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2018 | Buch

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Mechanical Properties and Working of Metals and Alloys

verfasst von: Prof. Amit Bhaduri

Verlag: Springer Singapore

Buchreihe : Springer Series in Materials Science

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik"

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Über dieses Buch

This book is intended to serve as core text or handy reference on two key areas of metallic materials: (i) mechanical behavior and properties evaluated by mechanical testing; and (ii) different types of metal working or forming operations to produce useful shapes. The book consists of 16 chapters which are divided into two parts. The first part contains nine chapters which describe tension (including elastic stress – strain relation, relevant theory of plasticity, and strengthening methods), compression, hardness, bending, torsion – pure shear, impact loading, creep and stress rupture, fatigue, and fracture. The second part is composed of seven chapters and covers fundamentals of mechanical working, forging, rolling, extrusion, drawing of flat strip, round bar, and tube, deep drawing, and high-energy rate forming. The book comprises an exhaustive description of mechanical properties evaluated by testing of metals and metal working in sufficient depth and with reasonably wide coverage. The book is written in an easy-to-understand manner and includes many solved problems. More than 150 numerical problems and many multiple choice questions as exercise along with their answers have also been provided. The mathematical analyses are well elaborated without skipping any intermediate steps. Slab method of analysis or free-body equilibrium approach is used for the analytical treatment of mechanical working processes. For hot working processes, different frictional conditions (sliding, sticking and mixed sticking–sliding) have been considered to estimate the deformation loads. In addition to the slab method of analysis, this book also contains slip-line field theory, its application to the static system, and the steady state motion, Further, this book includes upper-bound theorem, and upper-bound solutions for indentation, compression, extrusion and strip drawing. The book can be used to teach graduate and undergraduate courses offered to students of mechanical, aerospace, production, manufacturing and metallurgical engineering disciplines. The book can also be used for metallurgists and practicing engineers in industry and development courses in the metallurgy and metallic manufacturing industries.

Inhaltsverzeichnis

Frontmatter

Mechanical Properties of Metals and Alloys

Frontmatter

Chapter 1. Tension

Abstract

Engineering and true strain and stress, and their relationship, Poisson’s ratio and volume strain. Generalized Hooke’s law for a triaxial state of stress. Relationship between principal normal and shear stresses and explanation with Mohr’s stress circle. Mechanisms of plastic deformation of crystalline solids: slip and twinning. A brief introduction to dislocations. Reasons of strain hardening, relationship between yield strength and grain size, and effect of stacking fault energy on the extent of strain hardening and twinning. Various strengthening methods. Yielding criteria, invariant functions of stress and strain, and flow rules. Discussion of various types of stress–strain curve in tension. Empirical relationship for flow curve, strain-hardening coefficient, tensile instability, stress field at the neck. Different elastic (linear and nonlinear) and inelastic tensile properties, geometry of tensile specimen and ductility measurement. Influence of temperature, strain rate and testing machine on tensile properties. Notch tensile test and tensile fracture. Problems and solutions.

Amit Bhaduri

Chapter 2. Compression

Abstract

Standard specimen, elastic and plastic range, stress, strain and strain rate, brittle and ductile materials in compression. Advantages over tension test. Bauschinger effect. Barreling and buckling in compression test and remedial measures against them. Critical column stress for buckling. Various compressive failures. Problems and solutions.

Amit Bhaduri

Chapter 3. Hardness

Abstract

Classification of hardness measurement and precautions to avoid erratic measurement. Measurement of hardness with Mohs’ scale, file test and Herbert pendulum. Brinell hardness: principle, method with loading period and derivation of expression showing hardness. Indenters and loads for standard and non-standard tests. Condition to obtain a constant hardness for the same material. Advantages and disadvantages. Meyer hardness: definition, expression and its load sensitivity. Meyer’s law and condition to obtain the same hardness. Rockwell hardness: principle, loads, indenters, direct-reading hardness dial, hardness scale, method of testing, expression showing hardness, and advantages. Rockwell superficial hardness: principle and expression showing hardness, hardness scale, merits and demerits. Vickers hardness: principle, indenters and loads, derivation of expression showing hardness, operational method, and minimum test piece thickness. Advantages and disadvantages, and comparison with Brinell hardness. Microhardness (Knoop hardness): principle and derivation of expression showing hardness, penetrators and loads, advantages and disadvantages. Monotron hardness: principle and expression, indenters and hardness scales, advantages and disadvantages. Shore scleroscope: principle, mass effect of test piece and advantages. Poldi impact hardness: principle and expression, determination of Brinell hardness with supplied table, advantages and disadvantages. Nanohardness: indenters, derivation of expression showing hardness with Berkovich indenter, determination of contact depth of penetration, correction for machine compliance, correction due to imperfect geometry of indenter tip, and errors due to pile-up. Consideration of Martens hardness. Relationship to flow curve and prediction of tensile properties. Problems and solutions.

