Range Of Compressive Stresses Research Articles

Research on the residual stress of stainless steel pipe after overlay repair

The weld overlays are widely used to repair metal butt welds or piping components by depositing weld metal on the outside surface of the welds and piping components. This paper presents the detailed residual stress distribution of girth weld in stainless steel pipe after butt welding and weld overlay repair by using finite element analysis. Two dimensional (2D) cross-section models, axisymmetric assumptions for piping girth welds are used to simulate the welding process in order to predict the residual stress distribution in the weld and base material. A project has been implemented to validate the analytical models used to perform welding residual stress analysis against measured residual stresses data in literature. It is found that the simulation results of butt welding are consistent with the experimental results in literature, which means that the analysis model and its results are accurate and reliable. A series of simulations are conducted to investigate the changing rules of influencing factors of overlay repair for stainless steel pipe. The results show that appropriate interpass temperature and heat input, increasing the thickness of overlay can effectively increase the range of compressive stress in pipe, so as to prevent and limit the generation and propagation of cracks. This research may provide an important support for the formulation of weld overlay repair standards in service.

Numerical study of full penetration single- and double-sided U-rib welding in orthotropic bridge decks

Under the repeated action of residual stress and wheel load caused by welding, fatigue cracks easily occur on the top plate-U rib welding of an orthotropic bridge deck (OBD). These affect the service life. To study the influence of different full-penetration welding methods on the residual stress and fatigue of OBD, this study compared the residual stress, welding deformation, and fatigue performance of full-penetration single- and double-sided welding through finite element analysis. The welding temperature and residual stress fields were simulated based on Goldak's double ellipsoid heat source model using the thermal elastic-plastic method. The numerical results were verified using measured data from relevant literature, and the two were in good agreement. The results showed that the longitudinal residual stress of the double-sided welded U-rib was larger than that of the single-sided welded U-rib, primarily in the compressive stress range, and the maximum deviation reached 99.44 MPa. The longitudinal displacement of single-sided welding along the weld direction was 0.060 mm lesser than that of double-sided welding, and the maximum vertical displacement perpendicular to the weld direction was 2.457 mm lesser than that of double-sided welding. For the same frequency of fatigue load (wheel load), the fatigue strength of single-sided welding was larger than that of double-sided welding, and the fatigue life increased by 29.7%. In this study, analysis models of the full-penetration single-sided and full-penetration double-sided welding were established, which could provide a reference for structural fatigue assessment using the two full-penetration welding techniques under the influence of residual stress.

Mechanical properties of partially bonded rock anchors in squeezing large-deformation soft rock tunnels

Partially bonded rock anchors are crucial structural tunnel support elements whose effectiveness depends on their interactions with the surrounding rock. This study combined laboratory experiments and numerical simulations to examine the mechanical behavior of partially bonded rock anchors under pull-out tests, focusing on the influence of bonded lengths. The axial strain of the anchor body and the vertical strain of the concrete block along the anchor axis were tested using distributed optical fibers. The results indicated that the anchor body stress remained relatively constant in the unbonded sections but gradually decreased as the depth into the bonded section increased. Simultaneously, the significant compressive stress range induced by the rock anchor in the concrete block decreased rapidly as the bonded length increased. Subsequently, the effects of different bonded lengths, unbonded section positions, and bonding combinations on the mechanical behavior and support effectiveness of partially bonded rock anchors in highly stressed soft rock tunnels undergoing substantial deformation were investigated using numerical simulations in ABAQUS. These findings suggest that rock anchors with longer bonded lengths have better control of the rock between the anchors. Simultaneously, the maximum axial stress of rock anchors tended to increase with longer bonded lengths. The rock displacement tended to be obviously larger when the unbonded section was set at the end of the rock anchors compared with when the unbonded section was set in the middle. The rock displacement was larger when the unbonded section was set at the outer end of the rock anchors, indicating that setting unbonded sections near the tunnel wall was detrimental to controlling rock deformation while improving structural safety. Setting one unbonded section near the tunnel wall and another unbonded section in the middle of the rock anchors resulted in excellent structural safety and rock deformation control. Furthermore, fully bonded rock anchors were compared with partially bonded rock anchors based on suitable bonding combinations in the deformation section of Muzhailing Tunnel. The results indicated that the fully bonded rock anchors experienced axial forces exceeding the yielding load in the early stages of support, with noticeable early yielding of the anchor plate. In contrast, the unbonded sections in the partially bonded rock anchors did not yield in either the bonded anchor body or the anchor plate. Partially bonded rock anchors exhibited better overall stability and reliability under high-deformation tunnel conditions.

