Volume 65, Issue 3

The effect of Fe, P and Mn on microstructure and fatigue properties of CuZnSn bronzes investigated with optical microscopy and scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, hardness, tensile and fatigue tests. The addition of Fe, Mn and P to Cu-Zn-Sn bronzes formed Cu 31 Sn 8 , Cu 6 Sn 5 , ZnSn 2 , PbSnS 2 , ZnS, Cu 2 S, FeZn 9 and FeZn 21 phases. These phases were deposited between the dendrite arms and were dissolved in the matrix in small amounts. Especially, these precipitated phases were effective in fatigue properties. The formation of Cu-Sn, Cu-Zn and Zn-Sn intermetallic phases emitted due to the addition of Fe, Mn and P increased the fatigue strength. The spread of ferrous phases caused an increase in mechanical properties. The beneficial effect of P addition on the fatigue life far surpassed that of Mn and Fe additives.

In this study, the effect of using boron products in the production of aluminium composite foam on the formation of pores and mechanical properties of the material was investigated. Metallic foam was produced by powder metallurgy method by adding borogypsum to the Al matrix and using boric acid (H 3 BO 3 ) as a pore former. Samples containing 5, 10 and 20 wt% borogypsum were prepared at initial pressing pressures of 420 MPa and 630 MPa and sintered at 550 °C for 3 h. As a result of microhardness measurements taken from the cell wall of foam samples with ∼40% porosity, it was determined that the hardness value increased as the borogypsum ratio increased. According to the results of the quasi-static compression test performed at a deformation rate of 10 −3  s −1 at room temperature, the hardness and strength values of 20 wt% borogypsum reinforced Al composite foam prepared at 630 MPa pressure increased. In addition, mechanical properties such as plateau tension and elastic modulus for each sample were theoretically determined with the Gibson–Ashby approach.

In this paper, eight-layer composite laminates were produced using twill and plain woven glass and carbon laminate fibers as a reinforcement element and as a matrix with epoxy resin. All laminates having the layup of [(0°/90°) 2 ] s but the hybrid laminate arrangement varies between the number of woven glass and carbon laminates. The buckling behaviour of woven composite laminates used for typical of the aerospace industry is investigated. Un-grooved and grooved with centered elliptical groove angles with 0°, 15°, 30°, 45°, 60°, 75° and 90° specimens were subjected to buckling tests. It was investigated how the woven type, laminate designation, and groove angles affect the buckling behaviour. Cut-out causes to decrease of buckling load of composite plates. It is understood that the buckling load increased with regard to the increase groove angle (from 0° to 90°) of the composite plates. As the laminate designation changed, the buckling load also changed significantly. The buckling load of composite plates is highly influenced by its weave type. As a fiber, it has been determined that the buckling behaviour of carbon fiber is better than glass fiber. In addition, it was concluded that the twill weave type is generally better than the plain weave type.

In this study, experimental and numerical crash analyses are carried out to reach an optimum bumper beam and energy absorber design for a passenger car. Design parameters have been created to determine the most crash-efficient bumper beam and energy absorber models. The models that are formed by using Taguchi tables are subjected to crash analysis, and the responses are obtained to find an optimal design. Response surface methodology is used to approximate the structural responses in crash analysis, and the optimum bumper beam and energy absorber models are obtained by the differential evolution algorithm. The optimum model is subjected to crash analysis in the Hyperform software without considering the sheet metal forming effect. Besides, the model is analyzed by incorporating forming history into the crash analysis. As a result of the numerical analysis, a new energy absorber and bumper beam model with the better crash performance and weight reduction are obtained.

This study aimed to improve mechanical properties, which decreased in the weld area, with deep cryogenic treatment at different holding times. In the study, firstly, the formation of heat damaging the welding area was observed. The temperatures in the welding zone were measured on the shoulder with a thermal camera, on the material surface, and inside the material with a thermocouple. The effects of these temperatures during welding on the surface topography and mechanical properties were investigated. The effect of tempering heat treatment after deep cryogenic treatment applied for 6, 12, 18, and 24 h was investigated. It has been observed that tempering after cryogenic treatment applied to 7xxx series aluminum alloys reduces the hardness of the nugget zone but increases the hardness in the heat unaffected zone. In addition, it was observed that deep cryogenic treatment applied at different holding times positively affected the hardness, tensile strength, and % elongation in the weld area.

