Failure Pressure Research Articles

Numerical analysis of repaired wall loss defect pipelines for optimum composite wrap thickness

The paper presents the numerical analysis of failure pressure of wall loss defect metallic pipelines and validate it with experimental results. An optimization of composite thickness for repair of wall loss defect pipeline is also carried out using numerical analysis. A nonlinear explicit FE code with constitutive models for metallic steel and composite material to failure modelling was used. Three different cases: non-defective pipe, wall loss defective pipe and composite repaired of defective pipe are considered. It was found that the numerical results are in good agreement with the analytical results in all the three cases. The theoretical failure pressure determined by ISO/TS 24817 standard for wall loss defect pipe is highly conservative compared to the numerical failure pressure for the given composite repair thickness. Additionally, the numerical study on optimization of repair thickness revealed that lower composite repair thickness can also sustain the designed failure pressure (composite repair thickness of 8.4 mm can sustain the same designed pressure instead of 16.1 mm thickness), which implies there is scope to further reduce the composite thickness, which ultimately reduce the repair cost.

Analysis of the adhesive thickness effect on failure pressure of metal/composite hybrid joints in pressurized blister tests

Composite repairs are increasingly being used to restore the work capability of pipelines with through-wall defects by corrosion. In this context international standards, such as ISO and ASME are the references to design this kind of repair and to qualify such systems. The referred standards do not take into account the adhesive layer thickness (h) on the model for the calculation of the failure pressure (Pcr), as well as for the calculation of the energy release rate (γ). In this work an experimental investigation evidences the influence of the adhesive thickness on the failure pressure. In order to achieve these results, pressurized blister tests were performed in which the geometrical parameter (h) varied from 0,5 mm to 2,0 mm. Ultimately, an empirical model to calculate Pcr as when the critical energy release rate (γLCL) is a function of the adhesive layer thickness was proposed.

Failure Characteristics of Coal Seam Floor and Risk Assessment of Water Inrush Caused by Underground Coal Mining

Failure characteristics of the coal seam floor above-confined aquifer are key to evaluating the water inrush risk from the floor in the deep mining. At present, based on the analysis of water inrush impact indicators, mathematical evaluation methods are often used to evaluate the water inrush risk of a mining floor. This study proposes a theoretical risk assessment method for water inrush from the floor considering the failure characteristics of the coal seam floor above-confined aquifer. The 11301# coalface in the Wanglou colliery, Shandong Province, is considered as a case study. The mechanical model of the mining floor stress along the coalface inclination direction was established, and the analytical solutions of the vertical, horizontal, and shear stress and floor failure depth were derived. The floor failure mode along the coalface inclination direction is similar to the letter “lying flat-B” and the maximum and minimum failure depth is around 13 and 6 m. Furthermore, the dynamic failure characteristics of the floor during coal mining were simulated. Subsequently, the thickness of the floor key aquiclude was determined and the water inrush coefficient exhibits a certain trend from increasing to becoming stable in the mining process, that is, from 0.05 to 0.08 MPa/m. The analytical solution of the critical water pressure for floor aquiclude failure was derived based on the limit equilibrium theory. That is, the ultimate water pressure 3.9 MPa is greater than the actual water pressure 2 MPa, and there is no floor water inrush risk. Taking these into account, the water inrush risk of the mining floor above-confined aquifer was comprehensively analyzed and evaluated. The findings were deemed to be consistent with the actual mining case.

Standards and methods for dent assessment and failure prediction of pipelines: A critical review

Dent, a common mechanical damage on pipelines, is associated with a significant local plastic deformation. Dents can cause pipeline failures, especially when they are combined with other types of defects such as gouges, fatigue, corrosion, and cracks. In this work, a systematic review of various assessment methods and standards for pipeline dents, including the combination of a dent with other defects, is conducted. Generally, the methods available today are not sufficiently accurate and reliable to assess pipeline dents, especially the dent-defect combinations. For plain dents on pipelines, both the depth-based criterion and the strain-based criterion are commonly used in engineering. Their main problems include inaccuracy and conservatism. For a dent combined with other defects, the existing assessment techniques are not mature enough to give reliable results. Both experimental testing and numerical modeling through finite element (FE) analysis are capable of investigating the influence of dents and dent-defect combinations on burst failure pressure of the pipelines, although an approximation to the reality is still the main difficulty existing in the experimental testing and FE analysis. Nowadays, relevant studies on assessment techniques for plain dents, a dent with fatigue and a dent with a single gouge have been common in literature. The combinations of a dent with corrosion or cracks have been rarely assessed due to complicated mechanisms involving a multi-physics coupling effect. Development of novel assessment methods by integrating mechanical stress and strain, electrochemical reactions and steel metallurgy will be a key topic to accurately assess the dent-defect combinations for improved pipeline integrity.

