Search Results (11)

Inspired by the Bouligand structure of the mantis shrimp’s dactyl club, in this study, we employed direct ink writing 3D printing technology to fabricate bioinspired gradient ceramic samples with varying gradient spacings and rotation angles. A rigid–flexible coupled bioinspired gradient ceramic–epoxy resin composite was successfully constructed based on epoxy resin infiltration. The effects of gradient variations and rotation angles on mechanical properties were systematically investigated with flexural strength and fracture toughness tests. The experimental results revealed that, at a fixed rotation angle, both the flexural strength and fracture toughness initially increased and then decreased with an increase in gradient spacing. The infiltration of epoxy resin significantly enhanced the mechanical performance of the composite samples. Specifically, the maximum flexural strength of 63.35 MPa was achieved at Δd = 0.08 and a rotation angle of 12°, while the highest fracture toughness of 2 MPa/m² was observed at Δd = 0.1 and a rotation angle of 12°. A failure analysis indicated that the introduction of gradient structures and epoxy resin infiltration altered the failure forms of traditional ceramics, with the primary toughening mechanisms including crack deflection, fiber pull-out, and crack branching. In this study, we successfully developed a rigid–flexible coupled bioinspired gradient ceramic–epoxy resin composite with excellent mechanical properties based on bioinspired design and gradient optimization, providing new insights and methodologies for the design and fabrication of high-performance ceramic materials. Full article

The study of biomimetics allows for the creation of various structures inspired by nature. This work investigates the impact of using a bio-inspired tool path for manufacturing porous plates via 3D printing. The Bouligand (or plywood-like) structure is prevalent in several biological components. Structures that mimicked the Bouligand design concerning the tool path were printed and compared to uniform plates produced with a rectilinear pattern through mechanical testing. Quasi-static and dynamic tests were conducted on specimens with infill densities ranging from 25% to 100%. Results indicated that the Bouligand pattern displayed superior specific energy absorption at 75% infill density. This bio-inspired path pattern also provided excellent elongation during quasi-static and dynamic failure—the fracture pattern of the bio-inspired path adhered to the Bouligand structure. In contrast, brittle failure was demonstrated by the specimen with a rectilinear pattern at varying infill percentages, while the bio-inspired pattern enhanced the toughness of the polymer specimens. Full article

Our study considered porous Bouligand structured polymer, comprising polymer fibres with porous spaces between them. These are more complicated structures than the non-porous Bouligand, since the addition of porosity into the material creates a secondary variable besides fibre pitch. There is currently no analytical model available to predict the modulus of such materials. Our paper explores the correlation between porosity, polymer fibre pitch angle, and flexural modulus in porous Bouligand structured polymers. Our structures were digitally manufactured using stereolithography (SLA) additive manufacturing methods, after which they were subjected to three-point bending tests. Our aim was to simply and parametrically develop an analytical model that would capture the influences of both porosity and polymer fibre pitch angle on the flexural modulus of the material. Our model is expressed as $E_f=E_{poro}(a{\theta }_f^3+b{\theta }_f^2+c{\theta }_f+d)$, and we derive this by applying non-linear regression to our experimental data. This model predicts the flexural modulus, $E_f$, of porous Bouligand structured polymer as a function of both porosity and pitch angle. Here, $E_{poro}$ is defined as the solid material modulus, $E_{solid}$, multiplied by porosity, $\varphi$ and is a linear reduction in the modulus as a function of increasing porosity, while ${\theta }_f$ signifies the polymer fibre pitch angle. This relationship is relatively accurate within the range of 10° ≤ θ_f ≤ 50°, and for porosity values ranging from $0.277\le 0.356$, as supported by our evidence to date. Full article

The helical arrangement of cardiac muscle fibres underpins the contractile properties of the heart chamber. Across the heart wall, the helical angle of the aligned fibres changes gradually across the range of 90–180°. It is essential to recreate this structural hierarchy in vitro for developing functional artificial tissue. Ice templating can achieve single-oriented pore alignment via unidirectional ice solidification with a flat base mould design. We hypothesise that the orientation of aligned pores can be controlled simply via base topography, and we propose a scalable base design to recapitulate the transmural fibre orientation. We have utilised finite element simulations for rapid testing of base designs, followed by experimental confirmation of the Bouligand-like orientation. X-ray microtomography of experimental samples showed a gradual shift of 106 ± 10°, with the flexibility to tailor pore size and spatial helical angle distribution for personalised medicine. Full article

