Oblique Edge Research Articles

Investigation of fracture behaviors in copper influenced by the angle of oblique edge nanocrack

Investigation of fracture behaviors in copper influenced by the angle of oblique edge nanocrack

Approaches to Control Crazing Deformation of PHA-Based Biopolymeric Blends.

The mechanical behavior of polymer materials is heavily influenced by a phenomenon known as crazing. Crazing is a precursor to damage and leads to the formation of cracks as it grows in both thickness and tip size. The current research employs an in situ SEM method to investigate the initiation and progression of crazing in all-biopolymeric blends based on Polyhydroxyalkanoates (PHAs). To this end, two chemically different grades of PHA, namely poly(hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV), were melt-blended with polybutyrate adipate terephthalate (PBAT). The obtained morphologies of blends, the droplet/fibrillar matrix, were highly influenced by the plasticity of the matrices as well as the content of the minor phase. Increasing the concentration of PBAT from 15 to 30 wt.% resulted in the brittle to ductile transition. It changed the mechanism of plastic deformation from single craze-cracking to homogeneous and heterogeneous intensified crazing for PHB and PHBHV matrices, respectively. Homogeneous tensile crazes formed perpendicularly to the draw direction at the initial stages of deformation, transformed into shear crazes characterized by oblique edge propagation for the PHBHV/PBAT blend. Such angled crazes suggested that the displacement might be caused by shear localized deformation. The crazes' strength and the time to failure increased with the minor phase fibers. These fibers, aligned with the tensile direction and spanning the width of the crazes, were in the order of a few micrometers in diameter depending on the concentration. The network of fibrillar PBAT provided additional integrity for larger plastic deformation values. This study elucidates the mechanism of crazing in PHA blends and provides strategies for controlling it.

Research on Optimal Design of Chip ESD Protection Circuit Based on CMOS Technology

A high frequency circuit based on ESD protection and a new type of power grounding clamp circuit are designed. The oblique edge interfinger diode is used to achieve the optimal design of layout and performance. The design of electrostatic discharge protection circuit and flowsheet were completed in Jazz0.18-micron silicon germanium BiCMOS process. The protection voltage of electrostatic discharge is 3000 V. Higher electrostatic protection level can be obtained by changing the bifurcation index of diode. Improved protection of up to 4500 volts can be achieved. Through the test of the chip, it is proved that the chip fully meets the design requirements and can realize various types of digital circuits.

The Fracture Behavior of REBCO Tape with Multiple Oblique Edge Cracks

The Fracture Behavior of REBCO Tape with Multiple Oblique Edge Cracks

Analytical solution of an orthotropic elasticity for a frictional rigid flat punch on a half plane with an oblique edge crack using a mapping function

A solution of an orthotropic elastic plane problem is derived for a frictional rigid flat punch on a half plane with an oblique edge crack. A mapping function is used for arbitrary configurations. No stress function using a mapping function seems to have been derived. The problem is solved as a Riemann–Hilbert problem. The final exact stress functions are represented by an irrational mapping function as a closed form. Stress components are represented by one complex variable. Arbitrarily shaped half plane problems can be solved by exchanging the mapping function. Therefore, once the analytical solution has been derived, calculating the stress components is simpler than for an isotropic problem. It is easier to use an irrational mapping function than to form a rational mapping function for an isotropic problem. As an example, the stress distributions are shown for a frictional coefficient and an oblique edge crack angle. Four elastic constants are expressed by two independent parameters.

Modulation of Cerium Carbonate Crystal Growth by Polyvinylpyrrolidone using Density Functional Theory.

