Interpretation of undrained creep tests in terms of effective stresses

1995 ◽  
Vol 32 (2) ◽  
pp. 373-379 ◽  
Author(s):  
Thomas C. Sheahan
Keyword(s):  
Shear Stress ◽  
Shear Strength ◽  
Strain Rate ◽  
Creep Behavior ◽  
Creep Rupture ◽  
Peak Shear Stress ◽  
Stress Levels ◽  
Static Yield ◽  
Undrained Shear ◽  
Undrained Creep

The paper provides an effective stress-based interpretation technique for undrained creep behavior in cohesive soils. This technique could ultimately be used to predict whether a particular applied shear stress level will lead to failure or creep rupture. During the primary phase of undrained creep at constant shear stress, the soil's strain rate decreases, which in turn leads to a decrease in the undrained shear strength. However, it has been shown for a number of soils that a minimum undrained strength, or upper yield strength (suy), is eventually reached regardless of further strain rate decreases. It has been postulated that this phenomenon is part of a time-dependent behavior framework in which the yield locus shrinks with decreasing strain rate until some limiting surface, the static yield surface (SYS), is reached. Such a surface has been the basis for a number of constitutive models in which it represents the inviscid, or rate independent, behavior. The peak shear stress on the SYS corresponds to suy. Data from previous experimental programs are presented to show the existence of the surface and its role in undrained creep behavior. Undrained creep shear stress levels above suy lead to creep rupture on the failure envelope; stress levels below suy cause creep to the SYS, where the stress state apparently stabilizes without failure. The value of suy can be used in a number of analyses in creep susceptible soils, and the static yield condition can be used in the field to determine whether measured pore pressures are exceeding predicted nonrupture levels. A method is proposed for simple determination of the SYS using constant strain rate undrained shear tests. Key words : clays, consolidated-undrained tests, creep, rate effects, rheology, shear strength.

Effect of the Strain Rate on the Twisting of Trabecular Bone from Women with Hip Fracture

2013 ◽  
Vol 135 (12) ◽  
Author(s):  
Ana C. Vale ◽  
Jennifer Faustino ◽  
Luís Reis ◽  
Ana Lopes ◽  
Bruno Vidal ◽  
...  
Keyword(s):  
Shear Stress ◽  
Shear Strength ◽  
Hip Fracture ◽  
Shear Modulus ◽  
Strain Rate ◽  
Trabecular Bone ◽  
Axial Load ◽  
Angular Displacement ◽  
Maximum Shear Stress ◽  
Lower Limbs

As one of the major functions of bone is to provide structural support for the musculoskeletal system, it is important to evaluate its mechanical strength. Bones may be subjected to multiaxial stresses due to bone pathologies, accidental loads which may lead to hip, wrist fracture, or to a prosthetic joint replacement. Twist loading may lead to fractures, especially involving long bones from lower limbs. The aim of this work was to study the effect of the strain rate on the shear properties of trabecular bone samples from women with hip fracture (from 65 to 100 years). Cylindrical samples were core drilled from human femoral heads along the primary trabecular direction. The cylinder's ends were polished and embedded in blocks of polymeric material which fit the grips of the testing device. Deformation rates of 0.005, 0.01, 0.015, and 0.05 s−1 were applied. Twisting tests were conducted with or without an applied axial load of 500 N. From the torque-angular displacement curves, the shear stress–strain curves were obtained. The maximum shear strength and the shear modulus (i.e. the slope of the linear region) were determined. A large scatter of the results of the shear strength and the shear modulus was found, which is probably related to the heterogeneity of nonhealthy human bone samples. There is no significant effect of the strain rate on the maximum shear stress and the shear modulus, either in tests undertaken with or without the application of an axial load. The effect of strain rate on nonhealthy bone trabecular twisting properties did not follow the trend observed on the effect of strain rate in healthy bone, where an increase is detected.

Nonuniform Temperature Distribution in Adiabatic Shear Band Using Measured Shear Stress-Shear Strain Curve in Torsion of Thin-Walled Tube Aluminium Alloy Specimen and Gradient-Dependent Plasticity

2006 ◽  
Vol 519-521 ◽  
pp. 865-870 ◽  
Author(s):  
X.B. Wang
Keyword(s):  
Shear Stress ◽  
Strain Rate ◽  
Shear Strain ◽  
Temperature Rise ◽  
Strain Curve ◽  
Local Temperature ◽  
Dependent Plasticity ◽  
Peak Shear Stress ◽  
Nonlinear Shear ◽  
Shear Strain Curve

