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The conventional forming limit curve (FLC) has been widely and successfully used as a failure criterion to detect localized necking in stamping. However, in stamping advanced high strength steels (AHSS), under certain circumstances such as stretching-bending over a small die radius, the sheet metal fails much earlier than predicted by the FLC. This type of failure on the die radius is commonly called “shear fracture.” In this paper, the laboratory Stretch-Forming Simulator (SFS) and the Bending under Tension (BUT) tester are used to study shear fracture occurring during both early and later stages of stamping. Results demonstrate that the occurrence of shear fracture depends on the combination of the radius-to-thickness (R/T) ratio and the tension/stretch level applied to the sheet during stretching or drawing. Based on numerous experimental results, an empirical shear fracture limit curve or criterion is obtained.

One of the issues in stamping of advanced high strength steels (AHSS) is the stretch bending fracture on a sharp radius (commonly referred to as shear fracture). Shear fracture typically occurs at a strain level below the conventional forming limit curve (FLC). Therefore it is difficult to predict in computer simulations using the FLC as the failure criterion. A modified Mohr-Coulomb (M-C) fracture criterion has been developed to predict shear fracture. The model parameters for several AHSS have been calibrated using various tests including the butter-fly shaped shear test. In this paper, validation simulations are conducted using the modified (M-C) fracture criterion for a dual phase (DP) 780 steel to predict fracture in the stretch forming simulator (SFS) test and the bending under tension (BUT) test. Various deformation fracture modes are analyzed, and the range of usability of the criterion is identified.

To improve the energy absorption capacity of front-end structures during a vehicle crash, a novel 12-sided cross-section was developed and tested. Computer-aided engineering (CAE) studies showed superior axial crash performance of the 12-sided component over more conventional cross-sections. When produced from advanced high strength steels (AHSS), the 12-sided cross-section offers opportunities for significant mass-savings for crash energy absorbing components such as front or rear rails and crush tips. In this study, physical crash tests and CAE modeling were conducted on tapered 12-sided samples fabricated from AHSS. The effects of crash trigger holes, different steel grades and bake hardening on crash behavior were examined. Crash sensitivity was also studied by using two different part fabrication methods and two crash test methods. The 12-sided components showed regular folding mode and excellent energy absorption capacity in axial crash tests.

The rotary engine provides high power density compared to piston engine, but one of its downside is higher oil consumption. A model of the oil seals is developed to calculate internal oil consumption (oil leakage from the crankcase through the oil seals) as a function of engine geometry and operating conditions. The deformation of the oil seals trying to conform to housing distortion is calculated to balance spring force, O-ring and groove friction, and asperity contact and hydrodynamic pressure at the interface. A control volume approach is used to track the oil over a cycle on the seals, the rotor and the housing as the seals are moving following the eccentric rotation of the rotor. The dominant cause of internal oil consumption is the non-conformability of the oil seals to the housing distortion generating net outward scraping, particularly next to the intake and exhaust port where the housing distortion valleys are deep and narrow.

The rotary engine provides high power density compared to piston engine, but one of its downside is higher oil consumption. In order to better understand oil transport, a laser induced fluorescence technique is used to visualize oil motion on the side of the rotor during engine operation. Oil transport from both metered oil and internal oil is observed. Starting from inside, oil accumulates in the rotor land during inward motion of the rotor created by its eccentric motion. Oil seals are then scraping the oil outward due to seal-housing clearance asymmetry between inward and outward motion. Cut-off seal does not provide an additional barrier to internal oil consumption. Internal oil then mixes with metered oil brought to the side of the rotor by gas leakage. Oil is finally pushed outward by centrifugal force, passes the side seals, and is thrown off in the combustion chamber.

In present paper, the process of joining aluminum alloy 6111T4 and steel HSLA340 sheets by self-piercing riveting (SPR) is studied. The rivet material properties were obtained by inverse modeling approach. Element erosion technique was adopted in the LS-DYNA/explicit analysis for the separation of upper sheet before the rivet penetrates into lower sheet. Maximum shear strain criterion was implemented for material failure after comparing several classic fracture criteria. LS-DYNA/implicit was used for springback analysis following the explicit riveting simulation. Large compressive residual stress was observed near frequent fatigue crack initiation sites, both around vicinity of middle inner wall of rivet shank and upper 6111T4 sheet.

Active regeneration systems for cleaning diesel exhaust can operate at extremely high temperatures up to 1000°C. The extremely high temperatures create a unique challenge for the design of regeneration structural components near their melting temperatures. In this paper, the preparation of the sheet specimens and the test set-up based on induction heating for sheet specimens are first presented. Tensile test data at room temperature, 500, 700, 900 and 1100°C are then presented. The yield strength and tensile strength were observed to decrease with decreasing strain rate in tests conducted at 900 and 1100°C but no strain rate dependence was observed in the elastic properties for tests conducted below 900°C. The stress-life relations for under cyclic loading at 700 and 1100°C with and without hold time are then investigated. The fatigue test data show that the hold time at the maximum stress strongly affects the stress-life relation at high temperatures.

