Effect Of Stress State Research Articles

Poromechanical controls on spontaneous imbibition in earth materials

Over the last century, the state of stress in the earth’s upper crust has undergone rapid changes because of human activities associated with fluid withdrawal and injection in subsurface formations. The stress dependency of multiphase flow mechanisms in earth materials is a substantial challenge to understand, quantify, and model for many applications in groundwater hydrology, applied geophysics, CO2 subsurface storage, and the wider geoenergy field (e.g., geothermal energy, hydrogen storage, hydrocarbon recovery). Here, we conduct core-scale experiments using N2/water phases to study primary drainage followed by spontaneous imbibition in a carbonate specimen under increasing isotropic effective stress and isothermal conditions. Using X-ray computed micro-tomography images of the unconfined specimen, we introduce a novel coupling approach to reconstruct pore-deformation and simulate multiphase flow inside the deformed pore-space followed by a semi-analytical calculation of spontaneous imbibition. We show that the irreducible water saturation increases while the normalized volume of spontaneously imbibed water into the specimen decreases (46–25%) in response to an increase in effective stress (0–30 MPa), leading to higher residual gas saturations. Furthermore, the imbibition rate decreases with effective stress, which is also predicted by a numerical model, due to a decrease in water relative permeability as the pore-space becomes more confined and tortuous. This fundamental study provides new insights into the physics of multiphase fluid transport, CO2 storage capacity, and recovery of subsurface resources incorporating the impact of poromechanics.

Verification of unified effective stress theory based on the effect of moisture on mechanical properties of fiber reinforced unsaturated soil

The unified effective stress theory based on suction stress (SSCC theory) enables the characterization of soils under both saturated and unsaturated conditions with one closed-form relationship. This study provides experimental verification of this theory through the unconfined compressive strength test (UCS) and indirect tensile test strength (ITS) on silty clay soil stabilized with fiber. A series of matric suction, ITS, and UCS tests were conducted to validate the SSCC theory through the representation of the results of ITS and UCS tests in terms of mean total stress (p) versus deviatoric stress (q) and mean effective stress (p`) versus deviatoric stress (q). The results of the validation procedures showed that the SSCC theory is applicable and valid at a range of 6%–16% of water content on the silty clay and the silty clay fiber-reinforced soils. There is a small fluctuation in the increase of ITS and UCS values with increasing fiber content due to randomly oriented distribution of the fiber. The addition of glass fiber does not significantly affect the capacity of water retention of the soil. It improves the condition of the mechanical soil properties at the end of construction more than of the effective stress condition.

Influences of Stress State, Temperature, and Strain Rate on Ductility of Pure Iron

In this study, the plastic response of pure iron DT8 at different stress states, temperatures, and strain rates is investigated. Specimens with different structures designed for different stress states are subjected to quasi-static uniaxial tension tests to investigate the effect of stress state on the fracture behavior of pure iron. Standard specimens at temperatures ranging from 100 to 900 °C are tested by a quasi-static uniaxial tension machine. Double-notch shear specimens are subjected to a universal electronic tensile testing machine and an improved split-Hopkinson pressure bar device with strain rates ranging from 0.0033 to 227450/s to investigate the effect of strain rate on the fracture behavior of pure iron. Results show that the flow stress of pure iron DT8 slightly increases with the increase in stress triaxiality before the material breaks. With the increase in stress triaxiality from 0.333 to 0.550, the fracture strain of pure iron DT8 decreases almost linearly from 1.949 to 0.898. With the increase in temperature, the fracture strain increases almost linearly from 1.43 at 100 °C to 3.19 at 900 °C. A blue brittleness effect occurs at about 300 °C, where the yield and tensile strengths of pure iron increase slightly. In the low strain rate range from 0.0033 to 800/s, the fracture strain of pure iron is almost stable at approximately 2.0. Then, the fracture strain increases with the further increase in strain rate. When the strain rate reaches 120850/s, the fracture strain reaches its peak value of 3.64. Thereafter, the fracture strain decreases rapidly as the strain rate increases. The fracture surfaces of the specimens take on different fracture morphologies with the increase in strain rate. The nature of the strain rate’s effect on material ductility is discussed.

