Search Results (31)

The rapid shift toward electric vehicles (EVs) has underscored the critical importance of battery pack crashworthiness, creating a demand for lightweight, energy-absorbing protective systems. This review systematically explores bio-inspired cellular structures as promising solutions for improving the impact resistance of EV battery packs. Inspired by natural geometries, these designs exhibit superior energy absorption, controlled deformation behavior, and high structural efficiency compared to conventional configurations. A comprehensive analysis of experimental, numerical, and theoretical studies published up to mid-2025 was conducted, with emphasis on design strategies, optimization techniques, and performance under diverse loading conditions. Findings show that auxetic, honeycomb, and hierarchical multi-cell architectures can markedly enhance specific energy absorption and deformation control, with improvements often exceeding 100% over traditional structures. Finite element analyses highlight their ability to achieve controlled deformation and efficient energy dissipation, while optimization strategies, including machine learning, genetic algorithms, and multi-objective approaches, enable effective trade-offs between energy absorption, weight reduction, and manufacturability. Persistent challenges remain in structural optimization, overreliance on numerical simulations with limited experimental validation, and narrow focus on a few bio-inspired geometries and thermo-electro-mechanical coupling, for which engineering solutions are proposed. The review concludes with future research directions focused on geometric optimization, multi-physics modeling, and industrial integration strategies. Collectively, this work provides a comprehensive framework for advancing next-generation crashworthy battery pack designs that integrate safety, performance, and sustainability in electric mobility. Full article

Auxetic structures, also known as metamaterials, exhibit a negative Poisson’s ratio under applied load and have found use across a variety of applications. This behavior may arise from material properties or from the structural design itself. Depending on the intended application, such structures can be subjected to either static or dynamic loading conditions. New geometries that potentially enhance energy absorption or damping in both static and dynamic conditions were investigated in this work, using the well-known Reentrant design reported in earlier research articles as a benchmark. As an alternative to the cellular limb angles employed in the well-known Reentrant model, the effect of radial limb radius was analyzed in the novel cell designs called Arched-Reentrant. Four alternative designs have been proposed, and all analyses were conducted in ANSYS-2025-R1. The specimens were manufactured by using the 3D printing method with thermoplastic polyurethane (TPU) material having a shore hardness of 95A. In the evaluation of the outcomes resulting from different designs, the specimens were analyzed under static, impulsive, and harmonic loading conditions. The energy absorption capacities of the samples were examined in relation to their design modifications. Within the scope of the study, it was observed that Arched-Reentrant structures are capable of absorbing higher amounts of energy under static loading and exhibit greater stiffness under dynamic loads compared to conventional Reentrant structures. The impulse analysis’s findings demonstrate that the suggested Arched-Reentrant-V3 model performs better, with over 50% less displacement and comparable reaction forces. In addition, the harmonic analysis findings show that the Arched-Reentrant-V3 model has lower ground reaction forces and displacement values. As a result, the suggested model can be regarded as an efficient damping component when dynamic loading occurs. Full article

This study aimed to examine the effect of the orientation angle of center facing arms on the elongation and strength of 3D-printed textiles with two different re-entrant cellular auxetic structures. An experimental research design, consisting of 6 (auxetic-structure textiles) × 3 (repetition), was employed. Star-shaped re-entrant auxetic structures (star re-entrant) with orientation angles of 25°, 30°, and 35° and floral-based star-shaped re-entrant auxetic structures (floral re-entrant) with orientation angles of 55°, 60°, and 65° were developed using the fused deposition modeling 3D-printing method through identifying commonly used auxetic structures in the 3D-printed textiles’ development. A statistically significant relationship was found between load and elongation of both star re-entrant and floral re-entrant. The findings indicated that 3D-printed textiles with both star re-entrant and floral re-entrant structures exhibited an enhanced elongation with the increase in orientation angle, making the textile products more flexible and potentially providing better wear comfort. However, the strength of both star re-entrant and floral re-entrant textiles was not significantly affected by the orientation angle of center facing arms. The findings demonstrated the potential to enhance the elongation of 3D-printed auxetic-structure textiles without compromising their strength for ensuing comfort by adjusting the orientation angle of center facing arms. Full article

