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In this paper, three-dimensional (3D) novel hybrid lattice structures with exceptional mechanical properties and energy absorbing performances were proposed, and experimental and finite element simulation comparisons were performed to demonstrate their potential in mechanical application. First, different types of basic cubic unit cells were designed for constructing three types of novel hybrid metamaterials, in which stepped circulation of different unit cells was conceived to generate architected metamaterials. Afterwards, quasi-static compression experiments and finite element simulations were performed to study the deformation process and failure mechanisms of as-fabricated hybrid metamaterials. The energy absorption efficiency, specific energy absorption (SEA) indicators, and energy absorption capabilities of different hybrid lattice metamaterials were compared and analyzed. The results show that the deformation mechanisms of novel hybrid lattice were beneficial for generating remarkable elevated densification strain, and the energy absorption efficiency can be tailored by altering the types or sizes of basic unit cells. Strain-hardening and bilinear features were also obtained.

In this paper, making use of the coupled deformation features of reentrant and tetrachiral lattices, innovative 3D chiral metamaterials are designed, in which their mechanical properties and deformation mechanisms are explored in details. Firstly, three types of innovative 3D chiral metamaterials are designed based on geometry topology in the x ¯ y ¯ plane, namely: tetrachiral, anti-tetrachiral and hybrid-tetrachiral, respectively. Secondly, the coupled tension and rotation deformation mechanisms of innovative 3D chiral metamaterials are investigated based on large deformation theories of representative unit cell. The theoretical formulas for extension stress, Poisson’s ratio and rotation angle of the square loop are derived, it is found that wide range of negative Poisson’s ratio can be obtained with the proposed 3D chiral metamaterials. Afterwards, tensile experiments are performed, and good agreements between theoretical, finite element and experimental results are presented, verifying the reliability of the theoretical models. Finally, influences of the geometry parameters on the mechanical behaviors of the proposed 3D auxetic metamaterials are also studied.

This paper investigates whether the Weibull parameters of the new local approach model for cleavage fractures are affected by the geometric size of the specimen. Based on the fracture test data of A508-C steel, low temperature round notched bar tensile specimens of A508-C steel with two different notch sizes are numerically simulated by using finite element analysis software ABAQUS, and the stress distributions are obtained. The Weibull parameters of two notched bars are calibrated by linear regression method. The results show that the Weibull parameters of the specimens with different notch sizes are different. This suggests that the calibration parameters are dependent on the notch size.

Bamboo based composite materials are widely used for structural components in building and textile industries. The structural hierarchy across different scales could enhance the strength and toughness of bamboo for load-bearing applications. Firstly, chemical components of bamboo fibril are described, and bamboo fibril specimens are fabricated through chemical solution processing; Secondly, functionally graded mechanical properties of macroscopic bamboo fibers are studied with tensile experiments, and relations between graded mechanical properties and microstructures are explored; Afterwards, hierarchical microstructure characterization of bamboo across different scales are performed using scanning electron microscopy (SEM), and mechanical properties of bamboo fibrils are tested using homemade in-situ micro-tension setup. The results indicate that the elastic modulus, ultimate strain and strength of bamboo fibers are: 5.952 GPa, 0.0136 and 81.13 MPa respectively. The Young’s moduli, ultimate strains and fracture strengths of the five fibril samples located in (10.478, 12.285) GPa, (0.0172, 0.0217) and (181.87, 230.50) MPa, respectively. These experimental results suggest that the modulus and ultimate strength of bamboo fibril are higher than that of bamboo fibers which are attributed to several main factors including the ages of the bamboo, bamboo species, multi-lamella structures of the fibrils, geometry differences of fibrils, etc.

