Search Results for plastic flow

This chapter covers the fundamentals of metal flow and the tools and techniques used to predict and control it. It begins by illustrating the local state of stress in a metal cylinder during upset forging and showing how stress components can be expressed in matrix form. It then explains how to determine the onset of yielding, which corresponds to the start of plastic deformation and the flow of metal within the workpiece. The chapter then goes on to present two important yield criteria, one based on shear stress (Tresca criterion), the other on distortion energy (von Mises criterion). It compares and contrasts the two methods and demonstrates their use as flow rules. It also explains how to calculate effective strain and strain rate and includes a brief discussion on the mechanical energy consumed during deformation.

The design and optimization of sheet metal forming operations is aided by tools and techniques that have been developed and refined over several decades. This chapter covers many of these methods and practices and explains where and how they are used. It begins by showing how the stress state at any point in a material can be expressed in different ways for different purposes. It then compares and contrasts some of the more widely used yield criteria and demonstrates the use of flow rules. It also explains how to calculate power, energy, and effective strain and strain rate and how hardening laws are used to predict strain-hardening behaviors.

This chapter discusses the factors that influence the load-deformation relationship at the heart of most metal forming operations. It describes the changes that occur in tensile test samples and the various ways test data can be plotted and analyzed, particularly for design purposes. It discusses the effect of normal and planar anisotropy, the development and use of flow stress curves, and how formability is usually measured and expressed. It explains how formability measurements serve as a guide for process and tool design engineers as well as others. It also discusses the development and use of forming limit curves and the extensive amount of information they provide.

This chapter deals with the effects of fatigue in rotating shafts subjected to elastic and plastic strains associated with bending stresses. It begins with a review of the basic approach to treating low-cycle fatigue in bending, explaining that the assumption that stress is proportional to strain is incorrect due to plastic flow, causing considerable discrepancy between measured and calculated stresses. Data plots of the axial and bending fatigue characteristics of a 4130 steel help illustrate the problem. A closed-form solution is then presented and used to analyze the effects of flexural bending on solid as well as hollow rectangular and round bars. The chapter also discusses the difference in the treatment of a rotating shaft in which all surface elements undergo the same stress and strain and a nonrotating shaft in which a few surface elements carry most of the load. The difference, as explained, is due to the volumetric effect of stress in fatigue.

Hydrogen damage is a form of environmentally assisted failure that results most often from the combined action of hydrogen and residual or applied tensile stress. This chapter classifies the various forms of hydrogen damage, summarizes the various theories that seek to explain hydrogen damage, and reviews hydrogen degradation in specific ferrous and nonferrous alloys. The preeminent theories for hydrogen damage are based on pressure, surface adsorption, decohesion, enhanced plastic flow, hydrogen attack, and hydride formation. The specific alloys covered are iron-base, nickel, aluminum, copper, titanium, zirconium, vanadium, niobium, and tantalum alloys.

This chapter presents a qualitative and quantitative overview of the stresses, strains, forces, and energy associated with metalworking processes and the tribological behavior of metals. It covers key concepts necessary for understanding metalworking tribology, including plastic deformation, yield criteria, flow strength, and the application of flow rules. It explains how to calculate the work involved in deformation processes, how to assess the propensity for fracture, how to determine temperature rise and strain distribution in the workpiece, and how to classify metalworking processes based on related tribology.

This chapter focuses on the processes and mechanisms involved in fatigue. It begins with a review of some of the early theories of fatigue and the tools subsequently used to obtain a better understanding of the fatigue process. It then explains how plasticity plays a major role in creating dislocations, breaking up grains into subgrains, and causing microscopic imperfections to coalesce into larger flaws. It also discusses the factors that contribute to the development and propagation of fatigue cracks, including surface deterioration, volumetric and environmental effects, foreign particles, and stresses generated by rolling contact.

The mechanical properties of a material describe the relations between the stresses acting on the material and its resulting deformations. Stresses capable of producing permanent deformations, which remain after the stresses are removed, are considered in this chapter. The effects of cryogenic temperatures on the mechanical properties of metals and alloys are reviewed in this chapter; the effects on polymers and glasses are discussed briefly. The fundamental mechanisms controlling temperature-dependent mechanical behavior, phenomena encountered in low-temperature testing, and the mechanical properties of some representative engineering metals and alloys are described. Modifications of test procedures for low temperatures and sources of data are also included.

Metals are used in many engineering applications because of their mechanical properties, particularly strength and ductility. This chapter explains how mechanical properties are measured and how to interpret the results. It describes the most widely used tests, including tensile tests; Rockwell, Brinell, Vickers, and Knoop hardness tests; and Charpy V-notch impact tests. The chapter also provides information on loading conditions that can lead to fatigue failure, and in some cases, counteract or prevent it.

This chapter introduces basic extrusion concepts, including types, processes, mechanics, and the principal variables and their effects on extrusion. The chapter defines the two basic types of extrusion commonly used in the aluminum extrusion industry, direct and indirect. The chapter discusses the mechanics of extrusion including plastic deformation and metal flow, plastic strain and strain rate, extrusion pressure, and extrusion force. The principal variables of extrusion, including billet material flow stress, extrusion ratio, dead-metal zone semiangle, speed of deformation, and extrusion temperature are discussed.