This study investigates the properties of structures with an ordered cellular internal configuration. Certain forms of the ordered internal structure contribute to the manifestation of auxetic properties. In this study, a hexagonal hourglass cell shape was chosen. The samples were 3D-printed with PLA and ABS filaments. The panels were subjected to out-of-plane compression. The Poisson ratio of the panels under compression was −0.06 for PLA samples and −0.05 for ABS samples. Tension tests were performed using two types of samples: type 1 with monolithic shoulders and type 2 with cellular shoulders. The average tensile strength of the type 1 samples was 0.482 ± 0.006 kN, whereas that of the type 2 samples was 0.416 ± 0.028 kN, which was 13.7% lower. The elongation at failure in the type 2 samples was 35% higher than that in the type 1 samples (1.85 ± 0.14 mm and 1.37 ± 0.08 mm, respectively). The higher deformation capacity of type 2 samples may be explained by the presence of an auxetic mesh over the entire sample. Auxetic properties are useful in numerous engineering fields. For civil engineering purposes, the blast-proof abilities of such structures are important. Thus, in future research, it is planned to create samples of fine-grain concrete with similar cellular structure. Full article

Auxetic honeycomb structures, known for their exceptional mechanical properties, are widely used as sacrificial layers to protect critical targets from extreme explosive loads. However, conventional double arrowhead auxetic honeycomb-core structures (DA-AHSs) encounter significant interfacial connectivity challenges, and scaling auxetic honeycombs with alternative cellular microstructures introduces further complexity. To overcome these issues, riveted and assembled double-trapezoidal auxetic honeycomb-core structures (DT-AHSs) were developed as a replacement for DA-AHSs. The deformation modes and energy absorption mechanisms of DT-AHSs were analyzed through theoretical methods and quasi-static testing. The results show that DT-AHSs energy absorption primarily relies on the yield deformation of the longer inclined walls and rotational deformation of the shorter inclined walls. Additionally, the shorter walls support auxetic behavior by stabilizing the deformation of the longer walls. These findings provide a basis for further exploration of the protective potential of DT-AHSs. Full article

The introduction of 3D printing technology has broadened manufacturing possibilities, allowing the production of complex cellular geometries, including auxetic and curved plane structures, beyond the standard honeycomb patterns in sandwich composite materials. In this study, the effects of cell design parameters, such as cell geometry (honeycomb and auxetic) and cell size (cell thickness and width), are examined on acrylonitrile butadiene styrene (ABS) core materials produced using fusion deposition modeling (FDM). They are produced as a result of the epoxy bonding of carbon epoxy prepreg composite materials to the surfaces of core materials. Increasing the wall thickness from 0.6 mm to 1 mm doubled the elastic modulus of the re-entrant structures (5 GPa to 10 GPa) and improved compressive strength by 50–60% for both geometries. In contrast, increasing cell size from 6 mm to 10 mm significantly reduced compressive strength by 80% (from 2.5–2.8 MPa to 0.5–0.6 MPa) and elastic modulus by 70–78% (from 9–10 GPa to 2–3 GPa). Flexural testing showed that the re-entrant cores, with a maximum load capacity of 148 N, exhibited more uniform deformation, while the honeycomb cores achieved a higher load capacity of 273 N but were prone to localized failures. These findings emphasize the directional anisotropy and specific advantages of auxetic and honeycomb designs, offering valuable insights for lightweight, high-strength structural applications. Full article

In the proposed study, the fatigue analysis of an axisymmetric chiral cellular structure and its modified form, made of stainless steel 316L, is carried out. The main goal of the original structure geometry was to absorb as much mechanical energy as possible with its auxetic behaviour. However, it was found through testing that its response could be improved by modifying the thickness of the struts through the structure. Representative models for the original and modified geometries were generated using a script adapted for this numerical simulation. Three different types of displacement in the shape of sine waves were used to load the structures. A hexagonal mesh was assigned and determined by convergence analysis. An existing material model with the necessary LCF parameters was assigned in the computational analyses. The data from multiple simulations were recorded and presented in graphs that showed how the fatigue life of the structures changed depending on the level of strain. We also analysed stresses and plastic deformations that occur in the structures. The results showed that, despite a better stress distribution, the fatigue life of the optimised structure was shorter in all cases. Full article