Recently, additive manufacturing is of interest, and there is a trend to study additively manufactured materials such as Inconel 718 and 316L stainless steel. Additive manufacturing brings the easiness of production of complex geometries, avoids expensive tools, helps achieve interesting microstructures and obtaining promising results for future applications. Since the additive procedure is sensitive to many fabrication variables thereby affecting the microstructure and mechanical properties. This motivation promotes investigating the additively manufactured microstructure of 316L stainless steel and Inconel 718. While 316L stainless steel was fabricated using an electron-based powder bed fusion manner, directed energy deposition was preferred for Inconel 718. Samples were examined utilizing optical and scanning electron microscopes. Results suggest processing of 316L stainless steel gives rise to the same porosity rate as Inconel 718. Bimodal equiaxed austenite grain morphology was observed whereas no dendrite presence was detected for 316L stainless steel. Additive manufacturing types do not cause a significant change in the level of porosity for Inconel 718 alloy. Unlike the case of stainless steel, additive manufacturing results in dendritic microstructure formation in Inconel 718 whereas powder bed fusion-type production triggers a better refinement compared to that of directed energy deposition.

Shear strain rate effect on crystallisation behaviour and characteristic temperatures of the three well-known glass formers in Cu–Zr binary amorphous system, namely Cu 50 Zr 50 , Cu 56 Zr 44 and Cu 64 Zr 36 , were investigated. The crystallisation behaviour of Cu 64 Zr 36 was uniquely found to be heavily dependent on shear strain rate. Crystallisation kinetics were studied through Isochronal transformation and isothermal transformation. The activation energy of crystallisation of each case was compared and contrasted. Johnson-Mehl-Avrami (JMA) analyses were also employed to study its kinetics behaviour. Finally, high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) combined with laser-assisted local electrode atom probe (LEAP) investigation revealed no detectable clustering or phase separation.

Pre-aged Mg-6Zn-1Gd-1Er alloy is a novel rapid aging hardening Mg alloy, and studying its hot deformation behavior has an important role in promoting the development of lightweight alloy materials. To study this, the flow stress curves of pre-aged Mg-6Zn-1Gd-1Er alloy at 180–380 °C and 10 −3 −10 s −1 were obtained by isothermal compression tests. The constitutive equations of the medium-high temperature deformation (MHTD) and the low-temperature deformation (LTD) were established, and their activation energies were 155.78 kJ mol −1 and 178.00 kJ mol −1 , respectively. Based on the constitutive equation analysis, the glide and climb of dislocations and the cross-slip of dislocations was the deformation mechanism during MHTD and LTD, respectively. In order to determine the appropriate hot processing parameters, the hot processing map of the pre-aged Mg-6Zn-1Gd-1Er alloy under 0.2–0.8 strain was constructed based on the dynamic material model. The hot processing maps indicate that this pre-aged alloy at low temperature (180–230 °C) and high strain rates (1–10 s −1 ) mainly occurs flow instability, and the optimal hot processing window appears at a 330–380 °C and 10 −3 to 10 −2  s −1 range. Furthermore, the deformation mechanism of the stable domain with high power dissipation efficiency in the hot processing map was continuous dynamic recrystallization, discontinuous dynamic recrystallization, and particle-stimulated nucleation mechanisms.

In industries like automotive and aerospace, the demand for structures with a high strength-weight ratio is increasing. Additive manufacturing (AM) studies and applications of AlSi10Mg material have increased due to the improvement of mechanical properties when the production is performed at high cooling rates in the laser-powder bed fusion (L-PBF) method. The study aims to investigate the effect of the AM process parameters on the microstructure features, and determine the mathematical relationship between yield strength and process parameters to obtain better mechanical properties. In this study, AlSi10Mg specimens are manufactured using L-PBF method with different process parameters. Microstructure images of the manufactured specimens are obtained by scanning electron microscopy. Melt pool width, eutectic cell size and diameter of Si precipitates are measured using the microstructure images. Parametric equations are generated between the process parameters and microstructural features including eutectic cell size and Si precipitate diameter. Thus, relationships between strengthening mechanisms and process parameters are established by integrating the generated equations into the related strengthening mechanisms. Consequently, the yield strength model of AlSi10Mg material is developed as a function of the process parameters of L-PBF method. It is found that the developed model estimates close results to the nano-indentation results.

