Internal Stress State Research Articles

Mechanical Properties of Iron Tailing Sand Grout Sleeve Joints and Force Analysis.

In this paper, the mechanical properties and internal stress condition of the reinforcing bar sleeve connectors with ferro-tailed mineral sand cementitious grout as filler material were analyzed as research objects. Firstly, an experimental study was carried out on the reinforcing bar sleeve connectors of iron tailing sand grout with a 40% substitution rate of mechanism sand to analyze the mechanical properties of different grout types, age, and reinforcement diameters under unidirectional tensile, high stress, and large deformation of repeated tensile and compressive stresses. Next, five groups of sleeve joints with different anchorage lengths were set up for unidirectional tensile tests. The results show that, with the decrease of the diameter of the reinforcement, the grip force and bond strength of the iron tailing sand grout on the internal reinforcement gradually increase. Under conditions of large deformation and high stress due to repeated tensile loading, the residual deformation and total elongation of iron tailing sand grout sleeve joints are satisfactory. Additionally, the restraining anchorage effect of iron tailing sand grout in the end section is small. The utilization rate and integrity of iron tailing sand grout in the initial anchorage section are better.

Mechanical characterisation of a structural battery electrolyte

Structural battery composites require a structural electrolyte to work. The structural battery electrolyte has a bicontinuous microstructure which enables its dual roles: mechanical load transfer and ion transport between the electrodes. These structural electrolytes are difficult to characterise mechanically via bulk tests. For this reason, no extensive characterisation of the mechanical properties of the structural battery electrolyte has been performed to date. In this study, we highlight the many challenges of these types of tests, including the complexity of sample manufacturing, preparation and testing. We further demonstrate a method to prepare test samples and to perform mechanical tests on the structural battery electrolyte. The executed test campaign provides measures of Young's modulus (approximately 412 MPa) and Poisson's ratio (0.34), as well as tensile (4.85 MPa) and compressive strength (32.66 MPa) and strain to failure (2.49 % and 28.11 % in tension and compression, respectively). In addition, cure shrinkage is investigated and found insignificant. These results are crucial for the further development of structural battery composites as they allow for accurate prediction of their internal stress states.

Numerical and experimental investigation on critical stresses due to rail cant

The track integrity is significantly affected by the internal stress state of the rail. The rail cant influences the flexural stress distribution on the rail foot, thereby shifting the critical stress locations. In this study, full-scale lab testing was done for heavy equivalent wheel loads (16–40 tonne) to measure the rail foot stresses. Further, the mathematical model for track design is modified considering the effect of rail cant on stress distribution and compared with the developed finite element model (FEM) and the experimental study conducted. It was observed that the FEM and modified model calculates the rail stresses with better accuracy of around 5% for heavy wheel loads. The rail cant cause redistribution of stresses, making the gauge corner critical to rail failures. It was observed that stresses at the gauge corner are 20% higher than at the field corner of the rail foot.

Silk Fibroin Film Decorated with Ultralow FeCo Content by Sputtering Deposition Results in a Flexible and Robust Biomaterial for Magnetic Actuation.

Magnetically responsive soft biomaterials are at the forefront of bioengineering and biorobotics. We have created a magnetic hybrid material by coupling silk fibroin─i.e., a natural biopolymer with an optimal combination of biocompatibility and mechanical robustness─with the FeCo alloy, the ferromagnetic material with the highest saturation magnetization. The material is in the form of a 6 μm-thick silk fibroin film, coated with a FeCo layer (nominal thickness: 10 nm) grown by magnetron sputtering deposition. The sputtering deposition technique is versatile and eco-friendly and proves effective for growing the magnetic layer on the biopolymer substrate, also allowing one to select the area to be decorated. The hybrid material is biocompatible, lightweight, flexible, robust, and water-resistant. Electrical, structural, mechanical, and magnetic characterization of the material, both as-prepared and after being soaked in water, have provided information on the adhesion between the silk fibroin substrate and the FeCo layer and on the state of internal mechanical stresses. The hybrid film exhibits a high magnetic bending response under a magnetic field gradient, thanks to an ultralow fraction of the FeCo component (less than 0.1 vol %, i.e., well below 1 wt %). This reduces the risk of adverse health effects and makes the material suitable for bioactuation applications.

