Download or read book Residual Stress Prediction in Laser Shock Peening Based on Finite Element Analysis and Mechanical Threshold Stress Model written by Chinmay J. Tophkhane and published by . This book was released on 2012 with total page 56 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis focuses on a physically based strain rate dependent plasticity model known as the Mechanical Threshold Stress (MTS) model proposed by Follansbee and Kocks. The objective is to develop an algorithm based on the tangent modulus method to resolve the constitutive equation represented by the MTS model and use it to analyze the material response under laser shock peening for the Ni alloy INCONEL 718 (IN718). A user defined subroutine has been developed and integrated with commercial software LS-DYNA. A parametric study is carried out to study the influence of various model parameters on the predicted residual stresses. The developed model is then applied in the study of residual stresses imparted on INCONEL 718 induced by laser shock peening (LSP) process. Finite element analysis is performed for the case of plate made of INCONEL 718 and the residual stress predictions are compared with experimental results. The model predictions are found to be in good agreement with the experimental results. To the best of author's knowledge, this is the first time that an MTS model has been developed for IN 718 with an integrated approach.

Download or read book Constitutive Modeling of Laser Shock Peening on Additive Manufactured Ti 6Al 4V written by Ruidong Wang and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Laser shock peening (LSP) is a mechanical surface treatment that induces plastic deformation and compressive residual stress in the material similar to shot peening. Pressure generated by the pulsed laser is far above the yield stress of the material and pulse duration is on the order of nanosecond. Finite element analysis is applied to simulate LSP and predict plastic deformation and residual stress through different constitutive models. The development of analytical model including model details, loading time history and constitutive model equations and parameters is discussed. Finally, results are presented for different constitutive models and experiment results are discussed.

Download or read book Measurement and Modeling of Laser Peening Residual Stresses in Geometrically Complex Specimens written by Adrian T. DeWald and published by . This book was released on 2005 with total page 338 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Finite Element Simulation of Laser Shock Peening Process written by and published by . This book was released on 2008 with total page 80 pages. Available in PDF, EPUB and Kindle. Book excerpt: Laser Shock Peening (LSP) is a relatively new material processing technology to enhance the operating service lives of engineering components. It has been applied to metal parts such as aircraft engine turbine blades, compressor blades and medical implants like human hip joints. In this process shock waves are generated in the material using a high powered laser beam which develops residual stresses in the material. It has been proved experimentally that the life cycle of laser shock peened components are higher than conventionally shot peened components. Although LSP process has been found to be effective, improper control of the process will lead to spallation in the material under certain conditions. The spallation within the material in the form of crack significantly reduces the operating life of the component. Currently there is no systematic modeling approach to predict the material response under LSP. As such, the objective of this thesis is to develop a comprehensive model for the predicting the material response as a result of the LSP process. More specifically a pressure model is first established to obtain the pressure loading based on laser pulse intensity. Using the pressure load as input the spallation response is simulated by developing a strain rate and temperature dependent material model. The material model is implemented along with a nucleation and growth based damage model. The material and dynamic fracture model is solved using a semi-implicit forward tangent modulus algorithm. A user defined subroutine (UDM) is written and combined with the analysis tool LS-DYNA. The new model is compared with reported experimental results and a parametric study is done to understand the influence of various processing parameters. The residual stress obtained from simulation is in good agreement with experimental results. The spallation results have not been verified due to lack of experimental data.

Download or read book Laser shock peening Performance and process simulation written by K. Ding and published by CRC Press. This book was released on 2006-01-24 with total page 182 pages. Available in PDF, EPUB and Kindle. Book excerpt: Laser shock peening (LSP) is a process for inducing compressive residual stresses using shock waves generated by laser pulses. It is a relatively new surface treatment for metallic materials that can greatly improve their resistance to crack initiation and propagation brought on by cyclic loading and fatigue. This book, the first of its kind, consolidates the scattered knowledge about LSP into one comprehensive volume. It describes the mechanisms of LSP and its substantial role in improving fatigue performance in terms of modification of microstructure, surface morphology, hardness, and strength. In particular, it describes numerical simulation techniques and procedures that can be adopted by engineers and research scientists to design, evaluate, and optimize LSP processes in practical applications.

