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Technical Paper

Trend toward weight reduction of automobile body in Japan

With society demanding automobiles that provide higher fuel efficiency, safety of occupants in collisions and that at the end of their service life can be recycled with low environmental impact, the steel industry is tackling the needs of the automobile industry by developing ever-higher performance steel materials and simulation technologies that can demonstrate the performance of steel materials at the development stage without the need for costly prototype testing. In this paper, weight reduction of automobile body in Japan will be discussed. The main items will be as follows: (1) Development of Automobile Steel Sheets, (2) Materials for Automobile Bodies, (3) Materials and Technologies (Tailored Blanks, Hydroforming and Locally Quenching) for Reducing the Weight of Panels and Reinforcing members, (4) Future Prospects.
Technical Paper

Time-domain Transfer Path Analysis for Transient Phenomena Applied to Tip-in/Tip-out (Shock & Jerk)

Tip-in/Tip-out of the accelerator pedal generates transient torque oscillations in the driveline. These oscillations may be amplified by P/T, suspension and body modes and will eventually be sensible at the receiver side in the vehicle, for example at the seat or at the steering-wheel. The forces that are active during this transient excitation are influenced by non-linear effects in both the suspension and the power train mounts. In order to understand the contribution of each of these forces to the total interior target response (e.g. seat rail vibration) a detailed investigation is performed. Traditional force identification methods are not suitable for low-frequent, transient phenomena like tip-in/tip-out. Mount stiffness method can not be used because of non-linear effects in the P/T and suspension mounts. Application of matrix inversion method based on trimmed body vibration transfer functions is not possible due to numerical condition problems.
Technical Paper

Perforation Corrosion of Automobiles - Field Car and Laboratory Investigation

In order to clarify the effect of design and materials of the hem as well as the climatic factors on perforation corrosion of the automobile doors, field car and laboratory investigation has been carried out Field car investigation revealed that corrosion of the hem can be minimized by using two side galvanized steel plus adhesives. The ratio of wet/dry environment was evaluated in laboratory on hemmed sample, and it was found that the design of the hem in conjunction with the various wet/dry ratio affected the corrosion rate differently.
Technical Paper

1D Modeling of Thermal Expansion Valve for the Assessment of Refrigerant-Induced Noise

Without engine noise, the cabin of an electric vehicle is quiet, but on the other hand, it becomes easy to perceive refrigerant-induced noise in the automotive air-conditioning (A/C) system. When determining the A/C system at the design stage, it is crucial to verify whether refrigerant-induced noise occurs in the system or not before the real A/C systems are made. If refrigerant-induced noise almost never occurs during the design stage, it is difficult to evaluate by vehicle testing at the development stage. This paper presents a 1D modeling methodology for the assessment of refrigerant-induced noise such as self-excitation noise generated by pressure pulsation through the thermal expansion valve (TXV). The GT-SUITE commercial code was used to develop a refrigerant cycle model consisting of a compressor, condenser, evaporator, TXV and the connecting pipe network.
Technical Paper

Direct Simulation for Aerodynamic Noise from Vehicle Parts

Flows around a forward facing step and a fence are simulated on structured grid to estimate aerodynamic noise by using direct simulation. Calculated results of sound pressure level show quantitatively good agreement with experimental results. To estimate aerodynamic noise from 3D complex geometry, a simplified side mirror model is also calculated. Averaged pressure distribution on the mirror surface as well as pressure fluctuations on the mirror surface and ground are simulated properly. However, calculated result of sound pressure level at a location is about 20dB higher than experiment due to insufficient spatial resolution. To capture the propagation of sound waves, more accuracy seems to be required.
Technical Paper

