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cladding of YBCO discs: a numerical approach
Journal of Materials Processing Technology 161 (2005) 36–41
Explosive compaction/cladding of YBCO discs: a numerical approach A.G. Mamalis a,∗ , I.N. Vottea a , D.E. Manolakos a , A. Szalay b , F. Marquis c a
Manufacturing Technology Division, Department of Mechanical Engineering, National Technical University of Athens, 9 Iroon Polytechniou, Zografou, Athens 15780, Greece b S-Metalltech, H-1122 Budapest, T´ oth, Lorinc.u, Hungary c Materials and Metallurgical Engineering, South Dakota School of Mines and Technology, Rapid City, SD 57701, USA
Abstract In order to manufacture metal-sheathed bulk superconducting discs, the explosive compaction/cladding technique, which combines explosive welding and compaction, was employed. In this paper, experimental and numerical investigations are reported on grooved metallic plates, filled with superconducting ceramic powder, subjected to explosive loading. The response of the metal and ceramic material during compaction is investigated by using finite element techniques and the dimensions of the compacts, pressure and temperature distributions are predicted. The numerical results obtained are compared with experimental observations, being in good agreement. © 2004 Elsevier B.V. All rights reserved. Keyword: Compaction; Metal-sheathed; YBCO discs
1. Introduction Shock consolidation is a widely used method for producing ceramic and metallic components for advanced structural applications. It is a process by which the particle surfaces are highly deformed producing inter-particle bonding in a one-step process. The consolidation of the powders is accomplished by the passage of a strong shock wave through the powders. In the case of high-Tc superconducting materials, the bad current conduction of the superconducting parts may be attributed to the contamination of the grain interfaces, usually, by normal phases produced during processing. Explosive powder compaction may consist a solution towards this direction, since the high shock pressures and local temperatures produced, lead to the creation of new clean grain boundaries and new large contact surfaces, by breaking the original grains and bringing these new surfaces into very close contact with each other. Thus, the compacted solid contains a variety of primarily line defects (dislocations) that would provide flux pinning centres in type II superconductors [1,2]. The optimization of the compaction process and the evaluation of the process parameters are of great interest for en∗
Corresponding author. Tel.: +30 210 772 3688; fax: +30 210 772 3689. E-mail address: [email protected] (A.G. Mamalis).
0924-0136/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2004.07.006
gineers and the finite element methods can help in explaining the mechanics of powder behaviour under applied stress, as well as in predicting the deformation of the compact, the pressure, density and stress distribution, during the process. Most of the finite element models are associated with the static consolidation, while the modelling of the explosive compaction, is not extensively considered, since it is difficult to provide the dynamic properties of powders and the related Hugoniot curves [3]. In this paper, the explosive compaction/cladding process, for producing metal-sheathed YBCO discs, is simulated by using the explicit finite-element code LS-DYNA3D. Taking into account that the simulation of ceramic powders is often based on constitutive models, originally developed for mineral materials, such as soils and clays, an assumption was made to describe the non-linear behaviour of the HTS powders by using the modified Drucker–Prager/cap elasto-plastic constitutive material model [4].
2. Experimental The experimental configuration of the superconducting disc consisted of an initial set-up angle of 0◦ and a standoff distance of 4 mm. The explosive used was an Amonit
A.G. Mamalis et al. / Journal of Materials Processing Technology 161 (2005) 36–41
37
Fig. 1. SEM micrographs of the superconducting powder (a) before and (b) after the explosive compaction.
Fig. 2. XRD patterns of the superconducting powder (a) before and (b) after the explosive compaction.
