Volume 64, Issue 5

In order to investigate the effects of environmental conditions on materials, industrial products or to meet long warranty periods of the products, various tests are performed in the climate test chambers. They have a multidisciplinary structure and should be designed according to different operating conditions. So obtaining the mathematical model of them and knowing the performance of dynamic behavior are significant both in the design phase and in the control of the designed system. In this study, a novel model is developed for numerical investigation of heating process of prototype climatic test due to the mentioned needs. A so-called temperature-dependent L-section line approach was developed. The insulation material was divided into seven segments. The thermal conduction coefficients of the insulation material, mass flow rate, and specific heat of the air were modeled as a function of temperature, as distinct from constant-coefficient lumped-parameter approaches. The simulation results were compared with the experimental results for different conditions, it was observed that the presented approach was compatible with the experimental results. This developed model is not only limited to climate test chambers, but can also be applied to different engineering disciplines such as control, energy, heat and mass transfer, building, and construction.

Aramid and poly( p -phenylene benzobisoxazole) (PBO) fibers are two of the most represented organic fibers possessing high strength, high modulus, excellent thermal stability, and chemical resistance, with great potential in oil and gas applications. The reliability of organic fibers for oil and gas applications were systematically evaluated by studying the corrosion behavior and mechanisms in high-temperature and high-pressure (HTHP) hydrogen sulfide (H 2 S) and carbon dioxide (CO 2 ) corrosive environments. Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), elemental analysis, density measurements, and single fiber tensile testing were conducted to study the surface morphology, chemical structure, crystal structure, thermal, and mechanical properties of aramid and PBO fibers, before and after corrosion. After corrosion, the crystallinities of aramid and PBO fibers decreased by 19.4 and 4.4%, respectively, whereas their tensile fracture strengths decreased by 50.34 and 28.18%, respectively. Hence, the corrosion resistance of PBO fiber is better than aramid fiber. The decrease in tensile properties of aramid and PBO fibers can be attributed to the higher internal porosity, more number of surface defects, and lower crystallinity after HTHP H 2 S/CO 2 corrosion. This work provides some fundamental information regarding the selection of high-performance organic fibers for oil and gas applications.

Additively manufactured γ-titanium aluminide has a high specific strength and temperature resistance. This opens new possibilities for future lightweight constructions for aerospace applications. The objective of this work was to characterize additively manufactured Ti–48Al–2Cr–2Nb alloy specimens, which were successfully manufactured by electron beam powder bed fusion. For microstructural characterization, the as-built state was investigated with light and scanning electron microscopy. In the electron backscatter diffraction analysis, the size and the orientation of the grains were observed. The pore size and distribution were examined in computer tomographic scans, which showed a near fully dense material with a relative density of >99.9%. Furthermore, the hardness curve over the building height was examined in hardness mappings. Thereby, a strong decrease in hardness could be observed with an increase in part height. To evaluate the reliability of the manufactured alloy, quasi-static compression tests were carried out at temperatures up to 650 °C. Within these tests, a high compression strength ( σ c , p ,0.2,650 °C  = 684 MPa) was determined, which implicated a potential substitution of nickel-based superalloy components in aerospace applications under compressive loads.

The impression creep behavior of a lead-based PbSn 16 Sb 16 Cu 2 alloy was studied at stresses in the range from 15 to 30 MPa and temperatures in the range from 333 to 393 K. XRD, SEM, and EDS techniques were used to analyze microstructural evolutions of the alloy before and after creep at different impression creep conditions. Results show that, in the range of experimental conditions, the calculated stress exponent and the creep activation energy of the alloy are 4.12 and 60.56 kJ mol −1 , respectively. Grain boundary diffusion-dominated dislocation climbing is the main impression creep mechanism of PbSn 16 Sb 16 Cu 2 alloy. Creep rate increases and creep resistance decreases with the increase of temperature and stress, respectively. Two reasons dominate the creep process: first, Sn is largely precipitated from the solid solution in the matrix, which weakens the overall strength of the matrix during the creep process; second, as temperature and stress increase, the atoms are vibrated more fiercely by thermal energy, which results in a softening of the matrix and SnSb phase.

