Papers by Keyword: Ductile Fracture

Abstract: Anisotropic mechanical behavior is investigated for an aluminum alloy of 6K21-IH T4 both in plastic deformation and ductile fracture. Anisotropic plastic deformation is characterized by uniaxial tensile tests of dog-bone specimens, while anisotropy in ductile fracture is illustrated with specimens with a central hole, notched specimens and shear specimens. All these specimens are cut off at every 15º from the rolling direction. The r-values and uniaxial tensile yield stresses are measured from the tensile tests of dog-bone specimens. Then the anisotropic plasticity is modeled by a newly proposed J2-J3 criterion under non-associate flow rule (non-AFR). The testing processes of specimens for ductile fracture analysis are simulated to extract the maximum plastic strain at fracture strokes as well as the evolution of the stress triaxiality and the Lode parameter in different testing directions. The measured fracture behavior is described by a shear-controlled ductile fracture criterion proposed by Lou et al. (2014. Modeling of shear ductile fracture considering a changeable cut-off value for stress triaxiality. Int. J. Plasticity 54, 56-80) for different loading directions. It is demonstrated that the anisotropic plastic deformation is described by the J2-J3 criterion with high accuracy in various loading conditions including shear, uniaxial tension and plane strain tension. Moreover, the anisotropy in ductile fracture is not negligible and cannot be modeled by isotropic ductile fracture criteria. Thus, an anisotropic model must be proposed to accurately illustrate the directionality in ductile fracture.

Abstract: The plastic behavior of the Ti-6Al-4V alloy includes several features as strength differential effect, anisotropy and yield strength sensitivity to temperature and strain rate. Monotonic tensions in the three orthogonal directions of the material are performed to identify the Hill '48 yield criterion. Monotonic compression and plane strain tensile tests are also included in the experimental campaign to identify the orthotropic yield criterion of CPB06. An assessment of the two models is done by comparing the yield loci and the experimental data points for different levels of plastic work. A first approach of the damage modelling of the Ti-6AL-4V alloy is investigated with an extended Gurson-Tvergaard-Needleman damage model based on Hill '48 yield criterion. Finite element simulations of the experiments are performed and numerical results allows checking force-displacement curves until rupture and local information like displacement and strain fields. The prediction ability of the Hill '48, CPB and extended Gurson models are assessed on simple shear and notched tensile tests until fracture.

Abstract: The high cycle fatigue of super duplex stainless steel of SAF 2507 was investigated by rotating bending fatigue test in both air and 3.5% NaCl environment. The results showed that there is no much reduction of the fatigue life in corrosive environment, which is 90% of the air fatigue strength. In air fatigue, failure happens in ductile mode with austenite grains having finer and straighter fatigue striations than ferrite grains. Width and spacing of striations vary with the orientation and locations when the second cracking occurs. It is not reliable to identify the phase by morphology of striations. In 3.5% NaCl environment, the fracture exhibits a mixed mode of cleavage and quasi-cleavage in ferrites and ductile in austenite grains.

Abstract: In this article, through changing the parameters of the slenderness ratio lambda and axial compression ratio of n, the eight experimental study of steel tube concrete bending members with circular cross section. To explore different slenderness ratio of lambda concrete-filled steel tube under low cycle loading, the damage form of artifacts, deflection change, the relationship between the load and strain, load (P) and displacement (Δ) curve, the axial deformation and stiffness degradation curve, displacement ductility coefficient and the change of parameters such as energy consumption, thus further elastic-plastic seismic response analysis of concrete filled steel tubular structures. Got by test data of load P - displacement Δ relation curve and stiffness degradation curve, the displacement ductility coefficient, the total energy consumption. To get round steel tube reinforced concrete member seismic performance is good, the ductility damage.

