Sheet Panels Research Articles

Fracture Toughness of 7075-T6 and -T651 Sheet, Plate, and Multilayered Adhesive-Bonded Panels

Fracture-toughness tests have been made of 7075-T6 sheet and -T651 plate and of multi-layered panels of the sheet and plate. The nominal net fracture strength and the critical fracture-toughness parameters (Kc and Gc) of multilayered adhesive-bonded panels are greater than those of sheet or plate of the same total thickness, because the individual layers may fracture independently, each developing shear surfaces. The fracture strength and critical stress intensity factor, Kc, for a 0.5-in. thick panel made up of eight layers of 0.063-in. sheet are approximately twice those of 0.5-in. plate. Multilayered metallurgically bonded panels do not exhibit any advantage over sheet or plate of the same thickness, if the metallurgical bond retards shear-surface formation on the individual layers. The plane-strain stress-intensity factor, determined at pop-in on multi-layered adhesive-bonded or metallurgically bonded panels, is independent of thickness or number of layers.

Panel Flutter and Divergence Criteria Design Guide for Flat Unbuckled Sheets

THE outer surfaces of aircraft are often constructed of thin sheet panels attached to a ‘rigid’ inner framework. Acting on such panels are the lateral forces due to air pressure and inertia, and there are mid‐plane forces due to aerodynamic heating or internal pressurization effects. Due to this combination of forces it appears that such panels can suffer either static or dynamic deformations known, respectively, as panel divergence and flutter.

The Shearing Rigidity of Buckled Sheet Panels

A formula giving the effective shearing rigidity of either flat or curved panels in the buckled state is developed from approximate theoretical considerations making use of the concept of effective width. Cases of panels buckled by compression, shear, or combined compression and shear are considered. The formula contains an experimentally determined exponent and gives values both for an effective shear modulus to be used in determinations of stress distributions and for a reduced effective shear modulus to be used in instability calculations. An experimental check is established.

Empirical Formulas for Allowable Compression Loads in Stiffened Sheet Panels

The author presents a general formula for the strength of any flat sheet-stiffener combination, the necessary empirical constants being given for a limited range of extruded stiffener shapes. I t is suggested that this formula may be utilized in laying out test schedules for other stiffener shapes for which such constants are not now available. Existing test results, if sufficiently broad in scope, may be used to determine the empirical constants for stiffener shapes other than those considered. The number of tests necessary to obtain design data for a given range of stiffener shapes and sizes may be greatly reduced by use of the formula, and determining the necessary empirical constants, rather than running a complete schedule of exhaustive tests, will expedite stress analysis procedure. I t is recommended that further tests be run to correlate the effects of rivet spacing.