Essential Mechanical Properties Research Articles

Comparative study on mechanical behavior of low temperature application materials for ships and offshore structures: Part I—Experimental investigations

Austenitic stainless steels (ASSs), aluminum alloys, and nickel alloys are potential candidate materials for cryogenic applications owing to their superior mechanical properties under low temperatures. In the liquefied natural gas (LNG) industry, these materials are widely used in the construction of thermal barriers for the insulation systems of storage tanks and LNG equipment. Among the typical material nonlinearities of ASSs, phase transformation induced plasticity (TRIP)-related nonlinear hardening characteristics have been experimentally and numerically reported in a number of detailed studies [1,2]; however, to the best of our knowledge, quantitative studies on aluminum and nickel alloys are not available for reference. Moreover, although these materials are used under various temperatures and strain rates, their temperature- and strain rate-dependent properties have not been determined thus far. In this study, a series of tensile tests is carried out under various temperatures (110–293 K) and strain rate (0.00016–0.01 s −1) ranges as a preliminary step in the overall process for understanding the material characteristics of ASSs, aluminum alloys, and nickel alloys. On the basis of the experimental results, the essential mechanical properties are summarized in a quantitative manner in terms of the temperature and strain rate. The strain-hardening rate and strain sensitivity, which can be used to describe cryogenic temperature dependent material nonlinearities, are also proposed for the selected materials.

Preparation SnO2 Nanolayer on Flexible Polyimide Substrates via Direct Ion-Exchange and in situ Oxidation Process

Tin oxide (SnO(2)) nanolayers were formed on flexible polyimide (PI) substrate via direct ion-exchange and in situ oxidation process utilizing pyromellitic dianhydride/4,4'-oxidianiline-based poly(amic acid) films as polyimide precursor. During an ion-exchange process, stannous ions were doped into the precursor by immersion in ethanolic solution of stannous chloride. Subsequent thermal treatment of the tin(II)-containing precursor at a constant heating rate not only imidized poly(amic acid) to PI but also converted stannous ions into SnO(2) clusters, which diffused and aggregated onto the surface of polymer matrix, forming continuous tin oxide layers. Inductively coupled plasma (ICP) was used to investigate the ion-exchange process. Changes in chemical structure of the poly(amic acid) film and the crystal structure of tin oxides were analyzed by attenuated total reflection-Fourier transform infrared (ATR-FTIR) and X-ray diffraction (XRD). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the microstructure of the PI/SnO(2) nanocomposite films. The nanocomposite film maintained essential mechanical property and thermal stability of pristine PI films.

A Structurally Flexible Protein Backbone for the MARTINI Coarse Grained Force Field

By reducing the level of description of a system as compared to atomistic models coarse grained (CG) molecular force fields allow simulating larger systems for longer time scales, thereby probing exciting properties of biological systems. It is our constant effort to improve their accuracy and range of applicability. The MARTINI CG model defines a library of beads or super-atoms corresponding to chemical entities (defined by 3-6 non-H atoms) for which the interaction strengths are parameterized against thermodynamic (partitioning free energies) and structural data extracted from experiments and simulations. Virtually any molecular topology can be built from a combination of beads that reproduces structural and thermodynamic available data for that particular molecule. Molecular topologies are available for a large variety of molecules including lipids, amino acids and proteins, and sugars. Here we present a refined version of the MARTINI force field for proteins in which restraining the secondary structure is not required anymore. This is achieved by restoring directionality in the backbone interactions. To do so a dipole (two net charges kept at a fix distance) is placed on the peptide bond of the backbone. We show that this simple representation coupled with a rigorous parameterization of the dipole and related bonded/non-bonded interactions is able to capture some essential mechanical and physicochemical properties of the polypeptide backbone. In particular the backbone may access both extended (β-sheet) and compact (α-helix) conformations using a single potential. A few simple test cases are shown to illustrate the structural flexibility of the new backbone and its ability to stabilize secondary structure elements in proteins. The potential is tested with both regular and polarizable MARTINI water models.

