### Browsing by Author "Karttunen, Anssi"

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Item Bridging plate theories and elasticity solutions(PERGAMON-ELSEVIER SCIENCE LTD, 2017) Karttunen, Anssi; von Hertzen, Raimo; Reddy, JN; Romanoff, Jani; Department of Mechanical Engineering; Texas A&M UniversityIn this work, we present an exact 3D plate solution in the conventional form of 2D plate theories without invoking any of the assumptions inherent to 2D plate formulations. We start by formulating a rectangular plate problem by employing Saint Venant’s principle so that edge effects do not appear in the plate. Then the exact general 3D elasticity solution to the formulated interior problem is examined. By expressing the solution in terms of mid-surface variables, exact 2D equations are obtained for the rectangular interior plate. It is found that the 2D presentation includes the Kirchhoff, Mindlin and Levinson plate theories and their general solutions as special cases. The key feature of the formulated interior plate problem is that the interior stresses of the plate act as surface tractions on the lateral plate edges and contribute to the total potential energy of the plate. We carry out a variational interior formulation of the Levinson plate theory and take into account, as a novel contribution, the virtual work due to the interior stresses along the plate edges. Remarkably, this way the resulting equilibrium equations become the same as in the case of a vectorial formulation. A gap in the conventional energy-based derivations of 2D engineering plate theories founded on interior kinematics is that the edge work due to the interior stresses is not properly accounted for. This leads to artificial edge effects through higher-order stress resultants. Finally, a variety of numerical examples are presented using the 3D elasticity solution.Item Design space for bifurcation buckling of laser-welded web-core sandwich plates as predicted by classical and micropolar plate theories(SPRINGER, 2020-11-05) Romanoff, Jani; Karttunen, Anssi; Varsta, Petri; Marine Technology; Department of Mechanical EngineeringThe strength of laser-welded web-core sandwich plates is often limited by buckling. In design of complex thin-walled structures the combination of possible structural and material combinations is basically infinite. The feasibility of these combinations can be assessed by using analytical, numerical and experimental methods. At the early design stages such as concept design stage, the role of analytical methods is significant due to their capability for parametric description and extremely low computational efforts once the solutions have been established for prevailing differential equations. Over the recent years significant advances have been made on analytical strength prediction of web-core sandwich panels. Therefore, aim of the present paper is to show impact of this development to the design space of web-core sandwich panels in buckling. The paper reviews first, briefly the differential equations of a 2-D micropolar plate theory for web-core sandwich panels and the Navier buckling solution for biaxial compression recently derived by Karttunen et al. (Int J Solids Struct 170(1):82–94, 2019) by exploiting energy methods. By comparing the micropolar and widely-used classical first-order shear deformation plate theory (FSDT) solutions, it is shown that the different equivalent single layer (ESL) formulations and plate aspect ratios have a significant impact on the practical outcomes of the feasible design space and this way motivating further developments for micropolar formulations from practical structural engineering viewpoint.Item Dynamic response of a cylinder cover under a moving load(2014) Karttunen, Anssi; von Hertzen, Raimo; Department of Applied MechanicsItem Exact elasticity-based finite element for circular plates(Elsevier Limited, 2017) Karttunen, Anssi; von Hertzen, Raimo; Reddy, Junthula; Romanoff, Jani; Department of Mechanical Engineering; Texas A&M UniversityIn this paper, a general elasticity solution for the axisymmetric bending of a linearly elastic annular plate is used to derive an exact finite element for such a plate. We start by formulating an interior plate problem by employing Saint Venant’s principle so that edge effects do not appear in the plate. Then the elasticity solution to the formulated interior problem is presented in terms of mid-surface variables so that it takes a form similar to conventional engineering plate theories. By using the mid-surface variables, the exact finite element is developed both by force- and energy-based approaches. The