Investigations of a nanostructured FeMnSi shape memory alloy produced via severe plastic deformation

Low-cost iron-based shape memory alloys（SMAs） show great potential for engineering applications. The developments of new processing techniques have recently enabled the production of nanocrystalline materials with improved properties. These developments have opened avenues for newer applications for SMAs. The influence of severe plastic deformation induced by the high-speed high-pressure torsion（HSHPT） process on the microstructural evolution of an Fe–Mn–Si–Cr alloy was investigated. Transmission electron microscopic analysis of the alloy revealed the existence of nanoscale grains with an abundance of stacking faults. The high density of dislocations characteristic of severe plastic deformation was not observed in this alloy. X-ray diffraction studies revealed the presence of ε-martensite with an HCP crystal structure and γ-phase with an FCC structure.

Exact mesh shape design of large cable-network antenna reflectors with flexible ring truss supports

An exact-designed mesh shape with favorable surface accuracy is of practical significance to the performance of large cable-network antenna reflectors. In this study, a novel design approach that could guide the generation of exact spatial parabolic mesh configurations of such reflector was proposed. By incorporating the traditional force density method with the standard finite element method, this proposed approach had taken the deformation effects of flexible ring truss supports into consideration, and searched for the desired mesh shapes that can satisfy the requirement that all the free nodes are exactly located on the objective paraboloid. Compared with the conventional design method,a remarkable improvement of surface accuracy in the obtained mesh shapes had been demonstrated by numerical examples. The present work would provide a helpful technical reference for the mesh shape design of such cable-network antenna reflector in engineering practice.

STUDY OF CONSTITUTIVE RELATIONS FOR PSEUDO-ELASTICITY AND SHAPE MEMORY BEHAVIOR

Constitutive relations are given for the description of the deformation behavior of shape memory materials. The deformation is the superposition of the elastic, the thermal and the phase transformation deformation caused by the transformation from one to the other among the high temperature phase, the low temperature phase and the stress induced phase. The phase transformation is controlled by the driving force, i.e., the Gibbs energy difference between the phases.

Multiscale Isogeometric Topology Optimization with Unified Structural Skeleton

This paper proposes a multiscale isogeometric topology optimization(ITO)method where the configuration and layout of microstructures are optimized simultaneously.At micro scale,a shape deformation method is presented to transform a prototype microstructure(PM)for obtaining a series of graded microstructures(GMs),where microstructural skeleton based on the level set framework is applied to retain more topology features and improve the connectability.For the macro scale calculation,the effective mechanical properties can be estimated by means of the numerical homogenization method.By adopting identical non-uniform rational basis splines(NURBS)as basis functions for both parameterized level set model and isogeometric calculation model,the isogeometric analysis(IGA)is integrated into the level set method,which contributes to improving the accuracy and efficiency.Numerical examples demonstrate that,the proposed method is effective in improving the performance and manufacturability.

A three-dimensional CFD study of the hydrodynamic behavior of equal and unequal-sized in-line methane bubbles at high pressure

The hydrodynamic behavior of multiple bubbles rising upward is a field of ongoing research since various aspects of their interaction require further analysis. Shape deformation, rise velocity, and drag coefficient are some of the uncertainties to be determined in a bubble upward flow. For this study the predictions of the three-dimensional numerical simulations of the volume of fluid（VOF） CFD model were first compared with experimental results available in the literature, serving as benchmark cases. Next, 28 cases of pairs of equal and unequal-sized in-line pairs of bubbles moving upwards were simulated. The bubble size varied between 2.0–10 mm. Breakthrough of the present study is the small initial distance of 2.5 R between the center of the bubbles. To provide a more practical nature in this study material properties were selected to match methane gas and seawater properties at deepsea conditions of 15 MPa and 4 ℃, thus yielding a fluid-to-bubble density ratio λ = 7.45 and viscosity ratio n = 100.46. This is one of the few studies to report results of the coalescence procedure in this context. The hydrodynamic behavior of the leading and trailing bubbles was thoroughly studied. Simulation results of the evolution of the rise velocity and the shape deformation with time indicate that the assumption that the leading bubble is rising as a free rising single one is not valid for bubbles between 2.0–7.0 mm. Finally, results of the volume of the daughter bubble exhibited an oscillating nature.

