Defining of the material models for stainless steels to be used in FE modeling

The aim of this work is to study the results of tensile tests for austenitic stainless steel type 304 and make accurate FE-models according to the results of the tests. Tensile tests were made at Central Research Institute of Structural Material, Prometey at Saint Petersburg and Mariyenburg in Russia. The test specimens for the tensile tests were produced at Lappeenranta University of Technology in a Laboratory of Steel Structures. In total 4 different tests were made, two with base material specimens and two with transverse butt weld specimens. Each kind of a specimen was tested at room temperature and at low temperature. By comparing the results of room and low temperature tests of similar test specimen we get to study the results of work hardening that affect the austenitic steels at below room temperature. The produced specimens are to be modeled accurately and then imported for nonlinear FEM- analyzing. Using the data gained from the tensile tests the aim is to get the models work like the specimens did during the tests. By using the analyzed results of the FE-models the aim is to calculate and get the stress-strain curves that correspond to the results acquired from the tensile tests.

Hygro-elasto-plastic behavior of planar orthotropic material

The mechanical and hygroscopic properties of paper and board are factors affecting the whole lifecycle of a product, including paper/board quality, production, converting, and material and energy savings. The progress of shrinkage profiles, loose edges of web, baggy web causing wrinkling and misregistration in printing are examples of factors affecting runnability and end product quality in the drying section and converting processes, where paper or board is treated as a moving web. The structural properties and internal stresses or plastic strain differences built up during production also cause the end-product defects related to distortion of the shape of the product such as sheet or box. The objective of this work was to construct a model capable of capturing the characteristic behavior of hygroscopic orthotropic material under moisture change, during different external in-plane stretch or stress conditions. Two independent experimental models were constructed: the elasto-plastic material model and the hygroexpansivity-shrinkage model. Both describe the structural properties of the sheet with a fiber orientation probability distribution, and both are functions of the dry solids content and fiber orientation anisotropy index. The anisotropy index, introduced in this work, simplifies the procedure of determining the constitutive parameters of the material model and the hygroexpansion coefficients in different in-plane directions of the orthotropic sheet. The mathematically consistent elasto-plastic material model and the dry solids content dependent hygroexpansivity have been constructed over the entire range from wet to dry. The presented elastoplastic and hygroexpansivity-shrinkage models can be used in an analytical approach to estimate the plastic strain and shrinkage in simple one-dimensional cases. For studies of the combined and more complicated effects of hygro-elasto-plastic behavior, both models were implemented in a finite element program for a numerical solution. The finite element approach also offered possibilities for studying different structural variations of orthotropic planar material, as well as local buckling behavior and internal stress situations of the sheet or web generated by local strain differences. A comparison of the simulation examples presented in this work to results published earlier confirms that the hygro-elasto-plastic model provides at least qualitatively reasonable estimates. The application potential of the hygro-elasto-plastic model is versatile, including several phenomena and defects appearing in the drying, converting and end-use conditions of the paper or board webs and products, or in other corresponding complex planar materials.

Komposiittivaipan moderni optimisuunnittelu ja toteutus

Tavoitteena tällä tutkimuksella on soveltaa modernin optimisuunnittelun keinoja komposiittimuovisen nestesäiliön lieriömäisen vaipparakenteen suunnittelemiseksi optimaalisen tyydyttäviksi valmistustekniikan ja kustannusten kannalta. Kuormituksia on kahdenlaisia. Säiliön sisällä on neste, joka tuottaa hydrostaattisen painekuorman ja järjestelmään kytketty puhallin tuottaa ulkoisen ylipaineen. Säiliöt ovat pystysäiliöitä ja ne tukeutuvat alustaan suoran pohjalaatan avulla. FEM- malleissa kuoren alaosat ovat jäykästi kiinnitettyjä ja yläosissa säteensuuntaiset siirtymät ovat estettyjä. Materiaaleiksi kuoreen on valittu kahdella eri menetelmällä lujitetut komposiittimateriaalit. Kantavan kerroksen toimintona on kantaa kuormat. Sulkukerros toimii korroosiosuojana ja sen lujuus on kantavaa kerrosta pienempi. Keinoina käytetään ensin innovatiivista suunnittelua optimaalisten lähtövaihtoehtojen ideoimiseksi ja valitsemiseksi jatkokehittelyä varten. Tavoitteena on asiakkaan tyytyväisyyden maksimointi huomioiden tuotteen kustannukset ja kesto. Yhtenä suunnittelun keinona on käytetty kuoriteoriaa ja komposiittien materiaalimalleja. Kestoehtoina on sovellettu komposiiteille soveltuvia kriteerejä. Toisena keinona käytetään FEM-laskentaa. Elementtityypiksi on valittu kaksiulotteinen kuorielementti, jossa on ortotrooppisen ainemallin mukaiset materiaaliominaisuudet. Jännitystuloksien merkittävyys keston kannalta selvitettiin Tsai-Hillin kriteerillä. Tuloksina saatiin ensin innovoitua rakenteelle kaksi päävaihtoehtoa, joita alettiin optimoida. Valitussa ratkaisussa on huomioitu kokonaisuus ja eri yksityiskohdat, kuten paino, jäykisteet kustannustehokkuus, valmistusnopeus, laatu, hävikit, päästöt, lujuus ja kilpailukykyinen myyntihinta. Yhteenvetona voidaan todeta, että käytetyt keinot ovat hyvin tehokkaita ja niillä voidaan suunnitella ja toteuttaa komposiittirakenteita, jotka tyydyttävät optimaalisesti loppukäyttäjän teknis- taloudelliset vaatimukset. Lisäksi tulokset osoittavat, että standardin ja FEM-laskennan ennustukset ovat lähellä toisiaan sylinterimäisillä kuoriosilla, mutta standardit suosittavat suurempia mittoja itse jäykisteille.

