Failure Analysis of Hat-Stringer-Stiffened Aircraft Composite Panels under Four-Point Bending Loading.

Hat-stringer-stiffened composite panels have been widely used in aircrafts. Accurate failure analysis of them is important for the safety and integrity of the fuselage. During the service period, these panels will bear not only the lateral force caused by the bending of fuselage, but also the radial pressure caused by the internal and external differential pressure during the take-off and landing of the aircraft. However, the latter case lacks investigation. Therefore, experimental and numerical studies for the static and fatigue failure of hat-stringer-stiffened composite panels under four-point bending loading have been performed in this work. To accurately predict the fatigue failure, a novel theoretical model has been proposed based on the fatigue damage theory. In addition, a user-defined subroutine USDFLD is developed for the implementation of the proposed theoretical model in Abaqus. Experimental results show that the main failure modes are the delamination of the skin and debonding between the girder flange and the skin. The experimental average value of the initial debonding load and displacement in static tests are 897.3 N and 10.8 mm, respectively. Predictions exhibit good agreement with experimental results with relative errors within 10%. Experimental average fatigue failure life of the specimens is 33,085 cycles, which is also close to the prediction with relative errors within 10%. This indicates the reliability and applicability of the established theoretical model and numerical method for predicting the failure of hat-shaped girder structures.

Cu-Catalyzed Enantioselective Atropisomer Synthesis via Thiolative Ring Opening of Five-Membered Cyclic Diaryliodoniums.

A Cu-catalyzed asymmetric thiolative ring opening reaction of five-membered diaryliodonium salts and potassium thioates for the synthesis of atropisomeric 2'-iodo-[1,1'-biphenyl]-2-yl thioates was realized. The optimal catalytic system, Cu(CH3CN)4PF6/(Ph)-bis(oxazoline), showed the best performance with respect to both yields and stereocontrol. Finally, the utility of these products was briefly demonstrated by the synthesis of an axially chiral P,S-ligand.

Microwave-assisted synthesis and antifungal activity of novel coumarin derivatives: Pyrano[3,2-c]chromene-2,5-diones.

A series of novel fused coumarin analogues pyrano[3,2-c]chromene-2,5-diones have been synthesized through an optimized microwave-assisted protocol. All target compounds were tested and evaluated for their antifungal activity against Botrytis cinerea, Colletotrichum copsica, Alternaria solani, Gibberella zeae and Rhizoctorzia solani. The bioassay results indicated that some of the compounds exhibited potent antifungal activities at concentration less than 50 ppm. For the compounds 5d, 6c and 7b, EC50 values against B. cinerea were as low as 0.141, 0.082 and 0.091 µM, respectively, which represents better antifungal activity than that of the commonly used fungicide Azoxystrobin. Compounds 5d (57%) and 6c (55%) also exhibited more effective control than Azoxystrobin (44%) against Colletotrichum capsica.