Cerium carbonate crystal morphology is predicted using density functional theory (DFT) simulations in this paper. In the nucleation phase, the ketone group in polyvinylpyrrolidone (PVP) will preferentially bind to Ce3+ to form complexes and provide heterogeneous nucleation sites for the system, prompting the nucleation of cerium carbonate crystals. In the growth stage, due to the adsorption of PVP, the probability of (120) crystal plane appearing in the equilibrium state is the greatest, resulting in the formation of hexagonal flake cerium carbonate crystals with (120) crystal plane as the oblique edge. Experimentally, hexagonal sheet cerium carbonate crystals were successfully prepared using PVP as a template agent. Therefore, DFT can be used to predict the morphology of cerium carbonate crystals, which not only elucidates the growth mechanism of cerium carbonate crystals, but also greatly reduces the experimental cost.

Effect of edge cracks on critical current degradation in REBCO tapes under tensile stress

The slitting process for manufacturing REBa2Cu3O7-δ (REBCO, RE = Rare earth) tapes of required width significantly improves the production efficiency and reduces production costs. However, edge cracks induced by the slitting process of wide REBCO tapes may cause premature degradation under high tensile stress in high-field magnets. Therefore, it is necessary to evaluate the effect of edge cracks of REBCO tapes on the critical current (Ic) degradation. Firstly, Ic degradation under artificial cracks was measured to validate the applicability of linear elastic fracture mechanics for the REBCO layer. The maximum circumferential stress criterion was used to derive the mixed-mode stress intensity factor of multiple oblique edge cracks. A semi-analytical model considering edge crack properties such as angle β, spacing d, and length a, was built to evaluate the critical load and critical crack. We found that when the stress intensity factor at the crack tip is below KIC=2.3 MPam, edge cracks did not propagate. We examined commercial REBCO tapes manufactured by two different processes, concluding that edge cracks in these tapes will not cause premature degradation.

Cutting Force Transition Model Considering the Influence of Tool System by Using Standard Test Table.

The cutting force prediction model usually uses the classical oblique transformation method, which introduces the orthogonal cutting parameters into the oblique milling edge shape, and combines the geometric parameters of the tool to convert the orthogonal cutting force into the actual cutting force, thereby predicting the cutting force. However, this cutting force prediction method ignores the impact of tool vibration in actual machining, resulting in a large difference between the prediction model and the actual measurement. This paper proposes a cutting force conversion model considering the influence of the tool system. The proposed model fully considers the impact of tool vibration on the cutting force. On the basis of the orthogonal model, superimposing the additional cutting force generated by tool vibration makes the predicted value of the model closer to the actual cutting force. The results of milling experiments show that the conversion model can obtain higher prediction accuracy. Moreover, compared with the original conversion model, the accuracy of the proposed model is significantly improved.

Stress analysis for an orthotropic elastic half plane with an oblique edge crack and stress intensity factors

The main purposes of the present paper are as follows: (1) to analytically derive the general solution (stress functions) for an orthotropic elastic half plane with a crack or a notch; (2) to derive the Riemann–Hilbert equation as the analytical method; (3) to solve the present problem using two methods, one is a Cauchy integral method and other is a Riemann–Hilbert method; and (4) to derive the general expressions of the stress intensity factor (SIF) for a crack problem. The stress functions obtained by the Riemann–Hilbert equation are compared with those obtained by Cauchy integral method. Then, it is confirmed that the same stress functions can be obtained. The stress functions are expressed by any elastic constants. Therefore, Mode I and II SIFs can be calculated for any elastic constants. Some examples are shown. It is stated from the results of the examples that the negative Mode I SIFs exist for certain oblique edge crack angles and elastic constants. Because the derived stress functions are expressed using a mapping function, other geometrical shapes can be analyzed by changing the mapping function.

