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.

 

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Material Science in surfboards

Summer hiatus for Made2Measure, but we thought that you might like this topical post from Engineering Breakdown! (Comments disabled – please post these at Engineering Materials’ site).

ENGINEERING BREAKDOWN

During my recent visit to the American West Coast, I had the opportunity to have a first contact with surfing. Although I didn’t have a totally satisfactory experience, I must say I found this sport quite interesting and, for that reason, I started asking some questions about the materials which are used to manufacture surfboards to my surfing expert brother. In this post I will introduce very briefly the main materials and a bit of comparison between their performance.


To begin with, the surfboards can be classified in two main categories with regards to the materials used in the outer part. For people who, like me, are not familiar with this sport, the way for identifying which of the two types of surfboards is in front of us is simply to look at the external appearance of the board itself. Trust me, anyone can spot the difference!

The first type corresponds…

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Made to Measure…Silicon Carbide Monofilaments

Who are you? Michael Rix

What is your role? EngD Research Engineer

What is your work about? Silicon Carbide Monofilaments for the Reinforcement of Titanium Metal Matrix Composites

I beg your pardon? Silicon carbide monofilaments are continuous fibres that are about as thick as a human hair and several kilometres in length. They are extremely strong, even at high temperatures, but like all ceramics they are brittle and therefore difficult to use in structural applications. Reinforcing titanium with these monofilaments takes advantage of the ceramic’s properties to produce a composite that is both stronger and lighter than monolithic titanium. Figure 1 shows a cross-sectioned composite with the fibres in a hexagonal array. My doctoral research with the University of Surrey and TISICS has been focussed on the development and characterisation of the monofilaments.

 

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Figure 1 – A secondary electron image of a metal matrix composite panel.  Note the bright dots in the centre of the fibres, which are the tungsten wire precursor on which the SiC is deposited by chemcial vapour deposition (CVD).

Why? Lightweight, high strength materials are desirable in many industries. In aerospace in particular reducing weight is always a priority for improving efficiency. Ceramics theoretically have extremely high specific strength but in practise they often fail to achieve this due to the wide range of defects that occur during their production. They are also difficult to incorporate into complex structures due to their brittle nature. The silicon carbide monofilaments produced at TISICS have a very narrow strength distribution as a result of a carefully controlled chemical vapour deposition (CVD) process. While the monofilaments are still brittle it is possible to design composites to take advantage of their strength while protecting them from damage by exploiting the toughness of the metal matrix.

And? My research looks at improving the CVD process by reducing its complexity and optimising the rate of production. The simplest metal matrix component requires several kilometres of monofilament—as much as possible of which should be made in a single length with no defects. I am also investigating the microstructure of the monofilament coating, which is important to the performance in composite.

So what? When the monofilaments are produced correctly, the resulting metal matrix composite exhibits double the strength of the equivalent titanium alloy with a reduction in density of up to 40%. Additionally, because it is possible to change the volume fraction of monofilaments within the matrix the properties of the composite can be tailored to specific design requirements.

Final Thought: Made to measure metal matrix composites using these silicon carbide monofilaments exploit the best properties of ceramics and metals to produce high performance composites for jet engines, air frames, landing-gear and pressure vessels.