Volume 62, Issue 10

The multi-material design presented contains EN AW-6016 aluminum and high strength CR330Y590T-DP steel. This dissimilar combination is an example of an affordable lightweight design solution, but it requires an adapted joining technology. Hybrid joining technologies such as selfpiercing riveting (SPR) in combination with a structural adhesive enables an assembly of such dissimilar material combinations. In addition to higher manufacturing costs for mechanical joining the design process still requires a great amount of effort. This study provides a simple approach for assessing hybrid joined multi-material connections. Therefore, tests for several combinations of the most relevant parameters on fatigue life (material properties, sheet thickness, load cases) were performed under quasi-static and cyclic loads. Based on the data acquired, it is shown that the fatigue life of hybrid joined connections can be estimated by superposing the contributing fatigue life of purely SPR and purely adhesive joints.

In this study, 6 mm thick plates of Al 6061 T6 alloy are joined by laser welding at four welding speeds (40 mm × s -1 , 35 mm × s -1 , 25 mm × s -1 , and 20 mm × s -1 ). The welded joints are made using a 4000 W fiber laser welding machine. The effect of laser welding speed on the pores formed in the weld seam was investigated. In this manner, it was found that with a change in laser welding speed the amount of pores formed in the structure also changed. In addition, after the welding process, macroscopic examinations, tensile tests and the hardness tests were made. As a result of the experiments performed, it was determined that, the laser welding speed was highly effective for pore formation.

Since the processing of plastics by additive manufacturing techniques, for example, fused deposition modeling, has become quite common, it is mainly used for the production of unique pieces for private consumption as well as for prototyping in industry. In order to professionally manufacture plastic components in large amounts, due to time, cost, and quality factors, injection molding is more suitable. Nevertheless, it is of great interest to print plastic parts in small batch series for technical tasks. In this paper, FDM-produced tensile samples, made from 16 materials, printed in three orientations, are compared to compression molded components. In addition to ordinary filaments, composite materials with metal-, carbon-, wood-, and stone-additives are also examined. While some cavities emerged in both printed and molded samples, the results support the hypothesis that the mechanical properties depend on the components’ densities.

The effects of H 2 O 2 solution addition and temperature on electrolytic pickling via Na 2 SO 4 solution to eliminate the metal oxide layers of an annealed 304L stainless steel were investigated by polarization technique. The experimental conditions involved a pure 190 kg × m- 3 Na 2 SO 4 solution and a mixture of 190 kg × m- 3 Na 2 SO 4 + 10 kg × m- 3 H 2 O 2 at 298, 318 and 333 K and pH 4. It was found that the addition of a 10 kg × m- 3 H 2 O 2 solution in 190 kg × m- 3 Na 2 SO 4 solution and an increase in temperature resulted in a decrease in the passive region of the polarization curves. The results from the SEM images, the XRD patterns and root-meansquare roughness showed that the surface of the annealed 304L stainless steel was smoother and fewer remaining oxide scales was found when pickling in 190 kg × m- 3 Na 2 SO 4 + 10 kg × m- 3 H 2 O 2 solution. However, no effects of the addition of 10 kg × m- 3 H 2 O 2 solution in 190 kg × m- 3 Na 2 SO 4 solution and temperature on pickling time at 298, 318 and 333 K were observed.

Metal-polymer-metal hybrid sandwich panels are gaining importance in various industrial applications due to their light weight and damping properties. When compared with composite materials, hybrid materials consisting of separate metal and thermoplastic parts can be recycled more easily. In addition to their applications in civil engineering, the aluminum-low density polyethylene-aluminum (Al-LDPE-Al) sandwich panels yield a potential use as light ballistic protection material. In this study, a standard hybrid panel of 3.2 mm polyethylene filling and 0.4 mm of two aluminum metal sheets was experimentally tested under ballistic impact. A finite element model was constructed via commercial software and validated through shooting experiments with a rifle under real conditions. The finite element model was used to simulate the oblique impact behavior of Al-LDPE-Al sandwich panels as a single layer, as 5 layers stacking and as a single layer equivalent of the stacked 5 layer. Results showed that the oblique impact does not have a significant effect on the single layer panel. Stacked layers, however, and the equivalent single layer of a stacked layer have the highest energy absorption under a 30° hitting angle.

