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TWO TYPES of bench wear tests employed by the General Motors Research Laboratories are described, and examples are given to illustrate the application of the tests to material development problems. It is shown that correlation of a bench test with service may be achieved even when the laboratory test conditions do not appear to duplicate service conditions exactly. It is postulated that this behaviour is related to the formation of certain types of surface films during the wearing process. Some preliminary results are given of a study of the influence of lubricant type and material composition on the formation of anti-wear films.

THE PURPOSE of this experiment was to determine the role of residual stresses in fatigue strength independent of other factors usually involved when residual stresses are introduced. It consisted of an investigation of the influence of residual stresses introduced by shotpeening on the fatigue strength of steel (Rockwell C hardness 48) in unidirectional bending. Residual stresses were varied by peening under various conditions of applied strain. This process introduced substantially the same amount and kind of surface cold working with residual stresses varying over a wide range of values. It was found that shotpeening of steel of this hardness is beneficial primarily because of the nature of the macro-residual-stresses introduced by the process. There is no gain attributable to “strain-hardening” for this material. An effort was made to explain the results on the basis of three failure criteria: distortion energy, maximum shear stress, and maximum stress.*

PEARLITIC malleable iron crankshafts are being used in the new Pontiac engine as a result of recent developments. This paper discusses the physical properties of pearlitic malleable iron such as elastic modulus, fatigue endurance, and tensile strength. According to the author, definite machining economies result from using pearlitic malleable iron crankshafts.

The thermal deflection associated with the conventional die heat treating procedure usually requires extra die grinding process to fine-tune the die surface. Due to the size of the production die, the grinding is time consuming and is not cost effective. The goal of the study is to develop a new die heat treating process utilizing the flexible laser heat treatment, which could serve the same purpose as the conventional die heat treating and avoid the thermal deflection. The unique look of the developed zebra pattern laser heat treating process is defined as the Zebra Line. The heat-treating parameters and processes were developed and calibrated to produce the laser heat treating on laboratory size dies, which were subjected to the die wear test in the laboratory condition. The USS HDGI 980 XG3TM steel was selected to be carried out on the developmental dies in the cyclic bend die wear test due to its high strength and coating characteristic.

Four multigrade engine oils, containing the same base oil plus SE additive package but VI improvers of differing shear stability, were evaluated in 80 000 km of high-speed, high-temperature vehicle service. Bearing, piston ring and valve guide wear, as well as oil consumption, oil filter plugging and engine cleanliness were all worse for the engines operated on the low-shear stability oils. The wear differences were traced to differences in high-shear-rate viscosity, while the cleanliness, filter plugging and oil consumption differences occurred because of excessive wear or polymer shear degradation. These results suggest that engine oil viscosity should be specified under high-shear-rate conditions.

The strain-life approach is now commonly used for fatigue life analysis and predictions in the ground vehicle industry. This approach requires the use of material properties obtained from strain-controlled uniaxial fatigue tests. These properties include fatigue strength coefficient (σf′), fatigue strength exponent (b), fatigue ductility coefficient (εf′), fatigue ductility exponent (c), cyclic strength coefficient (K′), and cyclic strain hardening exponent (n′). To obtain the aforementioned properties for the material, raw data from stable cyclic stress-strain loops are fitted in log-log scale. These data include total, elastic and plastic strain amplitudes, stress amplitude, and fatigue life. Values of the low cycle fatigue properties (σf′, b, εf′, c) determined from the raw data depend on the method of measurement and fitting. This paper examines the merits and influence of using different measurement and fitting methods on the obtained properties.

Commercially available Third Generation Advanced High Strength Steels (GEN3 AHSS) are qualified by automakers worldwide. With an excellent combination of strength and ductility, GEN3 AHSS are cold-formable and have shown potential to replace press hardenable steels (PHS) in structural applications. With overall formability equivalent to 590DP, U. S. Steel 980 GEN3 AHSS (980 XG3™ AHSS) may achieve cold-formed component geometries similar to those achieved by hot-formed PHS. Furthermore 980 GEN3 AHSS demonstrates a substantial increase in post-forming yield strength due to the combined effects of work-hardening and bake-hardening-thereby contributing strongly toward crash energy management performance. The technical challenges and attributes of cold-formed 980 GEN3 AHSS are explored in this paper for an automotive rear rail application (currently PHS), including: formability analysis, wrinkling elimination and springback compensation.