A B-spline material point method for deformation failure mechanism of soft–hard interbedded rock

Geological hazards related to soft–hard interbedded rock are frequent in rock engineering. The material point method (MPM) is a mesh-free numerical approach specifically designed for analyzing large deformations. Notably, significant grid-crossing errors frequently arise when material points traverse the underlying grid. To investigate the failure mechanism of soft–hard interbedded rock, an enhanced MPM incorporating B-spline basis functions and Voronoi polygon discretization is developed and subsequently validated through comparisons with uniaxial compression test data and other numerical methods. The numerical results of soft–hard interbedded rock specimens associated with different soft layer dips (SLD) and confining pressures indicate that the SLD has a great effect on compressive strength and crack extension at low confining pressure. Rocks from SLD-30° to SLD-75° correspond to the “sliding failure along discontinuities” failure mode and have lower compressive strength than rocks with other SLD angles. It is also demonstrated that the propagation of cracks leads to a significant alteration in the internal stress state of the rock, and that stress concentrations at the crack tip exacerbate the development of failure surface. Furthermore, the failure mode of soft–hard interbedded rock can be categorized into four types: (1) sliding failure across multiple discontinuities, (2) tensile fracture across multiple discontinuities, (3) sliding failure along discontinuities, (4) tensile-split along discontinuities.

The Character of Couples and Couple Stresses in Continuum Mechanics

In this paper, the concepts of moments and couples in mechanics are examined from a fundamental perspective. Representing a couple by its moment vector is very useful in rigid body mechanics, where the states of internal stresses and deformation are not studied. This is because only the moment of couples appears in the governing equation of moment equilibrium. On the other hand, when considering the state of internal stresses and deformation in continuum mechanics, not only the moment of couples but also the line of action of their constituent parallel opposite forces must be specified. In defining a well-posed problem for a continuum, including the governing equations of moment equilibrium or motion, boundary conditions, and constitutive relations, only the moment of couples (e.g., body couples, couple tractions, couple stresses) appear without specifying the line of action of the constituent parallel forces. Nevertheless, the physical state of stress and deformation in the continuum must be unique and determinate. Therefore, this physical requirement imposes some restrictions on the form of body couples, couple tractions, and couple stresses. Here, the uniqueness of interactions in the continuum is used to establish that the continuum does not support a distribution of body couples or a distribution of surface twisting couple tractions with normal moments. Furthermore, the mechanism of action of the couple traction as a double layer of shear force tractions is established, along with the skew-symmetric character of the couple stress moment tensor.

El Chichón volcanic activity before and after the Mw8.2, 2017, Chiapas earthquake, México. Is El Chichón ready to erupt?

El Chichón volcano is the most active volcano in the state of Chiapas, México, and experienced its last Plinian eruption (VEI = 5) in 1982. To better assess its volcanic hazard, we studied its readiness to erupt by estimating changes in its internal stress state. These stress changes are difficult to calculate accurately, for example in the absence of focal mechanisms, but their existence can be indirectly revealed by the presence of volcano-tectonic earthquakes, for example following a large tectonic earthquake. We show that the seismic rate recorded at El Chichón volcano increased slightly after the large Mw8.2 Tehuantepec earthquake of 8 September 2017, Chiapas. However, this rate quickly returned to its background level after only 2 months, without any external volcanic manifestations, suggesting that the volcano is not ready to erupt in the near future. Previous observations of slight increases in the volcanic seismicity rate following large earthquakes have been explained by the presence of active hydrothermal systems in the vicinity of the volcano. We propose a similar explanation for El Chichón volcano which is known for its large hydrothermal system. Furthermore, the characteristics of the 2017 seismicity (spatial and magnitude distributions), and the horizontal-to-vertical spectral ratio also confirm the presence of high amounts of water near the volcano. We show that the 2017 volcano-tectonic seismicity is of hydrothermal rather than magmatic origin, in agreement with recent independent geochemical and aeromagnetic studies.

