Elastic Defect Research Articles

Elastic strain-induced amorphization in high-entropy alloys

Elastic stability is the basis for understanding structural responses to external stimuli in crystalline solids, including melting, incipient plasticity and fracture. In this work, elastic stability is investigated in a series of high-entropy alloys (HEAs) using in situ mechanical tests and atomic-resolution characterization in transmission electron microscopy. Under tensile loading, the HEA lattices are observed to undergo a sudden loss of ordering as the elastic strain reached ∽ 10%. Such elastic strain-induced amorphization stands in intrinsic contrast to previously reported dislocation-mediated elastic instability and defect accumulation-mediated amorphization, introducing a form of elastic instability. Together with the first principle calculations and atomic-resolution chemical mapping, we identify that the elastic strain-induced amorphization is closely related to the depressed dislocation nucleation due to the local atomic environment inhomogeneity of HEAs. Our findings provide insights for the understanding of the fundamental nature of physical mechanical phenomena like elastic instability and incipient plasticity.

Bandgap and its defect band analysis of flexoelectric effect in phononic crystal plates

The wave equations of a novel model for the electro-elastic Kirchhoff plate containing the flexoelectric effect are constructed using a variational formulation. Through an Improved Plane Wave Expansion (IPWE) approach, the proposed wave equations are then applied to examine the elastic wave bandgap and defect band in a phononic crystal plate structure without or with a defect. The results demonstrate that the flexoelectric effect on the bandgap is apparent when the structure is at the submicron scale and fades as the scale increases. Moreover, at all length scales, the magnitude of the bandgap varies dramatically with lattice length and inclusion volume ratio. This suggests that the frequency and broadness of the bandgap can be tuned by modifying the volume percentage of inclusion, plate size parameters and lattice length. The dispersion curves of the defect model and corresponding mode shape at the defect band are also studied, which can indicate the applicability of the current model incorporating flexoelectric effect in energy harvesting and wave focusing. The novel model and these findings would help the design of MEMS/NEMS devices for enhanced wave guiding when flexoelectric-based electro-elastic fields are involved.

(Digital Presentation) Internal Friction, Mechanical Spectroscopy in SiO2/Si Wafers

In this work, after X-ray and electron irradiation, the outcomes of the evaluation dynamic characteristics of interstitial atoms Sij , vacancy V, and O-complexes were evaluated to account for the annealing conditions to derive specific structural defects in the SiO2/Si wafer. A non-destructive method, which allows the determination of the internal friction difference ΔQ-1/Q-1 0 of the elastic vibration structure defect density Nd and the depth of the broken layer hb , is offered for the SiO2/Si wafer. The method was developed, the installation was designed and manufactured for the excitation and registration of damped bending resonant oscillations in a SiO2/Si disc-shaped wafer with a thickness hSiO2 ≈ 100 nm, his = 300÷500×103 nm, and diameter D = 60÷100×10-3 m to measure the structurally sensitive internal friction Q-1 . Measurement of the internal friction background Q-1 0 at harmonic frequencies f0 and f2 allowed us to experimentally determine the nodal lines of the oscillating disks.

Regeneration of artificial injuries external ear elastic cartilage of rabbits after stem cells local injection

Introduction: Every year, a large number of patients from developed countries turn to surgical departments with the reconstruction problems of the auricle cartilage. A some of surgical procedures was developed to correct minor defects due to the low regenerative capacity of elastic cartilage. Stem cells can potentially differentiate into chondroblasts and chondrocytes and restore cartilage integrity. Many factors influence on the differentiation and proliferation of stem cells, which complicates the method application. Therefore, the investigation of using stem cells to regeneration elastic cartilage is relevant. Aim: clarification the regeneration features of the artificial defect of the rabbits’ ear elastic cartilage after the stem cells injection. Materials and methods: The investigation was conducted on rabbits of chinchilla breed aged 1.5 months, weighing 2.5 kg. Artificial lesions measuring 2 x 7-10 mm were simulated on the cartilaginous plate of the outer ear with a scalpel. 0.5 ml of stem cell suspension (~5 million) obtained from the umbilical cord of rabbits by enzymatic method was injected into the defect site. Histological sections of the cartilage defect were prepared. The samples were stained by Weigert and Azure II methods. The relative density of collagen, elastin fibers, oxyphilic and basophilic tissue elements was programmatically evaluated. Results and discussion: The amount of fibers in the native elastic cartilage was more on 35% of the relative dermis. The newly formed tissues at the damage cartilage was like to the dermis after 2 months. Similar results were found on ear in 2.5 and 3 months after surgery. Native cartilage on histological sections almost was not oxyphilic. Maybe a significant number of acidic components was masked it. Dense connective tissue contains almost equal amounts of both components. Thus, it is possible to trace changes in the intercellular matrix that will characterize the direction of the regeneration process. The area of elastic cartilage defect was characterized by a significant presence of oxyphilic elements after 2 months of the stem cells addition. The ratio of oxyphilic and basophilic components in the native elastic cartilage was about to zero. For the dermis was 1.4-1.5. Dense scar connective tissue was characterized by a ratio about 1. Based on the results obtained, was assumed that the direction of stem cell proliferation is determined shortly after injection. Conclusion: The addition of stem cells to the area of the artificially created elastic cartilage defect of the rabbit's ear was not allow to obtain stable regenerative processes of cartilage tissue and the restoration of the intercellular matrix to its original state. The process of stem cell differentiation contributes the formation of dense connective tissue of the scar, which may be due to the presence of proinflammatory cytokines, growth factors and other biologically active molecules. This was not creating the necessary conditions for the cartilage regeneration.

