Estimation of fractional critical tractive stress from fractional bed load transport measurements of unimodal and bimodal sediments

Experimental investigation on estimation of fractional critical tractive stress of nonuniform unimodal and bimodal sediment mixtures is reported. The observed data on fractional bed load transport rates for different flow strength, under equilibrium condition, have been used to estimate critical tractive stress (CTS) of each size fraction in sediment mixture from reference transport method (RTM). Further, the accuracy of these estimated CTS values are assessed by comparing the same with CTS values estimated using largest grain method (LGM). The estimated CTS values of individual size fractions for different sediment mixtures have been used to assess the performance of CTS relationship recently proposed by Patel et al. [12].     

Failure analysis of a martensitic stainless steel (CA-15M) roll manufactured by centrifugal casting. Part I: Material and fractographic characterization

The failure analysis of a martensitic stainless steel (CA-15M) roll manufactured by centrifugal casting and used in cast glass rolling was carried out by means of traditional characterization techniques (optical metallography, SEM, EDX microanalysis, tensile testing and XRD). The roll was in the as-cast condition and its microstructure featured large proportion of δ ferrite (between 20% and 27%) in a martensitic (α′) matrix, with the δ/α′ interfaces presenting an intergranular network of M₂₃C₆ carbides. The crack propagation began in the internal surface of the roll, with δ/α′ intergranular and transgranular cleavage in the “equiaxed region” of the casting, progressing to δ/α′ intergranular ductile fracture in the “columnar” and “chilled regions”. Tensile thermal stresses in the internal surface of the roll associated with microstructural embrittlement (network of interfacial carbide and microporosities) are thought to be the main causes for the premature failure of the roll. Finally, materials selection was performed to replace the CA-15M stainless steel with another class of stainless steel for centrifugal casting.     

预应力混凝土箱梁横向应力分布分析

对预应力箱梁的横向分布有效宽度进行了介绍,使用有限元软件ANSYS建立实体模型对某矮塔斜拉桥的中跨箱梁进行了分析,得出了箱梁的实际应力分布,并与杆系模型结果进行了对比,得出箱梁的有效分布宽度。     

Vacancy strengthening in Fe3Al iron aluminides

The room temperature strength of FeAl alloys can be increased significantly by freezing in the high thermal vacancy concentrations present at elevated temperatures. In contrast, because of their lower thermal vacancy concentrations, vacancy strengthening in quenched Fe₃Al alloys is believed to be much smaller and has not received much attention to date. In the present work, the influence of annealing time and quench temperature on the room temperature strength of extruded and recrystallized Fe₃Al alloys is evaluated. For aluminum concentrations between 28 and 32 at% and quench temperatures between 400 and 900 °C both the magnitude and the kinetics of strengthening are found to be consistent with reported values for the thermal vacancy concentrations and vacancy migration rates. To assess the potential contributions of other strengthening mechanisms, appropriate heat treatments will need to be designed in follow-on studies that alter microstructural features relevant to those mechanisms while maintaining a constant vacancy concentration.     

不锈钢焊接工字形截面残余应力分布试验研究

通过焊接加工10个不锈钢工字形截面试件（选材包括奥氏体型S30408和双相型S22253两种），采用分割法将试件截面切分成条带，量测释放的残余应变，计算得出截面的残余应力大小与分布形态。结果表明：试件截面的残余拉应力峰值低于材料的名义屈服强度，对于奥氏体型S30408和双相型S22253两种不锈钢试件的截面残余拉应力峰值分别约为其名义屈服强度的80%和60%。基于试验结果对现有简化分布模型的评估表明其应用的局限性，提出可以较准确描述不锈钢焊接工字形截面残余应力分布的建议简化模型，结合现有的其他试验数据，对建议简化分布模型的适用范围进行了验证和推广，可以为不锈钢结构构件的稳定性研究和设计提供参考。     

Risk and reliability assessment about a manufacturing issue in a power MOSFET for automotive applications

In the automotive semiconductor industry, risk assessments are requested by customers on quality incidents that happen in the assembly line or in field. More rarely, in a die business context, such a study is requested about a defect observed during the optical inspection performed by the customers on the known good dice after assembly. This article deals with the case of pin holes in the top metal surface of a MOSFET component. The risk assessment is addressing detection, occurrence and severity of the defect: this implies process and failure analysis. Also, reliability has been carried out, by completing accelerated and typical stress tests.     

