Intermittent Creep Research Articles

Impact analysis of repeated improper treatment of bridge site slopes to bridge across

The bridge site slope in Zhengjiawan has been renovated several times in response to the adverse geological conditions of the Zhengjiawan ancient landslide (ZAL) in China. However, improper control and treatment measures have caused the structural failure of the Zhengjiawan bridge (ZB). Based on long-term field monitoring data of rainfall, temperature, bridge deformation, and bridge site slope displacements, this paper analyses the impact of repeated improper treatment on bridge site slopes to bridge across. Furthermore, it summarized the interrelationship between bridge deformation and bridge site slopes under natural rainfall and improper treatment measure conditions, and proposed a set of solutions for bridge site slope control and treatment. The results show that the destruction of ZB is primarily attributed to the deformation of ZAL, natural rainfall is the main trigger controlling the intermittent creep of the ZAL, while the construction of anti-slide pile and deviation rectification of bridge abutment result in significant deformation of ZAL. The deformation of ZB and ZAL were synchronous, and the monthly displacement difference ranged from 0.18 to 5.19 mm. The failure of the ZB structure resulting from the ZAL is attributed to the insufficient shear strength of the weak loose soil comprising the landslide, which fails to withstand the sliding force induced by continuous heavy rainfall. Additionally, the original anti-slide pile inadequately controls the deformation of the landslide. By setting the second-row anti-slide pile, adding the cross-sectional area of the bridge pier foundation, and installing drainage pipes, the safety of the bridge is effectively guaranteed. The control and treatment of ZAL show that preventing bridge pier deformation should be prioritized followed by controlling and treating bridge site slopes, and this study provides insights into interactions between unstable landslide treatments and bridge structures which may serve as a reference for similar projects.

Acceleration Mechanism of Intergranular Cracking of Ni-Base Superalloy GH4169 under Creep Loading at Elevated Temperatures due to the Growth of δ-Phase

In order to quantitatively clarify the effect of δ-phase precipitation on the strength of grain boundary in Ni-based superalloy GH4169 at elevated temperatures, which is expected to be used in aircraft engines, intermittent creep tests at 800°C were conducted on specimens, and the microstructural changes were analyzed using EBSD analysis. The effects of δ-phase precipitation and creep damage were evaluated by micro tensile tests. It was confirmed that there is a large lattice mismatch between the δ-phase precipitated around the grain boundary and the matrix phase, and that dislocations and voids accumulate in the grain boundary. It was also suggested that the δ phase precipitation may be a stress-induced diffusion phenomenon. Furthermore, it was confirmed that the strength of this alloy decreased in the early period of creep, influenced by both creep damage and the precipitation of δ-phase.

Temporary Confined Water-Induced Landslide in the Binary Structure of a Gentle Slope: A Case Study of the Fanshantou Landslide

With the increase in rainfall, landslides occur on many gentle slopes in the mountainous areas of southeast China. Gentle slopes have a particular dual geological structure, i.e., the lower part is a gravel soil layer with good water permeability, and the surface layer is clay soil with relatively poor water permeability. Under conditions of heavy rainfall, a gentle slope with this structure is likely to collect temporary confined water. The intermittent creep of the upper slope is caused by the floating force of the temporary confined water, which causes landslide disasters. The conditions that bring about temporary confined water are related not only to the stratum structure, but also to the rainfall intensity and the initial height of the water table level. On the basis of the characteristics of the stratum of the gentle slope landslide on the front of Fanshantou Mountain, we constructed a hydrological model in GEO-STUDIO. We investigated the effect of different rainfall intensities and initial water table levels on confined water under continuous rainfall conditions and conducted a corresponding stability analysis. The results show that when both the initial water table level and the rainfall intensity are high, temporary confined water is formed rapidly, increasing the chance of a landslide disaster. The research results provide a theoretical basis for the treatment of landslides on similar gentle slopes in the mountainous areas of southeast China.

Disappearance of Martensitic Strengthened-Micro-Texture in Modified 9Cr-1Mo Steel Caused by Stress-Induced Acceleration of Atomic Diffusion at Elevated Temperatures

Modified 9Cr-1Mo steel is a heat-resistant steel developed for a steam generator in a FBR (Fast Breeder Reactor) and it has been applied to various thermal power plants. Recently, it was found that the fatigue limits did not appear up to 108 cycles at temperatures higher than 500oC. The reason for the decrease of the fatigue life was attributed to the change of the initially designed microstructure of the alloy. The initially dispersed fine lath martensitic texture disappeared at temperatures higher than 500°C, when the magnitude of the applied stress exceeded a certain critical value. In order to explicate the dominant factors of the change quantitatively, the change of the microstructure and the strength of the alloy were continuously observed by applying an intermittent fatigue and creep tests at elevated temperatures and EBSD analysis. It was found that there was a critical stress which caused the microstructure change at each test temperature higher than 500°C, and the activation energy of the change was determined as a function of temperature and the applied tensile stress. The dominant factor of the micro structure change was the stress-induced acceleration of the atomic diffusion of the component element of the alloy.