Characterization of Terfenol-D and Comparison With Predictions of a Thermodynamically Consistent Two-Input, Two-Output Model of Hysteresis

Since its discovery more than forty years ago, Terfenol-D has promised much but has not yet been fully exploited in applications.The main reason for this is that it shows significant hysteresis and other nonlinearities, such as saturation, which need to be modeled correctly in order to maximize the application potential. In this article, we focus on the characterization of a Terfenol-D sample with the intention of developing a predictive two-input (magnetic field and stress) and two-output (magnetic flux density and strain) model of magnetostriction that exhibits hysteresis and saturation and is compatible with the laws of thermodynamics. Compatibility with thermodynamics is essential to ensure that numerical simulations do not exhibit unphysical behavior. The model is based on the Preisach hysteresis operator and its storage function and may be interpreted as a two-input, two-output neural net with elementary hysteresis operators as the neurons. In order to estimate the parameters, it is necessary to collect data over a wide range of magnetic fields (-300 kA/m to 300 kA/m) and compressive stresses (up to 60 MPa). Using the rate-independent memory evolution properties of the Preisach operator, we split the parameter estimation problem into three numerically well-conditioned, linear least squares problems with constraints. We show that the model is able to fit experimental data for strain and magnetization over a wide range of magnetic fields and stress.

A Low-Stress Method for Determining Static and Dynamic Material Parameters for Vibration Isolation with the Use of VMQ Silicone.

Progressive urbanisation causes building users to be affected by increasing amounts of noise and vibrations that come from transportation and other building users. This article presents a test method that can be used to identify quantities of methyl vinyl silicone rubber (VMQ) necessary to carry out solid mechanics finite element method simulations such as Young's modulus, Poisson ratio, and damping parameters. These parameters are necessary to model the vibration isolation used for protection against noise and vibration. The article uses an original combination of dynamic response spectrum and image processing methods to determine these quantities. The tests were carried out using one machine for the range of normal compressive stresses of 64-255 kPa with cylindrical samples of various shape factors in the range of 1-0.25. The parameters for the simulation of solid mechanics in statics were obtained from image processing based on the deformation of the sample under load; for dynamic solid mechanics, the parameters were obtained from the response spectrum of the tested system. The article shows the possibility of determining the given quantities using the original method of the synthesis of dynamic response and FEM-supported image analysis, which states the article's novelty. Additionally, limitations and preferred ranges of sample deformation in terms of load stress and shape factor are presented.

A new micromechanical damage model for quasi-brittle geomaterials with non-associated and state-dependent friction law

In this paper, we shall present a new micromechanical damage model for capturing the mechanical behaviors of quasi-brittle geomaterials under a wide range of compressive stress. Two essential coupled non-linear mechanisms are taken into account: plastic deformation related to frictional sliding along the microcrack surfaces, and microscopic damage induced by the initiation and propagation of microcracks. Within the framework of thermodynamics and Mori–Tanaka homogenization scheme, free energy and thermodynamic forces, including the local stress applied on the microcracks and damage driving force are deduced. The main novelty of this work lies in presenting a new physically based non-associated and state-dependent friction law to capture the plastic distortion, in which the friction coefficient is no longer a constant but a state-dependent variable varying with the surface asperities of microcracks. The relationship between the friction coefficient and mean local stress, as well as microscopic damage is subtly defined. Intriguingly, a macroscopic strength criterion is derived as an inherent part of the proposed model without rotation of the principal stress. Moreover, semi-analytical stress–strain–damage relationships of the proposed model can be derived under conventional triaxial compression. These up-scaling analyses provide a powerful tool for parameter calibration. For application, the semi-implicit return mapping algorithm with plasticity-damage decoupling correction procedure (SRM-PDDC) is adopted for numerical implementation. To demonstrate the performance of the micromechanical model, we compare the model predictions with experimental data of quasi-brittle rocks in literature as well as the results obtained by Zhu et al. (2016). Finally, the applicable condition of the SRM-PDDC algorithm is discussed in detail.

