Inclusion engineering in FeMnAl steels

Low density high Mn and Al steels, or FeMnAl steels, show great promise for military vehicles and automotive applications in which high strength and toughness is a requirement. However, these steels are subject to processing challenges including development of oxide and nitride inclusions during melting and casting as well as a large as-cast grain size and heavy interdendritic segregation. This can lead to non-uniform heat treatment response and cracking during subsequent hot rolling. Adding up to 10%Al lowers the density of these steels by as much as 15%, unfortunately, this also results in large amounts of hard and faceted AlN inclusions that are known to reduce toughness. Inclusion engineering techniques in other cast alloys can mitigate the effect of harmful inclusions or decrease grain size, segregation, and microporosity and improve ductility and toughness. Unfortunately, there is limited understanding of inclusion evolution in FeMnAl steels and the inclusion engineering strategies to improve mechanical properties. The goal of this research is to explore potential nonmetallic inclusions as inoculants to refine the as-cast grain size as well as potential mitigation of detrimental AlN by soft and globular MnS co-precipitation. MnS was effective at coating most of the AlN inclusions. However, this produced a large overall inclusion population that reduced dynamic fracture toughness. The potential of Ti(C,N), Nb(C,N), and complex Ce-oxides to refine the as-cast grain size was investigated. A decrease in the columnar zone was observed with addition of FeSiMg+FeTi and Ce addition, however, the equiaxed grain size did not decrease. A low N melt practice with Ti additions was effective at eliminating AlN”--Abstract, page iv

A Hybrid Heuristic for a Broad Class of Vehicle Routing Problems with Heterogeneous Fleet

We consider a family of Rich Vehicle Routing Problems (RVRP) which have the particularity to combine a heterogeneous fleet with other attributes, such as backhauls, multiple depots, split deliveries, site dependency, open routes, duration limits, and time windows. To efficiently solve these problems, we propose a hybrid metaheuristic which combines an iterated local search with variable neighborhood descent, for solution improvement, and a set partitioning formulation, to exploit the memory of the past search. Moreover, we investigate a class of combined neighborhoods which jointly modify the sequences of visits and perform either heuristic or optimal reassignments of vehicles to routes. To the best of our knowledge, this is the first unified approach for a large class of heterogeneous fleet RVRPs, capable of solving more than 12 problem variants. The efficiency of the algorithm is evaluated on 643 well-known benchmark instances, and 71.70\% of the best known solutions are either retrieved or improved. Moreover, the proposed metaheuristic, which can be considered as a matheuristic, produces high quality solutions with low standard deviation in comparison with previous methods. Finally, we observe that the use of combined neighborhoods does not lead to significant quality gains. Contrary to intuition, the computational effort seems better spent on more intensive route optimization rather than on more intelligent and frequent fleet re-assignments

Panorama do mercado e da produção nacional de aeronaves leves

Bibliografia: p. 253-255.No Brasil, apenas 120 localidades são atendidas pela aviação comercial (transporte aéreo regular). A aviação geral – qualquer atividade de transporte aéreo, excetuando-se a aviação comercial e a aviação militar – atende a cerca de 3,5 mil localidades. Daí sua importância para a integração nacional, considerando- se a dimensão territorial do Brasil e sua carência de infraestrutura de transportes. Este artigo apresenta um panorama sobre o mercado mundial de aviões monomotores a pistão – os principais utilizados na aviação geral – e sobre os principais fabricantes nacionais dessas aeronaves. O desenvolvimento dessa indústria no país poderá reduzir o deficit na balança comercial no segmento, proporcionar a manutenção e o incremento de empregos com alta qualificação, fomentar a engenharia nacional mediante a concepção de projetos aeronáuticos nacionais e alavancar o aumento do produto interno bruto (PIB) e da renda do Brasil

Um algoritmo heurístico híbrido para minimizar os custos com a antecipação e o atraso da produção em ambientes com janelas de entrega e tempos de preparação dependentes da sequência.

Este trabalho de dissertação tem seu foco no problema de sequenciamento em uma máquina com penalidades por antecipação e atraso da produção. São considerados tempos de preparação da máquina dependentes da sequência de produção, bem como a existência de janelas de entrega distintas. Para resolução do problema, desenvolveu-se um algoritmo heurístico de três fases. A primeira fase baseada em GRASP e Descida em Vizinhança Variável para a geração da solução inicial, a segunda fase baseada em Busca Tabu para re namento da solução, e por m, a Reconexão por Caminhos como estratégia de pós-otimização, na terceira fase. Para cada sequência gerada pela heurística é utilizado um algoritmo de tempo polinomial para determinar a data ótima de início de processamento de cada tarefa. Os re- sultados computacionais mostraram que houve melhoria em relação a um algoritmo da literatura, tanto com relação à qualidade da solução nal quanto em relação ao desvio médio.This work deals with the single machine scheduling problem with earliness and tar- diness penalties. Sequence dependent setup times and distinct due windows are con- sidered. To solve this problem, a three-phase heuristic approach was developed. The rst phase is based on GRASP and Variable Neighborhood Descent to generate an initial solution; the second phase is based on a Tabu Search for solution re ning, and nally Path Relinking is used as a mechanism of post-optimization as a third pha- se. For each job sequence generated by the heuristic, an optimal timing algorithm is used to determine the completion time for each job in the job sequence. Computatio- nal experiments carried out show that previous algorithms found in related literature have been improved, regarding the quality of the nal solution and the average gap