The benefits of physical activity in middle-aged individuals for cardiovascular disease outcomes

Regular physical activity (PA) has a positive role in preventing cardiovascular disease (CVD). Due to a trend toward a more sedentary lifestyle, the middle-aged population (35–65 years) is at greater risk of developing CVD. It is well established that PA improves cardiorespiratory fitness and reduces the risk of cardiovascular mortality and cardiovascular events, including stroke, coronary heart disease, heart failure, hypercholesterolemia, atherosclerosis, diabetes, and blood pressure. PA can potentially decrease oxidative stress and systemic inflammation, which are the two main underlying mechanisms leading to CVD. By reducing CRP, TNF-α, INF-γ, NF-κB and increasing IL-10, IL-4, and IL-8, PA can prevent the initiation and progression of CVD in middle-aged adults, highlighting the importance of being physically active for this age group. The general recommendation for PA to prevent CVD is at least 150 min/week at a moderate level of intensity; the type of PA should be adapted to the fitness level and medical condition of the individual. However, standardized guidelines for middle-aged individuals with cardiovascular events still need to be established.

VALIDATION OF YOGA CAPSULE ON HYPERLIPIDEMIA

Background: -Prelude with the statement of health, is a state in which one is sound with physical, mental, social, and spiritual and absence any of above will be taken as unhealthy. There are a lot of factors which hamper the condition of health. Furthermore, hyperlipidemia is one of the conditions which leads one for disease and unhealthy. When Lipids increases in the blood or high level of fat is dissolved and ow through blood in circulatory system and this deposit in blood vessel's inner layer which creates blockages and hinder the smooth blood ow. Which is the risk factor for cardiovascular system, heart failure and high blood pressure. Hyperlipidemia also hamper the overall quality of life. Moreover, Yoga nowadays is being used as alternative medicine for the healthy lifestyle. The present study was conducted to validate and determine the effect of yogic practices on hyperlipidemia. According to the inclusion and exclusion c Methods: - riteria fortyeight pre-adult (18-24) & Adult (25-30) were selected for the study with the age range of 18 to 30 years (mean =26), selected biochemical dependent variables such as Total cholesterol (TC), Triglyceride (TG), High-density Lipoprotein (HDL), Non-Highdensity Lipoprotein (NHDL) and Low-density Lipoprotein (LDL) were measured Before and after intervention for each participant. Yoga capsules were intervened for 30 days. The pretest and posttest data were taken, saved, and tabulated to assess the efcacy of Yogic interventions. The simple random sampling technique was opted as selection procedure as per elimination standard (10%). After a four weeks Yoga intervention the Yoga capsule (Selected yogic Results: - practice) on day 30th posttest data were taken and assessed. The mean TC was 162.44 and 149.00 before and after the intervention respectively (P=2.495). The mean TG was 82.83 and 88.96 before and after the intervention respectively (P=0.074). The mean HDL was 48.37 and 43.57 before and after the intervention respectively (P=0.000859). The mean NHDL was 114.09 and 105.16 before and after the intervention respectively (P=2.5). The mean LDL was 97.52 and 84.51 before and after the intervention respectively (P=1.39). So, based on obtained results and evidence, it can be clearly seen that there was Conclusion: - a signicant change in the term of Total cholesterol, triglyceride, HDL, NHDL, LDL. We can say that the selective yogic practices signicantly effect the TC, TG, HDL,NHDL,LDL.

