Effects Of Stress Rate Research Articles

Global and Local Shear Behavior of the Frozen Soil–Concrete Interface: Effects of Temperature, Water Content, Normal Stress, and Shear Rate

The interface between soil and concrete in cold climates has a significant effect on the structural integrity of embedded structures, including piles, liners, and others. In this study, a novel temperature control system was employed to conduct direct shear tests on this interface. The test conditions included normal stress (25 to 100 kPa), temperature (ranging from 20 to −6 °C), water content (from 10 to 19%), and shear rates (0.1 to 1.2 mm/min). Simultaneously, the deformation process of the interface was continuously photographed using a modified visual shear box, and the non-uniform deformation mechanism of the interface was analyzed by combining digital image correlation (DIC) technology with the photographic data. The findings revealed that the shear stress–shear displacement curves did not exhibit a discernible peak strength at elevated temperatures, indicating deformation behavior characterized by strain hardening. In the frozen state, however, the deformation softened, and the interfacial ice bonding strength exhibited a positive correlation with decreasing temperature. When the initial water content was 16% and the normal stress was 100 kPa, the peak shear strength increased significantly from 99.9 kPa to 182.9 kPa as the test temperature dropped from 20 °C to −6 °C. Both shear rate and temperature were found to have a marked effect on the peak shear strength, with interface cohesion being the principal factor contributing to this phenomenon. At a shear rate of 0.1 mm/min, the curve showed hardening characteristics, but at other shear rates, the curves exhibited strain-softening behavior, with the softening becoming more pronounced as shear rates increased and temperatures decreased. Due to the refreezing of interfacial ice, the residual shear strength increased in proportion to the reduction in shear rate. On a mesoscopic level, it was evident that the displacement of soil particles near the interface exhibited more pronounced changes. At lower shear rates, the phenomenon of interfacial refreezing became apparent, as evidenced by the periodic changes in interfacial granular displacement at the interface.

Dynamic leaching behaviors of heavy metals from recycled coal gangue aggregate under loading conditions during solid backfill mining

In solid backfill coal mining, recycled coal gangue aggregate (RCGA) is subject to the combined effects of overlying strata stress and leaching by mine water in the goaf. This process causes heavy metals to be leached and released from RCGA, which can lead to groundwater contamination. In this study, the release patterns of heavy metals in RCGA under the coupled effects of stress, solution pH, and solution flow rate were investigated, and the interactions between RCGA and the surrounding environment were explored. The findings indicate that: (1) The combined action of effective stress and mine water promotes the leaching of heavy metals. Specifically, the leaching of Pb, Zn, and Mn of RCGA is primarily influenced by the pH value of the leaching solution, while the leaching of Cu and Cr of RCGA is more closely related to the stress level; (2) Acidic environments accelerate the release of carbonate-bound fraction (CAR) in elements, facilitating the transformation of Fe/Mn oxide-bound fraction (XXI) into soluble forms; (3) The leaching ratios (Lr) of heavy metals follow the order: LrZn > LrPb > LrMn > LrCu > LrCr. This research provides guidance for the safe application of RCGA in solid backfill coal mining.

Fractional damage model of cyclic behaviors for nano-silver paste

Sintered nano-silver paste, extensively utilized in electronic packaging technology, is crucial for evaluating the lifetime of electronic devices. In this paper, a fractional damage model is proposed to characterize ratcheting strain of nano-silver paste under cyclic loading. It can be achieved by incorporating a damage coefficient into the classical fractional model, which directly correlates the ratcheting strain with cyclic number. The power law damage coefficient describes well both the non-damage behavior within a limited number of cycles and the rapid increase of ratcheting strain at higher cyclic numbers. Furthermore, the effects of temperature or stress rate on ratcheting strain of sintered silver have been investigated to establish a quantitative relationship between parameters and loading conditions. It is also numerically validated by various experimental datasets. Ultimately, the damage coefficient is physically interpreted based on evolution of porosity.

