Residual stress craze and crack formation in poly(methyl methacrylate)

Abstract

Samples of poly(methyl methacrylate) with a central circular hole are compressed, and crazes form on or after unloading, provided that the strain attains or exceeds a threshold value ϵt. Crazes induced in air are transformed rapidly to cracks, but environmental crazes are more stable. These residual stress crazes form at the diameter of the hole on a plane perpendicular to the applied stress direction. In contrast, during loading, crazes form on the vertical plane containing the hole axis. Unloading crazes are relatively insensitive to changes in strain rate, whereas loading erazes have a pronounced rate dependence. Environmental residual stress crazing exhibits an apparent rate sensitivity at constant time, but the critical applied strain ϵt is essentially constant, irrespective of rate, if the sample is in contact with the environment for a sufficiently long time to ensure that the minimum ϵt is obtained. Residual stress crazes appear to initiate at the equator of the hole, and the maximum tensile residual strain, indicated by a strain gauge, occurs in this position.

An end of service life assessment of PMMA lenses from veteran concentrator photovoltaic systems

“…Because it cannot craze during plastic deformation, the molecular weight of 10,000 gmol -1 is identified as a critical threshold for PMMA, below which it becomes extremely brittle [2]. Surface roughness was found to reduce the critical strain required for craze formation [53]. There may then be an interaction with abrasion damage, e.g., airborne sand or abrasion from cleaning.…”

“…There may then be an interaction with abrasion damage, e.g., airborne sand or abrasion from cleaning. [66], is also often examined [46,53,66,74,77].…”