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Despite plenty of static and dynamic mechanical measurements and modeling for bulk polydimethylsiloxane (PDMS) specimens, a notable gap exists in comprehensively understanding the dynamic mechanics under large cycle, low strain conditions, especially for microscale samples. This study integrates tensile testing and nanoindentation techniques to compare dynamic mechanical response for bulk PDMS samples and μ-pillars. The results from cyclic tensile testing, which involved up to 10,000 cycles at a strain range of 10%–20%, indicate a stabilization of energy dissipation rate after the initial 25 cycles. This attributes to stress relaxation and strain hardening, validating by rapid dual-phase exponential decay in maximum stress, coupled with an incremental increase in elastic modulus. In comparison to tensile testing, μ-pillars exhibited a 0.82% reduction in stiffness, stabilizing ~600th cycle. Concurrently, there was an approximately twofold increase in approaching distance during the initial 120 cycles, and an approximately fourfold increase in dissipated energy over the first 80 cycles, before reaching a plateau. This lagging hysteresis effect attributes to the distribution of the resultant force, including top tension, bottom compression, and base tilt. Overall, this study illuminates temporal mechanical deformations in PDMS under two application scenarios, enhancing our understanding of PDMS mechanical behavior. [ABSTRACT FROM AUTHOR]

Boron Nitride Nanotubes (BNNTs), a 1D nanomaterial with extraordinary mechanical properties, are structurally like carbon nanotubes. BNNTs possess superior thermal stability of ∼900 °C, higher resistance to oxidation at elevated temperatures, and enhanced neutron shielding capacity. These benefits open a wider processing window for manufacturing BNNT-reinforced metal matrix composites (MMC) and hold promise for several structural applications, including radiation shielding. This critique presents the current status, challenges, and future scientific possibilities of BNNT-reinforced MMC. Particular emphasis is laid on the progress made in this area regarding the synthesis, manufacturing, and characterization of BNNT-MMCs to date. The challenges associated with various processing techniques, including additive manufacturing (AM), are discussed in the fabrication of BNNT-MMCs. The experimental mechanics and structure-property relationship modeling are examined in detail to establish the utilization of BNNT-reinforced MMCs. Additionally, prospective research areas with a huge untapped potential for BNNT-MMCs are suggested. The scientific framework behind these methods' chronological development is analyzed, and a pathway for subsequent advancement is projected. By providing a comprehensive overview, this critique aims to facilitate further progress in BNNT-reinforced MMCs. [ABSTRACT FROM AUTHOR]

There is a need to augment the mechanical strength of titanium alloys to take advantage of their low mass density for structural applications. Herein, the reinforcement potential of boron nitride nanotube (BNNT), a high‐aspect‐ratio nanomaterial with exceptional strength and thermal stability, to engineer nanocomposites based on Ti–6Al–4 V alloy, is interrogated. The stress‐transfer behavior at the matrix/filler interface is programmed by tweaking the extent of chemical reactions during sintering. A twofold improvement in indentation resistance after integrating BNNTs in the alloy due to the crack bridging mechanism is reported. There is a further 50% enhancement in hardness and stiffness as the sintering temperature is raised from 750 to 950 °C. This improvement is attributed to the escalated formation of TiN and TiB phases due to matrix–nanotube interfacial reactions at elevated temperatures. A novel indentation‐based in situ trench testing technique is employed to study the subsurface deformation mechanisms activated in the bulk of the composite specimen. The ceramic interphases promote the indentation resistance by acting as crack deflectors in the microstructure, which promotes the dissipation of mechanical work. These insights can be applied to designing Ti‐BNNT microstructures with desired mechanical properties and deformation characteristics. [ABSTRACT FROM AUTHOR]

High‐resolution printing afforded by two‐photon polymerization (2PP) has opened up vast design space, spanning over four orders of magnitude (sub‐μm to cm), unleashing the opportunity to fabricate architected materials with intriguing mechanical characteristics. This study seeks to exploit direct laser writing to print accordion‐shaped honeycomb lattices constituted of slender micro‐membranes to achieve in‐plane mechanical anisotropy. The deformation mechanisms governing orientation‐sensitive mechanical properties of the lattice are examined by in situ investigations in a scanning electron microscope. The microlattice displays greater flexibility, compliance, and strain hardening during in‐plane compression, whereas it is highly stiff and resistant to fatigue in the out‐of‐plane orientation. The high aspect ratio of accordion‐shaped cells imparts prominent in‐plane anisotropy, with longitudinal stiffness twice the transverse stiffness. Folding, interlocking, and compaction of micro‐walls are the major deformation mechanisms, inducing brilliant energy dissipation ability, with up to 87% mechanical work‐absorption. Digital image correlation analysis reveals that strain re‐distribution facilitated by hinges dictates the recoverability of the microlattice. This work provides useful mechanistic insights at the micrometer length scale for tuning the orientation‐sensitive mechanical response of mesostructures printed by 2PP. [ABSTRACT FROM AUTHOR]

