Microsecond time-resolved X-ray diffraction for the investigation of fatigue behavior during ultrasonic fatigue loading

Abstract

A new method based on time-resolved X-ray diffraction is proposed in order to measure the elastic strain and stress during ultrasonic fatigue loading experiments. Pure Cu was chosen as an example material for the experiments using a 20 kHz ultrasonic fatigue machine mounted on the six-circle diffractometer available at the DiffAbs beamline on the SOLEIL synchrotron facility in France. A two-dimensional hybrid pixel X-ray detector (XPAD3.2) was triggered by the strain gage signal in a synchronous data acquisition scheme (pump–probe-like). The method enables studying loading cycles with a period of 50 µs, achieving a temporal resolution of 1 µs. This allows a precise reconstruction of the diffraction patterns during the loading cycles. From the diffraction patterns, the position of the peaks, their shifts and their respective broadening can be deduced. The diffraction peak shift allows the elastic lattice strain to be estimated with a resolution of ∼10−5. Stress is calculated by the self-consistent scale-transition model through which the elastic response of the material is estimated. The amplitudes of the cyclic stresses range from 40 to 120 MPa and vary linearly with respect to the displacement applied by the ultrasonic machine. Moreover, the experimental results highlight an increase of the diffraction peak broadening with the number of applied cycles.

Effect of electric fields in low-dimensional materials: Nanofrictional response as a case study

“…2); this is expected, since such a crystallographic axis is parallel to the direction of the applied field E. As we discuss later on, some structure becomes unstable for field values beyond a certain threshold which depends on the material; for those values, the lattice parameters correspond to a transient configuration which belongs to a geometric path connecting two stable states. Such transient configuration can be detected by time-resolved crystallography techniques, capable to monitor structural changes occurring in very short time scales [61][62][63]. Concerning the phonon structure, we observe that an increase of the field produces a general hardening of the − A modes together with a softening of some sliding branches, which may become unstable beyond some critical E (E = |E|) value specific of the system.…”

Estimation of stress in specimens loaded with ultrasonic fatigue machines

“…The in situ time-resolved XRD method applied to ultrasonic fatigue tests is a recently developed technique detailed in [18,19]. Its principle is the estimation of the applied stress (through the measurement of the lattice strain) from the measured Δ2θ shift of the diffraction peak position on the 2D detector.…”

“…After each image acquisition, an additional small delay is applied to the trigger so that the next detector image is captured at a different stress level within the sinusoidal loading. The setup requires an electronic system that synchronizes the short electronic opening of the detector with the cyclic deformation applied by the piezo-electric machine, see [18] for further details.…”

“…The stress field within the specimen can then be estimated by computing the response of a modeled specimen with a 1D or 3D geometry loaded in push-pull mode, and assuming that the specimen behavior is purely elastic [9,10,16]. • More recently, Ors et al [18] developed a third method based on measurements of the elastic strain. The method requires that timeresolved X-ray diffraction (XRD) be carried out in situ at the loading frequency (20 kHz) on a synchrotron beamline.…”

The CirPAD, a circular 1.4 M hybrid pixel detector dedicated to X-ray diffraction measurements at Synchrotron SOLEIL

“…* Single Bunch Mode: acquisition with an ultra-short gate, down to 100 ns for time-resolved applications (Fertey et al, 2013;Ors et al, 2019).…”