Evidence of Martensitic Transformation in Fe-Mn-Al Steel Similar to Maraging Steel

The Fe-Mn-Al steels claim a low density, and some fall into the category of transformation-induced plasticity (TRIP) steel. In Fe-Mn-Al TRIP steel development, phase transformations play an important role. Herein, the martensitic transformation of an Fe-16.7 Mn-3.4 Al ternary alloy (wt pct) was experimentally discovered, whose equilibrium phases are a single phase of austenite at 1373 K and dual phases of ferrite and austenite at low temperature. Ferritic lath martensite forms in the prior austenite grains after cooling from 1373 K under various cooling rates via quenching, air cooling, and furnace cooling. The formation mechanism of the ferritic lath martensite is different from that of traditional ferritic lath martensite in steel and quite similar to that in maraging steel. A slight strain energy coupled with a small temperature gradient can lead to the formation of ferritic lath martensite in the Fe-Mn-Al alloy after cooling from high temperature. It is also found that micro-twins exist in the ferritic lath martensite.

Estudio de la evolución de flujos termocapilares inducidos con un laser IR en películas delgadas de agua para la manipulación de micro-objetos

Estudio de la evolución de flujos termocapilares inducidos con un laser IR en películas delgadas de agua para la manipulación de micro-objetos Evolution study of laser-induced thermocapillary flows for manipulation of micro-objects Johan E. Quispe y Emir Vela Departamento de Ingeniería Mecánica, Universidad de Ingeniería y tecnología - UTEC, Jr. Medrano Silva esquina con Av. Miguel Grau, Barranco DOI: https://doi.org/10.33017/RevECIPeru2015.0002/ Resumen En la actualidad, la micromanipulación ha adquirido un papel importante en el ensamblaje de microcomponentes electromecánicos, ya que hace posible manipular objetos a escala micrométrica de diferentes propiedades y formas geométricas para posteriormente realizar un ensamblado y así crear sistemas cada vez más multifuncionales. Igualmente, el campo de la medicina ha alcanzado grandes avances ya que la micromanipulación nos permite manipular células, moléculas y bio-partículas en general, para realizar estudios más profundos en lo que respecta al comportamiento de éstas. Así, se requiere de un método de micromanipulación que sea capaz de desplazar micro-objetos biológicos como componentes de una manera rápida, precisa y múltiple que permita un estudio o producción a gran escala. Los métodos preferidos a la escala micrométrica son los métodos de manipulación sin contacto, ya que éstos permiten la manipulación sin dañar y contaminar las muestras u objetos. Dentro de éstos, la utilización de microfluidos para desplazar objetos es de gran interés en la comunidad científica ya que los fluidos permiten arrastrar a los objetos según la dirección y velocidad del fluido, lo que produce una fuerza que desplaza a los micro-objetos. En este trabajo de investigación se presenta un estudio, a través de simulaciones, de la generación de flujos termocapilares en películas delgadas de un líquido como método de manipulación sin contacto. Este método se está volviendo una opción viable para desplazar objetos a esta escala debido a su alta dinámica que permite desplazar objetos a gran velocidad, y además utilizando un bajo consumo de energía para su generación. Este método consiste en establecer un pequeño gradiente de temperatura en la interface líquido-aire de una película delgada, el cual genera flujos toroidales, centrados en el foco caliente, que hacen posible el desplazamiento de los objetos en el interior del fluido, a través de una fuerza de arrastre que se establece. Este estudio nos permitió comprender cómo es la evolución temporal del flujo y cómo poder generarlos de manera controlada para lograr estrategias de manipulación eficientes y precisas. Se obtuvieron valores de velocidad del flujo del orden de para un haz laser infrarojo que genera aproximadamente 80 mW sobre la muestra. Además, existe una distancia radial con respecto al foco caliente donde sería más conveniente ubicar los objetos para manipularlos debido al perfil de velocidades que se establecen. También se demostró a través de las simulaciones que es posible establecer un tamaño de espesor de fluido para manipular objetos de un determinado tamaño. Descriptores: micromanipulación, flujo termocapilar, tensión superficial Abstract Nowadays, micromanipulation has an important role for assembly of micro-electromechanical components, because it enables to assemble very small components with different material properties and geometrical shapes in order to create complex multifunctional systems. Also, micromanipulation has contributed significantly in the field of medicine enabling manipulation of cells, molecules and bio-particles to study their behavior. Thus, a micromanipulation method that could move biological objects and microcomponents in an accurate, fast and multiple manner is needed. The preferred methods in the microscale are non-contact methods because they allow manipulating objects without damage or contamination. In this scope, microflows are very good candidates to drag micro-objects according to the flows direction and velocity, producing a drag force over the objects. In this research work, a study, through multiphysics simulations, on the thermocapillary flows generation within thin liquid layers is presented as a non-contact manipulation method. The high flows dynamics can move objects at high speed. This method consists of imaparting a very small temperature gradient at the liquid-air interface of a thin liquid layer, thus generating toroidal-shaped flows centered at the hot spot. So the objects inside the flows are dragged. This study allowed us to understand the temporal evolution of flows and how they could be generated in a controlled manner. Besides, it exists a radial distance with respect to the hot spot where is most suitable to place the objects to manipulate them at high speed due to the velocity profile. Flows speeds in the order of were obtained using an infrared laser of about 80 mW. Simulations results showed that it is possible to establish a liquid depth in order to manipulate objects with specific sizes. As a result, manipulation strategies are being carried out to accurately move objects at high speeds. Keywords: micromanipulation, thermocapillary flows, surface tension.

