Permanent Plastic Deformation Research Articles

Method for identifying the impact load condition of thin-walled structure damage based on PSO-BP neural network.

Thin-walled structures (TWS) were widely used in engineering equipment, and may be subjected to impact loads to produce different degrees of structural damage during application. However, it is a difficult problem to determine the impact load conditions for these structural damages. In this study, we developed a novel method of identifying the impact load condition of the thin-walled structure damage, which is based on particle swarm optimization-backpropagation (PSO-BP) neural network. First, the known impact position and velocity are applied to the finite element model (FEM) of the TWS to produce permanent plastic deformation, and to fit the characteristic shape of the deformation is needed by invoking the multivariate polynomial function. Then, the method is devoted to build a basic data set. With impact position and velocity as input and function coefficients as output, a model of extended PSO-BP neural network is established. Besides, the basic sample set is expanded to solve the lack of samples. Ultimately, utilizing the expanded total sample set as training data, function coefficients, impact position and velocity will be outputted. On the basis of the known functional coefficients of deformed surfaces, a model of predictive PSO-BP neural network is established and predicted. Furthermore, we predicted the collision position and velocity using a conventional BP neural network in the same way. Finally, the predicted impact position and velocity is compared with the analysis results of the FEM, which verifies that the PSO-BP neural network algorithm has high accuracy.

Analysis of Wedge Lock Washer using the Finite Element Method

Washers with a so-called wedge-locking effect are available for the engineering industry. The manufacturer assures, as confirmed by the Junker vibration test, that the tension in the thread increases when the screw is unscrewed. This is due to the appropriate geometry of the washers, which always work together in pairs. On the outside, the washers have serrations which, when tightening the screw, cut into the material of the clamped part, leaving a permanent plastic deformation. On the inside they have wedges, the angle of which is greater than the angle of the helix of the thread. The subject of this work is a study of creating a simulation model that takes into account the discussed effect of wedge lock of the washers. This model will be used in the future for simulation tests of washers with a different geometry than the one proposed by the manufacturer.

On Modelling Approaches to the Influence of Mechanical Deformation on the Micromagnetic Activity in a Mild Steel

In this study an attempt is made to develop a theoretical modelling by which the influence of certain mechanical deformation factors on the micromagnetic emission behavior of a low-carbon steel can reasonably be described and estimated. This modelling consists of a simple kinetics – kinematics – aided approach of the pinning state – controlled domain wall motion by which appropriate specific parameters are introduced. In this aspect the basic notion of specific micromagnetic activity (s.m.a.) is introduced by which the energetic strength of the activity is reflected. In this way, the synergetic effect of the quantitative (count rate) and qualitative (voltage) the detected micromagnetic Barkhausen emission (MBE) is taken into consideration. Thus it is possible, theoretically, to give a prediction of the general trend of changes in the s.m.a. under the influence of the tensile elastic as well as plastic deformation. For instance, one can demonstrate that tensile elastic deformation cannot influence the s.m.a. whereas plastic one leads to an increase in this. Furthermore, one can also predict that increasing permanent (residual) plastic deformation, obtained after unloading from prior tensile loading, leads to an obvious decrease in the s.m.a. Similar decrease in the s.m.a. can also be predicted for increasing rolling deformation by means of the same modelling approach used for the permanent tensile plastic deformation. Owing to the good agreement with the experimental results and the simplicity of the proposed theoretical approaches that can be seen as a promising valuable tool for further similar studies.

