Stress Mode Research Articles

Cyclic deformation response of annealed low-carbon steel: Insights from ratcheting and LCF experiments

Low cycle fatigue (LCF) and ratcheting experiments were carried out on annealed low-carbon steel at room temperature within a laboratory environment, utilising stress and strain control modes. The annealed low-carbon steel consistently demonstrates a cyclic softening response over its LCF lifespan, across all tested strain amplitudes. Notably, it was observed that ratcheting strain rises while ratcheting life declines with both rising mean stress and stress amplitude. Annealed low-carbon steel, being entirely ferritic and lacking precipitation or substitutional solid solution strengthening or hard phase strengthening, exhibits a restricted ability to withstand or alleviate the accumulation of ratcheting strain, particularly under very low mean stress conditions. In both LCF and ratcheting, significant substructure formation was detected. Nevertheless, there was no discernible difference in substructure formation between LCF and ratcheting when employing electron channelling contrast imaging techniques. The existing mean stress-based fatigue life prediction model has successfully forecasted ratcheting and LCF life within the 102–105 cycles range. A novel approach utilising modulus is introduced to characterise the cyclic hardening/softening behaviour of alloys in stress and strain-controlled experiments. The cyclic hardening model based on modulus effectively captures the responses observed in cyclic hardening/softening during LCF and ratcheting experiments.

Effect of confining pressure on the damage characteristics and mechanism of granite under ultra-high-frequency impact

Assisted ultra-high-frequency impact technology is a promising method for improving hard rock-breaking efficiency in geotechnical and petroleum engineering. However, previous studies did not consider the effects of in situ stress. In this study, triaxial ultra-high-frequency impact tests were conducted at confining pressures ranging from 0 to 20 MPa. Using nuclear magnetic resonance, infrared thermal radiation, crack dye penetrant, and scanning electron microscope tests, the influence of confining pressure on the macro, meso, and micro damage characteristics and mechanism of granite was revealed. The results indicate that with the increasing confining pressure, the porosity increment of small pores continuously decreases from 0.2% to −0.02%; the moderate pores first increase to a peak of around 0.18% before 6 MPa and then gradually decrease to around zero. The large pores began to increase after 8 MPa, increasing to around 0.05% when the confining pressure was 14 MPa. In addition, the failure mode first changed from tensile splitting damage to a relatively intact state with meso-damage, and finally, transverse shear fracture occurred owing to the higher shear stress and low mode II fracture toughness near the crack tips. These findings prove the effectiveness of ultra-high-frequency impact technology in weakening hard rock in deep strata.

Crashworthiness of AAG joints with a foam aluminum layer gusset plate

The gusset joint is the most widely used joint system in an aluminum alloy single-layer reticulated shell structure; it plays a vital role in the spatial grid structure. In this paper, the effects of different thicknesses of aluminum alloy gusset plates on the dynamic response and failure modes of aluminum alloy gusset (AAG) joints were studied by impact tests of three specimens. The test results show that the failure modes of AAG joints are a slight depression of the gusset plate, the local buckling of members, the local distortional buckling of members, and tearing of the lower flange and a web of members. The AAG joint inclines along the direction of the failed member and collapses. The finite element model of the AAG joint was established using ANSYS software. The stress, displacement, and deformation modes in the test and numerical simulation results were compared and analyzed, and the rationality of the numerical simulation results was verified. Based on the failure mode of the specimens, a design method for improving the impact resistance of AAG joints with aluminum foam layer gusset plate (AFLGP) is proposed. The numerical simulation results show that an AAG joint with an AFLGP effectively reduces the maximum peak value of impact loads through the deformation of the aluminum foam. In the elastic and elastic-plastic stages, AAG joint with AFLGP had better impact resistance, and the energy absorbed by its rods was 25.44% ∼ 30.36% lower than that of AAG joints alone. Finally, the influence of the thickness of the AFLGP on the impact force and energy absorption of the AAG joint was studied. The aluminum foam gusset layer plate is approximately twice as thick as the aluminum alloy gusset plate had the best protection effect on the AAG joint.

