Volume 56, Issue 11-12

In sheet metal forming, residual stress distributions are often accompanied by crystallographic texture. Incremental hole-drilling for stress analysis is only reliably applicable for isotropic materials. The objective of this study is to determine the influence of texture on residual stress analysis using conventional evaluation methods and to specify the application limits in case of textured material states. A systematic finite element simulation study for ideal texture orientations is conducted with respect to the strain gage rosette orientation. The results of the numerical investigations show that reliable stress analysis on strongly textured materials is not feasible using the existing evaluation method. The application limits are given for the application of commercially available evaluation software with respect to degree of anisotropy, stress state and strain gage orientation.

Finite element analysis (FEA) and experiments have been conducted to analyze the calibration coefficient for measuring residual stress in the ring core method. In this publication, firstly, the calibration coefficients were determined using FEA. Then, factors which affect the calibration coefficients were investigated, such as the tensile load applied to the components, the geometric sizes of the annular grove and the location of the strain gage. The results of FEA were consistent with the experimental results. The most appropriate geometric sizes of the annular groove and location of the strain gage were obtained. This study also defines the distortion energy parameter S to calculate and modify the calibration coefficients. Hence, it is reasonable to apply FEA to calibration coefficients in the ring core method.

For the measurement of tensile properties of materials, specimens with a rectangular cross-section are commonly used. However, the results are affected by the size of the specimen and the orientations. In this study, the rectangular cross-section specimens in both longitudinal (strain ratio r = 0°) and transverse (strain ratio r = 90°) directions were used to investigate the influence of specimen and orientation on the tensile properties of I-profile of IPE360 and IPE400 steel grade S235. For both I-profiles, four types of sixty dog bone samples with varying dimensions were tested. An electromechanical test machine together with contacting strain gauge and extensometer was used to perform standard tensile test procedures. The conclusion is drawn that specimen dimensions and orientation have a significant influence on the mechanical properties of both I-profile structural steel such as Young's modulus of elasticity, upper and lower yield strength, tensile strength, post-necking elongation and strain hardening rate, which increase with increasing thickness or decreasing gauge length.

The aim of this study was to develop a finite element model for predicting the transient temperature and stress fields during friction stir welding. For this purpose, a three-dimensional model based on the nonlinear finite element analysis (FEA) has been generated. The experimentally measured temperatures by using an infrared thermometer during experiments were compared to the results obtained by FEA. In the numerical simulations, mechanical and physical properties were considered depending on temperature. The effect of the rotational and transverse speeds on the distribution of temperature and stresses in the welded AA6061-T6 plates were examined. It was observed that the maximum temperature near the weld region increases with increasing rotational speed. The normal stresses, σ x and σ y also increase as the rotational speed increases. The temperature decreases as the tool transverse speed increases.

This study targeted the effects of heat treatment on the mechanical properties of high-strength steel bolts. High-strength steel bolt samples were manufactured by sequential cutting, cold forming, heading and heat treatment. All sample bolts were M12, and the material was 30MnB4. During the heat treatment, quenching and tempering were applied to high-strength steel. Stress-strain curves were obtained for the steel bolt samples after different heat treatments. The mechanical properties of the steel bolts, such as yield strength, tensile strength, hardness and elongation, were determined for the various heat treatments. It was concluded that heat treatment is an important process that changes the microstructure of the steel bolts and their mechanical properties. By heat treatment at different temperatures it is possible to obtain high-strength steel bolts with different properties.

Gas purging is necessary to provide a high quality of stainless steel pipe welding in order to prevent oxidation of the weld zone inside the pipe. AISI 321 stabilized austenitic stainless steel pipes commonly preferred in refinery applications have been welded by the TIG welding process both with and without the use of purging gas. As purging gases, Ar, N 2 , Ar +N 2 and N 2 + 10% H 2 were used, respectively. The aim of this investigation is to detect the effect of purging gas on the weld joint properties such as microstructure, corrosion, strength and impact toughness. Macro sections and microstructures of the welds were investigated. Chemical composition analysis to obtain the nitrogen, oxygen and hydrogen content of the weld root was done by Leco analysis. Ferrite content of the beads including root and cap passes were measured by a ferritscope. Vickers hardness (HV10) values were obtained. Intergranular and pitting corrosion tests were applied to determine the corrosion resistance of all welds. Type of the purging gas affected pitting corrosion properties as well as the ferrite content and nitrogen, oxygen and hydrogen contents at the roots of the welds. Any hot cracking problems are not predicted as the weld still solidifies with ferrite in the primary phase as confirmed by microstructural and ferrite content analysis. Mechanical testing showed no significant change according to the purge gas. AISI 321 steel and 347 consumable compositions would permit use of nitrogen rich gases for root shielding without a risk of hot cracking.

