Effects of constituent particle clusters on fatigue behavior of 2024-T3 aluminum alloy

Fatigue tests of 2024-T3 aluminum sheet were run to determine the effects of constituent particles and particle clusters on fatigue life for all three metallurgical planes. In addition, a model to account for crack coalescence within particle clusters was developed to determine if particle clusters can be more damaging than single particles as crack nucleation sites. On the LS and ST planes, cracks formed primarily at single particles or holes, indicating that coalescence was not an issue. On the LT plane, coalescence was observed when the particle clusters were aligned with the crack growth direction, and the life was reduced about 30%. The crack coalescence and growth model showed that varying the initial separation between two particles (potential cracks) causes at most about a 15–20% change in fatigue life over a separation range of 5 μm to 1200 μm for a pair of 50 μm² particles.     

M-A组织对拉伸和冲击性能的影响

用18Cr2Ni4WA钢研究了M－A组织对拉伸和冲击性能的影响。结果表明,粒状组织和粒状贝氏体的屈服强度ρp0.2／ρb、断面收缩率ψ和冲击韧度Ak与马氏体及M－A含量有很好的线性相关性,而且其与马氏体的线性相关性高于与奥氏体的线性相关性。     

反应蒸发沉积的纳米硅氧化硅薄膜的发光及其氧的存在形态

通过改变蒸发源、衬底温度和氧的流量 ,用反应蒸发法制备了不同晶粒尺寸的Si/SiOx 薄膜。用X射线衍射、X光电子能谱和红外光谱分别测试了薄膜的结构、组分及氧在薄膜中的存在形态。实验发现氧的存在形态与蒸发条件密切相关 :对以硅为蒸发源的样品 ,衬底温度较低时 ,以间隙氧形态存在。随着衬底温度的升高 ,SiOx 量逐渐增多 ,间隙氧逐渐减少 ,72 0℃以上产生SiO2 。氧流量的增加有利于间隙氧的生成和氧含量的增加 ;对以SiO为蒸发源的样品 ,衬底温度较低时 ,主要以间隙氧的形态存在 ,同时存在SiO2 和SiOx。随着衬底温度的升高 ,有利于SiOx 和SiO2 的增加。 80 0℃退火后 ,SiOx 增多 ,同时产生大量SiO2 白硅石。荧光光谱表明 :薄膜的发光跟氧的存在形态密切相关 ,其可能原因是纳米硅被大量宽禁带的SiO2 或SiOx基体包裹所产生的量子效应。     

Time Effects Relate to Crushing in Sand

Based on previously obtained experimental results, a mechanistic picture of time effects in granular materials is presented. Accordingly, time effects are caused by grain crushing, which in turn is time dependent, as indicated by static fatigue of brittle materials. Triaxial compression tests have been performed on Virginia Beach sand at high pressures, where grain crushing is prevalent, to study effects of initial loading strain rates on subsequent amounts of creep and stress relaxation. Grain size distribution curves were determined after each test and the amount of crushing, as characterized by Hardin’s breakage factor, is related to the energy input to the triaxial specimens. A pattern emerges that indicates the importance of crushing for the axial and volumetric strains, while rearrangement and frictional sliding between intact grains play much smaller roles in the stress-strain and volume change behaviors of granular materials at high stresses and shear strains. Because particle crushing is a time-dependent phenomenon described as static fatigue or delayed fracture, the close relation between time effects and crushing in granular materials is established.     

Variation in blood pressure is associated with white matter microstructure but not cognition in African Americans.