Relationship between monotonic and cyclic behavior of saturated soft clay in undrained triaxial compression tests

Cyclic loading–induced deformation of soil is a common problem in engineering practice. In current practice, however, monotonic triaxial tests are more commonly used due to the availability of apparatus and ease of operation. Thus, it would be very useful and practical if monotonic triaxial tests could be used to evaluate the behavior of soil under cyclic loading. This study aims to find an explicit relationship between monotonic and cyclic behavior of saturated soft clay. Six monotonic and nine cyclic triaxial compression tests were conducted on undisturbed saturated soft clay under an undrained condition. The test results showed that the monotonic and cyclic tests shared the same stress–strain surface in a three-dimensional p′–q–εa space (p′, effective mean principal stress; q, deviatoric stress; εa, axial strain). It was also found that it is possible to evaluate the effective stress states of cyclic tests at two specific numbers of cycles, using corresponding monotonic tests. Based on these two findings, a simple procedure is proposed to predict the peak axial strain for the saturated soft clay under different cyclic loadings based on the monotonic tests and only one cyclic test, which was further verified against additional test data from the previous literature.

Combined effects of porosity and stress state on the failure behavior of laser powder bed fusion stainless steel 316L

Two primary variables that impact failure behavior of ductile metals are defects and stress state. These factors are especially critical in additively manufactured materials, as components made by additive manufacturing (AM) can have complex shapes that result in the material being subjected to multiaxial stresses under load, and these materials may also contain internal porosity due to AM processing. This study experimentally investigates the effects of both internal pores and stress state on the ductile failure behavior of laser powder bed fusion additively manufactured 316L stainless steel through the introduction of intentional penny-shaped pores of varying size at the center of samples whose geometries result in different stress states. It was found that strain to failure depended strongly on stress triaxiality until a large pore size with a diameter of 1200 µm (4% cross-sectional area of the sample gauge sections), while strain to failure was independent of stress triaxiality, and only a function of pore diameter, with larger pores (9% cross-sectional area or larger).

Permeability Evolution of an Intact Marble Core during Shearing under High Fluid Pressure

The progressive shear failure of a rock mass under hydromechanical coupling is a key aspect of the long-term stability of deeply buried, high fluid pressure diversion tunnels. In this study, we use experimental and numerical analysis to quantify the permeability variations that occur in an intact marble sample as it evolves from shear failure to shear slip under different confining pressures and fluid pressures. The experimental results reveal that at low effective normal stress, the fracture permeability is positively correlated with the shear displacement. The permeability is lower at higher effective normal stress and exhibits an episodic change with increasing shear displacement. After establishing a numerical model based on the point cloud data generated by the three-dimensional (3D) laser scanning of the fracture surfaces, we found that there are some contact areas that block the percolation channels under high effective stress conditions. This type of contact area plays a key role in determining the evolution of the fracture permeability in a given rock sample.

ЛОКАЛИЗАЦИЯ ПЛАСТИЧЕСКОЙ ДЕФОРМАЦИИ ТЕХНИЧЕСКИ ЧИСТОГО ТИТАНА В СЛОЖНОМ НАПРЯЖЕННОМ СОСТОЯНИИ ПРИ ВЫСОКОСКОРОСТНОМ РАСТЯЖЕНИИ

