Transition Radius Research Articles

Driven injection of a polymer into a spherical cavity: A Langevin dynamics simulation study* *Project supported by the Natural Science Foundation of Zhejiang Province, China (Grant No. LY20A040004) and the National Natural Science Foundation of China (Grant Nos. 11604232 and 11974305).

The injection of a self-avoiding flexible polymer into a spherical cavity under a driving force is studied by using Langevin dynamics simulation. For given polymer length (N) and driving force (f), the polymer can be completely injected into the cavity only when the radius of the cavity is larger than a transition radius (R eC). The dependence of R eC on N and f can be described by a scaling relation R eC ∝ N 1 / 3 f −δ . The value of δ changes from 4/15 in the small f region to 1/6 in the moderate f region due to the screening of the excluded-volume interaction between monomers. We find the complete injection time (τ) decreases monotonously with increasing the cavity radius or decreasing the polymer length. The simulation results are in good agreement with the theoretical predictions from the free energy analysis and a simple kinetic model.

Assembly history of massive galaxies

In this paper we present the new deep images from the VEGAS survey of three massive (M* ≃ 1012 M⊙) galaxies from the MUSE Most Massive Galaxies (M3G) project, with distances in the range 151 ≤ D ≤ 183 Mpc: PGC007748, PGC015524, and PGC049940. The long integration time and the wide field of view of the OmegaCam at the VST allowed us to map the light and color distributions down to μg ≃ 30 mag arcsec−2 and out to ∼2Re. The deep data are crucial for estimating the contribution of the different galaxy components, in particular the accreted fraction in the stellar halo. The available integral field observations with MUSE cover a limited portion of each galaxy (out to ∼1Re), but from the imaging analysis, we find that they map the kinematics and stellar population beyond the first transition radius, where the contribution of the accreted component starts to dominate. The main goal of this work is to correlate the scales of the different components derived from the image analysis with the kinematics and stellar population profiles from the MUSE data. The results were used to address the assembly history of the three galaxies with the help of theoretical predictions. Our results suggest that PGC049940 has the lowest accreted mass fraction of 77%. The higher accreted mass fraction estimated for PGC007748 and PGC015524 (86% and 89%, respectively) combined with the flat λR profiles suggest that a great majority of the mass has been acquired through major mergers, which have also shaped the shallower metallicity profiles that are observed at larger radii.

The Effects of Large-scale Magnetic Fields on the Model for Repeating Changing-look AGNs

Abstract Periodic outbursts are observed in several changing-look (CL) active galactic nuclei (AGNs). Sniegowska et al. suggested a model to explain the repeating CL in these AGNs, where the periodic outbursts are triggered in a narrow unstable zone between an inner advection-dominated accretion flow and outer thin disk. In this work, we intend to investigate the effects of large-scale magnetic fields on the limit cycle behaviors of CL AGNs. The winds driven by magnetic fields can significantly change the structure of thin disk by taking away the angular momentum and energy of the disk. It is found that the period of outburst in repeating CL AGNs can be substantially reduced by the magnetic fields. Conversely, if we keep the period unchanged, the outburst intensity can be raised by several times. These results can help to explain the observational properties of multiple CL AGNs. Besides the magnetic fields, the effects of transition radius , the width of the transition zone ΔR, and the Shakura–Sunyaev parameter α are also explored in this work.

Accretion Geometry in the Hard State of the Black Hole X-Ray Binary MAXI J1820+070

Abstract We study X-ray spectra from the outburst rise of the accreting black hole binary MAXI J1820+070. We find that models having the disk inclinations within those of either the binary or the jet imply significant changes of the accretion disk inner radius during the luminous part of the hard spectral state, with that radius changing from >100 to ∼10 gravitational radii. The main trend is a decrease with the decreasing spectral hardness. Our analysis requires the accretion flow to be structured, with at least two components with different spectral slopes. The harder component dominates the bolometric luminosity and produces strong, narrow, X-ray reflection features. The softer component is responsible for the underlying broader reflection features. The data are compatible with the harder component having a large scale height, located downstream the disk truncation radius, and reflecting mostly from remote parts of the disk. The softer component forms a corona above the disk up to some transition radius. Our findings can explain the changes of the characteristic variability timescales, found in other works, as being driven by the changes of the disk characteristic radii.

