Volume 65, Issue 7

B-pillars designed from B1500HS boron steel were compared for roof crushing situations for three different hardness values in the study’s scope. Simulations were also performed for designs where different parts of the B-pillar have different hardness values (tailored properties). For this purpose, roof crushing analyses were conducted, and results were compared in energy absorption and peak crushing force. The highest peak crushing force was obtained from the upper part T25 and lower part T400 heat-treated B-pillar. Upper part T400 and lower part T25 heat-treated B-pillar gave the highest energy absorption value. Since the energy absorption value of the upper part T25 and lower part T400 heat-treated B-pillar is low, the upper part T400 and lower part T25 heat-treated B-pillar provides the second-highest peak crushing force was chosen for use in the optimization. Single and multi-objective optimization studies were conducted to maximize peak crushing force and specific energy absorption for the upper part T400 and lower part T25 heat-treated B-pillar. The optimal B-pillar with tailored properties has an advantage over the base B-pillar, which could be used for B-pillar design.

A spherical indentation strain method was proposed to determine surface residual stress in this study. Through numerical simulation, the effect of the material properties and residual stress on the plastic zone around the indentation was investigated, and the ideal strain measurement region appropriate for diverse materials was identified. Meanwhile, the presence of residual stress in material will cause the strain increment in the strain measurement area near the indentation to change. Based on the relationship among strain increment, residual stress and material mechanical properties, the calibration equation of residual stress for different materials were established. A portable residual stress loading device was developed and combined with the indentation test to calibrate the 316 L and 304 stainless steel of nuclear welding joint material. The reliability of this method was verified, and it provides convenience for the calibration of the residual stress of stainless steel materials.

A variable load effective wear machine was designed, analyzed using the finite element method, and manufactured after its strength was verified. The creation of the solid design model and the finite element analysis were performed in the SolidWorks program. In the wear machine, the abrasive, attached to a plate that can move linearly back and forth, is in contact with the surface of a material to be tested in a fixed position. In the system, the movement is repeated periodically twice in each cycle. The operation of the design system is explained by the calculation of the reaction force and strength under different loads, depending on certain settings. The wear machine was able to operate successfully for a maximum of 30 N loads and up to 30 min in the wear tests. Compared to linear motion wear machines operating with constant speed and a constant load effect, the manufactured wear machine can better explain the wear mechanism between contact materials as a “constant load-variable load effect”.

Multi-principal filler materials via a high-entropy design have been reported to successfully finish the dissimilar metal joining of Al alloy to steel and to reduce the amount of Fe-Al IMCs in weld metals. However, few studies have concentrated on the corrosion and wear resistance of the Al/steel dissimilar weld metals by using multi-principal filler materials. In this study, the joining of Al 6061 alloy to 304 stainless steel served as the research object. Three types of filler materials including CoZnCuMn 0.8 Si 0.2 , FeCoCrNiMn, and AlSi12 powders were used. The effects of multi-principal filler materials on the corrosion behavior and wear resistance of the weld metals were evaluated. It was found that the weld metals by using multi-principal filler materials presented the contents of chemical elements in the range of 5–35 at%. The thermodynamic environment with a low Δ G mix was formed in the weld metals. Compared to the AlSi12 sample, the FeCoCrNiMn sample had excellent corrosion resistance in NaCl solution, whereas the CoZnCuMn 0.8 Si 0.2 sample had excellent corrosion resistance in HCl solution. Moreover, the weld metals by using multi-principal filler materials had a better wear resistance compared to that of the AlSi12 sample. The wear loss of the CoZnCuMn 0.8 Si 0.2 and FeCoCrNiMn samples was 4.5% and 11.4% of that of the Al 6061 alloy, respectively. Abrasive wear was the main wear mode for the weld metals by using multi-principal filler materials.

This research investigates the improvement of impact toughness by changing isothermal heat treatment time for an alloy having high boron/chromium constituents. Different boron contents (0.5–5.00 wt% B) were added into high chromium steel by sand casting. Along with JMatPro program, dilatometry used to calculate critical temperatures and transformation diagrams as well. After austenization at 1050 °C for an hour, at 390 °C high B/Cr alloys isothermally heat treated for three different time intervals (24, 96, and 168 h). According to experimental findings, isothermal heat treatment enhanced hardness and impact toughness of the alloys (excluding 3.10 and 4.75 wt% boron containing alloys) due to the elimination of microsegregations and lowering carboboride sharpness. However, for every alloy wear resistance was not affected by isothermal heat treatment because carbide/boride fraction controls wear properties of the high B/Cr alloys. According to scanning electron microscope microstructures, cleavage fracture, and plowing were observed in isothermally heat treated specimens. It is noted that, isothermal heat treatment time showed no effect in mechanical properties of the high B/Cr alloys because the large amount of alloying elements shifted the phase transformation curve longer times which was more than JMatPro estimations.

