Search Results

Fatigue behavior of aluminum alloys under multiaxial loading was investigated with both cast aluminum A356-T6 and wrought alloy 6063-T6. The dominant multiaxial fatigue crack preferentially nucleates from flaws like porosity and oxide films located near the free surface of the material. In the absence of the flaws, the cracking/debonding of the second phase particles dominates the crack initiation and propagation. The number of cracked/debonded particles increases with the number of cycles, but the damage rate depends on loading paths. Among various loading paths studied, the circle loading path shows the shortest fatigue life due to the development of complex dislocation substructures and severe stress concentration near grain/cell boundaries and second phase particles.

Crashworthiness is one of the most important performances of vehicles, and the front rails are the main crash energy absorption parts during the frontal crashing process. In this paper, the front rail was simplified to a thin-walled beam with a cross section of single-hat which was made of steel and aluminum. And the two boards of it were connected by riveting without rivets. In order to optimize its crashworthiness, the thickness (t), radius (R) and the rivet spacing (d) were selected as three design variables, and its specific energy absorption was the objective while the average impact force was the constraint. Considering the error of manufacturing and measurements, the parameters σs and Et of the steel were selected as the uncertainty variables to improve the design reliability. The algorithm IP-GA and the approximate model-RBF (Radial Basis Function) were applied in this nonlinear uncertainty optimization.

The work-hardening response of TRIP780 steel subjected to strain-path changes was investigated using two-stage tension experiments. Large specimens were prestrained and then sub-sized samples were subjected to tension along various directions. The influence of strain-path changes on flow stress and work hardening performance was discussed in detail. The specific plastic work was calculated to compare the kinematic hardening behaviour after strain-path changes. The results showed that transient hardening was observed for TRIP780 sheets subjected to orthogonal strain-path change. The strain-hardening exponent (n-value) was influenced by prestraining levels and the strain path. The n-value exhibited a greater decrease under an orthogonal strain-path change. Prestraining can delay the onset of high work hardenability of TRIP steels. It is meaningful for the safety design of vehicles.

Hot forming process of ultrahigh strength boron steel 22MnB5 is widely applied in vehicle industry. It is one of the most effective approaches for vehicle light weighting. Dynamic recovery is the major softening mechanism of the boron steel under austenite state at elevated temperatures. Deformation mechanism of the boron steel can be revealed by investigation on the behavior of dynamic recovery, which could also improve the accuracy of forming simulations for hot stamping. Uniaxial tensile experiments of the boron steel are carried out on the thermo-mechanical simulator Gleeble3800 at elevated temperatures. The true stress-strain curves and the relations between the work hardening rate and flow stress are obtained in different deformation conditions. The work hardening rate decreases linearly with increasing the flow stress.

The price of fossil fuels and the increasing inexorable energy crisis have become vital issues for everyone. Tongji University EconoPower Racing Team was established to participate in the “Honda EconoPower Cup” annually. Every contestant in the competition must finish a certain distance in the fixed time, with the gasoline supplied by the committee. After that the committee will measure the fuel consumption of every team and calculate the distance per liter fuel (the farther the better) to determine the champion. In order to enhance the EP vehicle's achievement we've made some improvements, such as framework, body, engine's optimization and so on. In this passage we mainly state some details of our research approaches in framework, steering, transmission, shape and driving strategy. The main technologies were: friction reduction, lightweight, enhancement of power train efficiency, tire selection and driving strategy.

The effects of biodiesel on the swelling of the elastomers and plastics and the corrosion of metals are studied by the immersion tests. The results indicate that biodiesels make little corrosion effect on aluminum, steel and little swelling impact on plastics, but a significant corrosion may be taken place on cooper and brass for some sourced biodiesels. For nitrile-butadiene rubber, the variation of swelling properties in biodiesels is slightly higher than that in diesel. For the non-diesel-resistant elatomers, the variation of swelling properties is lower than those in diesel. The production process and biodiesel source have an influence on the result of elastomer swelling and corrosion. The relationship between the impact of biodiesel on materials and biodiesels properties are also discussed.

Carbon Fiber Reinforced Plastic (CFRP) tube is an important material for the lightweight design of automotive structures. Simulation method of CFRP thin-walled tubes subjected to axial compression using MAT54 in LS-DYNA was investigated. Based on the two-layer shell model combined with MAT54, failure strategy and the parameters sensitivity of the model were discussed in detail. Then the simulation model was verified by using duplicate specimens comprised of carbon fiber/epoxy unidirectional prepreg tape. Furthermore, the modeling methods of crush trigger and different types of loading speed were analyzed. In addition, based on the method of equal energy absorption, energy absorption performance of thin-walled circular and square tubes made from four materials including mild steel, high strength steel, aluminum alloy and CFRP were also compared.

