Volume 66, Issue 7

In this article, the development of MoBeMeG , a modular device for bending-corrosion-fatigue investigations and variable specimen geometry in corrosive media with galvanic isolation between the test chamber and the test system, is presented. The main application is the investigation of hybrid laminates with high potential for galvanic corrosion, e.g., aluminum ∪ carbon fiber–reinforced plastics, focusing on the description of failure mechanisms and failure evolution at the interface under the influence of bending-corrosion-fatigue loading. The anvil distances are adjustable for the application of varying specimen geometries while retaining the full functionality of the test chamber and securing a full flexible testing possibility without the necessity of new constructions. The test engineering development results in considerable time savings as well as unparalleled efficiency enhancement in terms of bending-corrosion-fatigue performance assessments.

Corrosion assessment of steel-reinforced concrete specimens submerged in synthetic brine water with various chloride concentrations for 1–16 weeks was performed. Mass loss measurements combined with electrochemical techniques – half-cell potential, linear polarization (LP), and electrochemical impedance spectroscopy (EIS) – were employed. The results obtained from all corrosion assessments – on-site testing (half-cell potential measurements), laboratory scale (LP and EIS measurements), and destructive testing (mass loss or immersion measurements) – exhibited remarkable consistency, complementarity, and mutual supportiveness. Corrosion rate (CR) values from mass loss were close to those obtained from LP and EIS. The corrosion resistance decreased with increasing chloride concentration and immersion time, as indicated by the highest CR, Ca 2+ , and Fe 2+ concentrations, and the lowest half-cell potential and polarization resistance. X-ray photoelectron spectroscopy investigation on the corroded steel surface revealed Fe(III) oxides and hydroxides and Fe(III) (FeCl 3 ), corresponding to the reduction in polarization resistance in the LP and EIS results.

The fatigue life extension approaches played an important role in ensuring the safety of marine engineering structures. This study conducted an in-depth analysis of the S–N curves of welded structures under different service environments and different fatigue life extension approaches, and found that the comprehensive life extension process of welding toe polishing and coating (the fatigue life was extended by 15–33 times compared to untreated samples) was the most significant approach under dry air medium environment. The comprehensive life extension process of welding toe polishing and coating (the fatigue life was extended by 10–25 times compared to untreated samples) was the most significant approach under salt spray corrosive medium environment. Moreover, the S–N curve and related parameters of welded joints of semi-submersible platform under different environmental media conditions and different combinations of fatigue life extension approaches were studied in depth, which had important guiding significance for practical life extension tools of jacket platform T-joints in practice.

Vehicle lightening efforts, low fuel consumption and low CO 2 emission have become an important target in the automotive industry without compromising safety and comfort. By reducing vehicle weights, fuel consumption and CO 2 emissions are significantly reduced. In this context, the next generation steels are constantly being developed in terms of high strength, forming, weld ability, low cost in matters such as vehicle lightening and impact safety. In this study, side-impact performance of the next generation steels that can be used for the body B-Pillar part as part of vehicle lightening was examined. In finite element analysis, Usibor 1500, TWIP 980, TRIP 800, DP 1000 materials and three different metal sheet thicknesses (1.3–1.5–1.8 mm) were used for the B-Pillar part. All results obtained were compared in terms of energy absorption ability, formability, weld ability, cost and weight.

Constant amplitude fatigue tests were conducted on 6061/7075 dissimilar aluminum alloy laser welded lap specimens, as well as weld line cross-section hardness measurements. The fatigue test results show that the specimens exhibit multiple fracture modes that exit near the weld seam. The microhardness data on weld line cross-section from 7075 side to 6061 side display a sharp change and the softening phenomenon is serious. The hardness variation in heat affected zone of laser welding is very shallow, and its hardness is close to that of the base material. It was found that there are slag inclusions and pores in the weld seam when observing the fatigue fracture surface using SEM, and a small amount of secondary cracks were generated. However, stress concentration plays a dominant role in causing specimen fracture under fatigue loading, rather than welding defects. Defective specimens are found to have higher fatigue strength. The fatigue life prediction results obtained by the notch stress method and the hot spot stress method are both conservative and fall within two factor lines. The hot spot stress method has relatively higher accuracy for life prediction. The accuracy of both methods in predicting life is influenced by the location of the fracture.