central, nonstandard feature of the interior solution, and the finite element based on it, is that the interior stresses of the plate act as surface tractions on the plate edges and contribute to the total potential energy of the plate. Finally, analytical and numerical examples are presented using the elasticity solution and the derived finite element.Item Experimental determination of spring parameters of a nonlinear mass damper in a ship structure(2019-06-17) Jalava, Juho; Laakso, Aleksi; Karttunen, Anssi; Insinööritieteiden korkeakoulu; Romanoff, JaniItem HOMOGENIZED AND NON-CLASSICAL BEAM THEORIES IN SHIP STRUCTURAL DESIGN - CHALLENGES AND OPPORTUNITIES(2019) Romanoff, Jani; Karttunen, Anssi; Goncalves, Bruno Reinaldo; Reddy, Jn; Department of Mechanical Engineering; Marine Technology; Texas A&M University; Bensow, R; Ringsberg, JThe paper gives an overview of the recent developments on the application of homogenized, non-classical beam theories used to predict the micro- and macrostructural stresses in the design of marine structures. These theories become important when ultralight-weight marine structures are developed and one needs to explore the regions where the length scales of beam openings are in the range of the characteristic lengths of the beams or when lattice/frame-type beams are used to reduce the weight of ship structures. The homogenized beam models are based on non-classical continuum mechanics that allow local bending inside the beams. This added feature allows the treatment of size effects with great accuracy. The resulting analytical and finite element models have special features in terms of shape functions and iterative solutions in non-linear problems. Non-classical beam models enable localization processes that recover the microstructural effects from homogenized solutions accurately and the models are able to handle limit states of serviceability and ultimate strength. The non-classical models are validated by experiments and 3D FE simulations of periodic beams and plates. The non-classical beam theories converge to the physically correct solutions for wider range of beam parameters than the classical beam theories do.Item Identification of the viscoelastic parameters of a polymer model by the aid of a MCMC method(2014) Haario, Heikki; von Hertzen, Raimo; Karttunen, Anssi; Jorkama, Marko; Department of Applied MechanicsItem Kehärakenteen siirtymien mallinnus elementtimenetelmällä(2013-11-25) Rytömaa, Samuli; Karttunen, Anssi; Insinööritieteiden korkeakoulu; Mikkola, TommiItem Levinsonin palkkiteorian esittely ja soveltaminen(2015-04-15) Partanen, Samuli; Karttunen, Anssi; Insinööritieteiden korkeakoulu; Mikkola, TommiItem A nonlinear couple stress model for periodic sandwich beams(ELSEVIER SCI LTD, 2019-03-15) Reinaldo Goncalves, Bruno; Karttunen, Anssi; Romanoff, Jani; Department of Mechanical Engineering; Marine TechnologyA geometrically nonlinear model for periodic sandwich structures based on the modified couple stress Timoshenko beam theory with von Kármán kinematics is proposed. Constitutive relations for the couple stress beam are derived assuming an antiplane core and then extended for a generic periodic cell. A micromechanical approach based on the structural analysis of a unit cell is proposed and utilized to obtain the stiffness properties of selected periodic sandwich beams. Then, a localization scheme to predict the stress distribution over the faces of the selected beams is defined. The present model is shown to be equivalent to the thick-face sandwich theory for a linear elastic antiplane core cell. Numerical studies validate the present model against three-dimensional finite element models and the thick-face sandwich theory, and compare it with the conventional Timoshenko and couple stress Euler-Bernoulli beam theories. The present model is shown to predict deflections, stresses and buckling loads with good accuracy for different periodic cell setups. The model is able to describe elastic size effects in shear-flexible sandwich beams and the core stiffness influence on membrane and bending stress resultants.Item A numerical study of traveling waves in a viscoelastic cylinder cover under rolling contact(2013) Karttunen, Anssi; von Hertzen, Raimo; Department of Applied Mechanics; Department of Mechanical EngineeringItem Palkin ja laatan stabiliteettitarkastelu elementtimenetelmällä(2013-04-23) Huovinen, Heikki; Karttunen, Anssi; Insinööritieteiden korkeakoulu; Marquis, GaryItem Reiällisen levyn jännitysanalyysi elementtimenetelmällä(2012-04-19) Häsä, Riikka; Karttunen, Anssi; ; Insinööritieteiden korkeakoulu; Marquis, GaryItem Resonance phenomena of