Impact fracture toughness

Fig. 7.5. (a) Transverse impact fracture toughness and (b) fiber pull-out length versus testing temperature for carbon fiber-epoxy matrix composites with and without PVAL coatings on fibers. After Kim and... 

Fig. 7.8. (a) Normalized impact fracture toughness and (b) interlaminar shear strength (ILSS) of carbon fiber-epoxy matrix composites as a function of glycidyl acrylate/methyl acrylate (GA/MA) interlayer... 

Fig, 7.16, Impact fracture toughness (O) and interlaminar shear strength (ILSS, ) of carbon fiber-epoxy matrix composites with varying number of nylon sheets as delamination promoters. After Havre (1977). 

Previous work pursued the model analytically, for a linearly elastic [5] (or, later, non-linearly elastic [6]) material with constant thermal properties. The analytical model explained several measured fracture properties of thermoplastics the magnitude of impact fracture toughness and its dependence on impact speed [7] and the absolute magnitude of resistance to rapid crack propagation [8]. Recent results have shown that the impact fracture properties of some amorphous and crosslinked polymers show the same rate dependence [11],... 

Bohme, W. (1998). Application of Dynamic Key Curves (DKC) on the determination of the Impact Fracture Toughness, Kjd of Plastics at High Rates of Loading > 1 m/s , FI-IWM, Freiburg. 

Plati, E. and Williams, J. G. (1975b) Effect of temperature on the impact fracture toughness of pol5uners, Polymer, 16, 915-920. 

Flexural experiments were carried out in three-point loading geometry with inner span being 20 mm, and crosshead speed 1 mm/min. The impact fracture tests were conducted in a Zwick impact tester using Charpy specimens 4x10x50 mm. They contained razor-sharp initial cracks of 1,2,3,4 and 5 mm in the depth direction. The impact fracture toughness (G ) was obtained using the equation of Plati and Williams [7]. 

Tjong S C, Xu S A, and Mai Y W (2003) Impact fracture toughness of short glass fiber-reinforced polyamide 6,6 hybrid composites containing elastomer particles using essential work of fracture concept, Mater Sci Eng A 347 338-345. 

Using a method based on the ESIS impact fracture toughness test, the effect of impact speed on a thermoplastic can be isolated for a Charpy-like impact bend geometry. 

For a polyoxymethylene (POM), on the other hand, impact data (Fig. 3) do not conform to the thermd decohesion model at all. The minimum predicted impact fracture resistance of this material is f/D,min = 2.21 kJ m"2 at 23°C, but most impact fracture toughness results (Fig. 3) are at least 50% higher than this and there is no sign of a region of -2/3 power impact speed dependence, l ere is a further increase in at displacement rates far too low to be considered as impact or for die thermal decohesion mechanism to be viable. Viscoelastic crack blunting is a much more likely explanation. It seems most likely that the craze mechanics assumed by the thermal decohesion model simply do not apply to POM. 

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