Impact of atmospheric dryness on solar-induced chlorophyll fluorescence: Tower-based observations at a temperate forest

Solar-induced chlorophyll fluorescence (SIF) is widely accepted as a proxy for gross primary productivity (GPP). Among the various SIF measurements, tower-based SIF measurements allow for continuous monitoring of SIF variation at a canopy scale with high temporal resolution, making it suitable for monitoring highly variable plant physiological responses to environmental changes. However, because of the strong and close relationship between SIF and absorbed photosynthetically active radiation (aPAR), it may be difficult to detect the influence of environmental drivers other than light conditions. Among the drivers, atmospheric dryness (vapor pressure deficit, VPD) is projected to increase as drought becomes more frequent and severe in the future, negatively impacting plants. In this study, we evaluated the tower-based high-frequency SIF measurement as a tool for detecting plant response to highly variable VPD. The study was performed in a mixed temperate forest in Virginia, USA, where a 40-m-tall flux tower has been measuring gas and energy exchanges and ancillary environmental drivers, and the Fluospec 2 system has been measuring SIF. We show that a proper definition of light availability to vegetation can reproduce SIF response to changing VPD that is comparable to GPP response as estimated from eddy covariance measurement: GPP decreased with rising VPD regardless of how aPAR was defined, whereas SIF decreased only when aPAR was defined as the PAR absorbed by chlorophyll (aPARchl) or simulated by a model (Soil Canopy Observation, Photochemistry and Energy fluxes, SCOPE). We simulated the effect of VPD on SIF with two different simulation modes of fluorescence emission representing contrasting moisture conditions, ‘Moderate’ and ‘Soil Moisture (SM) Stress’ modes. The decreasing SIF to rising VPD was only found in the SM Stress mode, implying that the SIF-VPD relationship depends on soil moisture conditions. Furthermore, we observed a similar response of SIF to VPD at hourly and daily scales, indicating that satellite measurements can be used to study the effects of environmental drivers other than light conditions. Finally, the definition of aPAR emphasizes the importance of canopy structure research to interpret remote sensing observations properly.

A reconstruction method for structural stress distribution of wind turbine tower using optimised mathematical model

Wind turbine towers experience complex dynamic loads during actual operation, and these loads are difficult to accurately predict in advance, which may lead to inaccurate structural strength assessment during the structural design phase, thereby posing safety risks to the wind turbine tower. Therefore, a reconstruction method for structural stress distribution of wind turbine tower was developed based on modal expansion and linear superposition theory to estimate the full-field stress distribution of a tower, which can be used for online monitoring of structural strength. The dynamic stress distribution of the tower is assumed to be the superposition of several structural modal stress distributions, in the reconstruction method for structural stress distribution developed in this study. The modes with the greatest contribution to the wind turbine structural response were selected based on the modal effective mass, and used for the base functions of an initial mathematical model for the reconstruction of structural stress distribution of the tower, in which many candidate strain gauge locations and directions were considered. Then, the initial mathematical model was expressed as a linear system of equations. Two numerical examples were used to verify the accuracy and stability of the initial mathematical model for the reconstruction of structural stress distribution of the tower, and the reconstruction results indicate that the initial mathematical model combined with the Moore–Penrose inverse algorithm can provide stable and accurate reconstruction results. However, the initial mathematical model uses too many sensors, which is not conducive to engineering applications. Therefore, D-optimal and C-optimal design methods were used to reduce the dimensions of the initial mathematical model, optimise the system of equations, and determine the location, direction and number of strain gauges. Finally, the numerical examples of stress distribution reconstruction show that dimensionality reduction of the mathematical model leads to higher accuracy, in which the C-optimal design algorithm providing a more robust reconstruction outcome.

