Rate Of Change In Stress Research Articles

Earthquake Growth Inhibited at Higher Coulomb Stress Change Rate at Groningen

AbstractGas extraction from the Groningen gas field resulted in significant induced seismicity. We analyze the magnitude‐frequency distribution of these earthquakes in space, time and in view of stress changes calculated based on gas production and reservoir properties. Previous studies suggested variations related to reservoir geometry and stress. While we confirm the spatial variations, we do not detect a clear sensitivity of b‐value to Coulomb stress changes. However, we find that b‐value correlates positively with the rate of Coulomb stress changes. This correlation is statistically significant and robust to uncertainties related to stress change calculation. This study thus points to a possible influence of stress change rate on the probability of the magnitude of induced earthquakes.

Measurement of stress characteristics in flexible multi-thin-film substrates using tomography common optical path interferometry

Flexible displays are lightweight, thin, flexible, and impact-resistant, making them a major trend in the display industry. However, their short lifespan is a significant challenge. Thus, improving process parameters and extending product life through advanced measurement technology is crucial. Therefore, this study proposes using tomography common optical path interferometry (TCOPI) to measure and analyze the tomography stress characteristics of multi-thin-film flexible substrates in the folding direction. For polyethylene terephthalate (PET) and polyimide (PI), three thicknesses of indium tin oxide (ITO) were coated on the PET, graphene/PET, and graphene/PI flexible film substrates, and an automatic sliding-folding test platform was used to fold each flexible film substrate. Moreover, this study used TCOPI to measure and analyze the change in residual stress and the sheet resistance of the samples before and after folding. Additionally, this study conducted inward and outward folding tests on graphene/PET/graphene and graphene/PI/graphene substrates to analyze tomographic stress and sheet resistance in the folding direction. After 11,000 folding tests, the graphene/PET/graphene sample exhibited smaller stress and sheet resistance change rates compared to the graphene/PI/graphene sample, as measured by TCOPI. Consequently, the graphene/PET/graphene sample demonstrated better resistance to folding stress in this batch manufacturing process. Specifically, for the graphene layer of the graphene/PET/graphene sample, the minimum absolute value of the stress change rate before and after folding reached 5%. At the same time, the minimum sheet resistance value change rate was 8%. Based on the tomography stress measurements, suggestions for fine-tuning process parameters are provided to improve the flexible film substrate’s folding endurance.

Bone mineral density changes around the stem correlate with stress changes after total hip arthroplasty: A study using thermoelastic stress analysis.

Thermoelastic stress analysis (TSA) was used to evaluate stress changes over the entire surface of a specimen. This study aimed to assess the relationship between femoral stress distribution, analysed using TSA and changes in bone mineral density (BMD) after total hip arthroplasty (THA). Stress changes in the simulated bone before and after taper-wedge stem insertion were measured using the TSA. Stress changes were compared with BMD changes around the stem 1 year after surgery in a THA patient (58 hips) with the same taper-wedge stem. Subsequently, we compared the correlation between stress changes and BMD changes. TSA revealed significant stress changes before and after stem insertion, with prominent alterations in the proximal medial region. The BMD changes at 1 year post-THA exhibited a 15%-25% decrease in the proximal zones, while Zones 2-6 showed a -6% to 3% change. Notably, a strong positive correlation (0.886) was found between the stress change rate and BMD change rate. This study demonstrated a high correlation between femoral stress distribution assessed using TSA and subsequent BMD changes after THA. The TSA method offers the potential to predict stress distribution and BMD alterations postsurgery, aiding in implant development and clinical assessment. Combining TSA with finite element analysis could provide even more detailed insights into stress distribution. Case series (with or without comparison).

Wood sandwich softening behavior via coupling of moisture and heat

The controllability of the position and thickness of the compressed layer in the sandwich compression wood is primarily based on the yield stress distribution during a hydrothermal treatment. In this study, the variation law of the yield stress of poplar wood was analyzed in the moisture content (MC) range of absolute dryness to saturation and the temperature range of 30–210℃. A prediction model of wood yield stress response to MC and temperature was developed and the formation of sandwich compression was analyzed. The yield stress of the wood was influenced by the thermal effect and plasticizing effect. In the process of increasing temperature and MC, the yield stress decreased gradually. And the yield stress change rate was 0.29–0.46 MPa in the MC range of 5–10%. The prediction model of wood yield stress was developed by a multiple linear regression analysis. This example demonstrated that coupling distributions of MC and temperature were formed upon heating at 180℃, which led to a gradient distribution of the glass transition temperature and yield stress inside the wood. This phenomenon resulted in the sandwich softening behavior under the coupling of moisture and heat, which was the key formation mechanism of sandwich compressed wood.

