Creep Characteristics Research Articles

Structural design and motion characteristics analysis of dual-mode active swing arm tracked robot

Focusing on the demand for complex terrain traversal capability of mobile robots, this paper presents a mobile and creep dual-mode tracked robot configuration with capability of autonomous extrication, in response to solving the problem of tracked robots trapped due to insufficient obstacle-crossing capability. Based on the geometrical characteristics of parallelogram and its dynamic computation on the ground, a topological configuration of mobile tracked mechanism with the ability of creep is studied. An integrated structural design method of mobile chassis that integrates the swing arm and the tracked mechanism is proposed and a dual-mode active swing arm tracked robot structural model is established. The mobile and creep characteristics of the dual-mode active swing arm tracked robot are revealed through comparative simulations in multiple working conditions; Through the prototype tests in such typical working conditions as climbing, turning and obstacle-crossing, the feasibility of creep for the robot is verified and it is proved that the obstacle-crossing ability can be effectively improved. The research results provide theoretical support for improving the adaptability and possibility of mobile robots in complex terrain.

Impact of PVA-coated aggregate on concrete impermeability and creep characteristics under hydraulic pressure and development of a creep model

In marine engineering projects such as sea dikes, concrete must exhibit both exceptional impermeability and plastic deformation to prevent cracking and subsequent internal corrosion due to synergistic deformation with the foundation. This study enhances the interface transition zone (ITZ) and plastic deformation of concrete by applying a PVA film to the aggregate surface. We use nuclear magnetic resonance to investigate the internal pore distribution and conduct permeability tests to assess its impermeability. Utilizing a self-developed triaxial hydraulic creep apparatus, we tests the concrete's creep performance under hydraulic pressure. Compared with conventional waterproof concrete, the findings reveal that the PVA film on the aggregate surface significantly increases the water penetration pressure of the concrete and markedly enhances the momentary deformation and creep deformation under hydraulic pressure, significantly extending the time to creep. Furthermore, the study proposes a creep model incorporating a fractional derivative-based dashpot model, combined with the Burgers model. This research offers a novel approach and theoretical support for developing impermeable and plastic concrete suitable for marine engineering applications.

The role of Ni minor additions on the mechanical characteristics of Sn-1.5Ag-0.5 wt.% Cu (SAC155) Pb-free solder alloy

AbstractMicrostructure analysis, thermal behavior, and tensile creep characteristics of the Sn-1.5Ag-0.5Cu-x wt.% Ni (SAC155-xNi, x = 0, 0.05, 0.1, 0.2, and 0.5 wt.%) solder alloys have been examined. The Ni additions have greatly modified the microstructure of Ni-free alloy into bulky fibrous eutectic regions and included the contemporary (Cu, Ni)6Sn5, and (Ni, Cu)3Sn4 IMCs. Ni additions slightly increased solidus temperature and melting temperature of them. The results of tensile creep resistance have shown dependence on Ni content and testing temperatures due to bulky fibrous eutectic regions and finer IMCs. Creep rates vary with Ni content across all temperatures and stresses. The SAC155-0.05Ni alloy has the lowest and the SAC-0.0Ni alloy has the highest creep rates at all tested conditions. The delicate dispersed IMCs of Ag3Sn and Cu–Ni–Sn resulted in a significant increase in stress exponent (n$$\approx $$ ≈ 5–8), enhancing its deformation resistance. The $$n$$ n values of alloys decrease as the testing temperature rises due to a change in the dominant creep mechanism. The average values of activation energy (Q) of SAC155-xNi alloy ranged from 60.20 to 68.02 kJ/mol. These Q values are coherent to the process of pipe self-diffusion through dislocation cores.

