Designing Weldments E-Book

Ramesh Singh

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 332

Veröffentlichungsjahr: 2022

Beschreibung

Designing Weldments An important tool for professionals wishing to enhance their understanding or those who are new to the subject, Designing Weldments bridges that gap between structural engineers and a deeper understanding of the welding engineering within the structures. In modern-day construction, welding is the primary method to join various members of any structure. Welds are required to meet various types of load in tension, compression, torsion, and perform in static or cyclic loading conditions. The weld has to be at least as strong as the parent metal to meet the demands of various stress working on the structure. It should meet the structural requirement, add value to the integrity of the structure, and prevent failures. However, many design engineers lack even a fundamental insight or a basic understanding of essential welding processes and design requirements. Simply copying a few joint configurations in a drawing will not suffice. All-embracing and readable, Designing Weldments delivers a deeper understanding of many design factors that play a critical role in the design. The book clarifies welding design principles and applications. With this reference in hand, designers will have expert knowledge to consider very early on in the project, the implications of the choice of what type of weld to use for joining structural members, and how the component is made. The author explains the many welding techniques developed over the years, as well as some of which are still evolving. The reader will also find in this book: * Rules of thumb for saving time and money in the design phase of a project. * An insider's view for choosing the proper welding approach to ensure the overall strength of a structure. * Offers structural engineers a deeper understanding of the weld within their structures. * Clarifies welding design principles and applications, limiting the necessity to redesign the structure. Audience The intended market for this book is professionals working on the infrastructural projects in shipbuilding, construction of buildings, bridges, offshore platforms, wind towers for renewable energy, and other structures that join plates, pipes, and pipelines in power plants, manufacturing, and repair.

Leseprobe

Table of Contents

Cover

Title Page

Copyright

List of Figures

List of Tables

Foreword

Preface

1 Properties and Strength of Material

1.1 Introduction

2 Properties of Metals

2.1 Material Properties

3 Design: Load Conditions

3.1 Design of Welds

3.2 Design by Calculations

4 Design of Welds and Weldments

4.1 Introduction

4.2 Full Penetration Welds

4.3 Partial Penetration Welds

4.4 Groove Welds

4.5 Weld Grooves

4.6 Fillet Welds

4.7 About Fillet Weld

4.8 Weld Design and Loading

4.9 Sizing Fillet Welds

4.10 Fillet Welds in Holes and Slots

4.11 Designing Calculations for Skewed Fillet Weld

4.12 Treating Weld as a Line

4.13 Design of Tubular Connections

4.14 Design for Cyclic Loading

4.15 Aluminum

4.16 Welding Aluminum

4.17 Design for Welding Aluminum

4.18 Distribution of Stress in Aluminum Weld Design

4.19 Heat and Distortion Control

5 Introduction to Welding Processes

5.1 Introduction

5.2 Shielded Metal Arc Welding (SMAW)

5.3 Gas Tungsten Arc Welding

5.4 Gas Metal Arc Welding

5.5 Flux Cored Arc Welding (FCAW)

5.6 Submerged Arc Welding (SAW)

5.7 Electroslag Welding (ESW)

5.8 Plasma Arc Welding

5.9 Stud Welding

5.10 Oxyfuel Gas Welding

5.11 Hyperbaric Welding

5.12 Application of Welding Processes

6 Welding Symbols

6.1 Introduction

6.2 Common Weld Symbols and Their Meanings

6.3 Fillet Welds

6.4 Groove Welds

6.5 Bevel Groove Welds

6.6 Plug and Slot Welds

7 Structural Design and Welding Specifications, and Other Useful Information

7.1 Introduction

7.2 Structural Welding Codes

7.3 Useful Engineering Information

Index

Also of Interest

End User License Agreement

List of Tables

Chapter 2

Table 2.1 Properties of materials.

Table 2.2 Modulus of elasticity of common engineering metals.

Chapter 3

Table 3.1 Load components of design formulas and symbols used.

Table 3.2 Member components and symbols used in the formula.

Table 3.3 Member components (stress and strain) and symbols used in the formula.

Table 3.4 Shear modulus of elasticity (modulus of rigidity of some common materi...

Chapter 4

Table 4.1 Type of weld joints.

