Uticaj koncentracije napona i pojave prsline na preostali radni vek biomaterijala za rekonstruktivne pločice
Influence of stress concentracion and crack initiation on remaining life of biomaterials for reconstructive plates
Author
Vučetić, FilipMentor
Sedmak, AleksandarCommittee members
Radaković, ZoranGrbović, Aleksandar
Čolić, Katarina
Milošević, Miloš
Metadata
Show full item recordAbstract
Biomaterijali namenjeni za izradu ortopedskih rekonstruktivnih pločica su boljih
mehaničkih karakteristika u odnosu na kosti, a ipak u velikom broju slučajeva dolazi do otkaza
pločica usled zamornog oštećenja. Jasno je da otkazi pločica za fiksaciju preloma dovode do problema
u procesu lečenja i potrebe za ponovnom operacijom pacijenata. Pored materijala i geometrije,
iskustvo i znanje ortopedskog hirurga su jedan od najbitnijih faktora koji doprinose učestalosti
zamornih otkaza pločica. U slučaju neadekvatne ugradnje pločice će biti podvrgnute preopterećenju
od samog početka eksploatacije, što pogoduje inicijaciji prsline.
Jedan od najčešće korišćenih biokompatibilnih materijala za unutrašnju fiksaciju preloma kostiju je
dvofazna alfa-beta legura titana Ti-6Al-4V. Cilj istraživanja doktorske disertacije je da se utvrdi
ponašanje rekonstruktivnih biomedicinskih pločica u prisustvu prslina na mestima koncentracije
napona i da se utvrdi brzina rasta prslina za različite geometrije, na os...novu čega im je moguće
proceniti integritet i preostali radni vek. U tu svrhu, eksperimentalno su određene zatezne
karakteristike i parametri mehanike loma legure Ti-6Al-4V u cilju korišćenja podataka u numeričkim
simulacijama, dok su udarne karakteristike ispitane na instrumentiranom klatnu u cilju boljeg
razumevanja ponašanja samog materijala. Umesto komplikovanih eksperimentalnih ispitivanja,
primenjeni su postupci numeričkih simulacija ponašanja ortopedskih pločica od Ti-6Al-4V legure
titana u prisustvu zamornih prslina, opterećenih na savijanje u četiri tačke, prvenstveno zbog
nemogućnosti primene mernih folija na geometrijama pločica. Takođe, numeričke simulacije
predstavljaju bržu i jeftiniju alternativu eksperimentalnim ispitivanjima. Geometrija i modeli pločica
rađeni su u programu CATIA, a simulacija rasta prsline proširenom metodom konačnih elemenata
(PMKE) u programu ANSYS. U simulacijama je korišćeno opterećenje (moment savijanja) koje se
javlja na čovekovoj potkolenici tokom hoda, a uzete su u obzir i različite telesne mase pacijenta: 60,
90 i 120 kg. Analiza je rađena za 5 različitih geometrija pločica. Analiza je rađena isključivo sa
mehaničkog aspekta, dok uticaj korozivne sredine čovekovog organizma i biokompatibilnost
materijala nisu uzeti u razmatranje.
Postoji više metoda za tretiranje materijala u cilju poboljšanja njegovih određenih karakteristika.
Jedan od načina za poboljšanje površinskih karakteristika materijala je lasersko ojačavanje materijala
(LSP). Razlog za primenu laserskog ojačavanja na leguri titana je istraživanje mogućnosti lokalnog
poboljšanja mehaničkih karakteristika i mikrogeometrijskih karakteristika površine, kao i unošenja
pritisnih zaostalih napona koji bi doprineli otpornosti na iniciranje prslina, naročito na mestima
koncentracije napona. Ispitivanja su rađena na tri grupe uzoraka i pod tri različita tretmana
pikosekundnim laserom Nd:YAG. Analiza je rađena sa aspekta mikrostrukture, površinske hrapavosti
i mikrotvrdoće.
Biomaterials intended for orthopaedic plates manufacturing are of much higher mechanical
properties relative to the bone itself and still there are many cases where those plates fracture in
service with fatigue as the main failure mode. This causes the problem with healing process and
requires that the patients undergo another surgery. Apart from materials and geometry, experience
and knowledge of the orthopaedic surgeon is one of the important factors contributing to the
frequency of fatigue failures. If incorrectly implanted, plates will be subjected to overloading from
the start, which is convenient for crack initiation.
One of the most commonly used biocompatible materials for internal bone fixation is two phase
alpha-beta titanium alloy Ti-6Al-4V. Focus of this doctoral dissertation is to determine the behaviour
of reconstructive biomedical plates in the presence of cracks at the stress concentration locations and
to obtain crack growth rates for different plate geometries which a...re to be used as a basis for structural
integrity and life assessment. Experimental investigations of tensile and fracture mechanics
parameters of Ti-6Al-4V alloy were conducted to be used in numerical simulations, while impact
characteristics, tested on instrumented Charpy pendulum, were investigated for the purpose of better
understanding of the material. Instead of complicated experimental four point bend testing of
orthopaedic plates in the presence of cracks, numerical simulations were employed, mainly due to
inability of measurement foils to be used on given plate geometries. Also, numerical simulations are
time and cost efficient when compared to experimental testing. Geometries and models of plates are
defined in CATIA software, while extended finite element method (XFEM) crack growth simulations
were made in ANSYS. Loads (bending moments) correspond to the ones occurring in human tibia
during gait cycle for different body weights: 60, 90 and 120 kg. Analysis was conducted on 5 different
plate geometries. Analysis was done only from the mechanical aspect and the influence of corrosive
environment of the human body was not taken into consideration.
There are many methods for treatment of materials for the purpose of improving its certain
characteristics. One of the methods for surface characteristics improvement is laser shock peening.
Reason for utilising the laser shock peening on titanium alloy is to research the possibilities of local
improvement of mechanical and micro-geometrical properties, as well as inducing the compressive
residual stresses which should contribute to the crack initiation resistance, especially at the stress
concentration locations. Testing was conducted on three types of samples under three different
treatments with picosecond laser Nd:YAG. Analysis was made from the aspect of microstructure,
surface roughness and microhardness.
Faculty:
Универзитет у Београду, Машински факултетDate:
11-02-2021Projects:
- Developed new methods for diagnosis and examination mechanical structures (RS-MESTD-Technological Development (TD or TR)-35040)