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The compressive creep performance of Ti alloy is critical for the application of submersibles due to the pressure hull of deep-diving equipment mainly subjected to the seawater pressure during its service. The compressive creep behaviors and the corresponding deformation mechanism of Ti–6Al–4V ELI alloy under different applied stress amplitudes were investigated. It was found that the stress threshold for Ti–6Al–4V ELI alloy produced significant compressive creep damage was 0.8 times yield strength (Rp0.2), and the primary mechanism was {101‾0}⟨112‾0⟩ prismatic slip. Specifically, a large number of prismatic slips were preferentially activated in the αp grains with a relative high Schmid factor when the applied stress amplitude was greater than 0.8Rp0.2. As the applied stress amplitude increases, the prismatic slips were also activated in the αlath. Meanwhile, the Burgers relationship between αlath and βlamellae gradually destroyed due to the dislocation pile-up at the αlath/βlamellae interface. This investigation provides data support for the compressive creep performance evaluation of Ti–6Al–4V ELI pressure hull.

Creep, as a long-term deformation characteristic of shotcrete, significantly influences the load-bearing performance and durability of tunnel support structures. This study conducted creep tests on shotcrete under varying stress levels. The results reveal that shotcrete exhibits linear creep response within the stress range of 30%–40%, while the critical stress range for nonlinear creep response occurs between 40% and 50%. Employing SEM-EDS and XRD analysis methods, the impact of accelerator on the microstructure evolution and creep mechanism of shotcrete is explored. The accelerator accelerates the hydration of C3S, promoting the generation of AFt and C–S–H gel, leading to rapid solidification of the matrix and enhanced early strength. With the consumption of SO42− ions, AFt gradually transforms into AFm, resulting in increased matrix porosity. This phenomenon contributes to the reduced later-stage strength and substantial creep deformation of shotcrete. Based on experimental outcomes, this study evaluates the applicability of existing creep calculation models to shotcrete.

Thermomechanical loads are normally applied to refractory materials throughout their service life whichever is their practical use (e.g. steel ladle, rotary kiln furnaces). Among all the phenomena that the refractories are exposed to, the influence of creep behaviour is essential in determining their performance. Creep of refractories is usually represented by simple creep laws such as Norton-Bailey, which lack the capacity for generalization. The theta projection creep method, on the other hand, was proposed in the twentieth century to predict the creep of metals and alloys across different temperatures and stresses. The model is represented by one exponential equation capable of representing the complete creep curve, and coefficients that are temperature and stress-dependent, thus enabling the representation of complex nonlinear creep behaviour. Since refractories have similar creep responses to metals, the theta projection creep model is validated to characterize the compressive creep behaviour of alumina-spinel refractories at temperatures between 1200 and 1500 °C. Creep data from steady-state and transient temperature creep tests are used to calibrate the model. A regression by the least square method is applied to calculate the model's parameters. The model shows good flexibility in fitting the test data of the alumina-spinel refractory over the three creep stages. A temperature and stress dependence model is derived for the theta coefficients, reducing the number of material parameters necessary to describe the material's behaviour. The experimental creep curves are presented, as well as the curves resulting from the identified parameters. The implications of the chosen creep data set on the definition of the model and its adequacy for this novel application are discussed. [ABSTRACT FROM AUTHOR]

Titanium alloys have great potential as candidate materials for deep-sea facilities. Long-term creep deformation behavior of the pressure-bearing structures made of titanium alloys under alternating compressive stress has a direct impact on structural stability. The compressive creep evaluations of Ti-6Al-4V extra low interstitial (ELI) alloys with basketweave microstructure under alternating stresses have been carried out by a uniaxial compressive creep tester. The compressive creep deformations have strong stress sensitivity due to the larger creep strain by the higher applied compressive stress. The dislocation densities in a and β phases increase with the increase of applied compressive stresses. The dislocation slip and dislocation multiplication occur in a phases accompanied by high dislocations density in α phases caused by compressive deformation. The large strain concentration occurs at the grain boundaries of α/β phase due to dislocation plug after creep, which causes the grain boundary pinning. The compressive creep deformation of Ti-6Al-4V ELI alloys under alternating stress is a decelerating creep process and controlled by dislocation slip. The slight refinements of the grains and hardening have been confirmed after creep. The synergistic effects of dislocation multiplication, grain boundary pinning and grain refinements lead to strengthening the Ti-6Al-4V ELI alloys and decelerating the compressive creep. [ABSTRACT FROM AUTHOR]

In this paper, the effects of compressive pre-deformation and successive pre-artificial aging on the compressive creep aging behavior and microstructure evolution of the Al-Cu-Li alloy have been studied. Severe hot deformation mainly occurs near the grain boundaries during the compressive creep initially, which steadily extends to the grain interior. After that, the T1 phases will obtain a low radius–thickness ratio. The secondary T1 phases in pre-deformed samples usually only nucleate on dislocation loops or Shockley incomplete dislocations induced by movable dislocations during creep, which are especially prevalent in low plastic pre-deformation. For all pre-deformed and pre-aged samples, two precipitation situations exist. When pre-deformation is low (3% and 6%), solute atoms (Cu and Li) can be consumed prematurely during pre-aging at 200 °C, with dispersed coherent Li-rich clusters in the matrix. Then, the pre-aged samples with low pre-deformation no longer have the ability to form secondary T1 phases in large quantities during subsequent creep. When dislocation entangles seriously to some extent, a large quantity of stacking faults, together with a "Suzuki atmosphere" containing Cu and Li, can provide the nucleation sites for the secondary T1 phase, even when pre-aged at 200 °C. The sample, pre-deformed by 9% and pre-aged at 200 °C, displays excellent dimensional stability during compressive creep because of the mutual reinforcement of entangled dislocations and pre-formed secondary T1 phases. In order to decrease the total creep strain, increasing the pre-deformation level is more effective than pre-aging. [ABSTRACT FROM AUTHOR]