Cyclic behavior and damage mechanism of 304 austenitic stainless steel under different control modes

In this work, low cycle fatigue experiments under both strain and stress control modes with different loading levels were conducted on 304 austenitic stainless steel at ambient temperature to discuss the influence of loading mode and level on the cyclic response and physical mechanism. The results demonstrated that the cyclic response generally exhibited three stages: primary cyclic hardening, subsequent cyclic softening, and the secondary hardening finally. The degree of each hardening and softening stage was depended on not only the loading modes but also the strain/stress level. Accelerated cyclic softening and retarded secondary hardening occurred under the stress mode, which made a higher low-cycle fatigue life during stress cyclic loading than that for the strain control mode, especially at relatively high strain/stress level. The secondary hardening stage, occupying the main portion of the lifetime, was proved to be associated with the development of martensitic phase and the extension and intersecting of stacking faults or micro-twin.

Deciphering the regulatory landscape of murine splenic response to anemic stress at single-cell resolution

AbstractStress erythropoiesis can be influenced by multiple mediators through both intrinsic and extrinsic mechanisms in early erythroid precursors. Single-cell RNA sequencing was conducted on spleen tissue isolated from mice subjected to phenylhydrazine and serial bleeding to explore novel molecular mechanisms of stress erythropoiesis. Our results showed prominent emergence of early erythroblast populations under both modes of anemic stress. Analysis of gene expression revealed distinct phases during the development of emerging erythroid cells. Interestingly, we observed the presence of a "hiatus" subpopulation characterized by relatively low level of transcriptional activities that transitions between early stages of emerging erythroid cells, with moderate protein synthesis activities. Moreover, single-cell analysis conducted on macrophage populations revealed distinct transcriptional programs in Vcam1+ macrophages under stress. Notably, a novel marker, CD81, was identified for labeling central macrophages in erythroblastic islands (EBIs), which is functionally required for EBIs to combat anemic stress. These findings offer fresh insights into the intrinsic and extrinsic pathways of early erythroblasts' response to stress, potentially informing the development of innovative therapeutic approaches for addressing anemic-related conditions.

Biomechanical evaluation of the ST-knot: A new suture for flexor tendon repair

PurposeAlthough tendon lacerations are common, there is currently no consensus on choice of suture. Easy and fast sutures that impart enough strength to allow mobilization are needed. This study compared the ex vivo biomechanical strength (force required to create a 2 mm tendon gap) of a novel suture (ST-knot) with that of a conventional suture (double Kessler). Materials and methodsForty fresh deep flexor tendons from porcine forelimbs were used. Both repaired tendon ends were mounted on standard traction jaws of an axial traction machine at an initial distance of 40 mm for all tendons. A high-definition camera was used to determine the force forming a 2 mm gap. Ten tendons in group 1 (ST-knot) and 10 in group 2 (double Kessler) were prepared with PDS 4.0 (single thread for Kessler, double thread for ST-knot). Tendons in groups 3 (ST-knot) and 4 (double Kessler) were repaired with PDS 1.0 using the same principle. ResultsThere was no significant difference in the force required to form a 2 mm tendon gap between groups 1 and 2, and this trend was identical when using a stronger thread in groups 3 and 4. The maximum force before rupture, mode of repair failure, stress and stiffness were also comparable, with no significant differences between groups 1 and 2, or between groups 3 and 4. ConclusionsThe ST-knot showed comparable results to the double-Kessler knot, whichever the thread used. Because it involves fewer steps than conventional techniques and is easy to perform, the ST-knot may offer a therapeutic solution, particularly in complex trauma with multiple tendon injury.

Experimental Study on the Stress and Failure Mode of a Shield Tunnel Lining Under Asymmetric Thrust

This paper develops the "formation–shield tunnel segment–reaction frame model test system." The force and failure modes of the segment under different curvature radii and different left- and right-hand thrusts are compared and analyzed. The analysis results include the following. (1) Under asymmetric thrust, the axial force, bending moment, and deformation of the segment present an asymmetric distribution. With the increase in the ratio of the thrust between the lateral and inner jacks of the turn, the loading step of the damage inside the segment lining structure is advanced. (2) With the increase in the radius of curvature, the bending moment and deformation of the segment lining decrease, but the magnitude of the sudden change in the axial force of the segment structure increases accordingly. (3) The failure locations of the segment structure are mostly concentrated at the joints between the vault and the arch. With the increase in the jack thrust ratio, the cracks caused by segment structure failure also increase, transverse crack extension occurs where the force on the outside of the turn is large, and the peeling phenomenon occurs.

