A Fracture‐Mechanics Study of ZnSe for Laser Window Applications

Abstract

Fracture‐mechanics studies of chemically vapor‐deposited ZnSe show that this material has a low fracture toughness and is susceptible to water‐(moisture‐) dependent slow crack growth. Investigations of biaxial flexural strength indicate that fracture (in this configuration) is controlled primarily by surface flaws and that macrofracture mechanics adequately describe the propagation of typical preexisting flaws in this ZnSe. Crack growth can be detected consistently by the acoustic emission technique; fracture in air is preceded by precursor events which occur up to 2 s prior to catastrophic propagation. Failure diagrams generated from the slow‐crack‐growth parameters show that the lifetime requirements of the laser window can be achieved by overload proof‐testing to a proof ratio of 1.35 when the proper proof‐test precautions are implemented.