There are several reflector types commonly used as a basis for establishing system performance and sensitivity. Included among them are spheres and flat-bottom holes (FBH), notches, side-drilled holes (SDH), and other special purpose or designs. Table 1 summarizes these reflectors characteristics and uses.  Spherical reflectors are used most often in immersion testing for assessing transducer sound fields. Spheres provide excellent repeatability because of their omnidirectional sound wave response. The effective reflectance from a sphere is much smaller than that received from a flat reflector of the same diameter due to its spherical directivity pattern.  Flat reflectors are used as calibration…

A crack can propagate through a material because of the concentration of stress at its tip, where the forces acting on the material are magnified. The propagation of a crack depends on the interaction between the applied load, material properties, and the size and shape of the crack. Reasons Why a Crack Propagates: Stress Concentration: At the tip of a crack, stress is much higher than in the rest of the material due to the geometry of the crack. The stress intensity factor (K) describes the stress field near the crack tip, and when K exceeds the material's fracture toughness…