Download or read book Residual Stress Fields Due to Laser pulse generated Shock Waves written by Scott Allen Noll and published by . This book was released on 2000 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt: Laser shock peening (LSP) is a material processing technique that imparts compressive residual stresses, which in turn enhance the materials ability to resist crack initiation/propagation. SHOCKWAVE, a finite element program developed at The Ohio State University, is used to predict the residual stress fields for one-sided and two-sided LSP on a common industrial metal, Ti-6A1-4V. Close attention was paid to constitutive modeling, mesh refinement, and correlating the analytical results with experiments. Both one-sided and two-sided LSP techniques were analyzed for multiple peak pressures and base material thickness. The residual stress field was successfully predicted for one-sided LSP and moderately well for two-sided LSP. The challenges for two-sided LSP are discussed and a plan for further investigation is given. Plastic strains are calculated to be on the order of 1-2% penetrating to a depth of 1 to 2 mm. Compressive residual stresses at the surface are found to be 1/3 to 2/3 the yield strength of the metal. Strain rates were calculated at 106 s-1 at the front of the shock wave. To predict the residual stress, the constitutive relations must account for the effect of strain rate for one-sided LSP and also be able to model Baushinger effect for the two-sided LSP.

Download or read book Prediction of Residual Stress Random Fields in Selective Laser Melted Aluminum A357 Components Subjected to Laser Shock Peening written by Mohammad Issa Hatamleh and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This work aims to develop a procedure to simulate laser shock peening treatments more efficiently, and to characterize the major differences in laser peening effects for cast and additively manufactured (selective-laser-melted) metallic specimens fabricated from A357 aluminum alloy. In addition, residual stresses (RS) are to be predicted probabilistically as a random field, allowing rigorous determination of RS values for a desired reliability. Laser shock peening (LSP) is a surface treatment technique that induces compressive RS near the surface of target metal components to improve fatigue life. Developing an LSP process using physical experiments is very expensive and time-consuming. To address this issue, finite element methods (FEM) have been widely used to simulate the LSP process and predict RS. Conventionally, almost all material constitutive models used in LSP prediction of RS involve deterministic parameters. Therefore, the predicted RS profiles do not reflect real-world variations in the material or uncertainties in the LSP process. Moreover, prediction of RS as a random field has not been done. While the effect of LSP on cast alloys has been studied extensively, few researchers have investigated the effects of LSP on metallic specimens produced by additive manufacturing processes such as selective laser melting (SLM). Therefore, the objectives of this research are: (1) Develop a procedure to simulate the LSP process with reduced computational time; (2) Conduct experimental and numerical studies to understand the effects of LSP on SLM A357 aluminum alloy; (3) Create a probabilistic approach to quantify the material constitutive model parameters as a joint probability distribution of correlated random variables; and (4) Demonstrate a technique to efficiently generate stochastic maps of the resulting RS random fields, enabling improved reliability analysis for desired RS values. To increase LSP simulation speed, a new systematic procedure is developed using modal analysis and generalized variable damping profiles with the “single explicit analysis using time dependent damping” (SEATD) FEM approach. To begin understanding the effects of LSP on A357 aluminum alloy specimens produced by SLM, true-stress-strain curves of both as-built (AB) and laser shock peened SLM samples are obtained through transverse tensile tests. An initial hypothesis on the effects of LSP during tension testing is formulated and subsequently tested using SEATD approach. To quantify the plasticity-Johnson-Cook (J-C) material model parameters as a joint probability distribution of correlated random variables for heat-treated (HT) and as-built (AB) SLM A357, the Bayesian inference (BI) probabilistic approach is utilized. Also proposed in this work are two BI-quantified-techniques called, respectively, the Multidimensional-BI method and the Spatial-Posterior-Prior-Probability-Mass-Function (SPP-PMF) method. Both can be used to efficiently predict RS as a random field, thus providing far greater insight into the practical ability to attain desired RS. For identical LSP treatments, it is determined that the material models are significantly different for the SLM and the conventional cast A357 aluminum alloys, resulting in much lower overall magnitude of compressive RS in the SLM-alloy. In addition, stochastic maps of the resulting random stress fields for LSP treatments on specific SLM A357 components are generated using the approach described herein.