Non-Linear Elasticity of Skeletal Myosins is Essential for Collective Force Generation in Muscle

Muscle contraction occurs through the rotation of the myosin heads pulling actin filaments past myosin filaments. In order to achieve contractions efficiently, it is crucial for myosins to generate force collectively and to minimize the interference between motors. In the previous studies, it was suggested that the elasticity of myosin is linear so that myosins generate the large drag force opposing to muscle contraction if negatively strained. However, none of the previous studies has investigated the elasticity of single myosin explicitly in the negative strain region. Therefore, we investigated the elasticity of single skeletal myosins in both the positive and negative strain directions. In the absence of ATP, single myosins embedded in synthetic myosin-rod filaments were tightly bound to actin filaments and were stretched and shortened repeatedly by oscillating the two trapped beads on the both ends of acting filament manipulated by optical tweezers. The elasticity of myosins was characterized by obtaining the force-displacement curves, where forces on myosin heads were estimated by measuring the displacement of two beads, and displacements of myosin heads were obtained by tracking the position of quantum dots attached to the actin filament. We found that the elasticity is non-linear, in which stiffness is high (∼2.8 pN/nm) and low (∼0.02 pN/nm) in the positive and negative strain regions. The non-linear elasticity ensures high force generation with a small stretching of the elastic portion, and minimizing the drag force of negatively-strained myosins. Furthermore, the estimates of the actin sliding distance by the non-linear elasticity model were more consistent with experimental results observed in 20μM ATP than those by the linear elasticity model. Therefore, the non-linear elasticity might be an essential mechanical property of single myosin designed for the collective force generation in muscle.

Processing, Microstructure and Mechanical Properties of Air Plasma‐Sprayed Ceria–Yttria Co‐stabilized Zirconia Coatings

Abstract: Thermal barrier coatings (TBCs) are widely adopted to protect mechanical components in gas turbine engines operating at high temperature. Basically, the surface temperature of these components must be low enough to retain material properties within acceptable bounds and to extend component life. From this standpoint, air plasma‐sprayed (APS) ceria and yttria co‐stabilized zirconia (CYSZ) is particularly promising because it provides enhanced thermal insulation capabilities and resistance to hot corrosion. However, essential mechanical properties, such as hardness and Young’s modulus, have been less thoroughly investigated. Knowledge of Young’s modulus is of concern because it has a significant effect on strain tolerance and stress level and, hence, on durability. The focus of the present study was to determine the mechanical properties of APS CYSZ coatings. In particular, X‐ray diffraction (XRD) is adopted for phase analysis of powders and as‐sprayed coatings. In addition, scanning electron microscopy (SEM) and image analysis (IA) are employed to explore coating microstructure and porosity. Finally, the Young’s modulus of the coating is determined using nanoindentation and a resonant method. The results obtained are then discussed and a cross‐check on their consistency is carried out by resorting to a micromechanical model.

Young's Modulus of Thermal Barrier Coating and Oxidation Resistant Coating Bonded to Stainless Substrate by Four-Point Bending

Young's modulus of thermal barrier coating (TBC) is one of the most essential mechanical properties on the designing of high performance TBC system. This paper describes one of the round-robin test results of New Energy and Industrial Technology Development Organization's (NEDO's) project titled “the survey-research of standardization on testing methods for thermo-mechanical performance of ceramic thermal barrier coatings”, for the fiscal years of 2006 and 2007. The bending method of the coating bonded to substrate is straightforward in preparing the specimen and loading to the specimen. Previous study has offered recommended testing methods and proper geometries of the specimens for the Young's modulus of thermal barrier coating and the bond coating. This paper confirmed that the recommended method and the geometry of the specimen provided the reasonable estimation as far as the other type of substrate material. It was also confirmed that the ratio of coating thickness to substrate thickness should be high and the threshold ratio was independent of the substrate material.

A low-dimensional model for the red blood cell

The red blood cell (RBC) is an important determinant of the rheological properties of blood because of its predominant number density, special mechanical properties and dynamics. Here, we develop a new low-dimensional RBC model based on dissipative particle dynamics (DPD). The model is constructed as a closed-torus-like ring of 10 colloidal particles connected by wormlike chain springs combined with bending resistance. Each colloidal particle is represented by a single DPD particle with a repulsive core. The model is able to capture the essential mechanical properties of RBCs, and allows for economical exploration of the rheology of RBC suspensions. Specifically, we find that the linear and non-linear elastic deformations of healthy and malaria-infected cells match those obtained in optical tweezers experiments. Through simulations of some key features of blood flow in vessels, i.e., the cell-free layer (CFL), the Fahraeus effect and the Fahraeus-Lindqvist effect, we verify that the new model captures the essential shear flow properties of real blood, except for capillaries of sizes comparable to the cell diameter. Finally, we investigate the influence of a geometrical constriction in the flow on the enhancement of the downstream CFL. Our results are in agreement with recent experiments.

