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

Determining fracture toughness for soft, highly dissipative, solids has been a challenge for several decades. Amongst the limited experimental options for such materials is the essential work of fracture (EWF) method. However, EWF data are known to be strongly influenced by specimen size and test speed. In contrast to time-consuming imaging techniques that have been suggested to address such issues, a simple and reproducible method is proposed. The method accounts for diffuse dissipation in the specimen while ensuring consistent strain rates by scaling both the sample size and testing speed with ligament length. We compare this new method to current practice for two polymers: a starch based food and a polyethylene (PE) tape. Our new method gives a size independent and more conservative fracture toughness. It provides key-data, essential in numerical models of the evolution of structure breakdown in soft solids as seen for example during oral processing of foods

Under the combined influence of an aggressive environment and applied stress, engineering thermoplastics may undergo a phenomenon known as environmental stress cracking (ESC). This can result in adverse effects such as embrittlement and premature failure in service, due to the growth of environmentally-induced cracks to critical sizes, with little to no fluid absorption in the bulk material. Fracture mechanics is proposed as a suitable scheme to study and quantify ESC, with the aim being to obtain characterising data for different polymer-fluid combinations of interest, as well as to develop a reliable fracture mechanics test protocol. In the proposed method, slow crack growth is monitored to assess the effect of a range of applied crack driving forces (K, or alternatively G) on observed crack speeds, as opposed to simply measuring time-to-failure. This paper presents the results of experiments performed on the following materials: linear low density polyethylene (LLDPE) in Igepal solution and high impact polystyrene (HIPS) in sunflower oil. A discussion of the various issues surrounding the data analysis for these long-term tests is also included, as the attainment of consistent and repeatable results is critical for a method to be internationally standardised, which is a goal of the European Structural Integrity Society (ESIS) Technical Committee 4 from whose interest this work is drawn

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