Although the correlated rare-earth nickelate perovskites (such as SmNiO3) exhibit remarkable metal to insulator transitions (MIT) beyond conventional semiconductors, their respective variations in mechanical properties during MIT remain yet unknown. Exploring the intrinsic mechanical properties of SmNiO3 is largely prohibited since it is theoretically impossible to grow the single crystalline samples in a large size as required for conventional characterizations. For the first time, we performed nano-indentation tests of preferentially oriented SmNiO3 films with thickness approaching micrometer scale epitaxy on single crystalline LaAlO3 substrates, and the corresponding temperature-dependent mechanical properties are characterized. As-grown SmNiO3 thick films experience sharp transitions in electrical resistivity across MIT, while their insulating phases exhibit thermistor transportation behaviors with the negative temperature dependence of resistance within a broad range of temperature. Nano-indentation tests at room and elevated temperature regions (25–200 °C) are performed for harvesting the Vickers hardness and elastic modulus at different temperatures. In addition, it is also interesting to note that these mechanical properties remain relatively stable during MIT, despite the structural twisting in their NiO6 octahedron during the MIT as previously known for SmNiO3. The SmNiO3 is shown to be relatively soft among the family of perovskite oxides, while its mechanical properties are insensitive to increase temperature across its metal to insulator transitions. It paves the way for further applying rare-earth nickelates in the field of correlation electronics.

Synchrotron radiation X-ray micro-computed tomography (SR-µCT) is a 3D imaging technique that is widely employed for the characterization of defects in advanced materials and structures. In this study, we characterize several typical defects in octettruss and re-entrant 3D lattice structures by using SR-µCT. The 3D micro-lattice structures are manufactured using projection micro litho stereo exposure (PµLSE) additive manufacturing technology. The as-fabricated 3D lattice samples are characterized using optical microscopy, and subsequently, by SR-µCT. Further more, a statistical analysis is performed to characterize the surface roughness and internal defects qualitatively, whereby the statistical geometrical parameters of struts along different directions and strut joints are analyzed and classified. Consequently, several typical defects are identified: (1) holes at the joints of the strut and irregular diameter deviations of the strut in the octet-truss lattice structure; (2) irregular diameter variations, bulges, dislocations, grooves, accumulations, and torsion in the re-entrant lattice structure. All of these defects are related to the building direction, the weight of the structure, bubbles, dust, and impurities during the PµLSE additive manufacturing process.

Synchrotron radiation absorption based and phase-contrast X-ray tomographic microscopy techniques are applied for observation and identification of the 3D features of bamboo fiber and parenchyma ce...

In recent years, metal additive manufacturing (AM) are widely employed for industrial applications, such as: biomedical, aerospace, automotive, marine and offshore sections. AM demonstrated superior manufacturing efficiencies and economic advantages for advanced lightweight industrial components with unlimited arbitrary topological layouts and complex internal microstructures, and are also employed for fabrication of auxetic materials and structures. In this paper, damage characterizations and mechanical behaviors of selective laser melting (SLM) fabricated 3D re-entrant lattices are investigated based on in-situ interrupted micro-CT test, and simulation based on geometric reconstructed models are performed for exploring the underlying failure mechanisms. Firstly, theoretical models for predicting the mechanical properties of 3D re-entrant lattice are developed, such as stiffness, Poisson's ratio and strength, etc. Secondly, the geometrical errors and fabrication defects of 3D re-entrant lattices are analyzed based on 3D micro-CT scanning, in-situ micro-CT interrupted compression tests are performed for studying the deformation process and failure mechanisms. Finally, image finite element models with the detailed information of the shape, position and distribution of defects of the 3D reentrant lattices are constructed from 3D tomographic images, and numerical simulations are performed for studying the effects of the defects on the mechanical performances of the SLM additive manufactured 3D re-entrant lattice structures. It is shown that the failure behavior of the reentrant lattice is governed not only by its topology, but also by the geometric defects and surface defects. Moreover, the proposed interrupted in-situ micro-CT mechanical loading experiments and image finite element approaches can also shed lights on the relations between fracture failure around the edge and the powder adhesion. The damage evolution process is compared with the numerical simulation results to verify the materials failure modes.

Auxetic chiral structures consisting of circular ring nodes and tangentially connected ligaments are engineered systems that exhibit excellent flexibility, vibration attenuation, impact resistance performances. In this paper, the out-of-plane dynamic crash behaviors of anti-tetrachiral, hexachiral and hierarchical chiral structures are studied. The energy absorption efficiency, plateau stress, peak stress of chiral structures with different ligament length, node radius, ligament thickness and level of structural hierarchy under different external crashing conditions are compared, and identical mass per area of different unit cell configurations are assumed. It is found that anti-tetrachiral structure is able to generate higher plateau stress and better energy absorption efficiency than hexachiral structures. Making use of the mechanical benefits of structural hierarchy, novel hierarchical chiral structures are proposed for improving the crash energy absorption abilities of chiral structures, and relations between crash energy absorption performances and unit cell geometries are explored, such as: energy absorption efficiency, plateau stress of chiral structures. Based on systematical analysis, optimized chiral and hierarchical chiral cellular structure can be designed for impact energy absorption in protective sandwich structures.