Formation and characterization of cobalt oxide layers on polyimide films via surface modification and ion-exchange technique

Polyimide (PI) films with thin cobalt oxide (Co 3O 4) layers on both film sides have been prepared via a surface modification and ion-exchange technique. The method works by hydrolyzing the PI film surfaces in aqueous potassium hydroxide solution and incorporating Co 2+ into the hydrolyzed layers of PI film via subsequent ion exchange, and followed by thermal treatment in ambient atmosphere. The PI composite films were characterized by Attenuated total reflection-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffractions, scanning electron microscopy, transmission electron microscopy and thermogravimetric analyses, as well as surface resistance and mechanical measurements. By varying the absorbed cobalt ion content, a series of PI/Co 3O 4 composite films with insulative to semiconductive surfaces were obtained. The room temperature surface resistances of the semiconductive composite films reached to about 10 7 Ω. The Co 3O 4 particle formed on PI film surfaces was in the range of 10–40 nm. The final composite films maintained the essential mechanical properties and thermal stability of the pristine PI films. The adhesion between surface Co 3O 4 layers and PI matrix was acceptable.

Hypoplastic modelling of moisture-sensitive weathered rockfill materials

For broken rock materials under stress the process of weathering and consequently the degradation of the solid hardness may be accelerated under water. Thus, the resistance of particles against abrasion and breakage can be strongly influenced by a change of the moisture content of the grains. The focus of this paper is on modelling the essential mechanical properties of moisture-sensitive weathered coarse-grained rockfill materials using a hypoplastic constitutive model. The model takes into account the current void ratio, the effective stress, the strain rate and a moisture-dependent degradation of the solid hardness. Creep and stress relaxation during the process of degradation of the solid hardness are also included. It is shown that the results obtained from numerical simulations are in good agreement with experiments carried out with weathered granite.

Strength Testing and Analysis of Fatigue Crack Growth in Selected Aircraft Materials

Strength Testing and Analysis of Fatigue Crack Growth in Selected Aircraft MaterialsThe study has been intended to determine the most essential mechanical and fatigue properties as well as impact strength of the 30HGSNA steel, to gain own data on the above-mentioned characteristics of materials to be used further on in numerical analyses of life estimates of aeronautical structural components. The scope of the study comprised the following assignments:- determination of the most fundamental mechanical properties and impact strength of materials- low-cycle fatigue testing and evaluation of the Manson-Coffin curves- high-cycle fatigue testing and evaluation of the Wöhler curves- investigation into fatigue crack growth rates at constant and variable load-cycle amplitudes (determination of curves da/dN = f(ΔK, R), coefficients in Paris and NASGRO equations, coefficients in the Wheeler models of delay, the value of Kth(R))- crack toughness testing under the plane-state-of-strain conditions at room temperature (determination of the KIc(R)).The strength/fatigue testing was carried out in the Laboratory for Materials Strength Testing of the AFIT's Division for Aeronautical Systems Reliability and Safety, the lab being accredited by the Polish Centre for Accreditation (Accreditation Certificate No.: AB 430).

Fabrication of Highly Reflective and Conductive Double-Surface-Silvered Layers Embedded on Polymeric Films through All-Wet Process at Room Temperature

An easy technique is developed to fabricate highly conductive and reflective double-surface-silvered polyimide films at room temperature by the incorporation of silver ions in surface-modified polyimide, and subsequently by the in situ reduction of silver ions in alkaline containing aqueous glucose solution. Surface properties of the silvered composite films were investigated as a function of treatment time and reducing environment, respectively. Sheet reflectivity and conductivity can be controlled by adjusting the potassium hydroxide (KOH) etching and reducing conditions. The excellent silver-polymer adhesive property is based on a "tree roots" like micro/nanostructure of the silver layers. The essential mechanical properties of the silvered films were maintained as their inside matrix is intact during the whole procedure. Different properties between one film's double-side surfaces were investigated during the fabricating process. Films were characterized by inductively coupled plasma (ICP), X-ray diffraction (XRD), contact angle (CA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), four point probe instrument, and ultraviolet (UV) spectrophotometer.

