Cutting-tool performance in the end milling of carbon-fiber-reinforced plastics

Carbon-fiber-reinforced plastics (CFRPs) are no longer the exclusive domain of aerospace industries and nowadays find more applications in the automotive and consumer industries. The growing volume of these materials increases the need for their efficient machining. However, the machinability of CFRPs is a rather complex task due to the heterogeneity and the considerable number of parameters influencing the cutting process. The cutting tool has long been recognized as an important factor influencing both surface quality and dimensional accuracy. Hence, in this paper, tool performance is investigated in the end milling of CFRPs. The effect of tool geometry and coatings on the cutting forces, dimensional accuracy and surface quality were experimentally examined for side and slot milling

Preparation, thermal analysis, and mechanical properties of basalt fiber/epoxy composites

In this study, basalt fiber-reinforced polymer (BFRP) composites with epoxy matrix, 20 layers, and volume fraction of fibers Vf = 53.66%, were prepared by a hand lay-up compression molding combined method. The fabric of the basalt fibers is in twill 2/2 weave. Through dynamic mechanical analysis (DMA), their viscoelastic behavior at elevated temperatures and in various frequencies was explored, whereas thermomechanical analysis (TMA) took part in terms of creep recovery and stress-relaxation tests. Moreover, the glass transition temperature (Tg) of the BFRP composites was determined through the peak of the tanff curves while the decomposition of the BFRP composites and basalt fibers, in air or nitrogen atmosphere, was explored through thermogravimetric analysis (TGA). The mechanical behavior of the BFRP composites was investigated by tensile and three-point bending experiments. The results showed that as the frequency is raised, the BFRP composites can achieve slightly higher Tg while, under the same circumstances, the storage modulus curve obtains a less steep decrease in the middle transition region. Moreover, the hand lay-up compression molding hybrid technique can be characterized as efficient for the preparation of polymer matrix composites with a relatively high Vf of over 50%. Remarkably, through the TGA experiments, the excellent thermal resistance of the basalt fibers, in the temperature range 30-900 °C, was revealed. © 2020 by the authors.TBU in Zlin [IGA/FT/2020/004

Effects of core softness and bimodularity of fibreglass layers on flexural stiffness of polymer sandwich structures

This paper deals with the study of the flexural stiffness of the sandwich structures based on fibreglass and polymeric foams. The influence of geometrical and material parameters on the resulting effective flexural stiffness of the sandwich structure is being studied experimentally, analytically and by using FEM models. The effective modulus of elasticity of the sandwich-structured element is being studied and its theoretical and model dependencies on the flexibility of the foam core and bimodularity of the fibreglass layers are being investigated. The achieved results are compared with the experimentally observed values. This study shows that it is necessary to pay special attention to the issue of flexural stiffness of the walls when designing sandwich shell products in order to prevent possible failures in the practical applications of these types of structures. © The Authors, published by EDP Sciences, 2017.TBU in Zlin [IGA/FT/2017/002

Vpliv vrste in števila plasti na utrditev upogibne trdnosti in zdržljivosti pri utrujanju satastih sendvičnih konstrukcij

nefunkční DOIThis research paper deals with an investigation of the flexural properties measured in a three-point bending test depending on the type and number of the E-glass prepreg layers applied to the facing sides of the resulting sandwich structure used for floor panels in the transport industry. The values of the low-cycle fatigue were measured according to the values of the flexural strength obtained from the static test. Cycling was performed at (70, 60 and 50) % values of the ultimate flexural load. Moreover, a decrease in the flexural strength and stiffness depending on the number of cycles was also studied. For the production of samples, one type of aluminum honeycomb core and various phenolic prepregs with different numbers of layers were used. These samples were produced with two, in practice commonly used methods – compression molding and vacuum bagging. The measured results show that the production technology has a certain influence on the mechanical behavior in bending and the fatigue life of sandwich structures. The experimental results proved that the type of prepreg (defined by the reinforcing fabric and the amount of resin) and the number of layers also affect the properties of these structures. All the obtained results provide useful information for designing the sandwich structures for the transport industry.Članek obravnava preiskave lastnosti pri upogibu, izmerjene s trito~kovnim upogibnim preizkusom, v odvisnosti od vrste in {tevila plasti E-stekla na utrditev, uporabljenih na ~elni strani sendvi~nih konstrukcij, ki se uporabljajo v transportu za talne plo{~e. Vrednosti malocikli~ne utrujenosti so bile izmerjene skladno z vrednostmi upogibne trdnosti, dobljenimi pri stati~nem preizkusu. Cikli~no obremenjevanje je bilo izvr{eno pri (70, 60 in 50) % vrednosti upogibne trdnosti. Poleg tega je bilo preu~evano tudi zmanj{anje upogibne trdnosti in togosti v odvisnosti od {tevila ciklov. Za pripravo vzorcev je bila uporabljena ena vrsta sataste osnove iz aluminija in razli~ne fenolne plasti za utrjenje z razli~nim {tevilom plasti. Ti vzorci so bili izdelani z dvema obi~ajnima metodama – s tla~nim litjem in vakuumskim pakiranjem. Izmerjeni rezultati ka`ejo, da ima tehnologija izdelave dolo~en vpliv na mehansko vedenje pri upogibanju in utrujanju sendvi~nih konstrukcij. Rezultati eksperimentov so pokazali, da vrsta plasti za utrjanje (dolo~ena s tkanino za utrjanje in koli~ino smole) in {tevilo plasti tudi vplivata na lastnosti teh konstrukcij. Vsi dobljeni rezultati zagotavljajo koristne informacije za konstruiranje sendvi~nih konstrukcij v transportni industriji.Web of Science49451951

