Volume 60, Issue 11

Nanocrystalline nickel-iron microstructures, manufactured by means of an electrochemical deposition process via electrolyte solutions, were investigated to collect relevant information for the use of nickel-iron for micro-components. By varying the current density, nickel-iron coatings can be set to show specific grain sizes, iron content, lattice strains and textures. Uniform microstructures exist in each of the deposited nickel-iron coatings. The grain sizes determined using x-ray analysis (XRD) cover a range of 6 to 17 nm. XRD texture analyses parallel to the deposition plane resulted in {111} and {200} orientations. To characterize the material's mechanical properties indentation hardness measurements and micro-bending tests were performed. For a 0.01 %-offset bending yield strength (R p0.01 *), grain sizes of 6 to 17 nm clearly demonstrate Hall-Petch behavior. In addition, the investigations show lower work hardening and lower values for remaining edge strain at fracture for decreasing grain size. In contrast to R p0.01 *, the Young's modulus, indentation modulus, indentation hardness values and the bending strength, within their scatter bands, all remain largely unaffected by the different microstructures. Overall, all measured strength and hardness values of the considered nanocrystalline microstructures are very high in comparison to microcrystalline microstructures.

On pistons for diesel direct injection engines, the thermally high loaded bowl rim is exposed to high-cycle mechanical and high-cycle thermal loading during each combustion event in addition to the thermal cycling induced by variable engine loading, e. g. between idle and full load. This combined loading at various overall temperatures during engine operation contributes to material damage and finally to a limited service life. In the past, the high-cycle thermal loading has neither been experimentally investigated nor incorporated into a numerical model for lifetime estimation. The work described in this paper deals with the setup of an experimental test procedure on samples taken from components for which the effects of slow temperature cycling, fast temperature cycling and mechanical cyclic fatigue loading can be combined in different ratios. The aim of the investigation is to characterize the sample lifetime with respect to varied test conditions in order to differentiate alloy- or process-related material variations in support of process and material development.

Pores in additive manufactured metal parts occur due to different reasons and affect the part quality negatively. Few investigations on the origins of porosity are available, especially for Ni-based super alloys. This paper presents a new study to examine the influence of common processing parameters on the formation of pores in parts built by laser metal deposition using Inconel 718 powder. Further, a comparison between the computed tomography (CT) and the Archimedes method was made. The investigation shows that CT is able to identify different kinds of pores and to give further information about their distribution. The identification of some pores as well as their shape can be dependent on the parameter setting of the analysis tool. Due to limited measurement resolution, CT is not able to identify correctly pores with diameters smaller than 0.1 mm, which leads to a false decrease in overall porosity. The applied Archimedes method is unable to differentiate between gas porosity and other kinds of holes like internal cracks or lack of fusion, but it delivered a proper value for overall porosity. The method was able to provide suitable data for the statistical evaluation with design of experiments, which revealed significant parameters on the formation of pores in LMD.

Metal foam is a high-porosity engineering material which has many outstanding properties such as light weight, high specific strength and stiffness, large energy absorption during impact and good thermal transportation. The impregnation of metal foams with polymers produces a new types of composites such as interpenetrating phase composites (IPCs) or co-continuous composites due to the interconnection on a macroscopic level of individual phases as a co-continuous 3-D network. The coexistence of the metal and polymer phases allows each to contribute its prominent properties to the composite. This innovative composite material is a potential candidate for applications in the automotive and aerospace industries. The present study aims to develop two IPCs from open-cell Al foams of 20 ppi impregnated with silicone or epoxy resin. The compressive behavior and energy absorption characteristics of IPCs are also examined and compared. The results show that although both IPCs have a similar foam structure with similar density, the disparities in the properties of impregnated polymers lead to distinct mechanical properties. The combination of Al foam and polymers, both silicone and epoxy resin, results in IPCs stiffer than either of the two individual materials by themselves. Higher stiffness was found in IPCs with epoxy resin, owing to brittle nature of the resin. Energy absorption capacity was also increased when compared with the original Al foam.

This paper investigates the fatigue and static strength variation of 40 Cr steel which has been subjected to cyclic torsion below the fatigue limit. The experimental results show that an improvement in fatigue strength can be exhibited if low-amplitude cyclic torsion and loading cycles are properly selected. The static strength can also be strengthened through the improvement of fatigue strength. It should be added that there is no significant static strength change in the first 50 % of the fatigue damaging process.