High‐Temperature Creep Properties of an Additively Manufactured Y2O3 Oxide Dispersion‐Strengthened Ni–Cr–Al–Ti γ/γ’ Superalloy

The effects of the modification of a high‐γ' Ni–8.5Cr–5.5Al–1Ti (wt%) model superalloy with 0.5 wt% Y2O3, manufactured by laser powder bed fusion, on the microstructure and compressive creep resistance, are investigated. Compared with the base alloy, the oxide dispersion‐strengthened (ODS) alloy exhibits 8–10 times slower creep rates at 800 °C, over a wide range of compressive stresses (35–250 MPa). Two creep regimes are observed: diffusional creep, hypothesized to be due to grain boundary sliding, and dislocation creep, with stress exponents n of 2 and 5, respectively. Compared with the horizontal direction, the vertical build direction is characterized by lower creep rates, due to the vertically elongated grain structure. Nonetheless, the ODS alloy's weakest (horizontal) direction shows better creep resistance than the non‐ODS alloy in its strongest (vertical) direction, despite a higher number of as‐built defects (slag, cracks) in the ODS alloy. The strengthening potential of ODS modification of additively manufactured nickel‐based superalloys is thus demonstrated. The development of successful commercial ODS nickel superalloys for additive manufacturing processing requires further additions of grain boundary strengthening elements as the dispersoids do not significantly increase the grain boundary strength, as their cracking is prevalent in the ODS alloy.

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

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

Study on bonding compression-shear performance between industrial green fiber-reinforced concrete and old concrete

Industrial green fiber-reinforced concrete, a new hybrid high performance environmental protection material, can be made by adding recycled steel fibers into concrete in a certain proportion. As a composite material used in the construction industry, it can provide a new research direction for national green and sustainable development. This paper studied the interface bonding mechanism of normal steel fiber-reinforced old and new concrete and industrial green fiber-reinforced concrete and old concrete by using a self-made new fixture, and discussed the influence of compressive stress, types of steel fibers and recycled steel fiber content on the bonding compression-shear performance of specimens. The results show that the bonding compression-shear performance of specimens gradually increases with the increases of the compressive stress acting perpendicular to the shearing surface within the range of low compressive stress, and when the compressive stress is from 0.2 MPa to 1.0 MPa, the increased amplitude of the bonding compression-shear performance of specimens gradually increases, when the compressive stress is from 0.6 MPa to 1.0 MPa, the increased amplitude of the bonding compression-shear performance of specimens reaches the maximum, and when the compressive stress is from 1.0 MPa to 1.4 MPa, the increased amplitude of the bonding compression-shear performance of specimens decreases. Under the same conditions, the effect of the recycled steel fibers on improving the bonding compression-shear performance between old and new concrete is better than normal steel fibers. The bonding compression-shear performance between old and new concrete gradually increases with the increases of the volume ratio of recycled steel fibers, and when the fiber content is from 0.0 % to 1.0 %, the increased amplitude of the bonding compression-shear performance of specimens gradually increases, when the fiber content is from 0.5 % to 1.0 %, the increased amplitude of the bonding compression-shear performance of specimens reaches the maximum, and when the fiber content is from 1.0 % to 1.5 %, the increased amplitude of bonding compression-shear performance of specimens decreases. The simulation results of industrial green fiber-reinforced concrete and old concrete specimens with fiber content of 1.5 % under different compressive stresses are basically in agreement with the experimental results. This study can provide references for the research of bonding compression-shear behavior of steel fiber-reinforced old and new concrete materials and the recycling of steel wire from waste tires.

Mean stress sensitivity of sintered iron and steel

Abstract There is a well-based correlation between the pulsating amplitude σ A(R = 0) and the alternating amplitude σ A(R = – 1) in fatigue testing of sintered iron and steel which permits to predict the mean stress sensitivity and the pulsating amplitude if the alternating endurance limit σ A(R = – 1) has been measured. Without loss of precision the relationship can be extended from smooth unnotched specimen geometries to notched geometries if only the stress concentration factor is known. The coefficients of the predictive equation depend on the brittleness of the material, a systematic approach to take the brittleness into account is still missing. In Haigh diagrams, the slope of the σ A–σ m diagram with tensile mean stresses can be linearly extrapolated also into the compressive mean stress range σ m < 0.

