Mechanical Engineering

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Performance of a production system depends on breakdown-free operation of equipment and processes. Maintenance and quality control play an important role in achieving this goal. This paper presents an integrated model for joint optimization of preventive maintenance and quality control policy with cumulative sum (CUSUM) control chart parameters. Two types of maintenance policies are considered, namely minimal corrective maintenance and imperfect preventive maintenance. The proposed model enables the determination of the optimal value of each of the five decision variables, i.e. sample size (n), sample interval (h), the reference value (K), the decision interval (h1) and preventive maintenance interval (tPM), that minimize the expected total system cost per unit time. A numerical example is presented to demonstrate the effect of the cost parameters on the integrated design of preventive maintenance and quality control policy. It also compares the system performance employing the proposed integrated approach with that obtained by considering maintenance and CUSUM chart independently. Substantial economic benefit of 19 \% is seen in the joint optimization. © 2015, Springer-Verlag London.

(SoE) School of Engineering

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International Journal of Advanced Manufacturing Technology

Integrated design of preventive maintenance and quality control policy parameters with CUSUM chart

Orthotropic composite materials exhibits higher specific strength and stiffness; hence extensively used in various industrial and engineering applications such as aerospace, armored and automobile etc. During their service life, these critical engineering components are subjected to thermo-elastic loads. These loading conditions generate local thermal stress concentration near the crack/voids present in the structures, which leads to sudden failure of engineering components. Therefore, the study of crack tip stress field under thermo-elastic loading becomes very important to understand the effect of lamina orientation on the strength of orthotropic composite components. The presented work deals with XFEM formulation and implementation to simulate 3-D orthotropic fracture problems under thermo-elastic loading environment. In XFEM based formulation, meshed topology does not exhibit any geometrical discontinuity. All desired discontinuity can be captured by enriching primary variable approximations by additional mathematical functions (Heaviside and crack front enrichment functions). These enrichment functions are derived from theoretical background of the problem under consideration. The crack surface element enriched by Heaviside function whereas, crack front elements treated by orthotropic crack front asymptotic functions. Mixed mode stress intensity factors are computed by domain based interaction integral approach. Few example of 3-D orthotropic thermo-elastic crack problem is presented to illustrate the effectiveness and robustness of proposed method. © 2015 AIP Publishing LLC.

AIP Conference Proceedings

Thermo-elastic failure simulation of 3-D orthotropic composites by XFEM

Slurry erosion is a complex process with number of interacting variables (operating and material parameters). We study the interaction between erodent concentration and impingement angle using experimental and computational fluid dynamics (CFD) techniques. Experiments were performed using a high velocity slurry erosion test rig at a constant velocity with dilute slurries of water and sand particles. Concentration of sand in water was varied from 0.01wt% (100ppm) to 0.5wt% (5000ppm) at three sample orientations (30°, 60° and 90°). Six different targets, three bulk materials (aluminum, cast iron, and stainless steel) and three thermal sprayed coatings (Ni+20, 40, and 60wt% of Al2O3) were used for slurry erosion tests. Experimental results showed a significant interaction between erodent concentration and impingement angle. The concentration variation showed larger influence on erosion rate for sample held normal to the slurry jet compared to glancing angle. The degree of interaction was different for different materials. CFD simulations showed higher particle-to-particle interactions for sample at glancing angle compared to that at normal angle. This probably explains the low contribution of concentration variation at glancing angle compared to the normal angle. Further, the effect of concentration on erosion rates was also influenced by the restitution coefficient (function of material and impact parameters). For a high restitution coefficient materials, the change in slurry concentration showed minimum effect on erosion rate compared with low restitution coefficient materials. © 2015 Elsevier B.V.