Recent toxicological and epidemiologic studies have shown that diesel emissions have been a significant toxic air contaminant. Catalyzed DPF (CDPF) not only significantly reduces the PM mass emissions (>90%), but also further promotes carrier self-regeneration and oxidize more harmful gaseous pollutants by the catalyst coated on the carrier. However, some ultrafine particles and potentially harmful gaseous pollutants, such as VOCs species, originally emitted in the vapor-phase at high plume temperature, may penetrate through the CDPF filter. Furthermore, the components and content of catalyst coated on the CDPF could influence the physicochemical properties and toxicity intensity of those escaping ultrafine particles and gaseous pollutants. In this work, (1) we investigated the influence of precious metal content as a variable parameter on the physicochemical properties and catalytic activities of the small CDPF samples.

The maximum equivalent plastic strain (EPSmax), which can be achieved in the gauge region of a cruciform specimen during in-plane biaxial tensile tests, is limited due to early fracture on the cruciform specimen arm. In this paper, a theoretical model was proposed to determine the factors related to the EPSmax of a cruciform specimen following ISO 16842: 2014. Biaxial tensile tests were carried out to verify the theoretical analyses. Results show that the material strength coefficient (k) has no effect on the EPSmax, and EPSmax increases with the increase of the material hardening exponent (n) and the cross-sectional-area ratio (c) of the arm region to the gauge region. It is found that the applied load ratio (α) has an effect on EPSmax, which decreases as the load ratio increases from 0:1 (i.e. uniaxial tension) to 1:2 (i.e. plane strain state) and then increases as the load ratio increases to 1:1 (i.e. balanced biaxial tension).

For a practical pad design, a magnetic shielding layer is imperative which is made of ferrite, aluminum or some other metallic material. However, once the magnetic shielding layer is added, not only the mutual inductance but also the self-inductance of the coupling coils vary with the lateral misalignment which is inevitable for a human driver. The change of self-inductance will also result in the mistuning problem in the resonant circuit, which can significantly reduce the transmission efficiency of the whole wireless power transfer (WPT) system. This paper proposed a method of parameter identification of self-inductance based on the least square in order to solve the mistuning problem. In order to verify the proposed method, both the simulation model and the experiment set-up are built.

This study investigated the plastic deformation behavior of 304 stainless steel thin-walled tubes under axial compression by means of numerical calculation and theoretical analysis. It was found that the plastic deformation length of thin-walled tube determined the formability of folds and the work done in the whole axial compression process. To reveal the relation between the range of plastic deformation length and tube geometry parameters, regression equations were established using the quadratic regression orthogonal design method. Experiments were conducted to validate the equations. The process windows for forming a single fold and tube joining at ends had been printed ultimately. The results showed that the regression equations can accurately predict the range of plastic deformation length for forming a single fold.

With the degradation of lithium-ion batteries, the battery safety performance changes, which further influences the safe working window. In this paper, the pouch ternary lithium-ion battery whose rated capacity is 4.2 Ah is used as the research object to investigate the impact of the high-temperature calendar and cyclic aging on tolerance performance. The overcharge-to-thermal-runaway test is performed on the fresh cell and aged cell (90% SOH). The inflection point of voltage for aged cells appears earlier than that of the fresh cell, while the voltage corresponding to the inflection point is the same for them, which means that the voltage at which lithium plating occurs is the same. However, the voltage plateau and the crest voltage before thermal runaway of aged cell are significantly higher than that of the fresh cell. Besides, ohmic heat, reversible heat, and side reaction heat make contribution to the thermal runaway triggering.

Carbon fiber reinforced plastic (CFRP) composite materials have gained particular interests due to their high specific modulus, high strength, lightweight and perfect corrosion resistance. However, in reality, CFRP composite materials cannot be used alone in some critical places such as positions of joints with hinges, locks. Therefore, metal reinforcements are usually necessary in local positions to prevent structure damage. Besides, if uncertainties present, obtained optimal structures may experience in failures as the optimization usually pushes solutions to the boundaries of constraints and has no room for tolerance and uncertainties, so robust optimization should be considered to accommodate the uncertainties in practice. This paper proposes a mixed topology method to optimize metal and carbon fiber reinforced plastic composite materials simultaneously under nondeterministic load with random magnitude and direction.

The influence of heat flow and cooling water characteristics on motor temperature cannot be accurately reflected by the traditional motor temperature analysis method. In order to study the motor and its key components’ temperature characteristics under different temperatures and flow rates of cooling water, this paper establishes the lumped parameter transient thermal model which includes cooling water module, based on a 50kW permanent magnet synchronous motor. The transient and steady temperature is calculated through this model together with the motor loss calculation module in the electric drive system model. The influence of different temperature and flow rate of cooling water on motor and its key components’ temperature characteristics is compared. During the modeling process, the motor body is divided into 14 parts, based on the internal heat flow path of the motor. The thermal resistance of each key component and cooling water is calculated.

