Stress Relaxation Research Articles

Dissecting tunica responsibility in arterial stress relaxation: Smooth muscle need not apply.

Stress relaxation is considered a property of smooth muscle. Rings of thoracic aorta with/without perivascular adipose tissue (PVAT) stress relax. However, rings of isolated PVAT, containing no organized smooth muscle, also stress relax. We hypothesize that smooth muscle is not necessary in the individual tunicas of the aorta for stress relaxation to occur. Histochemical staining and isometric contractility were performed on whole or tunicas of the thoracic aorta from the male and female Dahl salt-sensitive (SS) rats on normal diet. Masson Trichrome (MT) and Verhoeff Van Gieson (VVG) staining validated the isolation of the different tunicas. Stress relaxation was measured after cumulative amounts of passive tension were applied in the presence or absence of extracellular Ca2+, followed by challenge with the a1 adrenergic agonist phenylephrine (PE, 10-5 M). Results: Stress relaxation occurred in all tunicas at each passive tension regardless of Ca2+. PE-induced contraction was observed in tissues containing smooth muscle (media, whole vessel) but not in the adventitia and aPVAT with Ca2+. No contraction was observed with no Ca2+. All tunicas of the rat thoracic aorta stress relax, doing so without dependence on smooth muscle or Ca2+. PVAT demonstrated the greatest ability to stress relax. .

Investigation of microscale brittle fracture opening in diamond with olivine inclusion using XFEM and cohesive zone modeling

Inclusions trapped in diamonds are a fundamental source of information to probe the Earth’s interior, provided that the pressure conditions at which the diamond grew are correctly determined.This study explores the traditional assumptions in geothermobarometry for olivine-in-diamond host-inclusion systems by employing extended finite element methods (XFEM) and cohesive zone models (CZM) to quantify the contributions of brittle fractures to the relaxation of the residual stress of inclusions. Our analysis was performed assuming that the host-inclusion system does not contain fluids and that the unfractured minerals are elastically isotropic. Our models show that the damage initiation is solely dependent on the shape of the inclusion and on the fracture strength of the diamond host, while the fracture nucleation is influenced by both the size of the inclusion and the toughness of the diamond. Our findings indicate that, in dry systems, the amount of relaxation of residual stress of the inclusion due to the opening of brittle fractures is much lower than that due to the elastic interaction between the host and the inclusion. Moreover, the pressure release due to fractures is not substantially affected by the shape of the inclusion. We also show that the total relaxation of the residual pressure due to the combined effect of the elastic interaction and of the brittle deformation is lower than what is observed in natural samples, even when assuming fracture strength and toughness lower than those reported from experiments on single crystals of diamond. Such discrepancies suggest that in natural olivine-diamond systems additional mechanisms such as viscous or plastic deformation and/or the presence of preexisting defects and fluids in the host might play a relevant role in the relaxation of the residual stress. These findings underscore the need for advanced numerical tools that consider the complex interplay of the geometry of the host-inclusion system, the fracture properties, and the presence of fluids and defects in order to build more accurate models to constrain the geological history of diamonds.

Localized Heating Assisted Laser Shock Peening without Coating Enhances Mechanical Properties of Ti6Al4V Alloys

Room-temperature laser shock peening without coating (RT-LSPwoC) is the mainstream method for surface strengthening, yet it induces tensile residual stress on the surface during rapid heating and cooling. Warm LSPwoC, combining the benefits of dynamic strain aging and LSPwoC, exhibits higher performance than RT-LSPwoC. However, overall high-temperature is time- and resource-consuming, and it is prone to causing thermal stress relaxation during processing, making it unsuitable for large-scale applications. In this paper, a novel localized heating assisted LSPwoC (LHA-LSPwoC) method, utilizing a continuous wave laser for local heating, is proposed. Additionally, the deep physics-informed neural network model, embedded with physical formulas, is designed for process optimization. It enables rapid and accurate responses for an extensive number of cases (40 cases with an average deviation below 1%), overcoming the drawbacks of traditional numerical simulations that are time-consuming and difficult to efficiently handle numerous cases. Compared to RT-LSPwoC, LHA-LSPwoC samples have higher dislocation density and higher grain refinement, demonstrating higher hardness and residual stress, particularly superior fatigue performance. The mechanism of LHA-LSPwoC is discussed, and thermally coupled finite element simulations and molecular dynamics calculations are conducted to provide theoretical support. The proposed method is cost-effective and flexible, showing outstanding potential for industrial applications.