Electron beam melting (EBM) is a powder bed additive manufacturing (AM) technology for small and medium-sized Ti-6Al-4V components. In this study, EBM-built Ti-6Al-4V tensile specimens were joined using tungsten inert gas (TIG) welding and laser beam welding (LBW) to form large-scale components. Weld morphology, defects, mechanical properties, and microstructure of joints made by LBW and TIG welding were compared. It was found that the pore sensitivity of EBMed Ti-6Al-4V is extremely high. In EBM, the most common defect is pores, but this has been ignored as parts are broken at welding zone. Large pores are distributed along the edge of the weld in TIG welding, whereas in laser welding they are distributed at top of the weld. LBW has a much smaller grain size in the weld center than TIG welding. The TIG welded sample has more heat at the weld boundary. Mechanical properties of TIG welded parts were superior to laser welded parts. The main reason for this is that the weld cross section is larger than the center. In addition, in the microstructure examination of TIG welding, it was observed that the weld had fewer defects than laser welding. Also, the elongation of all specimens is very low.

With regard to the application of thin-film hot-dip galvanizing to a welded steel tube structure in vehicle construction, several test series were carried out to investigate the potential for hydrogen embrittlement caused by the pretreatment media used in the galvanizing process. Here, C-ring specimens were produced from the materials E355 and C75 in different tempering states, treated in a hydrochloric acid-based operational pickle, and then tested under constant strain rate or constant load. The results show that under the investigated pickling conditions, no hydrogen-induced embrittlement effect occurs up to a hardness of 470 HV in the case of material E355 and 500 HV in the case of material C75. Only in the case of 550 HV and 600 HV, both for C75, was a tendency to embrittlement observed; this effect was more pronounced after treatment with the freshly prepared pickle than in the operating pickles. The two test methods used showed consistent results.

Various types of defects can impact the mechanical or aesthetic properties of stamped sheets, and the phenomenon of springback (SB) is one of them. SB is complicated, and it is hard to simulate it precisely because it is related to many factors such as tooling geometry, material properties, friction, and boundary conditions. In this article, the SB of V-stretch bended samples with uncoated and coated steel is experimentally and numerically investigated. The steel samples are coated with a thin layer of several metals (zinc, tin, nickel, and chromium). This investigation takes into account the influence of various parameters such as the coating thickness, its roughness, the punch depth, the blank holding force (BHF), and the change in the material’s yield strength. A self-developed two-dimensional elastoplastic finite element code was developed using Abaqus/standard. In this work, we also show that the SB angle is smaller for uncoated sheet, higher BHF, higher surface roughness, lower coating thickness, lower stretching height, and lower yield strength.

Optimization of the heat recovery devices such as heat exchangers (HEs) and cooling towers is a complex task. In this article, the widely used fin and tube HE (FTHE) is optimized in terms of the total costs by the novel gradient-based optimization (GBO) algorithm. The FTHE s have a cylindrical tube with transverse or longitudinal fin enhanced on it. For this study, various constraints and design variables are considered, with the total cost as the objective function. The study reveals that the GBO provides promising results for the present case study with the highest success rate. Also, the comparative results suggest that GBO is the robust optimizer in terms of the best-optimized values of the fitness function vis-à-vis design variables. This study builds the future implications of the GBO in a wide range of engineering optimization fields.

Large number of pre-mature failure cases of spline half-shafts of loader automobile rickshaws were encountered by an industry in Lahore, Pakistan. Unexpected fracture of the spline-region of half-shafts were reported shortly after the shafts were put to service. This paper presents the findings of a systematic investigation that was carried out to find the root cause of the failure. Visual inspection, mechanical characterization, microstructural analysis, and chemical composition analysis were used to study the failure. It was revealed that the failure was torsional fatigue fracture in nature, with crack initiating from one of the machining marks present near the spline-root. Main cause of failure was found to be stress concentration at machine marks present on the surface, especially the ones closer to spline-roots, resulting in crack initiation. Moreover, other factors like presence of manganese sulfide (MnS) inclusions and improper material had also contributed towards crack propagation and final fracture.