The benefits of tailored lattice topologies are limited in elevated temperature conditions without a clear understanding about the interplay between the metamaterial structure and the creep response of the base material. This study showed that the metamaterial structure causes the lattice compressive creep behavior to differ largely from that of bulk structures of the same base material. Inconel 625 FCCZ lattices and solid round bar specimens were crept in compression at two elevated temperatures and at three stress levels. The solid round bar specimens experienced only small increases in the steady state creep rate with a steady state exponent of 0.35 and 0.63 at 550°C and 650°C. The solid round bar specimens did not exhibit a deformation mechanism change over the temperatures and stress levels tested. The FCCZ lattices exhibited much larger changes in creep rates with changing stress and temperature with a steady state exponent of 18.3 and 20.2 at 550°C and 650°C, respectively. Additionally, the lattice specimens experienced three different failure behaviors with increasing temperature and stress from stable creep, to progressive buckling, and finally rapid collapse. Highlights: Compressive creep rupture life of lattices were temperature and stress dependent.Topology of the lattice dominated compressive creep behavior compared to base material.Magnitude of initial strut deflection controlled creep life of lattice specimens. [ABSTRACT FROM AUTHOR]

Microstructural characteristics and high-temperature creep behavior of the Mg–4Y‒xRE (x = 1, 2, 3 wt%) (WE41, WE42, WE43) alloys were investigated by compressive creep testing at 523–598 K under the applied stresses in the range 75–275 MPa for dwell times up to 5400 s. The effects of increasing rare earth (RE) elements on creep resistance of the materials were studied and it was shown that WE43 has the highest creep resistance. Cuboidal phases of Mg24Y5 in all alloys and formation of eutectic structure of Mg-Mg12RE in WE42 and WE43 alloys with considerable thermal stability were responsible for enhancement of creep resistance of the tested alloys. Creep stress exponent values were in the range of 4.1–4.4, 4.0–4.4 and 4.0–4.6 for WE41, WE42, WE43, respectively. The respective activation energies were found to be 168, 169 and 173 kJ mol−1 for the WE41, WE42, WE43. The values of stress exponent and activation energies implied that dislocation creep was the dominant deformation mechanism, in which slip occurs by cross slip of dislocations.

The room temperature compressive creep behavior is a key issue for the titanium alloys welded structural components served in deep-sea environment. In the present work, the compressive creep behavior of different areas for TC4 titanium alloy joints with vacuum electron beam welding was systematically studied, and it is found that the fusion zone (FZ) of TC4 titanium alloy joints has the minimum creep strain rate. This is mainly because the creep deformation of TC4 titanium alloy is mainly controlled by the movement of dislocations in the α or α′ phases, the size of α′ phase in FZ is small, and thus the dislocation slip is limited. MD simulation results have further revealed that the room temperature compressive creep nature of α-Ti can be regarded as a dynamic hysteresis phenomenon in plastic strain and is dominated by the dislocation movement. • The compressive creep behavior of TC4 titanium alloy joints was investigated. • The fusion zone of TC4 titanium alloy joints has the minimum creep strain rate. • The creep deformation is controlled by the movement of dislocations in the α phases. [ABSTRACT FROM AUTHOR]

Ultrahigh-performance concrete (UHPC) is a new class of concrete, differentiated from conventional concrete by clear distinctions in its material behaviors. Understanding and managing time-dependent properties is necessary for the appropriate use of any concrete-like material. This study investigated the time-dependent properties of a suite of commercially available UHPC-class materials, with the goal being to characterize the behaviors then propose predictive performance models. To achieve the goal of this study, compressive creep and shrinkage experiments encompassing different environmental conditions were completed. The objectives of this research were as follows: (1) quantify the compressive creep behavior of different UHPC-class materials; (2) assess the effects of strength, maturity, and loading age on UHPC creep and develop predictive equations; (3) investigate unrestrained shrinkage behaviors of UHPC-class materials; (4) evaluate the effects of different environments, including low-humidity and high-humidity and sealed conditions, on compressive creep and unrestrained shrinkage of different UHPC-class materials and develop predictive equations; and (5) determine the coefficient of thermal expansion (CTE) of UHPC-class materials at different ages. [ABSTRACT FROM AUTHOR]