Table 4.2 Flare groove weld sizing.

Table 4.3 Allowable stress and strength level for steel welds.

Table 4.4 Allowable unit load on steel fillet welds.

Table 4.5 Z loss table.

Table 4.6 Minimum weld size for PJP welds.

Table 4.7 Fillet weld (leg) size for skewed fillet -tee welds.

Table 4.8 Minimum fillet weld sizes.

Table 4.9 Stress on welds for different loading.

Table 4.10 CJP joints designed for T-K-Y tubular structures.

Table 4.11 Suggested allowable stress range in steel weldments.

Table 4.12 Aluminum alloy designation system.

Table 4.13 Cast aluminum designation and numbering system.

Table 4.14 Temper designation letters and meaning.

Table 4.14 Effect of service temperature on, as welded and heat treated and aged...

Chapter 5

Table 5.1 Master chart of welding and joining processes.

Table 5.10.1 Fuel gas characteristics.

Table 5.12 Application of various welding and joining processes for different ty...

Chapter 7

Table 7.1 Mechanical properties of various metals.

Table 7.2 Mechanical properties of copper grades and alloys.

Table 7.3 Mechanical properties of aluminum and its alloys, with temper.

Table 7.4 Mechanical properties of various grades of Austenitic stainless steels...

Table 7.5 Comparison of mechanical properties of grades of steel.

Table 7.6 HSS rect property table.

Table 7.7 Metric to US standard unit conversion.

List of Figures

Chapter 1

Figure 1.1 A typical strain and stress diagram, describing various elements of t...

Chapter 2

Figure 2.1 A typical strain and stress diagram, describing various elements of t...

Figure 2.2 Low temperature behavior of metals.

Chapter 3

Figure 3.1 Deflection in a cantilever beam.

Figure 3.2 Typical tensile test specimen.

Figure 3.3 Column under compressive load. (a) Straight beam, (b) column starts t...

Figure 3.4 Bending.

Figure 3.5 Bending stresses.

Figure 3.6 Simply supported beam.

Figure 3.7 Shear in a structure.

Chapter 4

Figure 4.1 Types of weld joints.

Figure 4.2 Types of weld joints.

Figure 4.3 Double flare joint.

Figure 4.4 Fillet weld with weld nomenclatures.

Figure 4.5 Transvers fillet weld.

Figure 4.6 Theoretical throat of a fillet weld.

Figure 4.7 Fillet weld under tensile load.

Figure 4.8 Fillet weld in shear load.

Figure 4.9 Fillet weld in shear load.

Figure 4.10 Combined fillet and groove weld.

Figure 4.11 Skewed joints.

Figure 4.12 Weld as a line (no area).

Figure 4.13 Weld as line, and mathematical relationships of various elements.

Figure 4.14 Example of calculations treating weld as a line.

Figure 4.15 Welded tubular connections, T, K, and Y and nomenclature, inserted w...

Figure 4.15.1

Figure 4.16 Joint design for PJP groove weld in simple T, K, and Y tubular conne...

Figure 4.17 Applicable location of PJP groove weld design.

Figure 4.18 Weld set up for same size members.

Figure 4.19 Load on the tubular welded connections.

Figure 4.20 Impact of cyclic loading on the strength of steel and weld metal.

Figure 4.21 Fatigue categories.

Figure 4.22 Typical approaches to aluminum weld design.

Figure 4.23 Distribution of tensile strength across the aluminum weld.

Figure 4.24 Typical extrusions used to design joint geometry.

Figure 4.25 Showing the transition of two different thicknesses for butt weld.

Figure 4.26 Lap joints (a) and (b).

Figure 4.27 Angular distortion, double-sided fillet welds in a T-joint.

Figure 4.28 Weld CG and neutral axis.

Figure 4.29 Angular distortion, single-sided groove weld in a butt joint.

Chapter 5

Figure 5.10.1 Oxy-fuel cutting process.

Figure 5.10.2 Oxyacetylene gas jet and nozzle design.

Figure 5.10.3 Propane gas jet and nozzle design.

Chapter 6

Figure 6.1 The structure of welding symbol.

Figure 6.2 Use of pointing reference line arrows in welding symbols.

