Vol.3, No 13, 2003 pp. 613-622
UDC 620.1 539.219.2

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AN ENGINEERING CONCEPT TO ACCOUNT
FOR CRACK-TIP CONSTRAINTS
H. J. Schindler
Mat-Tec SA, Unterer Graben 27, CH-8401 Winterthur, Switzerland

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It is one of the main advantages of engineering fracture mechanics that the user has not to deal with the local stress- and strain-field in detail. Instead, the local loading state and fracture behaviour is characterized by overall parameters like J or K and their critical values. Unfortunately, the transferability of these parameters is restricted to similar conditions concerning crack-tip constraints. However, to take the effects of non-equal constraints into account in a fracture assessment procedure, an elastic-plastic analysis of the crack-tip region has to be performed. This requires a computational effort which is usually beyond the possibilities within an engineering analysis. Therefore, simplified procedures are needed. A promising possibility is suggested in the present paper, where a new constraint parameter ? is introduced. It has two main advantages: First, it can be obtained easier than the commonly used Q-parameter, and second, it is related to the fracture toughness parameters by closed-form equations.

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TEHNIČKI KONCEPT OBJAŠNJENJA
NAPREZANJA VRHOVA PRSLINA Jedna od glavnih prednosti tehničke mehanike loma je to što korisnik ne mora da se detaljno bavi lokalnim oblastima napona i dilatacije. Umesto toga, lokalno stanje opterećenja i ponašanje loma okarakterisani su globalnim parametrima poput J i K i njihovim kritičnim vrednostima. Nažalost, prenosivost ovih parametara ograničena je na slične uslove u vezi sa vezama vrhova prslina. Medjutim, da bi se posledice nejednakih veza uzele u obzir u proceduri procene prsline, mora se izvršiti elastično-plastična analiza oblasti vrha prsline. To zahteva računski napor koji obično prevazilazi mogućnosti tehničke analize. Stoga su potrebne pojednostavljeni postupci. Obećavajuca mogućnost se predlaže u ovom radu, gde se uvodi novi parametar veza I. On ima dve glavne prednosti: prvo, do njega se može doći lakše nego do Q-parametra koji se obično koristi, i drugo, on je povezan sa parametrima žilavosti loma putem jednačina sa zatvorenom formom.