Automotive Structural Components Research Articles

Zero-emission joining methods for low-load automotive structural components

Zero-emission joining methods for low-load automotive structural components

Investigating the creep resistance of E-glass/polyester composite for automotive structural components

This study was focused on investigating the influence of fiber-to-matrix weight ratios on the creep behavior of a composite material made from E-glass fiber and polyester resin. The aim was to assess the practical applicability of the composites for aircraft and vehicle structural parts by checking creep strength. The test specimens were prepared using the hand layup method, combining E-glass fiber and polyester resin. Three different fiber-to-matrix weight ratios (65/35, 55/45, and 35/65) were selected and the test specimens were manufactured according to the ASTM D2990 standard. The tests were conducted on each weight ratio using creep loads of 20, 30, and 40 N., and finite element analysis (FEA) was performed to substantiate the experimental results. Based on the experimental and simulation results, it was observed that the composite with a fiber weight ratio of 65/35 has 62.43 Mpa stress and 7.59 mm deformation. This exhibited favorable creep behavior and higher deformation resistance compared to the other compositions. The finite element analysis results were in good agreement with the experimental findings. This suggests that this weight composition could be preferred for vehicle structural parts. The agreement between the experimental and finite element analysis results further validates the practical applicability of the composite material.

Fracture behaviors of the 1500 MPa-grade anti-oxidation hot-stamped steel: Measurement, numerical simulation and experimental validation

Ultra-high strength hot-stamped steel has been increasingly and widely used for the improvement of the collision safety and lightweight level. The 1500 MPa-grade anti-oxidation hot-stamped steel (AHS-1500), as a newly developed hot-stamped steel, is promising in the automotive industry due to its advantages of anti-oxidation, high strength, high hardenability, and no coating. It is necessary to figure out its fracture failure behaviors and further predict the fracture risk for promoting the large-scale application. In this paper, the fracture behaviors of the AHS-1500 steel plate are investigated by experiments and simulation. The fracture tests are conducted under static and dynamic loads by considering various stress states, namely uniaxial tension, notched static tension, shear, punching, center-hole static tension, and VDA bending. The fracture failure behaviors are obtained. Moreover, an Swift+Hockett-Sherby combined hardening model is adopted to extrapolate the post-necking flow stress to obtain the stress-strain relation at large strains. A fracture failure model is further established based on the GISSMO fracture failure criterion to accurately describe the failure behaviors under various stress states. The nonlinear fracture failure strain and the necking instability strain are determined with the consideration of the influence of element size and strain rate. Finally, the three-point bending experiment of a cap beam part is conducted and simulated to verify the effectiveness of the proposed model. The simulated results match the experimental ones very well, with the absolute relative errors of only 1.4 % and 4.6 % for the peak force and peak displacement, respectively. This research is favourable for contributing to high-precision numerical analysis for the design of automotive structural components and providing technical support for large-scale promotion of the AHS-1500 steel.

Impact Strain Signal Characteristics of Al and Mg under Instrumented Charpy Test

Impact strain signal is used to examine strain signal patterns under various parameters. Impact is a complicated phenomenon that occurs within a millisecond timeframe. Material toughness is measured by the energy absorption recorded by the Charpy machine and closely related to the specimen fracture deformation. By utilizing the strain gauge and data acquisition, the impact strain signal provides additional data regarding impact duration, maximum strain value and the area under curve for a deeper understanding of the impact problem. A material with high toughness has great energy absorption and the capability to withstand high impact load. Although magnesium is lighter in weight compared to aluminium, aluminium is a better corrosion-resistant material and is stronger, which makes it more suitable to be fabricated as automotive structural components. Tensile test is typically used for investigating a material’s mechanical properties. In the automotive industry, materials are required to have good crashworthiness. This study investigates the relationship between the energy absorbed with the power spectral density and the area under strain–time graph for different materials, impact speeds, and material thicknesses. Furthermore, the relationship between the stress–strain curve and impact strain signal were examined. In this study, the behaviour of two materials, namely Aluminium 6061-T6 and Magnesium AM60, was investigated using instrumented Charpy test, by referring to the impact strain signal pattern result. For the experiment, strain gauge attached to the Charpy machine striker was employed and linked to the data acquisition system. Charpy impact specimen has three different thicknesses; 10 mm, 7.5 mm and 5 mm. Impact speed is at 3.35 m/s and 5.18 m/s. Results show a correlation between energy absorbed with strain energy. Strain energy obtained is directly proportional to the energy absorbed. Aluminium 6061-T6 has the highest energy absorption, maximum strain, and strain energy under power spectral density graph compared to Magnesium AM60. Relation of strain signal from Charpy test and stress–strain curve from tensile test shows a significant finding where the material deforms and fracture points are identified through the signal pattern and curve. Thus, the strain signal pattern can be used to predict material behaviour.

