查看更多>>摘要：In order to reduce the failure accidents of dynamic seal ring and rubber core of conventional rotary control head, a novel rotary control head for coalbed methane underbalanced drilling is developed in this paper. According to the material selection requirements of the rubber core and dynamic seal assembly, the mechanical properties experiments of hydrogenated nitrile rubber materials with three different formulations were carried out. According to the design scheme of the rotary control head, the toothed slip ring combined seal is selected, and the finite element analysis and experimental research are carried out on the seal. Finally, through the field test, the working performance of the novel special rotary control head for coalbed methane is tested. The experimental results show that there is no leakage in the static and dynamic sealing system during the application period. It shows that the designed sealing system is reliable.
查看更多>>摘要：Secondary combustion in a power plant gas turbine occurs when liquid fuel is collected after shutdown or unsuccessful start-up and, for some reasons, was not drained. The pool of liquid is ignited by hot gases during a subsequent start. This uncontrolled combustion causes explosion and the turbine blades suffer very high temperature short exposure that leads to extensive blade damage. In the present research, the effect of very high temperature short exposure on microstructural evolutions and mechanical properties, which occurs during secondary combustion, has been investigated. The microstructure of the blades was evaluated by field emission scanning electron microscope (FESEM). The mechanical properties of the blades were investigated by room temperature and high temperature tensile test and hardness test. The results showed that both primary and secondary gamma' particles were dissolved during secondary combustion and then reprecipitated after the turbine trip. Dissolution and reprecipitation phenomena occurred in the upper area of the blade airfoil section. This dissolution of gamma' particles led to deterioration of mechanical properties during secondary combustion and ultimately, extensive blades failure. Furthermore, the MC carbide degeneration into M23C6 and eta phase was also observed in the microstructure which was attributed to the increase in temperature during secondary combustion. The hardness of the damaged blade was not uniform along the longitudinal direction of the blade due to the microstructural evolution. The fracture surface of the damaged blades indicated that cracks were propagating along the interdendritic regions.
查看更多>>摘要：The internal bore of a machine gun barrel is subjected to the complex effects of cyclic hightemperature and mechanical loadings during the continuous shooting process, resulting in the accumulation of bore damages and eventually the end of the lifespan. The correlation between the ballistic performances and the material properties is a critical issue for the development of gun barrels with a long lifespan. However, it is still not fully understood yet. In this study, the thermomechanical analysis of the strength degradation of 30SiMn2MoVA gun barrel steel during continuous shooting is investigated. Irregular rifling deformation of the failed machine gun barrel with a 12.7 mm caliber was observed. Mechanical tensile tests revealed that severe softening occurs in the 30SiMn2MoVA steel when the temperature exceeded 600 degrees C, where the yield strength decreased significantly from 862 MPa at room temperature to 114 MPa at 700 degrees C. Transmission electron microscope observations further revealed that the recrystallization of martensitic lath and the growth of cementite softened the gun barrel steel. Moreover, the finite element models are established using the Abaqus software for the evolution of the temperature and stress of the internal wall within 180 cycles. This shows that the peak temperature increases to 730-740 degrees C and the peak total stress exceeds 246 MPa during 170-180 cycles, which is much higher than the yield strength of 30SiMn2MoVA gun barrel steel. Therefore, the strength of gun barrel steel at 700 degrees C can be suggested as the key parameter for the development of long-life gun barrels for continuous shooting.
Kim, JoonieeChoi, Young-ManOkamoto, KojiJo, Byeongnam...
11页
查看更多>>摘要：A novel prediction model for the buckling failure load of 304 stainless steel under compression was developed using lead-antimony (Pb-Sb) alloys. The temperature-dependent modulus of elasticity of 304 stainless steel was characterized by changing the Sb concentration of the Pb-Sb alloys from 0 to 15 wt%. Slender Pb-Sb plate columns with a rectangular cross section were fabricated by casting. Buckling tests were performed with Pb-Sb alloys under compression at room temperature and compared with numerical simulations that considered the nonlinearity of the specimen, such as initial bending. Based on the buckling failure load and the modulus of elasticity measurements, the linear relationship between the normalized buckling failure loads and the normalized modulus of elasticity was obtained for both Pb-Sb alloy and 304 stainless steel. The relationship between these two correlations makes it possible to predict the buckling failure load of 304 stainless steel at elevated temperatures up to 1200 degrees C.
Sasso, Ricardo AparecidoKoga, Guilherme YuukiCruz, Dennis CoelhoFigueira, Gustavo...
16页
查看更多>>摘要：Sugar-alcohol industries are affected by unexpected and costly interventions caused by loss of efficiency of key components, stoping the production for maintenance. The main station suffering severe degradation is the shredder, where rotating hammers are subjected to abrasive wear from mineral contaminants and corrosion from the sugarcane juice. This work presents a failure analysis of hammers removed from an on-site shredder of a sugar-alcohol industry in Brazil. First, the materials were chemically and microstructurally characterized. Second, the resistance against abrasive wear and corrosion in sugarcane juice was assessed, respectively, by dry sand/rubber wheel test, and cyclic potentiodynamic polarization. Finally, the results were discussed in conjunction to propose the cause of the failure of the rotating hammer. The base material was a carbon steel (~0.3 wt% C), protected by a ferrous coating with high content of Cr (22.2 wt%) and C (4.4 wt%). Ferritic stainless steel (410 stainless steel) was included in the study due to its increased use in sugar-alcohol industries. The coating showed greater resistance to abrasive wear compared to the carbon steel and 410 stainless steel. The superior wear resistance of the coating was ascribed to the large fraction of hard carbides, which acted as effective reinforcement to prevent excessive removal of the soft matrix. 410 stainless steel performed better against the corrosive effects of sugarcane juice, due to the Cr being distributed in solid solution in a single ferritic structure, which ensured the formation of a protective passive film. Nevertheless, the coating was susceptible to corrode, since carbides in excess cause interfaces depleted in Cr, representing preferential points for corrosion. The cracks initially present in the coating allowed the penetration of the sugarcane juice, and subsequent detachment of the coating by impact, exposing the base material to severe abrasion and corrosion with large volume loss. Greater control during the coating preparation process and the use of base material with greater corrosion resistance such as 410 stainless steel could significantly extend the life of the hammers.
