El presente artículo es una aproximación a la situación laboral y jurídica de los afrodescendient... more El presente artículo es una aproximación a la situación laboral y jurídica de los afrodescendientes, esclavizados y libertos, en la frontera uruguayo-brasileña, en la segunda mitad del siglo XIX, particularmente en lo que hace a su captura y secuestro para ser vendidos como mano de obra esclavizada cuando ya estaba abolida la esclavitud en el Uruguay. A diferencia del proceso de liberación ocurrido en Montevideo y sur uruguayo, la persistencia de mano de obra servil, ya sea como esclavos reconocidos en su condición de tal o como peones contratados, formulismo legal adoptado para disfrazar su condición de esclavizados ante las leyes uruguayas, persistió hasta finales del siglo XIX en las estancias de la frontera norte y este de ese país. Con el fin del tráfico negrero atlántico, se desarrolló en esos territorios un intenso tráfico subregional que abasteció la demanda de
Composites Part A: Applied Science and Manufacturing, 1998
A consolidation model based on transient three-dimensional heat transfer for the resistance weldi... more A consolidation model based on transient three-dimensional heat transfer for the resistance welding of thermoplastic-matrix composite lap-shear specimens is established. The consolidation occurring in the resistance welding process was studied in terms of intimate contact and autohesion processes. Effects of power level on the time to achieve full intimate contact were determined. The influence of the consolidation pressure on the degree of intimate contact was investigated. Different welding configurations of lap-shear specimens were evaluated, i.e. APC-2 laminate/PEEK film, APC-2 laminate/PEI film and CF-PEI laminate/PEI film. The bonding time was compared with experimental electrified times, and close agreement was obtained. Local thermal degradation in the heating element was discussed for high power levels. A processing window for the CF-PEI/PEI configuration was established, which showed close agreement with that determined experimentally.
The heat treatable Al-Si-Mg based 6xxx alloys are becoming increasingly attractive for automotive... more The heat treatable Al-Si-Mg based 6xxx alloys are becoming increasingly attractive for automotive skin panel applications where high formability and in-service dent resistance are basic requirements. The use of standard 6xxx alloys in the T4 condition can not fully utilize the strengthening potential of the alloys due to a low temperature and a short duration in most commercial paint bake cycles. Recent progress in developing T4P (pre-aged) 6xxx alloys has substantially improved the paint bake response (PBR). However, the set-up of processing parameters can have a strong impact on the PBR of the final components. The current work presents the results of laboratory simulation of natural ageing effect on the PBR of the T4P 6xxx alloys. The work focuses on the natural ageing between the solid solution heat treatment (SSHT) and pre-ageing operation; the natural ageing in the pre-aged material; and their effect on the T4P strength and final strength after paint bake cycle. Differential s...
ABSTRACT The use of Al-Mg-Si-(Cu) heat treatable 6xxx alloys is steadily increasing in the automo... more ABSTRACT The use of Al-Mg-Si-(Cu) heat treatable 6xxx alloys is steadily increasing in the automotive industry. The possibility of weight reduction of the cars in combination with the good formability and high in-service dent resistance of these alloys, make them a favorable material for body panel applications. One of the most common, environment-friendly and easy to perform processes used to join aluminum sheets, is the hemming joining operation. This operation heavily relies on the bendability of the sheets, because they are bent to an angle of 180° over of a radius equal to their thickness. Tearing or cracking of the outer bent surface are often very common. In this study we attempt to understand the relations between the microstructural features of the sheets and their hemming behavior. The hemming experiments are performed in laboratory conditions and the results are discussed together with the data obtained from crystallographic, microstructural and textural investigations. Relations between the hemming appearance, chemical composition, natural aging time and dispersoid’s density are found and discussed.