The adaptability of metaheuristics is proliferating rapidly for optimizing engineering designs and structures. The imperative need for the fuel-efficient design of vehicles with lightweight structures is also a soaring demand raised by the different industries. This research contributes to both areas by using both the hybrid Taguchi salp swarm algorithm-Nelder–Mead (HTSSA-NM) and the manta ray foraging optimization (MRFO) algorithm to optimize the structure and shape of the automobile brake pedal. The results of HTSSA-NM and MRFO are compared with some well-established metaheuristics such as horse herd optimization algorithm, black widow optimization algorithm, squirrel search algorithm, and Harris Hawks optimization algorithm to verify its performance. It is observed that HTSSA-NM is robust and superior in terms of optimizing shape with the least mass of the engineering structures. Also, HTSSA-NM realize the best value for the present problem compared to the rest of the optimizer.

The existence of some problems in joining Al and Mg alloys using classical fusion welding methods causes limitations in the use of Mg and Al alloys in common structures. Friction stir welding (FSW) is a solid-state welding method for joining materials having same or different properties at temperatures below their melting points. In this study, dissimilar alloys AZ31B Mg and Al6061 were joined by FSW at a feed rate of 34 mm·min −1 and at different tool rotational speeds (600 and 700 rpm) and material positions. During the welding process, AZ31B Mg plate was positioned at the advancing side and Al6061 was located at the retreating side, and moreover, the two alloys were also positioned vice versa. Tensile strength and microhardness tests were performed to examine the mechanical properties of the welded specimens. The microstructures of the welded zones were examined by obtaining the optical microscopic (OM) and scanning electron microscopic (SEM) images. The highest welding strength was obtained from the specimen welded at a tool rotational speed of 600 rpm, at a feed rate of 34 mm·min −1 and by locating AZ31B Mg on the advancing side.

The effect of different joint angles and joint types in adhesively bonded joints was investigated. Two joint types were chosen to examine the effect of the joint type. A total of 12 samples were produced at six different angles (30°, 45°, 52°, 60°, 75°, and 90°) to examine the effect of joint angle on the scarf and double butt–lap joint types. St 37 steel was used as the adherend material. The adhesion distance, sample thickness, and adhesion area were kept constant in the samples. There were differences in the sample widths to make the angle change by keeping the adhesive bonding length constant. 3M Scotch-Weld DP810 epoxy adhesive was used as the adhesive. The adhesive thickness was chosen as 0.1 mm. An axial tensile load was applied to the samples, and the results were recorded and evaluated. When scarf and double butt–lap joint samples are compared with each other according to their angles, it was seen that double butt–lap joints were more successful in samples with 30, 45, and 52° joint angles, and scarf lap joints were more successful in samples with 60, 75, and 90° joint angles.

The aim of this study is to determine the structural effects of different delamination types on buckling behavior of the E-glass/epoxy with [0] 8 , [90] 8 , [±45] 4 orientation angles and aramid/epoxy with [±45] 4 orientation angle of the composite plates. The buckling behaviors of the layered composites with three different artificial delamination geometries namely, RECDel (rectangular delamination), SQRDel (square delamination), and CIRDel (circle delamination) as well as with different delamination locations (at depth ratios of t / h  = 0.25 and t / h  = 0.5) were investigated under compression load experimentally. The boundary conditions were clamped for loaded ends while they were freed for the other edges. The dimensions of rectangular composite plates were selected as 150 mm (L) × 25 mm (b) × 2.32 mm (h). Five specimens for each parameter of delaminated composite plates were tested to get the average buckling load. The test results showed that load values of the aramid/epoxy load values were higher than load values of the glass/epoxy load values regardless of the similarity of the buckling loads for t / h  = 0.25 and t / h  = 0.5 depth ratios. Furthermore, it is possible to conclude that the performance of both the glass/epoxy and the aramid/epoxy buckling are strongly influenced by the layered orientation configurations.

In this work, we studied the pull-out behavior of glass, basalt, and carbon rovings embedded in fine-grain concrete and geopolymer. Smooth rovings from the bobbin and coated rovings extracted from the fabric were both studied. A matrix made of fine-grained concrete and geopolymer was used to determine the interaction between roving and matrix during pull-out. The use of these matrices provides an economical consumption of concrete used in building structures. In addition, the bonding effect between coated roving and matrix was also investigated. As a result, it was observed that the bonding strength in a matrix made of fine-grained concrete is higher than that of a geopolymer. Smooth roving exhibited a minimal bonding characteristic irrespective of the matrix. The best anchoring is achieved by the coated roving extracted from the fabric and the strength characteristics of the roving itself are not critical.