In this work, the effect of a triaxiality stress state on the mechanical behavior and fracture of commercially pure titanium VT1-0 (Grade 2) in the range of strain rates from 0.1 to 1000 s−1 is studied. Tensile tests are carried out using a servo-hydraulic testing machine Instron VHS 40 / 50-20 on flat specimens with a constant cross-sectional area and on flat specimens with a notch. To study the effect of the complex stress state on the ultimate deformation before fracture, the samples with the notch of various radii (10, 5, 2.5 mm) are used in the experiments. Phantom V711 is employed for high-speed video registration of specimen’s deformation. Deformation fields in a working part of the sample are investigated by the digital image correlation method. It is shown that the effect of the strain rate on the ultimate deformations before fracture has a nonmonotonic behavior. An analysis of strain fields in the working part of the samples shows that the degree of uniform deformation of the working part decreases with an increase in the strain rate. At strain rates above 1000 s−1, the shear bands occur at the onset of a plastic flow. Commercially pure titanium undergoes fracture due to the nucleation, growth, and coalescence of damages in the bands of localized plastic deformation oriented along the maximum shear stresses. The results confirm that the fracture of commercially pure titanium exhibits ductile behavior at strain rates varying from 0.1 to 1000 s−1, at a triaxiality stress parameter in the range of 0.333 ≤ η <0.467, and at a temperature close to 295 K.

Influence of Particle Size and Moisture on the Compression Behaviour of D-G-S

Most studies in geotechnical engineering have focused on soil behavior under low pressures, low stress levels which are typically encountered in many geotechnical projects. But high stresses can lead to particle breakage of even the strongest soil minerals. In addition, many weak-grained soils, such as decomposed granites, carbonate sands, and volcanic ashes, are also crushable and compressible under normal working loads. Hardin stated the degree to which particles are crushed during shearing depends on many factors, such as particle-size distribution, state of effective stress and effective stress path, void ratio, particle hardness, and presence or absence of water. However, these studies have focused mainly on dry particles and the influence of water on the crushing properties of particles has not been sufficiently studied. It is important to mention that characterization of the behavior of D-G-S (decomposed granite soil) is important because this material is commonly used for construction in many engineering projects in Japan and Korea. Therefore, in this patter in order to investigate the influence of particle size and moisture on compression characteristics of D-G-S, single-particle crushing and one-dimensional compression tests were carried out on three types of D-G-S as well as on quartz-rich silica sand under both dry and wet conditions. Results showed that it can be seen that there is a relationship that the crushing strength decreases as the particle size increases. this result was clarified that the same result can be obtained not only in Silica but also in D-G-S. and the initial crushing strength of a single particle was reduced and strength variability increased due to the weakening effects induced by the presence of water. Moreover, it was observed that the one-dimensional compression behavior of decomposed granite soil was related to the initial crushing strength. Finally, the magnitude of initial crushing strength was also affected by the degree of weathering of the soil.

Effect of Stress State on Plastic Behavior, Deformation Mechanism and Texture Evolution of an Mg-Gd-Y Alloy: Experiment and Multi-Scale Simulation

Effect of Stress State on Plastic Behavior, Deformation Mechanism and Texture Evolution of an Mg-Gd-Y Alloy: Experiment and Multi-Scale Simulation

Experimental study of the stress state and strain rate dependent mechanical behaviour of TRIP-assisted steels

This paper presents an investigation into the effect of different stress states and strain rates on the austenite-to-martensite transformation during plastic straining of a Q&P steel. Different stress states are imposed to the steel using purposed-designed samples. The sample geometries, including in-plane shear, dogbone and plane strain samples, are optimised by finite element modelling. Tensile tests are performed at different strain rates of 0.001 s-1, 10 s-1 and 500 s-1. Digital image correlation is used to capture the strain fields during the entire deformation process. The mechanical results indicate a positive strain rate sensitivity for both the shear and plane strain specimens and a negative strain rate sensitivity for the dogbone sample. In addition, the influence of the strain rate on the strain level is more pronounced for the shear than for the plane strain specimens and for the dogbone samples.

Physical modeling of deformation and filtration processes in low-permeability reservoir rocks when implementing the directional unloading method

This article describes the results of physical modeling of deformation and filtration processes in low-permeability reservoir rocks of the Achimov deposits of the Urengoy gas condensate field. The experiments were carried out on a unique true Triaxial Independent Loading Test System (TILTS) of the Institute for Problems in Mechanics of the Russian Academy of Sciences. The effect of the non-uniform triaxial stress state on the character of deformation and filtration processes in rocks was studied. Real stresses that occur in the bottomhole formation zone when the pressure in the well decreases were created in the rock specimens. Experiments were carried out to simulate the stress state at the walls of the open hole and at the tip of the perforation hole. The geomechanical approach is shown to be promising for creating ways to improve the quality of wells; in particular, the adaptation of the directional unloading method for the conditions of a given reservoir is considered. These studies are essential both in fundamental scientific and practical terms to substantiate technological solutions in the development of fields with low-permeability reservoirs.

