High Creep Research Articles

Acoustic Emission-Based Structural Health Prediction and Monitoring: A Comprehensive Review

In this paper, we report a detailed overview of non-destructive techniques, specifically Acoustic emission, for structural health monitoring in engineering applications. The review comprehensively covers the application of the AE technique for data related to damping and attenuation of structural components made from various material types, including conventional and non-conventional materials. Also, this paper systematically emphasizes research related to data collection processes of variable structural elements, such as stress concentration areas, sensor placement, and methodological monitoring. In addition, the analysis discussed in the review encompasses research that has utilized the AE method to examine the performance of metal and concrete building elements in risky situations, such as high temperatures and creep factors, with and without any visible signs of damage. We also examine various solution techniques, such as empirical wavelet transforms, finite element solutions, and differential quadrature for conventional materials’ damage analysis. Furthermore, the review emphasizes using waveform schemes to assess the vulnerability of damages in unconventional materials, such as laminated composite structures with different geometrical shapes. The paper concludes by presenting an overview of the current state of the AE technique in structural health monitoring and discusses potential future developments. This review is a valuable reference for professionals and researchers engaged in engineering applications related to structural health monitoring.

Preferential nucleation of (O, Y/La/Ce/Hf)-core nano-clusters in multi-element micro-alloyed ferritic alloys: A first-principles study

The high creep strength and high radiation resistance of nanostructured ferritic alloys (NFAs) have been generally attributed to the high-density precipitation of (O, Y)-core nano-clusters and nano-oxides. In this work, the early-stage nucleation of (O, X)-core (X = La, Ce, and Hf) nano-clusters (NCs) with respect to (O, Y)-core NCs in multi-element micro-alloyed NFAs was investigated using first-principles calculations. Their competitive precipitation preference and possible growth sequence were predicted. The (O–O) pair was suggested as the most fundamental core of all types of NCs. Yttrium always has the strongest affinity with the (O–O) pairs to initiate the nucleation of NCs during the early-stage nucleation. Under the absence or depletion of yttrium, other types of (O, X)-core (X = La, Ce, Hf) structures could form, leading to different nucleation paths with the preference ordering of (O, La)-core > (O, Ce)-core > (O, Hf)-core. NC nucleation and composition in NFAs would, thus, strongly depend on the number availabilities of micro-alloying solute species in the neighborhood of the (O–O) pairs.

The γ/γ′ microstructure in CoNiAlCr-based superalloys using triple-objective optimization

Optimizing several properties simultaneously based on small data-driven machine learning in complex black-box scenarios can present difficulties and challenges. Here we employ a triple-objective optimization algorithm deduced from probability density functions of multivariate Gaussian distributions to optimize the γ′ volume fraction, size, and morphology in CoNiAlCr-based superalloys. The effectiveness of the algorithm is demonstrated by synthesizing alloys with desired γ/γ′ microstructure and optimizing γ′ microstructural parameters. In addition, the method leads to incorporating refractory elements to improve γ/γ′ microstructure in superalloys. After four iterations of experiments guided by the algorithm, we synthesize sixteen alloys of relatively high creep strength from ~120,000 candidates of which three possess high γ′ volume fraction (>54%), small γ′ size (<480 nm), and high cuboidal γ′ fraction (>77%).

Constructing a rigid-flexible grid structure for simultaneously strengthening and toughening bamboo flour/plastic composites through the introduction of continuous carbon fabric meshes via multi-layer co-extrusion

The defects of low strength, brittle fracture, and creep deformation of traditional wood–plastic composites (WPCs) significantly limit their applications as high-value-added products. This study aimed to develop advanced WPCs with high strength, toughness, and creep resistance via a structural design. A continuous rigid-flexible grid structure, sandwiched by carbon fabric mesh prepreg (CFMP) and casting film (MSF) with high toughness, was introduced into bamboo flour/high-density polyethylene composites (BPCs) via a multi-layer co-extrusion technology. The sandwiched grid structure was in-situ cured in the near-surface layers of BPCs to form a multi-layer composite (BPC-CFMP-F) during co-extrusion. The tensile strength, flexible strength, and impact strength of BPC-CFMP-F were 68.4 MPa, 89.0 MPa, and 22.5 kJ m−2, which are 138.3%, 96.4%, and 87.6% higher than those of BPCs, respectively, and the thermal expansion and 1000-hr creep strain of BPC-CFMP-F decreased by 45.8% and 61.7%, respectively. The simultaneous strengthening and toughening of BPCs were attributable to the rigid-flexible grid structure and the strong interfacial bonding between CFMP and BPCs and the surface- and core-layer BPCs through the grid of CFMP. Owing to these unique features, BPC-CFMP-F is a promising advanced composite with high strength, toughness, excellent creep resistance, and thermal stability for high value-added applications.

