Volume 60, Issue 9

The novel, additive manufacturing technique, continuous lattice fabrication, combines the advantages of continuous fiber-reinforcement with those of additive manufacturing. This enables the generation of fiber-reinforcement within a single layer and especially along an out-of-plane load path inside all spatial dimensions. This study is a test-related evaluation of sandwich panels with lattice core structures modifying a compression test. The specimens were manufactured differentially via plug and bond and automatically using continuous lattice fabrication. Additionally, the spatial arrangement of the rods within the lattice core structure varied in terms of base area. The ultra-lightweight sandwich panels have lattice core structures with core densities < 10 mg × cm −3 . The material testing was performed by a modified compression test at room temperature. The damage analysis of the single rods shows current deficits and future potentials for optimization of lattice core structures. It could be shown that sandwich panels exhibit a compression strength of up to 0.30 MPa at a core density of 6.57 mg × cm −3 . Using a dimensionless lightweight index demonstrates a mechanical performance on a level comparable with that of selected core materials.

Cu-based powder metallurgy friction material is technically one of the most important powder metallurgy friction materials due to its high conductivity, high strength, good thermal properties and wear endurance. In this paper, nano-carbon reinforced Cu-based powder metallurgy friction materials were prepared by hot isostatic pressing (HIP). Microstructure and mechanical properties of nano-carbon reinforced Cu-based powder metallurgy friction materials with different nano-carbon content were systematically investigated. The microstructures of the nanocomposites were examined by optical microscopy (OM), X-ray diffraction (XRD), back scattered electron imaging (BSE), scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS). Mechanical properties were determined from micro-hardness, shear strength and compressive strength. The fracture and strengthening mechanisms of nano-carbon reinforced Cu-based powder metallurgy friction materials are explored on the basis of the microstructure and composition of the nanocomposites along with the formation and function of the interface. The nano-carbon mainly enhances the nanocomposites by load transfer and obstruction of dislocation. The synergistic effect of multi-walled carbon nanotubes (MWCNTs)and graphene improves the dispersion but hinders the densification process. The interfaces between carbon and copper are the main source of cracks, and the nanocomposites are mainly composed of brittle fracture.

TiO 2 micro powder was deposited onto an aluminum substrate by atmospheric plasma spraying resulting in 200 μm thick coatings. These coatings were characterized, whereby typical layer properties like porosity, layer thickness and hardness were investigated. Subsequently, a thermo-mechanical load was applied to the TiO 2 coating by friction stir processing. This testing procedure indicates several advantages. First, specific load cycles can be applied at high accuracy using specific parameter sets. Secondly, different tool geometries can be used for testing, resulting in countless possible load cases and testing scenarios. As a result, the thermal properties of the TiO 2 coating were investigated and compared as a function of a stepwise increased testing load. To complete the experimental results, a numerical simulation of the testing process was set up to estimate the transient heat flow of the TiO 2 coating during friction stir processing.

In this study, blends were developed based on poly (lactic acid) (PLA) containing chitosan (CHS) extracted in our laboratory and an organically modified montmorillonite (cloisite 30B) at different amounts from 1 to 4 (in wt.-%). Tensile samples were prepared using twin-screw extrusion followed by injection molding, and films were obtained by press compression. The morphological and mechanical results showed a phase segregation and poor adhesion between the polymers. Indeed, the elongation at break and thermal stability had undergone a major decrease when adding chitosan to the PLA matrix. Glass transition temperature (T g ), melt temperature (T m ) and recrystallization temperature (T c ) decreased with the addition of chitosan, whereby an increase in crystallinity indicated a nucleation effect showing the same results as with the addition of cloisite 30B. An interesting effect of cloisite 30B was found when it was incorporated into the PLA/CHS blend especially with respect to a 4 wt.-% of cloisite 30B amount. The loss of elongation at the break was partially compensated and the thermal stability and crystallinity were improved. The water vapor permeability (WVP) and water vapor transmission rate (WVTR) of PLA/chitosan blends were higher than those for the neat PLA. By incorporating the C30B into the PLA/CHS blends, very interesting and good barrier properties were recorded as compared to neat PLA and PLA/CHS composites.

Kurzfassung Bei der Herstellung von Stahltragwerken nach DIN EN 1090 sowie bei der allgemeinen Materialprüfung ist die Messung der Härte Bestandteil der normgerechten Bauteilprüfung. Dabei wird zumeist die konventionelle stationäre Vickershärteprüfung gefordert. Beispielsweise werden bei der Erzeugung von thermischen Schnittkanten obere Grenzwerte für die Härte vorgeschrieben, die es folglich zu überprüfen gilt. Die Ermittlung der tatsächlich vorliegenden Härte an derartigen technischen Oberflächen stellt sich in der Praxis jedoch als schwierig dar, da die hohen Härten verfahrensbedingt nur in dünnen Schichten vorliegen und die zugänglichen Oberflächen der Schnittkanten Schneidriefen aufweisen. Die umständliche Verfahrensprüfung und die normgerechte Härtemessung an metallografischen Schliffen sind selbstverständlich möglich, aufgrund des hohen experimentellen Aufwands jedoch nicht immer praxistauglich. Im Zusammenhang mit der rechtlichen Produkthaftung, die für jedes gefertigte Bauteil gewährt werden muss, besteht unmittelbarer Bedarf an einem Verfahren zur verlässlichen Ermittlung der Härte, auch an nicht normgerecht vorbereiteten Oberflächen.

