Sheet metal forming processes, especially deep drawing processes give diverse results by various materials. Extreme differences occur between steel sheets and aluminum sheets. The main causes of this variance are anisotropy, elastic modulus and microscopic material properties. The aim of this thesis is to evaluate the deep drawing properties and also to develop suitable process parameters for aluminum and steel sheets by finite element simulation. In the simulation, the commercial dynamic-explicit code PAM-STAMP has been used. The reliability of the finite element package was verified by a comparison with the NUMISHEET 2002 benchmarks. Additionally, a commercial part is numerically simulated for experimental verification. The results of the simulations have been compared with several experiments that were performed in Metallurgical and Materials Engineering and Mechanical Engineering Departments. Finally, the simulation results are compared with analytical expressions for verification of results. The materials investigated for the deep drawability comparison is a deep drawing quality mild steel and an aluminum alloy designated as 6111-T4. For experimental verification St4 steel is used. Results are in agreement with the fact that aluminum and steel materials behave differently upon deep drawing in terms of the onset of failure, wrinkling and final shape. Aluminum is found to be less formable than steel for cup drawing operations.

In this investigation, SCCs were prepared by keeping the total mass of cementitious materials (cement and fly ash) constant at 500 kg/m3, in which 30, 40, 50, 60, and 70% of cement, by weight, was replaced by the high-lime and low-lime fly ash. For comparison, a control SCC mixture without any fly ash was also produced. The fresh properties of the SCCs were observed through, slump flow time and diameter, V-funnel flow time, L-box height ratio, U-box height difference, segregation ratio and the rheological parameters (relative yield stress and relative plastic viscosity). Relations between workability and rheological parameters were sought. Setting times and temperature rise of the SCC were also determined. The hardened properties included the compressive strength, split tensile strength, drying shrinkage and permeation properties (absorption, sorptivity and rapid chloride permeability tests) up to 360 days. The results obtained indicated that it is possible to produce SCC with a 70% of cement replacement by both types of fly ash. The use of high volumes of fly ash in SCC not only improved the workability and permeability properties but also made it possible to produce concretes between 33-40 MPa compressive strength at 28 days.

Ultrasonic testing of concrete is often used for the assessment of its uniformity, strength, modulus of elasticity, durability and etc. therefore, the related parameters of testing such as the transducer frequency, the specimen geometry and etc. are well-known. On the other hand, most of the concrete properties are affected by the cement and the mechanical as well as some durability properties of cements are determined through cement mortars. Applications of ultrasound on determining the properties of cement mortars are quite limited. Therefore, the required specimen dimensions, transducer frequencies have not yet been established for cement mortars. In this study, ultrasonic pulse velocity (UPV) of mortars was determined with different transducers of different frequencies for different size ans shape of specimens. Within the scope of the experimental program, three different ultrasonic frequencies (54 kHz, 82 kHz, and 150 kHz) were utilized and the relation between ultrasonic testing frequency and specimen shape was experimentally investigated. It was concluded that the mechanical properties of mortar was adversely affected by the water-to-cement ratio. It was also observed that, when the length/wavelength ratio increases, the measured UPV with different transducer frequencies tends to converge to a single value. Finally, it was also concluded that an increase in moisture content of the mortar mixtures causes an increase in UPV and a decrease in compressive strength.

Ultra high temperature ceramics (UHTC) are candidate materials for high temperature applications such as leading edges for hypersonic flight vehicles, thermal protection systems for spacecraft, and rocket nozzle throat inserts due to their extremely high melting points. Tantalum and Niobium Carbide (TaC and NbC), with melting points of 3950°C and 3600°C, respectively, have high resistivity to chemical attack, making them ideal candidates for the harsh environments UHTCs are to be used in. The major setbacks to the implementation of UHTC materials for these applications are the difficulty in consolidating to full density as well as their low fracture toughness. In this study, small amounts of sintering additive were used to enhance the densification and Graphene Nanoplatelets (GNP) were dispersed in the ceramic composites to enhance the fracture toughness. While the mechanisms of toughening of GNP addition to ceramics have been previously documented, this study focused on the anisotropy of the mechanisms. Spark plasma sintering was used to consolidate both bulk GNP pellets and near full relative density TaC-NbC ceramic composites with the addition of both sintering aid and GNP and resulted in an aligned GNP orientation perpendicular to the SPS pressing axis that allowed the anisotropy to be studied. In situ high load indentation was performed that allowed real time viewing of the deformation mechanisms for enhanced analysis. The total energy dissipation when indenting the bulk GNP pellet in the in-plane GNP direction was found to be 270% greater than in the out-of-plane orientation due to the resulting deformation mechanisms that occurred. In GNP reinforced TaC-NbC composites, the projected residual damaged area as a result of indentation was 89% greater when indenting on the surface of the sintered compact (out-of-plane GNP orientation) than when indenting in the orthogonal direction (in-plane GNP orientation) which is further evidence to the anisotropy of the GNP reinforcement.

