Determination of fracture resistance of pipeline materials by examination of the new ring-shaped specimen exposed to tension

[I. Trajković]

157 str.

Tehnolobko inženjerstvo - Inženjerstvo materijala / Technological Engineering - Materials Engineering

Cilj ove disertacije je razvoj metode za određivanje otpornosti prema lomu i obte enju materijala cevovoda, pre svega namenjene ispitivanju tankozidnih cevi za koje ne postoje standardne procedure za ispitivanje. U ovom radu je prikazan pregled trenutnog stanja istra~ivanja iz ove oblasti, sa posebnim naglaskom na razvoj nestandardnih epruveta, tehnika i pomo nih alata za ispitivanje mehanike loma cilindri nih struktura. Takođe, opisana su dosadabnja istra~ivanja sprovedena primenom eksperimentalnih i numeri kih metoda. U eksperimentalnom delu istra~ivanja, prikazani su rezultati dobijeni ispitivanjem novih epruveta tipa PRNT (Pipe Ring Notched Tension) i epruveta tipa SENT (Single Edge Notched Tension) od plasti nih (PLA – polylactide acide i PA12 – polyamide) i metalnih materijala ( elik P235TR1 i P235GH). Epruvete od plasti nih materijala izrađene su tehnikama aditivne proizvodnje: FDM (Fused Deposition Modeling) za PLA materijal i SLS (Selective Laser Sintering) za PA12 materijal, dok su epruvete od metala izrađene na CNC laserskoj mabini i erozimatu. Sve epruvete ispitane su na univerzalnoj mabini za ispitivanje materijala Shimadzu AGS-X 100 kN korib enjem alata specijalno projektovanog za geometriju epruveta oblika prstena, kao bto je PRNT. Rad mabine za ispitivanje materijala pratio je rad Aramis 2M sistema za opti ka merenja polja pomeranja i deformacija koje se javljaju usled delovanja sila u pravcu zatezanja epruveta. Sistem Aramis 2M bazira se na metodi digitalne korelacije slika (DIC – Digital Image Correlation), bto je omogu ilo precizno merenje parametara ije su vrednosti zasnovane na trodimenzionalnom kretanju jednog segmenta. Zahvaljuju i eksperimentalnim ispitivanjima doblo se do uvodnih parametara za numeri ka ispitivanja koja su sprovedena na modelima PRNT i SENT a to su sila, pomeranje, CMOD (Crack Mouth Opening Displacement) i CTOD-δ5 (Crack Tip Opening Displacement). Numeri kim putem, primenom metode kona nih elemenata na navedene dve geometrije pri razli itim dimenzijama doblo se do vrednosti parametara mehanike loma (J-integral, KI - faktor intenziteta napona) iji je uporedni prikaz dat u ovom radu. Formirani su dijagrami zavisnosti odnosa parametra KI za PRNT i SENT modele za razli ite geometrije epruvete i inicijalnog obte enja. Numeri kim putem dobijene su vrednosti parametra ηpl za razli ite dimenzije modela PRNT i SENT. Dobijene vrednosti rezultata merenja i prora una, kao i ponovljivost postupka, daju zna ajne dokaze da je razvijena metoda pogodna za primenu na tankozidnim cilindri nim geometrijama. Na osnovu navedenog mo~e se zaklju iti da postupak ispitivanja PRNT epruveta ima potencijal za korib enje kao nestandardna metoda za ispitivanje tankozidnih cevi.

The goal of this dissertation is the development of a method for determining the resistance to fracture and damage of pipeline materials, primarily intended for the testing of thin-walled pipes for which there are no standard testing procedures. This dissertation contains an overview of the current state of research in this area, with special emphasis on the development of non-standard test specimens, techniques and auxiliary tools for testing the fracture mechanics of cylindrical structures. Also, previous research conducted using experimental and numerical methods is described. In the experimental part of the research, the results obtained by testing new test specimens of the PRNT (Pipe Ring Notched Tension) type and SENT (Single Edge Notched Tension) type made of polymer materials (PLA - polylactide acid and PA12 - polyamide) and metal materials (steel P235TR1 and P235GH) are presented). Test specimens made of plastic materials are made using additive manufacturing techniques such as FDM (Fused Deposition Modeling) for PLA material and SLS (Selective Laser Sintering) for PA12 material, while metallic specimens are made on a CNC laser machine and erosimat. All specimens were tested on a Shimadzu AGS-X 100 kN universal material testing machine using a tool specially designed for ring-shaped specimen geometry, such as the PRNT. The operation of the material testing machine was accompanied by the operation of the Aramis 2M system for optical measurements of displacement fields and deformations that occur due to the action of forces in the direction of the tensile loading. The Aramis 2M system is based on the method of digital image correlation (DIC), which enabled the precise measurement of parameters whose values are based on the threedimensional movement of one segment. Thanks to the experimental tests, the initial parameters for the numerical calculations that were carried out on the PRNT and SENT models were obtained: force, displacement, CMOD (Crack Mouth Opening Displacement) and CTOD-δ5 (Crack Tip Opening Displacement). Numerically, using the finite element method, the values of the parameters of the fracture mechanics (J-integral, KI - stress intensity factor) were obtained for the mentioned two geometries with different dimensions, the comparative presentation of which is given in this paper. Diagrams of the dependence of the ratio of the KI parameter for PRNT and SENT models for different test specimen geometries and initial damage were formed. Values of the parameter ·pl were obtained numerically for different dimensions of the PRNT and SENT models. The obtained values of the measurement and calculation results, as well as the repeatability of the procedure, provide significant evidence that the developed method is suitable for application on thin-walled cylindrical geometries. Based on the above, it can be concluded that the test procedure of PRNT test tubes has the potential to be used as a non-standard method for testing thin-walled pipes.

epruvete oblika prstena izložene zatezanju, ravna epruveta za zatezanje sa ivi nom prslinom, digitalna korelacija slika, faktor intenziteta napona, J-integral, mehanika loma, cevovod

621.643:539.412(043.3)

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