Characterisation of crack tip fields under non-uniform fatigue loading

The paper analyses previously reported work, which uses digital image correlation to measure fatigue crack closure. As well as determining crack opening loads, the information on crack shape may be used to estimate the stress intensity factor, as well as other parameters in more complex models of crack tip fields. A number of specimens were subjected to single overload cycles, which produced a significant retardation in crack growth rate. The method previously applied to the analysis of constant amplitude loading is here used to analyse the single overload case. The stress intensity factor history is found to be very different in the two cases and the consequences of this observation for analysis of fatigue crack propagation are discussed

Localized structures of electromagnetic waves in hot electron-positronplasmas

The dynamics of relativistically strong electromagnetic (EM) wave propagation in hot electron-positron plasma is investigated. The possibility of finding localized stationary structures of EM waves is explored. It is shown that under certain conditions the EM wave forms a stable localized soliton-like structures where plasma is completely expelled from the region of EM field location.Comment: 14 pages, LaTeX, 1 figure can be obtained upon request through email to [email protected]

Deregulated microRNAs in neurofibromatosis type 1 derived malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNST) are aggressive cancers that occur spontaneously (sporadic MPNST) or from benign plexiform neurofibromas in neurofibromatosis type 1 (NF1) patients. MPNSTs metastasize easily, are therapy resistant and are frequently fatal. The molecular changes underlying the malignant transformation in the NF1 setting are incompletely understood. Here we investigate the involvement of microRNAs in this process. MicroRNA expression profiles were determined from a series of archival, paired samples of plexiform neurofibroma and MPNST. Ninety differentially expressed microRNAs were identified between the paired samples. Three downregulated microRNAs (let-7b-5p, miR-143-3p, miR-145-5p) and two upregulated microRNAs (miR135b-5p and miR-889-3p) in MPNST were selected for functional characterization. In general, their differential expression was validated in a relevant cell line panel but only partly in a series of unpaired, fresh frozen tumor samples. As part of the validation process we also analyzed microRNA expression profiles of sporadic MPNSTs observing that microRNA expression discriminates NF1-associated and sporadic MPNSTs. The role of microRNAs in cancer progression was examined in NF1-derived MPNST cell lines by transiently modulating microRNA levels. Our findings indicate that some microRNAs affect migratory and invasive capabilities and Wnt signaling activity but the effects are distinct in different cell lines. We conclude that miRNAs play essential regulatory roles in MPNST facilitating tumor progression

Towards good practice guidelines for the contour method of residual stress measurement

Accurate measurement of residual stress in metallic components using the contour method relies on the achievement of a good quality cut, on the appropriate measurement of the deformed cut surface and on the robust analysis of the measured data. There is currently no published standard or code of practice for the contour method. As a first step towards such a standard, this study draws on research investigations addressing the three main steps in the method: how best to cut the specimens; how to measure the deformation contour of the cut surface; and how to analyse the data. Good practice guidance is provided throughout the text accompanied by more detailed observations and advice tabulated in Appendi

Three-dimensional earthquake analysis of roller-compacted concrete dams

Ground motion effect on a roller-compacted concrete (RCC) dams in the earthquake zone should be taken into account for the most critical conditions. This study presents three-dimensional earthquake response of a RCC dam considering geometrical non-linearity. Besides, material and connection non-linearity are also taken into consideration in the time-history analyses. Bilinear and multilinear kinematic hardening material models are utilized in the materially non-linear analyses for concrete and foundation rock respectively. The contraction joints inside the dam blocks and dam-foundation-reservoir interaction are modeled by the contact elements. The hydrostatic and hydrodynamic pressures of the reservoir water are modeled with the fluid finite elements based on the Lagrangian approach. The gravity and hydrostatic pressure effects are employed as initial condition before the strong ground motion. In the earthquake analyses, viscous dampers are defined in the finite element model to represent infinite boundary conditions. According to numerical solutions, horizontal displacements increase under hydrodynamic pressure. Besides, those also increase in the materially non-linear analyses of the dam. In addition, while the principle stress components by the hydrodynamic pressure effect the reservoir water, those decrease in the materially non-linear time-history analyses. © 2012 Author(s). CC Attribution 3.0 License

Earthquake performance evaluation of three-dimensional roller compacted concrete dams

