<i>In situ</i> observation of strain and phase transformation in plastically deformed 301 austenitic stainless steel

To inform the design of superior transformation-induced plasticity (TRIP) steels, it is important to understand what happens at the microstructural length scales. In this study, strain-induced martensitic transformation is studied by in situ digital image correlation (DIC) in a scanning electron microscope. Digital image correlation at submicron length scales enables mapping of transformation strains with high confidence. These are correlated with electron backscatter diffraction (EBSD) prior to and post deformation process to get a comprehensive understanding of the strain-induced transformation mechanism. The results are compared with mathematical models for enhanced prediction of strain-induced martensitic phase transformation

Measurement of Creep Deformation across Welds in 316H Stainless Steel Using Digital Image Correlation

Spatially resolved measurement of creep deformation across weldments at high temperature cannot be achieved using standard extensometry approaches. In this investigation, a Digital Image Correlation (DIC) based system has been developed for long-term high-temperature creep strain measurement in order to characterise the material deformation behaviour of separate regions of a multi-pass weld. The optical system was sufficiently stable to allow a sequence of photographs to be taken suitable for DIC analysis of creep specimens tested at a temperature of 545 °C for over 2000 h. The images were analysed to produce local creep deformation curves from two cross-weld samples cut from contrasting regions of a multi-pass V-groove weld joining thick-section AISI Type 316H austenitic stainless steel. It is shown that for this weld, the root pass is the weakest region of the structure in creep, most likely due to the large number of thermal cycles it has experienced during the fabrication process. The DIC based measurement method offers improved spatial resolution over conventional methods and greatly reduces the amount of material required for creep characterisation of weldments

Damage in dual phase steel DP1000 investigated using digital image correlation and microstructure simulation

Microstructure failure mechanisms and void nucleation in dual-phase (DP) steels during deformation have been studied using a combination of in situ tensile testing in a scanning electron microscope (SEM), digital image correlation (DIC) and finite element (FE) modelling. SEM images acquired during in situ tests were used to follow the evolution of damage within the microstructure of a DP1000 steel. From these images, strain maps were generated using DIC and used as boundary conditions for a FE model to investigate the stress state of martensite and ferrite before the onset of the martensite phase cracking. Based on the simulation results, a maximum principal stress of about 1700 MPa has been estimated for crack initiation in the martensite of the investigated DP1000 steel. The SEM image observations in combination with the FE analyses provide new insights for the development of physically-based damage models for DP-steels

Investigation on trailing-edge noise sources by means of high-speed PIV

The noise generation of turbulent flows over surfaces and around edges of airplanes and automobiles is a general design problem and its importance increases in times of growing traffic in this globalizing world. Turbulent boundary layers near the trailing-edge of a surface are known to generate intense, broadband scattering noise as well as surface pressure fluctuations. The wake of vortices shed depends on the trailing edge thickness and results in the emission of narrow band noise. The noise generating mechanisms depend essentially on the radial components of the velocity fluctuations in respect to the trailing edge. Resulting forces may also cause model vibrations, which are additional low frequency noise sources. In this feasibility study the high-speed PIV (HS-PIV) technique is applied to an investigation of the spatial and temporal development of coherent structures in a turbulent flat-plate boundary layer flow in the vicinity of the trailing-edge (TE). It is expected that with time resolved PIV data obtained in the region immediately up- and downstream of the TE an identification of noise sources and their correlation with the flow structure movement will be possible. On the basis of a large number of time resolved instantaneous velocity vector fields the technique enables also the possibility of determining several statistical quantities of fluid mechanical significance: average velocity profiles, velocity fluctuations (u´, v´), rms-fields, probability density functions and space-time-correlations of the velocity fluctuations and the z-component of vorticity. The far field noise intensity, which is radiated locally at the position of the TE, measured simultaneously with the instantaneous velocity fields by a directional microphone at 80 kHz sample rate. A phenomenological link between noise and flow structure movement by a comparison of the pressure -time -history of the far field with the time-velocity vector fields directly at the noise source is one objective of this investigation. A connection of the velocity fluctuation structures to the far field noise by means of space-time-correlations is a first step towards an identification of the noise generating flow structures

Nicht-lineare Laser-Raster-Mikroskopie. Teilvorhaben: Massive parallelprocessing zur Beschleunigung der Zweiphotonenmikroskopie Abschlussbericht

SIGLEAvailable from TIB Hannover: F02B644 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman