Search query: superhard, negative poisson's ratio

Related papers:

abstract: Auxetic structure and tunable phase transitions are fascinating properties for future application. Herein, we propose two three dimensional (3D) carbon honeycombs (CHC) known as Cmcm CHC and Cmmm CHC. Based on first principles calculations, these novel 3D materials exhibit auxeticity with a fascinating negative Poisson's ratio, which stems from (i) the puckered structure of Cmcm CHC along the tube axis and (ii) significant change of angle dominant deformation for Cmmm CHC in the armchair direction. In addition, the moderate strain drives semimetal to semiconductor phase transition in CHCs, which thoroughly establishes its C C bond formation. In the meantime, two new phases, namely P63/mmc CHC and P6/mmm CHC, form and exhibit semiconductor characteristics. Our results also show that Cmcm CHC and P63/mmc CHC are superhard materials. The outstanding negative Poisson's ratio and phase transition properties make CHCs highly versatile for innovative applications in microelectromechanical and nanoelectronic devices.
author_names: Yanchun Li

Shuaiwei Wang

Bao-cheng Yang
title: Auxetic Carbon Honeycomb: Strain Tunable Phase Transitions and Novel Negative Poisson's Ratio
venue: ACS omega
year: 2021

abstract: Abstract Superhard titanium diboride (TiB2) coatings (Hv> 40 GPa) were deposited in Ar atmosphere from stoichiometric TiB2 target using an unbalanced direct current (d. c. magnetron. Polished Si (0 0 1) stainless steel, high speed steel (HSS) and tungsten carbide (WC) substrates were used for deposition. The influence of negative substrate bias, Us, and substrate temperature, Ts, on mechanical properties of TiB2 coatings was studied. X ray diffraction (XRD) analysis showed hexagonal TiB2 structure with (0 0 01) preferred orientation. The texture of TiB2 coatings was dependent upon the ion bombardment (Us increased from 0 to 300 V) and the substrate heating (Ts increased from room temperature (RT) to 700 degC) All TiB2 coatings were measured using microhardness tester Fischerscope H100 equipped with Vickers and Berkovich diamond indenters and exhibited high values of hardness Hv up to 34 GPa, effective Young's modulus E*=E/(1 n) ranging from 450 to 600 GPa; here E and n are the Young's modulus and Poisson's ratio, respectively, and elastic recovery We80% TiB2 coating with a maximum hardness Hv73 GPa and E*580 GPa was sputtered at Us= 200 V and Ts=RT. Macrostresses of coatings s were measured by an optical wafer curvature technique and evaluated by Stoney equation. All TiB2 coatings exhibited compressive macrostresses.
author_names: Marian Mikula

Branislav Grancic

Vilma Bursikova

Adrian Csuba

M Drzik

Stefan Kavecky

Andrej Plecenik

Peter Kus
title: Mechanical properties of superhard TiB2 coatings prepared by DC magnetron sputtering
year: 2007

abstract: The article reports on structure and mechanical properties of Ti B alloy films sputter deposited from a sintered TiB 2 target using an unbalanced dc magnetron. We present results of a systematic investigation of the effect of negative substrate bias, U s substrate ion current density i s and substrate temperature, T s on properties of Ti B films. The X ray diffraction (XRD) analysis shows that the Ti B films consist of the hexagonal TiB 2 phase with the typical (0001) texture only. The TiB x films are over stoichiometric with the ratio x=B/Ti=2.4. All Ti B films sputter ion plated in argon magnetron discharge are superhard films with hardness H>40 GPa and exhibit high values of (i) effective Young's modulus E*=E/(1 v 2 up to approximately 600 GPa and (ii) elastic recovery, W e up to approximately 82% here E and v are the Young's modulus and the Poisson's ratio, respectively. Besides, it was found that the value of the Bragg's angle 20 of the (0001) reflection line can be easily controlled by the energy delivered to the film during its growth by (I) the substrate heating T s and (2) ion bombardment (U s i s The angle 20 of the (0001) reflection increases with increasing T s from 300 to 550 degC and decreasing U s from 150 to 50 V. In this range of process parameters, the energy E p delivered to the growing film per condensing atom by ion bombardment can be adjusted to a value, at which the (0001) reflection from sputtered films is close to that of the TiB 2 (0001) powder standard. These films exhibit a low macrostress, which approaches to zero. It enables to sputter thick (up to 8 mm) superhard (H>40 GPa) Ti B films. The optimum value of E p is achieved when the Ti B film is sputtered at U s 50 V, i s 1 mA/cm 2 T s =550 degC with a deposition rate a D =52 nm/min. The Ti B film prepared under these conditions exhibits a maximum hardness of H77 GPa, measured using a computer controlled microhardness tester Fischerscope H100 at the Vickers diamond indenter load L=50 mN.
author_names: Filip Kunc

