Volume 62, Issue 6

Material extrusion-based additive manufacturing techniques such as fused deposition modeling or fused filament fabrication are developing from prototyping applications to serial components. The aim of this study is to properly characterize an additively manufactured polymer with the corresponding process-induced defects. To this effect, varied manufacturing orientations of fused filament fabrication were tested with a single-batch material manufactured by injection molding serving as a reference. Scans were carried out via micro-computed tomography to assess the void content and distribution with respect to quality. Local material performance was investigated via quasi-static and cyclic tests under tensile loading. The quasi-static tensile tests indicated a significant reduction of Young’s modulus, tensile strength, and strain at fracture for the additively manufactured polymer. The mechanical investigations with cyclic loading intensified this trend of clear reduced mechanical properties due to process-induced defects. The quality assessment revealed void volume contents of the additively manufactured polymer of up to 6.5 % and a void distribution dependent on manufacturing orientation. The results of this study are valuable as design guidelines for highly stressed components and serve as a basis for further characterizations of process-induced defects.

The oxide scales of hot-rolled, annealed hot-rolled, and shot blasted annealed hot-rolled AISI 304L stainless steel with 0.2-0.4 wt.-%Cu and 1.0-1.7 wt.-%Mn were investigated by XRD. Mn but not Cu showed its effects on the oxide compounds. In the hot-rolled state, the oxide compounds consisted of Fe 2 O 3 and Cr 1.5 Mn 1.5 O 4 in all tested steels. Mn-rich (Fe,Mn) 2 SiO 4 was found in the oxide of the tested steel with 1.2 wt.-%Mn while Mn3O4 was found in the oxide of the tested steel with 1.7 wt.-%Mn. The addition of Mn promoted the formations of Cr 1.5 Mn 1.5 O 4 , Mn-rich (Fe,Mn) 2 SiO 4 and Mn 3 O 4 . The oxide compounds developed from Fe 2 O 3 to (Fe 0.6 Cr 0.4 ) 2 O 3 or Cr 1.3 Fe 0.7 O 3 , Cr 1.5 Mn 1.5 O 4 to CrMn 2 O 4 and Mn-rich (Fe,Mn) 2 SiO 4 to (Fe,Mn) 2 SiO 4 after the annealing process. The shot blasting process of annealed hot-rolled 304L stainless steel descaled the outer oxides as (Fe0.6Cr0.4)2O3 and (Fe,Mn) 2 SiO 4 and revealed the inner oxides Cr 1.3 Fe 0.7 O 3 , CrMn 2 O 4 and Cr 2 O 3 . The results clearly showed that the fraction of CrMn 2 O 4 increased according to the Mn content.

This paper investigates the mechanical properties of two selective lasermelted aluminum alloys (AlSi10Mg and AlSi3.5Mg2.5) under high strain-rate uniaxial loading. Accelerated tensile tests were performed under various strain-rate decades ( . ε = 4.7 × 10-3 up to 250 s-1) to determine the load-speed-specific changes in the mechanical properties. As a result of the primary laser-based shaping process, the microstructure and characteristics change was entirely comparable to the conventional manufacturing of aluminum parts. Based on an ultrafine microstructure, parts achieve high strength along with a brittle fracture behavior. Modifications for applications requiring high ductility (e. g., the crashloaded structural parts of a car body) can be made through specific heat treatment strategies. The experimental results demonstrate that a significant increase in ductility (factors 4-5) with a concurrent decrease in strength can be obtained compared to the as-built state. In high-speed tests, the tensile strength of both alloys rose strain-rate dependently around 10 %, and the elongation at break increased relatively by ≈ 15 % for AlSi10Mg and ≈ 10 % for AlSi3.5Mg2.5.

Metastable phases can be shifted to a different state by thermal loads on components. This leads to structural changes and precipitation. Within the scope of this investigation, a coating is applied to a solution annealed and a quenched and tempered substrate of the same chemical composition by means of a cold PVD process. The investigation is based on the process of polymer extrusion without additives. The substrate examined is 1.2379 tool steel. The substrate is used as a screw extruder material and is exposed to operating temperatures of up to 400 °C. A titanium layer is applied which is used in practice as an adhesion promoter and is in direct contact with the substrate. An annealing temperature above 500 °C results in special carbide hardening. These should show a worse layer adhesion than the metal bonds of the solution annealed sample. The aim is to investigate whether a difference is measurable or negligible. The loads during polymer extrusion are simulated by means of bending and pin-on-disk tests. The 3-point bending test simulates the mechanical load during extrusion. The pin-on-disk test simulates the friction between the extrusion screw flank and the extrusion cylinder. The substrate is characterized before and after sample preparation. Wear measurements are carried out using CLSM and SEM. The surface topography is recorded and then evaluated for comparison.

