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51.
Strain-rate effects on concrete behavior 总被引:5,自引:0,他引:5
Gianluca Cusatis 《International Journal of Impact Engineering》2011,38(4):162-170
In this paper, a previously developed meso-scale model for concrete, called the Confinement Shear Lattice (CSL) model, is extended in order to include the effect of loading rate on concrete strength and fracturing behavior. The rate dependence of concrete behavior is assumed to be caused by two different physical mechanisms. The first is a dependence of the fracture process on the rate of crack opening, and the second is the viscoelastic deformation of the intact (unfractured) cement paste. In this study, the first mechanism is described by the activation energy theory applied to the ruptures occurring along the crack surfaces, whereas the second mechanism is modeled by the Microprestress-Solidification theory. The developed model is calibrated and validated on the basis of experimental data gathered from the literature. 相似文献
52.
Byeongho KimByoungsoo Kang Yongho Park Ikmin Park 《Materials Science and Engineering: A》2011,528(18):5747-5753
The effect of Pd addition (0, 2, and 4 wt%) on the microstructure and creep properties of permanent mold AZ61 (Mg-6Al-1Zn) alloy has been studied. The results indicate that Pd addition introduces a lamella-shaped Al4Pd phase at the grain boundary, in addition to the Mg17Al12 (β) phase. The addition of Pd also suppresses the precipitation of the Mg17Al12 phase and residual Al at grain boundaries during solidification. These effects lead to an improvement in the creep behavior of AZ61. Moreover, extended steady-state creep and reductions in both the minimum creep rate and total creep strain are also observed in the case of 4 wt% Pd addition. 相似文献
53.
HAYNES 282 and HAYNES 230 nickel-based superalloys were subjected to cold rolling deformation and heat treatments in order to investigate processing-microstructure-property relationships to understand the effects of thermomechanical processing on their microstructure and tensile-creep behavior. The sheet materials underwent four cycles of 20% reduction in thickness followed by a solution treatment. The resultant microstructures were characterized using electron backscattered diffraction and electron microscopy, and the high-temperature (973-1088 K (700-815 °C)) creep and fatigue behavior was evaluated and compared to the commercially available sheet alloys. The thermomechanical processing treatments did not significantly affect the grain boundary character distribution and almost half of all the boundaries in the microstructures were twin boundaries. The creep resistance was shown to degrade with the additional thermomechanical treatments, which resulted in finer equiaxed grain sizes. The HAYNES 282 alloy was shown to be significantly more creep resistant than the HAYNES 230 alloy. The fatigue behavior indicated that creep ratcheting occurred more prominently in the HAYNES 230 alloy than in the HAYNES 282 alloy and this was explained to be a result of the superior creep resistance exhibited by the HAYNES 282 alloy. Overall, this study suggests that additional energy-intensive processing treatments, beyond those involved in the commercially available sheet products, may not be beneficial for additional creep resistance. 相似文献
54.
Microstructure evolution in a 3%Co modified P911 heat resistant steel under tempering and creep conditions 总被引:1,自引:0,他引:1
A. Kipelova R. KaibyshevA. Belyakov D. Molodov 《Materials Science and Engineering: A》2011,528(3):1280-1286
Microstructure evolution was studied in a 3%Co modified P911 heat resistant steel during creep tests at 873 and 923 K to failure, which occurred in 4103 and 4743 h, respectively. The tempered martensite lath structure consisted of packets, blocks and laths. The average spacing of high-angle boundaries and the mean transverse lath size were about 1.9 μm and 360 nm, respectively. Various second phase particles precipitated upon tempering. Fine M(C, N) carbonitrides with an average size of about 30 nm were homogeneously distributed throughout the tempered martensite laths, while relatively coarse M23C6 carbide particles (average size 120 nm) were located at internal boundaries. The tempered martensite lath structure was rather stable upon aging for about 4 × 103 h. The boundary precipitates of M23C6 and Laves phases, which appeared during creep tests, exerted a high pinning pressure on low-angle lath boundaries and high-angle packet/block boundaries. The growth of martensite structural elements during the tests correlated with the coarsening of second phase particles. Quantitative relations of pinning and driving pressures for low- and high-angle boundaries are discussed. 相似文献
55.
56.