Friction Bit Joining (FBJ) is a recently developed spot joining technology capable of joining dissimilar metals. A consumable bit cuts through the upper layer of metal to be joined, then friction welds to the lower layer. The bit then snaps off, leaving a flange. This research focuses on FBJ using DP980 or DP590 steel as the lower layer, AZ31 magnesium alloy as the top layer, and 4140 or 4130 steel as the bit material. In order to determine optimal settings for the magnesium/steel joints, experimentation was performed using a purpose-built computer controlled welding machine, varying factors such as rotational speeds, plunge speed, cutting and welding depths, and dwell times. It was determined that, when using 1.6 mm thick coupons, maximum joint strengths would be obtained at a 2.03 mm cutting depth, 3.30 mm welding depth, and 2500 RPM welding speed. At these levels, the weld is stronger than the magnesium alloy, resulting in failure in the AZ31 rather than in the FBJ joint in lap shear testing.

Understanding the mechanisms that control the mechanical behavior of microscale actuators is necessary to design an actuator that responds to an applied actuation force with the desired behavior. Micro actuators which employ a diaphragm supported by torsional hinges which deform during actuation are used in many applications where device stability and reliability are critical. The material response to the stress developed within the hinge during actuation controls how the actuator will respond to the actuating force. A fully recoverable non-linear viscoelastic response has been observed in electrostatically driven micro actuators employing torsional hinges of silicon covered with thin metal films. The viscoelastic response occurs over a time period of 50 minutes at an operating temperature of 35°C. This viscoelastic phenomenon is similar to that reported in articles addressing anelastic behavior associated with viscous grain boundary slippage and dislocation bowing. In order to investigate this viscoelastic response as a function of metal film composition and thickness, bi-layer torsional hinge actuators consisting of Si with a deposited metal layer were designed to exhibit similar stress levels as the electrostatically driven micro actuators. The test devices were fabricated using common semiconductor fabrication techniques. The actuators were micromachined by deep etching 100mm diameter, 425µm thick, double side polished, single crystal (100) wafers to create a 4.5µm thick device layer. Subsequent etching of the device layer released the fixed-fixed torsional hinge test actuators. Physical vapor depositions of Au, Al and Al-Ti in two different thicknesses (100nm, and 150nm) were deposited in order to investigate the impact of metal film thickness and composition on the viscoelastic response. Grain sizes of the deposited films were estimated using backscattered electron images. Rotational actuation of the test actuators was achieved by using a modified Ambios XP-1 surface profiler that applies a constant force of 0.28mN while measuring the displacement of the actuator with respect to time. The viscoelastic response was observed in the test devices with Au and Al thin films indicating that this phenomenon is attributable to the stresses induced on the torsional hinge. Results indicate that the viscoelastic response was not observed in AlTi thin films consisting of 0.3at% titanium. Two theoretical models are presented that discuss the mechanism associated with the viscoelastic response as well as a method for inhibiting these mechanisms by the addition of an alloying element to form a second phase precipitate.