The strain-rate-dependent tensile failure and energy-absorbing behavior of sheet molding compounds

Sheet molding compounds (SMCs) as an alternative material for low-cost and lightweight automotive structural components require special attention to their failure behavior and collision safety. This study aims to analyze the energy-absorbing response and variability of unsaturated polyester matrix SMCs under the range of strain rates from 10−3/s to 500/s through quasi-static and dynamic tensile tests. Additionally, the tensile process and fracture morphology were characterized using Digital Image Correlation and Scanning Electron Microscopy to reveal the underlying rate-dependent failure mechanism. The results demonstrate a pronounced positive correlation between the tensile strength and absorbed energy of SMCs with strain rates. Specially, the absorbed energy exhibits substantial variability, primarily attributable to the plastic damage behavior during the nonlinear phase. A transition in the failure mode from debonding to pseudo-delamination, accompanied by a more extensive failure area at high strain rates, serves as the main mechanism for enhancing the material energy absorption capacity.

Nanodiamond-structured zinc composite coatings with strong bonding and high load-bearing capacity.

The aerospace and automotive industries find that relying solely on the intrinsic resistance of alloys is inadequate to safeguard aircraft and automotive structural components from harsh environmental conditions. While it is difficult to attribute accidents exclusively to coating failure due to the involvement of multiple factors, there are instances where defects in the coating initiate a wear or degradation process, leading to premature and unplanned structural failures. Metallic coatings have been introduced to protect the aircraft mainly from wear due to the extreme temperatures and moisture exposure during their service life. Bare metallic coatings have a limited lifespan and need to be replaced frequently. Herein, the strength and wear resistance of zinc (Zn) coating is enhanced using varying concentrations of diamond particles as an additive in the Zn matrix (Zn-D). The dispersion strengthening mechanism is attributed to the high hardness (70 HRC), and reduced friction-of-coefficient (0.21) and dissipation energy (4.6 × 10-4 J) of electrodeposited Zn-D7.5 (7.5 g l-1 of diamond concentration) composite coating. Moreover, enhanced wear resistance with minimum wear volume (1.12 × 10-3 mm3) and wear rate (1.25 × 10-3 mm3 N-1 m-1) of the Zn-D7.5 composite coating resulted in perfect blending of diamond with Zn. The improved hardness and wear resistance for Zn-D7.5 (optimum 7.5 g l-1 diamond concentration) is due to the steadiness between well-dispersed diamonds in Zn and enrichment in load-bearing ability due to the incorporation of diamond particles. Electronic structure calculations on the zinc-diamond composite models (two configurations adopted) have been performed using the density functional theory (DFT) approach, and the in silico studies appeared to facilitate meaningful and evocative outcomes. Zn-doped diamond (C10@Zn) without hydrogen (H) atoms (binding energy: 418 kcal mol-1, i.e. showing an endothermic reaction and thermodynamically not favourable) was detected to be more stable than the Zn-doped diamond (C10H16@Zn) consisting of hydrogen (H) atoms (binding energy: -33.3 kcal mol-1, i.e. showing an exothermic reaction and thermodynamically preferable). Thus, a composite coating of zinc and diamond can be a suitable candidate for the aerospace and automotive industries.

