Quasicontinuum Simulation of the Effect of Lotus-Type Nanocavity on the Onset Plasticity of Single Crystal Al during Nanoindentation

Stress concentration around nanosized defects such as cavities always leads to plastic deformation and failure of solids. We investigate the effects of depth, size, and shape of a lotus-type nanocavity on onset plasticity of single crystal Al during nanoindentation on a (001) surface using a quasicontinuum method. The results show that the presence of a nanocavity can greatly affect the contact stiffness (Sc) and yield stress (σy) of the matrix during nanoindentation. For a circular cavity, the Sc and σy gradually increase with the cavity depth. A critical depth can be identified, over which the Sc and σy are insensitive to the cavity depth and it is firstly observed that the nucleated dislocations extend into the matrix and form a y-shaped structure. Moreover, the critical depth varies approximately linearly with the indenter size, regarding the same cavity. The Sc almost linearly decreases with the cavity diameter, while the σy is slightly affected. For an ellipsoidal cavity, the Sc and σy increase with the aspect ratio (AR), while they are less affected when the AR is over 1. Our results shed light in the mechanical behavior of metals with cavities and could also be helpful in designing porous materials and structures.

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Reactive Balance Control for Legged Robots under Visco-Elastic Contacts

Applied Sciences ◽

10.3390/app11010353 ◽

2020 ◽

Vol 11 (1) ◽

pp. 353

Author(s):

Thomas Flayols ◽

Andrea Del Prete ◽

Majid Khadiv ◽

Nicolas Mansard ◽

Ludovic Righetti

Keyword(s):

Inverse Dynamics ◽

State Of The Art ◽

Balance Control ◽

Contact Stiffness ◽

Poor Performance ◽

Admittance Control ◽

Inverse Dynamics Control ◽

Rigid Contact ◽

Reactive Balance ◽

Shed Light

Contacts between robots and environment are often assumed to be rigid for control purposes. This assumption can lead to poor performance when contacts are soft and/or underdamped. However, the problem of balancing on soft contacts has not received much attention in the literature. This paper presents two novel approaches to control a legged robot balancing on visco-elastic contacts, and compares them to other two state-of-the-art methods. Our simulation results show that performance heavily depends on the contact stiffness and the noises/uncertainties introduced in the simulation. Briefly, the two novel controllers performed best for soft/medium contacts, whereas “inverse-dynamics control under rigid-contact assumptions” was the best one for stiff contacts. Admittance control was instead the most robust, but suffered in terms of performance. These results shed light on this challenging problem, while pointing out interesting directions for future investigation.

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Effects of microstructure and lattice misfit on creep life of Ni-based single crystal superalloy during long-term thermal exposure

International Journal of Materials Research (formerly Zeitschrift fuer Metallkunde) ◽

10.1515/ijmr-2020-7774 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Wenyan Gan ◽

Hangshan Gao ◽

Haiqing Pei ◽

Zhixun Wen

Keyword(s):

Single Crystal ◽

Rupture Life ◽

Precipitation Amount ◽

Lattice Misfit ◽

Thermal Exposure ◽

Phase Evolution ◽

Creep Rupture ◽

Simultaneous Increase ◽

Creep Life ◽

The Matrix

Abstract According to the microstructural evolution during longterm thermal exposure at 1100 °C, the creep rupture life of Ni-based single crystal superalloys at 980 °C/270 MPa was evaluated. The microstructure was characterized by means of scanning electron microscopy, X-ray diffraction and related image processing methods. The size of γ’ precipitates and the precipitation amount of topologically close-packed increased with the increase in thermal exposure time, and coarsening of the γ’ precipitates led to the simultaneous increase of the matrix channel width. The relationship between the creep rupture life and the lattice misfit of γ/γ’, the coarsening of γ’ precipitate and the precipitation of TCP phase are systematically discussed. In addition, according to the correlation between γ’ phase evolution and creep characteristics during thermal exposure, a physical model is established to predict the remaining creep life.

