Crack propagation analyses with CTOA and cohesive model: Comparison and experimental validation

Abstract

Two numerical crack propagation models, namely the cohesive model and the CTOA model, are compared regarding their ability to predict the crack propagation behaviour of fracture specimens made of thin walled Aluminium sheets, which can be simulated using plane stress assumption. The experimental database is presented and it is shown, how the various quantities are measured by different techniques (optically and with various clip gauges). It is explained how the respective parameters for the numerical models are determined by use of a selected set of fracture specimens. Other types of specimens are then used to validate the simulations with these parameters. In order to investigate the behaviour of the models under different constraint conditions and the transferability of their parameters, C(T) specimens are used for parameter evaluation and M(T) specimens for validation. It is shown that for all types of specimens, a single set of parameters can be used for both models.

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

“…[115][116][117][118]), applications of the cohesive model, frequently combined with investigations of the CTOA concept are found in [71] in this issue and elsewhere (e.g. [74,113,114,119]). Note that this list is by no means complete.…”

Residual strength prediction of a complex structure using crack extension analyses

“…Recently, transferability has been shown from C(T) specimens to M(T) and cruciform specimens for 3 mm thick aluminium material, see [15]. Further validation seems appropriate on this issue to define a criterion for the applicability of shell meshes to slender structures.…”

Comparison of different stress-state dependent cohesive zone models applied to thin-walled structures

“…At crack initiation the maximum value is higher than H = 0.65, slightly reducing to H = 0.62 after some amount of crack extension. Finally, ductile fracture of another specimen is predicted, which has successfully been simulated already in [16] without triaxiality dependent parameters. The M(T) specimen (width 2W = 300 mm) investigated here, has a high triaxiality in front o f the crack tip, slightly lower than the C(T) specimen, but not varying much with crack extension, see Fig.…”

“…The material used for validation and comparison of the two cohesive approaches is an aluminium alloy Al 5083 [16], which is used in shipbuilding and automotive industry. For quantities that are available from the experiments on fracture specimens: Force, F , remote elongation (v LL for the C(T) specimen and ∆l for the M(T)), the crack tip opening displacement, CTOD-δ 5 , and the crack extension, ∆a.…”