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- All Subjects: aluminum
- Genre: Academic theses
- 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