Onset of dynamic void coalescence in porous ductile solids

This paper investigates void growth and coalescence in porous ductile solids under dynamic loading condition. A physical definition for the onset of void coalescence in porous ductile solids under dynamic loading is proposed. The onset is deemed to occur when the third invariant of the tensorial form of the Hill–Mandel condition attains a zero value. The definition allows for systematic investigations on the effects of dimensionless stress rate κ and stress state, defined by the stress triaxiality T and Lode parameter L, on the onset of void coalescence via micromechanical analyses. The analyses reveal that the critical macroscopic effective strain for the onset of void coalescence displays an increasing–decreasing transition trend as the dimensionless stress rate increases, for all levels of T and L considered. The macroscopic effective strain at the transition is identified as the “ductile–brittle” transition strain. The dimensionless stress rate at which the transition strain occurs is found to be relatively constant. A mapping in the κ−T space for L=−1, representative of a generalized uniaxial tension typical in spall fracture experiments, is established which depicts regions where coalescence and non-coalescence can take place, as well as the ductile–brittle regions demarcated by a ductile–brittle transition curve. The results also show that the critical void volume fraction and macroscopic effective strain at the onset of void coalescence are insensitive to inertia at high stress triaxialities at L=−1.

Shear behavior of a two-component non-water reactive foamed polyurethane (TNFPU) grouting material under different stress levels

The two-component non-water reactive foamed polyurethane (TNFPU) material utilized in structural restoration scenarios may experience shear failure when subjected to multifaceted external factors, potentially culminating in structural instability or even failure. Consequently, it is imperative to conduct a thorough examination of the shear properties of TNFPU material. A series of direct shear tests were conducted to investigate the impact of factors such as density, normal stress, and shear rate on the shear properties of TNFPU material. These properties encompass shear strength, shear modulus, peak shear displacement, shear deformation, and shear dilation angle. The findings underscore the density and normal stress had more significant effects on the shear properties of TNFPU material. Conversely, the impact of shear rate on shear performance was relatively modest and exhibited a diminishing trend as density increased. Notably, a specific discovery emerged: the effects of density, normal stress, and shear rate on the shear properties of TNFPU displayed pronounced distinctions before and after reaching a critical density threshold of 0.51 g/cm³ . Furthermore, the study revealed a phenomenon of shear dilation and contraction transformation when the density or normal stress exceeded a certain critical value.

Laboratory study on the effect of stress cycling pattern and rate on seismicity evolution

Recent laboratory and field studies suggest that temporal variations in injection patterns (e.g., cyclic injection) might trigger less seismicity than constant monotonic injection. This study presents results from uniaxial compressive experiments performed on Red Felser sandstone samples providing new information on the effect of stress pattern and rate on seismicity evolution. Red Felser sandstone samples were subjected to three stress patterns: cyclic recursive, cyclic progressive (CP), and monotonic stress. Three different stress rates (displacement controlled) were also applied: low, medium, and high rates of 10−4 mm/s, 5 × 10−4 mm/s, and 5 × 10−3 mm/s, respectively. Acoustic emission (AE) waveforms were recorded throughout the experiments using 11 AE transducers placed around the sample. Microseismicity analysis shows that (i) Cyclic stress patterns and especially cyclic progressive ones are characterized by a high number of AE events and lower maximum AE amplitude, (ii) among the three different stress patterns, the largest b-value (slope of the log frequency-magnitude distribution) resulted from the cyclic progressive (CP) stress pattern, (iii) by reducing the stress rate, the maximum AE energy and final mechanical strength both decrease significantly. In addition, stress rate remarkably affects the detailed AE signature of the events classified by the distribution of events in the average frequency (AF)—rise angle (RA) space. High stress rates increase the number of events with low AF and high RA signatures. Considering all elements of the AE analysis, it can be concluded that applying cyclic stress patterns in combination with low-stress rates may potentially lead to a more favourable induced seismicity effect in subsurface-related injection operations.