Crystal orientation and material type related suppression to the graphitization wear of micro diamond tool

According to the Hencky stress theorem and J-C constitutive equation, a cutting force model is established for the diamond turning process when using micro diamond tool, through which the stress distributions on tool rake face and flank face are calculated. A stress model is further developed to calculate the stress distribution on the cutting edge region by using the stress intensity factor theory of fracture mechanics, into which the influences of crystal orientation of rake and flank faces are integrated. With consideration of elastic modulus and defect density of diamond crystal, the critical stress for graphitization of diamond tool is also deduced in response to different crystal orientations and types of diamond material. Finally, cutting experiments are performed to validate the theoretical predictions. Results show that the experimental observations agree well with the theoretical predictions. Such satisfactory consistency confirms that the natural cape Ia diamond as tool material and the (100) crystal plane as tool faces can effectively inhibit the graphitization wear of micro diamond tool.

Ab initio point defect calculations for structural properties of a model austenitic steel alloy

We present first-principles density functional theory calculations of atomic properties relevant to the material strength of an austenitic (face-centered-cubic) steel alloy, ${\mathrm{Fe}}_{0.70}{\mathrm{Ni}}_{0.12}{\mathrm{Cr}}_{0.18}$. While alloys in this class appear nonmagnetic macroscopically because their local magnetic moments are disordered, significant deviation from experiment can result when calculating properties using nonmagnetic calculations or magnetically ordered calculations. To overcome these difficulties, in this paper we employ a magnetic sampling method with spin-polarized density functional theory to approximate magnetically disordered states by averaging over several static configurations. Using this approach, we calculate elastic and point defect properties, which are then used to evaluate the dominant solid-solution strengthening contribution to the yield strength. Moreover, since the local composition can interact with strain fields, whether externally applied or induced by dislocations, diffusion can give rise to local changes in mechanical properties. We therefore calculate contributions to the vacancy-mediated diffusivity from the formation and migration terms in the activation energy, and the harmonic-transition-state-theory prefactor which depends on the vibrational states of the initial and transition states. While the prefactor is very sensitive to noise and therefore only loosely constrained by our calculations, the activation energies and yield stress values obtained from paramagnetic calculations are in good agreement with available experimental results.

Arteriomegaly with synchronous true aneurysms; Management of Common Femoral Artery and Profunda Femoris Artery aneurysms in a 70-year-old male - A case report.

Introduction and importanceArteriomegaly is characterized by an abnormal elastic defect of arterial vessels, which causes them to become elongated and tortuous. This raises the risk of limb loss due to thromboembolism, bleeding, infection, aneurysmal degeneration, dissection, or rupture. Despite asymptomatic presentations, surgical intervention could be warranted to plummet the morbidity and mortality associated with this pathology.Case presentationWe report the case of a 70-year-old male who presented with intermittent claudication in the left lower limb at a 100 m. Clinical examination revealed a pulsatile mass in the left groin with absent pulses in the left Popliteal and Pedal arteries. Radiology demonstrated a diffuse enlargement of the Abdominal Aorta with an infrarenal AAA, a L-CFA aneurysm, and a L-PFA aneurysm accompanied by occlusion of the L-SFA. Open surgical repair was achieved.Clinical discussionOur patient was managed by arterial ligation and surgical excision of both concomitant aneurysms where we placed a Dacron graft from the L-CIA to the branch of the L-PFA whilst placing a supported ePTFE graft from the previously mentioned Dacron graft of the deep femoral branch to the left below-knee Popliteal Artery.ConclusionArteriomegaly is considered an exceptionally rare and progressive disease. Patients affected by this pathology have higher incidence rates of aneurysmal degeneration and even loss of the affected limb, especially if it's a peripheral aneurysm. Bypass surgical repair is feasible with positive outcomes, and it is prophylactic against the wide spectrum of dire consequences for patients.

