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Copyright of Journal of Mechanical Strength / Jixie Qiangdu is the property of Zhengzhou Research Institute of Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

When the thermal maturity of the Longmaxi Formation in the southern Sichuan Basin is too high, the pore structure of shale becomes poor. Therefore, to investigate the effect of organic matter thermal maturity on shale pore structure, a study was conducted. Using the Longmaxi Formation shale in the southern Sichuan Basin as an example, the intrinsic relationship between shale porosity, pore structure parameters, organic matter laser Raman maturity, and organic matter graphitization degree was examined using X-ray photoelectron spectroscopy, particle helium porosity measurement, organic matter micro-laser Raman spectroscopy, and gas adsorption experiments. The results indicate that thermal maturity is the macroscopic manifestation of the graphitization degree of organic matter, and the correlation coefficient between the two is 0.85. A thermal maturity of 3.5% (with a corresponding organic matter graphitization degree of 17%) aligns with the highest values of shale porosity, pore volume, and pore-specific surface area across all pore size conditions. The evolution model of shale pore structure can be divided into two stages. The first stage is characterized by a thermal maturity between 2.0% and 3.5% (with a corresponding degree of graphitization of organic matter between 0% and 17%). During this stage, the number and connectivity of micro-macropores increase with increasing thermal maturity. The second stage is marked by a thermal maturity between 3.5% and 4.3% (with a corresponding degree of graphitization of organic matter between 17% and 47.32%). Basement faults are present, leading to abnormally high thermal maturity, poor preservation conditions, continuous generation of micropores, better connectivity, and a reduced number of pores. Medium macropores with good connectivity suffer from gas loss in the fracture network, leading to the collapse and disappearance of pores. The results mentioned in the statement have an important guiding role in the efficient exploration of shale gas in the Longmaxi Formation in the southern Sichuan Basin. [ABSTRACT FROM AUTHOR]

Achieving sustainable resource management is essential to address the rising demand for ecosystem services. The absence of targeted vegetation restoration based on ecological function positioning has, nevertheless, made it challenging to effectively combat the ecological decline. This study attempted to classify four dominant ecological function areas based on the assessment of water conservation, soil retention, habitat quality, and food supply and determined the vegetation coverage threshold by exploring the trade‐offs among ecosystem services and constraint effects between ecosystem services and vegetation coverage. The results highlighted the impacts of ecosystem services on vegetation coverage across the years 1990, 2000, 2010, and 2020 and established differentiated ecological restoration targets. The optimal vegetation coverage in the water conservation area was found to be 58%–63%, in the soil retention area was 52%–56%, in the food supply area was 34%–40%, and in the habitat quality area was 65%–70%. Finally, the study identified the subwatersheds with reasonable vegetation coverage, excessive restoration, and those that failed to reach the optimal vegetation coverage to develop targeted restoration strategies for each subwatershed according to its unique vegetation conditions. This study provides valuable insights into the specification of differentiated vegetation coverage targets and serves as a useful tool for more effective ecosystem planning and management. [ABSTRACT FROM AUTHOR]

The leak-before-break design concept is based on J-R curves, which are obtained by J-R tests on various types of specimens and are known to be dependent on the cyclic load history. The J-R curves of standard specimens suggested by the American Society for Testing Materials are determined based on quasi-static tensile loading. However, seismic loading induces a reverse cyclic loading that alternately applies a tensile and a compressive load to nuclear plant piping. Therefore, it is very important to obtain the fracture toughness characteristics under reverse cyclic loading for the integrity estimation of nuclear plant piping. The objective of this paper is to study the effects of reverse cyclic loading on the fracture toughness characteristics of SA312 TP316L stainless steel, which is a nuclear plant piping material. J-R tests on a flat, equivalent stress gradient specimen with varying incremental displacement were carried out. The test results were reviewed by comparing the J-R test results under quasi-static loading. In addition, the safety margin of the nuclear plant piping was evaluated using a crack driving force diagram method. For the SA312 TP316L stainless steel, the results showed that the J-R curves were decreased with a decrease in the incremental displacement. When the incremental displacement was set to 0.25 mm, the unstable crack growth point value was about 73.0% of those for the quasi-static loading conditions. [ABSTRACT FROM AUTHOR]

Green credit policy (GCP) has dual attributes of being both an "environmental regulation" and a "financial instrument". Understanding its role in facilitating industrial green transformation is crucial. However, there is limited theoretical and empirical evidence on the impact of GCP on industrial green transformation. This research fills this gap by comprehensively investigating the impacts and mechanisms of GCP on industrial energy intensity (EI) in China, considering both incentive and constraint effects. Theoretically, the environmental and financial impacts of GCP are merged into a unified analytical framework based on a heterogeneous enterprise model. Empirically, diverse empirical methods, including difference-in-differences (DID), difference-in-differences-in-differences (DDD), and mediating effects models, are adopted to examine whether GCP can promote green innovation or accelerate financial constraints. Results show that (1) GCP significantly decreases EI, especially among high-polluting enterprises (HPEs). The impact of incentives is far greater than that of constraints. (2) Regarding the incentive effect, energy substitution and innovation offsets exert a primary influence on reducing EI. (3) The constraint effect is caused primarily by rising financing and pollution abatement costs. (4) Heterogeneity analysis shows that the inhibiting effect of GCP is more significant in non-state-owned enterprises, underdeveloped financial markets, and abundant energy endowments. This paper provides a theoretical framework and new empirical evidence for policymakers to design effective policies for promoting industrial green transformation. [ABSTRACT FROM AUTHOR]