Acoustic Emission during Intermittent Creep in an Aluminum–Magnesium Alloy

The use of high-speed methods to measure deformation, load, and the dynamics of deformation bands, as well as the correlation between the intermittent creep characteristics of the AlMg6 aluminum–magnesium alloy and the parameters of the acoustic emission signals, has been studied experimentally. It has been established that the emergence and rapid expansion of the primary deformation band, which generates a characteristic acoustic emission signal in the frequency range of 10–1000 Hz, is a trigger for the development of a deformation step in the creep curve. The results confirm the accuracy of the mechanism of generating an acoustic signal associated with the emergence of a dislocation band on the external surface of the specimen.

Mechanism of low-frequency discrete acoustic emission during intermittent creep of aluminum alloy

A correlation between the dynamics of deformation bands and the discrete acoustic emission during the intermittent creep of the AlMg6 alloy using a high-speed video recording with a time resolution to 50 μs has been studied. A trigger of a macroscopic deformation step in the creep curve is the nucleation and the broadening of the primary deformation band that generates a characteristic acoustic emission signal with duration of several milliseconds. The results confirm the mechanism of generating an acoustic emission signal related to the cooperative dislocations outcrop on the specimen external surface.

Nonlinear dynamics of deformation bands in aluminum–magnesium alloy in the creep test

Various types of plastic instabilities that emerge in intermittent creep have been studied experimentally for AlMg6 aluminum–magnesium alloy. It has been shown that intermittent creep exhibits threshold dynamics. The deformation step on the creep curve of amplitude is ~1–6% and begins when the rate of the preceding continuous creep attains a certain critical value. In the course of evolution of the step, the strain rate varies in the interval that spans more than two orders of magnitude, and transitions occur between different dynamic regimes of type A and B characterized by different stress drop regularity levels in the force response. Nonlinear aspects of the deformation behavior of the alloy in the intermittent creep conditions are considered.

On-and-off dynamics of a creeping frictional system.

We report on the dynamics of a model frictional system submitted to minute external perturbations. The system consists of a chain of sliders connected through elastic springs that rest on an incline. By introducing cyclic expansions and contractions of the rest length of the springs, we induce the reptation of the chain. Decreasing the amplitude of the perturbation below a critical value, we observe an intermittent creep regime characterized by alternated periods of reptation (flowing state) and rest (quiescent state). A further decrease of the perturbation leads to the disappearance of the reptation. The width of the transition region between the continuous creep and the full stop (i.e., the range of excitation amplitudes where the intermittent creep is observed) is shown to depend on the difference between the static (μ(s)) and the dynamic (μ(d)) friction coefficients. For μ(s) = μ(d) the intermittent creep is not observed. Studying the statistical features of the intermittent creep regime for any given perturbation amplitude, we find that the time the system resides in each state (flowing or quiescent) suggests that: i) reptation events are uncorrelated, and ii) rest events are history dependent. We show that this latter history dependence is consistent with the aging of the stress state inside the chain of sliders during the quiescent periods.

Wind‐formed gravel bed forms, Wright Valley, Antarctica

Bed forms composed of gravel size particles (≈50% of particles >4 mm) are observed in the Wright Valley of the McMurdo Dry Valley system in Antarctica. These bed forms are characterized by a very asymmetrical shape with a mean aspect ratio of 0.025 (standard deviation 0.005), mean wavelength of 2.7 m (±0.49 m), and a mean height of 0.06 m (±0.01 m). Particle size analysis of the bed form sediments shows bimodality with a peak near 9 mm and another between 0.5 mm and 0.25 mm. Time‐integrated sediment trap samples of horizontal saltation and creep flux indicate the flux of particles ≥4 mm during the two‐year monitoring period was extremely low. Measurements of the horizontal displacement of tracer particles (14 mm, 12 mm, 10 mm, 8 mm, and 6 mm diameter) placed onto the bed forms corroborate the low particle flux measurements and limited movement of particles. The bed forms share form and grain size characteristics with both ripples and mega‐ripples, showing poor sorting of particles across a single wavelength except for a slight coarsening at the crest similar to ripples, but their sinuosity suggest that transverse instabilities affect their formation similar to mega‐ripples. Based on the data for the prevailing environmental conditions it can be argued that the Wright Valley form is an expression of gravel particles moved solely by highly intermittent creep processes. This also argues for the need for a very long period of time for their evolution, on the order of centuries.

