Stress-strain Constitutive Model Research Articles

Evaluation of Wellbore Stability by Small Parameter Perturbation Nonlinear Elastoplastic Model

Abstract Wellbore instability is a frequent occurrence during drilling and a popular research topic among petroleum workers. Most of the previous studies simplified the hardening stage and ignored or classified it into the elastic stage. Engineering practice shows that the total stress–strain process of rock can more truly reflect the bearing and deformation characteristics of rock. This study establishes a total stress–strain constitutive model by combining the perturbation index equation with the linear elastic equation. Additionally, the physical model of rock around the well is presented using the total deformation theory for the plastic zone. The stress field of the rock surrounding the well is analyzed based on the physical model of the rock surrounding the well, taking into account the influence of rock strength and geostress state. The relationship between rock strength, geostress state, drilling fluid density, and plastic radius is given. The calculation method of drilling fluid density limit is also given. The practical application demonstrates that the stability of a borehole wall can be evaluated by analyzing the size and direction of the plastic radius, as well as the distribution of radial, tangential, and shear stress for various combinations of stress states and rock strengths. The maximum shear stress is always found in the softening zone, which is also the region where wellbore instability is most likely to happen. Therefore, the area within the softening radius is regarded as an unstable area, and the softening radius can be used to determine the range of wellbore instability.

Axial compression stress-strain relationship of lithium slag rubber concrete

Replacing cement with lithium slag and fine aggregate with rubber in concrete solves waste disposal, reduces material consumption, boosts sustainability, and enhances concrete performance. A set of prismatic concrete specimens with varying proportions were designed and experimentally tested in order to study the compressive stress-strain behavior of lithium slag rubber concrete (LSRC). The main factors affecting the specimens were lithium slag substitution ratio (SL=0%, 10%, 20%, 30%) and rubber substitution ratio (SR=0%, 5%, 10%, 15%). The results demonstrated that the LSRC exhibited good integrity during the damage. Furthermore, the incorporation of lithium slag (LS) was found to effectively compensate for the reduction in compressive strength due to the incorporation of rubber. When 10% of the fine aggregate was replaced with rubber and 20% of the cement was substituted with lithium slag, the axial compressive strength, elastic modulus, and peak strain of the tested specimens increased by 21.57%, 6.92%, and 17.26%, respectively. Compared with ordinary concrete, LSRC has good toughness, impact resistance and durability with minimal loss of strength, and has broad application prospects in engineering fields (such as airports, highways, housing expansion joints, concrete floors and railway concrete sleepers, etc.). Based on the experimental data, simplified modified equations to predict the compressive strength, elastic modulus, peak strain and axial stress-strain constitutive model of LSRC were proposed, so as to promote the development of LSRC.

Shear failure characteristics and stress-strain relationship of Moso bamboo parallel to the fibers

Bamboo is susceptible to longitudinal splitting, which is mainly driven by its shear properties parallel to the fibers. In this work, bowtie tests including 124 Moso bamboo internode and node specimens were conducted to investigate the shear behaviors of Moso bamboo in shear parallel to the fibers. Based on the test results, the difference in shear strength between internode and node specimens using the analysis of variance (ANOVA) was quantitatively evaluated. The distribution of shear strength was fitted using Normal, Log-normal, and Weibull distributions, and the corresponding standard value was calculated using the non-parametric method. The design value was obtained based on reliability analysis. Additionally, prediction formulas for shear strength were fitted using univariate and multiple regression analyses based on outer diameter, wall thickness, and density. Various shear stress-strain constitutive models were established and validated. The research results indicated that there is no statistically significant difference in shear strength between internode and node specimens with the value of 17.17 MPa and 17.48 MPa, respectively. The distribution of shear strength followed the Normal and Log-normal distributions, but not the Weibull distribution. The standard value and design value of shear strength were 14.91 and 9.47 MPa, respectively. The shear strength was found to be negatively correlated with the outer diameter and wall thickness, but positively correlated with the density. The recommended strength prediction formulas and stress-strain constitutive models match well with the test results. This study can serve as a reference for the improvement of bamboo standard and design basis of Moso bamboo.

