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Author:Weckman, Kenneth
Title:Performance of friction based locking mechanisms used in implantable actuators
Kitkalukitusmekanismiin perustuvien implantoitavien aktuaattorien suorituskyky
Publication type:Master's thesis
Publication year:2011
Pages:97 + [15]      Language:   eng
Department/School:Elektroniikan laitos
Main subject:Elektroniikan valmistustekniikka   (S-113)
Supervisor:Paulasto-Kröckel, Mervi
Instructor:Hallila, Harri ; Vuorinen, Vesa
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  1558   | Archive
Keywords:intramedullary nails
contact mechanics
Herzian theory
implant metals
locking mechanism
theory applicability
luuydinnaula
kontaktimekaniikka
Hertzin teoria
implanttimetallit
lukitusmekanismi
teorian soveltuvuus
Abstract (eng): In the development of a new telescopic intramedullary nail, for the fixation and distraction of bone, the performance of the locking mechanism is one of the major research areas.
The main property of interest is its load bearing capability compared to its backlash.
Here, the contact mechanics between the locking component and the locking surfaces are vital.
In addition, the importance of the material and geometrical properties cannot be neglected.
This thesis will set out to investigate how the changes in the properties of a locking mechanism affect its backlash.

The Hertzian theory is the most widely used contact theory, in the simulation between the contacts of two elastic solids.
However, due to the limitations of the Hertzian theory other contact models were evaluated.
In this thesis, the backlash of the locking mechanism was investigated in two locking surface material configurations: titanium alloy and stainless steel.
The optimized dimensions in the locking component were the radius and length of the roller.

The experimental results show that the Hertzian based Puttock & Thwaite model corresponds best to the measured values.
However, since increasing the length of the contact surface decreases the backlash only up to a certain value a correction factor is included to the model.
With the correction factor the model matches to the measured values well.
The results indicate that the optimum roller to use has the length-to-diameter ratio of 1.0.
In addition, the locking surfaces should have as high Young's modulus as possible.
Abstract (fin): Luiden fiksaatioon ja pidennyshoitoon kehitettävän teleskooppisen luuydinnaulan kehitystyössä lukitusmekanismin suorituskyky on yksi päätutkimuskohteista.
Sen oleellisin ominaisuus on mekanismin kuormankantokyky verrattuna välykseen, missä lukituskomponentin ja lukituspintojen välinen kontaktimekaniikka on tärkeä.
Lisäksi, materiaalin ja geometristen tekijöiden osuutta ei voida unohtaa.
Tässä diplomityössä tutkitaan kuinka lukitusmekanismin ominaisuuksien muutos vaikuttaa sen välykseen.

Hertzin teoria on eniten käytetty kontaktiteoria simuloidessa kahden kiinteän elastisen kappaleen kontaktia.
Toisaalta, koska Hertzin teorialla on rajoituksensa, muitakin kontaktimalleja arvioitiin.
Tässä työssä lukitusmekanismin välystä tutkittiin käyttäen lukituspintana kahta eri materiaalikonfiguraatiota: titaaniseosta sekä ruostumatonta terästä.
Optimoidut dimensiot lukituskomponentissa olivat rullan säde sekä pituus.

Kokeelliset tulokset osoittavat, että Hertzin teoriaan perustuva Puttock & Thwaite:n malli sopii parhaiten mitattujen arvojen kanssa.
Koska kontaktipituuden kasvu pienentää välystä vain tiettyyn arvoon saakka, on mallia täydennetty korjauskertoimella.
Korjauskertoimen kanssa malli sopii hyvin yhteen mitattujen arvojen kanssa.
Tulokset osoittavat, että optimirullalla on pituus-halkaisija suhde 1,0.
Lisäksi, saatujen tulosten mukaan lukituspinnoilla pitäisi olla mahdollisimman korkea kimmokerroin.
ED:2012-05-08
INSSI record number: 44414
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