Investigating the potential influence of tectonic earthquakes on active volcanoes of Vanuatu

It is intuitive to think that an earthquake near a volcano could disrupt its equilibrium and potentially trigger an eruption. But this cause-and-effect link is far from obvious for active volcanoes with an unknown internal stress state and the complexity of its magma-hydrothermal processes. This phenomenon is clearer in continental-oceanic subduction zones where volcanoes generally have closed-vent systems, differentiated high-viscosity magma, and active hydrothermal systems. This phenomenon is less well known in oceanic-oceanic subduction zones, where volcanoes often have open-vent systems, low-viscosity mafic magma, and hypothetic hydrothermal systems. The Vanuatu oceanic-oceanic subduction is an ideal zone to perform such study due to a high-seismic rate and volcanoes with different characteristics. The Vanuatu volcanoes display both open- and closed-vent systems, low and relatively high viscosity magma that enhance different types of volcanic activities (such as lava lakes, strombolian eruptions, high-eruptive columns, phreatic activity), and potential active hydrothermal systems. We compiled and identified sixty-nine cases of earthquakes potentially triggering volcanic activities on Vanuatu volcanoes from 1913 to 2018. Our findings indicate that the triggered volcanic responses occur co-seismically or shortly (at most 2–3 months later) after the earthquake, that the activated volcanoes are mainly located at near-field distances of the potentially triggering earthquake, implying a strong influence of static stress changes. Using the value of the seismic density energy, we suggest that the mechanism of the Vanuatu volcanic responses is due to changes of the permeability within active hydrothermal systems at Lopevi and Ambrym volcanoes in addition to the well-established ones, at Ambae, Garet, and Yasur volcanoes.

Study of Phase Transformations and Interface Evolution in Carbon Steel under Temperatures and Loads Using Molecular Dynamics Simulation

Carbon steel materials are widely used in mechanical transmission. Under different temperature and pressure service conditions, the microscopic changes of stress and strain that are difficult to detect and analyze by experimental means will lead to failure deformation, thus affecting their operational stability and life. In this study, the molecular dynamics method is used to simulate the heating–cooling phase transition process of common carbon steel materials. Austenite transformation temperatures of 980 K (0.2 wt.%) and 1095 K (0.5 wt.%) are acquired which is determined by the volume hysteresis before and after transformation, which is consistent with the results of JMatPro phase diagram analysis. The internal stress state of the material varies between compressive stress and tensile stress due to the change of phase structure, and the dislocation characteristics during the phase transition period are observed to change significantly. Then, an α/γ two-phase interface model is constructed to study the migration of the phase interface and the change of the phase structure by applying a continuously changing external load. At the same time, the transition pressure of α→ϵ is obtained with a value of 37 GPa under three different initial loads showing the independence of the initial load and the historical path. Based on the molecular dynamics simulation and the phase diagram calculation of the carbon steel, the analysis method for the microstructure transformation and the stress–strain behavior of the phase interface under the external load can provide a reference for the design of microstructure and mechanical properties of alloy steel in the future.

Підхід до визначення напружено-деформованого стану стрижнів з композиційних матеріалів з урахуванням внутрішнього самоврівноваженого напруженого стану

