This article provides an overview of the structural design process and discusses the life-limiting factors, including material defects, fabrication practices, and stress. It details the role of a failure investigator in performing nondestructive inspection. The article provides information on fatigue life assessment, elevated-temperature life assessment, and fitness-for-service life assessment.

Life assessment of structural components is used to avoid catastrophic failures and to maintain safe and reliable functioning of equipment. The failure investigator's input is essential for the meaningful life assessment of structural components. This article provides an overview of the structural design process, the failure analysis process, the failure investigator's role, and how failure analysis of structural components integrates into the determination of remaining life, fitness-for-service, and other life assessment concerns. The topics discussed include industry perspectives on failure and life assessment of components, structural design philosophies, the role of the failure analyst in life assessment, and the role of nondestructive inspection. They also cover fatigue life assessment, elevated-temperature life assessment, fitness-for-service life assessment, brittle fracture assessments, corrosion assessments, and blast, fire, and heat damage assessments.

High-volume additive manufacturing (AM) for structural automotive applications, along the lines of economically viable technologies such as powder metallurgy, castings, and stampings, remains a lofty goal that must be realized to obtain the well-known advantages of AM. This article presents two key opportunities for AM related to automotive applications, specifically within the realm of metal laser powder-bed fusion: alloys and product designs capable of high throughput. The article also presents the general methodology of alloy development for automotive AM. It provides examples of unique designs for reciprocating components in elevated-temperature applications that are also exposed to demanding tribological conditions. The article also discusses the future of AM for automotive applications.

Aluminum wrought products, castings, welds, and fasteners are used in many structural applications where they are required to safely support a load. It is useful to design aluminum structural components with its structural properties in mind from conceptualization rather than attempting to mimic components of other materials. This article discusses design specifications, design requirements and methods, and material properties used in aluminum structural design. These properties include tensile yield strength and tensile ultimate strength, welding, and ductility. The article describes various factors that affect the strength of two categories of aluminum structural components, namely members and connections. Design requirements for aluminum bolts, rivets, screws, and pins are provided. The article concludes with a discussion on the considerations for serviceability, namely deflections and vibrations.

Optimized modeling of fracture-critical structural components and connections requires the application of elastic-plastic fracture mechanics. Such applications, however, can require sophisticated analytical techniques such as crack tip opening displacement (CTOD), failure assessment diagram (FAD), and deformation plasticity failure assessment diagram (DPFAD). This article presents the origin and description of FAD and addresses R6 FAD using J-integral. It details the fracture criteria of BS 7910. The factors to be considered during the use of FAD and the applications of FAD are also reviewed.

This article discusses the fundamental variables involved in fatigue-life assessment, which describe the effects and interaction of material behavior, geometry, and stress history on the life of a component. It compares the safe-life approach with the damage-tolerance approach, which employs the stress-life method of fatigue life assessment. The article examines the behavior of three different metallic materials used in the design and manufacture of structural components: steel, aluminum, and titanium. It also reviews the effects of retardation and spectrum load on component life. The article concludes with case studies of fatigue life assessment from the aerospace industry.

Modeling will help reduce machining problems and thereby enable more rapid introduction of high-performance materials and components. This article discusses the technical needs of aircraft engine and airframe structural components and modeling of heat-treat-induced residual stress by finite-element residual-stress analysis. It describes the two-dimensional (2-D) and three-dimensional (3-D) procedures involved in finite-element residual-stress analysis. The article deals with the 2-D and 3-D machining distortion validation on engine-disk-type components. It describes methods for obtaining machining-induced residual stresses, including detailed finite-element analysis of the cutting process, the simple fast-acting mechanistic model, and the semi-empirical linear stress model. The article concludes with information on the modeling benefits and implementation of modeling in a production environment.

This article describes two analysis methods that are used to determine the life of aircrafts: fatigue life and fracture mechanics methods. The life limiting factors that control the durability of the aircraft are also discussed. The article provides an overview of the various approaches to corrosion identification and prevention. These include safe-life, fail-safe, and damage tolerance approaches. The article discusses their application to the process of extending the life of aircraft structural components.

