ABSTRACT
Talcum reinforced polypropylene was enhanced with a soft type of polypropylene in order to increase the impact strength and damage tolerance of the material. The soft phase was incorporated in the form of continuous interlayers, where the numbers of layers ranged from 64 to 2048. A blend with the same material composition (based on wt% of the used materials) and the pure matrix material were investigated for comparison. A plateau in impact strength was reached by layered architectures, where the matrix layer thickness was as small or smaller than the largest talcum particles. The most promising layered architecture, namely, 512 layers, was subsequently investigated more thoroughly using instrumented Charpy experiments and tensile testing. In these tests, normalised parameters for stiffness and strength were obtained in addition to the impact strength. The multilayered material showed remarkable impact strength, fracture energy and damage tolerance. However, stiffness and strength were reduced due to the addition of the soft phase. It could be shown that specimens under bending loads are very compliant due to a stress-decoupling effect between layers that specifically reduces bending stiffness. This drawback could be avoided under tensile loading, while the increase in toughness remained high.
ABSTRACT
The application of material extrusion-based additive manufacturing methods has recently become increasingly popular in the medical sector. Thereby, thermoplastic materials are likely to be used. However, thermoplastics are highly dependent on the temperature and loading rate in comparison to other material classes. Therefore, it is crucial to characterise these influences on the mechanical properties. On this account, dynamic mechanical analyses to investigate the application temperature range, and tensile tests at different crosshead speeds (103, 101, 10-1 and 10-3â¯mms-1) were performed on various 3D-printable polymers, namely polyetheretherketone (PEEK), polylactide (PLA), poly(methyl methacrylate) (PMMA), glycol-modified poly(ethylene terephthalate) (PETG), poly(vinylidene fluoride) (PVDF) and polypropylene (PP). It was found that the mechanical properties of PEEK, PLA, PMMA and PETG hardly depend on temperature changes inside the human body. PVDF and PP show a significant decrease in stiffness with increasing body temperatures. Additionally, the dependency of the stiffness on the strain-rate is increasing between PLA, PP, PEEK, PETG, PMMA and PVDF. Besides the mechanical integrity of these materials (strength, stiffness and its strain-rate and temperature dependency inside the body), the materials were further ranked considering their filling density as a measure of their processability. Hence, useful information for the selection of possible medical applications for each material and the design process of 3D-printed implants are provided.
