We present a passive vibration compensation approach in scanning white-light interferometry (SWLI). A pointwise distance measuring interferometer (DMI) obtains fast temporal distance changes during the white-light depth-scan of an aerial-measuring Michelson white-light interferometer for topography measurement. Both interferometers share a part of the optical path so that the measurement spot of the DMI is within the field of view of SWLI. With the real positions of the interferometer with respect to the measuring object during the depth scan known from DMI measurements, we can compensate for the influence of unintentional distance changes caused by environmental vibrations or scanner nonlinearities. By reordering of the captured image frames and improved correlogram interpolation, we are able to reconstruct correct signals from completely distorted (and unusable) SWLI signals. Although the basic idea of the system already has been published, we improved the signal reconstruction technique so that the specimen's topography measurement can be obtained with the same accuracy as without any vibrations or scan distortions influence. In addition, we demonstrate the feasibility of the approach by different practical measurements with and without vibrations.

Hard phases such as martensite regions affect micro-crack extension by blocking the plastic zone ahead of the crack tip, but also by changing the crack opening which can be taken as loading quantity for cracks. This paper deals with the measurement of crack opening for microcracks in a ferrite/martensite dual phase steel. The methods used are in-situ testing in the SEM, X-ray tomography, and digital image correlation. It was found that martensite regions affect the relative displacement of the crack phases both at the crack tip and in the crack wake.

Zusammenfassung: Weiẞlichtinterferometer sind hochauflösende optische Messgeräte zum dreidimensionalen Messen von Mikrostrukturen. Der Einsatz solcher Messgeräte in maschinennaher Umgebung abseits schwingungsgedämpfter Labore wird durch Umgebungsschwingungen erschwert oder sogar unmöglich gemacht. Daher wird nach Algorithmen oder modifizierten Anordnungen gesucht, um den Einfluss der Störschwingungen zu kompensieren bzw. aus den Ergebnissen herauszurechnen. In diesem Beitrag wird ein passives Kompensationsverfahren vorgestellt, mit dem der Einfluss einer monofrequenten Störschwingung kompensiert werden kann. Dazu wird ein punktförmig messendes Laserinterferometer verwendet, das in das Weiẞlichtinterferometer (WLI) integriert ist und parallel zur Weiẞlichtmessung mit höherer zeitlicher Auflösung das Interferenzsignal des Lasers aufzeichnet. Die Bestimmung des jeweiligen Abstands zwischen WLI und Messobjekt erfolgt nachträglich durch Fourieranalyse, wobei die erforderlichen Parameter wie Frequenz, Amplitude und Phasenlage der Störschwingung aus dem Amplituden-bzw. Phasenspektrum des Interferenzsignals ermittelt werden. Diese Information wird genutzt, um die gestörten WLI-Korrelogramme zu korrigieren. Anschlieẞend kann die Oberflächentopographie auf konventionelle Weise mit Hilfe der Hüllkurven-und der Phasenauswertung bestimmt werden. Schlüsselwörter: Weiẞlichtinterferometrie, Schwingungskompensation, Michelson-Laserinterferometer, Insitu-Messung, Frequenzanalyse.Abstract: White-light interferometers (WLI) are highresolution optical instruments for 3D measurements of micro objects. Till now, the use of such systems in closeto-machine-applications is difficult or nearly impossible due to environmental vibrations. For this reason new algorithms or modified setups are required that compensate for the influence of vibrations or remove them from measured interferograms. In this paper we introduce a novel passive technique for compensating the influence of singlefrequency vibrations from measured data. For this purpose we integrate a point-wise measuring laser interferometer into a WLI and capture its interference signal with high temporal resolution during the depth-scan. After the measurement is finished we evaluate the laser interference signal in the frequency domain and obtain amplitude, frequency, and phase of the disturbing vibration. With this knowledge we obtain real distance changes during the depth scan and correct the WLI correlograms. Based on this procedure it is possible to calculate the surface topography from the corrected dataset in the conventional way by envelope peak of phase evaluation.

Physically small cracks in a ferritic martensitic steel were analyzed in the SPring-8 synchrotron facility. Change in the crack shape under static and cyclic loading could be determined in addition to the crack shape by mounting micro-specimens in an inbeam loading stage. Additional information can be gained by comparing three-dimensional images of the crack faces using volumetric digital image correlation. The displacement field on the crack faces is then available which, in turn, can be correlated to the microstructure determined by serial sectioning and orientation microscopy.

The formation and the three-dimensional shape of slip bands in a fatigued dual phase steel were analyzed with the purpose of understanding the relation between fatigue crack initiation and the topography development on the specimen surface. Fatigue tests with small dog-bone-shaped specimens were conducted under fully reversed axial loading (R = -1) with a constant stress amplitude and were interrupted when the first slip bands occurred and at defined numbers of load cycles, respectively. Subsequently the surface topography of the specimen was investigated with a white light interferometer with hundredfold magnification and high numerical aperture (NA = 0.9) which allows analyzing the surface of individual grains. The results were confirmed by additional atomic force microscopy measurements. Based on this analysis the height, width and length of the slip bands are known at different stages of the fatigue process. The results obtained using white light interferometry and AFM, were checked by cutting individual slip bands with the help of focused ion beam thus revealing the true shape of the slip bands.