Papers by Keyword: Fatigue Fracture

Abstract: The fractured coiled tubing of TS90 steel grade Φ50.8 mm ×3.96 mm in a certain oilfield was analyzed through macroscopic observation, magnetic powder inspection, physical and chemical properties testing, microstructure analysis and SEM analysis. The results showed that the coiled tubing fracture belonged to fatigue fracture and the fatigue crack originated from the area of cyclic friction on the outer surface of the tubing. The cyclic axial plastic stress of the tubing in service caused micro-cracks in the source area and finally led to fatigue fracture failure of the tubing.

Abstract: In order to explore the mechanism of tribological fatigue fracture in PEEK (Poly-ether-ether-ketone) polymer mechanical element application, one-point contact type RCF (rolling contact fatigue) tests were carried out by using a PEEK shaft with an artificial defect. An alumina ball contacted a PEEK shaft specimen under maximum Hertzian stress 380 MPa. Flaking and internal fatigue crack propagation under the rolling track of the tested PEEK shaft were investigated through 2.5D layer observation method. The main fatigue crack occurred near the artificial defect on the rolling track of the PEEK shaft, and propagated into depth direction. In addition, the main fatigue crack branched due to internal shear stress. The branching crack as internal fatigue crack propagated into the ball’s rolling direction. After the linkage of the branching crack and another semicircular surface crack, the horseshoe-shaped flaking as tribological fatigue fracture occurred on the rolling track of the PEEK shaft.

Abstract: One conventional domed slotted rupture disc, which was fabricated with Inconel 600 alloy, was used in reaction kettle. It was burst after only 2000 times of operational circles. The burst causes were investigated. Morphologies of the fracture were observed by scanning electron microscope and the relatively chemical compositions were analyzed by energy dispersive spectrometer. Meanwhile, metallographic microstructures were also observed and analyzed for the material of the failure of the rupture disc. The results show that the bursting of the rupture disc was caused by fatigue fracture.

Abstract: Observation of fracture surface in metal fatigue is one of the most significant procedures to get insight into the cause and mechanism of crack initiation and propagation. In the present study, age-hardened 2017-T4 and 7075-T6 Al alloys having the extrusion texture were fatigue tested in low and high humidities, and their fracture surfaces were examined using a three dimensional (3D) surface analyzer. In addition to the microscopic observations conducted, it is shown that these 3D analyses provide important information on the difference in crack propagation depending on the stress level and environment.

Abstract: This research aims to investigate micro-crack on a failed for helical gear transmission which was to adjust the engine to increased horsepower. The helical gears made are from chromium steel JIS-SCr 420. The spectrophotometer test machine was used to detect chemical composition, Mechanical properties were evaluated by Vickers hardness and microstructural analysis with an optical microscope, which the crack of the surface layer and energy dispersive spectroscopy using a scanning electron microscope. The results showed that the fracture characteristic of the helical gear’s surface was expected to beach marks and break away. It can be seen that the mixing failure area of oxide inclusion with carbide surrounding before the liquid state of material will be solidified which caused the failure cause of this helical gear. The summary analysis results can be accorded with the assumption of this research and which help prolong service life of the component.

Abstract: The research deals with determination of the breaking cause of the screws used to attach the truck cabins. Scanning electron and light optical microscopy were used for engineering investigation of the fracture cause. Fractographical and structural analysis revealed fatigue mechanism of the screw fracture with morphology corresponding to the combination of tensile and bending stresses. Based on the acquired results a structural adjustment was recommended to the customer.

Abstract: The mechanical properties and microstructural features of 1561 aluminum alloy weldments processed by single-wire MIG welding and CMT TWIN welding are investigated. The microstructure and mechanical properties of welded joints were studied by nondestructive testing, metallurgical test, scanning electron microscopy test, fatigue and tensile test. It is revealed that the welding efficiency of CMT TWIN welding is more than six times as much as single-wire MIG welding. It can be easy to find weld zone (WZ), fusion line (FL), heat affected zone (HAZ) and base metal (BM) with different characteristics in the metallographic specimen. In weld zone, the particle phase sizes are smaller than that of base material, but the densities of particle phase are increased. The sample fatigue strength of CMT TWIN welding is higher than the singe-wire MIG welding. It is suggested that the CMT TWIN welding has several advantages compared with single-wire MIG welding.

Abstract: Tribological fatigue failure of the machined PEEK shaft was investigated through the one-point type rolling contact fatigue test between a PEEK shaft and an alumina ball, in order to explore fatigue fracture mechanism of frictional parts working at high frequency in various mechanical elements. Due to Hertzian contact of cyclic compressive stress, the subsurface crack occurred within approximately 300 μm depth from thesurface and propagated along the rolling direction. After that, the subsurface crack propagation direction changed toward the surface. The flaking occurred on the raceway of the PEEK shaft when the subsurface crack reached to the PEEK shaft surface.

Abstract: This paper take a bolt-ball node network frame factory building collapse in shanxi as the research background,it suddenly had a partial collapse after used 13 years. Based on the field testing,fracture analysis and theoretical calculation with the finite element analysis software ABAQUS and MIDAS,including the simulating of the M33 high streng bolt’s stress concentration factor and the analysis of the grid structure’s force conditions, we found the cause of the high strength bolt’s fatigue fracture ,and finally,we concluded that this was a rare low cycle fatigue destruction under the action of indirect dynamic load.

Abstract: The low cycle fatigue behaviour of TA29 titanium alloy blisk forging at 300°C, 400°C, 500°C, 600°C were studied. The cyclic stress response, the stress-strain behaviour, the fatigue life and the fractograph were observed and analyzed. Through the double logarithm linear regression, the Coffin-Manson model parameters of TA29 titanium alloy at different temperatures were obtained. The results showed that the fatigue life decreases as the strain amplitude increases. Also, the testing temperature has a significant effect on the low cycle fatigue properties of TA29 titanium alloy. At the same level of the strain amplitude, the fatigue life and the peak value of cyclic stress decrease, while the plastic strain component in total strain amplitude increases with the increase of testing temperature. On the basis of the fractograph of fatigue specimens, the initiation of crack is mainly on the surface of the specimen. Fatigue striations can be seen clearly at fatigue crack propagation area. The fatigue striations in stable fatigue crack propagation area were broadened, and the propagation area was reduced and the final rupture area was increased with the increase of testing temperature.