Upper fracture transitions

Figure 1337 Schematic comparison of the brittle-ductile temperature transition in four different tests ( ) Hertzian indentation (lower transition), (2) plastic-elastic indentation (upper transition), (3) Double cantilever beam (lower transition) and (4) notched bar (upper transition). (Reproduced from Puttick, K.E. (1980) The correlation of fracture transitions. ). Phys. D, 13, 2249. Copyright (1980) Institute of Physics.)...

This change may be due to chemical decomposition or evaporation of residual styrene monomer or a combination of factors. The resin degrades at the upper end of the temperature range, but an increase in matrix toughness was observed over the range 10-40°C for a similar polyester [38] (Fig. 4.4). The increase was accompanied by a brittle-to-ductile transition, with changes in the fracture surface characteristics. 

The glass transition temperature corresponds to the upper temperature limit of heat resistance of plastics. The lower hmit of thermal performance is a brittleness temperature (a temperature at which polymers can be fractured even at small deformations). This lower limit of performance temperature is about 10-170°C below the glass transition temperature. It depends on the type of polymer, its strength properties, and plasticizer type and content. 

The Charpy tests are performed according to the RSE-M, with instrumented ISO tups. The transition curves of the absorbed energy, the lateral expansion and the fracture appearance are determined. The RTndt shift is deduced from the transition temperature shifts at an absorbed energy of 56 J and lateral expansion of 0.9 mm. The measured values are compared to the upper-bound predictions calculated according to the RSE-M Code. 

Notch Impact toughness Energy Lateral expansion % shear fracture Dynamic T41J/ Vk, Tq3j, use To,89 mm 7 50% Blunt Charpy V-notch (CVN) impact test e.g., ASTM E 23, EN ISO 148. Obtain curve fit to data vs test temperature, determine various transition temperature indices, e.g., T41J, and upper shelf energy (USE). Initiation and propagation test ... 

Other modeling developments include the work of EricksonKirk and EricksonKirk (2006a) on a so-called upper-shelf fracture toughness master curve, and by EricksonKirk and EricksonKirk (2006b) on linking of the Wallin Master Curve in the transition region and the EricksonKirk upper-shelf master curve in a model that predicts the temperature dependence of ferritic steels for both brittle and ductile behaviour. A more detailed discussion of the Master Curve concept and development is available in Planman and Server (2012). 

EricksonKirk M and EricksonKirk M (2006b), The relationship between the transition and upper-shelf fracture toughness of ferritic steels, Fatigue Fracture of Engineering Materials Structures, 29, 9-10, 672-684. 

Neutron irradiation of steels used in the construction of nuclear reactor pressure vessels can lead to the embrittlement of these materials - an increase in the ductile-to-brittle transmission temperature and a decrease in the fracture energy - which can limit the NPP. Embrittlement is manifested as a reduction in the fracture toughness and a shift in the ductile-to-brittle transition temperature (DBTT) to higher values, as shown schematically in Figure 4.17. The upper limits on neutron fluence for RPV materials are listed in Table 4.12 [52]. 

---