Three-Dimensional CTOA and Constraint Effects During Stable Tearing in a Thin-Sheet Material

Abstract

A small strain theory, three-dimensional elastic-plastic finite element analysis was used to simulate fracture in thin sheet 2024-T3 aluminum alloy in the T-L orientation. Both straight and tunneled cracks were modeled. The tunneled crack front shapes as a function of applied stress were obtained from the fracture surface of tested specimens. The stable crack growth behavior was measured at the spec&en surface as a function of applied stress. The fracture simulation modeled the crack tunneling and extension as a function of applied stress. The results indicated that the global constraint factor, ag, initially dropped during stable crack growth. After peak applied stress was achieved, ag began to increase slightly. The effect of crack front shape on ag was small, but the crack front shape did greatly influence the local constraint and through-thickness crack-tip opening angle (CTOA) behavior. The surface values of CTOA for the tunneled crack front model agreed well with experimental measurements, showing the same initial decrease from high values during the initial 3mrn of crack growth at the specimen's surface. At the same time, the interior CTOA values increased from low angles. After the initial stable tearing region, the CTOA was constant through the thickness. The three-dimensional analysis appears to confirm the potential of CTOA as a two-dimensional fracture criterion. NOMENCLATURE

Investigation of crack-tip plasticity in high volume fraction particulate metal matrix composites

“…This confirms an earlier review by Parks [28] and agrees with the results discussed in [20,30,31] where FE analyses were compared with CTOA or CTOD measurements.…”

“…Indeed, it has been increasingly understood in the past decade that surface measurements are affected by 3-D effects [28][29][30], and that caution must be exercised in analysis of experimental data. For instance, it has been shown that plane-stress approximations are not sufficient to fit experimental measures such as the crack-tip opening angle (CTOA) or the crack-tip opening displacement (CTOD) (which are the surface measurements of crack-tip loading that are the most commonly performed), whereas 3-D analyses yield much better agreement [20,[30][31][32].…”

“…To the best of our knowledge, such comparisons between elastic-plastic strain fields observed by experiment and numerically computed have rarely been performed. Three-dimensional constraint effects have, rather, been assessed by correlating numerical computations with other measurements, which are more directly accessible such as the CTOA, the CTOD or load-displacement curves [20,[31][32][33][34][35][36]. A second goal of this investigation is therefore to evaluate the significance of three-dimensional ''constraint'' effects with these half-metal/half-ceramic composite materials.…”

Fracture and damage mechanics modelling of thin-walled structures – An overview

“…The CTOA is than the angle enclosed by the upper and lower lines, L 1 and L 2 . A special case of optical measurement is the digital image correlation method [39,[41][42]. In [43] the authors, following earlier attempts, use a digital camera technique for investigating relatively tough pipeline materials.…”

Obliczenia Numeryczne Wytrzymałości Resztkowej Poszycia Statków Powietrznych z Uszkodzeniem Wielomiejscowym

“…Krytyczny kąt rozwarcia szczeliny jest jedynym parametrem tego kryterium. Kryterium CTOA zostało z powodzeniem zaimplementowane w obliczeniach wytrzymałości resztkowej połączeń nitowych [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Większość z prezentowanych wyników obliczeń była uzyskana przy pomocy programu FRANC3D współpracu-jącego z komercyjnym solwerem STAGS.…”