Wrought high Nb containing (high Nb-TiAl) alloys are potential materials for low pressure turbine blades in aero-engines. The performance and microstructure evolution under high temperature creep condition is of importance to the service stability of these materials. In this study, the internal strain and FWHM evolution of an extruded TNB-based high Nb-TiAl alloy during compressive creep are characterized by in-situ high energy X-ray diffraction (HEXRD) technique for the first time. The compressive creep test was conducted under a constant load of 300 MPa at 900 °C for 10 h in vacuum. The final creep strain is approximately 1.72 %. The microstructure and phase constitution after creep shows little difference from that before creep. Lattice strain analysis shows that γ phase is plastically deformed while the α 2 phase deforms elastically due to the low creep strain. The lattice strain of α 2 grains is dependent upon the deformation of surrounding γ grains. Creep induces dynamic recovery, exerting a softening effect. A high number of dislocations are visible in the γ lamellae while almost no dislocations exist within the α 2 lamellae. α 2 lamellae are partially decomposed and refined via the α 2 →γ transformation. • γ phase deforms plastically while the α 2 phase deforms elastically during creep. • The lattice strain of α 2 grains is dependent upon the deformation of γ grains. • Dynamic recovery first occurs in the <110>γ//LD and <002>γ//LD oriented grains. • The α 2.→γ phase transformation happens during compressive creep. [ABSTRACT FROM AUTHOR]

The influence of thermal exposure on the compressive creep behavior of (TiB + TiC + Y 2 O 3)/α-Ti composites and the matrix alloy at different conditions was studied. The results showed that the α-Ti lamellae coarsened and β-Ti laths dissolved into pieces after thermal exposure. After compressive creep, there occurred significant dynamic recrystallization, which is characterized by fine equiaxed grains. Discontinuous dynamic recrystallization is the main recrystallization mechanism, while continuous dynamic recrystallization is the minor mechanism. The increase in creep temperature will increase the possibility of continuous dynamic recrystallization. The occurrence of dynamic recrystallization will significantly soften the titanium matrix, thereby increasing creep strain. The improved compressive creep resistance after thermal exposure comes from the precipitated silicides and stacking faults. During the compressive creep process, the size and quantity of silicides increase, and the S1 type silicides introduced by thermal exposure have a strong pinning effect on dislocations. Serious dislocation pile-ups have formed around the stacking faults. The stacking faults distributed inside α-Ti lamellae will suppress β-Ti dissolution, improving the interface stability and effectively reducing creep rate. • The reasons for the enhanced creep properties by thermal exposure were analyzed. • Dynamic recrystallization mechanism during compression process was discussed. • The response of silicides and stacking faults to creep and DRX were revealed. [ABSTRACT FROM AUTHOR]

In this paper, the effects of compressive pre-deformation and successive pre-artificial aging on the compressive creep aging behavior and microstructure evolution of the Al-Cu-Li alloy have been studied. Severe hot deformation mainly occurs near the grain boundaries during the compressive creep initially, which steadily extends to the grain interior. After that, the T1 phases will obtain a low radius–thickness ratio. The secondary T1 phases in pre-deformed samples usually only nucleate on dislocation loops or Shockley incomplete dislocations induced by movable dislocations during creep, which are especially prevalent in low plastic pre-deformation. For all pre-deformed and pre-aged samples, two precipitation situations exist. When pre-deformation is low (3% and 6%), solute atoms (Cu and Li) can be consumed prematurely during pre-aging at 200 °C, with dispersed coherent Li-rich clusters in the matrix. Then, the pre-aged samples with low pre-deformation no longer have the ability to form secondary T1 phases in large quantities during subsequent creep. When dislocation entangles seriously to some extent, a large quantity of stacking faults, together with a “Suzuki atmosphere” containing Cu and Li, can provide the nucleation sites for the secondary T1 phase, even when pre-aged at 200 °C. The sample, pre-deformed by 9% and pre-aged at 200 °C, displays excellent dimensional stability during compressive creep because of the mutual reinforcement of entangled dislocations and pre-formed secondary T1 phases. In order to decrease the total creep strain, increasing the pre-deformation level is more effective than pre-aging.

The high-temperature compression creep of additive-free β/α silicon carbide ceramics fabricated by rapid hot pressing (RHP) was investigated. The creep tests were accomplished in vacuum at temperature range 1500 °C–1750 °C and compressive loads of 200 MPa to 400 MPa. Under investigated condition the RHP ceramics possessed the lowest creep rate reported in the literature. The observed strain rates changed from 2.5 × 10−9 s−1 at 1500 °C and a lowest load of 275 MPa to 1.05 × 10−7 s−1 at 1750 °C and a highest load of 400 MPa. The average creep activation energy and the stress exponent remain essentially constant along the whole range of investigated parameters and were 315 ± 20 kJ∙mol−1, and 2.22 ± 0.17, respectively. The suggested creep mechanism involves GB sliding accommodated by GB diffusion and β−α SiC phase transformation. [ABSTRACT FROM AUTHOR]

Creep behavior is very important for the selection of refractory materials. This paper presents a methodology to measure the compressive creep behavior of fired magnesia materials at elevated temperatures. The measurements were carried out at 1150–1500 °C and under compression loads from 1–8 MPa. Creep strain was calculated from the measured total strain data. The obtained creep deformations of the experimental investigations were subjected to detailed analysis to identify the Norton-Bailey creep law parameters. The modulus of elasticity was determined in advance to simplify the inverse estimation process for finding the Norton-Bailey creep parameters. In the next step; an extended material model including creep was used in a finite element analysis (FEA) and the creep testing procedure was reproduced numerically. Within the investigated temperature and load range; the creep deformations calculated by FEA demonstrated a good agreement with the results of the experimental investigations. Finally; a finite element unit cell model of a quarter brick representing a section of the lining of a ferrochrome (FeCr) electric arc furnace (direct current) was used to assess the thermo-mechanical stresses and strains including creep during a heat-up procedure. The implementation of the creep behavior into the design process led to an improved prediction of strains and stresses.

