Investigation Into Laser Shock Processing

Laser shock processing is a good candidate for surface industry due to its rapid processing, localized ablation, and precision of operation. In the current study, laser shock processing of steel was considered. The numerical solutions for temperature rise and recoil pressure development across the interface of the ablating front and solid are presented. The propagation of elastic-plastic waves in the solid due to recoil pressure loading at the surface is analyzed and numerical solution for the wave propagation was obtained. An experiment was conducted to ablate the steel surfaces for shock processing. Scanning electron microscopy was carried out to examine the ablated surfaces shock processing while transmission electron microscopy was conducted to obtain dislocation densities after the shock processing. It was found that surface hardness of the workpiece increased in the order of 1.8 times of the base material hardness, and the dislocation was the main source of the shock hardening in the region affected by laser shock processing

Entropy Analysis in Pipe Flow Subjected to External Heating

Abstract: In the present study, heat transfer and entropy analysis for flow through a pipe system is considered. The Reynolds number and the pipe wall temperature effects on entropy distribution and total entropy generation in the pipe are investigated. Numerical scheme employing a control volume approach is introduced when solving the governing equations. Steel is selected as pipe material, while water is used as fluid. It is found that increasing pipe wall temperature and Reynolds number increases the entropy production rate, in which case, entropy generation due to heat transfer dominates over that corresponding to fluid friction

Focusing of phase change microparticles for local heat transfer enhancement in laminar flows

Phase change material (PCM) suspensions have received wide spread attention for increased thermal storage in various thermal systems such as heat sinks for electronics and solar thermal applications. To achieve further heat transfer enhancement, this paper investigates the effect of focusing micron-sized phase-change particles (PCMs) to a layer near the heated wall of a parallel plate channel. A numerical model for fully-developed laminar flow with a constant heat flux applied to one wall is developed. Melting of the focused PCMs is incorporated using a temperature-dependent effective heat capacity. The effect of channel height, height of the focused PCM stream, heat flux, and fluid properties on the peak local Nusselt number (Nu∗) and the averaged Nusselt number over the melting length (Nu[subscript melt]) are investigated. Compared to the thermally-developed Nusselt number for this geometry (Nuo = 5.385), Nu[subscript melt]and Nu∗ enhancements of 8% and 19% were determined, respectively. The local heat transfer performance is optimized when the PCMs are confined to within 30% of the channel height. The present work provides an extended understanding of local heat transfer characteristics during melting of flowing PCM suspensions, and offers a new method for enhancing heat transfer performance in various thermal-fluidic systems

Laser nitriding method of making phosphor bronze with surface-embedded titanium carbide particles

The laser nitriding method of making phosphor bronze with surface-embedded titanium carbide particles involves coating a cleaned phosphor bronze workpiece with a thin film formed of a carbonaceous layer mixed with nanosize particles of titanium carbide. The titanium carbide forms about 5 wt % of the thin film, and the phosphor bronze workpiece is composed of about 6.0 wt % tin, about 0.1 wt % phosphorous, and about 93.9 wt % copper. A laser beam is then scanned over the thin film formed on the phosphor bronze workpiece. Coaxially and simultaneously with the laser beam, a stream of nitrogen gas is sprayed on the thin film formed on the phosphor bronze workpiece in order to provide the workpiece with a nitride coating having nanoparticles of titanium carbide embedded therein

Modelling the influence of laser drilled recast layer thickness on the fatigue performance of CMSX-4

This paper introduces a novel approach to fatigue life prediction modelling considering the laser drilling effect on film cooling holes of turbine vanes. The methodology proposed is based on a stress-life model such as the Basquin law and the introduction of manufacturing damage effect. The proposed empirical model gives a unique versatility compared to other stress-life models by considering surface damage such as the recast layer produced by the laser drilling process. The proposed empirical model has been thoroughly tested and validated using existing fatigue data. The statistical analysis shows that the proposed model is adequate for estimating the fatigue life of laser drilled specimens considering the recast layer thicknesses effect. The proposed model also can estimate the life of untested specimens even when only a small sample of fatigue data is available, thereby reducing the required testing data

Thermomechanical modelling of laser surface glazing for H13 tool steel

A two-dimensional thermomechanical finite element (FE) model of laser surface glazing (LSG) has been developed for H13 tool steel. The direct coupling technique of ANSYS 17.2 (APDL) has been utilised to solve the transient thermomechanical process. A H13 tool steel cylindrical cross-section has been modelled for laser power 200 W and 300 W at constant 0.2 mm beam width and 0.15 ms residence time. The model can predict temperature distribution, stress–strain increments in elastic and plastic region with time and space. The crack formation tendency also can be assumed by analysing the von Mises stress in the heat-concentrated zone. Isotropic and kinematic hardening models have been applied separately to predict the after-yield phenomena. At 200 W laser power, the peak surface temperature achieved is 1520 K which is below the melting point (1727 K) of H13 tool steel. For laser power 300 W, the peak surface temperature is 2523 K. Tensile residual stresses on surface have been found after cooling, which are in agreement with literature. Isotropic model shows higher residual stress that increases with laser power. Conversely, kinematic model gives lower residual stress which decreases with laser power. Therefore, both plasticity models could work in LSG for H13 tool steel

