Forensic Polymer Engineering

Why Polymer Products Fail in Service

Peter Rhys Lewis

• Publisher: Woodhead Publishing
• Year: 2016
• Print ISBN: 9780081010556
• eBook ISBN: 9780081007280
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Forensic Science
• Index: Technology & Engineering

Forensic Polymer Engineering: Why Polymer Products Fail in Service, Second Edition presents and explains the latest forensic engineering techniques used in the investigation of failed polymer materials that are illustrated with a very large number of detailed case studies which show the different types of failure and the forensic engineering techniques used in their investigation. In this updated edition, new case studies have been added to include patent disputes and failed products such as spiral wound wall storage tanks, lithium battery explosions, water bottle failures, and breast implant failures (such as the PIP scandal). New images demonstrating failure have been included, and images from the previous edition are reproduced in color and enhanced with additional explanatory detail. With a dedicated focus on polymeric materials, the book includes details on the experimental techniques that are used to characterize the materials, particularly in cases of failure. Finally, the book has information on the fabrication of polymer devices, as manufacturing flaws often play a role in failure. - Demonstrates the latest forensic engineering techniques used in the investigation of failed polymer components - Presents detailed case studies that illustrate different types of failure in polymer components, fittings, and medical devices - Examines the role of manufacturing in product failure with an overview of faults recognized in methods, design, and material selection - Provides an integrated approach to polymer failures that covers everything from basic materials properties, through to the experimental techniques required to study them

Chapter 1

Introduction

Abstract

Understanding polymer product failure needs some background to the science of polymers, especially the types of bond which occur in them between individual atoms, and the way those bonds determine their physical and chemical properties. Polymers are molecular chains of identical repeat units although they can be modified by adding different repeat units to make copolymers and are dominated by the ease with which carbon bonds to itself. Product failure modes include mechanical failure such as fracture. Product design may weaken its strength through inappropriate stress raisers in their shape, and there are ways in which such defects can be minimized if not eliminated. Failure through chemical attack is controlled by the type of chain bonding and includes both chain scission as well as environmental attack by various agents. Investigating failures requires a special set of skills in analysing different kinds of evidence, especially witness statements and the surviving physical remains, as well as being able to access literature in the public domain, which has expanded greatly in recent years.

Keywords

Bonding; Chain degradation; Chain length; Expert evidence; Failure; Fracture; Hydrolysis; Molecular weight; Oxidation; Thermoplastic; Thermoset

1.1. Product failure

It comes as no surprise that products have a limited life in service. But what many might find surprising is the very great range of possible causes of failure, from a large and now very diverse range of materials. The failure modes of most metals are well established, simply because most have been used in service for many years. They have been well studied both in the laboratory and in practical applications, so there is a voluminous literature on the way they fracture, or fail in other ways. That of course does not stop further failures, but it does make failures from known causes less likely. Engineers and designers have a large property database available to them to check whether or not a particular metal or alloy is fit to be used under a specified set of circumstances. Such is not the case with most non-metallic materials, especially those that have been discovered or invented within the recent past, especially polymers. Their failure mechanisms are the subject of this book, but the usual academic approach of separating the failure mechanism from the product which fails has not been taken, but rather discuss each incident as a case study in its own right.

Case studies are important for several reasons. First, product failures must be discussed in context, when the cause or causes of failure can be related to the way in which the product has been used (or abused). Second, if further failures of a particular type are to be prevented in future, then the causes must be identified so as to take remedial measures. It necessarily implies that all the product features which are relevant to its failure have to be examined for establishing the causal chain of events leading to its final demise. The first step in establishing the causal chain is simply to provide a chronology of events, so that each step is isolated and sequenced. Only then can the causes be tackled, using appropriate analytical tools. The details of each incident have to be described so that the critical facts can be sorted from the mass of irrelevant detail. This enables a fuller picture of the accident to be achieved, and it is also much more interesting to the reader if he or she wishes to draw parallels with related incidents within their own experience. There is no better way of illustrating the basic principles of polymer technology than by way of a detailed case study. It focuses attention on a specific aspect of the polymer structure, or the way it has been made, or the design of the product which has failed.

So by way of prelude to the case studies described in this book, it is essential to provide the technical backdrop to the diversity of polymers used in products today. They provide properties unavailable in metals, such as transparency, low weight, high strength and insulation. Low weight is at a premium for transport of goods and people, and one area where polymers have e...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• Preface to the Second Edition
• Preface to the First Edition
• Acknowledgements
• Chapter 1. Introduction
• Chapter 2. Sample Examination and Analysis
• Chapter 3. Medical Devices
• Chapter 4. Storage Tanks
• Chapter 5. Small Containers
• Chapter 6. Pipes and Fittings
• Chapter 7. Polymer Seals and Sealants
• Chapter 8. Tools and Ladders
• Chapter 9. Transportation Failures
• Chapter 10. Consumer Products
• Chapter 11. Conclusions
• Index