Search Results

Welding induced residual stresses are an important factor to consider when evaluating fatigue design of welded automotive parts. Fortunately, design engineers have various residual stress mitigation technologies at their disposal for improving the fatigue performance of these parts. For this purpose, it is essential to understand the relationship between the residual stresses and fatigue performance quantitatively as well as qualitatively. It has been widely accepted that tensile residual stresses in welded structures are as high as the material yield strength level. Therefore, the fatigue strength of welded joints is governed predominantly by the applied stress range, regardless of the load ratio. However, in stress relieved components the tensile residual stress level is not as high, and the weld fatigue behavior is more influenced by the load ratio.

Even under uniaxial loading, seemingly simple welded joint types can develop multi-axial stress states, which must be considered when evaluating both the fatigue strength and failure location. Based on the investigation of fatigue behavior for the multi-axial stress state, a procedure for fatigue behavior of welded joints with multi-axial stress states was proposed using an effective equivalent structural stress range parameter combined normal and in-plane shear equivalent structural stress ranges and the master S-N curve approach. In automotive structures, fatigue failure is often observed at weld end, which often show a complex stress state. Due to simplified weld end representation having a sharp right-angled weld corner, the fatigue failure prediction at the weld end tends to be overly conservative due to the excessive stress concentration at the right-angled weld termination.

Lightweight, optimized vehicle designs are paramount in helping the automotive industry meet reduced emissions standards. Self-piercing rivets are a promising new technology that may play a role in optimizing vehicle designs, due to their superior fatigue resistance compared with spot welds and ability to join dissimilar materials. This paper presents a procedure for applying the mesh-insensitive Battelle Structural Stress Method to self-piercing riveted joints for fatigue life prediction. Additionally, this paper also examines the development of an interim fatigue design master S-N curve for self-piercing rivets. The interim fatigue design master S-N curve accounts for factors such as various combinations of similar and dissimilar metal sheets, various sheet thicknesses, stacking sequence, and load ratios. A large amount of published data was collapsed into a single interim S-N curve with reasonable data scattering.

As the automotive industry seeks to remove weight from vehicle chasses to meet increased fuel economy standards, it is increasingly turning to composites and aluminum. In spite of increasing demands for quality aluminum alloy spot welds that enable more fuel efficient automobiles, fatigue evaluation procedures for such welds are not well-established. This article discusses the results of an evaluation Battelle performed of the fatigue characteristics of aluminum alloy spot welds based on experimental data and observations from the literature. In comparison with spot welds in steel alloys, aluminum alloy spot welds exhibit several significant differences including a different hardness distribution at and around the weld, different fatigue failure modes, and more. The effectiveness and applicability of the Battelle structural stress-based simplified procedure for modeling and simulating automotive spot welds has previously been demonstrated by Battelle investigations.

Weld fatigue evaluation using the mesh-insensitive Battelle structural stress method has been applied to fusion welds, resistance spot welds and non-welded components. The effectiveness of the Battelle structural stress procedure has been demonstrated in a series of earlier publications for welded structures with different joint types, plate thicknesses, and loading modes. In this paper, a weld fatigue evaluation procedure using the Battelle structural stress method is proposed for friction stir welds currently being used in the automotive and aerospace industries. The applicability of the Battelle structural stress procedure is demonstrated by comparing fatigue life predictions for friction stir welded specimens to well-documented test data from the literature. Different specimen types, plate thicknesses and loading ratios were analyzed for several aluminum alloys.

In this paper, the applicability of the finite element-based, mesh insensitive Battelle structural stress method is demonstrated for fatigue life predictions of notched specimens (non-welded) with different specimen types, and notch shapes. Well-documented notch fatigue data were analyzed using the Battelle structural stress fatigue evaluation procedure, including notched plate fatigue data for steel and aluminum alloys. The effectiveness of the Battelle structural stress procedure has been demonstrated in a series of earlier publications for welded structures with different joint types, plate thicknesses, and loading modes. Here, a similar Battelle structural stress procedure suitable for finite element modeling and service life simulations is proposed for structures with notches. Unlike weld fatigue data, the crack propagation portion of the fatigue life associated with a notch does not always dominant the total number of cycles to failure.

In this paper, the Battelle structural stress method for evaluating the fatigue life of welded joints is applied to weld-bonded joints. In order to overcome the complexity of modeling and analyzing both crack paths in weld-bonded joints, a superposition approach is proposed as a reasonable and effective alternative for fatigue design purpose. The superposition approach for evaluating the fatigue life of weld-bonded joints uses two simplified finite element (FE) models: a spot weld model and an adhesive bond model. Each simplified FE model is required to represent the fatigue behavior properly and to minimize the modeling effort without sacrificing the accuracy of the results. The superposition concept can be used in practice if the life evaluation results using the superposition are comparable with the experiments. For the spot welds, the recently developed simplified procedure and master fatigue S-N curve is employed [1].