One of the characteristics of Titanium alloys is that they are prone to creep due to the service conditions under high-pressure, such as deep-sea equipment. The compressive properties and deformation mechanism of Ti-6Al-4V-xSi-ySc alloys at room temperature are investigated in this study. The alloy samples are subjected to uniaxial compressive and creep tests. The obtained compression creep properties at room temperature follow the power-law function, and creep is mainly found in the first and second stage. Si and Sc are observed to improve the creep properties where the latter shows significant effect. This can be attributed to the strengthening of the solid solution of Si and Sc. Sc and Si strengthen the α and β phases respectively. The stability of these phases contributes to increasing the creep resistance of Titanium alloys. The creep resistance mechanisms of the alloys involve dislocation movement and twins.

A polymer-bonded explosive, also called PBX or plastic-bonded explosive, is an explosive material in which explosive powder is bound together in a matrix using small quantities (typically 5%–10% by weight) of a synthetic polymer. A PBX substitute material was made from sugar granules and polymer binder. Its compressive creep properties were investigated at room temperature. The creep deformation was found to depend strongly on the applied stress amplitude. Under an applied stress near the strength, creep deformation developed and reached the final rupture very quickly. A power law relationship, ε˙=4.14×10−8σ2.5,$\dot \varepsilon = 4.14 \times {10^{ - 8}}{\sigma ^{2.5}},$ was established between steady creep rate and applied stress. Microscopic observations show that the damage mechanism processes include mainly the intergranular and transgranular fractures, binder fracture, and peeling. Both porosity and granule size decrease almost linearly with increasing applied stress.

Compressive creep experiments were utilized to investigate the influence of small additions of 0.25 at.% Mn and 0.10 at.% Mo on the creep resistance of a cast Al-0.08Zr-0.02Sc-0.01Er-0.10Si at.% alloy. The Mn- and Mo-modified alloy displays significantly enhanced creep resistance at 300 and 400 °C, due to solid-solution strengthening and the formation of two types of precipitates: Al 3 (Zr,Sc,Er)(L1 2)-nanoprecipitates and α-Al(Mn,Mo)Si submicron platelets or cuboidal-shaped precipitates. The creep threshold stresses at 300 and 400 °C are 37 and 24 MPa, respectively, versus 19 and 15 MPa for the unmodified alloy. At 300 °C, the creep exponent n is found to change from 4.4 in the base alloy, to 3 in the modified alloy, consistent with a change from climb- to glide-controlled dislocation creep. The Mn- and Mo-modified alloy exhibits an as-cast grain-structure, which is finer (~0.35 mm versus 0.6 mm) and more equiaxed grains than the unmodified alloy, which is anticipated to enhance deformation by diffusional-creep. Nevertheless, diffusional-creep resistance at 400 °C remains high for the modified alloy, due to precipitation of submicron α-Al(Mn,Mo)Si-precipitates at grain boundaries (GBs). At 400 °C, the diffusional creep threshold-stress is ~14 MPa, three times that of the unmodified alloy, which also display fewer and coarser Al 3 (Zr,Sc,Er)(D0 23) precipitates at GBs. Creep resistance in the modified alloy does not deteriorate after 16 days of stress testing at 400 °C, highlighting the excellent coarsening resistance of the L1 2 - and α-precipitates. This new castable, heat-treatable aluminum alloy therefore represents an important technological advance for utilization at higher temperatures under stress. The modification of a castable Al-0.08Zr-0.02Sc-0.005Er-0.10Si at.% alloy, by the joint addition of 0.25Mn and 0.08Mo, produces a drastic increase in high-temperature mechanical properties, at temperatures as high as 400 °C, due to the dual precipitation of coarsening resistance Al 3 M (L1 2) nano-sized precipitates and α-Al(Mn,Mo)Si precipitates, as well as solid solution strengthening and grain boundary strengthening. Image, graphical abstract [ABSTRACT FROM AUTHOR]

To investigate the effects of over-lordotic curvature after lumbar fusion on the stress and deformations of the adjacent intervertebral discs under constant compressive loads. Two-level ovine specimens—including three vertebral bodies with two discs—were divided into two groups: Group A (to observe external deformation) and Group B (to observe internal stress and deformations of the discs). Each group consisted of three models: a) intact model, b) increased stiffness + unchanged curvature fusion model, and c) increased stiffness + curvature fusion model. Models were tested at a vertebral pressure of 0.4 MPa for 30 min. Creep deformations and stress distributions in the superior adjacent intervertebral discs were analysed using finite element models. Stiffness angle of the curvature model was increased by 5° and compared with the intact and stiffness models. In Group A, there was no significant deformation in the superior and adjacent intervertebral discs (P > 0.05), whereas creep deformations of the Group B discs increased significantly. Maximum deformations, with increases of approximately 3.7-fold and 2.8-fold in the vertical and horizontal directions, respectively, occurred at the anterior annulus fibrosus. The vertical and sagittal stress concentrations at the anterior annulus fibrosus had maximum differences of 1.0 MPa and 1.2 MPa, respectively. Under a continuous compressive load, over-lordotic fusion significantly increases the stress and deformation gradient of the nucleus polposus and annulus fibrosus in the superior, adjacent intervertebral disc, increasing the risk of damage and secondary degeneration of these discs when subjected to daily static loads. • The effects of over-lordotic curvature on intervertebral discs were investigated. • The stress deformation in ovine lumbar specimens was analysed. • Results indicate that the curvature increases stress and deformation gradients. • The curvature increases the risk of degeneration in intervertebral discs. [ABSTRACT FROM AUTHOR]

