Lifetime Assessment of Load‐Bearing Polymer Glasses: An Analytical Framework for Ductile Failure

Abstract

The most widespread application of polymers in structural applications is their use as pipe material for e.g., gas distribution systems. Pipes have a design lifetime of typically 50 years, which rules out real‐time lifetime assessment methods. Here, an engineering approach is presented, which makes it possible to predict long‐term ductile failure of loaded glassy polymers based on short‐term tests. The approach is based upon the hypothesis that failure is governed by accumulation of plastic deformation up to a critical strain. A pressure‐modified Eyring relation is employed to calculate the accumulation of plastic strain for any simple loading geometry. It is demonstrated that the approach can produce accurate quantitative time‐to‐failure predictions for loaded PC specimens and uPVC pipe segments.

Time-dependent failure of amorphous poly-d,l-lactide: Influence of molecular weight

“…This approach proves very useful for the prediction of the strain rate-and temperature dependence of the yield stress of solid polymers, and also allows prediction of plastic flow rates at a given applied stress and temperature (Bauwens-Crowet et al, 1969, 1974Mindel and Brown, 1973;Sherby and Dorn, 1958). Through introduction of a critical level of deformation, e cr , the time to failure under constant stress (creep rupture) can also be estimated (Bauwens-Crowet et al, 1974;Coleman, 1956;Engels et al, 2010;Janssen et al, 2008;Visser et al, 2010) …”

Influence of physical aging on impact embrittlement of uPVC pipes

“…The proposed hypothesis can only be employed when the influences of strain rate, temperature and physical aging on the yield behaviour of uPVC are characterised, as performed in previous works. 7,25 In these papers, the yield behaviour of uPVC was assumed to be thermorheologically simple: only one relaxation mechanism, the a process related to the glass transition temperature, was considered to contribute to the yield behaviour. This assumption holds for low strain rates and/or moderate temperatures.…”

“…The solid lines represent the result of equation (4) using the parameters summarised in Table 2. The parameters related to the a relaxation were calculated from the parameters as determined earlier 25 for the different uPVC grades. The parameters that account for the contribution of the b relaxation were adopted from the study of Bauwens-Crowet et al 38 The pre-exponential factors : e 0,a and : e 0,b were obtained using a reference 3 Cross-sectional view of set-up (schematically) for instrumented falling weight test 4 Markers show yield stress as measured in uniaxial tension at range of strain rates and temperatures: two regimes are indicated, a regime and azb regime; solid lines represent description of equation (4) using material parameters given in Table 2 Table 2 Values for parameters in equation (6) …”

“…7,25 Remarkably, the aging kinetics is significantly different. The activation energy for the gas pipe grade is about half the value found for the material used in this paper.…”

“…The excellent agreement of the solid lines compared with the experimental data allows two conclusions to be made. First, for the a regime, the deformation kinetics of the gas pipe grade uPVC characterised in Ref 25. is equal to the deformation kinetics of the uPVC grade used here.…”