Analysis and test of superplastically formed titanium hat-stiffened panels under compression

Four hat-stiffened titanium panels with two different stiffener configurations were fabricated by superplastic forming/weld brazing and tested under a moderately heavy compressive load. The panels had the same overall dimensions but differed in the shape of the hat-stiffener webs; three panels had stiffeners with flat webs and the other panel had stiffeners with beaded webs. Analysis indicated that the local buckling strain of the flat stiffener web was considerably lower than the general panel buckling strain or cap buckling strain. The analysis also showed that beading the webs of the hat stiffeners removed them as the critical element for local buckling and improved the buckling strain of the panels. The analytical extensional stiffness and failure loads compared very well with experimental results

Material characterization of superplastically formed titanium (Ti-6Al-2Sn-4Zr-2Mo) sheet

The aerospace industry has focused considerable interest on the near-alpha titanium alloy Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) because of both its high-temperature properties and its superplastic forming (SPF) capabilities. This paper describes current research to characterize selected mechanical properties of Ti-6242 sheet in the SPF-strained condition, both with and without heat treatment, and compares the results with those obtained on as-received material. Tensile and creep tests were conducted, and metallographic analysis was performed to show the effect of 100 to 700 percent SPF strain on titanium properties. Analysis shows that as a result of SPF processing, both tensile and yield strengths, as well as elongation, are moderately reduced. Creep tests at 800 F and 1000 F show that the SPF processed material displays superior creep resistance compared with the as-received material. A post-SPF duplex-anneal heat treatment had no beneficial effect on tensile and creep properties

Experimental Study of a Hot Structure for a Reentry Vehicle

A large structural model of a reentry vehicle has been built incorporating design concepts applicable to a radiation-cooled vehicle. Thermal-stress alleviating features of the model are discussed. Environmental tests on the model include approximately 100 cycles of loading at room temperature and 33 cycles of combined loading and-heating up to temperatures of 1,6000 F. Measured temperatures are shown for typical parts of the model. Comparisons are made between experimental and calculated deflections and strains. The structure successfully survived the heating and loading environments

Test of superplastically formed corrugated aluminum compression specimens with beaded webs

Corrugated wall sections provide a highly efficient structure for carrying compressive loads in aircraft and spacecraft fuselages. The superplastic forming (SPF) process offers a means to produce complex shells and panels with corrugated wall shapes. A study was made to investigate the feasibility of superplastically forming 7475-T6 aluminum sheet into a corrugated wall configuration and to demonstrate the structural integrity of the construction by testing. The corrugated configuration selected has beaded web segments separating curved-cap segments. Eight test specimens were fabricated. Two specimens were simply a single sheet of aluminum superplastically formed to a beaded-web, curved-cap corrugation configuration. Six specimens were single-sheet corrugations modified by adhesive bonding additional sheet material to selectively reinforce the curved-cap portion of the corrugation. The specimens were tested to failure by crippling in end compression at room temperature