Michal Petru

Development of fire shutters based on numerical optimizations

This article deals with a prototype concept, real experiment and numerical simulation of a layered industrial fire shutter, based on some new insulating composite materials. The real fire shutter has been developed and optimized in laboratory and subsequently tested in the certified test room. A simulation of whole concept has been carried out as the non-premixed combustion process in the commercial final volume sw Pyrosim. Model of the combustion based on a stoichiometric defined mixture of gas and the tested layered samples showed good conformity with experimental results – i.e. thermal distribution inside and heat release rate that has gone through the sample.

Numerical Modelling of Behaviour of Surface Finishing of Composite Materials

The article describes and compares the course of the resistance test of a treated surface against the impact of gravel with the model of the test process. The two series of composite samples with surface treatment underwent a so-called gravel test, followed by the evaluation of the test results. Simultaneously with the tests, the material models of the tested composites were created. The input values obtained were used to create a FEM model. The model describes the response of the surface treatment to the impact of the object i.e. gravel of the given size and weight/number. The modelling results were compared with the results of real tests.

Improving Electromagnetic Shielding Ability of Plaster-Based Composites by Addition of Carbon Fibers

The size of electromagnetic shielding in plaster composites by the means of different volume fractions of carbon fibers was studied in this paper. Conventional types of plaster, which are commonly used in industry, that is, cement, lime, gypsum, and lime cement (Thermo UM), were the base materials of the created composites. The fundamental idea of improving the electromagnetic shielding properties was verified based on a numerical simulation conducted by means of electromagnetic module in Comsol Multiphysics. The carbon microfibers with the above-critical length of 8 mm were added as the reinforcing and simultaneously shielding element into the plaster samples. From the viewpoint of the mechanical properties, fibers shorter than the critical length do not provide sufficient reinforcement. The samples were created at three different volume fractions of the dispersion and one without any reinforcement for the possibilities of their mutual comparison. The results of the carried measurement show that the electromagnetic shielding in the plaster composite grows with the increase of fiber content within the tested ratio proportionately. Also, the dependency of shielding ability on the inner material moisture has been studied. Any measureable influence of the moisture content on to the total shielding effect has not been found. Only in the lime plaster reinforced with fibers, the increased moisture could significantly decrease the shielding effect.

Improvement of the Acoustic Attenuation of Plaster Composites by the Addition of Short-Fibre Reinforcement

Noise attenuation is a key contemporary issue associated with the protection of human health. In this study, the possibilities of affecting acoustic properties of plaster composites by the addition of short-fibre reinforcement are described. The improvement of attenuation abilities was first verified using a simple numerical model with a pure plaster followed by using a reinforced plaster. The model results revealed a mutual correlation between the fibre ratio and dissipated acoustic energy. Hence, typical plasters used in the building industry (e.g., plaster, lime cement, and cement) are used as the base materials of the tested composites. The reinforcing dispersion in the form of short fibres (basalt and glass) with a defined length was selected after evidence from previously reported studies and after the comparison of some other fibres with respect to the trade-off between the rendered mechanical properties and cost. Transfer functions of the tested samples were measured using an impedance tube with two microphones, followed by the calculation of the total acoustic absorption. On the other hand, cement and plaster materials exhibited a low damping ability, and the absorption could be considerably increased by the addition of fibres, especially in the area around 1 kHz. In contrast, the UM plaster exhibited good damping properties even without the dispersion, and the addition of improper fibres such as glass ones possibly worsened the properties. The acoustic attenuation of the plaster composites can be improved by the appropriate combination of the base material and fibre dispersion. However, it is not possible to generalise this improvement for all possible combinations.

Possibilities of the Additional Damping of Unidirectional Fiber Composites by Implementation of Viscoelastic Neoprene and Rubber Layers

The aim of the presented work is to assess modal, transmission, and damping characteristics of layered carbon plates. The base is to carry experimental analysis verified by FEM model, which evaluates the vibration transfer of tested composites and describes possibilities of additional damping by implementation of viscoelastic layers. Preimpregnated carbon fibers known as prepreg were used for creation of the samples composed of four (2 constant and 2 variable) layers. The task was to assess impact of changing the fiber orientation on the transfer function and individual modal characteristics. As another option, testing of some additional damping materials was included. Neoprene and thin rubber coat were added as an outside damping element when the neoprene ply was inserted also among the layers. Expected dependence of the plies orientation onto the shape of the transfer function and even swapping of some of MOD characters (bending, torsion, and their combinations) have been found. The use of the additional damping materials is also possible but the right combination of the individual plies layout and stacking sequence is the most significant part. The results had been statistically analyzed and showed that the created layered shell FE models could be used to describe the behavior.