Automotive Lightweight Research Articles

LCF/TMF Model Based Approach for the Prediction of Fatigue Life of Components in Lightweight Automotive Engines

The life prediction of mechanical components in presence of Thermo-Mechanical Fatigue (TMF) is a crucial issue of the design activity. In the combustion engine, that action looks rather difficult because of a superposition of several damage phenomena. Some TMF models are currently available in the literature, but they include many parameters, whose calibration usually requires an onerous testing activity. Therefore, industry requires an assessment of those techniques, to be implemented through some simplified and reliable procedures. In this paper, the prediction of TMF life of a lightweight engine component is based on a new procedure, exploiting the isothermal Low-Cycle Fatigue (LCF) and creep tests, some theoretical approaches applied to TMF and numerical modeling. The A356 Aluminum Alloy is analyzed, as an example of strategic material used to design the new automotive lightweight engines. The calibration of TMF models based on the isothermal LCF and creep tests was found reliable. The fatigue life prediction looks compatible with some preliminary experimental results. Therefore, the proposed approach is suitable to simplify the design procedure, to decrease costs, especially related to testing, and to perform a preliminary trade-off activity of the engine layout.

A micromechanical-based finite element simulation of process-induced residual stresses in metal-CFRP-hybrid structures

Automotive lightweight design is a considerable measure to meet the worldwide need for reducing CO2 emissions. However, the lightweight potential of common materials like high strength steels or aluminium is limited. Hybrid materials allow to combine metals and CFRP in a manner to offset the drawbacks of every single material and reach an optimum of mechanical properties (Wang et al., 2016). Nonetheless, an essential shortcoming of hybrids are thermally induced residual stresses after cooling down from moulding temperature, driven by varying coefficients of thermal expansion and chemical shrinkage of the FRP.For a reliable prediction of the residual stress evolution in hybrid-structures during curing and after cooling down, a numerical homogenization technique of representative unit cells is proposed to calculate effective cure-dependent properties. Starting from a heterogeneous microstructure, a thermo-chemical-mechanical constitutive model for the curing process of the epoxy resin is presented and applied to two representative volume elements (RVE). The transition between the micro- and macro-scale is done by using a numerical homogenization framework. The effective cure-dependent properties predicted by the homogenization are used to simulate the curing-process and analyses the residual stresses of a metal-CFRP plate. The results are compared with experimental data obtained by the incremental hole drilling measurement.

A New Approach to Implement High Strength 7075 Aluminum for Automotive Application

Aluminum alloys offer high specific strength than advanced high strength steels, making them preferred candidates for automotive light weighting. Among them, AA7075 aluminum alloy offers significantly higher strength than 5xxx and 6xxx alloys and is considered an attractive candidate by automotive OEMs for structural applications such as door intrusion beams, B pillars etc. There are several challenges in implementing AA7075, such as long artificial aging time to reach peak strength, joining method and corrosion resistance. In this study, an artificial aging practice that significantly reduces aging time was explored and its influence on mechanical properties of AA7075 was investigated in comparison with conventional peak age practice. In addition, this practice offers a potential solution for joining through self-piercing riveting. Moreover, the effect of artificial aging on corrosion, specifically intergranular corrosion (IGC) and stress corrosion cracking (SCC) was evaluated. The results are discussed with in depth analysis and correlation with microstructure.

Approach for assessment of suitable automotive component ranges for the application of multi material design

Abstract Multi material design (mmd) represents the ideal compromise for the automotive lightweight design of the future with its capability of weight-reduced components at acceptable costs and practicability in large-scale production. At present, there are only limited selection strategies available for the goal-oriented identification of potential multi material areas in the vehicle. In order to develop a selection strategy for potential areas of application of the design method, the properties and conversion factors of existing components in hybrid construction methods from the automotive industry and research were investigated. In this contribution, the relevant influencing factors from component design, material selection, production and joining technology as well as cost planning are identified and their interaction is investigated. Based on a Pareto-Analysis in combination with the evaluation of a component study, significant effects could be identified regarding structural automotive components in mmd. The identified effects and their interaction are classified into a network of dependent variables. The “Network of mmd potentials” serves as a result of this contribution the basis for the development of an regression model for the indication of the feasibility of components in mmd.