Stable dispersion of boron nitride nanotube (BNNT) in a solvent is a critical challenge that has restricted the development of potential applications. In this study, stable BNNT aqueous dispersions are obtained by direct tip sonication in water without any surfactant and organic solvent. BNNTs are functionalized with hydroxyl groups (OH) as a result of the tip sonication‐assisted hydrolysis. The energy from tip sonication results in the disentanglement of the as‐received BNNT clusters and partial B‐N bond cleavage to unzip nanotubes. Using the BNNT aqueous dispersion, a transparent, strong, and ductile OH‐BNNT‐reinforced polyvinyl alcohol (PVA) multifunctional nanocomposite film is prepared. Tensile fracture strength, Young's modulus, and elongation at failure of 1.0 wt% OH‐BNNT/PVA nanocomposite film increased by 46%, 55%, and 45%, respectively, in comparison with pure PVA film. The addition of a mere 1.0 wt% BNNT contributed to a significant (25%) improvement in thermal conductivity. Simultaneous improvement in mechanical and thermal properties is attributed to the superior intrinsic properties of homogenously dispersed BNNTs and strong interfacial interactions between OH‐BNNT and PVA chains. [ABSTRACT FROM AUTHOR]

Herein, boron nitride nanotube (BNNT)–reinforced Ti alloy composites with 1 wt% BNNT (3 vol%) are successfully fabricated by spark plasma sintering (SPS). This study addresses two challenges affecting the performance of BNNT–metal matrix composites: i) the dispersion of high‐surface‐energy BNNTs by an ultrasonic‐assisted technique and ii) the control of reactions at the metal/nanotube interface. High‐energy ultrasonic vibrations were effective in the dispersion of entangled BNNTs, and sintering at low (750 °C and 555 MPa) and high (950 °C and 60 MPa) temperature regimes resulted in relative densities of 97% and 99%. Reducing sintering temperatures by up to 35% compared to those used in conventional sintering is effective in minimizing brittle interfacial products. Also, the composites sintered at high‐temperatures/low‐pressure benefit from the rapid densification (10 min) achieved in the SPS process limiting the extent of reactions (TiB2, TiB). Compressive properties show composites sintered at low and high temperatures exhibit increases of 46% and 50% in yield strength, respectively, as compared to the Ti alloy. Strain hardening exponents of 0.8 and 0.5 characterize the capabilities of the composites to arrest plasticity in the presence of BNNTs, reaction phases, and twin boundaries pinning dislocations. This study unravels the potential of a low‐temperature/high‐pressure processing window for Ti‐BNNT composites. [ABSTRACT FROM AUTHOR]

Boron nitride nanotube (BNNT) is integrated in AZ31 magnesium alloy by field‐assisted powder metallurgy route. A mat of BNNT is sputter‐coated with pure Mg and then sandwiched between AZ31 alloy powders. This layered composite is consolidated by spark plasma sintering (SPS). A high processing pressure of 400 MPa aids in intimate alloy–nanotube adhesion due to localized deformation. Thermal diffusion between AZ31 and BNNT (at 400 °C sintering temperature) results in the formation of Mg3N2 and AlN nanophases at the interface. Due to ultrafast Joule heating during SPS, the reactions are kinetically controlled, and only trace amounts of products are formed without compromising the characteristics of the nanotubes. The interphases aid in reactive bonding between AZ31 and BNNT, which is essential for load‐bearing applications. In situ double cantilever loading of the composite inside the scanning electron microscope shows that the nanotubes bridge, resist, and delay crack propagation. These findings demonstrate the promise of thermally stable BNNTs as reinforcement for engineering lightweight Mg‐based structural composites. [ABSTRACT FROM AUTHOR]

