Notch Problems Research Articles

Cost-Effective Zero-Voltage and Zero-Current Switching Current-Fed Energy-Recovery Display Driver for ac Plasma Display Panel

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A new cost-effective zero-voltage and zero-current switching (ZVZCS) current-fed energy-recovery display driver for a plasma display panel (PDP) is proposed. It features a simpler structure, less mass, and lower cost of production. Furthermore, since all power switches are turned on or off under zero-voltage or zero-current switching, it has several favorable advantages such as an improved electromagnetic interference (EMI), low switching losses, and reduced burden on the cooling system. Particularly, since the current source built in the inductor can compensate the large gas-discharge current, main inverter switches have the reduced current stress and turnon timing margin. Therefore, the undesirable voltage notch problem caused by the improperly controlled gate signal can be solved, which enables the panel to light at lower voltage such as 143 V compared with about 165 V of the prior circuit. To confirm the operation, validity, and features of the proposed circuit, experimental results from a prototype built with 6-in test PDP are presented. </para>

Cost Effective Zero-Voltage and Zero-Current Switching Current-Fed Energy-Recovery Display Driver for AC Plasma Display Panel

A new cost effective zero-voltage (ZVS) and zero-current switching (ZCS) current-fed energy-recovery display driver for a plasma display panel (PDP) is proposed. It features a simpler structure, less mass, and lower cost of production. Furthermore, since all power switches are turned on or off under ZVS or ZCS, it has several favorable advantages such as an improved electromagnetic interference, low switching losses, and reduced burden on the cooling system. Particularly, since the current source built in the inductor can compensate the large gas-discharge current, main inverter switches have the reduced current stress and turn-on timing margin. Therefore, the undesirable voltage notch problem caused by the improperly controlled gate signal can be solved, which enables the panel to light at lower voltage such as 143 V compared with about 165 V of the prior circuit. To confirm the operation, validity, and features of the proposed circuit, experimental results from a prototype built with a 6-in test PDP are presented

Modelling crack initiation by means of finite fracture mechanics

AbstractIn this study, a generally applicable hybrid criterion for brittle crack initiation overcoming deficiencies of classical approaches is applied to regular and singular stress concentrations. Possible formulations of the resulting optimisation problem for the failure load are discussed. Examples demonstrate the capability of the model to cover relevant effects as well as a versatile finite element analysis procedure for notch problems. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Antiamyloid Drugs May Offer Hope for AD

Antiamyloid Drugs May Offer Hope for AD

An Extension of the Complex Variable Method in Plane Elasticity to Domains with Corners: A Notch Problem

A severe limitation on the complex variable method in plane elasticity is the requirement that the region in which the stresses and strains are sought admits a rational conformal mapping into the half-plane or the unit circle. Of course, this limitation has not prevented the solution of many fundamental and interesting problems. However, the extension of this method to more general regions remains a source of debate. We here present an attempt in this direction. If the conformal mapping of the region is an algebraic function, it is still possible to find mathematical conditions defining the complex-valued stress function, but its explicit representation now requires the solution of a singular, linear, complex-valued, integro-differential equation.

910 Error Estimation and Adaptive Refinement for Extended FEM

In this research, we try to investigate and improve the accuracy of extended finite element method (X-FEM) with posteriori error estimation and adaptive refinement scheme. X-FEM allows the modeling of arbitrary geometric features in regular fixed mesh descriptions. However, to improve the accuracy of analysis, optimal mesh is needed based quantitative error estimation. We proposed h-adaptive X-FEM scheme by combining least squares based solution recovery and ZZ error norm definition. The evaluation of our method is performed in two problems such as a pulled infinite elastic notch problem and optimal sizing design.

A New Conception on Fatigue Plasticity and Its Application to Notch Problems

A New Conception on Fatigue Plasticity and Its Application to Notch Problems

Predicting the fretting fatigue limit for spherical contact

One of the most relevant factors controlling fatigue crack propagation under fretting conditions is the steep stress gradient produced in the material by contact loads, a situation also found in notch problems. This suggests that crack growth can be analysed using methodologies similar to those employed in notched components. In this work, we assess the ability of various methods originally used in notched components to predict fatigue failure in specimens undergoing fretting fatigue with spherical contacts. The effect of the local changes in the stress ratio along the crack path was considered in all cases. The predictions thus obtained are compared with a number of experimental results for Al-7075-T6.