The joint form plays a vital role in the rapid assembly of precast bridge decks for steel–concrete composite bridges. Existing research primarily focuses on studying the shear performance of joints through direct shear tests, which is insufficient to fully reflect the mechanical behavior of joints under the constraint of prefabricated bridge deck panels during actual vehicular traffic. Considering situations such as vehicle loads and external forces acting on precast bridge decks, this study investigates the shear performance of epoxy joints under constraint through an improved shear test. The influence of constraint force, shear key details and interface defects on the shear performance of epoxy joints is investigated. The results reveal that the shear test method employed in this study can realistically reflect the shear performance of epoxy joints in precast bridge decks. Both active and passive constrained epoxy joint specimens exhibited no interface cracks, and their failure modes were identified as shear failure between mid-span supports. Compared with passive constraint, the shear-bearing capacity of epoxy joint specimens under active constraint was increased by 86.1~130.6%. Among the epoxy joint specimens with depth–height ratios of 15/110, 25/110, 35/110 and 45/110, the joint with a depth of 35 mm demonstrated the highest shear strength. Furthermore, the shear performance of epoxy joints significantly deteriorated when the interface defects exceeded 30%, resulting in the failure mode transforming from shear failure to interface failure. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Advanced nuclear reactors are currently moving toward longer fuel cycles and higher burnup levels. Besides, high burnup levels can improve fuel economy and reduce the total amount of spent fuel in reactors. The formation of high burnup fuel particle is closely related to the failure behavior of ceramic dispersion fuel, and it is of great significance to focus on the strength analysis and cracking behavior of high burnup fuel particle. The representative volume element of dispersion fuel was innovatively established in this paper, and the heterogeneity of pore size and position in high burnup fuel particle was considered, corresponding parametric modeling and mechanical simulation procedure of high burnup fuel particle was realized automatically. The impacts of mechanical property of matrix, distance between fuel particles, ambient hydrostatic pressure and damaged layer on the strength of the fuel particles were analyzed systematically. The results show that the distance between fuel particles increases, the less possibility of crack initiates from the fuel particle. The existence of damaged layer will increase the risk of cracking of the fuel particles slightly. Due to the stress interference of the heterogeneous pores, crack initiates from multiple sites within the fuel particle, and the danger zones are more possibility located at the outer space, which is consistent with the experimental observations. Besides, danger zones within the high burnup fuel particle were characterized by larger pores and pore strings. It can be inferred that the formation of larger pores is probably due to the continuous coalescence of small pores and their surrounding pores. The constraint pressure of matrix on the fuel particle is not a constant, specially, it fluctuates significantly, and its average value increases linearly with the ambient hydrostatic pressure. Increasing the elasticity modulus of the matrix will inhibit the cracking behavior of the fuel particle, which reveals that the matrix should be designed more stronger and tougher. The higher the ambient hydrostatic pressure, the less likely the fuel particle will crack. While shortening the distance between fuel particles, and the impact degree of ambient hydrostatic pressure reduces. This work realizes the accurate calculation of the internal stress field of high burnup fuel particle and establishes a high burnup fuel cracking strength evaluation model based on fine microstructure modeling. Besides, this paper provides an analytical method and numerical reference for the failure study and optimal design of dispersion fuel under high burnup conditions.

The influence of the scale effect on the strength of mechanically inhomogeneous welded structures with a soft zone was studied. The investigated welded samples were made of two 12Kh18N10T austenitic steel plates and a low-carbon ferritic insert connected between them by two dissimilar welded joints performed by electron beam welding. Tensile strength as a function of soft zone relative thickness for tensile specimens was plotted. It was shown that with a relative thickness of the soft zone in the range from 0.2 to 0.5, the scale effect did not manifest during tension. This can be explained by low plastic compressive deformations in the soft zone after heat treatment, which typically lead to a decrease in the constraint effect due to the Bauschinger effect. [ABSTRACT FROM AUTHOR]

One of the challenges of managing grasslands sustainably is the conflict between the different ecosystem services they provide. This is especially evident in the Qinghai-Tibetan Plateau (QTP) region, where fragile alpine ecosystems make balancing the needs of grassland conservation and development difficult. However, our current understanding of the relationships and drivers of ecosystem services in degraded alpine shrub meadows on the QTP is insufficient. To address this, we studied forage provisioning and water retention services in a degraded alpine shrub meadow in the northeastern QTP. We analyzed the changes and relationships between these services at different levels of degradation and identified those factors that influenced ecosystem service relationships. The results showed that the forage supply service and the water retention service of the alpine shrub meadow increased and decreased by 23.6% and 27.07%, respectively, due to degradation. The trade-offs between these two services varied depending on the degree of degradation, with light and moderate degradation showing a preference for water retention service, and heavy and extreme degradation showing a preference for forage supply. Water retention was constrained by forage supply and both services showed an exponential function form of decay. The physical and chemical properties of the soil in the alpine shrub meadow remained relatively stable during the degradation process, with only soil organic carbon (SOC), total potassium (TK), and total nitrogen (TN) decreasing significantly. SOC may have indirectly influenced the relationship between the two services by affecting water retention. This study provides insights into alpine shrub meadow management and conservation on the QTP. [ABSTRACT FROM AUTHOR]

When the thermal maturity of the Longmaxi Formation in the southern Sichuan Basin is too high, the pore structure of shale becomes poor. Therefore, to investigate the effect of organic matter thermal maturity on shale pore structure, a study was conducted. Using the Longmaxi Formation shale in the southern Sichuan Basin as an example, the intrinsic relationship between shale porosity, pore structure parameters, organic matter laser Raman maturity, and organic matter graphitization degree was examined using X-ray photoelectron spectroscopy, particle helium porosity measurement, organic matter micro-laser Raman spectroscopy, and gas adsorption experiments. The results indicate that thermal maturity is the macroscopic manifestation of the graphitization degree of organic matter, and the correlation coefficient between the two is 0.85. A thermal maturity of 3.5% (with a corresponding organic matter graphitization degree of 17%) aligns with the highest values of shale porosity, pore volume, and pore-specific surface area across all pore size conditions. The evolution model of shale pore structure can be divided into two stages. The first stage is characterized by a thermal maturity between 2.0% and 3.5% (with a corresponding degree of graphitization of organic matter between 0% and 17%). During this stage, the number and connectivity of micro-macropores increase with increasing thermal maturity. The second stage is marked by a thermal maturity between 3.5% and 4.3% (with a corresponding degree of graphitization of organic matter between 17% and 47.32%). Basement faults are present, leading to abnormally high thermal maturity, poor preservation conditions, continuous generation of micropores, better connectivity, and a reduced number of pores. Medium macropores with good connectivity suffer from gas loss in the fracture network, leading to the collapse and disappearance of pores. The results mentioned in the statement have an important guiding role in the efficient exploration of shale gas in the Longmaxi Formation in the southern Sichuan Basin.

The leak-before-break design concept is based on J-R curves, which are obtained by J-R tests on various types of specimens and are known to be dependent on the cyclic load history. The J-R curves of standard specimens suggested by the American Society for Testing Materials are determined based on quasi-static tensile loading. However, seismic loading induces a reverse cyclic loading that alternately applies a tensile and a compressive load to nuclear plant piping. Therefore, it is very important to obtain the fracture toughness characteristics under reverse cyclic loading for the integrity estimation of nuclear plant piping. The objective of this paper is to study the effects of reverse cyclic loading on the fracture toughness characteristics of SA312 TP316L stainless steel, which is a nuclear plant piping material. J-R tests on a flat, equivalent stress gradient specimen with varying incremental displacement were carried out. The test results were reviewed by comparing the J-R test results under quasi-static loading. In addition, the safety margin of the nuclear plant piping was evaluated using a crack driving force diagram method. For the SA312 TP316L stainless steel, the results showed that the J-R curves were decreased with a decrease in the incremental displacement. When the incremental displacement was set to 0.25 mm, the unstable crack growth point value was about 73.0% of those for the quasi-static loading conditions.