Nano-silica and Ground Granulated Blast Furnace Slag Blended Concrete: Impact of Temperature on Stress–Strain Constitutive Model

Nano-silica and Ground Granulated Blast Furnace Slag Blended Concrete: Impact of Temperature on Stress–Strain Constitutive Model

Numerical Modeling of Steel Fiber Reinforced Recycled Concrete Filled Steel Tube Column Under Cyclic Loading

A finite element model (FEM) was created with the aim of analyzing the behavior of steel fiber reinforced recycled concrete (SFRRC)-filled steel tube columns under combined cyclic loading and monotonic axial load. The FEM considered the effect of steel tube confinement on the inner concrete behavior under cyclic loading. The numerical model was described in detail, with a focus on modeling the materials involved (normal concrete, SFRRC, and steel) under cyclic loading. A constitutive concrete model - with and without considering confinement - was based on utilizing a concrete damaged plasticity (CDP) model. The steel tube - concrete core interface was modeled by a surface-to-surface contact. A stress-strain constitutive concrete model, confined by circular steel tubes, was implemented, and validated using experimental results from the literature. The developed FEM considered various parameters: steel tube thickness, volume ratios of steel fibers, besides strengths of both concrete core and the steel tube. The FEM results showed great similarity to the under- cyclic- loading tested columns. The results indicated that the concrete confining pressure must be considered in CDP model. A good correlation between numerical and experimental findings was obvious, including failure modes, and hysteretic curves of load-displacement.

Mechanical property and frost resistance of phase–change/NanoSiO2 concrete in a low–temperature environment

To study the effect of phase–change materials and nanomaterials as new composite materials on the mechanical properties and frost resistance of concrete, it is beneficial for low–carbon and environmentally friendly buildings to be achieved. The effects of freeze–thaw cycles and different preloading strains were considered. ICT scanning was performed, and the compression performance of composite–modified concrete (CMC) were tested. The internal pore structure and strength indicators of the CMC were analyzed during uniaxial compression. Meanwhile, by conducting uniaxial compression tests on CMC at different temperatures, changes in the mechanical properties during real–time freezing and thawing processes were obtained. The results demonstrated that the fractal dimension grows and the compressive performance of the CMC declines as the number of freeze–thaw cycles and preloading strain increases. The proportion of spheroids in the internal pore shape gradually decreases, whereas the proportions of rods, discs, and blades increases. CMC effectively delays the rise or fall of internal temperature during the freeze–thaw process and reduces its internal structural deterioration. Compared with the freeze–thaw effect, an increase in the preloading strain has a more notable impact on the compressive performance of CMC. A stress–strain constitutive model is proposed for a 10 % microencapsulated phase–change materials and a 1.5 % nanoSiO2 composite–modified concrete (10 mPCMs/1.5 NS CMC), influenced by temperature, through regression analysis. Meanwhile, under low temperatures, the degradation of mechanical properties of 10 mPCMs/1.5 NS CMC and the influence of different preloading strains are considered, leading to the development of stress–strain constitutive models for freeze–thaw cycles and different preloading conditions.

Uniaxial compressive stress-strain model of Molybdenum tailings concrete after high-temperature exposure

