Volume 64, Issue 10

The advanced aluminum–lithium alloy is used in aircrafts fuselage. Based on the combination of fatigue test and digital image correlation technique, the influence of pre-corrosion and in situ corrosion damage on the fatigue performance of 2198-T8 aluminum–lithium alloy was investigated. The integrated evolution process of fatigue crack and strain distribution fields of two types of the damaged sheets were captured and evaluated by the digital image correlation technique. The results reveal a declining tendency of in situ corrosion fatigue life with the rise of solution temperature, as well as the decrease of flow rate. But, at increasing the NaCl concentration, the fatigue life tends to decrease first and then increase. The observed fatigue behavior and related phenomena are directly associated with fracture morphology such as micro-cracks and corrosion pits. The analysis indicates a competition mechanism between fatigue and corrosion, the fatigue damage dominates the failure process under lower NaCl concentration on the contrary to the higher one that the corrosion damage is the dominant factor. Considering the effect of flow rate on the surface adhesion, the crack tends to initiate at the position of low flow rate. The simulation on the flow field presents an attractive similarity with experimental results.

Wire arc additive manufacturing (WAAM) is an additive manufacturing (AM) technology that uses a modified robotic welding machine to manufacture parts in a layer-by-layer pattern. In the current study, a 308L stainless steel (SS) cylindrical component was manufactured by WAAM technique using gas metal arc welding (GMAW) process. The mechanical and microstructural characteristics of the deposited WAAM 308L SS cylinder were investigated. The microhardness of the WAAM SS cylinder varied slightly along the building direction. The lower zone of the cylinder showed higher hardness than the middle and upper zones. The tensile strength (TS), yield strength (YS) and elongation (EL) of the WAAM 308L cylinder are 331–356 MPa, 535–582 MPa, and 44–51% in the longitudinal, transverse and diagonal orientations, respectively. The microstructure of the WAAM SS cylinder is characterized by austenite dendrites that grow vertically and residual ferrite that exists within the austenite matrix. The results show that the properties of 308L SS cylinder produced by the GMAW-WAAM technique is matching with wrought 308L SS alloy (YS: 360–480 MPa, UTS: 530–650 MPa and EL: 35–45%). Therefore, the GMAW-WAAM 308L SS technique is found to be suitable for industrial use to manufacture stainless steel components.

In this study, the mechanical properties of a 7075-T6 aluminum alloy were investigated experimentally and numerically. Tensile tests were carried out at various temperatures (25–400 °C) and cross-head speeds (1–200 mm min −1 ). The results showed that the tensile strength of the aluminum alloy decreased with increasing deformation temperature. Also, the temperature had more effect on the mechanical properties than on the strain rate. The fracture morphology of test specimens was investigated using a scanning electron microscope. The bending behavior of aluminum alloy at elevated temperatures was investigated with finite element simulations. It obtained a good correlation with the validation study, and it can be predicted as the high-temperature behavior of aluminum alloy with finite element simulations. The analysis results show that the temperature dramatically affects the load-carrying capacity of aluminum. The load-carrying capacity and the absorbed energy values of aluminum alloy decreased with the increasing temperature on bending behavior.

In this study, low velocity single and repeated impact behaviors of 3D printed curved honeycomb cellular panels that can be used for impact protection are investigated. The energy absorbing capacity of the 3D printed honeycomb curved panels is predicted by evaluating the results. In addition, the changes in the fundamental free vibration frequencies of the panels subjected to impact are examined to have an idea about the presence of the damage. The effect of curvature on the damage mechanisms of 3D printed honeycomb panels is studied by examining the contact force–deformation curves, energy profile diagrams, and SEM images. The experimental results indicate that the radius of curvature of the cellular panels highly affects the impact and free vibration behavior, and the change in the natural frequency due to the impact damage is more considerable for ABS than PLA.

For a reliable, strength-compliant and fracture-resistant design of components and technical structures and for the prevention of damage cases, both the criteria of strength calculation and fracture mechanics are essential. In contrast to strength calculation the fracture mechanics assumes the existence of cracks which might further propagate due to the operational load. First, the present paper illustrates the general procedure of a fracture mechanical evaluation of fatigue cracks in order to assess practical damage cases. Fracture mechanical fundamentals which are essential for the calculation of the stress intensity factors K I and the experimental determination of fracture mechanical material parameters (e.g. threshold Δ K I,th against fatigue crack growth, crack growth rate curve) are explained in detail. The subsequent fracture mechanical evaluation on the basis of the local stress situation at the crack tip and the fracture mechanical material data is executed for different materials and selected crack problems. Hereby, the main focus is on the material HCT590X as it is the essential material being investigated by TRR285.

