Deformation-Based Processing of Materials

Behavior, Performance, Modeling, and Control

Heng Li, Mingwang Fu

• Publisher: Elsevier
• Year: 2019
• ISBN:
  9780128143827
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Deformation Based Processing of Materials: Behavior, Performance, Modeling and Control focuses on deformation based process behaviors and process performance in terms of the quality of the needed shape, geometries, and the requested properties of the deformed products. In addition, modelling and simulation is covered to create an in-depth and epistemological understanding of the process. Other topics discussed include ways to efficiently reduce or avoid defects and effectively improve the quality of deformed parts. The book is ideal as a technical document, but also serves as scientific literature for engineers, scientists, academics, research students and management professionals involved in deformation based materials processing.

• Covers process behaviors, such as non-uniform deformation, unstable deformation, material flow phenomena, and process performance
• Includes modelling and simulation of the entire deformation process
• Looks at control of the preferred deformation, undesirable material flow, avoidance and reduction of defects, and improving the dimensional accuracy, surface quality and microstructure construction of the produced products

Chapter 1

Introduction to Deformation-Based Manufacturing

Abstract

This chapter presents a brief introduction to the deformation-based processing of materials on a technical fundamental and theoretical basis. The issues related to deformation-based materials processing technology, process behavior and product performance, bottlenecks in manufacturing of products via deformation of materials, undesirable deformation in the process, deformation defects and their underlying mechanisms, defect prediction, modeling and simulation of the entire deformation process, the undesirable deformation control, etc., are summarized and articulated here. Once these issues are addressed, how to achieve defect-free deformation and control the deformation to ensure the needed geometries and the tailored properties are elucidated and delineated are discussed. This chapter also covers the main contents of the book.

Keywords

Deformation-based materials processing; inhomogeneous deformation; deformation defects; modeling and simulation; shape and geometry achieving; properties tailoring

1.1 Introduction

Deformation-based processing of materials is one of the most important ways to manufacture parts and components due to its high productivity, low production cost, excellent material utilization, and superior properties of fabricated parts. This manufacturing process has been widely used to shape materials into the desirable geometries as well as tailor the properties of deformed parts. Sheet and bulk metallic products fabricated by deformation-based manufacturing process are extensively applied in different industry clusters, ranging from computer, home appliance, medical devices, consumer electronics, automobile to aerospace industries. Among the four basic manufacturing processes, that is, casting, machining, joining, and deformation, deformation-based materials processing can remarkably exploit the ability of material plastic flow in the solid state to produce components with enhanced material properties. It is also well recognized that about 70% of metallic products are handled by deformation-based manufacturing [1,2].

Deformation processing is frequently used in conjunction with other processes such as casting, machining, welding and heat treating to transform raw materials to finished and assembly-ready discrete parts. The deformation process, along with the other manufacturing processes mentioned above, has been at the kernel of the modern mass production chain for shaping of the geometries of parts and components and tailoring of the required properties because it involves the severe metal flow and the metallurgical evolution of materials.

Nowadays, the high demands for shorter development lead-time, lower production cost, better dimensional accuracy and improved overall quality have created new challenges in deformation-based manufacturing for the companies to use this technology to maintain and enhance their competitiveness and technological cutting-edge in marketplace. As an efficient manufacturing technology, deformation-based materials processing has been revitalized to meet the increasing demand for lightweight and high-performance products, and to address the escalating concerns about environmental impact, energy consumption and material utilization in manufacturing arena [3,4].

In deformation-based manufacturing, nonuniform stress and strain distributions are frequently induced. When inappropriate thermal–mechanical loading is applied, unstable deformation can occur and cause various multiscale defects along with issues such as damage, ductile fracture, compressive instability, surface roughening, etc. [5]. The occurrence of different types of defects directly affects the behavior and performance of the deformation process and the quality of the deformed parts, limiting the applications of deformation-based materials processing and manufacturing [6]. There are also many challenging problems as well as upstream research topics to explore in terms of deformation behavior and process performance. If these challenges are addressed—how to control deformation, assure product quality, and avoid defect formation—it would be possible for this unique manufacturing process to grow.

This chapter presents an introduction to deformation-based processing of materials from three aspects: deformation of materials, processing classification, and process behavior and product performance. The desirable and undesirable deformation behaviors are discussed, and the deformation-induced defects and flow instabilities are classified and articulated in terms of the geometry and shape-related defects, and the property and performance-related ones. An epistemological understanding of the challenges in achieving accurate shaping along with tailoring bespoke properties and performance of deformed parts is given. Multiscale and multiphysics modeling and simulation of the entire deformation process as well as the robust and optimal design of defect-free forming process, tailoring of the needed properties, and assuring the required quality. This chapter summarizes the above-described issues and systematically addresses them in the subsequent chapters in this book.