An electrostatic spraying technique was used to synthesize 3D graphene foam (GrF)‐reinforced polyurethane (PU) composites. Glass transition temperature (Tg) of PU increased from 120 to 148°C after 3.3 vol% GrF addition. Strong interfacial bonding accounts for the improvement in Tg of PU‐GrF composites. Energy dissipation behavior is probed at multiple load scales to examine the intrinsic and structural damping characteristic. Micro‐scale damping at 1 mN and 1,000 Hz exhibited loss tangent value (tan δ), which is 200% higher and 3 times faster than PU. Nano dynamic mechanical analysis of PU‐3.3 vol% GrF composite demonstrated up to 383% tan δ improvement than of PU at 5 μN dynamic load. Physical mechanisms including rippling effect and weak van der Waals forces in graphene account for the high energy dissipation of PU‐GrF composite. This study suggests that PU‐GrF nanocomposites have the potential to serve as a good damping material in vibrating systems. POLYM. COMPOS., 40:E1862–E1870, 2019. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Polylactic acid (PLA) and graphene reinforced polylactic acid (PLA‐graphene) composites have been fabricated by three‐dimensional (3D) fused deposition modeling (FDM) printing. Indentation creep resistance was analyzed in terms of the strain‐rate sensitivity index of PLA (0.11) and PLA‐graphene (0.21). Enhanced creep resistance in PLA‐graphene is attributed to the restriction of the polymeric chains by graphene, caused by low strain rates identified during secondary creep. The tribological properties of PLA and PLA‐graphene composites were evaluated by ball‐on‐disk wear tests. Wear resistance was increased by a 14% in PLA‐graphene as compared to PLA. A two‐stage coefficient of friction (COF) behavior has been observed for PLA‐graphene. Initially, PLA‐graphene exhibits a 65% decrease in COF as compared to PLA. During the second stage, PLA‐graphene approached similar COF behavior and value of PLA (∼0.58). PLA‐graphene composites have shown significant improvement in creep and wear resistance demonstrating 3D printing to be a novel manufacturing route. POLYM. COMPOS., 39:3877–3888, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Boron Nitride Nanotube (BNNT) is a promising reinforcement for developing strong and lightweight metal matrix composites due to its brilliant mechanical properties and excellent high‐temperature oxidation resistance. In this study, layered composites of aluminum and BNNT are fabricated by a multi‐step process comprising of hot pressing, rolling, and annealing. Less than 0.1 wt% of ultra‐long nanotubes (up to 200 μm in length) are used to induce superior strengthening. For achieving enhanced mechanical properties, nanotubes are de‐agglomerated and chemically dispersed in an aqueous solution before introducing between the layers of aluminum sheets. Application of pressure (up to 10 MPa) and temperatures (up to 300 °C) during rolling and hot pressing induces a bonding between aluminum sheets and nanotubes. Scanning electron microscopy reveals that the nanotubes survive these conditions, suggesting superior thermal and mechanical endurance of BNNT. The nanohardness and elastic modulus of the composites are found to improve by 52% and 17%, respectively, by merely 0.045 wt% BNNT addition. BNNT reinforced composites exhibit up to 13% improvement in ultimate tensile strength. The improvement in mechanical properties is ascribed to effective load transfer from the aluminum matrix to the long nanotubes via interfacial shear stress and enhancement of dislocation density. [ABSTRACT FROM AUTHOR]

Ultra-long Boron Nitride Nanotubes (100-200 µm) based layered Al-BNNT-Al composites are fabricated by spark plasma sintering, followed by cold rolling. The BNNT mat is sputter coated with Al to engineer strong metal-nanotube interface. The BNNTs exhibit perfect alignment along the cold rolling direction. The tensile strength of the composite is found to be 200 MPa, which is 400% greater than the strength of pure Al (≈40 MPa). Young's modulus of this sandwich composite (≈134 GPa) is found to be double the modulus of pure Al (≈70 GPa) (with standard deviations less than 10%). Strengthening is explained by three major mechanisms: superior load transfer for long BNNT reinforcement, improvement in matrix-nanotube bonding due to trace amount of interfacial product formation, and crack bridging by directionally aligned long nanotubes. [ABSTRACT FROM AUTHOR]

Graphene foam reinforced multifunctional ceramic composite is fabricated in this study. Graphene foam has a 3D macroporous architecture, which is filled with a low temperature co‐fired (LTCC) ceramic phase. The composite microstructure is engineered by three‐step fabrication scheme: infiltration of porous graphene foam with ceramic slurry, solidification to form a green body, and finally, pressure and temperature‐assisted sintering to produce a dense composite with intimate ceramic/graphene interface. Graphene foam is found to retain its 3D structure. The interconnected network of nodes and branches induces superior fracture toughness, load‐bearing capacity, and thermal − electrical transport characteristics. Addition of mere 0.18 wt% graphene foam results in a 480% improvement in the fracture energy. Sub‐surface examination reveals extensive crack deflection due to graphene foam's cellular units, highlighting the advantage of a 3D filler. Graphene foam also induces an impressive electrical conductivity of 165 S m−1 in an otherwise insulator ceramic. In situ infrared thermal imaging demonstrates enhanced thermal transportability in ceramic due to graphene foam. These findings attest the significance of 3D graphene foam to develop multifunctional ceramic composites in load‐bearing structures, thermal management, and electro‐mechanical devices. The synthesis scheme presented here is promising for facile and scalable manufacturing of this new class of materials. [ABSTRACT FROM AUTHOR]