Energy Harvesting under Large Temperature Gradient – Comparison of Silicides, Half-Heusler Alloys and Ceramics

This paper reports about a new four-step analysis method for thermoelectric (TE) materials. While the Seebeck coefficient is usually measured under small temperature gradient, we report here the measurement of TE materials under large temperature gradient. The examined materials were Ag- and Bi-doped Mg

ON MODELS FOR VISCOELASTIC MATERIALS THAT ARE MECHANICALLY INCOMPRESSIBLE AND THERMALLY COMPRESSIBLE OR EXPANSIBLE AND THEIR OBERBECK–BOUSSINESQ TYPE APPROXIMATIONS

Viscoelastic fluid like materials that are mechanically incompressible but are compressible or expansible with respect to thermal stimuli are of interest in various applications ranging from geophysics and polymer processing to glass manufacturing. Here we develop a thermodynamical framework for the modeling of such materials. First we illustrate the basic ideas in the simpler case of a viscous fluid, and after that we use the notion of natural configuration and the concept of the maximization of the entropy production, and we develop a model for a Maxwell type viscoelastic fluid that is mechanically incompressible and thermally expansible or compressible. An important approximation in fluid mechanics that is frequently used in modeling buoyancy driven flows is the Oberbeck–Boussinesq approximation. Originally, the approximation was used for studying the flows of viscous fluids in thin layers subject to a small temperature gradient. However, the approximation has been used almost without any justification even for flows of non-Newtonian fluids induced by strong temperature gradients in thick layers. Having a full system of the governing equations for a Maxwell type viscoelastic mechanically incompressible and thermally expansible or compressible fluid, we investigate the validity of the Oberbeck–Boussinesq type approximation for flows of this type of fluids. It turns out that the Oberbeck–Boussinesq type approximation is in general not a good approximation, in particular if one considers "high Rayleigh number" flows. This indicates that the Oberbeck–Boussinesq type approximation should not be used routinely for all buoyancy driven flows, and its validity should be thoroughly examined before it is used as a mathematical model.

Safety and Durability Pavement in Super Long Tunnel

In order to solve the problem of design and construction of pavement structure in the long tunnel, through the analysis of pavement using domestic and overseas, combined with the factors of primary carrying capacity, small temperature gradient in the long tunnel, the Continuously Reinforced Concrete Pavement(CRCP) is proposed, which has characteristics of better durability, strong structure integrity and comfortable driving. Mini excavator auxiliary framing construction, layered pouring concrete, lap joint construction of welded steel have solved a series of problems of the relatively small space of construction, the lower concrete vibrators affected by the steel mesh and reinforced scene lashing. So continuously reinforced concrete pavement using welded steel fabric can be used as a major road structure in long tunnel.