Creep Characteristics Research Articles

FRP–soil interfacial mechanical properties with molecular dynamics simulations: Insights into friction and creep behavior

AbstractThe fiber‐reinforced polymer (FRP) has attracted much attention in civil engineering due to its durability and cost‐effectiveness. The soil–FRP structure interface plays an essential role when the FRP is adopted in geotechnical engineering, but its fundamental interfacial behavior remains unclear. In the present study, the atomistic models of silica representing sand, water film representing the lubricated condition, and cross‐linked epoxy representing FRP are constructed to investigate the FRP–sand interfacial properties at the nano‐scale through molecular dynamics (MD) simulations. The epoxy model geometry and forcefield are first validated by comparing the thermodynamic and mechanical parameters with experimental and simulation measurements. The silica–epoxy interfacial tribological and rheological behavior is then explored by conducting friction and creep simulations under dry and lubricated conditions. The friction force has been found linearly dependent on the normal load and increases with the sliding velocity while decreasing against water content. The modified Amontons law for the adhering surface could describe the silica–epoxy interfacial friction well. The shear stress level influences the creep characteristics with primary, secondary, and tertiary (or rupture) creep modes. The results of this study at the nano‐scale can be further developed to enhance the current contact laws of sand–FRP structure in micromechanics‐based modeling approaches.

Modelling the creep behavior of Gossypium hirsutum cotton fibers based on their physical and mechanical properties

In this work, we investigated the cotton fibers behavior utilizing the analogical modelling method. The aim was to establish the relationships between single and bundle cotton fibers physical and mechanical properties. This study was focused on the creep behavior of cotton fibers. The bundle fibers behaviors to creep tests were modeled considering the correlations between the physical and mechanical results of single ones. Results showed that cotton fibers are viscoelastic and their creep response in single or bundle fibers fitted to a three-element model; the Zener’s model. Furthermore, the tested fibers were classified per length to limit the variability effect. Moreover, Principal Component Analysis (PCA) was employed for data analysis, enabling the identification of correlations between the physical properties and creep behavior of both individual fibers and fiber bundles. This comprehensive study serves as a valuable benchmark for understanding the creep characteristics of cotton fibers.

Creep Characteristics of a Strongly Weathered Argillaceous Sandstone Sliding Zone and the Disaster Evolution Mechanism of the Huaipa Landslide, China

The creep characteristics of sliding zones strongly influence slope deformation and long-term stability, as well as the occurrence of landslide catastrophes. In this paper, large-scale triaxial creep tests were performed on the strongly weathered argillaceous sandstone sliding zone of the Huaipa landslide in the Henan Province, China, to study its creep characteristics and long-term strength in natural and saturated states. Three-dimensional numerical simulations were conducted to analyze the deformation creep law and catastrophic evolution mechanism of the slope after excavation and rainfall. The results show that the sliding zone underwent appreciable creep deformation prior to failure, and that the progression of specimen damage with an increasing stress level followed decay creep → steady creep → accelerated creep. The stress level played a decisive role in the creep deformation, with higher stress levels resulting in higher instantaneous displacement, creep displacement, and longer times required to reach steady creep. The stress level also determined the specimen’s creep stage. When the stress level was low, the adjustment of the specimen’s internal structure was dominated by air space compression and particle movement, whereas particle fragmentation mostly occurred at high stress levels. The long-term rock strength was approximately 62–66% of the instantaneous strength, the internal friction angle decreased by approximately 8° relative to the instantaneous strength, and the cohesion decreased by approximately 30%. The slope foot unloaded and deformed owing to the excavation of a bauxite mine at its front edge, after which the slope deformed via creep. The landslide disaster occurred when the deformation was significantly accelerated and the slope started to slide as a whole once the sliding zone became water saturated owing to continuous rainfall. The simulation results indicate that the landslide can be divided into a front edge bulging zone, central sliding zone, and trailing edge tension zone, which provides valuable insight on the creep deformation evolution process and the disaster mechanism of the landslide under the action of front edge excavation and rainfall.