To investigate the effect of high-temperature exposure on the mechanical properties of molybdenum tailings concrete, 75 cubes and 150 prisms of molybdenum tailings concrete were tested, by considering five heating temperatures (20, 200, 400, 600, and 800 ℃) and five replacement ratios (0, 25, 50, 75, 100%). The failure modes, mass loss rate, and mechanical properties of the specimens were analyzed in detail. The experimental results indicate that with an increasing heating temperature, the color of the blocks became lighter, accompanied by gradually intensifying phenomena such as skin peeling and crack propagation. At 800 ℃, many small cracks at the fracture site of the blocks after splitting failure, and obvious fracture zones in the block under axial compression failure were observed. With an increasing temperature, the mass loss rate and peak strain of the molybdenum tailings concrete show a linear growth trend, reaching the maximum amplitude at 800 ℃ (7.85% and 192.5%), whilst the molybdenum tailings concrete splitting tensile strength, peak stress, and elastic modulus showed a decreasing trend, reaching the maximum amplitude (404%, 61.7%, and 84.9%). By increasing replacement ratios, the mass loss rate of the molybdenum tailings concrete shows a linear growth trend, with a maximum increase of 1.07%. The mechanical properties of the concrete at all temperatures show a trend of first increasing and then decreasing. A 25% replacement ratio can improve the deterioration of the molybdenum tailings concrete after high-temperature exposure, with the maximum amplitude increase of the peak stress, peak strain, and elastic modulus being 24.3%, 12.4%, and 21%, respectively. Based on the test data, the prediction formulas of the mechanical properties of molybdenum tailings under different high-temperature and molybdenum tailings replacement ratios are fitted. The existing constitutive equations are modified to establish the stress-strain constitutive model of molybdenum tailings concrete after high-temperature exposure, of which results are in good agreement with the test data.

Dynamic mechanical behavior of steel fiber reinforced-recycled aggregate concrete subjected to uniaxial loading

The objective of this study was to investigate the dynamic mechanical performance of steel fiber reinforced-recycled aggregate concrete (SFRAC) under uniaxial loading. A total of 22 groups of cylindrical samples, each measuring 100 mm × 200 mm, were subjected to uniaxial compression. The investigation placed particular emphasis on examining the influence of variables such as the strain rate, volume fraction of steel fiber (Vsf), volume fraction of polyvinyl-alcohol (PVA) fiber (Vpf) and substitution ratio of recycled coarse aggregate (SRCA) on the failure modes, stress-strain curves and deformation ability. The results revealed that the incorporation of steel fibers and PVA fibers enhanced the overall integrity of fractured samples, and induced changes in the failure modes. In particular, the maximum increase in uniaxial compressive strength attributed to strain rate, Vsf and Vpf reached up to 15.0%, 23.57% and 8.57%, respectively. Although the inclusion of recycled aggregates had no significant influence on the failure mode, it decreased the compressive strength by up to 16.34%. Finally, a dynamic stress-strain theoretical constitutive model was established in this paper. The predictions derived from this model closely aligned with the experimental stress-strain curves obtained during the conducted tests. This study provides valuable insights for applications of SFRAC in structural engineering.

Mechanical Properties and Damage Constitutive Model of Thermally Damaged Basalt

Nuclear power is a high-quality clean energy source, but nuclear waste is generated during operation. The waste continuously releases heat during disposal, increasing the adjoining rock temperature and affecting the safety of the disposal site. Basalt is widely considered a commonly used rock type in the repository. This study of basalt’s mechanical characteristics and damage evolution after thermal damage, with its far-reaching engineering value, was conducted by combining experimental work and theory. Uniaxial compression tests were conducted on basalt exposed to 25 °C, 500 °C, 700 °C, 900 °C, and 1100 °C conditions, and acoustic emission (AE) equipment was utilized to observe the acoustic emission phenomenon during deformation. This study was carried out to examine the mechanical characteristics, the sound emission features, the progression of damage laws, and the stress–strain framework of basalt after exposure to different types of thermal harm. As the temperature rises, the rock’s maximum strength declines steadily, the peak strain rises in tandem, the rock sample’s ductility is augmented, the failure mode changes from shear to tensile failure, and cracks in the failure area are observed. At room temperature, the acoustic emission signal is more vigorous than in the initial stage of rock sample loading due to thermal damage; however, after the linear elastic stage is entered, its activity is lessened. In cases where the rock approaches collapse, there is a significant surge in acoustic emission activity, leading to the peak frequency of acoustic emission ringing. The cumulative ring count of acoustic emission serves as the basis for the definition of the damage variable. At room temperature, the damage evolution of rock samples can be broken down into four distinct stages. This defined damage variable is more reflective of the entire failure process. After exposure to high temperatures, the initial damage of the rock sample becomes more extensive, and the damage variable tends to be stable with strain evolution. The stress–strain constitutive model of basalt deformation is derived based on the crack axial strain law and acoustic emission parameters. A powerful relationship between theoretical and experimental curves is evident.

