Entire Stress Range Research Articles

Analysis of cubic perovskite oxide AgNbO3 under stress conditions: Potential for photovoltaic and high-temperature applications - A DFT study

In the family of perovskite materials, perovskite oxide gained considerable attention from researchers in diverse fields, due to their flexible chemistry. Here, cubic perovskite oxide AgNbO3 was studied using DFT via CASTEP code, to explore the key properties under varying stress conditions ranging from 0 to 100 GPa. Phase stability was confirmed by XRD analysis. Electronic properties confirmed the increasing trend in the band gap from 1.422 eV to 1.722 eV, with increasing stress. Optical characteristics reveal high absorption, conductivity, and lower loss function. Significantly, the elastic constants (C11, C12, and C44) satisfy the Born-stability criteria, ensuring the mechanical stability of the considered compound. Moreover, the Poisson ratio, Pugh's ratio (B/G), Frantsevich ratio, Cauchy pressure (PC), and anisotropic factor ensure the ductile nature as well as an anisotropic character over the entire stress range. The positive trajectory in phonon density confirms the thermal stability. Thermodynamically, the studied material shows high-temperature stability with a higher value of applied stress as confirmed by Debye temperature (θD). Furthermore, an inverse association of enthalpy and total entropy with free energy was observed. Based on these findings, confidently suggested that the considered cubic perovskite oxide, AgNbO3, can be efficiently used for photovoltaic and high-temperature applications.

Mechanical Properties of Rock Salt from the Kłodawa Salt Dome-A Statistical Analysis of Geomechanical Data.

Rock salt is a potential medium for underground storage of energy resources and radioactive substances due to its physical and mechanical properties, distinguishing it from other rock media. Designing storage facilities that ensure stability, tightness, and safety requires understanding the geomechanical properties of rock salt. Despite numerous research efforts on the behaviour of rock salt mass, many cases still show unfavourable phenomena occurring within it. Therefore, the formulation of strength criteria in a three-dimensional stress state and the prediction of deformation processes significantly impact the functionality of storage in salt caverns. This article presents rock salt's mechanical properties from the Kłodawa salt dome and a statistical analysis of the determined geomechanical data. The analysis is divided into individual mining fields (Fields 1-6). The analysis of numerical parameter values obtained in uniaxial compression tests for rock salt from mining Fields 1-6 indicates an average variation in their strength and deformation properties. Upon comparing the results of Young's modulus (E) with uniaxial compressive strength (UCS), its value was observed with a decrease in uniaxial compressive strength (E = 4.19968·UCS2, R-square = -0.61). The tensile strength of rock salt from mining Fields 1-6 also exhibits moderate variability. An increasing trend in tensile strength was observed with increased bulk density (σt = 0.0027697·ρ - 4.5892, r = 0.60). However, the results of triaxial tests indicated that within the entire range of normal stresses, the process of increasing maximum shear stresses occurs linearly ((σ1 - σ3)/2 = ((σ1 + σ3)/2)·0.610676 + 2.28335, r = 0.92). A linear relationship was also obtained for failure stresses as a function of radial stresses (σ1 = σ3·2.51861 + 32.9488, r = 0.73). Based on the results, the most homogeneous rock salt was from Field 2 and Field 6, while the most variable rock salt was from Field 3.

Fatigue life prediction of aluminum alloy T‐welded joints root failure based on equivalent crack method

AbstractThis study proposes an equivalent crack life prediction method for root cracks in T‐welded joints. An equivalent initial defect is used to describe the severity of the weld defect. Fatigue life prediction is achieved based on equivalent fracture parameters and high‐stress fatigue life reference points fitted to obtain a P‐S‐N curve for the entire stress range. Taking the 6082‐aluminum alloy T‐welded joints as the object, the test data under tensile load P‐S‐N curve fitting and crack growth simulation were carried out to compare and verify the applicability under constant and equivalent spectral load. This method enables deterministic fatigue life prediction with less testing and cost. Meanwhile, the approach incorporates the uncertainty of the physical model of the weld into the P‐S‐N curve, simplifying the process of calculating the probabilistic fatigue life.

