- Email: [email protected]
Uni-directional porous metal fabricated by rolling of copper sheet and explosive compaction
Materials Letters 170 (2016) 39–43
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Uni-directional porous metal fabricated by rolling of copper sheet and explosive compaction Matej Vesenjak a,n, Kazuyuki Hokamoto b, Shohei Matsumoto c, Yasuo Marumo c, Zoran Ren a a
Faculty of Mechanical Engineering, University of Maribor, Smetanova 17, 2000 Maribor, Slovenia Institute of Pulsed Power Science, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan c Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan b
art ic l e i nf o
a b s t r a c t
Article history: Received 12 November 2015 Received in revised form 12 January 2016 Accepted 30 January 2016 Available online 1 February 2016
A new type of porous metal with uni-directional pores (UniPore) has been developed using the explosive compaction fabrication process of rolled copper foil with plastic spacers. The interface bonding in the novel UniPore metal structure has been investigated by metallographic analysis. The mechanical properties of the new rolled UniPore specimens with different porosities have been determined by experimental compressive testing in transversal and longitudinal directions. & 2016 Elsevier B.V. All rights reserved.
Keywords: Copper Explosive compaction Explosive welding Uni-directional porous metal Mechanical properties
1. Introduction Porous metals have become an important building material in various modern engineering designs [1], due to their particular mechanical and thermal properties. Porous metals with uni-directional pores (UniPore structures) have been developed recently [2]. These materials are very similar to well-known gasar or lotus porous metals [3–5]) but additionally assure a constant crosssection (not irregular as usual for other porous materials [6,7]) through the whole specimen length with perfectly isolated pores between each other (Fig. 1a). This is achieved with unique fabrication method based on the explosive compaction of thin metal pipes [8,9]. The UniPore structure has an attractive combination of mechanical [8,9] and thermal [10] properties. However, the preparation procedure, which includes filling all inner pipes with paraffin to avoid complete compaction, has to be done very carefully to avoid any left over air bubbles in the pipes which would result in closed pipes during the compaction process. The moderate welding condition to form the wavy interface is not satisfied in some regions between the inner pipes due to varying collision inclination angle of pipes because of their round outer interface surface [8]. Additionally, the inner metal pipes with diameter n
Corresponding author. E-mail address: [email protected] (M. Vesenjak).
http://dx.doi.org/10.1016/j.matlet.2016.01.143 0167-577X/& 2016 Elsevier B.V. All rights reserved.
o3 mm and wall thickness 40.2 mm are very difficult to obtain and their cost is very high. For these reasons a new fabrication method of UniPore structures is proposed in this paper. It is based on rolling of cheap thin metal foil with acrylic spacer bars positioned on one surface and the subsequent explosive compaction. Once the thin foil is accelerated uniformly between the spacers, the welding condition related with the collision angle is considered stable, similar to the conventional explosive welding process [11]. It should be noted that the outer dimensions, size of the pores, thickness of the internal walls and consequently the porosity can be easily adjusted for individual application needs. The microstructure of the new rolled UniPore specimens with different porosities has been investigated by the metallographic analysis, while their compressive behaviour in longitudinal and transversal direction has been determined with experimental testing.
2. Fabrication of rolled UniPore specimens The new fabrication procedure of uni-directional metal copper UniPore comprises of i) preparation of the green specimen and ii) explosive compaction inducing the mechanism of explosive welding. Two different thin copper foils (JIS-C1100) with thicknesses of 0.3 and 0.4 mm were used to study their suitability for
40
M. Vesenjak et al. / Materials Letters 170 (2016) 39–43
Fig. 1. Original UniPore structure made of explosively compacted copper pipes (a), rolling of copper foil with acrylic spacer bars (b), rolled foil inserted into the copper tube (c), experimental assembly for explosive compaction (d), recovered sample after compaction (e), structure with internal wall thickness of 0.3 (f) and 0.4 mm without (g) and with centre copper core (h).
Fig. 2. Microstructure of samples cross-section, welding interface (a), interfaces with separation (b) isolation between pores (c).
