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- All Subjects: aluminum
- All Subjects: MEMS
- Creators: Solanki, Kiran
- Status: Published
Description
Aluminum alloys and their composites are attractive materials for applications requiring high strength-to-weight ratios and reasonable cost. Many of these applications, such as those in the aerospace industry, undergo fatigue loading. An understanding of the microstructural damage that occurs in these materials is critical in assessing their fatigue resistance. Two distinct experimental studies were performed to further the understanding of fatigue damage mechanisms in aluminum alloys and their composites, specifically fracture and plasticity. Fatigue resistance of metal matrix composites (MMCs) depends on many aspects of composite microstructure. Fatigue crack growth behavior is particularly dependent on the reinforcement characteristics and matrix microstructure. The goal of this work was to obtain a fundamental understanding of fatigue crack growth behavior in SiC particle-reinforced 2080 Al alloy composites. In situ X-ray synchrotron tomography was performed on two samples at low (R=0.1) and at high (R=0.6) R-ratios. The resulting reconstructed images were used to obtain three-dimensional (3D) rendering of the particles and fatigue crack. Behaviors of the particles and crack, as well as their interaction, were analyzed and quantified. Four-dimensional (4D) visual representations were constructed to aid in the overall understanding of damage evolution. During fatigue crack growth in ductile materials, a plastic zone is created in the region surrounding the crack tip. Knowledge of the plastic zone is important for the understanding of fatigue crack formation as well as subsequent growth behavior. The goal of this work was to quantify the 3D size and shape of the plastic zone in 7075 Al alloys. X-ray synchrotron tomography and Laue microdiffraction were used to non-destructively characterize the volume surrounding a fatigue crack tip. The precise 3D crack profile was segmented from the reconstructed tomography data. Depth-resolved Laue patterns were obtained using differential-aperture X-ray structural microscopy (DAXM), from which peak-broadening characteristics were quantified. Plasticity, as determined by the broadening of diffracted peaks, was mapped in 3D. Two-dimensional (2D) maps of plasticity were directly compared to the corresponding tomography slices. A 3D representation of the plastic zone surrounding the fatigue crack was generated by superimposing the mapped plasticity on the 3D crack profile.
ContributorsHruby, Peter (Author) / Chawla, Nikhilesh (Thesis advisor) / Solanki, Kiran (Committee member) / Liu, Yongming (Committee member) / Arizona State University (Publisher)
Created2014
Description
The study of response of various materials to intense dynamic loading events,
such as shock loading due to high-velocity impacts, is extremely important in a wide
variety of military and industrial applications. Shock loading triggers extreme states,
leading to high pressures and strain rates, and neglecting strength is a typical
approximation under such conditions. However, recent results have shown that strength
effects are larger than expected, so they must be taken into account. Recently,
hydrodynamic instabilities, the most common being the Rayleigh-Taylor (RTI) and
Richtmyer-Meshkov (RMI) instabilities, have been used to infer the dynamic strength of
materials at high pressure conditions. In our experiments and simulations, a novel RMI
approach is used, in which periodic surface perturbations are made on high purity
aluminium target, which was laser ablated to create a rippled shock front. Due to the
slow linear growth rate of RMI, the evolution of the perturbations on the back surface of
the sample as a result of the rippled shock can be measured via Transient Imaging
Displacement Interferometry (TIDI). The velocity history at the free surface was
recorded by spatially resolved laser velocimetry. These measurements were compared
with the results from the simulations, which were implemented using rate independent
and rate dependent material models, to characterize the dynamic strength of the
material. Simulations using the elastic-perfectly plastic model, which is rate
independent, failed to provide a value of dynamic yield strength that would match
experimental measurements of perturbation amplitudes. The Preston-Tonks-Wallace
(PTW) model, which is rate dependent model, worked well for aluminium. This model
was, in turn, used as a reference for calibrating the rate dependent Steinberg-Lund
model and the results from simulations using the calibration models were also compared
to experimental measurements.
such as shock loading due to high-velocity impacts, is extremely important in a wide
variety of military and industrial applications. Shock loading triggers extreme states,
leading to high pressures and strain rates, and neglecting strength is a typical
approximation under such conditions. However, recent results have shown that strength
effects are larger than expected, so they must be taken into account. Recently,
hydrodynamic instabilities, the most common being the Rayleigh-Taylor (RTI) and
Richtmyer-Meshkov (RMI) instabilities, have been used to infer the dynamic strength of
materials at high pressure conditions. In our experiments and simulations, a novel RMI
approach is used, in which periodic surface perturbations are made on high purity
aluminium target, which was laser ablated to create a rippled shock front. Due to the
slow linear growth rate of RMI, the evolution of the perturbations on the back surface of
the sample as a result of the rippled shock can be measured via Transient Imaging
Displacement Interferometry (TIDI). The velocity history at the free surface was
recorded by spatially resolved laser velocimetry. These measurements were compared
with the results from the simulations, which were implemented using rate independent
and rate dependent material models, to characterize the dynamic strength of the
material. Simulations using the elastic-perfectly plastic model, which is rate
independent, failed to provide a value of dynamic yield strength that would match
experimental measurements of perturbation amplitudes. The Preston-Tonks-Wallace
(PTW) model, which is rate dependent model, worked well for aluminium. This model
was, in turn, used as a reference for calibrating the rate dependent Steinberg-Lund
model and the results from simulations using the calibration models were also compared
to experimental measurements.
