Browsing by Author "Lane, Ryan Jeffrey"

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    Experimental and Computational Micromechanics of Aluminum Cerium Alloys and Selective Laser Melted 316L Stainless Steel
    Lane, Ryan Jeffrey (Virginia Tech, 2023-06-07)
    Over time science has provided us with new materials and fabrication techniques making it possible to design and create more complex engineering components for service. If we are to include these materials in damage tolerant design efforts, engineers need to understand when/where degradation will occur in the engineering component. To do so it is imperative that micromechanical studies be conducted to understand the material behavior of the microstructural features including phases, build pattern features, and microstructural imperfections including cracks of new materials to validate any future modeling efforts. This dissertation will discuss the experimental and computational micromechanics of extruded and cast aluminum cerium alloys and selective laser melted 316L stainless steel. In Chapters 2 and 3, micromechanical experiments and computational efforts are carried out on extruded 52:1 Al-8Ce-10Mg alloy. Using in-situ scanning electron microscopy tensile testing microcracking is observed in Al11Ce3 intermetallic after yield in the bulk alloy. In-situ digital image correlation tests observe the load sharing characteristics between the Al(Mg) matrix and the Al11Ce3 intermetallic before and after microcracking. Finally, that failure process is determined to be coalesce of microvoids leading to ductile damage failure. These results are used to create an experimental-computational framework to develop a crystal plasticity finite element model for extruded Al-8Ce-10Mg alloys. The calibrated model is used to perform multiple simulations evaluate the possible effect changes intermetallic content and grain orientation texture have on the mechanical strength of the alloy. The experimental and computational framework are expandable to other material systems not just Al-Ce alloys. In Chapter 4, in-situ scanning electron microscopy tensile testing is used to investigate how the matrix and intermetallic phases contribute to the failure behavior alloy of cast Al-11Ce- 0.4Mg alloy. The in-situ tests shows that after multiple points of crack nucleation, crack coalescence causes the subsequent failure to occur in the Al(Mg) matrix phase of the alloy, as seen by tortuous behavior. The cause of this crack behavior is determined to be due to the high strength match between the matrix and intermetallic phase, strong metallurgical bond between the two phases, and the size effect created by large eutectic colonies created during casting. The results of the experimental work are used to propose a 3D multiscale computational model of cast Al-Ce alloys. In Chapter 5, micromechanical experiments are carried out on SLM 316L Stainless Steel with four different sets of varied processing parameters. Discontinuous yielding is observed in the lowest energy density sample caused by the strong [110] texture, optimal for dislocation slip, in the loading direction. The in-situ loading experiments are also able to capture the melt pool track deformation and crack formation that leads to the failure of these samples. This highlights the importance of micromechanical experiments for additive manufactured materials.
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    Study of Wave Propagation in Damaged Composite Material Laminates
    Lane, Ryan Jeffrey (Virginia Tech, 2018-12-12)
    The characteristics of carbon fiber composites have enabled these materials to be accepted as replacements for metal parts in industry. However, due to their unsymmetrical material properties, carbon fiber composites are susceptible to damage, such as a delamination, which can cause premature failure in the structure. This has resulted in the need for nondestructive testing methods that can provide quick, reliable results so that these parts can be tested while in service. In this study, an approach was examined that involved a pencil lead break to excite multiple wave modes in a composite plate in an effort to identify key characteristics based on the wavespeed and frequency. These characteristics were then compared to models based on boundary conditions to generate dispersion curves using the transfer matrix method for whole composite plates that were either undamaged or damaged. To first test this approach, experiments were performed on multilayer isotropic plates and then on a composite plate. The results for all cases showed that modes could be excited by the pencil lead break in the undamaged region of the plates that were not theoretical possible in a delaminated region. Also modes that were specific to the delaminated region were excited and this allowed for a clear comparison between the two regions. This approach could be placed into practice to provide routine testing to detect delamination for in-service, carbon fiber composite parts.