Effect of water on the rock strength and creep behavior of green mudstone

The weakening of rock mass after immersion substantially affects slope stability. Considering the mudstone in the north slope of the Fushun West Open pit as the research object, we investigated the failure and creep characteristics of mudstone under different immersion times and confining pressures. For this, we used a self-developed experimental apparatus that applies biaxial compression loading in a water immersion environment. Water significantly changed the strength and failure mode of the mudstone. The increase in confining pressure limits the expansion of the crack aperture, reduces the rock strength-weakening coefficient, and delays the rock weakening time. The change in cohesion is primarily responsible for the weakening of shear strength during immersion. Based on the creep test results, the creep curve of the soaking specimen was identical to that of the dry specimen in the initial phase. The weakening effect of water on the specimen increased as the soaking duration increased, due to which the creep curve of the soaking specimen gradually approached that of the saturated specimen. Water entered the microcracks and reacted with the rock interior, accelerating rock failure. Consequently, the soaking specimen had the lowest stress level for creep failure and the shortest failure time. The results of this experiment provide a reference for the long-term stability of the flooded slope.

Creep behavior and characterization analysis of Mg-1.8Zn-0.3Ca alloy:a molecular dynamics analysis

The addition of Zinc (Zn) and Calcium (Ca) on the Magnesium (Mg) has invoked better biocompatibility in various orthopedic applications. But this addition (Zn and Ca) leads to inducing greater modifications in the creep characteristics. In this current study, a study on the creep characterization of Mg-1.8Zn-0.3Ca alloy has been examined using molecular dynamics analysis. The creep analysis has been focused on numerous grain sizes and creep environments such as temperature and pressure to analyze its effect on the creep performance and its features. Further, the creep performance, radial distribution function, dislocation length, and structural and microstructural transformation under various grain size and deformation time has been confirmed by the modifications in the deformation mechanism and its features under various grain size and creep conditions.

Comparison of deformation behavior between creep and fatigue on siltstone and its modified damage model

AbstractIn order to reveal the deformation behavior similarity between creep and fatigue, a series of creep and cyclic load tests were performed on siltstone under various load levels. First, the mechanical characteristics of creep and fatigue were compared, by analyzing the strength, ultimate strain, and steady deformation rate of siltstone. Then, a modified fatigue damage creep model was established by connecting a viscoplastic damage element in series with Burgers mode. Finally, the applicability of the model was verified, and the model parameters were analyzed. The results show that the fatigue failure of siltstone is controlled by fatigue strength and limit strain. The modified fatigue damage creep model can accurately describe the whole deformation process of siltstone under cyclic load test. Compared with creep test, the cyclic load hardly affects the elastic modulus of this model. However, the viscosity coefficient of this model is greatly weakened by the cyclic load.

A Roadway in Close Distance to Coal Seam in Deep Mine: Location Selection and Supporting Practice based on Creep Characteristics of Surrounding Rocks

A Roadway in Close Distance to Coal Seam in Deep Mine: Location Selection and Supporting Practice based on Creep Characteristics of Surrounding Rocks

Investigation of Damage and Creep for Bedding's Carbonaceous Slate with Chemical Erosion Effect.

Tunnel projects in the southwestern mountainous area of China are in full swing. According to the tunnel burial depth, structural characteristics, and chemical erosion environments of the Lixiang railway tunnel, carbonaceous slate specimens obtained in the field were taken to experimentally investigate the physical, mechanical, and creep characteristics of the bedding's slate specimens after chemical erosion. The results of scanning electron microscopy (SEM) indicate that chemical erosion leads to internal damage in the carbonaceous slate specimens, and the internal damages are increasing with the increase of erosion days. Moreover, the specimens' ultrasonic test (UT) results prove that specimens with smaller bedding angles suffer a more serious erosion and induce more internal cracks. Under conventional triaxial compression conditions with 40 MPa of confining pressures, the conventional triaxial compressive strength (σs) decreases with the decrease of the bedding angle and the increase of erosion days, and the failure modes of the specimens are mainly controlled by oblique shear fractures and accompanied by the occurrence of slip dislocation fractures between the bedding inclination. Under creep conditions with 40 MPa of confining pressures, the final deformations of specimens are increasing with the increase of erosion days, which means the longer the erosion days, the greater the deformations. The failure modes of the specimens under creep conditions are controlled by shear fractures, and for the specimen with a 60° bedding angle and long-term erosion, there are block separations and many cavities along the shear planes. Therefore, more attention should be paid to prevent serious failure of the surrounding rock if the surrounding rock has a bedding angle of 60° or suffers long-term erosion.

