Elastic Mechanical Properties Research Articles

Composite Superelastic Aerogel Scaffolds Containing Flexible SiO2 Nanofibers Promote Bone Regeneration.

Repairing irregular-shaped bone defects poses enormous challenges. Scaffolds that can fully fit the defect site and simultaneously induce osteogenesis and angiogenesis hold great promise for bone defect healing. This study aimed to produce superelastic organic/inorganic composite aerogel scaffolds by blending silica nanofibers (SiO2 ) and poly (lactic acid)/gelatin (PLA/gel) nanofibers; the content of SiO2 nanofibers is varied from 0-60 wt% (e.g., PLA/gel, PLA/gel/SiO2 -L, PLA/gel/SiO2 -M, and PLA/gel/SiO2 -H for 0%, 20%, 40%, and 60% of SiO2 nanofibers, respectively) to produce a range of scaffolds. The PLA/gel/SiO2 -M scaffold has excellent elasticity and good mechanical properties. In vitro experiments demonstrate that the silicon ions released from PLA/gel/SiO2 -M scaffolds promote the differentiation of rat bone marrow-derived mesenchymal stem cells into osteoblasts, enhancing alkaline phosphatase activity and bone-related genes expressions. The released silicon ions also promote the proliferation of human umbilical vein endothelial cells and the expression of vascular endothelial growth factors, thereby promoting angiogenesis. The assessment of these scaffolds in a calvarial defect model in rats shows good potential of PLA/gel/SiO2 -M to induce bone regeneration as well as promote osteogenesis and angiogenesis. Overall, these organic/inorganic composite scaffolds have good biological activity, which may have broad applications for tissue engineering.

Silk Fiber Multiwalled Carbon Nanotube-Based Micro-/Nanofiber Composite as a Conductive Fiber and a Force Sensor.

Silk cocoon fibers (SFs) are natural polymers that are made up of fibroin protein. These natural fibers have higher mechanical stability and good elasticity properties. In this work, we coated multiwalled carbon nanotubes (MWCNTs) on the surface of SFs using a simple stirring technique with vinegar as the medium. This SF-MWCNT micro-/nanofiber composite was prepared without any adhesives. The characterization results revealed that the SF-MWCNT micro-/nanofiber composite exhibited excellent electrical conductivity (995 Ω cm–1), tensile strength (up to 200% greater elongation), and durability characteristics. In addition, this micro-/nanofiber composite shows a change in resistance from 1450 to 960 Ω cm–1 for an applied mechanical force of 0.3–1 N kg–1. Based on our findings, SF-MWCNT micro-/nanofiber composite-based conductive fibers (CFs) and force sensors (FSs) were developed.

First-Principles Study on the Elastic Mechanical Properties and Anisotropies of Gold–Copper Intermetallic Compounds

In this study, first-principles calculations were utilized to investigate the lattice constants, elastic constants, and mechanical properties of gold–copper (Au–Cu) intermetallic compounds (IMCs), including AuCu3, AuCu, and Au3Cu. We also verified the direction dependence of the Young’s modulus, shear modulus, and Poisson’s ratio of the compounds. The calculated lattice parameters agreed with the experimental data, and the single-crystal elastic constants, elastic modulus E, shear modulus G, bulk modulus B, and Poisson’s ratio ν were calculated. For the Young’s and shear moduli, AuCu3 showed the highest anisotropy, followed by AuCu and Au3Cu. The Poisson’s ratios of AuCu3 and Au3Cu crystals were isotropic on (100) and (111) crystal planes and anisotropic on the (110) crystal plane. However, the Poisson’s ratio of the AuCu crystal was anisotropic on (100) and (111) crystal planes and isotropic on the (110) crystal plane.

First-principle study on the effects of hydrogen in combination with alloy solutes on local mechanical properties of steels

The first-principle calculation method has been utilized to study the effects of hydrogen in combination with alloy elements on the mechanical properties of iron-based super-cells, with the aim to bring new insight in the design of hydrogen-resistant steels. It is found that hydrogen prefers the second and third tetrahedral interstitial sites of the alloy solutes. Nb/Zr/Mo/W/Al alloyed super-cells dropped the most in the bulk modulus by hydrogen addition. Ni/Nb/Cu/Co/Zr dropped the most in the shear modulus/Young's modulus/hardness. The underlying influencing mechanisms on the elastic mechanical properties are discussed in perspective of atomic parameters/density of states/charge density/difference charge density/Bader charge analysis.