The EIS behavior, corrosiveness, and seepage structure of sand of varied water content were studied by means of electrochemical impedance spectroscopy under the three-electrode system. The results show that the effect of void geometry on the impedance modulus disappears at the high frequency range. However, the impedance modulus is greatly affected by the pore geometry and the effect is greater for standard sand with increased randomness when the frequency is under 5 Hz. The pore structure of standard sand increases Re by an order of magnitude and the increase is more obvious when water content is low. By contrast, Rt decreases with increasing water content. The corrosiveness of the sand system increases with increasing water content. The electrochemical process of a wet sand system shifts from a kinetic control process to a material transfer control process as frequency changes from a high to a low range. The hydraulic radius, a parameter of the seepage structure, fluctuates between 0.01 and 0.03 mS. The magnitude of W, showing a change in tortuosity T, fluctuates between 10 −5 and 10 −6 .

These days, a lot of metal scraps are generated by the automobile industry since the use of vehicles is increasing globally. As the production of automobile increases, the use of aluminum alloys has been increasing in automobile applications. Since the resources for the production of primary aluminum are getting scarce and the production of primary aluminum is highly expensive, production of components using secondary aluminum alloy in the form of scraps is highly essential. The present study deals with the re-melting of aluminium alloy scraps and the production of secondary aluminum alloy through a gravity die casting process. An investigation of its microstructure, chemical composition and mechanical properties such as hardness, tensile strength and an impact test have been performed and compared with the properties of primary and standard aluminum alloy. Porosity of secondary aluminum alloy is observed macroscopically. In addition a radiograph test was performed to study the internal defects of the secondary aluminum alloy.

For the evaluation of adhesive quality, the prevailing situation shows that standardized mechanical tests do not generate significant quality parameters as they indicate merely the maximum bonding strength of the specimen under investigation. Furthermore, most product data sheets provided by adhesive manufacturers supply only a few technical parameters (i. e. maximum tensile strength), which, from a technical point of view, limits the selection criteria for adhesives. Considering this fact, adhesive selection can be very dangerous when relying on bonding strength alone. This is crucial for industries where human safety has top priority, such as aeronautical, automotive or medicine. Consequently, the present study introduces a new approach, using both fracture mechanics and a special test arrangement for adhesively bonded composites to overcome the above mentioned handicaps. The key benefit of this novel evaluation concept is its ability to monitor the post-cracking behavior of bonded interfaces in a stable and steady manner even for brittle adhesives. This is a major advantage over commonly practiced techniques, both from a mechanical and a fracture mechanical point of view, as they basically tend to measure instability if brittle interfaces come about. To demonstrate this new technique, experiments were conducted on six different adhesives kindly provided by SIKA and MUREXIN. The results found opposite interactions between adhesive bonding strength and fracture resistance, meaning that high tensile strength values do not automatically lead to the best results. Such findings show that the selection of adhesives with the help of fracture analysis seems quite desirable for the future.

S275 structural steel is a popular low carbon steel type that can be used in many different general engineering and structural applications. These steels are widely used in steel construction, maintenance, machinery and manufacturing industries. Welded joints of this steel used in the mentioned industrial areas are important. In this study, 10-mm thick S275 structural steel sheets were joined by using gas metal arc welding (GMAW) and flux cored arc welding (FCAW) methods. Tensile, bending, and hardness tests were performed to determine the mechanical properties of the welded samples. In addition, metallographic investigations were carried out to determine the microstructural properties of the weld zones. As a result of the microstructural studies, it was found that different structures such as grain boundary ferrites, polygonal ferrites, Widmanstatten ferrites and acicular ferrites are formed in the weld metal and coarse-grained region. It was determined that the hardness of the weld metal was higher than HAZ and base metal in all welding parameters. The highest tensile and bending strengths were obtained from those samples joined by using the FCAW method. As a result of the tensile test, separation occurred in the transition region between the weld metal coarse-grained regions.

