SS
S. Shroff
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1
In multi-stage launch vehicles, the adjacent stage re-enters the Earth atmosphere. Once the stage is re-entering the atmosphere, the low-melting-point materials melt and the inner parts will be exposed to excessive heat. With heat increasing, the parts will break into debris. Some of the fragments will burn in the atmosphere, others will crash into the Earth’s surface. Since there is a lack of knowledge about the re-entering physics, Demise Observation Capsule (DOC) project is started. The DOC collects information about the re-entry progress of launch vehicle stage, where it is mounted on. Several launchers and stages are considered to investigate the effect of the location on the DOC’s configuration. In an ideal situation, the DOC can be placed on all stages/parts of launch vehicles and at the same time it is optimized for that location. A generalized design concept that fits on several locations and stages, will reduce the cost and effort. Therefore, the thesis objective is to determine whether it is feasible to have a generalized DOC or an optimized DOC per location and load case. Additionally, the current DOC is designed for four locations and the second objective of this thesis is to optimize the current DOC and shift its center of gravity to the nose of the DOC. For this reason, the main research questions are as follows: Is it feasible to generalize the DOC concept design so that it will fit on every ESA launcher and stage and meet the predefined requirements and will withstand environmental loads while general operability of the DOC is guaranteed? How can the center of gravity be shifted on the DOC to its nose under the current designed loads such that the DOC can be made more stable?
...
In multi-stage launch vehicles, the adjacent stage re-enters the Earth atmosphere. Once the stage is re-entering the atmosphere, the low-melting-point materials melt and the inner parts will be exposed to excessive heat. With heat increasing, the parts will break into debris. Some of the fragments will burn in the atmosphere, others will crash into the Earth’s surface. Since there is a lack of knowledge about the re-entering physics, Demise Observation Capsule (DOC) project is started. The DOC collects information about the re-entry progress of launch vehicle stage, where it is mounted on. Several launchers and stages are considered to investigate the effect of the location on the DOC’s configuration. In an ideal situation, the DOC can be placed on all stages/parts of launch vehicles and at the same time it is optimized for that location. A generalized design concept that fits on several locations and stages, will reduce the cost and effort. Therefore, the thesis objective is to determine whether it is feasible to have a generalized DOC or an optimized DOC per location and load case. Additionally, the current DOC is designed for four locations and the second objective of this thesis is to optimize the current DOC and shift its center of gravity to the nose of the DOC. For this reason, the main research questions are as follows: Is it feasible to generalize the DOC concept design so that it will fit on every ESA launcher and stage and meet the predefined requirements and will withstand environmental loads while general operability of the DOC is guaranteed? How can the center of gravity be shifted on the DOC to its nose under the current designed loads such that the DOC can be made more stable?
Application of C/PEKK UD Tape for Welded Aircraft Movables
A trade study for a single aisle aircraft rudder
In a strive to further improve the performance of Aircraft movables the performance of Carbon fibre PolyEtherKetoneKetone (C/PEKK) on component level was assessed in this study. In this study 3 concepts were designed for a fictitious Next Signle Aisle aircraft (NSA) rudder to perform a trade-off between the two composite materials and the two stiffening concepts. An existing C/PPS multi-rib rudder concept is used as a reference. Specified requirements were elaborated to create a C/PEKK based multi-rib rudder redesign. Two multi-rib concepts, each with a different minimum skin thickness, were made and compared. The weight and cost of these two concepts was found to be nearly equal. Alternative stiffening concepts for the multi-rib were generated in collaboration with experts. Grid-stiffening (GS) of the skin using a short fibre reinforced composite was selected. The GS skin allowed most of the ribs to be omitted so that part count and assembly effort could be reduced. The multi-rib concept proved to be the lightest, regardless of the used material. The Technology Readiness Level (TRL) of some manufacturing processes for C/PEKK is low and requires more development. The C/PEKK rudder shall be a viable option in the near future when all envisioned manufacturing concepts and welding of C/PEKK tape become available. The GS rudder requires more research and development. The short fibre material and manufacturing process of the grid have a low TRL and are not yet qualified. A discrete model of the GS skin is also required to better understand the behaviour of the rudder. Thus the GS rudder is expected to be a viable solution in the long term future.