Flexible nanocomposite sensors hold significant promise in various applications, such as wearable electronics and medical devices. This research aims to tailor the flexibility and sensitivity of 3D-printed piezoresistive nanocomposite pressure sensors through geometric design, by exploring various simple cellular structures. The geometric designs were specifically selected to be 3D printable with a flexible material, allowing evaluation of the impact of different structures on sensor performance. In this study, we used both experimental and finite element (FE) methods to investigate the effect of geometric design on piezoresistive sensors. We fabricated the sensors using a flexible resin mixed with conductive nanoparticles via a Stereolithography (SLA) additive manufacturing technique. Electromechanical testing was carried out to evaluate the performance of four different sensor designs. Finite element (FE) models were developed, and their results were compared with experimental data to validate the simulations. The results demonstrated that auxetic structure exhibited the highest sensitivity and lowest stiffness both in experimental and FE analysis, highlighting its potential for applications requiring highly responsive materials. The validated FE model was further used for a parametric study of one of the promising simple designs, revealing that variations in geometric parameters significantly impact piezoresistive sensitivity. These findings provide valuable insights for advancing the development of pressure sensors with tailored sensitivity characteristics. Full article

This paper proposes an innovative multi-material approach for introducing auxetic behaviour to syntactic foams (SFs). By carefully designing the size, shape, and orientation of the SFs, auxetic deformation behaviour was induced. Re-entrant hexagon-shaped SF elements were fabricated using expanded perlite (EP) particles and a plaster of Paris slurry first. Then, an auxetic pattern of these SF elements was arranged within a stainless-steel casting box. The empty spaces between the SF elements were filled with molten aluminium alloy (A356) using the counter-gravity infiltration casting technique. The cast auxetic composite had a bulk density of 1.52 g/cm³. The cast composite was then compressed under quasi-static loading to characterise its deformation behaviour and to determine the mechanical properties, especially the Poisson’s ratio. The cast composite deformation was auxetic with a Poisson’s ratio of −1.04. Finite Element (FE) simulations were conducted to understand the deformation mechanism better and provide means for further optimisation of the geometry. Full article

In this work, a simple and environmentally friendly process combining low pressure (vacuum) and mechanical compression is proposed to convert recycled polypropylene (PP) foams (28 kg/m³) into low density foams (90–131 kg/m³) having negative tensile and compressive Poisson’s ratios (NPR). The main objective of the work was to determine the effect of processing conditions (vacuum time, temperature and mechanical pressure). Based on the optimized conditions, the tensile Poisson’s ratio of the resulting auxetic foams reached −1.50, while the minimum compressive Poisson’s ratio was −0.32 for the same sample. The foam structure was characterized via morphological analysis (SEM) to determine any changes related to the treatment applied. Finally, the tensile and compressive properties (Young’s modulus, strain energy, energy dissipation and damping capacity) are also presented and discussed. It was observed that the mechanical properties of the resulting auxetic foams were improved compared to the original PP foam (PP-O) for all tensile properties in terms of modulus (19.9 to 59.8 kPa), strength (0.298 to 1.43 kPa) elongation at break (28 to 77%), energy dissipation (14.4 to 56.3 mJ/cm³) and damping capacity (12 to 19%). Nevertheless, improvements were also observed under compression in terms of the energy dissipation (1.6 to 3.6 mJ/cm³) and the damping capacity (13 to 19%). These auxetic foams can find applications in sport and military protective equipment, as well as any energy mitigation system. Full article

Cellular structures subjected to compressive loads provide a reliable solution for improving safety. As a member of cellular material, auxetic metamaterials can enhance performance according to the definition of the negative Poisson ratio. In conjunction with Rapid Prototyping by Additive Manufacturing methods, complex structures can be manufactured using a wide range of materials. This paper debuts the development process of a reliable material model that is useful for the numerical simulation, and further details and investigates the performance indicators of an auxetic structure, namely anti-tetra-chiral. These indicators are related to the force developed during the plateau stage, the length of the plateau stage, and the nominal dimensions of the structure to avoid buckling during compression. Two new indicators discussed in this paper aim to provide a complete set of performance indicators. The first analytical solution provides the displacement of the circular nodes during the compression. The second analytical solution estimates the strain developed in the ligaments. Considering the performance of the processed material, this analysis aims to determine whether the structure can develop the complete plateau stage or whether premature failure will occur. Full article