Wear

Interplay between erodent concentration and impingement angle for erosion in dilute water-sand flows

Slurry erosion is a degrading phenomenon usually observed in machineries dealing with particle-laden fluid such as hydro power plants, ship propellers, pump impellers, valves, and connecting pipes. The low erosion resistance of commonly employed structural materials prompts the use of different surface modification techniques. Among several types of surface modification techniques, thermal spraying has achieved a significant recognition worldwide due to its versatile nature. In this chapter, slurry erosion behavior of thermal sprayed coatings has been discussed with special emphasis on the contribution of different coating related parameter. It has been observed that microstructure play an important role in determining the slurry erosion performance of thermal spray coatings. Different microstructural features such as splat boundaries, pores, un-melted particles, and cracks are detrimental for the thermal spray coatings exposed to erosive environment. A parameter useful for identification of primary erosion mechanism for thermal sprayed coatings is also discussed. © 2015, IGI Global. All rights reserved.

Thermal Sprayed Coatings and their Tribological Performances

Slurry erosion behavior of thermal spray coatings

Sun is a great source of energy. Solar Energy is non-polluting and one of the most efficient and affordable energy alternatives available today. Solar energy can be utilised in two ways either in the form of thermal energy or electrical energy using photovoltaic (PV). The conversion efficiency of photovoltaic depends upon its operating temperature. The operating temperature of photovoltaic module is maintained as low as possible by withdrawing/utilizing the thermal energy associated with it. The thermal energy available on the PV module can be carried away by flowing any fluid (water, air etc.) above it. This type of system is known as hybrid photovoltaic thermal (PVT) system. In the present study, the analytical expressions for temperature dependent electrical efficiency have been derived for opaque and semitransparent PV module with water flow. Then comparison between efficiencies have been done for different climatic condition of New Delhi, India. Then it is observed that there is remarkable change in efficiency when water is flow on the top of the surface of PV module. © 2015 IEEE.

International Conference on Energy Economics and Environment - 1st IEEE Uttar Pradesh Section Conference, UPCON-ICEEE 2015

Effect of water flow on PV module: A case study

This work aims at asymptotically accurate dimensional reduction of non-linear multi-functional film-fabric laminates having specific application in design of envelopes for High Altitude Airships (HAA). The film-fabric laminate for airship envelope consists of a woven fabric core coated with thin films on each face. These films provide UV protection and Helium leakage prevention, while the core provides required structural strength. This problem is both geometrically and materially non-linear. To incorporate the geometric non-linearity, generalized warping functions are used and finite deformations are allowed. The material non-linearity is handled by using hyper-elastic material models for each layer. The development begins with three-dimensional (3-D) nonlinear elasticity and mathematically splits the analysis into a one-dimensional through-the-thickness analysis and a two-dimensional (2-D) plate analysis. The through-the-thickness analysis provides the 2-D constitutive law which is then given as an input to the 2-D reference surface analysis. The dimensional reduction is carried out using Variational Asymptotic Method (VAM) for moderate strains and very small thickness-to-wavelength ratio. It features the identification and utilization of additional small parameters such as ratio of thicknesses and stiffness coefficients of core and films. Closed form analytical expressions for warping functions and 2-D constitutive law of the film-fabric laminate are obtained. © 2015 AIP Publishing LLC.

VAM applied to dimensional reduction of nonlinear multifunctional film-fabric laminates

