İsMail Özen

The growing demand for lightweight, crashworthy structures in aerospace, automotive, and protective engineering has motivated the development of sandwich panels with high stiffness-to-weight ratios and strong energy absorption. This study investigates the crashworthiness of additively manufactured polylactic acid (PLA) sandwich panels with biomimetics-based helicoidal cores. Rather than reproducing the Bouligand architecture of the mantis shrimp dactyl club as a fiber laminate, the progressive rotational principle was abstracted and applied to the walls of three-dimensional cellular cores. Square, octagonal, and circular unit-cell topologies were combined with gradual angular (10°) and orthogonal (90°) rotational arrangements, yielding six core configurations manufactured by fused deposition modeling (FDM). Drop-weight impact tests were conducted at 50 J, complemented by nonlinear explicit finite element analyses that were first validated against experiments and then extended to 100 J, including a mesh convergence study and sequence-angle variants (20° and 45°). Results show that the angular arrangement generally yields higher crash force efficiency, with the octagonal-angular core reaching the highest CFE (70.77% at 50 J), while orthogonal arrangements provide higher mean crash forces for cylindrical and octagonal cores. Increasing the layer-sequence angle from 20° to 45° raised the mean crash force by up to 15% and markedly improved resistance to face-sheet perforation, with the square-angular 45° configuration offering the best balance of efficiency and mean resistance. The findings demonstrate that sequential wall rotation is an effective multi-metric design parameter whose benefits depend on the underlying cell topology.

Cellular porous structures are used as an alternative to blocking structures in in-dustrial fields where multi-functionality and mechanical efficiency are necessary. Many industries, such as automotive, aerospace and defense, utilize the benefits of these structures due to their high specific strength, outstanding noise and vibration damping abilities, thermal shielding, and superior specific energy absorption capacities. This study aims to reveal energy absorbing behavior and deformation mechanisms under compression load of Gyroid and Diamond cell based triply periodic minimal surface (TPMS) structures manufactured by powder bed fusion (PBF) technology. The TPMS lattice structures fabricated using AlSi10Mg material were designed in different relative densities according to cell wall thickness and cell number. Crushing behaviors of these structures were numerically investigated with a commercial Ls-Dyna finite elements (FE) software. The numerical results were obtained in a good agreement with the experimental data. The FE analysis facilitated understanding of the deformation damage mechanisms and stress distribution on the cell surfaces of the TPMS lattice structures designed with different relative densities. The findings of the study demonstrated that peak stress values computed during crushing of the TPMS lattice structures go up significantly with increasing relative density. Crush force efficiency (CFE) and energy absorption capacity of the TPMS lattice structures remarkably varied depending on deformation damage mechanisms occurred during crushing process. The highest CFE values for the Diamond and Gyroid cell-based lattice structures was obtained as 54% and 51%, respectively. Moreover, it was found that specific energy absorption capacity of the Diamond cell based TPMS lattice structures is 50% more than that of the Gyroid cell based TPMS lattice structures with close relative densities.

The removal of some pollutants in the Sakarya River was investigated in this study. Sakarya River located in Turkey flows from the northeast of Afyonkarahisar City to the Black Sea. Nineteen different micropollutants including trihalomethanes (THMs), haloacetic acids (HAAs), endocrine disrupting compound (EDC) and pharmaceuticals personal care product (PPCP) groups, and water quality parameters such as dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm wavelength (UV₂₅₄), hardness, and conductivity values were examined. To remove the micropollutants and improve the water quality, the treatment was performed with ozone, microfiltration (MF), and ultra-filtration (UF) membranes. The highest treatment efficiency was obtained with 1 mg/L ozone dosage and UP005 UF membrane. The trihalomethan formation potential (THMFP) and haloacetic acid formation potential (HAAFP) decreased with ozone + membrane at a concentration of 79 and 75%, respectively. After the treatment with ozone + membrane, the concentration of the micropollutants in the EDC and PPCP group remained below the detection limit. It was found that by using only membrane and only ozone, the maximum DOC removal efficiency achieved was 46 and 18%, respectively; and with ozone + membrane, this efficiency increased up to 82%. The results from the High-Pressure Size Exclusion Chromatography (HPSEC) analyses pointed that the substances with high molecular weight were converted into substances with low molecular weight after the treatment. The Fourier Transform Infrared (FTIR) analysis results showed that the aromatic and aliphatic functional groups in water changed after the treatment with ozone and that the peak values decreased more after the ozone + membrane treatment.