Three types of representative unit cell (RUC) of [±θ/904]S composite laminates and cracked plies were created to obtain the constitutive model of the cracked plies and to compare their accuracy of the calculation. The RUCs represent the damaged laminates, cracked plies, and cracked plies with additional constraints. A correction factor was defined to improve the accuracy of transverse modulus estimation using the RUC of cracked plies with constraints. The correction factor and numerical results were discussed to illustrate the constraint effect of the adjacent plies on the cracked plies in terms of stiffness, orientation, and thickness. [ABSTRACT FROM AUTHOR]

In order to examine the dynamic response of a girder-orbit-moving load coupling system considering the constraint effect of the orbit extension, an analytical calculation method for the dynamic response of the girder-orbit system with arbitrary boundary conditions under a moving load is proposed based on the finite Fourier transform. Using the analytical calculation method, the dynamic response of the girder-orbit system with orbit extension at different moving load speeds is calculated, and the calculated results are compared with ANSYS finite element numerical calculation to examine the effect of moving load speed, orbit and girder flexural stiffness, interlayer spring stiffness, and orbit extension length on the dynamic response of the system. Results show that the analytical calculation results are in good agreement with the ANSYS calculation results, verifying the correctness of the analytical calculation method. The amplitude-moving load velocity relationship curve of the girder-orbit system dynamic response is a waveform curve. The interlayer spring stiffness, orbit flexural stiffness, and orbit extension length have significant effects on the dynamic response of the orbital layer, but the effect on the dynamic response of the girder layer is not significant. [ABSTRACT FROM AUTHOR]

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents fracture mechanics analysis results for various cracks located at pressurized water reactor pressure vessel nozzle crotch corners taking into consideration constraint effect. Technical documents such as the ASME B&PV Code, Sec.XI were reviewed and then a fracture mechanics analysis procedure was proposed for structural integrity assessment of various nozzle crotch corner cracks under normal operation conditions considering the constraint effect. Linear elastic fracture mechanics analysis was performed by conducting finite element analysis with the proposed analysis procedure. Based on the evaluation results, elastic-plastic fracture mechanics analysis taking into account the constraint effect was performed only for the axial surface crack of the reactor pressure vessel outlet nozzle with cladding. The fracture mechanics analysis result shows that only the axial surface crack in the reactor pressure vessel outlet nozzle has the stress intensity factor exceeding the low bound of upper-shelf fracture toughness irrespectively of considering the constraint effect. It is confirmed that the J-integral for the axial crack of the outlet nozzle does not exceed the ductile crack initiation toughness. Hence, it can be ensured that the structural integrity of all the cracks is maintained during the normal operation.

Nuclear power plants should be strictly protected against earthquakes. Especially in nuclear power pressure vessels, there are a lot of dissimilar metal welded joints（DMWJ）. They are the weak link owing to their highly heterogeneous microstructure; mechanical; thermal; and fracture properties, and some defects that occur at different positions within the DMWJs. To ensure the safety of nuclear power pressure vessels, it is important to examine the fracture behavior of DMWJ in detail. In addition to the earthquake loads, constraint is an important factor affecting the fracture behavior of DMWJ. To understand this behavior, both constraint and earthquake loads must be considered. In this study, taking nuclear safe end DMWJ as the research object, four single edge-notched bend（SENB） specimens with central crack under different constraints were selected. Different vertical earthquake loads under five earthquake intensities and three actual earthquakes were applied to the specimen respectively by mass acceleration application method. The fracture behavior of DMWJ under various vertical earthquake loads and the interaction between vertical earthquake load and constraint were numerically simulated. The results showed that with the increase of earthquake intensity, the J-R curve of DMWJ gradually decreases. In contrast to the DMWJ with high constraint, the decrease of J-R curve of the DMWJ with low constraint is more obvious. It is related to the fracture mode of DMWJ under different constraints. Under the actual earthquake, the change of J-R curve is related not only to the earthquake magnitude, but also to the acceleration time history curve of earthquake wave.

Identifying the multiscale relationships of ecosystem services (ESs) and their influencing factors is helpful for scientific decision-making and regional sustainable development. Different from previous studies on trade-off and synergy relationships, this paper introduced a new perspective of the constraint effect and reports a third type of service relationship. This paper first assessed four typical ESs in the Pearl River Delta region, including water conservation (WC), soil conservation (SC), habitat quality (HQ), and natural recreation (NR). Applying segmented quantile regression, constraint lines for scatter plots of NR and three other ESs were extracted on 8 scale series. The key features of constraint lines were analyzed, and the multiscale constraint effects of four types of environmental factors on ESs were identified. The results showed that (1) NR-SC and NR-WC had a hump-shaped constraint relationship, while NR-HQ had a linear constraint relationship. The NR service not only has an amplifier effect on the trade-off and synergy strength relationship of other services, but its threshold range is also an important reference for realizing a win–win situation; (2) The threshold and key characteristics of the constraint line are closely related to the maximum and range values of vegetation coverage, slope, and landscape diversity; (3) Environmental factors had five constraining effects on ESs: hump-shaped, positive convex, negative convex, U-shaped and exponential, which not only limited the upper boundary of the ES supply but also had lower boundary constraint effects on specific services; and (4) When the vegetation coverage reached 70 %, the average annual precipitation reached 2000 mm, and the landscape diversity reached approximately 0.4, the total amount of ESs approached the maximum value. When the slope is close to 7.5°, monitoring of vegetation and soil erosion needs to be strengthened to reduce ecological risks. The application of the constraint line method in analyzing complex influence relationships has been proven to visualize nonlinear relationships and quantify the optimal values of influencing factors. It will help maintain the long-term stability of the entire ecosystem and become an effective tool for multiscale regional ecological planning.

To investigate the effects of stirrup ratio and connection type of stirrups on axial compression performance of stirrup-confined concrete-filled steel tubular (CFST) stub column, experiments were conducted on 16 CFST stub columns. The axial compressive bearing capacity and ductility of square and circular CFST stub columns with welded and non-welded stirrups were studied. Besides, numerical models of the stirrup-confined CFST stub columns were established to validate whether the numerical modeling method for welded stirrup-confined CFST column is suitable for the non-welded counterparts. Then, the applicability of the formulas for the axial compressive bearing capacity of the large stirrup ratio CFST stub column was investigated. The results indicated that the stirrups have a significant constraint effect on the steel tube and improve the axial compressive bearing capacity and ductility of the CFST stub column obviously. The effects of the stirrups on the square composite column are more significant than the circular composite column. The welded stirrups are more effective on the bearing capacity and ductility. The numerical modeling method and formulas are suitable for the non-welded stirrup-confined and large stirrup ratio CFST stub columns.

