1.1Introduction
1.2Analytical Modeling and Computer Simulation
1.2.1Operations Prediction Using Analysis
1.2.2Simulation
1.2.3Computer Languages and Tools
1.3Digital Design and Rapid Prototyping
1.3.1Computer-Aided Design Technology
1.3.2Biologically Inspired Design and Manufacturing
1.4Advances in Fabrication and Machining Techniques
1.5Joining Techniques
1.6Use of In Situ or Recycled Materials and Structure
1.7Nondestructive Evaluation, Nondestructive Testing, and Structural Health Monitoring
1.8Summary/Conclusions
Acknowledgment
References
Internet Links
1.1Introduction
Parts, structures and systems conception, fabrication, processing, operation, and retirement from service have equivalences to biological systems’ life stages, from conception, through aging, to grave. In recent years, numerous advances have been made in all the technology areas that are used throughout the “life” stages, from design, through production, to recycling. The significant developments in digital tools have been a major contributor to the enabling of the enormous capabilities that have emerged, and they include the simulation and testing of many production steps even before producing a physical prototype. The emerging processes include methods of precision subtractive and additive manufacturing. The subtractive processes consist of using blades, drill bits, water jets, or laser beams to remove material from products and shaping them as three-dimensional (3D) objects. On the other hand, additive processes consist of applying and/or depositing successive material layers to form desired shapes (e.g., 3D printing), and many of these processes have been considered science fiction until not too long ago. They may involve using combinations of materials and configurations for producing complex configurations and structures. This book covers some of the latest advances in manufacturing and processing of materials and structures from conception to retirement, providing a snapshot of the state-of-the-art. This chapter briefly reviews the state-of-the-art of the manufacturing and processing methods in the digital era.
1.2Analytical Modeling and Computer Simulation
Using software tools supported by analytical modeling and computer simulation is critical to designing structures and systems. This is accomplished using mathematical models, also known as analytical models, which may or may not have a closed form solution. The models involve solving equations that describe changes in a system behavior that are expressed as mathematical functions in analytic form. In contrast, numerical models are discrete time- or space-related procedures used for obtaining system behavior and the solutions are represented by numbers arranged in a generated table and/or graphical form. Since the mathematical solution of analytical models can be very complex, numerical solutions are widely used, and computer tools allow performing the analyses efficiently and very fast. Obtaining an analytical or numerical solution to a mathematical model involves the generation and interpretation of graphs that show the system’s behavior over time and space and its sensitivity to variations in the key parameters present in the model. One disadvantage of analytical solutions is that, if they exist, they are often very mathematically challenging to obtain.
1.2.1Operations Prediction Using Analysis
In physics and engineering, analysis is used to predict the operation and performance of a structure or system that is being designed and produced. Analysis is also used in business applications where a variety of statistical techniques, including predictive modeling, machine learning, and data mining, are used to analyze the current and historical facts in order to infer behavior and make prediction of future trends or unknown events. For the latter, predictive models use patterns that have been extracted from historical and transactional data and identify risks and opportunities. The developed models determine the relationships between the many factors that are involved in order to assess the risks or potentials related to a specific set of conditions for decision making. The analyses are executed on computers of various sizes and capabilities using variety of computation functions and software features.
One of the most important numerical techniques that are used to solve problems is the finite element method (FEM), which is also referred to as finite element analysis (FEA). This technique determines for partial differential equations (PDEs) approximate solutions to boundary value problems under different boundary conditions. Effectively, large problems are subdivided into smaller, simpler segments called finite elements. The simple equations that model the finite elements are then combined into a larger system of equations that model the complete problem being solved. Then, by minimizing a related error function, variational methods are used to approximate a solution. The process involves dividing the problem domain into many subdomains, each representing a set of element equations to the original problem. The element equations are simple equations that locally approximate the original complex equations, and they are often PDEs. For the final calculation, the set of equations are combined into a global system of equations.
To divide a complex problem into small elements, mesh generation techniques are used and software programs are coded with FEM algorithms. In recent years, meshless techniques (Atluri and Shen, 2002; Liu, 2002) and equation-free techniques (Kevrekidis and Samaey, 2009) have emerged. The subdividing of the full domain into simpler parts has several advantages in solving complex problems. The advantages include easier representation of the total solution; addressing local effects; as well as accurately representing complex geometry and material properties that are dissimilar. There are various widely used FEM tools, and they include the following:
NASTRAN (www.mscsoftware.com/product/msc-nastran) is a FEA program that was originally developed in the late 1960s for the National Aeronautics and Space Administration (NASA) by Stephen Burns of the University of Rochester. In 1971, NASTRAN has been first released to the public by the NASA’s Office of Technology Utilization. MacNeal-Schwendler Corporation was one of the original developers of the publicly available NASTRAN code. It was originally written to help in designing more efficient space vehicles, including the Space Shuttle. NASTRAN is widely used to analyze the behavior of elastic and inelastic structures of any size or shape. This FEA program is used today throughout the world in aerospace, automotive, and marine industries to perform such analyses as linear elastic static and dynamic analyses. This computer program consists of several modules, and its source code is integrated in a number of different software packages that are distributed by several companies. It is primarily written in the computer language FORTRAN, and it is compatible with a large variety of computers and operating systems ranging from small workstations to largest supercomputers. Its modules consist of a collection of subrouti...
