Milan Žaludek

Manufacturing and Mechanical Characterization of Bio-Based Laminates and Sandwich Structures

Jute fabric is well-known reinforcing material in composite science, however, there is a necessity to treat these fabrics to reduce moisture uptake and improve properties. Nevertheless, every modification increases the cost and reduces the possible applications. Presented research deals with an investigation of possibility to use untreated jute in various fabric weight as a reinforcing material in sandwich structures facings. Untreated jute reinforcements and two types of cork cores were saturated in one step during vacuum infusion creating a lightweight sandwich composite. All samples were mechanically tested in three-point bending test. Experimental results showed the most appropriate material combination and produced sandwich structure are proposed for design applications.

The Limits of Vacuum Infusion Technology during the Production of Filled Polymer Composite Systems

The vacuum infusion process (VIP) is suitable for production of bigger prototypes and low-series production, but their utilization is increasing because their low investment cost, comparability with high-tech technology (pre-preg), possibility to produce sandwich structures in one step and many various advantages.We verify the possibility of VIP to produce various prototypes with increasing degree of flame retarders, specifically aluminium hydroxide (ATH), which fulfil regiments to mechanical and Fire-Smoke-Toxicity (FST) properties according EN 45 545. Mechanical properties we confirmed by testing of bending properties according EN ISO 178 and tensile properties according EN ISO 527-4. FST properties were confirm by flammability test with hot wire according EN ISO 60695-2-11.

Optimization of the Material of External Fixator with FEM Simulation

Patients and surgeons with tibia fracture using external fixator are worried about a higher weight of metal fixator´s construction and therefore also poor manipulation ability with this tool [1]. During the last few years the bone tissue engineering has improved significantly and along with that also material development has increased [2,3]. Therefore patients requirements can be achieved by optimizing the material composition of this product. The main objective of this research is a weight reduction by material and design changes of the external fixator. Another aim is the evaluation of the final model. The model of innovative fixator was created and also computed in software CATIA V5-6 using finite element method simulation. Appropriate forces were applied and the simulation was performed. Results of FEM simulation indicate that the final weight of complete product declined significantly after application of carbon-fiber composite. Test results also suggest that the rigidity and the stability of complete fixator are safe. Hence this research describes that application of carbon fiber composite into the external fixator design is an important improvement of the external fixator.

Effect of Processing Parameters on Mechanical Properties of 3D Printed Samples

3D printing technology enables the production of functional components in small quantities which can be used as end-use parts. The mechanical properties of the final product define its quality and determine its success or failure in a given application. One at the various additive manufacturing technologies - Fused Deposition Modelling is very often used due to its relatively low cost and the availability of 3D printers and thermoplastic materials. During the process, there are many factors that can affect the mechanical properties of the final product. The temperature of the extrusion nozzle and the layer thickness are two of the basic process parameters. The objective of this work is to investigate the effect of these two processing parameters on the final mechanical properties of the 3D printed samples from acrylonitrile butadiene styrene. Mechanical testing includes the tensile and flexural strength, as well as tensile and flexural modulus.