Materiaalimallin määrityksestä kylmämuovattujen putkipalkkien K-liitosten FE-analyysissä

Työssä on tutkittu kylmämuovattujen nelikulmaisten putkipalkkien K-liitosten mallinnusta epälineaarisella elementtimenetelmällä. Työn tärkeimpänä tavoitteena on ollut kehittää putkipalkin osien materiaalimalleja siten, että liitosten kestävyyttä voidaan tutkia laboratoriokokeiden ohella luotettavasti myös elementtimenetelmällä. Toisena tavoitteena on ollut tutkia, voidaanko putkipalkkien liitosten mitoitusohjeita turvallisesti soveltaa kylmämuovatuille putkipalkeille, joissa valmistusprosessi aiheuttaa muutoksia materiaaliominaisuuksiin, erityisesti muodonmuutoskykyyn. Työssä tehtyjen laboratoriokokeiden ja elementtianalyysien perusteella elementti-menetelmä on käyttökelpoinen työkalu putkipalkkiliitosten staattista kestävyyttä määritettäessä, kun materiaalimallit on määritetty oikein. Erityisesti liitoksen käyttö-rajatilan mukaisen kestävyyden laskennassa elementtimenetelmällä saadaan hyvin laboratoriokokeita vastaavia tuloksia. Tehdyt laboratoriokokeet osoittavat myös, että Eurocode 3:n mukaisia putkipalkkien liitosten mitoitusohjeita voi turvallisesti käyttää kylmämuovatuille putkipalkeille.

Kylmämuovattujen putkipalkkien X-liitosten äärikestävyyden ja jäykkyyden määrittäminen sekä materiaalimallin kehittäminen

Työssä on tutkittu elementtimenetelmän avulla kylmämuovattujen nelikulmaisten putkipalkkien materiaalimallin kehittämistä ja putkipalkkien X-liitosten jäykkyyden ja äärikestävyyden määrittämistä. Työn tavoitteena on tutkia kylmämuovauksen vaikutuksia putkipalkkiprofiilin materiaaliominaisuuksiin materiaalikokeiden ja elementtianalyysien avulla sekä kehittää putkipalkille anisotrooppista materiaalimallia. Työssä määritettyjä materiaalimalleja on sovellettu X-liitosten elementtimalleihin, joiden käyttäytymistä on verrattu äärikestävyyskokeiden tuloksiin. Tutkimuksen perusteella Eurocode 3:n mitoitusohjeita voidaan turvallisesti soveltaa kylmämuovattujen putkipalkkien X-liitosten laskennassa. Työssä tehtyjen materiaalikokeiden ja elementtianalyysien perusteella materiaalin anisotrooppisuuden vaikutus liitoksen kestävyyteen on vähäistä, ja putkipalkin pituussuuntaista materiaalimallia voidaan soveltaa myös kehäsuuntaisille materiaaliominaisuuksille. Materiaalikokeiden simulointi osoittaa, että elementtimenetelmää voidaan käyttää materiaalimallin määrittämisen apuvälineenä.

Development of finite elements for analysis of biomechanical structures using flexible multibody formulations

The absolute nodal coordinate formulation was originally developed for the analysis of structures undergoing large rotations and deformations. This dissertation proposes several enhancements to the absolute nodal coordinate formulation based finite beam and plate elements. The main scientific contribution of this thesis relies on the development of elements based on the absolute nodal coordinate formulation that do not suffer from commonly known numerical locking phenomena. These elements can be used in the future in a number of practical applications, for example, analysis of biomechanical soft tissues. This study presents several higher-order Euler–Bernoulli beam elements, a simple method to alleviate Poisson’s and transverse shear locking in gradient deficient plate elements, and a nearly locking free gradient deficient plate element. The absolute nodal coordinate formulation based gradient deficient plate elements developed in this dissertation describe most of the common numerical locking phenomena encountered in the formulation of a continuum mechanics based description of elastic energy. Thus, with these fairly straightforwardly formulated elements that are comprised only of the position and transverse direction gradient degrees of freedom, the pathologies and remedies for the numerical locking phenomena are presented in a clear and understandable manner. The analysis of the Euler–Bernoulli beam elements developed in this study show that the choice of higher gradient degrees of freedom as nodal degrees of freedom leads to a smoother strain field. This improves the rate of convergence.

