Sami Holopainen

Sami Holopainen
Tampere University | UTA · Department of Civil Engineering

D.Sc. (Tech.)

About

31
Publications
2,500
Reads
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167
Citations
Citations since 2016
16 Research Items
157 Citations
201620172018201920202021202205101520253035
201620172018201920202021202205101520253035
201620172018201920202021202205101520253035
201620172018201920202021202205101520253035
Additional affiliations
October 2019 - August 2020
University Bourgogne Franche-Comté
Position
  • Professor
Description
  • Part-time position. Research and teaching of mechanics of materials.
November 2017 - present
Finnish Patent and Registration Office (FPRO)
Position
  • Lecturer
Description
  • Lectures in FPRO and Aalto University (Aalto Pro): https://www.aaltopro.fi/en/programs/patentit-teollisuus-tekniikka
February 2013 - present
Tampere University
Position
  • PostDoc Position
Education
February 2013
Tampere University
Field of study
  • Engineering Mechanics
September 2008 - November 2011
Lund University
Field of study
  • Solids Mechanics
September 1997 - January 2001
Tampere University
Field of study
  • Department of Structural Engineering

Publications

Publications (31)
Article
The objective of this work is to investigate the influence of damage mechanisms on inhomogeneous deformation behavior of amorphous glassy polymers. The mechanical properties of glassy polymers are strongly influenced by the microstructure which is typically described by network models. In order to improve the network model predictions at large mult...
Article
The objective of this work is to model the mechanical behavior of glassy polymers during non-monotonic loadings involving softening/hardening characteristics, transient effects and plastic instabilities. The microstructure of a glassy polymer has a strong influence on the mechanical properties and it is typically described by network models. The pr...
Article
Full-text available
The main goal of the present paper is to introduce certain duals and transpositions of a high-order tensor playing an important role in continuum mechanics. Emphasis is also placed on the comparison of the duals and the transpositions. In contrast to the duals, the transpositions depend on a metric of an underlying metric space. A high-order tensor...
Article
The constitutive model for glassy polymers proposed by Arruda and Boyce (BPA model) is reviewed and compared to experimental data for long-term loading. The BPA model has previously been shown to capture monotonic loading accurately, but for unloading and long-term behavior, the response of the BPA model is found to deviate from experimental data....
Article
Full-text available
When investigating materials to be utilized, attention inevitably focuses on their resistance over the service life. Despite the popularity of amorphous polymers, ranging from their applications in structural components to their ability to increase the toughness of biocomposites, the investigation of their short- to long-term resistance has been co...
Article
The deformation behavior of solid polymers under isothermal, quasi-static loadings is investigated. A comprehensive test program consisting of tension, torsion, and combinations thereof was conducted on a polycarbonate polymer under both monotonic and long-term cyclic loadings. The effects of different loading modes, creep load conditions, mean str...
Article
A number of constitutive models have been developed for solid polymers to describe the large deformation behavior. However, most of the existing models rely on a purely elastic or hyperelastic initial response when they are incapable of accurately predicting the cyclic stress-strain hysteresis loops. In this work, therefore, a compact cyclic viscoe...
Article
Full-text available
This article gives a computational continuum mechanics answer to a question of how much heat is generated, in terms of temperature rise, during controlled shear band formation in a rock like material. This problem is treated as adiabatic heating due to mechanical dissipation at the material point level. Assuming that only the compressive strength o...
Article
Full-text available
In this work, an extension of a previously developed continuum based high-cycle fatigue model is enhanced to also capture the low-cycle fatigue regime, where significant plastic deformation of the bulk material takes place. Coupling of the LCFand HCF-models is due to the damage evolution equation. The high-cycle part of the model is based on the co...
Article
Amorphous solids, such as certain polymers, alloys, and polymer-based composites,are increasingly used materials in engineering components and thus, their fatigue behavioris of utmost importance. The article presents a unified approach suitable for modeling bothisothermal high cycle and low cycle fatigue behavior. The emphasis is placed on the duct...
Article
Full-text available
An approach suitable for modeling viscoelastic-viscoplastic response with isothermal fatigue damage in amorphous solids is proposed. The theory explicitly accounts for frame-indifference and dependence of the free energy on both the viscoelastic-viscoplastic deformation and fatigue damage in a thermodynamically consistent manner. The damage evoluti...
Article
Full-text available
A very general continuum based approach to model both low- and high cycle fatiguebehaviour is described. The approach allows for both isotropic and anisotropic properties undervery general random multiaxial loading histories.
Article
Full-text available
In this paper a computational implementation of a continuum based transversely isotropic high-cycle fatigue model is described. The key idea of that model is the moving endurance surface where the movement is described by a back stress type tensor, the evolution of which is described by a rate type equation. Furthermore, damage accumulation is also...
Article
Full-text available
In this paper evolution equation based multiaxial fatigue model is applied to the analysis of fretting fatigue of a cantilever test specimen made of EN 10083-1 steel. The adopted high-cycle fatigue model is based on the concept of evolving endurance surface and damage evolution equation. For the endurance surface a simple linear relationship betwee...
Article
In this article, we propose an approach suitable for modeling isothermal fatigue in amorphous polymers. The theory is formulated in a rate form within continuum mechanics framework without the need to measure damage changes per loading cycles. Using the approach, contribution of ratcheting to fatigue of polycarbonate (PC) was investigated and the r...
Conference Paper
Full-text available
In this work, a unified low-and high-cycle fatigue model based on continuum mechanics is developed. The high-cycle part of the model is based on the concepts of a moving endurance surface in the stress space with an associated evolving isotropic damage variable. The low-cycle part of the model is formulated as a traditional nonlinear isotropic and...
Article
A continuum approach is proposed for modelling multiaxial high-cycle fatigue of solids which exhibit transversely isotropic fatigue properties. The approach is an extension of the original isotropic model proposed by Ottosen, Stenström and Ristinmaa in 2008, which model is based on the concept of a moving endurance surface in the stress space and o...
Conference Paper
Given the pressure on improving performance of labor-intensive services in the public sector, systematic decision support approaches for work planning within a field of a pertinent process and operations management have met with increasing success. However, due to a complex work pattern and multiple conflicting attributes, the issue has proven diff...
Conference Paper
Full-text available
The transpositions and duals of a tensor have numerous applications in many fields of mechanics. They are needed for calculation of a tensor norm, for the definition of pull-backs and push-forwards, and in connection with tensor symmetrizations. Considering the literature of mechanics, the transpose of a bilinear map or a second order tensor is wel...
Conference Paper
Full-text available
This paper considers two different damage formulations for modeling high-cycle fatigue of materials. The underlying fatigue model is formulated within continuum mechanics framework with the concept of a moving endurance surface. Such a model has a unique feature that it allows for the concepts of fatigue limits and damage accumulation during the loa...
Conference Paper
Full-text available
In this paper a computational implementation of continuum based transversally isotropic fatigue model is described. The key idea of the continuum based HCF-model is the moving endurance surface where the movement is described by a back stress type tensor, the evolution of which is described by a rate type equation. Furthermore, damage accumulation...
Article
In this work, supplier selection is applied to scheduling and ranking of employees. Ranking and selection of employees is considered an assembly of multiple criteria which feature turns the problem challenging. Identifying significant ingredients of the problem, the approach is split into the two linear subproblems involving employee timetabling an...
Conference Paper
Full-text available
In this work, supplier/vendor selection is applied to scheduling and ranking of employees. Ranking and selection of employees considered is an assembly of a multiple criteria which feature turns the problem challenging. Identifying significant ingredients of the problem, the approach is split into the two linear subproblems involving employee timet...
Article
This research deals with the nonlinear anisotropic material with large strains affected generally from large rotations. Consequently many difficulties arises, as the caring about objectivity or spatial covariance. For that, the theory and the modeling aspects have been researched and published only during couple of the latest decades [1], [2]. Addi...
Article
1.Abstract A continuum-based design sensitivity analysis (DSA) applied to the thickness design of the anisotropic elasto-plastic shell structures is developed. Since main interest lies in developing path-following algorithms for solving sensitivity problems of elasto-plasticity, such an incremental or a step-by-step formalism will be employed to im...

