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An Introduction to Lagrangian Mechanics begins with a proper historical perspective on the Lagrangian method by presenting Fermat's Principle of Least Time (as an introduction to the Calculus of Variations) as well as the principles of Maupertuis, Jacobi, and d'Alembert that preceded Hamilton's formulation of the Principle of Least Action, from which the Euler-Lagrange equations of motion are derived. Other additional topics not traditionally presented in undergraduate textbooks include the treatment of constraint forces in Lagrangian Mechanics; Routh's procedure for Lagrangian systems with symmetries; the art of numerical analysis for physical systems; variational formulations for several continuous Lagrangian systems; an introduction to elliptic functions with applications in Classical Mechanics; and Noncanonical Hamiltonian Mechanics and perturbation theory.This textbook is suitable for undergraduate students who have acquired the mathematical skills needed to complete a course in Modern Physics.
On Fracture Mechanics A major objective of engineering design is the determination of the geometry and dimensions of machine or structural elements and the selection of material in such a way that the elements perform their operating function in an efficient, safe and economic manner. For this reason the results of stress analysis are coupled with an appropriate failure criterion. Traditional failure criteria based on maximum stress, strain or energy density cannot adequately explain many structural failures that occurred at stress levels considerably lower than the ultimate strength of the material. On the other hand, experiments performed by Griffith in 1921 on glass fibers led to the conclusion that the strength of real materials is much smaller, typically by two orders of magnitude, than the theoretical strength. The discipline of fracture mechanics has been created in an effort to explain these phenomena. It is based on the realistic assumption that all materials contain crack-like defects from which failure initiates. Defects can exist in a material due to its composition, as second-phase particles, debonds in composites, etc. , they can be introduced into a structure during fabrication, as welds, or can be created during the service life of a component like fatigue, environment-assisted or creep cracks. Fracture mechanics studies the loading-bearing capacity of structures in the presence of initial defects. A dominant crack is usually assumed to exist.
The chapters of this book summarize the lectures delivered du ring the NATO Advanced Study Institute (ASI) on Computational Methods in Mechanisms, that took place in the Sts. Constantin and Elena Resort, near Varna, on the Bulgarian Coast of the Black Sea, June 16-28, 1997. The purpose of the ASI was to bring together leading researchers in the area of mechanical systems at large, with special emphasis in the computational issues around their analysis, synthesis, and optimization, during two weeks of lectures and discussion. A total of 89 participants from 23 count ries played an active role during the lectures and sessions of contributed papers. Many of the latter are being currently reviewed for publication in specialized journals. The subject of the book is mechanical systems, Le. , systems composed of rigid and flexible bodies, coupled by mechanical means so as to constrain their various bodies in a goal-oriented manner, usually driven under computer con- trol. Applications of the discipline are thus of the most varied nature, ranging from transportation systems to biomedical devices. U nder normal operation conditions, the constitutive bodies of a mechanical system can be consid- ered to be rigid, the rigidity property then easing dramatically the analysis of the kinematics and dynamics of the system at hand. Examples of these systems are the suspension of a terrestrial vehicle negotiating a curve at speeds within the allowed or recommended limits and the links of multiaxis industrial robots performing conventional pick-and-place operations.
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