Methylglyoxal crosslinking increases the fracture toughness of gelatin hydrogels

The development of biocompatible hydrogels with high strength and toughness is an ongoing challenge in many tissue engineering and drug delivery applications. Glutaraldehyde crosslinking of gelatin is widely used but increases cell toxicity. We crosslinked bovine gelatin using glutaraldehyde (Control) and methylglyoxal (MGO), a metabolic by-product during non-enzymatic collagen crosslinking, and assessed changes in the material properties of the hydrogels. Scanning electron micrographs show large pores with plate-like walls in MGO hydrogels that help retain water. Monotonic compression tests demonstrate nonlinear stress-strain behaviors. MGO samples had 96% higher moduli as compared to Control hydrogels that had moduli of 4.77 ± 0.73 kPa (n = 4). A first-order Ogden model fits the data from Control and MGO hydrogels well as compared to the Mooney-Rivlin model and neo-Hookean hyperelastic models that fit the Control samples alone. We used cavitation rheology to quantify the maximum pressure for bubble failure in the hydrogels using blunt needles with inner radii of 75, 150, 230, and 320 μm, respectively. Pressures in the bubbles increased linearly with time and dropped sharply following a critical value. High-speed videography studies demonstrate a symmetry break from large spherical bubbles in soft control hydrogels to small ellipsoidal bubbles in stiffer MGO samples. We used the critical pressures to quantify the fracture energies of the hydrogels. MGO treatment increased the fracture energy by 274% from 12.92 J/m2 for control gels. Finally, we show that analytical equations for cavitation based on Ogden and Mooney-Rivlin models present challenges when computing the fracture toughness of hydrogels.

Effectiveness of exhaled nitric oxide for the prediction of non-invasive left atrial pressure in older people: a cross-sectional cohort study.

During left-sided heart failure (HF), left atrial and pulmonary venous pressure increase, which may lead to pulmonary congestion. Previous cohort studies, examining participants with symptomatic HF or rheumatic heart disease, suggest a relationship between increased left atrial pressure (LAP) and fractional exhaled nitric oxide (FeNO). To examine the strength of association between FeNO and echocardiographic assessment of LAP by the E/e' ratio, to determine if FeNO could be used to identify those with elevated LAP. This cross-sectional cohort study examined a subset of the OxVALVE cohort aged ≥65 years. Data collection was undertaken in primary care practices in central England. Each participant underwent a focused cardiovascular history and clinical examination. Standard transthoracic echocardiographic (TTE) assessment was performed on all participants, with the E/e' ratio calculated to obtain a validated surrogate of LAP. FeNO was measured in 227 participants. FeNO was higher in males compared with females and no different in participants with asthma, chronic obstructive pulmonary disease (COPD), or those using inhaled steroids. Participants with a high E/e' (>14) were older, with a higher proportion of females than males. There was no relationship between E/e' and FeNO, either when measured as a continuous variable or in the group with high E/e'. FeNO was not found to be an accurate predictor of elevated LAP in a primary care setting.

Buckling behaviour of auxetic domes under external pressure

In view of ongoing great interest in novel materials exhibiting Negative Poisson Ratio (NPR), the current study examines its influence on buckling behaviour of externally pressurized​ torispherical pressure vessel closures. Failure pressures are computed for the range of Poisson’s ratio: −1.0 ≤ν < 0.5. The following wall constructions are considered: (i) single auxetic layer, (ii) outer metallic skin supported on inside by an auxetic layer, and (iii) sandwich with auxetic core. Both metallic and auxetic layers are assumed to be isotropic, and exhibit elastic, perfectly plastic behaviour.Results of this numerical study show that the inclusion of auxetic can lead to 89% gain in failure pressures above auxetic-free configuration of the wall. The range of analysed diameter-to-wall thickness ratio varied between 666 and 2000. Two layer wall construction (metallic skin supported by auxetic layer), was found to exhibit better performance than the equivalent sandwich configuration.

Failure pressure prediction by defect assessment and finite element modelling on pipelines containing a dent-corrosion defect

Dent-corrosion defects are a typical combination of defects and pose a significant threat to the safety and integrity of energy pipelines. In general, the corrosion features rather than dents are considered the primary factor of fitness-for-service of pipelines containing a dent-corrosion defect. In this work, a finite element (FE) based model was developed to predict the failure pressure of pipelines containing a dent-corrosion defect and investigate its dominant factor. Parametric analysis results demonstrated that the presence of dents reduced the failure pressure of corresponding pipelines containing a single corrosion defect. The dominant factor of the failure pressure changed from corrosion feature to dent feature if (1) an increase in dent depth and a decrease in the pipe diameter-to-thickness ratio, (2) exceeding the critical dent depth by 8% of diameter (D), and (3) below the critical indentation radius by 10%D. Longitudinal dent gave a significant reduction of the failure pressure, making dent feature a dominant factor; Oppositely, the effect of the circumferential dent was marginal.