Incremental shape rolling of top-hat shaped automotive structural and crash components

Incremental shape rolling of top-hat shaped automotive structural and crash components

Room Temperature Stamping of High-Strength Aluminum for Lightweight Structural Automotive Components

Room Temperature Stamping of High-Strength Aluminum for Lightweight Structural Automotive Components

Effect of pre-strain on high cycle fatigue property of TWIP steel

A commonly used material in vehicle structure is twinning-induced plasticity (TWIP) steel. In addition, during auto safety structural parts process, the material is pre-strained to different levels. Therefore, the influence of pre-straining on fatigue life needs to be examined for design and life assessment. Based on the current test data, due to the different types of steel and loading methods, the fatigue life of the material will show an increase or decrease with the increase of pre-strain level. The results of this study are compared with the recommended S-N fatigue, and the applicability and conservative levels of fatigue life curves are discussed to consider the influence of material pre-strain on the fatigue life assessment of automotive structural components.

Effect of retained austenite on the fracture behavior of a novel press-hardened steel

• Effect of RA on both the tensile and bending properties of the PHS has been studied. • RA with various mechanical stabilities and volume fraction are obtained via tuning the degree of auto-tempering of martensite during die quenching. • The tensile performance is improved with increasing of volume fractions of RA in the novel PHS. • The mechanical stability, rather than volume fraction of RA, has significant impact on the bendability of the PHS. Tensile and bending properties are two critical attributes of press hardened steels (PHSs) for automotive body structural components. However, the research on these properties of PHSs with retained austenite (RA), which is introduced to improve the mechanical properties, has not been well reported. In this study, the effect of RA on the quasi-static uniaxial tensile and three-point bending behaviors has been systematically investigated for a newly developed Cr and Si alloyed PHS. RA with various degrees of mechanical stabilities was obtained by tuning the auto-tempering of martensite through the control of the die contact pressure during the press hardening process. Mechanically stable RA provides the optimal combination of tensile and bending performance, while the PHS with RA of poor mechanical stability has a deteriorated bending toughness as manifested by a reduction of bending angle from approximately 61.6° to 56.8°. However, its tensile properties, in contrast, are the best in terms of the product of ultimate tensile strength and total elongation (15.9 GPa %). This is mainly attributed to the unstable RA on the outermost surface of the bending sample. The unstable RA can easily transform into brittle martensite under local plane strain and strain gradient conditions in the bending test compared with uniaxial stress in the tensile test, promoting crack initiation and propagation. Furthermore, the effect of martensitic auto-tempering or contact pressure on the quantity and stability of RA are also discussed. This study would provide a useful reference to guide hot stamping process optimization for the newly developed Cr and Si-containing press-hardened steel.

Microstructural Evolution of a Hot-Stamped Boron Steel Automotive Part and Its Influence on Corrosion Properties and Tempering Behavior

Boron-manganese steel 22MnB5 is extensively used in structural automotive components. Knowledge about its microstructural evolution during hot stamping and resistance spot welding (RSW) is extremely relevant to guarantee compliance with application requirements. Particularly, corrosion properties are critical to the application of uncoated sheet steels. However, microstructural studies are usually simplified to top-hat geometries, which might not be fully representative of the complex thermomechanical cycles locally faced by a real component. Therefore, the present work brings an extensive characterization of a hot-stamped 22MnB5 automotive B-pillar in terms of microstructure, hardness and corrosion resistance, which were correlated with a reverse engineering of the process using numerical simulation. Physical simulations of the subcritical heat affected zone (SCHAZ) of RSW were done to assess the influence of microstructure on martensite tempering. Results showed that the component undergoes a complex strain distribution along its body during hot stamping. Most heavily strained regions presented higher amounts of ferrite, leading to poorer corrosion resistance, since ferrite behaves as an anode. Physical simulations of the SCHAZ showed that the softening degree due to martensite tempering is solely affected by peak temperature, while other microstructural features appear to exert negligible or no influence.