ABSTRACT Hot-torqued samples of alloy AA 5182, with and without Cu (0.5 wt.%) additions, were inv... more ABSTRACT Hot-torqued samples of alloy AA 5182, with and without Cu (0.5 wt.%) additions, were investigated by polarized light optical microscopy, hardness measurements and transmission electron microscopy (TEM). A previous study (Ratchev et al., Mater. Sci. Eng. A222 (1997) 189) on the hot ductility of these materials was further extended to include the role of dislocation cell formation and recovery. TEM investigations have shown that after hot torsion some of the elongated grains contained a dislocation cell structure. An average of four such cells (in one dimension) may correspond to a small-equiaxed grain visible (with relatively sharp contrast) under polarized light optical microscopy. Development of long-range misorientations in the cell-forming regions is suggested to be the mechanism for their easy optical visibility. Much higher dislocation density and total absence of high angle boundaries in the cell-forming regions rule out possibilities of dynamic recrystallization. Decreased cell size and increased cell misorientation (both local and long range) were observed with increasing strain. This in turn may indicate a combination of deformation/recovery as the formation mechanism. Observed higher recoverability in the material with larger interparticle spacings may inhibit the formation of plastic instabilities or strain localizations (Hughes, Acta Metall. Mater. 41(5) (1993) 1421; Kuhlmann-Wilsdorf, Mater Sci. Eng. A113 (1989) 1; Wagner et al., Acta Metall. Mater. 43(10) (1995) 3799; Gil Sevillano et al., Prog. Mater. Sci. 25 (1981) 379; Dillamore et al., Metal Sci. 13 (1979) 73). This explains previous observations (Ratchev et al., Mater. Sci. Eng. A222 (1997) 189) on improved hot ductility in materials with large interparticle spacings.
The growing demand for more fuel-efficient vehicles to reduce energy consumption and air pollutio... more The growing demand for more fuel-efficient vehicles to reduce energy consumption and air pollution is a challenge for the automotive industry. The characteristic properties of aluminium, high strength stiffness to weight ratio, good formability, good corrosion resistance, and recycling ...
752 Aluminium Alloys - ICAA5 600 г Position 10 Position 12 Position 7 -^ 41 .0 44.0 Figure 6: X R... more 752 Aluminium Alloys - ICAA5 600 г Position 10 Position 12 Position 7 -^ 41 .0 44.0 Figure 6: X Ray diffractographs from positions 7, 10 and 12 Hasenclever [3] has reported that precipitation of Fe atoms occurs in a AA1050 alloy ingot during cool-down from soak which further ...
El presente artículo es una aproximación a la situación laboral y jurídica de los afrodescendient... more El presente artículo es una aproximación a la situación laboral y jurídica de los afrodescendientes, esclavizados y libertos, en la frontera uruguayo-brasileña, en la segunda mitad del siglo XIX, particularmente en lo que hace a su captura y secuestro para ser vendidos como mano de obra esclavizada cuando ya estaba abolida la esclavitud en el Uruguay. A diferencia del proceso de liberación ocurrido en Montevideo y sur uruguayo, la persistencia de mano de obra servil, ya sea como esclavos reconocidos en su condición de tal o como peones contratados, formulismo legal adoptado para disfrazar su condición de esclavizados ante las leyes uruguayas, persistió hasta finales del siglo XIX en las estancias de la frontera norte y este de ese país. Con el fin del tráfico negrero atlántico, se desarrolló en esos territorios un intenso tráfico subregional que abasteció la demanda de
Composites Part A: Applied Science and Manufacturing, 1998
A consolidation model based on transient three-dimensional heat transfer for the resistance weldi... more A consolidation model based on transient three-dimensional heat transfer for the resistance welding of thermoplastic-matrix composite lap-shear specimens is established. The consolidation occurring in the resistance welding process was studied in terms of intimate contact and autohesion processes. Effects of power level on the time to achieve full intimate contact were determined. The influence of the consolidation pressure on the degree of intimate contact was investigated. Different welding configurations of lap-shear specimens were evaluated, i.e. APC-2 laminate/PEEK film, APC-2 laminate/PEI film and CF-PEI laminate/PEI film. The bonding time was compared with experimental electrified times, and close agreement was obtained. Local thermal degradation in the heating element was discussed for high power levels. A processing window for the CF-PEI/PEI configuration was established, which showed close agreement with that determined experimentally.
