Lifetime predictions

To account for the poor reproducibility in accelerated aging, statistical approaches have been proposed, such as the nonparametric statistics which relies on performance comparison with a control material. The control material should be as similar as possible to the tested polymer in terms of structures, size, and shape, and its weathering durability should be well established in the specified exposure test. One useful approach to reduce error analysis was to compare a test property, not as a function of time or absorbed radiation, but relative to another 

Two main areas where major advances can be expected in the future include integral characterization of the degraded polymer, and realistic modeling of degradation kinetics. 

All these theories need to be confirmed by experimental verification and tested for their general applicability to different polymer systems. 

Kubelka-Munk scattering coefficient [m ] relative spectral damage scission indice temperature [°C] 

2 Handbook of Polymer Degradation, S. Halim Hamid, ed., Marcel Dekker, New York, 2000. 

---

E. R. Bixon and D. Robertson, "Lifetime Predictions for Single Base PropeUant Based on the Arrhenius Equation," in Fifth International Gun Propellant and Propulsion Symposium, ARDEC, Dover, N.J., Nov. 1991. 

Actual lifetime of the plant equipment. Corrosion monitoring provides data, which must then be analyzed with additional input and interpretation. However, only estimates can be made of the lifetime of the equipment of concern. Lifetime predictions are, at best, carefully crafted guesses based on the best available data. 

Quantitative Quantum Yield/Lifetime Predictions from Electron Transfer Quenching... 

L. Matisova-Rychla and J. Rychly, Inherent relations of chemiluminescence and thermooxidation of polymers, In R.L. Clough, N.C. Billingham and K.T. Gillen (Eds.), Advances in Chemistry, Series 249 Polymer Durability, Degradation, Stabilization and Lifetime Prediction. American Chemical Society, Washington, DC, 1996, p. 175. 

Lifetime prediction of plastic pipes is performed by extrapolating from higher loads and lower times to lower loads and higher times, remembering to use only data corresponding to brittle , low energy ruptures to the right of the knee in the curve (see Section 4.9). 

Pressurised pipes for water and gas provide an example of design lives being predicted with confidence on the basis of a large assembly of data, of benchmark quality control tests for existing products, and of two-parameter accelerated testing for new ones. Some types of pipe are particularly sensitive to pressure extremes. Lifetime prediction cannot however take into account poor installation conditions. 

Weathering is an example of where lifetime prediction is based largely on service life experience under normal or severe conditions as well as accelerated testing. If sufficient allowance is made for the variation between accelerated and natural weathering, and in natural weathering itself, the predictions can be regarded as very satisfactory. 

In practice, most lifetime prediction is based on service experience. Depending on the industry concerned, this can take the form of planned examination of components at the end of their service life or be limited to the explanation of warranty returns. Experience with polymers is now sufficiently long for service experience to be a prime source of information for components with lifetimes of up to 35 years. The construction industry provides a good example of systematic listing of component lifetimes, related to minimum quality levels and modified according to the service conditions. The electrical industry applies statistical methods to life components and predict failures. This, however, strays into the general field of engineering component lifetimes. In this book we are concerned with materials rather than components. 

Hase s trajectory value for the association rate constant, /cp of 1.04 cm- s maybe used in conjunction with the above Langevin value of the collisional stabilization rate constant to yield a unimolecular dissociation rate constant of 3.75 x 10 ° s and a lifetime of 27 ps. In each case, these values are in excellent agreement with the order of magnitude of lifetimes predicted by Hase s calculations for cr/CHjCl collisions at relative translational energies of 1 kcal mor , rotational temperatures of 300 K, and vibrational energies equal to the zero-point energy of the system. 

In a more recent work, Joens [158] has assigned the structures of the Hartley band using a Dunham expansion, that is equilibrium point quantization. The lifetime predicted by his analysis is extremely short, equal to 3.2 fs, while the symmetric stretching period is of 30 fs. Recall, however, that the interpretations in terms of equilibrium point expansions and in terms of periodic orbits are strictly complementary only for regular regimes. 

A complete investigation leading to a nonempirical lifetime prediction model would thus involve the following steps ... 

Practical Aspects of Thermal Aging Lifetime Prediction... 

Johnston RT, Morrison EJ (1996) In Clough RL, Billingham NC, Gillens KT (eds) Polymer durability degradation, stabilisation and lifetime prediction, Advances in Chem Series-249. American Chemical Society, Washington, p 651... 

Dependence of Bias Stress on Operating Conditions Lifetime Predictions... 

J. Verdu, X. Colin, B. Fayolle, and L. Audouin, Methodology of lifetime prediction in polymer aging. J. Testing Eval., 35(3), 289-296 (2007). 

S. Halim Hamid and I. Hussain, Lifetime prediction of plastics. In Handbook of Polymer Degradation, 2nd edn., S.S. Halim Hamid (ed.), Dekker, New York, pp. 699-726, (2000). 

Schwetlick K and Habicher W D (1996) Action mechanism of phosphite and phosphonite stabilizers, In Polymer durability degradation, stabilization and lifetime prediction, Clough R L, Billingham N C and Gillen K T (Eds), Adv Chem Ser 249 349-358. 

Calculations using Langmuir s equation show that the lifetime of very small volatile droplets in air is surprisingly short. But for large drops the lifetimes predicted by Langmuir s equation appear to be approximately correct, as indicated by experimental measurements. 

Fig. 4.21 Monkman-Grant curves for experimental and commercial grades of silicon nitride. The results from seven different studies are plotted on the same graph. With the exception of the data by Kossowsky et al., 116 data tend to plot within a relatively narrow band. Within a factor of three in lifetime prediction, all of these data can be represented by the dashed line. It is this line that is plotted in Fig. 4.17 with data from high temperature alloys.

---