ContributorsGopalakrishnan, Ashish (Author) / Peralta, Pedro (Thesis advisor) / Rajagopalan, Jagannathan (Committee member) / Solanki, Kiran (Committee member) / Arizona State University (Publisher)
Created2017
Description
Nanocrystalline (NC) and Ultrafine-grained (UFG) metal films exhibit a wide range of enhanced mechanical properties compared to their coarse-grained counterparts. These properties, such as very high strength, primarily arise from the change in the underlying deformation mechanisms. Experimental and simulation studies have shown that because of the small grain size, conventional dislocation plasticity is curtailed in these materials and grain boundary mediated mechanisms become more important. Although the deformation behavior and the underlying mechanisms in these materials have been investigated in depth, relatively little attention has been focused on the inhomogeneous nature of their microstructure (particularly originating from the texture of the film) and its influence on their macroscopic response. Furthermore, the rate dependency of mechanical response in NC/UFG metal films with different textures has not been systematically investigated. The objectives of this dissertation are two-fold.
The first objective is to carry out a systematic investigation of the mechanical behavior of NC/UFG thin films with different textures under different loading rates. This includes a novel approach to study the effect of texture-induced plastic anisotropy on mechanical behavior of the films. Efforts are made to correlate the behavior of UFG metal films and the underlying deformation mechanisms. The second objective is to understand the deformation mechanisms of UFG aluminum films using in-situ transmission electron microscopy (TEM) experiments with Automated Crystal Orientation Mapping. This technique enables us to investigate grain rotations in UFG Al films and to monitor the microstructural changes in these films during deformation, thereby revealing detailed information about the deformation mechanisms prevalent in UFG metal films.
The first objective is to carry out a systematic investigation of the mechanical behavior of NC/UFG thin films with different textures under different loading rates. This includes a novel approach to study the effect of texture-induced plastic anisotropy on mechanical behavior of the films. Efforts are made to correlate the behavior of UFG metal films and the underlying deformation mechanisms. The second objective is to understand the deformation mechanisms of UFG aluminum films using in-situ transmission electron microscopy (TEM) experiments with Automated Crystal Orientation Mapping. This technique enables us to investigate grain rotations in UFG Al films and to monitor the microstructural changes in these films during deformation, thereby revealing detailed information about the deformation mechanisms prevalent in UFG metal films.
ContributorsIzadi, Ehsan (Author) / Rajagopalan, Jagannathan (Thesis advisor) / Peralta, Pedro (Committee member) / Chawla, Nikhilesh (Committee member) / Solanki, Kiran (Committee member) / Oswald, Jay (Committee member) / Arizona State University (Publisher)
Created2017
Description
In real world applications, materials undergo a simultaneous combination of tension, compression, and torsion as a result of high velocity impact. The split Hopkinson pressure bar (SHPB) is an effective tool for analyzing stress-strain response of materials at high strain rates but currently little can be done to produce a synchronized combination of these varying impacts. This research focuses on fabricating a flange which will be mounted on the incident bar of a SHPB and struck perpendicularly by a pneumatically driven striker thus allowing for torsion without interfering with the simultaneous compression or tension. Analytical calculations are done to determine size specifications of the flange to protect against yielding or failure. Based on these results and other design considerations, the flange and a complementary incident bar are created. Timing can then be established such that the waves impact the specimen at the same time causing simultaneous loading of a specimen. This thesis allows research at Arizona State University to individually incorporate all uniaxial deformation modes (tension, compression, and torsion) at high strain rates as well as combining either of the first two modes with torsion. Introduction of torsion will expand the testing capabilities of the SHPB at ASU and allow for more in depth analysis of the mechanical behavior of materials under impact loading. Combining torsion with tension or compression will promote analysis of a material's adherence to the Von Mises failure criterion. This greater understanding of material behavior can be implemented into models and simulations thereby improving the accuracy with which engineers can design new structures.
ContributorsVotroubek, Edward Daniel (Author) / Solanki, Kiran (Thesis director) / Oswald, Jay (Committee member) / Mechanical and Aerospace Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
With the advancements in technology, it is now possible to synthesize new materials with specific microstructures, and enhanced mechanical and physical properties. One of the new class of materials are nanoscale metallic multilayers, often referred to as nanolaminates. Nanolaminates are composed of alternating, nanometer-thick layers of multiple materials (typically metals or ceramics), and exhibit very high strength, wear resistance and radiation tolerance. This thesis is focused on the fabrication and mechanical characterization of nanolaminates composed of Copper and Cobalt, two metals which are nearly immiscible across the entire composition range. The synthesis of these Cu-Co nanolaminates is performed using sputtering, a well-known and technologically relevant physical vapor deposition process. X-ray diffraction is used to characterize the microstructure of the nanolaminates. Cu-Co nanolaminates with different layer thicknesses are tested using microelectromechanical systems (MEMS) based tensile testing devices fabricated using photolithography and etching processes. The stress-strain behavior of nanolaminates with varying layer thicknesses are analysed and correlated to their microstructure.
