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Energy absorption structures and devices, such as car bumpers, are designed to transform the kinetic energy into another form of energy in a controlled and predictable way. Focus of this dissertation was to enhance energy absorption of common crashworthiness structures, such as crash tubes and honeycombs by using novel geometrical patterns. Ideas were explored using combination of experiments and finite element simulations. Firstly, the tensile properties and fatigue behavior of polyethylene terephthalate glycol (PETG) components manufactured by fused filament fabrication (FFF). The objective of this study was to quantify anisotropy of PETG coupons by testing against four raster orientations—longitudinal, transversal, diagonal and crosshatched. Quasi-static tensile tests were performed on two specimen types that yielded the highest ultimate tensile strength (UTS) and modulus of elasticity for longitudinal specimens, with measured UTS of 48.04 MPa and E=1623.28 MPa. Tensile–tensile fatigue tests with a stress ratio of R = 0.1 were performed at 90, 80, 70 and 60% of nominal UTS of each specimen type. S–N curves displayed the highest fatigue life of the longitudinal specimen followed by the crosshatched specimen at 80–90% UTS stress level. Finally, a fractography analysis conducted on fatigued specimens displayed signs of plastic failure in all specimens. Secondly, we designed three biomimetic honeycombs (BH) inspired by microstructure inspired of oak, palm, and cedar. The main objective of this study was to compare the crushing behavior and mechanical properties under in-plane compression tests. A few samples of each BH were fabricated using fused filament fabrication, a 3-D printing technique, and used for experimental and numerical investigation. Crushing behavior of BH-oak and cedar was very similar to commonly observed in hexagonal honeycombs, with predominant ‘V’ or diagonal shear band. Numerical simulations were found to be in a good correlation with experimental results what implied high repeatability and good quality of the prints. Results showed that BH-Cedar demonstrate higher strength by about 30% than BH-Oak and BH-Palm that is associated with more vertical unit cell alignment. Finally, the structural response and crashworthiness performance of circular thin-walled grooved tubes were investigated under axial loading. Star-like grooving patterns were introduced using CNC machining to a relatively short and thin tubes to enhance crashworthiness performance. Experimental and numerical analysis have been conducted to investigate influence of various geometrical patterns on crushing behavior and crashworthiness. It was found that several different multi-lobe diamond deformation modes can be triggered for a tube with constant D/t=59.25 ratio. Generally, an increased number of lobes and folds led to higher specific energy absorption (SEA) and crush force efficiency (CFE), up to 31% and 34.5%, respectively. Parametric studies showed that groove depth can be used to achieve desirable deformation mode that increase both SEA and CFE simultaneously. Also, it was demonstrated that 4-lobe diamond mode deformation can be triggered for a wide range of D/t tubes. For example, tube 4h3v developed a stable 4-lobe pattern exhibiting two incomplete folds for t=1.75 mm (D/t=33.38) and a stable 4-lobe pattern with three complete folds for t=0.65 mm (D/t=91.15).