Band 61, Heft 3

Stress concentration factors (SCF) related to specific geometries, loadings and stress quantities can be calculated efficiently using approximate equations. Those relations are typically based on metamodeling via the results of linear elastic analyses. Existing equations for the, technically speaking, very important circular shafts with shoulder fillets or U-shaped notches under bending, torsion or tension/compression can be appropriated, for example, from the DIN 743-2 : 2012-12. Using these relations requires compliance with underlying constraints and assumptions. For example, equations from that code do not provide SCFs larger than 6 and refer only to the maximum principle stress. Furthermore, DIN 743-2 : 2012-12 does not provide SCFs for combined loading, i. e. simultaneous bending, torsion and tensile/compressive loading. This paper presents new and improved equations based on sampling computational finite element simulations and subsequent regression analyses. Multiple improvements could be achieved: The six equations for circular shafts with shoulder fillets or U-shaped grooves derived from DIN 743-2 : 2012-12 were simplified down to two equations. Despite this simplification, the new equations have been generalized for combined loading and include SCFs larger than 6 as well. Choosing between various equations for each type of loading is no longer necessary. Only one equation for each of the two basic geometries is needed. Moreover, two further equations which refer to von Mises equivalent stress have been added. Although the new equations are easier to handle and allow for an estimation of stress concentration factors larger than 6, the accuracy of the new equations is higher than the accuracy of DIN 743-2 : 2012–12 when compared to SCFs derived from finite element simulation as reference values.

A material mechanical model provides basic data for numerical simulation and technological optimization during the forming process. In this paper, the flow behavior of the hot compressive deformation 0.3 wt.-% Si non-orientation electrical steel were investigated by thermal simulation tests, and a constitutive model was built based on a new modeling method. The thermal simulation tests conducted on a Gleeble 1500 thermo-mechanical simulator over a range of temperatures from 750 to 1050 °C and strain rates from 0.1 to 10 s −1 . To predict the hot deformation process of the silicon steel, a constitutive model based on the multiple regression method was developed. Prediction results showed that the proposed model can track deformational behavior accurately. The model was applied to finite element (FE) simulation, and the FE calculation results matched the industry production data satisfactorily.

Tungsten heavy alloys (WHAs) are widely used in many aerospace and defence applications such as radiation shields, kinetic energy penetrators etc. In the current work, attempts were made to join WHA rods (8 mm in diameter) using rotary friction welding techniques. The WHA rods were prepared via conventional liquid phase sintering and had a two phase microstructure containing tungsten particles of spherical shape and surrounded by a solid solution matrix of Fe, Co and Ni. Rotary friction welding process parameters were successfully optimized and a sound weld with a narrow weld interface without any defects was obtained. The weld interface was found to be of a uniform width of around 150 μm throughout the weld interface and showed very fine fragmented tungsten particles with a refined matrix phase. Moreover, the thermomechanically affected zone (TMAZ) elongated tungsten particles were clearly seen to react normally to the compressive force direction. Further, the heat-affected zone width was so narrow that it was not detected in the current study. Microhardness at the interface showed increased hardness when compared with the base material indicating that the microstructural refinement occurred during friction welding. Tensile tests carried out at room temperature as per ASTM-E8, showed lower strength and ductility when compared with the base material (tested along the hot-working direction). The fractography of the fractured surface of the base material and weld sample confirmed that the ductile mode of fracture had occurred.

Laser speckle photometry (LSP) is an innovative, non-destructive monitoring technique based on the detection and analysis of thermally or mechanically activated speckle dynamics in a non-stationary optical field. With the development of speckle theories, it has been found that speckle patterns carry information about surface characteristics. Therefore, LSP offers a great potential for the characterization of material properties and monitoring of manufacturing processes. In contrast to the speckle interferometry method, LSP is very simple and robust. The sample is illuminated by only one laser beam to generate a speckle pattern on the surface. The signals obtained are directly recorded by a CCD or CMOS camera. By appropriate optical solutions for the beam path, typically, resolutions of less than 10 μm are reached if larger areas are illuminated. LSP is definitely a contactless, quick and quality relevant material characterization and defect detection method, allowing process monitoring in many industrial fields. Examples from online biotechnological monitoring and laser based manufacturing demonstrate further potentials of the method for process monitoring and controlling.

