Stress Release Rate Research Articles

An analytical solution to ground stresses induced by tunneling considering ground surface boundary conditions and gravity

Accurately predicting the stress distribution around the tunnel is crucial for designing safe and economical support systems. The stress distribution is closely related to the ground stress release induced by tunneling, as well as the initial gravity stress and boundary conditions. In this study, a two-dimensional analytical model considering the ground surface boundary conditions and gravity is presented to investigate the stress field around the tunnel. Then, a numerical model was developed to validate the proposed analytical model. Finally, parametric analyses were conducted, and the limitations of the load calculation method of the code for design of shield tunnel in China were discussed. The results indicate that: (a) Tunnel excavation induces stress redistribution in the soil, resulting in a soil arching effect around the tunnel. This arching effect causes nonlinear load changes around the tunnel. (b) The soil mass around the tunnel can be divided into undisturbed and disturbed zones. Above the tunnel, the disturbance range is C-2D(C and D represent the burial depth and the tunnel diameter), while below and on both sides of the tunnel, the disturbance ranges are 4D and 1.5D, respectively. (c) Once the stress release rate reaches 0.6, a combined arching effect zone, consisting of both major and minor principal stresses, is formed in the disturbance zone above and below the tunnel. (d) The load distribution pattern calculated by the code for design of shield tunnel in China is gourd-shaped, and this calculation method is insufficient for accurately evaluating the load around the tunnel. The research results can provide a reference for the design of the shield tunnel.

Stress, Strain, or Energy? which one is superior predictor of fatigue life in notched Components? a novel Machine Learning-Based framework

This paper introduces an efficient framework for accurately predicting the fatigue lifetime of notched components under uniaxial loading within the high-cycle fatigue regime. For this purpose, various machine learning algorithms are applied to a wide range of materials, loading conditions, notch geometries, and fatigue lives. Traditional approaches for this task have mostly relied on one of the mechanical response parameters, such as stress, strain, or energy. This study also concludes which of these parameters serves as a better measure. The key idea of the framework is to use the profile (field distribution represented by some points) of the mechanical response parameters (stress, strain, and energy release rate) to distinguish between different notch geometries. To demonstrate the accuracy and broad applicability of the framework, it is initially validated using metal materials, subsequently applied to specimens produced through additive manufacturing techniques, and ultimately tested on carbon fiber laminated composites. This research demonstrates the effective use of all three parameters in estimating fatigue lifetime, while stress-based predictions exhibit the highest accuracy. Among the machine learning algorithms investigated, Gradient Boosting and Random Forest yield the most successful results. A noteworthy finding is the significant improvement in prediction accuracy achieved by incorporating new data generated based on the Basquin equation.

Characterization of stability and support force of loess caves in northwest China

Numerous manually excavated loess caves are present within a cultural relic protection zone in the northwestern region of China. The collapse of these caves frequently leads to the cracking, tilting, and even collapse of ancient buildings above, posing a severe threat to the safety of cultural architectural relics. Investigating the stability and characteristics of deformation and failure in loess caves is essential for effectively reinforcing and protecting cultural relics. A two-dimensional model of a loess underground cavern was developed using OptumG2. The stability and modes of deformation and failure in the underground cavern were analyzed through the augmentation of soil gravity and the strength reduction method. This analysis determined the cavern's safety factor, force, deformation and damage mode, and the plastic zone's progression. Numerical simulations analyzed the force characteristics of the support structure under different stress release ratios. The findings revealed that, with the implementation of an anchor rod concrete lining support scheme, the most probable failure mode is a shear failure, initiating at the arch foot. The ground's stress release rate does not influence the safety factor of the cavern but rather the material, design, and strength of the support structure. However, the magnitude of the internal forces acting on the supporting structure by the soil in the cavern is related to the degree of ground stress release. When applied during significant stress release, support structures may experience reduced internal forces, albeit with more substantial stratum displacement; opting for an appropriate stress release when applying support structures is crucial for achieving optimal stratum displacement and lining internal forces.