Download or read book On the Optimization of Laser Shock Peening Induced Residual Stresses written by Sergey Chupakhin and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: There is a strong economic motivation of the aircraft industry to explore novel residual stress-based approaches for the fatigue life extension, repair, and maintenance of the growing fleet of ageing aircrafts, although the effect of residual stresses is not taken into account by the established damage tolerance evaluation methods. Laser shock peening - the most promising life enhancement technique - has already demonstrated great success in regard to the mitigation of fatigue crack growth via deep compressive residual stresses. However, no comprehensive model exists which allows the prediction of generated residual stress fields depending on the laser peening parameters. Furthermore, the hole drilling method - a well-established technique for determining non-uniform residual stresses in metallic structures - is based on measuring strain relaxations at the material surface caused by the stress redistribution while drilling the hole. However, the hole drilling method assumes linear elastic material behavior and therefore, when measuring high residual stresses approaching the material yield strength, plastic deformation occurs, which in turn leads to errors in stress determination. In the light of these two points, the present work aims to optimize the laser shock peening process in regard to high residual stress profiles, their correct measurement by the hole drilling method and demonstration of the fatigue crack growth retardation through the laser peening treatment on the laboratory scale. First, the methodology for the correction of the residual stresses approaching the material yield strength when measuring by the hole drilling is established and experimentally validated. The correction methodology utilizes FE modelling and artificial neural networks. In contrast to the recent studies, the novelty of this methodology lies in the practical and elegant way to correct any non-uniform stress profile for a wide range of stress levels and material behaviors typically used in industrial applications. Therefore, this correction methodology can be applied in industry without changing the procedure of hole drilling measurement. Second, the laser shock peening process is optimized in regard to the generated residual stress profiles using design of experiments techniques. The strategy involves laser peening treatment with different parameters and subsequent measurement of induced residual stress profiles through hole drilling. The measured stress profiles are subjected to correction using the neural network methodology. After that the regression model is fitted into the experimental data in order to find the relationship between the laser peening parameters and the stress profiles' shapes. In the final stage, it is experimentally demonstrated that the established regression model provides an accurate prediction of the residual stress profile when using defined laser peening parameters and vice versa. Third, the regression model obtained in the design of experiments study is used for generating the desired residual stresses in the C(T)50 AA2024-T3 specimens for the fatigue crack propagation test. Significant retardation of the fatigue crack propagation of specimens due to the presence of deep compressive residual stresses is experimentally demonstrated on the laboratory scale.

Download or read book Prediction of Residual Stresses in Laser Glazing and Laser Powder Deposition Processes Using FEM written by Prashanth Kumar Tirukovelluri and published by . This book was released on 2007 with total page 376 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of the research is to develop a three-dimensional finite element model for predicting residual stresses that evolve during the Laser Powder Deposition of thin-walled builds using commercially available finite element software, ABAQUS/Standard [5]. The research work was started by developing a finite element model of Laser Glazing process, which is relatively simple when compared to Laser Powder Deposition in modeling perspective as there is no dynamic addition of material. The experience gained from modeling of Laser Glazing was applied to develop a finite element model of Laser Powder Deposition for prediction of residual stresses. The numerical model of Laser Glazing is based on sequentially coupled thermo-mechanical theory and Laser Powder Deposition process on fully coupled thermo-mechanical theory. To simplify the models, symmetry of geometry and boundary conditions were taken into account. In both the models temperature dependent material properties were included. Also, latent heat corresponding to melting was taken into account. The material was defined as elastic-perfectly plastic. The results predicted by the thermal model of Laser Glazing are comparable with analytical solution and are also validated with the results obtained from carefully designed experiments. In the case of finite element model of Laser Powder Deposition, it can be concluded that the results obtained are reasonable based on previous experimental studies by others.

