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Technical Paper

Vehicle Road Simulation Testing, Correlation and Variability

2005-04-11
2005-01-0856
In this paper, responses from a vehicle's suspension, chassis and body, are used to demonstrate a methodology to optimize physical test results. It is well known that there is a variability effect due to an increase of wheel unsprung mass (due to loads measurement fixturing), tire pressure, speed, etc. This paper quantifies loading variability due to Wheel Force Transducer (WFT) unsprung mass by using a rainflow cycle counting domain. Also, presents a proving ground-to-test correlation study and the data reduction techniques that are used in road simulation test development to identify the most nominal road load measurement. Fundamental technical information and analytical methodology useful in overall vehicle durability testing are discussed. Durability testing in a laboratory is designed to correlate fatigue damage rig to road. A Proving Ground (PG) loading history is often acquired by running an instrumented vehicle over one or more PG events with various drivers.
Technical Paper

The Effect of HIP Processing on the Properties of A356 T6 Cast Aluminum Steering Knuckles

2004-03-08
2004-01-1027
Hot Isostatic Pressing (HIP) has been routinely used to densify castings for aerospace and medical applications for over 30 years. While HIP is widely known to improve the toughness and fatigue life of castings through the healing of internal porosity, it has been perceived as too expensive for most cast aluminum alloys for automotive applications. Recent developments suggest that the cost effectiveness of certain special HIP processes should be revisited due to reductions in process cost and improvements in throughput. This paper will evaluate the Densal® II process applied to a front aluminum steering knuckle. Two casting processes representing differing levels of relative cost and quality were evaluated. The first was Alcoa's VRC/PRC process, a metal mold process with bottom fill, evacuation before fill and pressurization after fill. This is considered to be a premium quality, but higher cost casting process that is already qualified for this application.
Technical Paper

Stamping and Crush Performance of Dual Phase Steel

2001-10-16
2001-01-3074
Traditionally, high-strength low-alloy (HSLA) steel is used for automotive vehicle weight reduction in the North American automotive industry. Dual phase (DP) high strength steel has gained great attention because it provides a combination of high strength and good formability. The main advantage of DP steel is the high ratio of tensile strength to yield strength, which provides more flexibility in stamping and higher energy absorption in a component crush event. This study compares the performances of DP and HSLA steel grades in stamping processes and component crush events, as shown in a typical automotive unibody inner rail. Simulation results show that DP steel offers more uniform strain distribution, improved formability, and better crush performance than conventional HSLA steel.
Technical Paper

Reliability-Based Fatigue Strength Testing by the Staircase Method

2004-03-08
2004-01-1288
The staircase fatigue testing method is a recognized method for determining the fatigue limit of powertrain components. The purpose of this paper is to improve upon existing standards by adding common practices that will ensure a higher degree of statistical accuracy in the data. This includes specifying appropriate sample sizes, stress increments and initial load conditions, as well as making suggestions for appropriate methods of analyzing the data. Two methods (Dixon and Mood method and probit analysis method) are selected and compared in terms of relative percent difference on four parameters (mean, standard deviation, B10 fatigue strength and B50 fatigue strength). The staircase data are obtained by simulations from normal and lognormal fatigue limit distributions.
Technical Paper

Pump Noise Reduction Using Shainin Statistical Engineering Methods

2001-04-30
2001-01-1542
Historically, pump noise can be a contributor to customer dissatisfaction with automatic transmissions. In this paper, a Shainin experiment was conducted to identify all probable root causes for pump noise on a production RWD transmission. Sample transmissions were selected following subjective evaluations. Noise was objectively measured in the lab using a microphone and an accelerometer. The study was conducted following a systematic Shainin statistical engineering methodology, which included the following major steps: selection of the test measure using the isoplot technique, selection of Best of Best (BOB) and Worst of Worst (WOW) transmissions, assessment of assembly variation, component search, and pair-wise comparisons. The study successfully highlighted the key variables on the drive gear involute profile, which are now being tightly controlled for improved noise characteristics.
Technical Paper

Proactive Ergonomic Verification Through Human Biodynamic Modeling and Digital Simulation

1999-09-28
1999-01-3371
An extensive digital simulation study on lift devices that interact with human operators in DaimlerChrysler automotive assembly plants has been initiated and deployed. This digital mock-up of human-machine workcells is to scientifically evaluate and further certify a number of typical commercial lift devices that are served in car-assembly operations. The entire model is based on human biomechanical Jacobian relationship, as a fundamental kinematic structure, to predict human body instantaneous joint-torque distribution when the human is working with a certain payload. The developed modeling and simulation system will play a pivotal role in proactive ergonomic prediction, verification and digital certification in car advance manufacturing engineering processes.
Technical Paper

