TB6钛合金疲劳小裂纹扩展行为

为了研究TB6钛合金自然萌生小裂纹的扩展行为,针对单边缺口拉伸试样开展室温下不同应力比(R=0.1,0.5)的小裂纹扩展实验,采用复型法观测了小裂纹的萌生与扩展情况。结果表明:同一应力比下,随着应力等级的降低,小裂纹的萌生寿命由占全寿命的60%增加到80%,但应力等级对TB6钛合金小裂纹扩展速率没有明显影响。裂纹早期扩展速率受微观组织的影响大,TB6钛合金扩展速率转变临界值是200μm,一旦裂纹长度达到200μm,裂纹扩展速率将不受取向不同的晶界或晶粒影响而迅速提升。TB6钛合金疲劳小裂纹起源于试样缺口根部,所有试样的裂纹大部分为角裂纹,疲劳小裂纹萌生寿命占全寿命的绝大部分。     

缺口应力集中系数对TC4 ELI合金低周疲劳性能的影响

研究了缺口应力集中系数不同的深海潜水器耐压壳用TC4 ELI(Extra-low-interstitial)合金板材在恒总应变幅控制下的低周疲劳行为。结果表明,在应变幅较低(0.7%以下)和应变幅较高(0.8%和0.9%)条件下的光滑试样在循环初期分别发生了循环硬化和循环软化,而缺口试样在0.2%～0.7%应变幅条件下的循环初期均发生了循环硬化。通过循环载荷作用下材料滞回能的变化描述了TC4 ELI合金试样低周疲劳的损伤程度,得到了缺口应力集中系数与低周疲劳性能参数之间的关系,建立了相对裂纹萌生寿命预测模型。利用该模型能较好地预测缺口应力集中系数较低的TC4 ELI合金在高应变幅条件下的相对疲劳裂纹萌生寿命。     

残余压应力对45钢疲劳裂纹萌生寿命的影响

本文研究了４５钢不同缺口半径及经预压，喷丸处理后对试样弯曲疲劳裂纹萌生寿命的影响。研究结果表明：随着试样缺口根部半径的增大，试样的弯曲疲劳裂纹萌生寿命增加。     

缺口对7A85铝合金拉伸性能和疲劳性能的影响

在光滑试样表面预制深度为0.1 mm和0.2 mm的环状缺口，研究了不同缺口尺寸对7A85铝合金拉伸性能和疲劳性能的影响，并分析了7A85铝合金含缺口试样的疲劳断裂机理。结果表明，随着缺口深度由0 mm增加至0.2 mm, 7A85铝合金试样的抗拉强度、断后伸长率和疲劳强度分别下降了6%、47.5%、44.4%。缺口对7A85铝合金塑性的影响远大于拉伸强度，且其抗拉强度与疲劳强度呈线性关系。试样疲劳缺口系数随着缺口尺寸和循环次数的增加而增大。7A85铝合金试样的疲劳裂纹源通常是富铁的第二相颗粒，环状缺口根部应力集中促进了多疲劳裂纹源萌生，多个裂纹源同时扩展使得试样有效承载面积快速减少，导致疲劳寿命急剧缩短。     

TC21合金315℃高周疲劳光滑和缺口试样断口分析

开展了TC21研究合金光滑和缺口试样的315℃高周疲劳实验,并对疲劳断口进行详细观察,研究了缺口对TC21合金疲劳寿命的影响.结果表明,光滑和缺口试样的疲劳强度比值随循环寿命降低而降低;光滑试样的失稳疲劳裂纹长度随循环应力升高而降低;瞬断区所承受的断裂应力随循环应力升高而降低;这说明裂纹失稳决定试样的断裂,缺口试样断口有多个裂纹源,以缺口试样名义应力乘以应力集中因子与光滑试样的应力相等作为比较时,缺口试样主裂纹长度大于光滑试样的裂纹长度,缺口试样的裂纹扩展寿命更长.     

