Experimental and modelling investigation of the mechanical behaviour of chocolate at quasi-static and elevated strain rates
File(s)
Author(s)
Elezoglou, Thrasyvoulos-Konstantinos
Type
Thesis or dissertation
Abstract
Chocolate is a highly complex, multi-phase composite. Its mechanical properties strongly depend on the applied strain-rate. The novelty of the research lies on the comprehensive investigation of chocolate’s behaviour from low to high strain rates, the use of these data to construct material models, and the comparison between experimental and numerical results. Furthermore, cyclic compression tests unveil the difference between the loading and unloading Young’s Moduli of chocolate. This study can reveal insights about the appropriate handling and transportation of chocolate to prevent the development of cracks in the products and thus, reduce food waste. Monotonic compression tests were conducted at constant speeds of ranging from 0.001 m/s to 6 m/s, while monotonic tension tests were conducted at 0.001 m/s, and 0.01 m/s. Uniaxial cyclic compression tests were performed at 1 mm/min, and 10 mm/min. At the high-speed tests, dynamic effects were observed which caused oscillations in the Load-Displacement curves. An analysis to investigate and eliminate these oscillations was also conducted. Experimental results demonstrated that the strength of chocolate increases with strain rate, while there are different clusters of almost identical Young’s Moduli corresponding to low (≤0.1 m/s) and high speeds (>0.1 m/s). Cyclic tests showed that the Young’s Modulus calculated from the unloading path is 1.5 to 4 times larger than the one calculated from the loading path. Comparisons between quasi-static compression and tension results demonstrated that chocolate is stiffer in tension but stronger in compression. Finite Element Analyses simulated the uniaxial compression tests using several models and showed that the Drucker-Prager hardening model captures adequately and in a unified way the different behaviour of chocolate in compression and tension. Finally, micromechanical modelling of chocolate and comparison with analytical models was also performed, and the results were close to the experimental Young’s Modulus evaluated from uniaxial compression unloading.
Version
Open Access
Date Issued
2024-04-01
Date Awarded
2024-08-01
Copyright Statement
Attribution-Non Commercial-No Derivatives 4.0 International Licence (CC BY-NC-ND)
Advisor
Charalambides, Maria
Dear, John
Sponsor
Engineering and Physical Sciences Research Council
Mondelez UK R&D Limited (Firm)
Publisher Department
Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)
Rights Embargo Date
2025-07-31