The mechanical properties of 3D printed polymers parts are process parameter dependent. Defects such as inadvertent voids between deposited rasters and layers lead to weakness in produced parts, which results in inferior mechanical properties as compared to injection molding. An alternative method to change energy absorption and stiffness of a polymer is hybrid additive manufacturing (AM). Hybrid-AM is the use of additive manufacturing with one or more secondary processes that are fully coupled and synergistically affect part quality, functionality, and/or process performance. In this study, fused filament fabrication (FFF) was coupled with layer-by-layer shot peening to study the dynamic mechanical properties of ABS 430 polymer using dynamic mechanical analysis (DMA). FFF is a heated extrusion process. Shot peening is a mechanical surface treatment that impinges a target with a stochastically dispersed, high velocity stream of beads. Compressive residual stress was imparted to preferential layer intervals during printing to modify the elasticity (stiffness), viscosity, toughness, and glass transition temperature. Viscoelastic and dynamic mechanical properties are important to the performance of polymers in automotive, aerospace, electronics, and medical components. Coupling printing and peening increased the storage and loss moduli as well as the tangent delta. DMA results suggest that preferential layer sequences exist that possess higher elasticity and better absorb energy upon sinusoidal dynamic loading.
Metal additive manufacturing (AM) is employed to make highly complex low volume components, which often have demanding performance requirements. Current challenges in the metal AM field include control of porosity and microstructure, development of process-structure-property relationships, and simplification of the AM parameter space. These challenges are exacerbated in multiphase materials, such as Ti6Al4V, that are important for the biomedical, aerospace, and energy industries. Integrated in situ and ex situ non-destructive evaluation methods are proposed to address these challenges. In this work, in situ and ex situ ultrasound measurements are conducted on Ti6Al4V parts made using a hybrid Directed Energy Deposition (DED) system. The hybrid capabilities of the system are exploited to quantify part geometry, while ultrasound is used to measure phase velocity and attenuation in situ on a layer-by-layer basis. Furthermore, the phase velocity, attenuation, and backscatter responses of these AM and Hybrid AM parts are quantified ex situ and compared with those from conventionally manufactured Ti6Al4V parts to evaluate the role of microstructural complexity. The results highlight the improved geometric information offered by a hybrid AM system to quantify microstructure and elastic properties of parts in situ. The need for realistic complex microstructures to be integrated within model-based ultrasonic microstructural predictions is also discussed.
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