Gradient-dependent plasticity where a characteristic length is involved to consider the microstructural effect (interactions and interplaying among microstructures due to the heterogeneous texture) and the measured nonlinear shear stress-shear strain curves for different loading strain rates are used to calculate the distribution of local temperature rise in adiabatic shear band (ASB) for aluminum-lithium alloy specimen of thin-walled tube in dynamic torsion test. ASB is assumed to initiate just at peak shear stress in the specimen. The temperature rise in ASB is decomposed into the uniform temperature rise in strain-hardening stage and the nonuniform temperature rise in strain-softening stage. The former depends on the measured nonlinear shear stress-shear strain curve prior to the peak, the density, the work to heat conversion factor and the heat capacity. The latter is related to the softening branch of the measured nonlinear shear stress-shear strain curve, the internal length parameter and the physical parameters. For binary Al-Li alloy, the predicted maximum temperatures in ASB are 413K at strain rate of 2000s-1 and 433K at strain rate of 2600s-1. These peak temperatures are lower than the recrystallization and phase transformation temperatures. Higher loading strain rate results in higher pre-peak and post-peak temperature rises, steeper profile of local temperature and higher peak local temperature in ASB. These predictions qualitatively agree with the previously analytical solution for ductile metal exhibiting linear strain-softening behavior beyond the peak shear stress based on gradient-dependent plasticity.

Undrained shear strength properties of organic harbor mud at low consolidation stress levels

2011 ◽  
Vol 48 (3) ◽  
pp. 388-398 ◽  
Author(s):  
Benjamin Friedrich Schlue ◽  
Tobias Mörz ◽  
Stefan Kreiter
Keyword(s):  
Shear Strength ◽  
Large Scale ◽  
Strength Properties ◽  
Undrained Shear Strength ◽  
Ex Situ ◽  
High Plasticity ◽  
Compression Time ◽  
Stress Levels ◽  
Strong Surface ◽  
Undrained Shear

Dredging operations in European harbors for maintenance of navigable water depth produce vast amounts of harbor mud. Between 2005 and 2007, the second largest harbor construction project in Germany was designed as a pilot study, using dredged harbor mud as backfill material to avoid expensive deposition or ex situ treatment. During this project, strong surface deformations of the backfill highlighted the need for an improved assessment of undrained shear strength of naturally liquid harbor mud. The strength of harbor mud cannot be measured accurately under corresponding low in situ effective stress levels by standard laboratory tests. Therefore, a large-scale oedometer cell with a diameter of 22 cm was designed, providing the opportunity to perform vane shear measurements during consolidation. This study shows that East Harbor mud is a very sensitive, organogenic clay of extremely high plasticity, exhibiting very small undrained shear strength when compared with other cohesive soils. Both the peak and residual undrained shear strengths are shown to increase about 3%–4% per log-cycle increase in secondary compression time (days).

Finite element modeling of partially embedded pipelines in clay seabed using Coupled Eulerian–Lagrangian method

2015 ◽  
Vol 52 (1) ◽  
pp. 58-72 ◽  
Author(s):  
Sujan Dutta ◽  
Bipul Hawlader ◽  
Ryan Phillips
Keyword(s):  
Finite Element ◽  
Shear Strength ◽  
Strain Rate ◽  
Deep Water ◽  
Strain Softening ◽  
Mesh Size ◽  
Undrained Shear Strength ◽  
Band Formation ◽  
Offshore Pipelines ◽  
Undrained Shear

Vertical seabed penetration and lateral movement of deep-water offshore pipelines are simulated using the Coupled Eulerian–Lagrangian (CEL) approach in Abaqus finite element (FE) software. Abaqus CEL has been used in some previous studies to simulate large-deformation behavior of offshore pipelines; however, the effects of strain rate and strain-softening on undrained shear strength (su) have not been considered. In this study, the effects of these factors are critically examined. The available built-in models in Abaqus CEL cannot account for these factors directly, especially the strain rate; therefore, the development of user subroutines is required. In the present study, a simple but realistic soil constitutive model (published by Zhou and Randolph in 2007) that considers the effects of strain rate and strain-softening on su is implemented in Abaqus CEL. The effects of FE mesh size and shear band formation on penetration resistance are discussed based on a comprehensive FE simulation. Lateral analyses are performed for “light” and “heavy” pipes in clay seabed having a linearly increasing undrained shear strength profile for smooth and rough pipe–soil interface conditions. The FE results are compared with previous theoretical, numerical, and centrifuge test results. Based on the present FE analyses, it is shown that, similar to the remeshing and interpolation techniques with small strain (RITSS) technique developed at the The University of Western Australia, the Abaqus CEL can successfully simulate the response of partially embedded pipelines in deep-water clay seabed, provided strain rate and softening dependent clay models are implemented. A methodology to implement such a model using Abaqus user subroutine is also presented.

scholarly journals Root Tensile Resistance of Selected Pennisetum Species and Shear Strength of Root-Permeated Soil

