Title Validacija numeričkih modela mehaničkoga ponašanja životinjskih i ljudskih kostiju Title (english) Validation of numerical models of mechanical behavior of animal and human bones Author Martin Surjak Mentor Janoš Kodvanj (mentor)Mentor Dragica Bobinac (komentor)Committee member Zdenko Tonković (predsjednik povjerenstva)Committee member Janoš Kodvanj (član povjerenstva)Committee member Dragica Bobinac (član povjerenstva)Committee member Tanja Jurčević-Lulić (član povjerenstva)Committee member Nikica Daraboš (član povjerenstva)Granter University of Zagreb Defense date and country 2015-12-22, Croatia Scientific / art field, TECHNICAL SCIENCES Universal decimal classificationUDC ) 51 - Mathematics 612 - Physiology 502/504 - Environmental science. Conservation of natural resources. Threats to the environment and protection against them Abstract Primjena metode konačnih elemenata postaje nezaobilazna u biomehanici i medicini, osobito pri numeričkom modeliranju kosti ili sustava kost – implantat. Budući da je koštano tkivo nehomogen materijal, primjena računalne tomografije (engl. Computed Tomography – CT) vrlo je važna u razvoju numeričkih modela kostiju. Na osnovi CT-a može se vrlo precizno rekonstruirati geometrija kosti i odrediti gustoća svakoga pojedinog voksela. Gustoća kosti povezana je s modulom elastičnosti, no ta veza nije jednaka za svaku kost. U ovom istraživanju kost je na razini konačnog elementa modelirana kao linearno elastičan materijal s izotropnim svojstvima, dok u mreži konačnih elemenata modul elastičnosti varira s gustoćom kosti tako da je cijela kost modelirana kao nehomogeni materijal. Pravilan odabir relacije koja povezuje gustoću i modul elastičnosti znatno utječe na rezultate računalnih simulacija, stoga je potrebno validirati numeričke modele eksperimentalnim in vitro ispitivanjem svježih kostiju. Danas se u biomehaničkim istraživanjima, ponajprije jer se lakše nabavljaju, često koristimo životinjskim kostima. Konkretno, svinjske i ovčje kosti zbog svoje su građe, oblika i dimenzija prikladne za testiranje medicinskih implantata namijenjenih ljudima. Većina relacija gustoća – modul elastičnosti dostupnih u literaturi, ograničena je na ljudski femur (bedrena kost) te je upitna njihova primjenjivost na ostale ljudske ili životinjske kosti. Cilj predloženoga doktorskog rada jest in vitro eksperimentalno ispitivanje svježih životinjskih i ljudskih kostiju primjenom metode korelacije digitalne slike (engl. Digital image correlation – DIC) za mjerenje pomaka i deformacija. Metoda korelacije digitalne slike suvremena je beskontaktna metoda koja omogućuje mjerenje cijelog polja pomaka na površini mjernog objekta i sve se češće primjenjuje za ispitivanje bioloških tkiva. S obzirom na to da daje kao rezultat cijelo polje pomaka i deformacija, metoda je kvalitetan alat za validaciju numeričkih modela kostiju. Spomenuta metoda omogućuje bolji uvid u mehaničko ponašanje kosti te realnije prikazuje njezin mehanički odziv na narinuto opterećenje. Predloženo istraživanje obuhvaća numeričko modeliranje kosti na temelju računalne tomografije, te na osnovi usporedbe s eksperimentom, definiranje relacija gustoća – modul elastičnosti za pojedine vrste kostiju. Za veći dio istraživanja korištene su svježe svinjske i ovčje kosti, uglavnom zbog njihove pristupačnosti.
Abstract (english) The finite element method has become an indispensable tool in biomechanics and medicine, especially when the bone or the bone-implant system are modeled numerically. Since the bone tissue material is inhomogeneous, the application of computed tomography (CT) plays a major role in the development of numerical bone models. Based on the CT scan the bone geometry can be precisely reconstructed and the denstiy of each voxel can be determined. The bone density is related to the modulus of elasticity, whereby this relation is not the same for each bone. In this research the bone is at the finite element level modeled as a linear elastic material with isotropic properties. In finite element mesh the modulus of elasticity varies with the bone density so the global bone model was modeled as inhomogeneous material. The proper choice of relation between density and modulus of elasticity of the bone has a big impact on the numerical simulation results, therefore it is necessary to validate numerical models with the experimental in vitro testing of fresh bones. In today's biomechanical investigations, animal bones are often used, mostly because of their availability. In particular, swine and sheep bones are, due to their structure, shape and dimensions, suitable for testing medical implants intended for humans. Most of density-elasticity relations in the literature are limited to the human femur, and their applicability to other human or animal bones is questionable. The aim of this doctoral thesis is in vitro experimental testing of fresh animal and human bones using the digital image correlation (DIC) method for the displacement and strain measurement. The DIC method is a modern non-contact method that enables measurement of displacement fields on the surface of a measured object and has been increasingly used in the biological tissue testing. Since as a result the method produces the displacement and strain field, it represents a quality tool for the validation of numerical models of bones. The mentioned method will give a better insight into the mechanical behavior of bones and show the mechanical response of bone to the applied load in a more realistic manner. The proposed investigation involves numerical modeling of the bone based on computed tomography and a comparison with experimental results, as well as defining the relations between density and modulus of elasticity for certain types of bones. The greater part of the investigation will be carried out on fresh swine and sheep bones primarily because of their accessibility.
Keywords
računalna tomografija
mjerenje polja pomaka
gustoća kosti
modul elastičnosti
biomehanika
Keywords (english)
computed tomography
displacement field measurement
bone density
modulus of elasticity
biomechanics
Language croatian URN:NBN urn:nbn:hr:235:545011 Study programme Title: Mechanical Engineering and Naval Architecture Type of resource Text File origin Born digital Access conditions Open access Terms of use Created on 2020-04-23 19:06:18