Armor steel samples were exposed to corrosion for 24, 72, 168, and 720 h in two different corrosive media. The corrosion rate was determined using mass loss, measurement of the concentration of components in the corrosive medium solution, and Tafel extrapolation methods. Before and after corrosion experiments, the tensile properties, surface characteristics, and phase structures of the samples were examined. The surface analyses were performed using the SEM technique combined with EDX analyses, and the phase analyses were performed by X-ray diffraction. The corrosion rate determined by the mass loss method was 0.02 ± 0.01 mm year −1 for the 3.5 wt% NaCl medium and 2.66 ± 0.16 mm year −1 for the 1 M HCl medium. The corrosion rate values determined by the Tafel extrapolation method were 0.02 ± 0.01 mm year −1 in the 3.5 wt% NaCl medium and 1.21 ± 0.01 mm year −1 in the 1 M HCl medium. There was a decrease in the tensile, yield strengths, and elongation to fracture values of the corroded samples compared to the non-corroded samples. While intergranular ductile fracture occurred in samples exposed to 3.5 wt% NaCl medium, there were features reminiscent of the brittle fracture in samples exposed to the 1 M HCl/168 h medium.

Bone tissue loss may occur in bone structures, which are one of the elements that provide the body’s endurance and movement of living things, due to situations such as falling, hitting, or cancer formation. In bad scenarios, applications such as an external plate or internal rod addition are made to regain the old durability of the structure. At the same time, full or semi-prosthesis applications can be made in cases where the original bone structure cannot be preserved. With today’s advanced possibilities, lattice structures can be produced effortlessly with the additive manufacturing (AM) method. Here, the formation of the structure that can show anisotropic behavior depending on the production and the effect of the roughness caused by the production quality should also be seen in the process plan. In this study, it was aimed to compare the durability of titanium (Ti-6Al-4V) and magnesium (ZK60) materials for humeral half prosthesis using cubic-based lattice structure and to show their differences compared to the original bone structure. Maximum stress and deformation values were obtained by performing analyses with the finite element method on the lattice semi-humerus prosthesis obtained with this aim. Reliability analysis was made on the data obtained, and parameter optimization of the lattice structure was aimed. As a result of the study, it was seen that the lattice structure with 65% porosity compared to the reference values is reliable and with the same reliability rate, magnesium provides approximately 60% lightness compared to titanium.

The mechanical properties of bio-core sandwich composite structures fabricated in different configurations were investigated experimentally and numerically in this study. Balsa woods with thicknesses of 4, 6, 8, and 10 mm were used in the core element. Glass fiber/epoxy composites with 8 and 12 layers at [0°] 2s , [0/90°] s , and [±45°] s fiber orientation zones were used on the bottom and top surfaces of the sandwich structure. The effects of external surface fiber arrangement variation, the number of layers, and core thickness increase on the flexural damage load of sandwich structures produced by the vacuum infusion method were investigated. For this purpose, a three-point bending test was applied to the sandwich specimens. Maximum damage load values were determined using the three-point bending test performed in accordance with ASTM C-393 standard. Experimental and numerical data were compared with the finite element model created in the ANSYS package program. As a result of the tests, the damaged specimens were visualized and the types of damage to the balsa wood and composite element were determined.

The main objective of this study is to investigate the microstructure and wear resistance of AISI 316L austenitic stainless steel (ASS) cladding deposited over mild steel (MS) of grade IS 2062 using constant current (CC-GMAW) and pulsed current gas metal arc welding (PC-GMAW) processes. The PC-GMAW process was employed to overcome the problems of wider heat affected zone (HAZ), coarse grained deposited weld metal microstructure, lower penetration depth, higher dilution and reinforcement height encountered in CC-GMAW used for cladding of AISI 316L steel over mild steel. The microstructural features of cladded region were analyzed using optical microscopy (OM). The wear rate of cladded specimens was studied using pin-on-disc method and the morphology of wear surfaces was studied using scanning electron microscopy (SEM). The microhardness distribution of cladded region was analyzed and correlated to the wear performance of cladded specimens. The results showed that PC-GMAW cladding exhibit greater hardness and wear resistance compared to CC-GMAW cladding. It is correlated to the grain refinement offered by current pulsing in weld region of PC-GMAW cladding. The PC-GMAW cladding showed 5.22% increases in weld metal deposition compared to CC-GMAW cladding. The, PC-GMAW cladding showed 23.72% reduction in dilution of weld compared to CC-GMAW cladding. The PC-GMAW cladding disclosed 15.83 improvement in weld overlay hardness compared to CC-GAMW cladding. The PC-GMAW showed 20.18% average reduction in wear rate compared to CC-GMAW cladding.