Summary: Nowadays, the grouted splice sleeve and grouting‐anchoring overlap‐joint of steel bars are widely used as a connection method between precast concrete elements. However, the further development of these connection methods in the engineering is limited because of the high construction cost and complex construction technology in China. Hence, a precast concrete reinforcement connector, that is, double‐pipe connector (D‐P connector) based on strong lapping concept, was proposed, and the feasibility of the D‐P connector was validated by tensile tests, and the failure pattern and mechanical properties of the specimens were observed. Then, the wall panel specimens that connectors were surrounded by concrete were tested to prove the constraint effect of surrounding concrete on the connecting members. Finally, the influences of the parameters, including grout strength, grout height, and connector length, on the failure pattern and mechanical properties of the specimens were investigated. The results show that the influence of the parameters on the performance of the specimens is insignificant, demonstrating that the infill material was mainly used to fix the relative positions of the bar and the D‐P connector. To save cost effectively, high‐strength grout could be replaced by common cement slurry, and the length of D‐P connector could be properly reduced. [ABSTRACT FROM AUTHOR]

The joint form plays a vital role in the rapid assembly of precast bridge decks for steel–concrete composite bridges. Existing research primarily focuses on studying the shear performance of joints through direct shear tests, which is insufficient to fully reflect the mechanical behavior of joints under the constraint of prefabricated bridge deck panels during actual vehicular traffic. Considering situations such as vehicle loads and external forces acting on precast bridge decks, this study investigates the shear performance of epoxy joints under constraint through an improved shear test. The influence of constraint force, shear key details and interface defects on the shear performance of epoxy joints is investigated. The results reveal that the shear test method employed in this study can realistically reflect the shear performance of epoxy joints in precast bridge decks. Both active and passive constrained epoxy joint specimens exhibited no interface cracks, and their failure modes were identified as shear failure between mid-span supports. Compared with passive constraint, the shear-bearing capacity of epoxy joint specimens under active constraint was increased by 86.1~130.6%. Among the epoxy joint specimens with depth–height ratios of 15/110, 25/110, 35/110 and 45/110, the joint with a depth of 35 mm demonstrated the highest shear strength. Furthermore, the shear performance of epoxy joints significantly deteriorated when the interface defects exceeded 30%, resulting in the failure mode transforming from shear failure to interface failure.

Dryland ecosystem services (ESs) have been severely harmed by global environmental changes and increased human activities. To improve ESs, it is necessary to understand how they interact in drylands. In this study, we selected Ordos dryland, which is situated in northern China, as the study area to assess its four key ESs—food supply (FS), carbon storage (CS), water yield (WY), and habitat quality (HQ)—and to identify the hotspots of multiple ES supply. Furthermore, we studied the constraint effects between ESs in Ordos in 2000, 2010, and 2020 and used a spatial trade-off model to map the trade-off and synergy areas of ESs from 2000 to 2010 and from 2010 to 2020. The results indicated that all four ESs in Ordos increased significantly over the study period. The hotspots for the supply of multiple ESs also increased in areal extent during this period, and the state of the regional ecological environment continued to improve. The constraint effect between ESs showed that as the CS increased, its constraint effect on WY and FS decreased and then increased, whereas its constraint effect on HQ only decreased; as the WY increased, its constraint effect on HQ decreased and then increased, and its constraint effect on FS continued to decrease; as the FS increased, its constraint effect on HQ continued to increase. From the change in the area of ESs trade-offs and synergies, there was an increase in the area of positive synergy for four pairs of ESs in Ordos, which were CS-WY, CS-HQ, WY-HQ, and FS-HQ. These findings help in establishing a scientific foundation for the management and optimization of ESs in drylands.

[Display omitted] • A more accurate higher-order asymptotic solution of 3D V-notch and crack front tip fields is established theoretically. • The constraint effect in 3D fracture cannot be simply separated into in- and out-of-plane parts. • A new 3D fracture parameter A 2 T related to the out-of-plane stress factor T z is proposed. • The constraint levels of 3D specimens can be characterized and quantified by combining A 2 T with T z. As one of the most important topics studied in creep fracture mechanics, mechanics fields at 3D sharp V-notch front tip in creeping solids have drawn remarkable attention at present. In this paper, the higher-order asymptotic analysis is carried out for 3D sharp V-notch front tip fields in creeping solids subjected to mode Ⅰ loading, and a 3D higher-order term solution is theoretically proposed by introducing the out-of-plane stress factor T z to establish the 3D nonlinear governing equations of front tip fields. The present higher-order asymptotic solution for 3D sharp V-notch can naturally be degenerated to that for 3D crack. It is found that the stress exponents and angular distribution functions of higher-order terms for 3D notch and crack are highly related to T z. The proposed 3D higher-order term solution overall shows better agreement with the FEA results than the existing 3D leading-term solution and 2D higher-order term solutions available in the literature, especially for smaller notch angle and shorter ligament lengths. Based on the 3D higher-order asymptotic solution, a new fracture parameter A 2 T is given and combined with T z to characterize 3D constraint effect. It is noted that the effects of A 2 T and T z on 3D constraint are highly interlinked rather than simply separated into in-plane and out-of-plane parts. The present 3D higher-order asymptotic solution can promote the understanding and characterization of 3D constraint effect and is of great significance in the evaluation of 3D fracture behavior and structural failure assessment under creep conditions. [ABSTRACT FROM AUTHOR]

• Dependency of constraint effect intensity on material and stress regime is addressed. • A parameter, K z , is proposed for the characterization of constraint effect intensity. • A generalized constraint-dependent CCG rate equation based on K z is established. • Advantage of the K z is demonstrated through comparison with existing parameters. The introduction of creep fracture constraint parameter offers the possibility of accurately obtaining the CCG rate for specimens/structures subject to different constraint levels through the establishment of constraint-dependent CCG rate equation. However, experimental evidence indicates that the existing constraint-dependent CCG rate equation is generally material- and stress regime-dependent. It is noted that the dependencies may be attributed to the intrinsic difference in creep failure mechanisms of materials, which has not been fully considered by previous constraint parameters. To cope with the dependencies, a parameter, K z , for characterizing the intensity of constraint effect is proposed in this work based on the representative rupture stress, which could better reflect the operative creep failure mechanism sustained by the material. To justify the parameter, finite element analysis is carried out for five different materials based on experimental data available in the literature. Results show that, compared to the existing constraint parameters, R * and A c , the K z is capable of characterizing the crack-tip constraint level under the influence of creep failure mechanism. Furthermore, a generalized constraint-dependent CCG rate equation is established based on the K z , which overcomes the material and stress regime dependencies of the existing equation. Finally, to clarify the advantage of the K z , further comparison between the new parameter and the existing parameters is made. [ABSTRACT FROM AUTHOR]

