Maria Lißner

Testing low-impedance materials such as polymeric foams under dynamic compression presents challenges for traditional Hopkinson-type methods, which often fail to maintain stress equilibrium or transmit sufficient force. This study introduces a modified Direct Impact Hopkinson Pressure Bar (mDIHPB) system with an intermediate loading stage, addressing some of these limitations. Closed-cell Rohacell IG-71 foam was tested at strain rates of 100-1000/s, demonstrating improved resolution and reliability in material characterisation, supported by a numerical model. A rate-dependent foam model was developed and calibrated using low-rate experimental data, and subsequently implemented in the Abaqus/Explicit solver to validate the experimental method and provide insight into stress wave interactions and deformation mechanisms. This numerical framework complements the experimental setup, offering predictive capability and a foundation for future dynamic testing of low-impedance materials. Compared with conventional SHPB and DIHPB techniques, the mDIHPB enables longer pulse durations, enhanced force sensitivity, and effective observation of foam deformation through densification, providing a compact and versatile solution for low-impedance material testing at medium-to-high strain rates.

Testing methodologies integrating wedge-loaded double cantilever beam (WDCB) methods with digital image correlation (DIC) are promising for measuring the Mode I interlaminar fracture toughness of fiber-reinforced composites owing to the ability to bypass

Current mouthguard test methods require improvement, as the impact energies during traditional testing do not reflect the higher energy that can be observed in actual use during sport. A new data set of ball speeds experienced during the sport of field hockey was obtained. These ball speeds have then been used to estimate impact energies. This information was used to subsequently develop a new test method consisting of a high-speed camera and drop tower. Observations show an increase in energy experienced by the mouthguard for higher-impact energies. The work carried out showed that current testing methods for sports mouthguards use lower-energy impacts than experienced during the sport of field hockey. The new method that is proposed allows for a more realistic representation of real-world impacts.

Ethylene-Vinyl Acetate (EVA) is the most popular material for manufacturing mouthguards. However, EVA mouthguards are problematic, for example inconsistent thicknesses across the mouthguard. Additive manufacturing provides a promising solution to this problem, as it can manufacture mouthguards with a greater precision. This paper compares the energy dissipation of EVA, the current material used for mouthguards, to various designs of a 3D printed material, some of which contain air cells. Impact testing was carried out at three different strain rates. The Split-Hopkinson bar was used for medium and high strain rate tests, and an Instron test rig was used for low strain rate testing. The best performing design dissipated 25% more energy than EVA in the medium and high strain rate testing respectively while the low strain rate testing was inconclusive. This research has shown that additive manufacturing provides a viable method of manufacturing mouthguards. This opens up the opportunity for embedding electronics/sensors into additive manufactured mouthguards.

Experimental results from 3D printed TPC (thermoplastic copolyester) compression specimens were used to develop a combined experimental-numerical framework to support the design of e.g. 3D printed mouthguards. First, a commercially available material model capable of representing the strain-rate dependent behaviour of materials undergoing large deformations is identified. Second, experimental results from solid 3D printed compression specimens are used to calibrate the identified material models. Third, 3D printed compression specimens with two different cavity geometries are used to assess the ability of the material model to accurately reproduce the experimental observations. The numerical investigation indicates a good representation of the strain rate dependent experimental results of 3D printed specimens.