Anisotropic microstructure, nanomechanical and corrosion behavior of direct energy deposited Ti–13Nb–13Zr biomedical alloy

The present study investigates the anisotropic microstructure, nanomechanical and corrosion behavior of Ti–13Nb–13Zr biomedical alloys, which were fabricated using the direct energy deposition (DED) method. The microstructure of the as-deposited material was studied using a field-emission scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). We found anisotropic mechanical behavior using nanoindentation from strain rate sensitivity and creep tests. For the maximum load of 50 mN, the x-y plane (normal to the building direction) shows better indentation hardness and lower strain rate sensitivity value (0.014) compared to the x-z plane (0.022) (parallel to the building direction). The difference in the indentation hardness was mainly attributed to the smaller equiaxed prior-β grains and finer α’ martensitic laths on the x-y plane. In terms of creep behavior, the x-y planes show better creep strength than the x-z plane. Meanwhile, both planes show a very high creep exponent, which signifies a similar creep mechanism, i.e., dislocation based. Moreover, we further found the anisotropic corrosion behavior using electrochemical tests. Corrosion results reveal that the x-y plane is more corrosion-resistant than the x-z plane. In summary, the x-y plane of the direct energy deposited Ti–13Nb–13Zr alloy possesses better strength and corrosion resistance due to its finer microstructure.

Modifying Microstructure and Mechanical Properties of Mo-Nb Single Crystals via Thermal Annealing

Molybdenum-Niobium (Mo-Nb) single crystals possess excellent mechanical properties, such as high strength and low creep rate at high temperatures, which leads to Mo-Nb single crystals’ potential application in the irradiated and aerospace environment. Mechanical properties at high temperatures are closely related to structural defects, including the density of dislocation and low-angle grain boundaries in a single-crystal Mo alloy. It is well known that the density of defects is mainly contributed to by processing and annealing. To clarify the microstructural evolution of Mo-Nb single-crystal alloys, thermal annealing tests with temperatures varying from 1100 °C to 1700 °C were conducted. Two Nb contents (3 at.% and 6 at.%) were chosen to investigate the effect of Nb content on the thermal stability (≤1700 °C) of single-crystal Mo-Nb alloys. Samples with high Nb content (6 at.%) soften after annealing, while ductility at room temperature obviously enhances In the low Nb content (3 at.%) sample, however, hardening and softening occur after low (1100 °C) and high temperature annealing, respectively. The evolution of mechanical properties could be mainly attributed to the change of density in the low-angle grain boundary. Furthermore, the changing Nb element and dislocation density during annealing are still important to the strength and ductility of Mo-Nb single crystals.

Effect of Fe additions on microstructure and mechanical properties in near-eutectic Al–Ce alloys

The effects of adding 1 or 3 wt % Fe to a near-eutectic Al–10Ce alloy are investigated in terms of their as-cast and aged microstructures, thermal stability, and creep resistance. A 1 wt% Fe addition forms fine, Chinese-script Al10CeFe2 and Al11Ce3 eutectic phases without loss of microhardness as compared to the Fe-free Al–10Ce alloy, unlike in traditional cast Al-alloys where detrimental coarse phases are observed when adding Fe. Adding 3 wt% Fe increases hardness significantly while forming primary Al10CeFe2 in a coarse rod morphology. These near-eutectic Al–10Ce–1Fe and hyper-eutectic Al–10Ce–3Fe alloys, after thermal exposure at 400 and 425 °C for up to 384 h, show only a small loss in microhardness, indicating excellent coarsening resistance. Compressive creep measurements performed at 300 °C show similar trends: (i) near-eutectic Al–10Ce–1Fe performs quite similarly to near-eutectic Al–10Ce and (ii) hyper-eutectic Al–10Ce–3Fe exhibits much improved creep resistance, similar to near-eutectic Al–10Ce–5Ni with costly Ni additions, and much better than hyper-eutectic Al–13Ce. After surface laser remelting to simulate laser powder-bed fusion, the near-eutectic Al–10Ce–1 Fe alloy exhibits greatly refined Al10CeFe2 and Al11Ce3 eutectic phases with a doubling in microhardness, indicating a strong potential for laser-based additive manufacturing. Cast Al–Ce–Fe-based alloys show great promise as low-cost alloys with high creep- and coarsening-resistance for use at high temperatures, with the high Fe tolerance enabling the use of recycled aluminum with high Fe contamination.

