Made to Measure Future

You may have noticed that we’ve missed a couple of posts recently.  Mark and I are looking at how the site operates, formats, PR and various other factors, so we’ve put the posts on hold for a little while.  It won’t be for too long and we’re hoping to have a refresh of the site and new content up soon.  In the meantime, watch this space!

We’d love to hear from you as well – what has worked well?  What’s not so good?  What would you like to see more off?  Use the contact form below to drop us a line.

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Made to measure…Delaminations

Who are you?: Osman Ajmal

What is your role?: PhD Researcher

What is your work about?: Locating and measuring the growth of embedded delaminations in composite materials.

I beg your pardon?: Delaminations are one of the more prevalent forms of defects in composite materials such as Fibre Reinforced Polymers (FRPs). Non-Destructive Evaluation (NDE) is used to determine the position and size of delaminations during testing.

OK. Why?: FRPs are used in a wide variety of industries. They have applications as components of cars, aeroplanes, spacecraft and even sporting goods! By understanding how these defects in structural elements behave under different loading scenarios, these materials can be better tailored for different applications.

And?: My work compares existing and novel methods to detect these defects. Figure 1a is a finite element model of a typical specimen with an embedded defect, whilst Figure 1b shows a typical output from the real specimen, monitored by Digital Image Correlation (DIC).  Analysis of the DIC data gives, in this case, longitudinal surface strains which can be used to detect the presence of delaminations.

dic.png

Figure 1: Longitudinal strain contours of composite laminate specimen with an embedded square shaped artificial delamination in three point bending. (a) Finite Element Modelling (b) Digital Image Correlation

So what?: By comparing different NDE techniques to each other and to FEA, my work aims to determine the “resolution” of the different techniques. This is done by comparing the results of different techniques for the testing of the same structural elements and the same loading scenarios. By using artificial inserts, model defects can be created during the manufacturing process. During testing, these defects can be monitored: because the size of the delamination is known, the NDE technique can be assessed against what it   should detect, and if possible calibrated accordingly.

Final thought: The wide range of readily applicable NDE techniques are literally ‘made to measure’ defects in structural elements. It is important to determine how well they do this for delaminations in the composites used in modern cars, aeroplanes, ships and all the rest.

 

Made to Measure…Microscopy

Who are you? Rebecca Tung
What is your role? Undergraduate Medical Engineer on industrial placement in the Microstructural Studies Unit at the University of Surrey
What is your work about? I help to prepare and characterise materials using a variety of techniques, predominantly scanning electron microscopy based techniques.

I beg your pardon? Materials can be examined in a scanning electron microscope (SEM), which produces an electron image, to reveal microstructure and topography. In addition, the chemical composition of the material may be analysed which can help to determine the properties of a material.

What is a SEM? Scanning electron microscopes use a beam of accelerated electrons as a source of ‘illumination’. Electron microscopy offers a much higher spatial resolution than light microscopy and can reveal either microstructure or surface topography. When the beam interacts with the sample surface, some complex physical processes occur. This results in the emission of secondary electrons, backscattered electrons as well as X-rays. The detection of these three signals enables: (i) imaging of the surface topography, (ii) imaging of the microstructure and (iii) measuring the chemical composition. In the micrographs below, the difference between the detection of backscattered electrons and secondary electrons can be seen. Figure 1 shows the same Vickers hardness indent in a brittle material imaged with the two types of emitted electron. The behaviour of the low energy secondary electrons (Figure 1a) and high-energy backscattered electrons (Figure 1b), along with appropriate electron detectors, gives different information about the specimen.

Microscopy

Figure 1 – Comparison of Scanning Electron Microscopy modes: a) secondary electron image (the bright white areas suggest ‘charging’) and b) back scattered electron image.

And? Analysis of a material with a SEM offers not only increased resolution (therefore higher useful magnification) but the benefits of studying any combination of topography, microstructure and chemistry. Modern microscopes have multiple electron detectors that give different combinations and emphasis of information. Other possibilities include variable pressure microscopy which enables wet specimens to be studied and a focused ion beam capability which enables specimens to be sectioned and studied in 3D.

So what? The characterisation of engineering materials is essential for the goal of understanding microstructure-property-processing relationships. The SEM is arguably the most flexible technique that contributes to this goal.

Final Thought: SEM offers a variety of analytical techniques, which makes it a versatile tool for characterisation of materials. The capabilities of the JEOL 7100F SEM, at the University of Surrey, which is my favourite instrument, make it suitable for studying the whole range of engineering materials—it really is an instrument that is Made 2 Measure!