Piston rings are large contributors to friction losses in internal combustion engines. To achieve higher engine efficiency, low friction ring packs that can maintain good sealing performance must be designed. To support this effort, simulation tools have been developed to model the performance of piston rings during engine operation. However, the challenge of predicting oil consumption, blow by, and ring pack friction with sufficient accuracy remains. This is mostly due to the complexity of this system. Ring dynamics, deformation, interaction with liner and piston, gas and lubricant flow must all be studied together to make relevant predictions. In this paper, a new curved beam finite element model of piston rings is proposed. Ring structural deformation and contact with the liner are treated on two separate grids. A comparison with ring models in the literature and analytical solutions shows that it can provide accurate results efficiently.

Automotive structural parts made out of Advanced High Strength Steel (AHSS) are often produced in a multistage forming process using progressive dies or transfer dies. During each forming stage the steel is subjected to work hardening, which affects the formability of the steel in the subsequent forming operation. Edge flanging and in-plane edge stretching operations are forming modes that are typically employed in the last stage of the multistage forming processes. In this study, the multistage forming process was simulated by pre-straining a DP980 steel in a biaxial strain path with various strain levels followed by edge flanging and in-plane edge stretching. The biaxial prestrains were obtained using the Marciniak stretch test and edge flanging and in-plane edge stretching were accomplished by the hole expansion test using a flat punch and a conical punch, respectively.

Aftertreatment system design involves multiple tradeoffs between engine performance, fuel economy, regulatory emission levels, packaging, and cost. Selection of the best design solution (or “architecture”) is often based on an assumption that inherent catalyst activity is unaffected by location within the system. However, this study acknowledges that catalyst activity can be significantly impacted by location in the system as a result of varying thermal exposure, and this in turn can impact the selection of an optimum system architecture. Vehicle experiments with catalysts aged over a range of mild to moderate to severe thermal conditions that accurately reflect select locations on a vehicle were conducted on a chassis dynamometer. The vehicle test data indicated CO and NOx could be minimized with a catalyst placed in an intermediate location.

As the piston pin works under significant mechanical load, it is susceptible to wear, seizure, and structural failure, especially in heavy duty internal combustion engines. It has been found that the friction loss associated with the pin is comparable to that of the piston, and can be reduced when the interface geometry is properly modified. However, the mechanism that leads to such friction reduction, as well as the approaches towards further improvement, remain unknown. This work develops a piston pin lubrication model capable of simulating the interaction between the pin, the piston, and the connecting rod. The model integrates dynamics, solid contact, oil transport, and lubrication theory, and applies an efficient numerical scheme with second order accuracy to solve the highly stiff equations. As a first approach, the current model assumes every component to be rigid.

The first 3 cycles in the cold crank-start process at 20°C are studied in a GDI engine. The focus is on the dependence of the HC and PM/PN emissions of each cycle on the injection strategy and combustion phasing of the current and previous cycles. The PM/PN emissions per cycle decrease by more than an order of magnitude as the crank-start progresses from the 1st to the 3rd cycle, while the HC emissions stay relatively constant. The wall heat transfer, as controlled by the combustion phasing, during the previous cycles has a more significant influence on the mixture formation process for the current cycle than the amount of residual fuel. The results show that the rise in HC emissions caused by the injection spray interacting with the intake valves and piston crown is reduced as the cranking process progresses. Combustion phasing retard significantly reduces the PM emission. The HC emissions, however, are relatively not sensitive to combustion phasing in the range of interest.

A new ring pack model has been developed based on the curved beam finite element method. This paper describes the first part of this model: simulating gas pressure in different regions above piston skirt and ring dynamic behavior of two compression rings and a twin-land oil control ring. The model allows separate grid divisions to resolve ring structure dynamics, local force/pressure generation, and gas pressure distribution. Doing so enables the model to capture both global and local processes at their proper length scales. The effects of bore distortion, piston secondary motion, and groove distortion are considered. Gas flows, gas pressure distribution in the ring pack, and ring structural dynamics are coupled with ring-groove and ring-liner interactions, and an implicit scheme is employed to ensure numerical stability. The model is applied to a passenger car engine to demonstrate its ability to predict global and local effects on ring dynamics and oil transport.

