Relationship between Thermal Diffusivity and Mechanical Properties of Wood

This paper describes an experimental study of the relationships between thermal diffusivity and mechanical characteristics including Brinell hardness, microhardness, and Young’s modulus of common pine (Pinus sylvestris L.), pedunculate oak (Quercus robur L.), and small-leaf lime (Tilia cordata Mill.) wood. A dependence of Brinell hardness and thermal diffusivity tensor components upon humidity for common pine wood is found. The results of the measurement of Brinell hardness, microhardness, Young’s modulus, and main components of thermal diffusivity tensor for three perpendicular cuts are found to be correlated. It is shown that the mechanical properties correlate better with the ratio of longitude to transversal thermal diffusivity coefficients than with the respective individual absolute values. The mechanical characteristics with the highest correlation with the abovementioned ratio are found to be the ratio of Young’s moduli in longitude and transversal directions. Our technique allows a comparative express assessment of wood mechanical properties by means of a contactless non-destructive measurement of its thermal properties using dynamic thermal imaging instead of laborious and material-consuming destructive mechanical tests.

Numerical Investigation into the Influence of Grain Orientation Distribution on the Local and Global Elastic-Plastic Behaviour of Polycrystalline Nickel-Based Superalloy INC-738 LC

Polycrystalline nickel-based superalloys tend to have large grains within component areas where high loads are dominant during operation. Due to these large grains, caused by the manufacturing and cooling process, the orientation of each grain becomes highly important, since it influences the elastic and plastic behaviour of the material. With the usage of the open source codes NEPER and FEPX, polycrystalline models of Inconel 738 LC were generated and their elastic and crystal plasticity behaviour simulated in dependence of different orientation distributions under uniaxial loading. Orientation distributions close to the [100] direction showed the lowest Young’s moduli as well as the highest elastic strains before yielding, as expected. Orientations close to the [5¯89] direction, showed the lowest elastic strains and therefore first plastic deformation under strain loading due to the highest shear stress in the slip systems caused by the interaction of Young’s modulus and the Schmid factor.

Bending stiffness of circular multilayer van der Waals material sheets

We study the bending stiffness of symmetrically bent circular multilayer van der Waals (vdW) material sheets, which corresponds to the non-isometric configuration in bulge tests. Frenkel sinusoidal function is employed to describe the periodic interlayer tractions due to the lattice structure nature and the bending stiffness of sheets is theoretically extracted via an energetic consideration. Our quantitative prediction shows good agreement with recent experimental results, where the bending stiffness of different types of sheets with the comparable thickness could follow a trend opposite to their Young's moduli. Based on our model, we propose that this trend may experience a transition as the thickness decreases. Apart from the apparent effects of Young's modulus and interlayer shear strength, the interlayer distance is also found to have an important impact on the bending stiffness. In addition, according to our analysis on the size effect, the bending stiffness of such symmetrically bent circular sheets can steadily own a relatively large value, in contrast to the cases of isometric deformations.

Engineering shape memory and morphing protein hydrogels based on protein unfolding and folding

Engineering shape memory/morphing materials have achieved considerable progress in polymer-based systems with broad potential applications. However, engineering protein-based shape memory/morphing materials remains challenging and under-explored. Here we report the design of a bilayer protein-based shape memory/morphing hydrogel based on protein folding-unfolding mechanism. We fabricate the protein-bilayer structure using two tandem modular elastomeric proteins (GB1)8 and (FL)8. Both protein layers display distinct denaturant-dependent swelling profiles and Young’s moduli. Due to such protein unfolding-folding induced changes in swelling, the bilayer hydrogels display highly tunable and reversible bidirectional bending deformation depending upon the denaturant concentration and layer geometry. Based on these programmable and reversible bending behaviors, we further utilize the protein-bilayer structure as hinge to realize one-dimensional to two-dimensional and two-dimensional to three-dimensional folding transformations of patterned hydrogels. The present work will offer new inspirations for the design and fabrication of novel shape morphing materials.

One-Pot Preparation of Hydrophilic Polylactide Porous Scaffolds by Using Safe Solvent and Choline Taurinate Ionic Liquid

Polylactides (PLAs) are a class of polymers that are very appealing in biomedical applications due to their degradability in nontoxic products, tunable structural, and mechanical properties. However, they have some drawbacks related to their high hydrophobicity, lack of functional groups able to graft bioactive molecules, and solubility in unsafe solvents. To circumvent these shortcomings, porous scaffolds for tissue engineering were prepared by vigorously mixing a solution of isotactic and atactic PLA in nontoxic ethyl acetate at 70 °C with a water solution of choline taurinate. The partial aminolysis of the polymer ester bonds by taurine -NH2 brought about the formation of PLA oligomers with surfactant activity that stabilized the water-in-oil emulsion. Upon drying, a negligible shrinking occurred, and mechanically stable porous scaffolds were obtained. By varying the polymer composition and choline taurinate concentration, it was possible to modulate the pore dimensions (30–50 µm) and mechanical properties (Young’s moduli: 1–6 MPa) of the samples. Furthermore, the grafted choline taurinate made the surface of the PLA films hydrophilic, as observed by contact angle measurements (advancing contact angle: 76°; receding contact angle: 40°–13°). The preparation method was very simple because it was based on a one-pot mild reaction that did not require an additional purification step, as all the employed chemicals were nontoxic.