Harmonic Excitation Response of Standard Ultrasonic Horn Designs for Machining Nomex Honeycomb Core Composite

Ultrasonic horn plays a vital role in achieving vibration amplitude at tool end (VATE) by enhancing output displacement of piezoelectric ultrasonic transducer suitable for efficient machining of advanced composites. Higher vibration amplitude enhances ultrasonic machining quality, surface integrity and dimensional accuracy of Nomex honeycomb composite (NHC) while reducing cutting forces. Furthermore, low stress concentrations allow ultrasonic tool to have more safety factor and longevity. Ultrasonic horn is designed to enhance displacement amplitude of piezoelectric ultrasonic transducer and get optimum VATE while keeping stresses in acceptable limits to avoid failure at very high operating frequency of ultrasonic machining system. In this research, variety of standard ultrasonic horns (SUH) were designed with same length and end diameters; and were tested under similar operating conditions, using finite element method. The ultrasonic actuation of the horn exploits the first axial mode of horn vibration. Harmonic response analysis was carried out to determine axial modal frequencies (AMF), VATE, stresses, and factor of safety for performance evaluation. VATE attained by step horn was found to be greatest among all other SUHs for frequency ratio greater than one, but may be prone to early failure due to high stress concentrations. VATE achieved by third order Bezier, Gaussian, exponential, catenoidal, conical and second order Bezier horns were found less than that of step horn by 11.7 %, 16.6 %, 16.7 %, 17 %, 16.73 % and 18 % respectively. However, 44.2 %, 43.43 %, 42.5 %, 43.5 %, 42.8 % and 37.67 % reduction of stresses was achieved by Gaussian, exponential, catenoidal, conical, second and third order Bezier horns respectively. Outcomes of present work would be beneficial for designers, researchers, scientists, and manufacturers of ultrasonic machine tool to select appropriate SUH designs according to requirements.

The use of deep borehole imaging data in reconstruction of active stress mode at a polymetallic deposit of intrusive genesis

The use of deep borehole imaging data in reconstruction of active stress mode at a polymetallic deposit of intrusive genesis

Effects of Cold Stress Mode on Nutrient Composition, Energy Metabolism and Oxidative Stress During the Ecological Ice-temperature Retention Period of the Milky Oyster, Crassostrea Gigas

Effects of Cold Stress Mode on Nutrient Composition, Energy Metabolism and Oxidative Stress During the Ecological Ice-temperature Retention Period of the Milky Oyster, Crassostrea Gigas

Numerical Analysis of Effect of Plastic Change in Volume and Stress Mode in Boundary Value Problems of Plasticity

Numerical Analysis of Effect of Plastic Change in Volume and Stress Mode in Boundary Value Problems of Plasticity

Characterization and Identification of NPK Stress in Rice Using Terrestrial Hyperspectral Images.

Due to nutrient stress, which is an important constraint to the development of the global agricultural sector, it is now vital to timely evaluate plant health. Remote sensing technology, especially hyperspectral imaging technology, has evolved from spectral response modes to pattern recognition and vegetation monitoring. This study established a hyperspectral library of 14 NPK (nitrogen, phosphorus, potassium) nutrient stress conditions in rice. The terrestrial hyperspectral camera (SPECIM-IQ) collected 420 rice stress images and extracted as well as analyzed representative spectral reflectance curves under 14 stress modes. The canopy spectral profile characteristics, vegetation index, and principal component analysis demonstrated the differences in rice under different nutrient stresses. A transformer-based deep learning network SHCFTT (SuperPCA-HybridSN-CBAM-Feature tokenization transformer) was established for identifying nutrient stress patterns from hyperspectral images while being compared with classic support vector machines, 1D-CNN (1D-Convolutional Neural Network), and 3D-CNN. The total accuracy of the SHCFTT model under different modeling strategies and different years ranged from 93.92% to 100%, indicating the positive effect of the proposed method on improving the accuracy of identifying nutrient stress in rice.