Polydimethylsiloxane enabled triple-action water-resistant coating with desirable relaxation rate in clear aligner

Clear aligners undergo rapid stress relaxation in warm, moist oral environments, compromising therapeutic effectiveness and longevity of treatment. To develop an innovative multilayer composite material with improved stability and reduced stress release, we have engineered an innovative coating characterized by the surface aggregation of polydimethylsiloxane (PDMS), which imparts a pronounced hydrophobic effect. In addition, the chemically and physically cross-linked structure of the coating reduces the free volume created by molecular chain rearrangement owing to the presence of water molecules, thereby minimizing water penetration into the coating. Concurrently, the coating’s internal structure is enriched with numerous polar functional groups to capture water molecules that penetrate into the inside of the coating. Through combination of these mechanisms, water molecules are effectively sequestered, thereby impeding their penetration into the polyethylene terephthalate glycol (PETG) substrate. The impact of the polydimethylsiloxane content on the triple-action water-resistance mechanisms was thoroughly examined using attenuated total reflection (ATR)-Fourier transform infrared (FTIR), water absorption rate, water swelling rate, and X-ray photoelectron spectroscopy. The low surface energy cross-linked polyurethane coating is applied to the polyethylene terephthalate glycol (PETG) substrate to create a novel composite material with specific mechanical properties and reduced stress relaxation. The composite material remains stable in simulated oral environment with linear swelling rate of 0.58 % upon water absorption. Additionally, the stress release rate of the composite material within 336 h is notably lower (23.64 %) than that of PETG (62.29 %).

Thermomechanical-induced cracking model for ceramic matrix composite laminates subjected to thermal gradients and transients

Regarding the potential damage and failure issues that may occur in high-temperature transient environments during the service process of ceramic matrix composite laminates, the present work proposes a multi-layer thermomechanical induced crack initiation model for ceramic matrix composite laminates subjected to thermal gradients and transients. This model can determine the history of temperature, deformation, and stress distribution within each layer of the material, as well as the steady-state energy release rate of all possible crack locations. Then the influence of bending constraints on material stress distribution and energy release rate is investigated, finding that maximum stress and energy release rate values are significantly lower without bending constraints compared to those under bending constraints. Furthermore, the study explores the impact of material structural parameters and boundary conditions on the energy release rate of ceramic matrix composite laminates, providing direct insights for designing laboratory tests and evaluating the lifespan of these materials under in-service conditions.

Analytical solution for the interfacial stress and energy release rate at failure initiation of the three-point bending test (ISO 14679:1997)

Determining adhesive failure in adhesively bonded joints is still challenging in the field. While the three-point bending test (3PBT) (ISO 14679:1997) has been helpful in identifying critical forces and displacements related to bond strength, it only allows for a qualitative assessment of the bond line. Recently, a new quantitative methodology has been developed to determine critical stress and fracture toughness using the coupled stress–energy criterion and the 3PBT. However, these assessments require a significant effort using semi-analytical or finite element (FE) analysis. Therefore, the present study proposes a reliable set of analytical equations to determine peel and shear stress distributions using a weak interface formulation and 1D Euler–Bernoulli approach. More precisely, a particular numerical method computes the integration constants from these equations. A new method has been proposed for calculating the interfacial stiffness in peel and shear mode, based on the material and geometrical parameters of the geometry. This method differs from the previous approach, where the interfacial stiffness was calibrated from the experimental behavior of the test. The whole approach has been validated through experimental and numerical analysis, including the costly 3D FE analysis. An analytical expression for interfacial energy release is suggested, developed following the works of Fraisse and Schmit on J-integral assessment of sandwich-type overlaps and depending on the applied force and a rotation, which could be experimentally measured. Therefore, this work is significant progress in determining bond strength using a simple mechanical test and equations applicable to various industries.

