Petr Kulhavý

Testing of Tensile Properties of Carbon Prepreg Composite Rods with Adding of a Non-Composite Part

The global development of carbon composite materials has been devoting constantly in still more companies and research institutions. Pre-saturated fabrics known as prepregs have a significant position in this field. The common problem of many worldwide authors is how to determine their tensile strength. The problem with tensile load is mainly due to the extremely high strength of fibers filaments and structural fragility of the thin width of formed profiles. Therefore, indirect methods are usually used. They are based on a determination of the resonant frequencies or on a conversion of values obtained e.g. with bending test. In our case, some experiments have been based on the idea of added a non-composite material into the final structure. The aim of this work was also to find an appropriate modification of a surface of the additional element with regard to a mutual interaction, surface microstructure and mechanical properties of the resulting composite part.

Vibration and Noise Reduction Analysis of Sheet Metal Structures with Damping Layer

Vibration reduction in term of lower acoustic noise level increases e.g. the passenger comfort, fulfills acoustic manufacturing standards, decreases the transportation influence on the environment etc. The basic sheet metal structure is complemented with damping layer which absorbs the vibration energy. The frequency response experiment analysis of the component structure with damping material helps to validate the separate material models used for predictive simulations.

Study of Mechanical Properties and Modeling of Flax Reinforced Composites

This article deals with assessment of mechanical properties and possible technical usability of flax prepreg composite materials. Mechanical properties of materials are the decisive factor for selection of their suitable industrial application. The main step was to describe the process of acquiring basic mechanical properties of one layer. Then, these properties were used for creation of a numerical model of a primary laminate and subsequently for modeling a multilayered composite. The performed FEM model has been verified based on the experimentally tested samples in tensile and flexural loading.

Model verification of material properties of wound composite rods in tensile loading

The aim of this work is to find a suitable reinforcement in terms of mutual compatibility, surface microstructure, and mechanical properties of the resulting carbon composite parts. Two types of samples in layout + 45° / 0° / ± 45° / 0° / −45° and + 45° / 0° / −45° with a total thickness of 1.8 mm, wound on a rounded polyurethane core from several carbon rovings, were experimentally tested in the area of low elastic deformation up to 1 mm. In order to obtain basic engineering constants the tensile tests of whole parts failure have been carried out. Subsequently, several material and numerical models were developed in order to describe the problem of composite tensile loading. The model was solved by two approaches, specifically a layered shell and a layered solid. Considerable differences have been found in the properties of the real (experimental) and theoretical model based on the declared properties of the individual components. Probably due to the manufacturing imperfections and the porosity in the resulting material, the values of the basic engineering constants of the laminate of the resulting laminate reach lower values. This had to be solved by adjusting the material model of the used dispersion and matrix. The real arising failures were described by using the failure criteria for several time steps of the model solution and compared to the real experiment with quite good agreement.

Experimental Analysis and Optimization of Vibrations of a Clamping Device by Using Hyperelastic Elements

Nowadays composite frames can be used, for its specific properties, in many fields of industry. Lightweight composite frames can be significant structural components in some transportations, flights and military applications. The main problem is how to use automatic applications for winding filaments of the carbon fibres on a closed spatial shaped core of product frames, that has been still doing by the hand manufacturing. For automatic production could be used unique prototype of robotic technology, which allows winding of the carbon fibres on closed shape into the core of a frame. The biggest problem of the clamping device, used for the closed frames, are their vibrations and resonance caused due to the rotary motions. The vibrations and resonance negatively affect the process of carbon fibres winding. Experimental measurements were carried out to determine the acceleration on individual arms of the clamping device, which reaches to 2.5±0.6 g. Minimizing of the vibration was performed by a hyperelastic elements which reduce vibrations to 0.4±0.15g.

Numerical Model of the Static Loading of a Stitched Seam in the Composite Cover of Car Seat

Fundamental knowledge of the mechanical properties of used materials are the basic preconditions for a successful construction of a final product. For seam as well as the reliability of its strength in some cases we need to know certainty when there will be the malfunction. In this study a spun of polyester thread were sewn on a material used for car seat cover. A single or multiaxial loading either static or dynamic has been used in the field of automotive textiles as well as for conventional materials. There is no standard method of measurement for the determination of dynamic strength of sewn seams and therefore it was necessary to construct a device that may measure the strength of seams under dynamic stress. It was carried out an experimental determination of the tensile strength under a static and shock loading for the textile part itself, then for the thread and also for them all together. A lot of very sophisticated numerical models of the individual materials structures in the world generally exist but considerably less is in this field taken into account the behavior of the whole.The aim of this work is with using the commercial software ANSYS create a contact numerical model that will be able to predict behavior of stitched seams and can be used instead of the classical experiments.