This paper deals with the auxetic deformation behavior of periodically perforated aluminum sheets and their application for lightweight design. If commercially available metal sheets are provided with perforations, this can significantly change the mechanical properties of the sheets. For example, with certain perforation patterns, it is possible to achieve a negative Poisson's ratio in the sheet plane. Such material behavior is called auxetic. Macroscopic auxetic behavior can be explained by mechanisms that are based on the geometry of the perforation. Sheets are made of an isotropic aluminum alloy, provided with periodic perforation patterns and are mechanically characterized in tensile tests. The investigations focus on an exemplarily pattern with rectangular perforations leading to the auxetic behavior of the sheet. By means of passive thermography, highly stressed areas of the samples can be identified in situ and nondestructively during tests. The experimental results are verified in numerical simulations. The insights gained will help to better understand the mechanisms underlying the mechanical behavior of auxetically perforated sheet metal. Based on this, concepts for possible applications of auxetically perforated sheets in lightweight design can be developed for the future.

The fracture toughness (K IC ) of high strength casing steel (1130 MPa) has been determined by a three-point-bend specimen. Three specimens with thicknesses of 5 mm, 8 mm and 10 mm, respectively have been used to observe the effect of thickness on the fracture toughness of steel. The analytical formula of the relationship between the fracture toughness and material thickness of high strength casing (1130 MPa) is proposed based on the energy theory and on linear elastic mechanics. The values of fracture toughness, K, measured by three thicknesses of parent metals are combined with the quantitative model of the relationship between fracture toughness and specimen thickness. The material constant (and κ) are calculated by using the least squares method. Furthermore, an analytic formula for the relationship between fracture toughness and specimen thickness is proposed which allows for the calculation of the K IC value. Plane-strain fracture toughness (K IC = 133.94 MPa × m 1/2 ) is a fixed value only if the thickness of the specimen exceeds 43 mm. Fracture toughness values of different thicknesses of high strength casing are derived by fracture toughness tests of several thicknesses based on the model in question in order to save manpower and material resources. This method is also significant for measuring the fracture toughness of other OCTG, since their thicknesses do not meet the requirement of the standard test methods. For the present, it provides general methods and reference rules for obtaining the K IC of other metallic OCTG.

Laser butt welding was carried out for the joining of 5A06 aluminum alloy sheet by using 6 KW fiber laser. The effect of welding speed on the surface morphology, microstructure, micro-hardness, tensile strength and porosity were studied by means of optical microscopy (OM), a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), a Vickers hardness tester and a universal mechanical tensile test. The results show that the weld macro morphology tends to be smooth and the surface defects are reduced with an increase in welding speed. The heat-affected zone was very small due to the large cooling rate. The columnar dendrites grow from the fusion line along the direction of the temperature gradient. The microstructure of the weld zone was in the form of equiaxed grains. The micro-hardness of the weld was lower than that of the base material. The micro-hardness and the tensile strength were gradually increased with an increase in welding speed. When the welding speed is 12 mm × s −1 , the micro-hardness and the tensile strength were increased to 96.5 % and 56.2 % of the base mental, respectively. The porosity ratio decreased at first, and then increased with the increase in welding speed. The lowest porosity ratio was 1.99 % when the welding speed was 12 mm × s −1 . In summary, the quality of the weld was better when the welding speed was 12 mm × s −1 .

The aim of this study is to determine the correlation of ultrasound velocity with the physico-mechanical properties of sandstonefrom Jodhpur, India. The relationship between dry density, the Schmidt hammer rebound number, the point load strength index, and uniaxial compressive strength with ultrasound velocity are investigated. Ultrasonic P-wave velocity measurement is a simple, portable, and a non-destructive technique which can be carried out in situ as well as in the laboratory without the availability of core samples. Sandstone specimens were collected from various locations in Jodhpur, India and tested in the laboratory. The empirical equations depicting the relationship between physico-mechanical properties and ultrasound velocity were derived by regression analysis yielding reasonably good correlations. To check the sensitivity of the correlations, a t-test was performed which also confirms the validity of the equations proposed.

Gallium doped zinc oxide (ZnO:Ga) thin films were deposited on glass substrates by means of r.f. magnetron sputtering at room temperature, non-reactively. Both the wet chemical etching behavior and the influence of etching time variations on ZnO:Ga films were investigated. 0.1 % HCl was used as an etchant and the etching time varied in small increments. The thickness of the etched films was determined using scanning electron microscopy (SEM). The etching depth of the ZnO:Ga thin films increased from 13 to 58 % and the resistivity was 10 −3 Ω × cm at different etching times. X-ray diffraction (XRD) results revealed that etching did not influence the crystal structure in a clear way. The (002) peak intensity to thickness ratio reached its maximum at 15 s while full width at half maximum (FWHM) was determined as the minimum. Morphological investigations were conducted using both high resolution scanning electron microscopy (HRSEM) and atomic force microscopy (AFM). The surface of the etched films became rougher and the root mean square (RMS) values increased according to etching time; at 15 s etching the RMS value was calculated to be 8.48 nm. The optical transmittance was measured using an ultraviolet–visible (UV–VIS) spectrophotometer and decreased from 86.60 to 82.50 % while haze increased from 0.85 to 16.68 %.

