Wave propagation in a microbeam based on the modified couple stress theory

Kocaturk, Turgut,Akbas, Seref Doguscan Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.46 No.3

This paper presents responses of the free end of a cantilever micro beam under the effect of an impact force based on the modified couple stress theory. The beam is excited by a transverse triangular force impulse modulated by a harmonic motion. The Kelvin-Voigt model for the material of the beam is used. The considered problem is investigated within the Bernoulli-Euler beam theory by using energy based finite element method. The system of equations of motion is derived by using Lagrange's equations. The obtained system of linear differential equations is reduced to a linear algebraic equation system and solved in the time domain by using Newmark average acceleration method. In the study, the difference of the modified couple stress theory and the classical beam theory is investigated for the wave propagation. A few of the obtained results are compared with the previously published results. The influences of the material length scale parameter on the wave propagation are investigated in detail. It is clearly seen from the results that the classical beam theory based on the modified couple stress theory must be used instead of the classical theory for small values of beam height.

Geometrically non-linear static analysis of a simply supported beam made of hyperelastic material

Kocaturk, T.,Akbas, S.D. Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.35 No.6

This paper focuses on geometrically non-linear static analysis of a simply supported beam made of hyperelastic material subjected to a non-follower transversal uniformly distributed load. As it is known, the line of action of follower forces is affected by the deformation of the elastic system on which they act and therefore such forces are non-conservative. The material of the beam is assumed as isotropic and hyperelastic. Two types of simply supported beams are considered which have the following boundary conditions: 1) There is a pin at left end and a roller at right end of the beam (pinned-rolled beam). 2) Both ends of the beam are supported by pins (pinned-pinned beam). In this study, finite element model of the beam is constructed by using total Lagrangian finite element model of two dimensional continuum for a twelve-node quadratic element. The considered highly non-linear problem is solved by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. In order to use the solution procedures of Newton-Raphson type, there is need to linearized equilibrium equations, which can be achieved through the linearization of the principle of virtual work in its continuum form. In the study, the effect of the large deflections and rotations on the displacements and the normal stress and the shear stress distributions through the thickness of the beam is investigated in detail. It is known that in the failure analysis, the most important quantities are the principal normal stresses and the maximum shear stress. Therefore these stresses are investigated in detail. The convergence studies are performed for various numbers of finite elements. The effects of the geometric non-linearity and pinned-pinned and pinned-rolled support conditions on the displacements and on the stresses are investigated. By using a twelve-node quadratic element, the free boundary conditions are satisfied and very good stress diagrams are obtained. Also, some of the results of the total Lagrangian finite element model of two dimensional continuum for a twelve-node quadratic element are compared with the results of SAP2000 packet program. Numerical results show that geometrical nonlinearity plays very important role in the static responses of the beam.

Post-buckling analysis of Timoshenko beams made of functionally graded material under thermal loading

Kocaturk, Turgut,Akbas, Seref Doguscan Techno-Press 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.41 No.6

This paper focuses on post-buckling analysis of functionally graded Timoshenko beam subjected to thermal loading by using the total Lagrangian Timoshenko beam element approximation. Material properties of the beam change in the thickness direction according to a power-law function. The beam is clamped at both ends. The considered highly non-linear problem is solved by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. As far as the authors know, there is no study on the post-buckling analysis of functionally graded Timoshenko beams under thermal loading considering full geometric non-linearity investigated by using finite element method. The convergence studies are made and the obtained results are compared with the published results. In the study, with the effects of material gradient property and thermal load, the relationships between deflections, end constraint forces, thermal buckling configuration and stress distributions through the thickness of the beams are illustrated in detail in post-buckling case.

Post-buckling analysis of Timoshenko beams with various boundary conditions under non-uniform thermal loading

Kocaturk, Turgut,Akbas, Seref Doguscan Techno-Press 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.40 No.3

This paper focuses on post-buckling analysis of Timoshenko beams with various boundary conditions subjected to a non-uniform thermal loading by using the total Lagrangian Timoshenko beam element approximation. Six types of support conditions for the beams are considered. The considered highly non-linear problem is solved by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. As far as the authors know, there is no study on the post-buckling analysis of Timoshenko beams under uniform and non-uniform thermal loading considering full geometric non-linearity investigated by using finite element method. The convergence studies are made and the obtained results are compared with the published results. In the study, the relationships between deflections, end rotational angles, end constraint forces, thermal buckling configuration, stress distributions through the thickness of the beams and temperature rising are illustrated in detail in post-buckling case.

