Residual Creep Research Articles

Towards Photocrosslinkable Lyotropic Blends of Organosolv Lignin and Hydroxypropyl Cellulose for 3D Printing by Direct Ink Writing.

Polymer blends containing up to 70% organosolv lignin content and lyotropic cellulose derivatives have been established as "lignin inks" for direct ink writing of fully biobased 3D parts. However, a fast-crosslinking mechanism is needed to improve throughput and design space. In this paper, UV-photocrosslinkable organosolv lignin/hydroxypropyl cellulose inks are formulated through doping with common photocrosslinkers. The most potent photocrosslinkers for neat hydroxypropyl cellulose, lignin and their blends are determined through a series of DOEs. Hydroxypropyl cellulose is significantly more amenable to photocrosslinking than organosolv lignin. The optimal photocrosslinkable ink formulations are printable and exhibit up to 70% gel content, although thermal post-curing remains essential. Chemical, thermal, and mechanical investigations of the photocrosslinked 3D parts evidence efficient crosslinking of HPC through its hydroxyl groups, while lignin appears internally plasticized and/or degraded during inefficient photocrosslinking. Despite this, photocrosslinkable inks exhibit improved tensile properties, shape flexibility, and fidelity. The heterogeneous crosslinking and residual creep highlight the need to further activate lignin for homogeneous photocrosslinking in order to fully exploit the potential of lignin inks in DIW.

Tunable Dual Self-Healing Composite Coatings with Self-Assembled Structures Regulated by Janus Nanoparticles.

The durability of concrete structures can be enhanced in a convenient and permanent manner through the surface protection of cementitious materials with composite polymer coatings. However, polymer coatings are susceptible to various mechanical and physical deterioration in complex and variable environments. In this paper, the theory of polymer microstructure regulation was employed to improve the sustainability of the protective performance of composite coatings. The self-assembled core-shell structure regulated by amphiphilic Janus nanoparticles is employed to modify the tunable polystyrene acrylate-polysiloxane self-healing coatings. The results demonstrate that the adhesion strength of the prepared self-assembled coating reached 3.7 MPa, which is sufficient to resist the damage to the microstructure of cementitious materials caused by physical erosion, seepage, and ionic corrosion. The self-healing coating, regulated by Janus particles, exhibited a residual creep of only 57.03% and a maximum loss angle tangent of 0.381. Furthermore, the material exhibited a superior shape memory function due to the presence of strong hydrogen bonding. The regulated self-healing coating repaired the polymer structural damage under mechanical and thermal deformation by bridging and filling effects. The coating demonstrated a tensile strength recovery of up to 71.23% in a wetted state, accompanied by a rapid restoration of its electrochemical properties and corrosion resistance. Furthermore, the self-healing emulsion penetrates the substrate defects and forms numerous polymer crystalline particles that effectively fill the microcracks.

Electrochemical Characterization Method of Laves Phase in 9Cr Martensitic Heat-Resistant Steel and Creep Life Prediction

The Laves phase formed during the long-term creep of 9% Cr heat-resistant steels plays an important role in their high-temperature mechanical properties. Detecting and quantifying the Laves phase is one of the main problems in predicting the creep residual life. This study detects and quantifies the Laves phase in various 9% Cr heat-resistant steel samples by anodic polarization. Both T92/P92 samples after creep and 9Cr ferritic martensitic samples after thermal ageing precipitate Laves phase particles, and the content of the Laves phase increases with the service time. Comparing the results obtained by the electrochemical method with those obtained by the traditional SEM observation method, it can be found that there is a similar two-stage linear relationship between the two results in all materials, which is related to the diameter change of Laves phase particles during service. According to the correlation between the Laves phase content and creep time, an extrapolation method for the prediction of the residual creep life is proposed. The results show that the creep life of P92 can be predicted by using the dissolved charge density of the Laves phase with high prediction accuracy. This method has the potential to evaluate the service states of materials and predict the long-term creep life in the industrial field.