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Sound absorption performance of flexible polyurethane/silicon dioxide perforated coating composites

Textile Research Journal ◽

10.1177/00405175211015516 ◽

2021 ◽

pp. 004051752110155

Author(s):

Min Peng ◽

Xiaoming Zhao ◽

Weibin Li

Keyword(s):

Silicon Dioxide ◽

Sound Absorption ◽

Woven Fabric ◽

Perforation Rate ◽

Cavity Depth ◽

Resonant Frequencies ◽

The Matrix ◽

Absorption Performance ◽

Traditional Sense ◽

Flexible Polyurethane

Perforated materials in the traditional sense are rigid, usually dense, costly and inflexible. For this study, polyester/cotton blended woven fabric as the base fabric, nano-SiO2 (silicon dioxide) as the functional particles and PU (polyurethane) as the matrix were selected. Accordingly, flexible PU/SiO2 perforated coating composites with different process parameters were developed. The inﬂuence of the nano-SiO2 content, perforation diameter, perforation rate, number of fiber felt layers and cavity depth on the sound absorption coefficient were investigated. The resonant frequencies of materials with different cavity depths were evaluated by both theoretical calculation and experimental method. It was found that the flexible perforated composite has good sound absorption and mechanical properties, and has great potential for applications requiring soft and lightweight sound absorption materials.

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Growth of single crystals in the (Na1/2Bi1/2)TiO3–(Sr1–xCax)TiO3 system by solid state crystal growth

Journal of Advanced Ceramics ◽

10.1007/s40145-021-0481-2 ◽

2021 ◽

Author(s):

Phan Gia Le ◽

Huyen Tran Tran ◽

Jong-Sook Lee ◽

John G. Fisher ◽

Hwang-Pill Kim ◽

...

Keyword(s):

Crystal Growth ◽

Solid State ◽

Single Crystal ◽

Single Crystals ◽

Piezoelectric Properties ◽

Single Crystal Growth ◽

Crystal Growth Rate ◽

Large Strains ◽

Growth Technique ◽

The Matrix

AbstractCeramics based on (Na1/2B1/2)TiO3 are promising candidates for actuator applications because of large strains generated by an electric field-induced phase transition. For example, the (1−x)(Na1/2Bi1/2)TiO3-xSrTiO3 system exhibits a morphotropic phase boundary at x = 0.2–0.3, leading to high values of inverse piezoelectric constant d*33, which can be further improved by the use of single crystals. In our previous work, single crystals of (Na1/2B1/2)TiO3-SrTiO3 and (Na1/2B1/2)TiO3-CaTiO3 were grown by the solid state crystal growth technique. Growth in the (Na1/2B1/2)TiO3-SrTiO3 system was sluggish whereas the (Na1/2B1/2)TiO3-CaTiO3 single crystals grew well. In the present work, 0.8(Na1/2Bi1/2)TiO3-0.2(Sr1−xCax)TiO3 single crystals (with x = 0.0, 0.1, 0.2, 0.3, 0.4) were produced by the solid state crystal growth technique in an attempt to improve crystal growth rate. The dependence of mean matrix grain size, single crystal growth distance, and electrical properties on the Ca concentration was investigated in detail. These investigations indicated that at x = 0.3 the matrix grain growth was suppressed and the driving force for single crystal growth was enhanced. Replacing Sr with Ca increased the shoulder temperature Ts and temperature of maximum relative permittivity Tmax, causing a decrease in inverse piezoelectric properties and a change from normal to incipient ferroelectric behavior.

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Influences of the γ′ Phase on the Mechanical Properties of a Nickel-Based Single Crystal Superalloy

Materials Science Forum ◽

10.4028/www.scientific.net/msf.1023.45 ◽

2021 ◽

Vol 1023 ◽

pp. 45-52

Author(s):

Xiao Yan Wang ◽

Meng Li ◽

Zhi Xun Wen

Keyword(s):

Mechanical Properties ◽

Solid Solution ◽

Single Crystal ◽

Tensile Properties ◽

Room Temperature ◽

Solution Treatment ◽

Single Crystal Superalloy ◽

Original Material ◽

Solid Solution Treatment ◽

The Matrix

After solid solution treatment at 1335°C for 4 hours and cooling to room temperature at different rate, the nickel-based single crystal superalloy were made into three kinds of nickel-based single crystal superalloy materials containing different size γ′ phases, respectively. The tensile test of I-shaped specimens was carried out at 980°C, and their effect of γ′ phase microstructure on the tensile properties was studied. The results show that the yielding strength of the material air-cooled to room temperature was lower than that with cooling rate at 0.15°C/s, but both of them were lower than the yielding strength of original material. Little difference was found on the elastic modulus of I-shaped specimens made of three kinds of materials. When the cubic degree of the γ′ phase is higher and the size is larger, the tensile properties of the material is better, which can be attributed to the larger size and narrower channel of the matrix phase that lead to higher dislocation resistance.

