1. Deformation behaviour of optimised three-dimensional axisymmetric chiral auxetic structuresNejc Novak, Alen Grebo, Matej Borovinšek, Lovre Krstulović-Opara, Zoran Ren, Matej Vesenjak, 2025, original scientific article Abstract: Background/Objectives: Developing functional tissue constructs via 3D bioprinting relies heavily on scaffold architecture, demanding precise mechanical tunability and highresolution feature fidelity. Methods: This paper presents a novel approach utilising photocurable resins and resin 3D printing to fabricate auxetic axisymmetric chiral structures (ACSs), which can be used for advanced scaffold engineering. Results: The experimental tests showed that the optimised ACS (optACS) possess superior mechanical properties compared to their non-optimised counterpart. Both analysed structures possess an auxetic behaviour up to 40% longitudinal strain, with a Poisson’s ratio of about −0.1. Conclusions: This auxetic capability is promising for biomedical applications, particularly in developing enhanced stents or tissue scaffolds.
Keywords: auxetic, axisymmetric chiral structures, 3D printing, mechanical testing, deformation behaviour, optimisation
Published in DKUM: 10.12.2025; Views: 0; Downloads: 4
 Full text (1,77 MB)
This document has many files! More... |
2. Integrated design, simulation, and experimental validation of advanced cellular metamaterialsNejc Novak, Zoran Ren, Matej Vesenjak, 2025, original scientific article Abstract: Cellular metamaterials offer supreme properties for engineering, medicine, and defence, but their transition to industrial use faces design, fabrication, and characterisation challenges. This review provides an overview of 20 years of advancements in cellular structures, from open-cell foams to triply periodic minimal surfaces (TPMS), presenting novel fabrication techniques (e.g., explosive compaction for UniPore structures) and demonstrating validated computational models for optimising graded auxetic and hybrid TPMS lattices. The study indicates that porosity and base material primarily govern energy absorption, with closed-cell foams and TPMS outperforming other geometries. Additive manufacturing enables spatially graded designs with tailored mechanical properties. This work accelerates the development of next-generation metamaterials for crash absorption, blast protection, and biomedical devices.
Keywords: cellular structures, metamaterials, experimental testing, computational simulations, mechanical properties
Published in DKUM: 09.12.2025; Views: 0; Downloads: 2
Full text (1,84 MB)
This document has many files! More... |
3. Quasi-static and impact behaviour of polymer-metal interpenetrating phase TPMS compositesNejc Novak, Oraib Al-Ketan, Anja Mauko, Lovre Krstulović-Opara, Shigeru Tanaka, Matej Borovinšek, Boštjan Vihar, Uroš Maver, Kazuyuki Hokamoto, Matej Vesenjak, Zoran Ren, 2025, original scientific article Abstract: Interpenetrating phase composites (IPC) are materials with two or more mutually continuous, interconnected phases. This structure allows each phase to retain its properties, while together they exhibit enhanced synergistic properties. In this work, polymer-metal IPCs with Triply Periodical Minimal Surface (TPMS) structures were fabricated and tested for their mechanical properties at different impact velocities (ranging from 0.1 mm/s to 250 m/s). Samples. The samples comprise a stainless steel reinforcement phase and two polymeric matrices (silicone and epoxy). Computed tomography was used to evaluate the internal structure and the fabrication quality. The results showed that the samples were thoroughly infiltrated with polymeric filler, achieving a high degree of homogeneity in the composite. The compression tests of silicone-filled IPCs showed an increase in stiffness. Still, the Specific Energy Absorption (SEA) was not improved due to the non-optimal stiffness ratio between the polymeric matrix and the metallic reinforcement phase. However, using epoxy as the matrix resulted in the SEA enhancement of 38 %. This is attributed to the interlocking mechanism between the two phases, which improved the macroscopic mechanical properties. The compression tests showed significant strain rate hardening due to the base material’s strain rate sensitivity and the inertia effects.
Keywords: TPMS, interpenetrating phase composite, polymer filler, hybrid structure, experimental testing, mechanical properties, strain rate effect
Published in DKUM: 26.05.2025; Views: 0; Downloads: 14
Full text (10,05 MB)
This document has many files! More... |
4. In-plane deformation behavior and the open area of rotating squares in an auxetic compound fabricPolona Dobnik-Dubrovski, Nejc Novak, Matej Borovinšek, Matej Vesenjak, Zoran Ren, 2022, original scientific article Abstract: A conventional compound fabric was used to develop a modern, multifunctional material
with an auxetic behaviour and a tailored open area for particle filtration. Such material was produced
using traditional textile technology and laser cutting, to induce a rotating squares unit geometry. The
behaviour was investigated of three different rotating unit cell sizes. The laser slit thickness and the
length of the hinges were equal for all three-unit cells. The tensile properties, Poisson’s ratio and
auxetic behaviour of the tested samples were investigated, especially the influence of longitudinal
displacement on the fabric’s open area and the filtered particle sizes (average and maximum). Results
show that the developed compound fabric possesses an average negative Poisson’s ratio of up to
−1, depending on the applied auxetic geometry. The larger rotating cell size samples offer a higher
average negative Poisson’s ratio and a higher breaking strength due to the induced slits. The findings
highlight the usefulness of patterned cuts in conventional textile materials to develop advanced
auxetic textile materials with tailored geometrical and mechanical properties.
