Gauge Part Research Articles

Low-temperature superplastic behavior of nanostructured Al-Zn-Mg-Cu alloy

The evolution of Al-Zn-Mg-Cu alloy microstructure during high pressure torsion at room temperature and subsequent low-temperature superplastic deformation is studied. The formation of a nanostructured state in Al-Zn-Mg-Cu alloy made it possible to implement a superplasticity (SP) effect at 170 °C and a strain rate of 5 × 10−4 s−1. The deformation relief of the gauge part of an Al-Zn-Mg-Cu alloy sample at the stage of steady-state SP flow is analyzed. Low-temperature superplastic deformation is stated to take place due to grain boundary sliding. High formability of nanostructured alloy under biaxial tension at a temperature of 170 °C is recorded.

Building blocks of the flavourful SMEFT RG

A powerful aspect of effective field theories is connecting scales through renormalisation group (RG) flow. The anomalous dimension matrix of the Standard Model Effective Field Theory (SMEFT) encodes clues to where to find relics of heavy new physics in data, but its unwieldy 2499 × 2499 size (at operator dimension 6) makes it difficult to draw general conclusions. In this paper, we study the flavour structure of the SMEFT one loop anomalous dimension matrix of dimension 6 current-current operators, a 1460 × 1460 submatrix. We take an on-shell approach, laying bare simple patterns by factorising the entries of the matrix into their gauge, kinematic and flavour parts. We explore the properties of different diagram topologies, and make explicit the connection between the IR-finiteness of certain diagrams and their gauge and flavour structure. Through a completely general flavour decomposition of the Wilson coefficient matrices, we uncover new flavour selection rules, from which small subsystems emerge which mix almost exclusively amongst themselves. We show that, for example, if we neglect all Yukawa couplings except for that of the top quark, the selection rules produce block diagonalisation within the current-current operators in which the largest block is a 61 × 61 matrix. We provide all the ingredients of the calculations in comprehensive appendices, including SM and SMEFT helicity amplitudes, and explicit results for phase space integrals and gauge contractions. This deconstruction of the matrix, and its resulting block-diagonalisation, provides a first step to understanding the IR-relevant directions in the SMEFT parameter space, hence closing in on natural places for heavy new physics to make itself known.

Prediction of Crack Initiation Based on Energy Storage Rate during Low-Cycle Fatigue of Austenitic Stainless Steel.

The low-cycle deformation of 304L austenitic stainless steel was examined in terms of energy conversion. Specimens were subjected to cyclic loading at the frequency of 2 Hz. The loading process was carried out in a hybrid strain–stress manner. In each cycle, the increase in elongation of the gauge part of the specimen was constant. During experimental procedures, infrared and visible-range images of strain and temperature fields were recorded simultaneously using infrared thermography (IR) and digital image correlation (DIC) systems. On the basis of the obtained test results, the energy storage rate, defined as the ratio of the stored energy increment to the plastic work increment, was calculated and expressed in reference to selected sections of the specimen. It was shown that, before the specimen fracture in a specific area, the energy storage rate is equal to zero (the material loses the ability to store energy), and the energy stored during the deformation process is released and dissipated as heat. Negative and close-to-zero values of the energy storage rate can be used as a plastic instability criterion on the macroscale. Thus, the loss of energy storage ability by a deformed material can be treated as an indicator of fatigue crack initiation.

A novel method based on the Seebeck effect for analyzing the behavior of the PLC band and type A serration

In the present study, a new technique for analyzing dynamic strain aging (DSA), which causes the Portevin-Le Chatelier (PLC) band and type A serrations in a tensile curve, was proposed. The analytical technique is based on the thermoelectric phenomenon known as the Seebeck effect. The variation of the voltage of the gauge part was monitored by the four-wire voltage measurement method during tensile tests. The voltage was additionally changed by a thermo-electromotive force induced by the local deformation heat of the PLC band, i.e. the Seebeck effect. The voltage change led to serrations in the voltage vs. strain (or time) curve. The voltage serrations more clearly exhibited the nucleation and propagation of the PLC band and a critical strain for DSA, which is crucial for investigation of the DSA mechanism, compared to stress serrations in tensile flow curves.