Experimental study on the static and dynamic elastic stiffness of rock samples from a shale oil reservoir

Shale reservoirs play essential roles in numerous geoengineering applications, including storing CO2 and radioactive waste and producing hydrocarbons. To fulfill these applications, the mechanical properties of shale are of great interest so that people can locate shales with preferred sealing or frackable characteristics. One can estimate the static stiffness related to the rock deformation from the dynamic stiffness derived from the wave velocity through some empirical correlations. However, a gap exists between dynamic and static stiffness in sedimentary rocks. Anisotropy further complicates the prediction of the static stiffness from the dynamic stiffness of shale. This paper investigates the link and contrast between the dynamic and static stiffness and the effects of anisotropy by performing triaxial tests on two shale samples cored in the vertical and horizontal directions from a shale oil reservoir in China. We analyze the effects of stress (strain) rate, stress (strain) amplitude, and the base level of deviatoric stress. The secant Young’s modulus is found to decrease with the increasing stress rate or stress amplitude. By introducing the nonlinear elastic theory, Young’s modulus can be expressed as a linear function of axial strain, where the slope is related to the stress sensitivity of the static stiffness, and the intercept is associated with the elastic property at the infinitesimal strain. The slopes and intercepts of linear functions are negatively correlated. Furthermore, six linear fittings from the two samples in the three tests are found to link with the strain amplitude, the base stress level, and anisotropy. This study provides insights into the prediction of static stiffness from dynamic one. With proper models of dynamic-static transition, seismic or wireline logging measurements can assist in solving engineering issues. People can better ensure the quality of the geomechanical model and reduce the cost of various engineering applications.

Effect of the concentration of carbon nanotubes (CNTs) on the rheological behavior in a lubricating oil of plant-derived lubricant

Nanofluids have attracted a lot of attention since their significant enhancement in thermal properties, however there are few reports on the study of the viscosity of nanofluids from an experimental point of view. In this work, the rheological behavior of functionalized multi-walled carbon nanotubes (F-MWCNTs) and coated with MoS2 (MWCNTs-MoS2) in a commercial palm oil as base fluid was evaluated. The purification and functionalization process of the MWCNTs was performed by acid leaching and investigated by FTIR, and stable nanofluids were prepared with MWCNTs concerning time. The rheological behavior of nanofluids with MWCNTs was performed as a function of temperature at different concentrations (0.1, 0.5 and 1% wt.). The effect of time, temperature, shear rate and shear stress versus shear rate were determined. The results indicate that the nanofluid behaves as a Newtonian fluid independently of the MWCNTs concentrations and temperatures evaluated. The viscosity index increases by 16% at a concentration of 1% wt. of F-MWCNTs and for nanofluids added with MWCNTs-MoS2 had significant effect on the effect of temperature.

Rate-dependent multiaxial life prediction for polyamide-6 considering ratchetting: Semi-empirical and physics-informed machine learning models

The rate-dependent multiaxial fatigue life of PA6 is investigated by conducting a series of stress-controlled multiaxial fatigue tests involving the ratchetting. Based on the obtained experimental results and the critical plane approach, a semi-empirical life-prediction model is proposed, in which the effects of loading path, stress level, and stress rate are considered. To avoid the simplifications included in the semi-empirical model, a hybrid life-prediction model combing the critical plane approach and neural network is further developed for obtaining better accuracy and applicability. In addition, to compensate the insufficiency of data samples, two physical constraints (i.e., restricting the space of model parameters and generating domain knowledge-based data samples) are designed. The results demonstrate that: the hybrid model presents a better prediction accuracy than that of semi-empirical one; furthermore, by embedding the designed constraints into the hybrid model to steer the training of NN, the physically consistent solution is obtained and the extrapolation performance of modified hybrid model is significantly improved.

