Techniques for Postfracture Analysis

Abstract

Adhesives are used nowadays in an uncountable number of applications in everyday life, especially applications where a failure in service may lead to economic loss, injury, or death. In these cases, the ability to determine the causes of failure is essential. This chapter discusses the latest forensic engineering techniques used in the investigation of failed adhesive-bonded joints. An overview of the examination and analysis methodology is introduced in first place; the sequence of steps is important in order to guarantee that no vital information is lost along the way, avoiding cross contamination of fractured surfaces. Visual inspection, microscopy techniques – optic, electronic, and atomic probe microscopies – preparations methods for observation of the fractured surfaces – dissection, etching, coating – physical and chemical characterization methods – Raman microprobe, x-ray spectrometry, infrared analysis, thermal methods – are introduced as convenient tools for supporting the investigation on postfractured specimens. The fracture morphologies of adhesive joints are considered in relation to their locus of failure and directional stability of crack propagation. Mode of loading and strain rate influence on the failure morphologies of the surfaces are illustrated. Fatigue and creep failures imprint specific signatures on the fractured surfaces and are briefly introduced. Several case studies are shown to highlight some aspects of the general procedures and techniques that were previously described. Cases are grouped in three different categories: failures due to overload and design deficiencies, failures due to material and manufacturing defects, and failures due to in-service factors.