22 research outputs found
Interaction Between Solid Copper Jets and Powerful Electrical Current Pulses
The interaction between a solid copper jet and an electric current pulse is studied. Coppe
VĂ€xelverkan mellan cylindriska penetratorer och keramiska och elektromagnetiska pansar
Armoured vehicles have traditionally used steel armour as protection against penetrators such as projectiles and shaped charge jets. The latter produce a thin stretching metal jet, usually of copper, with a tip velocity of about 7-8 km/s. In order to obtain more weight-efficient solutions, there is a search for lighter materials and other protection techniques. In this thesis, ceramic and electromagnetic armours are studied. Ceramic materials are lighter than steel, and their high compressive strength makes them useful as armour materials. Electromagnetic armour consists of two metal plates connected to an electric power supply capable of delivering a strong current pulse. A conductive penetrator passing through both plates is destroyed by the effects of the resulting current. Tests of the ceramic armour materials alumina and boron carbide were performed with reverse impact technique, which signifies that a target assembly (ceramic confined in a metal cylinder) was launched by a gun towards a projectile placed in front of the gun barrel. By this technique yaw was eliminated, but the geometric scale had to be very small. Therefore, we studied scaling laws for ceramic armour through a series of tests with direct impact technique and projectile diameters from 2 to 10 mm. The small scale has the advantage that flash X-ray photography can be used to photograph the projectile inside the ceramic target. The phenomenon of interface defeat or dwell was also demonstrated. It signifies that the ceramic, at least for a short time, can withstand the impact pressure so that the projectile just flows out onto the target surface. A transition velocity, above which dwell does not occur, was determined. Simulations were performed with the continuum-dynamic code Autodyn and by use of a model for the brittle ceramic materials by Johnson and Holmquist. The simulations reasonably well represented the penetration behaviour above the transition velocity. They also did below, if under this condition the ceramic model was forced to remain undamaged. The performance of electromagnetic armour was tested against a shaped charge jet. The jet was registered with shadowgraph flash X-ray photography between the plates and after passing through the plates. The current through the jet and the voltage over the plates were also registered. The current caused heating leading to melting and even vaporization. The magnetic Lorentz force compressed the jet radially, and as this effect increases with decreasing jet radius, instability may arise. Explosions in the compressed regions resulted in a fragmented jet with disk-shaped fragments which are less effective penetrators than the elongated fragments obtained in the absence of current. We also performed a theoretical study, in which the penetrator was subjected to small elastic strains only and the current was constant. The magnetic field was determined by FFT, and the stresses due to the Lorentz force were calculated with a semi-analytical method. The velocity skin effect was demonstrated
VĂ€xelverkan mellan cylindriska penetratorer och keramiska och elektromagnetiska pansar
Armoured vehicles have traditionally used steel armour as protection against penetrators such as projectiles and shaped charge jets. The latter produce a thin stretching metal jet, usually of copper, with a tip velocity of about 7-8 km/s. In order to obtain more weight-efficient solutions, there is a search for lighter materials and other protection techniques. In this thesis, ceramic and electromagnetic armours are studied. Ceramic materials are lighter than steel, and their high compressive strength makes them useful as armour materials. Electromagnetic armour consists of two metal plates connected to an electric power supply capable of delivering a strong current pulse. A conductive penetrator passing through both plates is destroyed by the effects of the resulting current. Tests of the ceramic armour materials alumina and boron carbide were performed with reverse impact technique, which signifies that a target assembly (ceramic confined in a metal cylinder) was launched by a gun towards a projectile placed in front of the gun barrel. By this technique yaw was eliminated, but the geometric scale had to be very small. Therefore, we studied scaling laws for ceramic armour through a series of tests with direct impact technique and projectile diameters from 2 to 10 mm. The small scale has the advantage that flash X-ray photography can be used to photograph the projectile inside the ceramic target. The phenomenon of interface defeat or dwell was also demonstrated. It signifies that the ceramic, at least for a short time, can withstand the impact pressure so that the projectile just flows out onto the target surface. A transition velocity, above which dwell does not occur, was determined. Simulations were performed with the continuum-dynamic code Autodyn and by use of a model for the brittle ceramic materials by Johnson and Holmquist. The simulations reasonably well represented the penetration behaviour above the transition velocity. They also did below, if under this condition the ceramic model was forced to remain undamaged. The performance of electromagnetic armour was tested against a shaped charge jet. The jet was registered with shadowgraph flash X-ray photography between the plates and after passing through the plates. The current through the jet and the voltage over the plates were also registered. The current caused heating leading to melting and even vaporization. The magnetic Lorentz force compressed the jet radially, and as this effect increases with decreasing jet radius, instability may arise. Explosions in the compressed regions resulted in a fragmented jet with disk-shaped fragments which are less effective penetrators than the elongated fragments obtained in the absence of current. We also performed a theoretical study, in which the penetrator was subjected to small elastic strains only and the current was constant. The magnetic field was determined by FFT, and the stresses due to the Lorentz force were calculated with a semi-analytical method. The velocity skin effect was demonstrated