Effects of laser shock peening on microstructure and mechanical properties of TIG welded alloy 600 joints

Abstract Laser shock peening (LSP) is a competitive surface strengthening technology for post-weld treatment. In this work, tungsten inert gas (TIG) welded joints of Alloy 600 were treated by LSP to enhance the mechanical properties. The results showed that the tensile residual stress in weld surface was transformed into the compressive stress state after LSP. LSP treatment caused a significant improvement in microhardness and dislocation density in the weld surface. The tensile strength and yield strength of joints after peening on the full gauge part of tensile samples were increased by 10% and 75%, respectively. However, the fatigue life could be improved much more by only peening on the fusion zone and heat affected zone than that of samples peened on the full gauge part. The peening region played a crucial role on the difference of tensile and fatigue properties due to the residual stress distribution, dislocation strengthening and work hardening induced by LSP.

Macroscopic and microscopic characterizations of Portevin-LeChatelier effect in austenitic stainless steel using high-temperature digital image correlation analysis

Using digital image correlation (DIC) analysis in an Fe-19Cr-13Ni-0.2C austenitic stainless steel (mass%), the tensile deformation behavior accompanied with the Portevin-LeChatelier (PLC) effect was investigated at high temperatures of 723-823 K under various applied strain rates of 10−4 s−1–5 × 10−3 s−1. With the help of the DIC analysis, the global strain in the gauge part of a tensile specimen and the local strain in a PLC band were precisely measured regardless of the lowering machine stiffness at a high temperature. The high-temperature DIC analysis could identify the critical strain and strain rate conditions where stress-strain curve indicated serrated flow. The analytical results revealed that dynamic strain aging in the austenitic stainless steel was controlled by the pipe diffusion of Cr atoms. Further, it was also confirmed that the local strain gently increased in a gauge part through a PLC band propagation, which promoted a repeatable A-type PLC band propagation in the same direction. Furthermore, the local strain was discontinuously developed by the repeatable formation of PLC bands; consequently, the local strain rate became remarkably high within a PLC band. In addition, the local strain rate in the PLC band monotonically increased with the increase in the number of PLC bands. From this viewpoint, it was discovered that necking deformation occurs suddenly at the PLC band, when the local strain rate exceeds the critical value, where dynamic strain aging is ineffective.

Deformation of Corset-Shaped Specimens during Cyclic Heating

The deformation that develops in a corset specimen during its cyclic heating is analyzed. The plastic deformation in the central part of the specimen, where usually fracture is localized, reaches a very large value of 6–7% (for the thermal conditions typical of thermal fatigue research). This is explained by mechanical deformation due to external cyclically compressed and expanded specimen shoulders, which are rigidly constrained only from the heads. A thermocyclic diagram for a flat corset specimen is given; it differs significantly from the diagram for specimens with a long gauge part (for example, the Coffin technique). Corset specimens are recommended for full-scale tests of products by changing their shape (modeling dangerous regions of the products) and plastic deformation in a wide range.

Teukolsky formalism for nonlinear Kerr perturbations

We develop a formalism to treat higher order (nonlinear) metric perturbations of the Kerr spacetime in a Teukolsky framework. We first show that solutions to the linearized Einstein equation with nonvanishing stress tensor can be decomposed into a pure gauge part plus a zero mode (infinitesimal perturbation of the mass and spin) plus a perturbation arising from a certain scalar (‘Debye–Hertz’) potential, plus a so-called ‘corrector tensor’. The scalar potential is a solution to the spin −2 Teukolsky equation with a source. This source, as well as the tetrad components of the corrector tensor, are obtained by solving certain decoupled ordinary differential equations involving the stress tensor. As we show, solving these ordinary differential equations reduces simply to integrations in the coordinate r in outgoing Kerr–Newman coordinates, so in this sense, the problem is reduced to the Teukolsky equation with source, which can be treated by a separation of variables ansatz. Since higher order perturbations are subject to a linearized Einstein equation with a stress tensor obtained from the lower order perturbations, our method also applies iteratively to the higher order metric perturbations, and could thus be used to analyze the nonlinear coupling of perturbations in the near-extremal Kerr spacetime, where weakly turbulent behavior has been conjectured to occur. Our method could also be applied to the study of perturbations generated by a pointlike body traveling on a timelike geodesic in Kerr, which is relevant to the extreme mass ratio inspiral problem.