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In a strive to further improve the performance of Aircraft movables the performance of Carbon fibre PolyEtherKetoneKetone (C/PEKK) on component level was assessed in this study. In this study 3 concepts were designed for a fictitious Next Signle Aisle aircraft (NSA) rudder to perform a trade-off between the two composite materials and the two stiffening concepts. An existing C/PPS multi-rib rudder concept is used as a reference. Specified requirements were elaborated to create a C/PEKK based multi-rib rudder redesign. Two multi-rib concepts, each with a different minimum skin thickness, were made and compared. The weight and cost of these two concepts was found to be nearly equal. Alternative stiffening concepts for the multi-rib were generated in collaboration with experts. Grid-stiffening (GS) of the skin using a short fibre reinforced composite was selected. The GS skin allowed most of the ribs to be omitted so that part count and assembly effort could be reduced. The multi-rib concept proved to be the lightest, regardless of the used material. The Technology Readiness Level (TRL) of some manufacturing processes for C/PEKK is low and requires more development. The C/PEKK rudder shall be a viable option in the near future when all envisioned manufacturing concepts and welding of C/PEKK tape become available. The GS rudder requires more research and development. The short fibre material and manufacturing process of the grid have a low TRL and are not yet qualified. A discrete model of the GS skin is also required to better understand the behaviour of the rudder. Thus the GS rudder is expected to be a viable solution in the long term future.
Over the past decade, wind turbine towers have grown taller and wider to support high capacity turbines. It may, therefore, be prudent to investigate materials alternative to steel to mitigate an increase in tower mass, cost, and complexities in transportation & manufacturing associated with the steel towers. The current research focuses on the preliminary design of economically feasible composite wind turbine towers.Some of the project objectives involve setting up the design tool for tubular and lattice tower made up of Glass Fiber Reinforced Plastic (GFRP) and Carbon Fiber Reinforced Plastic (CFRP) material, preliminary design of possible joining techniques, setting up the cost model for various manufacturing approaches and assembly techniques and comparison of composite towers to steel tower design regarding mass and cost. The design tool will incorporate all the essential load cases, structural and geometric constraints and will help to analyze the composite towers with various hub heights and for 2.1 MW and 5 MW turbinecapacities.Loads and constraints are estimated through the literature study. Preliminary design of the tubular tower has been carried out using an analytical approach. For the lattice towers, a Finite Element Method (FEM) approach using Matlab was the suitable method to perform the analysis. A minimum first natural frequency constraint of 0.27Hz and 0.22Hz have been incorporated during the design for 2.1MW and 5MW turbine capacity towers respectively. For the joint design, bolted and adhesive joints are considered and the failure modes associatedwith these joints have been incorporated into the design to get an estimate of the joint mass and cost. The cost modeling of composite structures was done using the parametricequations that fit the Process Cost Analysis Database (PCAD) cost model in the region of interest. These parametric equations are usually functions of the surface area of the structure, perimeter, the number of plies and the complexity of the part. The final part involves comparison of the GFRP and CFRP towers with steel towers and comments on the feasibility of the composite towers.CFRP tubular and lattice towers show a mass reduction of up to 60% for lower hub height towers (<=100m), but this advantage decreases with height. Due to the high material cost, the CFRP towers are at least 3-4 times costlier than steel towers. For the GFRP material system, up to 35% mass reduction was found in the tubular design with lower hub height (<=100m). 5MW-100m hub height GFRP tubular tower showed the highest mass advantage (35%) and was the closest in cost to the steel design with the GFRP tower being 4% costlier. The GFRP lattice towers showed a similar trend with up to 35% but were at least 27% costlier than steel tower due to the high material and joint costs.The only region where composite currently shows any promises of mass and cost feasibility is for smaller hub heights (<=100m) and on tubular towers. The major existing difficulties with steel towers are for heights in the range of 125-150m, and in this region, the composite tower design does not show mass or cost advantages. Based on the results of the various trade studies and optimized designs, it was concluded that the composites do not hold a definitive promise as an alternative material for wind turbine towers over steel. With the current technology and understanding of the tower designs, the mass advantage promised by composite towers is not enough for composites to be deemed a viable option that can thrive in a competitive market for renewable energy. Thus a few scopes for future research are provided that can help in strengthening the understanding of the composite tower design
