A fracture mechanics approach to characterising the environmental stress cracking behaviour of thermoplastics

Abstract

Environmental stress cracking (ESC) is known to affect certain thermoplastics and occurs under simultaneous exposure to both applied stress and a hostile environment. The combination of these can cause a crack to form from a flaw in the material; upon reaching a critical size, the crack may accelerate thus causing catastrophic failure in the component. Various tests have been utilised to measure the resistance of different polymers to ESC, but these are often material- and application-specific and overlook the different stages of the failure process. In the present work, a fracture mechanics approach has been developed and applied, with a view to developing a test method that has wide applicability and provides both insight into the failure mechanisms as well as information for engineering design. Experimental results are presented for the following polymer-environment combinations: linear low-density PE in Igepal solution, HIPS in sunflower oil, and PMMA in methanol. It is shown that the representation of the results in the form of G versus crack velocity and G versus time can distinguish between materials of varying ESC resistance, identify the important regions of the failure process, and enable component life prediction

Time-temperature equivalence in environmental stress cracking of high-density polyethylene

“…Fracture mechanics has been successfully applied to the study of fracture in viscoelastic materials, as reported in several instances in the existing scientific literature [11][12][13][14]. Its use has been extended directly to study ESC of several systems [15,16], including: polystyrene in oil [17][18][19], polyethylene in various detergents [20][21][22] and polyethyleneterephtalate in sodium hydroxide [23].…”

A comparison between $K$ and $G$ approaches for a viscoelastic material: the case of environmental stress cracking of HDPE

“…From the intersection of the air and environment branches, critical interaction times * and critical crack growth rates ̇ * were evaluated. These parameters, previously observed in (Chang and Donovan, 1990;Ward et al, 1991;Ayyer, Hiltner and Baer, 2008;Andena et al, 2013;Kamaludin et al, 2017), reveal if a given environment will influence the fracture behaviour of a polymer. As a matter of fact, Environmental Stress Cracking will occur under conditions of or corresponding to fracture times that are longer than * and propagation rates lower than ̇ * .…”

“…This approximation, which constitutes the basis of the so-called pseudo-elastic approach, was found to be adequate to describe the behaviour of a variety of polymeric materials, among which were also some nonlinear viscoelastic materials. For instance, and were used for the analysis of the Slow Crack Growth (SCG) and Environmental Stress Cracking (ESC) of several polymers (Williams and Marshall, 1975;Frassine et al, 1996;Kamaludin et al, 2017), including: -toughened polymethyl methacrylate (Mariani et al, 1996;Pini et al, 2018) -high impact polystyrene (Andena et al, 2013(Andena et al, , 2016Kamaludin et al, 2016) -polybutene (Andena et al, 2009) -polyethylene (Chan and Williams, 1983;Brown, 1986, 1987;Chang and Donovan, 1989;Rink et al, 2003;Frank, Pinter and Lang, 2009;Contino et al, 2016Contino et al, , 2018Kamaludin et al, 2016) Assumptions on the validity of these two fracture parameters and of Equation (1) are supported by the accurate description of the fracture behaviour of the polymers considered in these works.…”

Formation Criterion of Hydrogen-Induced Cracking in Steel Based on Fracture Mechanics

“…Therefore, we assumed that the hydrogen in the material acted as the external load or residual stress. An additional load was needed to form a stress concentration around the crack tip during the crack propagation [21]. In this experiment, the hydrogen charged into the sample had the effect of a load, promoting the crack propagation [22][23][24].…”

“…The decrease in K IC due to hydrogen atoms was verified by MD simulations, as shown in Figures 14 and 15. Moreover, the hydrogen atoms can be driven to the crack tip by stress [35], as indicated by Equation (21), as the location of the crack tip is the place with the highest stress value around the crack:…”