Friction-damage coupled models and macroscopic strength criteria for ice-saturated frozen silt with crack asperity variation by a micromechanical approach

This paper aims to present physical friction-damage coupled models and derive macroscopic nonlinear strength criteria for ice-saturated frozen silt. Two material scales are considered here. The material at the mesoscale is composed of a frozen silt matrix and embedded mesocracks. At the microscale, the frozen silt matrix is composed of elastic mineral grains and elastic ice crystals. Considering this microstructure, for the ice-saturated frozen silt, the plastic deformation is related to frictional sliding along the mesocracks, and damage is due to the propagation of mesocracks. We obtain the effective elastic properties with a two-step linear Mori-Tanaka homogenization procedure. For the second homogenization step, we deduce the macroscopic stress-strain relations and local thermodynamic forces associated with damage and plasticity. Then, an energy release-based damage criterion is developed to capture the evolution of damage, and a friction sliding criterion with an associated/nonassociated local plastic flow rule is introduced to describe the rate of plasticity. The friction sliding criterion considers the variation of surface asperities of mesocracks as a result of pressure melting and damage evolution. In this context, associated/nonassociated multiscale friction-damage models are established. Furthermore, associated/nonassociated macroscopic nonlinear strength criteria as inherent parts of the corresponding multiscale models are derived under a large range of compressive stresses. For application, a semi-implicit local numerical algorithm of the multiscale models is developed. The accuracy of associated/nonassociated multiscale models is assessed by comparing their numerical simulations with conventional triaxial compression (CTC) tests. Although the associated multiscale model correctly predicts the nonlinear strength behavior and axial deformation of the Lanzhou frozen silt under CTC tests with different temperatures, it fails to quantitatively reproduce volumetric deformation. Nonassociated multiscale model predictions with experimental data of volumetric deformation are significantly improved compared to the associated multiscale model.

A Phenomenological Primary-Secondary-Tertiary Creep Model for Polymer-Bonded Composite Materials.

This study develops a unified phenomenological creep model for polymer-bonded composite materials, allowing for predicting the creep behavior in the three creep stages, namely the primary, the secondary, and the tertiary stages under sustained compressive stresses. Creep testing is performed using material specimens under several conditions with a temperature range of 20 °C–50 °C and a compressive stress range of 15 MPa–25 MPa. The testing data reveal that the strain rate–time response exhibits the transient, steady, and unstable stages under each of the testing conditions. A rational function-based creep rate equation is proposed to describe the full creep behavior under each of the testing conditions. By further correlating the resulting model parameters with temperature and stress and developing a Larson–Miller parameter-based rupture time prediction model, a unified phenomenological model is established. An independent validation dataset and third-party testing data are used to verify the effectiveness and accuracy of the proposed model. The performance of the proposed model is compared with that of an existing reference model. The verification and comparison results show that the model can describe all the three stages of the creep process, and the proposed model outperforms the reference model by yielding 28.5% smaller root mean squared errors on average.

Investigations of internal stresses in high-voltage devices with deep trenches

Deep trenches, as essential elements of silicon chips used in electronic high-power and high-frequency devices, are known as starting points for dislocation generation under the influence of internal mechanical stresses resulting mainly from the difference in the thermal expansion coefficients between silicon and silicon dioxide. Since the electrical insulation of the devices requires a sequence of mechanical, chemical, and high-temperature processes during the preparation of the deep trenches, including the formation of an amorphous SiO2 edge layer, the emergence of the internal stresses is hardly avoidable. The method of cross correlation backscattered electron diffraction in the scanning electron microscope is used here to quantitatively determine the magnitude and local distribution of internal stresses in silicon around the deep trenches after four different process steps. For this purpose, Kikuchi diffraction images are recorded of the wafer cross section areas along lines perpendicular and parallel to the deep trenches. After Fourier transformation, these images are cross correlated with the Fourier transform of the diffraction image from a stressfree reference sample site. The well-established numerical evaluation of cross correlation functions provides the complete distortion tensor for each measuring point of the line scan, from which the stress tensor can be calculated using Hooke's law. It is found that the in-plane normal stress component σ11 perpendicular to the long edges of the deep trench is larger than the other stress components. That means it essentially determines the magnitude of the von-Mises stress, which was determined as a general stress indicator for all measuring points, too. A characteristic feature is the local distribution of the stress component σ11 with maximum tensile stresses of some hundred megapascals at transition between Si and amorphous SiO2 on the long edges of the deep trench, and with even higher maximum compressive stresses immediately below the bottom of the deep trench. At a distance of about 2 μm from the edges of a single deep trench, all stress components decrease to negligibly small values so that steep stress gradients occur. The range and distribution of tensile and compressive stresses are in accordance with finite element simulations; however, the measured stresses are higher than expected for all investigated states so that dislocation formation seems to be possible. The influence of the electron acceleration voltage on the determination of the internal stresses is discussed as well.