Evaluation of the damping capacity of common CAD/CAM restorative materials

ObjectivesTo evaluate and quantify the damping capacities of common CAD/CAM restorative materials (CRMs) and to assess their energy dissipation abilities by comparing loss tangent and Leeb hardness data. MethodsLeeb hardness (HLD), together with its deduced energy dissipation data (HLDdis), and loss tangent values recorded via dynamic mechanical analysis (DMA) were determined for 4 ceramic, 13 composite, and 2 polymer-based CRMs as well as 1 metal. For Leeb hardness, ten indentations per material were performed on two separate specimens (12.0 × 12.0 × 3.5 mm3) after water storage (24 h; 37.0 ± 1.0 °C). For DMA, ten specimens (16.00 × 4.00 × 1.00 mm3 ± 0.05 mm) per material were investigated in distilled water (37.0 ± 0.5 °C) with a dynamic force of 1 N at 1.5 Hz. Each data set was analyzed using two-way analysis of variance (ANOVA) with material type and material nested in material type as factors. Post-ANOVA contrasts were performed using a Bonferroni adjustment for multiple comparisons (α = 0.05). Correlations between different parameters were tested (Pearson, α = 0.05). ResultsHLDdis data revealed the significantly highest damping capacity for metal and the lowest values for ceramics with composites and polymers in between. However, for loss tangent, the metal together with lithium disilicate glass-ceramics exhibited the lowest damping effects and polymer materials the highest results with composites likewise in between. A strong dependency of the loss tangent results on the filler content of the investigated CRMs was indicated (r = - 0.822, p < 0.001), while a positive and only moderate correlation between loss tangent and HLDdis was observed (r = 0.565, p < 0.001), which conversely revealed a very strong correlation (r = 0.911, p < 0.001) if the metal was excluded from the calculation. ConclusionsAlthough HLDdis and loss tangent values both allowed a distinct differentiation of the damping capabilities of various CRMs and the respective material types, HLDdis data appeared to more accurately describe the damping capacity of CRMs as the energy dissipation mechanism of permanent plastic material deformation, that is commonly observed for metals and some composite-based CRMs, is equally captured. This finding could be particularly interesting for the future development of new CRMs with improved mechanical properties as HLDdis data determination in principle is a very efficient and simple technique to entirely specify unknown damping capacities of materials.

A new constitutive model for permanent deformation of blood clots with application to simulation of aspiration thrombectomy

As a first line option in the treatment of acute ischemic stroke (AIS), direct aspiration is a fast and effective technique with promising outcomes. In silico models are widely used for design and preclinical assessment of new developed devices and therapeutic methods. Accurate modelling of the mechanical behaviour of blood clot is a key factor in the design and simulation of aspiration devices. In this study we develop a new constitutive model which incorporates the unrecoverable plastic deformation of clots. The model is developed based on the deformation-induced microstructural changes in fibrin network, including the formation and dissociation of the cross-links between fibrin fibres. The model is calibrated using previously reported experimentally measured permanent clot deformation following uniaxial stretching. The calibrated plasticity model is then used to simulate aspiration thrombectomy. Results reveal that inclusion of permanent plastic deformation results in ∼ 15 % increase in clot aspiration length at an applied aspiration pressure of 100 mmHg. The constitutive law developed in this study provides a basis for improved design and evaluation of novel aspiration catheters leading to increased first-pass revascularization rate.

Prediction method for plastic dynamic response of hull plate subjected to ice floe impact

Objectives Polar ships are often subjected to ice floe impact during navigation, particularly, hull plates may suffer permanent plastic deformation under extreme ice impact loads, affecting the safety and working performance of the ship, and greatly increasing the maintenance costs. Therefore, it is necessary to propose a method to predict the dynamic plastic response of hull structure under ice floe impact loads. Methods This paper analyzes the energy sharing mechanism of ice-hull interaction based on the energy analysis method and rigid-plastic theoretical method to predict the plastic dynamic response of hull plates. An analytical formula for the dynamic response of a hull plate under ice floe impact is proposed, and comparisons between the analytical and numerical results are made. Results The comparisons show that the presented analytical method is reliable, this simplified theoretical analysis method can provide designers with rapid prediction regarding the maximal plastic deformation and collision force of a hull plate under ice floe impact. Conclusions The research has giving it great significance for engineering applications.

Curve Fitting for Damage Evolution through Regression Analysis for the Kachanov-Rabotnov Model to the Norton-Bailey Creep Law of SS-316 Material.

