Volume 58, Issue 10

Vulcanized fiber is a macromolecular cellulose-based composite material manufactured using the parchmentizing process. The cellulose is produced from the chemical digestion of plant-based raw materials (wood, cotton) or textile waste. Chemical additives used during manufacturing are completely removed. After the process, vulcanized fiber possesses improved properties concerning mechanical strength and abrasion as well as corrosion resistance in comparison to its raw materials. Concerning its economic life cycle assessment, low density, electrical insulating capability and balanced properties, vulcanized fiber has a potential, up to now unused, as a light and renewable structural material for applications in automotive or civil engineering industries. Research activities concerning the mechanical properties are insufficient and existing standards are out-of-date. In this work, for the first time a direction-dependent characterization of the process-related anisotropic mechanical properties of the material is realized with the aim to formulate an adequate material model for numerical simulations in the next step.

The main objective of this study is to estimate the accuracy of the method for the determination of material parameters based on laboratory data from a single experiment conducted on a sample working in a nonuniform stress state, registered by the digital image correlation system (DIC). The idea of the method is based on the inverse analysis, in which the material parameters are determined by the optimization procedures using the cost function being the result of comparison of the laboratory data with the results of FEM simulation, wherein the whole deformation areas are taken into account. This paper presents the method described above applied on the determination of isotropic hardening parameters for an aluminum alloy material. Tests were carried out on the aluminum plates with nonuniform geometry subjected to tensile deformation. A comparison of the effect of sample geometry on the results was made, and an analysis of the impact of variation of material parameters on the value of the cost function was carried out.

Engineering of micro parts is an increasingly important area of industrial activity and this field is rapidly developing further. Thus, the simulation of micro parts also becomes more and more important. As reliable material data is required to obtain accurate simulation results, test setups are also necessary to determine the material properties. An experimental setup for microtensile testing of stainless steel micro specimen (i. e., specimen with at least one dimension below 1 mm) to obtain material data in the temperature range from 20 to 350 °C is presented herein. Heating of the specimen is based on Joule (resistive) heating as it is done in macroscopic testing in Gleeble machines. Contactless measurement of temperatures is conducted by an infrared (IR) camera and the determination of strain by a combination of optical microscopy and digital image correlation (DIC). First samples were made from the stainless steel 17-4PH and the results obtained are presented and discussed in comparison with macroscopic properties of this material.

In this study, the flexural behavior of filled and unfilled honeycomb structures was experimentally examined. As filler material, waste materials of the furniture and marble industry were used. In this context, effects of the wastes of the furniture industry (i. e., pine sawdust) and of the marble industry (i. e., travertine powder) on the flexural behaviors of honeycomb structures were investigated by the three point flexural test. Honeycomb specimens were produced by using PLA plastic material in a 3D printer by rapid prototyping techniques. By changing cell sizes of the honeycomb structures used in the flexural tests, the relation between the waste filler materials and the cell size was also investigated. The flexural behavior of unfilled honeycomb specimens was at maximum for the specimens with small cell size. In the honeycomb structures filled with waste material, it was determined that the flexural loads of small cell sized specimens were decreased by approx. 10 % while the flexural loads of big cell sized specimens were increased by approx. 10 %. As a result, it was found that the flexural behavior of unfilled honeycomb structures with big cells which have low flexural behavior could be increased using waste filler material.

The stress concentration factor in a plate with a hole is very important for joints. There are many different types of joints and forms. Plates are usually connected with bolted, riveted and pin joints. Connection parts need to consist of hole/holes to make a joint using these machine elements. Machine parts are exposed to different stresses. In this study, the stress concentration factor in a plate with a circular hole under axial tension stresses was invegistated. The emprical (Peterson's) stress concentration factor (Kt) was compared with the results of analytical model, regression analysis (REGA), finite element analysis (FEA), artificial neural network (ANN) model. The stress concentration factor (Kt) was modeled using 5 different methods and the accuracy of Peterson's model was tested. The best results were obtained using ANN model. The emprical results and ANN predictions were compared by using statistical error analyzing the absolute fraction of variance (R 2 = 0.999999788), root mean square error (RMSE = 0.000934125) and mean error percentage (MEP = 0.033902049) with the test data. ANN model can be used instead of Peterson's model. K t was determined by the ANN with an acceptable accuracy.