ContributorsRajarajan, Santhosh Kiran (Author) / Rajagopalan, Jagannathan (Thesis advisor) / Oswald, Jay (Committee member) / Solanki, Kiran (Committee member) / Arizona State University (Publisher)
Created2019
Description
Thin films are widely used for a variety of applications such as electrical interconnects, sensors, as well as optical, mechanical, and decorative coatings. Thin films made of NiTi, commonly referred to as nitinol, have generated recent interest as they are highly suitable for high frequency thermal actuation in microelectromechanical devices because of their small thermal mass and large surface-to-volume ratio. The functional properties of NiTi arise from a diffusionless phase transformation between two of its primary phases: austenite and martensite. This transformation leads to either the shape memory or pseudoelastic effect, where inelastic deformation is recovered with and without the application of heat, respectively. It is well known that the mechanical properties of NiTi are highly dependent on the microstructure, but few studies have been performed to examine the mechanical behavior of thin NiTi films (thickness below 200 nm), which are expected to have grain sizes in a similar range. The primary intent of this work is the synthesis of NiTi thin films with controlled microstructures, followed by characterization of their microstructure and its relationship to the mechanical properties. Microstructural control was achieved by utilizing a novel synthesis technique in which amorphous precursor films are seeded with nanocrystals, which serve as nucleation sites during subsequent crystallization via thermal annealing. This technique enables control of grain size, dispersion, and phase composition of thin films by varying the parameters of seed deposition as well as annealing conditions. The microstructures and composition of the NiTi thin films were characterized using X-ray Diffraction, Electron Microprobe Analysis, High-resolution Transmission Electron Microscopy, Secondary Ion Mass Spectroscopy, Differential Scanning Calorimetry, as well as other complementary techniques. Mechanical properties of the films were investigated using uniaxial tensile testing performed using a custom microfabricated tensile testing stage. The NiTi thin films exhibit mechanical behavior that is distinct from bulk NiTi, which is also highly sensitive to small changes in microstructure and phase composition. These findings are rationalized in terms of the changes in deformation mechanisms that occur at small grain sizes and sample dimensions.
ContributorsRASMUSSEN, Paul (Author) / Rajagopalan, Jagannathan (Thesis advisor) / Solanki, Kiran (Committee member) / Sieradzki, Karl (Committee member) / Arizona State University (Publisher)
Created2021
Description
Surface Mechanical Attrition Treatment (SMAT) is a process used to coat metallic alloy surfaces with a nanocrystallized layer via mechanical abrasion. SMAT has garnered a significant amount of interest from the scientific community as a surface treatment technique due to the ability of this fine grain top layer to provide several benefits to its constituent alloy, namely significantly higher hardness, fatigue strength, and most pertinently, greatly improved corrosion resistance. Emerging research suggests that SMAT can also be used to apply powder coatings onto target substrates. A given substrate can be installed in a ball mill, where stainless steel balls coated with pure elemental powder deliver sustained impact onto the substrate, embedding the powders onto its surface. This paper will explore the process of coating aluminum 7075 coating with chromium powder via SMAT, and the effects doing so will have on the corrosion resistance properties of the aluminum 7075. Traditionally, high-strength alloys have been treated with chromium via the process of electroplating, where the alloys are subjected to a hexavalent chromium plating procedure that is known to risk releasing toxic carcinogens into the environment. Coating these alloys with SMAT could minimize such negative externalities, while yielding benefits unique to the SMAT coating process itself. Baseline corrosion testing reveals that the corrosion resistance properties of the aluminum 7075 improved marginally when exposed to SMAT without the addition of any chromium powder. A literature review conducted in this paper of select studies on SMAT coating also demonstrates that material properties intrinsic to aluminum 7075 and pure chromium powder, as well as interaction effects occurring between aluminum and chromium when subjected to mechanical alloying, could enable the SMAT coating of aluminum 7075 with chromium to result in greatly enhanced corrosion resistance properties. While this was not accomplished within the duration of the Honors Project due to logistical difficulties brought forth by the COVID-19 epidemic, the baseline corrosion testing performed, as well as the literature review of studies directly relevant to the matter, should hopefully provide some information of value in any future exploration of the topic.
ContributorsMcManus, Matthew Harada (Co-author, Co-author) / Solanki, Kiran (Thesis director) / Beura, Vikrant (Committee member) / School of Politics and Global Studies (Contributor) / Mechanical and Aerospace Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2020-05