Effect of Laser Processing on Strength and Portevin–Le Chatelier Serrated Deformation of Aluminum Alloy

The effect of surface processing by laser IR radiation on strength and Portevin–Le Chatelier serrated deformation of AlMg6 aluminum–magnesium alloy is experimentally studied. Laser processing consists in local “shots” on the surface at the nodes of a square grid in the gauge part of a flat sample. The conditions under which such laser processing causes an increase in the surface microhardness, ultimate tensile strength, and the critical strain of the first stress drop in the stress–strain curve; decreases the probability of deformation band formation; suppresses necking at the prefracture stage; and changes the main crack morphology. The possible mechanism of the effect of laser processing on band formation, serrated deformation, and alloy strength are discussed.

Short-term strength properties and features of high-temperature deformation of VVER reactor pressure vessel steel 15Kh2NMFA-A within the temperature range 20–1200 °C

The problem discussed in this work concerns the estimate of integrity of the VVER reactor pressure vessel in the severe accident. In particular, the main goal of discussed investigation is to determine short-term mechanical properties of ferritic-pearlitic vessel steel 15Kh2NMFA-A (2% Cr, 1% Ni, 0.5% Mn, 0.5% Mo) within the temperature range 20–1200 °C. This steel type is one of basic structure steel types used in fabrication of reactor pressure vessels of Russian design, particularly, the VVER vessels. To perform short-term tests of this steel, several lots of steel specimens 8 and 10 mm in diameter with gauge part of length 40–50 mm, correspondingly, were made. The test specimens were made of the fragment of unirradiated standard VVER-1000 reactor pressure vessel of Russian design fabricated by OMZ Group “Izhorskiye zavody” (Russia). The short-term tensile tests of steel specimens were performed both in air within the temperature range 20–1100 °C and in vacuum within the temperature range 900–1200 °C. Basing on the results of the tests, strength-and plastic/strain parameters of this steel (ultimate tensile strength, yield stress, tensile Young’s modulus, steel elongation at fracture, the coefficient of linear thermal expansion) were determined. The analysis of obtained results made it possible to reveal a series of singularities of 15Kh2NMFA-A steel strain. In particular, it was shown that in the temperature range 770–820 °C (Ac1-Ac3), the investigated steel undergoes inner phase/structure transformations, which have an essential influence on strength- and strain properties of investigated steel. The analysis of temperature effect on strength properties (ultimate tensile strength and yield stress) and Young’s modulus of this steel made it possible to reveal three temperature ranges in which these parameters have characteristic features of change. In the first of these ranges (the temperature values from 20 to ~650 °C), a moderate degradation of strength- and elastic properties of steel is observed. In the second range (from ~650 to 850 °C), a sharp decrease of values of steel strength and elasticity occurs, and at test temperature of more than 900 °C, a monotonous decrease of these mechanical properties is observed. The comparison of the results obtained in the present work with the earlier results of tests at temperature of more than 900 °C showed their satisfactory agreement.

Development of Multiaxial Creep Testing Machine for Miniature Specimen

High temperature components such as boiler tube and jet engine turbine blade undergo multiaxial creep damage. Although multiaxial creep testing investigation is required for safety high temperature components designing, there are few commercial testing machines which can conduct multiaxial loading at high temperature. A new miniature cruciform specimen, which has a 5 mm square size plane stress gauge part, was designed by using FE analysis. A biaxial tensile loading creep testing machine was also designed to conduct multiaxial creep testing. The testing machine has 2 kN loading capacity and 1 kW furnace. We had also developed a non-contact displacement measuring method for the miniature specimen. This method uses conventional optical camera to get the surface observation photograph. Chasing the trace of the target mark painted at surface of the specimen, we can get the displacement of the specimen. The calculated strain value obtained from the non-contact displacement measuring method corresponds with the strain gauge value at room temperature. By using the multiaxial creep testing machine and the non-contact observation system, we can investigate not only deformation of the testing specimen but also surface conditions of materials during the creep testing.

