Naslov
Elastoplastic Analysis of Circumferential Cracks in Pipes

Autori
Tonković, Zdenko ; Skozrit, Ivica ; Sorić, Jurica

Vrsta, podvrsta i kategorija rada
Radovi u zbornicima skupova, cjeloviti rad (in extenso), znanstveni

Izvornik
Proccedings of the 4th International Congress of Croatian Society of Mechanics / Matejiček, Franjo - Osijek : Grafika Osijek, 2003

Skup
4th International Congress of Croatian Society of Mechanics

Mjesto i datum
Bizovac, Hrvatska, 18.09.2003. - 20.09.2003

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
elastoplastic fracture analysis; J-integral evaluation; pipes; through-wall circumferential cracks; off-centre cracks; combined internal pressure and bending

Sažetak
Elastoplastic fracture analysis of cracks existing in engineering structures is very important in assessing their structural integrity in nuclear power, chemical, civil and mechanical engineering. The crack opening displacement and J-integral of a through-wall circumferential crack in a pipe are the fundamental quantities for evaluating the reliability of a cracked component. The J-estimation for this crack configuration under various loading conditions, such as pure bending, pure tension and combined bending and tension, has been considered in References [2-4]. A postulated through-wall crack size is often calculated on the basis of its symmetric placement with respect to the bend-ing plane [3, 4]. However, in reality, the off-centre cracks can occur due to random imperfections around the pipe circumference. Elastic and elastoplastic finite element solutions for the J-integral for a pipe containing off-centre through-wall cracks under pure bending have also been presented and the special influence functions have been introduced [2]. A realistic evaluation of pipes frac-ture response demands consideration of more complex loading condition including combined bend-ing and internal pressure. When fracture mechanics analysis is performed for through-wall cracked pipes subjected to internal pressure, it is a typical practice to transform the effect of pressure by the pressure-induced axial tension [3]. The hoop stress effect on the fracture response characteristics has been considered only in a limited number of studies [4]. Due to combined loading, a full para-metric investigation of off-centre cracked pipes requires an enormous amount of FE computations, and thus only a limited set of solutions for non-proportional and proportional loading have been tabulated by authors in References [5, 6]. The objective of the present paper is to provide additional reference data and to use it to obtain a new solution of the J-integral for pipes containing off-centre through-wall cracks subjected to combined internal pressure loads and bending, as shown in Figure 1. To achieve this goal, three-dimensional nonlinear finite element computations are performed within the finite element program ABAQUS [1]. The tension forces due to the pressure and pressure-induced hoop stresses are in-cluded. Under the assumption of small elastoplastic strain, the constitutive law characterizing the stress-strain response of mild steel is represented by the well-known Ramberg-Osgood model. Small, medium and large crack lengths with a variety of off-centre angles and radius-to-thickness ratios have been considered. In all tests, proportional loading approach is applied and the hoop stresses effect due to internal pressure is considered. Using finite element solutions, the effects of off-centred cracks and the loading on the J-integral are evaluated. The computational results show that the J values for off-centre cracks are smaller than those for symmetric cracks. This statement is excepted for the offset crack angle of j = 15&ordm ; ; ; ; where the J val-ues at the crack front I-II, which is farther away from the bending axis, are slightly higher than those for the symmetric centred crack. This demonstrates that for any crack size there is a limit-offset angle for which the J-integral values at the crack front I-II exceed those of the centred crack. Those effects are also described in [2] for cracks under pure bending and in [5, 6] for combined bending and internal pressure. The proposed analytical approximation of elastic correction factors would reduce the computa-tional effort in performing fracture analysis of pipes containing off-centre through-wall cracks sub-jected to combined internal pressure loads and bending. Further investigations should be directed towards the determination of the plastic correction factors and the limit-offset angles for the others typical crack lengths and their effects on the J-integral values.

Izvorni jezik
Engleski

Znanstvena područja
Strojarstvo

POVEZANOST RADA