The effects of adding 0.08 at.% Cr or 1 at.% Zn to a dilute Al-0.11Zr-0.005Er-0.02Si at.% alloy are studied in terms of the precipitation behavior of Al 3 Zr (L1 2 -structure) nanoprecipitates and the resulting alloy's creep resistance. Although Cr and Zn additions do not affect measurably the precipitation kinetics or coarsening resistance, the modified alloys exhibit changes in dislocation creep resistance at 300 °C: the creep threshold stress is decreased by 17% (2 MPa) in the Zn-modified alloy and increased by 25% (3 MPa) in the Cr-modified alloy. This is attributed to a modification of the lattice parameter of Al 3 Zr(L1 2), which affects the ease with which matrix dislocations climb over the nanoprecipitates. The Zn-modified alloy exhibits Al 3 Zr(L1 2) nanoprecipitates containing 6–7 at.% Zn, as determined by atom-probe tomography, which reduces the lattice parameter by 0.17% as a result of Zn substituting for Al on its sublattice, as calculated utilizing density functional theory. The Al 3 Zr(L1 2) nanoprecipitates in the Cr-modified alloy contain 0.10–0.20 at.% Cr (1.2–2.5 times more than the matrix) and 0.28–0.51 at.% Er (a 60- to 100-fold enrichment). Erbium, which increases the lattice parameter misfit of Al 3 Zr(L1 2) with the Al matrix, is confirmed to be particularly potent in increasing the creep resistance of aluminum alloys containing L1 2 nanoprecipitates. An alloy design methodology for creep resistance is also validated, whereby precipitate compositions measured by APT are input to DFT calculations to determine their effects on lattice parameter misfit. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Ultra-high performance concrete (UHPC) has super high strength, ductile behavior, and excellent durability, which is quite different from conventional concrete. Many aspects of UHPC (mixture design, mechanical properties, shrinkage behavior, engineering applications, etc.) have been widely investigated. However, the information about creep properties of UHPC is not sufficient, which is vital to engineers for safe structure design as well as for predicting the structure's long-term performance. Thus, this study systematically brings together the published research on UHPC creep behavior, and major contents are as follows: 1) introduce basic terms for UHPC creep and give comparisons with conventional concrete; 2) summarize the various influencing factors on UHPC creep (curing regime, loading age, stress level, load type, w/b, fibers, mixture compositions, humidity, specimen size, etc.); 3) explain the mechanism of UHPC creep, relaxation performance, creep prediction models or equations in specifications; 4) give engineering applications considering UHPC creep (long-term deformation, prestress loss, early-age restrained stress, etc.); 5) summarize creep coefficient data from literature and propose future perspectives. This review can give researchers and designers a comprehensive and better understanding of UHPC creep, and facilitate the development of safe provisions for UHPC structures considering creep effect. • The compressive creep coefficients of UHPC are between 0.17 to 2.47. • The tensile creep coefficients of UHPC are between 0.78 to 2.38. • Heat treatment has the most pronounced effect on reducing UHPC creep. • Earlier loading age and higher stress levels increase UHPC creep. • Studies report that UHPC's compressive and tensile creep differ a lot or are similar. [ABSTRACT FROM AUTHOR]

In this study, the compressive creep behavior of Ti–45Al–8Nb alloy fabricated by selective electron beam melting technology at 800 °C and 850 °C was investigated. This alloy is mainly composed of equiaxed γ grains, and minor α 2 and B2 grains. Creep results show that compressive creep behavior of this alloy is dependent on temperature, which is manifested in the significant increase of creep strain and creep rate with the increase of temperature. Through a multi-step creep test, the stress exponent n (2.65 at 800 °C and 3.65 at 850 °C) and activation volume V * (36.49 b 3 at 800 °C and 53.51 b 3 at 850 °C) were measured. Combined with kinetic analysis based on n and V * and TEM observation, compressive creep deformation of this alloy at 800 °C and 850 °C is dominated by dislocation motion, including dislocation slip and climb. Additionally, mechanical twinning also plays an important role in creep deformation. Driven by dislocation pile-ups or mechanical twins, discontinuous dynamic recrystallization (DDRX) occurs during creep. The degree of DDRX at 850 °C is greater. Sufficient DDRX greatly softens the alloy and accelerates creep rate, resulting in no steady-state creep stage at 850 °C. • Compressive creep behavior of SEBM-produced Ti–45Al–8Nb alloy with near-γ microstructure strongly depends on temperature. • A multi-step compressive creep test method was applied to establish creep kinetics. • Dynamic recrystallization mechanism during compressive creep was elaborated. • Compressive creep deformation behavior was discussed based on kinetics analysis and experimental observation. [ABSTRACT FROM AUTHOR]

