Tube bending is a widely used manufacturing process in the aerospace, automotive, and other industries. During tube bending, considerable in-plane distortion and thickness variation occurs. The thickness increases at the intrados (surface of tube in contact with the die) and it reduces at the extrados (outer surface of the tube). In some cases, when the bend die radius is small, wrinkling occurs at the intrados. In industry a mandrel is used to eliminate wrinkling and reduce distortion. However, in the case of a close bend die radius, use of a mandrel should be avoided as bending with the mandrel increases the thinning of the wall at the extrados, which is undesirable in the manufacturing operation. The present research focuses on additional loadings such as axial force and internal pressure which can be used to achieve better shape control and thickness distribution of the tube. Based on plasticity theories, an analytical model is developed to predict cross section distortion and thickness change of tubes under various loading conditions. Results from both the FEA and analytical model indicated that at the intrados the increase in thickness for bending with internal pressure and bending with combined axial pull and internal pressure was nearly the same. But in the case of bending with the combination of axial pull and internal pressure there was a significant reduction of thickness at the extrados. A parametric study was conducted for the case of bending with combined internal pressure and axial pull and it was seen that with proper selection of the pressure and axial pull wrinkling can be eliminated, thickness distribution around the tube can be optimized, and cross section distortion of the tube can be reduced. Predictions of the analytical model are in good agreement with finite element simulations and published experimental results. The model can be used to evaluate tooling and process design in tube bending.

The aim of the project is to develop a model, which is going to be used for mass reduction of a standard profile of aluminium seat rails in Aircraft structure. Using nonlinear analysis including plasticity and material failure laws the effect of changes in geometry vs. ultimate load is analysed (ABAQUS 6.11). First, the non-linear model used is validated with experimental testing: Boundary conditions and material properties are adjusted based on load displacement curves, strain gauges information and failure patterns. Less than 1% deviation is achieved between simulation and testing. An inclusion of material imperfection led to a 5% improvement of the results. Using the validated algorithm, a mass reduction is performed via geometry variation. / Ziel der Studie ist es ein adäquates Simulationsmodell zu entwickeln, welches zur Gewichtsreduzierung einer Standardprofil Aluminium Sitzschiene im Flugzeug verwendet werden kann. In einer nichtlinearen Analyse unter Berücksichtigung der Plastizität des Materials und von Materialfehlern wird die Auswirkung der Geometrieänderungen auf die maximale Traglast analysiert (ABAQUS 6.11). Zunächst wird das nicht-lineare Modell mit experimentell ermittelten Daten überprüft: Randbedingungen und Materialeigenschaften werden basierend auf Lastverschiebungskurven, Informationen von Dehnungsmessstreifen und Versagensmustern angepasst. Dabei wurden weniger als 1% Abweichung zwischen Simulation und Test erzielt. Die Berücksichtigung von Materialfehlern führte zu einer 5%-igen Verbesserung der Ergebnisse. Mit dem validierten Modell wird abschließend eine Gewichtsreduzierung mittels Geometrievariation durchgeführt.