Microstructure evolution and stress rupture properties of A286 superalloy in the 600 to 750 °C temperature range

To study the stress rupture properties of the A286 alloy in high temperature service environment, the stress rupture tests of A286 alloy at different temperature ranges and stress levels were carried out. Moreover, the Larson-Miller Parameter (LMP) for predicting the rupture life was established as LMP = (T + 273)(log t r + C) × 10−3, C = 22.3. The fracture morphology and the microstructure evolution of the stress rupture specimens were observed by scanning electron microscopy. The results show that for the stress rupture tests at 700 °C–750 °C/150–400 MPa, the precipitation of the closely arranged cellular η phase and the coarse MC at the grain boundary acted as the crack source. For the stress rupture test at 600 °C–700 °C/400–700 MPa, the coarse MC at the grain boundary led to stress concentration to give rise to crack initiation and propagation during deformation. With decreasing of temperature and increasing of stress, the fracture mode of the A286 alloy changed from the ductile fracture mode of microvoids to the brittle fracture mode of intergranular. The deformation mechanisms of A286 alloy at different temperatures and stress levels also have been systematically analyzed by transmission electron microscopy. The deformation mechanisms of A286 at different temperatures and stress levels were Orowan looping, microtwins and dislocation pairs shearing with Orowan looping and microtwins as the dominant deformation mechanisms. The critical transition radius of γ′ phase during the transition from dislocation shearing mechanism to Orowan looping mechanism was calculated.

Analysis and Optimization Study of Piston in Diesel Engine Based on ABC-OED-FE Method

In order to increase the reliability and service life of piston in a heavy-duty diesel engine, the geometric structure of piston was optimized based on its maximum temperature and maximum coupling stress. To begin with, the boundary conditions of thermal and stress fields are calculated, which include the heat produced by the combustion in cylinder, the friction-induced heat, and the heat transferred to cooling system. Then, the finite element model was established to calculate and analyse the temperature and thermal-mechanical coupling stress fields of the piston. By combining this simulation model with orthogonal experimental design methods, computations and analyses were performed to determine how the five geometric parameters (depth of intake and exhaust valve grooves, radius of valve grooves transition, radius of top of valve grooves, height of first piston ring groove, and depth of piston ring groove) influence the two evaluation indicators (maximum temperature and maximum stress of piston). Subsequently, using the proposed ABC-OED- FE (artificial bee colony, orthogonal experiment design, and fitting equations) method, the fitting equations between the geometric parameters and evaluation indicators were determined. Taking the minimum values of two evaluation indicators of piston as optimization objectives, artificial bee colony method was run to determine the values of parameters. At last, the two evaluation indicators of the optimized piston were computed. The results indicate that, after optimization, the maximum temperature of piston decreases to be 16.05 K and the maximum stress decreases to be 13.54 MPa. Both temperature and stress conditions of the optimized piston had been improved, which demonstrates the effectiveness of the optimization and the validity of the algorithm.

Departure from the Exact Location of Mean Motion Resonances Induced by the Gas Disk in Systems Observed by Kepler