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Over the past decade, wind turbine towers have grown taller and wider to support high capacity turbines. It may, therefore, be prudent to investigate materials alternative to steel to mitigate an increase in tower mass, cost, and complexities in transportation & manufacturing associated with the steel towers. The current research focuses on the preliminary design of economically feasible composite wind turbine towers.Some of the project objectives involve setting up the design tool for tubular and lattice tower made up of Glass Fiber Reinforced Plastic (GFRP) and Carbon Fiber Reinforced Plastic (CFRP) material, preliminary design of possible joining techniques, setting up the cost model for various manufacturing approaches and assembly techniques and comparison of composite towers to steel tower design regarding mass and cost. The design tool will incorporate all the essential load cases, structural and geometric constraints and will help to analyze the composite towers with various hub heights and for 2.1 MW and 5 MW turbinecapacities.Loads and constraints are estimated through the literature study. Preliminary design of the tubular tower has been carried out using an analytical approach. For the lattice towers, a Finite Element Method (FEM) approach using Matlab was the suitable method to perform the analysis. A minimum first natural frequency constraint of 0.27Hz and 0.22Hz have been incorporated during the design for 2.1MW and 5MW turbine capacity towers respectively. For the joint design, bolted and adhesive joints are considered and the failure modes associatedwith these joints have been incorporated into the design to get an estimate of the joint mass and cost. The cost modeling of composite structures was done using the parametricequations that fit the Process Cost Analysis Database (PCAD) cost model in the region of interest. These parametric equations are usually functions of the surface area of the structure, perimeter, the number of plies and the complexity of the part. The final part involves comparison of the GFRP and CFRP towers with steel towers and comments on the feasibility of the composite towers.CFRP tubular and lattice towers show a mass reduction of up to 60% for lower hub height towers (<=100m), but this advantage decreases with height. Due to the high material cost, the CFRP towers are at least 3-4 times costlier than steel towers. For the GFRP material system, up to 35% mass reduction was found in the tubular design with lower hub height (<=100m). 5MW-100m hub height GFRP tubular tower showed the highest mass advantage (35%) and was the closest in cost to the steel design with the GFRP tower being 4% costlier. The GFRP lattice towers showed a similar trend with up to 35% but were at least 27% costlier than steel tower due to the high material and joint costs.The only region where composite currently shows any promises of mass and cost feasibility is for smaller hub heights (<=100m) and on tubular towers. The major existing difficulties with steel towers are for heights in the range of 125-150m, and in this region, the composite tower design does not show mass or cost advantages. Based on the results of the various trade studies and optimized designs, it was concluded that the composites do not hold a definitive promise as an alternative material for wind turbine towers over steel. With the current technology and understanding of the tower designs, the mass advantage promised by composite towers is not enough for composites to be deemed a viable option that can thrive in a competitive market for renewable energy. Thus a few scopes for future research are provided that can help in strengthening the understanding of the composite tower design
The automotive industry has developed an interest in manufacturing structural parts from continuous fibre-reinforced polymers because legislation is becoming more strict on the permissible CO2 emission of newly produced vehicles. Additional requirements on the level of recyclability has raised the question if composite materials with a thermoplastic matrix in particular can be utilised in the body structure. From the perspective of cost sensitivity, the conventional automotive manufacturing chain has to remain as it is and requires the body structure to pass through the automotive paint shop and subjects all structural elements to significant hygrothermal loading. The objective of this research is to analyse the deformation behaviour of continuous fibre-reinforced thermoplastics subjected to hygrothermal loading characteristic for the automotive painting process.
Studying the theory behind viscoelastic problems revealed that numerical solutions to the integral form of the linear viscoelastic constitutive equations often pose a problem regarding computational memory usage because of the importance of strain history. Utilising a recursive formulation of the constitutive equations eliminated this problem and identified the required material parameters for the numerical model. Thermal expansion, hygroscopic shrinkage, polymer-chemical effects, and stress relaxation were the four phenomena that governed the deformation. Measurements with a dilatometer, a micrometer, and an analytical scale yielded quantitative results about hygrothermal expansion. Thermogravimetric analysis provided information on the moisture diffusion and dynamic mechanical analysis quantified the stress relaxation behaviour. Quasi-static tensile tests confirmed the linearity of the viscoelasticity and digital image correlation supplied the major Poisson’s ratio.
