Study of the nanometric grain size distribution in iron compacts obtained by mechanical milling

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Critical strain for dynamic recrystallisation. The particular case of steel

The knowledge of the flow behavior of metallic alloys subjected to hot forming operations has particular interest for metallurgists in the practice of industrial forming processes involving high temperatures (e.g., rolling, forging, and/or extrusion operations). Dynamic recrystallisation (DRX) occurs during high temperature forming over a wide range of metals and alloys, and it is known to be a powerful tool that can be used to control the microstructure and mechanical properties. Therefore, it is important to know, particularly in low stacking fault energy materials, the precise time at which DRX is available to act. Under a constant strain rate condition, and for a given temperature, such a time is defined as a critical strain (ec). Unfortunately, this critical value is not always directly measurable on the flow curve; as a result, different methods have been developed to derive it. Focused on carbon and microalloyed steels subjected to laboratory-scale testing, in the present work, the state of art on the critical strain for the initiation of DRX is reviewed and summarized. A review of the different methods and expressions for assessing the critical strain is also included. The collected data are well suited to feeding constitutive models and computational codes.Peer ReviewedPostprint (published version

A new device for determining the compression after impact strength in thin laminates

In this work a new device has been developed to estimate compression-after-impact (CAI) strength. This device allows the testing of laminates thinner than those recommended by CAI test standards. The proposed device is composed of a support structure, with a set of vertical ribs that stabilize the specimen during the test, increasing the buckling load. A numerical analysis was made to ensure that global buckling does not occur in the laminate during the CAI test, and that there is no interference with the damage area. Laminate specimens were tested with the proposed device and the ASTM device. For specimens 4.416 mm thick (thickness according to ASTM D7137 standard), the test results were similar with both devices. For thinner laminates, higher CAI strength was estimated with the proposed device than with the ASTM device, showing that the global buckling was delayed.The authors are indebted to the Foundation for Research, Development and Application of Composite Materials (FIDAMC) and Innovation Works (EADS) for the financial support of this work (project Ilia). Also, the authors acknowledge the collaboration of the mechanical laboratories in FIDAMC and in Department of Continuum Mechanics and Structural Analysis of University Carlos III of Madrid.Publicad

Life Cycle Assessment in Higher Education: Design and Implementation of a Teaching Sequence Activity

The latest studies show that to achieve the Sustainable Development Goals on education, there must be a focus on adequately training higher education students. In this work, we present a study about the Life Cycle Analysis of knowledge of products and processes of engineering students. This aspect is very relevant in engineering education since it has direct implications on sustainability. The first step was to identify what the learning problems were, and taking them into account, a specific teaching sequence was designed and implemented over three academic years. Two activities, on an increasing level of complexity, of the application of Life Cycle Assessment are shown in this paper. The first one is the Life Cycle Analysis comparison between two steel and polypropylene pieces. The second one is the Life Cycle Analysis comparison between three different ends of life of a polypropylene piece: mechanical recycling, incineration, and landfill. Data on the evolution of students’ marks while solving a “one step more difficult project” throughout these courses have been collected. The results show a generalized learning by the students about Life Cycle Analysis

Effect of thermal treatment on the interfacial shear toughness of an aluminium composite laminate

The microstructure and mechanical properties in the interface region of a multilayer composite laminate based on Al-Zn (Al 7075) and Al-Cu (Al 2024) alloys have been mainly characterized by EBSD and shear tests. It is shown that varying solution heat treatments affect the microstructure of the constituent aluminium alloys in the bonding region and, as a consequence, the interfacial mechanical properties. The increase in the solution treatment time improves the interfacial toughness of the multilayer aluminium laminate due to higher intrinsic toughness of the constituent aluminium alloys.Financial support from CICYT (Project MAT2003-01172 and MAT2006-11202) is gratefully acknowledged. C.M. Cepeda-Jiménez thanks the Spanish National Research Council (CSIC) for a I3P contract. We also thank F.F. González-Rodríguez for assistance during hot rolling. Finally, an especial mention in memory of P.J. González-Aparicio for his help and assistance with electron microscopy during all these years is made.Peer reviewe

Effects on nodular extracts of Alnus glutinosa (l.) Gaertn. on ammonification, nitrification and CO2 production in different soils

