Issue 35

O. Demir et alii, Frattura ed Integrità Strutturale, 35 (2016) 340-349; DOI: 10.3221/IGF-ESIS.35.39 342 For the prediction of fracture limit the determination of equivalent stress intensity factor (SIF) is essential. Several criteria exist to compute the equivalent SIF. One of them is Erdogan and Sih criterion. An equivalent SIF was given in Eq. (1). Pook [8] developed an in plane mixed mode criterion and proposed the following Eq. (8) that equivalent SIF can be obtained from the equation with substituting the K I and K II SIF. 1 2 2 th th th 0.08 0.83 0.75 II I I K K K K K K                        (8) Tanaka [9] introduced the concept of the equivalent SIF for mixed mode conditions and the equivalent SIF was defined by: 1 4 4 4 eq I II 8 K K K          (9) Another criterion developed for in plane mixed mode-I/II problems is Richard criterion [10, 11]. Richard proposed an equivalent SIF and crack deflection angle formulation and verified the formulations by a large number of experiments [12]. According to this criterion, if the proposed equivalent SIF exceeds a critical value, unstable crack growth occurs. The equivalent SIF and crack deflection angle were given by: 2 2 eq 1 1 4( ) 2 2 I I II IC K K K K K      (10) 2 0 155.5 83.4 II II I II I II K K K K K K                    (11) α 1 is a material parameter describes the ratio of K IC / K IIC and generally taken as 1.155. In this study, fracture experiments of CTS specimen and a new type of specimen called T-specimen, which has smaller dimensions and requires less material, are conducted to check the validity of some of the existing criteria for mixed mode- I/II fracture conditions and to develop a further refined mode-I/II fracture criterion. In Part 1 of the study, details and results of the finite element models including fracture submodels of CTS specimen and description of the test procedure for CTS and T-specimens are given. The outline of this paper is as follows: In the next section, experimental results of CTS and T-specimen are given. This is followed by comparisons of the experimental results with existing criteria and development of an improved mode-I/II fracture criteria. E XPERIMENTAL RESULTS OF MODE - I / II FRACTURE TESTS his section deals with experimental results of mode-I/II fracture tests of CTS and T-specimen. In the first sub- section, experimental results of CTS specimen are given in terms of fracture loads, crack lengths and crack deflection angles for all tests under different loading angles. The second sub-section contains experimental results of T-specimen under different loading angles performed. Results of CTS Specimen Experiments In this sub-section, results from the in-plane mixed mode fracture tests of CTS specimen are presented for different loading angles. In Part 1 of this article, details of the experimental set-up, including materials and equipment used, specimen preparation and testing procedure, are explained. Tab. 1 summarizes different cases tested. Critical fracture loads are determined by load-displacement curves and crack deflection angles are measured from the fracture surfaces. Also, a 25 mm-thick CTS specimen is tested for 30° loading angle and its results are given in the table. T