In a number of circumstances, the Kachanov–Rabotnov isotropic creep damage constitutive model has been utilized to assess the creep deformation of high-temperature components. Secondary creep behavior is usually studied using analytical methods, whereas tertiary creep damage constants are determined by the combination of experiments and numerical optimization. To obtain the tertiary creep damage constants, these methods necessitate extensive computational effort and time to determine the tertiary creep damage constants. In this study, a curve-fitting technique was proposed for applying the Kachanov–Rabotnov model into the built-in Norton–Bailey model in Abaqus. It extrapolates the creep behaviour by fitting the Kachanov–Rabotnov model to the limited creep data obtained from the Omega-Norton–Bailey regression model and then simulates beyond the available data points. Through the Omega creep model, several creep strain rates for SS-316 were calculated using API-579/ASME FFS-1 standards. These are dependent on the type of the material, the flow stress, and the temperature. In the present work, FEA creep assessment was carried out on the SS-316 dog bone specimen, which was used as a material coupon to forecast time-dependent permanent plastic deformation as well as creep behavior at elevated temperatures and under uniform stress. The model was validated with the help of published experimental creep test data, and data optimization for sensitivity study was conducted by applying response surface methodology (RSM) and ANOVA techniques. The results showed that the specimen underwent secondary creep deformation for most of the analysis period. Hence, the method is useful in predicting the complete creep behavior of the material and in generating a creep curve.

Finite element-based analysis of buckling-induced plastic deformation

In recent years, the investigation of adhesion properties of thin films on brittle substrates is receiving more attention due to the spread of thin film applications (coatings, protective layers, conductive layers in microelectronics, etc.). However, a basic approach for adhesion measurements proposed by Hutchinson and Suo almost three decades ago is still widely used due to its easy applicability. This approach uses thin film spontaneous buckling using residual compressive stresses in the film, however, it is based on Euler beam theory and accounts only for elastic behavior. Modern material combinations may lead to permanent plastic deformations, even under the controlled experimental conditions according to the elastic model. This work aims at investigating the plastic deformation influence on the experimental procedure according to Hutchinson and Suo by the means of the finite element analysis on the specific Mo-Cu-glass system. The deformations of spontaneously formed buckles are compared between purely elastic, (more realistic) elastic-plastic model and previously published experimental results together with quantification of the dissipated energy via the current finite element model. The comparison of the two numerical approaches shows non-negligible plastic deformations of the spontaneously formed buckles which has an effect on the film deformed shape (corresponding to the experimental observations) as well as on the portion of the shear loading at the delamination crack tip. This indicates that the plastic deformation during the buckling delamination may have some impact on the stability of the delamination crack.

A deep neural network inverse solution to recover pre-crash impact data of car collisions

In this work, we have successfully developed a data-driven artificial intelligence (AI) inverse problem solution for traffic collision reconstruction. In specific, we have developed and implemented a machine learning computational algorithm and built a deep neural network to determine and identify the initial impact conditions of car crash based on its final material damage state and permanently deformed structure configuration (wreckage).In this work, we have demonstrated that the developed machine learning algorithm as an inverse problem solver can accurately identify initial collision conditions in an inverse manner, which are practically unique if we use permanent plastic deformation as the forensic data signatures. In other words, we think that the massive plastic energy dissipation process and the related big data will make final structure damage state insensitive to the initial car collision conditions. Thus, it provides an inverse solution for car crash forensic analysis by reconstructing the initial failure load parameters and conditions based on the permanent plastic deformation distribution of cars. This approach has general significance in solving the inverse problem for engineering failure analysis and vehicle crashworthiness analysis, which provides a key contribution for the unmanned autonomous vehicle and the related technology.

Research on the Bearing capacity of aircraft metal skin with pit damage

Pit is a kind of damage form that often occurs in the daily operation process of aircraft. It is formed by permanent plastic deformation due to the impact of foreign objects. In addition to the stress concentration caused by structural geometric changes, it will also produce local residual stress in the interior. Its impact on fatigue cannot be evaluated only through the stress concentration analysis of structural geometric changes. In this paper, the bearing capacity of the damaged metal skin dent is studied. By establishing the finite element model, the stress of the intact structure and the dent with different width depth ratio is compared and analysed.