Hitsin juurenpuolen kriittisyys suurlujuus teräksillä

Kandidaatintyön tarkoituksena oli selvittää pienahitsin juuren kriittisyyttä. Työ oli saanut aiheen rakenneputki kokeiden yhteydessä tehdyistä havainnoista. Työssä tutustuttiin millaiset ovat pienahitsin mitoitus menetelmät ja tausta tutkimusta kuinka sitä sovelletaan käytäntöön suurlujuusteräksille. Työssä esitellään käytetyt tutkimusmenetelmät kuinka menetelmätriangulaatio saavutettiin. Tutkimuskysymyksenä oli hitsien kestävyyden mitoituksen riittävyys. Tutkimukset suoritettiin tarkastellen staattisesti kuormitettuja pienahitsejä. Pienahitsi kappaleista tehtiin laboratoriokoekappale ja FEM-laskentamalli joista vertailtiin tuloksia. Laboratoriokokeessa mittaus menetelmänä käytettiin DIC-mittausta, jolle voitiin tehdä jälkikäsittelyjä ja sieltä määrittää haluttuja datapisteitä. Laskennassa suurimmat jännityskeskittymät syntyivät hitsin kohdalle mutta vetokokeessa koekappaleeseen syntyi vauriot sularajalle ja vetokorvakkeen kiinnityshitsin rajaviivalle. Tällä kohtaa todettiin materiaalimalli riittämättömäksi, koska siihen ei ollut määritelty muutosvyöhykkeen parametreja.

New Operation Model for Maintenance Material Logistics in Paper Industry

This research report illustrates and examines new operation models for decreasing fixed costs and transforming them into variable costs in the field of paper industry. The report illustrates two cases - a new operation model for material logistics in maintenance and an examination of forklift truck fleet outsourcing solutions. Conventional material logistics in maintenance operation is illustrated and some problems related to conventional operation are identified. A new operation model that solves some of these problems is presented including descriptions of procurement and service contracts and sources of added value. Forklift truck fleet outsourcing solutions are examined by illustrating the responsibilities of a host company and a service provider both before and after outsourcing. The customer buys outsourcingservices in order to improve its investment productivity. The mechanism of how these services affect the customer company's investment productivity is illustrated.

Wood as a model material for medical biomaterials. In vivo and in vitro studies with bone and Betula pubescens Ehrh

Novel biomaterials are needed to fill the demand of tailored bone substitutes required by an ever‐expanding array of surgical procedures and techniques. Wood, a natural fiber composite, modified with heat treatment to alter its composition, may provide a novel approach to the further development of hierarchically structured biomaterials. The suitability of wood as a model biomaterial as well as the effects of heat treatment on the osteoconductivity of wood was studied by placing untreated and heat‐treated (at 220 C , 200 degrees and 140 degrees for 2 h) birch implants (size 4 x 7mm) into drill cavities in the distal femur of rabbits. The follow‐up period was 4, 8 and 20 weeks in all in vivo experiments. The flexural properties of wood as well as dimensional changes and hydroxyl apatite formation on the surface of wood (untreated, 140 degrees C and 200 degrees C heat‐treated wood) were tested using 3‐point bending and compression tests and immersion in simulated body fluid. The effect of premeasurement grinding and the effect of heat treatment on the surface roughness and contour of wood were tested with contact stylus and non‐contact profilometry. The effects of heat treatment of wood on its interactions with biological fluids was assessed using two different test media and real human blood in liquid penetration tests. The results of the in vivo experiments showed implanted wood to be well tolerated, with no implants rejected due to foreign body reactions. Heat treatment had significant effects on the biocompatibility of wood, allowing host bone to grow into tight contact with the implant, with occasional bone ingrowth into the channels of the wood implant. The results of the liquid immersion experiments showed hydroxyl apatite formation only in the most extensively heat‐treated wood specimens, which supported the results of the in vivo experiments. Parallel conclusions could be drawn based on the results of the liquid penetration test where human blood had the most favorable interaction with the most extensively heat‐treated wood of the compared materials (untreated, 140 degrees C and 200 degrees C heat‐treated wood). The increasing biocompatibility was inferred to result mainly from changes in the chemical composition of wood induced by the heat treatment, namely the altered arrangement and concentrations of functional chemical groups. However, the influence of microscopic changes in the cell walls, surface roughness and contour cannot be totally excluded. The heat treatment was hypothesized to produce a functional change in the liquid distribution within wood, which could have biological relevance. It was concluded that the highly evolved hierarchical anatomy of wood could yield information for the future development of bulk bone substitutes according to the ideology of bioinspiration. Furthermore, the results of the biomechanical tests established that heat treatment alters various biologically relevant mechanical properties of wood, thus expanding the possibilities of wood as a model material, which could include e.g. scaffold applications, bulk bone applications and serving as a tool for both mechanical testing and for further development of synthetic fiber reinforced composites.