Abstract: B₄C/Al composites of different boron carbide contenting were prepared by the liquid mixing method and hot-rolled to 3mm. Microstructure and mechanical properties of the rolled composite were analyzed after the stress relieving heat treatment. Results showed that: the distribution of boron carbide particles was uniform, and only a few particles appeared fractured. With Ti addition, a reaction product layer was fabricated surrounding B₄C particles, which acted as a diffusion barrier to separate B₄C particles from liquid aluminum to protect them. With the mass fraction of the B₄C particles increasing, it can improve the tensile strength but degrade the plasticity of the composites. The fracture surface of composites showed both ductile and brittle fracture characteristics and when the mass fraction of the B₄C particles increased the ductile fracture feature decreased.

Abstract: Scar formation in fine blanking was investigated by means of a particularly developed fine blanking tool and experimental evidence about significant the process parameters chamfer size of the blanking tools, V-Ring usage and clearance is given. Furthermore, a special purpose Finite Element code using the Arbitrary-Lagrange-Eulerian method with a process specific mesh generation is demonstrated and used for the determination of relevant parameters for prediction crack formation in 3D fine blanking simulations. The simulations shown, that a commonly used description of fracture strain as a function of stress and deformation state is not sufficient. In order to simulate scar occurrence on the blanking surface, the significant increase of fracture strain due to temperature rise because of plastic heat generation has to be taken into account. A possible way of measuring the temperature effect was shown in torsion tests at different initial temperature levels.

Abstract: In the process of plastic forming of metals, ductile fracture is an important factor influencing the improvement of forming limit of metals, while ductile fracture criteria can predict when and where ductile fracture occurs. Some conventional ductile fracture criteria based on mesoscopic void-damage and their application in different plastic forming of metals are introduced in this paper. And the ductile fracture criteria will be summarized into two categories: based on triaxial stress degree and based on maximum tensile stress. Because the triaxial stress degree and maximum tensile stress are a main factor deciding the occurrence of the ductile fracture.

Abstract: Ductile fracture of 2024-T3 aluminum alloy has been investigated under tensile and shear loading conditions. In order to predict rupture, a void–based meso–damage constitutive relationship which can deal with both tensile and shear problems is developed and implemented in commercial software ABAQUS. The tensile and shear fracture behaviors including the load–displacement response and crack propagation path, of 2024–T3 aluminum alloy are analyzed using the proposed approach and compared with experimental data. It is shown that the proposed approach can be used to predict the failure of ductile materials under complex loading conditions.

Abstract: The parallel crackswere prefabricated on both sides of theQ345 steel specimensand the tensile failure tests were performed.The effects of parallel crack spacing and crack length on the crack propagation behavior were studied and the fracture modes were investigated with electronic scanning microscope.The finite element analysis of tensile fracture process was also fulfilled based on the ductile metal damage theory, and the crack propagation and the crack stress field evolution around the crack tips were studied. The simulation was agreed with experimental results, and these analysis shows that the crack propagation related with double crack tip of horizontal distance ratio. When the longitudinal and horizontal distance ratio of the two crack tip is less than 1, the linkage between two cracks occurs, or two cracks expand independently. Simulation analysis shows that cracks deflect and connect with another one when the two high Mises plastic stress zones are met with each other; on the contrary, cracks propagate separately.

Abstract: It is possible to successfully propose the physical-metallurgical and structural conditions for the equilibrium between steel strength and toughness by designing structural parameters which have a positive effect on the relation between local and macroscopic fracture processes. In carbon steels and microalloyed steels for a wide range of technical uses, whose structure after heat treatment consists of a basic matrix of tempered lower bainite with precipitated carbides and sometimes other types of inclusions, toughness is dependent primarily on the size distribution of second phase particles, their volume ratio, and also the strength of the matrix/particle phase boundary and the mechanical properties of structural phases. By modelling and simulating the process of main crack formation during high-energy ductile fracture, it is possible to propose optimum physical-metallurgical and geometric parameters of steel structure in order to achieve the required relation between strength characteristics and toughness. This paper presents an analysis of results achieved in several tasks carried out to predict mechanical properties in ductile fracture, and it outlines potential future developments. The aims are to determine the limit characteristics of mechanical behaviour of structural steels which can be achieved with a view to the current structural situation and technological possibilities, and furthermore to propose future methods for determining relations between microstructure and toughness.