On the Analysis of Composite Processing Using Magnetic Resonance Imaging (MRI)

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Abstract
The utility of magnetic resonance imaging (MRI) as a means of non-destructively investigating the distribution of internal defects has recently been demonstrated by imaging the distribution of water-filled voids within pultruded rods. Manufactured from glass-filled nylon and polyester, the samples were soaked in a water bath at 80°C for 25 weeks allowing water to ingress. The same work, however, also highlights one of the major problems found in materials MRI, namely the quantification of results. As pointed out by the authors, the particular experimental conditions used to obtain the images discriminate in favour of mobile water molecules having long spin-spin relaxation times (T2), i.e. those in voids and defects. This is because the experimental echo times (Te) used were limited by hardware considerations to longer than 40ms. In the imaging experiment, the total signal observed is proportional to the echo amplitude, S(t), and

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