Experimental investigation on the quasi-static structural properties of carbon fibre/metal hybrids processed by roll forming

Carbon Fibre Reinforced Metal Hybrid (CFRMH) materials combine high specific strength and stiffness with excellent fatigue resistance and damage tolerance. They are a potential solution for lightweight automotive crash and structural components, but their application is limited due to the lack of cost-effective manufacturing technologies. This study presents a new method for the manufacture of long steel components that are reinforced with a carbon fibre patch via roll forming, a low-cost sheet metal forming process that is heavily applied in the automotive industry. For this, CFRMH sheets are first produced in a hot press and then roll-formed to hollow components that are structurally tested in a 3-point bending test. The material deformation after roll forming and the failure modes after the structural tests are analysed with optical microscopy. The results of this study show that part quality and forming defects after roll forming depend on the carbon fibre orientation and the forming temperature. Depending on the carbon fibre layup, an increase in specific energy absorption of more than 45.6% was achieved compared to the sole steel counterpart. This was related to an intact adhesion at the carbon fibre–steel interface after roll forming, which allowed the carbon fibre patch to effectively absorb the deformation energy. The results suggest that roll forming presents a low-cost alternative for metal hybrid part production with significant potential to reduce weight and increase the structural performance of future automotive components.

Microstructure-Based Modelling of Flow and Fracture Behavior of Tailored Microstructures of Ductibor® 1000-AS Steel

Emerging grades of press-hardening steels such as Ductibor® 1000-AS are now commercially available for use within tailor-welded blanks (TWBs) to enhance ductility and energy absorption in hot-stamped automotive structural components. This study examines the constitutive (hardening) response and fracture limits of Ductibor® 1000-AS as functions of the as-quenched microstructure after hot stamping. Three different microstructures consisting of bainite and martensite were obtained by hot stamping with die temperatures of 25 °C, 350 °C, and 450 °C. Mechanical characterization was performed to determine the hardening curves and plane-stress fracture loci for the different quench conditions (cooling rates). Uniaxial-tension and shear tests were conducted to experimentally capture the hardening response to large strain levels. Shear, conical hole-expansion, plane-strain notch tension, and Nakazima tests were carried out to evaluate the stress-state dependence of fracture. A mean-field homogenization (MFH) scheme was applied to model the constitutive and fracture behavior of the mixed-phase microstructures. A dislocation-based hardening model was adopted for the individual phases, which accounts for material chemistry, inter-phase carbon partitioning, and dislocation evolution. The per-phase fracture modelling was executed using a phenomenological damage index based upon the stress state within each phase. The results revealed that the 25 °C hot-stamped material condition with a fully martensite microstructure exhibited the highest level of strength and the lowest degree of ductility. As bainite was formed in the final microstructure by quenching at higher die temperatures, the strength decreased, while the ductility increased. The predicted constitutive and fracture responses in the hot-stamped microstructures were in line with the measured data. Accordingly, the established numerical strategy was extended to predict the mechanical behavior of Ductibor® 1000-AS for a broad range of intermediate as-quenched microstructures.

Effect of external loading on liquid metal embrittlement severity during resistance spot welding

Advanced high strength steels (AHSS) used in automotive structural components are protected using zinc coatings. However, the steel/zinc system creates the potential for liquid metal embrittlement (LME) during resistance spot welding (RSW). Manufacturing conditions, such as mechanical restraint, were simulated by external loading on the sample during welding. The results showed increased LME severity in all cases, but the material response to external loading was different depending on the material’s inherent susceptibility to LME. Therefore, the manufacturing conditions are more critical for certain AHSS grades. This work provides guidelines on process design for LME mitigation and awareness during manufacturing.

