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Technical Paper

Simulation of Friction-Induced Vibrations of Window Sealing Systems

In this study, friction-induced vibrations of the window sealing system of a vehicle were investigated using a detailed numerical model. A lumped element, single-degree-of-freedom model was first developed for verification of the numerical procedures. An approximate expression for the frequency of the stick-slip oscillations was obtained. The model indicated that the frequency decreased as the normal force and the difference between the static and kinetic friction coefficients were increased. Stick-slip oscillations were then simulated using a finite element model of a glass run seal using an explicit time marching method. The motion of the seal during the slipping phase was in the direction of the friction force. The peak frequency was found to vary according to the glass position on the seal surface. The results indicated that both the periods of the stick and slip phases of the seal motion affect the frequency of the stick-slip oscillations.
Technical Paper

On the Use of the Shear Punch Experiments in Determining Mechanical Properties of Various Dual Phase Steels

Dual phase steels are being extensively considered as a structural material for automobiles because of the favourable combination of strength and formability. Crashworthiness of these new steels is an area of great importance. High strain rate testing is one approach to measure the ability of materials to absorb energy in a crash situation. The objective of this paper is to examine the effect of the deformation rate on the mechanical properties of dual-phase and multi-phase steels. Shear-punch experiments are conducted both at quasi-static and dynamic rates for this purpose. The ease of preparation of shear punch specimens compared to the tension specimen makes this approach attractive in evaluating key mechanical properties, such as ultimate tensile strength (UTS) and ductility limits, of automotive materials mostly in sheet forms.
Journal Article

Microstructure Development in a Magnesium Alloy Tube during Ring Hoop Tension Testing and Warm Gas Forming

The evolution of microstructure in a Mg 3.4%AI-0.16%Zn-0.33%Mn alloy tube was studied during deformation by ring hoop tension testing (RHTT). When the tests were carried out at moderate temperatures and relatively high strain rates, the accompanying c-axis strains were mainly accommodated by twin formation. At temperatures above 200°C and the lowest strain rate (0.001s-1), the formation of voids in the partially dynamically recrystallized regions caused premature fracture. The microstructural development in hot gasformed samples was similar to that observed during RHTT testing. These results indicate that RHTT testing is an effective way of studying the deformation behavior of Mg alloys during tube gas forming.
Technical Paper

High Strain Rate Deformation Behavior of Advanced High Strength Steels for Automotive Applications

The high strain rate deformation behavior of commercially available dual phase steel was studied by means of split Hopkinson bar apparatus in shear punch mode with an emphasis on the influence of microstructure. The cold rolled sheet material was subjected to a variety of heat treatment conditions to produce several different microstructures. Dual phase microstructures with different fractions of martensite were obtained by changing intercritical annealing temperature and time. Various microstructures of ferrite plus pearlite, or acicular ferrite/bainite, or bainite and martensite/carbide were obtained by changing the cooling rate after annealing. The effects of low temperature tempering and bake hardening treatment were also investigated for some selected specimens.
Technical Paper

Electromechanical Clutch Actuator: Design, Analysis and Experiments

With the aim of producing innovative clutch actuation mechanisms for automotive transmissions, we are investigating a design based on power screws. The design strives to improve clutch actuation technology and minimize energy consumption by maintaining clutch lock-up independent of an external energy source. The system consists of a lead screw shaft-and-nut assembly, a clutch apply-plate, a set of wet clutch disks and a brushless DC motor. The clutch actuation assembly is separated from the clutch-pack via thrust bearings, which allows the use of a motor, while reducing the inertial load imposed by the conventional clutch-pack. A prototype of the design was fabricated and installed on a testbed, to mimic the installation of the actuator to replace the hydraulic components. A standard 12-disk clutch-pack of an automatic transmission was used within the apparatus. The formulation of the mathematical model of the entire testbed is described in this paper.
Technical Paper

Effect of Tempered Martensite Volume Fraction on Final Properties of Cold Rolled and Tempered Al TRIP Steel

Tempered martensite assisted steels are of recent research interest for good strength and ductility combination. This paper discusses the effect of tempered martensite volume fraction on the final properties of cold rolled and subcritically annealed Al containing TRIP steel. The samples were TRIP annealed and the retained austenite volume fraction was measured using X-ray diffraction technique. The steel samples were subsequently cold rolled to obtain strain induced martensite, deformed ferrite and bainite in the microstructure. The final tempered martensite volume fraction corresponds to the initial retained austenite volume fraction of the steel. The cold rolled TRIP steel samples were subsequently subcritically annealed at 500°C for 1 hour to obtain tempered martensite, fine ferrite and bainite. Shear Punch testing was used to evaluate the mechanical properties. The properties are analyzed and the results are discussed.
Technical Paper

Effect of Temperature and Strain Rate on Formability of AZ31 Magnesium Sheet Alloy

The deformation characteristics of a commercial AZ31 magnesium sheet alloy were investigated at elevated temperatures. Tensile experiments were conducted at temperatures 300°C, 400°C and 450°C and at strain rates, 0.001s-1, 0.01s-1 and 0.1s-1. Depending on the test temperature, fracture analysis of failed specimens revealed three different types of failure: (1) by moderate necking, (2) by interlinkage cavity, (3) by strong necking. Plastic strain ratios, r-values were derived from the strain ratios of width and thickness of the fractured tensile specimens. The r-value increased with increasing temperature and strain rate.
Technical Paper

Crystal Plasticity Modeling of the Slip Systems Activity in Mg Alloys at Higher Temperatures

Understanding the role of the slip systems and their evolution with temperature is critical to the correct simulation of the mechanical behavior of magnesium alloys. In this paper, relations are proposed for evolution of the CRSS values of different slip systems and strain-rate sensitivity factor, stating them as functions of temperature and strain-rate. These relations are used in conjunction with the Crystal Plasticity Finite Element (CPFE) model for prediction of stress-strain curves and r-values at elevated temperatures (75°C to 250°C). The new relations can predict the decrease in stress level, the anisotropy of the material, and the decrease in the difference between the r-values in the RD and the TD with the increase in temperature. The results confirm the trends predicted with Taylor-type and VPSC models. In particular, they confirm the high activity of the slip systems at higher temperatures.
Technical Paper

Advanced In-cycle and Cycle-to Cycle On-line Adaptive Control for Thermoforming of Large Thermoplastic Sheets

This paper presents a control system for the thermoforming of large sheets. The system has three main purposes: Its primary purpose is for cycle-to-cycle control of the sheet temperature map as predicted by the thermoforming simulation. Its secondary purpose is to tune the simulation to the actual process through on-line characterization of some of the material and machine characteristics so that the simulation's predictions are reconciled with the machine sensors outputs. Lastly it can characterize on-line a number of independent and fast acting sub-models that allow for in-cycle control of some process parameters.