Jindrich Musil

Paul H Mayrhofer

Christian Mitterer
title: Low stress superhard Ti B films prepared by magnetron sputtering
year: 2003

abstract: Abstract This paper presents an investigation on the nonlinear flexural vibrations of carbon nanotube reinforced composite (CNTRC) laminated cylindrical shells with negative Poisson's ratios in thermal environments. The material properties of the CNTRCs are temperature dependent and the functionally graded (FG) in a piece wise pattern in the thickness direction of the shell. An extended Voigt (rule of mixture) model is employed to estimate the CNTRC material properties. The motion equations for the nonlinear flexural vibration of FG CNTRC laminated cylindrical shells are based on the Reddy's third order shear deformation theory and the von Karman type kinematic nonlinearity, and the effects of thermal environmental conditions are included. The nonlinear vibration solutions for the FG CNTRC laminated cylindrical shells can be obtained by applying a singular perturbation technique along with a two step perturbation approach. The effects of material property gradient, the temperature variation, shell geometric parameter, stacking sequence as well as the end conditions on the vibration characteristics of CNTRC laminated cylindrical shells are discussed in detail through a parametric study. The results show that negative Poisson's ratio has a significant effect on the linear and nonlinear vibration characteristics of CNTRC laminated cylindrical shells.
author_names: Hui-shen Shen

Chong Li

J N Reddy
title: Large amplitude vibration of FG CNTRC laminated cylindrical shells with negative Poisson's ratio
year: 2020

abstract: Abstract Artificial auxetic materials with negative Poisson's ratio enable distinctive elastic response in the direction orthogonal to the loaded direction, i.e. shrinking when compressed and expanding when stretched, compared to conventional materials. Such distinctive mechanical characteristic makes auxetic materials unique in practice. Current studies in this aspect focus mainly on the realization of beam dominated microstructures such as re entrant and chiral lattices and of cellular microstructures with orthogonal elliptical hole pattern. In this study, a novel two dimensional auxetic microstructure is designed by introducing peanut shaped holes in solid bulk matrix. Compared to the microstructure with elliptical hole pattern, the present design can produce slightly larger negative Poisson's ratio and achieve significantly lower stress level. The samples consisting of a number of centimeter scale unit cells with the peanut shaped holes are fabricated efficiently via additive manufacturing technique. Experiment and finite element simulation of tensile test are carried out on the specific sample to demonstrate the auxetic effect of the present design and simultaneously verify the computational model. Finally, effects of some parameters on Poisson's ratio, which may control the auxetic behavior of the present microstructure, are discussed for better understanding deformation mechanism of the proposed auxetic material.
author_names: Hui Wang

Yuxuan Zhang

Wanqing Lin

Qing Hua Qin
title: A novel two dimensional mechanical metamaterial with negative Poisson's ratio
year: 2020

abstract: Abstract This paper reports a study on the large amplitude nonlinear vibration of carbon nanotube reinforced composite (CNTRC) laminated plates with negative Poisson's ratios in thermal environments. The constituent materials of CNTRCs are temperature dependent and the plate is functionally graded (FG) in a piece wise pattern in the thickness direction of plate. An extended Voigt (rule of mixture) model is adopted to quantify the CNTRC material properties of the laminated plate. The governing motion equations for the large amplitude vibration of FG CNTRC laminated plates are based on the Reddy's third order shear deformation theory and the von Karman type kinematic nonlinearity framework, and the thermal effects and the reaction from elastic foundation are taken into account. The nonlinear solution of the motion equation can be obtained by applying a two step perturbation approach. The effects of material property gradient, the temperature variation, stacking sequence as well as the foundation stiffness on the vibration characteristics of CNTRC laminated plates are examined and discussed in depth through a parametric study. The results show that negative Poisson's ratio has a significant effect on the linear and nonlinear vibration characteristics of CNTRC laminated plates.
author_names: Jian Yang