Post-buckling analysis of Timoshenko beams with various boundary conditions under non-uniform thermal loading

Turgut Kocaturk,Seref Doguscan Akbas 국제구조공학회 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.40 No.3

This paper focuses on post-buckling analysis of Timoshenko beams with various boundary conditions subjected to a non-uniform thermal loading by using the total Lagrangian Timoshenko beam element approximation. Six types of support conditions for the beams are considered. The considered highly non-linear problem is solved by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. As far as the authors know, there is no study on the post-buckling analysis of Timoshenko beams under uniform and non-uniform thermal loading considering full geometric non-linearity investigated by using finite element method. The convergence studies are made and the obtained results are compared with the published results. In the study, the relationships between deflections, end rotational angles, end constraint forces, thermal buckling configuration, stress distributions through the thickness of the beams and temperature rising are illustrated in detail in postbuckling case.

Post-buckling analysis of Timoshenko beams with temperature-dependent physical properties under uniform thermal loading

Akbas, Seref Doguscan,Kocaturk, Turgut Techno-Press 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.44 No.1

Post-buckling behavior of Timoshenko beams subjected to uniform temperature rising with temperature dependent physical properties are studied in this paper by using the total Lagrangian Timoshenko beam element approximation. The beam is clamped at both ends. In the case of beams with immovable ends, temperature rise causes compressible forces end therefore buckling and post-buckling phenomena occurs. It is known that post-buckling problems are geometrically nonlinear problems. Also, the material properties (Young's modulus, coefficient of thermal expansion, yield stress) are temperature dependent: That is the coefficients of the governing equations are not constant in this study. This situation suggests the physical nonlinearity of the problem. Hence, the considered problem is both geometrically and physically nonlinear. The considered highly non-linear problem is solved considering full geometric non-linearity by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. The beams considered in numerical examples are made of Austenitic Stainless Steel (316). The convergence studies are made. In this study, the difference between temperature dependent and independent physical properties are investigated in detail in post-buckling case. The relationships between deflections, thermal post-buckling configuration, critical buckling temperature, maximum stresses of the beams and temperature rising are illustrated in detail in post-buckling case.

Omalizumab as a Succesfull Therapy in Normocomplementemic Urticarial Vasculitis: A Series of Four Patients and Review of the Literature

( Ece Nur Degirmentepe ),( Kubra Kızıltac ),( Pırıl Etikan ),( Ralfi Singer ),( Bachar Memet ),( Emek Kocaturk ) 대한피부과학회 2019 Annals of Dermatology Vol.31 No.3

Urticarial vasculitis is an eruption characterized by inflamed itchy or painful red papules or plaques that resemble urticaria but last longer than 24 hours and heal with residual pigmentation or purpura. Histopathologically, urticarial vasculitis presents as leukocytoclastic vasculitis with perivascular infiltrate and fibrin deposits. The treatment options are oral antihistamines, oral corticosteroids, dapsone, colchicine and hydroxychloroquine. We report four cases with normocomplementemic urticarial vasculitis who were treated with omalizumab and a brief review of the literature on the use of omalizumab in normocomplementemic urticarial vasculitis. (Ann Dermatol 31(3) 335∼338, 2019)

Rare earth elements (REEs) investigation of fly ash placers in southwestern Taurides: footprints of alkaline potassic Gölcük volcanism, Turkey

Ali Tugcan Unluer,Zeynep Doner,Mustafa Kaya,Huseyin Kocaturk,Amr Abdelnasser,Mustafa Kumral,Murat Budakoglu,Mehmet Sezai Kirikoglu 한국지질과학협의회 2023 Geosciences Journal Vol.27 No.4

The importance of Rare Earth Elements (REE) is consistently rising for industrialized countries due to their widespread usage in various applications. Production of REE heavily relies on carbonatite-ijolite complexes and other alkaline magmatic products. With this perspective, the potassic-alkaline volcanism related fly ash placers in Burdur and Isparta regions (SW, Turkey) are considered as a valuable prospecting target for REE. This work primarily focuses on the REE enrichment features (geochemistry, mineralogy, provenance and alteration processes) of Burdur and Isparta fly ash placers for construing the REE behaviour. At last, formation modeling of studied deposits was established and the similarities between studied deposits and some World class REE deposits were presented. Main REE-bearing minerals of studied deposits were identified as chevkinite, britholite and fluorapatite with considerable amounts of LREE as well as Th, Fe and Ti. The geochemical analysis results show that most of ΣREE values (up to 1109 and 1233 ppm, respectively) were comprised by La, Ce, Nd and Pr elements. The smaller grain size is a key factor in REE enrichment by the effectof combined factors such as REE-bearing mineral’s average crystal size, distribution, and higher intensity weathering process. The interference of Ca from meta-sedimentary carbonate rocks have a negative effect on REE accumulation. Because of the good response for ore purification methods and promising results for some of the critical REE, Burdur and Isparta fly ash placers might be feasible in the future in case of tighter supply and increasing global demand.