Sandwich structures offer innovative alternative solutions to many weight-critical industrial fields due to their lightweight and very high flexural rigidity compared to conventional materials. A vast number of sandwich configurations can be produced from a variety of materials for use as face sheets and core as well as matrix. Although there are many sandwich structures available in the literature to obtain the desired mechanical and physical properties, the usage of very low-density core materials is very limited. In this study, carbon and glass fiber fabrics having woven plain and ±45 ° fiber orientations and industrial PVC foam core having extremely low density of 40 kg × m −3 and 48 kg × m −3 were used for manufacturing the sandwich panels. Eight different configurations were constructed by hand lay-up followed by vacuum bagging. According to ASTM C393/C393M standard, the sandwiches were subjected to three-point bending (TPB) tests. After performing the TPB tests, the composite sandwich specimens were examined under a stereomicroscope to determine failure modes. The primary failure modes under quasi-static bending loading were found to be top face sheet failures due to fiber and matrix cracks and delamination, and core shear failures due to core crushing just below the top facing and core fractures. In addition, the consistency of the test results were verified and the effects of parameters were investigated by using statistical variance (ANOVA) and regression analysis. The study provides a valuable contribution to the literature regarding sandwich structures having extremely low-density foam core materials and may contribute to the material universe by introducing strong, stiff and lightweight sandwich composites. It provides a comprehensive comparison by considering the effect of different fiber types, fabric fiber orientations and core densities.

In this study, the impact response of laminated composite plates of various specimen dimensions under various impact energies has been investigated, experimentally and numerically. Glass/epoxy composites with [0 2 /90 2 /0 2 /90 2 ]s orientations were manufactured by the hand lay-up technique. Low velocity impact tests were conducted using a CEAST-Fractovis Plus impact test machine for specimens with net impact areas; SQR76 (square with 76 mm edge), SQR150 (square with 150 mm edge) and CIR76 (circle with diameter of 76 mm). Numerical analysis was also carried out via 3DIMPACT transient finite element code including matrix cracking and impact-induced delamination criteria. Absorbed energy and the damage size of specimens were investigated for various impact energies. Delamination areas obtained by finite element were in good agreement with those experimentally obtained up to 50 J of impact energy.

The present work deals with the three body abrasive wear behavior of sansevieria cylindrica fiber (SCF) and E-glass fiber (EGF) reinforced polyester resin (PR) composites. A dry sand rubber wheel (DSRW) test set up was used to test the three-body abrasive wear behavior of composites. Composites fabrication and testing were performed as per ASTM G65-04 standards. The composites were fabricated by varying the weight percentage (wt.-%) of SCF and EGF. The DSRW test was conducted by varying the sliding distance, 1000 m and 2000 m, and the applied load, 24 N and 36 N, at a constant speed of 200 rpm. The worn out surfaces of the composites were examined using a scanning electron microscope (SEM) and the mass loss, volume loss and the specific wear rate of the composites were determined. The wt.-% 30 SCF, wt.-% 20 EGF, wt.-% 50 PR composites revealed a better wear resistance as compared with all other combinations.

Currently besides the hand, color, structure and construction, the comfort characteristics of fabrics have become remarkable issues especially for intimate wear. Therefore, in this study, the synergistic effects of the antibacterial and wicking finishing processes on the comfort characteristics of the seamless knitted fabrics made of regenerated fibers, i. e. micro-modal and lyocell, were investigated and the effects of the lycra incorporation on the fabric structure was also explored. For the evaluation of the comfort properties, the seamless fabric samples were investigated in terms of vertical wicking capacity, transfer wicking, water vapor permeability and drying rate with the relevant textile material test methods. The statistical analysis was performed on the data obtained from the experimental work using Minitab and SPSS package programs. The incorporation of lycra into the fabric structure was found to reduce the vertical wicking capacity, transfer wicking and water vapor permeability of the fabric samples, mainly owing to the alterations it caused in the structure of the fabric by decreasing the porosity, affecting the pore distribution thoroughly and increasing fabric thickness and stitch density. Moreover, the lower wicking ability and water vapor permeability were determined as the factors of the decrease in the drying rates of the lycra incorporated fabric samples. The application of finishing treatments was shown to increase the vertical wicking capacity due to the capillary effect that might have been caused by the cracks and damages that were likely to occur on the surface of the cellulosic fibers during the wicking and antibacterial finishing treatments, whereas they were shown to decrease both the water vapor permeability and drying rate due to the reduction in the interfiber gaps caused by the coated surface of the fibers and the yarns, and the fiber-like structures on the fiber surface. On the other hand, according to the findings, the fiber type was found to have no significant effect on the vertical wicking capacity, transfer wicking, water vapor permeability and drying rate of the fabric samples. Finally, to select the best fabric alternative for the intimate wear, the hybrid AHP-TOPSIS approach was utilized.