OOA composite structures applicable in railway industry

Composite sandwich structures offers several advantages over conventional structural materials such as lightweight, high bending and torsional stiffness, superior thermal insulation and excellent acoustic damping. In the aerospace industry, sandwich composites are commonly manufactured using the autoclave process which is associated with high operating cost. Out-of-Autoclave (OOA) manufacturing has been shown to be capable of producing low cost and high performance composites. In this paper we present results of experimental testing of various sandwich materials according various standards and actual requirements in transport industry. We compared the different types of surface and paint systems, because these layers are the most important in contact with the surrounding environment and load conditions. In the experimental measurements were used various materials. For the core of the sandwich structure were selected aluminium honeycomb, aramid honeycomb and PET (Polyethylene terephthalate) foam core. Support layers were chosen two kinds of predimpregnated materials. The conditions of measurements were requirements for strength and rigidity, safety-flame resistance and reflectivity resistance. The samples were tested at the 3-point bending test according to standard EN ISO 178, by modified test to determine the force required to rapture threaded insert, by test of reflectivity according to UIC CODE 844-4 R and according to standard EN 45545-2 fire protection of railway vehicles. © The Authors, published by EDP Sciences, 2017.TBU in Zlin [IGA/FT/2017/002

Acoustic characteristics of composite structures used in train

This paper presents a study focused on sandwich structures as well-known train construction materials that are composed of two thin and rigid face sheets and a thick, low-density core material. For trains, the wheel-rail interface is the main source of noise, and the wheel-rail roughness, especially in the presence of rail corrugation, is the main excitation source transmitted to the interior and area for passengers. The purpose of the study is to optimize the acoustic properties of a composite sandwich panel used for train floors and walls. Sound absorption coefficient (α), noise reduction coefficient (NRC) and Transmission loss (TL) evaluations have been implemented and experimentally validated on a typical sandwich material used for trains. The opportunity to use a different material can be concretely calculated and modified for critical frequency ranges. Sound transmission loss levels of the structural components as the floor and wall of the train body, which are required of producers and customers, were tested in acoustic laboratory and acoustic devices according to ASTM and ISO standards. It is demonstrated that, for honeycomb and cork sandwich panels, acoustic response is not sensitive to cell size. For foam core sandwich panels, it is observed that different compositions with thin layers are effective in the frequency range of 50-1000 Hz. © 2020 Manufacturing Technology

Volume changes measurement of elastomers using 3D DIC

The presented research aims at measuring the volume changes of elastomers using digital image correlation (DIC) in the 3D configuration (stereo DIC). The deformation measurement method in stereo configuration was applied during the mechanical testing of two types of test specimens (dumbbells, cylinders) in uniaxial tension. In this configuration, two cameras were used. The test specimens were measured up to a specified strain value, and the measured data were used to obtain the strain dependence of Poisson’s ratio and the bulk modulus, which are crucial for hyperelastic models. The measurement results reveal that the stereo DIC method provides relatively less scattered data in the low-strain regions for dumbbell-shaped test specimens and is suitable for measuring various test specimen shapes

Flame resistance and mechanical properties of composites based on new advanced resin system FR4/12

Composite materials used in the transport industry and also in other sectors must have a certain degree of flame resistance. For this purpose, commonly used flame retardants are based on halogen compounds in the liquid state or aluminum hydroxide in the solid state. Solid flame retardants have a negative effect on the processing and mechanical properties. Low viscosity and rapid wettability of fibers are very important, especially in an resin transfer molding (RTM) process. Therefore, a new advanced matrix system based on phosphorus flame retardants was developed. The flame resistance and mechanical properties of the composite materials produced from the new resin system were tested. Furthermore, the processing parameters and tests are described in the article.Web of Science49582482

Possibilities of replacement of two side metal molds for the production of two facing side composite by one side mold

Presented research paper deals with possibilities of replacement of conventional mold materials by new, unconventional. Traditionally, laminate, wood or gypsum molds (in the case of small production series) are used for the production of composite parts. Furthermore, milled aluminum molds are conventionally used only for mass production. Due to this, thin metal sheet was prepared as an unconventional production mold for manufacturing of motorbike facing part. Vacuum bagging using prepared one side mold was chosen as the most appropriate technology. Normally, two facing sides are not commonly manufactured using this technology. Because of this, possibilities to create two facing sides at areas that are not in contact with mold itself were investigated. Presented results can help manufacturing companies with their production and considerably decrease manufacturing costs due to not necessity to use two side molds. © 2016. Published by Manufacturing Technology

Product dependability testing of polymer composite materials

This research paper deals with a proposal of the most appropriate methodology for dependability testing of products used in transport industry. Dependability is a global concept that includes terms of availability, reliability, durability, maintainability, supportability, etc. An important part of dependability is to find limit states of studied object, which are for PCM characterized by fiber cracking and delamination. Based on these specific failures, Building-Block Approach (BBA), which allows a systematic approach is often used for evaluation of composite constructions. Dependability evaluation consists of analysis and tests. Tests are always very time-consuming and expensive, because dependability is a property of objects with the strong stochastic character and therefore it is necessary to perform numerous measurements. Conversely, the analysis itself without verification may not achieve the desired results. For every test, it is necessary to develop the test plan and determine whether it is possible to use shortened or accelerated test. © 2016 Taylor & Francis Group, London