Experimental investigation of strain rate dependent damage mechanisms in DP1000 automotive steel

Present study aims to investigate the effect of stress state and loading rates on the damage mechanisms in a DP1000 steel using a welldesigned series of experiments. A specimen family comprising of central hole, in-plane shear and plane strain samples is applied to characterise damage under well-controlled stress states. The optimization of the specimen geometries is achieved using finite element simulations. To assess the influence of strain rate, quasi-static, intermediate and dynamic tests are performed on the designed samples. Local strain fields are obtained by digital image correlation. After testing, scanning electron microscopy is employed to systematically analyse the micromechanisms driving the damage in the investigated material. The underlying damage mechanisms are ferrite-martensite interphase debonding, martensite cracking and debonding at ferrite-ferrite grain boundaries. Stress state and strain rate are found to have distinct influences on triggering the underlying damage mechanisms.

Chemical-Mechanical Coupling Effects on the Permeability of Shale Subjected to Supercritical CO <sub>2</sub>-Water Exposure

The permeability of shale reservoir rock and caprock is the key parameters influencing the shale gas production and the storage security of CO2. In this study, the ScCO2-water exposure induced chemical-mechanical coupling effects on the permeability of shale was analyzed by a systematic research, including mineralogical analysis, pore structure analysis, uniaxial compression and permeability test at different stress and injection pressure of shale before and after ScCO2-water exposure. After ScCO2-water exposure, the pore volume and average pore size of shale increased, and the initial permeability of shale increased. At the stressed condition, the porosity and permeability of CO2-water treated shale sample is lower than the untreated shale sample. The uniaxial compressive strength and elastic modulus of shale were decreased after ScCO2-water exposure. The shale permeability was increased with the increase of injection pressure, and decreased with the increase of confining stress. The stress sensitivity of permeability in shale is stress-dependent, a higher effective stress corresponding to a lower stress sensitivity of permeability. The damage in the permeability (Δkd) of shale caused by the ScCO2-water exposure is also depending on the confining stress and injection pressure, at a higher effective stress condition, the damage in the permeability of shale is more significant.

Fatigue-driven failure criterion for progressive damage modelling and fatigue life prediction of composite structures

This paper attempts to assess fatigue lifetime of full-scale composite cabin by using experimental and numerical methods. With due consideration of multiaxial stress state and stress ratio effect, the governing equation for multiaxial fatigue-induced residual strength at an arbitrary stress ratio was derived. Based on multiaxial fatigue-induced residual strength concept, new fatigue-driven failure criterion was devised for progressive damage modelling and fatigue life prediction of composite structures. Quasi-static and step constant-amplitude cyclic loading tests were respectively performed to measure the load versus strain curves and to determine fatigue life and failure mode of full-scale composite cabins. It is shown from experimental observations that fatigue damage first appeared at upper left fillet of cutout, and then propagated from upper left fillet to the nearby countersunk hole, which was followed by the propagation along the circumference direction of cylinder until final failure. A progressive damage model based on fatigue-driven failure criterion was generated for damage mechanism modelling and fatigue life prediction of composite cabin, and the numerical results correlate well with the experimental findings, demonstrating the practical and effective use of proposed failure criterion.