Figure 6.3 Meaning of arrow pointing.

Figure 6.4 Significance of circle at the inflexion point of the arrow line.

Figure 6.5 Symbols to denote various types of welds.

Figure 6.6 Symbol of fillet weld.

Figure 6.7 How the fillet welds are shown for the given weld on top.

Figure 6.8 Typical fillet welds symbols and their as built appearance with size ...

Figure 6.9 Symbol and the as built: full dimensioning of a fillet weld, note the...

Figure 6.10 Symbol and As-built: Showing an intermittent fillet weld and its siz...

Figure 6.11 Symbols used to denote groove welds.

Figure 6.12 Sq. groove weld symbol and As-built.

Figure 6.13 V-groove welds and their as built, note the positioning of arrows.

Figure 6.14 Groove welds, full penetration and partial penetration welds note th...

Figure 6.15 Symbol and as built of a PJP weld that shows the depth of penetratio...

Figure 6.16 Symbol and as built of a bevel weld.

Figure 6.17 Symbol and as built of a U-groove weld.

Figure 6.18 Symbol and as built J-groove weld; note the positioning of arrow and...

Figure 6.19 Symbol and as built flare-weld note the practice of showing the dept...

Figure 6.20 Symbol and as built with desired dimensions of the weld, and supplem...

Figure 6.21 Symbol and as built and shown depth of desired and achieved weld pen...

Figure 6.22 A weld symbol and as built with the backing bar.

Figure 6.23 A symbol of a Plug-weld.

Figure 6.24 Shows the symbols and as built welds for both plug and slot welds.

Guide

Cover

Table of Contents

Title Page

Copyright

List of Figures

List of Tables

Foreword

Preface

1 Properties and Strength of Material

Index

Also of Interest

End User License Agreement

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Scrivener Publishing

100 Cummings Center, Suite 541J

Beverly, MA 01915-6106

Publishers at Scrivener

Martin Scrivener ([email protected])

Phillip Carmical ([email protected])

Designing Weldments

Ramesh Singh

This edition first published 2022 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA© 2022 Scrivener Publishing LLCFor more information about Scrivener publications please visit www.scrivenerpublishing.com.

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Library of Congress Cataloging-in-Publication Data

ISBN 978-1-119-86515-5

Cover images: supplied by the authorCover design by Russell Richardson

Set in size of 11pt and Minion Pro by Manila Typesetting Company, Makati, Philippines

Printed in the USA

10  9  8  7  6  5  4  3  2  1

List of Figures

Figure 1.1 A typical strain and stress diagram, describing various elements of tensile test.

Figure 2.1 A typical strain and stress diagram, describing various elements of tensile test.

Figure 2.2 Low temperature behavior of metals.

Figure 3.1 Deflection in a cantilever beam.

Figure 3.2 Typical tensile test specimen.

Figure 3.3 Column under compressive load. (a) Straight beam, (b) column starts to deflect with increasing load, (c) bending moment diagram, and (d) increased deflection with increased loading.

Figure 3.4 Bending.

Figure 3.5 Bending stresses.

Figure 3.6 Simply supported beam.

Figure 3.7 Shear in a structure.

Figure 4.1 Types of weld joints.

Figure 4.2 Types of weld joints.

Figure 4.3 Double flare joint.

Figure 4.4 Fillet weld with weld nomenclatures.

Figure 4.5 Transvers fillet weld.

Figure 4.6 Theoretical throat of a fillet weld.

Figure 4.7 Fillet weld under tensile load.

Figure 4.8 Fillet weld in shear load.

Figure 4.9 Fillet weld in shear load.

Figure 4.10 Combined fillet and groove weld.

Figure 4.11 Skewed joints.

Figure 4.12 Weld as a line (no area).

Figure 4.13 Weld as line, and mathematical relationships of various elements.

Figure 4.14 Example of calculations treating weld as a line.

Figure 4.15 Welded tubular connections, T, K, and Y and nomenclature, inserted within the figure is the description of joint parameters, its variation for Box and Circular sections.

Figure 4.15.1

Figure 4.16 Joint design for PJP groove weld in simple T, K, and Y tubular connections.

