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cyclic-plasticity
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An Investigation into the Wear of an Eutectoid Steel Based on the Low-Cycle Fatigue Theory with the Finite Element Method
, M.Sc. Thesis Sharif University of Technology ; Karimi Taheri, Ali (Supervisor)
Abstract
In sliding wear, the process of making debris takes place with different mechanisms. Previous works estimating the wear rate have been carried out based on contact mechanics and material failure mechanisms. In present work, the possibility of existence of low-cycle fatigue as the dominant mechanism in the wear of an as-cast eutectoid steel is investigated. Moreover, wear coefficient and the the volume loss per distance of that steel was predicted. At first, wear tests were done in order to obtain the wear trend of the steel in different loads. Then, regarding the roughness of the disk surface, a finite element model was built to simulate the sliding of the pin surface over the asperities...
Microporosity control and thermal-fatigue resistance of A319 aluminum foundry alloy
, Article Materials Science and Engineering A ; Volume 472, Issue 1-2 , 2008 , Pages 107-114 ; 09215093 (ISSN) ; Khalifehzadeh, R ; Akbari, M ; Khomamizadeh, F ; Sharif University of Technology
2008
Abstract
The objective of this work was to gain a quantitative and qualitative understanding of the degree to which porosity influences thermal-fatigue performance and other mechanical properties of A319 aluminum casting alloy over ranges of commercial interest. The number of cycles to failure for each test was recorded. An increase in porosity content caused degradation in thermal-fatigue life and other mechanical properties. The fractographic examinations identified the pores and some intermetallics as the key microstructural features which promote damage and thermal-fatigue crack initiation sites in the specimens. Crack initiation and propagation is expected to occur sooner in regions of higher...
Developing an Analytical Model for Predicting the Residual Stresses Induced by Shot Peening with Considering the Effect of Initial Surface Treatment
, Ph.D. Dissertation Sharif University of Technology ; Farrahi, Gholam Hossein (Supervisor) ; Mahmoudi, Amir Hossein (Co-Supervisor)
Abstract
Shot peening is a cold-working process commonly used in industry to improve the fatigue performance, stress corrosion resistance and surface nano-crystallization of metallic parts. This process extends fatigue life via two mechanisms: Preventing the crack growth due to compressive residual stresses and, preventing the crack initiation because of increased material hardness. These mechanisms are the results of the bombardment of the component's surface with small spherical particles. In this research, an analytical model is developed for estimating the residual stress distribution induced by shot peening process. The modifications of the developed analytical model are related to...
Considering cyclic plasticity to predict residual stresses in laser cladding of Inconel 718 multi bead samples
, Article Journal of Manufacturing Processes ; Volume 42 , 2019 , Pages 149-158 ; 15266125 (ISSN) ; Farrahi, G. H ; Movahhedy, M. R ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
A thermo-mechanical finite element model is developed to accurately predict residual stresses of the multiple beads laser cladding process, incorporating the cyclic plasticity into the analysis by utilizing the nonlinear kinematic hardening behavior. Finite Element results are presented for Inconel 718, a material for which the laser cladding process is widely used. The FE results are compared with the results of incremental center hole drilling conducted on three specimens with different clad beads to evaluate the effect of cyclic plasticity modeling on the residual stresses. The results indicate that incorporating the nonlinear kinematic hardening model into the analysis can reduce the...
Experimental and Numerical Study of Multi-track Laser Cladding to Evaluate Effects of Residual Stress on Fatigue Life
, Ph.D. Dissertation Sharif University of Technology ; Movahhedy, Mohammad Reza (Supervisor) ; Farrahi, Gholam Hossein (Supervisor) ; Shodja Razavi, Reza (Co-Supervisor)
Abstract
Laser cladding is a processing technique of layer-by-layer material deposition which is widely used to repair important components. However, tensile residual stresses generated in this process may result in detrimental effects such as crack, undesirable deformation and reduced fatigue life. A thermo-mechanical finite element model is developed to accurately predict residual stresses of the multiple beads laser cladding process with incorporating the cyclic plasticity into the analysis by utilizing the nonlinear kinematic hardening behavior. FE results are presented for Inconel 718, a material for which the laser cladding process is widely used. The FE results are compared with those of...
Effects of stress invariants and reverse loading on ductile fracture initiation
, Article International Journal of Solids and Structures ; Volume 49, Issue 13 , 2012 , Pages 1541-1556 ; 00207683 (ISSN) ; Hoseini, S. H ; Farrahi, G. H ; Sharif University of Technology
2012
Abstract
Recent research studies on ductile fracture of metals have shown that the ductile fracture initiation is significantly affected by the stress state. In this study, the effects of the stress invariants as well as the effect of the reverse loading on ductile fracture are considered. To estimate the reduction of load carrying capacity and ductile fracture initiation, a scalar damage expression is proposed. This scalar damage is a function of the accumulated plastic strain, the first stress invariant and the Lode angle. To incorporate the effect of the reverse loading, the accumulated plastic strain is divided into the tension and compression components and each component has a different weight...
Effect of severe shot peening on the fatigue life of the laser-cladded Inconel 718 specimens
, Article International Journal of Advanced Manufacturing Technology ; Volume 104, Issue 5-8 , 2019 , Pages 2619-2631 ; 02683768 (ISSN) ; Farrahi, G. H ; Movahhedy, M. R
Springer London
2019
Abstract
This paper presents the influence of the severe shot peening process on the fatigue life of the laser-cladded Inconel 718 specimens which can be employed during refurbishment of components enduring high mechanical cyclic loads such as gas turbine components. In order to quantitatively evaluate the destructive effect of laser cladding on the fatigue endurance, fatigue tests are first performed on the as-received and laser-cladded specimens. Then, microstructural analysis by scanning electron microscope (SEM) is carried out to identify the root causes of the drawback of laser cladding. Moreover, by employing a comprehensive laser-cladding FE analysis considering cyclic plastic material...