Comprehensive characterization mechanical properties of aerogels and their composites are important for engineering design. In particular, some aerogel composites were reported to have varied tension and compression moduli. But conducting tension tests is difficult for the reason that low strength and brittleness will lead to unexpected failure in the non-test area. A method is presented for measuring both the tension and compression moduli of a ceramic-fiber reinforced SiO 2 aerogel composite by bending via digital image correlation. First, the relationship between bending behavior and the tension/compression moduli was introduced for bimodular materials. Then a bending test was conducted to predict tension and the compression moduli of the ceramicfiber- reinforced SiO 2 aerogel composite via digital image correlation. In addition, uniaxial tension and compression tests of the aerogel composites were carried out, respectively for measuring tension and compression moduli. The tension and compression moduli measured were numerically similar to results obtained from uniaxial tests with a difference of less than 14 %.

In this study, the usability of a new submerged arc welding flux was investigated to develop the surface properties of Hardox steels. In the hardfacing welding processes for Hardox 400 steel, four welding speeds resulting in varied heat inputs were applied. Through an analysis of the chemical composition, microstructure examinations, hardness measurements and wear tests, the possibility of hardfacing properties control due to the change of process parameters were determined. In the experimental studies, the hardness of the hardfacing obtained at a welding speed of 30 cm × min- 1 was measured as 42 HRC while the hardness of the hardfacing obtained at a welding speed of 48 cm × min- 1 was measured as 57 HRC. Moreover, in the wear tests, results consistent with the hardness values were obtained. It was understood in the light of the results that the use of high carbon ferro-chromium 20 wt.-% in a submerged arc welding flux mixture may be useful in improving hardness and wear properties of Hardox steels through hardfacing welding processes.

Bolt production with a grade of 10.9 class quality made from AISI4140 material with a low thread rolling index is usually implemented in accordance with the thread rolling method (cold forming) in industrial applications. In this method, the effects of die revolutions and multiple passes are unknown in the thread forming process as the devices are usually operated with respect to geometrical dimensions but not the mechanical properties and microstructures of the material. In the literature there are few studies on microstructures of low-carbon steel having a higher thread rolling index in bolt production. This study experimentally examined the effects of the processing parameters on the mechanical properties and microstructures. Parameters such as forming speed and single or multi-pass influences were considered in the production of M12 × 1.75 and M20 × 2.5 fasteners widely used in industrial applications. The experiments identified the behavior of the mechanical properties, microstructures and micro-hardness of the AISI4140 material at two forming speeds (rpm) and three passes in the thread rolling process. Thus, significantly sensible outcomes as a function of processing parameters were obtained considering the thread strength viewpoints.

Diving depth is the criteria for designing the submarine pressure hull meant to achieve a definite collapse depth. In this study, a methodology to optimize a sandwich composite deep pressure hull is presented. Buoyancy factor (BF) minimization is considered as an objective function. The optimization process is achieved by ANSYS parametric design language (APDL). Composites failure criteria and structural stability are considered as constraints. Additionally, sensitivity analyses were conducted to analyze the effects of geometric parameters on optimal structural design. The results showed that, the utilization of a sandwich composite pressure hull for a deep submarine at extreme depths is not safe. Additionally, the results propose that the submarine designed should be able to operate at a maximum diving depth of up to 7500 m.