Vibro-acoustic FEA Modeling of Two Layer Trim Systems

This paper investigates the potential of using FEA poro-elastic Biot elements for the modeling carpet-like trim systems in a simplified setup. A comparison between FEA computations and experiments is presented for two layer (mass-spring) trim systems placed on a test-rig consisting in a 510×354×1.6 mm flat steel plate clamped in a stiff frame excited at its base. Results are presented for a given heavy layer with two different poro-elastic materials: one foam and one fibrous material. The investigations included accelerometer measurements on the steel plate, laser-doppler vibrometer scans of the heavy layer surface, sound pressure measurements in free field at a distance of 1 meter above the plate, as well as sound pressure in a closed rectangular concrete-walled cavity (0.5×0.6×0.7 m) put on top of the test-rig. Computations were carried out using a commercial FEA software implementing the Biot theory for poro-elastic media.
Technical Paper

Application of Vibration Damping Steel Sheet for Autobody Structural Parts

As a demand for vehicles of higher functionality grows, automakers and material suppliers are devoting increasing efforts to develop technologies for greater safety, lighter weight, higher corrosion resistance, and enhanced quietness. The resin-sandwiched vibration damping steel sheet (VDSS), developed as a highly functional material for reducing vehicle vibration and noise, has been used for oil pans1) and compartment partitions2). First applied for a structural dash panel of the new Mazda 929, a Zn-Ni electroplated VDSS which allows direct electric welding has contributed to greater weight reduction as well as improved quietness.
Technical Paper

Study of Formable High Strength Steel Sheets for Automotive Panels

Weight reduction of automobiles is one of the most highlighted subjects in automobile industry from the energy saving and clean environment points of view. A typical approach for the purpose is to use high strength steel sheets as well as optimizing designs and using low density materials. It is not, however, easy to apply high strength steel sheets to automotive panels because of their strict requirement for the shape-fixability although a high dent resistance is also required. Besides the use of bake hardening steels, two different high strength steel sheets, which are a continuously annealed extra-low carbon titanium-added IF steel and a low carbon TRIP steel which contains about six volume% of austenite, were assessed for the application to automotive panels in combination with a tension-controled press-forming technique and showed as good shape-fixability as a conventional box-annealed aluminum-killed DDQ steel sheet when high blank-holding-forces were applied.
Technical Paper

Properties of a Newly Developed Organic Composite Coated Steel Sheet for Automotive Use

The newly developed sheet steel lightly coated with an organic composite is as follows. Zn-Ni alloy plated sheet steel with a coating weight of 30 g/m2 and average Ni concentration of 11.5 ∼12.0 % is chromated through electrolysis. The coating weight of chromate film is 50 ∼90 mg/m2 in Cr. Furthermore, emulsified olefin-acrylic acid copolymer resin mixed with colloidal silica of particle size 7 ∼8 nm applied to a thickness of 1.0 ∼1.8 μm. Olefin-acrylic acid copolymer resin and colloidal silica are mixed at the rate of 100 and 30 (parts by weight). It maintains excellent corrosion resistance even after forming, C-ED paint corrosion resistance and paint adhesion. Furthermore, it has excellent perforation resistance. The product has excellent weldability and is well suited to continuous forming, too.
Technical Paper

The Development of Vibration Damping Steel Sheet For Automotive Use

Vibration Damping Steel Sheet (VDSS) for automotive use, which has a three layer structure of steel/viscoelastic resin/steel, has been studied. For automotive body panels, VDSS is required to have not only high vibration damping capability but also other properties such as bonding strength, formability, weldability and durability. In this research, the effect of resin layer on these properties was studied. It is found that VDSS which satisfies these properties can be made from thermosetting resin involving metal particles.
Technical Paper

Predictive Calculation of Idling Rattle in Manual Transmissions -Based on Experimental Measurements of Gear Vibration Occurring in Backlashes-