Although hypertension is a major risk factor for cerebrovascular disease (CVD) and is highly prevalent in African Americans, little is known about how blood pressure (BP) affects brain–behavior relationships in this population. In predominantly Caucasian populations, high BP is associated with alterations in frontal–subcortical white matter and in executive functioning aspects of cognition. We investigated associations among BP, brain structure, and neuropsychological functioning in 52 middle–older-age African Americans without diagnosed history of CVD. All participants underwent diffusion tensor imaging for examination of white matter integrity, indexed by fractional anisotropy (FA). Three regions of interest were derived in the anterior (genu) and posterior (splenium) corpus callosum and across the whole brain. A brief neuropsychological battery was administered from which composite scores of executive function and memory were derived. Blood pressure was characterized by mean arterial blood pressure (MABP). When controlling for age, higher MABP was associated with lower FA in the genu, and there was a trend for this same relationship with regard to whole-brain FA. When the sample was broken into groups on the basis of treatment for BP regulation (medicated vs. nonmedicated), MABP was related to genu and whole-brain FA only in the nonmedicated group. Neither MABP nor FA was significantly related to either neuropsychological composite score regardless of medication use. These data provide important evidence that variation in BP may contribute to significant alterations in specific neural regions of white matter in nonmedicated individuals without symptoms of overt CVD. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

烟草在线检测与异物剔除系统

以无屏闪光照系统作为光源，物料通过Y—Roller均散装置摊开后高速抛出时，CCD摄像机采集到物料图像并送入PC机；在光学滤色镜组的作用下，烟草与异物的色度值拉开，以便后续的识别与剔除处理；建立中心阈值库以加快判别阈值的确定，用浮动阈值提高判别阈值的机敏度，提高系统的识别率。系统原理样机对白纸、鸡毛等典型异物的识别率可达到60％以上。     

Comparison of spectral fluorescent signatures-based models to characterize DOM in treated water samples

Statistical procedures enable a multivariate analysis of the measurements to identify specific characteristics of the dissolved organic matter (DOM) fractions in raw natural water, including the concentrations. In this work, three already established models were used to predict the concentrations of fractions of DOM from spectral fluorescent signatures (SFSs): a general linear regression (GLR), loadings and scores of a principal components analysis (PCA), and a partial least squares regression (PLS). Details about the method undertaken to prepare the fractions were given. Water samples from surface water treatment plants in New Jersey were used for the testing. In all cases, PLS have shown much better biases and accuracies than GLR and PCA models. Hydrophilic neutral, however, showed poor performances (bias 33%) due to the isolation technique used. Recommendations were provided in order to improve the DOM characterization through SFS, which linked to PLS make a powerful and cost-effective surrogate parameter to characterize DOM.     

Modeling Permanent Deformation of Unbound Granular Materials under Repeated Loads

Finite-element analysis on a pavement structure under traffic loads has been a viable option for researchers and designers in highway pavement design and analysis. Most of the constitutive drivers used were nonlinear elastic models defined by empirical resilient modulus equations. Few isotropic/kinematic hardening elastoplastic models were used but applying thousands of repeated load cycles became computationally expensive. In this paper, a cyclic plasticity model based on fuzzy plasticity theory is presented to model the long-term behavior of unbound granular materials under repeated loads. The discussion focuses on the model parameters that control long-term behavior such as elastic shakedown. The performance of the constitutive model is presented by comparing modeled and measured permanent strain at various numbers of load cycles. Calculated resilient modulus from the complete stress-strain curve is also discussed.     

Effects of Particle Crushing in Stress Drop-Relaxation Experiments on Crushed Coral Sand

Stress relaxation and stress drop-relaxation tests have been performed to complement a test series performed to study strain rate, creep, and stress drop-creep effects on crushed coral sand. Drained experiments with constant effective confining pressure of 200 kPa were performed in which triaxial specimens of crushed coral sand were loaded to initial stress differences of 500, 700, and 900 kPa, followed by stress drops of 0, 100, 200, 300, and 400 kPa at which points the axial strains were kept constant while the axial stress relaxation and the volumetric strains were observed. The stress drops produced delays in initiation of stress relaxation that were proportional with the magnitudes of the stress drops. The experiments show that sands do not exhibit classic viscous effects, and their behavior is indicated as “nonisotach,” while the typical viscous behavior of clay is termed “isotach.” Thus, there are significant differences in the time-dependent behavior patterns of sands and clay. A mechanistic picture of time effects in sands is proposed.