polymer-covered cylinders under rolling contact(Aalto University, 2015) Karttunen, Anssi; von Hertzen, Raimo, Prof., Aalto University, Department of Applied Mechanics, Finland; Sovelletun mekaniikan laitos; Department of Applied Mechanics; Mechanics of Materials; Insinööritieteiden korkeakoulu; School of Engineering; Tuhkuri, Jukka, Prof., Aalto University, Department of Applied Mechanics, FinlandIn paper machines the paper is fed through the contact areas, the nips, between rolling cylinders which are often covered with polymers. A soft polymer nip gives the paper a glossy surface and a smooth thickness profile with uniform density. Although the use polymer covers is beneficial in terms of end-product quality, the covers also induce and suffer from harmful dynamic phenomena. In this dissertation two such phenomena, a self-excited vibration mechanism and a traveling wave phenomenon, were studied in detail to understand their essential features. At all instances, the studied system consisted of two steel-core cylinders with a polymeric cover on the other cylinder. The self-excited vibration mechanism was first investigated using a one-dimensional (1D) analytical model. It was found that the mechanism is active when the frequency of the cover deformation induced excitation is close to that eigenfrequency of the system, which corresponds to the eigenmode in which the cylinders are vibrating in opposite phases. The vibrations are strongest when the phase of the residual deformation of the cover leads the phase of the nip gap between the cylinders by 90 degrees. Next, simulations were performed using a two-dimensional (2D) plane strain finite element (FE) model and cover deformation patterns were obtained. The results from the 1D and 2D models were found to be in good agreement. Finally, the computational and obtained experimental results were compared to validate the model-based physical interpretations. The physical explanation given by the 1D analytical model for the self-excited vibration mechanism was found to be valid. The traveling wave phenomenon was first studied using a 2D plane strain FE model. A critical speed below which the traveling waves did not appear was calculated on the basis of a resonance condition using modal information from eigenmode analysis. After dynamic rolling contact simulations it was found that the traveling wave phenomenon is best described as a Rayleigh wave resonance in which contact-induced modified Rayleigh waves arise in the nip at critical and supercritical rolling speeds and the waves superpose to form a strong traveling wave. Next, a 1D analytical cover model was developed for an elastic cylinder cover with damping. It was found that the 1D model captures the essential features of the traveling wave phenomenon. The 1D model was developed further so that the cover material was described as a frequency-dependent viscoelastic polymer. The viscoelastic model offers a simple tool for calculating estimates for the critical speeds of polymer covers in industrial use.Item Stress concentration factor for interacting notch and subsurface pore(2017-10-30) Gebrehiwot, Silas; Karttunen, Anssi; Insinööritieteiden korkeakoulu; Remes, HeikkiMachineries, vehicles, ships and airliners have numerous components that inevitably have stress concentrations. These concentrations are mainly due to abrupt geometrical alteration caused by manufacturing processes and design. The magnitude of a stress concentration depends on the geometry, loading and interaction between two distinct geometrical features. Geometrical discontinuities occur in numerous forms; mostly as external surface notch or subsurface defects e.g., circular or elliptical porosities or inclusions. These surface and subsurface defects have long been identified as detrimental factors which reduce the fatigue life of components. To avoid catastrophic failures related to stress concentrations, detailed analysis of them in engineering design is required. This thesis focuses on the interaction of stress concentrations between a surface notch and a subsurface porosity. The motivation behind this thesis work has been the unavailability of related studies despite of its significance. The thesis work uses a stress averaging method of the tangential stress component to determine the maximum interacting stress concentration factors of semi-circular notch-hole and equivalent elliptical notch-hole configurations in a semi-infinite plate. The study of the maximum stress concentration factor of the notch-hole configurations uses global and local stress averaging techniques that strongly depend on the extent of notch-hole gap