Abstract The statistical results of transiting planets show that there are two peaks, around 1.5 and 2.0, in the distribution of orbital period ratios. A large number of planet pairs are found near the exact location of mean motion resonances (MMRs). In this work, we find that the depletion and structures of the gas disk play crucial roles in driving planet pairs out of the exact location of MMRs. Under such a scenario, planet pairs are trapped into exact MMRs during orbital migration first and keep migrating at the same pace. The eccentricities can be excited. Due to the existence of a gas disk, eccentricities can be damped, leading to a change in orbital period, which will make planet pairs depart from the exact location of MMRs. With depletion timescales larger than 1 Myr, near-MMR configurations are formed easily. Planet pairs have higher possibilities of escaping from MMRs with a higher disk aspect ratio. Additionally, with a weaker corotation torque, planet pairs can depart farther from the exact location of MMRs. The final location of the innermost planets in the systems are directly related to the transition radius from the optically thick region to the outer optically thin disk. While the transition radius is smaller than 0.2 au at the late stage of the star evolution process, the period of the inner planets can reach around 10 days. Our formation scenario is a possible mechanism for explaining the formation of near-MMR configurations with the innermost planet farther than 0.1 au.

Effect of aging temperature on the precipitation behavior and mechanical properties of Fe–Cr–Ni maraging stainless steel

Aging is an important heat treatment process for maraging stainless steel. During aging, the interaction between intermetallic compounds and dislocations has a significant impact on the mechanical properties of the material. In this article, the effect of aging temperature on the precipitation behavior and mechanical properties of Fe–Cr–Ni maraging stainless steel was studied by means of a three-dimensional atom probe (3DAP) and high-resolution transmission electron microscopy (HRTEM). The results show that coherent Ni3(Ti, Al) precipitates by heterogeneous nucleation from Ni/Ti/Al coclusters formed at defects (mainly dislocations) in the range of 350–450 °C, which leads to a rapid increase in strength and a sharp decrease in toughness. At 450–500 °C, the interface between Ni3(Ti, Al) and the matrix gradually changes from coherent to semicoherent, and an increase in the equivalent precipitate radius is accompanied by a decrease in their density. The tensile strength of the material reaches its peak value, and the toughness is improved. Within the range of 500–600 °C, Ni3(Ti, Al) continues to grow, aggregate and coarsen, and the amount of reverted austenite increases significantly. Both effects lead to a prominent decrease in the tensile strength and a substantial increase in toughness. The Ni3(Ti, Al) grows axially along the <111> dislocations through tube diffusion. The radial growth is parallel to [110]α and [11‾2]α, and the process is affected by the climbing and slipping of misfit edge dislocations. The strength increment of precipitates with different sizes formed at the peak aging temperature is calculated according to the critical transition radius, and the superposed results of the cutting and bypassing mechanisms during the yielding stage are found to be consistent with the experimental data, indicating that the two mechanisms work simultaneously. The findings provide a more accurate method for predicting the yield strength of materials.

Can Lense–Thirring Precession Produce QPOs in Supersonic Accretion Flows?

Abstract The timing properties of X-ray binaries are still not understood, particularly the presence of quasi-periodic oscillations (QPOs) in their X-ray power spectra. The solid-body regime of Lense–Thirring precession is one prominent model invoked to explain the most common type of QPOs, Type C. However, solid-body precession requires a specific structure that has not been examined in light of constrained properties of accretion flows. We assume in this paper, as solid-body precession requires, a disk separated into two flows at a transition radius r t : a cold outer flow and a hot inner flow (playing the role of the corona). We explore the physical structure of both flows using model-independent estimates of accretion parameters. We show that, in order to reproduce the observed X-ray spectra during luminous hard states, the hot flow must accrete at sonic to supersonic speeds, unreachable with typical viscous torques. As a result of this extreme accretion speed (or high α parameter), no region of the disk during these states lies in the “wave-like” regime required for solid-body precession. Furthermore, we expect the flow to align with the black hole spin axis via the Bardeen–Petterson effect inside a radius r break &gt; r t . As a consequence, the hot inner flow cannot exhibit solid body precession—as currently pictured in the literature—during luminous hard states. Since Type C QPOs are prevalent in these states, we conclude that this mechanism is unlikely to be responsible for producing Type C QPOs around stellar mass black holes.