Large closed cell aluminum foam components, produced through a powder metallurgical route, normally need multiple foamable precursors. The larger the size of components, the more precursors are required. The placement of precursors in the mold prior to sintering is important for a successful foaming. The present study shows that the initial precursor arrangement has a significant effect on the final foam structure and its mechanical properties. The largest foam expansion, close to the geometry of the mold, with more uniform pore distribution was found in the foam with the arrangement of four precursors, which were placed horizontally at the bottom of the mold in two layers. This was due to the delayed foam collapse as a result of the different onsets of individual precursor expansion. The difference in heat conduction of distinct precursor positions resulted in different cellular structural characteristics which strongly affect compressive behavior of the Al foams.

In this study, the effect of lubrications in biaxial forming zone was investigated and their performances in stretch forming process were compared. Two different ultra low carbon steel sheets which are extensively used in the industries, interstitial-free steel and galvanized steel, were tested. Three different lubrications were tested and changes in the right hand of the forming limit diagrams of the materials with different lubricants were determined by using out-of-plane formability test as well as limiting dome heights were obtained for each lubricant. Moreover, strain distributions of samples, which were stretched with dry and different lubricants, were evaluated experimentally and the effectiveness of lubricants is compared. As a result, it was observed that deep-drawing oil has the highest performance among all lubricants. Furthermore, galvanized steel has lower formability under all conditions when compared to interstitial-free steel.

In the present work, Si 3 N 4 -based composites were characterized by a relatively low friction coefficient in unlubricated sliding against a 100Cr6 steel ball. Si 3 N 4 -based composites containing different amounts of SiC were produced by spark plasma sintering at 1650 °C for 5 min with a uniaxial pressure of 40 MPa in a nitrogen atmosphere. In the wear test, the load, total distance and rotating speed were selected as 60 N, 120 m and 500 rpm, respectively. The wear tracks were examined by scanning electron microscopy (SEM) to estimate the wear mechanism. The results were evaluated using the friction coefficient-distance diagram. Si 3 N 4 -based composites showed significant decrement in wear by improving toughness with SiC powder reinforcement.

Sintered iron based compacts were welded by applying a high frequency induction process. The cross-sections of the compacts were square in shape so two different coil shapes, cylindrical and square, were studied with respect to the effect of magnetic flux. The effect of welding duration on the macrostructural changes and mechanical properties of the induction welded compacts were investigated for welding durations of 3, 5 and 10 minutes.

By combining detailed mathematical modeling of the physics involved in NDE with a broader and robust engineering approach based on the sequential steps of screening, modeling and optimization, it is possible to generate metamodels that can support NDE engineering efforts to evaluate the applicability of NDE in a wider context, as a complement to the repeatability, reproducibility and capability studies normally performed. The aim of the initial screening phase is to effectively evaluate and prioritize NDE control parameters from a wider perspective regarding the demands of a specific application and to prioritize parameters of lesser importance for the outcome on the basis of economic and practical considerations. The aim of the second and third steps is to study the influence of the important parameters and to perform sensitivity analyses of reproducibility and repeatability, for example, followed by procedure development, respectively. The methodology is straightforward when it comes to smooth response surfaces of lower order (up to second or third order). Generally, the recommendation for the screening phase is ‘to be bold’ for the definition of the experimental range for each parameter – meaning to make them as wide as possibly relevant for the specific application. For NDE applications not following the Berens assumption for POD studies, e.g., large cracks yield large response signals, such as the varying signal amplitudes from surface breaking notches in ultrasonic testing, the mentioned recommendation of ‘be-bold’ screening phase may lead to incorrect prioritization of parameters. In this publication, this is illustrated by how the width of the experimental range for the control parameters tested during screening actually influences the screening results. Two basic ultrasonic testing set-ups have been compared using the SimSUNDT simulation software package: surface breaking notch (SBN) and side drilled hole (SDH). Even though the results were anticipated, they pointed out the need to further develop the screening methodology supporting NDE engineering, especially when it comes to addressing the issue of applicability. Does the data collected tell us what we actually want to know about the tested application? Or does it only tell us something about the NDE method?