Compressive creep behavior and microstructural evolution of sand-cast and peak-aged Mg–12Gd–0.4Zr alloy at 250 °C

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 β1 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 <a> dislocations become the dominant creep mechanism for the sand-cast alloys. By contrast, the cross-slip of basal <a> dislocations and pyramidal <c + a> 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.

Effect of annealing twins, strain-recrystallization processing and δ-phase fraction on microtexture and evaluation of mechanical properties of nickel-based superalloy 718

The Nickel-based superalloy 718 is a precipitation-hardened material, especially by the ordered and coherent phases γ” (Ni3Nb) and γ″ (Ni3 (Al, Ti)). In addition to these phases, precipitation of carbides and δ-phase is possible. This material has high strength, creep, and corrosion resistance at temperatures up to 650 °C. However, despite the alloy’s outstanding performance under harsh environments, research effort has been put into optimizing its properties and increasing the operation temperature. Manipulation of microstructural parameters such as grain boundary character distribution (GBCD), microtexture, second phase fraction, etc. is frequently betaken in order ot achieve better properties. In this context, this work aimed to assess the influence of Thermomechanical Processing on the recrystallization texture of the material and its influence on the alloy’s mechanical behavior. The material was submitted to four iterative processing routes, composed of deformation-heat treatment cycles. The alloy’s microtexture data were obtained through the Electron Backscattered Diffraction technique. Data processing was performed using the MTEX toolbox, where Orientation Density Functions were obtained for microtexture analysis. It was observed that the deformation imposed during thermomechanical processing significantly affects the recrystallization texture of the material so that smaller deformations induce the formation of typical recrystallization texture components; on the other hand, high degrees of deformation lead to a retained deformation texture after annealing. Mechanical properties were evaluated by depicting the influence of different strengthening mechanisms and δ-phase fraction on yield strength and ductility, respectively. It was observed that the main strengthening parameters for the alloy were grain boundaries and intrinsic resistance (Pierls-Nabarro and solid solution), meanwhile ductility was greatly influenced by δ-phase and ∑3n boundaries fractions.

Enhanced creep stability in Inconel 718 deposited by induction-heating-assisted laser-directed energy deposition

This study investigated the creep stability enhancement of Inconel 718 by induction heating during the laser-directed energy deposition. The induction heating during the deposition fully dissolved the Laves phase, mitigated Nb segregation, and formed directionally solidified columnar grains. Based on the results of nanoindentation creep testing, the deposit utilizing induction heating exhibited high creep stability.

Revealing the influences of strain amplitudes on hybrid stress–strain controlled creep-fatigue interaction responses for 9 %Cr steel

The hybrid stress–strain controlled creep-fatigue interaction (HCFI) tests were performed on 9 %Cr steel at strain amplitudes ranging from ± 0.25% to ± 0.6%. The strain amplitude increase brings more possibilities of cracking but fewer crack deflections, along with some differences in LABs and grain size. But for HCFI tests with high creep damage, strain amplitude plays a minor role since considerable creep strain during stress holding is converted into fatigue strain even at low strain amplitudes. Additionally, a dwell indicator (DI) benchmarked against macroscopic LCF responses is proposed to evaluate strain amplitude-induced microscopic HCFI damage. When DI is approximately equal to (or greater than) 0.9, the differences in strain amplitudes can bring significant changes in internal degradation and fracture behaviors. When DI is close to (or lower than) 0.5, HCFI damage exhibits low sensitivity to strain amplitude.

Azine-Based dynamic covalent polyurethane elastomers with excellent mechanical and Creep-Resistant properties

Dynamic covalent bonds have received tremendous attention since they endowed classical crosslinked polymers with new properties, including self-healing, stimuli-responsive, anti-bacterial, and recycling properties. The dynamic crosslinked polymers combined the merits of thermoset and thermoplastic elastomers. However, the dynamic nature also compromised the heat resistance of dynamic crosslinked polymers, especially the creep resistance at high temperatures. Herein, a hexahydroxy azine crosslinker was synthesized and used to prepare a range of azine-based polyurethane elastomers (PUEs). The exchange reactions of small molecular model compounds revealed that the azine moieties could exchange fast at 150 °C. The resulting azine-based PUEs showed outstanding thermal stabilities and mechanical properties owing to the conjugated structure and related hydrogen bonds of azine. The obtained azine-based PUEs also exhibited a high creep temperature of 150 °C thanks to the relatively higher exchange temperature of azine moieties and high functionality of the azine crosslinker. The degradation process of azine-based PUEs displayed solvent and acid strength dependence. The excellent reprocessing properties of azine-based PUEs were attributed to the distribution of the azine moieties both in the backbone and crosslinking points. This study provides an alternative way to solve the creep resistance of dynamic crosslinked polyurethanes and a feasible method for the industrialization of the recyclable thermoset polyurethane elastomers.

