Design and build an elastic crosslinked network to strengthen and toughen soybean-meal based bioadhesive using organo-sepiolite and greener crosslinker triglycidylamine

Poor water resistance and curing layer brittleness are significant challenges of greener soybean meal (SM) adhesive promotion and application. In this study an elastic network was built to crosslink the SM adhesive and improve the cured layer toughness of the resultant adhesive. Long-chain organo-sepiolite (OSEP) was first prepared by compound modification using KH-560 and KH-602 silane coupling agents. Triglycidylamine (TGA), a greener crosslinking agent with a large number of effective epoxy functional groups, was then synthesized. SM-based adhesives were fabricated using SM, OSEP and TGA. Results indicated that an elastic network was fabricated by the cross-linked reaction of SM, OSEP, and TGA. The elastic network effectively improved the toughness of the resultant adhesive. The wet shear strength of the plywood (PlyW) bonded by SM with 1% OSEP (SM/TGA/OSEP-1 adhesive) increased by 60% to 1.25 MPa relative to that of the SM/TGA adhesive. This study provided a greener, simple and cheap method improving the toughness and wet shear strength of SM-based adhesive, which contributes to the industrialized application of the product.     

A note on the spheroidal modes vibration of an elastic sphere in linear viscoelastic fluid

Vibration characteristics of elastic nanostructures embedded in fluid medium have been used for biological and mechanical sensing, and also to investigate materials mechanical properties. An analytical approach based on the exact theory has been developed in this paper, to establish a new accurate and simple generalized frequency equation to predict spheroidal vibration of an elastic nanosphere, in a compressible viscoelastic fluid using linear Maxwell fluid model. To demonstrate the accuracy of the present approach, a comparison is made with the published theoretical results in the literature in some particular cases, which shows a very good agreement. Thus, the obtained frequency equation can be very useful to interpret the experimental measurements of vibrational dynamics of nanospheres and can serve as benchmark solution in design of liquid sensors.     

Application of acoustic methods for a non-destructive evaluation of the elastic properties of several typologies of materials

In solid phase materials, differently from what happens in the fluid phase, elastic waves propagate both through longitudinal and transverse waves. From the speed of propagation of longitudinal and transverse waves, it is possible to evaluate important elastic properties of the solids under study, namely the Young’s modulus, the Poisson’s coefficient, the bulk modulus and the shear modulus. This work suggests an accurate method for measuring wave propagation speeds in homogeneous and non-homogeneous materials with the purpose to evaluate their mechanical properties and the associated uncertainty.First of all, to assess the performance of the proposed methodology, based on the “pulse-echo” technique, in terms of accuracy and precision, measurements of wave propagation speeds have been carried out, in atmospheric conditions, in well-known homogeneous and isotropic materials, such as copper, aluminum, stainless steel and also polymethyl methacrylate (Plexiglas®), Teflon® and optical glass BK7. These results were compared with the values reported in literature (if present), showing how published speed of sound data are very disperse and not so reliable owing to the lack of a precise uncertainty evaluation and of the temperature value associated to the measurement. Then, the same experimental apparatus was used for measuring speed of sound as a function of temperature (from 274.15 to 313.15 K) for 304 stainless steel and oxygen free copper, showing a good accuracy of the results also for temperature conditions far from ambient. Finally, the same procedure was applied to a non-homogeneous solid, obtaining some very preliminary results in typical mediterranean building material, as Carrara marble.     

Electronic structure and peculiar bonding properties of NdNiMg5 from first principles

The newly found ternary compound NdNiMg₅ has been studied within DFT based methodologies. Results of cohesive energy, charge transfers, elastic constants and electron localized function mapping as well as electronic structure and bonding properties have been compared with those of isostructural binary NdNi. The calculation results have shown that Mg substructures interlayering NdNi – like slabs exhibit different magnitudes of charge transfers all within range of metallic behavior and the different Mg substructures selectively bind with Nd and Ni substructures. As a consequence an enhanced cohesion with respect to binary intermetallic NdNi is identified. The whole set of elastic constants and their combinations in orthorhombic symmetry confirm the mechanical stability of NdNiMg₅ with larger compressibility and less ductility (more brittleness) with respect substructures to NdNi. While in an intermetallic compound such as NdNi the bonding is ensured mainly by Nd–Ni interaction, in NdNiMg₅ Nd–Ni, Nd–Mg, Ni–Mg as well as Mg–Mg participate to the bonding and the extra electrons brought by Mg are found within bonding states thus illustrating furthermore the enhanced cohesion of the ternary versus the binary systems.     

