Issue 37

C. Riess et alii, Frattura ed Integrità Strutturale, 37 (2016) 52-59; DOI: 10.3221/IGF-ESIS37.08 55 np f . The reason for the differences is identified in the nonzero mean values of the paths. Non-proportionality is increased (  np f 0 365 . ) in the case of example c because of the translation of the perimeter centroid. Whereas the translation of the PC in example d produces a lower rotation of maximum shear planes at high stress levels. The shape of the peak in the middle diagram is more distinct than in example c. Therefore, the non-proportionality is much lower (  np f 0 093 . ). S YSTEMATIC PLANNING OF COMPONENT TESTS n order to expand the experimental database, new component tests with 2 load channels and a high degree of local non-proportionality are planned. The housing of a rear axle steering is chosen for these tests (see Fig. 3). The component is mounted onto a steel plate. One of the forces 1 F shall be applied at the front drill hole and shall be aligned in the x-z-plane. The second force 2 F shall be applied at the upper drill hole and shall be aligned with the centerline of the drill hole. Finally, the angle  (between x-axis and 1 F ) and the ratio of the forces   1 2 F F / remain as free variables for an optimization process. For a given combination of  and  the pseudo-elastic stress path t * ( , ) x  for all nodes can be attained by calculation of three unit load cases (ULC) ULC * ( ) x  :               1 ULC 1x 2 ULC 1z 3 ULC 2 t t a a t a * * * * , , , ( , ) sin( ) ( ) ( ) cos( ) ( ) . x x x x     (4) The relation between the scaling factors of the ULC 1 a , 2 a and 3 a and the free variables  and  is as follows:   2 1 2 1 3 1 2 2 a a 1 a 1 1 1 a a 1 t tan , tan an , .                   (5) The challenge of the optimization is that the location with the highest damage crit x is not known a priori. Depending on the choice of  and  the potential crack initiation site has to be determined numerically. Furthermore the change of crit x results in a non-steady objective function     np crit f f ,    x . That is why a genetic algorithm [10] is used to implement the optimization process. Figure 3 : Housing of a rear axle steering subjected to two load channels (left) and selective weakening of the component (right). Identification of the critical location x crit The fatigue assessment of non-proportional stress histories with rotating principal axis requires complex calculation algorithms, see [11, 12]. With regard to the optimization it is not necessary to perform a quantitatively precise damage calculation. It is rather important to qualitatively identify the critical location. Therefore, the identification of the critical locations is based on simple damage parameters and pseudo-elastic stresses. I