Prediction of First Ply Failure of Composite Pressure Vessels Under Internal Pressure: A review

Composite pressure vessels (i.e. types III and IV) are widely used for compressed natural gas (CNG) vehicles, as storage cylinders to reduce the weight while maintaining high mechanical properties. These vessels can achieve 70-80% of weight saving, as compared to steel vessels (type I). So, prediction of first ply failure and burst pressure of these vessels is of great concern. Thus, this paper involved a review of literature regarding the first ply failure and burst pressure of composite pressure vessels (types III and IV). The review included the researches related to the simulation, mathematical modeling, and experimental analysis. The study focused on simulation-related research more than others due to the complexities of mathematical modeling of such problems in addition to the high cost of experimental tests. The results indicated that the stacking sequence of layers, vessel thickness and the type of selected composites were the main factors that mainly affect the vessel burst pressure performance. Accordingly, the optimization in the vessel structure (composite fabric architecture) parameters plays an important role in the performance of burst pressure. This in turn will lead to a high vessel durability, longer life-time and better prediction of burst pressure. Furthermore, the study showed that the prediction of first ply failure is more important than burst pressure knowledge of pressure vessels because it gives an initial prediction of vessel failure before the final failure occurrence. This in turn, may prevent the catastrophic damage of vessel.

Effect of inclined layered soils on face stability in shield tunneling based on limit analysis

Owing to complex and lengthy geological processes, inclined layered soils are frequently encountered in geological and geotechnical engineering. Tunneling in such strata threatens and reduces the stability of tunnel face. Most existing studies only focus on the effect of horizontal layered soils on face stability. Therefore, to evaluate the stability of tunnel face when shield tunnel excavated along inclined layered soil, a 3D rotating rigid body collapse mechanism based on limit analysis is improved using discretization technique. The critical support pressure and failure mechanism derived from this method are practicable by the comparison with the results deduced by numerical simulation and existing researches. Several design charts for different occurrence of inclined strata are provided. The results show that the existence of inclined stratum will result in the asymmetric failure mechanism of tunnel face and the variation of active failure pressure. In addition, the proposed method is also used to analyze the stability of tunnel face under inclined ground. The results indicate that the dip of ground has a clear impact on the area of surface subsidence.

A generalized weighted yield criterion: Theoretical derivation and its application in the plastic failure analysis of pipeline with corroded defects

For the aim of predicting the failure pressure of pipelines accurately, a new yield criterion that embeds two physical parameters, i.e. the tension-compression ratio and the shear-tension ratio, is proposed by weighting the squares of the shear stresses. The yield criterion is proved to be universal and can convert into different yield criteria suitable for different materials. The experimental results show that the criterion can coincide well with the experimental data and can describe the yield characteristics of different materials very well. Base on the above research result, the mechanical analysis of a pipeline is executed based on the limit analysis method, and the analytical formulas of the burst pressures without and with defects are obtained by considering the strain-hardening behavior. The validation shows that both the theoretical values of burst pressures of pipelines with and without corroded defect based on the present yield criterion agree well with the experimental values. The sensitivity analysis is also carried out, which shows that the burst pressure of the uncorroded pipe decreases when the strain hardening exponent increases, while increases when the thickness-diameter ratio increases. In addition, the burst pressure of the corroded pipeline decreases when the defect depth or its length increases.

Timing of Treatment Outcomes and Risk Factors for Failure of BPAP in Patients Hospitalized for COPD Exacerbation.

Patients hospitalized for COPD exacerbation have an increased risk of mortality, particularly among those who fail bi-level positive airway pressure (BPAP) for hypercapnic respiratory failure subsequently requiring invasive mechanical ventilation. Therefore, we sought to investigate the treatment course of BPAP and factors associated with BPAP treatment failure. We performed a retrospective cohort study using real-world evidence to investigate subjects with COPD who were treated with BPAP during a hospitalization for COPD exacerbation. Treatment outcomes were defined within 7 d from BPAP initiation as either failure, persistent, or success. Failure was defined as death or progression to invasive ventilation. Persistent was defined as receiving BPAP during hospital day 7. Success was defined as liberation from BPAP prior to hospital day 7 and not meeting criteria for failure. Unadjusted multinomial logistic regression models were used to examine the association between BPAP treatment outcomes and 17 recipient characteristics. Among the 427 clinical encounters, 78% were successful, 10% were persistent, and 12% experienced failure. The median time to failure and success was 8 h and 16 h, respectively. Increasing age, body mass index (BMI), bicarbonate level, and creatinine level were significantly associated with either BPAP treatment failure, persistent treatment, or both. The first 8 h following initiation of BPAP is a critical time period where patients are at high risk for life-threatening decompensation. Careful consideration should be given to increasing age, BMI, bicarbonate level, and creatinine level as these factors were associated with BPAP treatment failure or persistent treatment.