TIG welding is an important joining technique for fabricating quality structural components with industrial capability. Dissimilar alloy plates were combined using double-sided tungsten inert gas (TIG) welding. Microstructure evaluation of joints were anayzed by using scanning electron microscopy, optical microscope, energy dispersion spectrometry, elemental mapping, electron back scatter diffraction. DSAW technique increased joint penetration and reduced distortion of joints. In the weld metal zone, austenite, delta ferrite and lath martensite were dominant. The weld pool had high density of Cr 7 C 3 and Fe 3 C phases and low density of CrFe 7 C 0.45 , FeNi, martensite, and Fe 3 Ni 2 phases.

Eight type of commercial cold work tool steels were heat treated to achieve the equal hardness of 650 HV. Heat-treated samples were investigated by optical and scanning electron microscopy (SEM), microhardness, and X-ray diffraction (XRD) to identify microstructural features and phases. The samples were examined in three distinct wear modes: adhesion, two-body wear using pin wear on SiC, and recycling plastic cutting machine, respectively. The wear surfaces of samples were analyzed by 3D scanning technology. The microstructure of steels determined their wear characteristics. For low sliding and higher cutting speeds, the order of adhesive wear performance of the steels was reversed due to the stress occurring in the cutting line. The wear rate of all samples was commensurate with load. In the recycling plastic cutting process, the sample with the minimum and homogeneously dispersed carbides exhibited the best wear performance. Tempering the S3 sample prevented crack formation and improved fracture toughness.

Quasi-unidirectional glass fiber non-crimp fabrics consist of a unidirectional main layer in the 0° direction stabilized by a backing layer in the 90° direction with a significantly lower amount of fibers. It is known that the backing layers impair the fatigue performance of respective reinforced plastics due to their orientation perpendicular to the main load direction. They act as damage initiators for the failure of the load-carrying unidirectional fibers. In the present work, the positive influence of the backing layers on the interlaminar fracture toughness energy – Mode I – G IC is demonstrated by tests in accordance with DIN EN 6033. The presence of backing fibers in the delamination plane can improve the G IC values by up to 43 %. Furthermore, results from evaluation according to DIN EN 6033 and ASTM D5528 are shown to have a good agreement, if the correction factor for large displacements recommended in the ASTM standard is not applied. If it is applied, however, there is a clear gap of up to 19 % between the two standards because the DIN simply does not provide a correction for large deflections.

Ni alloys are known to exhibit superior creep strength, chemical stability, and thermal resistance behavior at elevated temperatures. However, they also exhibit inadequate mechanical performance. Hence, the microstructures and, in relation to that, mechanical properties need to be improved. In this study, the effect of reinforcement of TiB 2 on microstructural and mechanical properties was evaluated. The Ni matrix is reinforced with TiB 2 particles. TiB 2 –Ni composites were successfully produced by the hot pressing method. Homogenously distributed TiB 2 particles were observed in the microstructure using the energy dispersive spectrometry (EDS) mapping technique. The hardness of the reinforced samples was considerably improved by 2.65–8.12 times compared to pure Ni and between the different content of borides. A three-point bending test was performed to examine the mechanical behaviors of the reinforced composites. The bending stress properties of metal matrix composite (MMC) were significantly influenced by TiB 2 content both positively and adversely. The optimum chemical content was determined based on bending tests and fractography. As a result, the 15 wt.% TiB 2 -reinforced sample exhibited superior microstructural (density), hardness, and bending properties compared to pure Ni and other reinforced samples with different ratios.

