Effect of microstructural length scales on spall behavior of copper

A systematic study to quantify the effects of specific microstructural features on the spall behavior of 99.999 pct copper has revealed a strong dependence of the failure processes on length scale. Shock loading experiments with Cu flyer plates at velocities ranging from 300 to 2000 m/s (or impact pressures from 5 to 45 GPa) using a 35-mm single/two-stage light gas gun revealed that single crystals exhibit a higher spallation resistance than fine-grained polycrystals and internally oxidized single crystals. However, in contrast to previously reported results, the fine-grained (∼8-μm) polycrystalline samples exhibit lower damage resistance than the coarse-grained (50- and 133-μm) samples. These observations have been analyzed in the context of the length scale inherent in each of these microstructures, and modeled using an analytical model developed recently. This article is based on a presentation given in the symposium “Dynamic Deformation: Constitutive Modeling, Grain Size, and Other Effects: In Honor of Prof. Ronald W. Armstrong,” March 2–6, 2003, at the 2003 TMS/ASM Annual Meeting, San Diego, California, under the auspices of the TMS/ASM Joint Mechanical Behavior of Materials Committee.     

Evaluation of the fatigue behavior of ductile irons with various matrix microstructures

The stress-failure (S-N) curves for ferritic irons, pearlitic irons, and austempered ductile irons (ADIs) have been determined under tension-tension loading with a stress ratio of 0.1. The effects of Ti contents of up to 0.10 wt pct (resulting from the deliberate use of Ti-containing steel scrap) on fatigue behavior were investigated. It was found that ferritic and pearlitic ductile irons can contain up to 0.10 wt pct Ti without any adverse effect on fatigue behavior. In ADIs, fatigue properties deteriorate at such high Ti contents. Tests were also conducted to investigate the effects of microstructural features on fatigue properties. It was found that the effect of the graphite nodule count (the number of graphite particles on a unit area of a polished surface) on the fatigue limit is significant only in ADIs. Scanning electron microscope (SEM) analysis has shown that cracks usually initiate from surface dross-type defects. However, in ADIs, fatigue cracks can also initiate at shrinkage cavities and at surface or subsurface locations. An offset bilinear S-N curve behavior (the linear S-N curve at higher stress levels is separated from the linear S-N curve at lower stress levels) has been observed in ADIs. This is attributed to surface residual compressive stresses, which prohibit fatigue crack initiation from surface positions at lower applied stress levels. In ferritic and pearlitic ductile irons, the offset bilinear S-N curve behavior is not observed because of the rapid relaxation of the residual compressive stresses.     

集装箱用高强耐候钢组织及腐蚀行为研究

利用动态相变仪分析Nb-Ti微合金化高强耐候钢在不同冷却速率下的显微组织变化规律,采用控轧控冷工艺获得高强热轧钢板,并通过72 h周期浸润腐蚀试验和腐蚀锈层元素分布分析对高强热轧钢板的腐蚀行为进行研究.结果表明：当冷却速度小于1℃/s时,变形后的奥氏体转变为铁素体、珠光体和贝氏体;随着冷却速率的增加,珠光体和铁素体逐渐减少并直至消失,贝氏体数量增加;采用控轧控冷工艺获得的高强钢板屈服强度为704 MPa,抗拉强度为753 MPa,伸长率为20.2%,-40℃低温冲击吸收功平均值为121 J;腐蚀后的实验钢与Q345B碳钢的相对失重率为52.11%,其表面锈层与铁基体结合紧密,表明Nb-Ti高强耐候钢在工业大气腐蚀环境下具有良好的耐腐蚀性能.     

On the choice of scales for task analysis.

101 incumbents of 25 service jobs rated their respective tasks on relative time spent, difficulty of learning, criticality, and overall importance. Although scale convergence varied as a function of job title, task criticality and importance ratings were similar and presented low to moderate levels of convergence with both time-spent and difficulty-of-learning ratings. Different composites of task importance were compared. All composites and the overall judgments of importance were moderately correlated with each other and showed similar levels of interrater agreement. Several conclusions regarding the choice of scales and the use of composites in task analysis are drawn. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On dislocation storage and the mechanical response of fine scale microstructures

For lamellar aggregates, a small size scale is attained where flow in a ductile layer occurs by the motion of single dislocations rather than dislocation arrays. Analysis of such a case indicates that the flow stress should follow an Orowan-type relation accompanied by rapid effective work hardening. Consequences for flow instability and fracture are considered.     