Contribution analysis of the cab-in-white for lightweight optimization employing a hybrid multi-criteria decision-making method under static and dynamic performance

To improve the complexity of traditional variable screening and the optimization efficiency of automotive lightweight design, an objective evaluation and screening method is proposed, using a hybrid multi-criteria decision-making (HMCDM) method combined with contribution analysis. Multi-objective optimization design is conducted for the static and dynamic performance of the cab-in-white (CIW). An implicit parametric model of the CIW was built to define complex shapes and size variables. The HMCDM and technique for order of preference by similarity to ideal solution (TOPSIS) methods combined with regression analysis were used to determine the final optimization parameters of the CIW. Non-dominated sorting genetic algorithm-II was used to determine the optimal design parameters to improve the bending stiffness, torsion stiffness and mass of the CIW without reducing low-order natural frequencies. Compared with empirical and TOPSIS-based screening methods, HMCDM is closer to the design requirements. The CIW’s mass was reduced by 31.36 kg and performance was improved.

Thermo-mechanical and morphological characterization of needle punched non-woven banana fiber reinforced polymer composites

The purpose of this study is to employ a novel technique for the fabrication of natural fiber reinforced polymer composites that could stand toe to toe with glass fiber composites in terms of thermo-mechanical properties without any chemical treatment. The reinforcement fibers were extracted from the pseudostem of the nendran banana plant. Later a non-woven fabric composite consisting of banana fibers reinforced with unsaturated polyester (UPE) matrix was fabricated using the needle punching technique. Composite specimens were subjected to tensile, flexural, hardness, quasi-static indentation (QSI) and dynamic mechanical analysis (DMA) test for evaluating mechanical properties. However, the optimal properties was achieved at 40 wt% fiber content with an increase in tensile and flexural strength of 36% and 33% for needle-punched banana fiber composites (NPBFC) compared with random banana fiber composites (RBFC) respectively. It was also evidenced from the load bearing capacity and hardness of NPBFC having 2420 N and 87 HRRW, proves its superiority over RBFC and comparable with RGFC. Further, the viscoelastic properties of UPE and NPBFC were analyzed. Subsequently, the characteristic bonds of cellulose were represented through infra-red spectroscopy and the crystallinity index was exposed through X-ray diffraction analysis. In addition, thermal analysis was done and the stability of the optimized NPBFC witnessed was up to 260 °C. Also, morphology-properties correlation was established. Finally, the experimental results were validated using theoretical models. This study concludes that the synthesized novel NPBFC endorses its potentiality as a probable reinforcement in industrial safety helmet, automotive door panel and light weight structural applications.

A study on acoustic characteristics of automotive magnesium composite dash panel

A dash panel is a plate that separates the engine compartment from the cabin and mainly serves to block engine noise. The effect of automotive lightweight design on sound insulation performance of the dash panel needs to be studied. In this paper, the study of acoustic characteristics of automotive magnesium composite dash panel was conducted in four steps. Firstly, the sound insulation performance of a basic magnesium alloy plate was investigated using finite element method/indirect boundary element method (FEM/IBEM) and was verified with corresponding sound insulation test. The result proved that the structural-acoustic coupling based FEM/IBEM was feasible for calculating the sound insulation. Secondly, finite element models of two bare (steel and magnesium alloy) dash panels were created and the FE model of the steel dash panel was verified with a constrained modal test. The sound insulation performance of the two bare dash panels of different materials was then predicted by developing their FEM/IBEM models, and the modal contribution was examined based on the partially-coupled modal assumption. It was found that although the weight was lightened the sound insulation performance did not deteriorate, and the performance was even better in some frequency bands after replacing steel with magnesium alloy. Thirdly, the sound insulation performance of composite dash panel applied with acoustic packages was studied. It was found that the sound insulation performance deteriorated in a low frequency band (0–1000 Hz) for certain acoustic packaging materials, and it was not always true that the thicker the acoustic package, the better the sound absorbing performance. Finally, the finite element-statistical energy analysis (FE-SEA) method was used to extend the sound insulation research of the composite dash panel to the full-frequency band. The results showed that acoustic packaging design of key areas could have significant acoustic optimization effects. Relevant discussions on the results were provided and conclusions were made.