The subject of this research is methods of stress-strain state analysis of composite structures. The goal is to develop a mechanism to explain the phenomenon of warping of thin-walled composite sections with a non-uniform cross-section under thermal loading and to synthesize a model to determine the forces in the section elements. The objectives of this study are to predict the deformed states of composite sections at the manufacturing stage and to determine the temperature stresses that occur at the manufacturing stage, as well as after the assembly of the structure. The methods used are related to the mechanics of materials and structures. The following results were obtained. The possible deformation forms of composite plates with an asymmetric structure are analyzed and the rationale for the appearance of such deformations is given. A model of the force interaction of elements in a folded section is proposed. The proposed model can be extended to most sections of load-carrying aircraft structures. Based on the analysis of the mechanics of thin-walled folded sections, the mechanism of the occurrence of complex bending-torsional deformation of long-dimensional sections made of composites with a non-uniform cross-section under the action of an internal self-equilibrium stress state caused by a change in temperature or shrinkage of the binder or both is explained. The analysis of this mechanism makes it possible to design composite sections with minimal warping and to propose engineering methods to compensate for unwanted spatial movements in the case of arbitrary loading of section elements. Conclusions. The scientific novelty of the obtained results can be summarized as follows. A mechanism for the deformation of rods made of dissimilar composite materials when the temperature changes (after extraction from the tool or during operation) is proposed considering the difference in Poisson's coefficients. A model for determining the forces acting on the perimeter of section elements was synthesized, and the corresponding formulas were obtained, which form the basis for the theory of off-center compression of rods. The direction of further research in this field is currently being planned.

Energy-dependent correlation between micro/nano-morphology and stress state of femtosecond laser-induced modification in fused silica

Due to the importance of stress control in the laser processing of brittle transparent dielectrics such as glass and crystal, investigating the evolution of laser-induced stress state and its manipulation mechanism is highly desirable for ensuring high-performance crack-free laser micro/nanostructuring of dielectrics. Herein, the internal stress state of a femtosecond laser-modified fused silica glass sample at a broad range of pulse energy from 0.34 to 3.5 μJ was evaluated using a cantilever displacement method. Two obvious transition zones in the variation of microscale displacement were identified and analyzed by polarized optical microscopy, scanning electronic microscopy, and confocal micro-Raman spectroscopy. A strong energy-dependent correlation between the evolution of the micro/nano-scale morphology and stress state in laser-induced structures has been investigated and discussed. The analyzed result is beneficial for developing high-efficiency and high-quality manufacturing of 3D large-scale and high-precision glass microstructures.

Determination of the Activity of the fimF Gene and Its N-Terminal Domain Disrupted Mutant on Biofilm Formation and Its Contribution to the Oxidative Stress Response in S. Typhimurium

Fimbriae is an important virulence factor which plays a key role in cell attachment and colonization of the intestinal mucosa during an infection of Salmonella, a pathogen that causes gastroenteritis and systemic infection in humans. In S. Typhimurium, type 1 fimbriae production strengthens the oxidative stress response. This study aimed to determine the effectiveness of the fimF gene and its N-terminal domain on biofilm formation in S. Typhimurium and their contribution to the oxidative stress response. Before the experiments to prove whether the N-terminal domain of the FimF protein is the region that determines the mechanism and function of the fimF gene; only the N-terminal domain of the fimF gene was cloned behind the pBAD promoter. As a result of biofilm experiments on polystyrene surfaces, it was determined that the biofilm production capacity was reduced significantly in mutant strains in terms of fimF and dam genes (p < 0.05). In the oxidative stress response experiment conducted in the presence of hydrogen peroxide (H2O2), it was determined that the mutant strains were more resistant to hydrogen peroxide than the wild-type strain, therefore Salmonella cells perceived the absence of Dam methylase enzyme and FimF protein as a critical internal stress condition and produced strong responses to these stress conditions. As a result of comparative analysis of the N-terminal domain cloned mutant strain with the wild-type, it was proven that the N-terminal domain of the protein in question acts as an adapter protein, due to its close similarities with the wild-type.