Acicular ferrite is a desirable microstructure in high strength low alloy steel weld metal. This is due to its improved toughness and the enhanced mechanical properties of the weld metal. Although the nucleation of acicular ferrite has been studied by many researchers, the exact mechanisms of its nucleation and growth are still under discussion and remained unclear. In this research work, the mechanism of acicular ferrite formation in the weld metal as cast structure has been clarified as diffusion controlled solid state phase transformation. This is based on the classic theory of nucleation and growth which can contribute to possible increase of nucleation sites and growth of intergranular ferrite in HSLA steel weld metal. Therefore, it could be considered that inclusions are not acting as a nucleation site for the intergranular acicular ferrite. Consequently, our results revealed that, in austenite transformation to pro-eutectoid and acicular ferrite, manganese as an austenite stabilizer alloying element is playing an important role in the nucleation and growth of the ferrite grains. It should be added that cooling rate accompanied with the presence of other alloying elements has influenced the type and morphology of the final ferrite microstructure and constituent products.

Using forming limit diagrams is the most convenient method for determining the forming limits of steel sheets. In this work, they were investigated primarily. Six diagrams were prepared for five different steel grades having different properties and then the effects of sheet thickness, r values, chemical and mechanical properties were compared for the forming limits by using these diagrams. The results revealed that the forming limit curves are shifted towards higher limit strains with the increase of the sheet thickness. Also, it was found that higher r values have a favorable effect on the limit strain values as indicated in the literature. Finally, it was seen from the diagrams that increasing of carbon ratio and strength properties has a negative impact on the formability.

In this study, submicron (APS = 200 nm) tungsten carbide (WC) ceramic particles were co-deposited with chromium metal (Cr) via electro-co-deposition system to fabricate WC-Cr metal matrix composite coatings. Instead of traditional electrodeposition cells, a new system was designed and coatings were fabricated using this system. Phase identifications of the coatings were performed by X-ray diffractometry (XRD) and surface morphologies were investigated using energy dispersive X-ray spectroscopy (EDS) with attached scanning electron microscope (SEM). Hardness values of the coatings were performed under 980.7 mN applied load using a microhardness tester. It was concluded that WC ceramic particles were physically adsorbed on the cathode surface and formed a composite structure with metal Cr and co-deposition of submicron sized ceramic particles with metals via electrodeposition system was strictly successful. In addition, with respect to the reference coatings, WC reinforced composite coatings depict an increased hardness up to twice its value. Frequency, as a parameter of pulse current, is determined as an effective parameter in co-deposition.

In this publication, a method was developed for the production of plastic parts for the use in low volume automotive production. The hollow parts having a complex geometry were produced in blown plastic injection molds. The part production method employed a combination of carbon fiber reinforced composites and rapid prototyping technology. Surface operations were applied on the core model and the effects of the surface quality were researched as a case study. The fused deposition modeling method was used to build the core from soluble material. This technique affected the inside surface roughness and quality of the final parts. As these types of components require smooth surfaces for good air flow and low resistance, the surface area of the physical model of the soluble core was unfortunately too rough to be used directly in the carbon fabric application process and consequently, required preliminary surface treatment in order to improve the surface quality of the manifold part. Specimens were fabricated using different surface treatments in order to determine the smoothest surface quality. The best result was obtained using the acetone-gelcoat post-processing method.

The influence of delaminations in the anisotropic carbon fiber reinforced plastics (CFRP) on laser- generated ultrasound is investigated. A 3D-finite element method is used to simulate the propagation of ultrasonic waves in CFRP with delaminations. The asymmetric properties and distortions as well as the wave reflection and attenuation at delamination interfaces are clearly shown. Measurements on CFRP specimens with circular delaminations above 2 mm in diameter are imaged by C-scans and correlated to the modeling results. The effects of ultrasound frequency, defect size and depth location are discussed. The results show that it is possible to decrease the influence of anisotropy in CFRP composites by choosing appropriate ultrasonic frequencies and controlling the laser parameters.