• As the crack length increases, the fracture toughness decreases. • A transfer model is established between fracture toughness and normalized T -stress. • The fracture toughness is fluctuational with specimen thickness due to LPBF defects and the change of fracture mode. Laser powder bed fusion (LPBF) is increasingly being used as an alternative to traditional manufacturing in the aerospace and biomedical industries. The effect of constraint on fracture performance is a crucial issue in assessing the integrity of engineering applications. This paper aims to better understand the fracture performance of Ti6Al4V components with different constraint levels produced by LPBF. Fracture toughness tests were performed on compact tensile (CT) specimens with varying crack length and specimen thickness. The results show that the fracture toughness decreases with increasing crack length, while the fracture toughness shows a large fluctuation with specimen thickness because of LPBF manufacturing defects. Both in-plane and out-of-plane constraint effects of a crack subjected to mode-I loading are analyzed by three-parameter K-T 11 - T 33 method. A correlation line between fracture toughness and normalized T 11 stress is established, which can be used to transform fracture properties of specimens with different constraint levels. [ABSTRACT FROM AUTHOR]

The creep fracture toughness of materials is required for the assessment of defective components at high-temperatures. Existing evidence indicates that creep crack-tip constraint state has a great influence on the fracture behavior of materials. In this work, the effect of constraint on creep fracture toughness was explored by conducting a series of creep crack growth tests on specimens with various thicknesses and loading modes. Results showed that the curves of creep fracture toughness with creep crack initiation time on the logarithmic scale for different groups of specimens were almost parallel with one another. Through the characterization of crack-tip constraint level for different groups of specimens in terms of a load-independent creep fracture constraint parameter, R *, the creep fracture toughness was found to increase with the decrease in the crack-tip constraint level. Moreover, evident effect of specimen geometry on creep fracture toughness was observed. Of all types of specimens, the CCT2 and CT10-SG exhibited the highest and lowest values of K c mat at the same t i , respectively. In addition, the K c mat was found to increase following a specimen group order of CT10-SG, CT10, CT5, SENT5, CT2, SENT2 and CCT2 at a given t i. Finally, a constraint-dependent creep fracture toughness equation was established for the Cr-Mo-V steel, which is expected for practical applications to improve accuracy of life assessment methods. Follow-up work on life assessment methods incorporating the constraint parameter R * is still necessary. [ABSTRACT FROM AUTHOR]

One of the challenges of managing grasslands sustainably is the conflict between the different ecosystem services they provide. This is especially evident in the Qinghai-Tibetan Plateau (QTP) region, where fragile alpine ecosystems make balancing the needs of grassland conservation and development difficult. However, our current understanding of the relationships and drivers of ecosystem services in degraded alpine shrub meadows on the QTP is insufficient. To address this, we studied forage provisioning and water retention services in a degraded alpine shrub meadow in the northeastern QTP. We analyzed the changes and relationships between these services at different levels of degradation and identified those factors that influenced ecosystem service relationships. The results showed that the forage supply service and the water retention service of the alpine shrub meadow increased and decreased by 23.6% and 27.07%, respectively, due to degradation. The trade-offs between these two services varied depending on the degree of degradation, with light and moderate degradation showing a preference for water retention service, and heavy and extreme degradation showing a preference for forage supply. Water retention was constrained by forage supply and both services showed an exponential function form of decay. The physical and chemical properties of the soil in the alpine shrub meadow remained relatively stable during the degradation process, with only soil organic carbon (SOC), total potassium (TK), and total nitrogen (TN) decreasing significantly. SOC may have indirectly influenced the relationship between the two services by affecting water retention. This study provides insights into alpine shrub meadow management and conservation on the QTP.

Material mismatch effect on the cracking behavior is an important topic for those welding structures. Characterization of the material constraint effect based on rigorously asymptotic solution is studied in this paper. Based on decomposition of the second order term, the constraint effect characterization parameter is decomposed as material constraint parameter and geometry constraint parameter. In general, the total constraint level for crack tip under undermatch condition is higher than overmatch condition. The specimen with positive biaxiality could lead to a higher constraint level compared with that of negative biaxiality. Geometry constraint effect and material constraint effect could not be separated independently from rigorously asymptotic solution for those cases with positive biaxiality. For a crack tip field under non-positive biaxiality, the material constraint effect can be characterized independently although it is approximate. For these conditions, the proposed material constraint effect and geometry constraint effected characterized are approximately independent on material mismatch factor, crack depth ratio and stress biaxiality. An empirical formula has been presented to characterize the geometry constraint effect and material constraint effect for the crack tip in the weldment under biaxial loading, which has been verified with fine accuracy. [ABSTRACT FROM AUTHOR]

Dissimilar metal joints (DMJs) are more common in the application of piping system of many industries. A 2- D and 3-D finite element analysis (FEA) is carried out on dissimilar metal Single Edged Notch Bending (DMSENB) specimens fabricated from ferritic steel, austenitic steel and Inconel – 182 alloy to study the behavior of DMJs with constraints by using linear elastic fracture mechanics (LEFM) principles. Studies on DMSENB specimens are conducted with respect to (i) dissimilar metal joint width (DMJW) (geometrical constraints) (5 mm, 10 mm, 20 mm, 30 mm and 50 mm) (ii) strength mismatch (material constraints) and (iii) crack lengths (16 mm, 20 mm and 24 mm) to study the DMJ behavior. From the FEA investigation, it is observed that (i) SIF increases with increase of crack length and DMJWs (ii) significant constraint effect (geometry, crack tip and strength mismatch) is observed for DMJWs of 5 mm and 10 mm (iii) stress distribution at the interfaces of DMSENB specimen exhibits clear indication of strength mismatch (iv) 3-D FEA yields realistic behavior (v) constraint effect is found to be significant if DMJW is less than 20 mm and the ratio of specimen length to the DMJW is greater than 7.4.