The moisture content of the subfloor has to be determined before installation to avoid damage to the floor covering. Only if readiness for layering is reached, can an installation without damage be expected in all cases. In general, three approaches exist to measure residual water content: determination of moisture content, determination of water release, or determination of the corresponding relative humidity. All three approaches are tested under laboratory conditions at eight screed types including two samples thicknesses in each case. Moisture content and water release are measured by sample weighing, the corresponding relative humidity is measured by embedded sensors. All three approaches are compared and correlated. The evaluations show only a weak correlation and, in several cases, contradicting results. Samples are considered ready for layering and not ready for layering at the same time, depending on the chosen approach. Due to these contradicting results, a general threshold for a risk of damage cannot be derived based on these measurements. Furthermore, the experiment demonstrates that the measurement of corresponding relative humidity is independent of the screed type or screed composition considered. This makes humidity measurement a potentially very promising approach for the installation of material moisture monitoring systems.

This study investigated the performance of the grinding parameters used in the cylindrical grinding process of AISI 5140 steel and identified optimum grinding conditions via the Taguchi optimization method. Experiments were carried out via the L 18 orthogonal array. Control factors for optimum surface roughness (Ra) values were determined by using the Taguchi method. Two different grinding wheels (SiC and Al 2 O 3 ), three different cryogenic samples (CHT, DCTT-15 and DCTT-30) and depth of cuts (100, 200 and 300 μm) were selected as control factors. The cylindrical grinding test results showed that optimal Ra values were obtained on specimens cryogenically treated for 30 h (DCTT-30). Linear and quadratic regression analyses were conducted for the experimental results. The correlation coefficients (R2) were found to be 0.957 and 0.993 with linear and quadratic regression models, respectively. Finally, confirmation tests were performed and showed that the optimization had been successfully implemented.

In this study, it was aimed to determine and compare the sinterability of aluminum-SiO 2 composites by conventional and fast sintering methods and to examine their tribological properties after the sintering process. For this purpose, 1, 3, 5, 9, and 15 wt.-% SiO 2 reinforced aluminum matrix composites were sintered by a conventional and induction sintering method at 600 °C after uniaxial cold pressing under 200 MPa pressure. The sintering was performed for 30 minutes for the traditional method and 5 minutes for induction sintering. After the sintering, the microstructures of the samples were examined, and their sintered densities and hardness were determined. In addition, the tribological properties of the samples were investigated by the pin-on-disc method, and the worn surfaces were examined after the tests.

The use of waste materials in concrete has been accelerated around the world recently. In this study, thermal and compressive strength properties of concrete doped with black tea waste are studied to assess the availability of using this type of waste in concrete. Black tea waste with 0.3 and 0.5 vol.-% were added to concrete mixtures. Thermal conductivity and effusivity of concrete with black tea waste were evaluated firstly, and load-bearing capacity of this biomass doped concrete were also investigated by the compressive test and Schmidt hammer test. The results showed that using black tea waste with 0.3 vol.-% slightly decreased the compressive strength of concrete whereas there was a considerable decrease in thermal conductivity. However, using black tea waste with 0.5 vol.-% causes an obvious decrease in compressive strength and a decrease in thermal conductivity of concrete which is not directly proportional with the amount of black tea. Therefore, with a small toleration of loss of compressive strength, black tea waste doped concrete can be produced with high volume fractions in order to have concrete samples with good thermal insulation for research purposes.

With respect to their relevance for wood-related technologies, moisturedependent elastic engineering parameters of Taurus fir (Abies Cilicica (Antoine et Kotschy) Carriere) are determined from ultrasound longitudinal (2.3 MHz) and shear (1 MHz) wave velocities. The dynamic Young’s and shear modules of characteristic axes and planes decrease significantly down to 17 % at increased moisture content due to decreased wave velocities. Moisture-dependent R 1 values of the modules range from 0.88 to 0.99. However, Poisson’s ratios exhibit inconsistent moisture dependent behavior. Remarkable differences between ultrasound findings and the published results from compression tests are observed. Generally, the elastic values of wood from ultrasonic testing are reported higher than from mechanical tests. In contrast we find lower values as well. The critical issue of different ultrasound velocity sensitivity at selected directions is highlighted.