Application of Sentinel-1 and-2 Images in Measuring the Deformation of Kuh-e-Namak (Dashti) Namakier, Iran

Kuh-e-Namak (Dashti) namakier is one of the most active salt diapirs along the Zagros fold–thrust belt in Iran. Its surface deformation should be measured to estimate its long-term kinematics. Ten Sentinel-2 optical images acquired between October 2016 and December 2019 were processed by using Co-Registration of Optically Sensed Images and Correlation (COSI-Corr) method. Forty-seven Sentinel-1 ascending Synthetic Aperture Radar (SAR) images acquired between April 2017 and December 2019 were processed by using Small Baseline Subset Synthetic Aperture Radar Interferometry (SBAS-InSAR) method. The deformation of Kuh-e-Namak (Dashti) namakier was measured using both methods. Then, meteorological data were utilized to explore the relationship between the kinematics of the namakier and weather conditions and differences in macrodeformation behavior of various rock salt types. The advantages and disadvantages of COSI-Corr and SBAS-InSAR methods in measuring the deformation of the namakier were compared. The results show that: (1) The flank subsides in the dry season and uplifts in the rainy season, whereas the dome subsides in the rainy season and uplifts in the dry season. Under extreme rainfall conditions, the namakier experiences permanent plastic deformation. (2) The “dirty” rock salt of the namakier is more prone to flow than the “clean” rock salt in terms of macrodeformation behavior. (3) In the exploration of the kinematics of the namakier via the two methods, COSI-Corr is superior to SBAS-InSAR on a spatial scale, but the latter is superior to the former on a time scale.

RESEARCH OF CORROSION RESISTANCE OF HOT-ROLLED PIPES SUBJECTED TO SURFACE PLASTIC DEFORMATION USING CORROSION INHIBITORS

The oil and gas industry is the main consumer of pipes of a wide grades and geometries, up to 18% of the total metal pool. The applied hot-rolled pipes have technological drawbacks in the form of scale on the surface, coarse-grained decarburized surface layers, high surface roughness. These factors are initiators and intensifiers of the development of corrosion and fatigue processes. Therefore, improving the corrosion resistance of hot-rolled pipes for the oil industry is an urgent task. To some extent, the problem is solved by the use of surface plastic deformation of (SPD) and various coatings – galvanizing, enameling, the use of inhibitors. Increasing the durability of machine parts by surface plastic deformation is widely used in industry to increase the resistance to low-cycle and high-cycle fatigue of machine parts. Surface plastic deformation is based on the ability of a metal surface to perceive permanent plastic deformation without breaking the integrity of the metal. SPD is one of the simplest and most effective technological ways to improve the performance and reliability of materials. Strengthening the surface layer of parts by plastic deformation is an effective way to increase their durability. Importantly, SPD improves resistance to corrosion and contact fatigue. At the same time, the use of only SPD does not solve the problem of corrosion resistance. The use of surface plastic deformation with a decrease in roughness increases the anti-corrosion properties of steel in non-aggressive environments with low humidity (closed storage). In the simulated conditions of aggressive environments, the degree of corrosion damage to steel subjected only to SPD increases sharply. The use of surface plastic deformation with corrosion inhibitors significantly increases the anticorrosive properties of the treated surface. Of the three materials used in these studies, the best result was shown by a corrosion inhibitor used for drinking water, as well as for protecting osmotic water lines, contains polyphosphate and sodium silicate. The obtained result is confirmed by three types of research carried out.

