Structural integrity fracture toughness

Fig. 38 Evolution of /u, the J-Integral accounting for the fracture toughness, and of the elongation at break, break> as a function of the long period, LP, (left) and the lateral size of /3-crystals, L300, (right). Tests have been performed at room temperature on injection molded samples at 1.5 m s-1 to determine /Icj and at 50 mm min 1 to measure ebreak-Mechanical and structural responses have been varied by varying the concentration of NU-100, the nucleating agent from 0 to 1300 ppm...

Mode I fracture tests were performed in three-point bending (SE(B)) at a low (lOmm/min) and a high (Im/s) loading rate according to the testing protocols that were developed by the European Structural Integrity Society - Technical Committee 4 (ESIS TC4) to determine fracture toughness in plastics by a linear elastic fracture mechanics approach, which have become now international standards [15,16]. 

Fracture toughness is a measure of a material s resistance to failure in the presence of a flaw of known or presumed size and a known or presumed stress. The relationship between the flaw (or crack) and the stress is designated the stress intensity, K. For structural integrity evaluations of RPVs, the plane-strain fracture toughness is designated Ki and is determined... 

If a ferritic RPV steel (body-centered-cubic structure) specimen experiences brittle cleavage fracture prior to the full development of a resistance curve, the /-integral value at the onset of fracture, / , is used to calculate an equivalent stress intensity factor, Kj, shown in Table 10.1 and Eq. 10.4. The specimen types used to measure Kj are essentially the same as those shown in Rg. 10.1. The Kj parameter is also used to determine the parameter To, the temperature at which the median fracture toughness (Kq) of a minimum specified number of IT specimens (25.4 mm thick) is 100 MPa Vm. This parameter. To, defines the fracture toughness transition temperature using the Master Curve concept developed by Wallin (1984). The Master Curve concept has been further developed as a consensus test standard in ASTM E 1921 (ASTM, 2013f) and is described in greater detail below. 

Fracture mechanics is a systems approach to estimate the relationship between the stresses, the flaw geometry, and the material properties as it relates to the structural integrity of the component under consideration. The primary objectives are to prevent failures, promote effective design, and make efficient use of materials. The modern approach seeks a parameter that is a measure of the material s toughness that is independent of the geometry, and can be used with stress analysis to predict fracture loads and critical crack sizes. Using this toughness value from a test specimen in the laboratory, the flaw sizes at which fracture will occur for the structural component used in service can be predicted. The reverse scenario is also... 

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