On the effective shear modulus of composite honeycomb sandwich panels

U radu je određen efektivni modul klizanja kompozitnog panela sa saćastom ispunom. Ovaj elastični koeficijent predstavlja veoma važnu karakteristiku kompozitnih panela, naročito 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 ploče (različitih tipova karbonskih vlakana, T300, AS4 u epoksidnoj matrici) kao i saćaste ispune (HexWeb EC engineered core). Polazeći od klasične teorije lamine, efektivni modul elastičnosti klizanja je određen za svaki sloj u kompozitnoj ploči. Ovi slojevi su spojeni u jedinstveni kompozitni sloj za različita usmerenja vlakana kao i debljine lamina. Elastični koeficijenti saćaste ispune HexWeb središnjeg sloja kompozitnog panela su izračunati koristeći teoriju Master Evans u cilju dobijanja ekvivalentnih vrednosti. Za proveru predloženog pristupa korišćen je metod konačnih elemenata, u cilju dobijanja polja pomeranja, deformacija i napona u kompozitnim pločama i saćastoj ispuni. Dva tipa numeričkih modela su upoređena: početni model, pri čemu su svi slojevi ploče modelirani sa svojim karakteristikama i drugi model kod kojeg su spojeni u jednu celinu sa svojim ekvivalentnim karakteristikama. Zaključeno je da se ekvivalentni metod određivanja modula klizanja kompozitnih panela sa saćastim ispunama može efikasno primeniti u slučajevima kada su gornja i donja kompozitna ploča simetričnog slaganja ili uopšte 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

Calculation of the effective shear modulus of composite sandwich panels

U radu je predstavljena metoda proračuna efektivnog modula smicanja kompozitnih panela sa sendvič ispunom. Ovaj koeficijent elastičnosti predstavlja vrlo važnu karakteristiku materijala, posebno kod konstrukcija koje su izložene čistoj torziji ili kombinaciji savijanja i torzije. Strukture koje su ispitivane u ovom istraživanju su ravne ploče načinjene od gornjeg i donjeg kompozitnog lica i ispunom (jezgrom) od šestougaonog kompozitnog sendvič materijala. Polazeći od klasične teorije laminata određen je efektivni modul smicanja gornje i donje ploče za svaki sloj u stoku (laminatu). Ovi slojevi platana se svode u jedan kompozitni sloj sa različitim orijentacijama vlakana i debljine. Da bi se verifikovao ovaj prilaz korišćen je Metod konačnih elemenata da bi se odredila pomeranja, deformacije i naponi u kompozitnim pločama i sendvič ispuni. Dva tipa numeričkih modela su upoređivani: početni model, gde su svi spojevi ploče modelirani sa svojim karakteristikama i drugi model kod kojeg su spojeni u jednu celinu sa svojim ekvivalentnim karakteristikama.Calculation Method for the effective shear modulus of composite plates with sandwich cores is presented. This elastic coefficient represents one very important material property especially in constructions subjected to pure torsion and combined bending - torsion. The structures investigated in this research are flat plates made of top and bottom composite facesheets and hexagonal composite material sandwich 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. To verify this approach Finite element method was used to determine the displacement, stress and strain field on Composite plates with Sandwich Cores. 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

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

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. (C) 2016 Elsevier Ltd. All rights reserved