6 high explosive and the ignition point was located at the centre of the explosive layer of 25 mm. The dimensions of the flyer Al plate and the parent Al disc were 100 mm × 100 mm × 4 mm and Ø100 mm × 36 mm, respectively, as can be seen in Fig. 4(a). A cylindrical groove of dimensions Ø30 mm × 15 mm was machined in the parent metal, filled with YBa1.95 K0.05 Cu3 Oy F0.05 + 7.5% Ag superconducting powder, which has been prepared by the solid-state reaction technique. The bulk density before explosive cladding was 50% of the theoretical density. Explosion was carried out in an explosive chamber by firing an electric detonator, resulting in the collapse of the flyer plate and the consolidation
of the powder [5]. According to experimental measurements, the thickness of the flyer plate was reduced to 2.5 mm and the diameter and height of the base plate was about 95 and 30 mm, respectively. After the explosive compaction, fracturing of the initial grains occurred and the compact consists of separate grains (no texturing), as can be seen in Fig. 1(a) and (b). The Y123 phase was dominant, while a partial decomposition occurred, as can be observed from comparison of the X-ray pattern of the powder before and after compaction, see Fig. 2(a) and (b), respectively. In the case of the four superconducting discs, the configuration consists of a flyer silver/copper plate, which was im-
Fig. 3. (a) SEM micrograph and (b) Tc measurements of the compacted superconducting powder.
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A.G. Mamalis et al. / Journal of Materials Processing Technology 161 (2005) 36–41
Fig. 4. (a) Experimental set-up, (b) initial finite element mesh, (c) experimental final deformation and (d) predicted final deformation of the sheathed aluminium disc.
Fig. 5. Distribution of pressure inside (a) the base and flyer metallic plates and (b) the ceramic disc at two different time steps of the simulation.
A.G. Mamalis et al. / Journal of Materials Processing Technology 161 (2005) 36–41
39
According to experimental measurements, the thickness of the flyer plate was reduced to 1.2 mm and the average diameter of the superconducting discs was 15.7 mm. After the explosive compaction, the superconductor’s microstructure and properties were characterized. Fig. 3(a) shows the microstructure of the YBCO compact, where separate grains are observed, with good cohesion, but no texturing is observed. The main size is smaller than 10 m, but there are also aggregates greater than 10 m. In order to determine the superconducting properties, measurements of the magnetic susceptibility were performed in a field of 10 G. The critical transition temperature was found Tc = 95 K, as can be seen from Fig. 3(b). Fig. 6. Distribution of density inside the ceramic disc.
3. Finite element modelling pacted, using a 30 mm layer of high-explosive, on a grooved aluminium/copper parent plate filled with superconducting powder. The dimensions of the flyer plate and the parent plate were 165 mm × 70 mm × 1.5 mm and 100 mm × 55 mm × 11 mm, respectively. Four grooves of dimensions Ø16 mm × 6 mm were machined in the parent metal and filled with superconducting powder. The flyer plate exceeds the parent plate for about 65 mm, since some time is needed for the development of a steady shock front. This part of the flyer plate is cut-off during the explosion due to plastic deformation. The experimental set-up is presented in Fig. 7(a).
A thermomechanical numerical analysis of the explosive compaction/cladding process was performed, using the explicit finite element code LS-DYNA3D. The macro-mechanical approach is adopted and the modified Drucker–Prager/cap elasto-plastic constitutive model is used to describe the superconducting powder [6]. The explosive material was described by the JWL equation of state and the metallic materials were modelled as elasto-plastic materials, taking into account the high deformation rate. More details for the materials used can be found in Refs [3,7]. Eight-node brick elements from the element library of the
Fig. 7. (a) Experimental set-up, (b) initial finite element mesh and (c) final deformation of the metal-sheathed superconducting discs.
40
A.G. Mamalis et al. / Journal of Materials Processing Technology 161 (2005) 36–41
Fig. 8. Distribution of pressure inside (a) the base plate and (b) the ceramic discs at two different time steps of the simulation.
FE code were used and interfaces to define the contact conditions between the different powders and the metals, as well as between the metals and the explosive material. In the case of the aluminium-sheathed superconducting disc, 24,532 brick elements and 29,870 nodes were used and a cross-section of the initial mesh of the configuration is presented in Fig. 4(b) For the four silver/copper bimetallic-sheathed YBCO discs, 47,665 brick elements and 60,886 nodes were used, as presented in Fig. 8(b).
