Stefan Golling

Absolute Measurement of Elastic Waves Excited by Hertzian Contacts in Boundary Restricted Systems

In most applied monitoring investigations using acoustic emission, measurements are carried out relatively, even though that limits the use of the extracted information. The authors believe acoustic emission monitoring can be improved by instead using absolute measurements. However, knowledge about absolute measurement in boundary restricted systems is limited. This article evaluates a method for absolute calibration of acoustic emission transducers and evaluates its performance in a boundary restricted system. Absolute measured signals of Hertzian contact excited elastic waves in boundary restricted systems were studied with respect to contact time and excitation energy. Good agreement is shown between measured and calculated signals. For contact times short enough to avoid interaction between elastic waves and initiating forces, the signals contain both resonances and zero frequencies, whereas for longer contact times the signals exclusively contained resonances. For both cases, a Green’s function model and measured signals showed good agreement.

The influence of contact time and event frequency on acoustic emission signals

Studies of acoustic emissions (AE) of rotating machine elements is often performed under a constant speed. There are few investigations on speed and contact time dependency of acoustic emission signals, even though some investigations have reported difficulties at elevated rotational speeds. Simplified experiments are, therefore, presented in this article to increase the understanding of the time dependency of acoustic emission signals. Hertzian impacts and tensile tests are used to study contact time, the time duration of an event and offset time, the time between events and accordingly the event frequency. The results of these model experiments indicate an indirect quadratic proportionality of acoustic emission amplitudes and contact time ( u max ∝ 1 / ( t c 2 ) ), as well as a proportional relationship between the root mean square and event frequency ( RMS ∝ f event ∝ 1 / t offset ). The relationship between contact time and the root mean square of acoustic emission signals is strongly dependent on the damping of the system.

Microstructural and mechanical study of press hardening of thick boron steel sheet

Press hardening has become a staple in the production of automotive safetycomponents, due to the combination of high mechanical properties and form complexity itoffers. However, the use of press ha ...

Modeling of multi-phase microstructures in press hardened components: plastic deformation and fracture in different stress states

Hot stamping or press hardening is an industrialized technique with the aim of improving material properties by heat treatment and forming of a component in a single production stage. Within the fi ...