Critical structural components must be fabricated from steels that exhibit adequate low-temperature fracture toughness because of the serious consequences of failure due to brittle fracture. This article reviews fracture resistance assessment procedures for welded joints and includes discussions on fatigue crack growth and fracture toughness. It presents the fracture toughness requirements specified by different design codes, summarizes the specifications for offshore structural steels provided by international standards organizations, and discusses the applications of these specifications. The article also focuses on advances made in steel technology and the impact of these advances on the fracture toughness of steel.

Tribology is the science and technology of interacting surfaces in relative motion. This article describes in detail the basic structural, operational, and interaction parameters of a tribosystem. The interaction parameters, which characterize the action of the operational parameters on the structural components in the system, consist of three important aspects: contact parameters, friction parameters, and wear parameters. These three aspects embody the complex mechanisms and relationships between the constituents of a tribosystem. The article concludes with information on the selection criteria of a material for wear applications.

Several methods are developed for the numerical solution of partial differential equations, namely, meshed-solution methods such as the finite-element method (FEM), finite-difference method, and boundary-element method; and numerical algorithms consisting of so-called meshed-solution methods. This article introduces the methods of so-called meshed solutions, with an emphasis on the FEM. It presents some basic differential equations that are used to model the responses of structures, components, processes, or systems with emphasis on continuum mechanics. The article provides an outline on the mathematical principles of solving differential equations. It also reviews linear structural problems to illustrate the concept of the FEMs.

This article describes the test techniques that are available for monitoring crack initiation and crack growth and for obtaining information on fatigue damage in test specimens. These techniques include optical methods, the compliance method, electric potential measurement, and gel electrode imaging methods. The article discusses the magnetic techniques that are primarily used as inspection techniques for detecting fatigue cracks in structural components. It details the principles and operation procedures of the liquid penetrant methods, positron annihilation techniques, acoustic emission techniques, ultrasonic methods, eddy current techniques, infrared techniques, exoelectron methods, and gamma radiography. The article explains the microscopy methods used to determine fatigue crack initiation and propagation. These include electron microscopy, scanning tunneling microscopy, atomic force microscopy, and scanning acoustic microscopy. The article also reviews the X-ray diffraction technique used for determining the compositional changes, strain changes, and residual stress evaluation during the fatigue process.

The design of structural components with nominally brittle materials is largely determined by their elastic moduli, density, and tensile strength. This article discusses some of the factors involved in the design and reliability through considerations of toughness and ductility of nominally brittle materials. It describes toughening by various bridging mechanisms, as well as process zone effects and their interaction with the bridging rupture zone. The article explains the phenomena that give rise to exceptional toughness and notch-insensitive mechanical behavior. It provides a schematic illustration of a basic cell model to characterize the inelastic strains that occur in ceramic-matrix composites and their dependence on the interface friction.

The stress-intensity concept is based on the parameter that quantifies the stresses at a crack tip. This article summarizes some stress-intensity factors for various crack geometries commonly found in structural components. Through-the-thickness cracks may be located in the middle of a plate; at the edge of a plate; or at the edge of a hole inside a plate. The article discusses uniform farfield loading in terms of point loading of a center crack and point loading of an edge crack. It tabulates the correction factors for stress intensity at shallow surface cracks under tension. Farfield tensile loading and part-through crack in a finite plate are also discussed. The article concludes with a discussion on through-the-thickness crack and part-through crack in a pressurized cylinder.

Shot peen forming is a manufacturing process in which local compressive residual stresses form thin sheet metals and structural components in one or more dimensions. This article discusses the principle of the process with an emphasis on fundamental mechanisms. It presents the basic considerations in the simulation of shot peen forming and provides information on single impact and multiple-impact peening simulations. The article describes the equipment and tooling used in the process. It also analyzes the influence of process parameters on shot peen forming and illustrates possible shapes and contours, which are producible by shot peen forming. The article concludes with a table that presents typical peen forming applications in the aircraft and aerospace industries.