Ab-initio study for the elastic stability, mechanical, electronic and optical properties of RuCrX (X = Si, Ge, Sn) half Heusler alloys

This paper contains the comparative study of elastic, mechanical, electronic and optical response of RuCrX (X=Si, Ge, Sn). Three independent second order elastic constants are computed and elasto-mechanical stability is checked. Mechanical parameters depicts the flexible and ductile nature. These materials are hard and stiffer, difficult to compress and have an excellent bond stretching minimization phenomenon. The higher melting temperatures make them candidate for the high temperature environment like aerospace and construction industries. The band gap and density of states study reveal the non-magnetic metallic nature of all these alloys. In addition, the Fermi surfaces are also calculated. The imaginary part of dielectric response function confirms the utility in opto-electronic devices and sensors.

Fractional description for the rate‐dependent viscoelastic response of tough hydrogels

AbstractMetal‐coordination mediated tough hydrogels have been considered as a promising materials for novel utilization in programmable actuation structures. However, the rate‐dependent mechanical behavior attributed to their intrinsic mechanical properties of mixed elasticity and viscosity, imposing a challenge for the realization of controllable deformations. In this work, the effect of stretch rate was incorporated into a variable fractional order model in order to describe and predict the rate‐dependent mechanical response of physically tough hydrogels. Firstly, we provide an iteration algorithm for model estimation and conduct simulations of the stress response under monotonic stretch to verify the applicability of proposed model. The performance of proposed model is compared with the existing model to validate its accuracy. Then, the present model is employed to describe the rate‐dependent stress response under cyclic loading. The change rule of related parameters with stretch rate is also unraveled by the present model, which is further utilized to test the model's predictive ability. Moreover, the physical meaning of variable order is qualitatively explored in conjunction with the evolution mechanism of dynamic bonds.

First-principles calculations on mechanical properties of Rh2MnZn Heusler alloy

Heusler alloys are a huge family of binary, ternary and quaternary compounds and contain a wide range of unique properties, which made Heusler compounds to be the efficient materials for diverse applications. When it comes to the commercial applications mechanical properties are worth of check on and turn out to be the significant factor in the processing and final use of the materials. These properties make the study proficient by examine the nature of material under external pressure. In this study, we estimated mechanical properties of Rh2MnZn full-Heusler alloy using the full-potential linearized augmented plane wave method (FP-LAPW) method within the density functional theory (DFT). We have obtained C11, C12 and C44 elastic constants due to cubic symmetry using Charpin method implemented in Wien2k code. Further, using these elastic constants mechanical properties such as bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, anisotropic factor and Cauchy’s pressure are calculated. These moduli depicted hardness, ductility and elastic anisotropy of the alloy.

Elastic properties of an additive manufactured three-dimensional vertex-based hierarchical re-entrant structure

This work proposes a new auxetic lattice based on replacing the vertexes of traditional three-dimensional re-entrant structural with self-similar configurations. Derived by Castigliano's second theorem, a theoretical model is built to predict its elastic mechanical properties, including the homogenized Young’s modulus and Poisson’s ratio in all three principal directions. The overlapped nodes of struts are considered in the theoretical model due to their excessive strut thickness. The analytical results exhibit good agreement with the numerical and experimental results. The effects of the geometric parameters, internal force species, and hierarchical magnitude on the elastic property are carefully studied. The findings suggest that the axial internal force in the new structure inhibits its auxetic effects in the three principal directions. Compared with the traditional three-dimensional re-entrant lattice with equal relative density, the vertex-based hierarchical one exhibits more comprehensive designability of auxetic effect and enables higher Young’s modulus with specific geometrical parameters. The findings in this study contribute to the metamaterial advancement and provide an option for engineering applications requiring programmable and controllable elastic properties.

