Characterization of Fatigue Crack Growth in Bonded Structures. Volume 1. Crack Growth Prediction in Bonded Structures
Final rept. Jul 1975-Feb 1977
NORTHROP CORP HAWTHORNE CA AIRCRAFT DIV
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This is the first of two volumes that present methods for solving crack problems in the metallic elements of adhesively bonded structures. There are six major sections in the report that cover the following topics 1. Methods of analysis, namely the finite element method and the integral equation method. Assumptions in the analysis and the influence of various parameters on the analytical results. 2. Criterion for the propagation of a debond. 3. Criterion for the crack transfer to a sound layer. 4. Verification test program. 5. Sensitivity of analysis to various parameters. 6. Limitations of the analysis. The stress intensity factors have been obtained for the geometries of 1 a cracked sheet with an adhesively bonded stringer, and 2 a two-layer, bonded structure with a center crack, an edge crack, and a crack at a hole. The influence of finite boundaries, adhesive methods, debond size, and bending on stress intensity factors has been studied. Comparison has been made of actual crack growth life and that based on analytical stress intensity factors. The crack growth life has been predicted analytically within ten percent of actual life. The influence of adhesive and adherend materials and thicknesses on crack growth life has been studied. The predicted debond sizes have been compared with those observed experimentally. A criterion for the cracking of a sound layer, based on load transfer to a sound layer, has been developed.
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