•The cyclic mechanical response of the auxetic structures FFF-printed by four different materials were revealed.•The auxetic structure properties were predicted by the mathematical equations of ...material property parameters.•The recovery behavior of the structure was simulated and useful information of structural design was provided.
The influence of lattice structural design on the mechanical property has been abundantly investigated, however, the effect of material on the load-carrying performance and energy absorption was seldom studied. In the current work, the auxetic structures fabricated using four materials including polyamide (PA), carbon fiber (CF) reinforced PA (PA/CF), polyether ether ketone (PEEK) and PEEK/CF were 3D-printed, and the compression performance and deformation behavior were compared and explored. The results showed that the deformation mode of auxetic structure were similar, which was not dependent on the material type. However, the compressive strength and modulus of the auxetic structure showed strong dependence on the material properties. Besides, PA and PA/CF auxetic structures displayed better rebound behavior after compression, which was perhaps attributed to the good resilience of PA resin. Therefore, mathematical equations were utilized to predict the compressive property based on the material parameters, showing a good agreement. On the other hand, the simulation of compression process was established and conducted, which confirmed the deformation process as experimental presented. The rebound behavior was further predicted by a loading-releasing cycle with different compression strains. Accordingly, the compression parameters showed great relations with material parameters but little effect on the deformation behavior.
Fatigue response of auxetic structures: A review Parente, João M.; Reis, Paulo N. B.; Berto, Filippo
Fatigue & fracture of engineering materials & structures,
August 2024, 2024-08-00, 20240801, Letnik:
47, Številka:
8
Journal Article
Recenzirano
The fatigue behavior of auxetic metamaterials is an interesting and recent research topic that will deserve future attention. How different geometries can interact with cyclic loadings is still an ...open question for these kinds of structures. Therefore, this review aims to provide an update on the state of the art on the fatigue response of auxetic structures, showing which research questions are open and possible future developments. As will be evident from this review, there is still room for further improvements that will allow these structures to become much more attractive for load‐bearing applications.
Re-entrant circular (REC) auxetic metamaterials have garnered significant attention in structural engineering due to their enhanced energy absorption capability and reduced stress concentration ...compared to traditional re-entrant auxetic configurations. However, there is considerable potential for further enhancing their design to achieve even greater energy absorption capabilities. This study introduces three novel REC auxetic structures (REC-S, REC-Star and REC-Flower) specifically designed to enhance energy absorption capabilities compared to traditional REC configurations. These structures are formed by deploying an S-shaped, a star, and a newly designed auxetic unit-cell (UC) named Flower into the REC framework and fabricated through 3D printing by using fused deposition modeling (FDM) techniques. Their deformation behavior and mechanical performance are assessed through quasi-static compressive experimental tests and finite element analysis (FEA), with good agreement obtained between the two sets of results. Based on the validated FEA, the effects of the geometrical parameters of the structures on specific stiffness (Es), specific energy absorption (SEA), and Poisson's ratio are further investigated. The results show that the newly designed structures outperform the traditional REC structure with equivalent relative densities (∆ρ) and the REC-Flower has the highest SEA for all relative densities, positioning it as a promising candidate for the next generation of REC structures.
•Three auxetic structures with auxetic unit-cells inside re-entrant cells proposed and fabricated by FDM printing method.•Their mechanical performances evaluated by FEM and experimental tests, confirming the accuracy of FEM.•REC-Flower structure showed superior stiffness and SEA, highlighting its potential as a next-generation REC structure.
The increasing demands of safety, cost reduction, or weight reduction on components call for new, multifunctional materials. Mechanical metamaterials, such as auxetic materials, provide enhanced ...properties due to a specially tailored microstructure. The negative Poisson's ratio of auxetics, for instance, increases the impact and thermal shock resistance. Herein, a parametrized model of a modified auxetic structure is simulated using the finite‐element software ABAQUS. Three out of five geometry parameters are varied between a minimum and maximum value to establish their impact on the energy absorption capacity and the Poisson's ratio using design of experiment (DoE). All eight resulting structures are additively manufactured by selective laser melting (SLM) and experimentally investigated under uniaxial compression to validate the simulations. The size of a unit cell has the biggest impact on both target values. Energy absorption capacity and Poisson's ratio are directly competing in optimization; hence, a compromise is necessary. The quasistatic compression experiments verify the simulation results up to the first collapse. Afterward, the specimens are brittle, which is not accounted for in the simulations, and this may result from the high process complexity of SLM manufacturing.
The 23‐full‐factorial testing plan identifies the strut thickness as the least influential geometry parameter for optimization of the energy absorption capacity and Poisson's ratio. The selective laser melting‐manufactured specimens display good accordance with the simulations, though in the experiments the specimens are brittle and bending dominated. Poisson's ratios up to −0.51 are reached in the experiments.
