4 research outputs found
On the effective shear modulus of composite honeycomb sandwich panels
U radu je odreÄen efektivni modul klizanja kompozitnog panela sa saÄastom ispunom. Ovaj elastiÄni koeficijent predstavlja veoma važnu karakteristiku kompozitnih panela, naroÄito kod kompozitnih konstrukcija koje su izložene uvijanju kao i kombinovanom uvijanju sa savijanjem. Analizirane strukture u ovom radu sastoje se od gornje i donje kompozitne ploÄe (razliÄitih tipova karbonskih vlakana, T300, AS4 u epoksidnoj matrici) kao i saÄaste ispune (HexWeb EC engineered core). PolazeÄi od klasiÄne teorije lamine, efektivni modul elastiÄnosti klizanja je odreÄen za svaki sloj u kompozitnoj ploÄi. Ovi slojevi su spojeni u jedinstveni kompozitni sloj za razliÄita usmerenja vlakana kao i debljine lamina. ElastiÄni koeficijenti saÄaste ispune HexWeb srediÅ”njeg sloja kompozitnog panela su izraÄunati koristeÄi teoriju Master Evans u cilju dobijanja ekvivalentnih vrednosti. Za proveru predloženog pristupa koriÅ”Äen je metod konaÄnih elemenata, u cilju dobijanja polja pomeranja, deformacija i napona u kompozitnim ploÄama i saÄastoj ispuni. Dva tipa numeriÄkih modela su uporeÄena: poÄetni model, pri Äemu su svi slojevi ploÄe modelirani sa svojim karakteristikama i drugi model kod kojeg su spojeni u jednu celinu sa svojim ekvivalentnim karakteristikama. ZakljuÄeno je da se ekvivalentni metod odreÄivanja modula klizanja kompozitnih panela sa saÄastim ispunama može efikasno primeniti u sluÄajevima kada su gornja i donja kompozitna ploÄa simetriÄnog slaganja ili uopÅ”te kvaziizotropna.In the presented paper the effective shear modulus of composite plates with honeycomb core is determined. This elastic coefficient represents one very important property, especially in constructions subjected to torsion and combined bending - torsion. The structures investigated in this research consisted of top and bottom plates (of different types of carbon fibers, T300, AS4 in epoxy matrix) and honeycomb core (HexWeb engineered core). Starting from classical lamination theory, the effective shear modulus of top and bottom plates was determined for each ply in the stack up sequence. These plies were 'lumped' into a single composite layer for different fiber orientations and plies thicknesses. Elastic coefficients for the HexWeb engineered core were obtained using Master and Evans relations for the equivalent properties of honeycomb cores. To verify this approach, finite element method was used to determine the displacement, stress and strain field on composite plates with honeycomb core. Two types of models were compared: the initial model where all the material components, plates and the core were modeled with their intrinsic properties and 'lumped' model with calculated effective elastic coefficients. It was found that the method of effective shear modulus calculation can successfully be used in situations where top and bottom plates are symmetric or quasi isotropic in general
Single rotor helicopter parasite drag estimation in the preliminary design stage
This paper presents the methodology for the rapid estimation of the single rotor helicopter parasite drag in the forward flight in the preliminary design phase. The aerodynamic drag of fuselage, main rotor hub, landing gear and the other, non-rotating defective surfaces contribute with more than 50% of the total power required for the forward flight at higher cruising speeds and therefore requires a more approximate determination in the design stages before the prototype development. The parasite drag determination is based on the evaluation of the basic value of The Equivalent Parasite Drag Flat Plate Area and its changes depending on the fuselage angle of attack. Plenty of the statistical indicators, aerotunnel tests results and the recent CFD investigations were taken into consideration during the process of developing and testing this methodology
Failure of mounting bolt of helicopter main gearbox support strut
The mounting bolt of helicopter main gearbox support strut was fractured into two pieces during the flight mission. The fracture occurred at the root of the first engaged thread of the bolt-nut assembly. Visual inspection of the fracture zone revealed cracks, formed by interlinking of corrosion pits, at the almost all thread roots of the bolt. Energy dispersive spectroscopy disclosed significant damage of the cadmium plating as well as the presence of large amounts of corrosion products at the bolt threads. Through the fractography and metallography analysis, it was found that the mounting bolt failed due to hydrogen-induced intergranular stress corrosion cracking (HI-IGSCC). The finite element (FE) analysis confirmed that the crack origin was located at the area with the maximum tensile stress in the bolt
Failure of mounting bolt of helicopter main gearbox support strut
The mounting bolt of helicopter main gearbox support strut was fractured into two pieces during the flight mission. The fracture occurred at the root of the first engaged thread of the bolt-nut assembly. Visual inspection of the fracture zone revealed cracks, formed by interlinking of corrosion pits, at the almost all thread roots of the bolt. Energy dispersive spectroscopy disclosed significant damage of the cadmium plating as well as the presence of large amounts of corrosion products at the bolt threads. Through the fractography and metallography analysis, it was found that the mounting bolt failed due to hydrogen-induced intergranular stress corrosion cracking (HI-IGSCC). The finite element (FE) analysis confirmed that the crack origin was located at the area with the maximum tensile stress in the bolt