石油钻杆材料G105在不同条件下的疲劳断裂

采用国产PQ-6型旋转弯曲疲劳试验机研究钻杆管体材料G105的弯曲疲劳性能以及H_2S腐蚀和缺口对试样弯曲疲劳性能的影响,利用金相显微镜和扫描电子显微镜对光滑试样断口、缺口试样断口以及H_2S腐蚀后试样断口进行微观形貌分析。结果表明:在光滑试样的疲劳极限载荷作用下,经过H_2S腐蚀后的光滑试样的疲劳寿命和缺口试样的疲劳寿命相当,材料的疲劳寿命都从106降低至104;缺口试样在缺口的高应力集中效应下,加快疲劳裂纹形核过程。H_2S腐蚀对钻杆疲劳性能影响的主要作用在于氢原子在材料内缺陷处聚集引起材料疲劳性能降低,缺口和H_2S腐蚀都会加快疲劳裂纹的扩展。材料疲劳断裂主要是因为试样在交变应力的作用下上产生滑移最后致使位错塞积而导致的。     

Stellite12钴基合金的疲劳性能及其断裂机理研究

采用三点弯曲疲劳法测得光滑试样和直缺口试样的S-N曲线以研究Stellite12钴基合金的疲劳性能,并通过断口形貌观察进一步探究该钴基合金的断裂过程。结果表明:光滑试样的疲劳极限为545 MPa,约为原始抗弯强度1552 MPa的25.4%;直缺口试样的疲劳极限约为101MPa,约为静态抗弯强度517.6MPa的19.1%。对于疲劳敏感性,光滑试样与直缺口试样的疲劳敏感性分别为397和31。此外发现疲劳裂纹多萌生于近表层聚集的碳化物处,同时表面缺陷也可诱发疲劳裂纹的萌生。疲劳裂纹的扩展主要表现为碳化物的穿晶断裂,钴基体在应力比R=0.1的疲劳加载条件下虽表现出一定的韧性且呈现出较多的撕裂脊,但也呈现出一定的脆性断裂模式,因此疲劳裂纹扩展模式为真疲劳与静态疲劳的混合模式。     

超声载荷下TC4钛合金的疲劳寿命分析

通过计算裂纹尖端应力强度因子及疲劳裂纹扩展速率da/d N,由C.Paris模型推导出安全寿命Nf,由Bathias公式计算"哑铃"状钛合金试样的裂纹扩展寿命。通过理论计算和有限元分析超声疲劳"哑铃"状试样,得出应力最大位置。利用有限元仿真和实验数据分析TC4钛合金疲劳寿命。在20 k Hz的超声疲劳试验中,试样的断口位置表明:TC4钛合金材料内部缺陷是试样萌生裂纹使断裂位置偏离最大应力处的主要原因。并得出疲劳裂纹萌生阶段寿命决定"哑铃"状试样的疲劳寿命。     

S135钻杆钢的拉扭复合加载疲劳行为

采用疲劳实验和回归分析相结合的方法,研究了S135钻杆钢在拉扭复合加载条件下的疲劳行为,并对疲劳断口进行了微观分析。结果表明:当τa/σeq=0.7时,由拉扭应力幅对应的当量应力表示的疲劳寿命公式可很好地描述S135钻杆钢的拉扭疲劳寿命规律;疲劳断口由疲劳源区、疲劳裂纹稳定扩展区和快速瞬断区组成,疲劳裂纹从试样表面萌生,并向试样内部扩展,且常为多疲劳源,不同疲劳源断口的连接和复合加载形成所谓的"屋脊"状特征;拉扭疲劳断裂试样裂纹源区的微观断口特征为明显的河流花样,裂纹扩展区的微观断口特征为疲劳条带与涟波状花样。     

超高强度钢中不同组织的疲劳超载效应

本文研究了超载对40CrMnsiMoVA 钢中准贝氏体组织和马氏体组织冲击疲劳裂纹起始寿命的影响。结果表明拉伸超载延长疲劳裂纹起始寿命 N_i,N_i 与试样缺口根部的残余应变ε_R 之间呈以下经验关系:N_i=N_i~0exp(mε_R);压缩超载缩短 N_i。准贝氏体组织的超载延寿效果明显地大于马氏体组织,认为这与准贝氏体组织具有良好的强韧性配合有关。还讨论了超高强度钢的超载延寿机制。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...     

Brainstorming for ISO Strategy 2016-2020

正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from     

CNAS Passes APLAC's PTP Review

正The review group of Asia Pacific Laboratory Accreditation Cooperation(APLAC)carried out a 4-day peer review of the proficiency testing provider(PTP)for China National Accreditation Service for Conformity Assessment(CNAS)from July 28 to 31,2014.CNAS passed the PTP review with excellent performance.Two senior peer reviewers of APLAC made a comprehensive,rigorous and detailed review of CNAS’s PTP accreditation activities,and made the on-spot inspection of the review groups in Shanghai and Shenzhen respectively.