Amit Bhaduri

Chapter 4. Bending

Abstract

Bending stresses, flexure formula and experimental method in pure bending. Beam design from economical and strength considerations of cross-sectional shapes. Modulus of elastic resilience and important variables affecting modulus of rupture. Yielding: discontinuous yielding and shape factor. Nonlinear stress–strain relationships for materials either deforming in the plastic range or exhibiting nonlinear elastic deformation. Shear stresses in elastically bent beam subjected to non-uniform bending moment. Problems and solutions.

Amit Bhaduri

Chapter 5. Torsion—Pure Shear

Abstract

State of stress and strain in torsion. Shear strain and its relation with angle of twist. Relation between shear modulus and Young’s modulus. Torsional stresses in elastic range. Relation between torque, shear modulus and angle of twist. Torque computation in practical applications. Polar moment of inertia, shear stress and angle of twist for solid and hollow cylindrical shaft and thin-walled tube subjected to torsion. Behaviour of thin-walled tubes of non-circular cross-section under torsion. Torsional stresses for plastic strains, and ultimate torsional shear strength or modulus of rupture. Shape of torque-angle of twist diagram for a solid or hollow cylindrical shaft and for a thin-walled tubular specimen of a ductile material subjected to torsion. Specimen and equipment for torsion test. Different elastic and inelastic properties in torsion. Comparison between torsion and tension tests with respect to state of stress and strain developed in each test and ductile behaviour of materials. Torsional shear stress–strain diagram from tensile flow curve and failure under torsion. Problems and solutions.

Amit Bhaduri

Chapter 6. Impact Loading

Abstract

Behaviour of materials under impact loads. Factors responsible for brittle cleavage type of fracture of normally ductile metals and alloys. Single-blow pendulum impact tests with notched bar, such as Charpy and Izod tests. Geometry of Charpy and Izod standard specimens with different types of notch and placement of specimens for tests in Charpy and Izod impact testers. Calculation of energy relations and correction for energy losses in impact test. Impact properties and transition temperature curves, and various criteria to define ductile–brittle transition temperature. Metallurgical factors affecting impact properties. Metallurgical embrittlement, such as tempered martensite embrittlement and temper embrittlement. Instrumented Charpy impact test. Additional large-scale fracture test methods, such as explosion-crack-starter test, drop weight test, Robertson crack-arrest test and dynamic tear test. Fracture analysis diagram and design philosophy using it. Problems and solutions.

Amit Bhaduri

Chapter 7. Creep and Stress Rupture

Abstract

Creep phenomenon. Creep curve and its different stages. Strain–time relations to describe the basic shapes of creep curves mathematically. A general empirical equation for time laws of creep. Creep rate–stress–temperature relations, showing influence of stress and temperature on steady-state creep rate. Effect of grain size on steady-state creep rate. Activation energy for creep, its determination and relation with activation energy for self-diffusion. Creep deformation mechanisms: dislocation glide, dislocation creep or climb–glide creep, diffusional creep (Nabarro–Herring creep and Coble creep), and grain boundary sliding. Deformation mechanism map. Stress-rupture test and its difference with the creep test. Concept of equicohesive temperature (ECT) and deformation features at ECT. Fracture at elevated temperature. Creep cavitation: wedge-shaped cracks and round or elliptically shaped cavities. Presentation of engineering creep data, and prediction of creep strength and creep-rupture strength. Prediction of long-time properties by means of parameter methods, such as Larson–Miller parameter, Orr–Sherby–Dorn parameter, Manson–Haferd parameter, Goldhoff–Sherby parameter and limitations of parameter methods. Stress-relaxation and step-down creep test. Creep-resistant materials for high-temperature applications and rules to develop increased creep resistance at elevated temperatures. Creep under multiaxial stresses. Indentation creep and method to obtain creep curve using Rockwell hardness tester. Problems and solutions.

