Fatigue strength of inner knurled interference fit joined by forming and cutting methods

The joining of machine parts by plastic forming is a common method for transmitting forces and torque. In drive trains, the ‘knurled interference fit’ has a high transmission capacity through the combination of frictional connection and form fit. In the present study, the shaft specimen made of C45 steel material is joined with an inner knurled hub made of 16MnCr5 case hardened steel. The influence of the joining process parameters on the torsional fatigue strength of the shaft-hub connection is investigated by means of experimental studies. The most important parameter is the chamfer angle of the knurled hub, which determines the rate of strain hardening in the material and differs between the cutting and forming joining processes. This study shows that knurled interference fit connections joined by forming achieve a higher fatigue strength and a higher maximum static torque than connections joined by cutting

Numerical Investigation of the Oxide Scale Deformation Behaviour with Consideration of Carbon Content during Hot Forging

Due to increasing product requirements the numerical simulation has become a powerful tool for the effective and efficient design of individual process steps as well as entire process chains. In order to model hot forging processes with finite element based numerical methods realistic models are required which consider the detailed mathematical description of the material behaviour during the forging process, the surface phenomena at die and workpiece as well as machine kinematics. Although this data exist for several steel grades, yet general mathematical models for steel groups based on alloying elements like carbon content are not available. In hot forging the surface properties are strongly affected by the growth of oxide scale, which influences material flow, friction as well as product quality of the finished components. The influence of different carbon contents on oxide scale growth and material behaviour is investigated by considering three different steel grades (C15, C45 and C60). For a general description of the material behaviour, an empirical approach is used to implement mathematical functions so as to express the relationship between flow stress and dominant influence variables like alloying elements, initial microstructure and reheating mode. The oxide scale consists of three different components namely wuestite, magnetite and haematite. In order to take the oxide scale into account, additional models are required to describe the growth kinematic and flow behaviour of the oxide scale components. The mathematical relationship between oxidation time, temperature, carbon content and oxide scale height is based on Arrhenius approach. The deformation behaviour of oxide scale is separately modelled for each component with parameterized flow curves. This paper gives first approaches on the numerical modelling of plastic deformation of oxide scale in a hot forging process. The main focus lies on the involvement of the different materials as well as the calculation and assignment of material properties in dependence of current process parameters by using subroutines. The numerical model and subroutines will be implemented in the FE-Software simufact.forming. A validation of the numerical model will be carried out by comparison of numerical results with experimental data

Accurate and Rapid Estimation of Phosphene Thresholds (REPT)

To calibrate the intensity of transcranial magnetic stimulation (TMS) at the occipital pole, the phosphene threshold is used as a measure of cortical excitability. The phosphene threshold (PT) refers to the intensity of magnetic stimulation that induces illusory flashes of light (phosphenes) on a proportion of trials. The existing PT estimation procedures lack the accuracy and mathematical rigour of modern threshold estimation methods. We present an improved and automatic procedure for estimating the PT which is based on the well-established Ψ Bayesian adaptive staircase approach. To validate the new procedure, we compared it with another commonly used procedure for estimating the PT. We found that our procedure is more accurate, reliable, and rapid when compared with an existing PT measurement procedure. The new procedure is implemented in Matlab and works automatically with the Magstim Rapid2 stimulator using a convenient graphical user interface. The Matlab program is freely available for download

Analysis of motoneuron responses to composite synaptic volleys (computer simulation study)

This paper deals with the analysis of changes in motoneuron (MN) firing evoked by repetitively applied stimuli aimed toward extracting information about the underlying synaptic volleys. Spike trains were obtained from computer simulations based on a threshold-crossing model of tonically firing MN, subjected to stimulation producing postsynaptic potentials (PSPs) of various parameters. These trains were analyzed as experimental results, using the output measures that were previously shown to be most effective for this purpose: peristimulus time histogram, raster plot and peristimulus time intervalgram. The analysis started from the effects of single excitatory and inhibitory PSPs (EPSPs and IPSPs). The conclusions drawn from this analysis allowed the explanation of the results of more complex synaptic volleys, i.e., combinations of EPSPs and IPSPs, and the formulation of directions for decoding the results of human neurophysiological experiments in which the responses of tonically firing MNs to nerve stimulation are analyzed

Impairment of Auditory-Motor Timing and Compensatory Reorganization after Ventral Premotor Cortex Stimulation

Integrating auditory and motor information often requires precise timing as in speech and music. In humans, the position of the ventral premotor cortex (PMv) in the dorsal auditory stream renders this area a node for auditory-motor integration. Yet, it remains unknown whether the PMv is critical for auditory-motor timing and which activity increases help to preserve task performance following its disruption. 16 healthy volunteers participated in two sessions with fMRI measured at baseline and following rTMS (rTMS) of either the left PMv or a control region. Subjects synchronized left or right finger tapping to sub-second beat rates of auditory rhythms in the experimental task, and produced self-paced tapping during spectrally matched auditory stimuli in the control task. Left PMv rTMS impaired auditory-motor synchronization accuracy in the first sub-block following stimulation (p<0.01, Bonferroni corrected), but spared motor timing and attention to task. Task-related activity increased in the homologue right PMv, but did not predict the behavioral effect of rTMS. In contrast, anterior midline cerebellum revealed most pronounced activity increase in less impaired subjects. The present findings suggest a critical role of the left PMv in feed-forward computations enabling accurate auditory-motor timing, which can be compensated by activity modulations in the cerebellum, but not in the homologue region contralateral to stimulation