It is generally known that the idling rattle in manual transmissions is caused by gear tooth portions that make repeated impact-generating vibrations in the backlashes. These vibrations result from rotational fluctuations of the flywheel induced by combustion in the engine. In the study reported here, the authors constructed an experimental setup using rotary encoders and a transient torsional angle converter that allowed the long-awaited direct measurement of impact-generating vibrations in the backlashes. Using this experimental result, the following ideas that the authors must pay attention for the numerical simulation are obtained. That is, transmission drag torque is to be input and treated as the offset value in the torque value of the torsional characteristics in the clutch disc, and coefficients of attenuation have great influence upon the calculation result.
Technical Paper

Theoretical Analysis and Proposition to Reduce Self-Excited Vibration of Automotive Shock Absorber

Knock noise induced by automotive shock absorbers has serious influence on driving comfort and vehicle quality. Some research focusing on knock noise had been introduced in the past. However there is the unidentified phenomenon that has been unnoticed. This paper describes the new theory to clarify one of the unidentified phenomenon and proposes the equation for stability assessment which is useful on designing stage of development. First of all, the characteristics of the unidentified rod vibration of shock absorbers are investigated experimentally. Second, the new theory is established on the basis of the non-linear physical model with friction forces between piston and cylinder. This theory shows that the unstable vibration, so called the Self Excited Vibration, can be induced by not only friction property but also structure of rod and piston. Third, the equation for stability assessment, which is useful on designing stage of development, is proposed on the basis of new theory.
Technical Paper

High-Strength Cold-Rolled Steels Produced by Continuous Annealing and Their Automotive Applications

In continuous annealing, accelerated cooling methods have recently found practical application in addition to conventional gas jet cooling or water jet quenching method. Moderate cooling rate of gas jet cooling or accelerated cooling makes it possible to utilize new high-strength steels with excellent properties. The faster cooling rate deteriorates ductility of steels. These newly developed steels are improved rephosphorized steels with high r̄-value and high bake hardenability, dual phase steels with superior ductility, Ti-stabilized high-strength steels with very high r̄-value, grain boundary hardening steels employing low temperature annealing, and unique ultra high-strength steels. This paper describes properties and process factors of these steels, and their applications to automotive.
Technical Paper

Effect of Strengthening Mechanism on Fatigue Properties of Hot-Rolled Sheet Steels

The influence of tensile strength on fatigue strength and the effect of strengthening mechanism on fatigue notch factor were investigated into conventional mild steels, HSLA steels, DP steels and TRIP steels. The grade of studied steels was altered from 440MPa to 780MPa. Not only smooth fatigue specimens with side surface ground and smooth fatigue specimens with laser-cut side surface but also fatigue specimens with a pierced hole were prepared for each of steel sheets. Fatigue tests were conducted in an axial load method. These experiments made it clear that the fatigue limits of smooth specimen increase along the tensile strength approximately independent of strengthening mechanism but those of notched specimen do not necessarily increase along the tensile strength. Namely, fatigue limits of DP steels and TRIP steels with notch increase in proportion to tensile strength although those of HSLA steels with notch do not increase.
Technical Paper

Comparison between Experiments and FEM Simulation of High Velocity Tensile Test Methods to Clarify Test Method's Influence of High Strength Steel

In order to examine the compatibility of improvement of crashworthiness with weight-saving of automobiles by using high strength steel, a combination analysis of Finite Element Method and Dynamic Mechanical Properties has been established. The material properties used in this analysis have been measured by “one bar method” high velocity tensile tests, which can examine the deformation behaviour of materials at an actual crash speed range (∼55km/h). As for the accuracy of this system, comparison between experiments and FEM simulation both of this test machine and other high-velocity-tensile-test machines have clarified the feature of one bar method and the metallurgical features of high velocity deformation. It was confirmed that the stress-strain curve measured by the one bar method agreed with that measured by the modified Split Hopkinson pressure bar method.
Technical Paper