Present study develops the experimental and finite element analysis of an auxetic piezoelectric energy harvester consisting of a cantilever, auxetic substrate, and piezoelectric layer. Firstly, five ...auxetic models with 1, 4, 9, 16, and 25 honeycomb auxetic cells are presented. Harvested power and stress distribution of the piezoelectric layer for these models are compared with plain piezoelectric energy harvester. All the analysis has been performed using the experimental tests and finite element method. Mesh size sensitivity analysis of the finite element model is presented, and it is verified by previous experimental studies. The model with 25 auxetic cells harvests more power than other models. Furthermore, comparing stress distribution on the piezoelectric layer of these models indicates that increasing the number of auxetic cells leads to increasing the average stress on the piezoelectric layer. The present investigation illustrates that harvested power of an auxetic energy harvester in resonant frequency could improve to twenty times more than a plain harvester. Besides, the new auxetic model with trapezoidal geometry is presented in the present paper. Utilizing this model as the substrate in a piezoelectric energy harvester leads to increasing the efficiency of the energy harvester by 82.5%. The damping ratio of the auxetic energy harvester has been measured by experimental investigation. Also, experimental analysis has been performed to find the optimum energy harvester circuit resistor. The density of the harvested power for the trapezoidal energy harvester with an optimum circuit resistor is 107% more than the rectangular energy harvester.
In the field of soft strain sensors, piezo-transmittance based strain sensors, which detect strains by optical transmittance change, have promising advantages of fast response, high sensitivity, ...long-term stability, and negligible effect from environmental factors. However, they feature low sensor-to-sensor and in-sensor uniformity as well as unpredictable response and high stiffness. This study exploits the gap control of an auxetic-patterned elastomer to develop a piezo-transmittance based strain sensor. Gap opening mechanism in the negative Poisson’s ratio metamaterial with rotating square structures makes the sensor free from these limitations; thus, achieving a designable response and low stiffness. In addition, high sensor-to-sensor ((root-mean-square deviation (RSD) < 3.5%) and in-sensor (RSD < 5%) uniformities are achieved by uniform metal-deposited light-blocking film. Finally, the developed sensor has been integrated with a solar cell and Bluetooth Low Energy (BLE) 4.0 to afford a self-powered wireless strain sensing system that is successfully applied to structural health monitoring and human motion monitoring.
A piezo-transmittance based strain sensor based on an auxetic structure with a gold-deposited elastomer is developed. Through this design, we accomplish high sensor-to-sensor and in-sensor uniformity. Furthermore, the gap opening mechanism allows an ultralow stiffness as well as a rational designability. The developed sensor is integrated into a self-powered wireless sensing system for structural health monitoring and human motion monitoring. Display omitted
•A piezo-transmittance based self-powered strain sensor is developed.•High sensor uniformity is accomplished using a uniform mechanical metamaterial.•The gap opening mechanism allows an ultralow stiffness and rational designability.•A self-powered wireless sensing system using solar cell and BLE is developed.•The system is utilized for structural health monitoring and human motion monitoring.
Auxetic structures exhibit unusual changes in size, expanding laterally upon stretching instead of contracting. This paper presents this effect in a failsafe mode in structures made of rigid squares. ...We applied the concept of auxetic structures made of rigid rotating squares (from Grima and Evans) and offer a novel solution for connecting them. By introducing axes of rotation on the surface of the squares, a reliable working system is obtained, free from stress, in which the squares can come into contact with each other and completely cover the surface of the structure, or, in the open position, form regularly arranged pores. Herein, we present a new 2D auxetic metamaterial that is mathematically generated based on a theoretical relationship of the angle between the edges of a square and the position of the axis of rotation. Physical models were generated in the form of a planar structure and in the form of a circular closed structure. Such physical models confirmed our initial considerations and the geometrical relationships, offering new application possibilities. The novel structure that was designed and manufactured for the purpose of the paper can be considered as a new proposal in the market of auxetic materials.
In the last decade, auxetic structures with a negative Poisson’s ratio have attracted the attention of experts in industries such as biomechanics, aerospace, and packaging due to their properties, ...such as energy absorption and high crack resistance. The preparation of these structures using smart polymers increases their attractiveness due to low energy expenditure at the destination and the deformation of two separate states by applying external stimuli. This study aimed to investigate the improved peanut-shaped structure that retains its auxetic properties at high elongation, the effects of changes in geometry and dimensions of the structure on the Poisson’s behavior, shape fixity ratio, and shape recovery ratio during the shape memory cycle. To this end, several samples were prepared using the 4D printing method of shape memory polymers, and laboratory results were compared with software simulations of the shape memory cycle. After validating the simulation results, more cases were examined by the modeling. The results showed that despite the complete recovery of samples, the Poisson’s ratio was not recovered. The changes in geometry and samples’ dimensions significantly enhanced their auxetic property. Due to obtaining a significantly high Poisson’s ratio by changing the geometric characteristics, this structure is suggested to be used in industrial applications such as aerospace.
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