Results are presented of a fatigue-strength investigation of a typical full-scale airplane wing structure. The tests were conducted by the resonant-frequency method, wherein concentrated masses were attached to the wing to reproduce flight stresses corresponding to load-factor values of 1 ± 0.625g over approximately 45 percent of the span. The results presented include the data obtained on the first two specimens of a more complete program.nAlthough the results cover 11 fatigue cracks, the amount of data is as yet insufficient to warrant definite conclusions. The data indicate a surprisingly small amount of spread in fatigue life even though all fatigue cracks did not originate at the same points. Computed effective stress-concentration factors for similar riveted joints varied from 2.55 to 3-15, whereas the one value computed for the corner of an inspection hole cut-out was 4.20. Neither the natural frequency nor the damping of the two test specimens appeared to be 'affected by fatigue damage until after a fatigue crack had originated) thus, indications are that the use of these parameters may not be adequate as a measure of the damage caused by fatigue in an airplane wing structure. The rate of fatigue crack growth was quite small until the crack had included approximately 7-5 percent of the tension material. Beyond this value, the rate of crack growth increased very rapidly.
展开▼