M. Vesenjak et al. / Materials Letters 170 (2016) 39–43
41
Fig. 3. Transversal and longitudinal compressive behaviour of rolled UniPore structures (strain increment Δε E0.15).
the explosive welding and quality of the welded interfaces for the purpose of this investigation. Thin foils made of other metallic materials can also be applied. The foils have been cut to width of 95 mm and length of 310 and 340 mm for preparation of the green specimens. Acrylic resin bars, white colour, with 1 mm in thickness, 2 mm in width and 95 mm in length have been cut from the extruded acryl resin plate and fixed to the copper foil at a regular patter along the longer edge with 3 mm offset. The first resin bar in the rolling direction was slightly bigger, 3 3 mm2, transparent, and was used to form the centre core hole in the final structure. In one specimen with the 0.4 mm thick foil the first acrylic resin core was substituted with a copper rod of 8 mm in diameter to form the solid centre core in the final structure. The thin copper foil was 340 mm long when using acrylic resin core and 310 mm when using copper centre rod. The copper foils with acrylic resin spacer bars/copper rod were then tightly rolled (Fig. 1b) and inserted into the outer copper pipe (JIS-C1220) with an outer diameter of 30 mm, wall thickness of 1.5 mm and 100 mm in length (Fig. 1c). The used copper pipes and foils as well as acrylic resin plates are all commercially available in Japan. The acrylic resin bars prevent complete compaction during explosion and basically reserve the space for the pores in the final UniPore structure. The final porosity can be easily adjusted with variation of the foil thickness, which is approximately equal to the internal wall thickness (t) in the final product, and the size of acrylic spacer bars. In comparison to the previously studied UniPore structures [2,8,9], where paraffin was used during the fabrication, the new approach using the thin acrylic bars allows to avoid any left-over air bubbles in the inner pipes while filling them with liquidised paraffin. Additionally, the thin copper foil is much cheaper in comparison to the thin copper pipes.
The specimens have been place in the explosive container made of PVC pipe and centred by PVC support plates (Fig. 1d). A sponge has been placed on top of the specimen to absorb and mitigate the shock wave in longitudinal direction. The explosive container was then fully filled with the primary explosive PAVEX (ANFO based and usually used for explosive welding, mass: 400 g, detonation velocity: 2.4 km/s, density: 530 kg/m3) provided by Kayaku Japan Co., Ltd. The primary explosive was ignited by an electric detonator with a small amount of SEP explosive (mass: 10 g, detonation velocity: 6.8 km/s, density: 1310 kg/m3) placed in the centre of the cover plate. During the explosive compaction, the outer copper pipe acts as the flyer tube [8,9]. As mentioned in the former paper [8], the velocity at the first collison toward the centre was estimated at 337 m/s with a gap of 1 mm under the pressure estimated at 0.763 GPa. Fig. 1e shows the retrieved sample after the explosive compaction. The acryl resin spacers were then removed by melting at increased temperature. Fig. 1f and g represent the porous cooper specimens with 0.3 and 0.4 mm internal wall thickness and achieved porosity of 0.42 and 0.38, respectively. The specimen with copper centre core and 0.4 mm internal wall thickness is shown in Fig. 1h with achieved porosity of 0.31. The samples were cut transversally for subsequent metallographic analysis and compressive tests. The average sample diameter (Fig. 1f, g and h) was equal to 23.4 mm (std. dev.: 0.4 mm). The height of the compressive specimens was equal to 10 mm in the case of transversal loading and 20 mm in the case of longitudinal loading. 3. Results and discussion The Fig. 1f, g and h suggest that good bonding was achieved close to the outer tube while the bonding was weak or even absent
42
M. Vesenjak et al. / Materials Letters 170 (2016) 39–43
Fig. 4. Engineering stress-strain relationships for transverse ( σ = F /(l∙d ) and ε=Δl/d ) and longitudinal ( σ = F /(π ∙d2/4) and ε=Δl/l ) compressive loading direction.
