Photonic crystals are able to change the macroscopic color by regulating the center wavelength of band gap with altering the lattice constant of nano-structures. Herein, stretchable photonic crystals, with periodic cylinder shaped air holes non-close-packed in triangular lattice, are designed and fabricated for mechanochromism in entire visible light range. Numerical simulation has verified the excellent mechanochromic ability for the proposed nano-structure. Then the stretchable photonic crystals with this structure are successfully prepared by nanoimprinting technology on PDMS. Subsequently, the mechanochromic properties of the prepared materials are studied, and color change over the entire visible light range from red to blue is observed under a small strain of 29%. In addition, cyclic stretching tests up to 2000 times show that the materials are capable of maintaining shape recovery ability as well as mechanochromic ability. Finally, a stretchable visual strain sensor is prepared using the stretchable photonic crystal. This sensor can distinguish three strain ranges below 30% of strain rate by its color change that offers a visual observation of strain ranges. The stretchable visual strain sensors is more sensitive to small strain than resistance sensors, which may have great potential for applications of visual monitoring stretching strain.

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A nanoindentation method is employed to measure the high temperature mechanical properties, including hardness H, Young's modulus E and fracture toughness K c , of 8YSZ (ZrO 2 z8 wt-%Y 2 O 3 ) thermal barrier coatings (TBCs) under as sprayed condition and after subjecting them to thermal oxidation. The tests are conducted on the surfaces of YSZ coatings at temperatures of 250 and 450uC. The expressions for indentation H and E are deduced analytically, and the influence of testing temperature and thermal oxidation on them is discussed. An expression for estimating the fracture toughness of the coatings is also derived. The estimated fracture toughness values for the as sprayed YSZ coatings in terms of stress intensity factor at 250 and 450uC are determined to be 1?58 and 0?84 MPa m 1/2 respectively. For the oxidised YSZ coatings, these values are 1?35 and 1?10 MPa m 1/2 respectively. This study proves that nanoindentation tests can be performed at elevated temperatures for YSZ based TBCs.