Bleeding risk in patients hospitalized for non-ST-segment elevation acute coronary syndromes in Switzerland: performance of the CRUSADE score

Abstract Background Evaluation of bleeding risk is critical to the management of patients with non-ST-segment elevation acute coronary syndromes (NSTE-ACS). The CRUSADE score is the most established tool to estimate major bleeding events following the index NSTE-ACS. Purpose We aimed to assess the performance of the CRUSADE score and the predictive utility of the individual score variables in contemporary European populations. Methods The CRUSADE score was studied in prospectively recruited Swiss patients with NSTE-ACS included in the multicentre SPUM-ACS study (n=4'787) and main findings were validated in the nation-wide AMIS Plus registry (n=46'939). Major bleeding during hospitalization was defined as Bleeding Academic Research Consortium (BARC) class IIIB, IIIC, IV, or V. Discrimination was evaluated by the area under the receiver operating characteristic curve (AUC). Multivariable-adjusted risk ratios (adj RR) were estimated for each of the 8 score variables. Hematocrit estimates were based on hemoglobin concentrations in AMIS Plus. Analyses were performed on complete and imputed data (multiple imputation using chained equations). Results CRUSADE showed poor discriminatory performance (SPUM-ACS: AUC, 0.65; 95% CI 0.57 to 0.72) and low balanced accuracy (SPUM-ACS: 0.50). Risk predicted by CRUSADE exceeded the observed risk across all predefined risk categories (very low, low, moderate, high, and very high). Decision curve analyses suggested little to no net benefit from using the score. Adjusting for other score variables, signs of heart failure (adj RR, 3.83; 95% CI, 1.93 to 7.37), low hematocrit (adj RR, 2.16; 95% CI, 0.55 to 7.70; &amp;lt;31% vs. &amp;gt;40%), and low systolic blood pressure (adj RR, 2.70; 95% CI, 1.14 to 6.16; &amp;lt;100 mmHg vs. &amp;gt;121 mmHg) were the strongest predictors of major in-hospital bleeds in SPUM-ACS. These findings were similarly observed in AMIS Plus. Conclusion The CRUSADE score overestimates bleeding risk in NSTE-ACS. Among all 8 score variables, signs of heart failure, low hematocrit, and low systolic blood pressure are the strongest predictors of major in-hospital bleeds in contemporary patients with NSTE-ACS. Funding Acknowledgement Type of funding sources: Public Institution(s). Main funding source(s): Swiss National Science FoundationSwiss Heart Foundation

Experimental and numerical simulation of formed-in-place pipe liner for repairing water mains with void

The failure pressure of the rehabilitated pressure pipe-lined system is related to several factors including the void in the host pipe. In this paper, the internal pressure resistance test of FIPP (Formed-In-Place Pipe) liner spanning the circular voids of the host pipe is carried out. The relationship among the strain, vertical displacement and internal pressure of the FIPP liner is studied. A three-dimensional finite element model of the host pipeline-FIPP liner system was established based on ABAQUS to investigate the stress distribution disciplinarian of the FIPP lining surface and the stress loading path of critical elements were investigated. Considering the influence of circular voids with different diameters on the failure pressure of FIPP lining pipes, numerical study of DN300 FIPP lining with a wall thickness of 5 mm is carried out. The results show that the hoop stress in the center of the void is always greater than the stress in other positions. Axial rupture is the main failure mode of the FIPP lining under the hoop stress at the center point. The maximum stress criterion is accurate and reliable when used to estimate the failure pressure of the FIPP lining. The larger ratio of void diameter to pipe diameter leads to smaller failure pressure of the lining. These results support further trenchless rehabilitation technology development of FIPP lining design and widespread applications.

