The fact that a new text book introducing the essentials of computational chemistry contains more than 500 pages shows impressively the grown and still growing size and importance of this field of chemistry. The author’s objectives of the book, using his own words, are “to provide a survey of computational chemistry its underpinnings, its jargon, its strengths and weaknesses that will be accessible to both the experimental and theoretical communities”. This design as a general introduction into computational chemistry makes it an alternative to Andrew R. Leach’s well-established “Molecular Modeling” (Prentice Hall) and Frank Jensen’s “Introduction to Computational Chemistry” (Wiley), although the latter focuses on the theory of electronic structure methods. Cramer’s “Essentials” covers force field and molecular orbital theory, Monte Carlo and Molecular Dynamics simulations, thermodynamic and electronic (spectroscopic) property calculation, condensed phase treatment and a few more topics. Moreover, the book contains thirteen selected case studies sexamples taken from the literature sto illustrate the application of the just presented theoretical and computational models. This especially makes the text book well suited for both classroom discussion and self-study. Each chapter of “Essentials” covers a main topic of computational chemistry and will be briefly described here; all chapters are ended by a bibliography and suggested additional readings as well as the literature references cited in the text. In chapter 1 the author defines basic terms such as “theory”, “model”, and “computation”, introduces the concept of the potential energy surface and provides some general considerations about hardware and software. Interestingly, the first equation occurring in the text is not Schro ̈dinger’s equation, as is the case for most computational chemistry introductions, but the famous Einstein relation. The second chapter deals with molecular mechanics. It explains the different potential energy contributions, introduces the field of structure optimization, and provides an overview of the variety of modern force fields. Chapter 3 covers the simulation of molecular ensembles. It defines phase space and trajectories and shows the formalism of, and problems and difference between, Monte Carlo and molecular dynamics. In chapter 4 the author introduces the foundations of molecular orbital theory. Basic concepts such as Hamilton operator, LCAO basis set approach, many-electron wave functions, etc. are explained. To illuminate the LCAO variational process, the Hu ̈ckel theory is presented with an example. Chapter 5 deals with semiempirical molecular orbital (MO) theory. Besides the classical approaches (extended Hu ̈ckel, CNDO, INDO, NDDO) and methods (e.g., MNDO, AM1, PM3) and their performance, examples are provided from the ongoing development in that still fascinating area. Ab initio MO theory is presented in chapter 6; the basis set concept is discussed in detail, and, after some considerations from an user’s point of view, the general performance of ab initio methods is explicated. The next chapter covers the problem of electron correlation and gives the most prominent solutions for its treatment: configuration interaction, theory of the multiconfiguration self-consistent field, perturbation, and coupled cluster. Practical issues are also discussed. Chapter 8’s topic is density functional theory (DFT). Its theoretical foundation, methodology, and some functionals as well as its pros and cons compared to MO theory are presented together with a general performance overview. The next two chapters deal with charge distribution, derived and spectroscopic properties (e.g., atomic charges, polarizability, rotational, vibrational, and NMR spectra), and thermodynamic properties (e.g., zero-point vibrational energy, free energy of formation, and reaction). The modeling of condensed phases is addressed in chapters 11 (implicit models) and 12 (explicit models), which closes with a comparison between the two approaches. Chapter 13 familiarizes the reader with hybrid quantum mechanical/molecular mechanical (QM/MM) models. Polarization as well as the problematic implications of unsaturated QM and MM components are discussed, and empirical valence bond methods are also presented. The treatment of excited states is the topic of chapter 14; besides CI and MCSCF as computational methods, transition probabilities and solvatochromism are discussed. The last chapter deals with reaction dynamics, mostly adiabaticskinetics, rate constants, reaction paths, and transition state theory are section topics here sbut also nonadiabatic, introducing curve crossing and Marcus theory in brief. The appendix is divided into four parts: an acronym glossary (which is very helpful), an overview of symmetry and group theory, an introduction to spin algebra, and finally a section about orbital localization. A rather detailed index ends the book. The “Essentials” writing style fits the fascinating topic: one reads on and on andssurprise! sanother chapter has been absorbed. The text is complemented by a large number of black and white figures and clear tables, mostly self-explanatory with descriptive captions. The use of equations and mathematical formulas in general is well-balanced, and the level of math should be understandable for every natural scientist with some basic knowledge of physics. There are only a few minor shortcomings: for example, a literature reference cited in the text (“Beck et al.”, p 142) is missing in the bibliography; “Kronecker” is mistyped with o ̈; and the author completely forgot to reference Leach’s text book when referring to other computational chemistry introductions. However, the author has established a specific errata web page (http://pollux.chem.umn.edu/ ∼cramer/Errors.html) with all known errors. These will be corrected in the next printing or next revised edition, respectively. With its emphasis, on one hand, on the basic concepts and applications rather than pure theory and mathematics, and on the other hand, coverage of quantum mechanical and classical mechanical models including examples from inorganic, organic, and biological chemistry, “Essentials” is a useful tool not only for teaching and learning but also as a quick reference, and thus will most probably become one of the standard text books for computational chemistry.