The nodal force based Battelle structural stress method has shown its mesh insensitivity in the stress analysis of spot welds as well as fusion welds. In the conventional structural stress simulation procedure, the structural stress is calculated at the nodes along the nugget periphery. However, implementing a nugget into each spot weld is cumbersome and time consuming not only in preparing mesh for FE analysis but also in preparing a series of structural stress calculation after finishing the FE analysis. Therefore, the efficiency of the current Battelle structural stress practice for spot welds can be improved significantly for structures with a large number of spot welds. The simplified modeling procedure presented here delivers reliable structural stresses at spot welds and these stresses can then be utilized for fatigue life prediction using a master S-N Curve approach that is applicable to wide range of spot welding techniques.

Hydrogen-powered vehicles offer the promise of significantly reducing the amount of pollutants that are expelled into the environment on a daily basis by conventional hydrocarbon-fueled vehicles. While very promising from an environmental viewpoint, the technology and systems that are needed to store the hydrogen (H2) fuel onboard and deliver it to the propulsion system are different from what consumers, mechanics, fire safety personnel, the public, and even engineers currently know and understand. As the number of hydrogen vehicles increases, the likelihood of a rollover or collision of one of these vehicles with another vehicle or a barrier will also increase.

Biodiesel has been used to reduce petroleum consumption and pollutant emissions. B20, a 20% blend of biodiesel with 80% petroleum diesel, has become the most common blend used in the United States. Little quantitative information is available on the impact of biodiesel on engine operating costs and durability. In this study, eight engines and fuel systems were removed from trucks that had operated on B20 or diesel, including four 1993 Ford cargo vans and four 1996 Mack tractors (two of each running on B20 and two on diesel). The engines and fuel system components were disassembled, inspected, and evaluated to compare wear characteristics after 4 years of operation and more than 600,000 miles accumulated on B20. The vehicle case history-including mileage accumulation, fuel use, and maintenance costs-was also documented. The results indicate that there was little difference that could be attributed to fuel in operational and maintenance costs between the B20- and diesel-fueled groups.

This paper describes Battelle's effort to demonstrate a bio-based, environmentally friendly, Type I, non-glycol deicer, called D3: Degradable by Design Deicer™. AMS 1424 D tests conducted by SMI and AMIL indicate this aircraft deicing fluid (ADF) meets the established physical properties, material compatibility, corrosion resistance, and deicing performance requirements. Its biological oxygen demand (BOD5) and lethal concentrations (LC50) are less than half of conventional Type I propylene glycol (PG) ADF levels. Spray tests were conducted in the McKinley Climatic Chamber at Eglin Air Force Base, and aircraft flight tests were conducted at the Niagara Falls Air Reserve Station.

The objective of this project, which is supported by the U.S. Department of Energy (DOE) through the National Renewable Energy Laboratory (NREL), is to provide a comprehensive comparison of heavy-duty trucks operating on alternative fuels and diesel fuel. Data collection from up to eight sites is planned. Currently, the project has four sites: Raley's in Sacramento, CA (Kenworth, Cummins L10-300G, liquefied natural gas - LNG); Pima Gro Systems, Inc. in Fontana, CA (White/GMC, Caterpillar 3176B Dual-Fuel, compressed natural gas - CNG); Waste Management in Washington, PA (Mack, Mack E7G, LNG); and United Parcel Service in Hartford, CT (Freightliner Custom Chassis, Cummins B5.9G, CNG). This paper summarizes current data collection and evaluation results from this project.

Tailor-welded blanks (TWB) have been increasingly used in the automotive industry as an effective way to reduce weight and costs. Although some of the joining processes for TWB are relatively well known, little independent information exists regarding welding procedure effects on weld/HAZ properties, particularly their effects on form-ability and structural performance under various conditions. In this paper, advanced computational modeling techniques were used to investigate the effects of welding procedures on weld property evolution and its impact on the formability issues. Two case studies were presented. One is on TIG welding of 6000 series aluminum tailored blanks, where thermomechanical effects on weldability was analyzed. Its implication on weld performance during forming will be discussed. The other case is on laser-beam welding of high strength steel to mild steel with a non-linear weld. The detailed thermal history and residual stress development will be presented.