The aim of this study was to investigate the influence of aging parameters and initial roughness on the wear properties of the aluminum alloy AA 6082 (Al-Mg-Si). For this purpose, various heat treatments were carried out. Afterwards, the solutionized samples and artificially aged samples (at 185 °C for 3 and 6 h) were prepared in terms of two different average surface roughnesses via various grades of grinding. The wear behavior of the samples was investigated by a pin-on-disc wear test apparatus under four different applied loads (5, 10, 15 and 20 N) and five different sliding distances (250, 500, 750, 1000, 1250 and 1500 m). The sliding velocity was 30 cm × s −1 . After the wear tests, the mass loss was measured for all samples and the worn surfaces were examined by scanning electron microscopy (SEM). The wear test results clearly show that with increasing hardness, the mass loss decreases, and the mass loss of the worn surfaces increases with increasing sliding distance, test load and initial roughness.

In this study, lamination panels were fabricated using chopped strand mat (CSM) and woven roving fabric (WR) as reinforcement for two different types of specimens, type E b and type P b , respectively. By a combination of plain materials composite lamination structures were formed, with [CSM/0/90/CSM] 2s as an orientation layer for the structures. In this research study, the structural panel was produced by hand lay-up technique with a combination of unsaturated epoxy and polyester resin, separately. Therefore, with this publication, a characteristic combination of chopped strand mat/woven roving fabric, are presented. The experimental work for both types of specimens were performed by bending until the structure fails. The characteristics of different materials, i. e. the chemicals used and the composite lamination structure, were studied, because there are different types of damages in the structure of composite materials, such as delamination, matrix cracking, fiber-matrix damage and fiber pull-out. Furthermore, it can affect the behavior of composite materials in the whole structure. As a result, this process contributes to failure prevention, as the capabilities of the structures are known, before it can be used for any part, component or area. It was also shown that different configuration lamination layers influence the strength properties of the composite materials.

This study aims to investigate the response of AA6061-T6 conical tubes under oblique impact loading, for variations in filler density and tube material by using experimentally validated model. Good correlations between the numerical and experimental results were observed. The initial peak force and dynamic force increase from AA6061-T6 to carbon steel tubes and further increase with increasing filler density, leading to increased energy absorption capacity. Conversely, the initial peak force and dynamic force of empty and foam-filled AA6061-T6 conical tubes decrease with the introduction of oblique loading as the load angle increases from 0° to 20°, leading to reduced energy absorption capacity. Carbon steel is relatively more advantageous compared with AA6061-T6 in terms of energy absorption, whereas AA6061-T6 is comparable with carbon steel because of its lower initial peak force.

The purpose of this study is to investigate the effects of process parameters on adhesive wear resistance by using the Taguchi experimental design method. In this study, Cu-Ni/B 4 C p composites were produced by the powder metallurgy method and the effect on the adhesive wear resistance was investigated. Cu-Ni/B 4 C p composite materials were made by cold pressing methods and reinforced with 1% Ni as well as with 6, 12 and 18% B 4 C p , respectively. The sintering was carried out at 800 and 900°C for 60 minutes. The wear tests were performed by using block on ring test apparatus at loads of 5, 10 and 15 N at a rotation speed of 90 rpm and a wear distance of 250, 500 and 750 m, respectively. The results were evaluated by the calculated wear losses. The wear resistance increased with increasing B 4 C ratio.