Single-Stage Synthesis and Characterization of Reflective and Conductive Silver−Polyimide Films Prepared from Silver(I) Complexes with ODPA/4,4′-ODA

Reflective and surface conductive polyimide films were prepared by the incorporation of silver(I) acetate and trifluoroacetylacetone into a dimethylacetamide solution of the poly(amic acid) formed 3,3',4,4'-oxidiphthalic dianhydride (ODPA) and 4,4'-oxidianiline (4,4'-ODA). Thermal curing of (trifluoroacetylacetonato)silver(I)-poly(amic acid) films led to cycloimidization with concomitant silver(I) reduction, which yielded a reflective and conductive silver surface at selected silver concentrations if the film was cured to a final temperature of 300 degrees C for several hours. The metallized ODPA/4,4'-ODA films retain the essential mechanical properties of an undoped film and have good thermal stability, particularly under a nitrogen atmosphere. The bulk of the composite film was not electrically conductive. The use of (hexafluoroacetylacetonato)silver(I) and silver(I) tetrafluoroborate as sources of silver(I) with ODPA/4,4'-ODA yielded modestly reflective films that never developed conductivity. The silvered films prepared with (trifluoroacetylacetonato)silver(I) can be patterned using mask-etch techniques. Comparisons are made among four similar silver-polyimide systems, with the polyimides being ODPA/4,4'-ODA, BTDA/4,4'-ODA, BPDA/4,4'-ODA, and 6FDA/4-BDAF.

Numerical investigations of the interface behaviour between granular soil and a geogrid reinforcement

In this paper the interface behaviour between a cohesionless granular soil and a rigid geogrid reinforcement under shearing is numerically investigated using a continuum approach. Particular attention is paid to the influence of grain size, initial density, vertical pressure and fluctuations of the rotation resistance of soil particles interlocked within the geogrid cells. To model the essential mechanical properties of granular soil a micro-polar hypoplastic description is used which takes into account stress and couple stress, pressure dependent limit void ratios and the mean grain size as the characteristic length. The results obtained from the 2D-finite element calculations show that the interaction of the reinforcement with the soil material has a strong influence on the deformation of the soil around the reinforcement.

Influence of initial density of cohesionless soil on evolution of passive earth pressure

This paper focuses on the influence of the initial void ratio on the evolution of the passive earth pressure and the formation of shear zones in a dry sand body behind a retaining wall. For the numerical simulation a rigid and very rough retaining wall undergoing a horizontal translation against the backfill is considered. The essential mechanical properties of cohesionless granular soil are described with a micro-polar hypoplastic model which takes into account stresses and couple stresses, pressure dependent limit void ratios and the mean grain size as a characteristic length. Numerical investigations are carried out with an initially medium dense and initially loose sand using a homogeneous and random distribution of the initial void ratio. The geometry of calculated shear zones is discussed and compared with a corresponding laboratory model test.

The Slow Skeletal Muscle Isoform of Myosin Shows Kinetic Features Common to Smooth and Non-muscle Myosins

Fast and slow mammalian muscle myosins differ in the heavy chain sequences (MHC-2, MHC-1) and muscles expressing the two isoforms contract at markedly different velocities. One role of slow skeletal muscles is to maintain posture with low ATP turnover, and MHC-1 expressed in these muscles is identical to heavy chain of the beta-myosin of cardiac muscle. Few studies have addressed the biochemical kinetic properties of the slow MHC-1 isoform. We report here a detailed analysis of the MHC-1 isoform of the rabbit compared with MHC-2 and focus on the mechanism of ADP release. We show that MHC-1, like some non-muscle myosins, shows a biphasic dissociation of actin-myosin by ATP. Most of the actin-myosin dissociates at up to approximately 1000 s(-1), a very similar rate constant to MHC-2, but 10-15% of the complex must go through a slow isomerization (approximately 20 s(-1)) before ATP can dissociate it. Similar slow isomerizations were seen in the displacement of ADP from actin-myosin.ADP and provide evidence of three closely related actin-myosin.ADP complexes, a complex in rapid equilibrium with free ADP, a complex from which ADP is released at the rate required to define the maximum shortening velocity of slow muscle fibers (approximately 20 s(-1)), and a third complex that releases ADP too slowly (approximately 6 s(-1)) to be on the main ATPase pathway. The role of these actin-myosin.ADP complexes in the mechanochemistry of slow muscle contraction is discussed in relation to the load dependence of ADP release.