Adverse Effects of an Edge Diffractor in Seismic Reflection Interferometry

To understand steeply dipping events in seismic reflection interferometry (SRI), we derived an expression that describes the difference in travel time (Δτ) from a diffractor to two receivers in two dimensions. For a fixed receiver interval, the expression shows that Δτ is zero when the diffractor is at the midpoint of the paired receivers, increases with an apparent velocity of half the medium velocity as the diffractor moves toward either receiver, and remains constant for a diffractor located on the same side of both receivers. The horizontal portion of Δτ is slightly skewed during the normal moveout correction, yielding a maximum peak of the horizontally stacked trace at a slightly smaller time than Δτ. Accordingly, the diffracted waves have an apparent velocity slightly higher than half of the medium velocity in a horizontally stacked image. This conformed to virtual data for an elastic two-layer model with a vertical boundary. We then generalized the expression to three dimensions, in which listric travel time curves were predicted for an oblique edge diffractor, a vertex diffractor offline from the receiver pair, or a buried diffractor. Based on both two- and three-dimensional analyses of the edge diffractor, we tentatively interpreted the linear and listric dipping events observed in the passive SRI image across the Korean Peninsula to have been caused by diffractors near the intersection of the profile and geologic boundaries.

Isometric bending requires local constraints on free edges

While the shape equations describing the equilibrium of an unstretchable thin sheet that is free to bend are known, the boundary conditions that supplement these equations on free edges have remained elusive. Intuitively, unstretchability is captured by a constraint on the metric within the bulk. Naïvely one would then guess that this constraint is enough to ensure that the deformations determining the boundary conditions on these edges respect the isometry constraint. If matters were this simple, unfortunately, it would imply unbalanced torques (as well as forces) along the edge unless manifestly unphysical constraints are met by the boundary geometry. In this article, we identify the source of the problem: not only the local arc-length but also the geodesic curvature need to be constrained explicitly on all free edges. We derive the boundary conditions which follow. In contrast to conventional wisdom, there is no need to introduce boundary layers. This framework is applied to isolated conical defects, both with deficit as well, but more briefly, as surplus angles. Using these boundary conditions, we show that the lateral tension within a circular cone of fixed radius is equal but opposite to the radial compression, and independent of the deficit angle itself. We proceed to examine the effect of an oblique outer edge on this cone perturbatively demonstrating that both the correction to the geometry as well as the stress distribution in the cone kicks in at second order in the eccentricity of the edge.

Practical edge-based modulation transfer function measurement.

The accuracy and precision of the modulation transfer function (MTF) of a sampled imaging system are affected by the shift-variant nature of subpixel binning of the pixel values in edge-based methods. This study demonstrates that a binning phase selected from a small number of binning phases can achieve a practical precision criterion for the MTF measurement. Furthermore, the new method proposed in this paper approximates the non-aliased, fundamental MTF without edge angle estimation and the following subpixel binning. The algorithm simply averages the aliased MTFs calculated from the row-by-row edge gradients in the region of a bitonal edge image and removes an assumed aliasing component. This method is also applicable to an oblique and non-straight edge.

Investigations on edge quality and its effect on tensile property and fracture patterns of QP980

Advanced High Strength Steel (AHSS) sheet metals have been widely used in automotive structures due to its safety performance and lightweight potentials, and some AHSS materials have been found more sensitive to edge crack during the stamping process. The tensile property of the sheared edge has great influence on flangability for AHSS. In the present work, the effects of the blanking clearance and shear angle on the quality of the sheared edge and subsequent tensile property for QP980 have been investigated experimentally by microscope and sheared-edge tension test based on digital image correlation (DIC) technology. In addition, the tensile properties of the specimens prepared by wire electrical discharging machining (Wire-EDM) and laser cutting were tested as well. The results show that promising and stable sheared edge quality, and tension with postponed fracture can be achieved if the clearance ratio is set as 7% or 11% for QP980. During blanking with 5° or 10° oblique edge, the ratios of burnish zone and burr zone decrease simultaneously, and the subsequent tensile performance increases significantly. The oblique edge blanking obtains smaller and smoother burr, and the sheared surface benefits from less void damage. In addition, based on the fracture surface morphology and the tracking of the fracture process with DIC technology, two typical fracture patterns (oblique crack and transverse oblique crack) in tension test are illustrated. Oblique crack occurring on the specimens with good edge quality shows obvious necking phenomenon and belongs to the typical ductile fracture. While transverse oblique crack exhibiting with high frequency on the sheared specimens is typical edge fracture and shows mixed characteristics of ductile fracture and brittle fracture.

