NAL・STOL実験機のUSBフラップ構造は,原型機であるC-1輸送機の構造上の主たる設計変更部分の一つであるため,部分外板模型を製作し,音響疲労寿命を保証するための基礎データを得る目的で各種の試験を行った。前フラップ上面構造(C),主フラップの上面(A),下面(B)構造と,(A),(B)の外板板厚を下げた構造(D),(E)の総計五個である。これら五個の模型に対する試験項目は, (1)(A),(C),(D)に対して,200度Cまでの静的加熱試験 (2)(A)～(E)に対して,常温での振動特性試験 (3)(A),(C),(D)に対しては,高温音響加振下での応答歪みの計測と疲労試験を,また,(B),(E)に対しては常温で,応答歪みの計測と疲労試験を行う。の三項である。得られた結果は,次の通りである。 (1)(A),(D)は,熱座屈が発生した。しかし,(C)は発生しなかった。 (2)(A),(B),(C),(D)の固有振動数は,周辺単純支持解と,固定支持解の間にあり,両者の幾何平均と良い一致を示した。また,減衰係数は,材料固有の値に近かった。(C)の固有振動数は,定性的には,周辺固定の曲面板解に近かったが,定量的には,周辺単純支持の曲面板解に近かった。 (3)応答歪みの二乗平均平方根値は,小さく,また,固有振動数近傍に顕著な極値を持たなかった。各模型とも,疲労試験で何ら損傷を発生せず充分な耐音響疲労特性を有することが解った。以上の試験と平行して,供試体を一様加熱と音響加振を受ける平版と仮定して,応答歪み解析を行い,試験結果と比較すると共に,種々の方法で,USBフラップ外板の寿命推定を行った。その結果,応答歪み解析では,周辺単純支持による解が,試験結果の傾向を良く示したが,解析値そのものは,大きめな値となった。一方、寿命推定結果は,最も短い寿命推定値でも十分,設計寿命を保証する安全側の推定となった。
Since the USB flap of the NAL-STOL experimental aircraft is one of the primary design modifications of the original C-1 transport aircraft, an acoustic fatigue test of sub-structural models at elevated temperature was conducted to verify the safety of the flap structure during the planned flight evaluation program. The following five structral models were provided: upper surface (A) and lower surface (B) substructures of the main flap, upper surface substructures of the fore flap (C), and additional models for upper (D) and lower (E) surfaces with reduced panel thickness. All structural models consist of the face panel with stringers and ribs rivetted on the backside in # shape. Thus they are called “nine-bay” models, with the center bay being of primary importance. Test panels (A), (B), (D) and (E) are all flat but (C) has the same curveture as the actural flap structure. The material of the face panels and stiffeners of (A), (C) and (D) is Ti-6A1-4V alloy and that of (B) and (E) is 2024C-T3 alloy. The present test program comprises the following four items: (1)Static thermal loading up to 200C to detect the thermal buckling temperature of test panels (A),(C) and (D). (2)Vibration test by an electric shaker and impact test to identify the resonant frequencies, mode shapes and damping coeffidients. (3)The dynamic strain response measurement and its data processing to compare the results with the numerical simulation solution. (4)Acoustic fatigue test on test panels (A), (C) and (D) at elevated temperature and on (B) and (E) at room temperature. The conclusions reached by the present experiment are summarized as follows: (1)Thermal buckling occured on test panels (A) and (D), but not on (C). (2)Resonant frequencies of the flat test panels (A),(B), (D) and (E) fall in the range between those of clamped and those of simply supported plates. However resonant frequencies of (C) are very close to those of the simply supported plate. (3)The dynamic response strain spectrum has a significant frequency content in the 100～200Hz range besides the peaks at the resonant frequencies. (4)Through the prescribed fatigue test period, all structural models have proven themselves to be strong enough to resist both acoustic and thermal loading. No detectable damage was found on the panel face or around the rivet holes. Besides the laboratory verification, analytical treatment on the strain response has been analyzed and the fatigue life has been estimated on the assumption that the flat test panel was uniformly loaded by heat and noise. The strain responses of simply supported panel qualitively agreed with experiments in terms of the spectrum, but their R.M.S. values were larger than those determined measurement. All estimated lives based on both simulated and experimental strain histories suggested confirmation of the fatigue test results.
資料番号: NALTR0683000
レポート番号: NAL TR-683