Mechanism of Cr enhancement on stress relaxation resistance in Cu–Ni–Co–Si–Mg alloys

Mechanism of Cr enhancement on stress relaxation resistance in Cu–Ni–Co–Si–Mg alloys

A peridynamic method for creep and stress relaxation incorporating a novel fractional viscoelastic model

A peridynamic method for creep and stress relaxation incorporating a novel fractional viscoelastic model

Assessment of dwell-fatigue properties of nickel-based superalloy coated with a multi-layered thermal and environmental barrier coating

A three-layered experimental thermal and environmental barrier coating (TEBC) was deposited using air plasma spraying technology on cylindrical specimens of nickel-based superalloy MAR-M247. TEBC consists of mullite (Al6Si2O13) and hexacelsian (BaAl2Si2O8) upper layer, Y2O3 stabilised ZrO2 interlayer and CoNiCrAlY bond coat deposited on the grit-blasted surface of MAR-M247. The cyclic plastic response and damage mechanisms in uncoated and TEBC-coated MAR-M247 have been studied in isothermal dwell-fatigue tests conducted under strain control with constant strain amplitude at 900 °C. In each cycle, 5-minute dwells were introduced in both tensile and compression peaks of the hysteresis loop. Fatigue hardening/softening curves, stress relaxation curves, cyclic stress-strain curves and fatigue life curves are reported. Ceaseless mild softening has been found in both uncoated and TEBC-coated MAR-M247. TEBC-coated MAR-M247 showed an improved lifetime in the whole range of tested strain amplitudes. Data obtained from stress relaxation curves were used to assess the fraction of creep damage. The generalised damage accumulation rule was used to evaluate damage due to fatigue-creep-environment interaction. A study of the surface relief and internal microstructure using SEM and TEM helped to interpret the specifics of fatigue behaviour of uncoated and TEBC-coated material. The effectiveness of this newly developed TEBC, together with the dwell sensitivity of MAR-M247, were discussed from the perspective relevant to dwell-fatigue cyclic straining.

Rheology of mRNA-loaded lipid nanodumbbells

In one important chemical engineering unit operation of messenger ribonucleic acid (mRNA) vaccine manufacture, the precious mRNA payload is encapsulated in lipid nanoparticles (LNPs). Recent elegant cryogenic-transmission electron microscopy [Brader et al., Biophys. J. 120, 2766 (2021)] reveals that these lipid nanoparticles take the form of dumbbell suspensions. When encapsulating their mRNA payloads, these dumbbells can be both lopsided and interpenetrating, with the smaller of the two beads carrying the payload. In this work, we arrive at analytical expressions for these suspensions of lopsided lipid nanoparticle dumbbells encapsulating mRNA payloads. For this, we first exploit rigid dumbbell theory [Abdel-Khalik and Bird, Appl. Sci. Res. 30, 268 (1975)], which relies on the orientation distributions of the lopsided dumbbells, to predict the suspension rheology, and specifically to predict how this departs from Newtonian behavior. We next exploit elastic dumbbell theory [Phan-Thien et al., Phys. Fluids 36, 071707 (2024)], which also relies on the orientation distributions of the lopsided dumbbells and to which we add dumbbell stretching. Our results include analytical expressions for the relaxation time, rotational diffusivity, zero-shear viscosity, shear stress relaxation function, steady-shear viscosity and both the viscous part and minus the elastic part of the complex viscosity. We determine the rotational diffusivity of the mRNA-loaded lipid nanoparticle nanodumbbells from small-amplitude oscillatory shear measurements.

Stress Relaxation and Creep Response of Glassy Hydrogels with Dense Physical Associations.

Various glassy hydrogels are developed by forming dense physical associations within the matrices, which exhibit forced elastic deformation and possess high stiffness, strength, and toughness. Here, the viscoplastic behaviors of the glassy hydrogel of poly(methacrylamide-co-methacrylic acid) are investigated by stress relaxation and creep measurements. We found that the characteristic time of stress relaxation of the glassy gel is much smaller than that of amorphous polymers. The varying hydrogen bond strength leads to a broad distribution of structural activation energies, which in turn affects the range of characteristic time. In the presence of water, the weak hydrogen bond associations are easily disrupted under applied strain, enhancing segmental mobility and reducing relaxation time in the preyield regime, while in the postyield regime, the relaxation time increases slightly since the chain stretching increases the energy barrier. In creep tests, the creep strain rate accelerates at the initial stage due to stress-activated segments and then decelerates as chains are extensively stretched. The stress required for structural activation during creep is much lower than the Young's modulus of the gel, reflecting the poor structural stability. To further analyze the underlying mechanism of the glassy gel, a micromechanical model is established based on an extension on shear transformation zone theory. By incorporating a state variable for hydrogen bond density, this model can capture the intricate mechanical responses of glassy gels. Our findings reveal that glassy hydrogels are far from the thermodynamic equilibrium state, exhibiting rapid segment activation under external loading. This work provides insights to the dynamics and structural stability of glassy materials and can promote the design and applications of tough hydrogels.