1.2 Deformation of Materials

Deformation is one of the most important and ubiquitous physical phenomena in product production and service. The deformation of materials can be referred to as the change in the shape or size of materials caused by mechanical force, thermal loading or phase transformation, etc. Deformation is often represented by strain. From a mechanical behavior perspective, deformation can be classified as elastic and plastic deformation. During the deformation process, two main changes happen: the geometry change in the deformation body and the microstructure evolution of materials. Shape forming and properties tailoring are thus two key tasks in deformation-based manufacturing. To fully understand the potential deformation capability of materials, in-depth insight into the multiple physical mechanisms of materials should be systematically obtained [7–9]. In this section, the focus is first on the multiple mechanisms of deformation, and then the above-mentioned two key tasks are covered in detail.

1.2.1 Physical Mechanisms of Deformation

Fig. 1.1 demonstrates the schematic view of elastic and plastic deformation of metallic materials. When the stress does not exceed the yield stress of material, the material is in the elastic deformation stage and the deformation is recoverable. Materials in the plastic deformation stage, however, generally undergo the elastic deformation first, which involves temporary stretching or bending of the bonds between atoms, but the atoms do not slip past each other. Elastomers and shape-memory metals such as Nitinol exhibit significant elastic deformation. Soft thermoplastics and conventional metals, on the other hand, have a moderate elastic deformation range. Ceramics, crystals, and hard thermosetting plastics, however, generally undergo almost no elastic deformation. To represent the elastic deformation, Hooke’s law is generally used to describe the linear elasticity of materials while Young’s modulus represents the strength of the bonds of atoms as well as the density and directionality of the atoms. The nonlinear elasticity of materials is also a ubiquitous property and has different properties such as anelasticity, viscoelasticity, pseudoelasticity, and Bauschinger effect.

Figure 1.1 Schematics of elastic and plastic deformation.

When the stress is sufficient enough to permanently deform the materials, the deformation is then called plastic deformation, which involves the breaking of a limited number of atomic bonds via the movement of dislocations, as shown in Fig. 1.1. The force needed to break the bonds of all the atoms in a crystal plane all at once is very great. However, the movement of dislocations allows atoms in crystal planes to slip past one another at a much lower stress level. Since the energy required for the slip movement is the lowest along the densest planes of atoms, dislocations have a preferred travel direction within a grain of the material. Slip occurs when the shear stress applied exceeds a critical value. As can be seen, the experimentally observed value of the critical resolved shear stress is quite low as compared to the theoretically calculated value since dislocations already exist in the crystal structure as a result of imperfections (defects) in the crystal structure during solidification. There is thus no need to create a dislocation for deformation, but simply to start an existing one on the slip plane. In general, there are two basic types of dislocation movements: glide and climb. With glide, dislocations move along a surface defined by its line and Burger’s vector, and is considered as the conservative motion of dislocations. With climb, on the other hand, the dislocation moves out of the glide surface and thus becomes a nonconservation motion of dislocation.

For most crystal materials, plastic deformation is realized via slip movements. But for materials with fewer slip systems, such as body-centered cubic (BCC) and hexagonal close packed (HCP) metals, twinning is a vital means of deformation, as shown in Fig. 1.2. Twinning is a movement of planes of atoms in the lattice parallel to a specific (twinning) plane. Atoms in the twinning process move only a fraction of an interatomic space, leading to change of the lattice structure in the twinned region. The amount of movement of each plane of atoms in the twinned region is proportional to its distance away from the twinning plane. Therefore, twinning is a process of the rearrangement of local atoms in the crystal subjected to deformation, which causes the orientation change of the involved atoms in such a way to become a mirror image of the other part. The plane across which the two parts form the mirror images is called the twinning plane or composition plane. Like slip, twinning also occurs along certain crystallographic planes and directions. These planes and directions are referred to as the twin plane and twin direction. Twinning plays an important role in plastic deformation because it causes changes in plane orientation allowing further slips to happen.

Figure 1.2 Slip lines and twin bands: (A) schematic of slip bands; (B) slip bands in Waspaloy alloy [10]; (C) schematic of twin bands; (D) twin networks in magnesium alloy [11].

In addition to slip, twinning, or their combination and interplay in single crystals, there are other complex deformation mechanisms responsible for accommodating the large plastic deformation or inelastic strain of polycrystalline. More than one mechanism may be active under a given set of deformation conditions and some mechanisms cannot operate independently but must act in conjunction with another so that a significant permanent strain can be developed. Generally, the deformation mechanism map can be used to display the relationship among the three macroscopic variables, that is, stress σ_s, temperature T, and strain rate

. The various regions of the map represent the corresponding dominant deformation mechanisms under the different combinations of stress and temperature. Note that in a single deformation episode, the dominant mechanism may change with time, such as recrystallization to refine ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Preface
• Acknowledgments
• Chapter 1. Introduction to Deformation-Based Manufacturing
• Chapter 2. Deformation Inhomogeneity
• Chapter 3. Damage Evolution and Ductile Fracture
• Chapter 4. Deformation-Induced Compressive Instability
• Chapter 5. Deformation-Induced Springback Defects
• Chapter 6. Inhomogeneous Deformation-Induced Surface Roughening Defects
• Chapter 7. Inhomogeneous Deformation–Induced Flow Defects
• Chapter 8. Microstructure Abnormality-Related Defects
• Index