Development of a high-temperature double-layer bulge test for failure prediction in gas-based hot forming of a high-strength aluminium alloy

In order to meet the continuously increasing environmental concerns, automotive lightweight concepts of replacing steels with high strength aluminium alloys are one promising solution. Therefore, complex automotive structural components manufactured with new processes like rapid gas-based hot sheet metal forming can become a key factor from a forming technology point of view. A product and process development phase, which is mainly assisted by numerical simulations, mandates knowledge of the material forming limits under the process conditions. The aim of this work is to determine the FLD of a 6xxx precipitation-hardening aluminium alloy within the solution heat treatment temperature range under gas-based hot forming process conditions. For this purpose, a hydraulic double-layered bulge test, as introduced by Banabic, is used as the basis and a high-temperature test setup as well as a characterization methodology are established. FE simulations are utilized to optimize the specimen geometries aiming at specific strain paths. Experiments are conducted with the optimized specimen geometries and the high-temperature FLD is extracted. The FLD is further used in simulations for process parameter identification for failure-free gas-based hot forming of a laboratory scale benchmark component. Experimental validations showed the reliability of the methodology and the determined FLD for failure prediction in the novel forming process.

Effect of graphene oxide wrapped functional silicon carbide on structural, surface protection, water repellent, and mechanical properties of epoxy matrix for automotive structural components

This study is aimed to develop novel nanocomposites with enhanced structural, mechanical and electrochemical properties for automotive applications. Polymeric coatings have been widely used in the automobile industry for the corrosion protection of metallic materials. The (3-aminopropyl)trimethoxysilane (APTMS) functionalized SiC was encapsulated by graphene oxide (GO) as an effective nanofiller in the epoxy matrix (EP). The protective performance of epoxy coating on mild steel in the presence of different concentrations of graphene oxide wrapped silicon carbide nanoparticles was evaluated in seawater by electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM). The optimum percentage of graphene oxide embedded SiC nanoparticles in the epoxy matrix was found to be 2.0 wt% in which the coating has the least agglomeration and appropriate corrosion resistance. The EIS measurements showed an enhanced coating resistance of EP-GO/APTMS-SiC nanocomposite (6498.17 kΏ.cm2) after 720 h immersion in seawater compared to EP-SiC (1124.95 kΏ.cm2) and plain epoxy (1.21 kΏ.cm2) coatings. It was found that the coating resistance of the EP-GO/APTMS-SiC nanocomposite coating was around 31% higher than that of the EP matrix. SECM measurements confirmed that the least dissipation of ferrous ions were observed at the crack of the EP-GO/APTMS-SiC nanocomposite coated steel specimen (1.6 I/nA) due to the improved resistance for anodic dissipation of the coated substrate. FE-SEM/EDX examined that Si was reinforced in the degradation products which formed an excellent passive layer at the coating/steel interface. The results showed that the newly developed EP-GO/APTMS-SiC nanocomposite coating possessed superior corrosion protection and enhanced hydrophobic behaviors (WCA: 131º). Therefore, it was concluded that the EP-GO/APTMS-SiC coatings on mild steel displayed superior surface protection, water repellent, and mechanical behaviors in the marine environment for long periods of exposure. Thus, EP-GO/APTMS-SiC coatings on mild steel can be used in industrial and marine applications.

Artificial Intelligence Investigation on (Al‐Si‐Fe) Alloy Reinforced with Nanoceramic Particles by RSM

Al 4043 alloy is extensively used as a filler material for welding aluminum alloys, especially when welding alloys from the Al 6000 series. It is utilized in aerospace and automotive structural components. For longer life in automotive applications, the wear resistance of Al 4043 alloy must be improved. According to research, tungsten carbide has good wear resistance. In this research, Al 4043 alloy is reinforced with varying percentages (1, 3, and 5%) of nano‐sized tungsten carbide to increase wear resistance. Taguchi L27 orthogonal array is employed for the wear analysis. The Taguchi signal‐to‐noise ratio is used to determine the optimal parameters for minimizing wear and coefficient of friction. The regression model and artificial neural network are developed to predict the experimental results. The outcomes of the regression model and artificial neural network are compared to the experimental results to demonstrate both models’ efficacy. A confirmation test was carried out for the optimal process parameter. The result shows that the minimized specific wear rate of 0.12 mm3/Nm, coefficient of friction of 0.01, and frictional force of 1.02 N are achieved at the optimal combination.