DEM STUDY ON THE PENETRATION OF JACKED PILES INTO LAYERED SOFT CLAY

In order to explore the variation law of soil particle displacement and pile force around piles during penetration process, the DEM (Discrete Element Method) model is used to test the penetration of pile foundation in layered soft soil foundation. The variation law of pile penetration force, radial pressure at pile-soil interface, friction resistance at pile side, displacement field and force field between particles during penetration process is analyzed. Research shows: (1) The penetration force increases with the increase of penetration depth and pile diameter. The increase of pile diameter is beneficial to overcome the influence of unfavorable strata. (2) At the same penetration depth, with the continuous penetration of the pile body, the radial pressure gradually decreases, showing a significant degradation phenomenon. The reason for the degradation of lateral friction is essentially the degradation of the radial pressure. (3) The distribution of contact force chain in different soil layers is similar, but the range of action is different. The contact force in silt layer is obviously larger than that in silty clay layer. The compressive stress of the soil at the end of the pile transfers radially with tensile stress. With the increase of pile diameter, the compressive stress and tensile stress in soil layer are gradually increasing, and the influence range of compressive stress and tensile stress is also gradually increasing. (4) The displacement of the soil below the pile tip is triangular, and the soil at the pile tip is squeezed around under the action of the pile tip. The influence range of particle displacement in each soil layer is different, and the influence range of particle displacement in silt layer is obviously smaller than that in silty clay layer.

Relation between water permeability and chloride diffusivity of concrete under compressive stress: Experimental investigation and mesoscale lattice modelling

This paper presents experimental investigations and a lattice modelling of the water permeability and chloride diffusivity of concrete under compressive stress and then proposes relationships between these two transport properties. Two representative ordinary concretes usually used in structures, subjected to compressive loading and water seepage or chloride contact, are considered.Water permeability tests were performed on hollow cylindrical samples in which the water diffuses in the radial direction through the sample thickness from the outer to inner surfaces under three different pressure gradients 3, 4 and 5 atm. Four compressive stresses (20%; 40%; 60% and 80% of the compressive strength) were applied on the sample top surface during the water permeability measurement. Rapid Chloride Permeability Testing (RCPT) is used to evaluate the chloride diffusivity. RCPT was carried out on cylindrical cores under four different stress levels (0; 25%; 50% and 75% of the stress at ultimate load).Mesoscale hydro-mechanical lattice modelling is proposed to model the fluid flow and chloride ingress in concrete under stress. In such a model, concrete includes three constituents: cement, aggregates and interfacial transition zone (ITZ). A softening damage model is employed to describe the behaviour of the cement matrix and the ITZ, while the aggregates are assumed to be elastic. Hydro-mechanical parameters of concrete components are calibrated from the experimental results of both water permeability and chloride diffusion tests. The proposed model allows extrapolating the experimental results for higher compressive stress. A relation between water permeability and diffusivity coefficients is resulted from both experimental and numerical investigations for a large range of compressive stress.

Predictions of decreased surface roughness after shot peening using controlled media dimensions

Shot peening induces residual compressive stresses on metallic substrates, often used to decrease fatigue crack growth. The relationship between surface roughness and the magnitude of the stress can be affected by peening media size or the extent of peening. Generally, an ideal condition from shot peening would be a high compressive residual stress and a low surface roughness, but these tend to be inversely related. This study proposes a method for decreasing roughness and increasing residual stress concurrently using a distribution of shot sizes in a single shot peening passage based on finite element modeling that has been calibrated using by experimental results. Numerical models predict mixed shot sizes will create a smoother surface than using monodispersed shot at 100 % coverage. The residual stress profile for mixed shot sizes showed a broad range of compressive residual stresses in comparison with the largest impact ball size. This newly proposed method can improve the surface quality and the extent of the compressive residual stresses in a single-shot peening passage.