A VALUABLE VIEW ON EVALUATION OF GENERAL MECHANICAL PERFORMANCES PERTAINING TO Bi-2223 SUPERCONDUCTING CERAMICS WITH VANADIUM ADDITION

In this research, our scientific group investigates the effect of vanadium addition in the Bi-2223 superconducting matrix on the general mechanical performance features by the help of experimental microhardness measurements conducted by a small indenter between the well-defined stress loads of 0.245 N and 2.940 N. Moreover, we determine the key mechanical design parameters including the elastic moduli with the hardness, stiffness coefficients, fracture toughness, yield strength, brittleness index and its opposite behavior (ductility) in the applied test loads given using the experimental data deduced from the microindentation tests. According to the experimental findings, it is oberved that the presence of vanadium content in the Bi-2223 crystal structure surpasses seriously the general mechanical performance and related parameters due to the degradation in the quality of grain boundary couplings, crystal structure and basic structural quantities as a consequence of the increment in the structural problems, permanent plastic deformations, crack-producing flaws and dislocations. In other words, the augmentation of vanadium compounds in the Bi-2223 superconducting lattice brings about the considerable enlargement in the responsibility to the static indentation loads. Namely, the sensitive level to the applied loads increases rapidly with the vanadium concentration. We also search the variation of graphs between the Vickers hardness parameters and applied test loads. In this respect, all the materials prepared in this work exhibit the standard ISE (indentation size effect) characteristics but within the decrement trend as the vanadium content level increases. In more detail, the impurity atoms damage harshly the ISE feature of Bi-2223 type-II superconducting ceramics. Additionally, we discuss the change of plateau limit regions coincided with the permeant artificial structural problems in the graphics. The vanadium leads to shorten the applied test load values for the plateau limit regions of Bi-2223 materials, stemmed from the enhancement the general structural problems. To conclude, the vanadium inclusions are ploughed to improve the general mechanical performance features and key mechanical design parameters.

Experimental and Numerical Analysis for the Mechanical Characterization of PETG Polymers Manufactured with FDM Technology under Pure Uniaxial Compression Stress States for Architectural Applications

This paper presents the numerical and experimental analysis performed on the polymeric material Polyethylene Terephthalate Glycol (PETG) manufactured with Fused Deposition Modeling Technology (FDM) technology, aiming at obtaining its mechanical characterization under uniaxial compression loads. Firstly, with the objective of evaluating the printing direction that poses a greater mechanical strength, eighteen test specimens were manufactured and analyzed according to the requirements of the ISO-604 standards. After that, a second experimental test analyzed the mechanical behavior of an innovative structural design manufactured in Z and X–Y directions under uniaxial compression loads according to the requirements of the Spanish CTE standard. The experimental results point to a mechanical linear behavior of PETG in X, Y and Z manufacturing directions up to strain levels close to the yield strength point. SEM micrographs show different structural failures linked to the specimen manufacturing directions. Test specimens manufactured along X present a brittle fracture caused by a delamination process. On the contrary, test specimens manufactured along X and Y directions show permanent plastic deformations, great flexibility and less strength under compression loads. Two numerical analyses were performed on the structural part using Young’s compression modulus obtained from the experimental tests and the load specifications required for the Spanish CTE standards. The comparison between numerical and experimental results presents a percentage of relative error of 2.80% (Z-axis), 3.98% (X-axis) and 3.46% (Y-axis), which allows characterizing PETG plastic material manufactured with FDM as an isotropic material in the numerical simulation software without modifying the material modeling equations in the data software. The research presented here is of great help to researchers working with polymers and FDM technology for companies that might need to numerically simulate new designs with the PETG polymer and FDM technology.

Study on the wind uplift failure mechanism of standing seam roof system for performance-based design

Compared with the current popular performance-based design (PBD) method, the current research of scholars on structural performance as a PBD foundation is insufficient. By considering the failure process of a standing seam roof system as an example, the wind-resistant performance of a roof system is evaluated by studying the wind uplift failure mechanism. The deformation process of roof-system components is obtained using numerical simulations. The analysis shows that the interaction between the vertical plate and anti-wind clip occurs in three stages: from non-contact and no interaction to anti-wind clips restraint vertical plate deformation, and finally to vertical plates drive anti-wind clip rotation. The changes in the structural responses (seam displacement and contact stress) and damage during the failure process of the roof system are obtained through experiments. Analysis of the variation in the curve of the structural responses with the load shows that the increase in the structural responses also occurs in three stages. Combined with the damage sequence, the aforementioned three failure stages are found to correspond to three different damage stages. In the first stage, the roof system is in an elastic stage. Second, the roof system is in the yield stage, and curling undergoes partial separation, which results in an interspace that is adverse to roof waterproofing. In the third stage, permanent plastic deformation occurs in the roof system, which leads to roof ponding. It was observed that the three-stage failure process represents different performance levels of the roof system, and some results from this study can be used as a guide for the definition of roof-system performance level in the future.