Stress and energy release rate analysis of cross-ply carbon fiber-reinforced plastic laminate with transverse cracks subjected to ultrasonic vibration using a variational approach

Application of carbon fiber reinforced plastics (CFRP) to structures that are subjected to increasingly high numbers of cyclic loads is expected to expand, so evaluation of fatigue properties up to the very-high cycle regime is essential to prove their long-term reliability. Conventional fatigue testing is not practical for such conditions owing to the excessive time required; ultrasonic fatigue testing, which can be performed at a frequency of 20 kHz, is an effective alternative. Stress distribution in ultrasonic fatigue testing differs from that in conventional fatigue testing because the specimen is resonated. The stress distribution of cross-ply laminates with transverse cracks subjected to resonance was calculated using a variational approach. The energy release rate was calculated based on the results of a previous study on transverse crack initiation. The results of the stress analysis are in good agreement with those of finite-element analysis. Quantitative evaluation of transverse crack initiation was also conducted.

Impact of interfacial texture on failure behaviour of 8YSZ thermal barrier coatings under thermal cyclic loading

Thermal barrier coatings (TBCs) provide thermal protection for high-temperature components of aero-engines and steam turbines, but are susceptible to failure under thermal cyclic loads. The effective design of interfacial texture is one of the approaches to enhance the lifetime of ceramic TBCs. In this study, four types of interfacial textures were designed on the surface of substrates, and 8YSZ coatings of equal thickness were prepared using atmospheric plasma spraying, and thermal cycling tests were carried out. Meanwhile, the thermal cycle lifetime, microstructure evolution, residual stress, and energy release rate criterion were also studied. The optimal morphology and parameters of the texture are determined. It is found that the lifetime of the concave trapezoidal texture is the longest, with a deflection angle of 67°, diameter of 700 μm, depth of 500 μm, and spacing of 5 mm. This study can provide theoretical guidance for the interfacial texture design of ceramic TBCs.

Research on Excavation Method for Soft Rock Tunnel Based on Stress Release Rate

A test method for controlling the stress release rate of the tunnel by adjusting the confining pressure is proposed based on the engineering background of Dongmachang No. 1 Tunnel of Huali Expressway to explore a suitable excavation method of soft rock tunnel. Based on the relationship between stress release rate, displacement release rate, and longitudinal advance of excavation face, the model test of tunnel excavation is carried out. On this basis, combined with the horizontal loading test and field monitoring results, the influence of three excavation methods, the three-bench method, three-bench with reserved core soil method, and three-bench seven-step method, on the mechanical behavior of the tunnel is studied. The research shows that the load shared by the double-layer initial support is not equal, and the second-layer initial support only bears 20% of the pressure of the first-layer initial support; replacing the three-bench method with the three-bench core soil method and the three-bench seven-step method can reduce the deformation of the surrounding rock by 8.7~12.4%, and the load borne by the supporting structure is transferred from the second layer to the first layer. In order to take into account the safety and efficiency of tunnel construction, it is recommended to use the three-bench core soil method for excavation. The research results can provide a theoretical reference for the construction of related tunnel projects.

Stress-Release Rate Model for Measuring Working Stress in Concrete

Stress-Release Rate Model for Measuring Working Stress in Concrete

Mutual dependence of experimental and data analysis features in characterization of fiber‐matrix interface via microdroplets

AbstractThe accurate determination of interfacial strength in composites poses a significant challenge, a critical factor yet often complex due to the multitude of unknowns that affect the microbond (MB) test. This complexity arises not only from different individual parameters, but also from the combined effects of these parameters interdepending with each other. This study presents a thorough analysis of the MB test, carried out through numerous finite element simulations that take into account a wide range of parameters. This was achieved in the context of an experimentally validated reference test. In this study, 624 different numerical simulations were performed, each using a unique set of parameters defined for this investigation. The study demonstrates that even minor modifications to features such as a change in droplet behavior (change in ductility – simulated via different material models), the normalized error can range from −2.5% to 20.6% and −10% to 80%, for peak force () and force‐displacement area (), respectively. The negative percent values indicate lower magnitudes than the reference experimental data, while positive values suggest higher predicted magnitudes. In addition, residual stresses are identified as the second strongest in terms of mutual interaction and a key feature that interacts with other parameters. The results also show that typical comparisons using and are inadequate and misleading, suggesting the use of critical stress and critical energy release rate for more accurate qualitative comparisons about the interface. In this work, the interdependencies between the selected features are investigated with the reasoning based on the interfacial crack propagation and associated dissipative phenomena of the droplet.