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Afaff Emhemed Ettbeb ◽  
Zulfahmi Ali Rahman ◽  
Wan Mohd Razi Idris ◽  
Jumaat Adam ◽  
S. Abd. Rahim ◽  
...  
Keyword(s):  
Shear Stress ◽  
Shear Strength ◽  
Tensile Force ◽  
Mineral Fertilizer ◽  
Tensile Tests ◽  
Root Diameter ◽  
Slope Instability ◽  
Root Reinforcement ◽  
Significant Relationships ◽  
Peak Shear Stress

It is widely recognized that vegetation plays a significant role in contrasting slope instability through the root reinforcement. The main objectives of this paper are to evaluate the root tensile of selected Pennisetum species, namely, P. pedicellatum (PPd) and P. polystachion (PPl), and to determine the soil shear strength of root-permeated soil from these species. The selected species were initially planted in the polybags using the hydroseeding technique. A mineral fertilizer of NPK ratio 10 : 8 : 10 was adopted in the hydroseeding mixture. Routine watering program was applied twice a day throughout growth observation for six months. Four replications were prepared for each species including a set of control polybags, which contained only soil for reference and comparison. The results of root tensile tests revealed the significant relationships between root diameter and tensile force. In comparison, the PPl was still indicated by higher values of root tensile force than PPd. The presence of roots clearly has contributed to the shear stress of root-permeated soils. The root density based on root biomass measurement attributed to the higher value of peak shear stress as achieved by PPl than PPd. The combined effects of root tensile and the soil shear strengths of this selected species can be used as biological materials in slope protection against erosion.

Long-Term Creep and Creep Rupture Behavior of Woven Ceramic Matrix Composites at Elevated Temperatures

Materials ◽  
2004 ◽  
Author(s):  
Siarajus Salekeen ◽  
Mohammad M. Rahman ◽  
Hassan Mahfuz ◽  
Shaik Jeelani
Keyword(s):  
Matrix Composite ◽  
Creep Behavior ◽  
Elevated Temperatures ◽  
Ceramic Matrix Composite ◽  
Ceramic Matrix ◽  
Test System ◽  
Creep Rupture ◽  
Tensile Creep ◽  
Matrix Composites ◽  
Stress Levels

The strong interest in ceramic matrix composite for high temperature application arises primarily from their ability to retain good creep behavior. The objective of this work is to investigate the creep behavior of quasi-isotropic woven silicon carbide fabric reinforced silicon-nitrogen-carbon (SiC/SiNC) ceramic composite at stress levels which are above and below the monotonic proportional limit strength. Constant-load tensile creep-rupture tests were performed on SiC/SiNC ceramic matrix composite on an Instron 8502 material test system. The creep behavior of SiC/SiNC matrix composites were investigated at various temperatures (700°C and 1000°C) and stress levels (55%, 65% of ultimate strength, σult). The strain vs. time curves consisted of primary and secondary (steady state) creep regions were established. The stress exponent and activation energy of SiC/SiNC ceramic matrix composite were also determined at these temperatures. The creep data followed the traditional power law exhibiting an exponential relationship between creep rate and stress.

Stability threshold for cyclic loading of saturated clay

1989 ◽  
Vol 26 (1) ◽  
pp. 122-131 ◽  
Author(s):  
Guy Lefebvre ◽  
Denis LeBoeuf ◽  
Benoît Demers
Keyword(s):  
Shear Strength ◽  
Cyclic Loading ◽  
Strain Rate ◽  
Undrained Shear Strength ◽  
Triaxial Tests ◽  
Repeated Loading ◽  
Loading Test ◽  
Stability Threshold ◽  
The Stability ◽  
Undrained Shear

This paper presents the results of an experimental investigation performed to study the stability threshold under cyclic (repeated) loading, and the postcyclic static strength of a sensitive clay from the Hudson Bay region. The strain rate and structure effects were also studied by carrying out monotonic and cyclic triaxial tests at both slow and rapid strain rates or frequencies, and at confining pressures above and below the apparent preconsolidation pressure. The stability threshold for both structured and normally consolidated Grande Baleine clay is about 60–65% of the original undrained shear strength measured at the same strain rate as that used in the repeated loading test. The undrained shear strength and the failure envelope remain essentially unchanged if the repeated preloading is kept below the threshold. The clay structure remains unaltered by this preloading. Key words: clay, stability threshold, cyclic loading, earthquake, postcyclic strength.