An experimental study and failure mechanism analysis on dynamic behaviors of plain concrete under biaxial compression-compression

In order to explore the dynamic mechanical properties of concrete under biaxial compression-compression, a true triaxial instrument was used to conduct an experimental study on the dynamic mechanical properties of plain concrete under biaxial compression-compression. Eight different lateral compressive stresses (0 MPa~14 MPa) and four strain (10−5/s, 10−4/s, 10−3/s and 10−2/s) rate were considered. From this, the effects of lateral compressive stress and loading strain rate on the biaxial compression-compression properties of concrete were compared and analyzed by obtaining the failure modes, principal compressive stress-strain curves and related mechanical characteristic parameters of plain concrete under different loading conditions. The research results show that: with the increase of lateral compressive stress, the failure modes of concrete were developed from columnar failure at low lateral compressive stress to sheet-like failure at high lateral compressive stress. With the increase of lateral stress, the development trend of concrete failure mode decreased gradually under the influence of strain rate. With the increase of lateral compressive stress, the variation range of concrete principal compressive stress decreased first and then tended to be relatively stable under the influence of strain rate. With the increase of strain rate, the increase range of concrete principal compressive stress decreased under the influence of lateral compressive stress. The influence mechanism of lateral compressive stress and strain rate on biaxial compression-compression performance of concrete was analyzed. Meanwhile, based on Kupfer biaxial compression failure criterion, a biaxial compression dynamic failure criterion model considering the effect of loading strain rate on plain concrete was proposed. The research results provided an important theoretical basis for the application and development of concrete engineering.

The effects of TGO growth stress and creep rate on TC/TGO interface cracking in APS thermal barrier coatings

To design reliable thermal barrier coatings (TBCs), it is essential to elucidate the interface failure mechanism and establish a better life-prediction model. Up to now, how the variations of thermally grown oxide (TGO) growth stresses and creep rates affect the interfacial cracking behavior between top coat (TC) and TGO has not been clearly studied. In this work, the thermos-mechanical model with simplified cosine curve interface morphology in TBCs is developed utilizing numerical simulation software (ABAQUS). According to the calculated stress states of TC/TGO interface, the possible damage scenarios are inferred. On this basis, the interface crack nucleation and propagation is simulated by the surface-based cohesive behavior. General features of the interface crack are in good coincidence with previous conjectures. Furthermore, large TGO growth stresses will trigger off premature cracking, conversely, the formation of TC/TGO interface crack can be postponed due to large TGO creep rates. In addition, the dominant fracture mode of TC/TGO interface is impacted by the variations of TGO growth stresses as well as its creep rate. The position of interface fracture mode transition has been shifted to a certain extent.

Ratcheting Behavior of Sintered Copper Joints for Electronic Packaging

This study experimentally investigated the whole-life ratcheting behavior of sintered copper joints with consideration of the effects of stress rate, stress amplitude, mean stress, maximum stress, and stress ratio. Deformation of joints under cyclic load was measured by a noncontact displacement detecting system. In these joints, ratcheting strain and ratcheting strain rate were found to be sensitive to loading factors. For example, strain decreased as mean stress and stress amplitude decreased, and also as stress ratio and stress rate increased. Meanwhile, larger stress amplitude or mean stress reduced ratcheting fatigue life, while increasing stress ratio and stress rate increased fatigue life. The results indicate the modified Goodman model accounting for the effects of mean stress can usefully predict the ratcheting fatigue life of sintered copper joints at room temperature.

Effect of initial minimum principal stress and unloading rate on the spalling and rockburst of marble: a true triaxial experiment investigation

Hard rock often performs as brittle failures, such as cracking, spalling, and rockburst, induced by excavation in deep underground engineering. To understand the effect of the minimum principal stress and unloading rate on the spalling and rockburst of marble, unloading experiments were carried out by using true triaxial equipment combined with a high-speed camera, acoustic emission instrumentation, and scanning electron microscope. The experimental results showed that the failure process of marble specimens was more stable and less inclined to exhibit dynamic ejection with a low strain energy release per unit time under a low unloading rate. At the same time, the initial minimum principal stress controlled the marble’s failure mode by changing its mode from predominantly shear failure to shear-tension failure as the minimum principal stress decreased, similar to the spalling behaviors of surrounding rock observed in the underground tunnel. What’s more, the dynamic rockburst of the marble specimen was simulated under the condition with a high unloading rate, high initial minimum principal, and free face on the specimen. Based on these experimental investigations, a flowchart was also presented to estimate the possible failure mode of marble specimens under different initial minimum principal stress and unloading rate conditions, which would be conducive to the disaster prevention of hard rock in deep underground engineering.