This research effort explored the possibility of using interwoven conductive and nonconductive fibers in a composite laminate for structural health monitoring (SHM). Traditional SHM systems utilize fiber optics, piezoelectrics, or detect defects by nondestructive test methods by use of sonar graphs or x-rays. However, these approaches are often expensive, time consuming and complicated. The primary objective of this research was to apply a resistance based method of structural health monitoring to a composite structure to determine structural integrity and presence of defects. The conductive properties of fiber such as carbon, copper, or constantan - a copper-nickel alloy - can be utilized as sensors within the structure. This allows the structure to provide feedback via electrical signals to a user which are essential for evaluating the health of the structure. In this research, the conductive fiber was made from constantan wire which was embedded within a composite laminate; whereas prepreg fiberglass, a nonconductive material, serves as the main structural element of the laminate. A composite laminate was constructed from four layers of TenCate 7781 “E” fiberglass and BT250E-1 resin prepreg. Integrating the constantan within the composite laminate provides a sensory element which supplies measurements of structural behavior. Thus, with fiberglass, epoxy, and a constantan conductive element, a three-part composite laminate is developed. Test specimens used in this research were fabricated using a composite air press with the recommended manufacturer cure cycle. A TenCate BT250E-1 Resin System and 7781 "E" impregnated glass-fiber/epoxy weave was used. A constantan wire of 0.01” gauge diameter was integrated into the composite structure. The composite laminate specimen with the integrated SHM system was tested under tensile and flexural loads employing test standards specified by ASTM D3039 and D7264, respectively. These test methods were modified to determine the behavior of the laminate in the elastic range only. A tension and flexural delamination test case was also developed to investigate the sensitivity of the SHM system to inherent defects. Moreover, material characteristic tests were completed to validate manufacturer provided material characteristics. The specimens were tested while varying the constantan configurations, such as the sensor length and orientation. A variety of techniques to integrate the sensor were also investigated. Two different measurement methods were used to determine strain. Strain measurements were made with Instron Bluehill 2 software and correlated to strain obtained by the structural health monitoring system with the use of a data acquisition code written to interact with a micro-ohm-meter. The experimental results showed good agreement between measurements made by the two different methods of measurement. Observations discovered that varying the length of the sensor element improved sensitivity, but resulted in different prediction models when compared to cases with less sensor length. The predictions are based on the gauge factor, which was determined for the each test case. This value provides the essential relationship between resistance and strain. Experiments proved that the measured gauge factor depended greatly on the sensor length and orientation. The correlation was of sufficient accuracy to predict strain values in a composite laminate without the use of any added tools or equipment besides the ohm-meter. Analytical solutions to the loading cases were developed to validate results obtained during experiments. The solutions were in good agreement with the experimental results.

Over recent decades, the public tendency toward using the structural composite lumber (SCL), a common composite of wood made of wood strands or veneers glued and compressed together, as structural members (especially the main load bearing members such as beams and columns) has risen considerably. In contrast to the fast-paced market growth of these products, development is slow. The experimental development is gradual and time-consuming and the computational development is even slower. The objective of this project is to introduce appropriate numerical models for limit state analysis of a certain type of SCL material called PSL. Parallel strand lumber (PSL), has mesostructures characterized by the presence of voids that renders the mesostructure highly heterogeneous. In addition to material phase aberrations such as grain angle variations and defects, void heterogeneities play an important role in determining the failure modes and strength of PSL. In this study, virtual void structures were defined to form part of the input to finite element analysis of PSL for the purpose of investigating the sensitivity of strength to the void structure. Assuming the wood phase to be homogeneous and orthotropic, the following 2D and 3D characteristics of voids were investigated: volume fraction, volume, alignment and moments of inertia of voids, as well as second moment properties, lineal path function and chord length functions of the two phase mesostructure. In addition, a method was developed to generate virtual voids in order to simulate PSL and investigate the possible effects of the void distribution on material strength. An experimental program along with a statistical survey was conducted to quantify the mentioned characteristics of the voids in two 133 mm * 133 mm * 610 mm 2.0 E Eastern Species PSL billets. As expected, most of the voids lie on the longitudinal direction of the specimen and have approximately an ellipsoidal shape. Based on this shape data, the characteristics of the ellipsoids which best t the voids were calculated. Using the statistical data of the fitted ellipsoids, a random field of virtual ellipsoid shaped voids to simulate the mesostructure of PSL was generated. In this study, the simulation of PSL material is based on two simplifying assumptions: 1) The wood phase is continuum, homogeneous and orthotropic. While in reality, the wood phase consists of glued wood strands that are heterogeneous due to their mechanical variability and only roughly orthotropic on a macro scale as a result of the varying fiber angle; 2) Voids are the mere source of uncertainty. The linear elastic analysis of carefully defined (in mesostructural aspect) PSL models can be the first step of mechanical study of the material. The effective modulus of elasticity of material in presence of voids and the distribution of conventional, principal and effective stresses considering the effect of volume fraction and shape of the voids are the target of this preliminary study. Linear elastic uniaxial analyses showed good mechanical consistency between the models including actual void shapes and the models including ellipsoidal void representations. Also, they showed that the stress mutliaxiality at the tip of the voids is negligible. The study of mechanics of PSL is incomplete unless the question of material anisotropy is taken into consideration. PSL is brittle in tension and ductile in compression. The material heterogeneity increases the complexity of the problem by affecting the stress distribution in the member. A detailed nonlinear approach has been proposed in order to investigate the mechanical behavior of PSL structural members under different uniaxial loading scenarios. This approach introduces proper constitutive models for the wood phase along with good void generation techniques. In other words, this approach suggests what models should be used for the continuum-assumed wood phase to simulate its brittle behavior in tension and ductile behavior in compression; and moreover, tests the applicability and accuracy of ellipsoidal void representation. The models are calibrated using the results of experiments on PSL material. Because of the brittle behavior, all wood products show significant mechanical dependency to the member's size under tensile loading. Once good constitutive model and mesostructural simulation is found for tensile loading, it is easy to make and analyze PSL models with different sizes and investigate the effect of size on mechanical behavior. The simulation results have been compared to the available results of a previously done experimental study.