Stress-strain constitutive models along the grain of original bamboo based on classification

To establish the constitutive model of original bamboo, the tensile and compressive tests along the grain of original bamboo were investigated. The original bamboo was graded according to the elastic modulus, and a stress-strain constitutive model of original bamboo was proposed. The results of the study show that the tensile failure mode of original bamboo along the grain is brittle failure, and the compression along the grain is ductile failure. The bamboo was divided into three grades I, II, and III, and the proportion of II and II was more than 80%. A linear constitutive model was used for tension along the grain of original bamboo, a “three-fold” model was used for simplified constitutive model for compression along the grain, and the Sargin model was used for accurate constitutive model. The classification method proposed in this paper can result in the efficient utilization of bamboo resources, and the proposed constitutive model can promote the analysis and engineering application of original bamboo architecture.

Mechanical properties and stress-strain relationship of surface-treated bamboo fiber reinforced lightweight aggregate concrete

Bamboo fiber (BF) possesses advantages such as environmental friendliness, renewability, economic viability, and favorable mechanical properties, making it a promising material for improving the brittleness and tensile strength of concrete. Previous investigations have demonstrated a limited exploration of BF-reinforced lightweight aggregate concrete (LWAC). Current study concentrates on investigating the mechanical properties and stress-strain relationship of BF-reinforced LWAC. To achieve this, 7 groups of BF-reinforced LWAC specimens were subjected to compressive tests, splitting tensile tests, and prism compressive tests. The influence of BF content and length on the compressive performance, failure modes and stress-strain curves was studied. BFs effectively suppressed the development of internal cracks in LWAC, playing a role in crack resistance and toughness enhancement. Furthermore, BFs significantly improved the splitting tensile strength of concrete, while the compressive strength slightly decreased with the increase of BF content. After adding BFs, the splitting tensile strength of concrete increased by 8.2∼23.7%, and the compressive strength decreased by 3.6∼11.1%. Moreover, the BF length had almost no effect on the compressive strength of concrete, while when the BF length was 10–30 mm, the tensile strength increased by 5.3∼17.6%. Based on existing researches, strength conversion equations and stress-strain constitutive models of BF-reinforced LWAC were proposed, and the models provide a theoretical basis for the calculation and analysis of BF-reinforced LWAC components and structures.

Confinement mechanism of cross-shaped steel reinforced concrete columns

A novel confined concrete constitutive model for steel-reinforced concrete (SRC) columns with cross-shaped steel (CSS) sections is proposed. The model is based on the similar characteristics of descending branches in the stress–strain curves of confined and unconfined concrete (UCC), considering confinement degradation caused by buckling of the steel section or longitudinal reinforcement. The confined region of SRC columns with CSS sections was divided into four parts: highly steel-confined concrete (HSCC), partially steel-confined concrete (PSCC), stirrup-confined concrete (StCC) and UCC. Relevant effective confinement coefficient expressions were also derived. Simulations of existing tests showed that (a) the load–strain curves obtained using the modified stress–strain constitutive model agreed well with the experimental results, with the error in the descending branch less than 5%; (b) the HSCC region for SRC columns with CSS sections in the finite-element model was in good agreement with that in the proposed region division; (c) the simulation of confined concrete region boundaries for SRC columns with CSS sections were determined using plumb lines for improving the calculation efficiency.