Stability evaluation of rock pillar between twin tunnels using the YAI

The stability of rock pillar is crucial for ensuring the construction safety of twin tunnels with small clearance, especially when transitioning from the traditional left–right tunnel layouts to the up-down configurations due to complex and variable site constraints. However, there are limited researches on the evaluation and comparative study of the stability of these two types of rock pillars in twin tunnels. This paper introduces the yield approach index (YAI) as a measure to assess the stability of rock pillar in twin tunnels with small clearance, and various influencing factors including side pressure coefficient (SPC), stress release rate (SRR), and the thickness of rock pillar (characterised by the ratio of rock pillar thickness to tunnel diameter, RPT/TD) are considered in the analysis. The study compares and analyzes the stability differences of the rock pillar in different situations. It is observed that the two sides of up-down tunnels pose a higher risk while the rock pillar in the left–right configuration being the most vulnerable. The stability of the rock pillar between the up-down tunnels is significantly higher than that of the left–right tunnels under similar conditions. Moreover, the up-down tunnels exhibit greater sensitivity to SPC, whereas the left–right tunnels are more sensitive to SRR. Additionally, the study reveals that increasing the RPT/TD can effectively improve the stability of the rock pillar within a specific range (1/4 to 2/3). The research method and obtained results of this paper can provide some important references for the stability evaluation and design of twin tunnels with small clearance.

Surrounding rock pressure calculation based on time functions and stress release rate determination of deep soft rock tunnel: taking Zhonghe Tunnel as an example

On the basis of the Zhonghe Tunnel project of the An-Lan Expressway, the objective of this study was to determine the appropriate method of calculating the steel arch load and stress release rate during numerical simulation. First of all, based on the monitoring results of six similar tunnel sections where the surrounding rock exerts pressure on the steel arch, using time functions, the rock pressure time history curve could be fitted, two formulas for calculating stable rock pressure in deep tunnels were compared, and the calculation model suitable for the Zhonghe Tunnel project was constructed. Then, a simulation of the Zhonghe Tunnel was performed using Flac3D, and stress release was simulated using the Mana method. By comparing the surrounding rock characteristic curves and the initial support characteristic curves under different stress release rates, the impact pattern of the stress release rate on the support load was summarized, and an appropriate excavation stress release rate was determined based on the stable rock pressure value calculation. It was found that the Zhonghe Tunnel rock pressure calculation model could better depict the change in rock pressure over time based on the empirical formula and Weibull time function. A prediction of the steel arch load of the Zhonghe Tunnel could be made using this method, and the stress release rate of the numerically simulated rock excavation was determined to be 0.5. This study thus provides a basis for the future internal force analysis and support parameter design of support systems.

USP22 knockdown protects against cerebral ischemia/reperfusion injury via destabilizing PTEN protein and activating the mTOR/TFEB pathway.