Modeling and experiment on elastic region low defect jet polishing for fused quartz

This paper preliminarily designs array nozzles according to different nozzle processing time and flow requirements, and analyzes the pressure distribution and fluid velocity of different combination array nozzles by using flow field simulation. It is found that the array hole nozzles 5 × 5 and 10 × 10 can remove materials evenly during the actual process without damaging the surface of the workpiece. In addition, fused quartz is processed by using nano-SiO2 jet polishing. As the removal depth increased, the width to depth ratio gradually increased from 3.34 to 4.71, while the damage threshold also gradually increased from 5.56 J/cm2 to 6.78 J/cm2. Experimental results show that nano-SiO2 jet polishing can indeed blunt scratches and improve the laser damage ability of fused quartz.

IMPLEMENTATION OF THE DMAIC APPROACH FOR QUALITY IMPROVEMENT AT THE ELASTIC TAPE INDUSTRY

The scope of this research is in one of the textile industries with elastic tape produced on the weaving machine, which has decreased production due to production defects that do not meet the target. This research aims to determine the leading causes of dominant defects, increase the sigma level with Six Sigma methods, and propose improvements to be included in the Key Performance Indicators (KPI) method. The results of this study that the dominant factor causing the defect is the curved elastic tape defect, which consists of the machine factor, and the method. Factors driving the machine include the hook like a side thread lock that is often bent and the difference in the thickness of the tape between the left, middle and right. The causative factor of this method is checking the thickness of the elastic band only in the center position. The results of corrective actions impact increasing the sigma level by 10% from 3.3339 to 3.6832. In contrast, repair defects can reduce defects before repair by 18.92% and after repair by 9.23%. It is proposed to be included in the KPI so that the weaving department can control and be enthusiastic about continuous improvement.

A predictive strain-gradient model with no undetermined constants or length scales

A general meso‑scale (GM) crystal plasticity (CP) model was developed that accounts for lower-order (strain hardening) and higher-order (internal stress) effects of geometrically necessary dislocations (GNDs). It is predictive: no arbitrary parameters or length scales were invoked and no ad hoc numerical techniques were employed. It uses general stress field equations for GND content and a novel harmonization technique to enforce consistency of elastic long-range singular defect fields with applied elastic-plastic fields. The model facilitates implementation in commercial finite element programs without requiring special elements, special boundary conditions, or access to element shape functions. GM simulations confirmed, with improved accuracy, previously published predictions of the Hall-Petch effect, Bauschinger effect, and anelasticity. Previously unpredicted phenomena were also predicted: anelasticity and hysteresis for single Ta crystals and strain-hardening stagnation. The internal stresses (higher-order effect) dominate at large length scales, while at small length scales, the GND density hardening (lower-order effect) dominates. GM predicts that strain heterogeneity and consequent GND internal stresses are important factors in anelasticity.

Using the elastic modulus defect for diagnostics of plastic deformation of metal

A non-destructive method for assessing the plastic deformation of a metal after processing a product is proposed, based on a change in the elastic properties of the material. Keywords metal, elastic properties, modulus of elasticity, Poisson's ratio, plastic deformation, non-destructive method, tension. matlin@vstu.ru

Large Elastic Deformation and Defect Tolerance of Hexagonal Boron Nitride Monolayers

Monolayer hexagonal boron nitride can serve in optoelectronics or as a dielectric in graphene and other two-dimensional (2D) electronics due to its ultra-wide band gap. As there is no center of symmetry, monolayer hexagonal boron nitride (h-BN) also shows piezoelectricity. However, these applications require h-BN to sustain large uniform elastic deformation, which has yet to be demonstrated. Here, we report, by tensile testing, that a large elastic strain up to 6.2% is achieved for defect-scarce polycrystalline h-BN monolayers, with corresponding 2D Young’s modulus ∼200 N/m, close to the ideal value measured by atomic force microscopy (AFM). Furthermore, samples containing voids of ∼100 nm can be strained up to 5.8%. Atomistic and continuum simulations show that compared to the imperfections introduced during sample preparation, the elastic limit of h-BN is virtually immune to naturally occurring atomistic defects and is gradually lowered by submicrometer voids. The mechanical robustness of h-BN monolayers, along with the large uniform elasticity, is encouraging for strain engineering and piezoelectronics applications.