Hybrid machine learning model and predictive equations for compressive stress-strain constitutive modelling of confined ultra-high-performance concrete (UHPC) with normal-strength steel and high-strength steel spirals

Stress-strain constitutive model for confined ultra-high-performance concrete (UHPC) plays a pivotal role in the design and modelling of UHPC structures. However, while extensive research exists on the stress-strain responses of unconfined UHPC, a notable dearth of studies focuses on the stress-strain constitutive model for confined UHPC. Accordingly, this study introduces a novel hybrid machine learning (ML)-based stress-strain constitutive model for UHPC confined with normal-strength steel (NSS) or high-strength steel (HSS) spirals. Given the limited experimental data available, a numerical model was developed and validated against experimental results of confined UHPC. Subsequently, it was employed to generate a comprehensive dataset of confined UHPC stress-strain responses, which were then used to train the hybrid ML model. Hyperparameters of the model are subsequently optimized using Optuna along with a cross-validation technique. The optimized hybrid ML model exhibited exceptional accuracy in predicting the stress-strain response of confined UHPC with NSS or HSS spirals, as demonstrated by high coefficients of determination (R2) values ranging from 0.905 to 0.999 and low error metrics across varying stress levels and datasets. Moreover, the capability of the model to simultaneously predict both stress and strain responses was further validated through canonical correlation analysis (CCA). The results of the analysis demonstrated robust predictive performance of the model, with high CCA scores that ranged between 93.3% and 99.4%. To facilitate the practical implementation of the model, an end-to-end interactive software tool is developed. In addition, this study proposes predictive equations for the peak and ultimate stress-strain responses of confined UHPC. The evaluation of the developed predictive equations demonstrates their efficacy in accurately predicting the stress-strain responses of confined UHPC, as evidenced by the high R2 values, which ranged from 83–91%.

Mechanical and environmental performance of structural concrete with coal gangue fine aggregate

Using coal gangue sand as fine aggregate is a feasible solution for the sustainable development of construction engineering. The mechanical and environmental properties of the gangue fine aggregate concrete-filled steel tube (GFACFST) and reinforced gangue fine aggregate concrete (RGFAC) with different gangue fine aggregate replacement ratios (rGFA) were investigated experimentally and numerically. The results showed that the GFACFST and RGFAC with various rGFA showed similar failure modes. The stiffness of the stubs decreases with the increase in rGFA. The ultimate strength of the GFACFST and RGFAC decreases by 3.8 % and 12.4 % respectively when rGFA is 100 %. The ductility of GFACFST shows an ascending tendency with the increase in rGFA, resulting from the increase in the confining effect of the steel tube on the core concrete. The stress-strain constitutive model of gangue fine aggregate concrete is proposed for numerical modeling. A design method for the bearing capacity of GFACFST and RGFAC is proposed by considering various gangue fine aggregate replacement ratios of which results differ from the tested and simulated values in the range of ±5 % and ±11 %. The life cycle assessment analysis shows that the environmental impact of GFACFST is less than that of RGFAC at the same axial compressive strength. The improvement of the mechanical-environmental performance efficiency by increasing cross-section diameter is more significant than that by increasing steel ratio.

Study on damage characteristics and application of gypsum pillar strengthened with FRP