Two combustion systems were developed and optimized for an engine for a power cylinder of 0.8-0.9L/cylinder. The first design was a re-entrant bowl concept which was based on the combustion system of a smaller engine with roughly 0.5L/cylinder. The second design was a chamfered bowl concept, a variant of a reentrant bowl that deliberately splits fuel between the bowl and the squish region. For each combustion system concept, nozzle tip protrusion, swirl, and nozzle configuration (number of holes, nozzle flow, and spray angle) were optimized. Several similarities between combustion system concepts were noted, including the optimal swirl and number of holes. The resulting optimums for each concept were compared. The chamfered combustion system was found to have better part-load emissions and fuel consumption tradeoffs. Full load performance was similar at low speed between the two combustion systems, but the reentrant combustion system had advantages at high engine speed and load.

Powder metal based copper steels have found increased use in automotive applications, an example being powder-forged connecting rods. A characterization study was conducted to determine the effects of carbon content and manganese sulphide addition on the mechanical properties and machinability of these materials. Steel powder mixes containing 2% Cu and various graphite contents, with and without a MnS addition were pressed, sintered and forged to full density. Forged samples were then tested for tensile properties, hardness and fatigue strength. Machinability was determined by measuring tool life during drilling tests. It was found that increasing the carbon content from 0.28 to 0.69% has little effect on fatigue properties of powder-forged copper steels although the tensile, strength increased as expected. The addition of manganese sulphide did not affect the mechanical properties measured, but was found to significantly improve the machinability.

Particulate emissions from a production gasoline direct injection spark ignition engine were studied under a typical cold-fast-idle condition (1200 rpm, 2 bar NIMEP). The particle number (PN) density in the 22 to 365 nm range was measured as a function of the injection timing with single pulse injection and with split injection. Very low PN emissions were observed when injection took place in the mid intake stroke because of the fast fuel evaporation and mixing processes which were facilitated by the high turbulent kinetic energy created by the intake charge motion. Under these conditions, substantial liquid fuel film formation on the combustion chamber surfaces was avoided. PN emissions increased when injection took place in the compression stroke, and increased substantially when the fuel spray hit the piston.

Ford Motor Company has developed a new 3.5L V6 engine. The engine, called the Duratec35, represents a new architecture for Ford Motor Co. that will eventually power one in five Ford vehicles. The goals of the engine design were high output, fuel efficient, low emissions, and excellent NVH. This paper will describe the NVH process for the development of the engine, the NVH features included in the design, and the final results relative to the benchmarks.

A dynamometer-mounted four-cylinder Saturn engine was used to accumulate combustion chamber deposits (CCD), using an additized fuel. During each deposit accumulation test, the HC emissions were continuously measured. The deposit thickness at the center of the piston was measured at the beginning of each day. After the 50 and 35-hour tests, HC emissions were measured with isooctane, benzene, toluene, and xylene, with the deposited engine, and again after the deposits had been cleaned from the engine. The HC emissions showed a rapid rise in the first 10 to 15 hours and stabilization after about 25 hours of deposit accumulation. The HC increase due to CCD accumulation accounted for 10 to 20% of the total engine-out HC emissions from the deposit build-up fuel and 10 to 30% from benzene, isooctane, toluene, and xylene, making CCDs a significant HC emissions source from this engine. The HC emissions stabilized long before the deposit thickness.

The effect of temperature and preload on the bolt load retention (BLR) behavior of AZ91D and AE42 magnesium die castings was investigated. The results were compared to those of 380 aluminum die castings. Test temperatures from 125 to 175°C and preloads from 7 to 28 kN were investigated. The loss of preload for AZ91D was more sensitive to temperature than that observed for AE42, especially at low preloads. In general, retained bolt-load was lowest in AZ91D. All test assemblies were preloaded at room temperature and load levels increased when the assemblies reached test temperature. The load-increase was dependent on the preload level, test temperature, alloy, and results from thermal expansion mismatch between the steel bolt and the magnesium alloy components, mitigated by the onset of primary creep. Thermal exposure (aging) of AZ91D at 150°C improved BLR behavior.

A rapid compression machine for chemical kinetic studies has been developed. The design objectives of the machine were to obtain: 1)uniform well-defined core gas; 2) laminar flow condition; 3) maximum ratio of cooling to compression time; 4) side wall vortex containment; and, 5) minimum mechanical vibration. A piston crevice volume was incorporated to achieve the side wall vortex containment. Tests with inert gases showed the post-compression pressure matched with the calculated laminar pressure indicating that the machine achieved these design objectives. Measurements of ignition delays for homogeneous PRF/O2/N2/Ar mixture in the rapid compression machine have been made with five primary reference fuels (ON 100, 90, 75, 50, and 0) at an equivalence ratio of 1, a diluent (s)/oxygen ratio of 3.77, and two initial pressures of 500 Torr and 1000 Torr. Post-compression temperatures were varied by blending Ar and N2 in different ratios.