A Semiempirical Model for Post‐Yield Stress Instability in the Stress–Strain Response of 3D Lattice Structures under Compressive Loads

Mechanical behavior of lattice structures is important for a range of engineering applications. Herein, a new semiempirical model is proposed that describes the entire range of stress–strain response of lattice structures, including the stress‐instability region which is modeled as an oscillator. The model can be fit to individual stress–strain curves to extract elastic modulus, yield stress, collapse stress, post‐yield collapse ratio, densification strain, and the energy absorbed per unit volume. The model is fit to 119 unique experimental stress–strain curves from 13 research papers in literature covering four different lattice designs, namely, octet truss, body‐centered cubic with vertical members, body‐centered cubic, and hexagonal. Manufacturing methods (additive and conventional) and materials (metals and polymers) were also included in the analysis. The fitted model yields several new insights into the compression behavior of previously tested lattice structures and can be applied to additional lattice designs. Among other results, analysis of variance (ANOVA) reveals that the octet truss lattice demonstrates the highest post‐yield collapse ratio and the smallest normalized energy absorption per unit volume amongst the lattice structures investigated. The proposed model is a powerful tool for designers to quantitatively compare and select 3D lattice structures with the desired mechanical characteristics.

Shear thickening in dense bidisperse suspensions

Discrete-particle simulations of bidisperse shear thickening suspensions are reported. The work considers two packing parameters, the large-to-small particle radius ratio ranging from δ=1.4 (nearly monodisperse) to δ=4, and the large particle fraction of the total solid loading with values ζ=0.15, 0.5, and 0.85. Particle-scale simulations are performed over a broad range of shear stresses using a simulation model for spherical particles accounting for short-range lubrication forces, frictional interaction, and repulsion between particles. The variation of rheological properties and the maximum packing fraction ϕJ with shear stress σ are reported. At a fixed volume fraction ϕ, bidispersity decreases the suspension relative viscosity ηr=ηs/η0, where ηs is the suspension viscosity and η0 is the suspending fluid viscosity, over the entire range of shear stresses studied. However, under low shear stress conditions, the suspension exhibits an unusual rheological behavior: the minimum viscosity does not occur as expected at ζ≈0.5, but instead decreases with further increase of ζ to 0.85. The second normal stress difference N2 acts similarly. This behavior is caused by particles ordering into a layered structure, as is also reflected by the zero slope with respect to time of the mean-square displacement in the velocity gradient direction. The relative viscosity ηr of bidisperse rate-dependent suspensions can be predicted by a power law linking it to ϕJ, ηr=(1−ϕ/ϕJ)−2 in both low and high shear stress regimes. The agreement between the power law and experimental data from literature demonstrates that the model captures well the effect of particle size distribution, showing that viscosity roughly collapses onto a single master curve when plotted against the reduced volume fraction ϕ/ϕJ.

Shock compression of silver to 300 GPa: Wave profile measurements and melting transition

Recent in-situ x-ray diffraction (XRD) measurements on laser-shock compressed Ag foils demonstrated a face-centered-cubic to body-centered-cubic transformation at \ensuremath{\sim}150 GPa and melting between 172 and 197 GPa [Phys. Rev. Lett. 124, 235701 (2020)]. As a complement to the XRD work, we conducted plate impact experiments to obtain shock velocity and wave profile measurements on thicker Ag samples shock-compressed to peak stresses between 30 and 300 GPa. The shock velocity--particle velocity results were fitted very well by a linear relation over the entire stress range, providing an accurate determination of the Ag Hugoniot (locus of the stress-volume states achieved under shock compression). For peak stresses below 187 GPa and above 210 GPa---corresponding to the solid and liquid phases, respectively---the wave profiles show clean single waves. No wave profile features related to the fcc-bcc transformation at \ensuremath{\sim}150 GPa were observed, implying minimal volume change for the transformation. For stresses between 187 and 210 GPa, an initial jump was followed by a time-dependent increase in the particle velocity (20--80 ns risetime) to the peak state---corresponding to the solid-liquid mixed phase response. Unlike the solid and liquid response, the mixed-phase response cannot be readily analyzed analytically. Instead, numerical simulations incorporating an accurate multiphase equation of state for Ag---not currently available---are required to analyze the wave profiles measured at 187--210 GPa stresses. The present work shows the potential for using wave profile measurements to examine the melting transition under shock compression.