环烷酸对油水界面膜流变性质的影响研究

研究了环烷酸对油水界面膜界面张力、弹性模量、损耗模量以及界面膜破裂速率常数的影响,同时对环烷酸与沥青质之间的相互作用进行了测定。结果表明,环烷酸使得原油油水界面张力下降;弹性模量随着环烷酸加量以及振荡频率的增加都分别逐渐增大,并且最终都趋于平衡;在任何振荡频率值时,损耗模量都随着环烷酸加量先增大后减小;当环烷酸加量增加时,界面膜破裂速率常数降低。环烷酸与沥青质之间存在相互作用,随着环烷酸加量的增加,其对沥青质界面膜弹性模量的影响与对原油界面膜弹性模量的影响相似,表明环烷酸主要是通过与沥青质相互作用而促进乳状液稳定性的。     

Theoretical study of the structural,elastic, electronic and optical properties of XCaF3 (X = K and Rb)

The PLANE WAVE pseudo-potential method within density functional theory (DFT) has been used to investigate the structural, elastic, electronic and optical properties of XCaF₃ (X = K and Rb) insulating. The studied compounds show a weak resistance to shear deformation compared to the resistance to the unidirectional compression. KCaF₃ and RbCaF₃ are considered ductile. The elastic constants and related parameters were predicted. The stiffness is more important in KCaF₃, whereas, the lateral expansion is more important in RbCaF₃. KCaF₃ and RbCaF₃ have R- Г indirect band gap. The main peaks in the imaginary part of the dielectric function correspond to the transition from the occupied state F₋p to the unoccupied states Ca: s or K, Rb: p. At lower energies, KCaF₃ and RbCaF₃ show the same optical properties. Under pressure effect, the peaks of imaginary part of dielectric function were shifted toward high energy.     

Thermoelasticity of bodies with microstructure and microtemperatures

This paper is concerned with a linear theory of thermodynamics for elastic materials with microstructure, whose microelements possess microtemperatures. It is shown that there exists the coupling of microrotation vector field with the microtemperatures even for isotropic bodies. Uniqueness and continuous dependence results are presented. The theory is used to establish the solution corresponding to a concentrated heat source acting in an unbounded continuum.     

用三维弹性力学方法研究圆板的稳定问题

用三维弹性力学方法研究任意边界条件圆板的轴对称稳定问题，利用Ｈ变换和Ｓｔｏｃｋｅｓ变换，导出位移函数及其偏导数的一种新型双重极数式，并由数学弹性定理论的基本方程和边界条件建立的特征方程，求得最小临界载荷的精确解，文末以简支圆板为例进行数字计算，结果表明：在弹性失稳范围内，三维弹性力学方法求得的临界载荷略低于经典理论的结果，对于薄板的弹性稳定问题，经典板理论有足够的精度。     

Experimental analysis of the steady-state behaviour of beam systems with discontinuous support

This paper deals with the experimental analysis of the long-term behaviour of periodically excited linear beams supported by a one-sided spring or an elastic stop. Numerical analysis of the beams showed subharmonic, quasi-periodic and chaotic behaviour. Furthermore, in the beam system with the one-sided spring three different routes leading to chaos were found. Because of the relative simplicity of the beam systems and the variety of calculated nonlinear phenomena, experimental setups are made of the beam systems to verify the numerical results. The experimental results correspond very well with the numerical results as far as the subharmonic behaviour is concerned. Measured chaotic behaviour is proved to be chaotic by calculating Lyapunov exponents of experimental data.

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Sommario Il presente lavoro concerne l'analisi sperimentale del comportamento a regime di travi lineari, su supporti elastici nonlineari discontinui, eccitate periodicamente. L'analisi numerica dei sistemi in esame ha evidenziato risposte subarmoniche, quasi-periodiche e caotiche, nonchè l'esistenza, nel caso di trave con una molla laterale, di tre differenti percorsi verso il caos. La relativa semplicità dei sistemi di travi ha consentito di procedere ad una verifica sperimentale dei risultati numerici e della varietà dei fenomeni nonlineari da essi evidenziati. La corrispondenza fra risultati sperimentali e numerici è molto buona nel caso di risposta subarmonica. Il comportamento caotico sperimentale è stato convalidato attraverso il calcolo degli esponenti di Lyapunov a partire dai relativi dati.

     

A numerical approach to spherical indentation techniques for material property evaluation

In this work, some inaccuracies and limitations of prior indentation theories, which are based on experimental observations and the deformation theory of plasticity, are investigated. Effects of major material properties on the indentation load-deflection curve are examined via finite element (FE) analyses based on incremental plasticity theory. It is confirmed that subindenter deformation and stress-strain distribution from deformation plasticity theory are quite dissimilar to those obtained from incremental plasticity theory. We suggest an optimal data acquisition location, where the strain gradient is the least and the effect of friction is negligible. A new numerical approach to indentation techniques is then proposed by examining the FE solutions at the optimal point. Numerical regressions of obtained data exhibit that the strain-hardening exponent and yield strain are the two key parameters which govern the subindenter deformation characteristics. The new indentation theory successfully provides a stress-strain curve and material properties with an average error of less than 3%.