Near-infrared responsive shape memory hydrogels with programmable and complex shape-morphing

In this work,semi-crystalline nanocomposite hydrogels(i.e.,PAAmA_(11)A/GO gels)were synthesized by micellar copolymerization of acrylamide and N-acryloyl-11-aminoundecanoic acid(A_(11)A)in the presence of a large amount of sodium dodecyl sulfonate(SDS)micelles and GO nanosheets.The resulting hydrogels(SMHs)not only demonstrated high strength and high toughness,but also exhibited good shape memory property.Because of near-infrared(NIR)light absorbability of GO nanosheets,shape recovery and shape of PAAmA_(11)A/GO gels could be tuned by NIR irradiation.Moreover,bilayer hydrogels and trilayer hydrogels were also fabricated by the integration of shape-memorized PAAmA_(11)A/GO gel and elastic hydrophobic associated hydrogel(E-gel).Based on the NIR-responsive shape memory property and layered structure,shape deformation of bilayer hydrogels and trilayer hydrogels was rather different from the single PAAmA_(11)A/GO gel.Each kind of gel structure exhibited diverse and complex shapes via programmable NIR irradiation.More importantly,the shape morphing of NIR-SMHs-based hydrogels could mimic the hand and flower and be used as actuators.

Partial Shape Matching Without Point-Wise Correspondence

Partial similarity of shapes is a challenging problem arising in many important applications in computer vision,shape analysis,and graphics,e.g.when one has to deal with partial information and acquisition artifacts.The problem is especially hard when the underlying shapes are non-rigid and are given up to a deformation.Partial matching is usually approached by computing local descriptors on a pair of shapes and then establishing a point-wise non-bijective correspondence between the two,taking into account possibly different parts.In this paper,we introduce an alternative correspondence-less approach to matching fragments to an entire shape undergoing a non-rigid deformation.We use region-wise local descriptors and optimize over the integration domains on which the integral descriptors of the two parts match.The problem is regularized using the Mumford-Shah functional.We show an efficient discretization based on the Ambrosio-Tortorelli approximation generalized to triangular point clouds and meshes,and present experiments demonstrating the success of the proposed method.

Dual-responsive fiber-reinforced hydrogel actuators by direct ion patterning

Nature inspired deformable heterogeneous smart hydrogels have attracted much attention in many fields such as biomedicine devices and soft actuators.However,normal spatial heterogeneous hydrogel structures can only respond to single factor and take one action as set in fabrication.Herein,we report a pre-stretched metal-liganded shape memory hydrogel with fiber reinforced,P(AAc-co-AAm)/CCNFs-Fe3+(CCNFs:carboxylated cellulose nanofibers,AAc:acrylic acid,AAm:acrylamide),which can conduct shape deformation by solvent induction and ultraviolet(UV)light.The deformation pattern could be programmed by the deposing of ferroin ions.Also,the pre-stretched shape memory hydrogels could effectively produce cyclic actuation or complex shape actuation by UV light.More importantly,combining the solvent response with the light response enabled complex reversible actuations,such as simulating the bending and unfolding of fingers.The addition of CCNFs significantly enhanced the mechanical properties of the hydrogels.The hydrogels with 3 wt.%CCNFs showed an elongation at break of about 500%and a significant increase in tensile strength of 8.7-fold to 1.55 MPa after coordination with metal ions,which was able to meet the mechanical requirements of the bionic actuated hydrogels.This work demonstrated that combining light-programmed and light-responsive shape-memory hydrogels,complemented by another independent response property,could achieve complex and reversible programmed actuations.

Understanding the isoscaling relationship in the fissioning system with evaluated data

The isoscaling parameters aevai in the fissioning systems,i.e.,those extracted from the Evaluated Nuclear Data Library(ENDF/B-VIII.O)and the Joint Evaluated Fission and Fusion File(JEFF-3.3),show an obvious difference from simple statistic model prediction where only the symmetry energy plays the dominant role.To explain the aeVai as a function of the charge number of the fission fragment,a statistic scission point model is adopted.Our analysis shows that the effects of the shell correction,nuclear shape deformation,and intrinsic temperature of fission fragments are indispensable as well as the symmetry energy.Furthermore,an alternative method for extracting the intrinsic temperatures of fission fragments is proposed based on the isoscaling relationship in fission fragments.The intrinsic temperatures of the light fragments are higher than those of the heavy fragments.