Metallic coatings which provide a hydrogen diffusion barrier are thought to reduce hydrogen assisted cracking on stainless steel. The influence of a metallic layer on the hydrogen migration of AISI 304 stainless steel was investigated using a commercial electroplating layer of Ni and Au on a thin stainless steel coupon. Phase identification was performed using an X-ray diffractometer to determine the average thicknesses, measured from back-scattered scanning electron images. Regarding the ASTM G148-97 practice, the effective hydrogen diffusivities of AISI 304 austenitic stainless steel, nickel and gold were measured as 7.07 × 10 -13 , 2.72 × 10 -14 and 9.64 × 10 -16 m 2 × s -1 , respectively. In this work, a gold layer was found to be most effective for the prevention of hydrogen diffusion when compared with untreated and Ni-plated 304 stainless steel.

In this study, the mechanical behavior of titanium (ASTM Grade 2) alloy sheet, resistance spot welded with 5754 aluminum alloy, was investigated with respect to nugget formation and mechanical properties. The welding operations were performed using resistance spot welding at various welding currents (10, 12.5 and 15 kA), welding times (10, 15 and 20 cycles) and electrode forces (5, 10 and 15 kN). The weld nugget diameter and nugget center height, hardness, and tensile-shear test results of the welded samples were examined, and the mechanical properties were compared. As a result of the tests, it was seen that the welding parameters have a significant effect on the mechanical properties of the titaniumaluminum alloy welding joints. The tensile-shear load of the resistance spot welded joints increased as the welding current increased, and welding time increased for 15 cycles. On the other hand, when the electrode force increased, the tensile-shear load decreased markedly.

A physically based material model, taking into account the interdependence of material microstructure and yield strength, is presented for an Al 5182 series aluminum alloy for the simulation of friction stir welding using continuum mechanics approaches. A microstructure evolution equation considering dislocation density and grain size is used in conjunction with a description of yield stress. In order to fit experimental stress-strain curves, obtained from compression tests at various strain rates and temperatures, phenomenological relationships are developed for some of the model parameters. The material model is implemented in smoothed particle hydrodynamic research code as well as in the commercial finite element code Abaqus. Simulations for various strain rates and temperatures were performed and compared with experimental results as well as between the two discretization methods in order to verify the material model and the implementation. Simulations provide not only an accurate approximation of stress based on temperature, strain rate, and strain but also an improved insight into the microstructural evolution of the material.

This investigation explored the effect of temperature on the compressive behaviors and failure mechanism of three dimensional (3D) carbon/ epoxy five-directional braided composite laminates. The compression tests of 3D braided composite laminates were performed at six different temperatures, which are 20 °C (room temperature), 50 °C, 70 °C, 90 °C, 110 °C and 130 °C, respectively. Then the effect of temperature on the failure mechanism, stress-strain curves, compressive modulus and strength of the composite laminates were analyzed and compared to that at room temperature. The results have shown that the temperature had a significant effect on the compressive properties and failure mechanism of 3D braided composite laminates. At 20 °C and 50 °C, the 3D braided composite laminates failed by shear fracture, and the stress-strain curves exhibited obvious linear elasticity and a brittle failure feature. While, at higher temperatures (70 °C, 90 °C, 110 °C and 130 °C), it was found that the specimens exhibited obvious plastic kinking, and the stress-strain curves exhibited obvious non-linear trend and a plastic failure feature due to the epoxy resin matrix becoming softened and plastic. The compressive modulus and strength decreased as temperature increased. The compressive modulus and strength decreased by 92.3 % and 93.8 % when the temperature increased from 20 °C to 130 °C.

Fused deposition modeling is one of the most well-known additive manufacturing methods. It might be considered the easiest way to produce particle reinforced composites or unreinforced sheets which are biodegradable and used in the packaging industry as well as for custom products. In this study, polylactic acid (PLA) sheets were produced by 3D printing and thermoformed using a lab-scale thermoforming machine. This article aims to determine the deformation behavior of 3d printed PLA sheets during thermoforming. In addition to experimental work, finite element analysis was performed to investigate the prediction capabilities of Mooney-Rivlin and Ogden models for PLA sheets. In addition, the initial thickness of the sheet was optimized using FEA and a python script to obtain final uniform thickness distribution. Thanks to 3D printing’s capability for printing sheets of variable thickness, sheets of variable thickness were printed to verify the material models. As a result, based on the thickness distribution obtained from the experimental study, Mooney-Rivlin and Odgen material models were found to be inadequate for representing the actual deformation behavior of PLA sheets.