Effects of initial stress state on the subsurface stress distribution after ultrasonic impact treatment on thick specimens

Thick welded specimens with different initial stress states were prepared and treated with the ultrasonic impact treatment (UIT). The subsurface stresses before and after UIT were measured by the X-ray diffraction (XRD) method combined with layer removal. The measured results were corrected based on the finite element correction method. The effects of initial high tensile stress and low compressive stress on the in-depth after-UIT stress distributions were investigated. The results show that initial stress has no effects on the stresses induced by the UIT within 1 mm depth and within that depth, UIT can induce almost the same longitudinal and transverse stress curves beneath the surface with a peak compressive stress close to the material yield strength at the depth of near 0.6 mm and 0.8 mm. UIT induces almost the same longitudinal and transverse stresses along with the measured depth under initial low compressive stress state. While under the initial high tensile stress state, the initial stress dominates the final stress distribution over 1 mm depth. Initial high tensile stress (welding residual stress) can reduce the depth of the after-UIT compressive stresses to 62.5% to 75% of that under the initial low-compressive stress state.

A comparative study on methods for determining the hydraulic properties of a clay shale

SUMMARY A comprehensive characterization of clay shale behavior requires quantifying both geomechanical and hydromechanical characteristics. This paper presents a comparative laboratory study of different methods to determine the water permeability of saturated Opalinus Clay: (i) pore pressure oscillation, (ii) pressure pulse decay and (iii) pore pressure equilibration. Based on a comprehensive data set obtained on one sample under well-defined temperature and isostatic effective stress conditions, we discuss the sensitivity of permeability and storativity on the experimental boundary conditions (oscillation frequency, pore pressure amplitudes and effective stress). The results show that permeability coefficients obtained by all three methods differ less than 15 per cent at a constant effective stress of 24 MPa (kmean = 6.6E-21 to 7.5E-21 m2). The pore pressure transmission technique tends towards lower permeability coefficients, whereas the pulse decay and pressure oscillation techniques result in slightly higher values. The discrepancies are considered minor and experimental times of the techniques are similar in the range of 1–2 d for this sample. We found that permeability coefficients determined by the pore pressure oscillation technique increase with higher frequencies, that is oscillation periods shorter than 2 hr. No dependence is found for the applied pressure amplitudes (5, 10 and 25 per cent of the mean pore pressure). By means of experimental handling and data density, the pore pressure oscillation technique appears to be the most efficient. Data can be recorded continuously over a user-defined period of time and yield information on both, permeability and storativity. Furthermore, effective stress conditions can be held constant during the test and pressure equilibration prior to testing is not necessary. Electron microscopic imaging of ion-beam polished surfaces before and after testing suggests that testing at effective stresses higher than in situ did not lead to pore significant collapse or other irreversible damage in the samples. The study also shows that unloading during the experiment did not result in a permeability increase, which is associated to the persistent closure of microcracks at effective stresses between 24 and 6 MPa.

Effects of stress state, strain rate, and temperature on fracture behavior of in situ TiB2/2024 Al composite

To gain insights into the relationship between the fracture behavior and the unique microstructure of the in situ TiB2/2024 Al composite, systematic experiments were conducted over wide ranges of temperature (298–673 K), strain rate (0.001–4000/s), and stress triaxiality (−0.82–1.03). The results showed that the strengthening mechanism of the composite was related to Orowan strengthening and coefficient of thermal expansion (CTE) mismatch strengthening. Owing to the smaller particle size and sturdy interfacial bonding, the tensile strength of the in situ nano/submicron TiB2/2024 composite was higher than that of the ex situ composite and the in situ micron composite. Through a morphologic study by scanning electron microscopy (SEM), the microstructural deformation and crack propagation path were found to be largely dependent on the stress state, strain rate, and temperature. The melted matrix precipitated in the dynamic tensile fracture surface can hinder the crack propagation and is considered the determining factor that improves the ductility at room temperature. Furthermore, a 3D fracture locus in the space of the fracture strain, stress triaxiality, and the Lode angle parameter was formed. Finally, a new fracture criterion that considers the Lode angle parameter, the stress triaxiality cutoff value, and the coupling effect of strain rate and temperature was developed. The developed criterion exhibited a robust and accurate capability to describe the fracture behavior of the in situ TiB2/2024 Al composite.