A physical model test for the stress and deformation analyses in underground caverns containing block during excavation

To investigate the influence of block on the stress and deformation of underground cavern with high sidewall during excavation and unloading, a physical model test of an underground cavern containing block was conducted based on similarity theory. The response pattern of surrounding rock stress and displacement during excavation is analyzed, and the influence and mechanism of block on surrounding rock stress and deformation are revealed. Results show that stress conduction in the model is closely related to the structural plane during loading. The stress barrier and stress concentration phenomena occur when stresses pass through the structural plane. After the model is loaded, stress loss takes place when stresses are transmitted from the boundary to the interior. During the underground cavern excavation, the tangential stress of the surrounding rock decreases within a certain range of the sidewall and increases at both the top and the shoulder of the arch. The change rate of stress before and after excavation is used as an index to determine the surrounding rock stress zone, and the influence range caused by excavation is 2.0–2.5 times the cave span. Compared with the sidewall without block, the sidewall with block has a smaller radial stress unloading zone and a larger tangential unloading zone.

Mechanical properties and failure characteristics of sandstone under ramp loading paths

The revelation of the mechanical behaviors of rock in complex stress conditions is of vital importance for the safe exploitation of underground resources. In this paper, the ramp loading path was designed to elaborate the mechanical properties and failure characteristics of sandstone under the compound action of linear loading path and cyclic loading and unloading path. The strength, deformation, AE and failure characteristics of sandstone under ramp loading paths were obtained. The research achievements indicate that with the increase of the amplitude and decrease of the stress change rate, the peak stress decreases. Elastic modulus is more greatly affected by the linear path stress than by the cyclic disturbance. The irreversible strain curve is L-shaped under a single loading and unloading cycle. Under lower amplitudes and higher stress change rates, the loading and unloading response ratio fluctuates largely and decreases slightly. Under lower amplitudes and higher stress change rates, the deformation and failure of sandstone caused by stress growth under the linear path is the leading cause for total deformation and failure of sandstone. Under higher amplitudes and lower stress change rates, cyclic loading and unloading are the dominant factor for the failure of sandstone. The research results are of scientific value for evaluating rock failure.

The material deformation modes of monocrystalline gallium antimonide (GaSb) under nano-scratching

The deformation characteristics of GaSb are investigated by employing nano-scratch tests to understand the material removal mechanism during ultra-precision grinding. The nano-scratches are obtained by a cube-corner tip under the two linear normal load conditions (0–30 mN and 0–60 mN). The normal force/scratch distance-penetration depth curves and the characteristics of chips and cracks are analyzed to understand the transition mechanism of ductile to brittle removal. In addition, the maximum principal stress near the bottom of the scratch is calculated to analyze the deformation behavior. The results revealed that the deformation behavior of three zones of deformation is plastic deformation, the transition from plastic to brittle deformation, and brittle deformation, respectively. The change rate of stress is significant differences in the zone of brittle-ductile transition. The critical ratio between mean contact pressures and hardness in the transition region is determined as 0.39 and 0.21, respectively.

잠재성장모형을 활용한 대학생의 스트레스가 진로미결정에 미치는 종단적 영향관계 분석

This study examined the longitudinal effects of college students' stress on their career indecision using data from the 12th (2018), 13th (2019), and 14th (2020) rounds of the ｢Youth Panel Survey｣ conducted by the Korea Employment Information Service. A latent growth model analysis was conducted for the relationship. As a result of the study, first, the 12th, 13th, and 14th data of college students' stress and career indecision showed a tendency to gradually increase over time. Second, the initial value of stress had a significant positive effect on the initial value of career indecision. Third, the initial value of stress was not statistically significant in the change rate of career indecision. Fourth, the change rate of stress had a significant positive effect on the change rate of career indecision. Through this study, the longitudinal changes in college student stress and career indecision and the longitudinal effect of stress on career indecision were confirmed.