Amit Bhaduri

Chapter 8. Fatigue

Abstract

Fatigue fracture and its characteristic appearance. Various types of fluctuating stress cycle and its components. Standard fatigue test and S–N diagram. Fatigue properties, and reason for existence of fatigue limit. Statistical nature of fatigue and estimation of anticipated fatigue life by means of standard statistical procedure. Fatigue crack initiation through persistent slip bands, such as slip-band extrusions and slip-band intrusions. Fatigue crack growth: Stage I and Stage II. Crack growth rate and ‘Paris’ law. Cumulative fatigue damage with definitions of overstressing, understressing and coaxing. Methods of presenting S–N data, where mean stress is not zero. Design criteria for mean stress effects: Gerber relation, Goodman relation or Goodman diagram to prevent fatigue failure, and Soderberg relation to prevent yielding. Effects of stress concentration, specimen size, metallurgical variables, frequency of stress cycling, corrosive environment, low and high temperature on fatigue and thermal fatigue. Effects of specimen surface, such as its roughness, properties and residual stress on fatigue. Surface treatments beneficial to fatigue and metallurgical processes detrimental to fatigue. Cyclic strain-controlled fatigue, describing cyclic strain hardening and cyclic strain softening, and their dependency on material’s stacking fault energy. Low-cycle fatigue and Coffin–Manson relation. Total fatigue strain–life equation, and its plot approaching towards the plastic strain–life curve at large total strain amplitudes and the elastic strain–life curve at low total strain amplitudes. Creep–fatigue interaction, where suggested important design approaches are: cumulative damage rule, modification of Goodman law, frequency-modified fatigue relation and strain-range partitioning method. Increasing amplitude tests, such as step test and Prot test. Problems and solutions.

Amit Bhaduri

Chapter 9. Fracture

Abstract

Variation of interatomic bonding force (cohesive force) with interatomic spacing. Evaluation of ideal fracture strength (cohesive strength in an ideally perfect crystal). Relation of geometrical discontinuity (flaw) in a body with theoretical (or, elastic) stress concentration factor and material’s fracture strength. Effects of notch on material’s fracture behaviour: ‘notch strengthening’ and ‘notch weakening’. Distributions of elastic stresses ahead of a notch and of elastic/plastic stresses during local yielding in the vicinity of a notch in plane stress and plane strain conditions. Characteristic features of fracture process. Fractography describing dimpled fracture (different shapes of the dimple depending on the state of stress), cleavage fracture, quasi-cleavage fracture and intergranular fracture. Griffith theory of brittle fracture and its applicability. Modification of Griffith theory by Orowan relation for brittle metals. Modification by Irwin approach introducing ‘elastic strain energy release rate’, its significance and experimental measurement. Stress intensity factor and its expressions depending on the types of loading and the geometry of crack and specimen configurations. Different modes of crack surface displacement. Relationship between energy release rate and stress intensity factor. Plastic-zone size at crack tip and effective stress intensity factor due to crack-tip plasticity in plane stress and strain conditions. Fracture toughness: plane stress versus plane strain. Test to determine plane-strain fracture toughness and design philosophy using it. Problems and solutions.

Amit Bhaduri

Mechanical Working of Metals and Alloys

Frontmatter

Chapter 10. Fundamentals of Mechanical Working

Abstract

Classification of mechanical forming processes and their main objectives. Hot working and cold working, and their comparison. Cold-work-anneal cycle and temperature limits for hot working. Warm working, its purpose and advantages. Temperature change during working of deforming metal, depending on its ideal plastic deformation, friction at its interface with tools or dies, and heat transfer between them. Effects of strain rate in working processes. Effect of varying pressure and strain rate on allowable hot working temperature range. Friction: Coulomb’s law of sliding friction and factors affecting Coulomb’s coefficient of sliding friction (COF). Shear friction factor and sticking friction. Maximum value of COF under sticking condition according to Von Mises’ and Tresca yielding criteria. Difference and advantages of shear friction factor model over Coulomb’s model of friction. Evaluations of friction factor and COF by ring-compression test. Adverse as well as beneficial effects of friction on mechanical working. Material pickup on tools. Functions and characteristics of a lubricant. Lubrication mechanism: hydrodynamic or full-fluid or thick-film lubrication, boundary lubrication, mixed-film lubrication, solid lubricants and melting solids. Mechanics of working process: slab method, uniform-deformation energy method, slip-line field theory, upper- and lower-bound solutions and finite element method. Slip-line field theory: slip lines, Hencky’s slip-line equations, stresses and slip lines at the boundaries of a plastic body, simple state of stress, Hencky’s first theorem, numerical method of solution, application of slip-line field to static system and steady motion. Upper-bound technique: derivation of its equation, its solutions for indentation of a semi-infinite slab and for compression. Deformation-zone geometry in terms of reduction in area of work-piece for different deformation processes. Anisotropy of mechanical properties: crystallographic texture and mechanical fibering. Problems and solutions.