In this work, compressive creep behavior of Ti-43Al-6Nb-1Cr-1.5V alloy fabricated by vacuum induction skull melting technology was investigated at 800-950 °C. The results show that compressive creep behavior of this alloy strongly depends on temperature. At 800 °C and 850 °C, this alloy exhibits conventional three-stage creep characteristics with a well-defined steady-state creep stage, and creep strain is small. However, at 900 °C and 950 °C, this alloy exhibits unconventional creep characteristics, and creep strain increases sharply. Microstructure observation proves that this is mainly due to the occurrence of dynamic recrystallization (DRX). During creep, continuous dynamic recrystallization and discontinuous dynamic recrystallization appear simultaneously, but the latter is more significant. At 800 °C and 850 °C, creep deformation mainly depends on dislocation motion, while at 900 °C and 950 °C, DRX also greatly contributes to creep deformation. During creep, recrystallized grains preferentially form at β-segregation and α-segregation, and rising temperature from 850 °C to 900 °C facilitates the sharp increase of DRX fraction. The occurrence of DRX reduces dislocation density, which greatly softens the alloy. Besides, more α 2 grains generate at γ grain boundary and grain boundary/twin intersection during creep, and maintain Blackburn orientation relationship with γ grains. This is the result of stress-induced γ→α 2 phase transformation. • The compressive creep behavior of high Nb containing TiAl alloy exhibits a strong temperature dependence. • The dynamic recrystallization (DRX) mechanisms during compressive creep were revealed. • The correlation between DRX and macroscopic compressive creep behavior was established. • The stress-induced γ.→α 2 phase transformation was reported in present TiAl alloy during compressive creep. [ABSTRACT FROM AUTHOR]

The mechanical behavior of asphalt mixtures at high stress levels are characterized by non-linear viscoelasticity and damage evolution. A nonlinear damage constitutive model considering the existence of creep hardening and creep damage mechanisms in the entire creep process is proposed in this study by adopting the fractional rheology theory to characterize the three-stage creep process of mixtures. A series of uniaxial compressive creep tests under various stresses were conducted at different temperatures to verify the model. The results indicated that the model predictions were in good agreement with the creep tests. The relationship between the model parameters and applied stresses was established, and the stress range in which the mixture exhibited only creep consolidation was obtained. The damage to the asphalt mixture was initiated in the steady stage; however, it developed in the tertiary stage. A two-parameter Weibull distribution function was used to describe the evolution between the damage values and damage strains at different stress levels and temperatures. The correlation coefficients were greater than 0.99 at different temperatures, indicating that a unified damage evolution model could be established. Thus, the parameters of the unified model were related to material properties and temperature, independent of the stress levels applied to the mixtures.

Concrete undergoes shrinkage regardless of the influence of external forces. The deformation of concrete is crucial for the structural stability of high-rise and large-scale buildings. In this study, the shrinkage and compressive creep of 70–90 MPa high-strength concrete used in high-rise buildings were evaluated based on the curing conditions (sealed/unsealed), and the existing prediction models were examined. It was observed that the curing condition does not significantly affect the mechanical properties of high-strength concrete, but the use of limestone coarse aggregate increases the elastic modulus when compared to granite coarse aggregate. The autogenous shrinkage of high-strength concrete is greater than that of normal-strength concrete owing to self-desiccation, resulting in a large variation from the value predicted by the model. The drying shrinkage was observed to be similar to that predicted by the model. Compressive creep was affected by the curing conditions, compressive strength, loading level, and loading age. The compressive creep of high-strength concrete varied significantly from the prediction results of ACI 209; ACI 209 was modified based on the measured values. The shrinkage and compressive creep characteristics of high-strength concrete must be reflected to predict the deformation of an actual structure exposed to various conditions.

Strengthening mechanisms at ambient and elevated temperatures are studied in a cast Al-0.11Zr-0.02Si-0.005Er (at.%) alloy with a 2.86 at.% Ni addition, containing: (i) incoherent Al 3 Ni microfibers formed during eutectic solidification; and (ii) coherent, equiaxed Al 3 Zr (L1 2 -structure) nanoprecipitates created on subsequent aging. Strengthening contributions from microfibers and nanoprecipitates are cooperative at ambient temperature, over the full range of Al 3 Zr precipitation during under-, peak-, and over-aging states. In contrast, during compressive creep testing at 300 °C, the binary eutectic Al-Al 3 Ni alloy is not further strengthened by the Al 3 Zr nanoprecipitates, reflecting their lower number density (5.8 × 1022 m−3) in the regions between Al 3 Ni microfibers, where load transfer and/or microfiber/dislocation interactions provide strengthening. Also, when the Al-0.11Zr-0.02Si-0.005Er (at.%) alloy is modified with very low Ni concentrations of 0.07 at.%, without Al 3 Ni microfiber formation, the precipitation kinetics of Al 3 Zr(L1 2) are unaffected and negligible amounts of Ni are measured in the nanoprecipitates. The binary Al-2.86Ni at.% alloys with Al 3 Ni eutectic microfibers, with and without Al 3 Zr nanoprecipitates, are significantly more creep resistant at 300 °C than dilute Al-Sc or Al-Zr alloys strengthened solely by Al 3 Zr or Al 3 Sc nanoprecipitates. Unlike Al-Zr alloys, their upper service temperature is, however, limited to ∼400 °C, above which Al 3 Ni coarsening becomes rapid. [ABSTRACT FROM AUTHOR]