Prediction of creep characteristics of superalloy bolts based on itransformer and θ projection method

Prediction of creep characteristics of superalloy bolts based on itransformer and θ projection method

Unravelling the dominant influence of microsegregation on creep rupture behaviour of additively manufactured inconel 718

This investigation focuses on unravelling the dominant influence of microsegregation and microstructure altered due to heat treatment cycle variation on creep rupture behaviour of additively manufactured Inconel 718 (AM-IN718). Two microstructural variants differing in the fraction of recrystallized grains while δ-phase being absent, were produced. A typical heat treatment (HT) cycle includes the stress-relieving of the as-built specimens at 980 °C, followed by solution treatment at 1080 °C (STA1080, a partially recrystallized microstructural variant) or 1150 °C (STA1150, a fully recrystallized microstructural variant), and double ageing (soaking at 720 °C for 8h and subsequent furnace cooling, followed by 8h at 620 °C and air cooling).Detailed microstructural characterization of two microstructural variants through correlative microscopy revealed a prevalent existence of Nb-rich precipitate-free zones (PFZ) in STA1080 than in STA1150. Creep characterization of the two microstructural variants in the temperature range of 625–675 °C and at 500–750 MPa demonstrated superior creep resistance in STA1150. The correlation of kinetic analysis and comprehensive post-deformation microstructural characterization suggests grain boundary cavitation as the main damage/softening mechanism and the reason for the difference in creep rupture behaviour between the two microstructural variants. The long-term exposure heat treatment methodology demonstrates that PFZs are the major influencing factor responsible for microsegregation-dependent creep rupture behaviour. Interestingly, the presence of the δ phase within PFZs appeared to retard cavity coalescence and failure during creep, despite its usual detrimental role in creep resistance.

Dynamic wheel-rail interaction of a train crossing a turnout under traction/braking behaviour and research on rail wear of the turnout

In order to study the dynamic behaviour of a vehicle passing through turnouts under traction and braking conditions, as well as its influence on the wear of turnout rails, a high-speed vehicle-turnout rigid-flexible coupling dynamic model is established based on the coupling dynamic theory of vehicle and turnout, using China’s No. 18 high-speed turnout and CRH380 high-speed EMU as prototypes. The model is used to analyse wheel-rail creep characteristics, wheel-rail contact mechanics, and wheel-rail wear under traction and braking conditions. The results indicate that when a high-speed train passes through a turnout under traction or braking conditions, the longitudinal creepage of the wheel-rail will change due to the rotative speed difference generated by traction or braking. Furthermore, due to the existence of the lead curve, the longitudinal creep rate of the wheel-rail becomes even more complex when passing through the turnout in the diverging route. The calculations reveal that the traction behaviour of the train leads to a significant increase in wear at the front of the switch rail and nose rail, while the wear number of the switch rail in the heel of the frog after 6m increases significantly under braking conditions. The different impact characteristics of vehicle traction and braking conditions on turnout rail wear obtained in this study can provide guidance for optimizing and grinding the profiles of turnout rails at the throat of railway stations.

Research of creep parameters of VVER reactor steel 15Kh2NMFA-A AT temperatures of 500 – 1200°C

The paper is devoted to the study of the creep characteristics of 15Kh2NMFA-A vessel steel in the temperature range of 500 – 1200 °C, which can be achieved during emergency operating conditions of VVER-type nuclear reactors. An analysis of the creep curves of the 15Kh2NMFA-A steel in the studied temperature range obtained during specimens tensile tests was carried out with the construction of the parametric Larson – Miller relationship. It is shown that in the temperature range of 600 – 850 °C the generalized Larson – Miller temperature dependence has a changed slope, resulting in a high error in estimating the time to fracture of 15Kh2NMFA-A steel under creep conditions in this temperature range. To reveal the reasons for the change in creep resistance in the specified temperature range, the studies of the metal microstructure using optical and scanning electron microscopy on specimens in the initial state and after creep testing were carried out. Studies of the microstructure of steel have shown that in the temperature range of 600 – 700 °C, coagulation of V(CN) type carbonitrides occurs, leading to a change in the slope of the Larson – Miller parametric relationship. It is shown that in the temperature range of Ac1 – Ac3 there is an abrupt change in creep characteristics associated with phase transformations. The feasibility of dividing the Larson – Miller parametric relationship into several sections depending on temperature, taking into account structural changes in the steel, is substantiated, which makes it possible to increase the accuracy of estimating the destruction time of 15Kh2NMFA-A steel by at least an order of magnitude. Based on the results of the study, a calculated dependence of the long-term strength of steel on temperature was obtained on a basis of 6,24 and 120 hours.