Rapid heat-activated post-tensioning of damaged reinforced concrete girders with unbonded near-surface mounted (NSM) NiTiNb shape-memory alloy wires

Concrete girders can suffer from serviceability issues due to excessive cracking and deflection. In response to this problem, a novel heat-induced post-tensioning technique utilizing unbonded near-surface mounted nickel–titanium–niobium (NiTiNb) shape-memory alloy (SMA) wires was proposed and evaluated. SMAs are a class of smart materials that can recover seemingly permanent plastic deformation when heated. The post-tensioning forces, thus, can be generated by restrained heat-induced shape recovery of SMA wires. Material characterization tests showed that 3.92-mm diameter NiTiNb wires with 2.5% prestrain can generate recovery stress of approximately 500 MPa when actuated via Ohmic heating in a restrained condition. The proposed post-tensioning system was experimentally evaluated in reinforced concrete girders measuring 2.3 m in length and 23 × 41 cm in cross-sectional dimensions. The girders were initially cracked to simulate typical girder damage. NiTiNb wires were then installed in the bottom cover of the girders and anchored at both ends. Subsequently, the wires were actuated via Ohmic heating, which triggered shape-recovery and generated post-tensioning stresses in the girder. The post-tensioning technique reduced the crack widths by up to 74% (370 μm) and recovered the residual midspan deflection by up to 49% (1.52 mm) in the cracked girders. Following post-tensioning, flexural loading up to failure showed that the cracked stiffness and ultimate moment capacity of the girders had increased by up to 31% and 45%, respectively, with a relatively small NiTiNb reinforcement ratio of up to 0.17%.

Identification of Sudden Stiffness Change in the Acceleration Response of a Nonlinear Hysteretic Structure

The integration of discrete wavelet transform and independent component analysis (DWT-ICA) method can directly identify time-varying changes in linear structures. However, better metrics of structural seismic damage and future performance after an event are related to structural permanent and total plastic deformations. This study proposes a two-stage technique based on DWT-FastICA and improved multiparticle swarm coevolution optimization (IMPSCO) using a baseline nonlinear Bouc–Wen structural model to directly identify changes in stiffness caused by damage as well as plastic or permanent deflections. In the first stage, the measured structural dynamic responses are preprocessed firstly by DWT, and then the Fast ICA is used to extract the feature components that contain the damage information for the purpose of initially locating damage. In the second stage, the structural responses are divided at the identified damage instant into segments that are used to identify the time-varying physical parameters by using the IMPSCO, and the location and extent of damage can accordingly be identified accurately. The efficiency of the proposed method in identifying stiffness changes is assessed under different ground motions using a suite of two different ground acceleration records. Meanwhile, the effect of noise level and damage extent on the proposed method is also analyzed. The results show that in a realistic scenario with fixed filter tuning parameters, the proposed approach identifies stiffness changes within 1.25% of true stiffness within 8.96 s; therefore, it can work in real time. Parameters are identified within 14% of the actual as-modeled value using noisy simulation-derived structural responses. This indicates that, in accordance with different demands, the proposed method can not only locate and quantify damage within a short time with a high precision but also has excellent noise tolerance, robustness, and practicality.

