Modeling pipeline crevice corrosion under a disbonded coating with or without cathodic protection under transient and steady state conditions

Underground steel pipelines are protected by coatings and cathodic protection (CP). The pipeline corrosion occurs when the coating is disbonded away from a defect or holiday to form a crevice and the corrosion rate varies temporally and spatially in the crevice. In the presence of dissolved oxygen (O₂) in soil ground water, a differential O₂ concentration cell may develop in the crevice because O₂ diffuses more readily into the crevice through the holiday than through the disbonded coating. CP can decrease or eliminate the O₂ concentration cell depending on the potential applied at the holiday. Since the coatings are usually non-conductive, CP is unable to protect the steel surface deep inside the crevice. The transport of dissolved O₂, and that of dissolved carbon dioxide (CO₂) if present, into the crevice through holiday can be key to determining the crevice corrosion rate. In this work, the transient and steady state behavior of the corrosion process is investigated. The effect of the cathodic portion of iron vs. ferrous ion redox reaction on the crevice corrosion rate, which is often neglected traditionally, is further studied. At steady state, the effect of dissolved O₂ on the crevice corrosion rate and the added effect of dissolved CO₂ are mathematically modeled.     

不同铸轧条件下铸轧辊套热应力分析

依据建立的包括铸轧辊套在内的铝双辊铸轧的整体耦合数学模型,对铸轧辊套的热应力场进行了模拟计算;研究了在不同的铸轧工艺参数包括铸轧速度、带坯厚度、内冷强度、铸轧区长度的变化对铸轧辊套热应力的影响规律.结果表明:铸轧辊辊套内外表面热应力相差很大,且外表面受到拉压交变热应力的作用;铸轧速度提高,应力幅度减小;水冷强度增加,应力幅度增大;铸轧区长度增大,应力幅度减小.这就为优化铸轧工艺参数提供了依据.     

Kinetic thermodynamics as a physicochemical foundation for fabricating materials under conditions of self-assembly

A thermodynamic approach that allows creating materials with improved combination of properties is developed. The new theory is based on Gibbs thermodynamics, which is a very strict physical theory. Foundations of the phenomenological hierarchical kinetic quasi-equilibrium thermodynamics of quasi-closed systems are presented. It is assumed in the theory of kinetic thermodynamics that at any moment of time the state functions of the systems studied have real physical sense within a justified approximation. Hierarchical thermodynamics is applied successfully in studies of the processes of creation of materials under weakly nonequilibrium conditions and of the evolution of living systems.     

基于XFEM的复杂应力状态下疲劳裂纹扩展分析

以AZ31镁合金为研究对象,基于扩展有限元方法,对板件上0°、80°和90°这3种不同角度裂纹在9种不同应力状态交替载荷作用下的扩展形态进行数值模拟分析.结果 表明,不同应力状态交替载荷作用下,相同角度的疲劳裂纹扩展形态不同;相同应力状态交替载荷作用下,不同角度的疲劳裂纹扩展形态也不同;疲劳裂纹在受到交替拉应力作用时更...     

基于人工神经网络的AZ91镁合金高温流变应力模型研究

针对目前采用数理统计方法建立的流变应力模型的缺点，本文基于Gleeble-1500热模拟试验机等温压缩AZ91镁合金的实验数据。采用L—M算法的人工神经网络．建立了该合金高温塑性变形时流变应力预测模型。研究结果表明，采用神经网络对流变应力建模是可行的。其预测结果与实验值的平均误差小于4％，具有较高的预报精度和推广能力，同时能宏观反映出材料在塑性变形过程中的动态力学行为。     

Normalized coffin-manson plot in terms of a new life function based on stress relaxation under creep-fatigue conditions

A new life prediction function based on a model formulated in terms of stress relaxation during hold time under creep-fatigue conditions is proposed. From the idea that reduction in fatigue life with hold is due to the creep effect of stress relaxation that results in additional energy dissipation in the hysteresis loop, it is suggested that the relaxed stress range may be a creep-fatigue damage function. Creep-fatigue data from the present and other investigators are used to check the validity of the proposed life prediction equation. It is shown that the data satisfy the applicability of the life relation model. Accordingly, using this life prediction model, one may realize that all the Coffin-Manson plots at various levels of hold time in strain-controlled creep-fatigue tests can be normalized to make one straight line.     

