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Abstract
Additive manufacturing (AM) is a fabrication technique that allows for complicated geometries to be manufactured that might otherwise be challenging using more traditional methods. AM is often seen paired with topology optimization to reduce weight while maximizing the strength of the part. Another benefit of AM is the ability to reduce the part count of components by integrating multiple parts into one single piece, lowering both cost and weight. However, integrating multiple parts into one single piece eliminates the jointing interfaces which are typically a dominant source of damping due to friction in the joints. This source of damping from jointing interfaces is beneficial to the fatigue life of a component and without it, other sources of damping features are required.
One such method that has seen increasing interest is embedding damping features such as particle dampers within a component. This is done by leaving a small pocket of powder within strategic areas of an AM part during the printing process. In general, particle dampers are known to reduce the vibration in a system, though they are rather intricate and difficult to qualify their behavior. As a statement to their complexity, the literature covering particle dampers have mixed results on what type of particle damper structures work best and their overall effectiveness. Additionally, many works focus on particle dampers that utilize particles orders of magnitude larger than AM feedstock powder, which are typically 5-50 ?m in diameter. As a result, many of the conclusions made based on current design particle dampers might not be applicable to the design of one that is additively manufactured.
This thesis looks to develop some guidelines and analysis towards AM particle dampers using a simulation model and experimental data. A Discrete Element method (DEM) simulation model is used to capture and model the behavior and explicit motion of particles and their interactions. Reported experimental data on various AM cantilever beam geometries and pocket locations showed large variation in damping ratios. The DEM simulation model was able to predict the damping ratio of the experiments accurately. As there was a strong correlation to experimental damping ratios, the model can be used further to analyze and optimize alternative designs. For instance, parameter studies made in the simulation can be leveraged for design optimization, such as packing densities and pocket geometries. In addition to these analyses, nonlinearities such as subharmonic behavior and amplitude dependencies were observed, demonstrating that additional studies could be made on the nonlinearities of particle dampers.