Xu-Hao Huang

Hui-shen Shen
title: Nonlinear vibration of temperature dependent FG CNTRC laminated plates with negative Poisson's ratio
year: 2020

abstract: In this paper, a novel three dimensional (3D) unit cell structure with butterfly like perforations was designed, and negative Poisson's ratio and tunable stiffness were achieved in such a geometry. The Poisson's ratio and strain stress relationship of structures with different geometric parameters were determined using the finite element method (FEM) Samples with identical geometric variables to those of finite element models were fabricated via 3D printing technique, and their Poisson's ratios and stress strain relationships were experimentally determined and compared with the FEM results. Results showed that the proposed 3D cellular structures exhibit negative Poisson's ratios, and a minimal value of 0.7091 could be reached. The stress strain curve of each structure exhibited three distinct stages (elastic response, rib buckling and self contact) with different elastic moduli being observed at each stage, and demonstrated a tunable range of the compressive stiffness ratio between stages varying from 0.1866 to 1.4006(tunable stiffness) as determined by FEM analysis. Good agreement was found between the experimental results and FEM predictions. The design concept can be implemented and optimized for specific applications via geometric parameters manipulation.
author_names: Dong Sheng Li

Ruicong Gao

L Dong

Wing-Kai Lam

Fengpeng Zhang
title: A novel 3D re entrant unit cell structure with negative Poisson's ratio and tunable stiffness
year: 2020

abstract: A novel foam structure is presented, which exhibits a negative Poisson's ratio. Such a material expands laterally when stretched, in contrast to ordinary materials.
author_names: Roderic S Lakes
title: Foam Structures with a Negative Poisson's Ratio
venue: Science
year: 1987

abstract: Four dimensional (4D) printing, integrates transformation information into three dimensional (3D) printed structures, which means that 3D printed structures are able to change their shapes, properties, or functionalities over time. Here, two types of shape memory personalized vascular stents with negative Poisson's ratio structure are developed via 4D printing. The genetic algorithm is used to optimize the structure. Axial compression tests, radial compression tests and three point bending tests are carried out to study the mechanical properties of the stents. In addition, fluid structure interaction and stress distribution during the shape recovery process are investigated based on finite element method. The shape memory behaviors of the stents are excellent and in vitro feasibility tests demonstrate that the stents can expand the simulated narrow blood vessel rapidly. Therefore, 4D printed shape memory stents with negative Poisson's ratio structure are highly promising for the treatment of vascular stenosis.
author_names: Cheng-Li Lin

Lijin Zhang

Yanju Liu

Liwu Liu

Jin-song Leng
title: 4D printing of personalized shape memory polymer vascular stents with negative Poisson's ratio structure: A preliminary study
year: 2020

abstract: Abstract Nanocomposite materials, such as carbon nanotube reinforced composites (CNTRCs) have emerged as a novel engineering material. They have received growing attentions in various engineering sectors. The fabrication process has also offered the possibility to design and make this type of material to have desired features, such as being functionally graded (FG) or/and having negative Poison's ratio. This paper reports an investigation on the nonlinear flexural behavior of auxetic laminated beams with each layer is made of CNTRC. Each layer may have different CNT volume fractions and the functional grading occurs in the thickness direction of the beam in the piece wise pattern. The extended rule of mixture model is used to evaluate the temperature dependent material properties of CNTRCs. The governing equations for the nonlinear bending of FG CNTRC laminated beams are derived based on the high order shear deformation beam theory. These equations include the geometrical nonlinearity in the von Karman sense and take into account the thermal effect and the beam foundation interaction. The nonlinear bending solutions can be obtained by employing a two step perturbation approach. The nonlinear flexural responses of FG CNTRC laminated beams under a uniform pressure in thermal environments are revealed and examined in details through a parametric study. Results showed that the negative Poisson's ratio has a significant impact on the nonlinear flexural behavior of CNTRC laminated beams.
author_names: Jian Yang

Xu-Hao Huang

Hui-shen Shen
title: Nonlinear flexural behavior of temperature dependent FG CNTRC laminated beams with negative Poisson's ratio resting on the Pasternak foundation
year: 2020