This paper describes the results of a liquefied petroleum gas (LPG) fleet test conducted using para-transit, medium-duty vehicles. The vehicles were part of an active municipal fleet providing daily service on varying operating routes. Over a period of nine months, each vehicle was fueled with a series of butane/propane mixtures. The mixtures tested were HD5 LPG as the baseline fuel, 20 percent butane/80 percent propane, 30 percent butane/70 percent propane, and a final blend of 50 percent butane/50 percent propane by volume. The test vehicles showed improved fuel economy as the butane content increased in the fuel mixture, even without modification to existing LPG fuel systems. The improved fuel performance was consistent with the higher energy content of butane, compared to an equal volume of propane. The vehicles displayed no symptoms of performance or maintenance problems that would be related to operation of the fuel mixtures.

The effects of electrode wear on nugget development during resistance spot welding are major concerns in auto-body assembly and manufacturing. By considering detailed electrode-sheet interactions using advanced finite element modeling procedure, this paper presents a framework for detecting the electrode wear conditions and associated nugget development characteristics. Two important in-process parameters are studied in detail. They are the electrode movement and the dynamic resistance. It is found that the second-order derivative of the electrode movement and the first-order derivative of the dynamic resistance can be correlated in a fundamental form to identify the detailed nugget development process under various electrode wear conditions.

Natural Gas engines are viewed as an alternative to diesel power in the quest to reduce heavy duty vehicle emissions in polluted urban areas. In particular, it is acknowledged that natural gas has the potential to reduce the inventory of particulate matter, and this has encouraged the use of natural gas engines in transit bus applications. Extensive data on natural gas and diesel bus emissions have been gathered using two Transportable Heavy Duty Vehicle Emissions Testing Laboratories, that employ chassis dynamometers to simulate bus inertia and road load. Most of the natural gas buses tested prior to 1997 were powered by Cummins L-10 engines, which were lean-burn and employed a mechanical mixer for fuel introduction. The Central Business District (CBD) cycle was used as the test schedule.

The objective of this program, which is supported by the U.S. Department of Energy (DOE) through the National Renewable Energy Laboratory (NREL), is to provide an unbiased and comprehensive comparison of transit buses operating on alternative fuels and diesel fuel. The information for this comparison was collected from eight transit bus sites. The fuels studied are natural gas (CNG and LNG), alcohol (methanol and ethanol), biodiesel (20 percent blend), propane (only projected capital costs; no sites with heavy-duty propane engines were available for studying operating experience), and diesel. Data was collected on operations, maintenance, bus equipment configurations, emissions, bus duty cycle, and safety incidents. Representative and actual capital costs were collected for alternative fuels and were used as estimates for conversion costs. This paper presents preliminary results.

Economics is one of several key factors that must be considered by fleet operators and other decision makers as they move towards initiating or increasing the use of various alternative fuels in their fleet applications. Accordingly, the CleanFleet demonstration project was structured to generate and present a full set of comparable cost information for several of the leading alternative fuels. The cost information included the costs to acquire and modify vehicles, personnel training, facility modifications, capital and operating costs for fueling stations, and vehicle operating costs. These costs were used as the starting point for an analysis of the costs that a fleet operator might face in the 1996 time frame for implementing the use of compressed natural gas, propane gas, Phase 2 reformulated gasoline, or methanol (M-85). The cost estimates were incorporated into a popular spread-sheet used on personal computers to facilitate examining various options available to fleets.

Vehicle exhaust emissions measurements are reported for full-size panel vans operating on four alternative motor fuels and control gasoline. The emissions tests produced data on in-use vans. The vans were taken directly from commercial delivery service for testing as they accumulated mileage over a 24-month period. The alternative fuels tested were compressed natural gas, propane gas, California Phase 2 reformulated gasoline (RFG), and methanol (M-85 with 15 percent RFG). The control gasoline for the emissions tests was an industry average unleaded blend (RF-A). The vehicle technologies tested represent those options available in 1992 that were commercially available from Ford, Chrysler, and Chevrolet or which these manufacturers agreed to provide as test vans for daily use in commercial service by FedEx.

Fuel economy estimates are provided for the CleanFleet vans operated for two years by FedEx in Southern California. Between one and three vehicle manufacturers (Chevrolet, Dodge, and Ford) supplied vans powered by compressed natural gas (CNG), propane gas, California Phase 2 reformulated gasoline (RFG), methanol (M-85), and unleaded gasoline as a control. Two electric G-Vans, manufactured by Conceptor Corporation, were supplied by Southern California Edison. Vehicle and engine technologies are representative of those available in early 1992. A total of 111 vans were assigned to FedEx delivery routes at five demonstration sites. The driver and route assignments were periodically rotated within each site to ensure that each vehicle would experience a range of driving conditions. Regression analysis was used to estimate the relationships between vehicle fuel economy and factors such as the number of miles driven and the number of delivery stops made each day.