Attenuation law of concentrated stress under coal pillar of close coal seams and its application

When mining the multiple coal seams in close proximity, the coal pillar left in the goaf causes stress concentration in the floor. The layout of mining roadway in lower short distance coal seam is affected by the propagation of concentrated stress caused by the upper coal pillar. To determine the reasonable distance of the roadway in the lower coal seam outside the coal pillar, the attenuation law of concentrated stress outside the coal pillar boundary has been studied through simulation model, theoretical analysis, and example analysis. The results show that the concentrated stress of coal pillar decreases with the distance from the coal pillar. At the coal pillar boundary position, the stress change rate reaches the maximum in the floor with different depths, and the stress decreases rapidly in the floor strata outside the coal pillar. Under the same stress condition, the roadway layout in strata at different depths is different. The joint formula of stress and stress change rate was deduced to determine the reasonable horizontal distance of roadway outside coal pillar. The results obtained by the numerical simulation fitting formula and the theoretical calculation formula are close to each other when calculating an engineering example. The roadway pressure appearance is not obvious in the experiment and physical simulation, which indicates that the theoretical formula can satisfy the requirement of engineering calculation. The method provides a reference for roadway location selection under similar conditions.

Anelastic deformation in the lower crust and its implications for tectonic dynamics in Kyushu, Southwest Japan

Most of the seismicity in inland Kyushu, southwest Japan occur in the localized intraplate shear zones which are Beppu-Shimabara Graben (BSG) and left-lateral shear zone (LSZ). One of the largest fault systems in Japan (Median Tectonic Line—MTL), and subduction zone of the Philippine Sea Plate also exist near Kyushu. These suggest that the island arc, such as Kyushu has a complex deformation process. This study estimated the anelastic strain rate in the lower crust and the interplate coupling rate via inversion analysis using Global Navigation Satellite System data to elucidate the seismotectonics. Deformation in the lower crust and interplate coupling were modeled by cuboid volumetric sources and a back slip model, respectively. To stabilize the solution, a L2 regularization constraint was applied to the anelastic strain rate. Further, constraints on direction and smoothing to the slip deficit rate were applied. These strength of the constraints were determined via the minimum value of the Akaike Bayesian information criterion. The analyses showed that the anelastic strain rate of the BSG and LSZ was ∼0.6 ×10−6 yr−1, and BSG was related to MTL activity. The findings also suggest that this anelastic deformation in the lower crust created a stress concentration zone in the upper crust of BSG and LSZ, with a stress change rate of ∼6–10 kPa·yr−1. The value is consistent with the stress drop and recurrence interval of regional earthquakes, suggesting that the seismicity around BSG and LSZ is strongly influenced by anelastic deformation in the lower crust. It is also suggested that BSG and LSZ development is influenced by slab rollback, and a subducting ridge. Lastly, a comparison between the deviatoric stress field estimated using focal mechanisms and the anelastic strain rate suggests the existence of a shear zone consisting of weak faults south of BSG.

A Novel Motion Recognition Method Based on Force Myography of Dynamic Muscle Contractions.

Surface electromyogram-based pattern recognition (sEMG-PR) has been considered as the most promising method to control multifunctional prostheses for decades. However, the commercial applications of sEMG-PR in prosthetic control is still limited due to the ambient noise and impedance variation between electrodes and skin surface. In order to reduce these issues, a force-myography-based pattern recognition method was proposed. In this method, a type of polymer-based flexible film sensors, the piezoelectrets, were used to record the rate of stress change (RSC) signals on the muscle surface of eight able-bodied subjects for six hand motions. Thirteen time domain features and four classification algorithms of linear discriminant analysis (LDA), K-nearest neighbor (KNN), artificial neural network (ANN), and support vector machine (SVM) were adopted to decode the RSC signals of different motion classes. In addition, the optimal feature set, classifier, and analysis window length were investigated systematically. Results showed that the average classification accuracy was 95.5 ± 2.2% by using the feature combination of root mean square (RMS) and waveform length (WL) for the classifier of KNN, and the analysis window length of 300 ms was found to obtain the best classification performance. Moreover, the robustness of the proposed method was investigated, and the classification accuracies were observed above 90% even when the white noise ratio increased to 50%. The work of this study demonstrated the effectiveness of RSC-based pattern recognition method for motion classification, and it would provide an alternative approach for the control of multifunctional prostheses.