Влияние лазерной обработки на прочность и прерывистую деформацию Портевена-Ле Шателье алюминиевого сплава

AbstractThe effect of surface processing by laser IR radiation on strength and Portevin–Le Chatelier serrated deformation of AlMg6 aluminum–magnesium alloy is experimentally studied. Laser processing consists in local “shots” on the surface at the nodes of a square grid in the gauge part of a flat sample. The conditions under which such laser processing causes an increase in the surface microhardness, ultimate tensile strength, and the critical strain of the first stress drop in the stress–strain curve; decreases the probability of deformation band formation; suppresses necking at the prefracture stage; and changes the main crack morphology. The possible mechanism of the effect of laser processing on band formation, serrated deformation, and alloy strength are discussed.

Aspects of nonsupersymmetric string phenomenology

We consider a big class of chiral four-dimensional string models which bear [Formula: see text] gauge symmetry. Supersymmetry (SUSY) is spontaneously broken via the Scherk–Schwarz mechanism associated with two large internal dimensions. We study two central issues in nonsupersymmetric string phenomenology: the suppression of the cosmological constant and the decompactification problem. We identify a subclass of chiral nonsupersymmetric models with fermion–boson degeneracy leading to exponentially suppressed cosmological constant. In addition, we propose a novel solution to the decompactification problem related to the cancellation of the linear growth of the gauge part of the thresholds with a similar growth of the universal part. We show that the proposed mechanism resolves the decompactification problem related to the non-Abelian gauge couplings in approximately 40% of the models under consideration.

Holographic mutual information of two disjoint spheres

We study quantum corrections to holographic mutual information for two disjoint spheres at a large separation by using the operator product expansion of the twist field. In the large separation limit, the holographic mutual information is vanishing at the semiclassical order, but receive quantum corrections from the fluctuations. We show that the leading contributions from the quantum fluctuations take universal forms as suggested from the boundary CFT. We find the universal behavior for the scalar, the vector, the tensor and the fermionic fields by treating these fields as free fields propagating in the fixed background and by using the 1/n prescription. In particular, for the fields with gauge symmetries, including the massless vector boson and massless graviton, we find that the gauge parts in the propagators play an indispensable role in reading the leading order corrections to the bulk mutual information.

Cyclic deformation behaviour and stability of grain-refined 301LN austenitic stainless structure

Low cycle fatigue (LCF) behaviour of metastable austenitic 301LN stainless steel with different grain sizes – coarse-grained (13 μm), fine-grained (1.4 μm) and ultrafine-grained (0.6 μm) – produced by reversion annealing after prior cold rolling was investigated. Fully symmetrical LCF tests with constant total strain amplitudes of 0.5% and 0.6% were performed at room temperature with a low constant strain rate of 2×10-3 s-1. Microstructural changes in different positions within the gauge part of the specimens were examined by optical microscopy (polarized light) and electron backscatter diffraction (EBSD) technique; for quantitative assessment of the volume fraction of deformation induced martensite (DIM) a Feritscope FMP 30 was adopted. The cyclic stress-strain response and specific changes of hysteresis loop shapes in the very early stage of cycling are confronted with the character of DIM formation and its distribution in the whole volume of the material. A possible effect of strain rate (frequency of cycling) on the destabilization of austenitic structure during cyclic straining of materials with different grain sizes is highlighted.