Inspired by the bionic Bouligand structure, helicoidal carbon fiber-reinforced polymer composite (CFRPC) laminates have been proven to own outstanding out-of-plane mechanical properties. This work aims to further explore the excellent bending characteristics of helicoidal CFRPC laminated plates and find out the optimal helicoidal layup patterns. The optimization design of laminated plates stacked with single-form and combination-form helicoidal layup sequences are carried out by using the finite element method (FEM) and adaptive simulated annealing (ASA) optimization algorithm on the Isight platform. Then, the nonlinear bending responses of optimal helicoidal CFRPC laminated plates are investigated via the FEM for the first time. The helicoidal CFRPC laminated plates under three different types of boundary conditions subjected to transverse uniformly distributed load are considered. The numerical results reveal that the combination-form helicoidal layup sequences can decrease the dimensionless bending deflection of laminated plates by more than 5% compared with the quasi-isotropic plate and enhance the out-of-plane bending characteristics of CFRPC laminated plates effectively. The boundary conditions can significantly influence the nonlinear bending responses of helicoidal CFRPC laminated plates. Full article

Enhancing the impact resistance performance of carbon fiber-reinforced polymer (CFRP) laminates stands as a prominent research focus among various nations. Existing studies have shown a tendency towards arbitrary selection of the inter-ply helix angle values in CFRP laminates, which is accompanied by a limited number of samples representing the chosen helix angles. However, existing studies have shown a relatively random selection of spiral angle values between CFRP laminates, and the sample size of selected spiral angles is limited, posing certain limitations. In order to tackle this problem, we have employed a systematic arrangement of combinations to select the optimal helix angle for CFRP laminates. Inspired by the biological structures of Bouligand, we have sequentially chosen 19 distinct sets of helix angles, aiming to overcome the inherent limitations and enhance the research outcomes in this field. In this study, we established 19 finite element models to investigate the behavior of Bouligand-inspired CFRP composite panels under high-velocity bullet impact. The models were created by selecting 19 sets of helix angles within the range of 0 to 90° with a 5° interval. The results show that the energy absorption of the Bouligand layer-stacking composite plate is better than that of the conventional plate. The optimal spiral angles of the CFRP laminate are 25° and 30°, and the energy absorption characteristics of the laminate are the best at these angles. The impact resistance is also the best at these angles. The energy absorption of the Bouligand layer-stacking composite plate is 396% higher in absorbed internal energy and 361% higher in absorbed kinetic energy compared to the conventional layer-stacking composite plate, significantly improving the ballistic performance of the CFRP bulletproof material and providing a reference for the design of individual protection equipment. Full article

The current study focuses on the impact loading phase characteristic of thin first year ice in inland waterways. We investigate metal grillages, fibre reinforced plastic (FRP) composites and nature-inspired composites using LS Dyna. The impact mode is modelled as (a) simplified impact model with a rigid-body impactor and (b) an experimentally validated ice model represented by cohesive zone elements. The structural concepts are investigated parametrically for strength and stiffness using the simplified model, and an aluminium alloy grillage is analysed with the ice model. The metal–FRP composite was found to be the most favourable concept that offered impact protection as well as being light weight. By weight, FRP composites with a Bouligand ply arrangement were the most favourable but prone to impact damage. Further, aluminium grillage was found to be a significant contender for a range of ice impact velocities. While the ice model is experimentally validated, a drawback of the simplified model is the lack of experimental data. We overcame this by limiting the scope to low velocity impact and investigating only relative structural performance. By doing so, the study identifies significant parameters and parametric trends along with material differences for all structural concepts. The outcomes result in the creation of a viable pool of lightweight variants that fulfil the impact loading phase. Together with outcomes from quasi-static loading phase, it is possible to develop a lightweight ice-going hull concept. Full article

