Department of Mechanical Engineering

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We report an experimental study of evaporation due to controlled infrared (IR) heating from above from an initially saturated confined porous medium consisting of nearly ‘mono-disperse’ particles which has been rarely used earlier. We have used three diagnostic tools simultaneously, evaporation rate measurements using a precision weighing balance, surface temperature measurements using IR imaging, and fluorescein dye mixed with water to visualize the drying front and the evaporation sites. IR images show that the first stage, so-called constant rate period (CRP), was maintained due to films of water reaching the top surface from the saturated region below. Gradually reducing evaporation rate in stage 1 is shown to be related to ‘shrinking evaporating patches’ on the top surface, clearly revealed as lower-temperature regions in the IR images. End of CRP coincides with disappearance of the low-temperature patches. We give end of CRP in terms of the average depth (Lcap) of the liquid level from the top surface at that time. Lcap and duration of CRP are strong functions of the porous medium bead size, transition to stage 2 happening earlier for coarser spheres. The obtained Lcap values deviated from the predictions of Lehmann et al. (Phys Rev E 77(5):056309, 2008) which we show is due to a small range of pore sizes in the current experiments. For both water and highly volatile n-pentane, we show that Lcap normalized by a length scale derived from gravity-surface tension force balance goes like Bo0.20, for Bo varying from 2.0E − 04 to 1.0E − 01; Bo is the Bond number. Fluorescein dye imaging shows a different view of the evaporation stages. During CRP, highly concentrated deposits of the fluorescein dye particles, orange in colour, are seen in the top few bead layers. These orange deposits represent the sites on the beads surfaces where the evaporation has taken place. Even with external heating, evaporation from such a porous medium is limited to a finite depth from the evaporating end, similar to the observation by Lehmann et al. (2008) for isothermal evaporation in Hele-Shaw cell. © 2018, Springer Nature B.V.

World University root node

Transport in Porous Media

Evaporation From Confined Porous Media Due to Controlled IR Heating From Above

Kinematic Identification of TAL-BRABO Robot using Vision

Micro-milling has shown great potential in producing complex miniaturized components over wide range of materials. It can also fabricate micro-products in small batches efficiently and economically. In spite of these advantages, several challenges hinder its ability to produce components with better dimensional accuracy. Among several factors, tool deflection is one of the major sources of surface error on machined parts and features. Therefore, it is necessary to develop accurate and reliable process models to analyze and improve performance of the process. This study presents a methodology to determine cutting forces and surface error in the presence of tool deflections for micro-milling operation. Tool deflections have considerable influence on instantaneous uncut chip thickness. As tool deflection alters tooth trajectories and instantaneous uncut chip thickness, the rigid cutting force model needs to be modified suitably to consider the effect of deflections. This aspect has been incorporated in the model by modifying tool center location and tooth trajectories iteratively. The convergence of an iterative algorithm determining stable chip thickness is obtained by comparing RMS deviation of average chip thickness between two successive tooth passes. The axial variation of surface error due to tool deflections is estimated using surface generation mechanism. The proposed model is implemented in the form of a computational program to predict cutting force and surface error. The results of computational model are substantiated further by conducting machining experiments. It is shown that the proposed model predicts cutting forces fairly well in the presence of tool deflections. A comparison between predicted variation of surface error and 3D images of machined surface captured using optical microscope showed good qualitative agreement in the error profiles. © 2018, Springer-Verlag London Ltd., part of Springer Nature.

International Journal of Advanced Manufacturing Technology

Modeling of cutting force, tool deflection, and surface error in micro-milling operation

Polyether ether ketone (PEEK), a thermoplastic polymer with remarkable mechanical properties apart from being bio-inert and approved by Food and Drug Administration- U S (FDA), is a promising bio-material at load bearing sites such as bone implants. The major challenge in PEEK associated bio composites is its process ability. Several ways have been attempted in past and finally resolved the issue by inkjet binder customized technique and Selective Laser Sintering for PEEK composite. An alternate method is presented in this work with ingenious process ability of PEEK, a polymer replacement for bone Collagen and Hydroxyapatites, the bone reinforcement prepared from egg shells. The alternate way suggested in this work is economically attractive without significant compromise in quality of the composite prepared. © 2018 Trans Tech Publications, Switzerland.

