QUALIFICATION PROGRAM OF THE COMPOSITE MAIN ROTOR BLADE FOR THE MODEL 214B HELICOPTER.

The introduction of composite materials such as S-glass and E-glass in the 214B blade required the establishment of material strength values for design and special procedures for the qualification program. Extensive fatigue testing of coupons and structural elements was accomplished. In addition, full-scale blade testing was conducted. Data from the coupon and element tests were used to establish S-N curve shapes, environmental effects, and fatigue strength data for these materials. Also, statistical analysis was performed on coupon and element data to establish minimum scatter reductions for these materials. The mean S-N curves established by the results of testing the full-scale blade fatigue test specimens were reduced for scatter, and an additional reduction for environmental effects was taken as indicated by the results of the coupon and structural element tests. These adjusted curves were used to calculate the blade fatigue life by Miner's cumulative damage method. A study was conducted to compare measured strains with analytically predicted strains to substantiate the accuracy of analytical methods. Also, the fail-safe characteristics of the blade were demonstrated by a damage growth test of a partially failed blade. The results of this test substantiate the excellent fatigue and damage growth characteristics of the composite blade.