Failure under Monotonic Loading

The physics of failure of fluoropolymers on the microscale is caused by thermally activated breakages of secondary and primary bonds in the material. The chain scission leads to crack and void formation and ultimate failure. To model and predict these events typically requires an investigation on a larger length scale where a continuum mechanics approach can be used. 

There are four main types of models for predicting failure under monotonic loading. The first type is stress-based failure models. A stress-based failure model, in its most general form, can be written/(ct ) 0. Since stress is a tensor quantity, the failure model becomes a function of the six independent stress components. Thanks to the difficulty and the experimental effort needed to determine the six-dimensional failure envelope in stress space, the prob- 

It is currently not well established which failure model is most appropriate for predicting failure of fluoropolymers that are monotonically loaded to failure. Commonly used approaches include the maximum principal stress, the maximum principal strain, the Mises stress, the Tresca stress, the Coulomb stress, the volumetric strain, the hydrostatic stress, and the chain stretch. In the chain stretch model, the failure is taken to occur when the molecular chain stretch, calculated fromPl 

A direct comparison between these and other failure models has not been performed for fluoropolymers, but a recent study of UHMWPEl showed that, for UHMWPE, these models are very different. For example, it was shown that the chain stretch model is the most promising for predicting multiaxial deformation states, and that the hydrostatic stress, and the volumetric strain are not good predictors of failure. 

---

In Fig. 10.6 (a), the beam was repeatedly loaded at 85% static load-bearing capacity until final failure. After several cycles of loading, amplitude distributions of AE signals were measured under monotonous loading. With the increase in loading cycles, amplitude distributions shift to the... 

P W M Peters, Damage development in laminated plates under monotonic tensile loading . Proceedings European Symposium on Damage Development and Failure Processes in Composite Materials, eds I Verpoest and M Wevers, Leuven, KU-Leuven, 1987, pp 21-30. 

Wnuk, M.P. (1973b) Prior to failure extension of flaws under monotonic and pulsating loadings. Eng. Fract. Mech. 5, 379-396... 

---