Influence of corrosion on the integrity and service life of an artificial hip

[T. Smoljanić]

94 str.

Tehnološko inženjerstvo - Hemijsko inženjerstvo / Technological Engineering - Chemical Engineering

Biokompatibilni metalni materijali (BMM) su materijali koji su u kontaktu sa ćelijama, tkivima i telesnim tečnostima u ljudskom organizmu. Koriste se za zamenu ili nadogradnju komponenata u organizmu nadomeštanjem oštećenja nastalih zbog bolesti, starosti i nesrećnih slučajeva. Da bi BMM bili upotrebljeni kao implanti, treba da zadovolje sledeće uslove: izuzetna otpornost na korozivno dejstvo sredine u kojoj se nalaze, biokompatibilnost, dobre mehaničke osobine i otpornost na zamorno opterećenje. Do otkaza implanata, uključujući i veštačke kukove, najčešće dolazi zbog zamora materijala, odnosno usled stvaranja zamorne prsline u najkritičnijim delovima konstrukcije implanta, kao posledica dugotrajnog promenljivog opterećenja. Ovaj proces može biti u velikoj meri ubrzan pojavom korozije, koja dovodi do gubitka mase materijala, odnosno smanjenja nosećeg poprečnog preseka. Glavni cilj eksperimentalnih ispitivanja urađenih u okviru ove disertacije je bio da se utvrde mehaničke osobine legure Ti-6Al-4V neophodne za analizu ponašanja veštačkog kuka u prisustvu zamorne prsline, a koji su korišćeni za numeričke simulacije klasičnom i proširenom metodom konačnih elemenata i za analizu ponašanja kuka primenom parametara mehanike loma, odnosno za analitičko određivanje zamornog veka. Numeričkim simulacijama se nastojalo da se dobiju reprezentativni modeli ponašanja veštačkog kuka u prisustvu zamorne prsline, a eksperimentalnim ispitivanjima su obuhvaćene tri grupe epruveta i upoređeni su rezultati za epruvete izložene koroziji sa epruvetama ispitanim na vazduhu. Ispitivanjem parametara mehanike loma (faktora intenziteta napona), i eksperimentalno dobijenih vrednosti koeficijenata Paris-ove jednačine za brzinu rasta zamorne prsline, urađen je analitički proračun rasta zamorne prsline. Ovi rezultati su korišćeni kao osnova za razvoj i verifikaciju numeričkih modela. Eksperimentalnim, analitičkim i numeričkim pristupima dobijeni su rezultati koji su pokazali dobro međusobno slaganje i na realan način opisali ponašanje veštačkih kukova od legure Ti6Al4V pri kombinovanom dejstvu korozije i zamora.

Biocompatible metallic materials (BMMs) are materials that come into contact with cells, tissues and body fluids in the human body. They are used to replace or improve components in the body by replacing damage caused by disease, age or accidents. For BMMs to be used as implants, they must meet the following conditions: exceptional resistance to the corrosive effects of the environment in which they are used, biocompatibility, good mechanical properties and resistance to fatigue loading. Failure of implants, including artificial hips, is in most cases due to material fatigue, i.e. the development of a fatigue crack in the most critical parts of the implant structure as a result of long- term variable loading. This process can be greatly accelerated by the occurrence of corrosion, which leads to a loss of material mass, i.e. a reduction in the load-bearing cross-section. The main objective of the experimental investigations carried out in this dissertation was to determine the mechanical properties of the alloy Ti-6Al-4V required to analyze the behavior of the artificial hip in fatigue fractures. These were used for numerical simulations with the classical and extended finite element method and for the analysis of the behavior of the artificial hip with fracture mechanics parameters, i.e. for the analytical determination of the fatigue life. Numerical simulations were used to create representative models for the behavior of an artificial hip in the presence of a fatigue crack. Experimental tests were performed on three groups of specimens and the results for specimens exposed to corrosion were compared with specimens tested in air. The analytical calculation of fatigue crack growth was performed using fracture mechanics parameters (stress intensity factor) and experimentally determined values of the coefficients of the Paris equation for fatigue crack growth rate. These results served as a basis for the development and verification of numerical models. Using experimental, analytical and numerical approaches, results were obtained that showed good agreement and realistically described the behavior of artificial hips made of Ti6Al4V alloy under the combined effects of corrosion and fatigue

legura Ti-6Al-4V; korozija; rast zamorne prsline; integritet veštačkih kukova; proširena metoda konačnih elemenata; mehanika loma; dijagram analize loma; zamorni vek

Ti-6Al-4V alloy; corrosion; fatigue crack growth; hip implant integrity; extended finite element method; fracture mechanics; failure analysis diagram; fatigue life

66.018:615.461(043.3)

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