Magnetic induction tomography (MIT), a relatively new method of non-destructive testing, is applied to monitor the structural health of carbon fiber reinforced plastics (CFRP). MIT utilizes inductive coils to map the properties of an object. A 3D finite element model of the sensor operation with defects in different CFRP layers is developed to obtain the sensitivity profile and solve the MIT forward problem. Moreover, a linear back projection algorithm was performed to reconstruct images for on-line detection. The results showed that the voltage values induced in the detection coil increase significantly at the defect positions within the related layer. Moreover, the average voltage of the layer with the defect is always higher than at the other layers. This indicates that MIT can easily detect not only surface defects of CFRP but also internal defects successfully and localize them accurately in depth as well.

This experimental study aims to reveal the effect of the drill flute number on the thrust force, tool wear, tool life, chip morphology, surface hardness and microstructure in the drilling of a cast AZ91 magnesium alloy. The results showed that the cutting flute number and cutting parameters have an important effect on thrust force, tool life, wear, chip morphology, microstructure, and drilled hole hardness. When the 2-flute drill was used, less thrust force was generated during the drilling. On the other hand, less tool wear occurred with the 3-flute drill. In scanning electron microscopy (SEM) microstructural analyses, grain refinement was observed in the microstructure of the borehole surface although grain growth was also observed due to a rise in temperature. In addition, the microhardness of the borehole surface decreased as the number of holes increased, and the 2-flute drill bit provided holes with higher stiffness than the 3-flute drill bit.

The prediction of limit load on inlet pigtail pipe bends employed in a hydrogen reformer is one of the unresolved engineering tasks in chemical industries. This is because of the uncertainty and required extrapolation of the applicable data. In practice, the cross section of the inlet pigtail pipe bend becomes non-circular due to the bending process. This irregularity in shape extends when pipes are subjected to in-plane bending moment during plant operation. Ovality is the shape imperfection in a pipe bend considered for the present study. It affects the load carrying capacity and life cycle of the pipe bend. A three-dimensional finite element method is used to model and analyze a stand-alone, long radius inlet pigtail pipe bend. The pipe bend is modeled with a shape irregularity for which the percent ovality varies from 0 to 20. By considering ovality, it is shown that there is a significant effect in limit load due to in-plane bending moment. Also, the stress induced in the pipe bend geometry increases with the percentage of ovality. The allowable levels are obtained from finite elements analysis, considering various bend factors, and the closed form limit load solution is proposed, including the effect of ovality in pipe bend.

Graphene oxide exhibits many unique physicochemical properties and has been investigated widely in many areas. For the present contribution, graphene oxide, using flake graphite as a graphite precursor has been prepared by means of the modified Hummers method. By adjusting the oxidation processes, different graphene oxide products have been obtained. By characterizing the structure and performance of these graphene oxide products, it was discovered that graphene oxide prepared with a greater oxidant content and over a longer reaction time has a well-defined sheet size distribution and exhibits superhydrophilicity. The present work provides a simple method to control the sheet size distribution and the hydrophilicity of graphene oxide by simply adjusting the oxidation process.

Rotating shaft systems play many critical roles in rotating machinery. The performance of any rotating machinery is very dependent on vibrations generated by the rotating shaft. The selection of rotating shaft material is very important to meeting the enormous demand of industrial users on the capability of vibration resistance in rotating machinery. Recent requirements for using rotating shafts have heightened the need for the materials used. The heat treatment of material has received much attention over the last few decades. The research to date has tended to focus on material properties for resistance and strength rather than on dynamic behavior. The main objective of the present study is to experimentally investigate the role of induction surface hardening which is one of the most commonly used types of heat treatment on AISI 1045 steel dynamic behavior. Heat treatable AISI 1045 steel is among the most widely used in all industrial applications requiring more resistance and strength. It has received much attention over the past several decades due to its usage in rotating shafts, axles, crankshafts, and spindles. Induction surface hardening is used to sustain service life by increasing the surface hardness and vibration reliability of a material. Since induction hardened surface depth plays a very important part in the stability of the rotating shaft, three different hardened surface depths (0.5, 1.0, and 1.5 mm) are utilized. The results show that a hardened surface depth of 1.0 mm surprisingly and positively affects the dynamic behavior of the rotating shaft as compared to the hardened surface depths of 0.5 and 1.5 mm.

The major difficulty faced in a machining process is predicting the failure of cutting tools and analyzing the stipulated time for tool replacement. The former and latter can be achieved through a monitoring system that surveys the effective condition. This present research work is focused on analyzing tool condition by adopting a vibration signature during the machining of a hybrid aluminum alloy composite using various coolants. The experiments were conducted employing various tools under optimum process parameters utilizing vegetable based cutting oil as a coolant. During the machining process, a vibration signature from the workpiece was acquired using an NI 6221 M series DAQ card allowing for various time domain features to be extracted. The arithmetic mean and skewness significantly increased for dull tools. Based on the extracted features, a decision making algorithm for tool condition monitoring system has been proposed. The result shows that the features extracted increased consecutively with an increase in flank wear.