Materials Science Forum

PEEK composite scaffold preparation for load bearing bone implants

The research work explores the microstructure evolution and creeps rupture behavior of the shielded metal arc welded joint of reduced activation ferritic/martensitic P91 steel plate in the as-welded and different states of post weld heat treatment (PWHT). Two types of heat treatments were employed including (i) post weld heat treatment (PWHT) at 760 °C for 2 h and finally air cooled and (ii) re-austenitizing at 1040 °C for 60 min and air-cooled and tempered at 760 °C for 2 h, followed by air cooling (PWNT). The P91 steel plates were received in the cast and forged condition having fully tempered lath martensite with lath blocks, packet boundaries and prior austenite grain boundaries (PAGBs). In this research, microstructural evolution at fracture frontier of crept P91 weld sample, creep rupture life and effect of creep exposure time on microstructure evolution in the fine-grained heat affected zone (FGHAZ) were studied. The results show a dominating effect of PWNT treatment on fracture behavior and creep rupture life of the P91 welded joints. PWNT treatment results in negligible hardness variation across the transverse section of the weld joint. The creep rupture life of PWNT specimen was 594.895% higher as compared to that of PWHT specimen and 142.7% higher than that of the as-welded specimen for the similar condition of creep exposure (620 °C/150 MPa). In PWHT condition, the most common type IV cracking was observed. However, it was eliminated in PWNT specimens and fracture occurred form the base zone. The fracture frontier of crept PWNT specimen showed a higher amount of creep cavities that can be attributed to the formation of Laves phase. © 2018 Elsevier B.V.

Materials Science and Engineering A

Effect of post weld heat treatments on fracture frontier and type IV cracking nature of the crept P91 welded sample

In this study an attempt is made to generate the microstructure of short fibre composites through representative volume element (RVE) approach and then analyzed using mathematical theory of homogenization with periodic boundary conditions to estimate the homogenized or effective material properties. An algorithm, based on random sequential adsorption technique (RSA), has been developed to generate the RVE for such materials. The goal of the present study is to demonstrate the methodology to generate RVEs which are effective in predicting the stiffness of the short fibre composites with repetitiveness. For this purpose, RVEs for four different scenarios of fibre orientations have been developed using this technique. These four different scenarios are: Fibres are aligned in a direction; fibres are oriented randomly in one plane; fibres are randomly oriented in one plane and partially random oriented in other plane and finally, fibres are completely random oriented. For each case three to four different fibre volume fractions are studied with five different RVEs for each volume fraction. These four cases presented different material behaviour at macroscale due to random location and orientation of fibres. The effective properties obtained from numerical technique are compared with popular non RVE methods like Halpin–Tsai and Mori–Tanaka methods for the case where fibres are aligned in a direction and were found to be in good agreement. The variation in the predicted properties for a given volume fraction of any of the four cases studied is less than 1%, which indicates the efficacy of the algorithm developed for RVE generations in repetitiveness of predicted effective properties. The four cases studied showed gradual change in macroscopic behaviour from transversely isotropic, with respect to a plane, to a nearly isotropic nature. © 2017 Elsevier Ltd

Fulltext

International Journal of Solids and Structures

Development of an RVE and its stiffness predictions based on mathematical homogenization theory for short fibre composites