Development of hot deformation rheological model as exemplified by 1424 and V-1461 aluminum-lithium alloys

The article proposes a variant of the rheological model of hot deformation – the law of hyperbolic sine, which, in contrast to the standard one, takes into account not only the strain rate and process temperature, but also the strain ratio. Material constants included in the law of hyperbolic sine are replaced by polynomial functions of the strain ratio with coefficients calculated using the corresponding method developed. The paper describes applications of the rheological model proposed in low-density aluminum-lithium alloys 1424 of the Al–Mg–Li–Zn system and V-1461 of the Al–Cu–Li–Zn system, for which flow curves in the temperature range 400–480 °C and strain rate range 1–60 s–1 up to a strain ratio of 0.6 are defined by physical simulation at the Gleeble 3800 unit. The influence of the initial material state was also investigated – samples were taken from both the ingot and hot-rolled plates. Constants were determined for the rheological model of hot deformation including the Zener–Hollomon parameter and the law of hyperbolic sine for the entire range of stresses and strains. After approximating the dependences of the model parameters on true strains with a 4th degree polynomial law, a rheological model was created that describes the alloy behavior in the temperature-rate range under study. The features of changes in hyperbolic sine law parameters depending on the strain ratio were established. It was shown that, in general, parameters for the cast material are higher than for the rolled one. A comparison between the standard and proposed models showed that the use of the standard model over the entire strain interval leads to too high flow stress values (up to 12 %).

Endothelialization of PDMS-based microfluidic devices under high shear stress conditions

Microfluidic systems made out of polydimethylsiloxane (PDMS) offer a platform to mimic vascular flow conditions in model systems at well-defined shear stresses. However, extracellular matrix (ECM) proteins that are physisorbed on the PDMS are not reliably attached under high shear stress conditions, which makes long-term experiments difficult. To overcome this limitation, we functionalized PDMS surfaces with 3-aminopropyltriethoxysilane (APTES) by using different surface activation methods to develop a stable linkage between the PDMS surface and collagen, which served as a model ECM protein. The stability of the protein coating inside the microfluidic devices was evaluated in perfusion experiments with phosphate-buffered saline (PBS) at 10−40 dynes/cm2 wall shear stress. To assess the stability of cell adhesion, endothelial cells were grown in a multi-shear device over a shear stress range of 20−150 dynes/cm2. Cells on the APTES-mediated collagen coating were stable over the entire shear stress range in PBS (pH 9) for 48 h. The results suggest that at high pH values, the electrostatic interaction between APTES-coated surfaces and collagen molecules offer a very promising tool to modify PDMS-based microfluidic devices for long-term endothelialization under high shear stress conditions.

Wall slip of highly concentrated non-Brownian suspensions in pressure driven flows: A geometrical dependency put into a non-Newtonian perspective

Wall slip quantification using the classical Mooney slip analysis has produced physically unreasonable results for many complex fluids. Over the past decades, the assumption that the slip velocity is solely dependent on the wall shear stress has therefore been questioned. In this contribution, the influence of the radius of cylindrical dies on the wall slip velocity of highly concentrated non-Brownian suspensions in a high-pressure capillary rheometer is re-examined, by varying the rheology of the liquid phase. Water- and oil-based suspensions (solid volume fraction ~ 0.60, D4,3 ~ 5 µm) are made using liquid phases that have different flow indices (n = 0.22 – 1.00) and a variation in their thickener concentration (25 g/L – 350 g/L). All classical Mooney plots showed negative y-intercepts and the fit worsened with decreasing flow index. A modification to the Mooney analysis is proposed that includes a geometrical dependency of the slip velocity that scales with the flow index of the liquid phase. Proposed modified Mooney plots not only show positive y-intercepts, but also show a good fit (R2 > 0.99) over the entire range of shear rates (10 – 640 s − 1) and corresponding wall shear stresses. The geometrical dependency is thought to arise from the shear stress gradient within the extrusion die.

