Preface Free

This book deals with the fatigue and fracture of engineering materials. Although modern fatigue analysis and fracture mechanics are mathematical disciplines, and mathematical rigor is normally found in texts on fatigue and fracture mechanics, I have endeavored to construct a more basic book that balances the major points of fatigue and fracture analysis without burdening the reader with too much complex mathematical development.

This book is ideal for the engineer with a basic knowledge of materials that is just starting to be involved with either failure analysis or fatigue and fracture analysis. It also provides a sound technical groundwork for further study of more advanced texts. This book is useful for the experienced failure analyst that needs a more thorough background in fatigue and fracture mechanics, or for the fatigue and fracture engineer that needs to know more about failure modes.

The first chapter gives a high level introduction to fatigue and fracture and describes some of the noteworthy failures that have occurred during the industrial age from 1900 to date. As a result of these failures, many of which were brittle, unexpected, and catastrophic in nature, there have been numerous changes to design philosophy, and after World War II, the evolution of fracture mechanics. A number of the life limiting factors are also introduced, including material defects, manufacturing defects, stress concentrations, elevated temperatures, and environmental degradation.

The second chapter covers the basics of the static mechanical properties of materials. Included are tension, compression, shear, torsion, and combined stress. Both the engineering and true stress-strain curves are covered in some detail. The importance of stress concentrations and residual stresses are also included.

The third chapter explains the difference between ductile and brittle fracture modes from both a macroscopic and microscopic level. The general characteristics, the macrostructural and microstructural aspects of both ductile and brittle fractures are explained. The ductile-to-brittle transition in steels is covered. Finally, intergranular failures are discussed along with embrittling causes.

The fourth chapter provides an introduction to fracture mechanics. The chapter starts with the pioneering work that Griffith conducted on brittle fracture that led to the development of linear elastic fracture mechanics. For metals that exhibit high levels of ductility, elastic plastic fracture mechanics is presented. Toughness tests discussed include: Charpy V-notch, drop weight tests, linear elastic fracture toughness, and nonlinear fracture mechanics testing (J-integral). The last section covers the important variables that affect fracture toughness; yield strength, loading rate, temperature, material thickness, and material orientation and anisotropy.

The fifth chapter covers the basics of fatigue. Topics covered include: high cycle fatigue, low cycle fatigue, fatigue life prediction, cumulative damage, fatigue crack nucleation and growth, the fracture mechanics approach to fatigue crack growth, crack closure, geometrical and manufacturing stress concentrations, temperature effects, fatigue life improvement methods, and fatigue design methodologies.

With the background provided by the previous chapters on fracture mechanics and fatigue, the sixth chapter covers the fatigue and fracture of three different classes of engineering alloys–steels, aluminum alloys, and titanium and titanium alloys.

The seventh chapter covers the important topic of structural joints– mechanically fastened and welded. It should be noted that many failures often start at joints. Mechanical fastener topics covered include threaded fasteners in tension, shear, and bearing and how preload affects joint performance. For welding, stress concentrations due to joint configurations, weld shape, and discontinuities are discussed along with methods to improve the fatigue and fracture resistance of welded joints.

The eighth chapter covers the basics of fracture control and damage tolerance analysis. Fracture control is the concerted effort to ensure safe operations without catastrophic failure by fracture, while damage tolerance is the property of a structure to sustain defects or cracks safely, until such time that action is (or can be) taken to eliminate the cracks by repair or by replacing the cracked structure or component. Important topics include residual strength, crack growth prediction, and nondestructive inspection.

The next two chapters cover the fatigue and fracture of ceramics and polymers in the ninth, and continuous fiber polymer matrix composites in the tenth. Ceramics are inherent brittle materials, while polymers may be either highly ductile or brittle. The fracture and fatigue behavior of ceramics is briefly covered. For polymers (i.e., plastics), important topics covered include: thermosets and thermoplastics, viscoelastic behavior, static strength, fatigue strength, fatigue crack propagation, impact strength, and the environmental performance of plastics.

The fatigue strength of continuous fiber polymer matrix composites, especially those with carbon fibers, is excellent. However, composites have a low resistance to impacts. Therefore, the thrust of Chapter 10 is to discuss impact events and the effects of delaminations and other defects on structural performance. The so-called “building block approach” to composite structural certification used in the aircraft industry is briefly covered.

The eleventh chapter covers high temperature failures with an emphasis on creep and stress rupture. Creep deformation mechanisms and failure modes are discussed with an emphasis on metallurgical instabilities and environmental effects. Creep life prediction, creep-fatigue interaction, and design for creep resistance are also included.

The topic of wear is covered in the twelfth chapter. Types of wear discussed include: abrasive wear, erosive wear, grinding wear, gouging wear, adhesive wear, and fretting wear. This is followed by wear in which fatigue is a major contributor: contact stress fatigue, subsurface-origin fatigue, surface-origin fatigue, subcase-origin fatigue and cavitation fatigue. Wear prevention methods are discussed.

In the thirteenth chapter, on environmentally-induced failures, first, some basic principles of electrochemical corrosion are covered and then some of the various types of corrosion, with an emphasis on stress corrosion cracking and corrosion fatigue. This is followed by a short section on corrosion control. The last section deals with high temperature oxidation which usually occurs in the absence of moisture.

The steps in the failure analysis process are outlined in the fourteenth chapter: collection of background data and samples, preliminary examination, nondestructive and mechanical testing, macroscopic and microscopic examination, determination of failure mechanism, chemical analysis, analysis by fracture mechanics, and testing under simulated service conditions.

I have included an appendix on defects that can lead to fatigue and fracture. It gives some degree of detail on defects that can lead to failure, including design deficiencies, material and manufacturing defects, and service life anomalies. Major topics include ingot related defects, forging imperfections, sheet forming imperfections, casting defects, heat treating defects, and weld discontinuities.

I would like to acknowledge the help and guidance of the staff at ASM International; Scott Henry, Steve Lampman, Karen Marken, Bonnie Sanders, Madrid Tramble, and Diane Whitelaw, for their valuable contributions.