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Technical Paper

Effect of geometric parameters on folding of thin-walled steel tube under axial compression

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.
Technical Paper

Ultimate Breakage Load Calculation Method of Cold Gas Inflator Burst Disk

For cold gas Inflator, high refinement of ultimate load forecast is one key of Inflator development. At beginning, two methods based on implicit algorithm, Zero Curvature method and RIKS method were used for burst disk hydro-burst test ultimate pressure load calculation. After considering the effect of bursting disk stamping process, comparing with results of real test, the refinement of the two methods were above 97% both. Studying the corresponding relations between displacement and stress matrix of the center point of burst disk by RISK method. It was found that under ultimate load, the third principal stress vs. displacement curve of the central node shown extreme point, and load step of the point was corresponding the one of maximum pressure load. This shown that after reaching the ultimate load, the center of the bursting disc lost stability in the direction of thickness.
Technical Paper

Compressive and Bending Resistance of the Thin-Walled Hat Section Beam with Strengthened 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.
Technical Paper

Investigation of the Operating Conditions on the Water and Thermal Management for a Polymer Electrolyte Membrane Fuel Cell by One-Dimensional Model

Water and thermal management is an essential issue that influences performance and durability of a polymer electrolyte membrane fuel cell (PEMFC). Water content in membrane decides its ionic conductivity and membrane swelling favors the ionic conductivity, resulting in decreases in the membrane’s ohmic resistance and improvement in the output voltage. However, if excessive liquid water can’t be removed out of cell quickly, it will fill in the pores of catalyst layer (CL) and gas diffusion layer (GDL) then flooding may occur. It is essential to keep the water content in membrane at a proper level. In this work, a transient isothermal one-dimensional model is developed to investigate effects of the relative humidity of inlet gas and cell temperature on performance of a PEMFC.
Technical Paper

Topology Optimization of Metal and Carbon Fiber Reinforced Plastic (CFRP) Structures under Loading Uncertainties

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.
Technical Paper

Parameters Analyses and Identification for Rubber Bush Based on Theoretical Dynamic Model with Effects of Temperature and Preload

A series connection of the KVBC (Kelvin-Voigt and Bouc-wen) theoretical model of rubber bush in automobile suspension is established. The numerical calculation model is also developed through Matlab/simulation and 9 parameters are identified. Experiments are conducted on the rubber bush on a bench for dynamic and static characteristics and to supply appropriate and reliable data for parameter identification. Based on this, preload and temperature are taken into consideration in an ordinary KVBC model as two important additional factors. As a result, it leads to developing a novel model with new parameter identification, which is validated under different conditions. This new modeling method of rubber bush has three advantages. First, it shows improved accuracy for solving non-linear problems in a multi-body calculation, which is useful for researchers and vehicle engineers.
Technical Paper

Concurrent Optimization of Ply Orientation and Thickness for Carbon Fiber Reinforced Plastic (CFRP) Laminated Engine Hood

Carbon fiber reinforced plastic (CFRP) composites have gained particular interests due to their high specific modulus, high strength, lightweight and resistance to environment. In the automotive industry, numerous studies have been ongoing to replace the metal components with CFRP for the purpose of weight saving. One of the significant benefits of CFRP laminates is the ability of tailoring fiber orientation and ply thickness to meet the acceptable level of structural performance with little waste of material capability. This study focused on the concurrent optimization of ply orientation and thickness for CFRP laminated engine hood, which was based on the gradient-based discrete material and thickness optimization (DMTO) method. Two manufactural constraints, namely contiguity and intermediate void constraints, were taken into account in the optimization problem to reduce the potential risk of cracking matrix of CFRP.
Technical Paper

Investigation of Factors Controlling the Attainable Equivalent Plastic Strain in the Gauge Region of Cruciform Specimens

