Intermittent plasticity in individual grains

A study using high energy x-ray diffraction.

Understanding the behavior of metals undergoing deformation is critical to design for fuel efficiency, performance and safety/crashworthiness. Traditional engineering analysis treats metal deformation as a smooth motion, like a fluid, when in reality the flow is intermittent at finer length scales. Use of a new detector enabled the study of these intermittent bursts of deformation at the scale of individual crystals in a loaded test sample.
A metal component is polycrystalline, composed of many crystals or grains. At the scale of millimeters, the deformation of a metal appears to proceed smoothly, whereas at the microscopic scale the underlying processes occurring in individual grains proceed in fits and starts. In this collaboration between researchers at Cornell University, the University of Illinois at Urbana-Champaign, the Air Force Research Laboratory and the Advanced Photon Source of Argonne National Laboratory, a high-speed detector was used to study these microscale deformation bursts in a grain-by-grain manner.

>Read more on the CHESS website

Image: The MM-PAD is shown with the vacuum cover and x-ray window removed. The 2×3 arrangement of detector modules are the brownish squares in the center.  Each module consists of 128×128 square pixels, where each pixel is 150µm of a side. Each module is roughly 2 cm x 2 cm in size. There is a 5 pixel wide (0.75 mm) inactive area between adjacent modules. (This photo is of an MM-PAD with Si, instead of CdTe sensors; otherwise, the two types of MM-PADs look identical.)

Big science -literally- at ESRF

This is no ordinary experiment. With a huge detector in tow and a team of 15 scientists from Goethe University in Frankfurt (Germany), it is probably as big as science gets -literally.

A 4-metre-long lorry arrived at the ESRF with a precious load: a so-called COLTRIMS Reaction Microscope. The chamber is so big that it requires a crane to fit it into the experimental hutch of ID31. And lots of manpower to set the experiment up. The aim: to image the momentum distribution of one of the two electrons in the Helium atom without averaging over the momentum distribution of the other, offering the most complete and detailed view on electron correlation.

The COLTRIMS technique allows the team to measure event by event the initial state momentum of a Compton scattered electron of a Helium atom and, in coincidence with this, they measure the second electron’s momentum as it is shaken off.

>Read more on the European Synchrotron website

Image: The team was in high spirits throughout the two-week duration of the experiment.
Credits: M. Kircher.

X-ray detector for studying characteristics of materials

Sol M. Gruner’s group, Physics, has been a leader in the development of x-ray detectors for scientific synchrotron applications, and the team’s technology is used around the world. Their detectors utilize pixelated integrated circuit silicon layers to absorb x-rays to produce electrical signals. The wide dynamic range, high sensitivity, and rapid image frame rate of the detectors enable many time-resolved x-ray experiments that have been difficult to perform until now.

The detectors are limited by the silicon layer. Low atomic number materials such as silicon become increasingly transparent to x-rays as the energy of the x-rays rises. Gruner’s group is now developing a variant of their detector that will use semiconductors comprised of high atomic weight elements to absorb the x-rays and produce the resultant electrical signals. The Detector Group, led by Antonio Miceli, at the United States Department of Energy’s Advanced Photon Source (APS) will simultaneously develop the ancillary electronics and interfacing required to produce fully functional prototypes suitable for high x-ray energy experiments at the APS and CHESS.

>Read more on the CHESS website

Image: Sol M. Gruner, Physics, College of Arts and Sciences
Credit: Jesse Winter