Statistical elastic and fracture mechanical properties of quasi-brittle and ductile amorphous polymers

Statistical elastic and fracture mechanical properties of quasi-brittle and ductile amorphous polymers

Study on failure mechanism and sealing performance optimization of compression packer

In order to accurately describe the mechanical behavior of rubber materials, and the uniaxial tensile and uniaxial compression experiments of three common rubber materials of packer are carried out combined with the function requirements of the rubber cylinder of packer. In addition, the sealing performance of the compression packer is studied in the setting stage by using the finite element software based on the investigation and analysis of the hyper elastic mechanical properties and constitutive models of rubber materials in this paper. It is found that contact deformation of the rubber cylinder begins to accelerate as the time increases through the analysis. When the packer completes sealing process, the upper rubber cylinder mainly plays a sealing role, and excessive stress will cause the shoulder of the upper rubber cylinder to be compressed and fatigue failure. The contact sealing performance of expanded rubber cylinder under different radius clearance and different pressure difference is studied. Under the given wall thickness and radius clearance, the limit pressure load is applied, the rubber cylinder is in a safe working state, and the sealing width is close to the contact length of the rubber cylinder, which ensures good sealing performance. Moreover, the rubber cylinder is in a good elastic deformation range without serious backlog.

A mechanical model of three-dimensional electrospun fiber scaffolds

Fiber scaffolds prepared by electrospinning method can be used for the repairing of soft tissues such as skin, and have been widely used in biomedical field. The mechanical properties of scaffolds needed to be considered in the process of preparing scaffolds. Based on the principle of statistics and the method of micromechanics, a mechanical model for calculating the elastic characteristics of fiber scaffolds with spatial random distribution characteristics was established. The model comprehensively considered the parameters such as mechanical properties of constituent units of fiber scaffolds, fiber diameter and fiber density. The quantitative relationship between the elastic mechanical properties of fiber scaffolds and their tissue unit parameters can be calculated, which provided a research basis for further research and improvement of the mechanical properties of three-dimensional fiber scaffolds.

Cylindrical compressible liquid inclusion with surface effects

Liquid-filled microchannels are common in biological tissues, such as blood capillaries and neuronal axons, which may often be regarded as cylindrical compressible liquid inclusions embedded in an infinite elastic matrix. How surface effects influence the elastic field and effective mechanical properties of such liquid inclusions remain elusive, especially when the inclusion size is at micro level wherein surface tension plays a significant role. We present first a theoretical model to analyze the elastic field of a cylindrical compressible liquid inclusion, with surface effects duly accounted for. We then use the solutions of our model, together with the Eshelby approach, to estimate the effective mechanical properties of a composite containing sparsely distributed cylindrical liquid inclusions. Different from previous studies, our model accounts for the nonlinear dependence of the normal vector and curvature of a liquid-solid surface upon surface deformation, achieved by expressing both as first order functions of surface displacement. We then linearize the deformation-induced surface curvature to simplify the problem and get the solution using linearized curvature. Predictions of our model demonstrate that surface effects prevent deformation of the liquid inclusion and increase stress concentration around the inclusion. Further, as the surface energy is increased, the effective Young's modulus of the two-phase composite first increases and then decreases, and the transition point is related to the bulk modulus of liquid; when the surface energy becomes sufficiently large, the effective Poisson ratio becomes negative. These results are useful for understanding and exploring the mechanical behaviors of a wide range of liquid-filled porous biological materials which contain distributed cylindrical pores, e.g., blood vessels, neuronal axons, dentinal tubules and hydrogel pores .

To Compare the Stress Magnitude on Roots of Mandibular Incisors at Different Inclinations With Different Arch Wires During Intrusion Mechanics—A Fem Study

Introduction: Force is applied through brackets in fixed mechanotherapy which generates stress in periodontal ligament and root of the teeth and is difficult to measure directly. Finite element analysis is used as a solution for understanding this biomechanical response. So the aims and objectives of this study were to evaluate the stress magnitude induced in the labial and lingual surface of mandibular incisors using superelastic NiTi arch wires of different cross-section at different inclination through finite element analysis. Materials and Methods: Finite element model of all mandibular teeth including periodontal ligament, alveolar bone, buccal tubes, brackets, and arch wire were constructed using mechanical elastic properties of the materials. Three different NiTi arch wires, round (0.016″), square (0.016″ × 0.016″), and rectangular (0.016″ × 0.022″), were placed into the bracket slots and models were constructed which were analyzed for stress distribution on root surface and periodontal ligament with 3 different cross-sections at 90°, 100°, and 110° with Ansys Version 14 software. Conclusion: Labial stress was found highest in round arch wire as compared to square and rectangular wire. Lingual stress was found to be slightly more in rectangular wire as compared to round and square arch wire.