Bridge performance undergoes time-varying changes when exposed to aggressive environments. While much work has been done on bridge reliability under corrosion, little is known about the effects of creep and shrinkage on the reliability of concrete bridges. In this paper, the CEB-FIP model for creep and shrinkage is applied by using finite-element (FE) analysis in conjunction with probabilistic considerations. Verification is made by comparing the analytical findings with existing test data. More specifically, a time-dependent reliability assessment is made for a composite prestressed concrete (PSC) box-girder bridge exposed to a chloride environment. This realized via an advanced probabilistic FE method. The postcracking behavior of the thin-walled box girder is described using composite degenerated shell elements, and importance sampling is used to improve the efficiency of the reliability analyses. It is shown that concrete creep and shrinkage dominate during the early stages of bridge structure deterioration. This is accompanied by a decrease in reliability owing to the combined action of creep, shrinkage, and corrosion. The reliability indexes for the serviceability and the tendon yielding limit state fall below the target levels prior to the expected service life. Therefore, early maintenance and/or repair measures are required. 相似文献
57.
A numerical formulation for the nonlinear quasi-viscoelastic (creep and shrinkage) analysis of steel-concrete composite beams that are curved in their plan is developed. The creep behavior of the concrete is considered by using the viscoelastic Maxwell-Weichert?model, in which the aging effect of the concrete is taken into account. Geometric nonlinearities and the partial shear interaction that exist at the deck-girder interface in the tangential (or longitudinal) direction and in the radial (or horizontal) direction owing to the flexibility of the shear connectors are considered in the strain-displacement relationship. The modeling based on the developed formulation is validated by comparisons with available results reported in the literature. The effects of initial curvature, partial interaction, and geometric nonlinearity on the time-dependent behavior of curved composite beams are illustrated in selected examples. 相似文献
58.
Cladding creep rupture is thought to be the most likely and limiting failure mechanism of spent fuel in dry storage. In spite of being highly unlikely, the current trend towards high burnups is drawing further attention to the potential creep effect on cladding integrity of fuels burnt over 45 GWd/tU.This paper explores the burnup influence on cladding creep during dry storage by modelling two different high burnup scenarios (51 GWd/tU and 67 GWd/tU). In addition, sensitivity of the results to the in-reactor average power and power history has been conducted. The computation tool used in this study has been an extension of FRAPCON-3.4 capable of simulating dry storage scenarios. Burnup and average linear power have been shown to make creep grow quite substantially during the first two years in dry storage, adopting a quasi-asymptotic trend from then on. However, even though this profile seems to have a generic nature, the net creep value reached depends not just on integral and average variables, but also on magnitudes describing the entire irradiation history, like linear power history. In none of the cases explored creep approaches the 1% threshold. In-reactor FGR modelling has been highlighted as a key element to get accurate estimates of creep. 相似文献
59.
The capabilities of structural bonding are more and more used. Estimating the abilities of an adhesive to endure repetitive loadings and to keep stable its mechanical properties along service life is an essential point to analyze in order to conduct fatigue assessments. The aim of this study is to develop a predictive tool for describing the fatigue behavior of an adhesive in an assembly under cyclic loadings. The approach developed analyzes the influence of viscosity on the mechanical behavior of an adhesive in an assembly based on monotonic and creep test results. Thanks to the evaluation of viscous phenomena, it is possible to predict the cyclic response of the adhesive. The experimental approach uses a unique bonded joint designed to limit the stress concentrations and with a maximum stress state in the center of the adhesive. In this paper, following the strategy developed under monotonic loading, experimental results under cyclic loading are presented for different types of loading using several load ratios and amplitudes. These results underline that the evolution of viscous deformations depends on the loading type. Under shear loading and for a ductile structural adhesive, the experimental results are well described using a viscoelastic–viscoplastic constitutive model with nonlinear viscous parameters. This model makes it possible to analyze the influence of different parameters on the mechanical response of bonded joints under cyclic shear loadings. 相似文献
60.
《Soils and Foundations》2021,61(6):1581-1596
Recent works have shown that delayed events of particle crushing are partially responsible of creep deformation in granular materials, and that Stress Corrosion Cracking promoted by high humidity within particles is the source of this mechanism. A number of experimental studies have focused on creep behaviour of water saturated samples and wetting-deformation after soaking dry material. However, there are few evidences of the effect of varying total suction in time-dependent deformation of partially saturated crushable material, and this mechanism have been rarely considered in constitutive models. The aims of this paper are to present experimental evidence of the effect of total suction on compressibility and creep of sandy sized samples from crushed rock, and to propose a simple one-dimensional elasto-plastic modelling approach based on the enhancement of an existing model. Oedometric compression tests at different total suctions are presented. The results show that compressibility and creep strains increase with both stress and humidity. The model proposed uses a time-dependent hardening law coupling suction with the amount of particle breakage. Based on preliminary calibrations, the model captures the effect of suction and time-dependent behaviour over a large range of total suction. 相似文献