Failure analysis of pitching wire for low speed wind tunnel (LSWT)

FAILURE ANALYSIS OF PITCHING WIRE FOR LOW SPEED WIND TUNNEL (LSWT). Pitching wire using one of support component in the aircraft model test for low speed wind tunnel (LSWT). It have operated six months, pitching wire failed through it was testing in the LSWT. To determine the caused was conducted fraktography examination by stereo mikroskop and scanning electron microscope (SEM), metallography by metalloplan microscope, tensile test by UPM 1000, and hardness test by Frank Finotest had been cried out. Visually in fracture area was found necking before fracture. Macroscopically the characteristic of surface fracture is ductile fracture caused by static tensile stresses. Under scanning olectron microscope (SEM), the surface fracture showed silky texture, fibrous, and dimples, as well as matte texture. The microstructure showed fine pealite and deformation ferrite as result during cold drawing in wire manufacturing. The microstructures have lamellar and globular oxide inclusion. Based on surface fracture characteristic, the failed pitching wire caused by applied iensile stress exceeded maximum tensile stresses; although the mechanical properties of pitching wire conform with piano wire grade B (JS 3522) is 206 kg/mm2.