Mechanical springs are used in mechanical components to exert force, provide flexibility, and absorb or store energy. This article provides an overview of the operating conditions of mechanical springs. Common failure mechanisms and processes involved in the examination of spring failures are also discussed. In addition, the article discusses common causes of failures and presents examples of specific spring failures, describes fatigue failures that resulted from these types of material defects, and demonstrates how improper fabrication can result in premature fatigue failure. It also covers failures of shape memory alloy springs and failures caused by corrosion and operating conditions.

Stress-relief heat treating of steel is the uniform heating of a structure to a suitable temperature below the transformation range, holding at this temperature for a predetermined period of time, followed by uniform cooling. This article provides information on the sources of residual stress, briefly describes the factors influencing the relief of residual stresses, and discusses the various thermal stress-relief methods. It contains tables that provide a summary of compressive and tensile residual stresses at the surface of parts fabricated by common manufacturing processes. The article presents the temperature range of alloy steels for stress-relief heat treating and describes the importance of stress relief of springs.

This article discusses the common causes of failures of springs, with illustrations. Design deficiencies, material defects, processing errors or deficiencies, and unusual operating conditions are the common causes of spring failures. In most cases, these causes result in failure by fatigue. The article describes the operating conditions of springs, common failure mechanisms, and presents an examination of the failures that occur in springs.

This article discusses stress relaxation testing on metallic materials, as covered by ASTM E 328. It reviews the two types of stress relaxation tests performed in tension, long-term and accelerated testing. The article illustrates load characteristics and data representation for stress relaxation testing used for the most convenient and common uniaxial tensile test. It concludes with information on compression testing, bend testing, torsion testing, and tests on springs.

This article discusses the failure mechanism of springs. It describes the critical application factors that affect spring fatigue performance. These include: material type and strength; stress conditions; surface quality; manufacturing processes; rate of application of load; and embrittlement or cracking. The article summarizes the methods of statistical analysis of S-N data for general comparisons of fatigue strength of spring steels. The fatigue performance of springs is illustrated by Goodman diagrams. The article also exemplifies the examination of failed springs.

Steel springs are made in many types, shapes, and sizes, ranging from delicate hairsprings for instrument meters to massive buffer springs for railroad equipment. The primary focus of this article is small steel springs that are cold wound from wire. Wire springs are of four types: compression springs (including die springs), extension springs, torsion springs, and wire forms. Chemical composition, mechanical properties, surface quality, availability, and cost are the principal factors to be considered in selecting steel for springs. Both carbon and alloy steels are used extensively. The three types of wire used in the greatest number of applications of cold formed springs are hard-drawn spring wire, oil tempered wire and music wire. Residual stresses can increase or decrease the strength of a spring material, depending on their direction. Steel springs are often electroplated with zinc or cadmium to protect them from corrosion and abrasion. Although some hot-wound springs are made of steels that are also used for cold-wound springs, hot-wound springs are usually much larger, which results in significant metallurgical differences. All spring design is based on Hooke’s law; charts and formulas are available to aid in the design of springs.

Lapping is the lower-pressure, lower-speed, and lower-power application of the use of fixed abrasives. This article begins with a discussion on the process capabilities of lapping and reviews the selection of abrasive and vehicle for lapping. It describes the methods of lapping outer cylindrical surfaces, namely, ring lapping, machine lapping between plates, centerless roll lapping with loose abrasives, and centerless lapping with bonded abrasives. In addition, the article discusses the methods employed for lapping of outer surfaces of piston rings, crankshafts, inner cylindrical surfaces, flat surfaces, end surfaces, spherical surfaces, balls, spring like parts, and gears. It also reviews the problems in flat and end lapping. The article concludes information on the use of lapping in accelerated wearing-in process for matching and aligning components of bearing assemblies.

This article is an atlas of fractographs that helps in understanding the causes and mechanisms of fracture of high-carbon steels and in identifying and interpreting the morphology of fracture surfaces. The fractographs illustrate the following: torsional fatigue fracture, hydrogen-embrittlement fracture, fatigue crack propagation, and corrosion fatigue of components made from high-carbon steels. The high-carbon steel components include bull gear, drive shaft, power boiler stoker grate, steel wheel, spring wire, suspension spring, automotive engine valve spring, power spring, cantilever-type spring, railroad rail, and seamless drill pipe.