Computer-digital technique for evaluating the geometry of the interface of the weld with the base metal

On the basis of the coordinate measuring machine CMM, there is a computer-digital technique for measuring the transition radius and the angle of conjugation of the metal with the base metal φ. It allows in automatic mode, with high accuracy and reliability, to determine the above parameters of welds, which are used in calculating stress factors and in assessing the fatigue strength of welded structures.

Interaction of a cold cloud with a hot wind: the regimes of cloud growth and destruction and the impact of magnetic fields

ABSTRACT Multiphase galaxy winds, the accretion of cold gas through galaxy haloes, and gas stripping from jellyfish galaxies are examples of interactions between cold and hot gaseous phases. There are two important regimes in such systems. A sufficiently small cold cloud is destroyed by the hot wind as a result of Kelvin–Helmholtz instabilities, which shatter the cloud into small pieces that eventually mix and dissolve in the hot wind. In contrast, stripped cold gas from a large cloud mixes with the hot wind to intermediate temperatures, and then becomes thermally unstable and cools, causing a net accretion of hot gas to the cold tail. Using the magneto-hydrodynamical code arepo, we perform cloud crushing simulations and test analytical criteria for the transition between the growth and destruction regimes to clarify a current debate in the literature. We find that the hot-wind cooling time sets the transition radius and not the cooling time of the mixed phase. Magnetic fields modify the wind–cloud interaction. Draping of wind magnetic field enhances the field upstream of the cloud, and fluid instabilities are suppressed by a turbulently magnetized wind beyond what is seen for a wind with a uniform magnetic field. We furthermore predict jellyfish galaxies to have ordered magnetic fields aligned with their tails. We finally discuss how the results of idealized simulations can be used to provide input to subgrid models in cosmological (magneto-)hydrodynamical simulations, which cannot resolve the detailed small-scale structure of cold gas clouds in the circumgalactic medium.

A unified accretion-ejection paradigm for black hole X-ray binaries

Context. We proposed in paper I that the spectral evolution of transient X-ray binaries (XrB) is due to an interplay between two flows: a standard accretion disk (SAD) in the outer parts and a jet-emitting disk (JED) in the inner parts. We showed in papers II, III, and IV that the spectral evolution in X-ray and radio during the 2010–2011 outburst of GX 339-4 can be recovered. However, the observed variability in X-ray was never addressed in this framework. Aims. We investigate the presence of low frequency quasi-periodic oscillations (LFQPOs) during an X-ray outburst, and address the possible correlation between the frequencies of these LFQPOs and the transition radius between the two flows, rJ. Methods. We select X-ray and radio data that correspond to 3 outbursts of GX 339-4. We use the method detailed in Paper IV to obtain the best parameters rJ(t) and ṁin(t) for each outburst. We also independently search for X-ray QPOs in each selected spectra and compare the QPO frequency to the Kepler and epicyclic frequencies of the flow in rJ. Results. We successfully reproduce the correlated evolution of the X-ray spectra and the radio emission for 3 different activity cycles of GX 339-4. We use a unique normalisation factor for the radio emission, f∼R. We also report the detection of 7 new LFQPOs (3 Type B, and 4 Type C), to go along with the ones previously reported in the literature. We show that the frequency of Type C QPOs can be linked to the dynamical JED-SAD transition radius rJ, rather than to the optically thin-thick transition radius in the disk. The scaling factor q such that νQPO ≃ νK(rJ)/q is q ≃ 70 − 130, a factor consistent during the 4 cycles, and similar to previous studies. Conclusions. The JED-SAD hybrid disk configuration not only provides a successful paradigm allowing us to describe XrB cycles, but also matches the evolution of QPO frequencies. Type C QPOs provide an indirect way to probe the JED-SAD transition radius, where an undetermined process produces secular variability. The demonstrated relation between the transition radius links Type C QPOs to the transition between two different flows, effectively tying it to the inner magnetized structure, i.e., the jets. This direct connection between the jets’ (accretion-ejection) structure and the process responsible for Type C QPOs, if confirmed, could naturally explain their puzzling multi-wavelength behavior.