Influence of Oblique Edge Blanking on the Online Punching Quality after Stretch Bending

The oblique edge punching was proposed to reduce the surrounding sag failure occurred under the large punching force during online punching after stretch bending. The finite element models under three different kinds of punches were stablished and the punching processes were simulated by using the DEFORM-3D software. Comparison between the flat-edge punch and the oblique edge punches were realized, and the optimal height of the oblique edge of the unilateral bevelled punch and the single-peak bevelled punch were obtained. Three kinds of punches were designed based on the simulation results, and the experiments for manufacturing the upper strip of the automobile door frame by the online punching after stretch bending were carried out. The results show that the depth of the surrounding sag of punching can be reduced significantly and the appearance quality can be improved effectively by the oblique edge blanking. The effect to reduce the depth of surrounding sag failure by the unilateral bevelled punch is better than that by the single-peak bevelled punch, and the depth of surrounding sag failure on the side near the edge tip of the unilateral bevelled punch is smaller than that on the side away from the edge tip.

Distance Calculation from Single Optical Image

Accurate and fast distance calculation with respect to a single optical image is useful for real-time 3D construction and acquisition, however currently rare distance calculation methods theoretically base on an optical single image, and the traditional distance calculation method with a single image has limitations due to assumption that the step edge in the image must be strictly horizontal or vertical, which is difficult to fulfill in real applications because the slope of a practical edge could be any other value except for zero and infinity. In this paper, a distance calculation method with a single defocused image containing an oblique step edge is proposed, and no special camera equipment or unique external condition is required. First, the basic theory of coordinate system rotation has been introduced to simplify the sampling process of neighbor points and eliminate the influence resulted from slope of the step edge; one-dimension point-spread-function of the original distance calculation method is expended to two-dimension, taking into account coordinate transform, and a comprehensive distance calculation based on an oblique step edge with any slope is deduced; The relationship between the precision of distance calculation and the slope of the step edge is analyzed and proved in theory. Finally, a serial of simulation are conducted to validate our proposed distance calculation method, and the experimental results prove the applicability, validity and high precision of our method.

Analytical Modeling of an Oblique Edge Crack in Rolling Contact Fatigue

Surface cracks represent a frequent cause of damage and even failure in rolling contacts, observed in gears, cams, rails, and so on. In the literature, different approaches have been applied to describe the crack behaviour by means of Fracture Mechanics parameters, such as the stress intensity factors (SIFs) and the J-integral. In this paper, a general procedure for dealing with plane problems is presented, which is based on Linear Elastic Fracture Mechanics hypotheses. It combines the Weight Function Method for evaluating the SIFs in a loading cycle with the Kolosov-Muskhelishvili complex variable approach for estimating the nominal stress field. In this way, a completely analytical procedure can be applied for a general loading condition, assuming that the real geometry can be simplified in a half-plane with an oblique edge crack. As test case, a travelling load has been considered representing a combination of three contributions: Hertzian pressure distribution, traction force due to friction, and pressurization of the crack faces. A comparison with literature results proved that the proposed approach can be an efficient tool for SIFs estimation and crack growth description.