Cyclic deformation behavior and microstructures of hydrided ZIRCALOY-4 under biaxial loading

Biaxial fatigue behavior of hydrided ZIRCALOY-4 (Zr-4) in the as-cold-worked (CW) and recrystallized (RZ) conditions under in-phase (IP) and out-of-phase (OP) cyclic loading was investigated. The CW Zr-4 showed cyclic softening followed by a saturation stage during biaxial cyclic loading. Additional cyclic softening was displayed in CW Zr-4 under OP loading with the phase lag of 30 and 60 deg. The additional softening level decreased as the phase lag increased. On the other hand, RZ Zr-4 showed cyclic hardening followed by a saturation stage, and additional cyclic hardening was obtained under OP loading. The additional hardening arose as the phase lag increased. Observation of the fracture surface showed that the biaxial fatigue failure of the CW Zr-4 under OP loading was controlled by crack initiation and propagation through the hydrides, while the nucleation and coalescence of microvoids were dominant in the failure of CW Zr-4 under IP loading and RZ Zr-4 under both IP and OP loading. The typical deformation substructure in CW Zr-4 specimens was composed of dislocation tangles together with parallel dislocation lines under IP and OP loading. Whereas the parallel dislocation lines were formed by prismatic slip for RZ Zr-4 under IP loading and OP loading with the lower phase lag, they developed into dislocation networks, loops, and debris as the phase lag increased under OP loading. The additional cyclic softening for CW Zr-4 was due to the relief of the anisotropic hardening mechanisms when the loading mode changed from IP to OP. The additional cyclic hardening of RZ Zr-4 under OP loading is attributed to an increase in the interaction between the primary dislocations and other dislocations from different slip systems.     

Clinical outcome measures and rating scales in multiple sclerosis trials

In this review, we analyzed clinical outcome measures used in multiple sclerosis (MS) clinical trials in which the primary goal is to slow or arrest progression of disease. In addition, we examined rating scales that quantify symptomatic complications of MS (for example, spasticity) and the current role of magnetic resonance imaging in MS treatment trials. Each proposed scale has advantages and deficiencies, and none meets all the criteria for an ideal outcome measure. The validity of trial design may be improved by using combinations of selected components of current scales as well as new instruments targeted to specific variables (such as motor strength). Symptom-specific rating scales are most appropriately used in trials of symptomatic therapeutic strategies for MS. Until serial magnetic resonance imaging changes are definitely known to predict long-term impairment and disability in patients with MS, clinical outcome measures will remain the primary means of assessing therapeutic efficacy in phase III clinical trials.     

On the consistency of individual classification using short scales.

Short tests containing at most 15 items are used in clinical and health psychology, medicine, and psychiatry for making decisions about patients. Because short tests have large measurement error, the authors ask whether they are reliable enough for classifying patients into a treatment and a nontreatment group. For a given certainty level, proportions of correct classifications were computed for varying test length, cut-scores, item scoring, and choices of item parameters. Short tests were found to classify at most 50% of a group consistently. Results were much better for tests containing 20 or 40 items. Small differences were found between dichotomous and polytomous (5 ordered scores) items. It is recommended that short tests for high-stakes decision making be used in combination with other information so as to increase reliability and classification consistency. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reliability and validity of scales for assessing behavior in epilepsy.

Behavior Rating Scales for Epilepsy (BRSE), developed to assess 8 characteristics that have been attributed to patients with epilepsy, were rated from a semistructured interview with 79 outpatients (aged 19–69 yrs) with epilepsy and from an independent interview with a friend or relative of each patient. Patients and observers also completed the Bear and Fedio Inventory (BFI) for assessing behavior change in epilepsy. Interrater reliability estimates exceeded .75 for 5 BRSE scales. Convergent and discriminant validity were demonstrated for all but 2 BRSE scales when comparing patient with observer-based rating. BRSE results showed correspondence with BFI-Observer scores for most scales but not with BFI-Patient scales. BFI-Observer scores also showed little association with BFI-Patient scores. The BRSE shows promise as a time-efficient, psychometrically sound assessment instrument for further research on behavioral aspects of epilepsy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)