Effects of compressive stress on electric-field-induced phase transition of antiferroelectric ceramics

In certain lead zirconate titanate compositions, the antiferroelectric (AFE) phase can be driven to the ferroelectric (FE) phase by electric field, and the induced FE phase can either revert to AFE or remain FE upon removal of the electric field. This results in a double or single hysteresis loop, respectively. To further explore the effects of the FE-AFE phase transition on electrical energy storage and conversion, two types of AFE ceramics were fabricated, and the effects of compressive stress on the AFE-FE phase transition were investigated. Compressive stress suppresses the volume increase associated with the AFE-FE transition, thus hindering the phase transition. Compressive stress also hinders polarization orientation in the FE phase, thus increasing the field necessary to achieve saturation polarization. For AFE compositions displaying a double hysteresis loop, the electrical energy storage performance can be enhanced by compressive stress. For the AFE compositions with a single hysteresis loop, the remanent polarization of the induced FE phase decreased and the coercive field did not change much within the range of compressive stress applied. In addition, the remanent polarization was reduced by 50% under a compressive stress of 126 MPa, indicating that this composition is a candidate for mechanical-electrical energy conversion.

Corrosion of Ti[sbnd]6Al[sbnd]4V orthopaedic alloy under stress

During in vivo function, implant surfaces are exposed to a corrosive environment as well as a wide range of tensile and compressive stresses. The objective of this study was to study the corrosion behavior of the Ti6Al4V orthopaedic alloy under different levels (ranging from plastic to elastic) of tensile stress, compressive stress, and combined tensile and compressive stresses in phosphate buffered saline 1X solution. The introduction of stress was found to alter the corrosion behavior of the Ti6Al4V alloy. The corrosion behavior was slightly improved under compressive stress while specimens under tensile stress showed weaker corrosion resistance compared to the specimens under zero stress. Nonetheless, the synergistic action of the tensile and compressive stresses considerably increased the corrosion activity of the specimens, more than that when they were just under tensile stress. The worst corrosion behavior was observed for the specimens under coupled elastic stress.

Comprehensive performance assessment of spacers in spiral-wound membrane modules accounting for compressibility effects

Net-type spacers are essential components of the spiral-wound membrane (SWM) modules employed in reverse osmosis (RO) desalination plants. Despite progress made in designing SWM modules in recent years, key issues related to feed-spacer characteristics (particularly spacer material properties in conjunction with their geometry), which affect module performance and membrane integrity, have been neglected by the research community. This paper focuses on the effect of compressive stresses, imposed on membrane spacers and envelopes during SWM-module fabrication to achieve module compactness and resistance to deformation during operation. A comprehensive method is presented (involving experimental and computational tools) which allows to quantify compressive stress effects, on the characteristics of spacer-filled membrane channels, and further to assess their impact on the key SWM-module operating parameters and on overall RO process performance. The method is demonstrated by assessing the performance of 26-mil commercial feed-spacer in an appropriate range of compressive stresses; it is interesting that modest nominal applied pressure, at the level of 1–2bar, tends to cause significant feed-spacer compression, channel-gap reduction and membrane indentations impairing the active layer. The novel method is considered most helpful for selecting appropriate feed-spacer material and geometric characteristics, for a membrane of particular mechanical properties.

A micro-mechanics based plastic damage model for quasi-brittle materials under a large range of compressive stress

In this paper, a new micro-mechanics based plastic damage model is proposed for quasi-brittle materials under a large range of compressive stress. The damage is due to initiation and propagation of micro-cracks while the plastic deformation is directly related to frictional sliding along micro-cracks. The two dissipation processes are then physically coupled. With the Mori-Tanaka homogenization procedure and thermodynamics framework, the macroscopic state equations are deduced and the local driving forces of damage and plasticity are defined. New specific criteria are proposed for the description of damage evolution and plastic flow. These criteria take into account the variation of material resistance to damage with confining pressure and the degradation of surface asperity of micro-cracks during the frictional sliding. An analytical analysis of macroscopic peak strength and volumetric compressibility-dilatancy transition is provided. A specific calibration procedure is further proposed for the determination of all model's parameters from conventional triaxial compression tests. The efficiency of the proposed model is verified against experimental data on three different materials and for a very large range of stress. All main features of mechanical behaviors of materials are well captured by the proposed model.