Papers by Keyword: Crack

Abstract: CoNiCrAlY bond coat (BC) and top ceramic coating (TCC) was fabricated on the GH99 super alloy by high velocity oxyfuel spray (HVOF) and air plasma spray (APS), respectively. Thermal cycling treatment was applied to the thermal barrier coatings (TBCs). The cross-sectional images of crack initiation and propagation of TBCs after treatment were investigated by scanning electron micrograph (SEM), meanwhile crack initiation and propagation in TBCs were analyzed based upon ABAQUS software using extended finite element method (XFEM). The results show that, crack initiation and propagation can be easily traced via microscopy at the interface areas in TBCs; after thermal cycling treatments, the crack associated with the TCC/TGO interface morphology initiates at interface peak area and propagates along TCC/TGO interface with thermal cycles; the interface roughness affects the crack magnitude in length and width obviously, the rougher the morphology, the bigger the crack is; the XFEM is a novel and effective method to well predict the crack initiation and calculate the crack propagation, and simulation and experimental results fit well.

Abstract: To a great extent，traffic accidents of liquefied gas tankers are caused by the defects inside the tankers themselves. Analyzing what causes the defects, and putting forward the corresponding prevention measures, to reduce accident risk, is of great significance. In this paper, the research object is a defective liquefied gas tanker in a propylene factory in Shandong. The defects in actual transportation process containing weld joints defects and anti-wave plates are analyzed, and the corresponding solutions are put forward on the basis of the literature analysis. The results show that the main causes of the defects are that the manufacture and processing did not correspond with design data. The defects repair of the liquefied gas tanker should be performed by qualified service units after specific repair plan and relevant formalities are put forward. The repaired liquefied gas tanker should be inspected qualified by the inspection organizations.

Abstract: Through analyzing the real collision process of a steel plate rolling sliding off a lorry and box girder flange of an overpass, the damage degree of box girder may be known, and in this article the collision process is also simulated by means of finite element method so that it may be obtained how the damaged girder collapses and the cracks propagate. Furthermore, the dynamic characteristics are studied during the collision process and the reliability of overpass section collision is analyzed from the angle of energy transfer and dissipation.

Abstract: Monitoring fatigue cracking of large engineering structures is a costly and time-intensive process. The authors present a low-cost smart coating sensor (SCS) consisted of driving layer, sensing layer and protective layer typically that can detect crack initiation and growth. The results show that the smart coating sensor can detect cracks above 300μm, corresponding to the increment of the sensing layer’s electric resistance at the level of 0.05Ω. Therefore, the development of SCS is of importance significance in the substitution of an existed inspection that requires substantial disassembly and surface preparation, and, thus, can find numerous applications in difficult-to-access locations on aircrafts.

Abstract: The cracks have emerged on the second lining of right tunnel for three months after tunneling in the Xin Chang Tunnel. The maximum crack depth is 264.0 mm which is explored by a RS-ST01C type ultrasonic tester. A fiber Bragg grating strain sensor is developed for measuring the surface strain of second lining. By converting the deflection of structure into the strain of displacement telescopic gauge, a fiber Bragg grating is mounted on two ends of gauge where suffers the strain, and as a result its Bragg wavelength will be shifted. The strain sensitivity and temperature sensitivity of the grating sensor are separately 0.677×10^-6/ and 0.968×10^-5 /°C. Grating sensors are installed on the corresponding linings according to the crack distribution. In an observation period of 51 days, the measurement results indicate that the lining cracks are derived from the tilted pressure of surrounding rock. After a backfill period of 29 days, the tunnel structures are gradually tending to be stability in the following operation period of 429 days.

Abstract: The research of impeller dynamic characteristics by modal analysis technology is a kind of practical and effective fault diagnosis method, which has the vital significance to realize the security of machinery. Crack and blade fracture often occur in centrifugal compressor impeller. In order to study the impeller dynamic characteristic with crack and the blade fracture, a three-dimension finite element model (FEM) was built using ANSYS program, and an experimental modal analysis was also carried out. The compared results show that the preceding four orders natural frequencies and vibration models are basically consistent, and those also verified the reliability of the simulation results. In addition, two kinds of failure mode were also simulated, such as crack and blade fracture. It concluded that all orders natural frequencies decrease clearly, compared with the normal impeller. How the severity of crack and blade fracture affects the natural frequency was also discussed.

Abstract: Residual stress produced on the surface of nanostructured ceramic coatings when they were grinded by diamond superhard abrasive wheel, these residual stresses affected directly the fracture strength, fatigue strength and corrosion resistance of the ceramic parts, they affected the surface quality of machined ceramic parts, and thus they affected the working reliability and the service life of ceramic parts. The tests show that the distribution of residual stress is directional, the residual compressive stress can make the hardness of the material increase, they can reduce the wear rate of the material, for the tested specimen, grinding surface whole residual stress σ is the sum up original residual stress σ₀ (existed in the part’s surface ) and grinding residual stress Δσ (formed by grinding process.), σ=σ₀ + Δσ.

Abstract: The volume of concrete surrounding the spiral case increases along with the increase of unit capacity of single-unit hydroelectric station. Once the spiral case concrete structure works with crack, its bearing capacity and safety stability will decrease seriously. Owing to the action of contraction stress induced by temperature variation, the spiral case concrete is often subject to cracking. There are a few temperature control researches on spiral case concrete during construction in the past, more severe, there are few researches on the sensitivity analysis of parameters and measures on temperature control. For this reason, based on the finite element analysis software ANSYS, the spiral case concrete of Xiluodu underground power plant is simulated. The temperature field and temperature stress field of different pouring temperature and concrete strength are analyzed and the temperature control measures with normal C30 concrete and 293.15K casting are recommended to prevent cracks accordingly. These measures, adopted by construction units are proved to be effective and also good references for similar projects.

Abstract: The efficiency offorging processes is significantly influenced by the tool and scrap costs whichin their turn depend on the life time of forging dies. The tools used for hotforging are subject to process-related high mechanical, tribological, chemicaland thermal-cyclic loads which usually interact with each other. In comparisonto other manufacturing methods, the resulting load spectrum leads to extensivewear and thus to the failure of forging dies after a short tool life. Toincrease the wear resistance of forging dies, duplex treatments consisting ofplasma nitriding and plasma deposition techniques were used to improve thesurface properties and hence to increase the die life time. By basicinvestigation of the wear mechanisms the potentials of newly developed vanadiumdoped chromium nitride and boron containing titanium nitride coating systemswere investigated. Within the presented work it is demonstrated that vanadium-dopedchromium nitride layers have a high wear reduction potential for hot forgingdies.

Abstract: The test rig of two-span rotor-bearing system with rub-impact and crack faults was constructed. The vibration of the rotor-bearing system was observed for different conditions, such as single rub-impact fault, double rub-impact faults and coupling faults of rubbing and crack. The 3D-waterfall spectrum of rotor system was used to analyze the dynamic characteristics of the system during faults. The results indicate there appears 6-superharmonic frequency component on double rub-impact faults. The amplitudes of subharmonic frequencies decrease obviously and it of superharmonic frequencies increases on coupling faults of rubbing and crack, and the superharmonic frequency components are different obviously in different span.