closer to the specimen centre due to apparent decrease in the collision velocity through the specimen depth caused by the arcrylic spacers disturbance of the foil velocity and deformation. Fig. 2 illustrates the quality of the interface bonding as a result of the explosive compaction. Metallographic analysis has shown that mostly good bonding conditions were established at the outer foil layers, as depicted in Fig. 2a (for 0.3 mm Cu with acrylic resin core). However, the welding interface showed planar structure not the wavy interface well known for the explosively welded interface. Fig. 2b (for 0.4 mm Cu with acrylic resin core) reveals also interfaces with separation due to lack of bonding at deeper foil layers. The detailed analysis also showed that majority of the pores were isolated between each other (upper Fig. 2c). Only in few cases close to specime centre some thin gaps remained (lower Fig. 2c) which was more pronounced at specimens with lower porosity (0.3 mm Cu with acrylic resin core). The welding interface showing planar structure is not an ideal interface bonding condition and is attributed to the low collision velocity of about 300 m/s which is close to the lower velocity limit of explosive welding [12]. It is estimated that the space between the outer pipe and the first foil layer was too narrow to achieve high enough collision velocity to assure proper explosive welding of all foil layers. The average Vickers micro-hardness of 98.9 and 91.0 HV has been measured on transversal cross-section of specimens after explosive compaction for the foil thickness of 0.3 and 0.4, respectively, while the hardness of as received copper foil was measured as 66.3 and 53.5 HV, respectively. The 32.9% and 41.2%
lower hardness of as received copper is a result of the work hardening during explosive compaction, as already observed previously [8,9]. The fabricated rolled UniPore structure is expected to exhibit a strong orthotropy under mechanical loading due to the uni-directional pore orientation. Therefore, the specimen compressive behaviour has been observed in transversal (specimens length: l¼ 10 mm) and longitudinal (specimens length: l¼ 20 mm) direction in respect to the direction of pores. The compressive specimens have been prepared and tested in accordance with ISO 13314:2011 [13,14]. The transversal and longitudinal compressive deformation behaviours of fabricated specimens with three different porosities are shown in Fig. 3. In case of transversal loading, the inner pipe filaments prevent the outer wall to freely bend and subsequently buckle. These transversal tensile stresses consequently cause rupture of bonding between cell walls at strains 40.5. In case of longitudinal loading, one non-symmetric fold was being formed through the complete deformation process approximately in the middle of all specimens (appearing after uniform deformation at strain of approx. 0.15). The engineering stress-strain response of tested specimens is presented in Fig. 4, where it is also compared to original UniPore structures with similar porosity [8,9]. The figures show a strong anisotropy and the typical compressive response of porous materials in transversal direction. The change in foil thickness influences the stiffness of the structure but it does not change the shape of the relationship. It can be noted that the specimens with
M. Vesenjak et al. / Materials Letters 170 (2016) 39–43
thicker foil experience higher stiffness and lower densification strain.
4. Conclusions The paper presents a new fabrication method of uni-directional porous metal based on rolling of copper foil with acrylic spacer bars and their bonding by explosive compaction with simple adjustment of pore size, internal wall thickness and porosity. This fabrication method proves to be far superior than the original UniPore compaction in terms of preparation time and raw material costs, while achieving similar mechanical properties as the original UniPore structure. The metallographic analysis has shown mostly effective bonding of foil and the compressive tests revealed low deviation of mechanical properties. The presented fabrication method is also suitable for thin foils made of other metallic materials.
Acknowledgements The paper was produced within the framework of research programme P2-063 entitled “Design of Porous Structures”, which is financed by the Slovenian Research Agency “ARRS”. The travel support of the JASSO, Japan Student Services Organization, is also appreciated. The support of AMADA Foundation is gratefully acknowledged.