4. Results and discussion 4.1. Explosive cladding of an aluminium-sheathed superconducting disc According to the simulation of the compaction/cladding of the superconducting disc, the flyer plate reaches the powder after 12 s, impacting on the superconductor with a 1100 m/s velocity, and it is cladded on the metal block after 50 s. After compaction, the thickness of the cladding plate was decreased from 4 to 2.6 mm, while the height of the metal block was reduced to 29 mm. The diameter of the superconductor was about 28 mm and its height 11.5 mm. The initial FE mesh of the configuration is presented in Fig. 4(b), whereas the final deformation of the metal-sheathed disc after the explosion and after the numerical simulation are shown in Fig. 4(c) and (d), respectively. The obtained pressure, acting on the metal and the ceramic, was in the range of 7 GPa, decreasing with time and towards the bottom of the disc, as observed in Fig. 5(a). The pressure inside the ceramic disc was lower, reaching the value of 1.5 GPa, since pressure decreases propagating from one material to the other, as indicated from Fig. 5(b). The density of the superconducting powder reached 80% of the theoretical value, meanly at the circumference of the disc, while at its centre it was about 75%, see Fig. 6. The maximum temperature of the aluminum and the superconductor was in the range of 100 and 300 ◦ C, respectively.
4.2. Explosive cladding of four silver/copper-sheathed superconducting discs According to the simulation the flyer plate reaches the base after 23 s, impacting on it with a velocity of 2000 m/s, and it is cladded on the metal base after 55 s. After compaction, the thickness of the cladding plate was decreased from 1.5 to 1.4 mm, while the average height of the metal base was 9 mm. The average values of the dimensions of the superconducting discs were Ø17.8 mm × 5.2 mm. The initial FE mesh of the configuration and the final deformation of the plates are presented in Fig. 7(b) and (c), respectively. The maximum pressures with values in the range of 6 GPa were achieved at the top of the parent plate (see Fig. 8(a)). The pressure inside the ceramic is smaller, due to the shock wave propagation from one material to the other (see Fig. 8(b)). The maximum pressures achieved were in the range of 2.5 GPa at the surface of the discs and near the interface with the metallic base.
5. Concluding remarks From the results reported above and similar conclusions made pertaining to the explosive compaction/cladding [5,7], it can be concluded that explosive compaction/cladding is not detrimental for the superconducting phase. The final deformed shape is calculated and found in good agreement with experimental measurements. Distributions of pressure inside the metal and the HTS throughout the whole process were predicted. The pressure obtained inside the superconductor was lower than that of the metal. The calculated density of the superconductor is in the in the range of 80% of the theoretical density, while the experimentally measured average density was in the range of 85%.
References [1] A.G. Mamalis, J. Mater. Process. Technol. 99 (2000) 1.
A.G. Mamalis et al. / Journal of Materials Processing Technology 161 (2005) 36–41 [2] A.G. Mamalis, D.E. Manolakos, A. Szalay, G. Pantazopoulos, Technomic Publishing Co., Lanchaster, PA, USA, 2000, pp. 280. [3] A.G. Mamalis, I.N. Vottea, D.E. Manolakos, A. Szalay, G. Desgardin, EXPLOMET2000, Proceedings of the International Conference on Fundamental Issues and Applications of Shock-Wave and High-StrainRate Phenomena, New Mexico, USA, June 2000. [4] H. Zipse, J. Eur. Ceram. Soc. 17 (1997) 1707–1713.
41
[5] A.G. Mamalis, I.N. Vottea, D.E. Manolakos, A. Kladas, in: Proceedings of the Fourth International Conference on New Theories, Discoveries and Applications of Superconductors and Related Materials (New3SC-4), San Diego, USA, January 2003. [6] Chou F.I., et al., J. Chin. Soc. Mech. Eng. 20 (1999) 287. [7] A.G. Mamalis, I.N. Vottea, D.E. Manolakos, Mater. Sci. Eng. B 90 (3) (2002) 254–260.
