Papers by Keyword: Mixed Mode Fracture

Abstract: The adhesive strength of ceramic - copper interfaces was measured in four point bending using a central notch for crack initiation. According to our method, plastic deformation may occur during the delamination process. FEM simulations were employed in order to separate elastic and plastic contributions to the energy consumption of the experiment. In conclusion, a novel delamination criterion based on the stress intensity at the crack tip was established. Here, the stress invariant J₃ is used as indicator for delamination of the interface. Agreement between experiments and theoretical interpretation is demonstrated for copper layers directly bonded to aluminum oxide.

Abstract: This paper analyses the role of cold drawing in the fatigue and fracture behaviour of pearlitic steels with distinct drawing degree (a hot rolled bar and a commercial prestressing steel wire). Fatigue crack growth develops globally in mode I and locally in mixed mode in both steels, the micro-crack deflection angle depending on the drawing degree. With regard to fracture behaviour, it takes place in mode I in the hot-rolled bar and in mixed mode (with a strong component of mode II) in the case of the cold-drawn wire, so that strength anisotropy appears in the drawn steel and a sort of directional toughness can be defined.

Abstract: The focus of this work is to investigate pre-cracked plate element fracture under mixed mode I/II loading. In order to look into element with inclined initial crack, the test procedure was also performed due to pure opening fracture (I mode) and in-plane shear mode (II mode). For this purpose, static and dynamic tests were performed with original testing device, in which the specimen was fixed in so called “Arcan disc”. The results showed fracture characteristics dependence under initial crack orientation angle, i.e. due opening mode, in-plane shear mode and mixed mode I/II fracture.

Abstract: Fracture line offset is the main defect in connecting rod fracture splitting processing, which seriously affects the using performance of connecting rod. In order to control this defect more effectively, the basic reason why this defect occurs was researched according to the theory of fracture mechanics, and the method of numerical simulation was used in this paper. The results show that when the applied load is nonparallel to the axis of a connecting rod, the first principle stress on the theoretical fracture surface is not perpendicular to the theoretical fracture line and the stress distribution is asymmetric on both sides of notches, which leads the type of fracture to turn into mixed mode I-II from mode I. As a result, the defect of fracture line offset occurs. Furthermore, the main factors leading to skew load were analyzed in actual production, and some effective measures were proposed to avoid the occurrence of this defect. This is significant in controlling the quality of connecting rod fracture splitting.

Abstract: The experimental procedures of mixed mode fracture of several ductile materials are investigated. The position and direction of crack initiation are determined according to a new method. The variations of fracture caused by different physical mechanisms are analyzed. Through studying the changing regularity of different fracture mechanisms, it is believed that the main ways of the fracture in ductile materials can be divided into three groups. They are traction fracture and two different types of shear fracture. Void nucleation, expansion and coalescing are the dominant mechanism of traction fracture. The formation and development of localized shear bands are the dominant mechanism of the two different types of shear fracture. Localized large plastic deformation will cause damage within the material. The fundamental factor, which causes the occurrence of fracture in the material, is a certain stress parameter at the dangerous point has reached the critical fracture value of the material. Based on those phenomena listed above, several fracture controlling parameters for different fracture forms have been discussed, and several new parameters, which affect various fracture forms, have been proposed.

Abstract: A variational technique has been developed to evaluate the static stress intensity factors of mixed mode problems with mesh free method in this paper. The stiffness is evaluated by regular domain integrals and shape functions are determined by both radial basis function (RBF) interpolation and moving least-square (MLS) method. The stress intensity factors are obtained by two boundary integrals with variation of crack length. The applications of proposed technique to two-dimensional fracture mechanics have been presented with several examples. Comparisons are made with benchmark solutions.

Abstract: Experimental methods that can be used in three-dimensional mixed mode fracture researches are investigated. The methods are capable of determining the initiation load, maximal load, crack tip opening displacement, crack tip slipping displacement and initiation angle of the mixed mode crack simply and conveniently. As an example, the effect of thickness on mixed-mode I/II fracture of a kind of aluminum alloy is revealed by the methods.

Abstract: The strain energy density factor approach under mixed-mode condition is used for the prediction of crack propagation in the orthotropic steel deck specimen, which is similar to that of existing suspension bridges. Stress intensity factor approach is used to compare with strain energy density factor approach for the fatigue crack growth analysis. The stress intensity factors are computed by numerical extrapolation using cracked models for the different crack length. The study shows that the fatigue crack propagation under mixed-mode condition is slower than that under mode I only. Parametric studies on the initial crack length, critical crack length and parameters related to crack growth equations are performed to show the influence of these parameters on the fatigue life.

Abstract: Conventionally, the bonding strength of bone-cement interface is obtained by mechanical strength testing which tends to produce large variability between specimens and test methods. In this work, interfacial fracture toughness of synthetic bone-cement interface has been determined using sandwiched Brazilian disk specimens. Experiments were carried out under selected loading angles from 0 to 25 degrees to achieve full loading conditions from mode I to mode II. Solutions for complex stress intensity factors as well as strain energy release rates were obtained for a sandwich disk with a finite interlayer using the finite element method. Phase angles were obtained at a fixed distance to the crack tip. The fracture loads were obtained from the load displacement curves and the values of interfacial fracture toughness were calculated from the fracture loads and the finite element J-integral solutions. The implication of this information on the assessment of fixation in acetabular replacements was discussed in the light of in-vitro fatigue testing of implanted acetabula.