Failure analysis used for remanufacturing of steel rolling components

The guide-pieces, used in the process line of steel roiling, were the important components. The guidepieces, which were slide contacting with the rolled-piece, had a high temperature and high speed. The wear was very serious. The results from failure analysis showed that there were three failure forms in the guide-pieces: the first was the wear during heat friction, the second was the heat fatigue under the cycle of deep heating and deep cooling, and the third was the impact rupture. Among them, the wear was the main reason. To the wear of guidepieces, there were four mechanisms, namely abrasive wear, adhesive wear, fatigue wear and corrosion wear. The failure analysis to the guide-piece laid the foundation for its remanufacturing.     

Experimental study on wear failure course of gas-valve/valve-seat in engine

The wear failure course of gas-valve/valve-seat in engine was investigated with a simulating tester. The results show that the failure of the contact conical surface is mainly caused by the elastic and plastic deformation and the fatigue micro-crack and spalling. The creep-deformation and corrosion atmosphere accelerated wear failure course at the high temperature. The wear failure course of the gas-valve/valve-seat in engine follows general wear rules of mechanical elements, but the rate of wear in the sharp wear stage is faster. Foundation item: Project supported by Postdoctoral Foundation of Central South University; project (04B035) supported by the Youth Foundation of Hunan Province Education Bureau     

Microstructure and wear resistance of electro-thermal explosion sprayed stellite coating used for remanufacturing

Electro-thermal explosion directional spraying was used to prepare the stellite coating on substrate of the AISI 1045 steel. The morphologies of cross-section and worn scar, porosity, distribution of elements, micro-hardness and wear resistance of the coating were determined by means of SEM, EDAX, micro-hardness tester and sliding wear tester. Because of the compact construction, good bonding and high hardness, the coating is characterized by good wear resistance. The results show that the mainly failure mode of the stellite coating is micro-plowing. Foundation item: Project(2003AA331130) supported by Hi-tech Research and Development Program of China; Project(50235030) supported by the National Natural Science Foundation of China     

Influence of oxides on high velocity arc sprayed Fe-Al／Cr3C2 composite coatings

Fe-Al/Cr3C2 coatings were sprayed on low steel by high velocity arc spraying(HVAS) technology. The influences of oxides on erosion, corrosion and wear behavior for high velocity arc sprayed Fe-Al/Cr3C2 coatings were studied. The results show that HVAS-sprayed Fe-Al/Cr3C2 coatings have good erosion, heat corrosion and wear resistance. The erosion resistance improves with the increase of the temperature. On one hand, the ferrous oxides are incompact, so they peel off the surface of the coatings easily during the high temperature erosion. On the other hand, compact Al2O3 films on the surface can protect the coatings.     

Failure analysis of wear of main clutch separating ring of heavy vehicles

The severe wear of separating ring is considered to be a main reason which leads to the improper declutch of the main clutch of heavy vehicles. The wear mechanism of the separating ring is not well understood. Scanning electron microscopy and transmission electron microscopy were employed to analyze the surface features and dislocation characteristics of the separating ring. The typical features of furrows and rolled tongue-like metal were found on the surface of separating ring by scanning electron microscopy observation, which can be considered as a major indication of the grain-abrasion. A zone of high density dislocation was noted on the subsurface of the separating ring by transmission electron microscopy observation, which implies the contribution of the severe impact on the surface of the separating ring in the wear process. The influences of the structure of the separating ring, the service condition and the in-service stress distribution on the wear behavior, were also analyzed. The results show that the failure of separating ring results from the impact wear and grain-abrasion together with the plastic deformation. Foundation item: Project(41327040101) supported by the Pre-research Fund of General Armament Department; project(51489010104QT0101) supported by the Fund of State Key Laboratory of Re-manufacture Technology     

Analysis of self-repair films on friction surface lubricated with nano-Cu additive

The surface modified nanocopper particles were prepared with chemical reduction method. The wear test was carried out on a T-11 ball-on-plate friction and wear tester made in Poland. The material of the upper sample was GCr15 and the counterpart was AISI-1045 steel. The morphologies of the worn surfaces of the samples were observed by optical microscope and scanning electron microscope, while the element distributions on the worn surfaces were determined by means of electron microprobe analysis. As the results, a film mainly made of Cu is formed on the worn surface. The film on the surface of the still upper sample is thicker than that formed on the revolving counterpart. At the edge of the groove of the worn surface made by the milling before test there is Cu element observed obviously, but there is not any Cu element in the bottom of the groove. A possible action mechanism of the film is suggested. The friction movement can induce reactivity of the metal and continuously produce activation surface. It benefits the film formed by nano-Cu in lubricant on the worn surface. Hardness and modulus of nano-Cu films were successfully measured and analyzed by the nanoindentation instrument. The results show that the hardness and modulus of the films are lower than those of the initial surface. Foundation item: Project (50235030) supported by the National Natural Science Foundation of China; Project (G1999065009) supported by the National Key Basic Research Special Foundation     