ШЕСТИПАРАМЕТРИЧЕСКИЙ КРИТЕРИЙ ПРОЧНОСТИ ДЛЯ БЕТОНА.

Based on the experiments conducted by the authors, a six-parameter failure criterion for concrete has been developed, which makes it possible to take into account the volumetric stress state in strength calculations of massive concrete and reinforced concrete structures. The developed strength criterion is adapted to a spatial eight-node finite element (solid type) and implemented in the PRINS software. To verify the developed criterion, the work provides a comparison with both experimental data and calculation results that meet other strength criteria widely used for concrete. A comparison of the results showed a reliable assessment of the strength of concrete in the mode of both low and high average stresses.

Synthesis of silica bearing sulfobetaine and sulfonic groups and their electrorheological response

Organically modified silica bearing amino groups (SiO2-NH2) was prepared by the simple sol-gel procedure followed by treatment with butanesultone to produce zwitterionic silica bearing sulfobetaine groups (SiO2-SB). This particle was then treated with sulfuric acid to prepared particles carrying both sulfonic acid and ammonium salt (SiO2-SO3H). These particles were characterized by different methods and dispersed in silicone oil (15 wt%) to evaluate the electrorheological (ER) performance. Thermogravimetric (TG) analysis, zeta potential and Fourier transform infrared (FTIR) spectroscopy confirmed the structure of the modified silica. The ER response was evaluated using controlled shear stress (CSR) and oscillatory mode. The SiO2-NH2 and SiO2-SB based fluids displayed the highest shear stress at low shear rate even without an applied electric field. However the higher ER efficiency and lower leakage current was observed for the fluid containing SiO2-SO3H. From dielectric analysis, it was demonstrated that the zwitterionic SiO2-SB particle provided faster relaxation time and larger permittivity difference. Thus, it is possible to conclude that the lower viscosity of the SiO2-SO3H based fluid without electric field also plays an important role for a good ER efficiency. Both SiO2-SB and SiO2-SO3H particles are suitable for producing ER fluids due to their better dielectric properties and relaxation time. The former also presented better sedimentation stability.

Failure criterion for concrete under volumetric stress state conditions

Based on the experiments conducted by the authors, a six-parameter failure criterion for concrete has been developed, which makes it possible to take into account the volumetric stress state in strength calculations of massive concrete and reinforced concrete structures. The developed strength criterion is adapted to a spatial eight-node finite element (solid type) and implemented in the PRINS software. To verify the developed criterion, the work provides a com-parison with both experimental data and calculation results that meet other strength criteria widely used for concrete. Thus, the compression and tension meridians of the developed fracture criterion were compared with experimental data, as well as with the Willam & Warnke criterion and the modified Drucker & Prager criterion with Mohr & Coulomb constants. A comparison of compression meridians shows that in the mode of low hydrostatic stresses , these criteria converge with each other and with experimental data. In the mode of average hydrostatic stresses , the criterion proposed by the authors and the Willam & Warnke criterion show similar results, while the modified Drucker & Prager criterion shows on 20% overestimation of the failure value. In the mode of high hydrostatic stresses , the Willam & Warnke criterion in com-parison with the proposed criterion and experimental data, gives an underestimated value of concrete failure.

Evaluating different models of maternal stress on stress-responsive systems in prepubertal mice.