Creep Motion of an Intruder within a Granular Glass Close to Jamming

We experimentally study the dynamics of an intruder dragged at a constant force in a horizontally vibrated monolayer of grains. At moderate packing fractions, the intruder moves rapidly as soon as the force is applied. Above some threshold value it has an intermittent creep motion with strong fluctuations reminiscent of "crackling noise". These fluctuations are critical at the jamming transition varphi_{J} unveiled in a previous study. The transition separates a regime with local free volume rearrangements from a regime where the displacement field is strongly heterogeneous and resembles force chain patterns.

Rate Dependence and Short-Term Creep Behavior of a Thermoset Polymer at Elevated Temperature

The inelastic deformation behavior of PMR-15 neat resin, a high-temperature thermoset polymer, was investigated at 288°C. The effect of loading rate on monotonic stress-strain behavior as well as the effect of prior stress rate on creep behavior were explored. Positive nonlinear rate sensitivity was observed in monotonic loading. Creep response was found to be significantly influenced by prior stress rate. The effect of loading history on creep was studied in stepwise creep tests, where specimens were subjected to a constant stress rate loading followed by unloading to zero stress with intermittent creep periods on both loading and unloading paths. The strain-time response was strongly influenced by prior deformation history. Negative creep was observed on the unloading path. In addition, the behavior of the material was characterized in terms of a nonlinear viscoelastic model by means of creep and recovery tests at 288°C. The model was employed to predict the response of the material under monotonic loading/unloading and multistep load histories.

Some aspects of the mechanical response of BMI 5250‐4 neat resin at 191°C: Experiment and modeling

AbstractThe inelastic deformation behavior of BMI‐5250‐4 neat resin, a high‐temperature polymer, was investigated at 191°C. The effects of loading rate on monotonic stress–strain behavior as well as the effect of prior stress rate on creep behavior were explored. Positive nonlinear rate sensitivity was observed in monotonic loading. Creep response was found to be significantly influenced by prior stress rate. Effect of loading history on creep was studied in stepwise creep tests, where specimens were subjected to a constant stress rate loading followed by unloading to zero stress with intermittent creep periods during both loading and unloading. The strain‐time behavior was strongly influenced by prior deformation history. Negative creep was observed on the unloading path. In addition, the behavior of the material was characterized in terms of a nonlinear viscoelastic model by means of creep and recovery tests at 191°C. The model was employed to predict the response of the material under monotonic loading/unloading and multi‐step load histories. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Ultrasonic Velocity Technique for Nondestructive Quantification of Elastic Moduli Degradation during Creep in Silicon Nitride

The ultrasonic velocity technique was used for nondestructive quantification of creep damage during interrupted tensile creep tests at 1400°C in an advanced silicon nitride to investigate the possibilities of this technique for creep damage monitoring in ceramic components. The longitudinal and shear wave velocities, Poisson's ratio, and Young's, shear, and bulk moduli linearly decreased with strain. Precise density change measurements indicated a linear relationship with a coefficient of proportionality of 0.69 between the volume fraction of cavities and tensile strain. Cavitation was identified as the main creep mechanism in the studied silicon nitride and the reason for ultrasonic velocity and elastic moduli degradation. The measurement of just the longitudinal wave velocity changes was found to be sufficient for quantification of cavitation during creep. The capability of the ultrasonic velocity technique for simple, sensitive, and reliable nondestructive monitoring of creep damage during intermittent creep was demonstrated in silicon nitride.

Growth of plastic shear zone and its duration inferred from theoretical consideration and observation of an ancient shear zone in the granitic crust

A new model for growth of plastic shear zone is proposed based on the basis of a theory of fluid dynamics coupled with a rheological constitutive function, and is applied to a natural shear zone. Mylonite, ultramylonite and other ductile fault rocks are well known to deform in a plastic flow regime. The rheological behavior of these kinds of rocks has been well documented as a non-linear viscous body, which is empirically described as , where : strain rate, τ: shear stress, Q: activation energy, R: universal gas constant, T: absolute temperature, and A and n are constants. Strain rate- and temperature-dependent viscosity is obtained by differentiating the equation, and simplified by substituting n = 1. Then, substitution of the equation into a diffusion equation, , derives an equation δ = 4[t/p · A exp(−Q/RT)]1/2, where δ: thickness of active layer of viscous deformation, ν: kinematic viscosity, and ρ: density. The duration of creep deformation along the ancient plastic shear zone (thickness: 0.076 m) is estimated to be around 760 s, in a temperature range from 300 to 500°C. This estimation is rather good agreement with intermittent creep during inter-seismic period, than steady state creep or co-seismic slip.