Abstract Mechanical testing of carbon containing refractories at high temperatures requires measures to protect the sample from oxidation. Therefore, special setups for tensile and compressive creep testing were developed to prevent the oxidation of carbon in the sample. A MgO-C refractory was selected for a case study. These developments allow the quantification of the tensile and compressive creep behaviour of MgO-C refractories at temperatures up to 1500 °C. The creep parameters are determined by an inverse evaluation method for the obtained experimental data. They enable the consideration of creep in a thermomechanical finite element simulation of refractory linings in service. [ABSTRACT FROM AUTHOR]

In the present work, the effects of the addition of C and Si on the compressive creep behavior of Ti-43.5Al–4Nb–1Mo-0.1B (TNM) alloy at 850 °C and 900 °C under 260 MPa were investigated. The results show that micro-alloying with C and Si can significantly strengthen the compressive creep resistance of TNM alloy. During compressive creep, obvious dynamic recrystallization occurs in TNM alloy, including major discontinuous dynamic recrystallization and minor continuous dynamic recrystallization. The development of dynamic recrystallization greatly softens the alloy, which leads to large creep deformation. Meanwhile, with the increase of creep strain, the bearing area increases and the actual stress decreases, which eventually results in the secondary creep behavior. In addition, the content of α 2 phase increases during compressive creep, which can be attributed to two phase transformations. After adding C and Si, the B2 phase content is decreased and the lamellar colony size is increased, which contributes to the improvement of creep resistance. In addition, fine and dispersed Ti 3 AlC and Ti 5 Si 3 particles precipitate in α 2 lamellae during compressive creep, and maintain definite orientation relationships with α 2 and γ phases. This will delay the decomposition of α 2 lamellae and greatly improve the lamellar stability. Then, the excellent lamellar stability will inhibit the development of dynamic recrystallization, thus effectively reducing the creep rate. • The multiple strengthening mechanisms of compressive creep resistance of TiAl alloys were clarified. • The precipitation of Ti 5 Si 3 and Ti 3 AlC will improve α 2 /γ lamellar stability during compressive creep. • The dynamic recrystallization mechanism during compressive creep was revealed. [ABSTRACT FROM AUTHOR]

The high-temperature strength and compressive creep resistance of TNM B1-type TiAl alloy modified with Y 2 O 3 nanoparticles are studied. The effect of equiaxed or lamellar microstructure on mechanical properties and deformation mechanisms is demonstrated. It is established that the lamellar microstructure provides higher strength compared to the equiaxed one at high temperatures. Microstructural studies of the samples, subjected to compressive creep, revealed that creep is governed by the dislocation mechanisms for the equiaxed alloy, while a combination of dislocation mechanisms, twinning, dynamic recrystallization, and dynamic recovery is typical for the lamellar alloy. In both types of alloys, Y 2 O 3 nanoparticles successfully act as reinforcement at 800 °C, while being prone to failure and facilitating microcrack nucleation at the nanoparticle/matrix interface at 1100 °C. [Display omitted] • Compression creep behavior of the Y 2 O 3 -reinforced TNM-B1 TiAl alloys was analyzed. • The effect of microstructure type on thermomechanical properties was demonstrated. • The creep activation energy of the alloys was determined to be 632–653 kJ/mol. • TEM studies were carried out to establish the primary deformation mechanisms. [ABSTRACT FROM AUTHOR]

A polymer-bonded explosive, also called PBX or plastic-bonded explosive, is an explosive material in which explosive powder is bound together in a matrix using small quantities (typically 5%-10% by weight) of a synthetic polymer. A PBX substitute material was made from sugar granules and polymer binder. Its compressive creep properties were investigated at room temperature. The creep deformation was found to depend strongly on the applied stress amplitude. Under an applied stress near the strength, creep deformation developed and reached the final rupture very quickly. A power law relationship, ε= 4.14 × 10-8 σ2.5 , was established between steady creep rate and applied stress. Microscopic observations show that the damage mechanism processes include mainly the intergranular and transgranular fractures, binder fracture, and peeling. Both porosity and granule size decrease almost linearly with increasing applied stress. [ABSTRACT FROM AUTHOR]

The characterization of thermal ratcheting behavior of high density polyethylene (HDPE) material coupled with compressive creep is presented. The research explores the adverse influence of thermal cycling on HDPE material properties under the effect of compressive load, number of thermal cycles, creep time period, and thermal ratcheting temperature range. The compressive creep analysis of HDPE shows that the magnitude of creep strain increases with increase in magnitude of applied load and temperature, respectively. The creep strain value increased by 7 and 28 times between least and maximum applied temperature and load conditions, respectively. The creep modulus decreases with increase in compressive load and temperature conditions. The cumulative deformation is evident in the HDPE material, causing a reduction in the thickness of the sample under thermal ratcheting. The loss of thickness increases with increase in the number of thermal cycles, while showing no sign of saturation. The thermal ratcheting strain (TRS) is influenced dominantly by the applied load condition. In addition, the TRS decreases with increase in creep time period, which is cited to the extended damage induced due creep. The results highlight the need for improved design standard with inclusion of thermal ratcheting phenomenon for HDPE structures particularly HDPE bolted flange joint. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the influence of ambient relative humidity on tensile creep of plain concrete amended with Ground Granulated Blast-furnace Slag and compares it with its influence on compressive creep. Tensile and compressive creep tests were carried out on concrete specimens of 34.49MPa compressive strength and 0.56 water/binder ratio at 51, 68 and 100% relative humidity. The results show a linear relationship between compressive creep and relative humidity; this cannot be said about tensile creep. Tensile creep was observed to be more sensitive to change in ambient humidity than compressive creep. Based on equal applied stress, tensile creep was found to be several times higher than compressive creep and the difference was greater in drying creep than in basic creep. On the basis of equal stress/strength ratio, tensile-to-compressive creep ratio was slightly less than 1 for drying creep and much less for basic creep. [ABSTRACT FROM AUTHOR]