In this paper, the quasi-static compression behavior of graded metallic auxetic reentrant honeycomb was firstly studied. Using the selective laser melting method, the unidirectionally-graded auxetic honeycomb (UGAH) and bidirectionally-graded auxetic honeycomb (BGAH) with the equal mass were fabricated to conduct the compression tests. The deformation mode, crushing stress and Poisson's ratio distribution of graded auxetic honeycombs were presented. Experiment results showed that the compression behavior of graded auxetic honeycomb was different from that of graded honeycomb with positive Poisson's ratio owing to the horizontal shrinkage deformation and the gradient distribution had effects on the crushing stress and Poisson's ratio. Then, a finite element (FE) model of the graded auxetic honeycomb was established and the calculation results were systematically compared with the experimental results. The effects of gradient distribution on the energy dissipation characteristics of the graded auxetic honeycomb were studied. The results showed that the energy dissipation of the UGAH was lower than that of the BGAH before the graded layer with the maximum cell-wall thickness was densified.

In-situ high temperature measurement in a scanning electron microscopy (SEM) environment is an important technique for exploring the microstructure evolution and crack propagation within refractory materials and other advanced alloys. In this paper, in-situ tensile fatigue experiments under SEM environment at room temperature and elevated temperature are performed for studying the fatigue performance and crack propagation process of selective laser melting (SLM) additive manufactured Al-Si10-Mg materials. Firstly, in-situ SLM additive manufactured Al-Si10-Mg fatigue tensile samples are prepared, and micro-CT are employed for the characterization of void defects within SLM additive manufactured Al-Si10-Mg with different laser scanning speeds and laser energy; Secondly, in-situ fatigue experiments are carried out under SEM environment at 25 °C, 100 °C, 200 °C, 300 °C, 400 °C, 500 °C and 600 °C, respectively. The fatigue mechanical behaviors, microstructure evolution and crack propagations of as-fabricated Al-Si10-Mg samples are characterized. Finally, micro-CT tomography 3D imaging techniques are employed for exploring the link between SLM defects and fatigue performances.

For end-on screw dislocations and inclined dislocations within thin transmission electron microscopy (TEM) foil, TEM diffraction contrast image is largely modified around piercing point due to free surface relaxation. Based on many-beam Schaeublin-Stadelmann equations, TEM diffraction contrast images simulation of inclined dislocations within thin pure Fe TEM foil are performed and the difference between isotropic and anisotropic dislocation models are studied. Image force are superposed onto bulk elastic field of dislocation in thin foil, the elastic distortions nearby the two emerging points of a straight inclined dislocation located in an elastically isotropic/anisotropic thin foil are expressed as semianalytical solution in Fourier space, and the semianalytical image stress solutions in Fourier space are implemented into CUFOUR for studying free surface relaxation effect on TEM diffraction contrast of dislocation. Simulation results suggest that the diffraction contrast at the ends of dislocation is modified drastically by image forces, and effects of anisotropy cannot be neglected. LAY DESCRIPTION: For end-on screw dislocations and inclined dislocations within thin transmission electron microscopy (TEM) foil, TEM diffraction contrast image is largely modified around piercing point due to free surface relaxation. Based on many-beam Schaeublin-Stadelmann equations, TEM diffraction contrast images simulation of inclined dislocations within thin pure Fe TEM foil are performed and the difference between isotropic and anisotropic dislocation models are studied. Image force are superposed onto bulk elastic field of dislocation in thin foil, the elastic distortions nearby the two emerging points of a straight inclined dislocation located in an elastically isotropic/anisotropic thin foil are expressed as semianalytical solution in Fourier space, and the semianalytical image stress solutions in Fourier space are implemented into CUFOUR for studying free surface relaxation effect on TEM diffraction contrast of dislocation. Simulation results suggest that the diffraction contrast at the ends of dislocation is modified drastically by image forces, and effects of anisotropy cannot be neglected.