A Novel Smart CFRP Cable Based on Optical Electrical Co-Sensing for Full-Process Prestress Monitoring of Structures.

Carbon-fiber-reinforced polymer (CFRP) is a type of composite material with many superior performances, such as high tensile strength, light weight, corrosion resistance, good fatigue, and creep performance. As a result, CFRP cables have great potential to replace steel cables in prestressed concrete structures. However, the technology to monitor the stress state in real-time throughout the entire life cycle is very important in the application of CFRP cables. Therefore, an optical-electrical co-sensing CFRP cable (OECSCFRP cable) was designed and manufactured in this paper. Firstly, a brief description is outlined for the production technology of the CFRP-DOFS bar, CFRP-CCFPI bar, and CFRP cable anchorage technology. Subsequently, the sensing and mechanical properties of the OECS-CFRP cable were characterized by serious experiments. Finally, the OECS-CFRP cable was used for the prestress monitoring of an unbonded prestressed RC beam to verify the feasibility of the actual structure. The results show that the main static performance indexes of DOFS and CCFPI meet the requirements of civil engineering. In the loading test of the prestressed beam, the OECS-CFRP cable can effectively monitor the cable force and the midspan defection of the beam so as to obtain the stiffness degradation of the prestressed beam under different loads.

Review on Creep Phenomenon and Its Model in Aircraft Engines

The aircraft is subjected to high-temperature and high-pressure conditions during flight, which renders it susceptible to the occurrence of creep phenomenon. Several academics have conducted extensive research on this issue. This research paper provides a comprehensive overview of the existing literature on creep phenomena in aircraft engines. First, several classical creep calculation models are enumerated and categorized as creep life calculation, creep-fatigue life calculation, and creep deformation calculation. Studies on creep phenomena are conducted in various components of aircraft engines, such as the engine’s turbine blades, turbine disks, and combustion chambers. The creep behavior of turbine blades in aircraft engines has been extensively researched. Furthermore, the protective measures aimed at mitigating creep are presented. Materials with high creep resistance can be used, and alternative fuels could be implemented. This paper provides an in-depth analysis of the advantages of creep in aircraft, presented in a favorable perspective. Finally, the prospective future research direction is discussed.

Experimental Study on the Time-Dependent Oedometric Compression Behavior of Calcareous Sand

A series of compression tests were carried out on two types of calcareous sand to study the time-dependent behavior of calcareous sand under oedometric conditions. Consolidation, creep, stress relaxation, and constant strain/stress rate tests were conducted. At the same time, the effects of input energy and grain shape on particle breakage were investigated. The test results show that a large amount of particle breakage occurs in the calcareous soils under different modes of loading, leading to a significant time effect on the oedometric compression responses. Under the same level of vertical stress, the large-grain calcareous sand has a higher creep or relaxation rate. Over-consolidated sand has a much smaller creep or relaxation response than normally consolidated sand, and the response decreases with an increase in the overconsolidation ratio. Loading rate has an influence on the compressibility of calcareous sand, especially when the particle breakage is significant. In addition, it is also shown that a unique relationship exists between the relative breakage and the input energy for the same kind of calcareous sand, which is independent of the loading mode.

Microstructure evolution and precipitation behavior in a Y2O3-bearing TiAl alloy during creep

The paper studies the microstructure stability of a Y2O3-bearing Ti–48Al–2Cr–2Nb alloy during creep. Tensile creep tests were performed at 800–850 °C under 100 or 275 MPa. Compared to thermal exposure, the low creep stress promotes the microstructure degeneration of lamellar colonies, mainly including α2-lath dissolution, γ-lath coarsening and βo phase precipitation. The high creep stress further accelerates the α2 → γ transformation, but goes against the precipitation of βo grains inside α2 laths. Similarly, more Cr-rich precipitates with the composition of Ti(Al, Cr)2 are observed in creep samples, which are identified as the C14-Laves phase. It has a {0001}C14//{111}γ and <101¯0>C14//<11¯0>γ orientation relationship with the γ phase. The high imposed stress also facilitates the precipitation behavior. It should be noted that there are a few C14-Laves phases precipitating along the Y2O3 interface by heterogeneous nucleation. The high strain energy around Y2O3 particles, especially under the high creep stress, contributes to the precipitation of C14-Laves phase not only at the Y2O3 interface, but also in the γ matrix.

