The title immediately brings to mind a standard reference of almost the same title [1]. The authors are quick to point out the relationship between these two works: they are complementary. The purpose of this work is to explain what is known about a selection of exact solutions. As the authors state, it is often much easier to find a new solution of Einstein's equations than it is to understand it. Even at first glance it is very clear that great effort went into the production of this reference. The book is replete with beautifully detailed diagrams that reflect deep geometric intuition. In many parts of the text there are detailed calculations that are not readily available elsewhere. The book begins with a review of basic tools that allows the authors to set the notation. Then follows a discussion of Minkowski space with an emphasis on the conformal structure and applications such as simple cosmic strings. The next two chapters give an in-depth review of de Sitter space and then anti-de Sitter space. Both chapters contain a remarkable collection of useful diagrams. The standard model in cosmology these days is the ICDM model and whereas the chapter on the Friedmann-Lema?tre?Robertson?Walker space-times contains much useful information, I found the discussion of the currently popular a representation rather too brief. After a brief but interesting excursion into electrovacuum, the authors consider the Schwarzschild space-time. This chapter does mention the Swiss cheese model but the discussion is too brief and certainly dated. Space-times related to Schwarzschild are covered in some detail and include not only the addition of charge and the cosmological constant but also the addition of radiation (the Vaidya solution). Just prior to a discussion of the Kerr space-time, static axially symmetric space-times are reviewed. Here one can find a very interesting discussion of the Curzon?Chazy space-time. The chapter on rotating black holes is rather brief and, for example, does not contain reference to the insights found by Pretorius and Israel [2]. This is perhaps justifiable in view of the many specialized texts devoted to the Kerr space-time (e.g. [3]). The large clear diagrams that one becomes accustomed to in this book show off the Taub-NUT (and related) space-times in the next chapter. After perhaps a somewhat standard discussion of stationary axially symmetric space-times, there is a very informative discussion of accelerating black holes. For example, the global structure of the C-metric is considered in detail. This is followed by a brief discussion of solutions for uniformly accelerating particles. The discussion of the Pleba?ski-Demia?ski solutions contains two very useful flow charts that help to systematize two rather complex families of solutions. After a somewhat brief discussion of plane and pp-waves, the authors give an extensive discussion of the Kunt solutions. I note here that after this text was in production the importance of the Kunt space-times as regards the characterization of space-times by scalar curvature invariants was made clear [4]. The discussion of the Robinson-Trautman solutions that follows is extensive, containing, for example, details of the singularity structure and of the global structure. The final formal chapter in this text covers colliding plane waves. This contains, for example, discussions of the Khan?Penrose, Ferrari?Iba?ez and Chandrasekhar?Xanthopoulos solutions. The text ends with a `final miscellany'. This covers a number of interesting topics, but I found the discussion of the Lema?tre?Tolman solutions rather weak (compare e.g. [5]). The book has two quite useful appendices covering 2-spaces and 3-spaces of constant curvature. To conclude, I will quote from the dust jacket: `The book is an invaluable resource for both graduate students and academic researchers working in gravitational physics'. I highly recommend it. References [1] Stephani H, Kramer D, MacCallum M, Hoenselaers C and Herlt E 2003 Exact Solutions of Einstein's Field Equations (Second Edition) (Cambridge: Cambridge University Press) [2] Pretorius F and Israel W 1998 Class. Quantum Grav.15 2289 [3] Wiltshire D, Visser M and Scott S (ed) 2008 The Kerr Spacetime: Rotating Black Holes in General Relativity (Cambridge: Cambridge University Press) [4] Coley A, Hervik S and Pelavas N 2009 Class. Quantum Grav. 26 025013 [5] Pleba?ski J and Krasi?ski A 2006 An Introduction to General Relativity and Cosmology (Cambridge: Cambridge University Press)

Exact Space-Times in Einstein's General Relativity

Black Holes The Membrane Paradigm

Among the various types of metal matrix composites, SiC particle-reinforced aluminum matrix composites (SiCp/Al) are finding increasing applications in many industrial fields such as aerospace, automotive, and electronics. However, SiCp/Al composites are considered as difficult-to-cut materials due to the hard ceramic reinforcement, which causes severe machinability degradation by increasing cutting tool wear, cutting force, etc. To improve the machinability of SiCp/Al composites, many techniques including conventional and nonconventional machining processes have been employed. The purpose of this study is to evaluate the machining performance of SiCp/Al composites using conventional machining, i.e., turning, milling, drilling, and grinding, and using nonconventional machining, namely electrical discharge machining (EDM), powder mixed EDM, wire EDM, electrochemical machining, and newly developed high-efficiency machining technologies, e.g., blasting erosion arc machining. This research not only presents an overview of the machining aspects of SiCp/Al composites using various processing technologies but also establishes optimization parameters as reference of industry applications.