43
References [1] L.J. Gibson, M.F. Ashby, Cellular Solids: Structure and properties, Cambridge University Press, Cambridge, 1997. [2] Hokamoto K, Torii S, Kimura A, Kai S. Japanese Unexamined Patent Application Publication, [No.2012-200748]. Japan Patent O[ffice2012]. [3] V.I. Shapovalov, Porous metals, MRS Bull. 19 (1994) 24–29. [4] H. Nakajima, Fabrication, properties and application of porous metals with directional pores, Prog. Mater. Sci. 52 (2007) 1091–1173. [5] T. Fiedler, C. Veyhl, I.V. Belova, M. Tane, H. Nakajima, T. Bernthaler, et al., On the anisotropy of lotus-type porous copper, Adv. Eng. Mater. 14 (2012) 1144–1152. [6] M. Ulbin, M. Borovinšek, Y. Higa, K. Shimojima, M. Vesenjak, Z. Ren, Internal structure characterization of AlSi7 and AlSi10 advanced pore morphology (APM) foam elements, Mater. Lett. 136 (2014) 416–419. [7] I. Duarte, M. Vesenjak, L. Krstulović-Opara, Variation of quasi-static and dynamic compressive properties in a single aluminium foam block, Mater. Sci. Eng. A 616 (2014) 171–182. [8] K. Hokamoto, M. Vesenjak, Z. Ren, Fabrication of uni-directional porous structure through explosive compaction using cylindrical geometry, Mater. Lett. 137 (2014) 323–327. [9] M. Vesenjak, K. Hokamoto, M. Sakamoto, T. Nishi, LKrstulović-Opara, Z. Ren, Mechanical and Microstructural Analysis of Unidirectional Porous (UniPore) Copper, Mater Design. 90 (2016) 867–880, http://dx.doi.org/10.1016/j.matdes. 2015.11.038. [10] T. Fiedler, M. Borovinšek, K. Hokamoto, M. Vesenjak, High-performance thermal capacitors made by explosion forming, Int. J. Heat. Mass. Trans. 83 (2015) 366–371. [11] M.A. Meyers, L.E. Murr, Shock Waves and High-Strain-Rate Phenomena Effects in metals, Springer, New York, US, 1981. [12] B. Crossland, Explosive welding of metals and its application, Oxford University Press, Oxford: New York, 1982. [13] M. Vesenjak, L. Krstulović-Opara, Z. Ren, Characterization of photopolymer cellular structure with silicone pore filler, Polym. Test. 31 (2012) 705–709. [14] I. Duarte, M. Vesenjak, L. Krstulović-Opara, Z. Ren, Static and dynamic axial crush performance of in-situ foam-filled tubes, Compos Struct. (2015) 124.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Uni-directional porous metal fabricated by rolling of copper sheet and explosive compaction Matej Vesenjak a,n, Kazuyuki Hokamoto b, Shohei Matsumoto c, Yasuo Marumo c, Zoran Ren a a
Faculty of Mechanical Engineering, University of Maribor, Smetanova 17, 2000 Maribor, Slovenia Institute of Pulsed Power Science, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan c Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan b
art ic l e i nf o
a b s t r a c t
Article history: Received 12 November 2015 Received in revised form 12 January 2016 Accepted 30 January 2016 Available online 1 February 2016
A new type of porous metal with uni-directional pores (UniPore) has been developed using the explosive compaction fabrication process of rolled copper foil with plastic spacers. The interface bonding in the novel UniPore metal structure has been investigated by metallographic analysis. The mechanical properties of the new rolled UniPore specimens with different porosities have been determined by experimental compressive testing in transversal and longitudinal directions. & 2016 Elsevier B.V. All rights reserved.
Keywords: Copper Explosive compaction Explosive welding Uni-directional porous metal Mechanical properties
1. Introduction Porous metals have become an important building material in various modern engineering designs [1], due to their particular mechanical and thermal properties. Porous metals with uni-directional pores (UniPore structures) have been developed recently [2]. These materials are very similar to well-known gasar or lotus porous metals [3–5]) but additionally assure a constant crosssection (not irregular as usual for other porous materials [6,7]) through the whole specimen length with perfectly isolated pores between each other (Fig. 1a). This is achieved with unique fabrication method based on the explosive compaction of thin metal pipes [8,9]. The UniPore structure has an attractive combination of mechanical [8,9] and thermal [10] properties. However, the preparation procedure, which includes filling all inner pipes with paraffin to avoid complete compaction, has to be done very carefully to avoid any left over air bubbles in the pipes which would result in closed pipes during the compaction process. The moderate welding condition to form the wavy interface is not satisfied in some regions between the inner pipes due to varying collision inclination angle of pipes because of their round outer interface surface [8]. Additionally, the inner metal pipes with diameter n
Corresponding author. E-mail address: [email protected] (M. Vesenjak).
