Creep Behavior Research Articles

Laboratory and numerical investigation of anisotropic creep behavior of transversely isotropic composite rock

Laboratory and numerical investigation of anisotropic creep behavior of transversely isotropic composite rock

Determination of creep behavior of vessel steel Q345R at elevated temperatures

Vessel steel Q345R is widely used in pressure applications in China due to its martensitic structure, often operating in high-temperature, high-stress environments. This study investigates its susceptibility to creep strain, which can lead to significant deformation and structural damage, compromising safety. Thermal creep tests for Q345R steel were conducted within the temperature range of 400 °C–600 °C under various stress ratios. Results indicate that, below 500 °C, stages I and II predominate creep curves, with stage II evolving slowly. However, as temperature rises, stage II becomes predominant, with stage III emerging earlier, especially under high stress, leading to accelerated creep and potential fracture. Temperature significantly influences creep rates, with even minor stress increments at elevated temperatures inducing substantial creep effects. Through fitting by creep strain curves, parameters for three different time hardening creep models were determined. Subsequently, material CREEP subroutines based on these models were developed and integrated into ABAQUS to simulate the entire creep test process. The simulation results validate the ability of calibrated creep models to accurately characterize Q345R steel's creep properties, facilitating the evaluation of safety in high-temperature service structures.

Well Integrity in Salt Cavern Hydrogen Storage

Underground hydrogen storage (UHS) in salt caverns is a sustainable energy solution to reduce global warming. Salt rocks provide an exceptional insulator to store natural hydrogen, as they have low porosity and permeability. Nevertheless, the salt creeping nature and hydrogen-induced impact on the operational infrastructure threaten the integrity of the injection/production wells. Furthermore, the scarcity of global UHS initiatives indicates that investigations on well integrity remain insufficient. This study strives to profoundly detect the research gap and imperative considerations for well integrity preservation in UHS projects. The research integrates the salt critical characteristics, the geomechanical and geochemical risks, and the necessary measurements to maintain well integrity. The casing mechanical failure was found as the most challenging threat. Furthermore, the corrosive and erosive effects of hydrogen atoms on cement and casing may critically put the well integrity at risk. The research also indicated that the simultaneous impact of temperature on the salt creep behavior and hydrogen-induced corrosion is an unexplored area that has scope for further research. This inclusive research is an up-to-date source for analysis of the previous advancements, current shortcomings, and future requirements to preserve well integrity in UHS initiatives implemented within salt caverns.

Reliability Risk Mitigation in Advanced Packages by Aging-Induced Precipitation of Bi in Water-Quenched Sn-Ag-Cu-Bi Solder.

Bi-doped Sn-Ag-Cu (SAC) microelectronic solder is gaining attention for its utility as a material for solder joints that connect substrates to printed circuit boards (PCB) in future advanced packages, as Bi-doped SAC is reported to have a lower melting temperature, higher strength, higher wettability on conducting pads, and lower intermetallic compound (IMC) formation at the solder-pad interface. As solder joints are subjected to aging during their service life, an investigation of aging-induced changes in the microstructure and mechanical properties of the solder alloy is needed before its wider acceptance in advanced packages. This study focuses on the effects of 1 to 3 wt.% Bi doping in an Sn-3.0Ag-0.5Cu (SAC305) solder alloy on aging-induced changes in hardness and creep resistance for samples prepared by high cooling rates (>5 °C/s). The specimens were aged at ambient and elevated temperatures for up to 90 days and subjected to quasistatic nanoindentation to determine hardness and nanoscale dynamic nanoindentation to determine creep behavior. The microstructural evolution was investigated with a scanning electron microscope in tandem with energy-dispersive spectroscopy to correlate with aging-induced property changes. The hardness and creep strength of the samples were found to increase as the Bi content increased. Moreover, the hardness and creep strength of the 0-1 wt.% Bi-doped SAC305 was significantly reduced with aging, while that of the 2-3 wt.% Bi-doped SAC305 increased with aging. The changes in these properties with aging were correlated to the interplay of multiple hardening and softening mechanisms. In particular, for 2-3 wt.% Bi, the enhanced performance was attributed to the potential formation of additional Ag3Sn IMCs with aging due to non-equilibrium solidification and the more uniform distribution of Bi precipitates. The observations that 2-3 wt.% Bi enhances the hardness and creep strength of the SAC305 alloy with isothermal aging to mitigate reliability risks is relevant for solder samples prepared using high cooling rates.