/pdf/a-review-on-conventional-and-nonconventional-machining-of-285cllwy57.pdf

A review on conventional and nonconventional machining of SiC particle-reinforced aluminium matrix composites

Supply chain has received a great deal of attention both in academia and industry The carbon emissions from supply chain activities are the major concern, therefore, many governments have implemented carbon taxes to promote energy conservation and emission reduction Under this background, the impact of the carbon taxes on supply chain and the related operational decisions become hot topics This paper aimed to review the researches on supply chain management under carbon tax First, the descriptive results and a bibliometric analysis of identified articles during 2010–2019 was presented to clarify the development in this field Then, content analysis is conducted to classify the selected articles into facility location decisions, supplier selection and order quantity, low carbon technology choice and investment, production planning, transportation decisions, pricing decisions, joint decisions and supply chain coordination under carbon taxes The research progress in these areas was systematically reviewed and summarized Finally, future directions were discussed from the perspectives of problem and method

Supply chain management under carbon taxes: A review and bibliometric analysis

Exact elasto-plastic analysis of rotating thick-walled cylindrical pressure vessels made of functionally graded materials

Wide applications of tube drawing process with using a fixed conical plug in manufacturing of thin-walled tubes have convinced the researchers to investigate and optimize this process in the past years. Current study deals with presenting an optimum curved die profile utilized in tube drawing process with fixed conical plug. Minimizing the required tensile stress in the process as well as reducing the stress which is applied to the die and plug has been considered as objectives of this study. Considering work-hardening behavior of material, the drawing stress of the process is analyzed based on incremental slab method theory. In addition to, plain strain condition is applied through the thin-walled tube. Furthermore, the obtained optimum die profile has also been simulated using ANSYS Workbench 18.0 and the results were compared with those of analytical method. It is found that the die profile could be determined based on the mechanical properties of the workpiece, reduction of cross section area, plug angle, and coefficients of friction. Results demonstrate that by applying an optimum die profile, the required tension stress in tube drawing process could considerably be reduced comparing to the same process with conical die profile.

Optimum curved die profile for tube drawing process with fixed conical plug

A two dimensional upper bound analysis of the ring rolling process with experimental and FEM verifications

In this article, an analytic solution for ring rolling process based on the slab method theory is presented, in which the non-uniformity of the normal and shear stresses across the section of the deforming material throughout the plastic region is considered. The friction factor multiplied by the shear yield strength (s = mk) is used to present friction between the main roll and the ring. The influence of the process parameters such as friction factor, feed speed, main roll rotational speed, and radii of the main roll and mandrel on process outputs is investigated. Complete expressions for the ring rolling pressure, force, and torque are obtained, and the position of neutral point is predicted. Comparison of the analytic results of this model with the experimental results of other investigators and FEM analysis show that they are in good agreement.

/pdf/slab-analysis-of-ring-rolling-assuming-constant-shear-2q20repm2b.pdf

Slab Analysis of Ring Rolling Assuming Constant Shear Friction

Laser welded blanks (LWBs) are semi-finished components typically manufacture by dissimilar materials, thicknesses, shapes, coatings, etc. After butt welding of the primary sheets, the product sheets are subjected to the sheet metal forming process. Formation of the heat-affected zones (HAZ) is typical in LWBs, which possess quite different mechanical properties than the base materials. Recently, laser beam technologies have been widely employed to weld different types of vehicles panels. In this study applying Nd:YAG laser welding, experimental and numerical investigations are carried out to evaluate the effects of process input factors on deep drawing process of LWBs. Laser beam power, welding speed, blank holder force (BHF), material properties, and friction coefficient are considered as process key input parameters. In addition, the laser welding and deep drawing processes were numerically simulated using Simufact Welding and Abaqus/Explicit software, Used the Simorgh supercomputer for heavy modeling calculations. Moreover, drawing depth, weld line movement, and energy absorption are taken into account as process main outputs or objective functions. Besides, using an advanced MATLAB code, multi objective optimization based on genetic algorithm is applied to determine the optimal design input parameters. It is observed that the critical stresses were taken place outside the weld zone and rupture due to high heat input of laser and metallurgical changes of the base metal occur in the pre-softening zone. In addition, the weld line displacement occurs as a result of plastic strain change of the weld joint that causes failure-prone zone creation as well as the adverse wrinkling. By considering weld line displacement and absorbed energy as multi-objective function, the optimal points is 1.15 mm and 0.21 KJ for weld line displacement and absorbed energy, respectively. Good agreement between the simulated and the experimental results revealed that the model would be appropriate for deep drawing of LWB process numerical simulation.

Multi-objective topology optimization of deep drawing dissimilar tailor laser welded blanks; experimental and finite element investigation

This paper aims at analyzing the deformation behavior of tailor welded blanks (TWBs), manufactured by laser beam welding (LBW) and gas tungsten arc welding (GTAW), through the deep drawing process....

Ali Parvizi

Papers

Optimum curved die profile for tube drawing process with fixed conical plug

A two dimensional upper bound analysis of the ring rolling process with experimental and FEM verifications

Slab Analysis of Ring Rolling Assuming Constant Shear Friction

Multi-objective topology optimization of deep drawing dissimilar tailor laser welded blanks; experimental and finite element investigation

Comparison between laser beam and gas tungsten arc tailored welded blanks via deep drawing