Creep Characteristics and Behavior of Fire Resistance Steel (FR355B) Exposed to High Temperatures

Creep Characteristics and Behavior of Fire Resistance Steel (FR355B) Exposed to High Temperatures

Creep characteristics and fractional rheological model of granite under temperature and disturbance load coupling

Creep characteristics and fractional rheological model of granite under temperature and disturbance load coupling

Analysis of the fault slip, creep, and coupling characteristics of the Maomaoshan-Laohushan-Haiyuan Fault using InSAR and GNSS measurements

Line-of-sight Interferometric Synthetic Aperture Radar (InSAR) observations are affected by long-wavelength errors and the inaccurate estimation of vertical deformation, thereby restricting horizontal slip rate estimations for strike-slip faults, such as the Maomaoshan-Laohushan-Haiyuan Fault (MMS-LHS-HY). To overcome this limitation, herein, InSAR (2016–2022) and Global Navigation Satellite System (GNSS) observations were combined and the Least Squares Variance Component Estimation (LS-VCE) method was used to obtain the Three-Dimensional (3-D) deformation field of the Haiyuan fault zone; subsequently, the slip-rate and coupling distributions were inverted. The results showed that: (1) Compared with the GNSS and leveling deformation velocities, the residuals of the 3-D deformation field obtained using the LS-VCE method combined with the GNSS and InSAR observations reached an RMS of 1 mm/a, significantly better than the deformation field obtained without GNSS data. (2) Vertical deformation from InSAR observations led to over- or under-estimation of the fault strike-slip rate, with the maximum influence on the shallow creep rate of 2.1 mm/a. (3) Based on the 3-D deformation field, fault slip rate, locking depth, and fault creep characteristics obtained from the elastic dislocation and elastic block models were consistent with each other. (4) The strike-slip rate of the MMS-LHS-HY fault gradually decreased from west to east, whereas the thrust rate gradually increased in the same direction. (5) Based on the 3-D deformation field, the creep range of the LHS fault was ∼40 km, with the mean shallow creep rate reaching 2.5 ± 0.1 mm/a, notably larger than the creep rate obtained by ascending InSAR observation alone.

Creep monitoring and parameters inversion methods for rock salt in extremely deep formation

When underground salt caverns are used for natural gas storage, the pressure difference between the inside and outside of the cavern will cause continuous creep deformation of the surrounding rock. Understanding the creep characteristics and constitutive model parameters of rock salt in actual formations is of great significance for guiding the construction and safe operation of gas storage facilities. In this paper, a creep contraction calculation model for slender cylindrical rock salt caverns was established firstly, based on the theory of complex variables and viscoelasticity. This model can calculate the radial displacement of the surrounding rock at any moment on the cross-section of the rock salt wellbore. Subsequently, two indirect monitoring methods for deep rock salt creep using the open hole section of the well were proposed based on this model, which involves using the cavern pressure change after wellhead closure and the liquid overflow rate after wellhead opening to indirectly reflect the deformation of underground rock salt. These two sets of field experiments can be used together to determine the values of the constitutive model parameters of rock salt creep under actual stress conditions. This theoretical framework was applied in the Ningjin Salt Cavern Gas Storage Project in China. Pressure monitoring was conducted for 150 days, and wellbore fluid overflow was measured for 45 h in a rock salt well at a depth close to 3000 m. The calculated results showed good agreement with the field monitoring data, and the parameters of the Burgers creep model for rock salt under actual conditions were determined. This demonstrates the strong feasibility of the monitoring method and the validity of the computational model. Finally, using the obtained creep parameters, a quantitative analysis of the creep contraction of the wellbore was performed considering factors such as internal pressure, in situ stress, and Poisson's ratio of the rock salt.

Nickel metal matrix composites reinforced with solid lubricants: A comprehensive review

Nickel metal matrix composites are suitable for aerospace and military applications due to their superior mechanical and tribological properties. The incorporation of reinforcing components in the nickel metal matrix composites significantly improves the specific strength, microhardness, wear resistance, frictional behavior, creep, and fatigue characteristics, as well as provides exceptional surface quality in comparison to typical engineering materials. The current study attempted to explore a review on nickel composites reinforced with various solid lubricants, along with their pros and cons. The study focuses on the issues like interfacial transition, agglomerating activity, and non-uniform particle dispersion. Several studies have been conducted to highlight the effect of solid lubricants on the microstructure, mechanical and tribological characteristics such as tensile strength, yield strength, ductility, hardness, friction, wear, and fatigue. In this review, the principal applications of various nickel matrix composites are also thoroughly examined.

