Engineering Fracture Mechanics最新文献

Interface cracks seriously affect the performance and service life of layered electronic devices. At nanoscale, the electric field concentration can be generated at the tip of insulating cracks by solely applying a uniform electric field loading, resulting in a large electric field gradient and thus inducing a significant converse flexoelectric effect. The deformation generated by the converse flexoelectric effect is expected to achieve crack shielding, however, its mechanism is still not clear. In this paper, the role of electric field gradients on interface crack behavior is studied by the collocation mixed finite element method (MFEM) and the J-integral. The result shows that the electric field gradient generated by a uniform electric displacement loading can reduce the J-integral of crack tips, achieving crack shielding. The result provides new ideas for the study of failure assessment, nanoscale fracture experiment and others.

To study the mechanical properties of coral aggregate seawater concrete (CASC), a combination of experiments and numerical simulations based on the HJC and K&C models was used, the failure mode and cube compressive/axial compressive/splitting tensile strength (f_cu, f_c, f_sp), complete stress–strain curve of CASC with different strength grades (C30 ∼ C55) and cement types (Portland cement, Basic magnesium sulfate cement) was studied, and the differences in the mechanical properties of CASC with lightweight aggregate concrete and ordinary aggregate concrete was revealed. The results show that: cube/prismatic/splitting tensile specimens of CASC mainly suffer from quadrangular cone damage/oblique damage/central cracking damage, respectively. BMSC can significantly reduce the brittleness and increase the ductility of CASC. A significant linear relationship between f_cu and f_c, f_sp for C30 ∼ C50 CASC was found and the corresponding transformations was established. The numerical model suitable for researching the mechanical properties of CASC was proposed, the errors between simulated and measured values of f_cu, f_c and f_sp of C30 ∼ C50 CASC were 2.5 % ∼ 3.1 %, 4.4 % ∼ 5.7 % and 2.7 % ∼ 4.4 %, respectively. Considering the characteristics of high brittleness of CASC, a more suitable stress–strain curve model is proposed, the accuracy can be improved by 1.6 % ∼ 5.9 %.

In order to analyze the mechanical behavior of plastic fiber bundle, a theoretical model considering elastic and plastic behavior of single fiber is established. Based on uniaxial tensile tests of polythene single fiber, elastoplastic mechanical properties, such as elastic modulus and plastic modulus, are obtained. Moreover, distributions of yield strength and breaking strength of single fiber are determined. The stress–strain curve of polythene fiber bundle is predicted by theoretical model. The correctness of this theoretical model is verified by uniaxial tensile test of polythene fiber bundle. All experimental data points are within the range predicted by theoretical model. Some key parameters which regulate mechanical behavior of single fiber are investigated theoretically. Results show that Weibull parameters of yield strength and breaking strength of single fiber have great effect on mechanical performance of fiber bundle. The concentration of distribution area of breaking strength can improve the overall fracture strength of fiber bundle. Results and conclusions in this investigation can extend and perfect fiber bundle model in terms of plastic behavior.

The Hoek-Brown strength criterion has been widely used to estimate the strength of intact rocks and rock masses, and has been continuously developed. However, in the latest version of the standard, the criterion still ignores the influence of the intermediate principal stress. To study the different effects of intermediate principal stress on rock failure under triaxial or multiaxial stress states, this paper proposes a modified three-dimensional H-B strength criterion, which can be reduced to the H-B criterion, three-dimensional Priest criterion, Jiang’s (2012) criterion, and the Cai criterion. Multiaxial test data of six intact rocks were used for validation and applicability analysis. The results show that the proposed criterion can well describe the trend of multi-axial test data of six kinds of rocks, and the average mismatch of the six types of rocks is controlled within 10 MPa, which is much smaller than the fitting error of the original H-B criterion, Mogi criterion and Jiang’s criterion, indicating that the criterion has a good prediction effect on rock strength. The proposed criteria can provide a basic theory for the future construction of in-situ rock mass strength.

Early-age cracking in massive concrete has long attracted research focus, essentially governed by the game between crack driving and resistance. However, cracking resistance aspect received inadequate attention. This study examines the impact of crack resistance properties development processes on shrinkage cracking law in early-age concrete, employing chemo-thermo-mechanical coupling phase-field model. Two quantitative evaluation indicators, namely the index of damage development and average growth rate of maximum damage, are introduced to characterize the process of damage and cracking. The findings demonstrate that the development processes of elastic modulus and tensile strength exert a considerable influence on shrinkage cracking process in early-age concrete, whereas the impact of fracture energy development process is insignificant. Multifactor analysis revealed substantial coupling effects among parameters. Additionally, an anti-crack reverse design method is proposed based on the global optimization analysis, which can guide the optimization design of shrinkage crack prevention and control in early-age concrete from both perspectives of crack driving and crack resistance.

The influences of elastic/plastic loading (100–220 MPa) on the creep behavior, mechanical properties, and corrosion behavior of creep-aged AA2050 alloys were investigated. The results show that the creep rate increased from 0.35 % to 0.61 % with the increase of stress from 100 MPa to 220 MPa. The creep rate was increased rapidly under plastic loading (220 MPa) due to the increased dislocation density. Meanwhile, the plastic loading shortened the peak-aged time of creep-aged alloys and achieved outstanding strength (UTS=534 MPa, YS=496 MPa, peak aged), which increased by 33 MPa and 32 MPa compared with elastic loading, respectively. The strength enhancement was attributed to the increase in dislocation density, weak oriented precipitation effect, and dense precipitation of T₁ phases. Additionally, compared with elastic loading, GBPs under plastic loading coarsened and distributed discretely, their elements content distributed evenly, and the Cu content increased. Therefore, the intergranular corrosion (IGC) depth and stress corrosion cracking (SCC) susceptibility index (I_SSRT) decreased from 174 μm, and 8.7 % to 121 μm, and 5.9 %, respectively. These findings pave a way in breaking curvature limit of creep aging technology.

High-temperature-assisted rock breaking is a promising technique, with conventional and microwave heating being widely used methods. Understanding the mechanisms of conventional and microwave heating on the dynamic mode-I fracture characteristics of rock is crucial for engineering applications. Dynamic mode-I fracture experiments were conducted on Notched Semi-Circular Bending (NSCB) specimens at 25, 200, 300, 400, and 500 °C under both heating methods. Additionally, a finite element-discrete element coupled numerical method was developed to simulate the dynamic mode-I fracture process in high-temperature granite. The study investigated the effects of both heating methods on the fracture process and morphological features of the rocks, revealing differences in damage mechanisms across various scales. Results indicated that both heating methods similarly influence the fracture toughness of granite, with fracture toughness initially remaining nearly unchanged and then rapidly decreasing, with 200 °C identified as the threshold temperature. Moreover, the fractal dimension increased exponentially with temperature. The fracture mechanisms associated with conventional and microwave heating were also discussed.