Download or read book Laser Shock Peening written by Shikun Zou and published by Springer Nature. This book was released on 2023-06-09 with total page 398 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book highlights the fundamentals and latest progresses in the research and applications of laser shock peening (LSP). As a novel technology for surface treatment, LSP greatly improves the resistance of metallic materials to fatigue and corrosion. The book presents the mechanisms, techniques, and applications of LSP in a systematic way. It discusses a series of new progresses in fatigue performance improvement of metal parts with LSP. It also introduces lasers, equipment, and techniques of newly developed industry LSP, with a detailed description of the novel LSP blisk. The book demonstrates in details numerical analysis and simulation techniques and illustrates process stability control, quality control, and analysis determination techniques. It is a valuable reference for scientists, engineers, and students in the fields of laser science, materials science, astronautics, and aeronautics who seek to understand, develop, and optimize LSP processes.

Download or read book Prediction of Residual Stresses from Laser Shock Peening written by William Richard Braisted and published by . This book was released on 2000 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Infuence of Curved Geometries on the Fatigue Life of Laser Peened Components written by Anoop Vasu and published by . This book was released on 2014 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt: Generating compressive residual stresses at the critical stress locations can prevent or delay structural component failure. Laser peening is a well-known method for inducing compressive residual stresses. The plastic deformation created by the planar shock waves near the surface regions is the major cause for the generation of compressive residual stresses. Apart from the planar waves, release waves at the border of impact are generated that act against the plastic deformation created by planar waves. This decrease of plastic deformation reduces the compressive residual stress generated near the surface regions of peened components. Laser peening of curved geometries creates compressive residual stresses - which is dissimilar to flat geometries - because of the influence of release waves on different curvatures. This research investigates the effects of reduction in the amount of plasticity in convex, concave, and flat geometries using the plastic dissipation energy as the measure of plastic deformation imparted on the component. Finite element models are created in Abaqus to predict the effects of "reduced plasticity" in residual stresses generated on curved geometries of laser peened components. An analytical formulation is derived based on the plasticity incurred inside the material and the results are compared with the prediction by numerical simulation. The consistency in the analytical formulation with the simulation model indicates the behavior of laser peening for curved geometries. However, the compressive residual stresses can relax due to the loading conditions and thus reduce the laser peening effectiveness. Under such a condition, re-peening or re-laser peening a component already in service can further increase its component life. This research develops a method to predict the optimal re-peening time for maximum fatigue life under realistic loading conditions. An optimization problem is set up to illustrate the application of this method to an aircraft lug problem. A novel surrogate modeling technique called the Sorted k-fold Approach (SKA) is developed to perform the optimization. Results from the investigation indicate that re-peening the component ~50-55% of its expected fatigue life maximizes the component's fatigue life. The proposed approach, proven to be able to obtain optimal process parameters for improving the fatigue resistance of the component, can significantly reduce the costs for experimental testing.

Download or read book Gradient Microstructure in Laser Shock Peened Materials written by Liucheng Zhou and published by Springer Nature. This book was released on 2021-06-12 with total page 241 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book introduces the fundamentals and principles of laser shock peening (LSP) for aeronautical materials. It focuses on the innovation in both theory and method related to LSP-induced gradient structures in titanium alloys and Ni-based alloys which have been commonly used in aircraft industries. The main contents of the book include: the characteristics of laser shock wave, the formation mechanism of gradient structures and the strengthening-toughing mechanism by gradient structures. The research has accumulated a large amount of experimental data, which has proven the significant effectiveness of LSP on the improvement of the fatigue performance of metal parts, and related findings have been successfully applied in aerospace field. This book could be used by the researchers who work in the field of LSP, mechanical strength, machine manufacturing and surface engineering, as well as who major in laser shock wave and materials science.

