The nonlinear response of cracked aluminum shells subjected to combined loads

The results of a numerical study of the nonlinear re-sponse of thin unstiffened aluminum cylindrical shellswith a longitudinal crack are presented. The shells areanalyzed with a nonlinear shell analysis code that accu-rately accounts for global and structural response phe-nomena. The effects of initial crack length on theprebuckling, buckling and postbuckling responses of atypical shell subjected to axial compression loads, andsubjected to combined internal pressure and axial com-pression loads are described. Both elastic and elastic-plastic analyses are conducted. Numerical results for afixed initial crack length indicate that the buckling loaddecreases as the crack length increases for a given pres-sure load, and that the buckling load increases as the in-ternal pressure load increases for a given crack length.Furthermore, results indicate that predictions from anelastic analysis for the initial buckling load of a crackedshell subjected to combined axial compression and inter-nal pressure loads can be unconservative. In addition,the effect of crack extension on the initial buckling loadis presented.IntroductionThe fail-safe design philosophy, when applied totransport aircraft fuselage structure, requires that thesestructures retain adequate structural integrity in the pres-ence of discrete-source damage or fatigue cracks. Onetype of damage frequently associated with the structuralintegrity of fuselage shell structures is a longitudinalcrack in the fuselage skin that is subjected to circumfer-ential stresses resulting from the internal pressure loads,and to axial stresses resulting from the vertical bendingand shearing of the fuselage that are induced by normalflight loads. The structural response of a transport fuse-lage structure with a crack is influenced by the localstress and displacement gradients near the crack and bythe internal load distribution in the shell. Local fuselageout-of-plane skin displacements near a crack can be large