Influence of loading sequence and residual stresses affecting the fatigue life of axle housing and crack path analysis using local approaches

The present work deals with the modification in linear damage accumulation using Palmgren-Miners rule which ignores the affects of loading sequence. Loading sequence plays a vital role in components like plates used in axle housing, as their loading pattern and its Stress Ratio ‘R’ continuously varies depending upon its application and the vehicle road terrain in which it operates. Loading cycles depending upon its severity induces strain hardening in the material due to its cyclic plasticity during the working conditions. This hardening affects the results in compressive residual stresses and its relaxation during the next stress cycle. One such loading condition in the axle housing has been taken as a case study and its strain hardening approach inducing residual stresses has been analyzed. It is found that if the affects of residual stress are taken into consideration, the life of the component is improved by 25.09% for the same sequence of loadings. It is also revealed from digital validation and experimental results that the transition radius is the most critical stress zone in the axle housing leading to housing cracks. The crack path analysis using local approaches helps to correlate the experimentation cracking path with the design calculations. 3-Dimensional approaches using finite element has revealed that the zone of maximum strain energy density in plate in the bending mode, is independent of its thickness and it depends only on the surface notch sensitivity.

The Fornax Deep Survey with VST

Context. This work is based on deep multi-band (g, r, i) data from the Fornax Deep Survey with the VLT Survey Telescope (VST). We analyse the surface brightness profiles of the 19 bright early-type galaxies (ETGs; mB ≤ 15 mag) inside the virial radius of the Fornax cluster (Rvir ∼ 0.7 Mpc), in the mass range 8 × 108 ≤ M* ≤ 1.2 × 1011 M⊙. Aims. The main aim of this work is to identify signatures of accretion onto galaxies by studying the presence of outer stellar haloes and to understand their nature and occurrence. Our analysis also provides a new and accurate estimate of the intra-cluster light inside the virial radius of Fornax. Methods. We performed multi-component fits to the azimuthally averaged surface brightness profiles available for all sample galaxies. This allows us to quantify the relative weight of all components in the galaxy structure that contribute to the total light. In addition, we derived the average g − i colours in each component identified by the fit, as well as the azimuthally averaged g − i colour profiles, to correlate them with the stellar mass of each galaxy and the location inside the cluster. Results. We find that in the most massive (1010 ≤ M ≤ 1011 M⊙) and reddest ETGs the fraction of light in, probably accreted, haloes (50%–90%) is much larger than in the other galaxies. All of these are located in the high-density region of the cluster (≤0.4Rvir ∼ 0.3 Mpc), belonging to the north-south clump (NS clump). Less massive galaxies (109 ≤ M ≤ 1010 M⊙) have an accreted mass fraction that is lower than 30%, have bluer colours, and reside in the low-density regions of the cluster. The colour profiles of the ETGs with the largest accreted mass fraction tend to flatten in the outskirts of the galaxy, that is beyond the transition radius from the central in situ to the ex situ accreted component. Inside the virial radius of the cluster (∼0.7 Mpc), the total luminosity of the intra-cluster light, compared with the total luminosity of all cluster members (bright galaxies and dwarfs), is about 34%. Conclusions. Inside the Fornax cluster there is a clear correlation between the amount of accreted material in the stellar haloes of galaxies and the density of the environment in which those galaxies reside. By comparing this quantity with theoretical predictions and previous observational estimates, there is a clear indication that the driving factor for the accretion process is the total stellar mass of the galaxy, which agrees with the hierarchical accretion scenario. Massive galaxies in the NS clump, with the largest accreted mass fractions, went through pre-processing in a group environment before this group merged with the main cluster early on. At the present epoch of the Fornax assembly history, these galaxies are the major contribution to the stellar density in the core of the cluster.