To flake the pure aluminum powder, ball grinding and forging are used. The mechanical properties of the forged B 4 Cp/Al composite are tested. The results show that ball milling can flake the pure aluminum powder. The alumina layer of Al 2 O 3 on the surface of aluminum powder are broken during the ball milling and can be dispersed in the matrix as reinforcement. The hardness of the forged aluminum with flaked Al is higher of 19.5% than that without flaked. The forging can increase ultimate tensile strength of the B 4 Cp/Al composite. Increasing B 4 C volume fraction, the average hardness of the forged B 4 C/Al composite with flaked Al powder gradually increases, relative density gradually decreases, ultimate tensile strength first increases and then decreases.

In this study, effect of homogenization on precipitation kinetics and mechanical properties during aging in AA7050 alloy was investigated. The billet material produced by direct chill method was homogenized at 470 °C for 12–20 h and then extruded to form T-profile. The electrical conductivity of the alloy aged at 120 and 185 °C for 0–36 h were measured and precipitation kinetics were calculated based on the relationship between increased electrical conductivity and amount of precipitates during aging. Time dependent precipitation fraction change curves using Avrami equations revealed that precipitation accelerated as the homogenization time increased due to increased nucleation and growth rates of precipitates. Peak hardness values in aging were reached depending on the increase in homogenization time, however, lower peak hardness (∼185 HV) was determined at 185 °C aging compared to the obtained ones (195–197 HV) at 120 °C aging. Depending on the increase in homogenization time, an increase trend in strength was detected in peak aged alloys. The application of longer time homogenization and subsequent aging caused an increase in strengths. The studied homogenization and aging conditions could be a useful guide for achieving the highest strength and ideal elongation values in commercial practice for the AA7050 alloy.

The focus of this study is manufacture of sandwich composites using palm and jute natural fibers with E-glass due to their high specific advantages such as lightweight, thermal insulation strength, biodegradability characteristics. The sandwich composites using in this study were fabricated using vacuum assisted resin infusion molding (VARIM) technique. The palm, jute and E-glass fibers were used as reinforcing materials, and PET foam core having a thickness of 10 mm was used as a core material. All specimens were then subjected to low velocity impact tests under various impact energy levels of 20 J, 30 J, 40 J, 50 J, and 60 J at room temperature. Force-time and force-deflection diagrams, maximum contact forces, contact times, and deflections corresponding to the peak forces, and absorbed energies of sandwich composites were obtained for each impact energy level in detail. Damages of sandwich composites are shown for selected energies. According to the obtained results, it was found out that the sandwich composite fabricated with palm fiber has a superior impact behavior in terms of maximum contact force compared to other configurations of sandwich composite (i.e., neat E-glass and jute reinforced E-glass).

Earing can be described as difference in cup wall height due to planar anisotropy of the sheet metals, and both prediction and minimization of this defect are critical steps of drawing process design to save material and production costs due to additional trimming operations. The finite element (FE) method is a practical design tool in this context. The accuracy of FE analyses is directly dependent on modeling material deformations using an effective plasticity model. In this study, a homogeneous orthotropic fourth-order polynomial stress function is presented and implemented into Ls-Dyna FE software by a user-defined material subroutine to predict the earing evolution of a strongly anisotropic aluminum alloy (AA2090-T3) in cup drawing. Primarily, the parameters of the function were calibrated using test data. The effects of element size, number of through-thickness integration points, and time-step size were investigated separately on the drawn cup’s earing profile and thickness strain distributions. It was observed that mass scaling factor related to time step size has a significant impact on the cup height and profile. Finally, simulations were repeated with optimum parameters to assess the performance of the plasticity model. The yield criterion successfully predicted the cup profile, earing amplitude, and thickness strain distributions.

Humanity is increasingly approaching the dream of making humanoid robots that have been imaginary for many years with advancing technology. Designs that are close to perfect in humanoid or animal-like robots emerge with the research and development studies carried out by researchers on this subject. In order to develop these robots, the movement mechanism of humans and animals must be examined again. Robots will work in place of people and can be used in wars with the development of these systems. In this study, the usability and performance of the linear actuator, which is widely used in various mechatronic systems as a linear motion provider, in the artificial muscle mechanism have been tested. Moreover, it tried to create a similar prototype by examining the working logic of skeletal muscle. The different aspect of the study is to indicate how the motion energy can be gained without using the conventional motors that are used in robot technologies. The artificial musculature is formed by arranging the electromagnets in a row, leaving a gap between them. The desired length of movement is formed as a result of the activated electromagnets gaining magnetism and closing the gap. In the study, the maximum load that the artificial muscle can pull according to the given voltage was 130.18 N and the average maximum gap length of each sarcomere was 1.68 mm. The efficiency of artificial muscle was found to be 56% compared to human muscle.

