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An experimental study on the impact response of foam core sandwich panels subjected to low velocity impact is performed. Panels with glass fiber laminated facesheets and polystyrene and polyurethane foam core with density of 32 kg/m3, respectively 100 kg/m3, were tested in impact on an INSTRON Ceast 9340 drop tower at different impact energies. The composite facesheets were made of epoxy resin, glass fiber roving of 500 g/m2 and short glass fibers of 3 mm in 5 different combinations. The effect of foam core and facesheet type on the resulting impact damage and contact force is analyzed. It was noted that higher impact energies introduce matrix damages and the partial fracture of the fibers which significantly change the force-displacement histories, particularly after the maximum impact force is reached. Also, the use of polyurethane foam core increased the impact damage indentation in size and depth compared to the panels with polystyrene core. Panels having facesheets only with short glass fibers show a very poor resistance compared to the ones with roving and are completely perforated even for the smallest impact energy.

Functionalization of silica nanoparticles is needed as to improve the mechanical performance of epoxy nanocomposites. Previous experience showed that direct dispersion of commercially available silica nanofillers does not improve significantly the mechanical properties of resulting nanocomposites. Different methods of fabrication are presented along with comments on the possibilities to improve the quality of obtained specimens. Both functionalized and unfunctionalized silica nanoparticles were added in three epoxy resins. The considered filling fraction was in most cases 0.1, 0.3 and 0.5 wt%. The obtained nanocomposites were subjected to monotonic uniaxial loading at room temperature. The static mechanical properties were not significantly changed regardless the filler type or percentage and type of epoxy resin.

The mechanical recyclability of the technical biopolymers polytrimethylene terephthalate (PTT), cellulose acetate butyrate (CAB), polybutylene succinate (PBS) and polyhydroxy alkanoate blend (PHBV/PBAT) was evaluated by assessing the effect of repeated polymer processing (extrusion without further compounding with virgin material or additives) on the material structure and mechanical properties. Reprocessing-induced hydrolytic degradation was found to be the prevalent aging mechanism of the investigated biopolymer grades. However, susceptibility to hydrolysis, and thus maintenance of the performance characteristics, differed strongly between the biopolymer types. To that effect, PTT and CAB especially exhibit a high potential for mechanical recycling. By taking advantage of appropriate additivation, the mechanical recyclability of PBS and PHBV/PBAT is also assumed to be high.

Poly(ethylene terephthalate) films with oriented lamellar structure were deformed in tensile experiments and investigated in situ using small angle X-ray scattering. The tensile direction was set parallel, normal and in an angle of 45° relative to the surface normal of the lamellae. Data were interpreted in terms of two-dimensional autocorrelation functions. The deformation of lattice spacing and lamellar orientation can largely be explained by affine transformations. The sample, where the lamellar surface normal was normal to tensile direction, developed a chequerboard type arrangement of crystalline parts. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

The rapid expansion of the Internet of Things (IoT) and consumer electronics is driving the demand for microelectromechanical systems (MEMS) in the area of wearables, smartphones, and home and building applications. MEMS sensor packages feature a variety of polymeric materials which can significantly affect their behavior under environmental loads as humidity or temperature. A broad range of different polymeric materials can be applied in the packages, but to get a good MEMS sensor performance, an optimized application tailored material combination should be applied. To analyze the effect of the applied material types an advanced simulation approach has to be considered. A hygro-thermo-mechanical simulation based on measured temperature and moisture dependent material properties is presented. As MEMS sensor packages are complex multimaterial systems, the main challenge is the modeling of the moisture discontinuities in the interfaces. The discontinuity of moisture concentration has been solved by using the solubility approach.

Fused filament fabrication is a material extrusion-based additive manufacturing technique that has been strongly growing in popularity, for it is accessible, versatile, and affordable. The 3D-printing of semi-crystalline polymers still faces major challenges, though. Apart from common issues such as shrinkage and warpage phenomena, a variety of process-related morphological and crystallographic changes can occur. Since these changes strongly influence the resulting material properties, it is crucial to understand the complex relationships between the material, its processing and final properties on a fundamental level. In this context, the present work examines the impact of different nozzle temperatures and printing speeds on 3D-printed polypropylene (PP) samples. One extreme parameter set (high nozzle temperature, low printing speed) reveals a homogeneous morphology, weak flow-induced orientations, isotropic thermal conductivities and a strong inter-layer diffusion. In contrast, the other extreme parameter set (low nozzle temperature, high printing speed) forms an inhomogeneous morphology with a complex growth of shish-kebab structures, a pronounced weld line morphology and a highly anisotropic behaviour. By in-depth analyses of four parameter sets, this paper offers novel insights into the complex formation of crystalline structures in 3D-printed semi-crystalline polymers and suggests how to purposefully design the property portfolio of these materials.

The present study was inspired by different industry projects in which a strong dependence of the fatigue fracture performance of POM on the processing conditions was observed. To examine the relationships under more reproducible conditions, plates of two different POM homopolymer resins (one significantly nucleated) were produced by compression molding and by injection molding under moderate conditions. For the injection molding, three different mold temperatures were used. At specific locations, the plates were analyzed concerning their hierarchical structure on the micro- and nanolevel and concerning their fatigue fracture performance. For the fatigue fracture performance, the dependence on the processing conditions was rather small for the nucleated resin but much more significant for the other resins. This dependence could not be related to morphological effects only, and thus, a combined effect of morphology and residual stresses was assumed.

In this study, different strategies to improve the mechanical properties of physically foamed high-density polylactic acid sheets were examined to produce polylactic acid foam sheets with tailor-made mechanical properties. The first part was the determination of the effect of different blowing agents (CO2 and N2) on the foam morphology. The second part of the study was the modification of the formulation. For this purpose, both a linear and a branching chain extender and a thermoplastic elastomer were used to improve the elongational properties (tensile modulus and strain at break) of the polylactic acid foam sheets. Additionally, the effect of the addition of cellulose fibers on the foam morphology and the mechanical properties was investigated. All experiments were carried out on a laboratory flat-film line. This extrusion line consists of a 30-mm single-screw extruder attached with a 250-mm flat sheet die. The results show a strong influence of the material formulation on the mechanical properties of the high-density foam sheets. Both the mechanical properties and foam morphology could be improved by the right material formulation. The addition of the thermoplastic elastomer leads to a better foam morphology and also to a reduced brittleness of the foam sheets. Furthermore, it could be demonstrated that cellulose fiber can be used as a nucleating agent for polylactic acid but causes a further decrease in the strain at break.

Materials used in high voltage applications have to meet a lot of regulations for their safety and functional usage during their lifetime. For high voltage applications the electrical properties are the most relevant designing criteria. However, the mechanical properties of such materials have rarely been considered for application dimensioning over the last decades. This article gives an overview of composite materials used in high voltage applications and some basic mechanical and thermo-mechanical characterization methods of such materials, including a discussion of influences on practically used epoxy based thermosets.