho * Department of Mechanical & Automotive Engineering, Kongju National University, Cheonan-si, Republic of Korea Abstract: The need for composites has been growing in various industries because it has high mechanical properties for weight as well as superior stiffness and strength. The composites addressed in this study are multi-pore aluminum foam and honeycomb whose have excellent impact energy-absorption capability. In this study, impact tests of aluminum foam and honey core sandwich composite with porous core are conducted in a bid to examine its mechanical properties. Different impact energies such as 50J, 70J, and 100J are applied to these specimens. The greater the impact energy is the shorter the duration of the maximum load. Maximum load is higher at foam than at honeycomb sandwich. At 50J test, the striker damages on the lower face at honeycomb but it does not damage at foam. At 70J test, it penetrates the specimen of composite at honeycomb but it does not penetrate at foam. On comparative study between impact behavior results of aluminum foam and honey core sandwich composite with porous core, stiffness at aluminum foam sandwich is superior than at aluminum honeycomb sandwich. The stabilities on aluminum foam and honeycomb core composite structure can be predicted by use of this experimental result. Keywords: Aluminum foam, aluminum honeycomb, composite, damage, impact energy, stiffness. 1. INTRODUCTION The requirement for metallic material has become increasingly severe, complex, and diverse [1-3]. A single material alone can hardly satisfy the requirements in properties such as rigidity, anticorrosion, abrasion-resistance, lightweight, heat-resistance, and sound insulation; thus, the study to satisfy the requirements in such a way of combining the materials has been underway [4]. As the composite material has superior mechanical properties as well as specific rigidity and strength, the need for it in automobile and aviation industry and for various structures has continued to grow [4-6]. A composite is a material produced by combining-forming 2 or more different materials so as to have unique properties which a single material lacks. It is the material produced by macroscopically combining two or more materials which are different in component or in shape [7]. As they usually have superior mechanical properties as well as specific rigidity and strength, the need in a wide range of industries has continued growing [8]. Among multi-pore materials, the core of aluminum foam or honeycomb can be controlled which also enables the control of density or maximum bearing load depending on intended use [9]. In this study, an impact experiments of foam core sandwich with porous cores and aluminum honeycomb core sandwich are conducted to examine its mechanical properties. The specimens are sandwich composites with aluminum foam and honeycomb cores where various impact energies such as 50J, 70J, and 100J were applied. By comparing the experimental impact results of aluminum honeycomb and foam core sandwich, the stability on composite structure with aluminum honeycomb or foam core sandwich can be predicted. The static bending test is introduced to apply the foam to obtain the other mechanical properties. 2. EXPERIMENT RESULTS Table 1 shows the material property of foam core and honeycomb core sandwich composite materials used in this experiment. Fig. (1) shows specimens of Al foam core and honeycomb core sandwich. The dimension of foam or honeycomb core sandwich *Address correspondence to this author at the Department of Mechanical & Automotive Engineering, Kongju National University, Cheonan-si, Republic of Korea; jucho@kongju.ac.kr Fig. (1). Specimens of Al foam core (a) and honeycomb core sandwich (b). specimen are shown in Fig. (2). The thickness of face sheet is 1 mm, its total height was 20mm, and its length and width are both 100mm. The adhesive agent used at manufacturing specimen has the adhesive strength of 0.4MPa as spray type. Its major components are add to isohexane, cyclohexane and SBR Latex Polymer. As the method bonding with core and face sheet, adhesive agent is spread to the adhesive surface with the layer of 0.2mm. 1 hour later, it is spread to the adhesive surface with the layer of 0.2mm once again. And then two specimens are bonded each other. After bonding, the thickness of adhesive agent between core and face sheet becomes 0.3 to 0.4mm as compressed state. More than 24 hours later after bonding, the experiment is carried out. The test using this striker is for 50J, 70J, and 100J impact energy. This experimental setup was set on the impact testing machine of Intron s Dynatup 9250 HV with the impact applied to the specimens by using a striker /14 $ Bentham Science Publishers