Microstructure and Mechanical Properties of Laser Repaired TC4 Titanium Alloy

Laser Additive Manufacturing (LAM) was employed to fabricate repaired specimens with wrought TC4 as the substrate and TC4 powders with low oxygen (O≤0.13wt%) as the cladding materials. The microstructure and mechanical properties of TC4 specimens fabricated by LAM and wrought billet were investigated comparatively. The results show that the macrostructure of the laser repaired specimen can be divided into three domains, including wrought substrate zone (SZ), heat affected zone (HAZ) and laser deposited zone (LDZ). The LDZ microhardness is equal to that of the SZ basically. And the HAZ microhardness is higher than that of both the LDZ and SZ slightly. The results of room temperature tensile test show that the strength and ductility of the wrought specimen are slightly higher than that of the laser repaired specimens. Meanwhile, the strength of the laser repaired specimen with repair ratio of 40% (i.e. area fraction of the LDZ on the transverse section of tensile specimen within gauge part is 40%)is slightly lower than that of 50% repaired specimen, but the ductility is higher than the latter. Therefore it is favorable to match the strength and ductility of the wrought substrate with the LDZ with low oxygen TC4 powders as the cladding materials, so as to improve the comprehensive properties of laser repaired TC4 titanium alloy. The wrought specimen tensile fracture presents a typical ductile characteristic, and the repaired specimen shows a complex fractograph. From the LDZ to the SZ, the tensile fracture presents a successive transformation from cleavage step to dimple fracture. It can be seen that there is a good corresponding relationship between the fracture morphology and the microstructure of the tensile specimens.

Research of wear resistance of bronze bushings during plastic vibration deformation

Optimum design parameters of the tool for vibration deformation of bronze bushings: the punch angle β=9°; the height of the punch gauge part – 4-5 mm are obtained. For treatment of parts, the vibration amplitude of 1.0 mm, the machining allowance of 0.4 mm and the plastic deformation force of 217 N/m 2 should be used. The analysis of the microstructure improvement of the parts treated by vibration deformation is presented. Under deformation, more fine grains are formed and favorable conditions for dislocation generation are created, which promotes an increase in the radial deformation rate. The obtained process parameters of vibration deformation of bronze bushings allow reconditioning of worn-out surfaces. They can also be used for treatment of new parts, thus increasing the wear resistance of operating surfaces by 1.2 times. The research results can be useful in the development and improvement of the processes of reconditioning “bushing” type parts.

Effect of metallurgical variables on the austenite stability in fatigued AISI 304 type steels

Low-cycle fatigue behavior, destabilization of austenite and emergence of deformation induced martensite (DIM) was investigated in wrought AISI 304 type (304, 304L, 348) austenitic stainless steels of diverse semi-product forms. The specimens fabricated from cylindrical bars, plates or thin sheets were cyclically strained with high strain amplitudes under total strain control in symmetrical push-pull at room and depressed temperatures to different stages of fatigue life. Quantitative and qualitative data on the formation, morphology and specific distribution of DIM in the volume of the material within the whole gauge part of the specimens are confronted with the respective cyclic stress-strain response and discussed in terms of characteristic chemical heterogeneity. This heterogeneity arises in the form of chemical banding due to the complex solidification behavior of AISI 304 type steels and its contemporary production route. Possible effect of additional solution treatment (various cooling rates due to quenching in different media) on DIM formation is discussed.

Entanglement of Distillation for Lattice Gauge Theories.

We study the entanglement structure of lattice gauge theories from the local operational point of view, and, similar to Soni and Trivedi [J. High Energy Phys. 1 (2016) 1], we show that the usual entanglement entropy for a spatial bipartition can be written as the sum of an undistillable gauge part and of another part corresponding to the local operations and classical communication distillable entanglement, which is obtained by depolarizing the local superselection sectors. We demonstrate that the distillable entanglement is zero for pure Abelian gauge theories at zero gauge coupling, while it is in general nonzero for the non-Abelian case. We also consider gauge theories with matter, and show in a perturbative approach how area laws-including a topological correction-emerge for the distillable entanglement. Finally, we also discuss the entanglement entropy of gauge fixed states and show that it has no relation to the physical distillable entropy.

On unification of gravity and gauge interactions

Considering a higher dimensional Lorentz group as the tangent symmetry, we unify gravity and gauge interactions in a natural way. The spin connection of the gauged Lorentz group is then responsible for both gravity and gauge fields, and the action for the gauged fields becomes part of the spin curvature squared. The realistic group which unifies all known particles and interactions is the $SO(1,13)$ Lorentz group whose gauge part leads to $SO(10)$ grand unified theory and contains double the number of required fermions in the fundamental spinor representation. Mirror fermions could acquire mass utilizing a mechanism employed for topological superconductors. Family unification could be achieved by considering the $SO(1,21)$ Lorentz group.