Human brain wrinkling has been implicated in neurodevelopmental disorders and yet its origins remain unknown. Polymer gel models suggest that wrinkling emerges spontaneously due to compression forces ...arising during differential swelling, but these ideas have not been tested in a living system. Here, we report the appearance of surface wrinkles during the
development and self-organization of human brain organoids in a micro-fabricated compartment that supports
imaging over a timescale of weeks. We observe the emergence of convolutions at a critical cell density and maximal nuclear strain, which are indicative of a mechanical instability. We identify two opposing forces contributing to differential growth: cytoskeletal contraction at the organoid core and cell-cycle-dependent nuclear expansion at the organoid perimeter. The wrinkling wavelength exhibits linear scaling with tissue thickness, consistent with balanced bending and stretching energies. Lissencephalic (smooth brain) organoids display reduced convolutions, modified scaling and a reduced elastic modulus. Although the mechanism here does not include the neuronal migration seen in
, it models the physics of the folding brain remarkably well. Our on-chip approach offers a means for studying the emergent properties of organoid development, with implications for the embryonic human brain.
•Assessment of mechanical and durability properties of rubber ash/fiber concrete.•Addition of rubber fibers in concrete mix increases flexural strength.•Reduction in elastic modulus indicates higher ...flexibility of rubber concrete.•Concrete containing rubber fibers is better in term of abrasion resistance.•Micro-structural study shows weak interfacial bonding.
Now a day’s natural sand is becoming scarcer and costlier due to its non-availability. Waste rubber tire as fine aggregates can be an economical and sustainable alternative to river sand. In this study attempt has been made to utilize waste rubber tire as partial replacement of fine aggregate in the form of rubber ash and rubber ash with rubber fibers (combined form) with three w/c ratios. Workability, compressive strength, flexural strength, density, water absorption, abrasion resistance, carbonation depth, static modulus of elasticity, dynamic modulus of elasticity and chloride ion penetration of rubber ash concrete and modified concrete (10% rubber ash and varied percentage of rubber fibers) have been obtained. Micro-structural study using XRD, EDAX and SEM has also been carried out in this work. It has been shown that flexural strength of rubber ash concrete decreases with the increase of percentage of rubber ash whereas flexural strength of modified concrete is increased with the increase of the percentage of rubber fibers content. The abrasion resistance, carbonation depth, modulus of elasticity and chloride ion penetration of rubber ash concrete and modified concrete were also affected by addition of rubber ash and rubber fibers in concrete.
Out-of-plane deformation patterns, such as buckling, wrinkling, scrolling, and folding, formed by multilayer van der Waals materials have recently seen a surge of interest. One crucial parameter ...governing these deformations is bending rigidity, on which significant controversy still exists despite extensive research for more than a decade. Here, we report direct measurements of bending rigidity of multilayer graphene, molybdenum disulfide (MoS2), and hexagonal boron nitride (hBN) based on pressurized bubbles. By controlling the sample thickness and bubbling deflection, we observe platelike responses of the multilayers and extract both their Young's modulus and bending rigidity following a nonlinear plate theory. The measured Young's moduli show good agreement with those reported in the literature (Egraphene>EhBN>EMoS2), but the bending rigidity follows an opposite trend, Dgraphene<DhBN<DMoS2 for multilayers with comparable thickness, in contrast to the classical plate theory, which is attributed to the interlayer shear effect in the van der Waals materials.
•The successful fabrication of FG-GPLRC is reported.•Micromechanics models to predict effective mechanical properties of GPLRC are reviewed.•A comprehensive review on the mechanical analyses of ...FG-GPLRC structures is presented.•Key technical challenges are identified and future research directions are discussed.
Owing to their superior mechanical properties, e.g. exceptionally high Young’s modulus, high strength, large specific surface area, and good thermal conductivity, graphene and its derivatives such as graphene platelets (GPLs) are excellent reinforcing nanofillers for composite materials. The most recently developed functionally graded graphene platelets reinforced composite (FG-GPLRC) where GPLs are non-uniformly dispersed with more GPLs in the area where they are most needed to achieve significantly improved mechanical performance has opened up a new avenue for the development of next generation structural forms with an excellent combination of high stiffness, light weight and multi-functionality. Research activities in this emerging area have been rapidly increasing since it was first proposed in 2017. The present paper (i) briefly reviews the mechanical properties of graphene and graphene composites; (ii) summarizes the characteristics of functionally graded materials (FGM) and reports the fabrication of FG-GPLRC; (iii) discusses the existing micromechanics models for the prediction of effective mechanical properties of GPLRC; (iv) presents a comprehensive review on the mechanical analyses of FG-GPLRC structures; and (v) discuss the key technical challenges and future research directions.