Fracture toughness test is an important method to monitor critical facilities' structural integrity and service life. Due to the limited storage space for test materials, these facilities may not provide sufficient specimens. Using sub-size specimen is one way to solve this problem. However, the resulting constraint loss often leads to errors in the measured fracture toughness. In terms of quantifying and correcting such deviations, a current research hotspot is the toughness scaling model (TSM for short) based on the Beremin model. This paper will apply the latest modified Beremin model to this TSM to study the scaled fracture toughness probability distribution. In the article, a new parameter calibration method is proposed to reduce the uncertainty of parameters used in the TSM. After that, the TSM based on the modified Beremin model is used to scale the fracture toughness of the sub-size specimens and compared with the standard specimens. The results show that the TSM still cannot accurately scale the entire J-integral probability distribution of small specimens. It is also found that the parameter α, which describes the J-integral distribution of the specimens, has a noticeable influence on the scaled fracture toughness, and this influence can be used to reduce the deviation of the scaled fracture toughness. [ABSTRACT FROM AUTHOR]

The increasing interest in fine-grained blocks requires a deeper understanding of the impact of block size on urban vitality. To date, limited empirical tests of the underlying relationships at the city level have been conducted using the ordinary linear-squares method, assuming a linear relationship. However, urban vitality is a complex system, thus making the use of linear regressions unfeasible because the assumption of homogeneity of variance would be violated. Therefore, the constraint line method was introduced to deepen the understanding of the relationship between block size and urban vitality. This paper employed a kernel density estimation of small catering businesses, point of interest density, social media check-in density, and comment density as proxies of urban vitality. Wuhan is the largest megacity in Central China and has been selected for this case study. When the block size increased to almost 0.08 km2, the maximum kernel density estimation value decreased sharply from above 2.70 to 1.60; when the block size exceeded 0.30 km2, vitality values tended to decrease very slowly. The maximum urban vitality measured by the other three indicators dropped an order of magnitude when the block size increased to 0.06 km2, then gradually slowed down, and tended toward a plateau when the block size increased beyond 0.20. Therefore, the dynamic process can be divided into three phrases with multiple critical thresholds of block size. These are approximately 0.06, 0.08, and 0.20 km2 ranked from the best to worst. The study indicates that block size has a nonlinear and threshold effect on urban vitality by constraining the maximum urban vitality. In general, the positive effect of small block size over urban vitality was confirmed, and additionally, urban planners should propose urban planning schemes with smaller residential blocks below 0.06 km2. [ABSTRACT FROM AUTHOR]

• Constraint effects on fracture toughness are predicted using an elastic–plastic phase field model and modified boundary layer formulations. • The influence of plastic material properties on the constraint effects in fracture toughness is investigated. • The cleavage toughness under different T- stress is predicted using our approach. • The novel framework successfully captures the constraint effects in fracture toughness. Fracture toughness is dependent on geometry according to a phenomenon known as the constraint effect on fracture toughness. In this paper, we propose a framework to predict constraint effects on fracture toughness using an elastic–plastic phase field model and modified boundary layer formulations. An elastic–plastic material was adopted because constraint effects are typically related to plastic deformation at the crack tip. Modified boundary layer formulations were used as loading methods to control phase field evolution at the crack tip. Numerical results indicate that fracture toughness increases with negative T -stress. The effects of yield stress and the linear hardening coefficient on constraint effects were also investigated. The results revealed that the variation in fracture toughness was greater in materials with low-strain hardening and yield stress compared to that in materials with high-strain hardening and yield stress. Finally, the variation in cleavage fracture toughness as predicted by our framework with a limited set of available experimental data was evaluated. The trend of the predicted results is consistent with that of the experimental results. [ABSTRACT FROM AUTHOR]

An estimating method, which conveniently and quickly predicts solutions of constraint parameter A in J-A two-parameter approach of elastic-plastic fracture mechanics (EPFM), was developed and successfully applied on three-dimensional (3D) cracked structures under both uniaxial and biaxial loading condition. The method (estimate formula) forA value estimate was developed theoretically first. Then, based on the obtained numerical solutions of parameter A from finite element analysis (FEA), the coefficient values of the proposed estimate formula were determined for 3D single edge cracked plate (SECP) structures under both uniaxial and biaxial loading, to estimate solutions of parameter A for 3D SECP. Through comparing predicted parameter A values with their FEA numerical solutions from authors and other researchers, it is validated that the proposed estimating method can be used well to predict A values for thin 3D cracked structures. It enables the application of the EPFM J-A two-parameter approach on practical engineering structure analysis and design of sensor and other mechanical systems.

A two-order asymptotic solution for sharp V-notch tip mechanics field in elasto-viscoplastic solids with power-law form under mode I loading is developed. The stress exponents and angular distributions for various notch angles and viscoplastic exponents for the second terms are reported. The stress exponent of the first order is singular and is non-singular except for low creep exponent with small notch opening angle. Compared with finite element results from several V-notched specimens, it is found that the two-order solution can have a better estimate for those cases with small notch opening angles, e.g., α = 30° under n = 5, than that of one-order solution regardless of viscoplastic extent, specimen type and loading level. One-order term solution is demonstrated to be sufficient to characterize the full field of sharp V-notch specimen for those conditions that elastic term is considered into higher order term, e.g., α = 60° under n = 5, in all specimens under various viscoplasticity extents. [ABSTRACT FROM AUTHOR]

The geometry of cracked pipe, loading condition and crack size all can have a strong effect on its resistance against crack-tip plastic deformation and crack growth. Usually, specimens listed in test standards (e.g. CT specimen) are applied to evaluate the fracture resistance (J-R) curves, which may cause excessive safety margin in leak-before-break (LBB) design of nuclear pipes. In this study, standard (CT) specimen and constraint designed specimens, including curved CT and compact pipe (CP) specimens were applied to measure the J-R curves of nuclear pipes. Finite element analysis (FEA) was applied to derive J-equations to calculate J-R curves for newly designed specimens. Constraint effects in these specimens and full-scale pipes under various loading conditions were compared according to crack-tip plastic deformation level. Then, safety margins in LBB design using these specimens were quantitatively analyzed by constructing the critical crack length lines. Both the tests and FEA results verified the validity of these constraint designed specimens for reducing conservatism. [ABSTRACT FROM AUTHOR]

AA2050-T84 alloy is widely used in primary structures of modern transport aircraft. AA2050-T84 is established as a low-density aluminum alloy with improved Young’s modulus, less anisotropy, and temperature-dependent mechanical properties. During flights, loading rate and temperature variation in aircraft engine subsequent parts are commonly observed. The present work focuses on the effect of loading rate and temperature on tensile and fracture properties of the 50 mm thick (2-inch) AA2050-T84 alloy plate. Quasi-static strain rates of 0.01, 0.1, and 1 s−1 at −20 °C, 24 °C and 200 °C are considered. Tensile test results revealed the sensitivity of mechanical properties towards strain rate variations for considered temperatures. The key tensile properties, yield, and ultimate tensile stresses were positive strain rate dependent. However, Young’s modulus and elongation showed negative strain rate dependency. Experimental fracture toughness tests exhibited the lower Plane Strain Fracture Toughness (KIC) at −20 °C compared to 24 °C. Elastic numerical fracture analysis revealed that the crack driving and constraint parameters are positive strain rate dependent and maximum at −20 °C, if plotted and analyzed over the stress ratio. The current results concerning strain rates and temperatures will help in understanding the performance-related issues of AA2050-T84 alloy reported in aircraft applications.