The demand for lightweight materials (aluminium and magnesium alloy) in structural applications is increasing due to strength ratio, corrosion resistance, formability, and recyclability. Fusion welding of aluminium and its alloy is difficult due to the formation of hot cracking, alloy segregation, porosity, etc. Henceforth, fusion welding is not an ideal process for joining aluminium and its alloy. Steel rivets are being used to join similar and dissimilar alloys in different joint configurations. Since the use of steel rivets, aircraft weight has increased drastically. Although, dissimilar metal corrosion has been encountered. These two are the main problems in structural fabrication industries. The solid-state welding friction stir welding process eliminates the issues mentioned earlier. This process can weld materials well below the melting point. Moreover, the formation of weld in the weld line could be achieved by severe plastic deformation and recrystallized grains. This metallurgical joint may replace the rivets.

The study aims to search for green, non-toxic bio-based plasticizers to replace traditional o-benzene petroleum-based plasticizers used in polyvinyl chloride films for automotive interior decoration. Three bio-based plasticizers – epoxy, polyester, and citrate were chosen and characterized based on refractive index, viscosity, and plasticizing efficiency. The three types of bio-based plasticizers were then applied to PVC films for automotive interiors. The odor rating, emission properties test, tensile test, dynamic thermomechanical test, low-temperature fatigue resistance test, and heat performance test were used to characterize the polyvinyl chloride film’s application properties. The results showed that the properties of epoxy plasticizer and polyester plasticizer are very close to those of traditional o-benzene petroleum-based plasticizers. In particular, polyvinyl chloride films prepared from polyester plasticizers have advantages in mechanical properties. The strength, elongation, and elasticity characteristics of PVC films plasticized with polyester bio-based plasticizer are 8.77 MPa, 533.92%, and 129.74 Nm, respectively. While the PVC films plasticized with epoxy bio-based plasticizer has an excellent heat resistance and aging resistance, with an initial gel temperature of 185.668 °C. However, the polyvinyl chloride film prepared with citrate plasticizer does not meet the requirements for application in automotive interiors due to its poor emission performance.

Lightweight magnesium (Mg) alloys are employed in a wide range of applications due to their high specific strengths. Nevertheless, some applications require improvement of the wear resistance of Mg alloys. The purpose of this study was to investigate the effect of the initial surface conditions, cold spray temperature, and coating material on the wear resistance of the cold sprayed coatings on WE43 Mg substrate. Blasted and sandpapered surfaces were coated with commercial powders of K-32 (Ni and Al 2 O 3 ) and K-714 (Zn, Ni, and Al 2 O 3 ). The coating materials were cold sprayed on blasted and sandpapered WE43 Mg surfaces at 500 °C and 600 °C. Surface roughness, thickness and wear resistance of the coatings were examined. Deposition efficiency was improved by raising the N 2 gas temperature. The samples with the greatest wear resistance were those that were coated with Zn, Ni, and Al 2 O 3 powder mixture on sandpapered surfaces at temperatures of 600 °C, where deposition efficiency is maximum. Cold spray coatings enhanced the wear resistance of the WE43 Mg substrate.

3D printing using multi-materials has been one of the most popular topics recently. Fused deposition modeling (FDM) is one of the most widely used techniques for the three-dimensional printing of plastics and composites by all industries. In this study, acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) were printed in the same structure with an independent double extruder FDM 3D printer. In the study, three different layer thicknesses (0.1 mm, 0.2 mm, and 0.3 mm), three different infill ratios (30%, 60%, and 90%) and three different infill types (hexagon, triangle, and 3D infill) were used. Tensile specimens were produced according to the ASTM D638 type-IV standard. Tensile specimens of 4 mm in thickness were produced in 1 mm ABS and PLA layers. As a result of the tensile tests, it has been seen that when PLA and ABS are used together in the same structure, the tensile strength increases significantly.

Friction stir welding (FSW) is superior to fusion welding for joining incompatible alloys. In FSW Al/Mg alloys, developing IMCs like Al 3 Mg 2 and Al 12 Mg 17 is almost predictable and undesirable. Continuous IMCs produce a simple fracture propagation path, increasing brittleness and reducing weld strength. AA5052-H32 and AA6061-T6 were joined with a scandium (Sc) strip in the current study to improve material flow and reduce brittleness. Interlayer added on these alloys are the military-grade aluminium alloys used in the production of ship hull constructions and armoured helicopters. During FSW, a threaded cylinder tool with a rotating speed (TRS) of 1600–2000 rpm, welding speed (WS) of 60–80 mm/min and tool pin depth (TPD) of 0.1–0.4 mm were used to create the weld joints. To improve the strength of the above material combination during FSW, a 2 mm thickness Sc interlayer was added. The mechanical and metallurgical characteristics of the weld joints were studied. The maximum ultimate tensile strength value obtained from the cylinder-threaded tool pin profile with 0.1 mm TPD presented 237.63 MPa. Experimental interpretations were employed using response surface methodology-box Behnken design (RSM- BBD). FSW variables’ influence was investigated using the analysis of variance (ANOVA) technique.