Non-Destructive Evaluation (NDE) of Polymer Matrix Composites

Vistasp M. Karbhari

• Publisher: Woodhead Publishing
• Year: 2013
• Print ISBN:
  9780857093448
• eBook ISBN:
  9780857093554
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

The increased use of polymer matrix composites in structural applications has led to the growing need for a very high level of quality control and testing of products to ensure and monitor performance over time. Non-destructive evaluation (NDE) of polymer matrix composites explores a range of NDE techniques and the use of these techniques in a variety of application areas.Part one provides an overview of a range of NDE and NDT techniques including eddy current testing, shearography, ultrasonics, acoustic emission, and dielectrics. Part two highlights the use of NDE techniques for adhesively bonded applications. Part three focuses on NDE techniques for aerospace applications including the evaluation of aerospace composites for impact damage and flaw characterisation. Finally, the use of traditional and emerging NDE techniques in civil and marine applications is explored in part four.With its distinguished editor and international team of expert contributors, Non-destructive evaluation (NDE) of polymer matrix composites is a technical resource for researchers and engineers using polymer matrix composites, professionals requiring an understanding of non-destructive evaluation techniques, and academics interested in this field. - Explores a range of NDE and NDT techniques and considers future trends - Examines in detail NDE techniques for adhesively bonded applications - Discusses NDE techniques in aerospace applications including detecting impact damage, ultrasonic techniques and structural health monitoring

Part I

Non-destructive evaluation (NDE) and non-destructive testing (NDT) techniques

1

Introduction: the future of non-destructive evaluation (NDE) and structural health monitoring (SHM)

V.M. Karbhari, University of Texas at Arlington, USA

Some elements of this chapter are adapted from Structural health monitoring of civil infrastructure systems published by Woodhead Publishing Limited.

Abstract:

As the use of fiber reinforced polymer matrix composites increases there is an increasing need for ensuring both a high level of quality control and that products and systems respond as required over extended periods of time. Thus, while there is a continuing need for methods of non-destructive evaluation (NDE), there is also a need to go further than just detection to the assessment of the effect of the defect on performance and life. It is important to keep in mind that the field is developing extremely rapidly and methods of testing and evaluation are increasingly being integrated with complex models and simulations along with technological advances that make it possible to combine specific methods with the means of assessment to enable rapid structural health monitoring (SHM) in the field.

Key words

non-destructive evaluation (NDE)

structural health monitoring (SHM)

defects

service life

capacity

durability

damage tolerance

design

performance

1.1 Introduction

As the use of fiber reinforced polymer matrix composites increases in applications ranging from aerospace and military field to those in civil infrastructure, the need for ensuring a high level of quality control is also increased. Simultaneously, there is a need to ensure that products and systems respond as required over extended periods of time. Thus, while there is a continuing need for methods of non-destructive evaluation (NDE), especially those capable of rapidly detecting even smaller sized defects, there is also a need to go further than just detection to the assessment of the effect of the defect on performance and life. This extension of NDE which includes the steps of diagnosis and prognosis is often known as structural health monitoring (SHM). While the focus of this book is on methods of NDE, it is important to keep in mind that the field is developing extremely rapidly and methods of testing and evaluation are being increasingly being integrated with complex models and simulations along with technological advances that make it possible to combine specific methods with the means of assessment to enable rapid SHM in the field. In many cases the SHM of a component, structure, or system can be conducted autonomously, or at least, without removing that item from service.

1.2 Non-destructive evaluation (NDE) and structural health monitoring (SHM)

Thompson (2009) attempted to provide differentiation between NDE and SHM by stating that NDE refers to ‘those situations in which the relative positions of a measurement system and the component under inspection can be manipulated with respect to one another,’ whereas SHM refers to ‘those situations in which fixed sensors are placed on a structure, either in-situ or ex-situ.’ While this does provide a means of differentiation at a simplistic level the use of the word ‘sensor’ has to be taken in the broadest context. One could also consider that NDE focuses on time-based, off-line, monitoring using passive systems that provide disparate and partial information about the condition of a material, component, or structure, facilitating time-based maintenance and an asset management approach that is time-consuming and could necessitate downtime. SHM, on the other hand, focuses on condition-based, on-line monitoring using combinations of active and passive systems that provide a comprehensive assessment of the ‘health’ of the material, component, or structure, facilitating proactive maintenance that results in ‘intelligent’ asset management.

Traditional NDE technologies are based on the detection of damage or defects (often caused during the manufacturing process or intrinsic in the raw constituent materials) which in the case of composites can range from air bubbles, voids, and blisters, fiber/fabric misalignment and/or wrinkling, fiber failure, matrix crazing and cracking, resin-rich or poor sites, layer separation and delaminations, as well as to aspects such as bond failures, crushing of cores and core shear. In addition aspects such as impact damage (both externally visible and internal), moisture entrapment and other aspects that could result in longer-term deterioration need to be pin-pointed and their extent determined. There are a range of NDE techniques used with composites and some of the most commonly used techniques can be classified as (a) visual inspection, (b) tap testing, (c) dye-penetrant testing, (d) stress-coating testing, (e) ultrasonic inspection, (f) acoustic emission techniques, (g) dielectric techniques, (h) X-ray radiography, (i) thermography, (j) eddy-current techniques, (k) microwave techniques, (l) Shearography, and (m) electron probe imaging. Each of these has its specific field of applicability although there is a level of overlap as related to defect size and accuracy of detection. Although a number of these techniques are ‘passive’, some are dependent on frequencies of excitation and a range is shown in Fig. 1.1.

1.1 Frequency spectrum for selected NDE techniques. UV = ultraviolet, ESR = election spin resonance, NMR = nuclear magnetic resonance. (After Summerscales, n.d.)

Irrespective of the NDE technique the key element is the detection of the smallest possible defect or damage sufficiently in advance of an event that causes failure. This essentially leads to the development of a ‘critical sized flaw’ representing a threshold beyond which ‘safe use’ cannot be guaranteed. Often this indicates a level beyond which defect growth (such as in the case of a crack) is rather rapid. This can be used in the development of a damage tolerance methodology as depicted in Fig. 1.2.

1.2 Concept of damage tolerance.

While concepts of damage tolerance have been used successfully and are increasingly effective, with the development of better and more refined and accurate methods of NDE the challenge is not just that of detecting damage. Rather, it is the use of sensing technologies in conjunction with materials and structural models (and simulations) to facilitate the inference of future behavior/response in terms of performance characteristics such as remaining capacity and life. The migration from NDE to SHM is thus a key aspect in the development of prognosis of the ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributor contact details
• Woodhead Publishing Series in Composites Science and Engineering
• Part I: Non-destructive evaluation (NDE) and non-destructive testing (NDT) techniques
• Part II: Non-destructive evaluation (NDE) techniques for adhesively bonded applications
• Part III: Non-destructive evaluation (NDE) techniques in aerospace applications
• Part IV: Non-destructive evaluation (NDE) techniques in civil and marine applications
• Index