We mimic a flapping wing through a fluid-structure interaction (FSI) framework based upon a generalized lumped-torsional flexibility model. The developed fluid and structural solvers together determine the aerodynamic forces, wing deformation and self-propelled motion. A phenomenological solution to the linear single-spring structural dynamics equation is established to help offer insight and validate the computations under the limit of small deformation. The cruising velocity and power requirements are evaluated by varying the flapping Reynolds number (20 ≤ Ref ≤ 100), stiffness (represented by frequency ratio, 1 ≲ w∗ ≤ 10) and the ratio of aerodynamic to structural inertia forces (represented by a dimensionless parameter Ψ (0.1 ≤ Ψ ≤ 3). For structural inertia dominated flows (Ψ ≤ 3), pitching and plunging are shown to always remain in phase (φ ≈ 0) with the maximum wing deformation occurring at the end of the stroke. When aerodynamics dominates (Ψ &gt; 1), a large phase difference is induced (φ ≈ π/2) and the maximum deformation occurs at mid-stroke. Lattice Boltzmann simulations show that there is an optimal w∗ at which cruising velocity is maximized and the location of optimum shifts away from unit frequency ratio (w∗ = 1) as Ψincreases. Furthermore, aerodynamics administered deformations exhibit better performance than those governed by structural inertia, quantified in terms of distance travelled per unit work input. Closer examination reveals that although maximum thrust transpires at unit frequency ratio, it is not transformed into the highest cruising velocity. Rather, the maximum velocity occurs at the condition when the relative tip displacemen. © 2018 Cambridge University Press.

Journal of Fluid Mechanics

Analysis of passive flexion in propelling a plunging plate using a torsion spring model

In recent years, integration of electric vehicles (EVs) has increased dramatically due to their lower carbon emissions and reduced fossil fuel dependency. However, charging EVs could have significant impacts on the electrical grid. One promising method for mitigating these impacts is the use of renewable energy systems. Renewable energy systems can also be useful for charging EVs where there is no local grid. This paper proposes a new strategy for designing a renewable energy charging station consisting of wind turbines, a photovoltaic system, and an energy storage system to avoid the use of diesel generators in remote communities. The objective function is considered to be the minimization of the total net present cost, including energy production, components setup, and financial viability. The proposed approach, using stochastic modeling, can also guarantee profitable operation of EVs and reasonable effects on renewable energy sizing, narrowing the gap between real-life daily operation patterns and the design stage. The proposed strategy should enhance the efficiency of conventional EV charging stations. The key point of this study is the efficient use of excess electricity. The infrastructure of the charging station is optimized and modeled. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.

Energies

A robust optimization for designing a charging station based on solar and wind energy for electric vehicles of a smart home in small villages

The effect of conventional normalizing and tempering (CNT) and double austenitization-based normalizing and tempering (DNT) heat treatments on the microstructure evolution and mechanical properties of creep strength-enhanced ferritic P91 steel were studied. CNT treatment was performed at 1,050°C and air cooled for 1 h and also at 760°C and air cooled for 2 h. In double austenitization- based normalizing heat treatment, steel was austenitized at 1,050°C and air cooled for 1 h and then normalized in a temperature range of 950°C -1,150°C for 1 h followed by water quenching. After the double normalizing, tempering is performed at 760°C for 2 h. A DNT treatment resulted in homogeneous microstructure formation that led to improved mechanical properties as compared to CNT treatment. The incomplete dissolution of precipitates in single-stage tempering resulted in incomplete martensitic structure formation. © 2018 by ASTM International.

Materials Performance and Characterization

Grain refinement of P91 steel using double austenitization treatment

P92 steels have been developed as a candidate material for power plant components that operate in a temperature range of 620o-650°C. A heterogeneous microstructure formation across the P92 weldments makes the wettability of P92 steel a serious issue. The other problem that arises in P92 steel weldments is the formation of δ-ferrite due to the presence of a higher weight percentage of ferrite stabilizers such as V and Nb. as well as W and Mo. In the present work, the shielded metal arc welding (SMAW) process was utilized to prepare the P92 steel weld joints. After welding, postweld heat treatment (PWHT) was performed at 760°C for 2 h. To characterize the weld joints, room-temperature tensile tests and microhardness measurements were performed in the as-welded and PWHT conditions. The subsequent PWHT resulted in a decrease in the hardness gradient across the weldments. The PWHT resulted in enhancing the : ductility of the weld joints. © 2018 American Welding Society. All rights reserved.

Welding Journal

Characterization of P92 Steel weldments in as-welded and PWHT conditions: Room-temperature tensile tests and microhardness measurements led to improving the ductility of the weld joints