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).
Technical Paper

Full Vehicle Dynamic Modeling for Engine Shake with Hydraulic Engine Mount

The statement of the engine shake problem is presented through comparing the quarter vehicle models with the rigid-connected and flexible-connected powertrain which is supported on the body by a rubber mount. Then the model is extended by replacing the rubber mount as a hydraulic engine mount (HEM) with regard to the inertia and resistance of the fluid within the inertia track. Based on these, a full vehicle model with 14 degree of freedoms (DOFs) is proposed to calculate the engine shake, which consists of 6 of the powertrain, 1 of the fluid within the inertia track of the HEM, 3 of the car body and 4 of the unsprung mass. Simulation analysis based on the proposed model is implemented, through which the conclusion is drawn that the HEM has great influence on the body and seat track response subjected to front wheel inputs, compared with the rubber mount.
Technical Paper

Numerical Simulation of CFRP Thin-Walled Tubes Subjected to Quasi-Static Axial Crushing

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.
Journal Article

Experimental Study of the Plasticity Responses of TRIP780 Steel Subjected to Strain-Path Changes

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.
Technical Paper

Design Improvement on Plastic Fuel Tank System with Model Bias Prediction

With the increasing development in automotive industry, finite element (FE) analysis with model bias prediction has been used more and more widely in the fields of chassis design, body weight reduction optimization and some components development, which reduced the development cycles and enhanced analysis accuracy significantly. However, in the simulation process of plastic fuel tank system, there is few study of model validation or verification, which results that non-risky design decisions cannot be enhanced due to too much consuming time. In this study, to correct the discrepancy and uncertainty of the simulated finite element model, Bayesian inference-based method is employed, to quantify model uncertainty and evaluate the simulated results based on collected data from real mechanical tests of plastic fuel tanks and FE simulations under the same boundary conditions.
Technical Paper

Dynamic Stress Experimental Study on Key Part of Port under Impact Load

The port structure consisting of spur pile, vertical pile and beam is subjected to impact loads, so its internal stress state of each point will rapidly change over time. Dynamic photoelastic method is used to study the dynamic stress and stress wave propagation. With epoxy resin and other materials, a photoelastic model of beam to column connection structure is processed and product. The dynamic response of the model under the impact load by the free fall is researched by the dynamic photoelastic method, and recorded by the new digital dynamic photoelastic system with a laser source and high-speed photography system. The internal dynamic stress propagation and distribution, the maximum shear stress and the dynamic stress concentration problems can be obtained by analyzing the dynamic response.
Technical Paper

The Research Progress of Dynamic Photo-Elastic Method

With the rapid development of computing technology, high-speed photography system and image processing recently, in order to meet growing dynamic mechanical engineering problems demand, a brief description of advances in recent research which solved some key problems of dynamic photo-elastic method will be given, including:(1) New digital dynamic photo-elastic instrument was developed. Multi-spark discharge light source was replaced by laser light source which was a high intensity light source continuous and real-time. Multiple cameras shooting system was replaced by high-speed photography system. The whole system device was controlled by software. The image optimization collection was realized and a strong guarantee was provided for digital image processing. (2)The static and dynamic photo-elastic materials were explored. The new formula and process of the dynamic photo-elastic model materials will be introduced. The silicon rubber mold was used without the release agent.
Technical Paper

Fatigue Life Prediction of Rubber Bushing in Engine Cradle

Fatigue defect and failure of rubber element widely used in mechanical systems could seriously affect the safety and reliability of systems in practical operation. Because rubber element is considered as hyperelastic material, traditional σ - N curve which is usually used in metal material for fatigue life analysis can not be used here. The fatigue life of rubber bushing in automobile engine cradle was analyzed by using the energy method. The Yeoh model coefficients were given by tensile test of natural rubber, and the estimating formula for fatigue life of natural rubber was obtained by finite element calculation and fatigue test. Maximum strain energy density was treated as the parameter of fatigue damage, then the rubber bushing fatigue life was calculated by the estimating formula. The results were verified by test of rubber bushing, which indicated that the model mentioned in this paper is accuracy enough.
Technical Paper

Material Compatibilities of Biodiesels with Elastomers, Metals and Plastics in a Diesel Engine

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.