Numerical Analysis of Flatback Trailing Edge Airfoil to Reduce Noise in Power Generation Cycle

Turbo machinery is an essential part in the power generation cycle. However, it is the main source of noise that annoys workers and users, and contributes to environmental problems. Thus, it is important to reduce this noise when operating the power generation cycle. This noise is created by a flow instability on the trailing edge of the rotor blade—an airfoil that becomes a section of the rotor blade of the rotating machine—manufactured as a blunt trailing edge (T.E.), with a round or flatback shape, rather than the ideal sharp T.E. shape, for the purposes of production and durability. This increases the tonal noise and flow-induced vibrations at a low frequency, owing to vortex shedding behind T.E. when compared with a sharp T.E. In order to overcome this problem, the present study investigates the oblique T.E. shape using numerical simulations. In order to do so, flow was simulated using large eddy simulation (LES) and the noise was analyzed by acoustic analogy coupled with the LES result. Once the simulation results were verified using the flatback airfoil measurements of the Sandia National Laboratories, numerical prediction was performed to analyze the flow and the noise characteristics for the airfoils, which were modified to have oblique trailing edge angles of 60°, 45°, and 30°. From the simulation results of the oblique T.E. airfoil, it could be seen that the vortex shedding frequency moves in accordance with the oblique angle and that the vortex shedding noise characteristics change according to the angle, when compared to the flatback T.E. airfoil. Therefore, it is considered that modifying the flatback T.E. airfoil with an appropriate oblique angle can reduce noise and change the tonal frequency to a bandwidth that is suitable for mechanical systems.

Weight function determinations for shear cracks in reinforced concrete beams based on finite element method

An efficient approach of evaluating the weight functions for the generally load applied faces of shear cracked RC beams with varying shear span/beam depth ratios is presented using the corresponding weight functions for the RC beams with two shear span/beam depth ratios. The shear cracked RC beam under applied load can be considered as an oblique edge crack elastic geometry under mixed load conditions if the nonlinear bridging force is evaluated according to a crack bridging model separately. With pure bend load conditions, both Mode I and II weight functions for the oblique edge crack geometries with three shear span/beam depth ratios for different crack length/beam depth ratios are evaluated through applying the Virtual Crack Extension technique with symmetric mesh around the crack-tip into finite element analysis, where all weigh function components exhibit orderly trends with respect to the changing shear span/beam depth. As a result, the weight functions for the shear crack RC beams with the other shear span/beam depth ratios can be calculated following the orderly trends. Since the crack-tip singular behaviors of fracture problems is observed only in the primary crack-face nodal weight functions, to facilitate application, the primary crack-face weight functions are formulated accurately as a function of crack length and distance away from the crack-tip employing the fitting and interpolation methods.

Interaction between a screw dislocation and an oblique edge crack in a half-infinite MEE solid

By using the complex variable function method, the interaction between a screw dislocation and an oblique edge crack in a half-infinite magnetoelectroelastic solid is investigated under remotely anti-plane mechanical and in-plane magnetoelectric loadings. The exact solutions in closed-form of the stress, electric displacement and magnetic induction are obtained by Cauchy integral formula and the technique of conformal mapping. The image force of the screw dislocation is then calculated by the generalized Peach–Koehler formula. The field intensity factors and energy release rate for the dislocation and crack are also derived explicitly. Numerical examples are provided to show the influences of the geometrical parameters of the crack and location of the dislocation on the field intensity factors, image force and energy release rate.

Vibration characteristics of fluid-conveying FGM cylindrical shells resting on Pasternak elastic foundation with an oblique edge

The flow-induced vibration characteristics (natural frequency and critical flow velocity) of FGM cylindrical shells partially resting on elastic foundation are investigated by an analytical method. These shells are completely filled with fluid or subjected to a flowing fluid. The cylindrical shells are partially surrounded by an elastic foundation with an oblique edge which is represented by the Pasternak model. The boundary edge of an elastic foundation lies in a plane that is oblique at an angle with the shell axis. The effective material properties of FGM models are predicted based on two homogenization methods such as Voigt and Mori-Tanaka models. Material properties vary continuously through the thickness according to a four-parameter power law distribution in terms of volume fraction of the constituents. The thermal effects are also included and the material properties of FGMs are assumed to be temperature-dependent. The fluid is described by the classical potential flow theory. The governing equation for eigenvalue problem is obtained using the Rayleigh-Ritz method. To validate the present method, numerical examples are presented and compared with the available existing results.