A finite element model has been developed that implements hygrothermal expansion and takes into account orthotropic linear viscoelastic behaviour by means of a material user subroutine. Adopting a sequential uncoupled simulation approach allowed the prediction of heat transfer, moisture diffusion, and stress distribution. A semi-numerical simulation approach enabled the calculation of the expansion of symmetric balanced laminates through classical laminate theory whilst taking into account the time- and temperature-dependency of the mechanical properties computed with a micromechanical model created for special orthotropic laminae. Sensitivity studies justified the usage of one-dimensional heat transfer- and moisture diffusion simulations. Moreover, mesh- and time step convergence studies revealed the sensitivity of the simulation to these parameters.
Dilatometer experiments with dry- and moisture saturated multi-directional specimens confirmed the correct calculation of hygrothermal expansion. Increasing in complexity, measuring the out-of-plane deformation of a clamped unidirectional tensile specimen subjected to a temperature profile that resembles the most severe thermal loading found in the automotive painting process confirmed a satisfactory agreement between the numerical results and the experimental data. Geometric compensation for the thermal expansion of the fixture and choosing graphite as construction material kept the thermal expansion of the fixture to a minimum. Components with the geometry of the roof bow that is currently in series production for the BMW 7 Series were manufactured by a thermoforming method to allow validation of the simulation with complex geometry. A proper agreement between the predicted deformation behaviour by the semi-numerical simulation and the optical measurements of the dry- and moisture saturated roof bows with various multi-directional lay-ups validated the functioning of the developed simulation. ...
Studying the theory behind viscoelastic problems revealed that numerical solutions to the integral form of the linear viscoelastic constitutive equations often pose a problem regarding computational memory usage because of the importance of strain history. Utilising a recursive formulation of the constitutive equations eliminated this problem and identified the required material parameters for the numerical model. Thermal expansion, hygroscopic shrinkage, polymer-chemical effects, and stress relaxation were the four phenomena that governed the deformation. Measurements with a dilatometer, a micrometer, and an analytical scale yielded quantitative results about hygrothermal expansion. Thermogravimetric analysis provided information on the moisture diffusion and dynamic mechanical analysis quantified the stress relaxation behaviour. Quasi-static tensile tests confirmed the linearity of the viscoelasticity and digital image correlation supplied the major Poisson’s ratio.
A finite element model has been developed that implements hygrothermal expansion and takes into account orthotropic linear viscoelastic behaviour by means of a material user subroutine. Adopting a sequential uncoupled simulation approach allowed the prediction of heat transfer, moisture diffusion, and stress distribution. A semi-numerical simulation approach enabled the calculation of the expansion of symmetric balanced laminates through classical laminate theory whilst taking into account the time- and temperature-dependency of the mechanical properties computed with a micromechanical model created for special orthotropic laminae. Sensitivity studies justified the usage of one-dimensional heat transfer- and moisture diffusion simulations. Moreover, mesh- and time step convergence studies revealed the sensitivity of the simulation to these parameters.
Dilatometer experiments with dry- and moisture saturated multi-directional specimens confirmed the correct calculation of hygrothermal expansion. Increasing in complexity, measuring the out-of-plane deformation of a clamped unidirectional tensile specimen subjected to a temperature profile that resembles the most severe thermal loading found in the automotive painting process confirmed a satisfactory agreement between the numerical results and the experimental data. Geometric compensation for the thermal expansion of the fixture and choosing graphite as construction material kept the thermal expansion of the fixture to a minimum. Components with the geometry of the roof bow that is currently in series production for the BMW 7 Series were manufactured by a thermoforming method to allow validation of the simulation with complex geometry. A proper agreement between the predicted deformation behaviour by the semi-numerical simulation and the optical measurements of the dry- and moisture saturated roof bows with various multi-directional lay-ups validated the functioning of the developed simulation. ...
The automotive industry has developed an interest in manufacturing structural parts from continuous fibre-reinforced polymers because legislation is becoming more strict on the permissible CO2 emission of newly produced vehicles. Additional requirements on the level of recyclability has raised the question if composite materials with a thermoplastic matrix in particular can be utilised in the body structure. From the perspective of cost sensitivity, the conventional automotive manufacturing chain has to remain as it is and requires the body structure to pass through the automotive paint shop and subjects all structural elements to significant hygrothermal loading. The objective of this research is to analyse the deformation behaviour of continuous fibre-reinforced thermoplastics subjected to hygrothermal loading characteristic for the automotive painting process.