Creep recovery of stress-annealed Zr-based metallic glass: Investigation based on the dynamic viscoelastic model

An isochronal creep recovery of a Zr-based material is discussed with a constructed dynamic viscoelastic model based on the Maxwell model concerning structural heterogeneity and relaxation. Creep strain retention occurs when elastically deformed and plastically deformed regions with long and short relaxation times, respectively, coexist upon stress-annealing treatment. Subsequently, the residual creep strain is released when relaxation is activated sequentially from the relaxation sites with the lowest activation energy during reheating. Stress-annealing temperature and time can affect the creep strain recovery magnitude and peak temperature for the corresponding strain rate, whereas the stress-annealing stress only affects the creep recovery magnitude. Therefore, this dynamic viscoelastic model offers new perspectives toward the understanding of metallic glasses.

A novel creep life prediction model for variable loads considering the sequence effect

Residual creep life prediction under variable creep loading is an important issue in structural design. The loading sequence has a significant effect on the rupture life, which refers to the sequence effect, including the temperature sequence at constant stress and the stress sequence at constant temperature. This paper investigates the creep life prediction model taking into account the sequence effect. First, the experimental results from the literature were collected to summarize the sequence effect they revealed. Then various creep life prediction models were reviewed and their main limitations were pointed out. A novel creep life prediction model was proposed based on the time fraction model. Finally, two-level tests were carried out on nickel-based superalloy FGH96 to validate the model. In addition, two-level and multi-level creep test results from public literature were used to validate. The results show that the proposed model effectively consider the sequence effect under various loading conditions.

Creep of autofrettaged thick-walled FGM cylindrical vessel

In this research work, the creep of thick-walled cylindrical vessels made of FGM with autofrettaged-treated was investigated using the analytical method. At different plastic depths and a variety of internal pressures for elastic modulus and yield stress constants ( n1 and n4), changes in residual creep strain rate (radial and circumferential) and final creep strain rate are investigated. The obtained results show that the circumferential stresses in the autofrettage have different values depending on the depth of the plastic. In the equivalent stress diagram, the resulting stress at the plastic points of the vessel reaches the yield stress of the FGM, and the stress decreases along the radius. If [Formula: see text] is increased from 1 to 1.8, the maximum creep strain rate decreases (for several n4, the dimensionless plastic depth is equal to 1.8). The results show that up to a dimensionless plastic depth of 1.5, the change in residual strain rate is negligible. The slope of the graphs for the dimensionless depths above 1.6 increases sharply. A comparison of the maximum circumferential stress as a function of plastic depth for the present work and the study by Darijani shows very good agreement between the two studies.

Residual Creep Life Assessment of High-Temperature Components in Power Industry.

A large percentage of power, petroleum, and chemical plants over the world were in operation for a long duration with the corresponding critical components being used beyond the design life of 30 to 40 years. It is generally more cost-effective to refurbish or modernize the degraded equipment or components, rather than to construct a new plant. Therefore, a reliable plant life extension assessment that can evaluate the critical components is needed. The key element in plant life extension is the residual life assessment technology. However, at present, there is still no general consensus among the industry players on the approach to adopt when performing residual life assessment for such a critical damage mechanism as creep. In this article, a three-level residual life assessment methodology is proposed as a general approach for high-temperature components prone to creep. A detailed validation of the selected guidelines and calculation models is also described. Eventually, an application of the three-level methodology to a real industrial case study is presented.

Prediction of the Residual Creep Life of SA335-P22 Steel Main Steam Pipelines

In this study, the comprehensive properties of a P22 high-temperature steam pipeline with moderate spheroidization were evaluated after more than 11,700 h of operation through a series of physico-chemical properties testing, especially for a creep test. The remaining life of the P22 high-temperature steam pipeline was analyzed and predicted by the θ parameter method, to guide the normal operation of the P22 high-temperature steam pipeline.

Posterolateral Corner Reconstruction Using Double Femoral Fixation With Adjustable Loop Cortical Suspension and Interference Screw

