Haris Ali Khan

This research focuses on enhancing the utilization of the Fused Deposition Modeling and Sintering (FDMS) process for metal parts by incorporating a pressing step to improve densification and mechanical properties. The study employed aluminum powder in a PLA matrix as the feedstock material and began with process window determination through Finite Element Analysis (FEA). This step mitigated issues such as excessive deformation and void/shrinkage formation in the mid-regions of the parts. Subsequently, defect-free parts underwent heat treatment for debinding and sintering, followed by a pressing operation. Density measurements were performed on three sample types: 3D printed parts, FDMS parts, and Fused Deposition Modeling, Sintering, and Pressing (FDMSP) parts. The FDMSP parts exhibited the highest density, highlighting the significant role of the pressing step. Compressive strength testing revealed an approximate 20% increase in strength for FDMSP specimens compared to FDMS specimens. Additionally, in-situ compression tests aided by µCT analysis revealed that the FDMS specimens initially exhibited a porosity of ∼40%, which decreased to ∼26% after applying a compressive force of 10 kN, underscoring the contribution of the pressing step to compaction. Furthermore, the tests showed an increase in aluminum agglomeration, attributed to the deformation of the PLA matrix under compression, facilitating the redistribution of aluminum particles. These findings confirm the pressing operation’s contribution to improving density and compressive strength, providing a pathway to enhance FDMS processes for metal part manufacturing.

Building upon previous researches that introduced an innovative foam core hybrid-sandwich composite structure for radome applications, showcasing promising performance under low-velocity impacts (LVIs), this paper delves into the assessment of damage tolerance and mechanics through Compression After Impact (CAI) testing. The primary objective is to analyze disparities in damage tolerance, damage mechanisms, displacements, deformations, energy absorption, and residual strengths resulting from LVIs followed by CAIs on dissimilar materials on opposite faces of the hybrid structure. The extent of damage is evaluated through Computed Tomography (CT) scans. During LVIs, impacts on the S glass face sheets side demonstrated different energy dispersion and absorption mechanisms, leading to variations in indent damage depths and widths across all impact energy levels, unlike the impact damages observed from the Kevlar side. During CAI testing, this difference becomes more evident, with Kevlar specimens (KS3 & KS5) showing greater indentation depths and narrower widths, and S glass specimens (SK3 & SK5) experiencing buckling. These effects are due to the unique damage absorption and dispersion properties of Kevlar and S glass. These variations prompted an in-depth investigation of the structure using CAI to comprehend damage tolerance and mechanisms under compressive loads. This study, unparalleled in existing literature, proposes hybrid sandwich structures with superior specific impact and residual strength compared to various composite sandwich structures documented in published literature, expanding their utility beyond radomes.

This research introduces an innovative hybrid sandwich composite structure tailored for specific applications, featuring a foam core and dissimilar face sheets made of Kevlar and S-Glass materials to address in-phase electromagnetic properties, UV protection, and impact response. Building on our prior work on design optimization for electromagnetic performance and aero/inertial loading, this paper investigates the low-velocity impacts (LVIs) response of the composite structure through drop-weight testing at various energy levels. Utilizing computed tomography (CT) scanning for damage analysis, distinct failure modes were observed for different face sheet combinations, with notable variations (energy absorption characteristics) in damage depth and width between the S-Glass and Kevlar face sheets. This study, unprecedented in existing literature, proposes hybrid sandwich structures with superior specific impact strength compared to various composite sandwich structures documented in the published literature expanding its utility beyond radomes.