Warm forming of aluminum alloys of has shown promising results for increasing the formability of aluminum alloy sheet. Warm forming is a term that is generally used to describe a sheet metal forming process, where part or all of the blank is formed at an elevated temperature of less than one half of the material’s melting temperature. The focus of this work is to study the effects of warm forming on Novelis X926 clad aluminum brazing sheet. Warm forming of clad aluminum brazing sheet, which is commonly used in automotive heat exchangers has not been studied. This work can be split into three main goals: i) to characterize the material behavior and develop a constitutive model, ii) to experimentally determine the effects of warm forming on deep drawing; and, iii) to create and validate a finite element model for warm forming of Novelis X926. For an accurate warm forming material model to be created, a temperature and rate dependant hardening law as well as an anisotropic yield function are required. Uniaxial isothermal tensile tests were performed on 0.5mm thick Novelis X926at 25°C (room temperature), 100°C, 150°C, 200°C, and 250°C. At each temperature, tests were performed with various strain rates between 7.0 E -4 /sec and 7.0 E -2 /sec to determine the strain rate sensitivity. Tensile tests were also performed at 0° (longitudinal), 45° (diagonal), and 90° (transverse) with respect to the material rolling direction in order to assess the anisotropy of the material. It was found that increasing forming temperature increases elongation to failure by 200%, decreases flow stress by 35%, and increases strain rate sensitivity. Barlat’s Yield 2000 yield function (Barlat et al., 2003a) and the Bergström work hardening law (van den Boogaard and Huétink , 2006) were found to accurately method model the material behavior. Warm deep drawing of 101.6 mm (4”) diameter cylindrical cups was performed using specially designed tooling with heated dies and a cooled punch. Deep drawing was performed on 228.6 mm (9“) and 203.2 mm (8”) diameter blanks of 0.5 mm thick Novelis X926. Deep drawing was performed with die temperatures ranging from 25°C to 300°C with a cooled punch. Teflon sheet and Dasco Cast 1200 lubricants were used in experiments. Different punch velocities were also investigated. 228.6 mm diameter blanks, which could not be drawn successfully at room temperature, were drawn successfully using 200°C dies. Increasing the die temperature further to 250°C and 300°C provided additional improvement in formability and reduced tooling loads. Increasing the punch velocity, increases the punch load when forming at elevated temperatures, reflecting the strong material rate sensitivity at elevated temperatures. A coupled thermal mechanical finite element model was developed using the Bergström hardening rule and the Yield 2000 yield surface using LS-DYNA. The model was found to accurately predict punch force for warm deep drawing using Teflon sheet as a lubricant. Results for Dasco Cast 1200 were not as accurate, due to the difficulties in modeling the lubricant’s behavior. Finite element simulations demonstrated that warm forming can be used to reduce thinning at critical locations, compared to parts formed at room temperature.

This thesis demonstrates the practicability of using Resonant Ultrasound Spectroscopy (RUS) in combination with Finite Element Analysis (FEA) to determine the size and location of a defect in a material of known geometry and physical constants. Defects were analyzed by comparing the actual change in frequency spectrum measured by RUS to the change in frequency spectrum calculated using FEA. FEA provides a means of determining acceptance/rejection criteria for Non-Destructive Testing (NDT). If FEA models of the object are analyzed with defects in probable locations; the resulting resonant frequency spectra will match the frequency spectra of actual objects with similar defects. By analyzing many FEA-generated frequency spectra, it is possible to identify patterns in behavior of the resonant frequencies of particular modes based on the nature of the defect (location, size, depth, etc.). Therefore, based on the analysis of sufficient FEA models, it should be possible to determine nature of defects in a particular object from the measured resonant frequency. Experiments were conducted on various materials and geometries comparing resonant frequency spectra measured using RUS to frequency spectra calculated using FEA. Measured frequency spectra matched calculated frequency spectra for steel specimens both before and after introduction of a thin cut. Location and depth of the cut were successfully identified based on comparison of measured to calculated resonant frequencies. However, analysis of steel specimens with thin cracks, and of ceramic specimens with thin cracks, showed significant divergence between measured and calculated frequency spectra. Therefore, it was not possible to predict crack depth or location for these specimens. This thesis demonstrates that RUS in combination with FEA can be used as an NDT method for detection and analysis of cracks in various materials, and for various geometries, but with some limitations. Experimental results verify that cracks can be detected, and their depth and location determined with reasonable accuracy. However, experimental results also indicate that there are limits to the applicability of such a method, the primary one being a lower limit to the size of crack – especially thickness of the crack - for which this method can be applied.