On twist springback of a curved channel with pre-strain effect

In the field of automotive lightweight manufacturing, the advanced high-strength steel (AHSS) sheet gets a pivotal position owing to a good match between the plasticity and superior strength. However, in the complex multi-step loadings, the twist springback phenomenon generated by irregular and curved stampings has arisen great concerns. In this article, the material DP500 is adopted for the twist springback analysis in a two-step loading experiment. First, the large bone-shaped specimen is deformed to 4% strain along the rolling direction. Subsequently, the forming blank, cut from the large specimen at different directions, is stamped in a die to form a 3D curved channel. Meanwhile, the simulation analysis of the two-step loading procedure is built for twist springback prediction. An advanced distortional hardening model incorporated with an attenuated modulus model is applied for exactly capturing the deformation features under mutative strain path. A deep analysis with regard to the residual stress and elastic modulus distribution is conducted to evaluate the pre-strain's influence on the twist springback of this curved part. The result shows that mutative strain path induced by the change of the pre-strain axis has a significant impact on the twist springback.

Materials for Automotive Lightweighting

Reducing the weight of automobiles is a major contributor to increased fuel economy. The baseline materials for vehicle construction, low-carbon steel and cast iron, are being replaced by materials with higher specific strength and stiffness: advanced high-strength steels, aluminum, magnesium, and polymer composites. The key challenge is to reduce the cost of manufacturing structures with these new materials. Maximizing the weight reduction requires optimized designs utilizing multimaterials in various forms. This use of mixed materials presents additional challenges in joining and preventing galvanic corrosion.

Dry and lubricated friction behaviour of thermal spray low carbon steel coatings: Effect of oxidational wear

The development of thermal spray steel coatings for Al-Si engine blocks with wear resistant cylinder bores constitutes an important aspect of automotive lightweighting strategy. In this work tribological behaviour of low carbon steel cylinder bore coatings produced by a plasma transferred wire arc (PTWA) method were studied using samples sliding against CrN coated top compression ring samples. The focus of the work was to study the role of oxidational wear on the friction behaviour of spray coatings consisting of α-Fe splats delineated by thin FeO layers. In-situ Raman spectroscopy was employed to observe the oxide transformations that occurred during dry and lubricated sliding tests conducted using a reciprocating tribometer. Lubricated sliding tests were performed within a speed range of 0.02–0.92 m/s covering the boundary and mixed lubrication conditions using a Polyol ester, POE, base oil with and without zinc dialkyldithiophosphate (ZDDP) addition. The use of ZDDP containing POE led to the generation of an amorphous carbon tribolayer incorporating ZnS and FePO4 nano-crystals that inhibited sliding-induced Fe2O3 debris formation, and consequently resulted in a reduced wear rate, but the steady-state coefficient of friction (COF) was higher during the boundary lubricated sliding. According to the Stribeck curves generated, the prevention of oxidational wear by the formation of oil residue layer delayed the transition from the boundary lubrication to the mixed lubrication regime.

Brazing filler metals

ABSTRACTBrazing is a 5000-year-old joining process which still meets advanced joining challenges today. In brazing, components are joined by heating above the melting point of a filler metal placed between them; on solidification a joint is formed. It provides unique advantages over other joining methods, including the ability to join dissimilar material combinations (including metal-ceramic joints), with limited microstructural evolution; producing joints of relatively high strength which are often electrically and thermally conductive. Current interest in brazing is widespread with filler metal development key to enabling a range of future technologies including; fusion energy, Solid Oxide Fuel Cells and nanoelectronics, whilst also assisting the advancement of established fields, such as automotive lightweighting, by tackling the challenges associated with joining aluminium to steels. This review discusses the theory and practice of brazing, with particular reference to filler metals, and covers progress in, and opportunities for, advanced filler metal development.

Tortuosity but Not Percolation: Design of Exfoliated Graphite Nanocomposite Coatings for Extended Corrosion Protection of Aluminum Alloys

Increased adoption of engineered aluminum alloys in vehicular components is imperative for automotive lightweighting, but such alloys are oftentimes prone to degradation upon exposure to corrosive ...