Creep in Nanostructured Materials

The creep behaviour and properties of nanostructured materials are attributed to their operating deformation mechanisms, which could be different from those in their coarse-grained counterparts. Accordingly, in this review, recent progress on the creep behaviour of nanostructured materials will be described. The results of large sets of tensile creep tests on selected more complex metallic materials are analysed for evaluating the effect of different SPD processing methods on creep resistance at high temperatures. The resultant creep characteristics are compared with those attained in unprocessed conditions of the same materials. By contrast to the creep behaviour of UFG pure metals SPD processing of more complex materials mostly exhibits no essentially improved creep resistance. Evaluated stress dependences of the creep rate and the creep life suggest that creep deformation mechanisms in UFG materials are similar to those operating in coarse-grained materials. However, creep mechanisms in SPD processed materials are not clearly resolved and this is due to complexity of phenomenon and very small number of studies that have been carried out before now.

InSAR Observations Reveal Variations in Shallow Creep on the Kangding Segment of the Xianshuihe Fault

AbstractInvestigating the spatiotemporal characteristics of aseismic shallow creep provides insights into interseismic steady-state and/or postseismic transient behavior of faults. In this study, we focus on the Kangding segment of the Xianshuihe fault in eastern Tibet, where the 2014 Mw 5.9 Kangding earthquake occurred. Previous geodetic observations in 1999–2021 identified apparent shallow creep along this segment; however, whether the aseismic slip is secular creep, afterslip of the 2014 Kangding earthquake, or the combined effect remains unresolved. We process descending and ascending Interferometric Synthetic Aperture Radar data in the 2014–2021 period and investigate the creep rate variations on the fault plane. Our results reveal an ∼55-km-long aseismic slip section between Huiyuan Temple and Kangding Airport, of which the ∼15-km-long section between Huiyuan Temple and Jinlong Temple is in steady creep at a rate of 13 ± 2.0 mm/yr. Along the remaining ∼40-km-long section that overlaps the rupture of the Kangding earthquake, the creep rate decays from ∼40 to 0 mm/yr between 2014 and 2019, implying that the aseismic slip here is most likely the postseismic afterslip. We also identify a northwestward migration of aseismic creep from Huiyuan Temple to Longdengba during 2017–2021, which might be related to fluid diffusion. On the basis of the aseismic slip distribution, we quantitatively calculate the moment budget on the Kangding segment. The results show that the Huiyuan Temple-Longdengba section can produce an Mw 6.9 earthquake. Despite the 2014 Kangding earthquake, which ruptured the ∼40-km-long Jinlong Temple-Kangding Airport section, the accumulated seismic moment since the last major earthquake in 1748 is still sufficient for an Mw 7.0 earthquake.

Nonlinear creep characteristics of extruded Poly (vinylidene fluoride-co-hexafluoropropylene) with high ß-phase content under extreme conditions: Design, characterization, and modeling

This study is concerned with the nonlinear creep characteristics of extruded Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) dominated by β-phase polymorphs over the temperature range 40 °C − 80 °C and tensile stress levels between 5 MPa and 12.5 MPa. The measured data using the developed experimental setup as well as the dynamic mechanical analyzer invariably suggested a nonlinearity taking place at temperatures near to 60 °C, where αc-relaxation began corresponding to 100 °C above the measured glass transition temperature of PVDF-HFP. The results from accelerated testing conditions indicated the transition to tertiary creep stage at 24% to 28% strain, irrespective of test condition, referred to as critical strain range. Following the identification of Findley power law model constant at different test conditions, a generalized temperature- and stress-dependent model was developed with only 7 constants. The comparisons between the measured and modeled data conveyed the model effectiveness in describing the nonlinear creep characteristics of the polymer over the measured temperature and stress levels. Time-temperature-compliance master curves were consequently constructed using the developed generalized model, which in combination with the critical strain failure criterion, provided the essential design data including the maximum allowable ranges of stress and temperature for achievement of 20 years creep life.