The effects of age and sex on the elastic mechanical properties of human abdominal fascia

BackgroundThe abdominal hernias become more prevalent with age, that can adversely affect life quality. The mechanical properties of abdominal wall layers are supposed to play a significant role in developing of an abdominal hernia.The objective of this study was to determine the mechanical properties of the human abdominal layer – fascia and the effects of age and sex on it for choosing the proper brand of hernia mesh. Methods78 samples harvested from 19 fresh cadavers were subjected to uniaxial tension tests and divided into four groups according to age. Group A corresponds to age up to 60 years, Group B to age 61–70 years, Group C to age 71–80 years and Group D to 81–90 years. Median stress–stretch ratio curves with respect to age, sex and direction of loading were obtained. Median values of the maximum tensile stress, stretch at maximum stress and elastic modulus calculated at 5% strain were determined. FindingsThe abdominal fascia showed large variations between specimens depending on age and sex. The stiffness of the fascia increased with age. There is statistically significant differences between the median curves of male samples (P = 0.008) and female samples (P = 0.019) according to age in the L direction. Statistically significant differences between the values of maximum stress (P = 0.01) and elastic modulus (P = 0.003) from Group C in the L direction and maximum stress (P = 0.03) from Group D in the T direction was established. InterpretationThe female samples are stiffer than male samples especially after 80 years.

Drying shrinkage properties of expanded polystyrene (EPS) lightweight aggregate concrete: A review

Expanded polystyrene (EPS) is currently being utilized in sustainable materials owing to its ultra-low density and superior thermal performance. It can be incorporated in concrete mixtures to replace coarse aggregate to produce lightweight aggregate concrete (LWAC). Concerning the high shrinkage development in LWAC, the present study reviews the available published articles regarding the drying shrinkage of lightweight concretes containing expanded polystyrene. According to the previous studies, the drying shrinkage development in expanded polystyrene concrete (EPSC) has been reported to be greater than that in conventional concrete, which must be considered for its application in the construction industry. It is mainly attributed to the low elastic modulus and mechanical properties of the EPS. However, incorporating additives and fibers can improve its shrinkage resistance properties. A comprehensive comparison of drying shrinkage magnitude between various LWAC showed that the drying shrinkage strain of EPSC is not generally higher than other types of LWAC; however, the density of EPSC was measured lower than that in other types of lightweight aggregate concretes.

Electrospun multifunctional nanofibrous mats loaded with bioactive anemoside B4 for accelerated wound healing in diabetic mice

With the worldwide prevalence of diabetes and considering the complicated microenvironment of diabetic wounds, the design and development of innovative multifunctional wound dressing materials are much wanted for the treatment of hard-to-heal wounds in diabetic patients. In the present study, anti-inflammatory ingredients loaded with nanofibrous wound dressing materials were manufactured by a promising blend-electrospinning strategy, and their capability for treating the diabetic wound was also systematically explored. A polymer blend consisting of Chitosan (CS) and polyvinyl alcohol (PVA) was electrospun into CS-PVA nanofibrous mats as control groups. In the meanwhile, a bioactive ingredient of Chinese medicine Pulsatilla, anemoside B4(ANE), with different contents were loaded into the electrospinning solution to construct CS-PVA-ANE nanofibrous mats. The developed CS-PVA-ANE wound dressing materials exhibited multifunctional properties including prominent water absorption, biomimetic elastic mechanical properties, and sustained ANE releasing behavior, as well as outstanding hemostatic properties. The in vitro studies showed that the CS-PVA-ANE nanofiber mats could significantly suppress lipopolysaccharide (LPS)-stimulated differentiation of pro-inflammatory (M1) macrophage subsets, and notably reduce the reactive oxygen species (ROS) generation, as well as obviously decrease inflammatory cytokine release. The in vivo animal studies showed that the CS-PVA-ANE nanofiber mats promoted the healing of diabetic wounds by significantly enhancing wound closure rates, accelerating excellent angiogenesis, promoting re-epithelization and collagen matrix deposition throughout all stages of wound healing. The present study demonstrated that CS-PVA-ANE nanofiber mats could effectively shorten the wound-healing time by inhibiting inflammatory activity, which makes them promising candidates for the treatment of hard-to-heal wounds caused by diabetes.