Directly searching method for slip plane and its influential factors based on critical state of slope

In order to determine the slip plane of slope directly by the calculation results of strength reduction method, and analyze the influential factors of slope stability, a numerical model was established in plane strain mode by FLAC3D for homogeneous soil slope, whose parameters were reduced until the slope reached the critical state. Then FISH program was used to get the location data of slip plane from displacement contour lines. Furthermore, the method to determine multiple slip planes was also proposed by setting different heights of elastic areas. The influential factors for the stability were analyzed, including cohesion, internal friction angle, and tensile strength. The calculation results show that with the increase of cohesion, failure mode of slope changes from shallow slipping to the deep slipping, while inclination of slip plane becomes slower and slipping volume becomes larger; with the increase of friction angle, failure mode of slope changes from deep slipping to shallow slipping, while slip plane becomes steeper and upper border of slip plane comes closer to the vertex of slope; the safety factor increases little and slip plane goes far away from vertex of slope with the increase of tensile strength. Foundation item: Project(20060533071) supported by the Doctoral Program Foundation of Higher Education of China; Project (20060400264) supported by China Postdoctoral Science Foundation; Project (50774093) supported by the National Natural Science Foundation of China; Project (1343-74236000014) supported by Graduate Student Innovation Foundation of Hunan Province, China     

Tribological properties and failure analysis of PTFE composites used for seals in the transmission unit

The sealing rings are one of the most important components as the sealing devices in the wet clutch unit of a heavy vehicle. The sealing ring, made from PTFE composites, was subjected to serious wear on the sealing surface, but the mating metal surface only had slight abrasion. A specialized test rig was designed for wear research and failure analysis of the sealing ring. The composition analyses of the ring material, working conditions and wear surface characteristics by visual inspection and tribological properties as well as microscopic analysis with scanning electron microscope was performed to determine the wear mechanism and failure causes. Results revealed that the wear of PTFE composites was characterized by abrasion and adhesion after a certain duration testing, and the wear mechanism changed to thermal fatigue and abrasive wear in the stage of intense wear. The thermal deformation and fatigue were primarily responsible for the rapid wear of the PTFE composites for the sealing rings.     

Experimental study on wear failure course of gas-valve/valve-seat in engine

The wear failure course of gas-valve/valve-seat in engine was investigated with a simulating tester. The results show that the failure of the contact conical surface is mainly caused by the elastic and plastic deformation and the fatigue micro-crack and spalling. The creep-deformation and corrosion atmosphere accelerated wear failure course at the high temperature. The wear failure course of the gas-valve/valve-seat in engine follows general wear rules of mechanical elements, but the rate of wear in the sharp wear stage is faster.     

Mechanism of zonal disintegration phenomenon in enclosing rock mass around deep tunnels

In order to study the mechanism of the zonal disintegration phenomenon (ZDP), both experimental and theoretical investigations were carried out. Firstly, based on the similarity law, gypsum was chosen as equivalent material to simulate the deep rock mass, the excavation of deep tunnel was modeled by drilling a hole in the gypsum models, two circular cracked zones were measured in the model, and ZDP in the enclosing rock mass around deep tunnel was simulated in 3D gypsum model tests. Secondly, based on the elasto-plastic analysis of the stressed-strained state of the surrounding rock mass with the improved Hoek-Brown strength criterion and the bilinear constitutive model, the maximum stress zone occurred in vicinity of the elastic-plastic interface due to the excavation of the deep tunnel, rock material in maximum stress zone is in the approximate uniaxial loading state owing to the larger tangential force and smaller radial force, the mechanism of ZDP was explained, which lay in the creep instability failure of rock mass due to the development of plastic zone and transfer of the maximum stress zone within the rock mass. Thirdly, the analytical critical depth for the occurrence of ZDP was obtained, which depended on the mechanical indices and stress concentration coefficient of rock mass. Foundation item: Projects(50525825, 90815010) supported by the National Natural Science Foundation of China; Project(2009CB724608) supported by the Major state Basic Research Development Program of China     