Bionic design and mechanical performance of spiderweb-inspired mesh fabrics

The mesh structure is widely applied due to its unique structure and exceptional performance, especially spider web structural materials, which have attracted widespread interest. However, the existing flexible spider web structural materials face problems such as low production efficiency and structural defects, constraining their practical application. This study proposed two types of no-knot mesh fabrics according to the topological structure of spider web and explored their mechanical properties. Both knitted loop divergent and ring spiral mesh fabrics showed excellent mechanical performance, with the ring spiral fabric demonstrating higher maximum failure forces (2217 N in tensile and 5738 N in bursting tests) and superior impact performance in terms of maximum impact force and energy absorption. Both fabrics exhibited similar creep behaviors and could withstand 70 J impact energy with an energy absorption rate around 90 %. This work may provide new strategies and inspiration for the preparation of high-performance flexible mesh materials and further helps in developing applications of spiderweb-inspired mesh fabrics in engineering fields.

Novel approach for predicting the creep behavior of ceramic fibers using dimensional analysis

Novel approach for predicting the creep behavior of ceramic fibers using dimensional analysis

Environmental Stress-Induced Fracture Behavior of Polypropylene Battery Separators: Insights into Creep Behavior and Mechanical Stability

Environmental Stress-Induced Fracture Behavior of Polypropylene Battery Separators: Insights into Creep Behavior and Mechanical Stability

The creep behaviors of red sandstone in northern Yunnan and its fractional order damage modelling considering relaxation time effect

The creep behaviors of red sandstone in northern Yunnan and its fractional order damage modelling considering relaxation time effect

The reduced order model for creep using dynamic mode decomposition

Given the computational challenges associated with finite element methods in analyzing creep behavior in high-temperature components, this work presents an advanced method for modeling thermal creep in complex structures through a reduced order model (ROM) developed via dynamic mode decomposition (DMD). The results indicate that the ROM using DMD can predict long-term structural responses related to creep based on short-term data with high accuracy, enhancing significantly computational efficiency. The application of ROM allows for the rapid estimation of creep effects in complex structures, like monoliths in the MegaPower reactor, thereby improving the design efficiency. The eigenvalues of the creep related ROM all fall in the unit circle on the complex plane, indicating that creep is a stable development process. The DMD with improved time mode coefficient can reconstruct strain-rate related plastic deformation and cyclic visco-plastic deformation process. Additionally, we derive the necessary stress updating algorithm and consistent tangent operator matrix for the 316H unified visco-plastic constitutive equation in 2023 edition ASME code, ensuring accurate modeling of material creep behavior under high temperatures in this paper. This work provides a valuable tool for the safe design and operation of critical components in nuclear engineering and other high-temperature applications.

Experimental study on creep-fatigue damage of hot central plant recycling asphalt mixture containing high RAP

The objective of this study is to delve into the nonlinear damage evolution mechanism of hot central plant recycling asphalt mixture under the influence of creep-fatigue interaction. A predictive model for lifespan, considering the interaction of temperature and load, was developed. Dynamic creep tests were conducted at different temperatures to assess the creep effect of the asphalt mixture under actual road temperature conditions. The investigation began by acknowledging the material's viscoelastic properties, thereby deriving the loss compliance value - a key indicator of temperature effects - using an equivalent conversion factor and a viscoelastic mechanics model. This allowed for the incorporation of creep behavior into the load system. Furthermore, to analyze the nonlinear damage mechanism and fatigue prediction mechanism, direct tensile fatigue tests were performed at different temperatures and different stress levels. The fatigue damage evolution law of hot central plant recycling asphalt mixture containing high RAP considering the creep effect was revealed, and the fatigue life evaluation method under the combined action of temperature and stress level was proposed. The results show that the fitting degree of the time-temperature conversion equation and the viscoelastic mechanics model to the test data is more than 0.9, and the derived loss compliance value better captures the creep effect. Based on the nonlinear creep-fatigue damage model, the damage law of high-RAP hot central plant recycling asphalt mixture was identified. The optimized fatigue life prediction model fully considers the combined effect of temperature and stress level and analyzes the influence parameters of the real state of pavement fatigue. The prediction accuracy is within the requirements of engineering applications. The model's predictive accuracy meets the criteria for engineering applications, enhancing the multifaceted damage coupling analysis approach for hot central plant recycling asphalt mixture and predict the service life of recycled pavements under complex conditions, establishing a groundwork for the prediction and assessment of long-lasting recycled pavements.

