Residual strength prediction of a complex structure using crack extension analyses

Abstract

The residual strength of a flat panel (thickness 7.6 mm) with five stringers, machined from a monolithic block of Al 2024-T351 material, which contained a crack that divided the central stringer, was to be predicted during a Round Robin organised by ASTM. The initial crack tips were right ahead of the stringers #2 and #4, respectively, so that crack branching along the skin and into the stringers occurred after initiation. The prediction has been achieved using finite element simulations including crack extension, for which a cohesive model was utilised. Conventional material properties, yield and ultimate strength as well as experimental results from M(T) specimens in terms of force, COD and Δa, were given. The residual strength prediction was performed in two steps: First the crack extension parameters for the cohesive model, the cohesive strength, T 0 , and the cohesive energy, Γ 0 , were determined by numerical reproduction of the results of the M(T) specimen. With the optimised parameters, the fivestringer panel was modelled. These steps were conducted by two different finite element models: by a shell and a 3D finite element mesh. It turned out that it is possible to analyse the structure with both models. In the 3D case, the residual strength prediction was conservative and the deviation of the predicted from the experimental value was below 9%. The results of the shell simulation were even closer to the experiment (deviation approximately 3%), but the simulation was non-conservative.

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

“…Note that the cohesive parameters determined for different separation laws are also different, as a result they should not be regarded as model independent material parameters. They are also different for two and three-dimensional simulations (see [71] in this issue).…”

“…[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]).…”

“…Although its applicability has been demonstrated in some cases [77][78] care should always be exercised. Scheider et al, in [71] give an example where the modeling of a stiffened structure by shell elements would cause unrealistic results due to undue deformation of the finite elements in the stiffener region. In order to cover the effect of necking Scheider and Brocks [79] propose the use of thickness-sensitive cohesive elements for shell structures.…”

Fatigue Crack Growth Behaviour in Friction Stir Welded Aluminium–Lithium Alloy Subjected to Biaxial Loads

“…Several studies have been performed in this context, e.g. [1][2][3][4][5]. Most of the work published concerning fatigue crack propagation in lightweight structures, e.g.…”

Application of the cohesive model for predicting the residual strength of a large scale fuselage structure with a two-bay crack

“…e.g. [28]. Earlier investigations carried out on a realistic fuselage component are based on the crack tip opening angle (CTOA) [29].…”