Magnesium (Mg) alloys with high concentrations of Gd additions are known to exhibit high strength and good creep resistance at elevated temperatures. However, the main mechanisms including microstructural evolution and dislocation configurations for clarifying the low creep rates of Mg–Gd–Zr alloys are still controversial. The present work investigates the compressive creep behavior of both the sand-cast and peak-aged Mg–12Gd–0.4Zr (wt.%) alloys at a fixed temperature of 250 °C under the applied stress range of 60–100 and 80–120 MPa, respectively. It is revealed that β' and β' F precipitates distribute alternately forming precipitate chains in Mg–Gd–Zr alloys. Furthermore, β'+β' F precipitate chains led to the honeycomb-like structure in the sand-cast alloy during the creep process, improving its creep resistance to some extent. Nevertheless, weakly strengthening β 1 precipitates occurred and detrimental β phases coarsened, which weakened the creep performance of the sand-cast alloy. However, the slight improvement of creep resistance in the peak-aged Mg–12Gd–0.4Zr alloy can be mainly attributed to the formation of precipitate-free zones (PFZs) and also the premature coarsening of β'+β' F precipitate chains. During creep, the cross slip of basal and prismatic dislocations become the dominant creep mechanism for the sand-cast alloys. By contrast, the cross-slip of basal dislocations and pyramidal dislocations is the dominant creep mechanism for the peak-aged alloys, which was arrested by precipitates then strengthening the creep resistance of peak-aged alloys. • The alternating distribution of β' and β' F phase occurred during creep. • Honeycomb structure appeared in sand-cast Mg-12Gd-Zr alloy during creep. • Aging treatment can marginally decrease the creep rate of Mg-12Gd-Zr alloy. [ABSTRACT FROM AUTHOR]

A hypoeutectic, Fe-modified Al–Ce–Ni alloy (Al–6Ce–3Ni-0.7Fe, wt.%) is studied in terms of microstructure, thermal stability, ambient temperature strengthening, and creep resistance. The as-cast microstructure consists of primary Al dendrites and interdendritic binary eutectic regions (Al–Al 11 Ce 3 and/or Al–Al 9 (Fe,Ni) 2), with micron/submicron lamellar spacing, depending on the location along the height of the ingot. The cast alloy exhibits excellent coarsening resistance at 400 °C, with mostly unchanged microstructure and microhardness after 6 weeks of aging, indicating good thermal stability of Al 11 Ce 3 and Al 9 (Fe,Ni) 2. Orowan strengthening and load transfer are identified as strengthening mechanisms at ambient and elevated temperature. A high volume fraction of the intermetallic phases (providing load transfer) and relatively coarse eutectic spacing (for modest Orowan strengthening) result in a moderate as-cast microhardness of 566 ± 32 MPa. Creep resistance at 300 and 350 °C is similar to a binary Al-12.5Ce eutectic alloy (with twice the Ce content) because of two countering effects: Al–6Ce–3Ni-0.7Fe shows a higher volume fraction of strengthening intermetallic phases, but it also exhibits a large fraction of primary Al dendrites which weaken the alloy. By contrast, the alloy, when laser-remelted at the surface, has a fully eutectic microstructure without primary aluminum dendrites achieved by high undercooling on solidification, with a refined network of eutectic phases that doubles the microhardness as compared to the cast alloy. Whereas coarsening is faster due to the shorter diffusion distances between the eutectic phases, hardness remains ∼30% higher than the as-cast alloy after ∼6 weeks aging at 400 °C. [ABSTRACT FROM AUTHOR]

In this paper, experimental results about the shrinkage and creep behavior of an alkali-activated slag concrete ( AAS-concrete) are presented. The autogenous shrinkage of AAS-concrete is pronounced at a relatively high water to binder ratio of 0.41. The ultimate value of autogenous shrinkage is determined to be higher than that of high-strength concrete ( HSC). The observed self-desiccation at a later concrete age can be one of the reasons for the autogenous shrinkage. In a drying environment of 65% relative humidity AAS-concrete exhibits a significantly higher total shrinkage compared to normal-strength concrete composed of Portland cement. In the contrary to normal and HSC carbonation shrinkage must not be neglected for AAS-concrete in the early concrete age. The sum of drying and carbonation shrinkage develops much more rapidly for AAS-concrete in the first weeks after the beginning of drying. Based on the experimental results the shrinkage behavior of AAS-concrete cannot be predicted by conventional models. The creep behavior of the AAS-concrete was investigated under sealed and unsealed conditions. The creep coefficients for both conditions are higher than those calculated when using conventional models. [ABSTRACT FROM AUTHOR]