Elastic and plastic mechanical properties of nanoparticle-based silica aerogels and xerogels

This paper reports and analyzes, for the first time, the effective Young's modulus and hardness of nanoparticle-based silica aerogels and xerogels with porosity ranging from 46 to 81%. Pure silica aerogel and xerogel monoliths were synthesized by (i) gelation of aqueous suspensions of silica nanoparticles on omniphobic substrates (PTFE or perfluorocarbon liquids), (ii) aging, (iii) drying at ambient temperature and pressure, and (iv) calcination. The aging and calcination conditions were varied to elucidate their effect on the mechanical properties of the monoliths. Both the effective Young's modulus and the hardness of the mesoporous slabs were measured by nanoindentation and were found to obey a power law as a function of the effective density. No effect of the synthetic conditions or structural parameters other than porosity were observed. Interestingly, the effective hardness was linearly proportional to the effective Young's modulus. The elastic properties of the present nanoparticle-based materials were compared with those of the molecular precursor-based silica aerogels and xerogels reported in the literature. A single relationship was proposed that can be used to estimate the effective Young's modulus of nanoparticle-based and molecular precursor-based silica aerogels and xerogels with porosity between 0 and 98% and Young's modulus between ∼10−4 and 70 GPa. Deposition of an alumina coating was also demonstrated as a way to increase the hardness of these mesoporous monoliths by a factor 2–13 for porosity of 40–73%. The experimental results and the accompanying analysis broaden the understanding of structure-property relationships in mesoporous silica and will help in the design and fabrication of mesoporous silica components.

Characterization of earplugs based on porous polyurethane (PU) and polyvinyl-chloride (PVC) polymers for human ear protection

Personal ear protection (PEP) is a device designed to reduce the effects of ambient noise on humans, thus limiting the risk of hearing damage. This damage mainly affects the entire auditory chain (from the tympanic membrane to the cochlea). The aim of this work is to carry out a study of the mechanical properties of the PEP studied to model it subsequently using the finite elements method (FEM). To this end, the aim of this paper will be the study of the morphological and mechanical performance of porous polymers to protect the human ear from vibrations. The influence of air content (Porosity rate, pore size and shape) on the elastic matrix and mechanical properties of porous polymers (Young's modulus and Poisson's ratio) produced from available commercial Polyurethane (PU) and Polyvinyl-Chloride (PVC) were examined and discussed. The authors present a mathematical model that is able to predict the Young’s modulus of porous polymers as a function of matrix characteristics, mechanical excitation and porosity percentage. Porosimeter, Scanning Electron Microscope (SEM) and Light Microscope (LM) techniques are used for morphological characterizations. PU and PVC earplugs are effective for sound reduction, so they can be used for other applications.

Elastic and Plastic Mechanical Properties of Lithium Measured by Nanoindentation

Elastic and Plastic Mechanical Properties of Lithium Measured by Nanoindentation

Conditions of elastic mechanical stability and elastic properties of crystal structures with different symmetry

A critical analysis of the conditions of elastic stability of crystal structures of different symmetry as restrictions imposed on their elastic constants cij has been carried out. It is shown that the conditions of elastic stability of all crystals, except for cubic ones, are described by polynomials from the second to sixth powers of their elastic constants cij. Necessary and sufficient conditions for the elastic stability of crystals of different symmetry are presented explicitly. Keywords: Elastic stability, Symmetry, Elastic constants, Stability conditions.