Investigation Of Crack Formation Research Articles

Investigation of Crack Formation and Propagation in AA7475 using Multiple Potential Drop Measurement

The direct current potential drop method (DCPD) is a well-known method for crack detection and crack length measurement in fatigue experiments. Recent Investigations have shown that with multiple potential drop measurements the location of crack initiation can be determined in round bars (Hartweg and Bär, 2019) and single edge notched specimens (Wiehler and Bär, 2020).In this work a more detailed investigation of crack initiation and propagation is undertaken on single-edge notched specimens. The specimens were equipped with three potential probes – on the frontside (Ufront), on the backside (Uback) and on the narrow side (Unarrow) of the specimen. During the fatigue tests all three potentials were measured simultaneously using amplifiers of the control electronics. The crack front was marked on the fracture surface by introducing overloads in defined intervals to allow a direct comparison between the measured potential drop and the real crack location and crack front geometry.In a first step relative Potentials Pi (i= front, back and narrow) were calculated by normalizing the actual potential on the potential of the crack-free specimen. To localize the crack initiation site and to eliminate temperature effects quotients of the potentials were formed by dividing Pfront and Pback by Pnarrow, respectively. By comparing the runs of the potential quotients plotted over the cycle number, the time of crack initiation and the location of the crack initiation site can be determined. In addition, the run of the quotients gives information about the shape of the crack front of long fatigue cracks.

Near-interface cracking in a TiN coated high speed steel due to combined shear and compression under cyclic impact loading

Hard coated tool steels are commonly used for metal working applications, where they are exposed to high levels of contact loads comprising normal and lateral force components. For such complex loading conditions, information on early stages of damage of hard coated steels is lacking. As these early stages provide information about damage mechanisms and possible weaknesses of the coated material, the current work investigates the damage behavior of the interface between a titanium nitride hard coating and a high speed steel. Specimens were subjected to cyclic impacts that combine shear and compression loading under unlubricated or lubricated conditions using an inclined impact tester. Investigation of crack formation below the substrate-coating interface by scanning electron microscopy on cross sections prepared by focused ion beam milling suggests that the predominating damage mechanism for unlubricated specimens is gradual coating wear. For lubricated specimens, the damage mechanisms are dominated by carbide fracture and fatigue crack growth between carbide and matrix occurring just below the substrate-coating interface.

An investigation of crack formation in surface paste disposal method for pyritic Pb–Zn tailings

Surface paste disposal method can be used to minimize environmental risks during storage of mine process tailings. There are some researches and industrial applications which prove success of the method. The surface paste disposal of mineral process tailings obtained from a Pb–Zn underground mine was simulated considering mine site conditions at laboratory scale in the study. The paste material was stored in the cabin/container layer by layer, and then, the cracks occurred after the paste formation of each layer were analyzed by image process. Meanwhile, leachate water collected from the bottom of the cabin was subjected to electrical conductivity (EC) analysis. Furthermore, the wetting–drying process was conducted to simulate the climatic conditions of the region. Additionally, some physical and geochemical parameters such as matric suction, volumetric water content, and oxygen consumption of the paste material were obtained using sensors displaced into different layers. The results of the crack analysis for each layer showed that the cracks intensity increased at lower layers. Moreover, the crack intensity and EC values of each layer showed a similar trend, and the crack intensity increased almost five times during the wetting–drying tests. The measured values of the parameters obtained from the tests indicated that the deposited paste material can be stabile during the deposition over the years under the climatic conditions of the region.

Investigation of Crack Formation in Ordinary Reinforced Concrete Beams and in Beams Strengthened with Carbon Fiber Sheet: Theory and Experiment

Investigation of Crack Formation in Ordinary Reinforced Concrete Beams and in Beams Strengthened with Carbon Fiber Sheet: Theory and Experiment

Sharp crack formation in low fluence hydrogen implanted Si0.75Ge0.25/B doped Si0.70Ge0.30/Si heterostructure

An approach to transfer a high-quality SiGe layer for the fabrication of SiGe-on-insulator wafers has been proposed based on the investigation of crack formation in H-implanted Si0.75Ge0.25/B-doped Si0.70Ge0.30/Si structures. The crack formation is found to be closely correlated to the concentration of B atoms doped in the buried Si0.70Ge0.30 layer. For H-implanted Si0.75Ge0.25/Si0.70Ge0.30/Si structures without B doping, no platelets or cracking is observed in the Si0.70Ge0.30 layer. Upon increasing the concentration of B doping in the buried Si0.70Ge0.30 layer to 2 × 1019/cm3, cracking occurs at the interfaces on both sides of Si0.70Ge0.30 interlayer, thus, resulting in the formation of continuous sharp crack confined in the ultrathin Si0.70Ge0.30 interlayer. With B doped ultrathin Si0.70Ge0.30 interlayer, the Si0.75Ge0.25 layer can be transferred to fabricate SiGe-on-insulator by H implantation with a fluence as low as 3 × 1016/cm2, which is only half of the typical fluence required for a conventional ion-cut process. Since cracking is confined in the ultrathin Si0.70Ge0.30 interlayer, the as-cut SiGe-on-insulator possesses a rather smooth surface with a roughness of 1.55 nm.

Investigation of crack formation on the Galvalume coating of roll formed roof panels

Roll forming of pre-coated and pre-painted sheet metal is a common industrial practice. Cracking of metal coating and/or paint at the sharp edges need to be considered and eliminated during the roll design phase of a new product. The sheet deformation in the lateral (transverse) direction during roll forming is a combination of pure bending and stretching in a step-by-step gradual deformation. Closed form equations of simple bending cannot model this type of deformation. Moreover, due to the free edges, approximations for draw bending cannot be used either, and thus the use of finite element analysis is necessary. In this paper, an investigation on roll forming of pre-coated and pre-painted roof panels have been conducted to eliminate the reported crack formation on the coating and paint. Finite element method was used to test various roll designs, and optimal roll geometry was proposed.

Investigation of crack formation during loading of brittle rock. Technical note : Pang, S S; Goldsmith, W Rock Mech Rock EngngV23, N1, Jan-March 1990, P53–63

Investigation of crack formation during loading of brittle rock. Technical note : Pang, S S; Goldsmith, W Rock Mech Rock EngngV23, N1, Jan-March 1990, P53–63

Investigation of crack formation during loading of brittle rock

The response of elastic/brittle targets to loading by conical-, wedge-and hemispherical-indenter shapes representing jackhammer bit tips was analyzed. Theoretical predictions of crack extent and direction are based on values of the maximum principal strains and the associated extension strain criterion in the target assuming a semi-infinite, homogeneous and isotropic solid. Corresponding static experiments using an MTS machine and dynamic percussive tests involving an encased circular target disk of Sierra granite have been conducted. The damage pattern consisting of a crater, a crushed zone, a region of multiple minor cracks as well a some longer fissures has been delineated. Comparison with theoretical predictions indicate that cracks are produced by maximum tensile strain, with their directions predicted well by the present theory. The upper bound predictions of the crack extent are also in reasonable accord. Deviations are due to the presence of inhomogeneities and anisotropies in the tests specimens.