Fatigue life prediction of crankshaft repaired by twin arc spraying

This paper used Baumel Jr. and Seeger’s approach estimating fatigue parameters of 48MnV with 3Cr13 coatings. The fatigue life of the crankshaft of a six-cylinder engine, repaired by twin arc spraying 3cr13 deposits, is respectively calculated using different damage model such as S-N method, normal strain approaches, SWT-Bannantine approaches, shear strain approaches, and fatemi-Socie method based on dynamical simulation and FE analysis of crankshaft. The results indicate that the traditional calculation is conservative and that the life of crankshaft repaired by arc spraying is sufficient. Foundation item: Project (50235030) supported by National Natural Science Foundation of China     

Residual fatigue strength of 48MnV crankshaft based on safety factor

Residual fatigue strength of 48MnV crankshaft was studied and analyzed based on safety factor. Three different status crankshafts were used to the hop-up tests, which maintain new after 500 h hop-up tests and after 1 000 h hop-up tests. Then, crankshafts were cut into unit cranks. The unit cranks were used to do endurance bending tests to get the residual fatigue strength. Finally, the results were analyzed based on safety factor. The results show that safety factor of crankshaft descends a little with the increase of the running time, and the residual safety factor is still much bigger than the endurable safety factor. Furthermore, after the crankshaft accomplishes a full life cycle, the residual fatigue strength of the crankshaft is enough to remanufacture and fulfill the next life cycle. Foundation item: Key Project (50235030) supported by the National Natural Science Foundation of China     

Fatigue properties of 48MnV steel with twin arc spraying 3Cr13 coatings

The fatigue behaviors of 48MnV steel, both uncoated and coated with different thicknesses of 3Cr13 deposits using twin arc spraying, were investigated. The fatigue properties of the 48MnV steel, determined under axial loading conditions, can be substantially decreased by coating 3Cr13 films, deposited by twin arc spraying. And the fatigue behavior of the thinner coatings is better than that of the thicker ones, of which the fatigue limits decrease by 9%–14%. The decrease in fatigue life attributes to the less mechanical properties of the coatings in comparison with those of the substrate, their relative bad bonding strength and trapped oxide or Al₂O₃ particles retain in the matrix after blasting responsible for the initiation of fatigue cracks. Foundation item: Project (50235030) supported by the National Natural Science Foundation of China     

Thermal partition of two asymmetric discrete heat sources by cold air curtain

A partition solution implemented by a cold air curtain for two asymmetric discrete heat sources in a two-dimensional rectangular enclosure was numerically studied. Main attentions were focused on the effects of Reynolds number, Grashof number, separation distance between heat sources, and buoyancy ratio. It is found that the airflow and heat transfer are not only determined by governing parameters, but also affected by boundary conditions. It is also found that nearly symmetry of flow structure corresponds to nearly thermal partition, and the symmetry can be enhanced when Reynolds number, separation distance and buoyancy ratio increase. In addition, it is observed that there is a minimum Reynolds number for obtaining nearly thermal partition, which increases when Grashof number increases. Foundation item: Project (50408019) supported by the National Natural Science Foundation of China     

The Influence of Some Key Parameters on Fatigue Life of Common Metallic Components

Ｆａｔｉｇｕｅｌｉｆｅｐｒｅｄｉｃｔｉｏｎｆｏｒｃｏｍｐｏｎｅｎｔｓｉｎｖｏｌｖｅｓｔｈｅｆｏｌｌｏｗｉｎｇｆａｃｔｏｒｓ :ｍａｔｅｒｉａｌ,ｌｏａｄ ,ｓｈａｐｅａｎｄｐｒｏｃｅｓｓｉｎｇｓｔａｔｕｓｏｆｃｏｍｐｏｎｅｎｔｓ .Ｗｈｅｎｎｏｍｉｎａｌ ｓｔｒｅｓｓｍｅｔｈｏｄｉｓｕｓｅｄｔｏｐｒｅｄｉｃｔｔｈｅｆａｔｉｇｕｅｌｉｆｅｏｆｃｏｍｐｏｎｅｎｔｓ ,ｔｈｅｐａｒａｍ ｅｔｅｒｓｒｅｆｌｅｃｔｉｎｇｔｈｅｓｅａｓｐｅｃｔｓａｒｅｔｈｅｍａｘｉｍｕｍｌｏａｄσｍａｘ,ｔｈｅｓｈａｐｅｉｎｄｅｘｎｏ…     

Numerical simulation on heat transfer performance of vertical U-tube with different borehole fill materials

Heat exchange performance of vertical U-tube heat exchanger was studied with two different borehole fill materials and CFD software. Borehole surface temperature and water temperature distribution were simulated on the condition of continuous operation for 8 h in winter with inlet water temperature being 10 ℃. The results show that there is no obvious difference on heat exchanger performance between the two different borehole fill materials.     