Amit Bhaduri

Chapter 11. Forging

Abstract

Classification of forging processes and different types of forging operations. Forging equipments, describing gravity drop hammer, power drop or steam hammer, mechanical forging press and hydraulic forging press. Open-die forging, coefficient of spread and its relation with bite ratio, ‘spread law’ with definitions of spread ratio and squeeze ratio. Closed-die forging or impression-die forging with discussion on some die design factors, such as flash and flash land ratio, draft angles, corner and fillet radii and location of parting line. Material loss due to scale formation, discard, croppings, slug waste, during forging. Plane strain forging of uniformly thick rectangular plate: distributions of pressure and longitudinal stress, average pressure and total load under conditions of Coulomb sliding friction, sticking friction and mixed sticking–sliding friction. Plane strain forging of strip with inclined dies: die pressure and strip thickness at neutral plane and its location. Forging of flat circular disk: distributions of pressure and longitudinal stress, average pressure and total load under conditions of Coulomb sliding friction, sticking friction and mixed sticking–sliding friction. Forging of circular disk by conical pointed dies: die pressure and condition for complete elimination of barrelling of the work-piece. Forging defects and fibre structure. Problems and solutions.

Amit Bhaduri

Chapter 12. Rolling

Abstract

Terminology of rolled product, different methods of rolling and quantities characterizing deformation. Classification of rolling mills. Different types of rolling mills, such as cluster mill, Sendzimir cold-rolling mill and planetary hot-rolling mill, pendulum mill, contact-bend-stretch mill, universal mill. Hot and cold-rolling practice. Deformation zone in rolling, angle of bite and artificial methods to increase it, neutral point (no-slip point) and no-slip angle. Ekelund expression for no-slip angle. Forward slip, its relation with no-slip angle, its measurement and importance. Elastic deformation of rolls: roll flattening and roll deflection. Simplified assessment of rolling load and Ekelund equations for loads in cold and hot rolling. Theory of rolling: derivation of differential equation of friction hill. Bland and Ford theory of cold rolling: roll pressure with no external tensions and with back and front tensions, no-slip angle, rolling load and torque, maximum allowable back tension, estimation of friction coefficient. Sims’ theory of hot rolling: roll pressure, no-slip angle, rolling load and torque, limitations of theory. Mean strain rate in flat rolling with sticking friction. Lever arm ratio and its estimation from Sims’ theory, torque and mill power. Minimum thickness of rolled product. Factors controlling rolling process. Gauge control by considering mill modulus line and plastic deformation curve for work-metal and factors affecting outgoing gauge of rolled product. Defects in rolled products. Fundamentals of roll-pass design: types and shapes of passes, gap and taper of sides in pass, pass arrangement, pass sequences used in rolling of billets to rods and square bars. Production of seamless pipe and tube by hot rolling using rotary piercing mill, plug mill, continuous mill, pilger mill and finishing mills, such as reeling, sizing, stretch-reducing and expanding mills. Problems and solutions.

Amit Bhaduri

Chapter 13. Extrusion

Abstract

Advantages and drawbacks of extrusion. Two basic methods of extrusion: direct and indirect, and their comparison. Extrusion equipments and dies. Metal flow during extrusion. Factors influencing extrusion process, such as type of extrusion, extrusion ratio, extrusion (ram) speed, approach angle of conical die and optimum semicone angle, friction and lubrication. Estimation of extrusion (ram) pressure and load for: open-die, indirect and hydrostatic extrusions, direct extrusions through conical converging die and square die under conditions of Coulomb’s sliding friction, full sticking friction and mixed sticking–sliding friction, prevailing, respectively, from the entry plane of conical die or from that of dead zone in square die to the entry to extrusion chamber. Strain rate in extrusion. Extrusion defects. Impact extrusion: direct (Hooker process) and indirect. Hydrostatic extrusion and its basic difference with conventional extrusion. Conventional hydrostatic and differential pressure hydrostatic extrusion. Advantages and disadvantages of hydrostatic extrusion. Seamless tube production by extrusion: using an external long fixed, floating or piercing type of mandrel, or without using a normal external mandrel (welding-chamber method). Extrusion of cable sheathing. Application of slip-line field to steady-state motion: 50% and \( 2/3 \) plane-strain frictionless extrusion. Upper-bound solution for plane-strain frictionless extrusion with an example. Problems and solutions.

