Daniel B. Hayden

Fatigue and Fretting of Self-Piercing Riveted Joints

The fatigue life and fretting characteristics of aluminum alloy 5754-O self-piercing riveted lap joints have been investigated experimentally and analytically. The experimental program involves a set of 27 cyclic tension tests on three different joints consisting of either 1 mm, 2 mm or 3 mm-thick sheet specimens. In most cases (85%), fatigue cracks are found to initiate on the faying surface of the upper sheet, adjacent to the hole, and at an angular location that lies on the sheet loading axis towards the loading end. Three-dimensional finite element analysis of the three joints has also been performed. Computed distributions of local stresses and rivet-sheet slips are interpreted in terms of experimental observations of fatigue life, crack initiation location and fretting damage observations. Significantly, the calculations provide a rationale for the surprising crack initiation location.© 2002 ASME

Estimation of Metal Hardening Models at Large Strains

Simulation accuracy of large strain deformation of sheet metals, such as that which occurs during hemming and vehicle crash situations, is limited because existing hardening laws (true stress vs. true strain relationships) are extrapolated from uniform elongation data and applied for post-uniform deformation. In this paper, a reverse-engineering method was developed to predict metal hardening laws at large strains beyond uniform elongation for sheet metals. The method required a standard uniaxial tensile test and finite element analyses (FEA), and was implemented as a custom computer code called GMSS (General Motors Stress-Strain). The true stress vs. true strain data pairs are determined when the load and displacement history of a tensile test specimen matches the FEA results using GMSS. Test cases showed that the true stress vs. true strain relationships at very large strains (75% for AA6111 aluminum, and 85% for DP600 steel) could be automatically generated using GMSS. This reverse-engineering method will provide General Motors with an easy-to-use tool for generating very accurate metal hardening laws for post-uniform deformation that can greatly improve the accuracy of FEA for formability (including hemming), and crashworthiness simulations.Copyright

An Automotive Instrument Panel Employing Liquid Crystal Displays

An instrument panel cluster consisting of five twisted nematic liquid crystal displays has been installed and tested in a 1975 Chevrolet Monte Carlo. The displays are: warning indicators, speedometer, clock/odometer, fuel gauge, and transmission indicator (PRNDL). Four modes transmissive, reflective, and color transreflective. The remaining displays all operate in the reflective mode. A heater system allows operation over a -40 deg C to +80 deg C temperature range. /GMRL/