Elastic Modulus Poisson's Ratio Research Articles

Effect of hydrogen on the mechanical, electronic, and thermodynamic properties of YMgNi4 alloys from first-principles calculations

Using the Density Functional Theory, we investigated the mechanical, electronic, and thermodynamic properties of YMgNi4 alloys and its two hydrides. The results of formation enthalpy and impurity formation energy indicate that an increase in H doping content contributes to the thermodynamic stability of YMgNi4 alloy, and the phonon dispersion curves show that these models are consistent with dynamic stability. Additionally, the elastic modulus Poisson's ratio and AU were studied using the Voigt-Reuss-Hill approximation method. The band structures and density of states confirm their metallic nature. The free energy and heat capacity were also calculated to further investigate the thermodynamic properties.

Lithofacies Types and Physical Characteristics of Organic-Rich Shale in the Wufeng-Longmaxi Formation, Xichang Basin, China.

The shale of the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation in the Xichang Basin is the main replacement horizon for the shale gas exploration being conducted in the Sichuan Province, except for the Sichuan Basin. The fine identification and classification of the types of shale facies are important for shale gas exploration and development evaluation. However, the lack of systematic experimental studies on rock physical characteristics and micro-pore structures leads to a lack of physical evidence for the comprehensive prediction of shale sweet spots. Therefore, the present study used different means, such as core observation, total organic carbon content (TOC), helium porosity measurement, X-ray diffraction analysis, and mechanical properties analysis, in combination with the analysis of the whole rock mineral composition and characteristics of shale, for the identification and classification of the lithofacies of the shale layer, the systematic petrology and hardness measurement of the shale samples with different lithofacies, and discussion of the dynamic and static elastic properties of the shale samples and the control factors. It was revealed that nine types of lithofacies existed in the Wufeng Formation- the Long11 sub-member in the Xichang Basin, among which moderate organic carbon content-siliceous shale facies, moderate organic carbon content-mixed shale facies, and high-organic carbon content-siliceous shale facies were the best lithofacies with the optimum reservoir conditions, providing sufficient space for shale gas accumulation. The siliceous shale facies mainly developed organic pores and fractures, and the pore texture was excellent overall. The mixed shale facies mainly developed intergranular pores and mold pores, with a preference toward pore texture. The argillaceous shale facies mainly developed dissolution pores and interlayer fractures, and the pore texture was relatively poor. The geochemical characteristics of the organic-rich shale samples with TOC > 3.5% revealed that the sample was composed of microcrystalline quartz grains as the rock support framework, while the intergranular pores were located between the rigid quartz grains, which exhibited hard pores in the analysis of their mechanical properties. In the relatively organic-poor shale samples with TOC < 3.5%, the quartz source was mainly terrigenous clastic quartz, and the sample was composed of plastic clay minerals as the rock support skeleton, while the intergranular pores were located between argillaceous particles, which exhibited soft pores in the analysis of their mechanical properties. The difference in the rock fabric of the shale samples resulted in an ″initial increase followed by a decrease″ trend of velocity with quartz content, with the organic-rich shale samples exhibiting low velocity-porosity and velocity-organic matter content change rate, and the two kinds of rocks were easier to distinguish in the correlation diagram of the combined elastic parameters such as the P-wave impedance-Poisson ratio and the elastic modulus-Poisson ratio. The samples dominated by biogenic quartz exhibited greater hardness and brittleness, while the samples dominated by terrigenous clastic quartz exhibited lower hardness and brittleness. These results could serve as a basis for logging interpretation and seismic ″sweet spot″ prediction of high-quality shale gas reservoirs in Wufeng Formation-Member 1 of the Longmaxi Formation.

Auxeticity and stiffness of random networks: Lessons for the rational design of 3D printed mechanical metamaterials

The emergence of advanced 3D printing techniques and the recent interest in architected materials have sparked a surge of interest in mechanical metamaterials whose unusual properties are defined by their highly ordered microarchitectures. Mechanical metamaterials with disordered microarchitectures have, however, not received as much attention despite their inherent advantages, such as robustness against the precise arrangement and design parameters of individual unit cells. Here, we computationally studied the elastic properties of two general types of disordered networks, namely, lattice-restricted and unrestricted networks that were made of beamlike elements and possessed mean connectivity values, Z, ranging between 2.5 and 7. We also additively manufactured a number of representative networks using selective laser sintering and showed that their deformations are consistent with our computational predictions. Unrestricted networks exhibited several advantages over the lattice-restricted ones including a broader range of achievable elastic modulus-Poisson's ratio duos as well as a higher probability of exhibiting auxetic and double-auxetic (i.e., auxetic behavior in both orthogonal directions) behaviors. Most interestingly, we could find unrestricted auxetic networks for high connectivity levels of up to 4.5, while no lattice-restricted auxetic networks were found for any connectivity level beyond 3.5. Given the fact that, according to Maxwell's criterion, 3.5 is the highest Z for which both of our lattice-restricted and unrestricted networks are bending-dominated, we concluded that unrestricted networks exhibit auxetic behavior well into their stretch-dominated domain. This is a promising observation that underlines the potential of unrestricted networks for the challenging task of designing stiff auxetic metamaterials in the stretch-dominated domain (i.e., Z = 4–4.5).

Multi-material 3D printed mechanical metamaterials: Rational design of elastic properties through spatial distribution of hard and soft phases

Up until recently, the rational design of mechanical metamaterials has usually involved devising geometrical arrangements of micro-architectures that deliver unusual properties on the macro-scale. A less explored route to rational design is spatially distributing materials with different properties within lattice structures to achieve the desired mechanical properties. Here, we used computational models and advanced multi-material 3D printing techniques to rationally design and additively manufacture multi-material cellular solids for which the elastic modulus and Poisson's ratio could be independently tailored in different (anisotropic) directions. The random assignment of a hard phase to originally soft cellular structures with an auxetic, zero Poisson's ratio, and conventional designs allowed us to cover broad regions of the elastic modulus-Poisson's ratio plane. Patterned designs of the hard phase were also used and were found to be effective in the independent tuning of the elastic properties. Close inspection of the strain distributions associated with the different types of material distributions suggests that locally deflected patterns of deformation flow and strain localizations are the main underlying mechanisms driving the above-mentioned adjustments in the mechanical properties.

Rational design of soft mechanical metamaterials: Independent tailoring of elastic properties with randomness

The elastic properties of mechanical metamaterials are direct functions of their topological designs. Rational design approaches based on computational models could, therefore, be used to devise topological designs that result in the desired properties. It is of particular importance to independently tailor the elastic modulus and Poisson's ratio of metamaterials. Here, we present patterned randomness as a strategy for independent tailoring of both properties. Soft mechanical metamaterials incorporating various types of patterned randomness were fabricated using an indirect additive manufacturing technique and mechanically tested. Computational models were also developed to predict the topology-property relationship in a wide range of proposed topologies. The results of this study show that patterned randomness allows for independent tailoring of the elastic properties and covering a broad area of the elastic modulus-Poisson's ratio plane. The uniform and homogenous topologies constitute the boundaries of the covered area, while topological designs with patterned randomness fill the enclosed area.

Measurements for dynamic deformation by mismatch white speckle method

This paper presents a simple method for measurements of dynamic deformation by mismatch white speckle method using dynamic photoelastic device. The method is able to measure not only large dynamic deformation[1], but also small dynamic deformation. Combined with dynamic isochromate pattern, the elastic modulus Poisson's ratio and dynamic material fringe value of the material measured can be obtained by the method.