Improved the mechanical properties of SiCf/SiC-GH536 joints by in-situ introducing better toughness MoNiSi phase to the brazing seam

Brazing, a crucial technology for connecting composites with metals, emerges as an effective solution to the intricate challenges posed by alternative joining methods. This investigation employs foam Ni and MoNi as intermediary layers to establish connections between silicon carbide reinforced silicon carbide composites (SiCf/SiC) and GH536 superalloy. The diverse joint structures, scrutinizing their intricate impact on the mechanical properties of the brazed joints are systematically explored in this study. Findings reveal distinctive characteristics depending on the intermediary layer: Ni foam widens the brazing seam, with a significant portion of Ni elements in the nickel foam adopting the Ni(s, s) form within the brazing seam. Meanwhile, MoNi foam as the intermediary layer prompts the in-situ formation of a substantial MoNiSi phase within the brazing seam. The alternation between the MoNiSi and FCC phases contributes to a harmonized internal stress state within the joint, resulting in an impressive strength of 106.7 MPa. This study delineates a novel technical trajectory for the practical engineering application of SiCf/SiC composites.

A discrete model for layered growth

We present a discrete model that captures the fundamental properties of layered deposition in a minimal setting. The model is based on simplified kinematics and allows for the onset of incompatible deformations between discrete layers of a growing stack. Thanks to the discrete nature of the model, we obtain an averaged formulation of mechanical equilibrium for the growing stack, leading to closed-form solutions that are both analytically simple and physically transparent. In particular, we are able to explain the origin of residual stress by the accumulation of incompatible deformations between adjacent layers. The model can also be regarded as an elementary approximation of additive manufacturing. Within this context, we are able to formulate the technologically relevant inverse problem that provides the deposition protocol required to produce a desired state of internal stress in an additively-manufactured stack. Another important aspect analyzed in the work is the role played by an ideal “glue” between the layers, whose presence is fundamental to prevent their sliding and whose mechanical behavior can quantitatively influence the final stress distribution in the stack. The simplicity of the model makes it possible to highlight how the controls exerted during deposition will have qualitative or quantitative effects on the final stress state of the stack.

Internal stress state of martensite in low-carbon steel: a phase-field study

Internal stress state of martensite in low-carbon steel: a phase-field study

Evaluation of the coefficient of lateral stress at rest of granular materials under repetitive loading conditions

Although the internal stress state of soils can be affected by repetitive loading, there are few studies evaluating the lateral stress (or K0) of soils under repetitive loading. This study investigates the changes in K0 and directional shear wave velocity (Vs) in samples of two granular materials with different particle shapes during repetitive loading. A modified oedometer cell equipped with bender elements and a diaphragm transducer was developed to measure the variations in the lateral stress and the shear wave velocity, under repetitive loading on the loading and unloading paths. The study produced the following results: (1) Repetitive loading on the loading path resulted in an increase in the K0 of test samples as a function of cyclic loading number (i), and (2) Repetitive loading on the unloading path resulted in a decrease in K0 according to i. The shear wave velocity ratio (i.e. Vs(HH)/Vs(VH), where the first and second letters in parentheses corresponds to the directions of wave propagation and particle motion, respectively, and V and H corresponds to the vertical and horizontal directions, respectively) according to i supports the experimental observations of this study. However, when the tested material was in lightly over-consolidated state, there was an increase in K0 during repetitive loading, indicating that it was the initial K0, rather than the loading path, which is responsible for the change in K0. The power model can capture the variation in the K0 of samples according to i. Notably, the K0 = 1 line acts as the boundary between the increase and decrease in K0 under repetitive loading.

An integrated statistical-thermodynamic model for fission gas release and swelling in nuclear fuels

We propose a new model for burst fission gas release induced by microcracking in ceramic nuclear fuels such as uranium dioxide. The model stipulates that the densities of defects in the fuel material, such as microcracks and fission gas bubbles on grain boundaries, evolve in accordance with the second law of thermodynamics. Central to the model is the notion of an effective temperature, conjugate to the configurational entropy of the fuel material, and directly linked to the burnup. The model predicts that microcracking, driven by the internal stress state of the fuel material, reduces the bubble storage capacity of grain boundaries, and accounts for burst fission gas release during rapid temperature transients that simulate power transients, reactor startup, and loss-of-coolant accident conditions.

