Who is the winner of a three point bending test? Hard PZT (PZT 4 and PZT 8) or Soft PZT (PZT 5A and PZT 5H)? The study by Abramovich et al. 2013 describes a three point bending test on 50 samples of each of these materials. The link to the article is here. The testing conditions were open circuit. 

The results show that PZT 5A and 5H are able to exhibit more strain and more stress in an off-resonance actuator scenario before fracture than hard PZT.

How do these results inform us regarding an ultrasonic transducer? Well, for high power applications, we traditionally think of hard PZT being the king due to its low heat generation and high Q. However, ultrasonic transducer transferring energy primarily through epoxy bonds, system Q is very low, and actually approximately equal between hard and soft PZT assembled devices.

 In that case, tolerance to high strain is important; the results in the article described here indicate that fracture limits of soft PZT are superior to hard PZT, thus it would be a superior choice for such an actuator. Very non-intuitive.