presentation speech
...ect last summer at Imperial College in collaboration with Nestle UK. I hoped to show that traditional mechanical methods can be applied to determine wafer strength. However the final aim of this project was to investigate the effects of moisture absorption in Kit Kats, which I believe is being done by my colleagues back at Imperial. In order to determine wafer strength, we have to choose a suitable test to perform. Compression testing is regularly used to determine the strength of food. It is easy and simple to apply and with such brittle material, it is hard to use tension testing since it cannot be gripped. However, the one disadvantage is that we have to know the structure of the material before performing any data analysis. Well, since we need to know the structure of the wafer in order to use the data obtained, it was decided to classify wafers as cellular foams. This isn’t the soap foam you may be thinking about but harder packing foam. This consists of an interconnected network of struts or beams and has a three dimensional open cell system, as shown here. How do these cellular foams fail? Two main failure modes have been identified. Buckling and fracture. Buckling is somewhat like bending, without any structure separation as shown here, while fracture means breaking away from the structure, as shown here. So after classifying the structure of the wafer and seeing how it fails, how then do we measure the strength of wafers? The simplest method is to obtain a stress strain curve, from which the gradient of the initial straight line gives a simple strength measurement which can be gauged against well known materials like steel or wood. Shown here is what a stress strain curve for brittle materials may look like, with the three most important regions pointed out, the initial linear elasticity region, from which the gradient gives the strength measurement, the brittle crushing region and the densification region. Well, now that we know what we are looking for, i.e. stress and strain values and what results we are expecting, i.e. the previously shown curve, we proceed to testing the wafer. The two formulas shown are the basic calculation that is computed to obtain the stress strain curve. Stress equals force over circular area. Strain equals to natural log of extension divided by original height. Further, what is shown is a simple compression test set up, with the machine recording the parameters needed and transferring this data to a computer, which makes it easier for us to analyze. And after successful tests, voila, we obtain the stress strain curve as ex...