Edge flanging represents one of the forming modes employed in multistage forming, and advanced high strength steels (AHSS) are more prone to edge cracking during sheared edge flanging than the conventional high strength steels (HSS) and mild steels. The performance of the sheared edge in flanging operation depends on the remaining ductility of the material in the sheared edge after the work hardening (WH) and damage produced by blanking and subsequent forming operations. Therefore, it is important to analyze the effect of work hardening produced by blanking and subsequent forming operations prior to edge flanging on the edge flanging performance. In this study, the effect of different forming operation sequences prior to edge flanging on the edge flanging performance was analyzed for a dual phase 780 steel.

Contacts or interactions commonly exist between adjacent components in automotive structures, and most of the time they dominate stress status of the components. However, when the routine pseudo stress approach is employed in fatigue life estimations, simulating contacts present special challenges. This may result in coarse stress status and corresponding coarser fatigue life estimations at the contact locations. In this paper, concept, development and procedures of two techniques to consider contacts in fatigue life estimations of automotive structures are described in detail. One is still pseudo stress approach based, but employs additional 1-D connection elements to simulate contacts. The other is nonlinear stress approach based, but equivalent constantly repeating cyclic critical load cases are introduced and utilized. The contacts are simulated by interface setup provided in the software.

Commercially available Generation 3 (GEN3) advanced high strength steels (AHSS) have inherent capability of replacing press hardened steels (PHS) using cold stamping processes. 980 GEN3 AHSS is a cold stampable steel with 980 MPa minimum tensile strength that exhibits an excellent combination of formability and strength. Hot forming of PHS requires elevated temperatures (> 800°C) to enable complex deep sections. 980 GEN3 AHSS presents similar formability as 590 DP material, allowing engineers to design complex geometries similar to PHS material; however, its cold formability provides implied potential process cost savings in automotive applications. The increase in post-forming yield strength of GEN3 AHSS due to work and bake hardening contributes strongly toward crash performance in energy absorption and intrusion resistance.

The more noise and vibration improvements are incorporated into our vehicles, the more customers notice squeaks and rattles (S&R). Customers increasingly perceive S&R as a direct indicator of vehicle build quality and durability. The high profile nature of S&R has the automotive industry striving to develop the understanding and technology of how to improve the S&R performance in the vehicle. Squeaks and itches make up a significant amount of Squeak and Rattle complaints found in today's vehicles. Squeaks and itches are the result of stick slip behavior between two interacting surfaces. Squeak itch behavior is dependent upon a large number of parameters including but not limited to: the material itself, temperature, humidity, normal load, system compliance, part geometry, velocity, surface roughness, wear, contaminants, etc. This paper will describe the analysis of sound data and friction data and the relationship between them.

Third generation advanced high strength steels (3GAHSS) are increasingly used in automotive for light weighting and safety body structure components. However, high material strength usually introduces higher springback that affects the dimensional accuracy. The ability to accurately predict springback in simulations is very important to reduce time and cost in stamping tool and process design. In this work, tension and compression tests were performed and the results were implemented to generate Isotropic/Kinematic hardening (I/KH) material models on a 3GAHSS steel with 980 MPa minimum tensile strength. Systematic material model parametric studies and evaluations have been conducted. Case studies from full-scale industrial parts are provided and the predicted springback results are compared to the measured springback data. Key variables affecting the springback prediction accuracy are identified.

Press hardenable ultra high strength steel (UHSS) is commonly used for automotive components to meet crash requirements with minimal mass addition to the vehicle. Press hardenable steel (PHS) is capable of forming complex geometries with deep sections since the forming takes place at elevated temperatures up to 900 degrees Celsius (in the Austenitic phase). This forming process is known as hot-stamping. The most commonly used PHS grade is often referred to as PHS1500. After hot-stamping, it is typically required to have a yield strength greater than 950 MPa and a tensile strength greater than 1300 MPa. Most automotive design and material engineers are familiar with PHS, the hot-stamping process, and their capabilities. What is less known is the capability of 3rd Generation advanced high strength steels (AHSS) which are cold stamped, also capable of forming complex geometry, and are now in the process of, or have recently completed, qualification at most automotive manufacturers.