Explosive compaction/cladding of YBCO discs: a numerical approach A.G. Mamalis a,∗ , I.N. Vottea a , D.E. Manolakos a , A. Szalay b , F. Marquis c a
Manufacturing Technology Division, Department of Mechanical Engineering, National Technical University of Athens, 9 Iroon Polytechniou, Zografou, Athens 15780, Greece b S-Metalltech, H-1122 Budapest, T´ oth, Lorinc.u, Hungary c Materials and Metallurgical Engineering, South Dakota School of Mines and Technology, Rapid City, SD 57701, USA
Abstract In order to manufacture metal-sheathed bulk superconducting discs, the explosive compaction/cladding technique, which combines explosive welding and compaction, was employed. In this paper, experimental and numerical investigations are reported on grooved metallic plates, filled with superconducting ceramic powder, subjected to explosive loading. The response of the metal and ceramic material during compaction is investigated by using finite element techniques and the dimensions of the compacts, pressure and temperature distributions are predicted. The numerical results obtained are compared with experimental observations, being in good agreement. © 2004 Elsevier B.V. All rights reserved. Keyword: Compaction; Metal-sheathed; YBCO discs
1. Introduction Shock consolidation is a widely used method for producing ceramic and metallic components for advanced structural applications. It is a process by which the particle surfaces are highly deformed producing inter-particle bonding in a one-step process. The consolidation of the powders is accomplished by the passage of a strong shock wave through the powders. In the case of high-Tc superconducting materials, the bad current conduction of the superconducting parts may be attributed to the contamination of the grain interfaces, usually, by normal phases produced during processing. Explosive powder compaction may consist a solution towards this direction, since the high shock pressures and local temperatures produced, lead to the creation of new clean grain boundaries and new large contact surfaces, by breaking the original grains and bringing these new surfaces into very close contact with each other. Thus, the compacted solid contains a variety of primarily line defects (dislocations) that would provide flux pinning centres in type II superconductors [1,2]. The optimization of the compaction process and the evaluation of the process parameters are of great interest for en∗
Corresponding author. Tel.: +30 210 772 3688; fax: +30 210 772 3689. E-mail address: [email protected] (A.G. Mamalis).
0924-0136/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2004.07.006
gineers and the finite element methods can help in explaining the mechanics of powder behaviour under applied stress, as well as in predicting the deformation of the compact, the pressure, density and stress distribution, during the process. Most of the finite element models are associated with the static consolidation, while the modelling of the explosive compaction, is not extensively considered, since it is difficult to provide the dynamic properties of powders and the related Hugoniot curves [3]. In this paper, the explosive compaction/cladding process, for producing metal-sheathed YBCO discs, is simulated by using the explicit finite-element code LS-DYNA3D. Taking into account that the simulation of ceramic powders is often based on constitutive models, originally developed for mineral materials, such as soils and clays, an assumption was made to describe the non-linear behaviour of the HTS powders by using the modified Drucker–Prager/cap elasto-plastic constitutive material model [4].
2. Experimental The experimental configuration of the superconducting disc consisted of an initial set-up angle of 0◦ and a standoff distance of 4 mm. The explosive used was an Amonit
A.G. Mamalis et al. / Journal of Materials Processing Technology 161 (2005) 36–41
37
Fig. 1. SEM micrographs of the superconducting powder (a) before and (b) after the explosive compaction.
Fig. 2. XRD patterns of the superconducting powder (a) before and (b) after the explosive compaction.