Mechanistic-empirical permanent deformation models: Laboratory testing, modelling and ranking

Abstract Geomaterials exhibit elastoplastic behaviour during dynamic and repeated loading conditions. These loads are induced by the passage of a train or vehicle which then generates recoverable (resilient) deformation and/or permanent (plastic) deformation. Modelling this behaviour is still a challenge for geotechnical engineers as it implies the understanding of the complex deformation mechanism and application of advanced constitutive models. This paper reviews on the major causes of permanent deformation and the factors that influence the long-term performance of materials. It will also present the fundamental concepts of permanent deformation as well as the models and approaches used to characterise this behaviour, including: elastoplastic models, shakedown theory and mechanistic-empirical permanent deformation models. This paper will focus on the mechanistic-empirical approach and highlight the evolution of the models, and the main similarities and differences between them. A comparison between several empirical models as well as the materials used to develop the models is also discussed. These materials are compared by considering the reference conditions on the type of material and its physical state. This approach allows for an understanding of which properties can influence the performance of railway subgrade and pavement structures, as well as the main variables used to characterise this particular behaviour. An innovative ranking of geomaterials that relate to the expected permanent deformation and classification (UIC and ASTM) of soil is also discussed because it can be used as an important tool for the design process.

Material Consequences of Hydrogen Dissolution in Palladium Alloys Observed from First Principles

Hydrogen embrittlement is one of the fundamental material science challenges to be faced under a potential “hydrogen economy”, as hydrogen will interact with the infrastructure for hydrogen production, storage, and transportation. While some embrittlement mechanisms have been proposed (especially for Fe), the behavior of dissolved hydrogen and impact on material properties is not fully understood in many systems relevant to hydrogen technologies. Here, hydrogen binding in pure Pd and alloys of Pd with Ag and Au was examined at a fundamental level from first principles in an attempt to elucidate how hydrogen-induced failure can be reduced in Pd alloys relevant to hydrogen production technologies. We show that PdAg and PdAu alloys (where the alloying metal is under 25%) likely suppress hydrogen-induced mechanical failure due to their reduced hydrogen solubility relative to pure Pd. This conclusion is based on our findings that alloying leads to higher vacancy stabilization and lower elastic constants upon hydrogen dissolution than for pure Pd but to unfavorable hydrogen dissolution beyond 25 at. %. The lowering of hydrogen solubility is strongly related to the combination of a lowering of the overall metal d-band center through alloy incorporation as well as changes to the metal Pauli repulsion factor, which is herein related to the metal matrix coupling element. Additionally, hydrogen loading and unloading were sequentially interrogated to mimic stress in storage materials. We find that permanent plastic deformation to the system is pronounced for alloyed systems, which in some cases made subsequent loading more favorable.

Failure analysis and solution study of 203 mm solid expandable tubular

The solid expandable tubular technology (SETT) is a permanent radial plastic deformation of the casing, which serves to block the leaking section and subsidize the casing. The difficulty of the SETT lies mainly in the material selection of the solid expandable tubular (SET) and the design of the expansion cone structure. The 20G steel casing pipe with 203 mm × 10 mm specification in dagang oilfield is subject to an expansion test with a variable-diameter expansion cone (an expansion rate of 20.2%), during which the casing pipe ruptured and failed. In this paper, the microstructure is analyzed by scanning electron microscope (SEM) and the failure analysis of SET is studied macroscopically by finite element analysis method, and the corresponding solution is proposed. The research shows that when the expansion ratio is 20.2% and the 20G steel casing is used as the material of SET, the maximum stress of SET during the expansion process exceeds the ultimate tensile strength of the material, the SET fracture fails, and 20G steel pipe is not suitable for use as materials of SET in the case of a large expansion ratio (20.2%). In this paper, the expansion cone is continuously optimized. It is found that the single-stage expansion cone is more conducive to the expansion operation than the variable-diameter expansion cone. The expansion cone chamfer and friction coefficient have a significant influence on the driving force, and should be fully lubricated during the expansion operation. In addition, this paper also prefers 316L steel material with better plasticity and toughness. It is found that 316L can expand successfully without failure at large expansion ratio. The research results provide a theoretical basis for the material selection of SET and the structural design of the expansion cone, and have important significance for ensuring the success of the expansion work.