An Evaluation Method for Effective Prestress of Simply Supported Prestressed Concrete Beams with Breathing Cracks

Loss of effective prestress and accurate detection of actual stress in existing precast prestressed concrete bridges are two major challenges in the bridge industry. In this respect, this research aims at an improved method for the critical decompression moment (DM) test of cracked sections depending on the stress change rate of tensile rebars. A calculation method for total effective prestress of prestressing strands in the tensile region is derived with the assumption of the plane section and pre‐decompression elastomer. The proposed method is verified by laboratory tests on beams and numerical analysis and by addressing effective prestress issues of existing simply supported beams. The determination results of the critical decompression state show that the proposed method (i.e., the stress change rate of tensile rebars‐load curve) is more sensitive and reasonable than the traditional stress increment, i.e., load curve method. The evaluation results of the total effective prestress are more reasonable than the traditional method based on the steel stress relief hole technique or frequency test results. Compared with the existing methods for estimating the prestress using the mid‐span deflection or crack width, the proposed method is more reasonable in theory and calculation. It provides a guide for the evaluation and reinforcement of aging bridges.

Millisecond dynamics of deformation bands during discontinuous creep in an AlMg polycrystal

Formation of bands of macroscopic strain localization during staircase creep in an AlMg polycrystal is studied by the acoustic emission (AE) technique and high-speed video recording with an image acquisition rate up to 50 000 frames per second. The simultaneous measurements by two methods allow us to distinguish different types of embryo deformation bands and concomitant AE signals, and to establish correlations between the band evolution and the acoustic response. It is found that the fastest stages of band formation, associated with its emergence to the surface and subsequent accelerated expansion, generate complex AE bursts in the frequency band ∼0.05-1 MHz. The correlations hidden in the complex structure of an individual acoustic burst are investigated by methods of statistical and fractal analysis. On the other hand, relationships between average parameters of various physical responses to discontinuous creep are assessed. Particularly, a close correspondence is found between the envelope of the acoustic burst and the rate of stress change during formation of a single deformation band. Evolution of dynamical behavior of embryo bands with increasing creep stress is discussed. Notably, a qualitative change in the AE waveform observed on approaching the ultimate stress is considered from the viewpoint of anticipation of the oncoming fracture.

Experimental Research of the Time-Dependent Effects of Steel–Concrete Composite Girder Bridges during Construction and Operation Periods

The present work aimed to study the effects of temperature changes and concrete creep on I-shaped steel–concrete composite continuous girder bridges during construction and operation processes. This study combined structural health monitoring data, an ANSYS finite element simulation, and the age-adjusted effective modulus method to obtain the variation laws of temperature and internal force in composite girders. Moreover, a temperature gradient model was proposed that is suitable for bridges in Hebei, China. In addition, a concrete creep experiment under unidirectional axial compression was performed using concrete specimens prepared from the concrete batch used to create the composite girder. The long-term evolution laws of the deflection and internal force of the composite girder were obtained by predicting the concrete creep effect. The measured data showed that the temperature variation trends of the steel beam and concrete slab were characterized by a sinusoidal curve without a temperature lag. The heating rate of the concrete slab was higher than the cooling rate. The prediction results showed that the internal force changes in the composite girder were characterized by three stages. The stress changes in the composite girder during the first 10 days were significant and the stress charge rate of the concrete slab, the steel girder and the shear stud can reach 5%–28%. The stress change rate decreased continuously during 10–90 days. The stress changed slowly and smoothly after 90 days. This research can provide feedback and reference for structural health monitoring and service safety control of similar I-shaped steel–concrete composite bridges.

