With the renewed current interest in high strength steel and aluminum automotive body and chassis components it has again become important to properly assess the effects of corrosion on the fatigue behavior of structures. The present work summarizes the past work on fatigue and corrosion and presents new results on current automotive materials. The Neuber plasticity correction method, used throughout fatigue software of the ground vehicle industry to account for localized plastic behavior during fatigue, was found to give a very simple and useful technique for the computation of fatigue life of materials in corrosion environments. Data is offered for many common automotive structural materials and a method is given to adapt finite element calculations to compute corrosion fatigue life.
A procedure for the computation of fatigue life of shafts subjected to variable amplitude independent bending and torsion loading is described. The elastic superposition technique, followed by a Neuber plasticity correction, also allows for the initial and possibly cyclic plasticity dependent residual stress states caused by induction hardening or other surface altering processing effects. The present study documents the formation and alteration of residual stresses caused by initial induction hardening and followed by a straightening process. Sample calculations are presented for two critical finite elements of a prototype shaft, and lives are predicted using a traditional equivalent axial stress and by a new procedure that searches for and computes lives at critical angles.
The paper describes the fabrication and testing of thin sheet metal uniaxial fatigue specimens that have been laminated to prevent buckling. When hot or cold rolled metal thicknesses are below 5 mm, the usual fatigue specimens, having a uniform gauge length of 7.5 mm or more, buckle in the short life region (∼10000 cycles) of strain-life testing. For thinner materials, non-standard specimen designs or anti-buckling guides have been used, but each of these solutions requires additional instrumentation. The results presented in this paper show that laminating multiple sheets of material together to increase the specimen's effective thickness raises the strain level for the onset of buckling of the standard uniaxial specimen. Constant and variable amplitude fatigue tests extending into the high-strain short-life region were performed. Fatigue life data for multiple layer specimens were in good agreement with those obtained for single layer specimens.
A highly adaptable fatigue testing computer system is presented for controlling single or multichannel test machines. The system imposes most common varieties of waveforms and also provides time synchronization between channels, such as in the case of variable amplitude biaxial load histories, and monitors various feedback signals for both data acquisition and alarm purposes. The program operates in a real-time Unix system as a separate stand-alone process. Communication with other users or the operator is done only through a reserved common block of shared memory. This feature allows control and monitoring of all tests over the computer network. A user can simply login remotely and check the test or start a data acquisition task from any workstation in the company, and then take the data files and analyze them on other computers. This paper describes the operation of the software, the methodology behind the hardware selection and the software structure.
Field data measurements of structural behavior are often made for use in the evaluation of component or vehicle durability. Traditional life prediction methods have utilized uniaxial fatigue concepts for life estimation. Much recent work has been undertaken to extend the life prediction methods to multiaxial strain states. The following work discusses issues related to the analysis of strain gage rosette data for use in structural durability assessment. In particular, methods for identification of critical orientation in multiaxial cyclic load analysis are evaluated.