Fatigue Life of Al-Honeycomb Core Composites Construction

The composite materials (CM) are increasingly replacing conventional structural and building materials. A special type of composite material is the polymer composite sandwich panel with a honeycomb core (PCHSP). PCHSPs have been used in aviation since the 1960s. First on tertiary structures, later on secondary and nowadays on primary structures. At present, PCHSPs are also used in the construction of land vehicles (cars and buses, railway trains, etc.). The design of the aircraft and land vehicles is stressed by flight and ground loads (surface loads: aerodynamic, volume loads: own weight, etc.). These are always random processes. This work deals with statistical analysis of PCHSP testing. The substance of evaluation is in the determination of PCHSP ́s lifetime. The issue of fatigue loading of PCHSPs is not fully explored and general conclusions have not been formed yet. Unlike metallic materials, where two standards [1] and [2] for metal fatigue testing used in the Czech Republic, however, there is no specialized standard describing testing and statistical evaluation of PCHSP ́s fatigue lifetime. There is only ISO 13003:2003 standard [3], which is applicable to composite materials (laminates) and the military standards; MIL-HDBK-23A [4]. There is a relatively small number of scientific publications dealing with the life fatigue test of PCHSPs. Only static tests on sandwich panels are included in the book [5] and fatigue tests of composite structures are described in [6] (laminates only). There is also a limited number of scientific articles dealing with PCHSPs fatigue tests [7, 8, 9, and 10]. The issue of fatigue testing of sandwich panels was solved in Czechoslovakia already in 1972 [11]. A PCHSP has specific fatigue life properties. The problem is complicated by the different properties of each of sandwich components. The PCHSPs tests are always tests of the structural element. Therefore, the complications resulting from the demands of adhesive bonding technology are increasing due to the known factors affecting the number of the achieved cycles, ie. stress values, structure of the individual components, geometric shape and dimensions. This also explains non-existent standard for the PCHSP ́s fatigue test. The fatigue testing methodology have to always include a statistical approach for the evaluation of the test results and with respect to the loading and conducted cycles itself we differ between low and high-cycle fatigue [12-16]. The statistical evaluation of the PCHSPs fatigue tests results is in a graphical representation using the classic S-N (Wöhler) curve and it determinines the reliability of the estimates of statistical variables. As a result, median of lifetime, the shortest life and the lower limit of fatigue life were investiquded in this work. During fatigue testing, it is advisable to monitor the formation and propagation of the sample ́s damage by infrared thermography. This non-destructive testing method is very well suited in CM and PCHSP testing and it has been validated in other experiments, eg. in [17].

Preparation and Dynamic Mechanical Analysis of Glass or carbon Fiber/Polymer Composites

Nowadays, glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP) composites are broadly used so it is essential their properties to be explored in depth. In this study, GFRPs and CFRPs were produced by vacuum bag oven method and their viscoelastic behaviour at elevated temperatures was investigated. In particular, by Dynamic Mechanical Analysis experiments properties such as storage modulus, loss modulus, tanδ and glass transition temperature were determined. The results showed that, apart from a very small increment in the low temperatures in some of the compounds, as the temperature increases the storage modulus of the composites decrease while the composite containing unidirectional glass fibers in longitudinal direction and 34% percentage of matrix achieved the higher storage and loss modulus. Furthermore, as the unidirectional fibers change direction from transverse to longitudinal the GFRPs exhibit much higher storage and loss modulus.

Detecting Water in Composite Sandwich Panels by Using Infrared Thermography

Honeycomb composite structures widely used in aviation are sturdy and light-weight but they may accumulate water from the atmosphere during aircraft operation. The presence of water in honeycomb cells leads to a higher airplane mass and excessive corrosion of aluminum cores, while the frozen water endangers panel integrity. This work describes the use of infrared thermography for detecting water trapped in aviation honeycomb cells.

Analysis of Mechanical and Impact Properties of Prepreg Composites under Elevated Temperature

This paper presents an experimental investigation of mechanical and impact properties of carbon and Kevlar-glass composites prepared from pre-impregnated materials. Namely, flexural performance in three-point bending at different temperatures is evaluated. Moreover, Charpy impact test and low-velocity impact test are also conducted for classification of impact properties and character of rupture. These all properties are important for material design of sport bike rims and many sport and other applications.

An Experimental Analysis of Bending Behavior of Sandwich Constructions for Transport Industry

In this work the mechanical performance of various sandwich constructions with respect to core material were experimentally evaluated. Sandwich structures were made of glass prepreg and three types of plastic core using vacuum bagging, technology traditionally used for production of parts for transport industry. The aim of this study is to analyze the impact of the core material type and its thickness on bending behavior at different environmental temperatures. Moreover, the effect of core layers compared to one layer core of same thickness was determined. Conducted research provided useful information of bending behavior and showed specific failure modes of individual sandwich constructions.

Experimental Characterization of Multiaxial Glass Laminates for Front End Cab

This research paper deals with an experimental investigation of mechanical properties of prepared composite panels. Flexural behavior in three-point bending test is measured. Composites are prepared in order to satisfy requirements for transport industry. Totally, three material compositions are tested with different multiaxial reinforcing fabric and polyester resin. All samples are produced by low-pressure vacuum infusion mainly used for large-scale composite parts. Furthermore, fire resistance of prepared laminates is tested and appropriate classification into corresponding categories is also done. Experimental results proved suitability of prepared glass fiber composites for application in transport industry.