2 24 Current Nanoscience, 2014, Vol. 10, No. 1 Kim and Cho Table 1. Characteristics of Foam Core and Honeycomb Core Sandwich Composite Materials Foam Core Sandwich Honeycomb Core Sandwich Material of face sheet Al-3003 Al-3003 Material of core Al-foam Al-3003 Mass of specimen 128g 78g Density of core 0.4g/cm 0.18g/cm Fig. (2). Dimensions of test specimen Result after Applying 50J Impact Energy Fig. (3) shows the cutting faces of Al foam core and honeycomb core sandwich specimens after applying 50J impact energy. The striker penetrated 12mm in case of specimen (a), and 21mm in specimen (b), showing that the striker generally caused damage to the middle of the core, penetrating the upper face sheet, but not damaging the lower face sheet. Fig. (4) shows the result in load and energy graph over the time after applying 50J impact energy to the Seeing the graph, maximum load appeared at 4.2ms with all specimens (a) and (b). Maximum load on specimen was 4.8KN on (a), and 4.5KN on (b) when the striker was penetrating upper face sheet before being gradually reduced. About 50J energy was applied during 15ms (a). About 40J energy was applied during 15ms (b). At the impact experiments of 50J, Such penetration up to 10mm caused the damage to the core, but not to the lower face sheet in case of aluminum foam. But this penetration up to 21mm caused the damage to the lower face sheet after penetrating the upper face sheet and the core in case of honeycomb core sandwich. At the impact experiments of 50J, the maximum loads in case of of aluminum foam become higher than honeycomb core sandwichs. penetrated 19mm in case of specimen (a) and 25mm in specimen (b). Viewing the result, the striker caused the damage to the core completely after penetrating the upper face sheet when applying 70J, unlike the case of 50J. Fig. (6) shows the result in load and energy graph over the time after applying 70J impact energy to the Seeing the graph, maximum load appeared at 3.5ms with all specimens (a) and (b). Maximum load on specimen was 5.5KN on (a) and 4.5KN on (b) when the striker was penetrating upper face sheet but it then reduced to 10ms (a) and 9ms (b) before increasing again significantly. Specimen (a) showed a gradual decrease before rising again. About 70J energy was applied during 15ms. Such increase seemed to be attributable to penetrating or causing severe damage to the lower face sheet. About 60J energy was applied during 15ms. At the impact experiments of 70J, the striker was penetrating the upper face sheet. It caused the damage to the lower face sheet at 10ms after penetrating the core in case of of aluminum foam. But it caused damage to the lower face sheet or penetrated at 14ms after going past the core in case of honeycomb core sandwich. At the impact experiments of 70J, the maximum loads in case of of aluminum foam become higher than honeycomb core sandwichs. Fig. (3). Cutting faces of Al foam core (a) and honeycomb core (b) sandwich composite after applying 50J impact energy Result after Applying 70J Impact Energy Fig. (5) shows the cutting faces of Al foam core and honeycomb core specimens after applying 70J impact energy. The striker Fig. (4). The graph showing the result after applying 50J impact energy to Al foam core (a) and honeycomb core (b) sandwich composite.

3 Comparative Study between Impact Behaviors Current Nanoscience, 2014, Vol. 10, No Fig. (5). Cutting faces of Al foam core (a) and honeycomb core (b) sandwich composite after applying 70J impact energy. which means it penetrated all of upper face sheet, core, and lower face sheet. Viewing such result comprehensively, the striker completely penetrated the specimen when 100J impact energy was applied, whereas it caused a slight damage to the lower face sheet when 70J was applied. Fig. (8) shows the result in load and energy graph over the period when 100J impact energy was applied to the Seeing the graphs of (a) and (b) on the specimens of Al foam core and honeycomb core sandwich, maximum loads appeared at 3.0ms, indicating 4.8KN on (a) and 4.6KN on (b), which were then rapidly reduced during the penetration of lower face sheet and then showed the second highest load at 10ms as that at 3ms, indicating 4.8KN on (a) and 4KN on (b), penetrating the lower face sheet. After penetrating the lower face sheet, it's rapidly reduced again as the case after penetrating the core. About 100J energy was also applied during 15ms. At the impact experiments of 100J, the maximum loads in case of aluminum foam become higher than honeycomb core sandwichs. By comparing the experimental impact results of aluminum honeycomb and foam core sandwich, stiffness at aluminum foam sandwich is superior than at aluminum honeycomb sandwich. Fig. (6). The graph showing the result after applying 70J impact energy to Al foam core (a) and honeycomb core (b) sandwich composite. Fig. (8). The graph showing the result after applying 100J impact energy to the specimen of Al foam core (a) and honeycomb core (b) sandwich composite. Fig. (7). Cutting faces of Al foam core (a) and honeycomb core (b) sandwich composite after applying 100J impact energy Result after Applying 100J Impact Energy Fig. (7) shows the cutting faces of the specimens after applying 100J impact energy to the specimen of Al foam core and honeycomb core sandwich composite. The striker penetrated 29mm deep Finally, the static bending test is also introduced to apply the foam to obtain the other mechanical properties. Fig. (9) shows the dimensions of the static bending test specimen. Four specimens with a height (h) of 25mm to 40mm at 5mm intervals are fabricated to specimen heights of 25, 30, 35, and 40mm and classified by cases 1, 2, 3, and 4, respectively. The length of the specimen is 200mm and the width is 25mm. Load block is designed with 30mm length and 25mm height and a 10mm hole in load-block and 25mm initial crack are provided [10]. MTS Landmark tester is used for the test. The test data is produced using a computer and the experimental scenes of each specimen are photographed using a camcorder. As seen in Fig. (10), the adhesive agent used at manufacturing specimen has the adhesive strength of 0.4MPa as spray type. The tape indicating the number and crack length is on the specimen. To obtain more accurate test data, a number of aluminum foam specimens by case are fabricated by FOAMTECH Co. and the mean