The instability of mine pillars has posed a serious threat to the safety of mines in China. In order to reduce the risk of pillar instability, this study used fiber-reinforced polymer (FRP) to reinforce gypsum specimens and conduct mechanical loading experiments. The study investigates the reinforcement effect of gypsum specimens with different height-diameter ratios and different FRP wrapping thicknesses, and analyzed the uneven distribution of constraint force along the height direction of FRP-reinforced gypsum specimens. An optimized wrapping method was proposed, and a stress–strain constitutive model for gypsum materials under optimized wrapping was established. By utilizing a statistical method based on strain energy density for heterogeneous rock damage identification, a simulation study was conducted on FRP-reinforced gypsum-like specimens. A comparative analysis was carried out with experimental results to verify the feasibility of the constitutive model. The research findings indicate that the use of FRP reinforcement significantly improves the uniaxial compressive strength and strain values of gypsum-like specimens. Moreover, the smaller the aspect ratio, the more pronounced the effect of FRP reinforcement on gypsum-like specimens. The stress–strain curve of FRP-reinforced gypsum-like specimens shows a distinct combination of curves and straight lines, which can be divided into two distinct stages based on different elastic moduli. The peak value of acoustic emission energy of FRP-reinforced gypsum specimens appears at the junction of the first and second stages of the stress–strain curve, and then the acoustic emission energy curve becomes relatively flat, with an increase in peak energy before failure. The constraint force acting on FRP-reinforced gypsum specimens exhibits an obvious uneven distribution along the height direction, based on which an optimized reinforcement scheme is proposed. Based on the established constitutive model, numerical simulation was conducted using real data from a specific mine. The research findings demonstrate that when the optimized reinforcement method is employed, the load-bearing capacity of the mine pillars was significantly enhanced. The maximum displacement was reduced by 33%, the maximum vertical stress was reduced by 3.2%, and the volume of the plastic zone was reduced by 39.87%.

Quantitative characterization of constitutive model of mudstone under uniaxial loading after immersion in acid solution by infrared radiation

The fracturing of coal and rock is a fundamental cause of mine disasters, such as coal pillar instability,water inrush and rock failure. To prevent the occurrences of these failures, it is important to accurately monitor and detect stress fractures in coal and rock. Furthermore, it is also essential to develop stress–strain constitutive models for an accurate and effective monitoring, early warning of coal and rock stress fracture process. The development of stress–strain constitutive model is the important basis for effectively realizing water conservation mining and rock strata control in mines. In this research, mudstone samples were collected from coal mining sites and mining faces. The mudstone samples were subjected to chemical corrosion using both strong acid and neutral solutions, followed by conducting infrared radiation observation experiments during uniaxial loading. The research findings revealed that 1) strong acid can promote the infrared radiation of the mudstone surface. The Average Infrared Radiation Temperature (AIRT) value of the mudstone corroded by the solution with pH 1.3 during uniaxial loading fracture is changed and noted 6.71 times to the solution with pH 7.3. 2) strong acid has an significant impact on the failure of mudstone samples. The mudstone corroded by the solution with pH 1.3 is mainly damaged by tension and shear composite cracks, while the mudstone corroded by the solution with pH 7.3 is primarily damaged by tension cracks. 3) A nearly linear relationship between the strain of mudstone during uniaxial loading and AIRT was found. This relationship defines a new index of deformation infrared radiation coefficient, allowing for the quantitative characterization between strain and infrared radiation. 4) A one-dimensional statistical damage constitutive model based on AIRT is established using Weibull distribution, while considering the stress–strain compaction stage. This model effectively predicts the stress of mudstone during uniaxial loading. The research results lay a theoretical and practical foundation for the monitoring and evaluation of rock stability in underground engineering such as coal mines, subways and tunnels.

Estimation of stress–strain constitutive model for ultra-high performance concrete after high temperature with an deep neural network based method

In order to better study and analyze the residual compressive behavior and stress–strain curve relationships of ultra-high performance concrete (UHPC) materials after high temperatures, high-temperature tests and uniaxial compression tests were carried out on 144 specimens in the temperature range of 20 °C-900 °C in this paper. The effects of different curing regimes and cooling regimes on the mechanical properties, apparent characteristic and stress–strain curves of UHPC after experiencing different temperatures were investigated respectively. As the target temperature increased, the stress–strain curves of all UHPC specimens gradually tended to be flatten, the peak point of the curve shifted to the right, the peak strain increased sharply, and the elastic modulus and proportional limits gradually decreased. The compressive strength and modulus of toughness of the UHPC specimens both increased and then decreased as the target temperature increased, with a critical temperature of 300 °C and 500 °C respectively. The Poisson's ratio of the UHPC specimens decreased and then increased as the target temperature increased, with a critical temperature of 500 °C. In addition, based on the experimental results, a Deep Neural Network (DNN) model with four hidden layers and 100 neurons in each layer was constructed to predict the complete residual stress–strain response of UHPC materials after high temperature. The training and validation of the DNN model was completed by pre-processing and segmenting the original dataset with the help of Pytorch deep learning libraries. The DNN model predicts stress–strain curves that are in excellent agreement with the UHPC test curves.

