Analysis of Engineering Structures and Material Behavior

Josip Brnic

• Publisher: Wiley
• Year: 2018
• ISBN:
  9781119329060
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Mechanical Engineering
• Index: Technology & Engineering

Theoretical and experimental study of the mechanical behavior of structures under load

Analysis of Engineering Structures and Material Behavior is a textbook covering introductory and advanced topics in structural analysis. It begins with an introduction to the topic, before covering fundamental concepts of stress, strain and information about mechanical testing of materials. Material behaviors, yield criteria and loads imposed on the engineering elements are also discussed. The book then moves on to cover more advanced areas including relationships between stress and strain, rheological models, creep of metallic materials and fracture mechanics. Finally, the finite element method and its applications are considered.

Key features:

• Covers introductory and advanced topics in structural analysis, including load, stress, strain, creep, fatigue and finite element analysis of structural elements.
• Includes examples and considers mathematical formulations.
• A pedagogical approach to the topic.

Analysis of Engineering Structures and Material Behavior is suitable as a textbook for structural analysis and mechanics courses in structural, civil and mechanical engineering, as well as a valuable guide for practicing engineers.

1
Introduction

1.1 The Task of Design and Manufacture

The design of structures and machines that need to be safe, reliable and economical, and the estimation of their service life at some point in time, has recently been based on iterative procedures, capacitive computers and numerical analysis. In recent times, a very powerful tool in the aforementioned analysis has been the finite element method.

Practically all fields of human activity are involved in design processes. Problems that need to be solved relate to transportation, buildings, water systems, communication systems, and so on [1]. The same goes for the production processes and metal‐forming processes by which products are created.

The designer (manufacturer) of the product needs to be familiar with the mechanical behavior of materials, specifically with such topics as deformation, fatigue and fracture. Emphasis is placed on methods (numerical and predictive) that can be useful in avoiding any kind of failure. Such methods usually take a mechanics viewpoint. The resistance of materials to failure is expressed by material properties such as tensile strength, yield strength, fracture toughness, creep resistance, and so on. Of course, an understanding of the data related to the mentioned material properties is also required. The main task in designing a structure is to ensure that the final product is the optimal one; i.e. it must meet its purpose, it must be economical and it must comply with the prescribed durability and safety requirements.

1.2 Factors that Influence the Design of Engineering Structures

When we use the word structure, we are usually referring to the design of a construction. Therefore, in engineering design we often use the words “structure” and “construction” interchangeably. However, in human life, the word “structure” can have another meaning: the structure of a process or system. The words “structures,” “machines” and “materials” are interrelated. Each machine is also a construction, but each structure does not have to be a machine. For example, a car has an engine. This engine is a kind of structure but it is not the primary structure (the body) of the car. Also, for example, the structure of an aircraft is not an engine. Many factors are involved in the design, optimization and production of the structure, such as:

• Purpose
• Materials
• Lifetime
• Safety
• Manufacturing technology.

With respect to the spatial position of elements that make up a structure, they may be combined in such a way as to produce planar or spatial structures (see Figure 1.1).

Figure 1.1 Types of structures. a–e) Planar structures. f–h) Spatial structures.

According to the relative proportions of dimensions of the structures (and their elements), structures may be categorized as:

• One‐dimensional systems (rods, beams, frames, arches, grillages, etc.);
• Two‐dimensional systems (plates, shells, disks);
• Three‐dimensional systems.

1.3 The Importance of Optimization in the Process of Design and the Selection of Structural Materials

In recent times, the processes of design and manufacture of structures have involved the application of optimization procedures. Optimization may be treated as the act of obtaining the best product under given circumstances [2]. Three main classes of structural optimization can be described:

• Sizing optimization;
• Layout/topology optimization;
• Shape optimization.

Sometimes material optimization is added as a special type of optimization. In any case, the optimization procedure that yields the optimal product includes both optimal design and manufacturing processes.