Background: The posterolateral corner (PLC) of the knee is a complex anatomic region of the knee comprising the popliteus tendon, the popliteofibular ligament (PFL), and the fibular collateral ligament (FCL). Treatment of PLC injuries is based on the degree of varus and rotational instability on preoperative examination and is recommended in grade 3 injuries.1,6 Technique Description: The key concept of this new surgical technique is to use adjustable loop cortical suspensory fixation implants for initial femoral fixation of the popliteus and the FCL grafts. This allows for individual tensioning of the grafts prior to definitive fixation with an interference screw. An anatomic fibular tunnel is initially created, followed by popliteus and FCL anatomic femoral socket drilling. A TightRope RT implant is attached to the popliteus end of the graft and secured through a bone tunnel on the medial femoral cortex initially. The popliteus end of the graft is then pulled into the femoral socket before tunneling the graft through the fibular tunnel. A second TightRope RT implant is secured to the FCL end of the graft before securing it to the medial femoral cortex through a bone tunnel and pulling the graft into the drilled femoral socket. An interference screw is first used to secure the graft at the fibular tunnel. The knee is then taken to 60° where the TightRope device is used to remove residual creep and optimize final tensioning prior to final fixation with interference screw in femoral socket. With the knee at 30° of flexion, neutral rotation, and slight valgus, the same steps are repeated for FCL graft. A posterolateral capsular shift is completed for additional stability. Results: Residual posterolateral corner instability or failure after reconstruction surgery has been reported in 6% to 9.4% of surgical reconstruction case.2,3,5 The use of cortical suspensory devices in PLC reconstructions allows independent dialing of optimal graft tension for both the popliteus and FCL reconstruction before final interference screw fixation, therefore presumably limiting any residual creep and allowing for a double femoral fixation of the graft. Discussion: We describe a novel technique for posterolateral corner reconstruction which allows for optimal and individual tensioning of the structures of the posterolateral corner. Given the technique still uses well-described and validated graft choices and anatomic landmarks for reconstruction, we expect this new technique to allow for similar if not improved outcomes when compared with current gold standard.4

Empirical relationships between hardness, replica and strain and their roles in health monitoring based life assessment for aged power plant materials

In this paper, for the first time, a holistic empirical lifing approach, which accommodates the on-site information of replica, hardness and strain, is established based on a large amount of outage inspection data on ageing high temperature parent ½Cr½Mo¼V (CrMoV) material and has been used to illustrate how such routinely collected inspection data can be better utilized to provide the plant operator with predictions of residual creep life. The model differentiates between long term and persistent thermal softening behaviour revealed by change in hardness over time and short-term creep cavitation that accelerates material damage. Importantly the models developed are designed to be used iteratively with surface replica and hardness data available from an outage inspection. The study shows that the availability of more data will enable further refinements, but more importantly it emphasises the importance of systematically capturing this data and processing at the time of inspection to forecast residual life and then updating and tuning the model periodically at future inspections. The capture of strain data from pipe diametral measurements is also a routine outage activity and this data is included in the case study to demonstrate the capabilities in the residual life forecast by the new methods.

Degradation of microstructural and mechanical properties with serviced turbine blades

To study the degradation of directionally solidified turbine blades with different service times, four parts of four cross sections are selected to examine their microstructure through scanning electron microscopy. The width of the γ-phase channel, γ’ volume fraction, types of carbides, and elemental composition are chosen to characterize the damage. Creep tests are carried out at four heights on the upper and lower parts of the turbine blades, and the residual creep life is determined. The degrees of degradation of the blades are examined based on the microstructures and creep test results of the samples with respect to various service times. The results indicate that the quantitative description of the microstructure is consistent with the experimentally obtained results for the remaining creep life. The relationships between the residual lives of the small samples and the width of the γ-channel and γ'-phase volume fraction are presented in a three-dimensional graph. Based on the creep damage model, a method for predicting the remaining life of the turbine blades in service is established. The predicted results of the remaining life fit well with the model results. • The study of serviced turbine blades can obtain first-hand information. • The volume fraction and size of the γ' phase are closely related to the mechanical properties. • The degradation degree of the same part of the blades increases with the large increase of service time. • There is a good correlation between the mechanical properties and the icrostructural features of the blades. • The quantitative description of the microstructure is consistent with the test results of the remaining creep life . • Based on the creep damage model, a method for predicting the remaining lives of turbine blades in service was established.