Behavior and mechanism of the stress buffer effect of the inside ceramic layer to the top ceramic layer in a double-ceramic-layer thermal barrier coating

The Double-Ceramic-Layer Thermal Barrier Coating (DCL-TBC) consists of a top ceramic layer (TC1), an inside ceramic layer (TC2), bond coat (BC) and alloy substrate. The top ceramic layer is made by new ceramic materials which has the lower thermal conductivity, such as LZ, LZ₇C₃, LMA etc. Although these materials have good high temperature performance and thermal insulation properties, their thermal expansion coefficients are very low which cause higher degree of mismatch with material properties of alloy substrate.     

过渡圆角对曲轴疲劳强度的影响

对发动机中的曲轴作了简要阐述,对曲轴表面淬火及残余应力进行了分析,在此基础上研究了淬火残余应力对曲轴强度的影响,以确保发动机工作的可靠性。     

悬挂式支座的薄壁储液壳薄膜应力的简化计算

分析薄壁壳体的应力时,采用薄膜理论,应力沿厚度均匀分布,壳体材料的强度可以合理利用,是最理想的应力状态。而传统的薄膜应力计算方法比较复杂。针对两种不同结构形式的薄壁储液壳进行应力计算,得出求解薄膜应力的简便计算方法,该方法适用于能应用薄膜理论计算的任何一种薄壁储液壳的两向薄膜应力。     

Hypothalamic-pituitary-adrenal axis activation and immune regulation in heat-stressed sheep after supplementation with polyunsaturated fatty acids

The aim of this study was to assess the effects of supplementation with polyunsaturated fatty acids from different sources on immune regulation and hypothalamic-pituitary-adrenal (HPA) axis activation in heat-stressed sheep. The experiment was carried out during the summer 2012. Thirty-two Comisana ewes were divided into 4 groups (8 sheep/group): (1) supplemented with whole flaxseed (FS); (2) supplemented with Ascophyllum nodosum (AG); (3) supplemented with a combination of flaxseed and A. nodosum (FS+AG); and (4) control (C; no supplementation). On d 22 of the experiment, cortisol concentrations in sheep blood were measured after an injection of ACTH. Cellular immune response was evaluated by intradermic injection of phytohemagglutinin (PHA) at 0, 15, and 30 d of the trial. Humoral response to ovalbumin (OVA) was measured at 0, 15, and 30 d. At 0, 15, and 30 d of the experiment, blood samples were collected from each ewe to determine production of T-helper (Th)1 cytokines (IL-12 and IFN-γ), and Th2 cytokines (IL-10, IL-4, IL-13), and concentrations of heat shock proteins (HSP) 70 and 90. Ewes supplemented with flaxseed alone had greater cortisol concentrations and a longer-lasting cell-mediated immune response compared with ewes in the control and other groups. Anti-OVA IgG concentrations increased in all groups throughout the trial, even though ewes in the FS+AG group had the lowest anti-OVA IgG concentrations at 15 d. The level of IL-10 increased in all groups throughout the experiment; the FS+AG group had the lowest IL-13 concentration at 15 and 30 d. The concentration of HSP 70 increased in AG ewes at the end of the experiment and decreased in FS ewes, whereas that of HSP 90 increased in FS ewes compared with FS+AG ewes. Flaxseed supplementation was found to influence in vivo HPA activation in heat-stressed sheep, resulting in increased cortisol concentrations, probably to meet increased energy demand for thermoregulation. Flaxseed supplementation also supported Th1 response via a complex cross-talk between IL-10, IL-12, and IFN-γ production.