Figure 4.17 Applicable location of PJP groove weld design.

Figure 4.18 Weld set up for same size members.

Figure 4.19 Load on the tubular welded connections.

Figure 4.20 Impact of cyclic loading on the strength of steel and weld metal.

Figure 4.21 Fatigue categories.

Figure 4.22 Typical approaches to aluminum weld design.

Figure 4.23 Distribution of tensile strength across the aluminum weld.

Figure 4.24 Typical extrusions used to design joint geometry.

Figure 4.25 Showing the transition of two different thicknesses for butt weld.

Figure 4.26 Lap joints (a) and (b).

Figure 4.27 Angular distortion, double-sided fillet welds in a T-joint.

Figure 4.28 Weld CG and neutral axis.

Figure 4.29 Angular distortion, single-sided groove weld in a butt joint.

Figure 5.10.1 Oxy-fuel cutting process.

Figure 5.10.2 Oxyacetylene gas jet and nozzle design.

Figure 5.10.3 Propane gas jet and nozzle design.

Figure 6.1 The structure of welding symbol.

Figure 6.2 Use of pointing reference line arrows in welding symbols.

Figure 6.3 Meaning of arrow pointing.

Figure 6.4 Significance of circle at the inflexion point of the arrow line.

Figure 6.5 Symbols to denote various types of welds.

Figure 6.6 Symbol of fillet weld.

Figure 6.7 How the fillet welds are shown for the given weld on top.

Figure 6.8 Typical fillet welds symbols and their as built appearance with size of the weld.

Figure 6.9 Symbol and the as built: full dimensioning of a fillet weld, note the length of the weld.

Figure 6.10 Symbol and As-built: Showing an intermittent fillet weld and its size. Shown is the size ¼ inch fillet weld that is 2-inch long and end to end spaced by 4-inches.

Figure 6.11 Symbols used to denote groove welds.

Figure 6.12 Sq. groove weld symbol and As-built.

Figure 6.13 V-groove welds and their as built, note the positioning of arrows.

Figure 6.14 Groove welds, full penetration and partial penetration welds note the sizing of PJP and positioning of arrow.

Figure 6.15 Symbol and as built of a PJP weld that shows the depth of penetration and also the effective throat.

Figure 6.16 Symbol and as built of a bevel weld.

Figure 6.17 Symbol and as built of a U-groove weld.

Figure 6.18 Symbol and as built J-groove weld; note the positioning of arrow and method to show PJP weld.

Figure 6.19 Symbol and as built flare-weld note the practice of showing the depth of the weld.

Figure 6.20 Symbol and as built with desired dimensions of the weld, and supplementary symbol to show backing bar.

Figure 6.21 Symbol and as built and shown depth of desired and achieved weld penetration.

Figure 6.22 A weld symbol and as built with the backing bar.

Figure 6.23 A symbol of a Plug-weld.

Figure 6.24 Shows the symbols and as built welds for both plug and slot welds.

List of Tables

Table 2.1 Properties of materials.

Table 2.2 Modulus of elasticity of common engineering metals.

Table 3.1 Load components of design formulas and symbols used.

Table 3.2 Member components and symbols used in the formula.

Table 3.3 Member components (stress and strain) and symbols used in the formula.

Table 3.4 Shear modulus of elasticity (modulus of rigidity of some common materials).

Table 4.1 Type of weld joints.

Table 4.2 Flare groove weld sizing.

Table 4.3 Allowable stress and strength level for steel welds.

Table 4.4 Allowable unit load on steel fillet welds.

Table 4.5 Z loss table.

Table 4.6 Minimum weld size for PJP welds.

Table 4.7 Fillet weld (leg) size for skewed fillet -tee welds.

Table 4.8 Minimum fillet weld sizes.

Table 4.9 Stress on welds for different loading.

Table 4.10 CJP joints designed for T-K-Y tubular structures.

Table 4.11 Suggested allowable stress range in steel weldments.

Table 4.12 Aluminum alloy designation system.

Table 4.13 Cast aluminum designation and numbering system.

Table 4.14 Temper designation letters and meaning.

Table 4.14 Effect of service temperature on, as welded and heat treated and aged welds.

Table 5.1 Master chart of welding and joining processes.

