Young's Modulus Measurement Techniques - Collaboration with Volkswagen Research

PhD researcher, Sully Khan, spent eight weeks at Volkswagen's research centre in Wolfsburg, Germany, with a view to obtaining accurate Young's modulus measurements for various samples.

Sully Khan
Sully Khan

Sully Khan is currently completing a PhD in developing high modulus composite steels for automotive applications with the Advanced Metallic Systems Centre for Doctoral Training and sponsored by Volkswagen Group Innovation. The overall aim of his PhD is to fabricate a steel which is high modulus and lightweight for new electric vehicle components. He has created a unique steel composite which required further investigation through a placement at Volkswagen's research site in Wolfsburg, Germany, which was recently successfully completed.

The current focus of Sully's work involves taking a steel composite which is reinforced with titanium diboride (TiB2) and analysing it both microscopically and mechanically. The thermomechanical processing route used to refine the alloy involves hot rolling and plane strain compression (PSC). 

The steps for the alloy fabrication and grain refinement
The steps for the alloy fabrication and grain refinement

This project heavily relies on the Henry Royce Institute (HRI) facilities present at The University of Sheffield, both at the Royce Discovery Centre (RDC) and the Royce Translational Centre (RTC), specifically the Consarc 10kg Vacuum Induction Melting (VIM) machine, FENN Hot Rolling Mill and ServoTest Thermomechanical Compression (TMC) machine. Additional equipment from Royce being utilised for this project includes the gas atomiser located and the FCT HP D25 Field-assisted Sintering Technology (FAST) machine. The latter equipment focuses on creating a steel composite via a powder metallurgy route to compare it to the traditional casting and thermomechanical processing route. 

The Vacuum Induction Melting and Hot Rolling stages were completed at the Royce Discovery Centre, University of Sheffield, by Dr Yunus Azakli, Alloy Manufacturing Research Lead, and Dr William Pulfrey, Advanced Metal Processing Engineering Lead, respectively, with work on the FAST heavily supported by Senior Engineering Technician, Nigel Adams. 

After the PSC stage, the samples are machined into miniature dog-bone size for tensile testing; these are small due to the original nature of the sample dimensions needed for PSC. The problem lies in the dog-bone samples which have a 12mm gauge length. This made it difficult to obtain accurate strain readings which in turn, generated noisy stress-strain plots due to the external extensometer using pins to measure distance with the aid of software, which had high uncertainty and fluctuated regularly. It is important for the linear region of a stress-strain graph to have little noise as this is where Young’s modulus is determined. The solution was to use a state-of-the-art laser extensometer from VW in Wolfsburg to address the fluctuation issue. The facilities also had a resonant frequency dynamic analysis (RFDA) machine which accurately determined the Young’s modulus in a non-destructive approach. Using the two methods in tandem, accurate Young’s modulus measurements were successfully obtained.

Sometimes an opportunity is not clear to see, but in the case that it presents itself to you, take advantage of it. My PhD is fully funded with a grant and organised through Advanced Metallic Systems (AMS) who kindly take care of all expenses. As I have an industrial sponsor, I recognised the importance of collaboration and with the help of VW and AMS I managed to meet friendly, dedicated and focussed colleagues who helped excel the progress of my PhD. I seized the opportunity given to me and I am very happy I did not brush it aside. A conversation is all you need to start something special.

Sully Khan, The University of Sheffield

This project was useful in understanding of how elongation characteristics change with different steel compositions which all had different temperature profiles during the final stage of PSC. This was present through obtained stress-strain plots and RFDA measurements. As well as Young’s modulus measurements, part of the project looked into observing TiB2 particles in a steel matrix. Through SEM, observations showed interesting TiB2 morphology and secondary phase particles formed during ferrous titanium and boron additions during VIM. This is unique for this alloy composition and processing route and will prove to be valuable for upcoming research. As the development for a new steel matrix composite (SMC) continues in this PhD, new micrographs and mechanical testing reveal that TiB2 has an effect on thermodynamic behaviour as well as mechanical properties. Improvements of SMC’s compared to standard steel alloys are prevalent and require further investigation to see how the volume fraction of TiB2 changes thermodynamic behaviour, elongation and modulus measurements. After finalising a composition which adheres to automotive vehicle requirements, new lightweight components can be fabricated for stiff electric car components which can reduce the overall weight of vehicles and therefore improve fuel economy and driving dynamic.

Tensile Samples - Sully Khan
Tensile Samples - Sully Khan

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