Analysis of an improved Nishihara creep model considering plastic strain accumulation

Rock-engineering structures, particularly subway excavation rock-engineering structures, are subjected to the long-term effects of external loading that may gradually damage and cause creep and severe plastic deformations or even progressive failure. The traditional Nishihara creep model cannot accurately describe the accelerated creep stage of rock with particularly obvious nonlinear characteristics. Based on this model, a damage variable that can consider the plastic strain accumulation is introduced in this study to replace the viscoplastic body in the traditional model with a damaged viscoplastic body and establish an improved Nishihara creep model. Using the superposition principle, the creep equations of the improved model in the one- and three-dimensional stress states are derived. The accuracy and rationality of the improved model are verified using uniaxial and conventional triaxial creep tests of mudstone and sandstone under different confining pressures. The improved model can not only accurately reflect the nonlinear characteristics of the creep curve in the decay and constant velocity stages but also describe the accelerated creep characteristics of mudstone and sandstone in a high-stress state. Its applicability and accuracy are superior to those of the traditional model. This study can provide a theoretical reference for subway tunnel excavation and stability analysis of deep roadway surrounding rocks.

Creep properties and energy evolution characteristics of weakly cemented rock under step loading

The contact mode of particles in weakly cemented mudstone (WCM) and the persistence of cemented materials, as well as the cemented particulate matter composed of them, lead to different mechanical response characteristics from general soft rock during loading, that is, rheological failure occurs under low stress. In order to study the creep characteristics and energy evolution characteristics of weakly cemented rock (WCR) in the western mining area of China, based on the triaxial graded loading creep test of WCR, the creep deformation and failure law of WCM under graded loading was studied, and the energy evolution characteristics of WCR in each creep stage were revealed by energy dissipation theory. The results show that with the increase of confining pressure, the fracture angle decreases, but the failure strength and volume expansion point show the opposite trend. In addition, due to the strong heterogeneity of WCR samples, the contact force between particles is different after loading, which makes the slip between particles and cements and then produces a completely different fracture form from other rocks. The energy growth in the deceleration and steady creep stages is mainly affected by the confining pressure. With the increase of confining pressure, the growth rate of dissipation energy Ud and total energy U gradually tends to be constant, but the growth rate of strain energy Ue remains at a high level. In the accelerated creep stage, the growth rate of strain energy Ue decreases rapidly, and the residual energy storage capacity does not change significantly with the increase of confining pressure. These results revealed the unique creep properties and energy evolution characteristics of the WCR, providing a theoretical basis for long-term stability control of roadways that are built with WCR.

Particle flow study on the microscale effects and damage evolution of sandstone creep

The creep damage of hard rock is significantly influenced by its microscopic parameters and pore structure. To explore the correlation between the macroscopic creep characteristics and microscopic properties of sandstone, the construction method of Clumps with random geometry (CRG) that can simulate the creep movement of minerals was proposed. Through seepage corrosion tests and uniaxial creep tests, a rock porous creep model was established, and the CRG model was used to investigate the evolution pattern of rock fracture and the relationship between macro and micro parameters. The results demonstrate that the creep parameters of red sandstone are significantly affected by its microporosity. When particles range from 0.05 to 2 mm, the instantaneous and creep mechanical properties of the CRG model are strongly dependent on contact parameters and porosity, but less sensitive to particles size. The simulation based on CRG is in good agreement with the laboratory tests, with a certain proportional relationship existing between the microscopic contact parameters of the numerical model and the macroscopic creep parameters of the laboratory test.

Study on Creep Characteristics and Long-Term Strength of Mud-Calcareous Conglomerates in the Three Gorges Reservoir Area

The study of the time-dependent properties of engineering rock masses is a frontier topic in rock mechanics. In this study, creep tests and stress relaxation tests were conducted on mud-calcareous conglomerates from the Three Gorges Reservoir Area, and the long-term strength values of the conglomerate specimens were determined via different methods based on the test curves. By comparing these mainstream long-term strength determination methods, it was found that each of these methods have their own drawbacks. For example, the transition creep method requires a high accuracy of the test curve and only obtains an approximate strength interval rather than an accurate value. The long-term strength values determined by the isochronous stress–strain curve method are strongly influenced by subjective factors, among other things. Therefore, this paper proposes a new method for determining long-term strength, called the steady-state creep rate method, based on stress intervals. By comparison, the long-term strength values determined via this method are in good agreement with the transition creep method, the volume expansion method, and the stress relaxation method.