The paper describes investigations and research work in order to develop a simple sensor for the quantification of spectral broadband energy dissipation of flash lamps at any point in space. Such flash lamps are often used as energy source during active thermography testing (TT). Here, the temperature transient of the sensor surface has to be recorded by the infrared camera that is already present. During the following data evaluation, the energy input into the investigated specimen can be determined. Two opposite concepts were considered: thermal thick and thermal thin probes. The direct comparison shows advantages for thermal thick probes based on the physics of thermal balance processes.

Kurzfassung Ziel dieser Untersuchungen war die Bewertung der Beständigkeit häufig eingesetzter Dichtungswerkstoffe, wie FKM, FVMQ, VMQ, EPDM, CR, CSM, IIR, PA, NBR und PUR in Kraftstoffen und Heizöl mit und ohne biogene Zusätze bei 20 °C, 40 °C und 70 °C. E10, E85, Dieselkraftstoff mit max. 5 % Biodiesel, ungealtertes und 2 Jahre gealtertes B10 (Heizöl mit 10 % Biodiesel), reiner Dieselkraftstoff, Heizöl und Kraftstoff Super Plus zählten zu den Testsubstanzen. Masse, Zugfestigkeit und Bruchdehnung wurden von den Prüfkörpern vor und nach der 84-tägigen Auslagerung in den Kraftstoffen und Heizöl bestimmt. Die visuelle Begutachtung einiger Elastomerprüfkörper zeigte eindeutig hohe Quellung bis zur partiellen Auflösung. Die Shore-Härte A und D (für PA) der Prüfkörper wurden vor und nach der 42-tägigen Auslagerung in den Kraftstoffen bestimmt. In den internationalen Normen wird zur Bewertung der Beständigkeit von Elastomeren kein Grenzwert der Reduzierung der Zugeigenschaften und der Shore-Härte definiert. Deshalb wurde für die Beständigkeitsbewertung ein Grenzwert von 15 % festgelegt. Zusammenfassend kann die Aussage getroffen werden, dass die Beständigkeit der Fluorpolymere FKM und FVMQ in den Kraftstoffen und Heizöl mit und ohne biogene Zusätze am besten ist.

In this work, anatase-type TiO 2 layers were prepared by deposition of precursor solution including titanium isopropoxide, ethanol and acetic acetylacetone on a FTO substrate using rapid expansion of supercritical solutions (RESS). The spraying to obtain a particulate coating of TiO 2 was carried out at 65 °C and 180 bar of supercritical carbon dioxide environment. Then, thermal annealing at 550 °C for 2 h was applied to coated substrates to obtain desired phase composition. The structural and optical properties of the film were evaluated by XRD, SEM and UV-Vis. SEM observation showed that the photoanode film has porous microstructure with interconnected spherical TiO 2 grains. TiO 2 film has a band gap of 2.6 eV.

The present study investigated the mechanical characteristics of epoxy strips reinforced with Cloisite 30B nanoclay. Epoxy materials were reinforced with different particulate fractions of chosen nanoclay and the specimens were investigated regarding mechanical properties such as tensile, impact and flexural strengths. The nanoclay content was varied from 2 to10 wt.-% of the total matrix in the matrices. The results showed that the mechanical properties of the composites mainly depended on the dispersion condition of the filler particles, particle size and aggregate structure. Improved tensile modulus, flexural modulus and impact strength in bending properties with less nanoclay content were observed and were found to decrease with increased filler content.

Engineering ceramic materials are one among the key components of technology due to their outstanding physico-mechanical properties like hardness, toughness, wear resistance and chemical stability at elevated temperatures. On the other hand, the stated unique properties of ceramics exhibit complexity during machining. Under such circumstances, online monitoring of cutting tools plays a major role. The present study involves acoustic emission (AE) testing technique for condition monitoring of machine tools. Various grades of alumina ceramics had been machined using SiC grinding wheel. Grinding process parameters like depth of cut and feed rate were varied. Introducing AE technique, the following parameters like energy, amplitude of grinding wheel wear and surface roughness of alumina ceramics were analyzed.