Ubiquitin-specific protease 22 (USP22) expression was reported to be increased in response to ischemic brain damage, but the biological role and underlying mechanism remain little understood. USP22 shRNA was intravenously injected into the mouse brain, and then a middle cerebral artery occlusion/reperfusion (MCAO/R) mouse model was constructed, and the infarct volume, neurobehavioral deficit score, cell apoptosis, oxidative stress, and autophagy in vivo were evaluated. Oxygen-glucose deprivation/reperfusion (OGD/R) treated pheochromocytoma-12 (PC12) cells were used as an in vitro model of ischemia/reperfusion. The effects of USP22 on proliferation, apoptosis, oxidative stress, and autophagy were explored by CCK-8, flow cytometry, ELISA, and Western blot assays. The relationship between USP22 and the phosphatase and tensin homolog (PTEN) was measured by Co-IP and Western blot assays. Both USP22 and PTEN were highly expressed in MCAO/R mouse brain tissues and OGD/R-induced PC12 cells. In vitro, USP22 knockdown strongly improved OGD/R-mediated changes in cell viability, apoptosis, oxidative stress, and lactate dehydrogenase (LDH) production in PC12 cells. USP22 bound to PTEN and stabilized PTEN expression by decreasing its ubiquitination. PTEN overexpression reversed the promoting effect of USP22 knockdown on cell viability and the inhibitory effects of USP22 knockdown on apoptosis, oxidative stress, and LDH release rate in PC12 cells subjected to OGD/R. PTEN silencing elevated the protein levels of p62, p-mTOR, TFEB, and LAMP1 and reduced the protein levels of LC3-II/LC3-I. USP22 expression levels were negatively correlated with mTOR expression levels, and USP22-shRNA-mediated expression of p62, p-mTOR, TFEB, and LAMP1 was reversed by rapamycin, an inhibitor of mTOR. In vivo, USP22 silencing significantly alleviated infarct volume, neurobehavioral impairments, cell apoptosis, oxidative stress, and autophagy in MCAO/R mice. USP22 knockdown exerts neuroprotective effects in cerebral ischemia/reperfusion injury by downregulating PTEN and activating the mTOR/TFEB pathway.

Stress Detection of Precast Pipe Piles Based on the Low-Loss Slotting Method

Tilting of buildings due to uneven settlement, construction quality issues or other problems is one of the critical accidents threatening the safety of buildings. In order to determine a reasonable solution with respect to the rectification of the tilting building, detection of the stresses of the substructure is necessary. In this study, a stress release method to test the stress of prefabricated pipe pile under loading is studied by combining experimental research and finite element numerical simulation. Based on various measurements, such as traditional strain gauges, vibrating wire strain gauges, and three-dimensional digital image correlation (DIC) tests, the relationship between local residual stress and actual stress of the slotted area at different load levels is determined. Meanwhile, the stress release process in slotted precast pipe pile was numerically simulated with ABAQUS to investigate the influence of the slotting dimension parameters on the stress release rate at different load levels. Based on 1042 sets of finite element modeling results of multi-parameter combination, the quantitative relationship between slot width, depth, spacing, prestress level and stress release rate is studied. An explicit prediction model of the stress release rate is given by regression analysis of combined test results and simulation data. With the prediction model, the stress condition of a loaded precast pipe pile can be accurately predicted based on low-loss slotting. Compared to the traditional stress release method, the proposed method has better controllability and applicability, less damage to the structure, and stronger anti-disturbance ability.

Relieving Residual Stress of 316L Stainless Steel by Acoustic/Thermal Composite Treatment

The influence of temperature, vibration time, amplitude, and other factors on the residual stress release effect was studied using the method of low-temperature heating and high-frequency ultrasonic vibration, and excellent control parameters were obtained. In addition, the influence of cutting weld reinforcement on the residual stress release was also studied. The results demonstrate that the highest relative residual stress release rate was 280.29%, the average release was over 150 MPa, and the efficiency was higher than that of the general stress release methods. After cutting the reinforcement, only a small part of residual stress was released, influencing the overall residual stress distribution relatively little. The experimental material was a butt-welded 316L stainless steel plate μ-X360s diffractometer, and this was used for measuring the residual stress.