The dynamic modulus of elasticity (
), specified by ultrasonic pulse velocity measurements, is often used, especially for concrete built into construction, to estimate the static modulus of ...elasticity (
). However, the most commonly used Equations for such estimations do not take into account the influence of concrete moisture. The aim of this paper was to establish this influence for two series of structural lightweight aggregate concrete (LWAC) varying in their strength (40.2 and 54.3 MPa) and density (1690 and 1780 kg/m
). The effect of LWAC moisture content turned out to be much more pronounced in the case of dynamic modulus measurements than for static ones. The achieved results indicate that the moisture content of the concrete should be taken into consideration in modulus measurements as well as in Equations estimating
on the basis of
specified by the ultrasonic pulse velocity method. The static modulus of LWACs was lower on average by 11 and 24% in relation to dynamic modulus, respectively when measured in air-dried and water-saturated conditions. The influence of LWAC moisture content on the relationship between specified static and dynamic moduli was not affected by the type of tested lightweight concrete.
A passive solid cannot do work on its surroundings through any quasistatic cycle of deformations. This property places strong constraints on the allowed elastic moduli. In this Article, we show that ...static elastic moduli altogether absent in passive elasticity can arise from active, non-conservative microscopic interactions. These active moduli enter the antisymmetric (or odd) part of the static elastic modulus tensor and quantify the amount of work extracted along quasistatic strain cycles. In two-dimensional isotropic media, two chiral odd-elastic moduli emerge in addition to the bulk and shear moduli. We discuss microscopic realizations that include networks of Hookean springs augmented with active transverse forces and non-reciprocal active hinges. Using coarse-grained microscopic models, numerical simulations and continuum equations, we uncover phenomena ranging from auxetic behaviour induced by odd moduli to elastic wave propagation in overdamped media enabled by self-sustained active strain cycles. Our work sheds light on the non-Hermitian mechanics of two- and three-dimensional active solids that conserve linear momentum but exhibit a non-reciprocal linear response.Active, non-conservative interactions can give rise to elastic moduli that are forbidden in equilibrium and enter the antisymmetric part of the stiffness tensor. The resulting solids function as distributed elastic engines that can perform work on their surroundings through quasistatic strain cycles.
Intrinsically stretchable conductors have undergone rapid development in the past few years and a variety of strategies have been established to improve their electro-mechanical properties. However, ...ranging from electronically to ionically conductive materials, they are usually vulnerable either to large deformation or at high/low temperatures, mainly due to the fact that conductive domains are generally incompatible with neighboring elastic networks. This is a problem that is usually overlooked and remains challenging to address. Here, we introduce synergistic effect between conductive zwitterionic nanochannels and dynamic hydrogen-bonding networks to break the limitations. The conductor is highly transparent (>90% transmittance), ultra-stretchable (>10,000% strain), high-modulus (>2 MPa Young's modulus), self-healing, and capable of maintaining stable conductivity during large deformation and at different temperatures. Transparent integrated systems are further demonstrated via 3D printing of its precursor and could achieve diverse sensory capabilities towards strain, temperature, humidity, etc., and even recognition of different liquids.
Freezing and thawing resistance is a key characteristic for concrete materials in cold weather conditions. In this study, the tensile properties and elastic modulus of ultra-high performance concrete ...(UHPC) under accelerated freeze-thaw cycles are characterized. Six series of UHPC specimens are experimentally tested with a well-designed direct tension test (DTT) method to capture complete tensile stress-strain responses. Both the dynamic and wave moduli of elasticity of UHPC are measured at specific cycles using the standard impact test and self-designed “smart aggregate” technology, respectively. Long term freezing and thawing cyclic conditioning of UHPC samples results in reductions of elastic modulus, tensile strength, strain capacity, and energy absorption capacity. The tensile stress-strain curves of UHPC demonstrate distinct descending with increasing freeze-thaw cycles, particularly in the strain softening region. The energy-based approach is found to be more sensitive and effective than the elastic modulus-based approach when evaluating material deterioration over time and capturing accumulative material degradation subjected to rapidly-repeated freezing and thawing actions. As from the test results, UHPC is characterized as a very durable cementitious material, but it is not inherently unconquerable. Extended freezing and thawing actions can still lead to deterioration of the material, with respect to its elastic modulus, tensile strength, energy absorption capacity, etc. As demonstrated, the DTT method can be used to effectively characterize the long-term performance of UHPC in tension under cold weather conditions.
Concretes with the same strength can have various deformability that influences span structures deflection. In addition, a significant factor is the non-linear deformation of concrete dependence on ...the load. The main deformability parameter of concrete is the instantaneous modulus of elasticity. This research aims to evaluate the relation of concrete compressive and tensile elastic properties testing. The beam samples at 80 × 140 × 1400 cm with one rod Ø8 composite or Ø10 steel reinforcement were experimentally tested. It was shown that instantaneous elastic deformations under compression are much lower than tensile. Prolonged elastic deformations under compression are close to tensile. It results in compressive elasticity modulus exceeding the tensile. The relation between these moduli is proposed. The relation provides operative elasticity modulus testing by the bending tensile method. The elasticity modulus's evaluation for the reinforced span structures could be based only on the bending testing results. A 10% elasticity modulus increase, which seems not significant, increases at 30-40% the stress of the reinforced span structures under load and 30% increases the cracking point stress.
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