Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Building and Real Estate | en_US |
| dc.contributor.advisor | Yam, C. H. Michael (BRE) | en_US |
| dc.creator | He, Qun | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/12997 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Experimental and numerical investigation on the cyclic and fatigue behaviour of high-strength steel Q690 | en_US |
| dcterms.abstract | High-strength steel (HSS) has become a prospective material in structural steel construction due to its superior yield strength and tensile strength. Its enhanced strength reduces the material usage and further substantially reduces the steel cost, corresponding foundation cost, transportation cost, and construction costs. In addition, reduced steel material usage decreases carbon footprints and thereby promotes sustainable construction. When HSSs are adopted in steel structures, they may experience ultra-low cycle fatigue (ULCF) failure when used in earthquake-resistant structures and high cycle fatigue (HCF) failure when used in bridges. However, the current studies on the fatigue behaviour of HSS structures are limited. Hence, this study aims at examining the ULCF and HCF behaviour of HSS, with a focus on Q690 steel. | en_US |
| dcterms.abstract | The ULCF behaviour of HSS Q690 was examined in two aspects, including its cyclic plasticity and ULCF failure criterion. A novel definition of stress state (including stress triaxiality and Lode angle parameter) was proposed to consider the effect of backstress during ULCF loading. Twenty-five material specimens were tested to study the effect of strain histories and stress states on the ULCF behaviour of HSS Q690. The test results showed that HSS Q690 exhibited cyclic softening behaviour and that its cyclic plasticity was independent of its strain amplitude and stress triaxiality but dependent on its equivalent plastic strain and Lode angle parameter. A constitutive model was then proposed to characterise the cyclic softening behaviour of HSS Q690 and the corresponding numerical algorithm was developed. Moreover, a new ULCF failure criterion was proposed based on micromechanical analysis using the novel definition of stress state. Subsequently, a UMAT subroutine of ABAQUS was developed for the finite element simulation of the cyclic plasticity and ULCF failure of HSS Q690. The proposed constitutive model was calibrated and validated using the material test results. To further validate the proposed constitutive model, the developed UMAT was adopted to predict the cyclic behaviour and ULCF behaviour of five beam-column specimens made of HSS Q690 from the existing literature. | en_US |
| dcterms.abstract | The HCF behaviour of HSS Q690 (including the S-N curve and fatigue life scatter) was examined from a microscopic perspective using the theory of crystal plasticity (CP). A new CP model was developed by modifying the evolution rules within the CP framework. To consider the influence of the material’s microstructure on the HCF behaviour of HSS Q690 using the proposed CP model, a representative volume element (RVE) model was created based on its microstructural characteristics (e.g., the distribution of grain size and orientation). The microstructure of HSS Q690 was characterised using the electron backscatter diffraction (EBSD) method. Subsequently, a series of material tests of HSS Q690, including tensile test, stress relaxation test, cyclic test, and HCF test (under mean stress of 0 and 0.4𝑓u), were conducted. The proposed CP model was calibrated using the material test results and further applied to compute the plastic deformation in the slip band of the RVE model. In addition, a fatigue model based on a fatigue indicator parameter (FIP), namely band-averaged energy dissipation density 𝑊𝑏𝑐𝑦𝑐, was adopted. It was calibrated using the computation results of RVE models and the HCF test results of HSS Q690 specimens under zero mean stress. The calibrated fatigue model reproduced the distribution and scatter of fatigue life for specimens under zero mean stress and predicted the HCF crack initiation life of specimens under a mean stress of 0.4𝑓u. Furthermore, the proposed CP model and fatigue model effectively predicted the HCF crack initiation life of five bolted connection specimens. | en_US |
| dcterms.extent | xxiv, 209 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2024 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.LCSH | Steel, High strength -- Fatigue | en_US |
| dcterms.LCSH | Steel, Structural -- Fatigue | en_US |
| dcterms.LCSH | Hong Kong Polytechnic University -- Dissertations | en_US |
| dcterms.accessRights | open access | en_US |
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