The effect of root nodule extracts from European alder (Alnus glutinosa [L.] Gaertn.) on the rates of amrnonification, nitrification and C02 production was evaluated in three soils of different physico-chemical characteristics. The extracts decreased net ammonification rate (up to a 43% respect to water control), probably because of an increase of immobilization rather than an effect of a speciffc inhibitor. The rate of nitrification was increased by the extracts (up to 40% from water control) because of the ammonium present in the extracts. An increase in C02 production showed that the nodule extracts stimulate microbial activity. This depended not only on the amount of organic matter introduced by the extracts but also to some activator of microflora.Se evalúa el efecto de extractos nodulares del aliso europeo (Alnus glutinosa [L.] Gaertn.) sobre las tasas de amonificación, nitrificación y producción de C02 en tres suelos de características físico-químicas diferentes. Los extractos reducen la tasa de amonificación (un 43% menor que en el control con agua), probablemente debida a un aumento de la inmovilización más que a un inhibidor especifico. La tasa de nitrificación crece por efecto de los extractos (un 40% respecto al control con agua) a consecuencia del amonio presente en éstos. El incremento de la producción de C02 muestra que los extractos estimulan la actividad microbiana. Esto no parece depender sólo del aporte extra de materia orgánica por los extractos, sino por algún activador especifico

Effects of nodular extracts of Alnus glutinosa (L.) Gaertn. on nitrogen fixation (Acetylene reduction assay) and denitrification in different soils

European alder (Alnus glutinosa [L.] Gaertn) nodules were maintained under conditions that allow their exudation (water stress). The effect of this nodular extracts colected on free nitrogen fixation (acetylene reduction assay [ARA]) and denitrification, was evaluated in three soils of significativelydifferent physico-chemicalcharacteristics. The comparisons with controls having different concentrations of glucose as carbon source suggest that, in the assayed conditions, the nodular european alder extracts activate ARA (up to 9.97% respect water control) and produces a partial inhibition of denitrification. The effects do not seem to be due neither to organic carbon nor to nitrate, but rather to specific activator(s) and inhibitor(s) of the processes considered.Nódulos radicales de aliso europeo [Alnusglutinosa (L.)Gaertn.] fueron mantenidos en condiciones que optimizan el proceso de exudación (estrés hídrico). Se evaluó el efecto de dichos extractos sobre la fijación libre de nitrógeno (ARA) y desnitrificación en tres suelos con diferencias significativas en sus características físico-químicas. Las comparaciones con diferentes controles, muestran que los extractos activan (en un 9.97%) el ARA y promueven una inhibición parcial de la desnitrificación. Los efectos no parecen causados por el aporte de carbono orgánico o de nitrato por parte de los exudados, sino por algún activador o inhibidor especifico de los procesos considerados

Aproximación al control de la microestructura de dos aceros microaleados con contenido medio de carbono en condiciones de conformado en caliente

El objetivo principal de este trabajo es estudiar el comportamiento a fluencia de dos aceros microaleados de contenido medio de carbono, en condiciones de conformado en caliente analizando su evolución microstructural a través de la dependencia del tamaño de grano recristalizado (Drec) con el parámetro de Zener-Hollomon, Z. Se observó que esta dependencia muestra un comportamiento bimodal asociado a la transición entre la recristalización dinámica cíclica y de pico simple. También, se ha observado que la variación del Drec normalizado por el vector de Burgers (b) con la tensión de estado estable sss a su vez normalizada por el modulo de cizalladura (m) exhibe el mismo comportamiento bimodal arriba mencionado. Debido a la complejidad de los dos aceros estudiados, el tamaño de grano recristalizado no se ajusta a la ecuación universal de Derby. Para explicar este comportamiento cabe pensar en el efecto de los precipitados y de la microestructura inicial sobre el tamaño de grano recristalizado. The main aim of the present investigation was to study the flow behaviour of two medium carbon microalloyed steels under hot forming conditions, and to analyse their microstructural evolution. The dependence of recrystallized grain size (Drec) on the Zener-Hollomon parameter Z shows a bimodal behaviour with transition from single to cyclic dynamic recrystallization. We also observed that the variation of Drec normalized by the Burgers vector (b) with the steady state stress sss normalized by shear modulus (m) shows the same bimodal behaviour cited above. The Derby’s universal equation reported in the literature for recrystallized grain sizes was not followed; it seems that the presence of fine precipitated particles has a clear effect on this disagreementPeer ReviewedPostprint (published version