Enhanced erodibility of deep-sea sediments by presence of calcium carbonate particles

Using an erosion chamber, erodibility experiments on two different deep-sea sediments (mainly clayey silt) acquired in the western Pacific Ocean have been conducted to estimate the erosion rate and its potential controlling factors. Overall, the erosion rates of both deep-sea sediments were in the range of 10−7–10−5 kg m−2 s−1 which was two or three orders of magnitude lower than that of sediments in shallow environments. Such erodibility, however, exhibited two contrasting patterns depending on the carbonate compensation depth (CCD), which determines carbonate contents in sediments. At one site (MC1), above the CCD, the sediments (carbonate content 18.32 ± 1.00 wt%) were easily resuspended by surface erosion, resulting in a high eroded mass (2.49 × 10−2 kg m−2 at shear stress of 0.6 Pa). At another site (MC4), below the CCD, the sediments (carbonate content 0.06 ± 0.04 wt%) were less resuspended by floc erosion, resulting in a low eroded mass (3.70 × 10−3 kg m−2 at shear stress of 0.6 Pa). Over the entire range of bed shear stress, the erosion rate above the CCD was about 1–6 times higher than that below the CCD. The difference in carbonate content between two sites caused different variations in the bed resistance with depth. The erodibility above the CCD was enhanced, probably due to the particle roughness and low bulk density. Once the bed shear stress exceeded about 0.39 Pa, the erosion type of MC1 shifted from depth-limited to transitional erosion. However, the erosion type of MC4 always remained depth-limited over the entire range of bed shear stress. These results underline the effect of calcium carbonate on resuspension and erosion behaviors of the deep-sea sediments.

Mechanical and optical response of polymethylpentene under dynamic compression

Polymethylpentene, commonly referred to by its trade name TPX (Mitsui Chemicals, Inc.), is a thermoplastic polymer that has the potential to be a useful window material for dynamic compression experiments. For such experiments, an optically transparent or a low x-ray absorptive window is often used to maintain stress within the sample during compression. TPX can be used as a low-impedance optical and x-ray window due to its good transmittance in most parts of the electromagnetic spectrum, very low density (0.83 g/cm3), and low x-ray absorption. In dynamic compression experiments, interferometry can be used to determine the particle velocity at the interface between the sample and window. However, velocimetry measures the rate of change of the optical path length, commonly referred to as the apparent particle velocity. An experimentally determined window correction factor is needed to ascertain the actual particle velocity from the measured apparent velocity. Here, we present the results of a series of dynamic compression experiments from 1 to 31 GPa designed to characterize the mechanical and optical response of TPX, determine the range of stresses over which TPX is transparent, and determine the window correction factor. The index of refraction was found to be essentially linear in density, resulting in a simple constant correction factor. TPX was found to remain largely transparent over the entire stress range examined.

Application of bending creep for examining effect of service conditions on creep response of steel

We demonstrate that creep testing of cantilevers in bending is suitable for evaluating steady-state creep parameters, including the stress exponent. In particular, a low alloy bainitic boiler tube steel, namely T11, in as-fabricated condition and after 27 years of service in a coal-fired power-plant were tested in bending at 600 °C at effective steady-state stresses of 100–200 MPa. Steady-state strain rates obtained from the bending tests matched reasonably well with those obtained from uniaxial compression tests performed at equivalent stresses, thereby unambiguously validating the bending test methodology for the entire range of stress. All types of samples showed a stress exponent of 6; however, the steady-state strain rates of the in-service samples were ~7 times larger than those of as-fabricated samples. Although this suggests a substantial loss in the creep resistance of the tubes at the end of the design-life, the “to-be-discarded” tube may still have considerable residual life. Microstructural evaluation of the samples revealed coarsening of carbides in bainite and metal enrichment of carbides, with excess of M6C, with exposure to the service conditions. A structure-property correlation is established to explain the experimental observations, and results are discussed in light of existing literature.