To overcome some drawbacks of using AHSS (Advanced High Strength Steel) in vehicle weight reduction, like brittleness, spot weld HAZ (Heat Affected Zone) softening and high cost, a new ridgeline strengthening technology was introduced and applied to the thin-walled structure in this paper. The energy absorption mechanism of thin-walled box structure with selective strengthened ridgelines under axial compressing load was discussed in first section. After this, the formulas of mean crushing force and corresponding energy absorption for square tube were theoretically discussed. To demonstrate prediction capabilities of formulas, a set of FE simulations of square tubes were conducted. Simulation results show that energy absorption capacity of square tube under quasi-static axial crushing load is dramatically improved by selectively strengthening their ridgelines.

To overcome some drawbacks of using UHSS (Ultra High Strength Steel) in vehicle weight reduction, like spot weld HAZ (Heat Affected Zone) softening, hard machining and brittleness, a new solution of ultra-high stress strengthening was proposed and applied to the ridgelines of thin-walled structures in this paper. Firstly, stress distribution characteristics, the laws of stress variation and the compressed plate buckling process of the rectangular thin-walled beam under compressive and bending load were analyzed in elastic plastic stage by theory and Finite Element (FE) simulation. Secondly, based on elastic plastic buckling theory of the compressed plate and stress distribution similarity of the buckling process of the thin-walled box structure, three factors influencing the ultimate resistance enhancement of thin-walled hat section beam were found, and the rationality and accuracy of cross section ultimate resistance prediction formulas were also verified by FE simulation.

The yield locus of a cold-rolled transformation-induced plasticity (TRIP780) steel sheet was investigated using a biaxial tensile test on a cruciform specimen. The effect of the key dimensions of the cruciform specimen on the calculation error and stress inhomogeneity was analyzed in detail using an orthogonal test combined with a finite element analysis. Scanning electron metallography (SEM) observations of the TRIP780 steel were performed. The yield curve of the TRIP780 steel was also calculated using the Von Mises, Hill '48, Hill '93, Barlat '89, Gotoh and Hosford yield criteria. The experimental results indicate that none of the selected yield criteria completely agree with the experimental curve. The Hill '48 and Hosford yield criteria have the largest error while the Hill '93 and Gotoh yield criteria have the smallest error.

The vehicle permanent magnet synchronous motor has the advantages of high power density, compact structure and small size, which makes it generate heat obviously in the process of energy conversion, which seriously affects the service life of the motor and the performance of permanent magnet. Predicting magnet temperature is a challenging task, in lab and various specialized applications, infrared sensors or thermocouples are used to measure the temperature, but it cost a lot. In order to predict the temperature field of the motor, the hysteresis characteristic test of the core material of the motor is carried out in this paper. The hysteresis characteristic and loss of electrical steel under different temperature, magnetic field intensity and magnetic field frequency are tested. It is found that the loss of electrical steel increases with the increase of magnetic induction intensity and magnetic field frequency.

In order to research the effect of process parameters (laser power, welding speed, wire-feed speed, spot diameter) on mechanical properties of Zn-coated Steel Laser Brazing Lap Joint for vehicle, the influence of welding parameters on energy input of brazing seam cross section was theoretically analyzed, and then a great number of laser brazing experiments of 0.7mm galvanized steel was carried out. After that, the tensile strength and micro-hardness tests were also done for well-formed joints of galvanized steel formed in the laser brazing. The results show that joints with good mechanical properties and surface morphology can be formed when laser power is in the range of 2500-3200W and the other parameters keep in a specified range. Joint performance significantly reduces when the value of wire-feed speed exceeds 3.0m/min for that a wider brazing seam cross section can’t be formed.

The catalyzed diesel particulate filter with Pt and Pd noble metals as the main loaded active components are widely used in the field of automobile engines, but the high cost makes it face huge challenges. Rare earth element doping can improve the soot oxidation performance of the catalyzed diesel particulate filter and provide a new way to reduce its cost. In this paper, thermogravimetric tests and chemical reaction kinetic calculations were used to explore the effect of Pt-Pd catalysts doped Ce, and La rare earth elements on the oxidation properties of soot. The results shown that, among Pt-Pd-5%Ce, Pt-Pd-5%La, and Pt-Pd-5%Ce-5%La catalysts, Pt-Pd-5%La catalyst has the highest soot conversion, the highest low-temperature oxidation speed, and the activation energy is the smallest. Compared with soot, this catalyst reduced T10 and T20 by 82% and 26%, respectively, meaning the catalytic activity of Pt-Pd-5%La catalyst was the best.