Effect of carbon fiber and graphite on the mechanical properties of conductive fine-grained concrete in textile reinforced concrete

In order to further explore the influence of single and double-doped carbon fiber and graphite on the mechanical properties of fine-grained concrete, compressive tests, flexural tests and uniaxial compressive tests were used. Researches show that the bending strength increases the most when 0.25% carbon fiber and 10% graphite are added in the fine-grained concrete. The ultimate failure modes of fine-grained concrete under uniaxial compression contains two types: split and shear. The double-doped conductive material can make up for the defects existing after the addition of single conductive material and improve concrete performance. Finally, based on the Kent and Park constitutive model and combined with the full-stress–strain curve image obtained by the test in this paper, a modified Kent and Park three-line function stress–strain constitutive model of fine-grained concrete was established.

Mechanical properties and constitutive model of the buckling restraint rebar under compression loads

AbstractBuckling of the longitudinal rebar is one of the main forms of plastic hinge failure in reinforced concrete (RC) columns after an earthquake. This rebar buckling significantly impacts the seismic bearing capacity and energy dissipation capacity. To restrain the development of longitudinal rebar buckling behavior and delay the degradation of lateral strength in RC columns, this paper developed a new type of buckling restraint rebar (BRR) consisting of three components: longitudinal rebar, a restraint sleeve, and foam material. First, the BRR mechanical properties under compression and tension‐compression cyclic loading were obtained through quasi‐static loading tests. Then, the BRR compression and tension‐compression cyclic loading processes were numerically simulated based on ABAQUS finite element software. The simulated results were compared with the test results. Finally, a stress–strain constitutive model for this new BRR was proposed based on this study. Results showed that the restraint sleeve could significantly enhance the lateral stiffness and the bearing capacity of longitudinal reinforcement after yielding. The compressive performance of BRR was mainly affected by the length and wall thickness of the sleeve. The cyclic performance was mainly affected by the length of the sleeve and the clearance between the sleeve and the reinforcement. The BRR constitutive model proposed in this paper can accurately reflect the influence of restraint sleeves on the stiffness of longitudinal reinforcement after yielding.

Multi-scale coupling numerical modeling of metallic strip flexible pipe during reel-lay process

Complex plastic deformation and local buckling may occur due to the nonlinear contact between the pipe and drum in the offshore pipeline laying by reel-lay method. In this paper, material performance tests are carried out to obtain the nonlinear stress-strain constitutive models for high density polyethylene (HDPE) material and steel strip. Meanwhile, full-scale tensile tests are also conducted to acquire the tension-strain correlation of metallic strip flexible pipe (MSFP). Then, shell element and solid element are combined to establish an ABAQUS multi-scale finite element model (FEM) for MSFP under the coiled laying condition. The proposed multi-scale FEM consists of three components, i.e. two simplified components and one fine component, which could accurately and efficiently simulate the mechanical properties of flexible pipe under the coiled laying condition. The results indicate that: due to the radial extrusion restriction of spiral steel strips, the Mises stress distribution of inner HDPE layer shows a more uniform spiral strip distribution than outer HDPE layer; the most dangerous condition for MSFP may be when it is just partially wound up on the drum; the effect of friction coefficient on the spiral steel strips seems obviously larger than the effects of traction force and drum diameter.