Pulse spray gas metal arc welding of advanced high strength S650MC automotive steel

With an increasing demand for safer and greener vehicles, mild steel and high strength steel are being replaced by much stronger advanced high strength steels of thinner gauges. However, the welding process of advanced high strength steels is not developed at the same pace. The performance of these welded automotive structural components depends largely on the external and internal quality of weldment. Gas metal arc welding (GMAW) is one of the most common methods used in the automotive industry to join car body parts of dissimilar high strength steels. It is also recognized for its versatility and speed. In this work, after a review of GMAW process and issues in welding of advanced high strength steels, a welding experiment is carried out with varying heat input by using spray and pulse-spray transfer GMAW method with filler wires of three different strength levels. The experiment results, including macro-microstructure, mechanical properties, and microhardness of weld samples, are investigated in detail. Very good weldability of S650MC is demonstrated through the weld joint efficiency > 90%; no crack in bending of weld joints, or fracture of tensile test sample within weld joint or heat affected zone (HAZ), or softening of the HAZ. Pulse spray is superior because of thinner HAZ width and finer microstructure on account of lower heat input. The impact of filler wire strength on weldability is insignificant. However, high strength filler wire (ER100SG) may be chosen as per standard welding practice of matching strength.

Comprehensive Enhancement in Thermomechanical Performance of Melt-Extruded PEEK Filaments by Graphene Incorporation.

A simple and scalable fabrication process of graphene nanoplatelets (GnPs)-reinforced polyether ether ketone (PEEK) filaments with enhanced mechanical and thermal performance was successfully demonstrated in this work. The developed PEEK–GnP nanocomposite filaments by a melt-extrusion process showed excellent improvement in storage modulus at 30 °C (61%), and significant enhancement in tensile strength (34%), Young’s modulus (25%), and elongation at break (37%) when GnP content of 1.0 wt.% was used for the neat PEEK. Moreover, the GnPs addition to the PEEK enhanced the thermal stability of the polymer matrix. Improvement in mechanical and thermal properties was attributed to the improved dispersion of GnP inside PEEK, which could form a stronger/robust interface through hydrogen bonding and π–π* interactions. The obtained mechanical properties were also correlated to the mechanical reinforcement models of Guth and Halpin–Tsai. The GnP layers could form agglomerates as the GnP content increases (>1 wt.%), which would decline neat PEEK’s crystallinity and serve as stress concentration sites inside the composite, leading to a deterioration of the mechanical performance. The results demonstrate that the developed PEEK–GnP nanocomposites can be used in highly demanding engineering sectors like 3D printing of aerospace and automotive parts and structural components of humanoid robots and biomedical devices.

Friction characterization and application to warm forming of a high strength 7000-series aluminum sheet

Tribological conditions are challenging when forming high strength aluminum alloys at elevated temperatures due to the sticking behavior of aluminum and potential material transfer to the die in the form of die pick-up. The current study examines the elevated temperature performance of several lubricants as well as a Physical Vapor Deposition (PVD) die coating, in conjunction with a 7000-series aluminum alloy sheet under conditions corresponding to warm forming of automotive structural components. Lubricant performance is characterized from the coupon-to-component level at temperatures in the range of 25–230°C. The classical coupon-level Twist Compression Test (TCT) is modified to perform elevated temperature experiments and used to rank the lubricants in terms of their steady-state coefficient of friction and resistance to lubricant breakdown as a function of temperature. It is found that both the friction coefficient and lubricant breakdown distance need to be considered for lubricant assessment. The studied PVD die coating is found to successfully mitigate lubricant breakdown for the FORGE EASE AL 278 at 230°C in the TCT. In parallel, warm forming experiments considering deep drawn cylindrical cups and U-channel rail sections (representative of a structural side member) are used to evaluate lubricant performance under real stamping conditions. The trends in forming performance (draw-in length, final blank perimeter, visual scoring, and forming force) confirm the lubricant ranking obtained from the TCT coupon tests, with the Teflon® PTFE film as the most effective followed by the FORGE EASE AL 278, OKS 536, and the LPS® Dry Film PTFE Spray Lubricant. For the highest test temperature, the LPS® Dry Film PTFE Spray Lubricant exhibits breakdown in the TCT at short sliding distances and results in fracture during deep drawing.