This work outlines the fatigue failure in a failed helical coiled compression spring of a passenger car used as a commercial vehicle. As a failure investigation case study, the fractured left rear axle suspension spring of the car is thoroughly examined. The fractographic investigations included the visual examination, spectroscopy, microstructure analysis, SEM and micro-hardness testing. The foremost causes of failure have been identified. From the SEM fractograph, microvoid coalescence is observed at the grain boundaries on of the fractured surface which eventually resulted in intergranular dimple rupture. Residual stress is also measured on the fractured surface through two-dimensional (2-D) imaging using a Debye Scherrer ring, with the conclusion that the spring under investigation experiences micro-stress due to the variation of theintergranular spacing resulting from the vibrations induced by overloading, road conditions and prolonged use which eventually results in a rupturing of the compression spring.

In today’s world, reducing fuel consumption is one of the most important goals for the automotive industry. For this reason, weight reduction is one of the main topics in this research and for various companies. In this research, topology optimization was conducted on a suspension arm as a means of ensuring balance in automobiles. Subsequently, the model, formed by topology optimization was filled with a lattice structure and re-optimized by size optimization to obtain optimum dimensions for the model. These operations are described as lattice structure optimization. Additive manufacturing (3D printer) is necessary to produce complex models (after topology and lattice structure optimization). A static analysis of the new models was conducted by using the finite element method, and the results were compared with those of the initial design of the model. As a result of the comparison, positive results were obtained, and it was shown that topology optimization and lattice structural optimization could be used in the design of vehicle elements. According to the results obtained from lattice structure optimization, design structure can be formed more reliably than via topology optimization. In addition, both configurations and layouts of the cellular structures have a special effect on the overall performance of the lattice structure.

In this research paper, a new surrogate-assisted metaheuristic for shape optimization is proposed. A seagull optimization algorithm (SOA) is used to solve the shape optimization of a vehicle bracket. The design problem is to find structural shape while minimizing structural mass and meeting a stress constraint. Function evaluations are carried out using finite element analysis and estimated by using a Kriging model. The results show that SOA has outstanding features just as the whale optimization algorithm and salp swarm optimization algorithm for designing optimal components in the industry.

In this study, the wear and microstructure properties of some coatings produced on Weldox 700 steel were investigated via a high-velocity oxygen fuel (HVOF) technique. For the coating types, NiCrBSi, WCCo and CoNiCrAlY-based coatings were selected. Microstructure and phase formation were examined via scanning electron microscopy (SEM), X-ray diffraction and X-ray energy dispersive spectrometry. Wear tests of the substrate and coatings were made using the ball-on-disc method. It can be seen from the SEM images that the coating layers are metallurgically/ mechanically connected to the substrate and have a mostly homogeneous structure. The hardness measurement was taken from the top of the coatings. The hardness values of the coatings were significantly higher than those of the substrate. The coated substrates exhibit a very good tribological performance compared with the substrate. Depending on the load, the wear rate and coefficient of friction of the coatings were much lower as compared with the Weldox 700 steel substrate.

This paper presents the growth kinetics of the boride layer formed on a boronized AISI 316 (X5CrNiMo17-12-2) stainless steel surface. Samples were boronized applying the Ekabor 2™ boronizing agent in an atmosphere controlled furnace at 1073, 1173 and 1273 K for 1, 2 and 3 h by the powder pack method. Surfaces of the samples which have completed the boronizing process were prepared for metallographic examinations. An optical microscope and an integrated image analyzer were used to measure the thickness of the boride layer formed on the surface of the samples. Due to the dual phase structure of the boride layer formed on the steels in order to see these phases in detail, an SEM (Scanning Electron Microscope) image of the sample was taken with the help of the back scattered electrons. In addition, for determination of the elements constituting these phases, elemental analysis was carried out with the help of an EDS (Energy Dispersive Spectroscopy) unit connected to SEM. Then XRD (Xray diffraction analysis) analyses were carried out to understand in detail which phases formed the boron layer. For hardness measurements of boride layers, a Vickers hardness device with 100 g weight was used. Finally, to determine the growth kinetics of the boronized samples, calculations were made with the help of the Arhenius equation and compared with the literature.