Technical and environmental evaluation of a new high performance material based on magnesium alloy reinforced with submicrometre-sized TiC particles to develop automotive lightweight components and make transport sector more sustainable

This study evaluated the use of submicrometre-sized particles based on titanium carbide from both technical and environmental points of view. The objective was to improve the mechanical properties of the magnesium alloy intended for use in the automotive component industry. To this end, an Al/TiC master compound containing 60wt.% of TiC was produced through a self-propagating, high-temperature synthesis process and embedded in a magnesium alloy by a mechanical stirring method. The life cycle assessment methodology was then used to evaluate the environmental impact of the manufacturing of the magnesium alloy reinforced with submicrometre-sized particles. X-ray diffraction and scanning electron microscopy techniques revealed the nature and purity of the TiC present in the material and revealed particle sizes below submicrometre range (300–500nm). The incorporation of TiC particles into the magnesium alloy resulted in improvements in yield stress and ultimate tensile strength of more than 10% and 18%, respectively, and increases in ductility values by 30%. Finally, the results indicated that the submicrometre particle production had a low environmental impact compared with the total impact associated with manufacturing the magnesium alloy reinforced with submicrometre-sized particles; the greatest environmental burden was attributed to the magnesium production stage. However, this impact is offset in the use phase of the vehicle, providing approximately 28,000km of mileage for a car.

Application of Tailor Rolled Blank in A-pillar stiffener of a certain automotive body

Tailor Rolled Blank(TRB) can be used for manufacturing A-pillar stiffener in an automotive body in order to achieve the goal of automotive lightweight on the premise of meeting requirements of strength and rigidity. In this paper, forming and springback simulations of A-pillar stiffener made of TRB were carried out. Aiming at springback and thickness transition zone(TTZ) movement defects, annealing and rib were adopted in order to lower springback and TTZ movement. Research findings show that after annealing is adopted, TTZ movement increases slightly, and meanwhile rib can diminish TTZ movement. Rib and annealing can lower springback of TRB A-pillar stiffener, especially springback on the thinner side, and springback of the whole TRB part becomes uniform.

Deep drawing of fiber metal laminates for automotive lightweight structures

Current challenges in the automotive industry are the reduction of fuel consumption and the CO2 emissions of future car generations. These aims can be achieved by reducing the weight of the car, which further improves the driving dynamics. In most currently mass-produced cars, the body accounts for one of the largest parts by weight, and hence designing a lightweight car body assumes great importance for reducing fuel consumption and CO2 emissions. Extremely lightweight designs can be achieved by using purely composite materials, which are very light but also highly cost intensive and not yet suitable for large scale production due to the necessity of manual processing. A promising approach for the automated, large-scale production of lightweight car structures with a high stiffness to weight ratio is the combination of high strength steel alloys and CFRP prepregs in a special hybrid material/fiber metal laminate (FML) – which can be further processed by forming technologies such as deep drawing. In current research work at the Chair of Forming and Machining Technology (LUF) at the University of Paderborn, innovative manufacturing processes are being developed for the production of high strength automotive structural components made of fiber metal laminates. This paper presents the results of technological and numerical research that is currently being performed at the LUF into the forming of hybrid fiber metal laminates. This paper focuses on the results of basic research and the individual measures (tool, process and material design) necessary for achieving the desired part quality.

Reply to Kim et al. (2019): Commentary on “Correction to: On the Calculation of fuel savings through lightweight design in automotive life cycle Assessments” by Koffler and Rohde-Brandenburger (2018)

In addition, the reply contains several arguments that speak against the allocation of engine friction losses in the context of automotive lightweighting. In conclusion, the authors cannot follow Kim et al's proposed solution and maintain their recommendation to follow the approach published in their 2010 methodology paper to assess the fuel savings due to automotive lightweighting for internal combustion engine (ICE) vehicles.