Table 5.10.1 Fuel gas characteristics.

Table 5.12 Application of various welding and joining processes for different types of metal and materials.

Table 7.1 Mechanical properties of various metals.

Table 7.2 Mechanical properties of copper grades and alloys.

Table 7.3 Mechanical properties of aluminum and its alloys, with temper.

Table 7.4 Mechanical properties of various grades of Austenitic stainless steels.

Table 7.5 Comparison of mechanical properties of grades of steel.

Table 7.6 HSS rect property table.

Table 7.7 Metric to US standard unit conversion.

Foreword

Designing Weldments by Ramesh Singh, addresses the importance of how properly designed welds in a structure can change the approach to its design, leading to greater structural integrity and potentially reduced cost. This book seeks to strengthen frequently neglected elements of design engineering involving structural load-bearing members of various metals, but particularly those of steel, and aluminum manufacture. Ramesh’s real-world experiences have led him to conclude that many engineers possess only a basic education about the welding. Consequently, many are ill-equipped with sufficient understanding of how welded structures respond to loading versus, for example, a wrought steel member in a structure. How do the presence of welds within the structure change stress types and concentrations, thereby having significant impact on the long term integrity of the structure? How can the designer take strategic advantage of welding technologies to strengthen the structural design while also reducing its weight and finished cost. Finally, this book also addresses the differences between a cast structure and a welded structure, and what factors need to be addressed when converting a cast structure design to a welded structure design, as might be done for a machine component.

The importance of the type of weld joint preparation, for full penetration, or partial penetration, butt weld or fillet weld, or a combination of fillet and groove welds is addressed in detail. The book also provides an introduction to various welding processes, materials of construction, and their classifications.

I have worked professionally with Ramesh for more than two decades. He is passionate about his work in metallurgy, corrosion, fabrication and welding, which spans more than half a century and multiple industries. Unlike many whose background is primarily academic; his knowledge has been acquired through practical experience in a variety of settings around the globe. An avid long distance bicycle rider, and dedicated marathon runner, Ramesh brings that same level of devotion and commitment to his profession.

Designing Weldments will be an important resource and reference tool for structural designers and engineers. The book is replete with illustrations, tables and figures to bring visual clarity and substance to the technical nomenclature necessary for such a complex subject.

W. M. Olson

Sr. Vice President | Operations

Gulf Interstate Engineering, in Houston TX

Preface

The idea of writing about the specifics of weld design has been in my mind for nearly all through my career. The concept of the Designing Weldments was inspired, and motivated by my experience with engineers that were often responsible for designing major structures for offshore platforms, PLEMS, risers, roads and bridges, and buildings etc.

Most of the time very excellent design concepts got bogged down due the limited knowledge the of the impact welding does on materials’ behavior, and how a welded structure is different from other materials say, an extruded structural member.

The subject is also complicated by the fact that different types, and grades of material have different metallurgical response to the fabrication processes, including welding which is a major component of such complex fabricated structural members. The details of metallurgical aspects of material is discussed in another book Applied Welding Engineering (ISBN 978-0-12-821348-3) published by the Elsevier publication. Interested readers are encouraged to read and reference this book.

While the basic engineering principles related to loading, and stresses remain same, as for the design of any other structural member, the presence of weld changes the stress locations, stress direction, and develops stress concentration points. This significant change, demands different approach to the calculations, and providing for those specific conditions. A structure with weld is no longer a straight forward member. The presence of weld in a structural member is not all that bad news, welds are complex part of any structure, with good understanding of them, welds can be designed to be useful and contributing part of any structure. Welds can, and are also used to strengthen and stiffen any structure. The knowledge of all these attributes helps improve the design of welded structures.

This book discusses properties of materials, as structure sensitive and insensitive properties, and how these properties affect the integrity of the structure, and how to evaluate these sensitive properties of material and use them to the advantage in design evaluation.

The book further discusses the design load conditions with various joint configurations, and placement of welds, and with the consideration of how they have been made, and inspected.

Weld types are discussed in details, and how the load is distributed through these welds. Where in the structure is the primary stress? What type of primary stress working on the weld? What is the stress category? These are all discussed and graphically shown for easy understanding.