In this study, the machinability of Stellite-6 coating was examined using a ceramic cutting tool. Orthogonal tube-cutting experiments were performed on a lathe and the data collected was evaluated by analysis of variance (ANOVA) to find out the percentage contributions of the key factors. Whisker reinforced ceramic inserts with ISO tool designations RNGN 1907 00T01020 were used for the machining trials and round type cutting tool inserts which are common in the manufacturing industry were chosen. Taguchi design of experiments was implemented to determine the optimal cutting parameters for analyzing the effects of the cutting speed and feed rate on the surface quality. Four cutting speeds and three feed rates were used during the turning operations to produce the regression model for Ra (average surface roughness) in terms of the actual parameter values. Hardness of the cutting inserts gets affected significantly at higher feed rate.

Surfaces are the primary contact zones between a biomaterial and its host organism. Surface treatment or coating provides a means to fulfill demanding structural and mechanical requirements of the prostheses. As well as, a number of studies have been performed on functionally graded materials (FGM) and their suitability for use as the biomaterial of choice in various prostheses. This study investigates the effect of utilizing the two concepts of FGM and coating, in designing new hip stem material. The results of this study concluded that the optimal FGM cemented stem is consisting of titanium at the upper stem layers graded to collagen at lower stem layers. The optimal functionally graded stem coated with collagen reduced the stress shielding by 51% compared to homogenous titanium stem coated with collagen. However, this optimal graded stem coated with hydroxyapatite showed a reduction of stress shielding by 57% compared to homogenous titanium stem coated with hydroxyapatite.

The weight and fuel savings offered by composite materials make them attractive not only to the military, but also to the civilian aircraft, space, and automobile industries. In these industries, bolted and riveted joints are extensively used as a primary method for structural joining. Bolted joints in composite materials have complex failure modes, and hence the demand for improving their performance exists. The main objective of this work is to improve the performance of bolted joints in composite structures by introducing nanoparticles/fibers around the expected failure zone. The literature on this issue showed shortcomings in the investigations of such materials. Most of the investigations in this field aimed to enhance the mechanical properties of epoxy materials, which cannot be used alone for high performance structural applications due to their low mechanical properties. In the present work, epoxy resin was modified with different types of nanofillers including multi walled carbon nanotubes (MWCNT). Nano-phased epoxy was used to fabricate different types of nanocomposites as well as nano-hybridized glass fiber reinforced composite laminates. Therefore, six different advanced materials were fabricated including a nanocomposite material (MWCNT/E), a quasi-isotropic nano-hybridized composite laminate (QI-GFR/MWCNT/E), a unidirectional nano-hybridized composite laminate (UD-GFR/MWCNT/E) and a control panel manufactured without nano-fillers (neat epoxy, QI-GFR/E, UD-GFR/E). The materials were characterized by tension and compression tests. The obtained properties are essential for the validation of respective finite element analysis. The results showed improvements in the tensile and compressive properties (strength and modulus) of the fabricated nanocomposites (MWCNT/E) compared with neat epoxy. The hybridized composite laminate with MWCNT showed high improvements in their mechanical properties compared to the composite laminates without nanofillers.

Parts made of composite materials are generally produced by near-net-shape technology. However, additional machining operations such as drilling are often required to facilitate components assembling. Drilling of composite materials is also a common process in the assembly of aerospace and automotive composite structures. During drilling, unlike the conventional materials, a few damage forms may take place. Among these damage forms, the delamination is the most important one. Therefore, the experimental studies carried out on drilling of CFRP composite materials for determining optimum processing parameters are of great importance. In this particular study, delamination in CFRP composites caused by drilling was investigated. The composite material was drilled under various spindle speeds, feed rates and drill point angles. The results showed that delamination and thrust forces were affected by cutting parameters. It was demonstrated that feed rate and drill point angle make the largest contribution to the overall performance.

In the present study, dimensional optimization of screw system elements, like shaft diameter, arm length and nut height, has been performed by tensile, torsional, and shear strength calculations via genetic algorithm. Genetic algorithm has been used to minimize the objective function work with the idea of natural selection. The volume of the designed screw device has been defined as the object function. The limit function is composed of the total stresses affecting the screw system. The algorithm was set up in this way, due to the fact that it relies on the principle of finding the best in a genetic process. Values of the variables within the limiting intervals ensure that the screw device has an optimum size.