Thermomechanical EBM‐based modeling of time‐dependent creep behavior in semicrystalline polymers: Competitive viscoelastic impact of amorphous and crystalline sections

AbstractIn this study, the creep behavior of semicrystalline polymers was investigated based on time‐dependent thermomechanical characteristics of the amorphous and crystalline sections. To this end, different equivalent box models (EBMs) with simple or complex structures were designed to interconnect the system components and cover all of their likely interactions. To induce time‐dependency to the model, a variety of viscoelastic models (e.g., Maxwell, Kelvin–Voigt, Maxwell representation of standard linear viscoelastic [SLV] model, Kelvin representation of SLV model, Burger and developed Bingham–Norton) were incorporated with the EBM structures as its crystalline/amorphous components. A specific strategy was devised in order to separately indicate the particular effects of crystalline and amorphous sections along with stress concentration on the temperature‐dependent creep behavior of the system. This approach combined with validating the theoretical data against the creep test results, performed at 20, 40, and 60°C, helped to indicate the most efficient structure for EBM and the best applicable viscoelastic model component. Accordingly, based on the findings of the present study, it was revealed that the series arrangement of the amorphous and crystalline model components, represented by the Burger viscoelastic model, could provide the best predictions regarding the temperature‐dependent creep in semicrystalline polymers.Highlights Creep behavior of semicrystalline polymers at different temperatures. Representing the crystalline and amorphous sections using viscoelastic models. Evaluating different interactions in the semicrystalline polymers using EBMs. Comparison of the efficiency of different viscoelastic model components in EBM. Distinct impact of crystalline and amorphous sections on the system properties.

Investigation on role of heat-treated barley husk biosilica on fatigue, creep, and dynamic mechanical behavior of cotton microfiber-vinyl ester composite

Investigation on role of heat-treated barley husk biosilica on fatigue, creep, and dynamic mechanical behavior of cotton microfiber-vinyl ester composite

Influence of powder particle size distribution on the creep performance of Ti-48Al-2Cr-2Nb alloy fabricated via electron beam-powder bed fusion

The effects of particle size distributions (PSDs) on the microstructure and creep behavior of Ti-48Al-2Cr-2 Nb fabricated via electron beam-powder bed fusion (EB-PBF) were investigated. Three PSDs of 45–150 (PSD-A), 38–150 (PSD-B), and 38–180 µm (PSD-C) were used as powder feedstock. Widening the PSD range decreased the relative density of fabricated parts and promoted the formation of banding microstructure. Moreover, samples fabricated with wider PSDs had a higher volume of lack-of-fusion (LoF) defects; however, the content of gas pores decreased significantly in PSD-C, which was related to the presence of coarse powder particles. The volume of the LoF defects in PSD-C was approximately 2.8 times of the same defects in PSD-A, which influenced the creep performance (at 750℃) and failure mechanism of Ti-48Al-2Cr-2 Nb. A longer steady-state creep period at different stress levels was identified for the samples fabricated with the narrowest PSD (45–150 µm). Widening the PSD span also caused weakness in the creep properties and data scattering at higher stress levels of 300 and 350 MPa. The LoF defects and coarse grains accelerated the crack initiation and propagation in Ti-48Al-2Cr-2 Nb during creep. This study represents the first report on the impact of PSD on the creep properties of TiAl alloys fabricated via EB-PBF, which offers new insights and enhances understanding of the powder-process-microstructure-property relationship.