Exploring the Role of Video Games in Reducing Academic Stress among Filipino Students

This qualitative study explores how Filipino undergraduate students perceive video games as a coping mechanism for academic stress. It examines student views on video games' benefits, identifies helpful game characteristics, and explores integration into academic routines. Through multiple-case analysis of ten student cases, the research generates individual case reports and a cross-case report. Four prominent themes emerge: video games offer stress relief and relaxation, foster social interaction and community, provide cognitive skill practice and development, and motivate time management. Consistent with prior research, the findings suggest video games can be a valuable resource for managing academic stress.

Stress relaxation of silt under excess pore water pressure impact from cone penetration test in Yellow River Delta

Stress relaxation of silt under excess pore water pressure impact from cone penetration test in Yellow River Delta

Characterization and Modelling of Microstructure Evolution and Flow Stress of Single-Phase Austenite and Ferrite Phases in Duplex Stainless Steels

This paper presents an experimental and modeling study to investigate and predict the microstructure evolution for single-phase austenite and ferrite steels with the chemistry of the corresponding phases in a duplex stainless steel SUS329J4L under hot forming conditions. For steels with the compositions corresponding to both austenite and ferrite phases, single-pass hot uniaxial compression tests, stress relaxation tests, and heat treatment tests have been conducted for a temperature range of 1000–1250 °C and strain rates ranging from 0.3 to 30 s−1. The dynamic and static recrystallization mechanisms, as well as the grain growth behavior, were studied, and the material parameters of each mechanism were identified for a semi-empirical microstructure model called StrucSim. Double-compression tests in the same temperature and strain rate range were performed to validate the model, and a good correlation of the flow stress between the experiment and simulation was observed.

Evaluating stress relaxation and creep-fatigue interactions in Alloy 617

ABSTRACT This paper investigates the creep-fatigue interactions of Alloy 617 for its exceptional high-temperature mechanical and physical resistance. We focus on modelling the stress relaxation curves under varying total strain ranges, with the primary goal of developing a comprehensive model to verify relaxed stress over extended hold times, up to 5,000 hours. The predictive performance of models fitted to short-term data is compared with long-term data, particularly in the context of the linear damage summation (LDS) model. Additionally, we analyse the fractured surfaces in relation to the creep-fatigue damage mechanism. Our findings identify three leading models – Jeong’s formula, the Power-law fit, and Peleg’s model – as effective representations of the stress relaxation behaviour in Alloy 617. The Peleg’s model is utilised for parameter extrapolation and offers significant predictive accuracy. We also propose an improved LDS diagram for Alloy 617, integrating our findings to enhance the understanding of creep-fatigue interactions and damage prediction accuracy.

Numerical Analysis of Heat Transfer and Flow Characteristics of Jeffrey Nanofluid Over Stretched Surfaces With MHD and Slip Effects

ABSTRACTThis study employs the Jeffrey fluid model to investigate stress relaxation in non‐Newtonian fluids, offering a more precise representation than conventional viscous models. It explores the influence of multiple slip conditions and magnetohydrodynamics (MHD) on Jeffrey fluid flow and heat transfer across irregular surfaces. Additionally, the impact of thermal radiation and internal heat sources on heat transfer is examined, essential for a comprehensive understanding of the system's thermal dynamics. Using the Buongiorno model, the diffusion and thermophoresis of nanoparticles within the flow are analyzed. Nonlinear coupled governing equations covering flow dynamics, heat transfer, and nanoparticle transport are transformed into ordinary differential equations (ODEs) through similarity transformations and solved numerically using the Runge–Kutta fourth‐order (RK4) method combined with shooting techniques. Results indicate significant effects of physical parameters on temperature, velocity, and mass profiles: a 20% decrease in temperature profiles with an increase in the dimensionless thermal slip coefficient from 0.1 to 0.5 and a 15% reduction in velocity profiles from a 0.1 unit increase in the magnetic parameter . The study also quantifies mass and heat transfer rates to elucidate their impacts. These findings have profound implications for engineering applications involving non‐Newtonian and nanofluids in complex geometrical configurations.