Tunnel stability analysis of coral reef limestone stratum in ocean engineering

The islands and coasts in the South China Sea have developed coral reefs, which are the basis for the development of ocean resources and the construction of ocean engineering. However, the biogenetic coral reef limestone in the sea has the physical properties of much porosity, low strength and low density, which is obviously different from the traditional geological rock mass during the underground engineering construction. So in this paper, surrounding rock stability of coral reef limestone stratum in tunnel excavation is studied by physical model tests and numerical simulation. Firstly, according to the similarity theory, quartz sand, barite powder, high strength gypsum, calcareous sand and cement are selected to configure the similar materials of coral reef limestone by the orthogonal ratio test and physical mechanics test. Secondly, the triaxial geomechanical model tests of tunnel excavation in coral reef limestone stratum are carried out. The influence of tunnel shape, support method and rock strength on the tunnel stability is studied by analyzing the variation laws of displacement and stress of the surrounding rock. Finally, the numerical calculation of tunnel excavation in coral reef limestone stratum is conducted and the results of physical model tests are verified. The influence of tunnel depth on the surrounding rock stability is further studied. The results show that: (i) Compared with the horseshoe shaped tunnel, the displacement of the circular tunnel at the haunch and springer is significantly increased, and the stress concentration phenomenon occurs. (ii) The stress release rate and displacement of surrounding rock decrease significantly when the anchor support is added or the strength of reef limestone increases. (iii) The stress release rate and displacement of surrounding rock increase with the tunnel depth, so the support strength of surrounding rock should be increased.

Joule heating effect on thermal stress for a bi-material interface crack

The electric-induced Joule heat plays a dominant role for the fracture and failure in electronic devices, particularly in those with bi-material interfaces, yet the effect of Joule heat on temperature elevation and thermal stress for a bi-material interface crack remains incompletely understood. To this end, we develop a coupled electro-thermo-mechanical model for the bi-material interface crack using the extended finite element method. A novel near-tip asymptotic function is introduced as the enrichment field in the finite element approximations of electrical potential and temperature, which well reproduces the singularities of electric current and heat flux near the bi-material interface crack. Using the domain form of the interaction integral, the complex stress intensity factors and energy release rate are evaluated for bi-material interface cracks. The results of several benchmarking tests demonstrate the accuracy and robustness of the proposed model. The effects of the Joule heat and the mismatch of material properties on the stress intensity factors and energy release rate at the interfacial crack tip are investigated. The results not only reveal the significant contribution of the Joule heating effect on temperature elevation, thermal stress, and energy release rate for a bi-material interface crack, but also provide practical suggestions on the optimal design of multilayered electronic devices to reduce thermal stress and prevent crack propagations.

Inverse analysis on mode II adhesive properties of PP film in fiber metal laminate using hybrid Levenberg–Marquardt methods

Fiber metal laminate constants of the metallic sheet and the fiber-reinforced composite sheet. FMLs can undergo delamination under transverse loads. Therefore, their nominal stress and energy release rate (ERR) should be experimentally derived to quantitatively evaluate their adhesive properties. However, the adhesive properties obtained experimentally contain some unavoidable errors. In this study, we propose an inverse analysis method to more accurately predict the mode II nominal stress and the ERR of a polypropylene film. First, an end-notched flexure test was conducted to obtain the mode II ERR, and a cohesive zone model was proposed to predict the delamination of the specimens. Next, we proposed the hybrid Levenberg–Marquardt methods to predict the mode II nominal stress and the ERR of the PP film. The methods were compared using the root mean square error to confirm whether each method escaped the local minimum and plateau regions, and the computational resources.

Quantitative evaluation of the constraint effect and stability of tunnel lining support

The surrounding rock stress release rate in a two-dimensional (2D) rock tunnel model and boundary problems in a three-dimensional (3D) rock tunnel model are the main factors that affect the results of modeling rock tunnels. We investigated the constraint effect of supporting structures and boundary effects of the 3D model based on the confinement convergence method. A rupturable lining unit was developed using FLAC3D to study the influence of the constraint effect on the surrounding rock stress release and influence range of the boundary effects. The results show that the 2D model stress release enhances the virtual support force generated by the support constraint effect by 3–5% of the initial rock stress. A comparison of field monitoring and numerical calculations of the Millin tunnel project shows that the 3D model boundary effect is nearly 1.5 times the tunnel span. The rupturable lining unit directly reflects the stress characteristics of concrete lining in practical engineering and provides support for the quantitative evaluation of tunnel engineering stability.