Characterization of Environmental Dust in the Dammam Area and Mud After-Effects on Bisphenol-A Polycarbonate Sheets

Owing to recent climate changes, dust storms are increasingly common, particularly in the Middle East region. Dust accumulation and subsequent mud formation on solid surfaces in humid environments typically have adverse effects on surface properties such as optical transmittance, surface texture, and microhardness. This is usually because the mud, which contains alkaline and ionic species, adheres strongly to the surface, often through chemical bonds, and is therefore difficult to remove. In this study, environmental dust and the after-effects of mud formed on a polycarbonate sheet, which is commonly used as a protective glass in photovoltaic cells. Ionic compounds (OH−) are shown to significantly affect the optical, mechanical, and textural characteristics of the polycarbonate surface, and to increase the adhesion work required to remove the dry mud from the polycarbonate surface upon drying. Such ability to modify characteristics of the polycarbonate surface could address the dust/mud-related limitations of superhydrophobic surfaces

Activation of GATA4 gene expression at the early stage of cardiac specification

The exclusionary protected area-based approach to biodiversity conservation has succeeded at several places,but at a significant social cost and conflict, especially in the developing country tropics.More inclusive approaches, including community-based conservation (CBC), its subset enterprise-based conservation(EBC), and payments-based conservation (PES) programs, have been tried in the past 15 years. A brief summary of the literature on socio-economic impacts of the exclusionary approach suggests that, although detailed studies and documentation is missing,impacts are significant, and the ethical argument against forced displacement quite strong. We then examine the potential of non exclusionary approaches from a broader perspective that values biodiversity gains as well as socio-economic ones. Our review suggests that (a) comprehensive socio–ecological and comparative studies of such initiatives are surprisingly scarce, (b) enterprise-based conservation offers some potential if design flaws, poor implementation, assumptions about homogeneous communities, and inattention to tenurial change and security are addressed, (c) payments-based programs require caution because of their focus on economic efficiency, and simplified assumptions regarding the nature of rights, biological information,monitoring costs, and state interventions, and (d) the alternatives to exclusion have often not been given adequate state support and space to function, nor is the ongoing neoliberalization of the political-economic system conducive to giving them that space, except when they fit the direction of this larger process

Influence of Yb:YAG laser beam parameters on Haynes 188 weld fusion zone microstructure and mechanical properties

The weldability of 1.2 mm thick Haynes 188 alloy sheets by a disk Yb:YAG laser welding was examined. Butt joints were made, and the influence of parameters such as power, size, and shape of the spot, welding speed, and gas flow has been investigated. Based on an iconographic correlation approach, optimum process parameters were determined. Depending on the distribution of the power density (circular or annular), acceptable welds were obtained. Powers greater than 1700 W, welding speeds higher than 3.8 m mm1, and spot sizes between 160 and 320 lm were needed in the circular (small fiber) configuration. By comparison, the annular (large fiber) configuration required a power as high as 2500 W, and a welding speed less than 3.8 m min�1. The mechanical properties of the welds depended on their shape and microstructure, which in turn depended on the welding conditions. The content of carbides, the proportion of areas consisting of cellular and dendritic substructures, and the size of these substructures were used to explain the welded joint mechanical properties

Optical method and neural network for surface roughness measurement and surface pattern classification

In this present study, two optical methods employing diffusive and specular reflections from the steel surfaces are considered to measure the surface roughness value (Ra). The first method is introduced for Ra > 2 fim while the second method is employed for 0.1 (im < Ra < 2 (im. The peak intensity of the reflected beam, and a Gaussian curve parameter of a Gaussian function, approximating the peak intensity of the reflected beam, are measured for the first and second methods, respectively. Since a unique Ra value exists for a surface, the data collected for each profile were combined to produce a profile representing the Ra value for that particular surface, which is Gaussian in nature. The relationship between Ra and the standard deviation of Gaussian function (SDGF) was developed. An experimental set up associated with both methods has been designed and built. In this case, a He-Ne laser beam was used to scan the workpiece surface while fiber optic probes were employed to collect the reflected beam. To calibrate the fiber optic probes, Ra is measured initially using a Bendix surface proficoder. A back-propagation neural network classifying the surface patterns resulting from the first method was developed. A network simplification based on the self-pruning of the weights was employed. Control chart patterns resembling the possible surface profiles were developed when training the network. It is found that, the resolution of the surface texture measurement improved considerably in the case of presently employed optical method. The neural network developed for this purpose could classify the resulting surface patterns successfully. Newly introduced selfpruning method results in an improvement in the network performance and minimisation of the network structure and computing time. The first scheme used in the second method gives an improved standard estimate of error. The linear relationship was found between the Ra values and SDGF of the reflected beam intensity. Higher the SDGF values result in higher surface roughness. However, the measurement is limited to a certain range of Ra values; in this case, the accuracy of the measurement drops considerably as the Ra value reduces below 0.1 um