Viscoelastic creep model and parameter inversion of bond interface in steel plate reinforced tunnel lining

The interface filler material (epoxy resin) used for reinforcing tunnel linings with steel plates exhibits time-dependent mechanical properties, commonly referred as creep behavior. The creep behavior of the filler material will significantly influence the long-term service performance of the reinforced tunnel, especially considering the design service life scale of 100 years. This paper presents an experimental test and mathematical modelling to illustrate the creep mechanical behavior of bond interfaces within shield tunnels reinforced with steel plates. It was observed that in the initial moments of stress application, the bond interface demonstrates an instantaneous response through elastic strain and on-set of creep deformation stage at maximum stress value. Three stages can be characterized in the creep deformation process: the decay creep stage, the steady-state creep stage and the accelerated creep stage. In the accelerated creep stage, the bond interface rapidly deteriorated after experiencing 90 % of the ultimate shear stress for 186 hours or 90 % of the ultimate tensile stress for 96 hours. Based on the fractional-order calculus theory and drawing inspiration from the modeling principles of classical component combination models, a constitutive equation that accurately characterizes the creep mechanical behavior of the bond interface between steel plates and concrete linings was formulated. The model parameters are inversely computed using the principle of least squares and the accuracy of this model is validated through a comparison with the results of the creep tests.

Evolution of Long-Term Load Reduction Using Borrowed Soil

AbstractThe effectiveness of load-reduction techniques often diminishes due to creep behavior observed in geomaterials, as loess backfill is used, the load reduction rate of high-filled cut-and-cover tunnels (HFCCTs) after creep will decrease by 10.83%, posing a threat to the long-term stability of deeply buried structures such as HFCCTs. Therefore, a geotechnical solution is crucial to ensuring sustained effectiveness in load-reduction strategies over time. This study utilizes a finite-difference method to examine three promising measures for mitigating creep effects. Our analysis focuses on the time-dependent changes in earth pressure atop the cut-and-cover tunnel (CCT) and the internal distribution of cross-sectional forces, including bending moment, shear force, axial force, and displacement. Results indicate that the creep behavior of load-reduction materials significantly influences the internal force distribution. Furthermore, sustained load reduction is achieved when utilizing low-creep materials like dry sandy gravel as backfill soil, which needs to be borrowed from other sites. Additionally, integrating concrete wedges with load-reduction techniques facilitates a more uniform stress distribution atop CCTs.

Effect of MgO-based expansive agent on strengths, volume stability, and microstructures of C80 SCC in steel tube arch

In order to meet the requirements of concrete filling, vibration, and pumping during the construction of the concrete-filled steel tube (CFST) arch bridge, the C80 expansive self-compacting concrete (SCC) is prepared using the absolute volume method. This research investigates the effects of MgO-based expansive agent (EA) and water-to-binder ratio (w/b) on the fresh properties, mechanical properties, autogenous shrinkage, and creep behaviors of expansive SCC. The microstructure of expansive SCC is analyzed by scanning electronic microscopy (SEM) and nuclear magnetic resonance (NMR). Results show that, as the MgO-based EA content increases from 5 % to 10 %, its effect on fresh properties of SCC is negligible. The addition of EA retards the hydration reaction of cement at early ages, thus delaying the strength development. However, the long-term mechanical strengths of the SCC are enhanced, due to the expansion product refines the microstructure at later ages. Moreover, the 14-day autogenous shrinkage of SCC with 10 % EA content is eliminated and shows the micro expansion (155.3 με). The microstructural analysis shows that the porosity of SCC with 10 % EA content is 1.8 % while the pore throat below 0.1 μm accounting for 55 % and the pore size above 30 μm is negligible. This research reveals the mechanism of the effects of MgO-based EA and w/b on the volume stability of the SCC, facilitating the application of expansive SCC in CFST composite structures.

