False-coloured X-ray diffraction images around the tip of crack C2 (detail from Fig. 2a). (a) Image 0037 at room temperature before heating of the crack C2. P1 marks the position where the opening of the crack is impeded. (b) Image 0045 at ∼598 K (ΔT ≃ 155 K). The image shows the opening crack which produces a huge strain field below P1 and a small one S1 directly above. (c) Image 0049 at 689 K shows increasing strain fields, the upper one into the  direction. A small-sized strained area S2 builds up near the tip. (d) Image 0060 at 788 K shows increasing strain at S1 above P1. (e) Image 0104 at 893 K. The strain fields below and above P1 have both increased in size and intensity. The thermal stress exceeds 24.8 MPa. (f) Image 0105 at 895 K. The crack C3 has developed to the left into the  direction in less than 0.72 s and the strain fields have significantly decreased in size and intensity.