This study explores the use of a recent metaheuristic algorithm called a reptile search algorithm (RSA) to handle engineering design optimization problems. It is the first application of the RSA to engineering design problems in literature. The RSA optimizer is first applied to the design of a bolted rim, which is constrained optimization. The developed algorithm is then used to solve the optimization problem of a vehicle suspension arm, which aims to solve the weight reduction under natural frequency constraints. As function evaluations are achieved by finite element analysis, the Kriging surrogate model is integrated into the RSA algorithm. It is revealed that the optimum result gives a 13% weight reduction compared to the original structure. This study shows that RSA is an efficient metaheuristic as other metaheuristics such as the mayfly optimization algorithm, battle royale optimization algorithm, multi-level cross-entropy optimizer, and red fox optimization algorithm.

Cold rolled steel plate is found in different applications. In manufacturing processes with high stretch ratios like bending or deep drawing, non-metallic inclusions, or segregations, which remain in the material during slab casting, can lead to ruptures of the plate. While not being visible optically, those inclusions are detectable by magnetic flux leakage inspection. Therefore, an online inspection system using giant magnetoresistance gradiometers was developed. The individual components were optimized by researching the magnetic properties of the cold rolled plate and natural as well as artificial defects on a laboratory setup for moving material simulation. Correlations between defect properties, inspection parameters and the resulting signals were determined. By optimizing components and configuration accordingly, a sensor module containing 48 sensors, signal conditioning, digitization, and an adjustable magnet was arrived at. Due to the necessarily small distance to the moving material, attention was paid to mechanical repeatability and ruggedness. An inclusion detection system, fully covering 1344 mm strip width, was installed in a coating line. Operating in production for over a year, the inspection system has shown high sensitivity and is, in addition to internal defects, able to detect various strip damages like roll marks and scratches.

Environmentally and hydrogen assisted cracking can occur during application of high-strength aluminum alloys. However, there are only few suitable laboratory procedures to characterize and evaluate the environmentally and hydrogen assisted cracking behavior of materials. By optimizing the hydrogen charging parameters and slow strain rate, a multidimensional test procedure was established, which could simulate the actual working environment and could realize the test and evaluation of hydrogen assisted cracking susceptibility in the laboratory. Moreover, it provides a new environmental adaptability evaluation method for the high-strength aluminum alloy materials.

Visually detecting irregularities on components is a complex process, influenced by physical, technical, and human factors. Current standards mainly focus on illuminance, demanding highest accuracy for it, without providing scientific justification. In this research, 63 inspectors visually inspected forgings, with and without crack-like indications. The influence of illuminance on probability of detection was investigated. Therefore, illuminance was varied in three steps (200 lx, 350 lx, 500 lx). Human factors (e.g., experience, motivation) were recorded by using questionnaires. The results show no significant difference in probability of detection between the three illuminance levels. Equal probability of detection rates could be achieved at illuminances below and at the required threshold (500 lx). A difference in illuminance was found between the measurement point and the test area of the respective participant. This leads to higher assumed illuminance than present on the component. Compared with the measurement accuracy of the used illuminance meter, none of these deviations could be used to explain the similar results at different illuminance. The fact that illuminance has a significant influence in detecting indications has been disproven for this case. Whether human factors can provide explanation for the results remains unclear. This will be investigated in further research.

Fused deposition modeling has become the most common 3D printing technology in both the industry and the private sector, due to its easy application and low price. Although some companies provide parameter sets that are perfectly adapted for their machines and filaments, a great variety of materials that can be processed on arbitrary printers are also available. Usually, the operator has to figure out ideal printing parameters in order to achieve high-quality results. In this work, an approach is presented relating the conclusions of differential scanning calorimetry, including the melting and glass transition temperatures and the decomposition points, to the printout quality. To give an overview of the common materials and to correlate the behavior of the printing parameters, 16 different filaments categorized into groups of plastics without additives, metals and carbon, woods, and stones have been investigated. Heat towers have been printed with each filament, whereby the individual floors in 5 °C steps represent the nozzle temperatures and show features for direct comparison. As a main result, it is shown that the optimal printing quality is achieved with temperatures on the colder end of the range between melting and decomposition.