Self-shaping of bioinspired chiral composites

Self-shaping materials such as shape memory polymers have recently drawn considerable attention owing to their high shape-changing ability in response to changes in ambient conditions, and thereby have promising applications in the biomedical, biosensing, soft robotics and aerospace fields. Their design is a crucial issue of both theoretical and technological interest. Motivated by the shape-changing ability of Towel Gourd tendril helices during swelling/deswelling, we present a strategy for realizing self-shaping function through the deformation of micro/nanohelices. To guide the design and fabrication of selfshaping materials, the shape equations of bent configurations, twisted belts, and helices of slender chiral composite are developed using the variation method. Furthermore, it is numerically shown that the shape changes of a chiral composite can be tuned by the deformation of micro/nanohelices and the fabricated fiber directions. This work paves a new way to create self-shaping composites.

A review on additive manufacturing of ceramic matrix composites

Additive manufacturing(AM)of ceramic matrix composites(CMCs)has enabled the production of highly customized,geometrically complex and functionalized parts with significantly improved properties and functionality,compared to single-phase ceramic components.It also opens up a new way to shape damage-tolerant ceramic composites with co-continuous phase reinforcement inspired by natural ma-terials.Nowadays,a large variety of AM techniques has been successfully applied to fabricate CMCs,but variable properties have been obtained so far.This article provides a comprehensive review on the AM of ceramic matrix composites through a systematic evaluation of the capabilities and limitations of each AM technique,with an emphasis on reported results regarding the properties and potentials of AM man-ufactured ceramic matrix composites.

Bioinspired design of hybrid composite materials

Mimicking the natural design motifs of structural biological materials is a promising approach to achieve a unique combination of strength and toughness for engineering materials.In this study,we proposed a 2D computational model,which is a two-hierarchy hybrid composite inspired by the ultrastructural features of bone.The model is composed of alternating parallel array of two subunits(A&B)mimicking‘mineralized collagen fibril’and‘extrafibrillar matrix’of bone at ultrastructural level.The subunit-A is formed by short stiff platelets embedded within a soft matrix.The subunit-B consists of randomly distributed stiff grains bonded by a thin layer of tough adhesive phase.To assess the performance of the bioinspired design,a conventional unidirectional long-fiber composite made with the same amount of hard and soft phases was studied.The finite element simulation results indicated that the toughness,strength and elastic modulus of the bioinspired composite was 312%,83%,and 55%of that of the conventional composite,respectively.The toughness improvement was attributed to the prevalent energy-dissipating damage of adhesive phase in subunit-B and crack-bridging by subunit-A,the two major toughening mechanisms in the model.This study exemplifies some insights into natural design of materials to gain better material performance.

Sinusoidally architected helicoidal composites inspired by the dactyl club of mantis shrimp

The impact region of the dactyl club of mantis shrimp features a rare sinusoidally helicoidal architecture,contributing to its efficient impact-resistant characteristics.This study aims to attain bioinspired sinusoidally architected composites from a practical engineering way.Morphological features of plain-woven fabric were characterized,which demonstrated that the interweaving warp and weft yarns exhibited a sinusoidal architecture.Interconnected woven composites were thus employed and helicoidally stacked to achieve the desired structure.Quasi-static three-point bending and low-velocity impact tests were subsequently performed to evaluate their mechanical performance.Under three-point bending condi-tion,the dominant failure mode gradually changed from fiber breakage to delamination with the increase in the pitch angle.Failure displacement and energy absorption of the heli-coidal woven composites were,respectively,43.89%and 141.90%greater than the unidirectional ones.Under low-velo-city impact condition,the damage area of the helicoidal woven composites decreased by 49.66%while the residual strength increased by 10.10%compared with those of the unidirectional ones,exhibiting better damage resistance and tolerance.Also,effects of fiber architecture on mechanical properties were examined.This work will shed light on future design of the next-generation impact-resistant architected composites.

Bioinspired polyimide film with fire retardant and gas barrier properties by gravity-induced deposition of montmorillonite

Flame retardants play a crucial role in improving theflame retardant properties of polymer materials.In recent years,environmental problems caused byflame retar-dants have attracted widespread attention.It is urgent to use green and effective methods to prepareflame retardant polymers.Bioinspired nanocomposites with lay-ered structures seem to provide effective ideas,but in general,their hydrophilic raw materials limit their applications in certainfields.Here,we prepared biomimetic composites with a layered“brick-and-mortar”structure by gravity-induced depo-sition using polyimide as the polymer matrix and montmorillonite(MMT)as thefiller.The well-arranged structures of the composite material could isolate oxygen and prevent combustible gases from escaping.The gas barrier performance has been greatly improved,in which the water vapor transmission rate and the oxygen trans-mission rate decreased by 99.18%and three orders of magnitude,respectively.Theflame retardant performance has also been improved,and its limiting oxygen index can reach 67.9%.The polyimide matrix can be converted to water-insoluble by ther-mal imidization of water-soluble poly(amic acid)salt precursors,which endows the composites with low hygroscopicity.The coating containing MMT can protect against polyurethane(PU)foam fromfire.During the conical calorimetric test,the coated sample self-extinguished,and the peak heat release rate,total heat release,and total smoke production are significantly decreased by 53.39%,40.69%,and 53.03%,respectively.Taking advantage of these properties,this work utilizes a facile method to prepare biomimetic composites with low moisture absorption,excellent gas barrier properties,andflame retardancy,which have great application potential.

Biological Waste Water Hyacinth (Eichhornia crassipes) Plant Powder Particle with Eggshell Filler-reinforced Epoxy Polymer Composite Material Property Analysis

In this study, water hyacinth powder-reinforced polymer composites with eggshell filler material are investigated for their mechanical, absorption, morphological, thermal, and characterization properties. Hyacinth powder particles have not been extensively studied in polymer composites. This study investigates the use of eggshell powder for composites made from hyacinth powder. The use of hyacinth powder improves the mechanical properties of composites. With the help of the powder particles, composite samples are produced by compression moulding using an epoxy polymer matrix. 5% eggshell filler varied from 18.25 to 33.64 MPa for tensile strength, 40.28–49.66 MPa for flexural strength, and 2.45–4.75 J for impact strength. X-ray diffraction and Fourier transforms can be used to determine chemical groups, function groups, and crystallinity indexes. Powder particles can be observed by scanning electron microscopes in terms of their bonding behavior, eggshell powder combinations, and primary- and secondary-phase material absorption. According to the research presented in this paper, commercial particleboard applications can benefit substantially from hyacinth powder particles reinforced with eggshell fillers.