A composite model for residual creep life assessment in T/P92 heat-resistant steel

In this paper, a composite model is proposed to describe the overall creep deformation by combining the power and logarithmic laws and considering the relationship between strengthening and softening in the creep deformation. The results demonstrate that the proposed composite model can fit well the creep curves of T/P92 heat-resistant steel under different stress and temperature values. Based on the relationship between the model parameter K and creep life, an extrapolation method of residual creep life denoted as the K-parameter method is proposed. The results demonstrate that the K-parameter method has high prediction accuracy for both low and high stress creeps under different temperatures. The proposed method has the potential for predicting the long-term creep life based on the primary creep data.

Rheological properties of dioctyl adipate-modified asphalt binder

ABSTRACT By referring to the successful application of a cold-resistant plasticizer in the plastic industry, dioctyl adipate (DOA) plasticizer was selected to improve the low-temperature performance of asphalt. Dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests were conducted to analyse the high and low temperature performance of plasticizer-modified asphalt binder. The residual creep rate ratio was put forward to evaluate the improvement effect of the anti-aging performance of asphalt binder. The rheological characteristics analysis shows that DOA could increase the viscous components in asphalt binder. However, with the increase of plasticizer content to 3.0%, the creep rate increased by 35% and the creep stiffness decreased by 39% at −24°C. The low temperature performance of DOA modified asphalt binder was improved by 30%. The residual creep rate ratio of the plasticizer-modified asphalt binder was more than 15% higher than base asphalt at the same temperature and softening point increment was 22.5% lower than base asphalt which means that the anti-aging performance was improved. Comprehensive analysis of the high and low temperature performance of DOA modified asphalt shows that the optimum content is 3.0%. Fourier-Transform Infrared Spectroscopy (FT-IR) indicates that the plasticizer and asphalt binder mainly undergo a physical blending reaction.

Evaluation of residual creep life of steels using macro-pillar creep testing and Omega method

Residual creep life evaluation is an essential part of Fitness-For-Service (FFS) assessment for engineering components operating at elevated temperatures. This paper elaborates a new evaluation approach based on macro-pillar compression testing (MPCT) and Omega method. The MPCT creep test was performed at the same stress level as the tensile creep test by adjusting the testing load using an algorithm, which is also provided in this paper. The barreling effect of MPCT creep test was corrected by two proposed parameters, which were calibrated using finite element method with 6 types of Cr-Mo alloys from API 579. Finally, a 1.25Cr-0.5Mo-Si steel was prepared for both MPCT and round bar tensile creep tests at 550 ℃ and different initial stress levels. The predicted residual creep life by MPCT has an error of 2.2% at 140 MPa, 6.4% at 160 MPa and 13.5% at 180 MPa.

A Grain Size-Dependent Equation for Creep Rupture Life of Grade 91 Steel Verified Up To 233,000 Hours

Abstract Grade 91 steel is widely used as steam pipes in ultrasupercritical (USC) steam boilers. In residual creep life assessment of the pipes by calculation, one needs creep rupture life of the steel as a function of stress and temperature in a time range longer than 105 h. Four regions with different creep rupture characteristics appear in a stress versus creep rupture life diagram of the steel. Main steam pipes made of the steel are used in a long-term region with low values of stress exponent and activation energy for creep rupture life (referred to as region G in this paper). Creep rupture lives of the steel in this region vary from heat to heat depending on their prior austenite grain size. This paper proposes a grain size-dependent equation representing creep rupture life of the steel in region G. The equation is verified with creep rupture data up to 232,833 h at 600 °C. Region G is absent in some heats with a large grain size. The equation can rationalize the absence in the heats. In a stress versus creep rupture life diagram of grade 92 steel, there is the same long-term region G. In the region, a creep rupture life of each heat is dependent on its grain size as is the case in grade 91 steel. The proposed equation accords well with the creep rupture lives of the grade 92 steel in region G.

Influence of creep deformation on sub-regional lumbar spine motion during manual lifting