In this study, the effect of the notch fabrication method (printing the notch on the part, and machining the notch) on the impact results of 3D-printed polylactic acid (PLA) was investigated. Sensitivity to build orientation was also noted in both test situations. The impact test specimens were printed using an FDM-based printer with or without a notch at various build and print orientations. Un-notched specimens were then machined to create notches. To simulate the impact effects, Ansys software was employed to create a finite element model, and the results of the finite element analysis were consistent with the experimental results. According to the findings, the impact strength of the specimens with 3D-printed notches increased by 11–38% compared to specimens whose notch was machined after the rectangular bars were 3D printed. In addition, it has been observed that the build and print orientations affect the impact strength.

Hydride formation in Zr-containing amorphous alloys as an experimental artifact was investigated utilizing atom probe tomography, transmission electron microscopy, and focused ion beam with normal and cryogenic conditions. The amount of hydrogen existing in the atom probe specimens decreased significantly by utilizing focused ion beam milling under cryogenic condition. Also, the formation of hydride was confirmed by diffraction pattern analysis in the remaining tip of the specimen after the atom probe tomography experiment. With those collected pieces of evidence, sources of hydrogen in the atom probe tomography were discussed.

Revision ceramic heads with titanium adapter sleeves are used in case of a femoral head revision in total hip arthroplasty to avoid ceramic fracture due to damaged tapers. Objective of the present study was to evaluate the taper connection strength of revision ceramic heads. Therefore, revision ceramic heads (Ø36 mm; adapter sleeve S) and standard ceramic heads (Ø36 mm; neck length S) were assembled with an axial load (2 kN) to titanium tapers with various damage modes (undamaged, truncated, and elevated). Subsequently, the heads were either pulled-off directly after assembly or after dynamic loading over 2.5 million cycles (sinusoidal 0.3 kN–3.0 kN). Pull-off forces of the revision heads (1.24 kN–1.66 kN) were up to 43.7% higher compared to standard heads (1.02 kN–1.48 kN) in dependency of the taper damage. After dynamic loading, the pull-off forces did not change in case of standard heads. The pull-off forces of the revision heads decreased in combination with the undamaged and truncated tapers but increased in combination with the elevated tapers. In conclusion, revision heads with adapter sleeves (size S) showed higher taper connection strength than standard heads both on undamaged and damaged tapers.

In this paper, the effects of particle reinforcement on the tensile, compression and flexural properties, as well as the influence of cross head speed on the quasi-static punch shear properties of glass/epoxy composites are investigated. Laminated composites, which are manufactured by hand lay-up method consist of six layers of stitched glass fibers. As the particle reinforcement materials, pinecone and acorn powders with 1, 2, 3, 4 and 5 wt% ratios are used for the manufacturing of composites. The quasi-static punch shear behaviour of composites is elucidated at a room temperature through the force – deformation curves and the energy graphs at different test speeds (i.e., 1, 10 and 20 mm min −1 ). According to the experimental findings of quasi-static punch shear tests, it is concluded that the maximum contact force of each composite increases along with the punch shear test speed. Compressive strength of the acorn reinforced specimens shows their highest compressive value at the particle amount of 5 wt%, while pinecone-reinforced composites exhibit their highest compressive strength at the particle ratio of 2 wt%.

Austempered ductile iron (ADI) has been preferred in a wide range of applications due its unique combination of high strength, good ductility, wear resistance and fracture toughness together with lower cost and lower density compared to steels. Magnetic Barkhausen noise (MBN) measurement offers a better alternative to traditional characterization techniques by being fast and non-destructive. A simple linear regression using only one single independent variable cannot correlate the MBN with the microstructure of ADI, since its microstructure is multi-component. Multiple linear regression analysis (MLRA) was used to build a model that uses the characteristic features of microstructural constituents as input parameters to predict the MBN. For that purpose, Cu-Ni-Mo alloyed ductile iron samples austempered between 325 and 400 °C and for 45–180 min duration were used. The results show that MBN is most sensitive to the size and shape of acicular ferrite and retained austenite. Moreover, MBN is almost insensitive to the size, morphology and volume fraction of graphite particles. This indicates that retained austenite pins the domain walls more effectively than the graphite particles. Considering the results MLRA, MBN technique can be used to characterize the ausferritic microstructure of ADI.