Forming Performance of Aluminum Alloy Sheets for Automobile Body Panels

Improvement of material characteristic values, adjustment of forming conditions as well as introduction of new forming technics are necessary to promote wide application of aluminum alloy sheets into automotive parts. 5000 series and 6000 series aluminum alloy sheets are concerned about the relationship between material characteristic values and fundamental forming ability required to apply them to automobile body parts as well as the effect of lubricant on their formability. The hardening parameters, n values, of them are larger than those of cold-rolled steel sheets. However, the r values and the local elongations are extremely small. The improvement of stretch formability owing to increase of n value is smaller than that of the steel sheets. Inferior deep drawability of the aluminum alloy sheets is due to low fracture resistance force caused by low r value.
Technical Paper

Development of High Strength Steel Sheet with Excellent Stretch Flange Formability for Automobile Application

With the aim of improving stretch-flange formability by further reducing carbides in steel, the authors studied the hole expansion ratio of a steel consisting entirely of ferrite and the factors governing the hole expansion ratio. Ultra low carbon steels adding Ti and/or Nb showed a higher hole expansion ratio than conventional steels, but their hole expansion ratio was not higher than the hole expansion ratio of bainitic steel reported before1). On the other hand, it was found from study of the relationship between hole expansion ratio and r-value of various steels, including cold-rolled interstitial-free steels, that the hole expansion ratio of a steel consisting only of the ferrite phase is strongly influenced by the minimum r-value and n-value and that it improves as the r- and n-values increase. The steel added Ti and/or Nb has a strong anisotropy of r-value, hence its minimum r-value is small. This is disadvantageous to hole expansion ratio.
Technical Paper

Strengthening of Surface Induction Hardened Parts for Automotive Shafts Subject to Torsional Load

The purpose of this study is twofold: to clarify the factors governing the torsional strength of surface induction hardened parts and, to present a method for strengthening automotive shaft parts for their weight reduction. The torsional strength against Mode III fracture can be expresssed by a new indicator, “equivalent hardness” defined as an average hardness weighted with the radius squared. If the equivalent hardness is continuously increased, the fracture mode change from Mode III to Mode I. The torsional strength against Mode I fracture is governed by grain boundary strength. Accordingly, the key-points in increasing the torsional strength of surface induction hardened parts are to raise the equivalent hardness and increase the grain boundary strength of the steel. By application of this method, the torsional strength of steel can be raised by 50%, which, in turn, enables about a 25% weight reduction for shaft parts.
Technical Paper

Extremely Formable Cold Rolled Sheet Steel with Ultra-High Lankford and n Values - Metallurgy and Formabilities

Extremely formable cold sheet steel with an ultra-high Lankford value of more than 2.5 and an n value of more than 0.27 has been developed. This steel is obtained due to the following factors; using extremely pure IF (Interstitial free) steel, immediate rapid cooling upon completion of rolling in the hot rolling process, a high reduction in the cold rolling process, and a high soaking temperature in the continuous annealing process. This steel sheet shows excellent deep drawability and stretch formability compared with conventional steel sheet (former IF steel and low carbon aluminum-killed steel) as a result of evaluating the limiting drawing ratio and limiting dome height, respectively. This excellent formability is also shown by the model forming tests for simulating the actual stamping of an oilpan and a side-panel. Furthermore, this steel shows the same spot-weldability as that of former IF steel, and zinc phosphatability similar to that of low carbon aluminum-killed steel.
Technical Paper

Recent Developments in Press Formability of Aluminum Alloy Sheets for Automotive Panels

Aluminum alloy sheets are used for automotive body-panels, but their small Young's modulus results in inferior shape-fixability than conventionally-applied steel sheets with similar strengths. Smaller radius of curvature, indicating better shape-fixability, is found at the center of a panel press-formed with higher blank holder force (BHF). Higher force can be applied for press-forming of alloy sheets with larger strain-hardening exponent (n value) induced by an increased addition of Mg. Recently-developed 5000 series alloy sheets containing 5.5 pct Mg and 0.3 pct Cu have an elongation over 33 pct at an ultimate tensile strength of 270 MPa and can be press-formed with better shape-fixability.