Ratcheting Fatigue Behavior of Modified 9Cr–1Mo Steel at Room Temperature

Fusion reactor components undergo asymmetric cyclic loading,that leads to a progressive increase in plastic strain and causes deterioration in life of engineering components. This investigation deals with fatigue behavior of modified 9Cr–1Mo steel at room temperature and presents the effect of mean stress (σm), stress amplitude (σa) and stress rate ( $$\dot{\sigma }$$ ) on fatigue life, deformation and fracture behavior under asymmetric cyclic loading. A series of fatigue tests were conducted under asymmetric stress-controlled loading with different combinations of σm (190–210 MPa), σa (400–420 MPa) and $$\dot{\sigma }$$ (50–450 MPa/s). The plastic strain increased with increase in σm and σa and the fatigue life was reduced, whereas increase in $$\dot{\sigma }$$ reduced the accumulated plastic strain and the cyclic life was increased. The deformation behavior and microstructural changes under the influence of the three parameters (σm, σa and $$\dot{\sigma }$$ ) were examined by tranmission electron microscope (TEM). With increase in the three parameters (σm, σa, $$\dot{\sigma }$$ ), the lath martensitic structure changed to subgrain structure along with dislocation cells and forest dislocations. Scanning electron microscopy revealed unique features of fractured specimens, with progressive reduction in diameter towards the fracture-end, fatigue striations on the tapered circumferential surface and dimples on the fracture surface.

Shear Stress in Schlemm\u2019s Canal as a Sensor of Intraocular Pressure

Elevated intraocular pressure (IOP) narrows Schlemm’s canal (SC), theoretically increasing luminal shear stress. Using engineered adenoviruses containing a functional fragment of the shear-responsive endothelial nitric oxide synthase (eNOS) promoter, we tested effects of shear stress and elevated flow rate on reporter expression in vitro and ex vivo. Cultured human umbilical vein endothelial cells (HUVECs) and SC cells were transduced with adenovirus containing eNOS promoter driving secreted alkaline phosphatase (SEAP) or green fluorescent protein (GFP) and subjected to shear stress. In parallel, human anterior segments were perfused under controlled flow. After delivering adenoviruses to the SC lumen by retroperfusion, the flow rate in one anterior segment of pair was increased to double pressure. In response to high shear stress, HUVECs and SC cells expressed more SEAP and GFP than control. Similarly, human anterior segments perfused at higher flow rates released significantly more nitrites and SEAP into perfusion effluent, and SC cells expressed increased GFP near collector channel ostia compared to control. These data establish that engineered adenoviruses have the capacity to quantify and localize shear stress experienced by endothelial cells. This is the first in situ demonstration of shear-mediated SC mechanobiology as a key IOP-sensing mechanism necessary for IOP homeostasis.

Life prediction for rate-dependent low-cycle fatigue of PA6 polymer considering ratchetting: Semi-empirical model and neural network based approach

Based on the experimental results in [1,2], a semi-empirical low-cycle fatigue life prediction model is constructed for a polyamide-6 (PA6) polymer, in which the rate dependence of fatigue life and the effect of ratchetting strain on the life are considered. Since the fatigue damage in PA6 is not only loading-cycle-dependent but also time-dependent, a function to describe the complicate effect of stress rate on the fatigue life is obtained. In the proposed model, the detrimental effect of ratchetting strain on the fatigue life is characterized by introducing a function of mean stress. Comparison of the predicted and experimental results shows that the proposed model presents a good prediction. Furthermore, the neural network based method is also used to correlate the low-cycle fatigue data of PA6. The results show that the established neural network based approach achieves a better prediction to the fatigue life of PA6 with the occurrence of ratchetting than that by the proposed semi-empirical model, which demonstrates a possibility to apply the neural network based machine learning method to deal with the fatigue of polymer.