The chapters also discusses the nomenclature of welds, especially that of fillet welds. The use of complex joint designs, and their application in tubular connections. And factors that affect such complex designs. Structures are not only made of steel, and iron, other materials are also used for structures, aluminum is other most common material used for construction. The properties and grades of aluminum is explained in the chapter. The unique properties of aluminum brings in other design challenges that needs engineers and designer’s attention.

A weldment cannot be without welding, a basic introduction to most common cutting and joining process is introduced in the book. For more detailed information of arc welding process, readers are direct to another book Arc Welding Process (ISBN 978-1-119-81905-9), published by Scrivener Publishing.

The knowledge of these welding specific structural challenges are often missing, or at least available in limited form, to the engineering and design groups. This deficiency is often filled by an experienced welding engineer. If no such help is available at the design stage, then those deficiencies are identified at the fabrication shop, and then corrective action, and reverse engineering ensues, causing costly repairs and delays. In the extreme cases if those design deficiencies are not caught intime and corrected, they lead to the structural failures. Often such failures occur several years in the service of the structure, and at that point very little can be attributed to the design failure. Phrases like “weld failed” and “weld became hard” are often used to pass of the cause of failures, pinning responsibility on welders, rather than finding if the weld was designed correctly.

There are number of construction codes that address these issues, some of them are mandated as national standards, AWS D1.1 and W59 in Canada are the examples, but there are several segments of fabrication, and construction that do not fall within the construction codes’ scope or jurisdictions. And there are also places where there is no national building codes to get any guidelines. The details of joint configurations, and its impact on the integrity of the designed structure can be determined before any fabrication or construction begins, and suitable modifications can be incorporated in the design, and shown on the construction drawings. That includes, inclusion of welding related instructions, use of universally accepted and understood welding symbols to specify specific types of weld edge preparations, necessary inspections (NDE), and use of specific welding procedure, distortion control, and necessary heat treatment, where it is required.

Designing Weldments intends to fill that serious gap, or at least bring awareness among engineers and designers to seek help of an experienced welding engineer when planning to design a structure, or replacing a cast, forged, or wrought component to a welded component.

Ramesh Singh

Katy, TX

February 2022

1Properties and Strength of Material

Synopsis

This chapter defines what is meant by the term weldment. How it is distinguished from other structures. What are the factors that should be considered in deciding the conversion of a Cast structure to a welded structure? This introduction chapter gives essential basic knowledge quired for design of weldments.

Keywords

Weldment, static, dynamic, structure, cast, forged, NDE, distortion

1.1 Introduction

A weldment is an assembly of various members of a structure that are joined by welding. The word structure may include from a simple joint of two members, for a trailer hitch, motor vehicle chassis, building frame, or a more complex joint of say a bridge-spurs of road over pass, construction of a ship, of an offshore platform, where multiple members are joined by welding in complex configurations to address varying static or dynamic stresses. The joining of different members by welding to create a complex structure is a preplanned activity with following basic objectives.

(i) to provide the intended purpose of the structure and

(ii) to be a reliable and safe structure.

Of course, the technical feasibility, ease of fabrication, availability of the material, and the cost are the other important factors that are associated and woven with the basic objectives, and all those are considered at the design stage.

Often to reduce the weight and/or the cost of a cast structures it may be selected for conversion to a welded structure. It may be noted with caution that a machines or a component constructed (Cast) out of a cast-steel or cast iron is not an automatic fit-design for welded design of the same component. This is a very common error among the designers of machine parts. Same caution also applies for any forged part, considered for the conversion to a welded design.

Figure 1.1 A typical strain and stress diagram, describing various elements of tensile test.

When welded design is used to convert Cast and Forged components, it can significantly reduce the cost of the component, the weight of the component, and also improve its aesthetics. But it needs very careful, and in depth study of both the designs, for usability, and the end objective of the component.

As a minimum the weldment designer should have good knowledge and experience of the following manufacturing processes.