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Projects

Projects (2)
Project
The goal is to find a unified low cycle-high cycle fatigue model based on continuum mechanics. The high-cycle part of the model is based on the concepts of a moving endurance surface in the stress space and an evolving isotropic damage variable. In this concept, originally developed Ottosen et al. (2007), the movement of the endurance surface (as a function of the stress history) is tracked by an evolving back stress type of stress tensor. This model avoids the cycle-counting techniques. The low-cycle part of the model is formulated as the classical J2-plasticity model with nonlinear isotropic and kinematic hardening. The low and high cycle components are combined so that first, in case of yielding, the stress is returned onto the yield surface and then the damage is computed using a single damage evolution law. In case of no yielding, the only contribution to the damage evolution is due to high-cycle fatigue model. The high-cycle fatigue damage is driven by the amount of violation of the endurance criterion while the low-cycle fatigue is driven by the equivalent plastic strain. The work is done in collaboration with Dr. Sami Holopainen and Timo Saksala at TUT and Professors Niels Ottosen and Matti Ristinmaa from Lund University.
Project
Manufacturers of metal alloys and polymer materials are interested in the assurance of components lifetime, especially when the lifetime cannot be easily inspected or may lead to a catastrophe in service. Due to the costly and time-consuming testing of long-term fatigue life, which still suffers from its sensitivity to environmental conditions and previous operation histories, there is a need to develop approaches that can simulate tests well.