Features and Constitutive Model of Hydrate-Bearing Sandy Sediment’s Triaxial Creep Failure

In the longstanding development of hydrate-bearing sediment (HBS) reservoirs, slow and permanent deformation of the formation will occur under the influence of stress, which endangers the safety of hydrate development projects. This paper takes hydrate-bearing sandy sediment (HBSS) as the research object and conducts triaxial compression creep tests at different saturation degrees (20%, 30%, and 40%). The results show that the hydrate-containing sandy sediments have strong creep characteristics, and accelerated creep phenomenon will occur under the long-term action of high stress. The longstanding destructive power of the specimen progressively raises with the increase in hydrate saturation, but the difference in the triaxial strength of the specimen progressively increases. This indicates that the damage to the hydrate structure during long-term loading is the main factor causing the strength decrease. Further, a new nonlinear creep constitutive model was developed by using the nonlinear Burgers model in series with the fractional-order viscoplastic body model, which can well describe the creep properties of HBSS at different saturation levels.

Algorithms and software for processing images of the structure of metallic materials for the purpose of determining creep characteristics

The paper contains a description of the approach, algorithms, and software tool for image analysis of deformed material structures. The developed approach is based on the analysis of the microstructure of the material to identify important factors that affect high-temperature deformation during creep in a heat-resistant nickel-based alloy, namely, the dimensions of the channels and their orientation. The developed software tool uses algorithms for converting images into binary black and white using the Otsu method. The intensity of the gradient at each point of the image is visualized using the Sobel operator. Fragment boundaries are determined using the Canny edge detector. Straight line segments are found using the Hough transformation. The software tool is implemented in the Python programming language using the OpenCV library. The main components are described and a flow chart of the program is provided. With the use of the developed software, the transformation of the known experimentally obtained images of the structures of the specimens from heat-resistant nickel-based alloy CMSX-4 deformed at a temperature of 1273K and in a wide range of stresses at different time moments was performed. The results of the analysis of the dimensions of the g-phase channels in the alloy using quantitative evaluation of transformed binary images are discussed. The found characteristics were matched to the value of the creep strain rate, which was determined by calculation based on known experimental data. The possibility of determining the transition from the secondary creep to the stage of avalanche-like growth of strains and hidden damage is shown. For the considered example, the location of the channels in the representative image was determined. A technique for correcting creep curves with the involvement of material structure image processing data is proposed.

Numerical simulation of the creep of a turbine blade made of a monocrystalline alloy

The article is devoted to the creep model of a monocrystalline alloy and the development of a methodology for identifying material parameters based on the results of physical experiments. A finite element analysis of the creep of a gas turbine engine blade was performed. Creep is one of the most dangerous types of deformation in the operating conditions of turbine blades. In the process of studying the problems of assessing the strength of turbine blades of aircraft engines and power plants, special attention should be paid to the study of stress redistribution during creep. The characteristics of the crystallographic structures of modern turbine blades have a very significant influence on the progress of the crack development process during engine operation. To date, turbine blades are manufactured by the method of single-crystal casting. This type of blade material structure is characterized by orthotropic mechanical properties. This study considers the steady-state creep model of an anisotropic heat-resistant single-crystal alloy with cubic symmetry. The authors carried out a numerical simulation of the material parameters using the well-known literary creep properties of single crystals. An algorithm is described that allows you to determine some creep characteristics of single crystals. The parameters of the given ratios can be obtained after conducting direct experiments, or based on micromechanical analysis, using the example of composite materials. The authors calculated the creep constants of a typical heat-resistant monocrystalline alloy as a result of the approximation of its creep curves, which were obtained experimentally. Based on the Norton-Bailey equation and using the Maple Release 2021.0 calculation complex, a graph of the dependence of the rate of creep deformation on the level of load applied to the material was plotted, and the minimum rate of deformation and creep constants were also determined. The results of the calculations were used for finite-element simulation of creep on the example of a solid-state model of a high-pressure turbine blade. Several series of calculations were carried out on the basis of the ANSYS Workbench complex, in particular, the calculation of the elastic problem when the blade is loaded by centrifugal forces, as well as the accumulation of creep deformations at different exposure times. Graphs of the change in equivalent stresses and creep deformations as a function of time are plotted.

