Fatigue cracks initiated from holes in several zones and structural components of the RRJ‐95 aircraft frames were investigated. Using the method of quantitative fractography, the crack growth duration in the wing panels during full‐scale bench tests and in the brackets of the in‐service airframe was estimated by measuring the spacing of meso‐beach‐marks (MBM) and fatigue striations. The applied program of bench test consisted of blocks of variable loads that were equivalent to the wing loading in flight and reproducing schematized flight‐cycle. It was shown that the duration of fatigue crack propagation in several structural components of the RRJ‐95 aircraft frames was approximately the same as for the crack nucleation duration. The total lifetime is sufficiently long for cracks in the structural components to be detected and reliably monitored with a large operating time interval between adjacent inspections.

ABSTRACT. The paper delivers a critical review of the research data on the crack initiation and crack growth patterns characteristic of the components of the spline-bolted joints between the propeller shaft and reducer shaft at An-24, An-26, and Il-18 aircrafts. Cracks in the shafts nucleated because of reduced bolt-fastening force. Actually, the bolt (bolts) failed first (also by fatigue) and then fatigue cracks nucleated and grew in the shafts, the spline surface fretting zones and/or sharp edges of the attachment (bolt-conducting) holes making the crack origin sites. The crack growth history shows itself through the regular Macro-Beach Marks, each mark sequentially pointing to the next loading event of the propeller shaft, i.e., to each next flight. The cracks cease growing for some while in the airscrews and their shafts just replaced to another aircraft. For the airscrew shafts, the critically assessed data show the crack growth period Np ranging as five to ten percent of a total running period N f . We recommend performing nondestructive inspection of the airscrew shafts on every 250-hour running period to ensure the safety flights.

Fatigue cracking of longerons manufactured from Al-alloy AVT-1 for helicopter in-service rotorblades was considered and crack growth period and equivalent of tensile stress for different blade sections were estimated. Complicated case of in-service blades multiaxial cyclically bending-rotating and tension can be considered based on introduced earlier master curve constructed for aluminum alloys in the simple case of uniaxial tension with stress R-ratio near to zero. Calculated equivalent tensile stress was compared for different blade sections and it was shown that in-service blades experienced not principle difference in this value in the crack growth direction by the investigated sections. It is not above the designed equivalent stress level. Crack growth period estimation in longerons based on fatigue striation spacing or meso-beach-marks measurements has shown that monitoring system introduced designer in longerons can be effectively used for in-time crack detecting independently on the failed section when can appeared because of various type of material faults or in-service damages.

Fatigue cracks initiated from holes in several zones and structural components of the RRJ-95 aircraft frames were investigated. Using the method of quantitative fractography the crack growth duration in the brackets of the in-service airframe and in the wing panels during full-scale bench tests was estimated the spacing of meso-beach-marks (MBM) and fatigue striations. The applied program of bench test consisted of blocks of variable loads that were equivalent to the wing loading in flight and reproducing schematized flight-cycle. It was shown that the duration of fatigue crack propagation in several structural components of the RRJ-95 aircraft frames was approximately the same as for the crack nucleation duration. The total lifetime is sufficiently long for cracks in the structural components to be detected and reliably monitored with a large operating time interval between adjacent inspections.