6 high explosive and the ignition point was located at the centre of the explosive layer of 25 mm. The dimensions of the flyer Al plate and the parent Al disc were 100 mm × 100 mm × 4 mm and Ø100 mm × 36 mm, respectively, as can be seen in Fig. 4(a). A cylindrical groove of dimensions Ø30 mm × 15 mm was machined in the parent metal, filled with YBa1.95 K0.05 Cu3 Oy F0.05 + 7.5% Ag superconducting powder, which has been prepared by the solid-state reaction technique. The bulk density before explosive cladding was 50% of the theoretical density. Explosion was carried out in an explosive chamber by firing an electric detonator, resulting in the collapse of the flyer plate and the consolidation
of the powder [5]. According to experimental measurements, the thickness of the flyer plate was reduced to 2.5 mm and the diameter and height of the base plate was about 95 and 30 mm, respectively. After the explosive compaction, fracturing of the initial grains occurred and the compact consists of separate grains (no texturing), as can be seen in Fig. 1(a) and (b). The Y123 phase was dominant, while a partial decomposition occurred, as can be observed from comparison of the X-ray pattern of the powder before and after compaction, see Fig. 2(a) and (b), respectively. In the case of the four superconducting discs, the configuration consists of a flyer silver/copper plate, which was im-
Fig. 3. (a) SEM micrograph and (b) Tc measurements of the compacted superconducting powder.
38
A.G. Mamalis et al. / Journal of Materials Processing Technology 161 (2005) 36–41
Fig. 4. (a) Experimental set-up, (b) initial finite element mesh, (c) experimental final deformation and (d) predicted final deformation of the sheathed aluminium disc.
Fig. 5. Distribution of pressure inside (a) the base and flyer metallic plates and (b) the ceramic disc at two different time steps of the simulation.
A.G. Mamalis et al. / Journal of Materials Processing Technology 161 (2005) 36–41
39
According to experimental measurements, the thickness of the flyer plate was reduced to 1.2 mm and the average diameter of the superconducting discs was 15.7 mm. After the explosive compaction, the superconductor’s microstructure and properties were characterized. Fig. 3(a) shows the microstructure of the YBCO compact, where separate grains are observed, with good cohesion, but no texturing is observed. The main size is smaller than 10 m, but there are also aggregates greater than 10 m. In order to determine the superconducting properties, measurements of the magnetic susceptibility were performed in a field of 10 G. The critical transition temperature was found Tc = 95 K, as can be seen from Fig. 3(b). Fig. 6. Distribution of density inside the ceramic disc.
3. Finite element modelling pacted, using a 30 mm layer of high-explosive, on a grooved aluminium/copper parent plate filled with superconducting powder. The dimensions of the flyer plate and the parent plate were 165 mm × 70 mm × 1.5 mm and 100 mm × 55 mm × 11 mm, respectively. Four grooves of dimensions Ø16 mm × 6 mm were machined in the parent metal and filled with superconducting powder. The flyer plate exceeds the parent plate for about 65 mm, since some time is needed for the development of a steady shock front. This part of the flyer plate is cut-off during the explosion due to plastic deformation. The experimental set-up is presented in Fig. 7(a).
A thermomechanical numerical analysis of the explosive compaction/cladding process was performed, using the explicit finite element code LS-DYNA3D. The macro-mechanical approach is adopted and the modified Drucker–Prager/cap elasto-plastic constitutive model is used to describe the superconducting powder [6]. The explosive material was described by the JWL equation of state and the metallic materials were modelled as elasto-plastic materials, taking into account the high deformation rate. More details for the materials used can be found in Refs [3,7]. Eight-node brick elements from the element library of the
Fig. 7. (a) Experimental set-up, (b) initial finite element mesh and (c) final deformation of the metal-sheathed superconducting discs.
40
A.G. Mamalis et al. / Journal of Materials Processing Technology 161 (2005) 36–41
Fig. 8. Distribution of pressure inside (a) the base plate and (b) the ceramic discs at two different time steps of the simulation.
FE code were used and interfaces to define the contact conditions between the different powders and the metals, as well as between the metals and the explosive material. In the case of the aluminium-sheathed superconducting disc, 24,532 brick elements and 29,870 nodes were used and a cross-section of the initial mesh of the configuration is presented in Fig. 4(b) For the four silver/copper bimetallic-sheathed YBCO discs, 47,665 brick elements and 60,886 nodes were used, as presented in Fig. 8(b).