http://dx.doi.org/10.1016/j.matlet.2016.01.143 0167-577X/& 2016 Elsevier B.V. All rights reserved.
o3 mm and wall thickness 40.2 mm are very difficult to obtain and their cost is very high. For these reasons a new fabrication method of UniPore structures is proposed in this paper. It is based on rolling of cheap thin metal foil with acrylic spacer bars positioned on one surface and the subsequent explosive compaction. Once the thin foil is accelerated uniformly between the spacers, the welding condition related with the collision angle is considered stable, similar to the conventional explosive welding process [11]. It should be noted that the outer dimensions, size of the pores, thickness of the internal walls and consequently the porosity can be easily adjusted for individual application needs. The microstructure of the new rolled UniPore specimens with different porosities has been investigated by the metallographic analysis, while their compressive behaviour in longitudinal and transversal direction has been determined with experimental testing.
2. Fabrication of rolled UniPore specimens The new fabrication procedure of uni-directional metal copper UniPore comprises of i) preparation of the green specimen and ii) explosive compaction inducing the mechanism of explosive welding. Two different thin copper foils (JIS-C1100) with thicknesses of 0.3 and 0.4 mm were used to study their suitability for
40
M. Vesenjak et al. / Materials Letters 170 (2016) 39–43
Fig. 1. Original UniPore structure made of explosively compacted copper pipes (a), rolling of copper foil with acrylic spacer bars (b), rolled foil inserted into the copper tube (c), experimental assembly for explosive compaction (d), recovered sample after compaction (e), structure with internal wall thickness of 0.3 (f) and 0.4 mm without (g) and with centre copper core (h).
Fig. 2. Microstructure of samples cross-section, welding interface (a), interfaces with separation (b) isolation between pores (c).
M. Vesenjak et al. / Materials Letters 170 (2016) 39–43
41
Fig. 3. Transversal and longitudinal compressive behaviour of rolled UniPore structures (strain increment Δε E0.15).
the explosive welding and quality of the welded interfaces for the purpose of this investigation. Thin foils made of other metallic materials can also be applied. The foils have been cut to width of 95 mm and length of 310 and 340 mm for preparation of the green specimens. Acrylic resin bars, white colour, with 1 mm in thickness, 2 mm in width and 95 mm in length have been cut from the extruded acryl resin plate and fixed to the copper foil at a regular patter along the longer edge with 3 mm offset. The first resin bar in the rolling direction was slightly bigger, 3 3 mm2, transparent, and was used to form the centre core hole in the final structure. In one specimen with the 0.4 mm thick foil the first acrylic resin core was substituted with a copper rod of 8 mm in diameter to form the solid centre core in the final structure. The thin copper foil was 340 mm long when using acrylic resin core and 310 mm when using copper centre rod. The copper foils with acrylic resin spacer bars/copper rod were then tightly rolled (Fig. 1b) and inserted into the outer copper pipe (JIS-C1220) with an outer diameter of 30 mm, wall thickness of 1.5 mm and 100 mm in length (Fig. 1c). The used copper pipes and foils as well as acrylic resin plates are all commercially available in Japan. The acrylic resin bars prevent complete compaction during explosion and basically reserve the space for the pores in the final UniPore structure. The final porosity can be easily adjusted with variation of the foil thickness, which is approximately equal to the internal wall thickness (t) in the final product, and the size of acrylic spacer bars. In comparison to the previously studied UniPore structures [2,8,9], where paraffin was used during the fabrication, the new approach using the thin acrylic bars allows to avoid any left-over air bubbles in the inner pipes while filling them with liquidised paraffin. Additionally, the thin copper foil is much cheaper in comparison to the thin copper pipes.