Characteristics of ITO films deposited on a PET substrate under various deposition conditions

ITO films, with a thickness of 150 nm to 160 nm, were deposited on an unheated hard coated PET substrate or non-alkali glass substrate via dc magnetron sputtering. Depositions were carried out under the following various conditions: total gas pressure (P_tot), dc sputtering power, target — substrate (T-S) distance, and O₂ or H₂ addition ratio. The ITO coated on the PET substrate showed relatively lower resistivity than that of the ITO coated on a glass substrate. Relatively small changes in the resistance (ΔR/R₀=0.4) of the films were obtained for each deposition condition for the ITO/PET deposited under a sputtering power of 70 W, P_tot of 0.5 Pa, and T-S of 50 mm. It has been confirmed that the results of the electrical property showed concurrence with the results of the bending test. Specifically, the films that have a good electrical property showed only a small change in resistance to the increasing cycle number for each deposition condition. Therefore, it can be assumed that the increased resistance of the ITO films could be due to the formation of micro defects such as micro-cracks and the micro detachment of the ITO film from the flexible PET substrate.     

基于变形历史的管线钢屈服强度预测模型研究

在管线钢管成形过程中,因为正反两个方向塑性变形发生不同程度的变化,使管体和毛坯板之间的屈服强度产生差异。以国内某厂生产的X90钢板为研究对象,采用正向预拉伸—卸载—反向压缩的试验方法,分析了在不同程度的预变形条件下,材料的反向屈服强度的变化规律。结果显示,随着预应变的增加,板料反向屈服强度呈现先降低后升高的趋势,预应变为5.455%时,反向屈服强度取得最小值。基于Hodge强化理论建立了这种材料的反向屈服强度预测模型,并通过ABAQUS二次开发,实现了X90管线钢单次反向加载条件下的屈服强度预测。验证结果表明:模型预测结果与实验结果吻合较好,相对误差未超过2%。     

Crack growth in a welded microalloyed steel under sulfide stress cracking conditions

In this work, the hydrogen sulfide stress-corrosion cracking (SSC) susceptibility of a welded API X-80 pipeline was investigated. For this purpose, steel welding was carried out normal to the rolling direction using a 60° single V-joint design. After welding, compact modified-wedge opening loading (M-WOL) fracture mechanics specimens were machined and loaded to an applied stress intensity factor, K_I, of 27 to 53 MPa√m. This was followed by specimen exposure to H₂S saturated synthetic seawater. Each of the M-WOL specimens contained the typical microstructures developed during welding, such as the weld metal (WM), base metal (BM), and heat affected zone (HAZ). No attempt was made to establish a unique K_ISCC for crack arrest because its significance was not clear. Qualitatively, the experimental outcome indicated that in mode I loading under a K_I of 40.3 MPa√m only the base metal region underwent SSC. Apparently, active anodic dissolution of the crack tip started the growth process, but it was followed by a transition to hydrogen induced cracking. At an applied K_I of 55 MPa√m and under similar exposure times, crack growth in the base metal was discontinuous and tended to follow the grain boundaries. Moreover, the HAZ exhibited the least SSC susceptibility as inferred from the relatively short crack propagation lengths (0.829 mm). In this case, it was found that the crack path was highly tortuous due to the presence of acicular ferrite and a refined grain structure. The most SSC susceptible condition was found in the weld metal where crack lengths of up to 4.2 mm developed. In this case, the presence of a relatively coarse dendritic structure coupled with interdendritic segregation provided a weak path for crack propagation.     

闭挤式精冲变形区应力状态对断裂损伤的影响

文章将考虑静水应力、最大主应力及应变历史对材料损伤影响的Brozzo断裂准则模型,用于闭挤式精冲的断裂预测。分析了变形区材料的应力、应变状态对材料断裂损伤的影响,并通过DEFORM-2D有限元软件的模拟及物理试验进行验证。研究表明,Brozzo断裂准则能比较精确地模拟闭挤式精冲过程,模拟结果与试验误差在6%以内;主、副凹模闭合时,变形区材料所受的压应力越大,越有利于抑制裂纹的产生和扩展;精冲过程中,凸模刃口附近材料的压应力大于主凹模刃口附近材料,裂纹首先出现在主凹模刃口处,材料开始产生裂纹时的有效应变,随压应力的增加而增大。     

The internal stress state in lamellar PST-crystals of the intermetallic alloy TiAl after compressive deformation

The microstructure of γ-based TiAl alloys often exhibits grains with an internal lamellar structure consisting of alternating γ-TiAl and α₂-Ti₃Al lamellae. Even in undeformed material, internal coherency stresses, due to the lattice misfit between the two phases and the tetragonality of the γ-phase are present. The goal of this work was to investigate the evolution of internal strains induced by compressive deformation of PST-specimens of the alloy TiAl at room temperature and at 800°C. The results of X-ray measurements of different peak profiles, performed with a special high-resolution double-crystal diffractometer are reported, which revealed the dependence of the deformation-induced internal strains on the orientation of the lamellar boundaries with respect to the axis of deformation.     