Essentials Of Computational Chemistry Theories And Models

Friction welding (FW) is a high quality, nominally solid-state joining process, which produces welds of high structural integrity. Rotary friction welding (RFW) is the most commonly used form of FW, while linear friction welding (LFW) is a relatively new method being used mainly for the production of integrally bladed disc (blisk) assemblies in the aircraft engine industry. Numerous similar and dissimilar joints of structural metallic materials have been welded with RFW and LFW. In this review, the current state of understanding and development of RFW and LFW is presented. Particular emphasis is placed on the process parameters, joint microstructure, residual stresses, mechanical properties and their relationships. Finally, opportunities for further research and development of the RFW and LFW processes are identified.

Linear and rotary friction welding review

EBSD analysis of evolution of dynamic recrystallization grains and δ phase in a nickel-based superalloy during hot compressive deformation

Linear friction welding (LFW) is a solid state joining process in which a joint between two metals can be formed through the intimate contact of a plasticised layer at the interface of the adjoining specimens. This plasticised layer is created through a combination of frictional heating, which occurs as a result of pushing a stationary workpiece against one that is moving in a linear reciprocating manner, and applied force. The process is currently established as a niche technology for the fabrication of titanium alloy bladed disc (blisk) assemblies in aeroengines, and is being developed for nickel based superalloy assemblies. However, interest is growing in utilising the process in a wider range of applications that also employ non-aeroengine metallic materials. Therefore, it is the objective of this report to provide a broad view of the capabilities of the LFW process for joining metals. This review paper will cover relevant published work conducted to date on LFW. The basics of the process and ...

Solid state joining of metals by linear friction welding: A literature review

Numerical simulation of linear friction welding of titanium alloy: Effects of processing parameters

In this work, Ti-6Al-4V alloy was jointed by linear friction welding (LFW). A sound weld of thickness about 65-115 μm was obtained under the present processing parameters. The weld consisted of a superfine a + β microstructure, which is associated with the quick heating and cooling processes involved in LFW. This superfine microstructure contributes to the higher hardnesses of weld (422 ± 11Hv 0.2 ) than that of parent Ti-6Al-4V (302 ± 20 Hv 0.2 ). The tensile properties of weld are comparable to or higher than those of parent Ti-6Al-4V.

Microstructure Characterization and Mechanical Properties of Linear Friction Welded Ti‐6Al‐4V Alloy

Finite element modeling of the linear friction welding of GH4169 superalloy

Friction welding (FW) is a collection of a series of friction-based solid state joining processes which can produce high quality welds of different components with either similar or dissimilar materials and has been attracting increasing attention. Due to the extreme condition encountered during FW and the highly thermomechanical coupled nature of FW, finite element methods have been widely developed to study the FW process. In the light of reasonable simplification, we developed several effective methods based on the ABAQUS environment. Initially 2D models were developed to investigate the complete FW process, where an implicit method with remeshing and map solution techniques and an explicit method with the Arbitrary Lagrangian Eulerian (ALE) adaptive mesh controls were proposed to effectively overcome the excessive element distortion by using the ABAQUS Standard and Explicit packages, respectively. In addition, a 3D model was also developed to obtain better simulation results with the help of the ALE adaptive mesh controls in the ABAQUS/Explicit package and the map solution technique in the ABAQUS/Standard package combined with the HYPERWORKS software. The experiments validate the feasibility and accuracy of the developed models.

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Tiejun Ma

Papers

Linear and rotary friction welding review

Numerical simulation of linear friction welding of titanium alloy: Effects of processing parameters

Microstructure Characterization and Mechanical Properties of Linear Friction Welded Ti‐6Al‐4V Alloy

Finite element modeling of the linear friction welding of GH4169 superalloy

Numerical Simulation of Friction Welding Processes Based on ABAQUS Environment