Studying the theory behind viscoelastic problems revealed that numerical solutions to the integral form of the linear viscoelastic constitutive equations often pose a problem regarding computational memory usage because of the importance of strain history. Utilising a recursive formulation of the constitutive equations eliminated this problem and identified the required material parameters for the numerical model. Thermal expansion, hygroscopic shrinkage, polymer-chemical effects, and stress relaxation were the four phenomena that governed the deformation. Measurements with a dilatometer, a micrometer, and an analytical scale yielded quantitative results about hygrothermal expansion. Thermogravimetric analysis provided information on the moisture diffusion and dynamic mechanical analysis quantified the stress relaxation behaviour. Quasi-static tensile tests confirmed the linearity of the viscoelasticity and digital image correlation supplied the major Poisson’s ratio.
A finite element model has been developed that implements hygrothermal expansion and takes into account orthotropic linear viscoelastic behaviour by means of a material user subroutine. Adopting a sequential uncoupled simulation approach allowed the prediction of heat transfer, moisture diffusion, and stress distribution. A semi-numerical simulation approach enabled the calculation of the expansion of symmetric balanced laminates through classical laminate theory whilst taking into account the time- and temperature-dependency of the mechanical properties computed with a micromechanical model created for special orthotropic laminae. Sensitivity studies justified the usage of one-dimensional heat transfer- and moisture diffusion simulations. Moreover, mesh- and time step convergence studies revealed the sensitivity of the simulation to these parameters.
Dilatometer experiments with dry- and moisture saturated multi-directional specimens confirmed the correct calculation of hygrothermal expansion. Increasing in complexity, measuring the out-of-plane deformation of a clamped unidirectional tensile specimen subjected to a temperature profile that resembles the most severe thermal loading found in the automotive painting process confirmed a satisfactory agreement between the numerical results and the experimental data. Geometric compensation for the thermal expansion of the fixture and choosing graphite as construction material kept the thermal expansion of the fixture to a minimum. Components with the geometry of the roof bow that is currently in series production for the BMW 7 Series were manufactured by a thermoforming method to allow validation of the simulation with complex geometry. A proper agreement between the predicted deformation behaviour by the semi-numerical simulation and the optical measurements of the dry- and moisture saturated roof bows with various multi-directional lay-ups validated the functioning of the developed simulation.
Studying the theory behind viscoelastic problems revealed that numerical solutions to the integral form of the linear viscoelastic constitutive equations often pose a problem regarding computational memory usage because of the importance of strain history. Utilising a recursive formulation of the constitutive equations eliminated this problem and identified the required material parameters for the numerical model. Thermal expansion, hygroscopic shrinkage, polymer-chemical effects, and stress relaxation were the four phenomena that governed the deformation. Measurements with a dilatometer, a micrometer, and an analytical scale yielded quantitative results about hygrothermal expansion. Thermogravimetric analysis provided information on the moisture diffusion and dynamic mechanical analysis quantified the stress relaxation behaviour. Quasi-static tensile tests confirmed the linearity of the viscoelasticity and digital image correlation supplied the major Poisson’s ratio.
A finite element model has been developed that implements hygrothermal expansion and takes into account orthotropic linear viscoelastic behaviour by means of a material user subroutine. Adopting a sequential uncoupled simulation approach allowed the prediction of heat transfer, moisture diffusion, and stress distribution. A semi-numerical simulation approach enabled the calculation of the expansion of symmetric balanced laminates through classical laminate theory whilst taking into account the time- and temperature-dependency of the mechanical properties computed with a micromechanical model created for special orthotropic laminae. Sensitivity studies justified the usage of one-dimensional heat transfer- and moisture diffusion simulations. Moreover, mesh- and time step convergence studies revealed the sensitivity of the simulation to these parameters.
Dilatometer experiments with dry- and moisture saturated multi-directional specimens confirmed the correct calculation of hygrothermal expansion. Increasing in complexity, measuring the out-of-plane deformation of a clamped unidirectional tensile specimen subjected to a temperature profile that resembles the most severe thermal loading found in the automotive painting process confirmed a satisfactory agreement between the numerical results and the experimental data. Geometric compensation for the thermal expansion of the fixture and choosing graphite as construction material kept the thermal expansion of the fixture to a minimum. Components with the geometry of the roof bow that is currently in series production for the BMW 7 Series were manufactured by a thermoforming method to allow validation of the simulation with complex geometry. A proper agreement between the predicted deformation behaviour by the semi-numerical simulation and the optical measurements of the dry- and moisture saturated roof bows with various multi-directional lay-ups validated the functioning of the developed simulation.