Isothermal low-cycle fatigue and fatigue-creep of Alloy 709 using an unified viscoplasticity modelling

An improved unified viscoplastic model (UVM) is proposed to simulate the cyclic viscoplastic behaviors of Alloy 709 under low-cycle fatigue (LCF) and creep fatigue interaction (CFI) loadings. And the effects of strain amplitudes and hold times on the model parameters as well as the relationship between the static recovery parameter and the accumulated inelastic strain are considered to reflect the evolutionary behavior of strain-stress hysteresis loops, the varying stress relaxation and cyclic hardening behavior. Moreover, an efficient numerical implementation is proposed using Voigt notation and implicit radial return method with Newton-Raphson iteration, and the consistent tangent operator (CTO) for the improved UVM can be simply solved using matrix operations. The proposed model accurately depicts the mechanical behavior of Alloy 709 at 750°C.

Single fiber pull-out investigation at different temperature and humidity conditions: Experimental characterization of the fiber-matrix interface in carbon fiber reinforced polyamide 6

This study investigates the effects of varying environmental conditions on the interfacial properties of carbon fiber-reinforced polyamide 6 (CF-PA6). The primary focus is the impact of temperature and humidity on the Interfacial Shear Strength (IFSS), debonding fracture toughness, and surface-specific work of friction. The study reveals that caused by polymer swelling both temperature and humidity lead to a relaxation of the radial residual stress within the interface and a subsequent reduction in IFSS. Notably, the effects of these factors appear to be superimposed up to the debonding of the fiber-matrix interface. Furthermore, while the debonding fracture toughness also follows a declining trend with an increase in both environmental factors, it displays non-linear characteristics, implying a coupled effect between temperature and humidity. The study also identifies that humidity alone significantly decreases the surface-specific work of friction, irrespective of the surrounding temperature, so that after debonding a simple superposition is not feasible. To ensure precise results, a microscale climate chamber was developed using the principle of deliquescence to maintain a constant relative humidity during testing. The findings offer valuable insights into the performance of CF-PA6 under varying environmental conditions, informing potential improvements in its design and application.

Experimental study and numerical simulation of short- and long-term shear stress relaxation behaviors of magnetorheological elastomers

An experimental study and numerical simulation of short- and long-term shear stress relaxation behaviors of nonaligned and aligned magnetorheological elastomers (MREs) were investigated. The aligned MRE was created by aligning micro-size carbonyl iron particles in chains in silicon rubber using an external magnetic field during the curing process, while the nonaligned MRE was fabricated without applying a magnetic field. The effects of permanent magnetic fields on the shear stress relaxation of the nonaligned and aligned MREs were examined using the double-lap shear stress relaxation test with a short-term period of 1200 s and a long-term period of 1.08×106 s. The shear stress and relaxation modulus of the nonaligned and aligned MREs increased considerably with the rise of magnetic flux density to about 500 mT and then enhanced slightly above 500 mT. The shear stress and relaxation modulus of the aligned MRE were considerably higher than those of the nonaligned one. The shear stress relaxation of the nonaligned and aligned MREs was numerically simulated using the fractional derivative viscoelastic Kelvin–Voigt model. The model parameters were identified by fitting the relaxation modulus to the short-term measured data of the MREs. The shear stress estimated from the investigated model with fitted parameters was in excellent agreement with the short-term experimental data of the MREs measured under different magnetic fields. Besides, the short-term model-fitted parameters were used to predict the long-term shear stress relaxation of the nonaligned and aligned MREs. The largest difference between model-predicted and long-term measured results for the nonaligned and aligned MREs was less than 1%. Therefore, the studied model can be used to predict the long-term shear stress relaxation of the nonaligned and aligned MREs.

