Search Results for statistics

Failure analysis can sometimes involve considerations of statistics and probability. This chapter reviews some of the basic types of statistical distributions in order to understand some basic principles in their use. The main focus is on the uses of the normal distribution, which is the most commonly used statistical distribution. The chapter also includes a section discussing the reliability and probability of passing.

This chapter provides an introduction to statistical process control and the concept of total quality management. It begins with a review of quality improvement efforts in the extrusion industry and the considerations involved in developing sampling plans and interpreting control charts. It then lays out the steps that would be followed in order to implement statistical testing for billet casting, die performance, or any other process or variable that impacts extrusion quality. The chapter concludes with an overview of the fundamentals of total quality management.

Statistics, data analysis, root cause analysis, and problem-solving processes play a key role in failure investigations. This chapter explains how to collect failure investigation data, how to build and maintain a database for company-related failures, and how to use corresponding statistics including type of failure, material, and root cause. It describes the purpose and benefits of conducting a root cause analysis and the factors, namely relative failure importance and company value, that determine when an investigation should be performed. The chapter also discusses the four-step problem-solving process as it applies to failure investigation, how to assemble an investigation team, and the details of organization and planning. It concludes with a case history of the Firestone 500 steel-belted tire failure, stressing the importance of a systematic approach to failure investigations.

A successful heat treating operation is determined by the ability to satisfy the customer's quality requirements consistently and economically. This chapter reviews the steps that are important to produce quality parts in heat treating with a brief practical explanation of each. The steps include selecting proper material and design of the part being treated; determining whether the process is capable of heat treatment; using statistical process control, control charting, and in-process inspection and testing; and applying statistical quality control and final testing (sampling) to verify the results.

This chapter discusses the factors that play a role in fatigue failures and how they affect the service life of metals and structures. It describes the stresses associated with high-cycle and low-cycle fatigue and how they differ from the loading profiles typically used to generate fatigue data. It compares the Gerber, Goodman, and Soderberg methods for predicting the effect of mean stress from bending data, describes the statistical nature of fatigue measurements, and explains how plastic strain causes cyclic hardening and softening. It discusses the work of Wohler, Basquin, and others and how it led to the development of a strain-based approach to fatigue and the use of fatigue strength and ductility coefficients. It reviews the three stages of fatigue, beginning with crack initiation followed by crack growth and final fracture. It explains how fracture mechanics can be applied to crack propagation and how stress concentrations affect fatigue life. It also discusses fatigue life improvement methods and design approaches.

This chapter covers the failure modes and mechanisms associated with boiler components and the tools and techniques used to assess damages and predict remaining component life. It begins with a review of the design and operation of a utility boiler and the materials used in construction. It then describes the various causes of failure in boiler tubes, headers, and steam pipes, explaining how and why they occur, how they are diagnosed, and how to mitigate their effects. The final and by far largest section in the chapter is a tutorial on damage and life assessment techniques for boiler components and assemblies. It demonstrates the use of various methods, including analytical techniques that estimate life expenditure based on operating history, component geometry, and material properties; predictive methods based on the extrapolation of failure statistics; methods that predict life based on dimensional measurements; methods based on metallographic studies; methods based on temperature estimates; and a method for estimating remaining life under creep conditions based on stress-rupture testing of service-exposed material samples. The chapter also discusses the use of fracture mechanics and presents a number of cases in which life assessments are made based on the integration of several methods.

This chapter gives a brief overview of the role of fatigue in component failures. It presents examples of fatigue failures along with statistics on the causes and costs of fatigue damage in various industries. It also includes a chapter-by-chapter summary of the content in the book, noting that the book deals primarily with fatigue at temperatures below the creep range with high-temperature fatigue being treated in a companion publication.

This appendix provides supplemental information on the metallurgical aspects of atomic structure, the use of dislocation theory, heat treatment processes and procedures, important engineering materials and strengthening mechanisms, and the nature of elastic, plastic, and creep strain components. It also provides information on mechanical property and fatigue testing, the use of hysteresis energy to analyze fatigue, a procedure for inverting equations to solve for dependent variables, and a method for dealing with the statistical nature of failure.

This data set contains the results of uniaxial tensile tests of a wide range of aluminum casting alloys conducted at high temperatures from 100 to 370 deg C, subzero temperatures from -269 to -28 deg C, and room temperature after holding at high temperatures from 100 to 370 deg C. In most cases, tests were made of several lots of material of each alloy and temper. The results for the several lots were then analyzed together graphically and statistically, and the averages were normalized to the room-temperature typical values. For some alloys, "representative" values (raw data) rather than typical values are provided.