Numerical modelling of crack growth profiles in integral skin-stringer panels

Integral (monolithic) structures can play a significant role in high efficiency structural design. According to the current technological manufacture methods, integral structures have an impact on fabrication cost and on weight reduction. However, until now, some critical aspects have limited the use of these structures. Conventional structures with mechanical or chemical (by adhesion) joints are advantageous because of their damage tolerant and fail safe behaviour. The presence of two separate parts, skins and stringers, guarantee the structural integrity of the component when propagating defects and cracks are present and are thus the key factor in aircraft structures. Focusing our attention on aircraft related structures, the aim of this paper is to show the application of numerical methodologies to evaluate the behaviour of integrally machined skin-stringer panels in the presence of propagating cracks. The described activity resulted from the Analytical Round Robin on Crack Growth and Residual Strength Prediction in Integral Structures proposed by ASTM Task Group E08.04.05 while different FE approaches for a single type integral panel with a propagating crack have been introduced in this paper. The crack growth evaluation based on the numerical models agrees well with the experimental results.