The shape memory polymer (SMP) is a new type of smart material that can produce a shape memory effect through the stimulation of the external environment. In this article, the viscoelastic constitutive theory of the shape memory polymer and the mechanism of the bidirectional memory effect of the shape memory polymer are described. A chiral poly cellular circular concave auxetic structure based on a shape memory polymer made of epoxy resin is designed. Two structural parameters, α and β, are defined, and the change rule of Poisson’s ratio under different structural parameters is verified by ABAQUS. Then, two elastic scaffolds are designed to assist a new type of cellular structure made of a shape memory polymer to autonomously adjust bidirectional memory under the stimulation of the external temperature, and two processes of bidirectional memory are simulated using ABAQUS. Finally, when a shape memory polymer structure implements the bidirectional deformation programming process, a conclusion is drawn that changing the ratio β of oblique ligament and ring radius has a better effect than changing the angle α of oblique ligament and horizontal in achieving the autonomously adjustable bidirectional memory effect of the composite structure. In summary, through the combination of the new cell and the bidirectional deformation principle, the autonomous bidirectional deformation of the new cell is achieved. The research can be used in reconfigurable structures, tuning symmetry, and chirality. The adjusted Poisson’s ratio achieved by the stimulation of the external environment can be used in active acoustic metamaterials, deployable devices, and biomedical devices. Meanwhile, this work provides a very meaningful reference for the potential application value of metamaterials. Full article

The objective of this study was to present a simple and environmentally friendly process combining low pressure (vacuum) and mechanical compression to convert low-density polyethylene (LDPE) foams into low-density foams (76–125 kg/m³) with negative tensile and compressive Poisson’s ratios (NPR). As a first step, four series of recycled LDPE foams (electronics packaging) with starting densities of 16, 21, 30 and 36 kg/m³ were used to determine the effect of different processing conditions including temperature and pressure. Based on the optimized conditions, the tensile and compressive Poisson ratios of the resulting auxetic foams reached −2.89 and −0.66, while the tensile and compressive modulus of the auxetic foams reached 40 kPa and 2.55 kPa, respectively. The foam structure of the samples was characterized via morphological analysis and was related to the mechanical properties before and after the treatment (i.e., foams with positive and negative Poisson’s ratios). The tensile and compressive properties (Young’s modulus, strain energy, energy dissipation and damping capacity) for these auxetic foams were also discussed and were shown to be highly improved. These auxetic foams can be applied in sports and military protective equipment. To the best of our knowledge, there is only one report on vacuum being used for the production of auxetic foams. Full article

In this paper, a novel auxetic structure with rotating squares with holes is investigated. The unit cell of the structure consists of four units in the shape of a square with cut corners and holes. Finally, the structure represents a kind of modified auxetic structure made of rotating squares with holes or sheets of material with regularly arranged diamond and square cuts. Effective and dynamic properties of these structures depend on geometrical properties of the structure. The structures are characterized by an effective Poisson’s ratio from negative to positive values (from about minus one to about plus one). Numerical analysis is made for different geometrical features of the unit cells. The simulations enabled the determination of the dynamic characteristic of the analyzed structures using vibration transmission loss, transmissibility, and mechanical impedance. Numerical calculations were conducted using the finite element method. In the analyzed cases of cellular auxetic structures, a linear elasticity model of the material is assumed. The dynamic characteristic of modified rotating square structures is strongly dependent not only on frequency. The dynamic behavior could also be enhanced by adjusting the geometric parameter of the structure. Auxetic and non-auxetic structures show different static and dynamic properties. The dynamic properties of the analyzed structures were examined in order to determine the frequency ranges of dynamic loads for which the values of mechanical impedance and transmissibility are appropriate. Full article

A designer of metallic energy absorption structures using additively manufactured cellular materials must address the question of which of a multitude of cell shapes to select from, the majority of which are classified as either honeycomb, beam-lattice, or Triply Periodic Minimal Surface (TPMS) structures. Furthermore, there is more than one criterion that needs to be assessed to make this selection. In this work, six cellular structures (hexagonal honeycomb, auxetic and Voronoi lattice, and diamond, gyroid, and Schwarz-P TPMS) spanning all three types were studied under quasistatic compression and compared to each other in the context of the energy absorption metrics of most relevance to a designer. These shapes were also separately studied with tubes enclosing them. All of the structures were fabricated out of AlSi10Mg with the laser powder bed fusion (PBF-LB. or LPBF) process. Experimental results were assessed in the context of four criteria: the relationship between the specific energy absorption (SEA) and maximum transmitted stress, the undulation of the stress plateau, the densification efficiency, and the design tunability of the shapes tested—the latter two are proposed here for the first time. Failure mechanisms were studied in depth to relate them to the observed mechanical response. The results reveal that auxetic and Voronoi lattice structures have low SEA relative to maximum transmitted stresses, and low densification efficiencies, but are highly tunable. TPMS structures on the other hand, in particular the diamond and gyroid shapes, had the best overall performance, with the honeycomb structures between the two groups. Enclosing cellular structures in tubes increased peak stress while also increasing plateau stress undulations. Full article