Download or read book Metals Abstracts written by and published by . This book was released on 1999 with total page 1014 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book High Repetition Rate Laser Shock Peening on Biodegradable Magnesium Alloys written by Hossein Kamkarrad and published by . This book was released on 2016 with total page 137 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recently, Magnesium based alloys have been identified as a potential bio-degradable material for implants. While the biggest advantage of magnesium based implants is that it eliminates the need for additional surgery for removal, magnesium corrodes within human body much faster than the cure of broken bones. Hence, reduction of corrosion rate in magnesium surface is important to successful implementation. Laser Shock Peening (LSP) as mechanical treatment has been used successfully on implant surfaces to reduce the corrosion rate. Having reviewed the literature in LSP, it can be seen that the lasers used are low repetition rate high power lasers. Owing to cost of low repetition lasers, high repetition laser shock peening (HRLSP) is introduced in this work. The general objective of this thesis dissertation is to develop HRLSP for low mechanical strength metals/alloys like Magnesium. To this end, a feasibility study of HRLSP was performed and pertinent laser parameters for successful peening of magnesium were evaluated. The finite element analysis using Abaqus Dynamic/Static was performed in both single shot mode as well as in multi shot mode. The simulation was used to predict the surface deformation on the peened area, magnitude of Compressive Residual Stress (CRS), and the propagation of CRS along the depth from the surface. The effect of laser parameters and scanning parameters on these values have been analyzed by Finite Element Analysis (FEA). Based on the results from the feasibility study, an experimental setup involving both optical as well as scanning arrangement was performed and design of experiment was done for peening. From the experiments, with two laser intensities at 0.91GW/cm2 and 2GW/cm2, peening was possible only at 2GW/cm2. The magnitude of peening was varied by changing the %overlap between subsequent spots, and the total number scans. Increasing the number of peened shots within the specimen surface area of 10 X 10 mm, increases the magnitude of CRS that was shown by Finite Element Analysis. Comparison of peened samples to unpeened samples showed significant improvements in the mechanical attributes, comparable to that seen in the literature. The hardness increased from 45 HV to 103 HV; Surface roughness (Ra) increased from 0.35 m to 3.3 m; surface wettability measured as function of contact angle reduced from 68.5° to 44.4°; and wear resistance improved from 5.5E-4 gr/s to 1.8E-4 gr/s. The results mentioned above clearly indicate the relationship between improvements in mechanical attributes to the magnitude of peening.