The work presented here builds on the practical and effective spot weld fatigue life prediction method, the structural stress method (SSM), that was developed at Stanford University. Constant amplitude loading tests for various spot weld joint configurations have been conducted and the SSM has been shown to accurately predict fatigue life. In this paper refinements to the structural stress approach are first presented, including a variable amplitude fatigue life prediction method based on the SSM and Palmgren-Miner's rule. A test matrix was designed to study the fatigue behavior of spot welds under tensile shear loading conditions. Constant amplitude tests under different R-ratios were performed first to obtain the necessary material properties. Variable amplitude tests were then performed for specimens containing single and multiple welds.

In this paper, the development of random vibration testing schedules for durability design verification of engine mounted products is presented, based on the equivalent fatigue damage concept and the 95th-percentile customer engine usage data for 150,000 miles. Development of the 95th-percentile customer usage profile is first discussed. Following that, the field engine excitation and engine duty cycle definition is introduced. By using a simplified transfer function of a single degree-of-freedom (SDOF) system subjected to a base excitation, the response acceleration and stress PSDs are related to the input excitation in PSD, which is the equivalent fatigue damage concept. Also, the narrow-band fatigue damage spectrum (FDS) is calculated in terms of the input excitation PSD based on the Miner linear damage rule, the Rayleigh statistical distribution for stress amplitude, a material's S-N curve, and the Miles approximate solution.

An accurate representation of proving ground loading is essential for nonlinear Finite Element analysis and component fatigue test. In this paper, a rainflow counting based multiple blocks loading development procedure is described. The procedure includes: (1) Rainflow counting analysis to obtain the relationship between load range and cumulative repeats and the statistical relationship between load range and mean load; (2) Formation of preliminary multiple loading blocks with specified load range, mean load, and the approximate cycle repeats, and construction of the preliminary multiple loading blocks; (3) Calibration and finalization of the repeats for preliminary multiple loading blocks according to the equivalent damage rule, meaning that the damage value due to the block loads is equivalent to that from a PG loading.

In August 2005, National Highway Traffic Safety Administration (NHTSA) proposed to increase the roof strength requirement under Federal Motor Vehicle Safety Standard (FMVSS) 216 from 1.5 to 2.5 times unloaded vehicle weight (UVW). To meet the new requirement with a minimum impact on vehicle weight and cost, the automotive community is working actively to develop improved roof architectures using advanced high strength steels (AHSS) and other lightweight materials such as structural foam. The objective of this study is to develop an optimized steel-only solution with low material and part-manufacturing costs. Since the new regulation will present a particular challenge to the roof architectures of large vans, pickup trucks and SUVs due to their large mass and size, a validated roof crush model on a B-Pillar-less light truck is utilized in this study.

Two on-line algorithms have been developed to acquire driveline component loads in terms of revolutions at torque and rainflow cycle counting matrix. These algorithms have been implemented in real-time on a standard engine controller unit and have been optimized for fast run-time and low memory requirements. The revolutions at torque algorithm is intended to count the number of driveshaft revolutions in each torque level for each gear and store the number of counts in the engine controller memory. The rainflow cycle counting algorithm is intended to count driveshaft torque cycles and to store the number of counts in a two dimensional “from-to” matrix format in the engine controller memory. The revolutions at torque histogram data and the rainflow cycle counting matrix are then downloaded from the vehicle using the data collection device. Download occurs when the vehicle is serviced at a dealership.

Robust optimization usually requires numerous functional evaluations, which is not feasible when the functional evaluation is time-consuming. Examples in automobile industry include crash worthiness/safety and fatigue life simulations. In practice, a response surface model (RSM) is often used as a surrogate to the CAE model, so that robust optimization can be carried out. However, if the error in the RSM is significant, the solution based on the RSM can be invalid. This paper proposes a method of finding multiple candidate solutions, all of which have similar predicted performances. This approach is effective in finding the close-to-optimum solutions when the model has error, and providing design alternatives. Examples are provided to illustrate the method.

Magnesium alloys are the lightest structural metal and recently attention has been focused on using them for structural automotive components. Fatigue and durability studies are essential in the design of these load-bearing components. In 2006, a large multinational research effort, Magnesium Front End Research & Development (MFERD), was launched involving researchers from Canada, China and the US. The MFERD project is intended to investigate the applicability of Mg alloys as lightweight materials for automotive body structures. The participating institutions in fatigue and durability studies were the University of Waterloo and Ryerson University from Canada, Institute of Metal Research (IMR) from China, and Mississippi State University, Westmorland, General Motors Corporation, Ford Motor Company and Chrysler Group LLC from the United States.