4. Results and discussion 4.1. Explosive cladding of an aluminium-sheathed superconducting disc According to the simulation of the compaction/cladding of the superconducting disc, the flyer plate reaches the powder after 12 s, impacting on the superconductor with a 1100 m/s velocity, and it is cladded on the metal block after 50 s. After compaction, the thickness of the cladding plate was decreased from 4 to 2.6 mm, while the height of the metal block was reduced to 29 mm. The diameter of the superconductor was about 28 mm and its height 11.5 mm. The initial FE mesh of the configuration is presented in Fig. 4(b), whereas the final deformation of the metal-sheathed disc after the explosion and after the numerical simulation are shown in Fig. 4(c) and (d), respectively. The obtained pressure, acting on the metal and the ceramic, was in the range of 7 GPa, decreasing with time and towards the bottom of the disc, as observed in Fig. 5(a). The pressure inside the ceramic disc was lower, reaching the value of 1.5 GPa, since pressure decreases propagating from one material to the other, as indicated from Fig. 5(b). The density of the superconducting powder reached 80% of the theoretical value, meanly at the circumference of the disc, while at its centre it was about 75%, see Fig. 6. The maximum temperature of the aluminum and the superconductor was in the range of 100 and 300 ◦ C, respectively.
4.2. Explosive cladding of four silver/copper-sheathed superconducting discs According to the simulation the flyer plate reaches the base after 23 s, impacting on it with a velocity of 2000 m/s, and it is cladded on the metal base after 55 s. After compaction, the thickness of the cladding plate was decreased from 1.5 to 1.4 mm, while the average height of the metal base was 9 mm. The average values of the dimensions of the superconducting discs were Ø17.8 mm × 5.2 mm. The initial FE mesh of the configuration and the final deformation of the plates are presented in Fig. 7(b) and (c), respectively. The maximum pressures with values in the range of 6 GPa were achieved at the top of the parent plate (see Fig. 8(a)). The pressure inside the ceramic is smaller, due to the shock wave propagation from one material to the other (see Fig. 8(b)). The maximum pressures achieved were in the range of 2.5 GPa at the surface of the discs and near the interface with the metallic base.
5. Concluding remarks From the results reported above and similar conclusions made pertaining to the explosive compaction/cladding [5,7], it can be concluded that explosive compaction/cladding is not detrimental for the superconducting phase. The final deformed shape is calculated and found in good agreement with experimental measurements. Distributions of pressure inside the metal and the HTS throughout the whole process were predicted. The pressure obtained inside the superconductor was lower than that of the metal. The calculated density of the superconductor is in the in the range of 80% of the theoretical density, while the experimentally measured average density was in the range of 85%.
References [1] A.G. Mamalis, J. Mater. Process. Technol. 99 (2000) 1.
A.G. Mamalis et al. / Journal of Materials Processing Technology 161 (2005) 36–41 [2] A.G. Mamalis, D.E. Manolakos, A. Szalay, G. Pantazopoulos, Technomic Publishing Co., Lanchaster, PA, USA, 2000, pp. 280. [3] A.G. Mamalis, I.N. Vottea, D.E. Manolakos, A. Szalay, G. Desgardin, EXPLOMET2000, Proceedings of the International Conference on Fundamental Issues and Applications of Shock-Wave and High-StrainRate Phenomena, New Mexico, USA, June 2000. [4] H. Zipse, J. Eur. Ceram. Soc. 17 (1997) 1707–1713.
41
[5] A.G. Mamalis, I.N. Vottea, D.E. Manolakos, A. Kladas, in: Proceedings of the Fourth International Conference on New Theories, Discoveries and Applications of Superconductors and Related Materials (New3SC-4), San Diego, USA, January 2003. [6] Chou F.I., et al., J. Chin. Soc. Mech. Eng. 20 (1999) 287. [7] A.G. Mamalis, I.N. Vottea, D.E. Manolakos, Mater. Sci. Eng. B 90 (3) (2002) 254–260.