This paper concerns the effects of hygrothermal ageing on the tensile behaviour of assymetric helicoidally stacked carbon fibre reinforced plastic (CFRP) composites. MR70 12P carbon fibre epoxy prepreg sheets were manufactured into laminated composites comprising constant inter-ply pitch angles ranging from 0${}^{°}$ to 30${}^{°}$. The composites were tested in tension (according to BS ISO 527-5:2009) as either dry unaged specimens or following hygrothermal ageing in seawater at the constant temperatures of 40 ${}^{°}$C and 60 ${}^{°}$C for 2000 h. Both tensile modulus and tensile strength are found to be detrimentally affected by hygrothermal ageing, and the extent to which ageing affects these properties is a function of the inter-ply pitch angle. Higher hygrothermal ageing temperatures are found to decrease the tensile modulus and strength ratios of asymmetric helicoidally stacked composites when compared against UD composites subjected to the same conditions and the strength and stiffness ratios of all composites when compared against unaged equivalents. Significantly, therefore, we show that the degradation of helicoidal composite properties under hygrothermal conditions, in general, occurs more rapidly than it does in UD composites, and thus the long-term use of helicoidal composites in immersed environments should take into account these differences. A second order relationship is observed for the mechanical properties of the composites when plotted against their inter-ply helicoidal pitch angles. As such, a mixtures model was modified to incorporate the observed effects of laminate inter-ply pitch angle and used to predict the tensile modulus of unaged composites. The predictions are within one standard deviation of the experimental arithmetic mean; however, the model can only be used for dry helicoidal composites, as ageing alters the microstructures in an irregular manner between the different sample sets. The development of this mixture model is useful as it provides a justifiably simple route to predicting the properties of dry helicoidal structures, albeit within the bounds of specific interply-pitch angles. Finite element analyses (Hashin failure) elucidate the plies that are most likely responsible for composite failure. The validity of these numerical predictions is evidenced by observing primary fracture paths in the composites. Finally, hygrothermal ageing is found to enable greater in-plane (mode III) twisting of individual laminates under loading, with certain laminate angles being more prone to twisting than others. Full article

Modern expansion and three-dimensional growth are rapidly altering the morphological features of traditional cities. This morphological phenomenon fully reflects the internal organization mode and composition rules of modern cities. This study draws on the research method of three-dimensional fractal, focusing on the situation where there is less research on the fractal form at the block scale, and conducts a fractal research on the three-dimensional form of a city at the meso and micro scales, in order to reveal the fractal characteristics of modern urban density. Based on fractal theory, the urban form of Shenyang, Northeast China, was quantitatively analyzed using the box-counting (Minkowski–Bouligand) method to calculate the two-dimensional (2D) and three-dimensional (3D) box dimensions of urban areas. Next, by analyzing the correlations between morphological indicators and 2D and 3D fractal dimensions, this study proposes cluster features of the correlation between the 3D fractal dimension and floor-area ratio. Then, this study summarizes the fractal characteristics of Shenyang’s urban form, based on the cluster analysis and spatial features of various urban areas within the city. The analysis results show the fractal dimension of Shenyang’s urban form to have characteristic expected values; fractal dimension clusters reflect spatial differences in the forms of different urban areas. The 3D D value of architectural morphology fractal in urban areas of Shenyang is between 2.41 and 2.70. From this, the representative characteristics of Shenyang’s urban form were obtained: first, it has the fractal characteristics of morphological hierarchy and system embeddedness; second, under unified and standardized management, its basic urban form structure displays the fractal characteristics of morphological similarity and system hierarchy; and third, its 3D urban form characteristics include the spatial accumulation of clusters and morphological patches, creating a patchwork of different building heights and densities, with the spatial clustering of density form highly correlated with the fractal dimension. The results of this research will provide reference samples for the morphological identification, design control, and design review of modern cities, and enrich the research results of the application of fractal theory to urban morphology at the meso and micro scales. Full article

Dense 3D point clouds were generated from Structure-from-Motion Multiview Stereo (SFM-MVS) photogrammetry for five representative freshwater fish habitats in the Xingu river basin, Brazil. The models were constructed from Unmanned Aerial Vehicle (UAV) photographs collected in 2016 and 2017. The Xingu River is one of the primary tributaries of the Amazon River. It is known for its exceptionally high aquatic biodiversity. The dense 3D point clouds were generated in the dry season when large areas of aquatic substrate are exposed due to the low water level. The point clouds were generated at ground sampling distances of 1.20–2.38 cm. These data are useful for studying the habitat characteristics and complexity of several fish species in a spatially explicit manner, such as calculation of metrics including rugosity and the Minkowski–Bouligand fractal dimension (3D complexity). From these dense 3D point clouds, substrate complexity can be determined more comprehensively than from conventional arbitrary cross sections. Full article

The dactylopodites of the Chinese mitten crab (Eriocheir sinensis) have evolved extraordinary resistance to wear and impact loading after direct contact with rough surfaces or clashing with hard materials. In this study, the microstructure, components, and mechanical properties of the dactylopodites of the Chinese mitten crab were investigated. Images from a scanning electron microscope show that the dactylopodites’ exoskeleton was multilayered, with an epicuticle, exocuticle, and endocuticle. Cross sections and longitudinal sections of the endocuticle revealed a Bouligand structure, which contributes to the dactylopodites’ mechanical properties. The main organic constituents of the exoskeleton were chitin and protein, and the major inorganic compound was CaCO₃, crystallized as calcite. Dry and wet dactylopodites were brittle and ductile, respectively, characteristics that are closely related to their mechanical structure and composition. The findings of this study can be a reference for the bionic design of strong and durable structural materials. Full article