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A least-squares method for the determination of the orientation matrix in single-crystal diffractometry

Acta Crystallographica Section A ◽

10.1107/s0567739470000712 ◽

1970 ◽

Vol 26 (2) ◽

pp. 295-296 ◽

Cited By ~ 5

Author(s):

K. Tichý

Keyword(s):

Single Crystal ◽

Least Squares ◽

Least Squares Method ◽

Reciprocal Vector ◽

Orientation Matrix ◽

The Matrix

An appropriate choice of the function minimized permits linearization of the least-squares determination of the matrix which transforms the diffraction indices into the components of the reciprocal vector in the diffractometer φ-axis system of coordinates. The coefficients of the least-squares equations are based on diffraction indices and measured diffractometer angles of three or more non-coplanar setting reflexions.

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Microstructure Evolution of a Single Crystal Superalloy after Tensile Fracture at Different Temperature

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.721.262 ◽

2013 ◽

Vol 721 ◽

pp. 262-265

Author(s):

Zhen Xue Shi ◽

Shi Zhong Liu ◽

J. Yu ◽

M. Han ◽

J.R. Li

Keyword(s):

Single Crystal ◽

Microstructure Evolution ◽

Stacking Faults ◽

Single Crystal Superalloy ◽

Tensile Fracture ◽

Matrix Channel ◽

Stress Orientation ◽

Transmission Electron ◽

Strength Behavior ◽

The Matrix

The tensile property tests of DD6 single crystal superalloy were performed at 25°C, 760°C and 980°C in air. Detailed microstructure evolution was carried out on the alloy to illuminate the γ phase and dislocation structure after tensile fracture by scanning electron microscope and transmission electron microscopy. The results show that the alloy has the maximum tensile strength and the minimum plasticity at 760°C. DD6 alloy has the same anomalous yield strength behavior with other single crystal superalloys. The γ phase hasve a little extension in the stress orientation after tensile fracture at 25°C. The γ phase morphology still maintains cubic after tensile fracture at 760°C. The γ phase is no longer cubic and changes into rectangular solid in the specimen tensile ruptured at 980°C. The vertical γ matrix becomes thinner and horizontal γ matrix becomes thicker slightly. The γ phase is no longer cubic and changes into rectangular solid. High density dislocations are present in the matrix channels and a lot of superlattice stacking faults are seen within γ phases in the sample tested at 25°C. A large quantities of superlattice stacking faults within γ phase and a lot of dislocations tangling in matrix channel are all present in the sample tested at 760°C. The dislocation networks have homogeneously formed at γ/γ interface in the sample tested at 980°C.

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Modeling and Experiment of the Critical Depth of Cut at the Ductile–Brittle Transition for a 4H-SiC Single Crystal

Micromachines ◽

10.3390/mi10060382 ◽

2019 ◽

Vol 10 (6) ◽

pp. 382 ◽

Cited By ~ 4

Author(s):

Peng Chai ◽

Shujuan Li ◽

Yan Li

Keyword(s):

Single Crystal ◽

Lateral Displacement ◽

Tangential Force ◽

Test System ◽

Depth Of Cut ◽

Critical Depth ◽

Berkovich Indenter ◽

Nose Radius ◽

Brittle Transition ◽

Critical Depth Of Cut

In this paper, a theoretical model of the critical depth of cut of nanoscratching on a 4H-SiC single crystal with a Berkovich indenter is proposed, and a series of scratch tests in a nanomechanical test system was performed. Through nanoindentation experimentation on fused quartz, the Berkovich indenter nose radius was indirectly confirmed using least squares. The range of critical depths of cut at the ductile–brittle transition was obtained by SEM observation, and the size of cracks was amplified with increasing scratching depth. The theoretical result of the critical depth of cut at the ductile–brittle transition for a 4H-SiC single crystal is 91.7 nm, which is close to the first obvious pop-in point of the relation curve between tangential force and lateral displacement. Repeated experimental results show good consistency and good agreement with other references.