Bioinspired, heredity-derived hierarchical bulk multifunctional copper alloys

Bioinspired hierarchical design demonstrates a promising microstructural solution to circumvent multiple intricate property trade-offs in artificial materials. However, it remains extremely challenging to tailor structural hierarchies feasibly and synthetically, particularly for bulk materials. Here, a counterintuitive strategy is reported–exploring multiscale microstructural heredities for highly-developed dendritic hierarchies in as-cast bulk alloys. During optimized thermomechanical processing, we carefully control these dendrites to be progressively deformed, elongated, aligned and refined, rather than completely destroying them as in conventional alloy processing paradigms. As such, a hierarchical fibrous lamellar (HFL) structure–resembling those of shell and bamboo–is controllably designed in a technologically-important CuCrZr alloy. This innovative HFL design promotes multiple synergetic micro-mechanisms with sequential multiscale interactions and salient biomimetic attributes, thereby affording exceptional multifunctionality, especially record-high strength–ductility–conductivity combination. At more fundamental levels, multiple previously inaccessible deformation and reinforcement mechanisms are activated by exploiting the HFL structure-enabled complex internal stress condition. They perform and interact at multi-length-scales from intense diversified dislocation trapping, massive stacking-fault proliferation, 9R-phase-assited nano-twinning, self-buffering shear bands to ever-intensified hetero-deformation-induced hardening. These scenarios even create superior, strain-rate-tolerant dynamic properties far exceeding conventional homogeneous-structured counterparts. Dendrites exist ubiquitously, yet generally undesirable, in metallic materials, whereas our ‘bioinspired, heredity-derived’ strategy counterintuitively utilizes them, realizing unprecedented high figure-of-merit multifunctionality.

Latent heat effects in inductive heating of shape memory alloy fibers

AbstractMotivation of the present work is an inductive heating process, used in manufacturing a new kind of improved ultra‐high performance concrete. In this novel material, fibers made out of shape memory alloys are used to increase the maximum possible fiber volume fraction, or to create an internal state of compressive stress. In contrast to other works, the underlying microstructure transformation from martensite to austenite is highlighted based on thermal analysis. Dynamic scanning calorimetry measurements are adapted as basis for development of a phenomenological phase transformation model. It relates local temperature and temperature rate to the rate of change of the phase indicator, modeling the transformation of martensite to austenite. Latent heat is considered by an enthalpy method, the inductive heating process is considered by a phenomenological model. Study results for a purely thermodynamic process of heating a single fiber embedded in concrete are presented. They show that latent heat effects delay phase transformation and the process of fiber activation is very sensitive to the induced heat. Furthermore, it is discovered that latent heat causes a strongly inhomogeneous state of transformation in radial direction of the fiber, which is of great importance for thermomechanical processes and the interpretation of experimental results.

Multi-axial load spectrum extrapolation method for fatigue durability of special vehicles based on extreme value theory

A method for the multi-axial load spectrum extrapolation based on extreme value theory has been proposed herein, for the first time to the best of our knowledge. The relationship between the internal damage of the structure with the external multi-axial load spectrum is first established prior to extrapolation. The multi-axial load spectrum is then equivalently synthesized into a uni-axial load spectrum based on the interaction between the external forces and the internal stress state of the structure. The basic theory of the time-domain multi-axial load spectrum extrapolation method is developed, including (1) the multi-axial load spectrum extrapolation model establishment; (2) the optimal threshold determination based on grey relational analysis (GRA); (3) the fitting of the distribution function parameters based on the Bayesian parameter estimation method; and (4) the judgment of phase relationship between each channel of the multi-axial load spectrum. The rationality of the method proposed in this paper is verified through an application example. In the example, the multi-axial load spectrum measurement of a special vehicle is introduced, and the proposed multi-axial extrapolation method is applied. Finally, the validation of the multi-axial load spectrum extrapolation method – in terms of the characterized comparison and the durability simulation – is performed.