Optimization of cutting conditions for single pass turning operations using a deterministic approach

An optimization analysis, strategy and CAM software for the selection of economic cutting conditions in single pass turning operations are presented using a deterministic approach. The optimization is based on criteria typified by the maximum production rate and includes a host of practical constraints. It is shown that the deterministic optimization approach involving mathematical analyses of constrained economic trends and graphical representation on the feed-speed domain provides a clearly defined strategy that not only provides a unique global optimum solution, but also the software that is suitable for on-line CAM applications. A numerical study has verified the developed optimization strategies and software and has shown the economic benefits of using optimization.     

On the model of solid state joint formation under superplastic forming conditions

The peculiarities of solid state joint (SSJ) formation under conditions of superplastic forming (SPF) were investigated for the titanium alloy VT6S (Ti-6Al-4V). The influence of annealing and SPF on the change of state of the alloy surface was considered. A significant role of grain boundary sliding (GBS) in the formation of both surface microrelief and SSJ was established. It was shown that SSJ formation under SPF conditions is primarily a deformation process. Corresponding schemes of the appearance of surface microrelief and SSJ formation are proposed.     

Modelling the orientation and direction dependence of the critical resolved shear stress of nickel-base superalloy single crystals

The orientation and direction dependence of the critical resolved shear stress was determined experimentally for the chromium-rich superalloy SC 16 at 650, 750 and 850°C and a constant strain rate of 10⁻³ s⁻¹. The results are used to establish an extended Schmid law for octahedral slip in the temperature and orientation range in which cross-slip pinning of dislocation pairs in the γ′ phase takes place. Normal Schmid behaviour was assumed for orientations near [111], for which cube slip was activated on a macroscopic level. Differences between some commercial superalloys are worked out and can be attributed to morphology and volume fraction of the γ′ phase. The orientation dependence and asymmetry effects increase in the order NIMONIC 105, SC 16, René N4. The orientation range where macroscopic cube slip can be expected increases in the same order. A close inspection of the parameters which are responsible for non-Schmid behaviour suggests that, in addition to cross-slip pinning, a matrix effect must be operating as well, partly counteracting the behaviour expected for mono-phase γ′ crystals.     

平面应力条件下TA15钛合金超塑性

采用受平面应力变形的锥形件和盒形件的气压胀形实验,研究TA15钛合金在不同温度的变形能力,通过显微组织观察和力学性能测试,分析变形过程中的组织变化和性能变化。结果表明,940℃时,材料达到最佳超塑性,锥形件最大高度为94.4mm,最小壁厚为0.1mm,且盒形件的力学性能较原始板材略有提高。在温度940℃和980℃变形时均有β相析出,且随着应变的增大,α相体积分数先减少后增加,组织粗化是导致材料失效的主要原因。     

The deformation and cooling of ceramic particles sprayed with a thermal radio-frequency plasma under atmospheric conditions

Common thermal-spray techniques use the strong acceleration of powder particles to produce dense ceramic coatings with high bond strength. The residence time of the powder particles within the plasma jet is correspondingly low, and only relatively small particles can be molten. In this work, on the contrary, an inductively coupled radio-frequency (RF) inductively coupled plasma (ICP) torch was used to spray large oxide-ceramic powder particles under atmospheric conditions. The slow plasma flow of a RF plasma leads to large residence times of the powder particles, so that the powder size of the feedstock can be 100 μm and more. It was observed that these particles will not be strongly accelerated in the plasma and that their velocity at the moment of impact is in the range of 10 to 20 m/s. Ceramic coatings were ICP sprayed with a low porosity and a high bond strength, similar to direct current (DC) or high-velocity-oxygen-fuel (HVOF) sprayed coatings. The morphology of ICP-sprayed particles on smooth steel surfaces, as a function of the surface temperature, is described and compared with DC plasma-sprayed splats. Furthermore, the degree of deformation was measured and determined by different models, and the pronounced contact zones formed between the pancake and the substrate were investigated. The ICP-sprayed ceramic coatings show some special properties, such as the absence of metastable crystalline phases, which are common in other spray technologies.