Prolonged or repetitive spine flexion induces creep deformation of posterior spine tissues allowing for increased intervertebral motion beyond ‘normal’ limits, which may influence sub-regional (intersegmental) spine motion during subsequent manual lifting tasks. Using spine skin-surface kinematics, intersegmental lumbar spine motion was recorded over 20 minutes of prolonged static spine flexion and a subsequent manual lifting task (2 lifts every 3 minutes, 30 minutes total) in 14 participants. Results demonstrated that mid to lower lumbar intersegmental levels (i.e. L2/L3 to L4/L5) experienced the greatest overall creep deformation and range of motion during both prolonged flexion and manual lifting; however, overall range of motion during manual lifting was unaffected. Additionally, creep deformation did not completely recover within 30 minutes. Future work should continue to investigate the influence of this residual creep, as well as how overall creep deformation impacts spine neuromuscular control and stability, and ultimately the development of low back disorders. Practitioner summary: Mid to lower lumbar spine levels (i.e. L2/L3 to L4/L5) experienced the greatest creep deformation and range of motion during both prolonged flexion and manual lifting. Repeated lifting following prolonged flexion may limit creep recovery; however, overall lifting kinematic motion remained unchanged.

Creep Characteristics and Fracture Mechanisms of a Ni‐Based Superalloy with δ Phases at Intermediate Temperatures

The creep and fracture characteristics of a Ni‐based superalloy with preprecipitated δ phases are researched at the intermediate temperatures (630–670 °C). The influences of external stress and temperature on the creep properties and rupture mechanisms are analyzed. It is observed that the creep rupture time decreases, whereas the minimum creep rate increases, as the creep temperature or external stress is raised. With raising the external stress, the failure pattern changes from the mixed intergranular/transgranular mode to the intergranular fracture. A Monkman–Grant (MG) model is established to characterize the relationship between the residual creep life and experimental parameters (external stress and temperature). The small error between the forecasted and measured residual creep life verifies that the established MG model can be applied to evaluate the creep life of the studied superalloy.

Effect of compressive creep on fracture toughness: application to thermomechanical fatigue (TMF) life prediction

An experimental procedure is developed to identify and quantify a connection between compressive creep and the evolution of fracture toughness. Specifically, it is determined that an accumulation of compressive creep leads to a reduction in fracture toughness. Insight into the mechanism responsible for this observed behavior is pursued. Fractography performed following the fracture toughness tests shows a transition from ductile to brittle failure caused by the presence of residual creep. The quantified effect of compressive creep on fracture toughness is applied in a thermomechanical fatigue (TMF) model to simulate crack propagation in the single crystal nickel-based superalloy PWA 1484. Considering the coupling between compressive creep and decreased crack resistance led to significantly improved TMF life prediction. Further application of the developed experimental procedure to fully quantify the evolution of fracture toughness as a function of creep accumulation will lead to greater TMF and structural life predictive capabilities. This finding has implications for a wide variety of materials and applications involving high temperature dwell fatigue including in the aerospace, energy, and manufacturing sectors.

Simplified approach for creep evaluation in superheaters

This paper is focused on the estimation of temperature distribution on superheater tube bundles for the consequent creep damage evaluation. The precision of estimated temperatures is very important because it significantly affects residual creep life. Conditions in the tube bundle can be simulated using CFD, however, a full 3D simulation would be computationally intensive and not fit for practical use. In order to mitigate this issue, the new approach considered in this paper uses a series of 2D CFD simulations in multiple sections using known inlet flow conditions. Those conditions have been investigated in previous work using 3D CFD simulation of flue gas flow starting in the combustion chamber and ending just before the superheater in the second pass. The paper also deals with possible temperature differences that may arise due to simplifications in the proposed approach. Lastly, the residual creep life is estimated using obtained temperature distribution on the tube bundle.

Degradation and reduction of small punch creep life of service-exposed Super304H steel

To ensure the safety and structural integrity of a power boiler in thermal power plants, residual life management of superheater tubes at elevated temperature is needed. Over the decades, small punch (SP) creep testing has been widely used as an effective method for measuring creep life and creep properties of the boiler tube materials. In this study, a series of SP creep tests were performed at 650 °C with virgin and service-exposed Super304H stainless steels. The service period was 54750 h and 68550 h, respectively. The residual creep rupture life of the 68550 h serviced Super304H material decreased significantly when it was compared with the virgin and 54750 h serviced materials. Coarsening of the M23C6 precipitates along the grain boundaries made the adjacent region Cr-depleted, which could accelerate the formation of creep cavities at the grain boundaries. These microstructural degradations reduced the creep rupture life of the service-exposed materials. The Larson–Miller curve and the Monkman–Grant relationship were applied to predict the creep rupture life of service-exposed Super304H steels from the measured short creep rupture data.