High Harmonic Generation and Molecular Orbital Tomography in Multielectron Systems: Beyond the Single Active Electron Approximation

It was recently shown that the highest molecular orbital of N2 could be reconstructed from a series of high harmonic measurements. Existing theories of high harmonic generation and orbital tomographic imaging are based on the single active electron approximation that ignores essential quantum mechanical properties such as the indistinguishability of identical particles and the Pauli exclusion principle. We show that, when fully antisymmetrized multielectron wave functions and electronic relaxation in the cation are considered, molecular orbital tomography records the image of the Dyson orbital plus exchange contributions from inner shells. The mixing of contributions from more than one molecular orbital gives access to additional wave function information. By utilizing the exchange term, harmonic emission from a closed-shell 4-electron system can be interpreted as a complete Hartree-Fock wave function.

Prestressed F-actin networks cross-linked by hinged filamins replicate mechanical properties of cells

We show that actin filaments, shortened to physiological lengths by gelsolin and cross-linked with recombinant human filamins (FLNs), exhibit dynamic elastic properties similar to those reported for live cells. To achieve elasticity values of comparable magnitude to those of cells, the in vitro network must be subjected to external prestress, which directly controls network elasticity. A molecular requirement for the strain-related behavior at physiological conditions is a flexible hinge found in FLNa and some FLNb molecules. Basic physical properties of the in vitro filamin-F-actin network replicate the essential mechanical properties of living cells. This physical behavior could accommodate passive deformation and internal organelle trafficking at low strains yet resist externally or internally generated high shear forces.

Preparation of highly reflective and conductive metallized polyimide films through surface modification: processing, morphology and properties

Silvered polyimide films have been prepared by potassium hydroxide hydroxylation of polyimide film surfaces and incorporation of silver ions through subsequent ion exchange. Thermal curing not only recycloimidized the poly(amic acid) into polyimide, but also reduced silver ions into silver atoms and near-atomic silver clusters, which diffused and aggregated to give reflective and conductive surfaces without need of the addition of reducing agents. Films were characterized by X-ray photoelectron spectrometer, transmission electron microscopy, scanning electron microscopy and tapping mode atomic force microscopy. The thickness of the silvered layers and the reflectivity and conductivity of the silvered films can be controlled. By this method, the double-sided silvered polyimide films with excellent reflective (reflectivity > 97%) and conductive surfaces (surface resistivity = 0.02 Ω cm−2) could be easily fabricated. Their essential mechanical properties could be maintained, and the silver–polymer adhesion was outstanding.

4005 引張・ねじり繰返し応力下におけるA2024材のクリープ変形挙動(S25-1 非弾性変形,S25 材料・構造の非弾性挙動・高温強度・損傷評価)

The machine components used at elevated temperatures are commonly subjected to cyclic stresses in addition to static stress. This problem is in the medium state between fatigue and static creep, being one of the essential mechanical properties needed for design of high temperature machine components. In the present study, fatigue-creep interaction tests were performed for A2024 under stress rate-controlled triangular tensile-torsional stress wave at elevated temperature. Then the creep constitutive equation under multi-axial cyclic stresses is proposed on the basis of the formula of extended Norton-Bailey, and creep deformation behavior was numerically analyzed in comparison with the test results. It was found that these calculations slightly underestimated measured creep curves.

Preparation of surface conductive and highly reflective silvered polyimide films by surface modification and in situ self-metallization technique

Double surface conductive and reflective flexible silvered polyimide films have been prepared by alkali hydroxylation of polyimide film surface and incorporation of silver ions through subsequent ion exchange. Thermal curing of silver(I) polyamate precursor leads to re-cycloimidization of modified surface with concomitant silver reduction, yielding a reflective and conductive silver surface approaching that of native metal. The reflective and conductive surface evolves only when the cure temperature rises to 300 °C. The metallized films usually retain the essential mechanical properties of the parent films. Films were characterized by transmission electron microscopy (TEM), scanning electron microscopy and tapping mode atomic force microscopy (AFM). AFM demonstrates that the diameter of close-packed silver particles of the silver layers was about 50–150 nm. TEM shows that thickness of silver layer on the polyimide film surface is about 400–600 nm.