Rational design of artificial micro-structured metamaterials with advanced mechanical and physical properties that are not accessible in nature is challenging and important. Making use of the node rotation and ligament bending deformation features of chiral materials, innovative reentrant and anti-chiral hybrid metastructures are proposed for vibration attenuation, where elastic rubber coated mass inclusions are distributed within the chiral circular ring nodes of unit cells. The bandgaps and wave attenuation mechanisms of the proposed reentrant and anti-chiral hybrid metastructures are explored, and finite element simulations are performed for analyzing the relation between wave attenuation properties and structural parameters. Then, coupled deformation mechanism of reentrant and anti-chiral hybrid metastructures are analyzed, it is found that the geometrical topology and node elastic mass inclusion distribution schemes have remarkable effects on the bandgaps of the metastructures. Meanwhile, the wave mitigations of the reentrant and anti-chiral hybrid metastructures are explored through tuning the structural parameters and mass inclusions distributions. Finally, the wave attenuation performances of sandwich panels with reentrant and anti-chiral hybrid cores are studied, thus demonstrating the promising engineering application potentials for vibration isolation.

The mechanical properties of the stent are of key importance to the mechanical integrity and performance reliability of stent-plaque-artery system, and an ideal stent should have good bending compliance, axial deformation stability, hoop strength and stiffness, larger radial expandable ability, etc. In this paper, innovative chiral stent designs with auxetic properties are proposed, and amplified stent sample is fabricated with SLS additive manufacturing technique. Firstly, through combining micro-CT tomography and image-based finite element analysis, the mechanical properties of as fabricated SLS stent are explored; Secondly, two series of stent samples are fabricated with SLS additive manufacturing techniques, and in-situ compression experiments are performed for studying the deformation mechanisms and auxetic mechanical behaviors of stents. Finally, effects of geometrical parameters on the tensile mechanical performance of these stents are studied with finite element analysis. The proposed chiral stent exhibits auxetic behaviors, and can be tailored through adjusting the unit cell design parameters, such as: struct numbers along circumferential directions, ligament lengths, and node radius.

Design of materials and structures with quite low coefficient of thermal expansion (CTE), even zero or negative CTE is important for industrial application where drastic temperature changes are encountered. In this paper, making use of the bending of bi-material beam and the unique deformation mechanism of chiral lattice structures, five sets of chiral lattice composite structures with tailorable CTEs are proposed, where synergic effects of rigid node rotation and bi-material ligament bending deformation are responsible for giant range of structural deformation due to temperature change, from positive CTE to negative CTE through adjusting the geometrical parameters of composite bi-material chiral unit cell, and the relationship between unit cell geometric parameters and CTEs of the structure are studied systematically through finite element analysis . Finally, design of bi-material cylindrical shells consisting of anti-tetra chiral unit cells are proposed, and its axial CTEs with different number of the unit cells along the circumferential are studied systematically, demonstrating the robust range of CTEs can be generated through adjusting the geometrical parameters of chiral bi-material unit cells. The proposed chiral structures demonstrated promising application potentials in industrial fields, such as: aerospace and microelectronics, where extremely high structural accuracy is required during harsh working temperature environment.

The high-performing biomimetic behaviors of crustaceans are the optimal results of long-time wise adaption to their living environment. One outstanding prototype is crab claw, which has the combining advantages of lightweight and high strength. To promote relevant engineering applications, it is imperative to explore its mechanical behaviors and structural characteristics. In this work, mechanical test and finite element analysis (FEA) are performed to reveal the fundamental mechanical properties and clamping behaviors of snow crab (Chionoecetes opilio) claw, respectively. A lightweight modeling method, parametric lofting modeling, for the 3D modeling of the claw is employed, which is compared with the traditional reverse engineering modeling method based on tomography image. Our results demonstrated that the hardness and modulus of the regions near the top of the claw are larger than those of the regions near of bottom of the claw. Moisture is a critical factor in controlling the tensile behavior of the claw and the wet specimens exhibit higher modulus and strength under tensile loading. Besides, The parametric lofting method is highly flexible and efficient in generating 3D geometrical model. The investigation of clamping behaviors provides not only insights into mechanical behaviors and intrinsic mechanisms but also a practical guide for their potential applications, such as designing high-performing artificial clamping muscles for clinical operations, aerospace applications, and robotics.