In recent years, traditional piezoelectric materials have been pushed to the limit in terms of performance because of countless novel applications. This has caused an increased interest in piezoelectric composites, which combine two or more constituent materials in order to create a material system that incorporates favorable attributes from each constituent. One or more of the constituents exhibits piezoelectric behavior, so that the composite has an effective electromechanical coupling. The composite material may also have enhanced properties such as stiffness, durability, and flexibility. Finite element analyses were conducted on a three-phase piezoelectric nanocomposite in order to investigate the effects of several design parameters on performance. The nanocomposite consisted of a polyimide matrix, beta-CN APB/ODPA, enhanced with single wall carbon nanotubes and PZT-5A particles. The polyimide and nan- otube phases were modeled as a single homogenized phase. This results in a two-phase nanocomposite that can be modeled entirely in the continuum domain. The material properties for the nano-reinforced matrix and PZT-5A were obtained from previous experimental efforts and from the literature. The finite element model consisted of a single representative volume element of the two-phase nanocomposite. Exact periodic boundary conditions were derived and used to minimize the analysis region. The effective mechanical, electrical, and piezoelectric properties were computed for a wide range of nanotube and PZT particle concentrations. A discrepancy was found between the experimental results from the literature and the computational results for the effective electrical properties. Several modified finite element models were developed to explore possible reasons for this discrepancy, and a hypothesis involving dispersion of the nanotubes was formulated as an attempt to explain the difference. The response of the nanocomposite under harmonic loading was also investigated using the finite element model. The effective properties were found to be highly dependent on the dielectric loss of the beta CN/SWNT matrix. It was also found that increasing the matrix loss enhanced piezoelectric performance up to a certain point. Exploiting this type of behavior could be an effective tool in designing piezoelectric composite materials.

The Coffin-Manson equations of Sn/Ag/Cu and Sn/Pb solder joints are presented in this thesis. The experimental results of CSP thermal cycle fatigue test and ball shear test are used to formulate Coffin-Manson equations. The maximum amplitude of equivalent plastic shear strain corresponding to these two experiments are employed. The MARC finite element package is used to calculate the plastic shear strain. Different published fatigue experiment results have been used to show the accuracy and the feasibility of these proposed equations. The 3-D finite element models of the BGA type¡¦s CSP and VCSEL assembly are employed to simulate the thermal cycling fatigue. Results indicate that the fatigue lifes of solder predicted by using the proposed equations have good agreement with those measured from experimental tests.

The purpose of the study is to better understand the factors that affect melt-wear in the armature-to-rail contact interface of an electromagnetic launcher (EML). In order to investigate the factors, the study uses finite element analysis (FEA) to vary parameters of a lab-scale EML at the Georgia Institute of Technology. FEA is used due to the complex nature of the system, which includes the geometry and various engineering aspects that the EML incorporates. The study focuses on an uncoupled analysis of the structural, electromagnetic (EMAG), thermal, and modal aspects. The reason for the uncoupled analysis was because the system was complex and there were computational limits. Also, by uncoupling the analysis fields, the way the parameters affected melt-wear could be viewed separately. The study varied the geometry of the armature, the stiffness of the rail system (compliance layer), and the material of the armature. The structural analysis was for the initial contact of the rail to the armature and found the von Mises stresses, contact area, and contact pressure. The EMAG analysis found the Lorentz forces in the system based on a current curve used in the lab-scale EML. The thermal analysis consisted of friction heating and Joule heating. The modal analysis was for the unstressed and pre-stressed armature. Based on the study conducted, it was found that aluminum would provide the best speeds due to its lighter mass, but lacked in the thermal resistance area. Tungsten provided the better thermal resistance, but lacked in the potential speed due to its heavier mass.

In the automotive industry uniaxial vibration testing is a common method used to predict the lifetime of components. In reality truck components work under multiaxial loads meaning that the excitation is multiaxial. A common method to account for the multiaxial effect is to apply a safety margin to the uniaxial test results. The aim of this work is to find a safety margin between the uniaxial and multiaxial testing by means of virtual vibration testing and statistical methods. Additionally to the safety margin the effect of the fixture’s stiffness on the resulting stress in components has been also investigated.