Parameter sensitivity analysis of stability of T-shaped rigid frame bridge by adopting swivel construction method

PurposeIn order not to affect the highway and railway traffic under the bridge during the construction process, bridges adopting swivel construction method are increasingly used at areas where the traffic is heavy. Previous studies are mostly conducted by assuming that the bridge is under its own stability conditions, without considering the impact of construction error, changes of external condition and wind-induced vibration on the stability of the bridge, which poses serious challenges to the bridge construction process. This paper aims to analyze the extent to which static load and fluctuating wind effect influence structural stability and to test the credibility of the structure.Design/methodology/approachA finite element calculation method is used to analyze a T-shaped rigid frame swivel bridge. A full bridge model was built, and a local model of the turntable structure established; the two are then combined means of node coupling. Subsequently, the three sensitivity indexes – deflection rate, stress change rate and the change rate of spherical hinges – are used to evaluate in what way the bridge stability is influenced under various factors.FindingsIt is found that the stability of the swivel bridge is quite sensitive to unilateral overweight, steel beam tension and wind-induced vibration effects but less sensitive to the change of bulk density. Also found is that the change of elastic modulus exerts some effects on deflection but has negligible effects on other stability indexes. Furthermore, the transverse unbalanced torque on the bridge generated by wind-induced vibration is an important factor in determining the size of the turntable, indicating that it is not just controlled by the weight of the bridge.Originality/valueAll factors affecting the stability of swivel construction are analyzed, and solutions to reduce the influence are proposed. The influence of wind-induced vibration effects on swivel construction is analyzed for the first time. It is pointed out that wind-induced vibration effects have great influence on the structure, and its influence could not be neglected.

Dynamic tensile process of blended fabric using finite element method

PurposeTensile property is one basic mechanics performance of the fabric. In general, not only the tensile values of the fabric are needed, but also the dynamic changing process under the tension is also needed. However, the dynamic tensile process cannot be included in the common testing methods by using the instruments after fabric weaving.Design/methodology/approachBy choosing the weft yarn and warp yarn in the fabric as the minimum modeling unit, 1:1 finite element model of the whole woven fabrics was built by using AutoCAD software according to the measured geometric parameters of the fabrics and mechanical parameters of yarns. Then, the fabric dynamic tensile process was simulated by using the ANSYS software. The stress–strain curve along the warp direction and shrinkage rate curve along the weft direction of the fabrics were simulated. Meanwhile, simulation results were verified by comparing to the testing results.FindingsIt is shown that there are four stages during the fabric tensile fracture process along the warp direction under the tension. The first stage is fabric elastic deformation. The second stage is fabric yield deformation, and the change rate of stress begins to slow down. The third stage is fiber breaking, and the change of stress fluctuates since the breaking time of the fibers is different. The fourth stage is fabric breaking.Originality/valueIn this paper, the dynamic tensile process of blended woven fabrics was studied by using finite element method. Although there are differences between the simulation results and experimental testing results, the overall tendency of simulation results is the same as the experimental testing results.

Laser-assisted cyclic chipless splitting for hard-to-cut thick wall tubes and fatigue fracture mechanism analysis

High-quality precision cropping of hard-to-cut thick wall tubes is urgently needed as the first process for precision forming of tubular parts. Due to the deficiencies of large cutting load and waste of chips and coolants in the present cutting methods, a laser-assisted cyclic chipless splitting (LACCS) method is developed, which prefabricates circumferential crack with large stress concentration by laser, and exerts cyclic rotary load at a low amplitude simultaneously to split the tube. The theoretical laser crack depth and critical loads are derivated for fatigue crack propagation and instant rupture, respectively, and an XFEM model based on cohesive damage criterion is established to reveal the fracture mode based on stress intensity factors. Finally, section quality and microfracture mechanism are investigated by experimental tests with different initial crack depths and load control curves. The results show that critical fatigue splitting load and instant rupture load gradually drop with crack depth at a decreasing rate; for crack depth of 0.7 mm, the critical loads are 0.67% and 34.36%, respectively, of that in the traditional cutting method. The type I crack is the primary fracture mode in this LACCS process, and the stress intensity factor KI varies as a cosine curve with peak amplitude of 436.09 MPa(m)1/2. Step-reduction frequency load can smoothly transite the crack propagation to final rupture, and obtains high-quality sections in 16–32 s, with outer roundness error of 0.6%, flatness error of 0.2–0.3 mm and final rupture area of 0.25–1.19 mm2. The fractographies typically show laser affected zone, cracks propagation zone and final rupture zone. Micro-cracks initiate from the tangency points on the laser notch curve with maximal stress change rate, and the ductile striations propagate with growth rate of 3.3–5.1 μm/cycle. Final rupture zone forms under shear stress, featured by quasi-parabolic dimples involving microvoid coalescence.

