Issue 41

P. Lopez-Crespo et alii, Frattura ed Integrità Strutturale, 41 (2017) 203-210; DOI: 10.3221/IGF-ESIS.41.28 208   number of data points number of terms in series (6) Fig. 6 shows the error for different levels of φ parameter. φ parameter represents the level of over-determination in the system of equations. Fig. 6 shows that increasing φ parameter produces better estimations of the SIF. The best estimations are observed for higher terms (5 and 6). For φ ≥40, the error is below 5%. For φ = 20 the error is smaller than 10% for all number of terms studied. Figure 5 : Effect of including or excluding the plastic zone in the collected data, i.e. setting R int =0 or setting R int =330 µ m . Figure 6 : Effect of the level of over-determination (i.e. φ parameter, as defined in Eq. 6). C ONCLUSIONS novel approach for estimating the SIF inside the bulk of engineering materials is described. The approach is based on fitting experimental data on an analytical model following a multi-point over-deterministic scheme. The experimental data are collected from the bulk of the material through powerful synchrotron X-ray diffraction. The analytical model describing the elastic field around the crack-tip is based on Williams development. The methodology is applied to a CT specimen made of bainitic steel. A detailed analysis of key parameters affecting the efficacy of the SIF evaluation is presented. The current study suggests that: 1. 3 or 4 terms in Williams’s expansion is often sufficient. 2. Data points should be included from across the full range of angles in front and behind the crack tip. A