This chapter discusses the fatigue behavior of bolted, riveted, and welded joints. It describes the relative strength of machined and rolled threads and the effect of thread design, preload, and clamping force on the fatigue strength of bolts made from different steels. It explains where fatigue failures are likely to occur in cold-driven rivet and friction joints, and why the fatigue strength of welded joints can be much lower than that of the parent metal, depending on weld shape, joint geometry, discontinuities, and residual stresses. The chapter also explains how to improve the fatigue life of welded joints and discusses the factors that can reduce the fracture toughness of weld metals.

This chapter describes the factors that affect the corrosion performance of aluminum assemblies joined by methods such as welding, brazing, soldering, and adhesive bonding. The factors covered include galvanic effects, crevices, and assembly stresses in products susceptible to stress-corrosion cracking.

This chapter describes joining by forming processes including riveting, clinching, crimping, and dieless joining techniques. It also discusses the fatigue behavior of clinched joints and the results of fatigue tests that compare clinched and spot welded joints.

An aircraft went down over water some 30 minutes into a flight. The wreckage was retrieved and the elevator linkage components were dismantled, cleaned, and reassembled. As the chapter explains, both the port and starboard hinge pins had fractured at a tack welded joint along a flange. Based on visual examination, SEM fractography, and chemical analysis, investigators concluded that the hinge pins were not made from the specified steel and were not properly treated after cadmium plating. The pins failed due to hydrogen embrittlement, which may have been aggravated by welding. The chapter provides several recommendations to avoid such failures in the future.

During fusion welding, the thermal cycles produced by the moving heat source causes physical state changes, metallurgical phase transformations, and transient thermal stresses and metal movement. This chapter begins by discussing weld metal solidification behavior and the solid-state transformations of the main classes of metals and alloys during fusion welding. The main classes include work- or strain-hardened metals and alloys, precipitation-hardened alloys, transformation-hardened steels and cast irons, stainless steels, and solid-solution and dispersion-hardened alloys. The following section provides information on the residual stresses and distortion that remain after welding. The focus then shifts to distortion control of weldments. Inclusions and cracking are discussed in detail. The chapter also discusses the causes for reduced fatigue strength of a component by a weld: stress concentration due to weld shape and joint geometry; stress concentration due to weld imperfections; and residual welding stresses. Inspection and characterization of welds are described in the final section of this chapter.

Many factors must be considered when welding dissimilar metals, and adequate procedures for the various metals and sizes of interest for a specific application must be developed and qualified. Most combinations of dissimilar metals can be joined by solid-state welding (diffusion welding, explosion welding, friction welding, or ultrasonic welding), brazing, or soldering where alloying between the metals is normally insignificant. This chapter describes the factors influencing joint integrity and discusses the corrosion behavior of dissimilar metal weldments.

Weldments made by the various welding processes may contain discontinuities that are characteristic of that process. This chapter discusses the different welding processes as well as the discontinuities typical of each process. It provides a detailed discussion on the methods of nondestructive inspection of weldments including visual inspection, liquid penetrant inspection, magnetic particle inspection, radiographic inspection, ultrasonic inspection, leak testing, and eddy current and electric current perturbation inspection. The chapter also describes the properties of brazing filler metals and the types of flaws exhibited by brazed joints.

Superalloys, except those with high aluminum and titanium contents, are welded with little difficulty. They can also be successfully brazed. This chapter describes the welding and brazing processes most often used and the factors that must be considered when making application decisions. It discusses the basic concepts of fusion welding and the differences between solid-solution-hardened and precipitation-hardened wrought superalloys. It addresses joint integrity, design, weld-related cracking, and the effect of grain size, precipitates, and contaminants. It covers common fusion welding techniques, defect prevention, fixturing, heat treatments, and general practices, including the use of filler metals. It also discusses several solid-state welding methods, superplastic forming, and transient liquid phase bonding, a type of diffusion welding process. The chapter includes extensive information on brazing processes, atmospheres, filler metals, and surface preparation procedures. It also includes examples of nickel-base welded components for aerospace use.

Leaks can occur as the result of several failure causes. This chapter reviews the causes, features, and impact of various types of leaks, namely gasket leaks, O-ring leaks, bond-joint leaks, weld leaks, polyvinyl chloride leaks, valve leaks, and structural leaks.