Download or read book Modeling the Residual Stress Distribution and Experimental Characterization of Shot Peening on AZ31B Rolled Sheet written by Amir Yazdanmehr and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The drive to reduce fossil fuel consumption due to its environmental impacts has generated renewed interest in employing magnesium (Mg), the lightest industrial metal, and its alloys in vehicle manufacturing. One of the qualifying metrics for structural application of Mg in transportation vehicles is its high durability. The low fatigue strength of these alloys has been an obstacle to using them in load-bearing components. Thus, methods for improving the fatigue properties of Mg alloys are of interest. Shot peening is a cold-working process employed to improve the fatigue properties of materials. The shot peening process induces compressive residual stress at the material's surface and at a layer in the order of a few hundred micrometers deep, which improves the fatigue life by retarding the crack initiation as well as growth; however, the increased surface roughness has a detrimental effect on fatigue life. These competing effects of peening have created interest in finding the optimum peening intensity that will maximize fatigue life. Modeling reduces the cost of experimentally evaluating optimum peening conditions. However, modeling the shot peening of Mg alloys remains complicated due to the anisotropic and asymmetric properties of wrought Mg alloys, and the complex unloading behavior and rate-sensitivity behavior of these materials. To address these challenges, a comprehensive experimental and numerical-analytical study of shot peening on AZ31B-H24 rolled sheet was conducted and is reported in this thesis. First residual stress distributions through the depth of the material were measured. Among the methods for residual stress measurement, X-ray diffraction (XRD) has attracted researchers' attention because: 1) it is a non-destructive method; 2) it can measure residual stress at the surface, and 3) the spatial resolution can be less than 0.3 mm. However, due to the low x-ray mass attenuation coefficient of Mg alloys, x-ray penetration in the material is significant which needs to be accounted for. The residual stresses in as-received and shot peened AZ31B-H24 rolled sheet samples were measured using the 2D-XRD method. The electro-polishing layer removal method was used to find the residual stress pattern through depth. Due to the high depth of penetration, a correction had to be made to account for the penetration depth. The results showed that the corrected residual stresses in a few tens of micrometers layer from the surface were different from the raw stresses. To better estimate the residual stress distribution in a few micrometers from the surface, the grazing-incidence x-ray diffraction (GIXD) method was applied to evaluate the stresses in the surface layer. This study also showed how small uncertainty in measuring the observed residual stress and in evaluating the depth of the polished area in layer removal leads to high uncertainty in the corrected residual stresses. The XRD results showed the creation of compressive residual stress through the depth as well as a good agreement between the XRD and hole-drilling and GIXD results. Modeling the shot peening process first requires an understanding of how Mg alloys behave at large strain values during loading-unloading. The tension-compression (TC) and compression-tension (CT) in the in-plane directions were obtained using an anti-buckling fixture. By comparing the compression part of the CT curves along the rolling direction (RD) with the ones using a cuboid sample, the negligible effect of using the anti-buckling fixture was shown. A novel fixture was designed to obtain the CT and TC curves in the through-thickness (normal direction: ND) of the rolled sheet, which is only 6.3 mm thick. FEM was employed to evaluate the consistent area for strain measurement using DIC in the designed setup. The CT and TC curves along ND were obtained using the new fixture. The results of the new fixture were verified by comparing the curves obtained by the new fixture in RD with those obtained by using the anti-buckling fixture. Different effects of shot peening on the AZ31B-H24 rolled sheet were characterized in this study by measuring the residual stress and micro-hardness distribution through the depth, followed by measuring surface roughness and texture evolution at the surface of samples shot peened under Almen intensities ranging from 0.05 mmN to 0.6 mmN. To obtain the optimum peening intensity, rotating bending fatigue tests were performed on peened samples at different intensities. It was found that increasing the peening intensity, increases the surface roughness and hardness at the surface layer. In addition, the depth of the maximum compressive stress and the depth of the induced compressive residual stress layer have a direct relation with the peening intensity. The material showed a high sensitivity to shot peening under different intensities, due to the over-peening effects in the peening on Mg alloys. Peening at the optimum intensity increases the fatigue strength moderately, from 130 MPa to 150 MPa. During investigations to find an accurate and a computationally efficient method for capturing the complex behavior of Mg alloys, it was found that stringent assumptions are needed to allow for a closed-form analytical solution when calculating residual stresses induced by shot peening. This limits the application of these models to idealized conditions. On the other hand, and because of the complex behaviors of Mg alloys, such as complex unloading behavior and rate-sensitivity, it is difficult to provide numerical solutions such as finite element that are capable of mimicking actual material's behavior once it is released from an over-strain loading state. Moreover, modeling full coverage shot peening condition is time-consuming and computationally expensive. A single-shot finite element model was combined with an analytical model using actual loading-unloading material behavior to propose a hybrid FEM-analytical model for prediction of the residual stress distribution in shot peening. First, the shot peening process was divided into a loading phase, modeling the impact of a shot and substrate, and an unloading phase, modeling the rebounding of the shot. Finite element was employed to model a single shot impingement on a substrate using the actual loading properties of the substrate. Using the results of the loading phase, an analytical model was proposed to predict stresses due to the unloading phase, using the actual unloading behavior of the material. The proposed hybrid model accounts for the actual behavior of a material, actual elastic-plastic contact analysis, strain rate effect, and friction. The model was then verified by predicting residual stresses induced in a SAE1070 and an Al2024-T351 sheet. Results were compared with the available experimental results and showed close agreements. The application of the proposed hybrid numerical-analytical model was extended to use with an asymmetric and anisotropic material that also has complex unloading behavior, i.e., Mg alloys. First, the loading state of material under peening and the effects of the material's asymmetry and anisotropy were discussed, then the numerical modeling of the loading step was provided. Finally, the actual unloading curves, measured using the designed fixture, of the material were used to estimate the residual stress profiles. The strain rate effect was also considered in the modeling. The results were matched closely with the XRD and hole-drilling experimental measurements.

Download or read book Residual Stress Measurement and Parametric Analysis of Laser Shock Peening of Aluminium Alloy 7075 with Different Thicknesses written by Sean Nicholas Van Staden and published by . This book was released on 2018 with total page 394 pages. Available in PDF, EPUB and Kindle. Book excerpt: