Coarsening resistance of M2C carbides in secondary hardening steels: Part I. Theoretical model for multicomponent coarsening kinetics

The development of very high-strength levels in many alloy steels is achieved by a secondary hardening reaction. In high Co-Ni steels containing the strong carbide-forming elements Mo, Cr, and W, secondary hardening is accomplished by the precipitation of fine-scale M₂C alloy carbides. Coarsening resistance of the M₂C precipitates depends on the alloy content of these elements, and there should be an addition to the alloy of these carbide-forming elements which optimizes the M₂C coarsening resistance. Current Lifshitz-Slyozov-Wagner (LSW) theory^[2,3] cannot properly be used to describe, the coarsening behavior of multicomponent carbides, which involves concentrations and diffusivities of two or more solutes and nonspherical carbide morphologies. A model is introduced for the coarsening resistance of multicomponent carbides. This model treats the coarsening of shape-preserving particle and is applicable to rodlike particles.     

Material-Model-Based Determination of the Shock-Hugoniot Relations in Nanosegregated Polyurea

Previous experimental investigations reported in the open literature have indicated that applying polyurea external coatings and/or internal linings can substantially improve ballistic penetration resistance and blast survivability of buildings, vehicles, and laboratory/field test-plates, as well as the blast-mitigation capacity of combat helmets. The protective role of polyurea coatings/linings has been linked to polyurea microstructure, which consists of discrete hard-domains distributed randomly within a compliant/soft matrix. When this protective role is investigated computationally, the availability of reliable, high-fidelity constitutive models for polyurea is vitally important. In the present work, a comprehensive overview and a critical assessment of a polyurea material constitutive model, recently proposed by Shim and Mohr (Int J Plast 27:868-886, 2011), are carried out. The review revealed that this model can accurately account for the experimentally measured uniaxial-stress versus strain data obtained under monotonic and multistep compressive loading/unloading conditions, as well as under stress relaxation conditions. On the other hand, by combining analytical and finite-element procedures with the material model in order to define the basic shock-Hugoniot relations for this material, it was found that the computed shock-Hugoniot relations differ significantly from their experimental counterparts. Potential reasons for the disagreement between the computed and experimental shock-Hugoniot relations are identified.     

Toward a model of social influence that explains minority student integration into the scientific community.

[Correction Notice: An erratum for this article was reported in Vol 103(1) of Journal of Educational Psychology (see record 2011-01898-001). The name of the author Mica Estrada-Hollenbeck should have read Mica Estrada. All versions of this article have been corrected.] Students from several ethnic minority groups are underrepresented in the sciences, indicating that minority students more frequently drop out of the scientific career path than nonminority students. Viewed from a perspective of social influence, this pattern suggests that minority students do not integrate into the scientific community at the same rate as nonminority students. Kelman (1958, 2006) described a tripartite integration model of social influence by which a person orients to a social system. To test whether this model predicts integration into the scientific community, we conducted analyses of data from a national panel of minority science students. A structural equation model framework showed that self-efficacy (operationalized to be consistent with Kelman's rule orientation) predicted student intentions to pursue a scientific career. However, when identification as a scientist and internalization of values were added to the model, self-efficacy became a poorer predictor of intention. Additional mediation analyses supported the conclusion that while having scientific self-efficacy is important, identifying with and endorsing the values of the social system reflect a deeper integration and more durable motivation to persist as a scientist. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

A Computational Investigation of the Multi-Hit Ballistic-Protection Performance of Laminated Transparent-armor Systems

Multi-hit ballistic-protection performance of a prototypical laminated glass/polycarbonate transparent armor is investigated using a series of transient nonlinear dynamics analyses of armor impact with a sequence of four M2AP full metal jacket (FMJ) armor-piercing bullets. All calculations were carried out using ABAQUS/Explicit commercial finite element program (ABAQUS Version 6.7, User Documentation, Dessault Systems, 2007), and the computational results obtained were compared to their experimental counterparts obtained by Dolan (Ballistic Transparent-armor Testing Using a Multi-hit Rifle Pattern, Bachelors, Thesis, Kettering University, December 2007). The comparison revealed that (a) The proposed computational procedure can reasonably well account for the observed multi-hit ballistic-protection performance of the laminated transparent armor; (b) The role of prior bullet hits in reducing armor??s ballistic-protection performance is clearly revealed; (c) The role of polycarbonate lamina in preventing glass fragments from entering the vehicle interior is clearly demonstrated; and (d) Experimentally observed inability of the transparent armor to defeat 0.50-caliber Fragment Simulating Projectiles (FSPs) is confirmed.     

Micro-mechanics based derivation of the materials constitutive relations for carbon-nanotube reinforced poly-vinyl-ester-epoxy based composites

The atomic-level computational results of the mechanical properties of Multi-Walled Carbon Nanotube (MWCNT) reinforced poly-vinyl-ester-epoxy obtained in our recent work [Grujicic M, Sun Y-P, Koudela KL (2006) Appl Surf Sci (accepted for publication, March)], have been utilized in the present work within a continuum-based micro-mechanics formulation to determine the effective macroscopic mechanical properties of these materials. Since the MWCNT reinforcements and the polymer-matrix molecules are of comparable length scales, the reinforcement/matrix interactions which control the matrix-to-reinforcement load transfer in these materials are accounted for through direct atomic-level modeling of the “effective reinforcement” mechanical properties. The term an “effective reinforcement” is used to denote a MWCNT surrounded by a layer of the polymer matrix whose thickness is comparable to the MWCNT radius and whose conformation is changed as a result of its interactions with the MWCNT. The micro-mechanics procedure yielded the effective continuum mechanical properties for the MWCNT-reinforced poly-vinyl-ester-epoxy matrix composite mats with a random in-plane orientation of the MWCNTs as a function of the following composite microstructural parameters: the volume fraction of the MWCNTs, their aspect ratio, the extent of covalent functionalization of the MWCNT outer walls as well as a function of the mechanical properties of the matrix and the reinforcements.     