VĂ€xelverkan mellan cylindriska penetratorer och keramiska och elektromagnetiska pansar
Armoured vehicles have traditionally used steel armour as protection against penetrators such as projectiles and shaped charge jets. The latter produce a thin stretching metal jet, usually of copper, with a tip velocity of about 7-8 km/s. In order to obtain more weight-efficient solutions, there is a search for lighter materials and other protection techniques. In this thesis, ceramic and electromagnetic armours are studied. Ceramic materials are lighter than steel, and their high compressive strength makes them useful as armour materials. Electromagnetic armour consists of two metal plates connected to an electric power supply capable of delivering a strong current pulse. A conductive penetrator passing through both plates is destroyed by the effects of the resulting current. Tests of the ceramic armour materials alumina and boron carbide were performed with reverse impact technique, which signifies that a target assembly (ceramic confined in a metal cylinder) was launched by a gun towards a projectile placed in front of the gun barrel. By this technique yaw was eliminated, but the geometric scale had to be very small. Therefore, we studied scaling laws for ceramic armour through a series of tests with direct impact technique and projectile diameters from 2 to 10 mm. The small scale has the advantage that flash X-ray photography can be used to photograph the projectile inside the ceramic target. The phenomenon of interface defeat or dwell was also demonstrated. It signifies that the ceramic, at least for a short time, can withstand the impact pressure so that the projectile just flows out onto the target surface. A transition velocity, above which dwell does not occur, was determined. Simulations were performed with the continuum-dynamic code Autodyn and by use of a model for the brittle ceramic materials by Johnson and Holmquist. The simulations reasonably well represented the penetration behaviour above the transition velocity. They also did below, if under this condition the ceramic model was forced to remain undamaged. The performance of electromagnetic armour was tested against a shaped charge jet. The jet was registered with shadowgraph flash X-ray photography between the plates and after passing through the plates. The current through the jet and the voltage over the plates were also registered. The current caused heating leading to melting and even vaporization. The magnetic Lorentz force compressed the jet radially, and as this effect increases with decreasing jet radius, instability may arise. Explosions in the compressed regions resulted in a fragmented jet with disk-shaped fragments which are less effective penetrators than the elongated fragments obtained in the absence of current. We also performed a theoretical study, in which the penetrator was subjected to small elastic strains only and the current was constant. The magnetic field was determined by FFT, and the stresses due to the Lorentz force were calculated with a semi-analytical method. The velocity skin effect was demonstrated
Implementering av strategier - En studie av handelshus i Göteborg
Bakgrund och problem: Ett företag kan ha strategier som Àr fullstÀndigt ÀndamÄlsenliga och
anpassade till företagets situation, dock Àr det av avgörande betydelse att de förankras i
organisationen samt att det finns en grundlÀggande förstÄelse för dem. Metoden att implementera strategier i ett företag kan dÀrmed ge effekt pÄ företagets förmÄga att uppnÄ
sina mÄl.
Syfte: Syftet med studien Àr att undersöka och beskriva om strategier implementeras i företag
samt vilken betydelse tillvÀgagÄngssÀttet har vid implementering av strategier. Vi vill se om det föreligger skillnader i synen pÄ strategier och implementering, dels mellan olika företag,
dels mellan personer pÄ olika nivÄer inom företagen.
AvgrÀnsningar: Det strategibegrepp som studien inriktas pÄ Àr affÀrsstrategi. Avsikten Àr inte
att nÀrmare granska och analysera de undersökta företagens verksamheter eller ekonomiska
redovisning. Föresatsen Àr inte att undersöka eller bedöma huruvida de strategier företagen valt Àr de rÀtta eller om de Àr relevanta för att uppnÄ företagets mÄl.
Metod: Studien Àr av kvalitativ art och det empiriska materialet insamlades genom personliga
intervjuer. UtgÄngspunkten i studien Àr den teoretiska referensram vi utformade med hjÀlp av
litteratur och forskningsartiklar inom Àmnet, mot vilken empirin stÀlldes.
Resultat och slutsatser: Det Àr av vÀsentlighet att strategival och metod för implementering av strategier följs Ät. Om sÄ inte sker Àr det svÄrt för företag att implementera sina strategier.
Oavsett val av perspektiv Àr det möjligt att implementera strategier och goda förutsÀttningar
skapas genom att hela organisationen medverkar och förstÄr företagets strategier. Personalens
delaktighet och en bra dialog inom företaget Àr tydliga tecken pÄ att strategier blir
implementerade.
Förslag till fortsatta studier: Ett förslag Àr att studera hur strategiimplementering fungerar
pÄ större företag, med mer resurser. Ett annat förslag pÄ undersökningsomrÄde Àr vilka
konsekvenser val av strategi och implementeringsmetoder fÄr pÄ graden av mÄluppfyllelse. Ytterligare ett förslag Àr att genomföra en studie pÄ företag som anser att deras strategier inte leder till mÄluppfyllelse för att se om misslyckandet beror pÄ att strategierna Àr fel
formulerade eller fel implementerade