Contact pressure distribution and support angle optimization of kiln tyre

Rotary kiln is the key equipment in many in-dustrial depart ments ,such as metallurgical indus-try ,building materialsindustry ,etc . Kilntyreis aloose ferrule on the shell ,supported by two roll-ers . The angle between the vertical line and theline linking roller center and tyre center is definedas tyre support angle . Accordingtothe postulationthat kiln load was transformed to the shell at thestation of tyre as uniformly distributed verticalforces ,and Alan et al[1 3]deduced the formula ofty…     

GH80A镍合金电子束焊接接头旋转弯曲高周疲劳行为研究

随着镍合金电子束焊接在工业中的大量应用,尤其是在航空发动机和燃气轮机等关键长寿命服役设备中的使用,有必要对镍合金电子束焊接接头的高周疲劳属性和断裂机理进行系统的分析研究。本文利用旋转弯曲高周疲劳试验机进行疲劳试验,获得了母材和焊接接头的应力-寿命(S-N)曲线和疲劳断口,同时利用扫描电镜（Scanning Electron Microscope,SEM）对疲劳断口进行了微观特征分析,确定了母材和焊接接头在不同应力幅下的疲劳裂纹萌生区和扩展区,分析了裂纹萌生区位置与应力幅的相互关系。最后,利用有限元分析了焊接接头热影响区微裂纹位置与大小对材料疲劳性能的影响。从现有的试验和模拟结果可以得到：1)母材和电子束焊接接头应力-寿命(S-N)曲线分布趋势一致,但焊接接头疲劳强度要低于母材,在靠近107周次时,两者疲劳强度差距最小;2)在高应力幅（低周疲劳寿命阶段）母材和焊接接头的疲劳裂纹均起源于试件表面并且都是多点萌生断裂,焊接接头疲劳断口位置位于焊接熔合区或热影响区;3)在低应力幅（高周疲劳寿命阶段）疲劳裂纹在试件次表面萌生,焊接接头疲劳断口位于热影响区或焊接母材靠近热影响区处;4) 通过有限元模拟发现微裂纹的存在有利于裂纹的扩展。在拉应力作用下,横向微裂纹更优于纵向裂纹沿着应力方向进行裂纹扩展;随着微裂纹尺寸增大,微裂纹间更易于相互贯通,形成更长的裂纹,从而降低了材料的疲劳性能。综上可知,电子束焊接仅仅影响材料的疲劳强度。疲劳断裂机理和母材一致都为穿晶解理断裂,疲劳裂纹萌生区域位置也和母材一样都受应力幅的直接影响。     

Automatic brush-plating technology for component remanufacturing

An automatic brush-plating system was developed for component remanufacturing. With this system, Ni/nano-alumina composite coatings from an electrolyte containing 20 g/L nano-alumina particles were prepared. Microstructure, surface morphology, microhardness and wear resistance of automatically plated coating and manually plated coatings were investigated comparatively. The results show that the automatically plated coatings are relatively dense and uniform and have lower friction coefficient of 0.089 under lubricant condition, when compared with manually plated coatings with friction coefficient of 0.14. Foundation item: Project(50235030) supported by the National Natural Science Foundation of China; Project(G1999065009) supported by the National Basic Research Program of China     

Analysis and calculation of thermal conductivity of rock in deep strata

The thermal conductivity of rock is an important parameter for the deep mine and the geothermal development. It is often not possible to measure the thermal conductivity of the rocks present in the deep strata, and the usual approach is to calculate thermal conductivity including mineralogy and porosity. The compositions of core samples from the MID01 borehole in the Bj?rk? area were determined, and the minera composition was classified. The calculation of the thermal conductivity of rock in the borehole was carried out, and the main factors for the thermal conductivity of rock were analyzed. The results show that the calculated thermal conductivity of rock is reliable and useful for the design and calculation of geothermal development in the Bj?rk? area. Foundation item: Project(50490274) supported by the National Natural Science Foundation of China; project supported by the Postdoctoral Science Foundation of China and Bj?rk? project supported by the Energy Agency of Sweden