John Joseph Francis Bonnen

The effect of bending overloads on torsional fatigue in normalized 1045 steel

Abstract Variable amplitude bending-torsion fatigue experiments were conducted on axle-shafts to determine the effects of overloads on the fatigue life of normalized SAE 1045 steel. Either periodic bending overloads or static bending loads were applied to these shafts to determine their effect on torsional fatigue. It was determined that these yield stress level bending excursions both decrease the torsional fatigue limit and shorten the torsional fatigue life at medium and long lifetimes. The magnitude of this effect is very similar to that of uniaxial overloads, and a multiaxial fatigue parameter was found which causes the uniaxial and multiaxial datasets to fall on a single parameter–life curve. It is postulated that the fatigue strength reduction is due to a reduction in crack face interaction which results in an increase in effective strain intensity.

The role of in-phase and out-of-phase overloads on the torsional fatigue of normalized SAE-1045 steel

Abstract Several researchers have demonstrated that, under both uniaxial and in-phase biaxial loading, periodic overloads of yield stress level magnitude can be used to eliminate the effects of crack-face interference. In the current research a series of experiments using either axial or torsional overloads were conducted in order to determine their effects on the torsional fatigue of normalized SAE1045 steel tubes. It was determined that, in the high cycle regime, both types of overload had the same impact on fatigue life. The effect on the torsional high cycle fatigue of axial/torsional mean stress following an axial/torsional overload was found to be minimal for both the zero mean and peak strain cases examined. Lastly, the results of these experiments were compared with similar fatigue data for this material from both axle-shafts and in-phase overload tests. This larger data set was then used to evaluate various multiaxial parameters, and it was found that the Fatemi–Socie–Kurath parameter yielded the best data correlation.

Electrohydraulic Sheet Metal Forming of Aluminum Panels

In this paper, we present results of testing from sheet metal forming trials using pulsed electrohydraulic technology. Pulsed electrohydraulic forming is an electrodynamic process, based upon high-voltage discharge of capacitors between two electrodes positioned in a fluid-filled chamber. Electrohydraulic forming (EHF) combines the advantages of both high-rate deformation and conventional hydroforming; EHF enables a more uniform distribution of strains, widens the formability window, and reduces elastic springback in the final part when compared to traditional sheet metal stamping. This extended formability allows the fabrication of aluminum panels that are difficult to make conventionally even of EDDQ steel, and it thereby vastly improves the number automotive weight reduction opportunities. The paper presents discoveries regarding chamber design, electrode erosion, forming, and results of finite element multiphysics simulations of system performance.

Analysis of Dynamic Loads on the Dies in High Speed Sheet Metal Forming Processes

During high-speed sheet metal forming processes, the speed at which the work piece contacts the die tooling is on the order of hundreds of meters per second. When the impact is concentrated over a small contact area, the resulting contact stress can compromise the structural integrity of the die tooling. Therefore, it is not only important to model the behavior of the workpiece during the high-speed sheet metal forming process, but also important to predict accurately the associated workpiece/tooling interface loads so that engineers can more confidently propose robust die tooling designs. The foundation to accurate predictions of contact stress on die tooling is a reliable contact model within the context of a finite element simulation. In literature, however, there exists no comprehensive guideline for establishing a contact model for high-speed sheet metal forming processes using the finite element method. In this paper, mathematically justified contact model recommendations are offered for the electrohydraulic forming (EHF) process.