An expanded catalogue of low surface brightness galaxies in the Coma cluster using Subaru/Suprime-Cam

ABSTRACT We present a catalogue of low surface brightness (LSB) galaxies in the Coma cluster obtained from deep Subaru/Suprime-Cam V- and R-band imaging data within a region of $\mathord {\sim }4$ deg2. We increase the number of LSB galaxies presented in Yagi et al. (2016) by a factor of $\mathord {\sim }3$ and report the discovery of 29 new ultradiffuse galaxies (UDGs). We compile the largest sample of UDGs with colours and structural parameters in the Coma cluster. While most UDGs lie along the red-sequence relation of the colour–magnitude diagram, $\mathord {\sim }16$ per cent are outside (bluer or redder) the red-sequence region of Coma cluster galaxies. Our analyses show that there is no special distinction in the basic photometric parameters between UDGs and other LSB galaxies. We investigate the clustercentric colour distribution and find a remarkable transition at a projected radius of $\mathord {\sim }0.6$ Mpc. Within this cluster core region and relative to the red-sequence of galaxies, LSB galaxies are on average redder than co-spatial higher surface brightness galaxies at the 2σ level, highlighting how vulnerable LSB galaxies are to the physical processes at play in the dense central region of the cluster. The position of the transition radius agrees with expectations from recent cosmological simulation of massive galaxy clusters within which ancient infalls are predicted to dominate the LSB galaxy population.

Fatigue Life Prediction of Lap Welds in Axle Housings Using Notch Stress Modelling Approach and Design Modifications to Overcome the Failure

Axle housing in the axle assembly of medium and heavy commercial vehicle is the structural load-bearing member supporting platform payloads for different road conditions which has an impact on the axle through the suspension systems. Axle housings are fabricated structures from hot formed structural plates integrated using MIG welding. This paper presents life prediction of one of the critical weld in the axle housing joining dome cover with the banjo housing as cracking of the weld leads to oil leakages and the entire transmission fails without oil. Failure of root crack in the weld noticed at 0.4 million cycles in indoor bench testing against the minimum life requirement of 0.6 million cycles. Similar failure noticed in customer vehicles in the range of 0.3 million km’s. To analyse the failure, life prediction using CAE is carried out as per IIW modelling guidelines of nominal stress and notch stress approaches of weld roots and toe. Analysis reveals weld roots act as weld notches and life calculation of the weld using notch stress approach, matches with the experimental results. Also, the stress concentration factors proposed by IIW for MIG weld match with the design-calculated results. Since the weld root stress is higher than the acceptance, design improvement is carried out to reduce the stress values. Banjo bowl transition radius is increased to have a higher section modulus there by stresses has been reduced from 580 to 320 MPa and life improvement in the weld root by 44% increase. Life correlation achieved from design-calculated values using notch stress approach with the experimental results. Also, field performance of the weld cracks leading to oil leakages in the housings of the customer vehicle has reduced by almost 90%, resulting in warranty cost reduction in the commercial vehicles.

From Super-Earths to Mini-Neptunes: Implications of a Surface on Atmospheric Circulation

Abstract It is well known that planets with radii between that of Earth and Neptune have been the most commonly detected to date. To classify these planets as either terrestrial or gaseous, typically we turn to mass–radius relations and composition curves to determine the likelihood of such a planet being rocky or gaseous. While these methods have set a likely transition radius of approximately 1.5 R ⊕, we cannot expect that any change between terrestrial and gaseous compositions will be a sharp cutoff, and composition curve predictions result in ambiguous designations for planets right near this transition radius. In this work, we present 3D general circulation models (GCMs) of transition planets, wherein we study the effects of a surface on observable quantities such as the latitudinal variations and eclipse depths. We present our updated GCM, validated on the circulation of Earth, before discussing our modeling choices for this transition planet. Finally, we discuss the results of this study and explore the prospects of detecting the presence of a surface through observations of secondary eclipses in the future.