Influence of different cooling methods on the creep characteristics and damage model of layered limestone after thermal treatment

In the actual underground energy extraction projects, the long-term stability of the well wall surrounding rock through the layered rock body often faces the influence of complex factors such as joints, thermal and cooling. The laminated limestone as a common rock type with obvious laminated structure and petroleum reservoirs, under high temperature environment can directly relate to the stability and safety of underground engineering structures. This paper investigates the creep characteristics of laminated limestone under high-temperature natural cooling and water cooling, analyzing the correlation between creep deformation, creep rate, long-term strength, and the angle of laminations, temperature, cooling mode. It then introduces a non-constant fractional-order cohesive body to construct an improved model based on these findings. The results indicate that under the same temperature and cooling method, as the lamination angle increases, the long-term strength shows a V-shaped trend, while the creep rate shows an inverted V-shaped trend. Specifically, the water cooling conditions at 500 °C (0°, 30°, 45°, 60°, and 90°) are 85.75 MPa, 71.24 MPa, 42.30 MPa, 61.52 MPa, and 87.40 MPa, respectively. For specimens with the same lamination angle, the creep mechanical properties of specimens cooled by water are more deteriorated than those cooled naturally. Taking the 100 °C action stratified limestone, long-term strength (0°, 30°, 45°, 60°, 90°) corresponding to natural cooling are 120.15 MPa, 106.12 MPa, 72.71 MPa, 91.43 MPa, and 123.32 MPa, respectively, while the long-term strengths corresponding to water cooling are 116.96 MPa, 100.97 MPa, 70.65 MPa, 85.34 MPa and 119.63 MPa, respectively. Finally, by comparing with the experimental results of nodular limestone under different cooling methods, it is found that the creep damage model proposed in this paper is not much different from the experimental curves, and it can effectively express the creep deformation and mechanical behavior of laminated limestone after high temperature. The results and findings are important for optimizing the design and prevention of potential underground energy extraction project disasters, and also provide important data support.

Characterization of low-temperature creep and stress relaxation of an iron-based shape memory alloy (Fe-SMA) using in-situ synchrotron diffraction

Iron-based shape memory alloys (Fe-SMAs) are e-merging materials with extensive application in civil structures owing to their unique properties, including the shape memory effect. However, it is crucial to understand the time dependent behavior of Fe-SMAs for their effective application as pre-stressing element. In particular, behavior at individual stress, the underlying mechanism, and the transformation kinetics have not been investigated yet. To address these important fundamental research gaps, in-situ compression creep and stress relaxation experiments with high-energy X-ray diffraction (HEXRD) of a Fe-17Mn-5Si-10Cr-4Ni-1(V,C) Fe-SMAs were conducted. The time-dependent behavior of the Fe-SMA was investigated at different stress levels with respect to the yield strength (YS) at room temperature. The experimental result showed that the material exhibits a creep strain of up to 1.84 % and 56 MPa relaxed stress at test stress of 769 MPa (1.6 σYS) within one hour of holding. Stacking fault probability and phase volume fraction quantification provide an understanding of the mechanisms based on different stress levels. The transformation kinetics traced from the characteristics of HEXRD peaks offer further insights on creep depending on the contribution of {hkl} families. The paper concludes with an evaluation of the existing models for predicting creep and stress relaxation of Fe-SMA.

Surface and bulk viscoelastic stability of solvent-stored bulk-fill resin-based composite

