•Plate lattice is constructed by placing a plate between two adjacent trusses.•The equivalent stiffness of cubic-plate is twice higher than that of cubic-truss at the same relative density.•The ...mechanical properties of plate-lattice attains the theoretical Hashin-Shtrikman (HS) upper bound.
In this study, a new type of lattice structure, namely plate–lattice, was investigated. The plate–lattice structure was constructed by placing a plate between two adjacent trusses. Theoretical analysis of Young's modulus on a simple cubic–truss and cubic–plate revealed that the Young's modulus of the plate–lattice was twice that of the lattice composed of trusses. Subsequently, further studies on more complex structures, such as octet–trusses and octet–plates, were conducted using the finite element method (FEM). Furthermore, the periodic boundary condition (PBC) was applied to a unit cell to reflect the response of an infinite structure. Additionally, equivalent Young's modulus, strength, and shear modulus were compared at the same density. The results indicated that the stiffness of the plate–lattices was more likely to realize the Hashin–Shtrikman theoretical upper bounds. The plate–lattice structure exhibited 2–3 times higher stiffness values, including Young's modulus and shear modulus, than those of the truss lattice structure. Furthermore, the Ashby charts of relative compressive modulus (E/Es) and relative strength (σ/σy) were plotted as a function of relative density, and the data indicated that the plate–lattice structure was a new low density structure, which could utilize materials to the maximum extent.
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The effects of B4C content on the specific stiffness and mechanical and thermal properties of pressureless-sintered SiC ceramics were investigated. SiC ceramics containing 2.5 wt% C and 0.7–20 wt% ...B4C as sintering aids could be sintered to ≥ 99.4% of the theoretical density at 2150 °C for 1 h in Ar. The specific stiffness of SiC ceramics increased from 136.1 × 106 to 144.4 × 106 m2‧s−2 when the B4C content was increased from 0.7 to 20 wt%. The flexural strength and fracture toughness of the SiC ceramics were maximal with the incorporation of 10 wt% B4C (558 MPa and 3.69 MPa‧m1/2, respectively), while the thermal conductivity decreased from ∼154 to ∼83 W‧m−1‧K−1 when the B4C content was increased from 0.7 to 30 wt%. The flexural strength and thermal conductivity of the developed SiC ceramic containing 20 wt% B4C were ∼346 MPa and ∼105 W‧m−1‧K−1, respectively.
In this paper, a novel mechanical metamaterial with controllable stiffness is proposed based on the structural topology and rational design of curved beam unit cells. First, both straight and curved ...beams are mechanically analyzed, and the corresponding stiffness of these two beams is compared. Second, various curved beam unit cells are presented based on fractal geometries, and lattice structures assembled from curved beam unit cells are optimally designed and precisely fabricated by means of 3D printing techniques. Finally, multi-layered mechanical metamaterials are proposed and mechanically tested, which exhibit advantages of improved specific stiffness and reduced spatial volume. The theoretical and experimental results are verified using the finite element method (FEM). This study proposes a novel design principle for mechanical metamaterials with adjustable stiffness using curved beam unit cells, which can provide a theoretical basis for the development of mechanical metamaterials and present promising potentials in versatile engineering applications.
The lattice truss structure is a porous lightweight periodic structure with high specific stiffness and specific strength. In this research, pyramid lattice truss structures were designed and ...manufactured by three-dimensional (3D) printing technology through horizontal printing and vertical printing manners, respectively. Quasi-static axial compression tests were conducted to study the mechanical properties and energy absorption of the pyramidal lattice truss structures. These two types of printed lattice truss materials had close strength and rigidity. However, the vertically printed lattice truss structures had excellent ductility and their struts never broken off during compression. Three post failure styles of the vertically printed lattice truss structures were observed, including strain-hardening, stable deforming and softening and depending on the slenderness ratio of the strut. Theoretic analysis and finite element method (FEM) were performed to investigate the compression behaviors of the vertically printed lattice truss materials. Appropriate printing method and relative density could make the 3D printed pyramidal structures achieve excellent specific energy absorption.