Design and Properties of 1000 MPa Strength Level Hot-Formed Steels Possessing Dual-Phase and Complex-Phase Microstructures

In cold forming for automotive lightweight design, advanced high strength steels (AHSS) lead to limited formability, high springback and press forces, low stretch flangeability, multiple operations for complex geometries and large scrap rates. Two sets of AHSS, namely ferritic-martensitic dual-phase (DP) steel and martensitic-bainitic complex-phase (CP) steel with some amounts of retained austenite (RA), were designed for the hot-forming route, which eliminates the above drawbacks and guarantees higher performance in the body-in-white (BIW). Design of four DP and four CP alloys was accomplished using JMatPro6.0 thermodynamic software and available literature. The alloys were manufactured in the laboratory in cold-rolled gauge of ~1.5 mm and subjected to hot-forming cycles including hot deformation (up to 20% strain), using a dilatometer and a Gleeble 3800 machine. The thermal cycles of the DP alloys included an intercritical reheating whereas in-situ austempering or slow continuous cooling followed by supercritical reheating was used for the CP alloys. The results showed that yield strength (YS) of 605MPa & 695MPa, ultimate tensile strength (UTS) of 1097MPa & 1242MPa with a total elongation (TE) of 12.6% & 14.1% can be achieved in the best performing DP alloys with a martensite content of 65% & 60 vol.%. The best CP alloys with austempering achieved YS of 673MPa & 699MPa, UTS of 983MPa & 1026MPa and TE of 9.2% & 13.6% with RA of 4%-12 vol.%. The continuously-cooled alloys achieved even better properties. Higher bendability at 1.0 mm gauge in the critical direction was achieved in the CP alloys (90o&107o) than in the DP alloys (73o&76o).

Mechanical Bending Property of Ultra-High Strength Steel Sheets IN Roll Forming Process

Ultra-high strength steel (UHSS) plays an important role in the automotive lightweight industry owing to its insubstantial weight and high specific strength. Roll forming is one of the effective forming processes for UHSS in the steel industry. In this study, the minimum bending radius is determined by roll forming experiments, taking into account the 1200MPa level of the V-profiled parts of UHSS. The ductile fracture criterion (DFC), which considers both the “tensile ductile fracture” and “shear ductile fracture,” is applied to predict the fracture of sheets in the roll forming process, where bending is the main deformation mode. A set of rolls is designed to investigate the fracture behavior in the roll forming process. In addition, finite element models (FEMs) are built and four sets of experiments are conducted to calibrate the fracture of the V-profiled parts for R/T = 1, 2, 3, and 4. Furthermore, the fracture time and fracture location of the V-profiled parts for R/T = 1 and 2 are predicted and the prediction results agree with the experimental results.

Influence of cathodic dip painting on the mechanical strength of material-adapted composite/metal joints

The flow drill joining concept (FDJ) allows the load adjusted joining of continuous fiber reinforced thermoplastics (FRTP) and metallic sheets without auxiliary joining elements. As there is no scathe done to the fiber reinforcement, a radial realignment of the fibers leads to high-strength joints with high lightweight potential. In terms of their use in automotive lightweight construction, an important requirement for joining technologies is the resistance to temperature loads and chemicals, applied in the production processes, e.g., in vehicle lacquering. Therefore, force flux aligned FDJ-joints were investigated in cross tension and shear testings, after passing through a serial cathodic dip painting (CDP) process. The results show that the CDP-treatment does not adversely affect the quasi-static properties of the tested FDJ-joints, as they resist shear loads up to 2900 N and cross tension loads of about 1100 N, both, before and after the lacquering process.

Non-Isothermal Crystallization Kinetics of Short Glass Fiber Reinforced Poly (Ether Ether Ketone) Composites.

Due to its excellent chemical and temperature resistances, short glass fiber reinforced poly (ether ether ketone) composite (SGF/PEEK) is a promising material for application in automotive lightweight. Processing conditions, such as cooling rate, need to be well controlled to obtain the optimal crystallite morphology of PEEK composites. Thus, in this paper, the non-isothermal crystallization kinetics and melting behavior of SGF/PEEK were investigated by differential scanning calorimetry (DSC) at different cooling rates, and the crystallite sizes were evaluated by the X-ray diffraction technique (XRD). Crystallization kinetics models and effective activation energies were evaluated to determine the crystallization parameters of the composites. The results suggest that a lower cooling rate enlarges the size of crystallites and enhances the uniformity of size distribution. The addition of glass fibers improves the nucleation rate owing to heterogeneous nucleation while decreasing the growth rate due to retarded movement of the polymer chain. The combined Avrami-Ozawa equation was shown to describe accurately the non-isothermal crystallization. The absolute value of the crystallization activation energy for SGF/PEEK is lower than that of pure PEEK.