distances. Three cases with relative notch-hole radii ratios of 20:1, 10:1, and 1:1 are investigated to determine the interacting stresses concentration factors with subsequent gap increments. In addition, the developed method is further utilized to analyse the interacting stress concentration factors of an equivalent elliptical notch and a hole that represents surface roughness with a subsurface porosity. The results of this work are compared with analytical solutions for two interacting holes and finite element simulations carried out using Abaqus simulation software. Based on the results, the stress averaging methods can be used to analyse the interacting stress concentration factors of notch-hole configurations with a specified range of gaps. The limitations of estimations using stress averaging approach are observed when the notch-hole gap is substantially reduced. The differences between the results obtained using stress averaging and the corresponding benchmarks of two holes solutions as well as finite element simulations are discussed. The study also discusses the limitations of using the stress averaging method in determining the interacting stress concentrations between semi-circular notch-hole and equivalent elliptical notch-hole configurations. In this study, porosity is represented by a circular hole. As the thesis is a single case of study in terms of relative notch-hole orientation, there is a variety of further study possibilities that could incorporate different notch-hole arrangements, loading conditions and varying material properties, which are suggested as possible future works.Item A Stress concentration factor for interacting surface notch and subsurface hole(2018) Gebrehiwot, Silas Zewdie; Remes, Heikki; Karttunen, Anssi; Department of Mechanical Engineering; Marine TechnologyWe propose a conservative method for the calculation of the maximum stress concentration factor (SCF) for an interacting notch-hole pair and for a double semi-circular notch (i.e., a notch that has an additional small semi-circular notch ahead of its tip). The method is based on a linearly elastic Airy stress function solution for a circular hole. The notch-hole and double notch configurations are aligned vertically with respect to uniform uniaxial (horizontal) stress. This means, a uniform horizontal tension is applied to a notch-hole pair that lie on a vertical axis. For the notch-hole pair, the maximum interacting SCFs are calculated for edge to edge gaps equal to hole sizes of 2.5a, 5a, 10a and 15a, where a is the hole radius. The analytical results are validated by 2-D finite element calculations. The presented simple approach provides good results with errors well below 10% in most cases compared to the detailed finite element analyses. Fatigue notch factors that can be thought of as the effective SCFs in fatigue analyses are determined. By using the simple approach, computationally costly finite element analysis can be avoided.Item Synthesis of experimental testing and fatigue behavior of laser stake-welded T-joints on medium-high cycle fatigue range(2017) Gallo, Pasquale; Romanoff, Jani; Karttunen, Anssi; Frank, Darko; Remes, Heikki; Department of Mechanical Engineering; Marine Technology; as2con - Alveus LtdThe paper presents a synthesis of experimental fatigue tests and theoretical studies of laser stake-welded T-joints in steel sandwich panels. The experiments indicate that the slope of the fatigue strength curves varies significantly depending on the type of loading the joint experiences, but also on the geometry. Therefore, the focus is on the influence of crack tip plasticity when the joints are loaded under tension and bending. This is investigated by two different approaches based on square root of J-integral. With this parameter, the experimental fatigue curves meet at the fatigue limit for all of the loading modes and geometries. To investigate the change in slope in the medium-high cycle fatigue range, the suitability of stress gradient and plastic zone size as defined by Irwin are studied. It is shown that the gradient of principal stress correlates well with the variation of slope, but it does not give a practical tool for fatigue assessment of the joints. Instead, based on the plastic zone approach,a new method is proposed that permits the estimation of number of cycles to failure under bending directly from the tension fatigue curve. The method is verified with experiments. (C) 2017 The Authors. Published by Elsevier B.V.Item Timoshenkon palkin leikkauskorjauskertoimen historiakatsaus(2014-04-14) Salerto, Samu; Karttunen, Anssi; Insinööritieteiden korkeakoulu; Mikkola, Tommi