Prediction of Draw Bead Coefficient of Friction Using Surface Temperature

2002-03-04
2002-01-1059
Sheet metal stamping involves a system of complex tribological (friction, lubrication, and wear), heat transfer, and material strain interactions. Accurate coefficient of friction, strain, and lubrication regime data is required to allow proper modeling of the various sheet stamping processes. In addition, non-intrusive means of monitoring the coefficient of friction in production stamping operations would be of assistance for efficiently maintaining proper stamping quality and to indicate when adjustments to the various stamping parameters, including maintenance, would be advantageous. One of the key sub-systems of the sheet metal stamping process is the draw bead. This paper presents an investigation of the tribology of the draw bead using a Draw Bead Simulator (DBS) Machine and automotive zinc-coated sheet steels. The investigation and findings include: 1) A new, non-intrusive method of measuring the surface temperature of the sheet steel as it passes through the draw bead.
Technical Paper

Methodology for Vehicle Box Component Durability Test Development

2004-03-08
2004-01-1690
During the initial vehicle design phase and as the first prototypes are built, extensive on-board instrumentation and data acquisition is required at the proving grounds (PG). The data is used for various types of testing and analysis. During this phase of development very few parts and assembly components are available for physical test. The objective is to develop a component test for the truck box. This test can be run without suspension parts during the early stages of the vehicle development. A further objective is to correlate the test to FEA models and actual Proving Ground full vehicle test results.
Technical Paper

Fatigue Analysis for Axle Differential Cases

2006-04-03
2006-01-0779
The recent trends of increasing driveline torque and use of traction control devices call for increasingly higher durability capacity from driveline components. Bench and vehicle durability tests are often used to validate designs, but they are not cost-effective and take months to complete. Traditional finite element analysis (FEA) procedures have been used effectively in the re-design of driveline components to reduce stress, and occasionally, to predict fatigue life. But in the case of certain rotating components, such as the Axle Differential Case, where the component sees large stress/strain fluctuations within the course of one complete rotation, even under constant input torque, historical fatigue analysis (when conducted) yields very conservative results. The axle differential case tends to be one of the weakest links in the rear axle assembly. Therefore, there is a crucial need for analytical methods to more accurately predict fatigue life to reduce testing time and cost.
Technical Paper

Effect of Forming Strain on Fatigue Performance of a Mild Automotive Steel

2001-03-05
2001-01-0083
The effect of forming strains on the fatigue behavior of an automotive mild steel, interstitial free steel, was studied after being prestrained by balanced biaxial stretch and plane strain. In the long life region, higher than 5×105 reversals, prestrain improves fatigue resistance. In the short life region, prestrain reduces fatigue resistance. At even shorter fatigue lives, the detrimental effect of prestrain diminishes. For plane strains, the fatigue behavior is anisotropic. In the direction perpendicular to the major strain, the steel exhibits much better fatigue resistance than in the direction parallel to the major strain.
Technical Paper

Drivetrain Torsional and Bending Vibration for a RWD Vehicle Interior Noise Development

2003-05-05
2003-01-1496
In a vehicle NVH development and refinement phase, it is necessary to understand the source of the noise and vibration from various powertrain and drivetrain mechanisms. The noise and vibration generated by a drivetrain in a vehicle is a complicate but significant source of physical mechanism, which might become important issues in early or later phase of the vehicle development. For the diagnostic purpose of the drivetrain, a rear-wheel drive (RWD) vehicle in early development phase has been used to measure the bending and torsional vibration of the drivetrain, as well as the vehicle interior noise simultaneously, while the vehicle is running up and down under quasi-steady state on a chassis dynamometer. The lower frequency resonances of torsional and bending vibrations from the drivetrain are correlated with the vehicle interior boom or overall loudness.
Technical Paper

Advances in Thixomolding Magnesium Alloys Part II

2003-03-03
2003-01-0181
Thixomolding (1) is a relatively new process in which the metallic slurry is injected into a die cavity tool at semi-solid or liquid temperatures to form near net-shape products from the solid feedstock. As part of on-going research into Thixomolding technology, this study continues the work of a previous study, that concentrated on magnesium alloys AZ91D and AM60B. The test samples were made with high, low and zero percent fraction solid. The test results of the thixomolded samples of the various percent fraction solid are compared to conventional high pressure die casting samples and there is a discussion of the why the Thixomolding process produces superior properties. In addition, a comprehensive corrosion resistance study was completed utilizing uncoated corrosion plates in an salt spray environment (ASTM B117).
Technical Paper

Achieving Acceptable Cp and Cpk Values in Sheetmetal Stampings

1999-09-28
1999-01-3193
Detail parts are approved during several different phases of the prototype build cycle. There is much pressure at all stages to meet strategic body quality targets. Parts stamped for assembly must meet a process capability requirement of Cpk>1.33. For final PSO (process sign off), as called out in the PPAP (Production Part Approval Process) manual, the requirement can be increased to meeting a Cpk>1.67. During the 2000 Neon part approval process, the PPAP requirements provided the guideline necessary for consistent buy-offs. However, on some critical parts the Cpk requirement made part approvals difficult to accomplish. Occasionally this caused resources to be focused in the wrong place. This paper will discuss how a requirement of Cpk>1.33 can make part approvals more difficult to achieve and change the entire application of a tolerance.
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