Microporosity of the Shuaiba Formation: The Link Between Depositional Character and Diagenesis in Sharjah, United Arab Emirates

Objectives/Scope This study focuses on assessing the uncertainties related to sedimentological heterogeneity and the diagenetic variability within the gas-condensate reservoirs of the Shuaiba Formation, Sharjah, United Arab Emirates. Methods, Procedures, Process For characterizing the sedimentology of the Shuaiba Formation, a lithofacies scheme has been developed on the basis of Dunham's (1962) and Embry & Klovan classification (1971). The lithofacies are grouped on the basis of their genetic relationships which also correspond to their depositional environment, and are designated as lithofacies associations. A pore-scale fabric/textural investigation was completed using conventional thin-section microscopy and Scanning Electron Microscopy (SEM). Results, Observations, Conclusions The Shuaiba sediments are characterized by skeletal-rich wackestone/packstones to floatstones deposited in an inner ramp setting. The stacking pattern of the inner ramp deposits define broad third order trends observed across the studied field.These trends are relatable to the regional sequence stratigraphic framework of Sharland et al. (2001). In higher order sequences, lateral variations in lithology occur, defining the reservoir heterogeneity, which are most likely forced by topographic/hydrodynamic variation as well as sea level changes. Reservoir quality distribution is controlled by various factors, including the depositional texture and allochem assemblage (abundance, type, and size). Diagenetic alteration of the textures played an important role in determining overall reservoir quality. The pore enhancing phases are defined by dissolution events, where later stage dissolution was the dominant phase to enhance micropores and also to create meso- to macropores which partially to completely negated the effect of previous cementing phases. In these Shuaiba deposits, the porosity comprises common matrix-hosted as well as grain-hosted micropores along with variably distributed intraparticle and rare mouldic meso- to macropores. The measured porosity ranges from very poor to moderate (0.5-17%) while permeability is very low to low (<0.001-1.49 mD). The detailed petrographic analysis highlighted that changes in micritic fabric shows a variation in the reservoir properties. From SEM observations, it was noted that microcrystalline calcite crystals of polyhedral to sub-rounded morphologies with intercrystalline contacts ranging from facial to sub-punctic, which display relatively a good microporosity developement, whereas crystals that show anhedral compact character with coalescent/fused intercrystalline contacts are rarely associated with any microporosity. Novel/Additive Information In addition to SEM characterization, porosity data and elastic properties (e.g., Young's moduli) generated from the interpretation of the well-log data, were used to investigate the prospective relationship between the microporous carbonates and elastic properties. The comparisons highlight that an increase in porosity values results in a decrease of Young's moduli values, thereby reflecting a decrease in the stiffness of the rock. On the other hand, the increase in porosity maybe linked to the evolution of anhedral, compact, micritic fabric to polyhedral/sub-rounded micritic fabric. The understanding of this relationship provides a powerful tool to be utilized in reservoir architecture prediction based on integrating the sedimentological framework and diagenetic overprint.

A design method for metamaterials: 3D transversely isotropic lattice structures with tunable auxeticity

A method for designing 3D transversely isotropic auxetic lattice structures is proposed. Based on it, two new auxetic structures have been designed. Systematically, their effective elastic properties are investigated computationally and analytically in all loading directions. The effective Young's moduli and Poisson's ratios within the transverse plane and those along the longitudinal direction are widely tunable by tailoring the structural geometry. Both structures exhibit transverse and longitudinal auxeticities concurrently as well as separately. The proposed auxetic structures expand the existing auxetic material space in terms of elastic anisotropy.

Laser Self-Mixing Sensor for Simultaneous Measurement of Young’s Modulus and Internal Friction (Invited)

The Young’s modulus and internal friction are two important parameters of materials. Self-mixing interferometry (SMI) is an emerging non-destructive sensing method that has been employed for various applications because of its advantages of simple structure, ease of alignment and high resolution. Some recent works have proposed the use of SMI technology to measure the Young’s moduli and/or internal frictions by measuring the resonance frequencies and damping factors of specimen vibrations induced by impulse excitation. However, the measurement results may be affected by frequencies of SMI fringes, and the implementation requires extra signal processing on SMI fringes. In this work, we developed an all-fiber SMI system without SMI fringes to measure the Young’s modulus and internal friction simultaneously. Simulations and experiments were carried out to verify the feasibility of the proposed method. Two specimens of brass and aluminum were tested. The experimental results show that the standard deviations of Young’s moduli for brass and aluminum are 0.20 GPa and 0.14 GPa, and the standard deviations of internal frictions are 4.0×10−5 and 5.4×10−5, respectively. This method eliminates the influences of the SMI fringe frequency on the resonant frequency and requires no signal processing on SMI fringes, contributing to its simplicity as a method for the measurement of the Young’s modulus and internal friction.