Repair of segmental bone defects with fiber-reinforced composite: a study of material development and an animal model on rabbits

The Repair of segmental defects in load-bearing long bones is a challenging task because of the diversity of the load affecting the area; axial, bending, shearing and torsional forces all come together to test the stability/integrity of the bone. The natural biomechanical requirements for bone restorative materials include strength to withstand heavy loads, and adaptivity to conform into a biological environment without disturbing or damaging it. Fiber-reinforced composite (FRC) materials have shown promise, as metals and ceramics have been too rigid, and polymers alone are lacking in strength which is needed for restoration. The versatility of the fiber-reinforced composites also allows tailoring of the composite to meet the multitude of bone properties in the skeleton. The attachment and incorporation of a bone substitute to bone has been advanced by different surface modification methods. Most often this is achieved by the creation of surface texture, which allows bone growth, onto the substitute, creating a mechanical interlocking. Another method is to alter the chemical properties of the surface to create bonding with the bone – for example with a hydroxyapatite (HA) or a bioactive glass (BG) coating. A novel fiber-reinforced composite implant material with a porous surface was developed for bone substitution purposes in load-bearing applications. The material’s biomechanical properties were tailored with unidirectional fiber reinforcement to match the strength of cortical bone. To advance bone growth onto the material, an optimal surface porosity was created by a dissolution process, and an addition of bioactive glass to the material was explored. The effects of dissolution and orientation of the fiber reinforcement were also evaluated for bone-bonding purposes. The Biological response to the implant material was evaluated in a cell culture study to assure the safety of the materials combined. To test the material’s properties in a clinical setting, an animal model was used. A critical-size bone defect in a rabbit’s tibia was used to test the material in a load-bearing application, with short- and long-term follow-up, and a histological evaluation of the incorporation to the host bone. The biomechanical results of the study showed that the material is durable and the tailoring of the properties can be reproduced reliably. The Biological response - ex vivo - to the created surface structure favours the attachment and growth of bone cells, with the additional benefit of bioactive glass appearing on the surface. No toxic reactions to possible agents leaching from the material could be detected in the cell culture study when compared to a nontoxic control material. The mechanical interlocking was enhanced - as expected - with the porosity, whereas the reinforcing fibers protruding from the surface of the implant gave additional strength when tested in a bone-bonding model. Animal experiments verified that the material is capable of withstanding load-bearing conditions in prolonged use without breaking of the material or creating stress shielding effects to the host bone. A Histological examination verified the enhanced incorporation to host bone with an abundance of bone growth onto and over the material. This was achieved with minimal tissue reactions to a foreign body. An FRC implant with surface porosity displays potential in the field of reconstructive surgery, especially regarding large bone defects with high demands on strength and shape retention in load-bearing areas or flat bones such as facial / cranial bones. The benefits of modifying the strength of the material and adjusting the surface properties with fiber reinforcement and bone-bonding additives to meet the requirements of different bone qualities are still to be fully discovered.

Value added logistics in supply and demand chain : COSTFIX : New operation model for maintenance material logistics in paper industry

This research report illustrates and examines new operation models for decreasing fixed costs and transforming them into variable costs in the field of paper industry. The report illustrates two cases – a new operation model for material logistics in maintenance and an examination of forklift truck fleet outsourcing solutions. Conventional material logistics in maintenance operation is illustrated and some problems related to conventional operation are identified. A new operation model that solves some of these problems is presented including descriptions of procurement and service contracts and sources of added value. Forklift truck fleet outsourcing solutions are examined by illustrating the responsibilities of a host company and a service provider both before and after outsourcing. The customer buys outsourcing services in order to improve its investment productivity. The mechanism of how these services affect the customer company’s investment productivity is illustrated.

Site index model approach for drained peatland forest stands

Tiivistelmä: Pituusboniteettisovellus ojitusalueiden metsille

A game theoretic simulation model for quality oriented timber supply to sawmills

Summary

A mouse model for improving cell survival of bisected cattle embryos

Selostus: Hiiren alkio mallina solukestävyyden parantamiseksi naudan alkioiden halkaisussa