The specimens have been place in the explosive container made of PVC pipe and centred by PVC support plates (Fig. 1d). A sponge has been placed on top of the specimen to absorb and mitigate the shock wave in longitudinal direction. The explosive container was then fully filled with the primary explosive PAVEX (ANFO based and usually used for explosive welding, mass: 400 g, detonation velocity: 2.4 km/s, density: 530 kg/m3) provided by Kayaku Japan Co., Ltd. The primary explosive was ignited by an electric detonator with a small amount of SEP explosive (mass: 10 g, detonation velocity: 6.8 km/s, density: 1310 kg/m3) placed in the centre of the cover plate. During the explosive compaction, the outer copper pipe acts as the flyer tube [8,9]. As mentioned in the former paper [8], the velocity at the first collison toward the centre was estimated at 337 m/s with a gap of 1 mm under the pressure estimated at 0.763 GPa. Fig. 1e shows the retrieved sample after the explosive compaction. The acryl resin spacers were then removed by melting at increased temperature. Fig. 1f and g represent the porous cooper specimens with 0.3 and 0.4 mm internal wall thickness and achieved porosity of 0.42 and 0.38, respectively. The specimen with copper centre core and 0.4 mm internal wall thickness is shown in Fig. 1h with achieved porosity of 0.31. The samples were cut transversally for subsequent metallographic analysis and compressive tests. The average sample diameter (Fig. 1f, g and h) was equal to 23.4 mm (std. dev.: 0.4 mm). The height of the compressive specimens was equal to 10 mm in the case of transversal loading and 20 mm in the case of longitudinal loading. 3. Results and discussion The Fig. 1f, g and h suggest that good bonding was achieved close to the outer tube while the bonding was weak or even absent
42
M. Vesenjak et al. / Materials Letters 170 (2016) 39–43
Fig. 4. Engineering stress-strain relationships for transverse ( σ = F /(l∙d ) and ε=Δl/d ) and longitudinal ( σ = F /(π ∙d2/4) and ε=Δl/l ) compressive loading direction.
closer to the specimen centre due to apparent decrease in the collision velocity through the specimen depth caused by the arcrylic spacers disturbance of the foil velocity and deformation. Fig. 2 illustrates the quality of the interface bonding as a result of the explosive compaction. Metallographic analysis has shown that mostly good bonding conditions were established at the outer foil layers, as depicted in Fig. 2a (for 0.3 mm Cu with acrylic resin core). However, the welding interface showed planar structure not the wavy interface well known for the explosively welded interface. Fig. 2b (for 0.4 mm Cu with acrylic resin core) reveals also interfaces with separation due to lack of bonding at deeper foil layers. The detailed analysis also showed that majority of the pores were isolated between each other (upper Fig. 2c). Only in few cases close to specime centre some thin gaps remained (lower Fig. 2c) which was more pronounced at specimens with lower porosity (0.3 mm Cu with acrylic resin core). The welding interface showing planar structure is not an ideal interface bonding condition and is attributed to the low collision velocity of about 300 m/s which is close to the lower velocity limit of explosive welding [12]. It is estimated that the space between the outer pipe and the first foil layer was too narrow to achieve high enough collision velocity to assure proper explosive welding of all foil layers. The average Vickers micro-hardness of 98.9 and 91.0 HV has been measured on transversal cross-section of specimens after explosive compaction for the foil thickness of 0.3 and 0.4, respectively, while the hardness of as received copper foil was measured as 66.3 and 53.5 HV, respectively. The 32.9% and 41.2%
lower hardness of as received copper is a result of the work hardening during explosive compaction, as already observed previously [8,9]. The fabricated rolled UniPore structure is expected to exhibit a strong orthotropy under mechanical loading due to the uni-directional pore orientation. Therefore, the specimen compressive behaviour has been observed in transversal (specimens length: l¼ 10 mm) and longitudinal (specimens length: l¼ 20 mm) direction in respect to the direction of pores. The compressive specimens have been prepared and tested in accordance with ISO 13314:2011 [13,14]. The transversal and longitudinal compressive deformation behaviours of fabricated specimens with three different porosities are shown in Fig. 3. In case of transversal loading, the inner pipe filaments prevent the outer wall to freely bend and subsequently buckle. These transversal tensile stresses consequently cause rupture of bonding between cell walls at strains 40.5. In case of longitudinal loading, one non-symmetric fold was being formed through the complete deformation process approximately in the middle of all specimens (appearing after uniform deformation at strain of approx. 0.15). The engineering stress-strain response of tested specimens is presented in Fig. 4, where it is also compared to original UniPore structures with similar porosity [8,9]. The figures show a strong anisotropy and the typical compressive response of porous materials in transversal direction. The change in foil thickness influences the stiffness of the structure but it does not change the shape of the relationship. It can be noted that the specimens with
M. Vesenjak et al. / Materials Letters 170 (2016) 39–43
thicker foil experience higher stiffness and lower densification strain.
