Jan Trnka

This study investigates the dynamic response of various chocolate types to direct impact at high strain rates, which has significant implications for practical applications such as production, packaging, and transportation. Five different chocolate types – extra dark, dark, milk, white, and ruby – were evaluated. Experiments were conducted using the Direct Impact Hopkinson Bar (DIHB) technique, which enables the study of the mechanical behaviour of materials at strain rates exceeding 10 ³ s-1. The influence of specimen length on the mechanical response of the chocolates was also examined. Impact responses were characterized in both the time and frequency domains. Results indicate that dark chocolate exhibited the highest resistance to impact loading. Furthermore, an enhancement in mechanical properties with increasing impact velocity was observed across all chocolate types.

Summary: The split Hopkinson pressure bar test is extensively used to characterize material at high strain rate. This method enables to evaluate strain, strain rate and stress in the specimen. The viscoelastic behavior of materials in study was described using of the complex elastic modulus. Three copolymers of high‐density polyethylene (PE‐HD) have been investigated, two unimodal types supplied by two chemical companies and one bimodal type. Structure of PE samples (pellets) was characterised by ¹³C NMR (Carbon‐13 nuclear magnetic resonance).

Acta Universitatis Agriculturae et Silviculturae Mendelianae Brunensis, the scientific journal of the Mendel University in Brno, Czech Republic

Paper deals with experimental research on the crushing of coffee beans of different kinds under quasi-static and dynamic compression. The process of the crushing is described in details. It has been shown that there is variability in the crushing strength values. A relation between crushing strength and the coffee grain shape is also studied. Roasted Arabica coffee (Coffea arabica) beans were used for analyses. Arabica coffees were produced in different countries. All Arabica samples were submitted to a light roast. The detail analysis of the experimental data shows that there is no significant relation between parameters describing the fracture behaviour of the grains and grain geometry. These parameters are also independent on the grain weight. Compression of the coffee grains leads to their crushing. The fracture force is different for the different kinds of the coffee. The same is fact valid also for the strain at the fracture and for the energy absorbed during the grain crushing. Dynamic loading leads to the increase in the fracture force of coffee grains in comparison with the quasi static loading.