Constitutive relationships of 21-4 N heat-resistant steel for the hot forging process

The Gleeble-1500D thermal simulator was used for the isothermal compression test of 21-4N heat-resistant steel under the T range of 1273–1453 K and ε˙ of 0.01–10s−1. Using the obtained stress - strain data, various parameters of the Fields–Backofen (F-B), the modified F–B (m–F–B) equations and the modified Zerilli–Armstrong (m–Z–A) equations were calculated respectively. The constitutive equations of 21-4N heat-resistant steel based on the F–B, the m–F–B and the m–Z–A were established. Second, the predictive ability of the three constitutive equations were evaluated using the correlation coefficient (R), average absolute relative error (AARE) and the relative error (r). Third, the established model was imported into Deform-3D to simulate the valve forging process of 21-4N heat-resistant steel, and the distribution rules of the effective stress, effective strain, temperature and damage condition of the forging were analyzed. Finally, a hot forging experiment was performed on a 160t hot die forging press. Results show that the flow stress of 21-4N heat resistant steel is affected by temperature, strain rate and strain. The m–F–B and m–Z–A models can describe the rheological behavior of 21-4N heat-resistant steel, while the original F–B model has a high predictive ability, but only under low temperature, low strain rate and small deformation. The simulation process can be completed successfully, indicating that the established models can be used for the simulation study of the thermal deformation of 21-4N heat-resistant steel and all models are correct. The results can provide some important basic data for the simulation of 21-4N heat resistant steel in the plastic deformation process.

Effect of Material Strength on Ductile Failure of Steel in Pressure Vessel Design

Abstract Pressure vessels and their components are commonly designed with the ASME Boiler and Pressure Vessel Codes. One of the requirements when pursuing the design by analysis route is to design these equipment against ductile local failure criterion provided in the codes. However, the ductile local failure criterion in the ASME codes only accounts for the stress triaxiality (T) as a stress state measure. Recent work has shown that ductile failure highly depends on the stress state characterized by both T and the Lode parameter L, which is related to the third deviatoric stress invariant. In this study, the effect of stress state characterized by both T and L is investigated for six different steel grades with different material strength levels. To establish the ductile failure loci for the six steel grades with respect to T and L, experiments were conducted on two different specimen geometries. The L parameter is controlled by the specimen configuration, where the round notched bar specimen corresponds to axisymmetric tensile conditions (L = −1) and the flat notched specimen corresponds to plane strain loading conditions (L = 0), whereas T is controlled by introducing a notch at the center of the specimens. A Lode sensitivity parameter (LS) is defined based on the experimental results and revealed that the steel grades with ultimate strength higher than a certain threshold value (450 MPa) exhibit sensitivity to the Lode parameter. The Lode sensitivity was quantified, and the results showed that the LS increases with increase in the ultimate strength of the steel grade. The results were incorporated to enhance the original ASME local failure criterion by accounting for T, L, and LS to accurately assess ductile failure in high-strength steels. The application of the enhanced failure locus in a design analysis of a pressure vessel made of a high-strength steel grade is demonstrated, which showed that the original ASME criterion, as compared to the enhanced criterion in this study, is not capable of predicting ductile failure and hence rendering a rather nonconservative design. It is concluded that the enhanced local failure criterion is recommended to be used for the design of pressure vessels and their components made of steel grades with an ultimate strength higher than the threshold value.

Microstructure-based RVE modeling of ductile failure induced by plastic strain localization in tailor-tempered 22MnB5 boron steel

To differentiate the ductile fractures caused by deformation incongruities between phases, 22MnB5 boron steel sheets consisting of diverse bainite-martensite fractions were studied. The microstructural characteristics of each phase in tailor-tempered boron steel were examined in tandem with the ductile fracture morphologies after undergoing varied stress states. A micromechanical model was proposed, including microstructural reconstruction using a 2D representative volume element (RVE) approach and a constitutive formulation of a dislocation density-based strain hardening model. The microstructure-based RVE model can be utilized to study the effects of stress states and the influence of microstructural characteristics on the failure mode of tailor-tempered 22MnB5.