Strain-rate-dependent stress-strain behavior of overconsolidated Hong Kong marine clay

2000 ◽  
Vol 37 (6) ◽  
pp. 1272-1282 ◽  
Author(s):  
Jun-Gao Zhu ◽  
Jian-Hua Yin
Keyword(s):  
Shear Strength ◽  
Hong Kong ◽  
Strain Rate ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Undrained Shear Strength ◽  
Rate Dependency ◽  
Marine Clay ◽  
Strain Rate Dependency ◽  
Undrained Shear

A total number of 24 consolidated undrained triaxial shear tests on reconsolidated saturated Hong Kong marine clay (HKMC) have been performed in both compression and extension shear states. The specimens were prepared in four different overconsolidation ratios (OCRs) and sheared at three different axial strain rates. The strain-rate dependency of undrained shear strength, pore-water pressure, stress path, and secant Young's modulus are investigated. The influence of OCR on the stress–strain–strength behavior of HKMC is also examined. The results of all tests are presented and interpreted. The interpreted results are compared with the results in the literature. For the HKMC with OCR varying from 1 to 8, the average value of the strain-rate parameter [Formula: see text] 0.15 is 5.5% for compression tests and 8.4% for extension tests. Most interpreted results are conclusive and consistent with the published results, whereas some results are not conclusive. A new parameter for describing the strain-rate dependency of undrained shear strength of overconsolidated soil is introduced.Key words: strain-rate effects, clay, overconsolidated, triaxial, shear strength, pore-water pressure.

scholarly journals Experimental Investigation on the Interfacial Debonding between FRP Sheet and Concrete under Medium Strain Rate

2019 ◽  
Vol 2019 ◽  
pp. 1-13
Author(s):  
Zihua Zhang ◽  
Yunyi Xiao ◽  
Ping Zhuge ◽  
Xiaocun Zhang
Keyword(s):  
Shear Stress ◽  
Strain Rate ◽  
Fracture Energy ◽  
Static Load ◽  
Concrete Strength ◽  
Interfacial Shear Stress ◽  
Interfacial Fracture ◽  
Interfacial Bond ◽  
Peak Shear Stress ◽  
Interfacial Fracture Energy

Fiber-reinforced polymer (FRP) composites have been widely used to strengthen the existing reinforced concrete (RC) structures to against static and dynamic loads. During the past decades, the interfacial bond behavior between FRP and the concrete substrate under static load has been systematically investigated by experimental and numerical approaches. In contrast, the interfacial bond performance under dynamic loads, e.g., impact and explosive loading, is still far away from well known, especially taking the strain rate effect into account. In this contribution, the single-lap shear test is conducted to sixty specimens at the medium strain rate between 1.0E−4/s and 5.0E−3/s. The effects of various system parameters, including the strain rate, concrete strength, type of FRP and adhesive, on the interfacial fracture energy, peak shear stress, FRP strain distribution, interfacial shear stress, and effective bond length, are thoroughly investigated. It has been revealed that the strain rate and concrete strength can significantly affect the interfacial fracture energy and peak shear stress. The specimen with CFRP sheet possesses higher interfacial shear stress but lower fracture energy than that with BFRP sheet. The adhesive with lower elastic modulus is helpful to improve interfacial energy dissipation under dynamic load. The effective bond length decreases with concrete strength and strain rate, mainly between 75 mm and 90 mm, which is significantly shorter than that under static load. Inspired from the Kulkarni and Shah model, a new model is proposed to evaluate the interfacial fracture energy and peak shear stress with respect to the strain rate, and the estimated values agree well with the experiments.

scholarly journals Large-Scale Direct Shear Test on Tire Slice Reinforced Crushed Concrete Particles

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Qiang Ma ◽  
Hang Shu ◽  
Jia Mou ◽  
Lihua Li ◽  
Zhenyi Zheng
Keyword(s):  
Shear Stress ◽  
Shear Strength ◽  
Shear Rate ◽  
Volume Content ◽  
Large Scale ◽  
Friction Angle ◽  
Vertical Load ◽  
Reinforcement Effect ◽  
Crushed Concrete ◽  
Peak Shear Stress

In order to study the mechanical properties of tire slices reinforced crushed concrete particles, a series of shear tests were carried out under the conditions of different vertical loads, different tire volume contents, and different shear rates. The test results show that the addition of tire slices can increase the internal friction angle and cohesion of concrete particles, therefore increase the shear strength of crushed concrete particles. The peak shear stress increases with the increase of vertical load. However, with the increase of the tire volume content, the reinforcement effect of the tire slices first increases and then decreases, and the effect is best when the tire volume content is 4%. Under the vertical load of 60 kPa, the reinforcement effect of 4% tire volume content is the best, and the peak shear stress increases by 46.53%. Additionally, the shear rate has a little effect on the peak shear stress. The larger the shear rate is, the smaller the shear displacement is and the faster the shear strength decreases. The smaller the shear rate is, the more gently the shear strength decreases.

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