Papers by Keyword: Mode II

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Authors: Barbora Mužíková, Pavel Padevět, Petr Bittnar, Jakub Antoš
Abstract: This paper is focused on testing in mode II. In this article there is presented the double-edge notched specimen based on the theory of the infinite plate to determine the critical factor KII. There are three approaches to this testing here. Firstly, the real test documented by photos and measured data to determine the value of the critical stress intensity was carried out. Secondly, the real test evaluated by the digital image correlation and finally the numerical model in Adina was made. The success of the testing was lower than has been expected (only 24 %). All three prescriptions were used for all 55 specimens. The highest value of KII is reached with the prescription without fly ash.
Authors: Krzysztof Gołoś, Michał Niepokolczycki
Abstract: FEM linear numerical analysis of stress distribution demonstrated that the model Zappalorto and Lazzarin for analysed V-hole ended notch, relatively correctly predicts the stress distribution at the tip of the notch, especially for small angles of opening. The maximum levels of hoop stress and a tangential for load Mode II strongly dependent on the radius of the notch. The stress reaches its maximum value at a certain distance from the tip of the notch, approximately equal to half of the hole circle radius. The most effective way to reduce the levels of maximum stress at the notch is to increase the radius. When changing radius of 0.5 mm to 2 mm can reduce the degree of stress concentration approx. 40%.
Authors: Majid R. Ayatollahi, David John Smith, M.J. Pavier
Abstract: Research studies for mode I cracks have shown that fracture toughness or the critical value of J for fracture initiation, Jcrit is not merely a material property but depends also on the geometry and loading configurations. The geometry dependency of fracture toughness can be attributed to the effect of the crack tip constraint. In this paper, the constraint effect is studies for the initiation stage in mode II ductile crack growth. Two major mechanisms of ductile fracture: 'void growth and coalescence' and 'shear band localization and de-cohesion' are considered. A boundary layer model is simulated using the finite element method and the effect of far-filed T-stress on the relevant stress parameters near the crack tip is studied. It is shown that the initiation of the ductile crack growth in mode II is influenced significantly by T for the mechanism of void growth and coalescence and is insensitive to T for the mechanism of shear localisation and de-cohesion.
Authors: Kazuro Kageyama, Isao Kimpara, Takahito Suzuki, Isamu Ohsawa, K. Esaki
Authors: M.R.M. Aliha, Mahdi Rezaei
Abstract: Crack growth path was investigated experimentally, numerically and theoretically using two test specimens subjected to pure mode II loading. The specimens were (a) the center cracked circular disc (CCCD) specimen subjected to diametral compression often called the Brazilian disc and (b) the diagonally loaded square plate (DLSP) specimen containing inclined center crack and subjected to pin loading. A few CCCD and DLSP specimens made of two brittle materials (i.e. marble rock and PMMA) were tested under pure mode II conditions. It was observed that the fracture initiation directions and the fracture paths for the tested specimens differed significantly and grew in two different trajectories. However, it was shown that the experimentally observed fracture paths for both specimens can be predicted theoretically very well by using the incremental crack growth method. Several finite element analyses were performed to simulate the whole fracture trajectories of the tested CCCD and DLSP specimens. At each increment, the direction of fracture initiation for the tip of growing crack was determined using the fracture parameters (i.e. stress intensity factors and T-stress) based on the modified maximum tangential stress (MMTS) criterion. The main difference in the fracture trajectory was found to be related to the magnitude and sign of the fracture parameters (which depend strongly on the specimen geometry and loading configuration) and also the type of tensile or compressive loading in the CCCD and DLSP samples.
Authors: Mario Guagliano, Majid R. Ayatollahi, Mahnaz Zakeri, Chiara Colombo
Abstract: According to classical definition of crack deformation modes, the constant stress term (Tstress) exists only in presence of mode I. However, some studies show that this term can exist in mode II problems as well; and significantly affect the elastic stress field around the crack tip. Based on the previous analytical results, T-stress changes the photoelastic fringe patterns from symmetric closed shapes to asymmetric and discontinuous loops. In this research, the effects of T-stress on the fringe patterns in mode II cracks is investigated experimentally. Test specimens are Brazilian disks made of polycarbonate, and thermal treatment is performed to remove the residual stresses after generation of the cracks. Observed isochromatic fringes are in good agreement with theoretical predictions. Also, experimental results indicate that this specimen contains a negative T-stress in pure mode II condition.
Authors: Nobusuke Hattori, S. Nishida, H. Yamamoto
Authors: Peter Davies
Authors: Kamila Czajkowska, Piotr Czarnocki, Zbigniew Lorenc
Abstract: Fatigue delamination of CF unidirectional laminates made of low temperature and vacuum bag cured prepreg, (out of autoclave-OOA), with MTM46 epoxy system was investigated under Mode II loading condition and the coefficients of the corresponding Paris equations were determined. The tests were carried out with the use of ENF beam specimens under displacement controlled conditions and at room temperature with the frequency, f=5Hz, and cycle parameter R=0.1. The crack length, a, was calculate based on the specimen compliance changes. For each specimen, for the entire range of load cycles, i.e. 1 nnmax, the a (n) relationship was approximated with the help of a single sigmoidal function and then the da/dn (n) relationship was determined. In addition, for the comparison purpose the 7-point approximation procedure recommended by ASTM E647 for the same purpose was applied. The differences in results produced by both the data reduction variants were presented for important variants stages and discussed.
Authors: Tomáš Vojtek, Jaroslav Pokluda, Anton Hohenwarter, Richard Pippan
Abstract: This work is focused on experimental study of micromechanisms of mode II and mode III fatigue cracks in metallic materials in the near-threshold regime. The resistance to fatigue crack growth can be divided to an intrinsic component (ahead of the crack tip) and an extrinsic component (shielding, closure), which is significantly higher than the intrinsic one. Fracture surfaces from the Ti6Al4V alloy and pure zirconium were observed in three dimensions. Experiments were conducted using a special device for simultaneous crack loading in modes II and III. Additionally, pure mode II and pure mode III experiments were done using CTS and torsion specimens, respectively. At the beginning of all experiments, crack closure was eliminated due to precracks generated under cyclic compressive loading. A common mechanism of local mode II advances was observed in both modes II and III. The results were similar to those of pure titanium. The hcp metals exhibit a transition behaviour between materials with coplanar shear-mode crack propagation and materials with a high tendency to deflect to the opening mode I.
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