查看更多>>摘要：Fatigue fracture is a common failure mode of steel structure, and it usually leads to steel structure failure. In this study, the fatigue damage of duplex 2205 stainless steel with different stress ratios was monitored based on acoustic emission (AE) technology. The fatigue crack growth length, stress intensity factor, fatigue crack growth rate, and the various characteristics of the count, amplitude, and average signal level (ASL) of AE parameters during the whole process were recorded. The results show that AE parameters count and amplitude can well characterize the three stages of fatigue crack initiation, steady-state growth and failure fracture. In the steady-state growth stage, the crack length prediction models based on single-factor and multi-factor of AE parameters suitable for different stress ratios were established and compared for the first time. The multi-factor model has the highest prediction accuracy and it can provide an effective basis for monitoring methods.
查看更多>>摘要：The cavitation erosion of Ti-Ni alloy is explored on a cavitating liquid jet with different standoff distances. The cavitation erosion characteristics of Ti-Ni alloy specimens are analyzed, and the influences that different standoff distances of the water jet have on cavitation erosion are explored. The results of cavitation erosion outcomes under different standoff distances of 6 mm, 8 mm, 10 mm, 12 mm, 14 mm and 16 mm show slight deformation, grain boundary cracking and formation of initial micro-pits, pits of maximum depth around 50 mu m, more pits of maximum depth around 80 mu m with micro-cracks, obvious plastic deformation traces with some pits, bulges and slip bands, respectively. When the Ti-Ni alloy is impacted by water jet with a standoff distance of 12 mm for 4 hrs, the surface microstructure undergoes substructural evolution and new fine grains form, with obvious stress concentration and dislocation accumulation appearing on the subsurface.
查看更多>>摘要：Ground fissures are a special urban geological disaster within the city of Xi'an. The differential settlement between strata can cause ground cracking and severely threatens the safe construction and operation of underground engineering. This study establishes a 3D-FDM calculation model of different intersection relationships between the segmented utility tunnel and the ground fissures using Flac 3D software. The influence of the intersection angles on the deformation and failure characteristics of the structure was analyzed. The results show that the segmented utility tunnel presents with the deformation characteristic of three-dimensional movement under the action of the ground fissures. The deformation between structures is primarily vertical dislocation, horizontal tension, and compression, indicating that the structure may be subjected to a bendingtorsion failure. The vertical settlement of the roof of the utility tunnel shows the deformation characteristics of three broken lines. The third and fourth structures have a significant differential settlement, showing a negative correlation with the intersection angle. The segmented measures can eliminate the void area at the bottom of the hanging wall in the utility tunnel; however, when the intersection angle is <= 30 degrees, the contact pressure at the bottom is close to 0, indicating that the intersection angle has a significant impact on the formation of the void areas. In addition, the calculation method of the vertical settlement of the segmented utility tunnel crossing the ground fissure zone is also proposed. It has proven to be effective in calculating the vertical deformation of the structure. This study provides scientific guidance for constructing utility tunnels within ground fissure development areas.
Maiorana, EmanueleTetougueni, Cyrille DenisZampieri, Paolo
15页
查看更多>>摘要：In order to know the safety margins and the critical zone of an important infrastructure such as a bridge, the response of the construction typology to extreme forces must be investigated. In this sense, in the literature, few numerical and experimental data are available concerning the response of steel bridges under explosive loads. The purpose of this work is to develop a coherent model, using the finite element analysis method, to verify the behaviour of such a structure and to focus on the collapse mechanism. As a case study, a typical network arch bridge was defined and meshed. Information about stresses, strains and displacement were collected as a function of the position and intensity of the slab damage. Finally, some useful observations were collected regarding the slab response, damage mechanisms and the role of the concrete class.
查看更多>>摘要：With the increasing speed of high-speed trains and the deteriorating operation environment of axle-box system, the dynamic performance of axle-box bearing directly affects the stability and safety of operation. In this paper, a bearing-vehicle-track coupling dynamic model is established, and its effectiveness is verified by field tests. The simulation results of the coupling dynamic model including wheel-polygonal wear show that the effect of high order polygonal wheel wear (17th - 21st order) on the axle-box system is greater than that of low order wheel wear (1st - 5th order). The frequency domain of axle-box vertical vibration acceleration excited by high order wheel-polygonal wear is mainly distributed in 400 - 600 Hz. The low order polygonal wheel wear amplitude has little effect on the bearing roller-outer raceway contact load. When the wear amplitude of 20th order polygonal wheel is 0.06 mm, the roller-outer raceway contact load is 27.22% higher than that when the wear amplitude is 0.04 mm. In order to avoid bearing failure caused by excessive bearing roller-raceway contact force, the amplitude of 20th order polygonal wheel wear should reduce to less than 0.04 mm.
NSTL
Elsevier