Kurzfassung Die Methode der Essential Work of Fracture ist ein Konzept der Fließbruchmechanik und eignet sich hervorragend zur Werkstoffoptimierung von duktilen Kunststoffen. Sie zeichnet sich, unter Beachtung gewisser Restriktionen, durch eine relativ einfache experimentelle Durchführbarkeit und Ergebnisinterpretation aus. Speziell die Gewährleistung des ebenen Spannungszustands, eine Grundvoraussetzung zur Anwendung dieser Methode, wird maßgeblich durch den gewählten Ligamentbereich der Prüfkörper beeinflusst. Mit der digitalen 3D-Bildkorrelation wird ein Verfahren vorgestellt, mit dem es möglich ist, sowohl die vollkommene Plastifizierung des Ligamentbereiches zu überprüfen als auch die minimal zulässige Ligamentuntergrenze zu definieren und zu überprüfen. Durch die mit digitaler 3D-Bildkorrelation unterstützte Werkstoffuntersuchung mit der Methode der Essential Work of Fracture ist es möglich, die Genauigkeit und die Verlässlichkeit der Ergebnisse zu steigern.

The present study outlines the optimization of process parameters in the EDM of AA7178-10 wt.-% ZrB 2 composites. The composites were fabricated by using stir casting and the mechanical properties are evaluated. The mechanical properties of AA7075, AA7178 and AA7178-10 wt.-% ZrB 2 composites were reported. Scanning electron microscope (SEM) and energy dispersive spectrometry (EDS) analysis were used to characterize the composites. The fabricated composite material was machined using different process parameters based on Taguchi's L9 orthogonal array. Parameters such as current (I), pulse on time (PT-on) and pulse off time (PT-off) were varied. The response variables measured for the analysis are material removal rate (MRR) and surface roughness (SR). From the SN Ratio (SNR) analysis, it was observed that, current is the significant factor affecting both MRR and SR. ANOVA analysis was carried out to determine the percentage contribution of each factor to the responses. Further, a verification experiment was performed to confirm the performance of optimum parameters.

In this study, severe plastic deformation (SPD) and wear behavior of AA 7075 allosy widely used in aerospace, automotive and defence industries, has been investigated. The equal channel angular pressing (ECAP) process was applied to achieve an ultra-fine grain structure of homogenized AA 7075 materials. Solid particle abrasion behavior was impressed into homogenized and ECAP' ed materials via a variable particle impingement angle (PIA) and acceleration pressure. Microstructure and wear behavior of the tested materials were investigated using scanning electron microscopy (SEM) and a surface profilometer. In the studies conducted, it was observed that an increase in the number of ECAP passes with the effect of SPD, reduced the solid particle wear behavior.

Historically, cutting force and surface roughness are known to be important performance indicators in conventional machining operations and are mainly affected by material type and the choice of cutting tool. One well-known method to improve cutting tool performance is covering these tools with durable ceramic coatings to protect them from wear and thermal degradation. This work elucidates the advantage of Al 2 O 3 and TiN coatings and presents important performance improvements in turning operation. Process parameters such as cutting speed, feed rate, cutting depth and tip radius were taken into consideration in a total of 540 experiments. The design of the experiment and a statistical analysis were performed to reveal significant process parameters. A special experimental setup was designed to measure in-situ cutting forces. The surface roughness of the machined surfaces was measured. An artificial neural network model was developed to predict optimum performance parameters.

In recent decades, research on soft robot manipulations and their materials attracted a huge momentum among various researchers. Selection of appropriate soft material is a vital role in robotic fingertip design, which enables the object to be held in proper orientation without slip and damage. Development of such an anthropomorphic type of soft hand requires knowledge about material selection, types of finger contact and the mechanism behind grasping. This research work presents a comprehensive comparison of six chosen soft materials with human skin for improved robotic manipulation. Extensive research is required to develop such soft hands for better manipulation becausein the final analysis, the human hand is the best soft manipulator as it conforms to objects easily through good contact with an object. In the past decades, many researchers have tried to replace metal hand of robots with appropriate soft materials to enable better manipulation. In this work, the magnitude of contact area, contact pressure and vertical depression of six soft materials was compared with human skin with respect to precision grasping. The simulation results clearly show that neoprene rubber exhibits a close relationship with the characteristics of human skin.

The austenitic nickel-chromium based super alloy Inconel 718 is considered a difficult material to machine due to a combination of nickel, iron and cobalt. The material exhibits mechanical strength and resistance to surface degradation under extreme pressure and heat. It employed widely in aerospace, jet engines, gas turbine etc. This research work focuses on the optimization of cutting variables for each performance measure obtained by employing grey-Taguchi techniques. The orthogonal array, grey relation analysis and analysis of variance are employed to study the performance characteristics in turning Inconel 718 using a carbide cutting tool insert. Further, a simulation model based on an finite element approach is proposed using DEFORM-3D software for the prediction of tool wear through Usui's tool wear model. The study highlights the optimum cutting conditions and a favorable range of the machining variable values. Finite element method results show that predicted tool wear values according to DEFORM-3D produce a useful and adequate level of accuracy.