Analysis of rock fracture deformation by normal stress is important for quantifying hydromechanical properties of fractured rocks that are related to a large number of geophysical problems and ...geoengineering applications. Experimental and numerical results for the closure of crystalline rock fractures subject to normal stress are presented in this study. An efficient high-resolution, half-space elastic–plastic contact model for analyzing the closure of crystalline rock fractures based on the Boussinesq’s solution is validated by high-precision and high-resolution experimental data. Using the validated elastic–plastic model, we investigate the correlation between fracture-specific stiffness and multi-scale surface roughness. The wavelet analysis method and the extended averaged slope magnitude for asperity heights (referred to as
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) are introduced to characterize the multi-scale surface roughness. The results show that the elastic–plastic contact model is effective and precise in modeling the closure of crystalline rock fractures, which matches better with the test results than the elastic model. The multi-scale features of surface roughness can be well characterized by the wavelet analysis and the extended roughness parameter
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. The specific stiffness is nonlinearly correlated with the multi-scale surface roughness that possibly follows a power law. The validated elastic–plastic contact model and the multi-scale surface roughness characterization methods, as well as the nonlinear correlation between the specific stiffness and the multi-scale surface roughness presented in this study, are helpful for evaluating the dependence of mechanical behaviors of rock fractures on its multi-scale surface roughness.
For the first time, a digital light processing (DLP) three-dimensional (3D) printer is implemented for additive manufacturing of sandwich beams with fiber reinforced facesheets and different core ...types without using adhesives. After characterizing the formulated thermosetting resin, sandwich beams with honeycomb and square core unit cells were printed in out-of-plane (OP) and in-plane (IP) arrangements, with and without woven glass fiber reinforcement in the facesheets. Meanwhile, using theoretical, micromechanical, and finite element (FE) approaches, the elastic properties and stiffness of sandwich beams were predicted. The stiffness measured from flex tests showed reliable agreement with predictions from analytical and finite element analysis (FEA) for most cases. Additionally, fiber reinforcement significantly increased specific stiffness of these structures, but did not affect the trends for different core geometries. The novel methodology presented here can open new doors for manufacturing advanced structures using DLP 3D printing technology.
Architected lattice materials, realized through artificial micro‐structuring, have drawn tremendous attention lately due to their enhanced mechanical performances in multifunctional applications. ...However, the research area on the design of artificial microstructures for the modulation of mechanical properties is increasingly becoming saturated due to extensive investigations considering different possibilities of lattice geometry and beam‐like network design. Thus, there exists a strong rationale for innovative design at a more elementary level. It can enhance and grow the microstructural space laterally for exploiting the potential of geometries and patterns in multiple length scales, and the mutual interactions thereof. A bi‐level design is proposed, where besides having the architected cellular networks at an upper scale, the constituting beam‐like members at a lower scale are further topology‐engineered for most optimum material utilization. The coupled interaction of beam‐level and lattice‐level architectures can enhance the specific elastic properties to an extreme extent (up to ≈25 and 20 times, depending on normal and shear modes, respectively), leading to ultra‐lightweight multifunctional materials for critical applications under static and dynamic environments.
A bi‐level design in lattice metamaterials is proposed, where besides having the architected cellular networks at an upper scale, the constituting beam‐like members at a lower scale are further topology‐engineered for most optimum material utilization. The coupled interaction of beam‐level and lattice‐level architectures can enhance the specific elastic properties to an extreme extent, leading to ultra‐lightweight multifunctional materials.
A theoretical foundation is developed for the active seismic reconstruction of fractures endowed with spatially varying interfacial conditions (e.g. partially closed fractures, hydraulic fractures). ...The proposed indicator functional carries a superior localization property with no significant sensitivity to the fracture's contact condition, measurement errors, or illumination frequency. This is accomplished through the paradigm of the F -factorization technique and the recently developed generalized linear sampling method (GLSM) applied to elastodynamics. The direct scattering problem is formulated in the frequency domain where the fracture surface is illuminated by a set of incident plane waves, while monitoring the induced scattered field in the form of (elastic) far-field patterns. The analysis of the well-posedness of the forward problem leads to an admissibility condition on the fracture's (linearized) contact parameters. This in turn contributes to the establishment of the applicability of the F -factorization method, and consequently aids the formulation of a convex GLSM cost functional whose minimizer can be computed without iterations. Such a minimizer is then used to construct a robust fracture indicator function, whose performance is illustrated through a set of numerical experiments. For completeness, the results of the GLSM reconstruction are compared to those obtained by the classical linear sampling method (LSM).
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