查看更多>>摘要：Corrosion fatigue damage can lead to degradation of engineering structures and components. As a major stage of the total corrosion fatigue life, the crack initiation of pitting corrosion and fatigue is studied. A continuum damage mechanics model for predicting the crack initiation life of pitting corrosion fatigue is presented based on a pure fatigue damage model and a fracture-mechanics-based pit-to-crack transition criterion. The synergistic effect of pitting corrosion and fatigue are quantified as a time-varying amplification of the fatigue stress field. The proposed model is validated by corrosion fatigue test data of two different metallic materials. The predicted curves of corrosion fatigue crack initiation life are in good agreement with the test data. The model demonstrates a good prediction of corrosion fatigue crack initiation life, i.e., corrosion fatigue life is always lower than fatigue life, and the lower the stress, the more significant the life reduction.
Ferreira, G., VCampos, E. R. F. S.Neves, R. S.Desmorat, R....
30页
查看更多>>摘要：In this contribution, a modification and application of the Lemaitre damage evolution law is proposed for the problem of fatigue life estimate under low number of cycles. For this, the denominator of damage, considered constant for Lemaitre, was replaced by a function dependent on the stress triaxiality. The new function has a nonlinear and thermodynamically consistent behavior. In addition, the evolution law of the backstress tensor is adopted as proposed by Desmorat, where there is no saturation of the limit value. The formulation is implemented in an academic tool for analysis at one Gauss point, through an implicit integration strategy of the flow equations. The Newton-Raphson method is used to solve a system of nonlinear equations, with two tensor and two scalar equations. Thus, in order to demonstrate the robustness of the model, experimental data from the literature for SAE 1045 and S460N steels are adopted. Proportional and nonproportional axial, torsional and multiaxial loading paths are simulated. Finally, the results have shown that the modification formulation is a good strategy to control the damage evolution in predicting fatigue life. In this sense, the calculated lives by the new proposal are within a scatter band of factor three, both under normal or torsional uniaxial loading conditions, as well as proportional or nonproportional multiaxial conditions.
Moni Ribeiro Filho, Sergio LuizTeixeira, Flavio NevesMonteiro Guimaraes, Luiz GustavoSilva, Jose Antonio...
19页
查看更多>>摘要：Power plants production's growth capacity has led to increased concerns about efficiency and reliability of steam turbines. Its components are prone to cracking and failure caused by creep and fatigue. The present work used Ansys (R) and nCode GlyphWorks (R) package to predict tensions and deformations. The methodology used allows calculate the level of structural damage caused to each work cycle. Analysis of the application of a chemical process on the rotor to improve failure resistance influenced the component life, avoiding corrosion fatigue. To create residual stresses on the surface of material was used Shot peening process. Thermal analysis results show that the rotor supports approximately 3.18 x 10(4) cycles, obtaining a maximum error of 12.5% compared to experimental reference. The shot peening process increased the rotor life by about 3000 h (10.5%) and changes in the heat treatment microstructure increased by 9.6% in number of cycles.
查看更多>>摘要：Although cylindrical and prismatic specimens are often used in laboratory tests, the differences between their deformation and failure characteristics remain unclear. Cylindrical and prismatic specimens of two rocks (marble and granite) were analyzed under various conventional triaxial conditions. The failed prismatic specimens exhibit multiple fractures intersecting in the cross section. With increasing confining pressure, the failure mode of the prismatic specimen changes from tensile failure to shear failure. In the progressive failure process of prismatic specimens, the two lateral strains epsilon(2) and epsilon(3) are the same before the peak, but some differences arise after some degree of post-peak failure, where the acoustic emission (AE) activity clearly increases. The mechanical parameters (peak strength, internal friction angle, cohesion, Young's modulus, and Poisson's ratio) determined for the cylindrical and prismatic specimens are consistent. However, a significant difference in the fracture morphology exists among them, even with similar change trends in the tensile-shear failure mode with confining pressure.
Sampaio, Rui F., VPragana, Joao P. M.Braganca, Ivo M. F.Silva, Carlos M. A....
19页
查看更多>>摘要：The formability limits of bulk metal forming in principal strain space and in the effective strain vs. stress-triaxiality space are characterized by an uncertainty region in which cracks may be triggered by tension (mode I of fracture mechanics) or by out-of-plane shear (mode III). The problem in obtaining experimental data in this region has been known for a long time and the main objective of this paper is to present a new upset formability test geometry that can effectively contribute to the characterization of the formability limits of bulk metal forming parts subjected to biaxial tension. Alongside with this objective, this paper also presents an analytical expression for converting the fracture forming limit line corresponding to crack opening by mode III in principal strain space into a hyperbolic fracture limit curve in the effective strain vs. stress-triaxiality space. The overall methodology employed by the authors combines experimentation along with analytical and numerical modelling, and the contents of the paper is a step towards diminishing the actual lack of knowledge regarding failure by fracture in bulk metal forming parts subject to stress-triaxiality values beyond uniaxial tension. Results show that a new uncoupled ductile fracture criterion built upon combination of the integrands of the Cockcroft-Latham and McClintock criteria can be successfully used to model the physics of the bulk metal forming limits for the entire range of stress-triaxiality values corresponding to cracking on free surfaces.
查看更多>>摘要：In the past few decades, extensive research on concrete modeling to predict behavior, crack propagation, microcrack coalescence by utilizing different approaches (fracture mechanics, continuum damage mechanics) were investigated theoretically and numerically. The presented paper aims to review the theoretical work of continuum concrete damage and plasticity modeling in part I of the work. The detailed theoretical work is presented with some of the supporting work related to multiscale modeling and phase-field modeling is also part of this paper. Few other applications related to rate-dependent models and fatigue in concrete are also discussed. In part II of this work, the review of numerical work limited to finite element is presented. Some open issues in concrete damage modeling and future research needed are also discussed in part II.
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