Diffusion assisted interaction of shear bands in metallic glasses

Shear bands were formed at room temperature in Zr44Ti11Cu10Ni10Be25 bulk metallic glass subjected to torsional deformation. Shear offset distribution was determined quantitatively for intersecting bands and compared to an elastic continuum shear defect model applied to similar band arrangements. The model reproduced the measured offset distribution, the residual stress field and different asymmetrical features of the band interaction. Differences between the model and the experimental results revealed the presence of a diffusion process for dilatational defects in shear band interaction.

Electronic structures, mechanical properties and defect formation energies of U3Si5 from density functional theory calculations

The uranium silicide U3Si5 has been utilized as the second phase in the UN-U3Si5 composite fuel. However, there have thus far been few theoretical investigations on its microscopic structure and mechanical behaviors. In this work, the electronic structures, elastic mechanical properties, Debye temperature and defect formation energies of U3Si5 are systematically studied by density functional theory. The crystalline structure of U3Si5 is determined to be a defective β-USi2 with a distorted lattice, in good agreement with the experimental observations. The theoretical results indicate that the U3Si5 is a metallic and brittle material and the chemical bonds in U3Si5 are found similar with those of U3Si2. We have also calculated formation energies of different types of point defects: vacancies, interstitials, and Frenkel pairs in U3Si5. The smaller Si atoms exhibit lower defect formation energies than U atoms with an isolated Si or U atom as the reference. Besides, the silicon vacancies are not prone to cluster. The volumes of supercells with interstitial and Frenkel pair defects are found to increase but single vacancies cause an opposite trend. This work may provide theoretical insights into the behavior of uranium silicide materials under irradiation.

Improved Finnis-Sinclair potential for vanadium-rich V–Ti–Cr ternary alloys

Abstract We have developed an improved Finnis-Sinclair (IFS) potential for vanadium-rich V–Ti–Cr random alloys with body-centred cubic structure. An extra exponential term is added to the original FS potential to enhance the repulsive interaction. The IFS potential is fitted to experimental crystal structure, cohesive energy and elastic constants of pure metals (V, Ti and Cr) and theoretical data of binary alloys (V 15 Ti, V 15 Cr and Ti 8 Cr 8 ). The good agreement of the predicted formation energies of mono-vacancy and self-interstitial of octahedral interstitial site, tetrahedral interstitial site, -dumbbell, -dumbbell, and -dumbbell with available experimental and theoretical data confirms the validity of our IFS potential in pure V. Furthermore, the agreement of elastic properties and defect properties of typical alloy (V–4Ti–4Cr) with experimental or DFT data also support the applicability of the IFS potential in V-rich ternary V–Ti–Cr alloys. Finally, this work also provides a reference to develop empirical potentials for other ternary alloys.

SURFACE NANOHARDNESS OF WEAR RESISTANT SURFACING IRRADIATED BY ELECTRON BEAM

The nanohardness, Young elastic modulus and defect substructure of the layer surfaced on the low carbon martensite Hardox 450 steel by the high carbon power wires with diameter of 1.6 mm of different chemical composition (containing such elements as V, Cr, Nb, W, Mn, Si, Ni, B) and two times additionally irradiated by the pulse electron beam were studied for the purpose of substantiated selection of coating material corresponding to the product operation conditions and the modes of subsequent electron beam treatment. The formation of the fused layer on the steel surface was carried out in the shielding gas medium containing 98 % Ar, 2 % CO 2 , with a welding current of 250 – 300 A and a voltage on the arc of 30 – 35 V. Modification of the deposited layer was carried out by irradiating the surface of the deposited layer by a high-intensity electron beam in the mode of melting and high-speed crystallization. The load on the inductor was 50 mN. Determination of the nanohardness and Young elastic modulus was carried out at 30 arbitrarily chosen points of the modified surface. The defect structure of the surface modified by of an electron beam of the surfacing was studied by scanning electron microscopy. A multiple increase in nanohardness and Young elastic modulus of the welded layer was revealed during electron-beam treatment according to the base material. It was found that the maximum hardening effect is observed at surfacing by a flux-cored wire containing 4.5 % of boron. It is shown that on the weld deposit surface formed by the wire with 4.5% of boron and additionally irradiated with an intense pulsed electron beam, the formation of a microcrack system on the surface of irradiation was revealed. Investigations of weld deposits, formed by non-boron-containing powder wires, have shown the absence of microcracks on the modified surface after pulsed electron beam treatment. The increase in the strength properties of the deposited layer modified by the electron beam is due to the formation of structures which crystallite sizes vary from tenths of a micrometer to one micrometer and contain second phases (borides, carbides, carbborides). A significant spread of the values of the nanohardness and the Young elastic modulus was established, which was apparently due to the inhomogeneous distribution of the strengthening phases.