It is critical to understand the airflow structures in the respiratory system toward increasing the drug delivery efficiency via inhalation. A whole-lung airway model is created by connecting a three-dimensional cast-based mouth–throat model and a one-dimensional conduit describing the other lung airways according to the literature. Constant displacement of the bottom surface in the geometrical model is used to simulate the respiratory process. Large eddy simulation with the dynamic structure sub-grid scale model is used to model the turbulent flow via a commercial computational fluid dynamics software, ConvergeTM. The innovative findings are as follows: (1) shear layer as well as vortical flow is observed in the lower airway at the inspiration phase; (2) the main airflow structures in the upper airway of this model are close to the case using the mouth–throat model; (3) the airflow structures, in particular the reversed laryngeal jet, are highly unsteady during the expiration phase. It is shown that this whole-lung airway model is suitable to analyze the airflow field in the upper airway but not in the lower airway, although it has been used a lot by a few researchers. More investigations should be carried out to study the dynamics of airflow structures during the expiration phase toward understanding airflow properties of human respiratory process.

To clarify the strengthening mechanism of coated/embedded graphene in metal matrix nanocomposites, nanoindentation responses of graphene-coated/embedded copper nanocomposites are investigated using molecular dynamics simulations, with the consideration of indentation force-displacement relation, stress distribution, evolution of microstructure and dislocation, and elastic recovery. Results show that two mechanisms, graphene layer bearing surface tensile stress disperses the contact stress and blocks the propagation of dislocations, contribute to the enhanced hardness and improved load bearing capacity, but one is often dominant for different nanocomposites. The former dominates in graphene-coated structure while the latter dominates in graphene-embedded structure, and the reinforcement is more obvious in the coated structure. The graphene delays the plastic deformation of matrix, and its elastic recovery is boosted due to the stress homogenization effect. The embedded graphene promotes the stress concentration and accelerates the plastic deformation of up Cu film, weakening its width elastic recovery. The observations will provide a practical guide for the mechanical optimization and design of metal-graphene nanocomposites.

The manufacturing of additives with projection micro litho stereo exposure (PμLSE) has provided an opportunity for the fabrication of metastructures with complex microstructures at micro-nano resolutions. However, the performance evaluation of as-fabricated metastructures is challenging. The benefit of synchrotron radiation-based 3D imaging techniques and advanced image processing methods makes it is feasible to study fabrication defects and damage processes of micro-nanoscale body-centered cubic (BCC) lattices manufactured with PμLSE. First, synchrotron radiation technology is used to capture the structural features inside the micro-lattice samples. Subsequently, several types of statistical defects-based image finite element models are adopted to analyze the failure process of the structure under compression loading. Finally, comparisons between in situ experiments and numerical simulation results are performed for verification. The method of the combined non-destructive testing of synchrotron radiation and image finite element technology provides a robust technique for evaluating the performances of additive-manufactured micro-lattice with complex microstructures.

The mechanical performance of reactor pressure vessel materials is an important factor in the safety and economics of the operation of a nuclear power plant. The ductile-to-brittle transition temperature tested by Charpy impact test is the key parameter for evaluating the reactor pressure vessel embrittlement. In this article, the study of thermal aging embrittlement of temperature sets of reactor pressure vessel surveillance Ni-Cr-Mo-V steel weld metal was conducted by Charpy impact test. The thermal aging effect on the impact fracture behavior was analyzed. The impact test of the three batches of weld surveillance sample indicated that the weld metal embrittled during thermal aging. The study of impact fracture and Auger electron spectroscopy indicated that the element P segregated to the grain boundaries and lowered their cohesion strength during the long-term thermal aging. Therefore, the non-hardening embrittlement of Ni-Cr-Mo-V steel welds in a reactor pressure vessel caused by segregation of impurity elements P occurs during thermal aging.