POLDI: Pulse Overlap time-of-flight Diffractometer

 

 

 

 

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Case study 1 - residual stress


Figure 1. Half model of the pump casing. The 5 lines indicate where the measurements have been done.

Residual stress was determined in a pump casing fabricated from a quenched aluminum alloy Al2104 TB, which constitute part of fuel transmission system in aircrafts. Figure 1 shows a half model of the pump casing.


Two sets of stress-free samples were used in this measurement to determine the corresponding do for the residual stress measurement (see also Figure 1). The first set included a cube of dimension 10mm×10mm×10mm cut out from a corner near a free edge of the sample and distant from the measurement zone. The second set consisted of a core of diameter 10mm electrodischarge- machined from an identically treated (quenched) sample through its centre which was sliced into 6 discs each of diameter 10mm and thickness of 5mm.


All three strain components were measured along 5 lines shown. Figure 2 displays the lattice parameter determined from the three strongest reflections along the central line through the thickness of the quenched sample. Here only the radial component is shown. The data points of the three reflections are on top of each other, indicating that intergranular stresses are negligible.


Figure 3 compares the measured residual stress distribution through the centre of the quenched specimen with finite element (FE) predictions of residual stresses. The agreement is excellent apart from a small region close to the top surface.


Courtesy: C. E. Truman et al, University of Bristol


Figure 2. Lattice parameter for three reflections measured in radial direction.

Figure 3. Residual stress in three directions compared to finite element calculations.