Maternal adversity during pregnancy influences neurodevelopment in human and model animal offspring. Adversity can result from stressors coming from many different directions ranging from environmental to nutritional and physiological to immune (e.g., infection). Most stressors result in fetal overexposure to glucocorticoids that have been directly linked to long- and short-term negative impacts on neurological health of offspring. Neuropsychiatric diseases postulated to have fetal origins are diverse and include such things cardiovascular disease, obesity, affective disorders, and metabolic and immune disorders. The experiments in the current study compare 3 stressors: prenatal exposure to dexamethasone (DEX), maternal high fat diet (HFD), and maternal caloric restriction (CR). Offspring of mothers with these treatments were examined prepubertally to evaluate stress responsiveness and stress-related behaviors in in male and female mice. Prenatal exposure to synthetic glucocorticoid, DEX, resulted in decreased neonatal body weights, reduced social interaction behavior, and hypoactive stress response offspring exposed to maternal DEX. Maternal CR resulted in decreased body weights and social interaction behavior in males and females and increased anxiety-like behavior and acute stress response only in males. HFD resulted in altered body weight gain in both sex offspring with decreased anxiety-like behavior in a female-biased manner. The idea that glucocorticoid responses to different stressors might serve as a common stimulus across stress paradigms is insufficient, given that different modes of prenatal stress produced differential effects. Opposite nutritional stressors produced similar outcomes for anxiety-like behavior in both sexes, social-like behavior in females, and a hyperactive adrenal stress response in males. One common theme among the three models of maternal stress (DEX, CR, and HFD) was consistent data showing their role in activating the maternal and fetal immune response. By tuning in on the more immediate immunological aspect on the developing fetus (e.g., hormones, cytokines), additional studies may tease out more direct outcomes of maternal stress in rodents and increase their translational value to human studies.

Concrete strength criteria for biaxial and triaxial state of stress

Based on the experiments conducted by the authors, a concrete strength criteria has been developed, which allows us to take into account biaxial and triaxial states of stress in strength calculations of massive concrete and reinforced concrete structures. The developed strength criteria is adapted to a spatial eight-node finite element (solid type) and implemented in the PrinCe programme. In order to conduct the developed criteria operational check, both experimental data and calculation results of other widely used strength criteria for concrete were compared. Thus, to verify the proposed criteria under triaxial compression, the calculation results were compared with experimental data as well as with the Willam-Warnke criterion and the modified Drucker-Prager criterion. The comparison shows that in the low hydrostatic stresses mode results of the above criteria converge both with each other and with the experimental data. In the medium hydrostatic stress mode , the criteria proposed by the authors and the Willam-Warnke criterion show close results, while the modified Drucker-Prager criterion, on the contrary, gives 20 % overestimation of concrete strength. Comparison of the results of concrete biaxial tests shows good agreement with the criteria developed by the authors. Thus, for heavy coarse concrete the differences in strength values were not more than 3,5 %, for heavy fineconcrete and expanded clay concrete — not more than 4 %.

Improved Performance and Bias Stability of Indium‐Tin‐Zinc‐Oxide Thin‐Film Transistors Enabled by an Oxygen‐Compensated Capping Layer

Herein, the effects of oxygen‐compensated capping layer (CCL) on the electrical performance and stability of indium‐tin‐zinc‐oxide (ITZO) thin‐film transistors (TFTs) are investigated. Two different channel structures, namely, single and dual channels, are tested for the ITZO TFTs. The dual‐channel layer is created by depositing an oxygen CCL on the oxygen‐uncompensated channel layer (UCL), while the single‐channel layer consists only of the oxygen UCL. It is found that the oxygen CCL is critical for enhancing the electrical properties of dual‐channel ITZO TFT and its stability under different stress modes such as dynamic stress, positive bias temperature stress, and negative bias illumination stress. The dual‐channel ITZO TFT exhibits a saturation field‐effect mobility of 16.69 cm2 V−1s−1, a threshold voltage of 6.80 V, and a subthreshold swing of 0.22 V dec−1. Furthermore, it is revealed that the higher metal‐oxide concentration and fewer defects in the dual channel lead to enhanced electrical performance and stability of the device. This work demonstrates the potential of utilizing the oxygen CCL for the highly reliable operation of oxide semiconductor TFTs.