The mechanism of tidal triggering of earthquakes at mid-ocean ridges

The strong tidal triggering of mid-ocean ridge earthquakes has remained unexplained because the earthquakes occur preferentially during low tide, when normal faulting earthquakes should be inhibited. Using Axial Volcano on the Juan de Fuca ridge as an example, we show that the axial magma chamber inflates/deflates in response to tidal stresses, producing Coulomb stresses on the faults that are opposite in sign to those produced by the tides. When the magma chamber’s bulk modulus is sufficiently low, the phase of tidal triggering is inverted. We find that the stress dependence of seismicity rate conforms to triggering theory over the entire tidal stress range. There is no triggering stress threshold and stress shadowing is just a continuous function of stress decrease. We find the viscous friction parameter A to be an order of magnitude smaller than laboratory measurements. The high tidal sensitivity at Axial Volcano results from the shallow earthquake depths.

Low-stress creep deformation in two opto-electronic glass-epoxy joints: Part II – Joint measurements and FEA

The creep deformation of two glass-epoxy adhesive joints, representative of joint designs used in opto-electronic devices, was measured at various temperatures and relatively low stress levels using a novel, ultra-sensitive method employing optical interference fringes. The adhesive creep models obtained in Part I were then used as the constitutive equations in finite element models of the joints with the objective of assessing the accuracy of the predictions of creep deformation at the low stresses typical of opto-electronic applications. Good agreement was obtained for both adhesives; however, the higher modulus adhesive was more complicated, exhibiting highly non-linear creep behavior as the stress levels approached zero. The lower modulus adhesive was shown to be linearly viscoelastic over the entire range of stresses encountered in the opto-electronic joints.

Non-linear stress-orientation behavior of flexible chain polymers under fast elongational flow

Closed-form analytical formulas are proposed for non-linear stress-orientation relation valid in the entire range of tensile stresses, intermediate and high, basing on the inverse Langevin chain statistics. Tensile force and orientation characteristics for single, flexible chain macromolecule are reconsidered in a closed-form Padè approximation of the inverse Langevin function in the entire range of chain extensions, as well as the dynamics of molecular deformation and orientation for systems of chains subjected to uniaxial elongational flow. Average stress and orientation tensors, not collinear in the non-linear range, as well as the tensile stress and axial orientation factor of the chain segments in the system are calculated. For the intermediate tensile stresses, the closed-form formula is derived in the first non-Gaussian term approximation of the inverse Langevin function with the assumption of dominating longitudinal elongation of the chains. The high-stress non-linearity formula is derived with the Padè and Peterlin modulus approximations and aligned chain end-to-end vectors by the flow. Both formulas are validated by exact numerical calculations without the assumptions and influence of the approximations is estimated. Ranges of applicability of the formulas are illustrated and examples of their application are presented.

Numerical Investigation on Plastic Strain Correction Factor in Simplified Elastic-Plastic Fatigue Analysis

A plastic strain correction factor is used in a simplified elastic-plastic fatigue analysis of nuclear power plant components. Numerical investigation on the plastic strain correction factor is presented for the case of the primary and secondary stress range exceeding three times the design stress intensity value under thermal-mechanical loadings. The plastic strain correction factor was computed separately by following the RCC-M code and applying the elastic-plastic finite element analysis. The influence of loading ratio, loading controlled mode and ambient temperature on the plastic strain correction factor was discussed. It was shown that the plastic strain correction factor computed from the RCC-M code is not as conservative as that from the complete elastic-plastic finite element analysis when the primary plus secondary stress range is close to three times the design stress intensity value. However, it is too conservative when the primary plus secondary stress range is more than three times the design stress intensity value multiplying parameter m (use in RCC-M code). Additionally, a new formula of plastic strain correction factor was proposed to provide a complete envelope curve to the entire primary plus secondary stress range.