Design of automation for telerobots and the effect on performance,operator situation awareness,and subjective workload

In this article we review and assess human‐centered level of automation (LOA), an alternate approach to traditional, technology‐centered design of automation in dynamic‐control systems. The objective of human‐controlled LOA is to improve human‐machine performance by taking into account both operator and technological capabilities. Automation literature has shown that traditional automation can lead to problems in operator situation awareness (SA) due to the out‐of‐the (control) loop performance problem, which may lead to a negative impact on overall systems performance. Herein we address a standing paucity of research into LOA to deal with these problems. Various schemes of generic control system function allocations were developed to establish a LOA taxonomy. The functions allocated to a human operator, a computer, or both, included monitoring system variables, generating process plans, selecting an “optimal” plan and implementing the plan. Five different function allocation schemes, or LOAs, were empirically investigated as to their usefulness for enhancing telerobot system performance and operator SA, as well as reducing workload. Human participants participated in experimental trials involving a high fidelity, interactive simulation of a telerobot performing nuclear materials handling at the various LOAs. Automation failures were attributed to various simulated system deficiencies necessitating operator detection and correction to return to functioning at an automated mode. Operator performance at each LOA, and during the failure periods, was evaluated. Operator SA was measured using the Situation Awareness Global Assessment Technique, and perceived workload was measured using the NASA‐Task Load Index. Results demonstrated improvements in human‐machine system performance at higher LOAs (levels involving greater computer control of system functions) along with lower operator subjective workload. However, under the same conditions, operator SA was reduced for certain types of system problems and reaction time to, and performance during, automation failures was substantially lower. Performance during automation failure was best when participants had been functioning at lower, intermediate LOAs (levels involving greater human control of system functions). © 2000 John Wiley & Sons, Inc.     

Synthesis and Hydrodesulfurization Properties of Noble Metal Phosphides: Ruthenium and Palladium

Silica-supported ruthenium and palladium phosphide catalysts (Ru₂P, RuP, Pd₃P, Pd₅P₂) were investigated for the hydrodesulfurization (HDS) of dibenzothiophene (DBT). The Ru and Pd phosphide catalysts were prepared by temperature-programmed reduction of hypophosphite-based precursors consisting of uncalcined or calcined Ru/SiO₂ or Pd/SiO₂ impregnated with ammonium hyposphosphite (NH₄H₂PO₂). The Ru₂P/SiO₂ and RuP/SiO₂ catalysts prepared from uncalcined precursors had smaller average crystallite sizes, higher CO chemisorption capacities, and higher HDS activities than the catalysts prepared from the calcined precursors, while the effect of preparation method on catalytic properties was less clear for the Pd₃P/SiO₂ and Pd₅P₂/SiO₂ catalysts. Following HDS testing at 673?K, X-ray diffraction analysis revealed that the Pd₅P₂/SiO₂ catalysts decomposed to give Pd₃P on the silica support, while the other phosphides exhibited good stability during the testing period. At temperatures at which high DBT conversion was observed (>598?K), the Ru and Pd phosphide catalysts were less active than sulfided Ru/SiO₂ and Pd/SiO₂ catalysts prepared from the uncalcined metal precursors.     

Correction to Estrada-Hollenbeck et al. (2010).

Reports an error in "Toward a model of social influence that explains minority student integration into the scientific community" by Mica Estrada-Hollenbeck, Anna Woodcock, Paul R. Hernandez and P. Wesley Schultz (Journal of Educational Psychology, np). The name of the author Mica Estrada-Hollenbeck should have read Mica Estrada. All versions of this article have been corrected. (The following abstract of the original article appeared in record 2010-22529-001.) Students from several ethnic minority groups are underrepresented in the sciences, indicating that minority students more frequently drop out of the scientific career path than nonminority students. Viewed from a perspective of social influence, this pattern suggests that minority students do not integrate into the scientific community at the same rate as nonminority students. Kelman (1958, 2006) described a tripartite integration model of social influence by which a person orients to a social system. To test whether this model predicts integration into the scientific community, we conducted analyses of data from a national panel of minority science students. A structural equation model framework showed that self-efficacy (operationalized to be consistent with Kelman's rule orientation) predicted student intentions to pursue a scientific career. However, when identification as a scientist and internalization of values were added to the model, self-efficacy became a poorer predictor of intention. Additional mediation analyses supported the conclusion that while having scientific self-efficacy is important, identifying with and endorsing the values of the social system reflect a deeper integration and more durable motivation to persist as a scientist. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Modeling design objects in CAD system for Service/Product Engineering

This paper proposes a new type of service CAD system utilized in Service/Product Engineering (SPE), a much-needed and novel engineering discipline within the background of servicification. In this research a design-object model was defined, and a prototype named Service Explorer was implemented. The model represents critical concepts such as value, costs, functions either of products or of service activities, and entities. Through its application to business cases such as selling washing machines, providing pay-per-wash service, and cleaning washing machines, the Service Explorer was proven to support designers as they describe and operate design objects. In the future we expect that the Service Explorer can help designers with generating new ideas.