4 26 Current Nanoscience, 2014, Vol. 10, No. 1 Kim and Cho Fig. (9). Dimension of the specimen. Fig. (12). Graph of reaction force due to time. Fig. (10). Boundary condition of experiment. value of the test is calculated and evaluated. The specimen is tied to the jig connected to the load cell and the test is carried out using a displacement controlled method. Displacement is vertically imposed on the bottom load cell only and the displacement speed is set at 30mm/min. According to the test result, the adhered part is segregated to the end of the specimen as indicated in Fig. (11). Fig. (13). Graph of energy due to displacement. Fig. (11). Segregated form of specimens. Fig. (12) is the graph showing the variation of reaction force depending on displacement of the specimen. In general, the higher the h, the height of the beam, the greater the maximum load. Fig. (13) is the graph showing the variation of energy depending on displacement on load line. The formula to calculate the P energy is stipulated in Equation 1: E = P (1) P is the energy pulled on load line in order to separate two bonded specimens. As seen in Fig. (8), data analysis indicates the higher the h, the height of the beam, the greater the energy. 3. CONCLUSIONS In this study, impact behavior results of aluminum foam and honey core sandwich composite with porous core are compared. Aluminum foam and honeycomb core sandwich composites can be applied to a variety of industries, and predictions of structural stability and verification are available. This study results from the impact tests of these composites are outlined as follows; 1) The point of time when the maximum load occurred was 4.2ms for 50J, 3.5ms for 70J, and 3ms for 100J, indicating that the greater the impact energy was the shorter the duration of the maximum load. 2) At the impact experiments of 50J, 70J and 100J, the maximum loads in case of of aluminum foam become higher than honeycomb core sandwichs. 3) At the impact experiments of 50J, Such penetration up to 10mm caused the damage to the core, but not to the lower face sheet in case of aluminum foam. But this penetration up to 21mm caused the damage to the lower face sheet after penetrating the upper face sheet and the core in case of honeycomb core sandwich. At the impact experiments of 70J, the striker was penetrating the upper face sheet. It caused the damage to the lower face sheet at 10ms after penetrating the core in case of of aluminum foam. But it caused damage to the lower face sheet or penetrated at 14ms after going past the core in case of honeycomb core sandwich. 4) At the impact experiments of 100 J in case of aluminum foam and honeycomb core sandwich composites, the maximum load

5 Comparative Study between Impact Behaviors Current Nanoscience, 2014, Vol. 10, No occurred at 3.0ms with 100J when the striker was penetrating the upper face sheet. It penetrated the lower face sheet at 10ms after penetrating the upper face sheet and the core. 5) On the experimental impact result, stiffness at aluminum foam sandwich is superior than at aluminum honeycomb sandwich. The static bending test is introduced to apply the foam to obtain the other mechanical properties. CONFLICT OF INTEREST The authors confirm that this article content has no conflicts of interest. ACKNOWLEDGEMENTS This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science, and Technology ( ). This work was supported by National Research Foundation through the Joint Research Program (Grant No. D00004). REFERENCES [1] Kim, T.W.; Kim, B.J.; Kim, Y.; Kim, H.I. Density and geometric characteristic of aluminum form for shock absorption performance, Annual Conference of KSME, Pyeongchang, Rep. of Korea, 2007, 12(1), pp [2] Kim, S.S.; Han, C.H.; Jang, J.S. Effects of the Sintering Variable on Impact Energy in MA 316L ODS and Wet 316L ODS Stainless Steels. J. Korean Powder Metall. Inst., 2010, 17(2), [3] Woo, K.D.; Kang, D.S.; Kim, S.H.; Park, S.H.; Kim, J.Y.; Ko, H.R. Microstructure and mechanical properties of nano-sized Ti-35%Nb-7%Zr-10% CPP composite fabricated by pulse current activated sintering. J. Korean Powd. Metall. Inst., 2011, 18(2), [4] Lee, S.K.; Cho, C.D.; Cho, J.U.; Bang, S.O. In-plane characteristics of Al foam core and Al honeycomb core sandwich composites with an indented damage, Annual Conference of KSME, Jeju, Rep. of Korea, 2011, 1, pp [5] Ramamurty, U.; Kumaran, M.C. Mechanical property extraction through conical indentation of a closed-cell aluminum foam. Acta Mater., 2004, 52(1), [6] Zhou, J.; Soboyejo, W.O. Compression compression fatigue of open cell aluminum foams: macro-/micro- mechanisms and the effects of heat treatment. Mater. Sci. Eng. A, 2004, 369(1-2), [7] Ohno, N.; Okumura, D.; Niikawa, T. Long-wave buckling of elastic square honeycombs subject to in-plane biaxial compression. Int. J. Mech. Sci., 2004, 46(11), [8] Zhu, H.X.; Thorpe, S.M.; Windle, A.H. The effect of cell irregularity on the high strain compression of 2D Voronoi honeycombs. Int. J. Solids Struct., 2006, 43(5), [9] Santosa, S.; Wierzbicki, T. Crash behavior of box columns filled with aluminum honeycomb or foam. Comput. Struct., 1998, 68, [10] Cho, J.U.; Kinloch, A.; Blackman, B.; Rodriguez, S.; Cho, C.D.; Lee, S.K. Fracture behavioure of adhesively-bonded composite materials under impact loading. Int. J. Prec. Eng. Manuf., 2010, 11(1), Received: May 3, 2012 Revised: February 14, 2013 Accepted: April 30, 2013