ObjectiveInvestigate the effect of solvent-storage on surface hardness and bulk creep of fast photo-cured bulk-fill resin-based composite (RBC) compared to conventionally irradiated bulk-fill RBCs. MethodsThree bulk-fill RBCs were studied: Tetric® PowerFill (fast photo-cured bulk-fill RBC) (TPF), Tetric EvoCeram® (EVO), and GrandioSO® x-tra (GSOx) (conventional). Disk-shaped specimens of clinically realistic thickness (4 mm) were prepared from each material for: Group A: surface measurements (18 mm diameter) and Group B: 4 mm diameter for bulk compressive creep measurements. Group A disks were light-cured from the upper ‘occlusal’ surface for either 3 s or 20 s according to the manufacturer’s recommendation. Martens hardness (HM) of both top and bottom surfaces of each specimen were measured. Group B: 4 × 4 mm cylindrical specimens were fully cured to measure bulk creep (CB). A 20 MPa static compressive stress was applied for 2 h, followed by 2 h of unloading. Strain deformation was recorded continuously for 4 h. Both Martens and bulk creep studies were performed under the following storage conditions at 37 °C: (i) dry at 24 h post curing (baseline), and (ii) after 7 and 30 d of storage in two different media: distilled water (DW) and 75 % ethanol/water (75 % E/W). ResultsAt baseline, HM for all materials ranged from 587 to 439 N/mm2 (top) and 398 to 342 N/mm2 (bottom). After 30 d of solvent-storage, more pronounced HM changes were observed, with the bottom surface being more affected. Normalised HM for TPF decreased by 44 % after 30 d in 75 % E/W. Maximum creep strain ranged from 1.1 % to 2.1 % at baseline, and after 30 d in 75 % E/W this increased from 1.9 % to 2.9 %. Depending on the material and storage condition, the percentage creep strain recovery after 30 d ranged between 65.2 % and 80 %. Increased filler loading in the bulk-fill RBCs decreased the creep strain magnitude and increased the surface hardness. SignificanceSolvent storage decreased the Martens hardness of both upper and lower surfaces and increased the bulk creep characteristics of bulk-fill RBCs. Nevertheless, there was a similar relative stability in surface hardness and viscoelastic stability of fast-cured PowerFill compared to conventionally irradiated RBCs.

Experimental study on the mechanical properties of red sandstone with fractures under different loading rates

In order to study the effects of crack inclination angle and loading rate on rock mechanical properties, creep characteristics, and failure characteristics. Taking homogeneous red sandstone with different fracture angles as the research object, uniaxial compression tests and uniaxial compression creep tests were conducted at different loading rates. The results showed that under the same fracture angle, the loading rate was positively correlated with the peak strength, elastic modulus, instantaneous strain, creep strain, and steady-state creep rate of the sample, while negatively correlated with the peak strain. At the same loading rate, the mechanical properties and creep properties of the sample were controlled by the crack inclination angle α. With the increase of α, the peak strength, peak strain, instantaneous strain, creep strain and steady-state creep rate decreased first and then increased, and the elastic modulus increased. On the basis of rock creep testing, it is also important to establish a creep model that conforms to the actual test situation for studying rock creep characteristics. However, many models currently used cannot accurately describe the three stages of rock creep, especially the accelerated creep stage. Therefore, based on Burgers elements, this paper introduces plastic damage bodies based on damage rates and software components based on fractional calculus, A new creep model was obtained and its rationality was verified through experimental results. The results showed that the fit between the model and experimental data was above 0.97, indicating that the model can better describe the three stages of rock creep, especially reflecting the non-linear characteristics of the accelerated creep stage.

Experimental study on the macroscopic and mesoscopic mechanical characteristics of deep damaged and fractured rock

Most of the rock surrounding deep roadways is in a fractured state; fractured rock has significant rheological properties, and the time-dependent mechanical properties of fractured rock affect excavation construction, support design, and long-term stability of deep roadways. Triaxial compression and mercury intrusion tests are conducted on the bearing characteristics of severely damaged and fractured rock samples, indicating the strength degradation properties of these samples. The evolution of the internal pore structure in damaged and fractured rock samples is analyzed in relation to changes in unloading points (pre-peak stage, peak point, and post-peak stage), leading to the establishment of a quantitative evaluation index for rock damage based on the porosity evolution. Short-term rheological testing is performed on rock samples with varying degrees of damage and fracture, demonstrating the evolution of creep and stress relaxation characteristics. The findings contribute to a deeper theoretical understanding of the post-peak mechanical properties of coal and rock masses, which hold significant theoretical implications and can inform research on long-term stability in underground engineering applications, such as deeply buried roadways, tunnels, and chambers.

Deciphering the Indentation Creep Characteristics and the Metallurgical Aspects of the 9Cr1MoVNb(P91) and SS316LN Dissimilar Butt Joint

Deciphering the Indentation Creep Characteristics and the Metallurgical Aspects of the 9Cr1MoVNb(P91) and SS316LN Dissimilar Butt Joint

New insights into oxidation and creep characteristics of T91 heat-resistant steel in martensitic and ferritic states

This study systematically compared the oxidation and creep characteristics of T91 steel in both martensitic and ferritic states. Findings indicate the formation of mixed oxides, including Fe3O4, (Cr, Mn)2O3, and MnCr2O4, during the oxidation process. In the ferritic specimens, the oxygen diffusion channel is restricted due to the transition of M23C6 carbide. Moreover, the ferritic steel exhibits poor creep life, and a strong α fibre texture was observed. For T91 steel, appropriate thermomechanical treatment can lead to uniform distribution of M23C6 carbides within the matrix, achieving the optimal precipitation strengthening effect and resulting in improved high-temperature properties.