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Phase Transformations in the Fe-Al System Studied by “In-Situ” Tem Heating

MRS Proceedings ◽

10.1557/proc-364-219 ◽

1994 ◽

Vol 364 ◽

Cited By ~ 2

Author(s):

A. Korner

Keyword(s):

Transition Temperature ◽

Single Crystal ◽

Domain Structure ◽

Type A ◽

Bimodal Distribution ◽

Dislocation Motion ◽

In Situ Tem ◽

Transmission Electron ◽

The Matrix

AbstractThe domain structure and the evolution of antiphase boundaries (APBs) have been investigated in Fe-Al by means of “in-situ” transmission electron microscopy (TEM) heating experiments. Single crystals with composition Fe22.1at%Al and Fe25.6at%Al have been used.The grown-in structure of the Fe22.1at%al single crystal is composed of DO3 ordered particles embedded in the disorderd ±-matrix. A bimodal distribution of the particles was found. Small ordered particles are in between the large precipitates which are surrounded by particle-free zones. Numerous of this large ordered precipitates contain APBs. Crossing the transition temperature to the disordered phase, the small particles dissolve into the ±-matrix and the large particles start to shrink by dissolving.The single crystal with composition Fe25.6at%Al was found to be completely DO3 ordered. The grown-in domains are separated by APBs of type a′0/2〈100〉. At temperatures far below the transition temperature to the B2 phase no significant change in the APB and domain structure has been detected. In contrast, a remarkable evolution in the APB structure has been observed approaching the transition temperature. Coarsening of the domains has been found. Furthermore, APBs of B2-type (a′0/4〈lll〉 shear) are dragged out by dislocation motion. B2- and DC3-type APBs react and junctions are formed. With increasing annealing time, the density of B2-type boundaries increases. The TEM image is dominated by B2-type boundaries linked by the D03-type boundaries. The DO3 superlattice spots are clearly excited approaching the transition temperature to B2. Above the transition temperature, the DO3 spots disappear completely and the diffraction pattern reveals B2 long range order.

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Enhanced erosion resistance of biopolymer-enriched B. subtilis NCIB 3610 biofilms

10.5194/biofilms9-56 ◽

2020 ◽

Author(s):

Elif Nur Hayta ◽

Oliver Lieleg

Keyword(s):

Erosion Resistance ◽

Biotechnological Applications ◽

Shear Forces ◽

Cavity Depth ◽

Biofilm Growth ◽

Promising Strategy ◽

The Matrix ◽

Rose Petal ◽

Surface Superhydrophobicity ◽

High Erosion Resistance

Erosion resistance is one of the advantages bacteria gain by producing biofilms. While it is undesirable for us humans when biofilms grow on medical devices or industrial pipelines, biofilms with a high erosion resistance can be advantageous for biotechnological applications. Here, we demonstrate how the erosion resistance of B. subtilis NCIB 3610 biofilms can be enhanced by integrating foreign (bio)polymers such as &#947;-polyglutamate (PGA), alginate and polyethylene glycol (PEG) into the matrix during biofilm growth. Artificial enrichment of the NCIB 3610 biofilms with these biopolymers causes a significant increase in the erosion resistance by slightly changing the surface topography: A decreased cavity depth on the surface results in an alteration in the mode of surface superhydrophobicity, and we obtain a state that is located somewhere between rose-petal like and lotus-like wetting resistance. Surprisingly, the viscoelastic and microscopic penetration properties of the biofilms are not affected by the artificial incorporation of (bio)polymers. As we obtained similar results with all the biopolymers tested (which differ in terms of charge and molecular weight), this indicates that a variety of different (bio)polymers can be employed for a similar purpose. The method introduced here may present a promising strategy for engineering beneficial biofilms such, that they become more stable towards shear forces caused by flowing water but, at the same time, remain permeable to nutrients or other molecules.

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