Interpretable Machine Learning Models for Prediction of UHPC Creep Behavior

The creep behavior of Ultra-High-Performance Concrete (UHPC) was investigated by machine learning (ML) and SHapley Additive exPlanations (SHAP). Important features were selected by feature importance analysis, including water-to-binder ratio, aggregate-to-cement ratio, compressive strength at loading age, elastic modulus at loading age, loading duration, steel fiber volume content, and curing temperature. Four typical ML models—Random Forest (RF), Artificial Neural Network (ANN), Extreme Gradient Boosting Machine (XGBoost), and Light Gradient Boosting Machine (LGBM)—were studied to predict the creep behavior of UHPC. Via Bayesian optimization and 5-fold cross-validation, the ML models were tuned to achieve high accuracy (R2 = 0.9847, 0.9627, 0.9898, and 0.9933 for RF, ANN, XGBoost, and LGBM, respectively). The contribution of different features to the creep behavior was ranked. Additionally, SHAP was utilized to interpret the predictions by the ML models, and four parameters stood out as the most influential for the creep coefficient: loading duration, curing temperature, compressive strength at loading age, and water-to-binder ratio. The SHAP results were consistent with theoretical understanding. Finally, the UHPC creep curves for three different cases were plotted based on the ML model developed, and the prediction by the ML model was more accurate than that by fib Model Code 2010.

Challenges related to elevated temperature during creep in a PM-HIP Ti-6Al-4 V alloy: The role of [formula omitted] dislocations and pyramidal [formula omitted] dislocations

In our current study, the impact of pre-creep treatment at 300 °C and 560 MPa for 1000 h on the subsequent creep behavior and properties at an elevated temperature of 400 °C have been examined. The characterization of the resulting creep deformation structure, including twins and dislocation morphology, was conducted using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). Additionally, we have focused on the fine crystallization behavior of the α phase during creep, as well as the study and discussion of the 〈a〉 dislocations and pyramidal 〈c+a〉 dislocations. Our findings indicate that the creep life at 400 °C and 560 MPa is significantly lower, by an order of magnitude, compared to samples without pre-creep treatment. During the pre-creep process at 300 °C, 〈a〉 dislocations were found to be active. Furthermore, the creep temperature was observed to reduce the critical resolved shear stress (CRSS) of pyramidal 〈c+a〉 dislocations, leading to increased dislocation activity at 400 °C compared to 300 °C. However, a substantial number of 〈a〉 dislocations activated during the pre-creep process were unable to accommodate the subsequent heating process, resulting in extensive intergranular fractures. Simultaneously, during the creep process, the α phase underwent marginal fine grain formation in the form of continuous dynamic recrystallization (CDRX), with its internal fine grain promoted by pyramidal 〈c+a〉 dislocations assisting 〈a〉 dislocation to form dislocation locks. These findings offer valuable insights into potential deformation mechanisms and failure causes of PM-HIP Ti-6Al-4 V alloy when subjected to elevated temperatures during creep.

Experimental study on mechanical damage and creep characteristics of Gonghe granite under real-time high temperature

It is significant to study the mechanical properties of hot dry rock (HDR) for the development of deep geothermal energy. At present, the creep behavior of granite under real-time high temperature is not fully understood. The creep behavior of granite at 25 ∼ 800°C was investigated by real-time high-temperature uniaxial compression and graded load creep tests, and the thermal damage mechanism of granite was studied by scanning electron microscopy (SEM) experiments. The paper systematically analyzes the evolution of mechanical indexes such as uniaxial compressive strength (UCS), elastic modulus, creep deformation, steady creep rate and long-term strength of granite under thermal-force coupling. The results show that the UCS and elastic modulus of granite increase with increasing temperature in the range of 25 ∼ 200 °C, and decrease with increasing temperature in the range of 200 ∼ 800 °C. The damage speed of granite is the fastest in the temperature range of 400 ∼ 600 °C. The steady creep rate of granite increases with the increase of temperature and stress level. The ratio of long-term strength to UCS decreases with increasing temperature, from 93.6% at 25 °C to 73.2% at 800 °C. The research results provide relevant thermal damage mechanical parameters and theoretical basis for the development of HDR.

Impact of structural anisotropy on compressive creep behaviors of composite rocks based on digital image correlation technology

Impact of structural anisotropy on compressive creep behaviors of composite rocks based on digital image correlation technology