Kinematics of simulated galaxies II: Probing the stellar kinematics of galaxies out to large radii

ABSTRACT We investigate the stellar kinematics of a sample of galaxies extracted from the hydrodynamic cosmological Magneticum Pathfinder simulations out to five half-mass radii. We construct differential radial stellar spin profiles quantified by the observationally widely used λ and the closely related (V/σ) parameters. We find three characteristic profile shapes: profiles exhibiting a (i) peak within 2.5 half-mass radii and a subsequent decrease; (ii) continuous increase that plateaus at larger radii typically with a high amplitude; (iii) completely flat behaviour typically with low amplitude, in agreement with observations. This shows that the kinematic state of the stellar component can vary significantly with radius, suggesting a distinct interplay between in-situ star formation and ex-situ accretion of stars. Following the evolution of our sample through time, we provide evidence that the accretion history of galaxies with decreasing profiles is dominated by the anisotropic accretion of low-mass satellites that get disrupted beyond ∼2.0 half-mass radii, building up a stellar halo with non-ordered motion while maintaining the central rotation already present at z = 2. In fact, at z = 2 decreasing profiles are the predominant profile class. Hence, we can predict a distinct formation pathway for galaxies with a decreasing profile and show that the centre resembles an old embedded disc. Furthermore, we show that the radius of the kinematic transition provides a good estimation for the transition radius from in-situ stars in the centre to accreted stars in the halo.

Assessment of the stress-strain state in the weld zone for the forklift truck frame

In the context of an ever-increasing complication of both the construction of building machines and mechanisms and the conditions of their operation, the issues of achieving reliability and durability of the main welded joints are actualized, since the quality of the welded joint determines the operability of the assembly and the machine as a whole. In this regard, ensuring satisfactory weldability and obtaining a better welded joint are necessary conditions of increased strength for welded structures on which the working bodies of construction machinery, as well as mechanisms and their assembly units are mounted. The article addresses the key issues of improving the reliability of welded structures of building machines. Special attention is paid to the problems of strengthening hazardous areas, as well as the restoration of such zones in the welded structures of construction machinery. As an example, the article considers the frame of a forklift truck equipped with a hydraulic manipulator. Particular emphasis is placed on the fact that when calculating the distances between welds, it is necessary to take into account its dependence on the welding conditions and the parameters of the frame structures of construction machines. The stress-strain state of the frame was evaluated by modeling the state of the structure in various situations. Using finite element analysis programs, it was found that it is possible to reduce local stresses that exceed the tensile strength of the material and cause the risk of microcracks due to the welding of overlays with short seams in a checkerboard pattern, as well as finding the optimal parameters of the welds taking into account the stress concentration. It was also established during the study that the greatest influence on the value by stress concentration factors is exerted by the radius of the transition from the base metal to the weld metal. An increase in the transition radius from 0.1 mm to 1.0 mm makes it possible to reduce the value of the stress concentration coefficient.

Experimental constraints on subglacial rock friction

AbstractSubglacial rock friction is an important control on the sliding dynamics and erosive potential of hard-bedded glaciers, yet it remains largely unconstrained. To explore the relative influence of basal melt rate, effective stress and ice temperature on frictional resistance, we conducted abrasion experiments in which limestone beds were slid beneath a fixed slab of ice laden with granitic rock fragments. Shear stress scales linearly with melt rate and cryostatic stress, confirming that both viscous drag and effective stress are first-order controls on the contact force in drained conditions. Furthermore, temperature gradients in the ice increase the contribution of viscous drag on basal shear stress. In all experiments, the relationship between melt rate and shear stress is best explained by a model that accounts for the effects of regelation and viscous creep on the bed-normal drag force. We interpret this to mean fluid flow around entrained clasts contributed to basal drag even at subfreezing temperatures. Incorporating premelting dynamics into the Watts/Hallet model for subglacial rock friction, we find that the predicted debris-bed drag decreases by approximately an order of magnitude, with a corresponding ~3.5 × increase in the transition radius. This is lower than we observe for ice slightly below the pressure melting point.