4. Conclusions The paper presents a new fabrication method of uni-directional porous metal based on rolling of copper foil with acrylic spacer bars and their bonding by explosive compaction with simple adjustment of pore size, internal wall thickness and porosity. This fabrication method proves to be far superior than the original UniPore compaction in terms of preparation time and raw material costs, while achieving similar mechanical properties as the original UniPore structure. The metallographic analysis has shown mostly effective bonding of foil and the compressive tests revealed low deviation of mechanical properties. The presented fabrication method is also suitable for thin foils made of other metallic materials.
Acknowledgements The paper was produced within the framework of research programme P2-063 entitled “Design of Porous Structures”, which is financed by the Slovenian Research Agency “ARRS”. The travel support of the JASSO, Japan Student Services Organization, is also appreciated. The support of AMADA Foundation is gratefully acknowledged.
43
References [1] L.J. Gibson, M.F. Ashby, Cellular Solids: Structure and properties, Cambridge University Press, Cambridge, 1997. [2] Hokamoto K, Torii S, Kimura A, Kai S. Japanese Unexamined Patent Application Publication, [No.2012-200748]. Japan Patent O[ffice2012]. [3] V.I. Shapovalov, Porous metals, MRS Bull. 19 (1994) 24–29. [4] H. Nakajima, Fabrication, properties and application of porous metals with directional pores, Prog. Mater. Sci. 52 (2007) 1091–1173. [5] T. Fiedler, C. Veyhl, I.V. Belova, M. Tane, H. Nakajima, T. Bernthaler, et al., On the anisotropy of lotus-type porous copper, Adv. Eng. Mater. 14 (2012) 1144–1152. [6] M. Ulbin, M. Borovinšek, Y. Higa, K. Shimojima, M. Vesenjak, Z. Ren, Internal structure characterization of AlSi7 and AlSi10 advanced pore morphology (APM) foam elements, Mater. Lett. 136 (2014) 416–419. [7] I. Duarte, M. Vesenjak, L. Krstulović-Opara, Variation of quasi-static and dynamic compressive properties in a single aluminium foam block, Mater. Sci. Eng. A 616 (2014) 171–182. [8] K. Hokamoto, M. Vesenjak, Z. Ren, Fabrication of uni-directional porous structure through explosive compaction using cylindrical geometry, Mater. Lett. 137 (2014) 323–327. [9] M. Vesenjak, K. Hokamoto, M. Sakamoto, T. Nishi, LKrstulović-Opara, Z. Ren, Mechanical and Microstructural Analysis of Unidirectional Porous (UniPore) Copper, Mater Design. 90 (2016) 867–880, http://dx.doi.org/10.1016/j.matdes. 2015.11.038. [10] T. Fiedler, M. Borovinšek, K. Hokamoto, M. Vesenjak, High-performance thermal capacitors made by explosion forming, Int. J. Heat. Mass. Trans. 83 (2015) 366–371. [11] M.A. Meyers, L.E. Murr, Shock Waves and High-Strain-Rate Phenomena Effects in metals, Springer, New York, US, 1981. [12] B. Crossland, Explosive welding of metals and its application, Oxford University Press, Oxford: New York, 1982. [13] M. Vesenjak, L. Krstulović-Opara, Z. Ren, Characterization of photopolymer cellular structure with silicone pore filler, Polym. Test. 31 (2012) 705–709. [14] I. Duarte, M. Vesenjak, L. Krstulović-Opara, Z. Ren, Static and dynamic axial crush performance of in-situ foam-filled tubes, Compos Struct. (2015) 124.