1. Casting and Forging process by which the original component is made of,

2. Welding and other joining processes,

3. Cutting and machining process,

4. Inspection and testing methods,

5. Fabrication activities and tools available for the task,

6. Properties of various materials,

7. Weldability of materials,

8. Effects of restrains on welds,

9. Distortion control,

10. Design for appropriate stiffness and or flexibility as desired of the structure,

11. Designing to address, required tension, compression and torsional load on the structure,

12. Weld and NDE symbols,

13. Knowledge of nondestructive inspection (NDE) methods, with their specific advantages and limitations.

14. Applicable codes, regulations and practices,

15. Selection of suitable weld design for welding.

The strength of steel is an important aspect of design, typically the tensile strength is used for the design purpose. A typical stress and strain diagram of steel shown the Figure 1.1 above with various strength related elements of the steel that can be determined by testing a specimen of the steel.

2Properties of Metals

Synopsis

This chapter discusses the properties of material, structure sensitive and structure insensitive properties are defined. How properties are determined for engineering applications. Behavior of metal in extreme environ conditions like heat and cold are introduced.

Keywords

Mechanical, physical, corrosion, modulus of elasticity, tensile strength, fatigue strength, cyclic loading, HAZ

2.1 Material Properties

Knowledge of the properties of the metal is an essential aspect of welding engineer’s ability to be a good welding engineer. This knowledge allows the engineer to choose the most suitable material to improve upon the cost and functioning of the component being designed.

Various metals and non-metals are used in fabrication and construction, they all possess certain specific properties that differentiates them from others to be more desirable for the specific demands of the design to be an engineering material. All these metal properties are assessed and classed in three specific metal properties that are relevant to the engineering evaluations, for the suitability for the project.

Metal properties can be classified as,

1. Mechanical properties

2. Physical properties and

3. Corrosion properties.

These are the primary properties however they can also be classified on the basis of their nuclear and optic properties. Further they can be classified on the basis of, if these properties are structure sensitive, or structure insensitive etc. Some details of these properties given the Table 2.1 below.

Table 2.1 Properties of materials.

General group

Structure-insensitive properties

Structure–sensitive properties

Mechanical

Elastic moduli

• Ultimate strength,

• Yield strength,

• Fatigue strength,

• Impact strength,

• Hardness,

• Ductility,

• Elastic limit,

• Damping capacity,

• Creep strength,

• Rupture strength.

Physical

Thermal Expansion,Thermal conductivity,Melting point,Specific heat,Emissivity,Thermal evaporation rate,Density,Vapor pressure,Electrical conductivity,Magnetic properties,Thermionic emission.

Ferromagnetic properties

Corrosion

• Electrochemical potential,

• Oxidation resistance

Corrosion of metals does affect some of the mechanical properties leading to metals failures.

Optical

• Color,

• Reflectivity.

Nuclear

• Radiation obsorbtivity,

• Nuclear cross section,

• Wavelength of characteristic X-rays

The following is the discussion on these material properties.

2.1.1 Structure Insensitive Properties

These are well stablished and defined properties of a metal. These properties are standard from one piece of metal to another, from the engineering aspect they do not change. These properties are verifiable and can be tested for verification. These can be calculated, rationalized by consideration of the chemical compositions and crystallographic structure of metal.

2.1.2 Structure Sensitive Properties

These properties are dependent upon chemical and microstructural details of the metal. These chemical and microstructural details get altered through the manufacturing and processing history of the metal. Even the size of the sample can affect these properties. All mechanical properties of metal except the Elastic Moduli are Structure sensitive properties. And all the physical properties except the Ferromagnetic properties are Structure insensitive properties of the metal. Corrosion, Optical, and Nuclear properties are all structure insensitive properties.

Now we briefly discuss these properties as they apply to metals in engineering application.

2.1.3 Mechanical Properties

Mechanical properties of metals make them useful for engineering applications. These properties make them strong, playable, to form shape and still retain their strength. Metals possess a combination of properties like toughness, strength and ductility that vary from metal to metal this variation allows the choice of specific metal for specific needs of the structure. These properties of some metals like steel, and aluminum can be altered and improved to make them more suitable for specific objectives.