There is great need to understand the mechanical properties of lead-free alloys—an alternative of lead-based alloys—to address the environmental problems associated with the use of lead-based materials in microelectronics. In this work, the microstructures of Bi57In26Sn17 lead-free alloy were examined using Optical Microscopy and Energy Dispersive X-ray Spectroscopy analysis. The micro-indentation technique was used to study the mechanical properties of Bi57In26Sn17 lead-free alloy. The experimental results of the hardness and contact modulus were presented and discussed. Local creep during the indentation was observed from the load-displacement curves. The Vickers hardness (HV) increases with the decrease of the indentation depth, suggesting that the alloy exhibits indentation size effect.

Piezoelectric materials in the forms of both bulk and thin-film have been widely used as actuators and sensors due to their electromechanical coupling. The characterization of piezoelectric materials plays an important role in determining device performance and reliability. Instrumented indentation is a promising method for probing mechanical as well as electrical properties of piezoelectric materials. The use of instrumented indentation to characterize the properties of piezoelectric materials requires analytical relations. Finite element methods are used to analyze the indentation of piezoelectric materials under different mechanical and electrical boundary conditions. For indentation of a piezoelectric half space, a three-dimensional finite element model is used due to the anisotropy and geometric nonlinearity. The analysis is focused on the effect of angle between poling direction and indentation-loading direction on indentation responses. For the indentation by a flat-ended cylindrical indenter, both insulating indenter and conducting indenter without a prescribed electric potential are considered. The results reveal that both the indentation load and the magnitude of the indentation-induced potential at the contact center increase linearly with the indentation depth. For the indentation by an insulating Berkovich indenter, both frictionless and frictional contact between the indenter and indented surface are considered. The results show the indentation load is proportional to the square of the indentation depth, while the indentation-induced potential at the contact center is proportional to the indentation depth. Spherical indentation of piezoelectric thin films is analyzed in an axisymmetric finite element model, in which the poling direction is anti-parallel to the indentation-loading direction. Six different combinations of electrical boundary conditions are considered for a thin film perfectly bonded to a rigid substrate under the condition of the contact radius being much larger than the film thickness. The indentation load is found to be proportional to the square of the indentation depth. To analyze the decohesion problem between a piezoelectric film and an elastic substrate, a traction-separation law is used to control the interfacial behavior between a thin film and an electrically grounded elastic substrate. The discontinuous responses at the initiation of interfacial decohesion are found to depend on interface and substrate properties.