Effect of stress rate on shear strength of aluminium alloy single lap joints bonded with epoxy/nanoalumina adhesives

Epoxy adhesive was reinforced with spherical-shaped and rod-shaped alumina nanoparticles. Quasi-static shear strength of aluminium alloy single lap joints was determined as a function of wt.% (0.5, 1.0, 1.5, and 2.0) of alumina nanoparticles in the compression loading. At quasi-static loading, the shear strength of joints with epoxy/nanoalumina adhesives was higher (1.3–1.8 times) than the joints with neat adhesive. Dynamic shear strength of joints with neat adhesive, and epoxy/nanoalumina adhesives containing 1.5 wt% of nanoalumina was analysed. A significant improvement (3–5 times) of dynamic shear strength of joints was obtained over quasi-static shear strength of joints. However, the static and dynamic lap shear strength of joints containing spherical nanoalumina was higher compared to the neat adhesive, and nanoadhesives containing rod-shaped nanoalumina.

Effect of kinematic hardening parameters on fatigue crack growth

The parametric study of the effect of material properties on fatigue crack growth (FCG) rarely has been addressed in literature. The consideration of plastic CTOD as crack driving force opened the opportunity to predict FCG rate numerically and therefore to develop parametric studies focused on the effect of loading, geometrical and material parameters. The objective here is to study the effect of kinematic saturation stress, XSat, and kinematic saturation rate, CX, on FCG using this numerical approach. The increase of the kinematic parameters reduced the plastic CTOD and therefore the FCG rate. The variation is non-linear and the rate of variation of δp decreases with the increase of XSat and CX. The effect of the kinematic saturation stress, XSat, is more relevant than the effect of kinematic saturation rate, CX. On the other hand, a small effect of kinematic hardening parameters on crack closure was found. Finally, the increase of the number of load cycles between crack increments produced a great reduction of crack closure but no effect of plastic CTOD on models without contact of crack flanks.

Numerical analysis of effect of thermal stress depending on pulling rate on behavior of intrinsic point defects in large-diameter Si crystal grown by Czochralski method

We analyzed the effects of thermal stress and pulling rate on the behavior of intrinsic point defects in a silicon (Si) single crystal grown by the Czochralski (Cz) method using a numerical approach. The thermal equilibrium concentration of the intrinsic point defects (vacancy, V, and self-interstitial Si atom, I) was simulated as a function of thermal stress, which was obtained via ab -initio calculations. Furthermore, the point defect dynamics in the crystal were solved within a framework of a two-dimensional (2D) axisymmetric steady-state global heat and mass transport model of Si crystal growth by the Cz method. The numerical simulations revealed that both magnitude and distribution of the thermal stress depend on the pulling rate. Moreover, they impact the formation and distribution of intrinsic point defects in a growing Si single crystal.

Quasi‐static and ratcheting properties of PEEK reinforced by carbon fibers under uniaxial and cyclic compression

AbstractUniaxial compression tests were carried out to investigate the mechanical properties of polyetheretherketone (PEEK) with different contents of short carbon fibers (CF). Results show that the mechanical strength of PEEK can be improved with a certain mass fraction of CF. In order to study the viscosity of PEEK, static creep tests were performed considering the effects of stress level and content of CF. It is found that CF enhances the creep resistance of PEEK and 20 wt% carbon fiber‐reinforced PEEK has the best performance. Moreover, the creep strain of the composites increases with increasing stress level. Subsequently, the ratcheting experiments under uniaxial cyclic compression with the stress‐controlled condition were conducted. It is shown that the ratcheting strain increases with increasing stress amplitude and the holding time of peak stress. However, the effects of stress rate and content of CF on ratcheting strain are opposite. Meanwhile, the dependence of ratcheting behavior on loading history was also investigated. The results show that ratcheting strain is significantly affected by loading history of stress amplitude due to cyclic hardening of the material, while the effect of loading history of stress rate on ratcheting strain is negligible.