This chapter reviews materials issues encountered in joining, including challenges involved in welding of dissimilar metal combinations; joining of plastics by mechanical fastening, solvent and adhesive bonding, and welding; joining of thermoset and thermoplastic composite materials by mechanical fastening, adhesive bonding, and, for thermoplastic composites, welding; the making of glass-to-metal seals; and joining of oxide and nonoxide ceramics to themselves and to metals by solid-state processes and by brazing. The classification, types, applications, and the mechanism of each of these methods are covered. The factors influencing joint integrity and the main considerations in welding dissimilar metal combinations are also discussed.

Beryllium has been successfully joined by fusion welding, brazing, solid-state bonding, and soldering. This chapter describes these processes in detail along with their advantages and disadvantages. It also addresses application considerations such as surface preparation, joint design, and testing.

Joining comprises a large number of processes used to assemble individual parts into a larger, more complex component or assembly. The selection of an appropriate design to join parts is based on several considerations related to both the product and the joining process. Many product design departments now improve the ease with which products are assembled by using design for assembly (DFA) techniques, which seek to ensure ease of assembly by developing designs that are easy to assemble. This chapter discusses the general guidelines for DFA and concurrent engineering rules before examining the various joining processes, namely fusion welding, solid-state welding, brazing, soldering, mechanical fastening, and adhesive bonding. In addition, it provides information on several design considerations related to the joining process and selection of the appropriate process for joining.

Boiler tube failures associated with material defects are often the result of poor quality control, whether in primary production, on-site fabrication, storage and handling, or installation. This chapter examines quality-related failures stemming from compositional and structural defects, forming and welding defects, design defects, improper cleaning methods, and ineffective maintenance. It also includes case studies and illustrations.

Solid-state welding processes are those that produce coalescence of the faying surfaces at temperatures below the melting point of the base metals being joined without the addition of brazing or solder filler metal. This chapter discusses solid-state welding processes such as diffusion welding, forge welding, roll welding, coextrusion welding, cold welding, friction welding, friction stir welding, explosion welding, and ultrasonic welding.

This chapter discusses the various methods used to join titanium alloy assemblies, focusing on welding processes and procedures. It explains how welding alters the structure and properties of titanium and how it is influenced by composition, surface qualities, and other factors. It describes several welding processes, including arc welding, resistance welding, and friction stir welding, and addresses related issues such as welding defects, quality control, and stress relieving. The chapter also covers mechanical fastening techniques along with adhesive bonding and brazing.

The nonferrous alloys described in this chapter include aluminum and aluminum alloys, copper and copper alloys, titanium and titanium alloys, zirconium and zirconium alloys, and tantalum and tantalum alloys. Some of the factors that affect the corrosion performance of welded nonferrous assemblies include galvanic effects, crevices, assembly stresses in products susceptible to stress-corrosion cracking, and hydrogen pickup and subsequent cracking. The emphasis is placed on the compositions, general welding considerations, and corrosion behavior of these alloys.

This chapter discusses the properties and compositions of steels used in pressure vessels, piping, boilers, rebar, and other structural applications. It covers fine-grained steels, quenched and tempered steels, and controlled rolled (thermomechanical treatment) steels. It also compares and contrasts steels used for concrete reinforcement and in various types of pressure vessels, and presents a metallographic study of the effects of welding on the micro and macrostructure of steel.

Boiler tubes subjected to cyclic or fluctuating loads over extended periods of time are prone to fatigue failure. Fatigue can occur at relatively low stresses and is implicated in almost 80% of the tube failures in firetube boilers. This chapter covers the most common forms of boiler tube fatigue, including mechanical or vibrational fatigue, corrosion fatigue, thermal fatigue, and creep-fatigue interaction. It discusses the causes, characteristics, and impacts of each type and provides several case studies.

This chapter discusses the extrusion characteristics of relatively soft aluminum alloys. It begins by identifying alloy designations within the class and the types of extrusions made from them. It then explains how extruded shapes and cross-sections are defined and how to analyze and assess important process variables such as runout, extrusion pressure, ram speed, and butt thickness. It also provides best practices for various operations and explains how to identify and remedy common extrusion defects.

This chapter covers the welding characteristics of titanium along with the factors that determine which welding method is most appropriate for a given application. It discusses the joinability of titanium alloys, the effect of heat on microstructure, the cause of various defects, and the need for contaminant-free surfaces and atmospheres. It describes common forms of fusion, arc, and solid-state welding along with the use of filler metals, shielding gases, and stress-relief treatments. It also discusses the practice of titanium brazing and the role of filler metals.