Steel rivets serve as a substitute material for connecting similar and dissimilar materials within the structural fabrication industries. However, the use of steel rivets can result in a significant increase in the structure’s weight and may trigger corrosion at the interface due to galvanic coupling. Combining dissimilar alloys through the fusion welding process poses numerous challenges for manufacturers and designers. A solid-state welding technique called friction stir welding (FSW) has been developed. FSW can effectively join materials without reaching their melting points, relying on severe plastic deformation and recrystallization to form a welded joint. The proper selection of the tool and process parameters is essential for achieving a sound weld. The findings of this study indicate that plastic deformation, material flow, and recrystallization play pivotal roles in the strength of the joint. This implies that FSW represents an ideal joining process for high-strength alloys and serves as a viable alternative to replace permanent joints like rivets.

In this article, a newly developed optimization approach based on a mathematics technique named the geometric mean optimization algorithm is employed to address the optimization challenge of the robot gripper, airplane bracket, and suspension arm of automobiles, followed by an additional three engineering problems. Accordingly, other challenges are the ten-bar truss, three-bar truss, tubular column, and spring systems. As a result, the algorithm demonstrates promising statistical outcomes when compared to other well-established algorithms. Additionally, it requires less iteration to achieve the global optimum solution. Furthermore, the algorithm exhibits minimal deviations in results, even when other techniques produce better or similar outcomes. This suggests that the proposed approach in this paper can be effectively utilized for a wide range of critical industrial and real-world engineering challenges.

Glass fiber-reinforced plastic (GFRP) pipes are widely used as buried pipes in petrochemical and other industries. At present, in-depth studies have been conducted on GFRP pipes in terms of internal hydrostatic pressure, axial compression, and cyclic internal pressure, especially limited research has been carried out on transverse load, especially stress relaxation behavior. In this study, GFRP pipes with three different component contents were subjected to different initial deflections at different temperatures and subjected to stress relaxation tests for 1000 h. The findings demonstrate that the stress relaxation behavior of GFRP pipes is not affected by the initial deflection. Rather, it is primarily influenced by temperature and sand entrapment content, which are identified as the key factors determining the stress relaxation behavior of GFRP pipes. In addition, the time-temperature superposition principle (TTSP) was used to pass the test results to obtain a smooth master curve and verify the applicability of TTSP on GFRP pipes. Subsequently, the relaxation performance of GFRP pipes was predicted after 50 years. This research result contributes to a more comprehensive understanding of the stress relaxation behavior of GFRP through accelerated testing and offers crucial insights into the application of GFRP pipes.

In this study, experimental analyses and numerical simulations of polyethylene terephthalate glycol (PETG) pedal pins with optimum production parameters are performed concerning mechanical properties. The aim of this study is twofold: first, the effect of the three-dimensional (3D) manufacturing process, which has a significant impact on the mechanical properties of the 3D-printed part, is realized experimentally. Second, the mechanical behavior of the 3D-printed clutch pedal pin is evaluated using both numerical simulation and experimental tests, which is an important application for lightweight vehicles. It is observed that the determined production parameters can significantly improve the mechanical behavior of the materials and the pin of the vehicle pedal mechanism can be replaced with a lighter structure. Thus, the results obtained in this paper are of the utmost importance for the manufacturer to choose the optimum manufacturing parameters of three-dimensional printed materials and their application to vehicle pedals and other possible parts.

Additive manufacturing enables the fabrication of versatile and cost-effective metallic-alloy components from a digital data model. This study explores the prospects of selective laser melting (SLM), an additive manufacturing technique, for fabricating Ti6Al4V alloy components from Ti6Al4V alloy powders. Selective laser melting parameters, such as laser power, scanning speed, powder thickness, hatching space, and scanning strategy, are carefully selected through a series of experiments. The metallurgical characteristics (microstructure, grain orientation, and phase composition), microhardness, and creep performance of the as-fabricated specimens are tested and analyzed. The kinetics of phase transformation and rupture mechanism are determined using advanced instrumental characterization tools, such as field emission scanning electron microscope, energy dispersive X-ray spectroscope, X-ray diffractometer, and transmission electron microscope.