An Improved Iterative Predictive Model for Grinding Residual Stress Considering Material Microstructure Evolution

Abstract During micro-grinding, multiple abrasive grains on grinding wheel circulate on the workpiece causing alternating mechanical and thermal loads which result in microstructure evolution. The microstructure evolution affects the flow stress of the material, which in turn affects force and temperature. This paper thoroughly investigates the cyclic iterative mechanism and proposes an analytical model to predict micro-grinding-induced residual stress. In this investigation, the flow stress model is developed considering temperature, strain, strain rate, yield stress, and material microstructure evolution, based on which, the micro-grinding force and temperature are calculated. On the basis, the evolution of grain size and phases transformation induced by force and temperature are calculated, in turn affected grinding force by flow stress. Then, the analytical model of residual stress is proposed incorporating the stresses induced by mechanical and thermal loadings as well as microstructure evolution. Moreover, the elastic or plastic deformation is determined according to Von-Mises criterion with the developed plastic modulus model in the stress relaxation process. Finally, the residual stress is measured to validate the improved iterative model. By comparing the traditional models, the results indicated that the developed cyclic iterative model obtains a higher accurate prediction of residua stress.

Stress Relaxation for Lead Iodide Nucleation in Efficient Perovskite Solar Cells.

Porous lead iodide (PbI2) film is crucial for the complete reaction between PbI2 and ammonium salts in sequential-deposition technology so as to achieve high crystallinity perovskite film. Herein, it is found that the tensile stress in tin (IV) oxide (SnO2) electron transport layer (ETL) is a key factor influencing the morphology and crystallization of PbI2 films. Focusing on this, lithium trifluoromethanesulfonate (LiOTf) is used as an interfacial modifier in the SnO2/PbI2 interface to decrease the tensile stress to reduce the necessary critical Gibbs free energy for PbI2 nuclei formation. The relaxed tensile stress facilitates the more porous PbI2 generation with larger particles and higher roughness, resulting in superior-quality perovskite films. Besides, this strategy effectively passivates the inherent electron traps of SnO2 and smooths the interfacial energy levels, boosting the charge extraction and transfer. As a result, a champion power conversion efficiency (PCE) of 25.33% (25.10% stabilized for 600 s) is achieved. Furthermore, the device demonstrates exceptional stability, retaining 90% of its initial PCE at its maximum power point tracking measurement (under 100mW cm-2 white light illumination at ≈55°C temperature, in N2 atmosphere) after 600 h.

Fast-Relaxing Hydrogels Promote Pancreatic Adenocarcinoma Cell Aggressiveness through Integrin β1 Signaling.

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a dense extracellular matrix (ECM) exhibiting high stiffness and fast stress relaxation. In this work, gelatin-based viscoelastic hydrogels were developed to mimic the compositions, stiffness, and fast stress relaxation of PDAC tissues. The hydrogels were cross-linked by gelatin-norbornene-boronic acid (GelNB-BA), thiolated macromers, and a 1,2-diol-containing linear synthetic polymer PHD. Controlling the thiol-norbornene cross-linking afforded tunable stiffness, whereas increasing PHD content led to hydrogels with PDAC-mimicking fast stress relaxation. In vitro studies, including proliferation, morphology, and mRNA-sequencing, showed that fast-relaxing hydrogels supported PDAC cell proliferation, epithelial-mesenchymal transition (EMT), and integrin β1 activation. Blocking integrin β1 in vitro led to upregulating EMT markers in both slow and fast-relaxing hydrogels. However, this strategy profoundly impacted tumor growth rate and reduced tumor size but did not alter metastasis patterns in an orthotopic mouse model. This suggests a need to further evaluate the antitumor effect of integrin β1 blockade.

Inhibition of DEK restores hematopoietic stem cell function in Fanconi anemia.

Hematopoietic stem cells (HSCs) are susceptible to replication stress, which is a major contributor to HSC defects in Fanconi anemia (FA). Here, we report that HSCs relax the global chromatin by downregulating the expression of a chromatin architectural protein, DEK, in response to replication stress. DEK is abnormally accumulated in bone marrow (BM) CD34+ cells from patients with FA and in Fancd2-deficient HSCs. DEK haploinsufficiency promotes chromatin relaxation, replication stress relief, and function recovery of Fancd2-deficient HSCs. Furthermore, inhibition of DEK restores the proliferation of FA CD34+ cells in vitro and enhances their engraftment in vivo. Mechanistically, the activating transcription factor 2 (ATF2), specifically phosphorylated ATF2 at Thr69/71, was identified as a promoter of DEK transcription. Fancd2 deficiency results in p38 hyperphosphorylation, which in turn phosphorylates ATF2 at Thr69/71, leading to DEK accumulation in HSCs. In conclusion, our findings establish a functional link between chromatin relaxation and replication stress tolerance in HSCs and highlight DEK as a target for FA.