Volume recovery of polystyrene: evolution of the characteristic relaxation time

We have developed a new experimental technique that uses intermittent temperature perturbations during volume recovery in order to obtain quantitative information concerning the evolution of the characteristic relaxation time for volume during structural recovery. The experiments are analogous to the intermittent creep experiments developed by Struik. Using an automated capillary dilatometer and a polystyrene sample, the time-temperature history dependence of the characteristic relaxation time for volume was investigated. Our preliminary results show that for the set of temperature down jumps and memory experiments investigated, the characteristic relaxation time appears to depend only on the instantaneous state of the material. However, the results are not totally consistent with the Tool–Narayanaswamy model/Kovacs–Aklonis–Hutchinson–Ramos model.

Vertical crustal movement in the Boso peninsula, South Kanto, Japan, as deduced from the adjustment of a geodetic network with signals

In the adjustment of a leveling network that is frequently resurveyed, we introduce corrections not only to the approximated heights of the stations but also to their rates of vertical movement, which are linear over time, as an unknown. Thus we can apply least-squares collocation to the problem, and have some cases corresponding to the rank deficiency of the design matrix in the observation equation. We have applied this method to the study of the vertical crustal deformation in the Kanto district, particularly to the Boso peninsula, Honshu, Japan. Rates of vertical crustal movement and their covariance matrices are deduced for two periods for the Kanto district (1) 1965–1978 and (2) 1978–1989, and for three periods for the Boso peninsula (1) 1965–1972, (2) 1973–1976 and (3) 1976–1988. The deduced rates range from −10 mm/yr to +10 mm/yr, and their standard deviations amount to ±11 mm/yr for the Kanto district. For the Boso peninsula, they range from −22 mm/yr to +6 mm/yr, and amount to ±5 mm/yr. This peninsula is very close to the convergent plate boundary between the Philippine sea plate and South Kanto, and the results of this analysis reveal the typical fluctuating behavior of the crustal movements associated with the subduction process during the interseismic period. The author interprets this episodic crustal movement as being due to intermittent creep dislocation along the deeper part of the interface between the Kanto district and the Philippine Sea plate.

Uniaxial and Biaxial Viscoplastic Behavior of SUS304 after Cyclic Preloading.

A series of tests for creep and biaxial ratchetting during cyclic loading were carried out to investigate the interaction between cyclic plasticity and creep or ratchetting of SUS 304 stainless steel. Specimens were subject to intermittent creep or biaxial ratchetting at several stress levels during cyclic tension-compression loading with the constant strain amplitude under the constant stress rate. The test results showed that the creep curve during cyclic loading could be explained by the so-called Bailey-Norton law, with stress levels measured from the current center of the yield surface which was determined by the hybrid constitutive equation for cyclic plasticity proposed by authors. Axial ratchet strain induced by cyclic shear stressing was expressed by the shear stress amplitude, the number of cycles and the axial stress level measured from the current center of the yield surface.

Some critical uniaxial experiments for viscoplasticity at room temperature

An austenitic AISI Type 304 stainless steel, a ferritic A533B pressure vessel steel and a Ti-7Al-2Cb-1Ta alloy were tested using a servocontrolled MTS axial-torsion testing machine. Tests involved changes in strain rate between 10 −8 and 10 −3 s −1 and intermittent creep periods of less than 1200 s duration. The tests show that inelastic work is not a suitable repository for modeling strain (work)-hardening and the Bauschinger effect is found to be rate dependent. Upon an increase in stress level, creep rate can decrease. This anomaly can be reproduced by a theory of viscoplasticity based on overstress previously proposed by the first author and his co-workers.

Surface faulting in Imperial Valley during the earthquake swarm of January–February, 1975

abstract Surface ruptures formed along a 10.4-km segment of the Brawley fault during the earthquake swarm of January and February, 1975, in central Imperial Valley, California. This newly recognized fault appears to branch northward from the Imperial fault about 8 km east-northeast of El Centro. Displacement at the surface was apparently vertical and reached a maximum of probably more than 0.2 m at Keystone Road. En echelon cracking suggested an incipient right-lateral component, but roads and irrigation canals were not laterally offset by the faulting. Surface cracks and most of the displacement probably developed suddenly at the time of the largest shock ( M 4.7) in the swarm on January 23. At Harris Road, vertical movement continued at least until March 24, but significant afterslip across the fault zone may have ceased by February 13. Vertical movement after the 13th apparently took the form of a relative subsidence centered on the fault with no important net slip across the fault. Pre-1975 historic displacements on the Brawley fault occurred in 1940 at the time of the M 7.1 Imperial Valley earthquake and probably as intermittent creep between 1940 and 1975.

Intermittent creep behaviour of glassreinforced polypropylene at elevated temperatures: effects of matrix to fiber coupling and pigments : Cessna, L. C., Jr, Proceedings, 29th SPE Conference, pp 372–377 (May 1971)

Intermittent creep behaviour of glassreinforced polypropylene at elevated temperatures: effects of matrix to fiber coupling and pigments : Cessna, L. C., Jr, Proceedings, 29th SPE Conference, pp 372–377 (May 1971)