Social sustainability, sustainable development and housing development: the experience of Hong Kong

In the experimental research of ultrasonic detection and characterization of cracks, laboratory specimens are indispensible. For surface-breaking cracks, the usual method for metals is fatigue growth and for brittle materials an indentor may be used to initiate the crack. The fabrication of interior crack specimen is generally more difficult. Diffusion bonding has been used in producing specimens containing simulated interior cracks and thin cracks have also been simulated by including yttria power between the diffusion bond surfaces.1 We report here a technique for inducing interior fracture cracks in transparent plastic resin with focused laser energy. Such specimens are useful for ultrasonic characterization of crack parameters such as size and orientation. This technique has the following advantages: (i) It is quite easy to implement; (ii) The induced damages are usually flat circular cracks which closely approximate the “penny-shaped crack” — the subject of many experimental and theoretical studies for ultrasonic scattering;2 and (iii) This method provides a variety of crack size and orientation for ultrasonic sizing experiments and the results may be compared with direct optical microscopic measurements