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2024 | Book

Algebraic Equations of Linear Elasticity

Novel Force-based Methods for Solid Mechanics with MATLAB®

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About this book

This book describes a second-generation force-based method emerging from a general formulation where the partial differential equations of elasticity are replaced by equivalent algebraic equations. These algebraic equations of linear elasticity can be used to solve statically indeterminate problems in

reduced forms that define either the new second-generation force-based approach or a new displacement-based approach. The new force-based method can serve as the basis for teaching students at many technical levels how to solve equilibrium problems directly for the forces present. In

elasticity courses, the derivation and use of the algebraic equations of linear elasticity can show how the difficulties of dealing with partial differential equations may be avoided by transforming those equations into algebraic equations with work-energy concepts. In a finite element course, a force-based finite element method can be described along with the traditional displacement-based approach to demonstrate how the two methods provide alternative ways for solving complex structural problems. Serving as a resource for including second-generation force-based methods in solid mechanics courses

of an engineering curriculum, and as a robust learning resource, the book is ideal for instructors and for students, practicing engineers, and researchers.

Table of Contents

Frontmatter
Chapter 1. Introduction
Abstract
This introduction outlines how work-energy principles can be used to transform the differential equations of linear elasticity into equivalent algebraic equations. Those equations can be reduced to two forms—(1) a displacement-based method like the method used in finite elements and (2) a new force-based method for the solution of statically indeterminate problems that combines equilibrium and compatibility equations, which is also called the second-generation force-based method. This force-based method is compared to an earlier first-generation force-based method. A discussion is given on how second-generation force-based methods can be applied to all the courses found in an engineering curriculum at the technical levels assumed for students in those courses.
Lester W. Schmerr Jr.
Chapter 2. Algebraic Equations of Linear Elasticity and Their Solutions
Abstract
A detailed derivation is given of the algebraic equations of elasticity that correspond to their differential equation counterparts. These algebraic equations are then reduced to two forms—one based on forces and another based on displacements. The new displacement approach is shown to be like the standard finite element method, where a stiffness matrix is used to solve for the displacements in statically indeterminate problems, but where the stiffness matrix is formed from equilibrium and inverse flexibility matrices. The force approach is based on equilibrium and compatibility equations and flexibility matrices where the compatibility equations are obtained from homogeneous solutions of the equilibrium equations. The reduced force-based and displacement-based methods are described in detail for a simple statically indeterminate problem using the symbolic algebra capabilities of MATLAB to demonstrate a highly efficient approach to solving problems at all technical levels in an engineering curriculum.
Lester W. Schmerr Jr.
Chapter 3. Force-Based Methods in Statics
Abstract
A new second-generation force-based method is used to solve statically indeterminate problems at the technical level of an engineering statics course. Two-dimensional and three-dimensional examples like those found in a statics course are treated with the force-based approach when there are too many unknown forces or moments to solve the problems with the equations of equilibrium alone. The symbolic algebra capabilities of MATLAB are combined with the force-based method to demonstrate a highly effective approach for solving problems in an engineering statics course. It is also shown how the displacements present in statically indeterminate problems can be found with the force-based method.
Lester W. Schmerr Jr.
Chapter 4. Force-Based Methods in Strength of Materials
Abstract
A new second-generation force-based method is used to solve statically indeterminate axial extension and torsion problems. To apply the method, it is shown how distributed forces and torques must be replaced by discrete forces and torques. Once all the unknown forces or torques are found, it is shown how singularity functions can be used to describe and plot the internal forces or torques. The alternative use of a pseudo stiffness matrix to determine the displacements and then subsequently the forces is also described. The relationship of the force-based method applied in this chapter to a force-based finite element method is also discussed.
Lester W. Schmerr Jr.
Chapter 5. Force-Based Methods in Advanced Strength of Materials
Abstract
A new second-generation force-based method is used to solve statically indeterminate beam bending and the extension, bending, and torsion of frames. To apply the method, it is shown how distributed forces, moments, and torques must be replaced by discrete forces, moments, and torques acting at nodes. Once all the unknown forces, moments, and torques are found, singularity functions are used to describe and plot the internal force, moments, and torques. The second moment area theorem is used to determine the flexibility matrix. The relationship of the force-based method applied in this chapter to a force-based finite element method is also discussed.
Lester W. Schmerr Jr.
Chapter 6. Force-Based and Displacement-Based Finite Elements
Abstract
The traditional displacement-based finite element method forms stiffness matrices for elements of a structure and assembles those elements into a global stiffness matrix that is then solved for the displacements and, subsequently, the forces. In the force-based method discussed in this book, a global equilibrium matrix is assembled from the equilibrium equations written at discrete nodes in the structure and then combined with compatibility equations to solve for the forces and, subsequently, the displacements. However, a global equilibrium matrix can also be assembled from element equilibrium matrices, in a process very similar to the displacement-based finite element method and is called here the force-based finite element method. Both force-based and displacement-based finite element methods are described with one-dimensional examples. Problems where there are nonzero-specified displacements are also considered. MATLAB displacement-based and force-based finite element scripts are presented.
Lester W. Schmerr Jr.
Backmatter
Metadata
Title
Algebraic Equations of Linear Elasticity
Author
Lester W. Schmerr Jr.
Copyright Year
2024
Electronic ISBN
978-3-031-66174-7
Print ISBN
978-3-031-66173-0
DOI
https://doi.org/10.1007/978-3-031-66174-7

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