Programa Bolsa Famí­lia e Descumprimento de Condicionalidades: O Ponto de Vista da Família

O artigo resulta de uma pesquisa que teve por objetivo compreender os fatores que concorrem para o descumprimento de condicionalidades por famí­lias beneficiárias do Programa Bolsa Família (PBF), do Munic­ípio de Belo Horizonte - MG. De natureza qualitativa, a pesquisa coletou depoimentos de 42 responsáveis por estas famí­lias. Como principal resultado ressalta-se que as famí­lias possuem conhecimento sobre as condicionalidades e avaliam positivamente a necessidade de cumpri-las. Contudo, são enfáticas quando apresentam argumentos que revelam que os fatores que mais concorrem para o seu não cumprimento são, de um lado, a recusa dos filhos em frequentar a escola, fato que se agrava quando atingem a adolescência e, do outro lado, a ausência de apoio por parte do poder público para superar esta situação. Decorre daí um dos maiores desafios do PBF no que diz respeito ao cumprimento das condicionalidades: a necessidade de qualificação das metodologias de acompanhamento social das famílias inseridas no Programa

AFS/FEF Student Technology Contest: Understanding the Role of Mo on К-Carbide Precipitation and Fracture of Lightweight Advanced High-Strength Steels

Fe-Mn-Al-C lightweight steels have great potential to replace Cr-Mo quenched and tempered steels where weight reduction is an important design variable. Previous research has centered around a fully austenitic cast composition of Fe-30Mn-9Al-0.9C-1Si-0.5Mo that achieves high strength through homogenous precipitation of κ-carbide during age hardening. However, the effect of varying Mo content and the corresponding effects on age hardening kinetics and resulting mechanical properties are not well documented. The current study investigates Mo additions in the range of 0-0.7% Mo on the microstructure, age hardening response, and toughness of a Fe-30Mn-9A-0.8C-1Si steel. Molybdenum was shown to decrease the age hardening response at 530 °C. Higher concentrations of Mo resulted in an increase in the Charpy V-notch impact toughness of aged specimens. Optical microscopy revealed that alloys with Mo additions had much less κ-carbide along grain boundaries in the aged condition and this decreased the propensity of intergranular fracture and increased toughness

A hybrid heuristic for a broad class of vehicle routing problems with heterogeneous ?eet

Abstract We consider a family of rich vehicle routing problems (RVRP) which have the particularitytocombineaheterogeneous?eetwithotherattributes,suchasbackhauls,multiple depots, split deliveries, site dependency, open routes, duration limits, and time windows. To ef?ciently solve these problems, we propose a hybrid metaheuristic which combines an iteratedlocalsearchwithvariableneighborhooddescent,forsolutionimprovement,andaset partitioning formulation, to exploit the memory of the past search. Moreover, we investigate aclassofcombinedneighborhoodswhichjointlymodifythesequencesofvisitsandperform eitherheuristicoroptimalreassignmentsofvehiclestoroutes.Tothebestofourknowledge, this is the ?rst uni?ed approach for a large class of heterogeneous ?eet RVRPs, capabl

Understanding the Role of Inclusions on the Dynamic Fracture Toughness of High Strength Lightweight FeMnAl Steels

High manganese lightweight steel alloys in the Fe-Mn-Al-C system are promising alternatives to quenched and tempered Cr and Mo steels for transportation and military applications. The understanding of nonmetallic inclusion formation and their effect on the mechanical properties is of extreme importance for further alloy development. Sharp and brittle AlN forms prior to the liquidus and has been shown to decrease notch toughness. Controlled additions of sulfur may promote soft and globular MnS that precipitates around AlN during solidification, thus mitigating their detrimental effect. The effect of controlled sulfur additions from 0.004 to 0.042%S was studied in a Fe-30%Mn-9%Al-1%Si-(0.9-1.2)%C-0.5%Mo steel. The main inclusions observed were AlN, MnS, and AlN-cored MnS. Charpy impact toughness was evaluated in the solution treated condition and in specimens aged to 329-340 HBN. Toughness is a function of the overall inclusion population. In aged specimens, same was true only for steels with 0.9% carbon; above 1%C the toughness was below 15 J for any sulfur content

Solving last-mile distribution problems after major earthquakes

International audienc