Micro-impact technique and its applications

Abstract

A micro-impact tester has been designed and built by using a piezoelectric impact hammer as an impactor driver. During the course of an impact process, force interactions between the impactor and target surfaces were monitored continuously by a miniaturized piezoelectric loadcell embedded in the flying head assembly. A 3-sided pyramidal diamond indenter (Berkovich indenter) was used as an impactor. After having fully characterized such an impact system, the trajectory of the impactor can be calculated by using the corresponding prerecorded impact force interaction in a simulation program. The contact and returning velocities, kinetic energy loss of the impactor, and the impact penetration curve are the key pieces of information obtained from the simulation. Furthermore, the impact morphology can reveal failure mechanisms of materials by providing details such as indent shapes, coating fragment, chipping, crack type and size, and other information which are useful in assessing the fracture toughness of testing materials. The micro-impact testing was carried out in the contact velocity ranging from 0.3 to 2.0 m/s. Three types of materials such as metal, glass, and amorphous carbon were used in studying their distinct mechanical behavior under high rate indentations. The correlations among the impact conditions, energy losses, impact morphologies, and material responses are illustrated and discussed.

New tools for structural testing - Piezoelectric impact hammers and acceleration rate sensors

“…12¡18 A completely different concept, which is based on a waveguide design to transform the blocking force of piezoelectric materials into a free-ying motion, was created by Chang and Wang 19;20 to achieve large motion for piezoelectrically driven mechanisms. This mechanism was later improved by Lee and Wu, 21 and Wu and Lee, 22 who added an on-line load cell into a free-ying object to detect impact force as well as to create a piezoelectric impact hammer system. The optimization process and many design modi cations to the aforementioned system will be discussed in detail herein.…”

Fabrication of a Piezoelectric Impact Hammer and Its Application to theIn-situNondestructive Evaluation of Concrete

“…The waveguide concept has been applied to design a high-speed piezoelectric-driven system for application in the printer industry by Chang and Wang. 9,10) Later, the mechanism was improved by Wu and Lee,11) which included an on-line load cell to detect the impact force for microimpact applications such as the study of the mechanical properties of amorphous carbon under high-rate indentation. The highspeed piezoelectric hammer has also been applied recently to the structural modal testing of a small metallic structure to give precise impact timing and positioning by Lee et al 12) To the best of our knowledge, the application of the waveguide-based piezoelectric hammer to the nondestructive evaluation (NDE) of concrete structure has not been reported.…”