To investigate the bearing behavior of symmetrical full-scale different strength concrete filled double skin steel tube (CFDST) stub columns, 19 full-scale specimens were designed, considering the slenderness ratio (λ); the compression strength of core concrete and sandwich concrete (fcki, fcko), the thickness of the inner and outer steel tubes (ti, to); the diameter of inner and outer steel tubes (Di, Do); and the tensile strength of the inner and outer steel tubes (fyki, fyko) as the main parameters. Nonlinear constitutive models for concrete considering constraint effect were adopted, and a finite element (FE) model was established using ABAQUS software. By comparing the results between simulations and experiments, the rationality of the modeling method was verified. Based on the FE model, the parameter analysis for CFDST columns were conducted, and the force mechanism, stress distribution, and deformation process were analyzed. The results showed that the axial compression bearing capacity (Nsu) increased significantly with an increase in fcki, to, Do, and fcko, while Nsu decreased gradually with an increase in λ. Finally, according to the calculated results of the specimens, the calculation formula for Nsu of full-scale composite columns was statistically regressed using 1stOpt software and showed a good agreement with the FE.

Displacement fields around the fatigue crack tip for a constant value of stress intensity factor (SIF) range were measured using digital image correlation (DIC) technique on the S355 J2 steel grade. The data obtained were resolved into the T‐stress evaluation and quantification of its influence on the fatigue crack growth rate. The higher order terms of the Williams expansion (WE) were calculated as well. The displacements of a set of points outside of the plastic zone were selected for application of the over‐deterministic method (ODM) to obtain several initial WE terms. The computed values of T‐stress show good agreement with finite element analysis and literature. It was shown by collected experimental displacement, that the level of constraint influences the fatigue crack propagation rate. [ABSTRACT FROM AUTHOR]

This work reported the abnormal constraint effect of graphene on the structural and optical properties of in situ grown Gr@WO 3 nanobrick (NB) hybrid nanomaterials. Stable hybrid Gr@WO 3 nanomaterials were synthesized through a one-step hydrothermal method, in which different graphene contents (0.1, 0.3 and 0.5 wt%) were directly introduced into the precursor solution of tungsten oxide. The existence of graphene in the nucleation phase of tungsten oxide NB decreased the crystallite size from 49.5 nm to 45.3 nm, increased the microstrain from 1.10% to 1.44% and the optical bandgap of the hybrid samples from 2.68 eV to 2.78 eV, and reduced the radiative recombination efficiency of tungsten oxide NB. The hybridization between graphene and tungsten oxide NBs was confirmed by X-ray diffraction and Raman scattering analysis. The optical properties of materials were studied based on the absorbance and diffuse reflectance spectra. In this work, we also proposed a reliable method to estimate the optical bandgap of the sample from the diffuse reflectance spectrum. These findings would introduce an alternative method of fabrication and enhance the understanding of in situ hybrid materials. [ABSTRACT FROM AUTHOR]

The effects of T -stress on the stress field, creep zone and constraint effect of the mode I crack tip in power-law creeping solids are presented based on finite element (FE) analysis in the paper. The characteristics of the crack tip field in power-law creep solids by considering low negative T -stress and high positive T -stress are studied in the paper. The differences of T -stress effect on the crack tip field between power-law creeping solids and elastoplastic materials are also clarified. A modified parameter is proposed to characterize the influence of T -stress on creep zone. The constraint parameter Q under both small-scale creep and large-scale creep with various T -stresses for the modified boundary layer (MBL) model and various specimens with different crack depths are given. The applicability and the limitation of the MBL model for creep crack are also investigated. The inherent connection between T -stress and Q -parameter is discussed. The investigations given in this paper can further promote the understanding of T -stress effect and constraint effect on the mode I creep crack. [ABSTRACT FROM AUTHOR]

The impact of high-velocity projectiles on fluid-filled containers can induce the hydrodynamic ram (HRAM) effect, leading to the creation of a cavity within the fluid. The evolution of this cavity is subject to the constraints imposed by the container. This study aims to investigate the decay of projectile velocity and the development of confined HRAM cavities using a combined approach involving experimental and analytical methods. In contrast to existing research, this study accounts for the varying projectile velocities during different HRAM phases. Furthermore, enhancements have been introduced to the established cavity model, encompassing refinements in pressure differentials both inside and outside the cavity, alongside adjustments to the radial extent of liquid disturbance. The effectiveness of these refinements has been substantiated through experimental evidence. The findings illuminate two prominent constraint effects exerted by the container on the dynamics of HRAM cavities. Primarily, it accentuates the disparity in HRAM cavity pressures between the interior and exterior environments, and this pressure differential follows an exponential decay with distance. Secondly, it profoundly influences the flow of liquid near the wall, resulting in a considerably slower contraction of the cavity near the wall compared to its expansion phase. The evolution of the HRAM cavity is observed to manifest across three distinct stages: the unconfined cavity expansion stage, the partial cavity confinement stage, and the full cavity confinement stage. [ABSTRACT FROM AUTHOR]

• Constraint effect is experimentally investigated on two different superalloys. • A coin-shaped small compact tension specimen for CCG test was developed. • Intensity of constraint effect varies simultaneously with creep fracture mechanism. • Connection between constraint effect intensity and fracture mechanism was explained. To further clarify the relation between the intensity of specimen size effect on creep crack growth (CCG) rate and operative creep fracture mechanisms, CCG testing and mechanism observation were carried out for two superalloys IN625 and IN783. Results show that the CCG data of different specimen types for IN625 basically coincide at 650 °C. In contrast, strong specimen size effect was observed in IN783 at 560 °C, that is, the CCG rate increases with the increase in specimen thickness, producing the largest CCG ratio of approximately seven. The load-line displacement and fracture mechanism analyses indicate that the IN625 specimens failed in a ductile and intergranular manner, while the IN783 specimens in a brittle and intergranular manner. The present study suggests that the influence of creep fracture mechanisms should be considered in the characterization of the specimen size effect on CCG rate. [ABSTRACT FROM AUTHOR]