In this paper, the stress on axially loaded metal sheets with elliptical holes reinforced by a double-sided composite patch was analysed. The metal sheets with elliptical holes were subjected to axial loading, although no load was applied along the edges of the holes. The central elliptical holes on the metal plates had different diameters. The overlap distance of composite patches, which were adhesively bonded on each side, was of varied lengths. Elasto-plastic stress analyses were examined by means of the finite element method (FEM). The experimental results were compared with numerical results and a convergence rate of 92 % was achieved.

The creep behavior of the extruded Mg alloys ZK60 and ZK60+1 %Y was investigated by means of the impression creep technique. The tests were carried out at a temperature in the range of 175–225 °C and under punching stress in the range of 25–100 MPa. The results showed that a 1 wt.-% yttrium addition could improve the creep resistance of ZK60. The creep mechanism of the extruded Mg alloy ZK60 consists of grain boundary diffusion by grain boundary sliding and that of the extruded Mg alloy ZK60+1 %Y grain boundary slip initiated by Mg. The microstructure of the extruded Mg alloy ZK60 consists mainly of the Mg phase and that of the Mg alloy ZK60+1 %Y in the extruded condition is composed of an α-Mg matrix and β-Mg 3 Zn 3 Y 2 phase. After the press-in creep, the extruded Mg alloy ZK60 precipitates MgZn 2 and MgZn phases and a small amount of the Zr-Zn phase, and the extruded Mg alloy ZK60+1 %Y precipitates MgZn 2 , MgZn, Y-Zn and the rare earth phase Mg-Y. The precipitation of the rare earth phase is represented by a discontinuous thin strip and a fine granular uniform distribution in the matrix. The precipitation of the rare earth compound phase shows high thermal stability, which can improve the creep resistance of the alloy. The Y-containing alloy ZK60 manifests higher threshold stress and better creep resistance due to the formation of the rare earth thermally stable particle.

Small-scale model specimens of concrete expanded plates at a scale of 1 : 5 were prepared based on the normal sizes of squeezed branch piles used in engineering applications. Load tests were conducted on the model specimens using an electro-hydraulic compression-testing machine. Through the tests, the complete load-displacement curves of expanded plates were obtained. The test results indicate that the failure mode of expanded plates under the experimental conditions is generally inclined to compression failure and that the major factors affecting the expanded plate's bearing capacity are the compressive strength of concrete, the height-to-width ratio of the expanded plate, and the disc diameter ratio of the expanded plate. Based on the test results, a bearing capacity calculation model for the expanded plate was established. Additionally, a practical calculation formula for the expanded plate's ultimate bearing capacity was derived, where a correlation coefficient (β) was considered to reflect the effects of the expanded plate's failure modes and forces on its bearing capacity. Considering the approximations of the failure modes and forces of expanded plates, a β value of 0.625 may be suggested. The computed bearing capacity values from the derived formula are in good agreement with the test results, as evidenced in the comparison and verification analyses. This study demonstrates the improvement in strength design and calculation theory of expanded plates.

Granite stone powder is a common type of stone-product industrial waste spreading over Fujian Province and other areas of China, causing serious environmental problems. This paper investigates the possibility of using granite stone powder to completely or partially replace quartz powder for preparing “Green” or “Eco” ultra-high performance concrete under autoclave curing regimes. The mechanical properties and microstructure of autoclaved ultra-high-performance concrete (UHPC) mixed with different replacement ratios of granite stone powders were tested. It was found that its mechanical properties still satisfied the original requirements even after total replacement of quartz powders by granite stone powders. Despite of a slight decrease in flowability after total replacement, flexural and compressive strength did not change significantly. The hydration product of flaky tobermorite crystal was found in both granite stone powder blended UHPC and in quartz powder blended UHPC, while the Ca/Si ratio varied slightly. Furthermore, the pore structure of unadulterated UHPC improved due to a larger population of harmless and less-harmful pores after quartz powder were replaced by granite stone powder.

In recent years, automobile, naval and aircraft structures are manufactured using composite materials reinforced with glass fiber, carbon fiber, etc., because of their high specific strength, good corrosion resistance, strength to weight ratio and applicability in saline environments. In this study, glass fiber reinforced plastic (GFRP), carbon fiber reinforced plastic (CFRP) and glass-carbon fiber reinforced plastic (GCFRP) laminated composites were manufactured by means of the hand layup process. Subsequently, a hole was drilled into each specimen of the above composites by means of conventional drilling and fine blanking and finally, the specimens were prepared as per ASTM standards D256, D790, D3039 and D 5868. A detailed study of the mechanical properties and micro-structure analysis of the above specimens and lap jointed specimen was carried out. It turned out that the tensile strength, impact strength and flexural strength of glass carbon hybrid fiber reinforced plastic composite was significantly higher as compared to the glass fiber reinforced plastic composite due to lower fiber breakage and fiber pull out in the fine blanking of the GCFRP.