Keywords: compound textile material, auxetic structure, open area, filtration, mechanical properties, Poisson’s ratio
Published in DKUM: 25.03.2025; Views: 0; Downloads: 12
Full text (2,67 MB)
This document has many files! More... |
5. Mechanism elucidation of high-pressure generation in cellular metal at high-velocity impactMasatoshi Nishi, Shigeru Tanaka, Akihisa Mori, Matej Vesenjak, Zoran Ren, Kazuyuki Hokamoto, 2022, original scientific article Abstract: Cellular metals exhibit diverse properties, depending on their geometries and base materials. This study investigated the mechanism of high-pressure generation during the high-velocity
impact of unidirectional cellular (UniPore) materials. Cubic UniPore copper samples were mounted
on a projectile and subjected to impact loading using a powder gun to induce direct impact of samples.
The specimens exhibited a unique phenomenon of high-pressure generation near the pores during
compression. We elucidate the mechanism of the high-pressure phenomenon and discuss the pore
geometries that contribute to the generation of high pressures.
Keywords: cellular metal, high-pressure, high-velocity impact, computational simulation, metal jet
Published in DKUM: 24.03.2025; Views: 0; Downloads: 6
Full text (3,90 MB)
This document has many files! More... |
6. |
7. Development of novel hybrid TPMS cellular lattices and their mechanical characterisationNejc Novak, Oraib Al-Ketan, Matej Borovinšek, Lovre Krstulović-Opara, Reza Rowshan, Matej Vesenjak, Zoran Ren, 2021, original scientific article Abstract: Uniform lattices composed of one type of lattice structure repeated periodically have been extensively investigated in literature for their mechanical and physical properties. Their promising properties, which include a desirable combination of high strength, stiffness and toughness, suggest that hybrid structures made of two or more lattice types can exhibit even more advantageous and desired properties. In this work, the mechanical properties of hybrid cellular structures designed using implicit functions are investigated both experimentally and numerically. Two proposed samples are investigated comprised of a Gyroid and a Diamond unit cells hybridised linearly and radially. First, a finite element computational model was utilised in LS-DYNA to capture the mechanical properties of the additively manufactured constituent lattices (i.e., Gyroid and Diamond) made of stainless steel 316L and tested under dynamic and quasi-static loading conditions. The model was validated for three different relative densities. Then, the validated computational model was then tested to predict the mechanical behaviour of the proposed hybrid lattices. Finally, the proposed hybrid lattices were fabricated and mechanically tested to obtain their mechanical properties. A good agreement between experimental and computational results was achieved. The validated computational models will be used to evaluate other designs of TPMS lattices and their crashworthiness performance for protective equipment applications.
Keywords: cellular materials, triply periodical minimal surface, hybrid lattices, experimental testing, computational modelling, multi-morphology
Published in DKUM: 27.11.2024; Views: 3; Downloads: 13
Full text (3,99 MB)
This document has many files! More... |
8. |
9. Behaviour of cellular metamaterials under impact loading conditions : doctoral disertationYunus Emre Yilmaz, 2024, doctoral dissertation Abstract: This doctoral thesis investigates cell-size-graded metallic and non-metallic Triply Periodic
Minimal Surface (TPMS) structures' behavior under varying loading rates. Using experimental
tests, analytical calculations, and advanced computer simulations, the research explores the
interplay between material properties, cell size grading, and deformation mechanisms under
different strain rates. The study focuses on enhancing the Direct Impact Hopkinson Bar (DIHB)
setup for accurate force and displacement measurements and pioneering a method for
quantifying inertial forces, critical at high strain rates.
Key findings show that cell-size grading significantly affects deformation patterns, with initial
deformation occurring in regions with smaller and lower stiffness cells across different loading
rates and TPMS geometries. The research also highlights topology's influence on mechanical
response, with photopolymer-based diamond structures showing superior energy absorption
and gas-atomized steel structures favoring gyroid configurations. This underscores the
importance of considering both topology and base material selection during TPMS design. The
study demonstrates the increasing prominence of inertial forces as deformation rates rise,
impacting structural response and failure likelihood in TPMS structures.
These insights inform the design of optimized cellular metamaterials for high-performance
applications requiring superior energy absorption and structural integrity under high loading
rates. The research advances material characterization techniques and computational
modelling capabilities, contributing to the development of next-generation cellular
metamaterials for broader engineering applications.
Keywords: Triply Periodic Minimal Surfaces, TPMS, Cell-size-grading, Impact, High-strainrate, Digital Image Correlation
Published in DKUM: 17.10.2024; Views: 0; Downloads: 43
Full text (46,48 MB) |
10. High strain rate hardening of metallic cellular metamaterialsNejc Novak, Matej Vesenjak, Zoran Ren, 2024, original scientific article Abstract: Strain rate hardening caused by the changed deformation mode is a fascinating phenomenon in cellular metamaterials where the material’s stiffness and energy absorption capabilities increase as the strain rate increases. This unique behaviour is attributed to a combination of micro-inertia effects, base material’s strain rate hardening and inertia effects. At high strain rates, the metamaterial’s inertia influences its deformation response, which changes to shock mode. This work briefly presents the geometry and fabrication of different metallic metamaterials. Then, it evaluates their mechanical response at different strain rates, ranging from quasi-static to intermediate dynamic and shock, determined by experimental and computational investigation. The three deformation modes can be separated into two critical loading velocities, unique for each metamaterial, which are also presented and compared in this work for various metamaterials. The investigations show that the deformation mode change in metallic metamaterials depends on their porosity. The critical velocities separating the deformation modes decrease with increasing porosity, i.e., decreased density of the metamaterial results in reduced critical loading velocities. The shock deformation mode in cellular metamaterials is thus attainable at much lower loading velocities than in homogeneous (nonporous) materials.
Keywords: metamaterials, cellular structures, high strain rate, experimental testing, computational modelling, compression loading, mechanical properties
Published in DKUM: 22.05.2024; Views: 204; Downloads: 29
Full text (3,42 MB)
This document has many files! More... |