Computational coupled large‐deformation periporomechanics for dynamic failure and fracturing in variably saturated porous media

AbstractThe large‐deformation mechanics and multiphysics of continuous or fracturing partially saturated porous media under static and dynamic loads are significant in engineering and science. This article is devoted to a computational coupled large‐deformation periporomechanics paradigm assuming passive air pressure for modeling dynamic failure and fracturing in variably saturated porous media. The coupled governing equations for bulk and fracture material points are formulated in the current/deformed configuration through the updated Lagrangian–Eulerian framework. It is assumed that the horizon of a mixed material point remains spherical and its neighbor points are determined in the current configuration. As a significant contribution, the mixed interface/phreatic material points near the phreatic line are explicitly considered for modeling the transition from partial to full saturation (vice versa) through the mixed peridynamic state concept. We have formulated the coupled constitutive correspondence principle and stabilization scheme in the updated Lagrangian–Eulerian framework for bulk and interface points. We numerically implement the coupled large deformation periporomechanics through a fully implicit fractional‐step algorithm in time and a hybrid updated Lagrangian–Eulerian meshfree method in space. Numerical examples are presented to validate the implemented stabilized computational coupled large‐deformation periporomechanics and demonstrate its efficacy and robustness in modeling dynamic failure and fracturing in variably saturated porous media.

Genetically predicted blood pressure, antihypertensive drugs and risk of heart failure: a Mendelian randomization study.

Elevated blood pressure (BP) was associated with higher risk of heart failure, but the relationship between BP-lowering via antihypertensive drugs and diminution of heart failure was inconclusive. This study aimed to estimate the causal association of BP with heart failure, and explore the effects of BP-lowering through different antihypertensive drug classes on heart failure risk using Mendelian randomization analysis with genetic variants as instrument variables. Genetic variants associated with BP were derived from UK Biobank ( n = 317 754) and the genome-wide association study (GWAS) meta-analysis of UK Biobank and International Consortium of Blood Pressure ( n = 757 601). Heart failure summary association data were contributed by HERMES Consortium (47 309 heart failure cases and 930 014 controls). Inverse variance weighted (IVW) was performed to estimate causality between exposure and outcome, and weighted median was utilized as sensitivity analysis, and Mendelian randomization-Egger regression was used to identify pleiotropy of instrument variables. Multivariable Mendelian randomization (MVMR) was applied to control for the confounders. Genetically predicted SBP and DBP were associated with heart failure [SBP: odds ratio (OR) = 1.355, 95% confidence interval (CI) 1.201-1.529; DBP: OR = 1.348, 95% CI 1.213-1.498] in UK Biobank. Likewise, in the GWAS meta-analysis of UK Biobank and International Consortium of Blood Pressure, the causal associations were observed between SBP, DBP and heart failure (SBP: OR = 1.237, 95% CI 1.188-1.289; DBP: OR = 1.337, 95% CI 1.245-1.437). Genetically determined β-blockers and calcium channel blockers (CCBs) were associated with lower risk of heart failure (β-blockers: OR = 0.617, 95% CI 0.453-0.839; CCBs: OR = 0.730, 95% CI 0.625-0.851). No association was found between angiotensin receptor blockers (ARBs) and heart failure (OR = 1.593, 95% CI 0.647-3.924). When adjusted for smoking, alcohol, physical activity, fruit and vegetable intake, the results were stable. Our study indicates causal associations between SBP, DBP, and heart failure, and suggests the preventive effects of heart failure by BP-lowering using β-blockers and CCBs.

Analysis of the impact factor of burst capacity models for defect-free pipelines

The research on the failure pressure of perfect pipeline is the basis of evaluating the bearing capacity of defective pipeline. The applicability of impact factor of theoretical and empirical failure pressure prediction models for thin-walled pipes are evaluated with 77 full-scale burst test data. Impact factors analyzed in this study include diameter D, strain hardening exponent n, flow stress and yield criterion. The diameter D and strain hardening exponent n have less effect on the prediction of failure pressure of defect-free pipeline, while the flow stress and yield criterion have significant influence on the prediction of failure pressure. For the failure pressure assessment of defect-free pipelines, average shear stress yield (ASSY) criterion is the best applicable criterion, followed by Tresca and von Mises yield criterion. 1.0σu is the most accurate calculation method of flow stress for failure pressure of defect-free pipeline.

Phase field modeling of concrete cracking for non-uniform corrosion of rebar

Non-uniform corrosion of rebar in reinforced concrete will lead to concrete cover cracking, thus significantly reducing the durability of structures. A 2D mesoscale phase field model was developed to explore the failure behaviors of corrosion-induced cracking. The expansion of rust was described by a time-dependent non-uniform corrosion model. The phase field regularized cohesive zone model was employed to study the cracking pattern. The proposed model was validated by available experimental results in publications. The effects of several geometric parameters, such as concrete cover thickness, rebar diameter, and clear spacing, on the crack pattern and crack width of single and multiple rebar models were investigated. Finally, the influence of the ratio of cover thickness to rebar diameter on the failure pressure was discussed.