Stress and strain analysis is a part of structural analysis. However, differences between the engineering analysis of a structure, the design process and the manufacturing process need to be explained [3]. While the analysis process is concerned with determining the behavior of an existing structure, the design process is intended to calculate sizes, shapes, topology and materials for a structure. Decreasing resources, both in terms of materials and production costs, require the optimization of these processes. In this sense, when choosing a material, its availability and convenience should be considered. Modern structural design is based on the criteria of optimal design, the use of finite element analysis of stress and strain and high‐capacitive computers. Consequently, as a result of both design and manufacturing processes, the market should be offered the best product.

Many engineering applications will be subjected to high temperature conditions, or high levels of load, or are intended to be used in conditions with aggressive environments. The materials chosen for structures such as ships, pressure vessels, bridges and so on have to withstand and resist all of these different operating conditions for the required lifetime of the structure. In accordance with this, it is important to know the properties of the various materials that need to comply with the conditions of service life. Physical, chemical and mechanical properties determine the utility of the material. In this sense, designers must be familiar with different types of structures, different types of materials as well as their properties and possible manufacturing processes [4]. Materials science is concerned primarily with the basic knowledge of materials while materials engineering is concerned with the use of this knowledge, i.e. how to transform materials into products. It is known that chemical composition, the processing path and the resulting microstructure define the properties of a material [5]. The kind of properties that depend on the microstructure are called structure‐sensitive properties (for example, yield strength and hardness). Processes such as cold rolling, hot rolling and so on provide the means to develop and control the microstructure. An engineering structure is designed, manufactured, maintained and controlled in order to guarantee that it does not fail and that it serves the purpose for which it was intended. Structure lifetime predictions and safety during service life are key indicators regarding a structure’s quality and reliability.

1.4 Commonly Observed Failure Modes in Engineering Practice

A structure is designed and manufactured for a specific purpose, with a certain safety level and for a certain lifetime. The purpose of the designed structure may be, for example, to carry a load, to transport something, to store a liquid or gas or whatever. Any mechanical failure, which may be defined as any change in size, shape or material properties, can make the considered structure incapable of performing its intended function. Engineering analysis of failures, a newly established discipline in engineering practice, is of the utmost importance in engineering practice. It is an approach to determining why and how an engineering member (component) has failed, because the particular failure has a cause of origin and a form of manifestation. Understanding why and how a failure occurred can be helpful in establishing improvements in design, manufacture and the use of structures, and may provide a means to avoid similar situations in the future. Despite all the possible failures, the number of successfully designed structures may be considered satisfactory. Although in engineering practice many types of failure may occur, the structure will have been designed and manufactured with the assumption that it does not contain a fault. With regard to failures, we may consider:

• The time at which they arose;
• Their causes (why the component failed);
• The modes of their manifestation (how the component failed).

In general, two main categories of failure can be distinguished:

• Pre‐existing failures/defects;
• Failures that arose in the design, manufacture, assembly, service life, maintenance, control processes, etc. [6–13].

Pre‐existing defects can arise in a material and may be defects stemming from imperfections.

Common causes of failure that can arise in processes such as design, manufacture, service life, maintenance, and so on include misuse (or abuse), design errors, improper choi...

Table of contents

• Cover
• Title Page
• Table of Contents
• Frequently Used Symbols and the Meaning of Symbols
• Principal SI Units and the US Equivalents
• SI Prefixes, Basic Units, Physical Constants, the Greek Alphabet
• Important Notice Before Reading the Book
• Preface
• About the Author
• Acknowledgements
• 1 Introduction
• 2 Stress
• 3 Strain
• 4 Mechanical Testing of Materials
• 5 Material Behavior and Yield Criteria
• 6 Loads Imposed on Engineering Elements
• 7 Relationships Between Stress and Strain
• 8 Rheological Models
• 9 Creep in Metallic Materials
• 10 Fracture Mechanics
• 11 The Finite Element Method and Applications
• Index
• End User License Agreement