The heat treatable Al-Si-Mg based 6xxx alloys are becoming increasingly attractive for automotive... more The heat treatable Al-Si-Mg based 6xxx alloys are becoming increasingly attractive for automotive skin panel applications where high formability and in-service dent resistance are basic requirements. The use of standard 6xxx alloys in the T4 condition can not fully utilize the strengthening potential of the alloys due to a low temperature and a short duration in most commercial paint bake cycles. Recent progress in developing T4P (pre-aged) 6xxx alloys has substantially improved the paint bake response (PBR). However, the set-up of processing parameters can have a strong impact on the PBR of the final components. The current work presents the results of laboratory simulation of natural ageing effect on the PBR of the T4P 6xxx alloys. The work focuses on the natural ageing between the solid solution heat treatment (SSHT) and pre-ageing operation; the natural ageing in the pre-aged material; and their effect on the T4P strength and final strength after paint bake cycle. Differential s...
ABSTRACT The use of Al-Mg-Si-(Cu) heat treatable 6xxx alloys is steadily increasing in the automo... more ABSTRACT The use of Al-Mg-Si-(Cu) heat treatable 6xxx alloys is steadily increasing in the automotive industry. The possibility of weight reduction of the cars in combination with the good formability and high in-service dent resistance of these alloys, make them a favorable material for body panel applications. One of the most common, environment-friendly and easy to perform processes used to join aluminum sheets, is the hemming joining operation. This operation heavily relies on the bendability of the sheets, because they are bent to an angle of 180° over of a radius equal to their thickness. Tearing or cracking of the outer bent surface are often very common. In this study we attempt to understand the relations between the microstructural features of the sheets and their hemming behavior. The hemming experiments are performed in laboratory conditions and the results are discussed together with the data obtained from crystallographic, microstructural and textural investigations. Relations between the hemming appearance, chemical composition, natural aging time and dispersoid’s density are found and discussed.
ABSTRACT Hot-torqued samples of alloy AA 5182, with and without Cu (0.5 wt.%) additions, were inv... more ABSTRACT Hot-torqued samples of alloy AA 5182, with and without Cu (0.5 wt.%) additions, were investigated by polarized light optical microscopy, hardness measurements and transmission electron microscopy (TEM). A previous study (Ratchev et al., Mater. Sci. Eng. A222 (1997) 189) on the hot ductility of these materials was further extended to include the role of dislocation cell formation and recovery. TEM investigations have shown that after hot torsion some of the elongated grains contained a dislocation cell structure. An average of four such cells (in one dimension) may correspond to a small-equiaxed grain visible (with relatively sharp contrast) under polarized light optical microscopy. Development of long-range misorientations in the cell-forming regions is suggested to be the mechanism for their easy optical visibility. Much higher dislocation density and total absence of high angle boundaries in the cell-forming regions rule out possibilities of dynamic recrystallization. Decreased cell size and increased cell misorientation (both local and long range) were observed with increasing strain. This in turn may indicate a combination of deformation/recovery as the formation mechanism. Observed higher recoverability in the material with larger interparticle spacings may inhibit the formation of plastic instabilities or strain localizations (Hughes, Acta Metall. Mater. 41(5) (1993) 1421; Kuhlmann-Wilsdorf, Mater Sci. Eng. A113 (1989) 1; Wagner et al., Acta Metall. Mater. 43(10) (1995) 3799; Gil Sevillano et al., Prog. Mater. Sci. 25 (1981) 379; Dillamore et al., Metal Sci. 13 (1979) 73). This explains previous observations (Ratchev et al., Mater. Sci. Eng. A222 (1997) 189) on improved hot ductility in materials with large interparticle spacings.
The growing demand for more fuel-efficient vehicles to reduce energy consumption and air pollutio... more The growing demand for more fuel-efficient vehicles to reduce energy consumption and air pollution is a challenge for the automotive industry. The characteristic properties of aluminium, high strength stiffness to weight ratio, good formability, good corrosion resistance, and recycling ...
752 Aluminium Alloys - ICAA5 600 г Position 10 Position 12 Position 7 -^ 41 .0 44.0 Figure 6: X R... more 752 Aluminium Alloys - ICAA5 600 г Position 10 Position 12 Position 7 -^ 41 .0 44.0 Figure 6: X Ray diffractographs from positions 7, 10 and 12 Hasenclever [3] has reported that precipitation of Fe atoms occurs in a AA1050 alloy ingot during cool-down from soak which further ...
Uploads
Papers by Peter Smet