Prediction of nanoindentation creep behavior of tungsten-containing high entropy alloys using artificial neural network trained with Levenberg–Marquardt algorithm

This paper describes the synthesis of tungsten-containing high-entropy alloys (HEAs). The synthesis method involves a powder metallurgy process, and spark plasma sintering (SPS) is used to compact the powder. XRD and SEM analyses of synthesized HEAs showed that the main phases formed were body-centered and face-centered cubic phases, and a sigma phase was also observed after sintering at 900 ℃. Furthermore, nanoindentation showed that the introduction of tungsten in HEA resulted in high hardness and elastic modulus, which ranged from 8.31 to 13.57 GPa and 197.21–209.43 GPa respectively. The indentation creep behavior was ascertained at room temperature. The HEAs exhibited a significant benchmark after the addition of a specific amount of W for further investigation because of their lower creep rate. Experimental creep displacement data were used for modeling by artificial neural networks (ANNs) in which the training has been performed by the Levenberg–Marquardt algorithm. The experimental creep displacement data and the ANN model predictions have an excellent agreement. The ANN model is reliable and can accurately forecast the room temperature creep behavior of HEAs. HEAs are promising candidates for use in elevated and wear-resistance applications, owing to their unique combination of high hardness and high creep resistance.

Experimental study on flexural performance of reinforced concrete beams strengthened by PET

AbstractPolyethylene terephthalate (PET) is a new type of fiber‐reinforced polymer (FRP) composite material, which has the characteristics of high performance, high toughness, high tensile fracture load, low elongation, low creep, no rust, and safety in use. The good performance of PET can significantly improve the mechanical properties of its components. A total of six reinforced concrete (RC) beams were produced in the test, one of which was a comparison beam, and the other five were reinforced with PET. In the test, the PET reinforcement spacing, number of reinforcement layers, and laying method were used as control variables, and an experimental study on the normal section bending performance of the specimen was performed. The test analyses the failure characteristics, crack width, bearing capacity, and deflection of the specimens under different reinforcement conditions. The test results showed that PET reinforcement can effectively inhibit the occurrence and development of cracks in RC beams and improve the ultimate bearing capacity and ductility of the components. The smaller the PET reinforcement spacing, the higher the ultimate bearing capacity; the greater the number of PET layers, the better the ductility of the specimen. Additionally, the economy, environmental protection, and portability of PET are of great significance for its application in practical engineering reinforcement.

Experimental study on tilting deformation and a new method for landslide prediction with retaining-wall locked segment

The destruction of the locked-segment type landslide is often accompanied by the destruction of the locked segment with cumulative effects. Investigating the failure mode and instability mechanism of locked-segment type landslides is crucial. The study uses physical models to examine the evolution of locked-segment type landslides with retaining-walls. It utilizes a variety of instruments (tilt sensors, micro earth pressure sensors, pore water pressure sensors, strain gauges, and others) to conduct physical model tests of locked-segment type landslide with retaining-wall and to reveal the tilting deformation and evolution mechanism of retaining-wall locked landslide under the condition of rainfall. The results showed that the regularity of tilting rate, tilting acceleration, strain, and stress change in the retaining-wall locked segment is consistent with the landslide evolution process, indicating that tilting deformation can be used as the criterion of landslide instability and that the locked segment plays a vital role in controlling the landslide stability. The tertiary creep stages of tilting deformation are divided into initial, medium, and high tertiary creep stages using an improved angle tangent method. This establishes the failure criterion for locked-segment type landslides with tilting angles of 0.34°, 1.89°, and 4.38°. In addition, the tilting deformation curve of a locked-segment type landslide with a retaining-wall is utilized to predict the landslide instability by the reciprocal velocity method.

Effect of Ru on Deformation Mechanism and Microstructure Evolution of Single-Crystal Superalloys under Medium-Temperature and High-Stress Creep.

In this work, the effect of the Ru element on the γ'-phase evolution and deformation mechanism in the fourth-generation Ni-based single-crystal superalloy was investigated. Results show that the Ru element alters the distribution coefficient of other elements in the alloy to produce reverse partitioning behavior, which leads to a difference in microstructure between 0Ru and 3Ru. The addition of Ru triggered the incubation period before the beginning of the primary creep stage, which depends on the creep temperature and stress during creep deformation. TEM results revealed that Ru addition inhibits the slip system {111}<112> at medium-temperature (760-1050 °C) and high-stress (270-810 MPa) creep, which brings a considerably low creep rate and high creep life to the Ru-containing alloy.