A multi-state modified embedded atom method potential for titanium

The continuing search for broadly applicable, predictive, and unique potential functions led to the invention of the multi-state modified embedded atom method (MS-MEAM) (Baskes et al 2007 Phys. Rev. B 75 094113). MS-MEAM replaced almost all of the prior arbitrary choices of the MEAM electron densities, embedding energy, pair potential, and angular screening functions by using first-principles computations of energy/volume relationships for multiple reference crystal structures and transformation paths connecting those reference structures. This strategy reasonably captured diverse interactions between atoms with variable coordinations in a face-centered-cubic (fcc)-stable copper system. However, a straightforward application of the original MS-MEAM framework to model technologically useful hexagonal-close-packed (hcp) metals proved elusive. This work describes the development of an hcp-stable/fcc-metastable MS-MEAM to model titanium by introducing a new angular function within the background electron density description. This critical insight enables the titanium MS-MEAM potential to reproduce first principles computations of reference structures and transformation paths extremely well. Importantly, it predicts lattice and elastic constants, defect energetics, and dynamics of non-ideal hcp and liquid titanium in good agreement with first principles computations and corresponding experiments, and often better than the three well-known literature models used as a benchmark. The titanium MS-MEAM has been made available in the Knowledgebase of Interatomic Models (https://openkim.org/) (Tadmor et al 2011 JOM 63 17).

Atomic interaction of the MEAM type for the study of intermetallics in the Al–U alloy

Interaction for both pure Al and Al–U alloys of the MEAM type are developed. The obtained Al interatomic potential assures its compatibility with the details of the framework presently adopted. The Al–U interaction fits various properties of the Al2U, Al3U and Al4U intermetallics. The potential verifies the stability of the intermetallic structures in a temperature range compatible with that observed in the phase diagram, and also takes into account the greater stability of these structures relative to others that are competitive in energy. The intermetallics are characterized by calculating elastic and thermal properties and point defect parameters. Molecular dynamics simulations show a growth of the Al3U intermetallic in the Al/U interface in agreement with experimental evidence.

Assessment of the dislocation bias in fcc metals and extrapolation to austenitic steels

A systematic study of dislocation bias has been performed using a method that combines atomistic and elastic dislocation-point defect interaction models with a numerical solution of the diffusion equation with a drift term. Copper, nickel and aluminium model lattices are used in this study, covering a wide range of shear moduli and stacking fault energies. It is found that the dominant parameter for the dislocation bias in fcc metals is the width of the stacking fault ribbon. The variation in elastic constants does not strongly impact the dislocation bias value. As a result of this analysis and its extrapolation, the dislocation bias of the widely applied austenitic stainless steels of 316 type is predicted to be about 0.1 at temperature close to the swelling peak (815 K) and typical dislocation density of 1014 m−2. This is in line with the bias calculated using the elastic interaction model, which implies that the prediction method can be used readily in other fcc systems even without EAM potentials. By comparing the bias values obtained using atomistic- and elastic interaction energies, about 20% discrepancy is found, therefore a more realistic bias value for the 316 type alloy is 0.08 in these conditions.

Small-Scale Effect on Longitudinal Wave Propagation in Laser-Excited Plates

Longitudinal wave propagation in an elastic isotopic laser-excited solid plate with atomic defect (vacancies, interstitials) generation is studied by the nonlocal continuum model. The nonlocal differential constitutive equations of Eringen are used in the formulations. The coupled governing equations for the dynamic of elastic displacement and atomic defect concentration fields are obtained. The frequency equations for the symmetrical and antisymmetrical motions of the plate are found and discussed. Explicit expressions for different characteristics of waves like phase velocity and attenuation (amplification) coefficients are derived. It is shown that coupling between the displacement and defect concentration fields affects the wave dispersion characteristics in the nonlocal elasticity. The dispersion curves of the elastic-diffusion instability are investigated for different pump parameters and larger wave numbers.