Crystalline properties of semicrystalline polymers are very important parameters that can influence the application area. The internal structure, like the mentioned crystalline properties, of polymers can be influenced by the production technology itself and by changing technology parameters. The present work is devoted to testing of electrospun and centrifugal spun fibrous and nanofibrous materials and compare them to foils and granules made from the same raw polymer. The test setup reveals the structural differences caused by the production technology. Effects of average molecular weight are also exhibited. The applied biodegradable and biocompatible polymer is polycaprolactone (PCL) as it is a widespread material for medical purposes. The crystallinity of PCL has significant effect on rate of degradation that is an important parameter for a biodegradable material and determines the applicability. The results of differential scanning calorimetry (DSC) showed that, at the degree of crystallinity, there is a minor difference between the electrospun and centrifugal spun fibrous materials. However, the significant influence of polymer molecular weight was exhibited. The morphology of the fibrous materials, represented by fiber diameter, also did not demonstrate any connection to final measured crystallinity degree of the tested materials.

Hybrid epoxy/vinyl ester (EP/VE) and epoxy/unsaturated polyester (EP/UP) resins were used as matrices to prepare unidirectional carbon fibre (CF) and carbon/glass fibre (CF/GF) reinforced composites targeting toughness of improvement. Hybrid resins were produced simultaneously (one-pot) and sequentially. (Thermo)mechanical properties of hybrid resins were determined in surface hardness, three-point bending, dynamic mechanical analysis (DMA), and differential scanning calorimetry (DSC) tests. Hybrid matrix composites with CF and CF/GF hybrid reinforcements were characterized with quasi-static mechanical (three-point bending) tests performed in 0° (longitudinal) and 90° (transverse) directions. In addition, flexural fatigue tests were run on UD composites.Interlaminar properties were deduced from in-plane shear strength (IPSS) test and 2 fractographic inspection in a scanning electron microscope. The EP/VE hybrid resin exhibited improved energy absorption compared to neat constituent resins in contrast to EP/UP. Using hybrid resins as matrix highly improved the toughness and durability of the corresponding composites. Improved energy absorption was attributed to the phase structure of the hybrid resins, which also positively affected the IPSS.

In this study epoxy/vinyl ester (EP/VE) based hybrid thermoset resin was developed and used as a matrix in unidirectional Keywords Hybrid resin · fatigue · composite · epoxy · vinyl ester · IPN IntroductionIn the field of thermoset polymer composites the researchers work on materials and their combinations which give more favourable mechanical properties. The thermoset structural composites have great strength and modulus, but their toughness properties are often worse than that of ductile metals and alloys or thermoplastic matrix polymer composites. These high performance materials usually give rigid reactions to quickly forthcoming actions, loadings. The solution for toughening can be found in the micro-, or nano-scale structure of the thermoset polymer. In the fibre reinforced composites usually the matrix is responsible for the toughness, therefore mainly the matrix should be modified to improve of this property [1,2].Basically, there are two different ways to create micro-, or nano-structure in the polymers. The first opportunity is the hybridization of the reinforcing materials with micro or nano sized particles. Nowadays this technique is quite popular among researchers and manufacturers, because of the easy reproducibility of these composites. The effectiveness of this third phase is based on the properties of the particle itself and on the surface to volume ratio that has main role in the quality of the adhesion. The specific surface can be extremely huge in case of nanoparticles. Another way to achieve micro-or nanostructured systems is to change the matrix morphology by blending. In this approach researchers try to make a mixture of different polymers, which are well distributed in each other and the border area of their phases (interphases) has large surface, where a lot of secondary bounds are present. One example of such structure is the interpenetrating polymer network (IPN) system, in which the different polymer phases are not separated, but the polymer chains penetrates into the other crosslinked structure of the other phase. In these systems a sort of synergistic effects there can be found. Due to this fact the IPN structure can absorb remarkable amount of energy by their flexible properties. This feature can be manifested in mechanical, thermal and thermo-mechanical properties too [1][2][3].The mentioned synergistic effects and the compatibility of mixed polymers affect the thermo-mechanical properties.

The essential work of fracture (EWF) method was adapted to determine the fracture toughness of poly(propylene-block-ethylene) (EPBC) based nanocomposites with different amounts (from 0 up to 5 wt.%) of synthetic boehmite alumina (BA). The dispersion of BA in the matrix was studied by transmission and scanning electron microscopies. Agglomerated micronscale along with well dispersed nanoscale BA particles were present in the EPBC matrix.By contrast to the neat EPBC, all nanocomposites failed by unstable necking. Therefore the energy partitioning concept of the EWF was adapted and attention paid to the yielding-related term. Both specific yielding-related essential and non-essential work of fracture parameters increased linearly with the product of the yield stress and elongation at yield derived from static tensile tests.2

This work combines modal analysis measurements with a novel 2D finite element plate model, which is capable to determine the delamination growth based on the change in the measured frequencies. The base of the presented method is a finite element model incorporating the Classical Laminated Plate Theory, and it is capable to estimate the eigenfrequencies of a rectangular plate with through-the-width delamination and straight crack front using arbitrary boundary conditions. The model contains special types of finite elements for modelling the delamination. This results a contact free model, which improves the simulation speed significantly. Using this model, the characteristic of the change of the eigenfrequencies with respect to the delamination growth can be obtained. These results can serve as reference, and according to the theoretical curves, the actual size of the delamination can be estimated based on the change in the measured frequencies. According to our measurement results, it can serve as a good reference for modal analysis. The experiment shows that the model can predict the effect of the delamination growth on the eigenfrequencies very well. Additional conclusions are drawn based on further numerical simulations, which can aid the model based modal analysis of composite plates.