Amit Bhaduri

Chapter 14. Drawing: Flat Strip, Round Bar and Tube

Abstract

Drawing: definition, purposes, demerits and fields of application. Drawing stress with friction for work-hardening and non-strain-hardening strip drawn through wedge-shaped dies. Frictionless ideal drawing stress. Maximum reduction of area in a single pass with and without friction. Drawing stress with friction for strip drawn through cylindrical dies. Treatments of work metal prior to drawing, such as heat treatment (recrystallization annealing, patenting), surface preparation (pickling, surface conditioning or coating), and pointing or chamfering. Drawing equipments, such as draw bench, multiple-die continuous and single-die block drawing machines, stepped-cone multiple-die drawing machine. Conical converging drawing die, describing internal profile geometry and functions of different zones of die nib. Drawing of rod and wire: dry drawing and wet drawing. Drawing load and power with friction, and with and without back tension, with and without consideration for work hardening. Frictionless ideal drawing stress without back tension. Maximum reduction of area in a single drawing pass: for non-strain-hardening rod or wire with and without friction and back tension, and for strain-hardening rod or wire with friction and back tension. Redundant deformation, redundant work factor and its effect on drawing stress. Variation of drawing stress with die-cone angle, describing optimum cone angle, dead-zone formation and shaving mode of flow. Tube drawing using fixed plug, floating plug or mobile mandrel. Stress and maximum reduction of area in a single pass for plug drawing and mandrel drawing. Tube sinking and stress for sinking. Stability condition of a floating plug. Application of slip-line field to frictionless plane-strain strip drawing through wedge-shaped dies. Upper-bound solution for frictionless plane-strain strip drawing through wedge-shaped dies, with an example. Problems and solutions.

Amit Bhaduri

Chapter 15. Deep Drawing

Abstract

Deep drawing: definition and fundamentals. Stresses and deformation in a deep-drawn cup. Deep drawing load and its components and their variations with punch movement. Derivation of mathematical expression for load and its comparison with Sachs relation. Formability: properties of work metal for optimal formability. Strain distribution in a forming operation determined by strain-hardening exponent, strain rate sensitivity and plastic strain ratio. Allowable maximum deformation level represented graphically as forming limit diagram. Deep drawability and its relation with plastic strain ratio. Conditions for optimal drawability. Measurement of drawability by drawing ratio using Swift cup test. Limiting draw ratio to express deformation limit in deep drawing. Effects of process variables that include drawing ratio and redrawing operations, profile radii of die and punch, punch-to-die clearance, drawing speed, friction and lubrication, restraint of metal flow, such as use of a blank holder. Effects of material parameters that include sheet thickness and anisotropy. Evaluation of formability of sheet metal using different type tests, such as Marciniak biaxial stretching test, Swift cup test, Ericksen and Olsen cup tests, Fukui conical cup test, hole expansion test and forming limit diagram using hemispherical punch method. Defects in deep-drawn components. Problems and solutions.

Amit Bhaduri

Chapter 16. High-Energy Rate Forming

Abstract

Principle of high-energy rate forming (HERF) or high-velocity forming (HVF) process, and its difference with conventional processes, reason to develop HVF process, and its fields of application, advantages and limitations. Principle of explosive forming process, and its distinction with conventional forming. Varieties of explosives and their properties. Standoff or unconfined or underwater (bulk head forming, free forming and cylinder forming) explosive forming technique: description with advantages and limitations, and sequence of forming operation. Effect of standoff distance, weight, types of explosives used and type of energy-transmitting medium on magnitude of peak pressure exerted on work-piece. Contact or confined explosive forming technique: description with advantage and disadvantage. Electromagnetic forming or magnetic pulse forming process: principle and discussion, advantages and limitations, various applications, such as expansion (bulging) or compression (shrinking) of a hollow cylindrical work-piece, or even a combination of both to attain a final shape, and forming of flat sheet metal to contours of die. Electrohydraulic forming or spark discharge forming or electric discharge forming or electrospark forming: description with fields of application and comparison of energy efficiency and peak pressure with explosive forming. High-energy rate forging and other HERF methods. Problems and solutions.

Amit Bhaduri

Backmatter

Titel: Mechanical Properties and Working of Metals and Alloys
verfasst von: Prof. Amit Bhaduri
Verlag: Springer Singapore
Electronic ISBN: 978-981-10-7209-3
Print ISBN: 978-981-10-7208-6
DOI: https://doi.org/10.1007/978-981-10-7209-3

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