Solute strengthening at high temperatures

The high temperature behavior of solute strengthening has previously been treated approximately using various scaling arguments, resulting in logarithmic and power-law scalings for the stress-dependent energy barrier versus stress τ. Here, a parameter-free solute strengthening model is extended to high temperatures/low stresses without any a priori assumptions on the functional form of . The new model predicts that the well-established low-temperature, with energy barrier and zero temperature flow stress , transitions to a near-logarithmic form for stresses in the regime and then transitions to a power-law form at even lower stresses . and remains as the reference energy and stress scales over the entire range of stresses. The model is applied to literature data on solution strengthening in Cu alloys and captures the experimental results quantitatively and qualitatively. Most importantly, the model accurately captures the transition in strength from the low-temperature to intermediate-temperature and the associated transition for the activation volume. Overall, the present analysis unifies the different qualitative models in the literature and, when coupled with the previous parameter-free solute strengthening model, provides a single predictive model for solute strengthening as a function of composition, temperature, and strain rate over the full range of practical utility.

Mechanical characteristics and microstructure of weld joint of high-temperature martensitic steel containing 9% Cr

The structure and mechanical characteristics of a weld joint of 10Kh9K3V2MFBR steel (0.097 C, 0.17.Si, 0.54 Mn, 8.75 Cr, 0.21 Ni, 0.51 Mo, 0.07 Nb, 0.23 V, 0.004 N, 0.003 B, 1.6 W, 0.15 Cu, and Fe for balance, wt %) have been studied; the joint was produced by hand welding in an argon atmosphere using 03Kh20N45M7G6B welding wire (0.3 C, 20 Cr, 45 Ni, 7 Mo, 6 Mn, and 1 Nb, wt %). The weld joint is divided into the zone of the base metal, a thermal effect zone, which consists of zones that contain fine and coarse original austenitic grains, and the zone of seam metal. It has been shown that the weld joint of 10Kh9K3V2MFBR steel possesses high strength characteristics at the room temperature under static loading and a satisfactorily impact toughness, which has the minimum value of 30 J/cm2 in the zone of the seam metal and does not depend on the temperature. With a decrease in the temperature from the room temperature to 253 K, a ductile–brittle transition occurs in the thermal effect zone. Creep tests carried out at the temperature of 923 K have shown that the long-term strength of the weld seam is lower than that of the base material in the entire stress range being tested. At stresses of 140 MPa or higher, the acceleration of creep in the weld seam is observed, while at low stresses of about 120 MPa, the rates of creep in the weld seam and in the base metal remain similar until the transition to the stage of accelerated fracture occurs. The difference in the values of the long-term strength is due to premature fracture, which occurs in the thermal effect zone with the finegrained structure.

Nucleation of dislocations in aluminum alloys with copper

The influence of copper impurities on the nucleation of dislocations in aluminum has been investigated using the method for determining the average lifetime of the metastable state. The primary data have been obtained using the molecular dynamics method. The obtained dependences of the dislocation nucleation rate on the shear stress in pure aluminum and aluminum solid solutions with copper have been plotted in the Arrhenius form. It has been found that, with an increase in the copper concentration, the activation parameters for these dependences decrease. It has been shown that an increase in the temperature leads to an increase in the sensitivity of the dislocation nucleation rate to stresses in aluminum solid solutions with 0.1–3.0 at % Cu, in contrast to pure aluminum in which the sensitivity is almost independent of the temperature. The dependences of the dislocation nucleation rate on the copper concentration and temperature over the entire range of stresses have been discussed based on the obtained approximations.

Modal acoustic emission of damage accumulation in C/C–SiC composites with different fiber architectures

The stress-dependent material behavior of carbon fiber reinforced ceramic matrix composites (C/C–SiC) was investigated with modal acoustic emission (AE) technique. AE observation is a promising health monitoring method which provides accurate location and identification of the recorded damage-related AE events. For a better understanding and identification of different damage mechanisms C/C–SiC composites with different fiber orientations were studied. Load/unload/reload tensile tests were performed and measurements were made over the entire stress range in order to determine the stress-dependence of acoustic activity for increasing damage states. In general it was found that in C/C–SiC composites a significant damage-related increase in AE energy was observed close to the ultimate tensile stress. Also, fiber architecture dependent differences during damage accumulation in terms of total number of AE events and their typical AE energy could be determined and correlated to different damage mechanisms.