Through a combination of both alloy selection and heat treatment gives design engineers a selection of mechanical properties in metals to choose from. During the fabrication process too, the applied heat, joining methods like welding and brazing choice of filler metal for welding all affect metal’s mechanical properties. Some of these properties are counter to each other; that is, if you increase one property the other may be lowered and vice versa. This leads to some compromises in selection process. This brings in the importance of fully knowing the properties of metals. To know the specific properties of metal in given condition and during its formation during fabrication it is essential to test and know exact properties of the material that is being used for design purpose.

In the following paragraphs a brief introduction to some of the mechanical properties is discussed.

2.1.3.1 Modulus of Elasticity

The ability of a metal to resist stretching (stain) under the stress is defined by the ratio of the two. This is called the Modulus of Elasticity and indicated by letter E. This is a constant value for specific metal. The Table 2.2 below gives Modulus of Elasticity values of some of the common engineering metals.

where;

Table 2.2 Modulus of elasticity of common engineering metals.

Metal

Modulus of elasticity, psi

Aluminum

9.0 × 10

6

Beryllium

42.0

Columbium

15.0

Copper

16.0

Iron

28.5

Lead

2.0

Molybdenum

46.0

Nickel

30.0

Steel, (Carbon and alloy steels)

29.0

Tantalum

27.0

Titanium

16.8

Tungsten

59.0

The elastic modulus is a structure sensitive property, (see Table 2.1) is not changed by metal’s gain size, cleanliness, by significant alloying, or by heat treatment. However, modulus of elasticity decreases with increasing temperatures, and the rate of change is not same for all metals.

The modulus indicates that, how much a beam would deflect elastically under the load, or a bar would elastically stretch, when loaded. In welding engineering the modulus is frequently used to determine the level of stress created in a piece of metal when it is forced to stretch elastically for a specific amount. In this case the stress (σ) can be determined by multiplying the strain (ϵ) by the modulus of elasticity (E) which is a constant for the given metal.

2.1.3.2 Tensile Strength

By far the most often used property is the metals’ ability to sustain the load while it is put under tensile strain. During testing, it is determined by the sustained load at which the test specimen breaks or the metal has lost its elasticity and entered in the Plastic state and deformed. This value is divided by the cross-section of the specimen being tested to obtain the Ultimate Tensile Strength (UTS) of the metal under test. The Figure 2.1 below is the tensile test graph of typical mild steel, it indicates the key points of mechanical behavior during the testing.

Figure 2.1 A typical strain and stress diagram, describing various elements of tensile test.

2.1.3.3 Yield Strength

The yield strength of a metal is the load at which the metal transits from being elastic to plastic. This load is reached at a point called yield point, however it also transits and peaks at one point, where metal exhibits total plasticity and YIELDS to the applied load. Both these points are shown in the Figure 2.1 above.

Note that there is a line at 0.2 percent offset, this value of the yield is often the engineering yield value that is used for design calculations.

2.1.3.4 Fatigue Strength

When a metal structure is subject to repeat (a cyclic load) loading, the metal is subject to specifically more stringent conditions. The cyclic loading fatigues the metal structure and reduces the life of the structure, and ultimately fractures and fail. Fatigue strength is an important mechanical property to know about the metal and welds if cyclic loading is one of the demands of the designed structure. Metal’s ability to sustain cyclic loading, for longer time of its design life is the Fatigue strength of that metal. Fatigue strength is a measures of load versus the time.

The fatigue fracture develops as each successive applied load advances the tip of the crack further to a point where the metal has no more ability to resist fracture. This type of crack progression is called stable growth of the crack. The rate of advance of the crack increases with the time and applied load, and the growth becomes unstable, and sudden failure occurs. It is important to know that any crack growth can occur only under cyclic loading in combination with residual tensile stresses in the metal itself, if there is a compressive stress, at the crack tip the crack growth will stop.

The stress that the metal can endure without fracture successively decreases as the number of cycles increases. Each successive stress cycle reduces the metal’s ability to sustain further.

For steel the fatigue strength is almost constant beyond about two million cycles. Several million more cycles are needed for steel to cause reduction in steel’s fatigue strength. Therefore, the Fatigue Limit becomes maximum stress or a range of stress which metal will be able to bear for infinite number of cycles without fracture, this is called the Endurance Limit. This leads us to the definition of the Fatigue Life. Fatigue life is the number of cycles of stress that the metal can sustain in the stipulated conditions.