The specimen is a reactor pressure vessel with a semi-elliptical surface crack with axial orientation and its 3D finite element numerical modeling is built. Based on J-A2 two parameters method,analysis is performed by considering constraint effect,at T = 561 K,p = 10 MPa. Three different aspect ratio（ a/c） and Ramberg-Osgood exponent（ n） is analylized,namely a/c = 1/2,1/3,1/5（ a = 20 mm,c = 40 mm,60 mm,100 mm） and n = 10,15,20. The corresponding J-integral and constraint parameter A2 is gained. The research results show that: J-integral increases with the decrease of aspect ratio a/c,and RambergOsgood exponent（ n） almost has no effect on J-integral. The increase of Ramberg-Osgood exponent（ n） will weaken the effect of aspect ratio a/c on A2. The most serious point is the deepest point of a crack.

Ecological restoration efforts to combat soil loss often fail to deliver the expected benefits despite enormous investments. Better understanding the close relationships between climate, vegetation, and non-linear ecosystem dynamics can help restoration activities meet their intended goals. The severely eroded Loess Plateau (LP) was selected for a case study to investigate the underlying drivers of soil retention change and their non-linear constraint impacts. The soil retention function was substantially enhanced during 2000–2015, while the water yield function was weakened. Both the favourable changes in climate conditions (i.e., increasing precipitation and declining evapotranspiration) and governmental policies for soil and water conservation and ecological restoration promoted vegetation restoration and expansion, thereby strengthening the soil retention function. Consequently, water and sediment yields declined significantly. The relationship between water yield and soil retention is non-linear and shows that the two ecosystem functions can be either in synergy or in trade-off according to the level of vegetation cover. We observed that the vegetation cover had an upper threshold (i.e., 50%) for controlling the soil erosion because of the limited water condition (rainfall), which implies that the effect of vegetation on reducing the water erosion reached its maximum capacity when the plant cover was 50%. Considering the limited water conditions in drylands, to minimize the trade-off between the water yield and soil retention and to maximize the effectiveness of ecological restoration programs, it is recommended that the overall vegetation cover in the LP be controlled at approximately 30–40%, i.e., without exceeding 50%. Currently, the non-linear constraint effects of the water condition and vegetation cover on the soil retention are yet to be thoroughly understood. Moreover, practical policy recommendations require further field-based observations and experimental studies. • The soil retention function change during 2000–2015 was assessed. • The non-linear boundary of limited water resources was investigated. • The ecological restoration strategies in degraded drylands were discussed. [ABSTRACT FROM AUTHOR]

This paper proposes a node release approach to estimate the fracture resistance curve, often known as the J‐R curve, for monotonic and cyclic fracture tests. The node release approach simulates the crack extension by releasing the constraints imposed on the node at the crack tip and estimates the J‐R curve by coupling the domain integral value with the corresponding crack extension. This proposed node release approach estimates closely the J‐R curve for SE(B) and SE(T) specimens subjected to monotonic loading. For SE(T) specimen under cyclic loading, this study implements the node release analysis in two approaches: (1) an equivalent monotonic analysis corresponding to the envelope of the cyclic load‐CMOD response and (2) a direct cyclic simulation. Both approaches lead to close estimations of the experimentally measured J‐R curve. The numerical analysis also confirms the path independence of the domain integral values in the direct cyclic simulation. [ABSTRACT FROM AUTHOR]

Abstract We report the formation of wrinkles with tunable wavelength in Ag films and Mo films deposited on polydimethylsiloxane (PDMS) and PDMS/Si substrates by magnetron sputtering at 50 °C. The PDMS-supported Ag films have the wrinkles with μm-sized wavelength, while the sub-μm-sized wrinkles are engendered in the Ag films on PDMS/Si substrates due to the constraint from the substrates. By contrary, Mo films with a similar thickness range exhibit wrinkles with μm-sized wavelength on the PDMS/Si substrates, much larger than that of Ag films on the same substrates. This indicates that the wrinkle wavelength in metal films depends closely on the substrates and the characteristics of metal films. The possible reasons for the discrepancy in wavelength between experiments and theoretical predictions are discussed. The wettability of the wrinkled surfaces is predominantly controlled by the length scale of the wrinkles. In the Ag films with sub-μm-sized wrinkles, droplet contact angle is highly sensitive to the surface roughness, i.e. , increasing quickly with the surface roughness. However, in the PDMS-supported Ag and PDMS/Si-supported Mo films both with μm-sized wrinkles, the contact angle raises slowly with the surface roughness. It is thus evident that a wettability spectrum derived from the wrinkling pattern can be artificially developed by tuning the wavelength in different length scales through controlling of substrates, metal films, and film thicknesses. Highlights • The wrinkles with tunable wavelength were created on metal film surfaces. • The wavelength can be tuned by the substrates, film constituent and thickness. • The wettability of the wrinkled surfaces was controlled by the wavelength. [ABSTRACT FROM AUTHOR]

Abstract In this work, enhanced theoretical analysis and finite-element (FE) simulation were carried out to evaluate the creep crack initiation times by coupling the stress-regime creep strain rate and creep ductility and constraint effect. Firstly, the enhanced theoretical approaches were derivated based on the ductility exhaustion model, 2RN (2 regimes Norton) creep model and the Fermi's fit (between the creep ductility and creep strain rate), and several analytical models of CCI prediction were proposed under the different stress field condition. Then the constraint effect was coupled into the enhanced C*-Q* approaches. The comparison of CCI time predictions between the FE solutions and the enhanced C*-Q* approaches verified the accuracy of the latter. Reasonable and conservative predictions of CCI time could be obtained from the theoretical solutions when the constraint effects were considered in the K-RR and HRR-RR controlled models when compared with FE solutions. The K-RR and solutions were accurate when initial stress intensity factor K was at low and high range, respectively. Finally, the accuracy of the enhanced approaches and the suitability of finite element simulation were validated by the experimental data of 316H steel. Highlights • Enhanced theoretical analysis and finite-element simulation are carried out to evaluate the creep crack initiation times. • 2RN creep model and Fermi's fit of creep ductility and constraint effect are coupled into the enhanced C*-Q* approaches. • K-RR and HRR-RR solution are accurate at low rage of initial stress intensity factor and high range respectively. • The accuracy of enhanced approaches and suitability of finite element simulation are validated by experimental data. [ABSTRACT FROM AUTHOR]