Analysis of dynamic disturbance and multistage shear creep damage evolution law of the weak intercalated layers in slope under the influence of coupled damage effect

Based on the damage characteristics of multistage shear creep in weak intercalated layers (carbonaceous mud shale) of slopes under the influence of dynamic disturbance, the effective bearing area method was used. A new coupled damage equation (dynamic disturbance damage, shear creep damage, and initial damage) was established through further derivation, and its applicability was demonstrated. The calculation method for the relevant coupled damage degrees was also provided. Furthermore, by targeting the three coupled damage factors and extending the Kachanov damage law, a time-dependent damage evolution equation for weak intercalated layers under the influence of the three coupled damage effects was established. The influence of different dynamic disturbance intensities on the evolution of multistage shear creep damage in weak intercalated layers of slopes under the influence of coupled damage effects was analysed. The results show that the damage to the rock mass caused by dynamic disturbance mainly occurs in the low-frequency stage (40–80 Hz). The instantaneous damage caused by dynamic disturbance to the shear plane of weak intercalated layers is not only affected by the intensity of the dynamic disturbance but also limited by the magnitude of the shear creep load. The influence of the dynamic disturbance intensity on the entire process of multistage shear creep damage of weak intercalated layers was analysed. With increasing of dynamic disturbance intensity, the cumulative coupled damage at the end of shear creep at all levels gradually exhibits linear evolution. The time-dependent coupling damage evolution process of weak intercalated layers was quantitatively characterized.

Fractional-order burgers model for coral concrete creep

With the rapid development of marine engineering construction, coral aggregate has been widely applied in practical engineering. Its creep characteristics must be emphasized, but only a few experimental studies have been conducted, and theoretical research has not yet been reported. In this study, based on the traditional Burgers rheological model and using the fractional order software components Able dashpot, constructs a fractional order creep model for coral concrete and provides a calculation method. Comparison shows that the traditional Burgers rheological model cannot adjust the creep rate and development degree in calculations, resulting in a large deviation between its predicted results and experimental values. However, the fractional order model established in this paper aligns with the creep development law of coral concrete, and its calculated values match well with experimental values, making it suitable for predicting the creep characteristics of coral concrete under different water-cement ratios. Sensitivity analysis of the fractional order can achieve effective control over the prediction of creep development in coral concrete in practical engineering. The fractional order creep model established in this paper can provide a basis for predicting and evaluating the long-term performance of coral concrete in practical engineering.

An experimental and theoretical study on the creep behavior of silt soil in the Yellow River flood area of Zhengzhou City

We took the silt soil in the Yellow River flood area of Zhengzhou City as the research object and carried out triaxial shear and triaxial creep tests on silt soil with different moisture contents (8%, 10%, 12%, 14%) to analyze the effect of moisture content on silt soil. In addition, the influence of moisture contents on soil creep characteristics and long-term strength was analyzed. Based on the fractional derivative theory, we established a fractional derivative model that can effectively describe the creep characteristics of silt soil in all stages, and used the Levenberg–Marquardt algorithm to inversely identify the relevant parameters of the fractional derivative creep model. The results show that the shear strengths of silt soil samples with moisture contents of 8%, 10%, 12% and 14% are 294 kPa, 236 kPa, 179 kPa and 161 kPa, respectively. The shear strength of silt soil decreases with increasing moisture content. When the moisture content increases, the cohesion of the silt soil decreases. Under the same deviatoric stress, the higher the moisture content of the silt soil, the greater the deformation will be. The long-term strength of silt soil decreases exponentially with the increase of moisture content. If the moisture content is 12%, the long-term strength loss rate of silt soil is the smallest, with a value of 32.96%. The calculated values of our creep model based on fractional derivatives have a high goodness of fit with the experimental results. This indicates that our model can better simulate the creep characteristics of silt soil. This study can provide a theoretical basis for engineering construction and geological disaster prevention in silt soil areas in the Yellow River flood area.