Issue 38

T. Inoue et alii, Frattura ed Integrità Strutturale, 38 (2016) 259-265; DOI: 10.3221/IGF-ESIS.38.35 263 Method for Reproducing Complex Stress When reproducing complex stresses or strains with the advanced testing machine, a stress or strain matrix is composed of stress or strain states that are generated by applying a unit load to each axis. In the elastic region, a stress in i direction (  i ) is described in the following expression using a force in j direction ( L j ) and a stress in i direction generated by applying a unit load in j direction ( S i , j ): S S S L S S S L S S S L 0 0,0 0,90 0,45 0 90 90,0 90,90 90,45 90 45 45,0 45,90 45,45 45                                   (3) Accordingly, loading conditions ([ L j ]) for generating arbitrary in-plane stress states ([  i ]) generated at the evaluation point of the test specimen are stated as: L S S S L S S S L S S S 1 0 0,0 0,90 0,45 0 90 90,0 90,90 90,45 90 45 45,0 45,90 45,45 45                                    (4) The inverse matrix in Eq. (4) is calculated by either measurement results using a rosette gauge by applying a unit load to each axis or numerical results using a FE model with the constraint conditions of the testing machine as shown in Fig. 4. y x z Full constraint : Constraint to z : 0 deg. loading case : 45 deg. loading case : 90 deg. loading case Constraint to y between nodes Constraint to 135 deg. Constraint to x between nodes Mechanical properties (SS400) Young’s modulus : 210 GPa Poisson’s ratio : 0.3 Evaluation point Figure 4 : FE model with constraint conditions of testing machine. E XPERIMENTAL RESULTS AND DISCUSSION Reproducibility of Complex Stress omplex stress states were reproduced in the center of the flat type test specimen as shown in Fig 3 (c) by the advanced testing machine. The stress states to be reproduced had been measured using a rosette gauge on the mechanical surface of actual transport machinery in operation. The reproduced stress was compared with the measured stress in Fig. 5. It was found that the reproduced stress history was in good agreement with the measured stress. The errors in each peak stress were within 10 %. C