Asymptotically-accurate dimensional reduction from three to two dimensions and recovery of 3-D displacement field of non-prestretched dielectric hyperelastic membranes are carried out using the Variational Asymptotic Method (VAM) with moderate strains and very small ratio of the membrane thickness to its shortest wavelength of the deformation along the plate reference surface chosen as the small parameters for asymptotic expansion. Present work incorporates large deformations (displacements and rotations), material nonlinearity (hyperelasticity), and electrical effects. It begins with 3-D nonlinear electro-elastic energy and mathematically splits the analysis into a one-dimensional (1-D) through-the-thickness analysis and a 2-D nonlinear plate analysis. Major contribution of this paper is a comprehensive nonlinear through-the-thickness analysis which provides a 2-D energy asymptotically equivalent of the 3-D energy, a 2-D constitutive relation between the 2-D generalized strain and stress tensors for the plate analysis and a set of recovery relations to express the 3-D displacement field. Analytical expressions are derived for warping functions and stiffness coefficients. This is the first attempt to integrate an analytical work on asymptotically-accurate nonlinear electro-elastic constitutive relation for compressible dielectric hyperelastic model with a generalized finite element analysis of plates to provide 3-D displacement fields using VAM. A unified software package 'VAMNLM' (Variational Asymptotic Method applied to Non-Linear Material models) was developed to carry out 1-D non-linear analysis (analytical), 2-D non-linear finite element analysis and 3-D recovery analysis. The applicability of the current theory is demonstrated through an actuation test case, for which distribution of 3-D displacements are provided. © 2014 Elsevier Ltd. All rights reserved.

International Journal of Engineering Science

Dielectric elastomers: Asymptotically-correct three-dimensional displacement field

Superhydrophobicity facilitates the development of self-cleaning, anti-biofouling, and anti-corrosion surfaces. The leaves of the lotus (Nelumbo nucifera) and taro (Colocasia esculenta) plants are well known for their self-cleaning properties. A hierarchical structure comprising papillae epidermal cells superimposed with epicuticular wax crystalloids of varying shapes, sizes, and orientations is an important aspect of the surface of these plant leaves. We fabricated two types of hierarchical structures biomimicking the surface topography of the lotus leaf. The hierarchical patterns successfully demonstrated the superhydrophobic state in comparison with nano and micro patterns. We used the finite element method (FEM) to simulate and understand the wetting process. The FEM simulations showed good correlation with the experimental results. FEM was helpful in understanding the wetting of enormously complex biological surfaces with relative ease, and it qualifies as a potential tool for designing superhydrophobic surfaces. Using the FEM framework, we further designed surfaces to optimize the order of the shapes in hierarchy. The results showed that the superhydrophobic surface with the lowest wetted area was obtained by placing shapes with smaller geometric angles at the top of the hierarchy. This arrangement of shapes provides the optimum combination of superhydrophobicity and surface integrity. This observation explains why the hierarchical structure of many superhydrophobic leaves follows this order. We also investigated the complex hierarchical structure of Salvinia minima. Owing to its remarkable ability to entrap air and pin the contact line, it exhibits superhydrophobicity along with the much-required Cassie state. These properties of Salvinia minima make it an excellent candidate for developing omniphobic surfaces. © 2015 IOP Publishing Ltd.

Bioinspiration and Biomimetics

The role of bio-inspired hierarchical structures in wetting

The atomic distribution in catalytically active metallic glass alloys, Pd43Cu27Ni10P20 and Pt57.5Cu14.7Ni5.3P22.5, was investigated using three-dimensional atom probe microscopy. Atom probe analysis showed uniform distribution of constituent elements for both the starting amorphous alloys, with no phase separation. Both the crystallized alloys showed eutectic microstructure with a very sharp interface (0.5 nm as determined from atom probe). The atomic distribution in the devitrified state is explained based on the "fragile liquid" behavior for these noble-metal glassy alloys. © 2015 Sanghita Mridha et al.

Fulltext

Journal of Nanomaterials

Atomic distribution in catalytic amorphous metals

Evolution of atomic distribution during devitrification of a zirconium-based bulk metallic glass, Zr41.2Ti13.8Cu12.5Ni10.0Be22.5, was investigated using three-dimensional atom probe microscopy. Atom probe analysis showed uniform distribution of constituent elements for the as-cast alloy, with no phase separation. The metallic glass was annealed at different temperatures to study the crystallization pathways and the length scale, distribution, and morphology of the phases formed. Devitrification was found to proceed via the formation of a metastable icosahedral phase. The devitrification pathway is explained based on "strong-liquid" behavior of this alloy. © 2015 Elsevier B.V. All rights reserved.