Tube bending is a widely used manufacturing process in the aerospace, automotive, and other industries. During tube bending, considerable in-plane distortion and thickness variation occurs. The thickness increases at the intrados (surface of tube in contact with the die) and it reduces at the extrados (outer surface of the tube). In some cases, when the bend die radius is small, wrinkling occurs at the intrados. In industry a mandrel is used to eliminate wrinkling and reduce distortion. However, in the case of a close bend die radius, use of a mandrel should be avoided as bending with the mandrel increases the thinning of the wall at the extrados, which is undesirable in the manufacturing operation. The present research focuses on additional loadings such as axial force and internal pressure which can be used to achieve better shape control and thickness distribution of the tube. Based on plasticity theories, an analytical model is developed to predict cross section distortion and thickness change of tubes under various loading conditions. Results from both the FEA and analytical model indicated that at the intrados the increase in thickness for bending with internal pressure and bending with combined axial pull and internal pressure was nearly the same. But in the case of bending with the combination of axial pull and internal pressure there was a significant reduction of thickness at the extrados. A parametric study was conducted for the case of bending with combined internal pressure and axial pull and it was seen that with proper selection of the pressure and axial pull wrinkling can be eliminated, thickness distribution around the tube can be optimized, and cross section distortion of the tube can be reduced. Predictions of the analytical model are in good agreement with finite element simulations and published experimental results. The model can be used to evaluate tooling and process design in tube bending.

Warm forming of aluminum alloys of has shown promising results for increasing the formability of aluminum alloy sheet. Warm forming is a term that is generally used to describe a sheet metal forming process, where part or all of the blank is formed at an elevated temperature of less than one half of the material’s melting temperature. The focus of this work is to study the effects of warm forming on Novelis X926 clad aluminum brazing sheet. Warm forming of clad aluminum brazing sheet, which is commonly used in automotive heat exchangers has not been studied. This work can be split into three main goals: i) to characterize the material behavior and develop a constitutive model, ii) to experimentally determine the effects of warm forming on deep drawing; and, iii) to create and validate a finite element model for warm forming of Novelis X926. For an accurate warm forming material model to be created, a temperature and rate dependant hardening law as well as an anisotropic yield function are required. Uniaxial isothermal tensile tests were performed on 0.5mm thick Novelis X926at 25°C (room temperature), 100°C, 150°C, 200°C, and 250°C. At each temperature, tests were performed with various strain rates between 7.0 E -4 /sec and 7.0 E -2 /sec to determine the strain rate sensitivity. Tensile tests were also performed at 0° (longitudinal), 45° (diagonal), and 90° (transverse) with respect to the material rolling direction in order to assess the anisotropy of the material. It was found that increasing forming temperature increases elongation to failure by 200%, decreases flow stress by 35%, and increases strain rate sensitivity. Barlat’s Yield 2000 yield function (Barlat et al., 2003a) and the Bergström work hardening law (van den Boogaard and Huétink , 2006) were found to accurately method model the material behavior. Warm deep drawing of 101.6 mm (4”) diameter cylindrical cups was performed using specially designed tooling with heated dies and a cooled punch. Deep drawing was performed on 228.6 mm (9“) and 203.2 mm (8”) diameter blanks of 0.5 mm thick Novelis X926. Deep drawing was performed with die temperatures ranging from 25°C to 300°C with a cooled punch. Teflon sheet and Dasco Cast 1200 lubricants were used in experiments. Different punch velocities were also investigated. 228.6 mm diameter blanks, which could not be drawn successfully at room temperature, were drawn successfully using 200°C dies. Increasing the die temperature further to 250°C and 300°C provided additional improvement in formability and reduced tooling loads. Increasing the punch velocity, increases the punch load when forming at elevated temperatures, reflecting the strong material rate sensitivity at elevated temperatures. A coupled thermal mechanical finite element model was developed using the Bergström hardening rule and the Yield 2000 yield surface using LS-DYNA. The model was found to accurately predict punch force for warm deep drawing using Teflon sheet as a lubricant. Results for Dasco Cast 1200 were not as accurate, due to the difficulties in modeling the lubricant’s behavior. Finite element simulations demonstrated that warm forming can be used to reduce thinning at critical locations, compared to parts formed at room temperature.