A roller compacted concrete (RCC) dam should be analyzed under seismic ground motions for different conditions such as empty reservoir and full reservoir conditions. This study presents three-dimensional earthquake response and performance of a RCC dam considering materially non-linearity. For this purpose, Cine RCC dam constructed in Aydin, Turkey, is selected in applications. The three-dimensional finite element model of Cine RCC dam is obtained using ANSYS software. The Drucker-Prager material model is considered in the materially nonlinear time history analyses for concrete and foundation rock. Furthermore, hydrodynamic effect was investigated in linear and non-linear dynamic analyses. Researchers observe that how the tensile and compressive stresses change by hydrodynamic pressure effect. The hydrodynamic pressure of the reservoir water is modeled with the fluid finite elements based on the Lagrangian approach. In this study, dam body and foundation are modeled with welded contact. The displacements and principle stress components obtained from the linear and non-linear analyses with and without reservoir water are compared each other. Principle stresses during earthquake were obtained at the most critical point in the upstream face of dam body. Besides, the change of displacements and stresses by crest length were investigated. Moreover demand-capacity ratio criteria were also studied under linear dynamic and nonlinear analysis. Earthquake performance analyses were carried out for different cases and evaluated. According to linear and nonlinear analysis, hydrodynamic water effect is obvious in full reservoir situation. On the other hand, higher tensile stresses were observed in linear analyses and then non-linear analyses were performed and compared with each other. © 2018 Techno-Press, Ltd

Linear and nonlinear response of concrete slab on CFR dam during earthquake

The joint between concrete slab and rockfill is designed as welded contact in the classical modeling of concrete-faced rockfill (CFR) dams and earthquake response of the CFR dams is determined by this method. In this study, linear and nonlinear response of Torul CFR Dam including interface element between concrete slab and rockfill were investigated for the duration of strong seismic excitation. The finite element analyses were performed by employing both cases, empty and full reservoir, to research the effect of the reservoir water on the earthquake response of the dam. The reservoir water was modeled with fluid finite elements by the Lagrangian approach. The Drucker-Prager model was used in nonlinear analyses for concrete slab, rockfill and soil materials. According to finite element analyses, displacement and stress components were increased by hydrodynamic pressure. The nonlinear response of the concrete slab was monitored about the peak ground acceleration (pga). This study reveals that the size of sliding zone increases with increasing acceleration amplitudes. © 2010 Elsevier Ltd

Non-linear response of the rockfill in a concrete-faced rockfill dam under seismic excitation

This study investigates the non-linear response of the rockfill in a concrete-faced rockfill dam under seismic excitation for various concrete slab thicknesses from 30 to 100 cm thick. The effect of the friction in the concrete slab rockfill interface on the non-linear response of the rockfill is also considered in the numerical solutions. The friction contact in the concrete slab joints is provided with contact elements based on the Coulomb’s friction law. The hydrodynamic pressure of the reservoir water is considered by the fluid finite elements based on the Lagrangian approach. Geometrical and material non-linear behaviours of the dam-foundation-reservoir interaction system are considered together in the finite element analyses. The Drucker–Prager model is used to obtain materially non-linear behaviour of the concrete slab. The multi linear kinematic hardening model is used for rockfill and foundation rock in the material non-linear analyses. Therefore, the uniaxial stress–strain relations of the rockfill and foundation rock are determined from the shear stress–shear strain relations of the gravel and rock, respectively. The principle compressive and tensile stresses of the rockfill are investigated along the horizontal section of the rockfill. According to numerical analyses, the most critical stresses occur in the upstream and downstream faces of the dam for the concrete slab thickness of 30 cm, while the optimum thickness for seismic performance is 58 cm. © 2014, © 2014 Taylor & Francis

Investigation of buckling behavior of laminated reinforced concrete plates with central rectangular hole using finite element method

This paper deals with change of buckling coefficients of symmetrically laminated reinforced concrete plates with a central rectangular hole under biaxial static compression loadings using finite element method. Composite structure of these plates has been constituted from four, six, eight and ten laminas including steel and concrete. The effect of change in central rectangular hole from the point view of size and direction on buckling coefficients is investigated in this study. Symmetrically laminated plates under biaxial in-plane loadings are taken into consideration in the analyses for simply supported and clamped boundary conditions. Obtained results are compared with each other according to a/L and b/L where a, b are the hole sizes and L is the length of the plate, respectively. Crown Copyright © 2008.2003-45-06-11This study is supported by Zonguldak Karaelmas University Scientific Research Fund (Project No. 2003-45-06-11)