A nacre mimicking layered composite consisting of multilayer graphene (MLG) flakes and copper is fabricated in this study by a two‐step process including cementation reaction and Joule heating via spark plasma sintering (SPS). In situ cementation reaction deposits copper nanodroplets on activated graphene flakes with the aid of reducer Magnesium metal. The copper‐coated graphene flakes are subjected to pressure and localized Joule heating, resulting in a hierarchical 3D architecture comprising of uniformly aligned graphene flakes firmly bonded together by intermediate copper layers. The lamellar microstructure is characterized by a heterogeneous variation of elastic modulus. The impact of this hierarchical structure on the composite's mechanical behavior is explored by indentation loading, revealing a four‐fold increase in the load bearing ability of MLG/Cu hybrid as compared to MLG monolith. The Nacre‐inspired MLG‐Cu hybrid exhibits work of indentation ≈22.4 mJ, which is 500% improvement over MLG monolith (≈3.7 mJ). Copper deposition on graphene significantly improves the inter‐layer adhesion and restricts the sliding, pull‐out, and delamination of graphene flakes. The intimate interfacial contact between the constituent layers of the 3D hybrid facilitates effective stress‐transfer, thereby improving the overall load‐bearing ability. The novel processing route proposed here can be applied to other 2D materials for developing bioinspired 3D architectures with superior mechanical properties for a wide range of applications. A nacre mimicking layered composite consisting of multilayer graphene flakes and copper is fabricated. Cementation reaction is employed to deposit copper particles on graphene sheets, followed by spark plasma sintering to consolidate the graphene/metal hybrid. The 3D architecture exhibits superior mechanical properties compared to pure graphene monolith, as the metal deposition provides intimate interfacial adhesion between graphene platelets. [ABSTRACT FROM AUTHOR]

Biomimetic on-chip tissue models serve as a powerful tool for studying human physiology and developing therapeutics; however, their modeling power is hindered by our inability to develop highly ordered functional structures in small length scales. Here, we demonstrate how high-precision fabrication can enable scaled-down modeling of organ-level cardiac mechanical function. We use two-photon direct laser writing (TPDLW) to fabricate a nanoscale-resolution metamaterial scaffold with fine-tuned mechanical properties to support the formation and cyclic contraction of a miniaturized, induced pluripotent stem cell-derived ventricular chamber. Furthermore, we fabricate microfluidic valves with extreme sensitivity to rectify the flow generated by the ventricular chamber. The integrated microfluidic system recapitulates the ventricular fluidic function and exhibits a complete pressure-volume loop with isovolumetric phases. Together, our results demonstrate a previously unexplored application of high-precision fabrication that can be generalized to expand the accessible spectrum of organ-on-a-chip models toward structurally and biomechanically sophisticated tissue systems.

Three-dimensional (3D) macroporous graphene foam based multifunctional epoxy composites are developed in this study. Facile dip-coating and mold-casting techniques are employed to engineer microstructures with tailorable thermal, mechanical, and electrical properties. These processing techniques allow capillarity-induced equilibrium filling of graphene foam branches, creating epoxy/graphene interfaces with minimal separation. Addition of 2 wt % graphene foam enhances the glass transition temperature of epoxy from 106 to 162 °C, improving the thermal stability of the polymer composite. Graphene foam aids in load-bearing, increasing the ultimate tensile strength by 12% by merely 0.13 wt % graphene foam in an epoxy matrix. Digital image correlation (DIC) analysis revealed that the graphene foam cells restrict and confine the deformation of the polymer matrix, thereby enhancing the load-bearing capability of the composite. Addition of 0.6 wt % graphene foam also enhances the flexural strength of the pure epoxy by 10%. A 3D network of graphene branches is found to suppress and deflect the cracks, arresting mechanical failure. Dynamic mechanical analysis (DMA) of the composites demonstrated their vibration damping capability, as the loss tangent (tan δ) jumps from 0.1 for the pure epoxy to 0.24 for ∼2 wt % graphene foam-epoxy composite. Graphene foam branches also provide seamless pathways for electron transfer, which induces electrical conductivity exceeding 450 S/m in an otherwise insulator epoxy matrix. The epoxy-graphene foam composite exhibits a gauge factor as high as 4.1, which is twice the typical gauge factor for the most common metals. Simultaneous improvement in thermal, mechanical, and electrical properties of epoxy due to 3D graphene foam makes epoxy-graphene foam composite a promising lightweight and multifunctional material for aiding load-bearing, electrical transport, and motion sensing in aerospace, automotive, robotics, and smart device structures.