Modeling the impact of microcracking on the thermoelasticity of porous and microcracked ceramics

The foundations of the Integrity Factor Model are laid down and the model is discussed. The calculation of the internal stresses in microcracked materials (as a function of temperature) is done on the basis of both the macroscopic dilation and the lattice expansion measured by diffraction. The derivation is made starting from first principles for a single crystal, and then extending the approach to polycrystals, including complex microstructures, such as those containing porosity, microcracks, and multiple phases. Focus is cast on the fundamentals of the relationship between material properties and microstructure of anisotropic crystals, and on the resulting macroscopic behavior. The model is validated against experimental data, with the examples of the microcracked β-eucryptite and porous microcracked aluminum titanate composite.     

Rheology of particulate rafts,films, and foams

Liquid foam exhibits remarkable rheological behavior although it is made with simple fluids: it behaves similar to a solid at low shear stress but flows similar to a liquid above a critical shear stress. Such properties, which have been proved to be useful for many applications, are even enhanced by adding solid particles. Depending on their hydrophobicity and size, the particles can have different geometrical configurations at the mesoscopic scale, that is, at the air–liquid interfaces, in the films, or in the interstices between the bubbles. In this review, we present rheological studies performed on granular rafts and films, on spherical armored interfaces, on gas marbles, and on aqueous foams laden with hydrophilic grains.     

Extracting uncrosslinked material from low modulus sylgard 184 and the effect on mechanical properties

Commercial silicone elastomers are commonly used in soft materials research due to their easily tunable mechanical properties. However, conventional polydimethylsiloxane (PDMS) elastomers with moduli below ∼100 kPa contain uncrosslinked free molecules, which play a significant role in their behavior. To utilize these materials, it is important to quantify what role these free molecules play in the mechanical response before and after their removal. We present a simple and inexpensive extraction method that enables the removal of free molecules from a lightly crosslinked sheet of Sylgard 184, a commercially available PDMS elastomer. The materials can contain a majority of free molecules yet maintain a thin and flat geometry without fractures after extraction. Subsequently, we compare the modulus, maximum stretchability, and hysteresis behavior with mixing ratios ranging from 60:1 to 30:1, before and after extraction. We show that the modulus, maximum stretchability, and dissipation increase upon extraction. Moreover, our approach offers a route to prepare crosslinked silicone elastomers with a modulus as low as ∼20 kPa without free molecules from a commercially available kit. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 343–351     

Quantitative mapping of elastic moduli at the nanoscale in phase separated polyurethanes by AFM

The micro phase separated nanoscale morphology of phase separated polyurethanes (PUs) was visualized by atomic force microscopy (AFM) height and phase imaging of smooth surfaces obtained by ultramicrotonomy. PUs were obtained from 4,4′-methylenbis (phenyl isocyanate) (MDI), 1,4-butanediol (BD) and poly(tetrahydrofurane) polyether polyol (PTHF). The segmented polyether PUs with varying stoichiometric ratio of the isocyanate and hydroxyl groups were prepared to investigate the effect of molar mass, as well as the type and number of end-groups on their morphology and mechanical performance.The PU samples studied show characteristic “fingerprint” AFM phase images. Novel dynamic imaging modes of AFM, including HarmoniX material mapping and Peak Force Tapping were used to assess the mechanical performance of phase separated polyurethanes quantitatively as a function of their molecular structure. The values of surface elastic moduli were determined with nanoscale resolution and were in excellent agreement for both AFM modes. While tensile testing provides a bulk average value for the elastic modulus of the elastomers, the novel AFM based elastic moduli mappings introduced enable the study of surface stiffness with nanoscale resolution in a quantitative way.     

The Measurement of Glass Elastic Modulus by Using of Newton＇s Ring Experiment

弹性模量是衡量物体抵抗形变能力的重要物理量,本文在对牛顿环这一大学物理经典实验研究的基础之上,对牛顿环仪进行了改装,从理论上分析光学平板玻璃与平凸透镜接触端暗斑大小与外力的关系。测定弹性模量,同时利用MTALAB进行数据处理。     

Influence of alloying elements on the mechanical and thermodynamic properties of ZrB12 ceramics from first-principles calculations

Although ZrB₁₂ is a promising advanced material because of the boron cuboctahedron cages, the hardness of ZrB₁₂ remains controversy. Here, we apply first-principles calculations to study the influence of transition metals (4d- and 5d-) on the hardness and thermodynamic properties of ZrB₁₂. The calculated hardness of ZrB₁₂ is 32.9 GPa, which is in good agreement with the previous theoretical result. Importantly, the calculated hardness of Re-doped ZrB₁₂ is up to 40.0 GPa, which is a potential superhard material. The essential reason is that the alloying element of Re enhances the localized hybridization of B B and Zr B atoms, and then forms the strong B B covalent bond and Zr B bond. The result is well demonstrated by the chemical bonding and lattice parameter. Here, our work shows that the alloying elements of Nb, Mo, and Re enhance the thermodynamic properties of ZrB₁₂. The Debye temperature of Re-doped ZrB₁₂ is 1225.2 K, which is larger than that of the parent ZrB₁₂ (1213.5 K).     

Measurement of the Low-Frequency Shear Modulus of Polymeric Liquids

Abstract

The present work describes the resonance method for measurement of a low-frequency (about 10⁵ Hz) complex shear modulus of liquids by the use of a piezoquartz crystal. The problem of interaction of an oscillating system of the type piezoquartz-liquid interlayer-cover plate is analyzed. From the analysis of the problem there follow three methods for measuring the elasticity modulus of liquids. The investigation results of a homologous series of polymethyl siloxane liquids are presented. It has been shown that as the molecular weight of the series being investigated increases, the elasticity modulus value also increases, while the mechanical losses angle tangent passes through its maximum.     

Trigonometric approximation in reflexive Orlicz spaces

The Lipschitz classes Lip(α, M) , 0 α≤ 1 are defined for Orlicz space generated by the Young function M, and the degree of approximation by matrix transforms of f ∈ Lip (α, M) is estimated by n-α .     

蜂窝板复合材料的等价弹性模量

运用复合法则计算蜂窝板复合材料的等价弹性模量, 并把此值与有限元法的分析数值计算结果进行比较, 指出在运用复合法则计算等价弹性模量时, 由于未考虑到蜂窝芯板与面板间的位移连续性条件, 其误差将很大; 提出了满足蜂窝芯板与面板间的位移连续性条件下的等价弹性模量理论分析的新的计算方法, 并且通过与有限元法的数值分析结果进行比较, 确认其有效性.