Evaluation of Food Fineness by the Bionic Tongue Distributed Mechanical Testing Device.

In this study, to obtain a texture perception that is closer to the human sense, we designed eight bionic tongue indenters based on the law of the physiology of mandibular movements and tongue movements features, set up a bionic tongue distributed mechanical testing device, performed in vitro simulations to obtain the distributed mechanical information over the tongue surface, and preliminarily constructed a food fineness perception evaluation model. By capturing a large number of tongue movements during chewing, we analyzed and simulated four representative tongue movement states including the tiled state, sunken state, raised state, and overturned state of the tongue. By analyzing curvature parameters and the Gauss curvature of the tongue surface, we selected the regional circle of interest. With that, eight bionic tongue indenters with different curvatures over the tongue surface were designed. Together with an arrayed film pressure sensor, we set up a bionic tongue distributed mechanical testing device, which was used to do contact pressure experiments on three kinds of cookies—WZ Cookie, ZL Cookie and JSL Cookie—with different fineness texture characteristics. Based on the distributed mechanical information perceived by the surface of the bionic tongue indenter, we established a food fineness perception evaluation model by defining three indicators, including gradient, stress change rate and areal density. The correlation between the sensory assessment and model result was analyzed. The results showed that the average values of correlation coefficients among the three kinds of food with the eight bionic tongue indenters reached 0.887, 0.865, and 0.870, respectively, that is, a significant correlation was achieved. The results illustrate that the food fineness perception evaluation model is effective, and the bionic tongue distributed mechanical testing device has a good practical significance for obtaining food texture mouthfeel information.

Study on the subsurface microcrack damage depth in electroplated diamond wire saw slicing SiC crystal

At present, the fixed-abrasive wire saw machining technology is widely used in the slicing process of SiC single crystal. And the subsurface microcrack damage depth of wire sawn SiC wafer is an important quality control parameter. In this paper, experimental and numerical analysis of the subsurface microcrack damage depth of single-crystal SiC in wire sawing is presented. A finite element model (FEM) which was used for simulation and calculation of subsurface microcrack damage depth in wire saw slicing SiC crystal wafer was established. The variations of maximum principal stress and stress change rate of sawn crystal and slice in wire sawing were analyzed, and the validity of the FEM was verified by sawing experiment. Further, microcrack damage depths under different ingot feed speeds and wire speeds were predicted and the influence of process parameters on microcrack damage depth was discussed. Research results show that the microcrack damage depth values of simulation are lower than the experimental measurement, but with a consistent change trend of a relative error is less than 15.92%. The subsurface microcrack damage depths of sawn wafer decrease with the increase of wire speed and decrease of feed speed. The research results can be helpful to develop precision and high quality slicing technology of SiC single crystal.

Study on electromagnetic radiation in crack propagation produced by fracture of rocks

The physics of electromagnetic radiation due to rock facture is complex, and understanding of this phenomena and its relationship with the extent of rock damage is imperative and remains challenging. In this paper, the relationship between the electric dipole moment and the stress change rate at the crack tip and the crack propagation characteristics are established. The stress change process is divided into three stages, the characteristics of electric dipole moment of each stage are analyzed. Simulation studies showed that the dipole frequencies, the angles between the electric dipole and detectors have a significant influence on the detection of those radiations. Self-expanding destructive experiments were designed and carried out for different types of rocks to observe more details of this phenomenon. In the rupture process of the sample, a number of electromagnetic radiation signals were detected. The duration of the signal is about 2 to 3 ms, and the interval between signals varies from 23 to 210 ms. The spectrum of the signal is between 4 kHz and 50 kHz. The complex variation of the signal spectrum and amplitude are due to the different electric dipoles produced by the different stages of crack propagation, and the change in the distance and angle of the radiation source from the detector during the crack propagation.