On the path dependence of the J-integral in notch problems

This study attempts to clarify the conditions under which the J-integral is path-independent in U- and V-shaped notch problems. The key is to determine the contribution to the J-integral evaluated in the global coordinate system from the second component of the J k -vector evaluated in the local coordinate system along the traction-free surfaces that form part of the integration path. It is found that the global J-integral is path-independent only if the projected contribution from the J 2-integral to J vanishes. The J-integral for a V-shaped notch is, strictly speaking, path-dependent even under remote symmetrical loading. This is due to the fact that, unlike in the case of a line- or plane-crack, the value of the J-integral calculated along a closed contour surrounding the V-shaped notch is dependent on the selection of the starting and ending points on the notch surface. In other words, the traction-free surface of the V-shaped notch does contribute to the J-integral due to the non-zero projected values induced from the J 2-integral. For a U-shaped notch, the path-independence of the J-integral is established if the integration path completely encloses the notch root. This is because both the upper and lower notch surfaces of the U-shaped notch are parallel to the geometric symmetrical line (the x 1-axis) and hence the projected values from the J 2-integral vanish. Furthermore, it is found that the small arc at the root of the notch (whether U- or V-shaped) also contributes to the J-integral even if the remote loading is symmetrical. These conclusions are derived by detailed analytical manipulations and by numerical examples; the analytical solution obtained by Lazzarin and Tovo [Int. J. Fracture 78 (1996) 3] and Lazzarin et al. [Int. J. Fracture 91 (1998) 269] for stress field in the vicinity of a notch root in an infinite elastic plane is used to calculate the contribution induced from the arc with different radii. Some useful results for studying the fracture and fatigue of notches are discussed.

Short History of Body Force Method and its Application to Various Problems of Stress Analysis

Body force method (BFM) was originally proposed in 1967 as a general technique for the stress analysis of notch and crack problems. The concept of BFM is to express the stress fields of elastic problems by means of superposition of point force solutions. In principle, any problem of individual shape and boundary conditions is transformed into a problem of an infinite region without any holes, cracks or external boundary. BFM has provided a number of highly accurate solutions. Some of these have been inserted in technical documents or handbooks. In this paper, firstly, a short history of BFM is described. Then the fundamental principle of BFM is explained. As numerical examples, some useful solutions of 2D and 3D crack problems are shown.

Study of the Plastic Stress Intensity Factor for V-Shaped Notch Problems

Study of the Plastic Stress Intensity Factor for V-Shaped Notch Problems

Quantitative Evaluation for Influence of Complex Surface Texture on Fatigue Limit Reliability from Mesocharacteristics. 1st Report. Stress Analysis of Infinite Plate with Complex Surface Profile.

The influence of surface roughness on fatigue limit is evaluated by a surface factor and a safe factor and they don't have the distinct physical meanings. To discuss a quantitative evaluation of surface roughness on fatigue limit reliability, the exact solution is given for a problem of an infinite plate with a complex profile under tension. The solution is obtained with the complex variable method. Some simple periodical notch problems are analyzed with the solution and also the method is shown to solve a problem of a complex profile.

Intensity of a Plastic Singular Stress Field at the Notch Tip

In the present study, the relation between the plastic and the elastic stress intensity factors, Kp and Ke, for various V-shaped notch problems is studied by using the finite element analysis. Detailed results for mode I under plane stress and plane strain conditions are investigated. Based on the numerical results, it is found that there is a one-to-one correspondence between Kp and Ke, even when the load is so large that the condition of the small scale yielding is not satisfied. Also, it is found that the values of Kp1-λe/Ke1-λp for various notch problems depend only on the notch opening angle γ and hardening exponent n. This enables one to evaluate the factor Kp for various notch problems without any plastic stress analysis.

Intensity of a Plastic Singular Stress Field at the Notch Tip.

In the present study, the relation between the plastic and the elastic stress intensity factors, Kp and Ke, for various V-shaped notch problems is studied by using the finite element analysis. Detailed results for mode I under plane stress and plane strain conitions are investigated. Based on the numerical results, it is found that the relation between Kp and Ke is independent of the notch depth and the scale of plastic zone. Also, it is found that values of K1-λep/K1-λpe for various notch problems only depend on the notch opening angle γ and hardening exponent n under plane stress and plane strain conditions. This enables one to evaluate the factor Kp for various notch problems without any additional plastic stress analysis.

Boundary integral equations for notch problems in an anisotropic half-space

A crack or a hole embedded in an anisotropic half-plane space subjected to a concentrated force at its surface is analyzed. Based on the Stroh formalism and the fundamental solutions to the half-plane solid due to point dislocations, the problem can be formulated by a system of boundary integral equations for the unknown dislocation densities defined on the crack or hole border. These integral equations are then reduced to algebraic equations by using the properties of the Chebyshev polynomials in conjunction with the appropriate transformations. Numerical results have been carried out for both crack problems and hole problems to elucidate the effect of geometric configurations on the stress intensity factors and the stress concentration.

Higher order fields for damaged nonlinear antiplane shear notch, crack and inclusion problems

Damaged nonlinear antiplane shear problems with a variety of singularities are studied analytically. A deformation plasticity theory coupled with damage is employed in analysis. The effect of microscopic damage is considered in terms of continuum damage mechanics approach. An exact solution for the general damaged nonlinear singular antiplane shear problem is derived in the stress plane by means of a hodograph transformation, then corresponding higher order asymptotic solutions are obtained by reversing the stress plane solution to the physical plane. As example, traction free sharp notch and crack, rigid sharp wedge and flat inclusion, and mixed boundary sharp notch problems are investigated, respectively. Consequently, higher order fields are obtained, in which analytical expressions of the dominant and second order singularity exponents and angular distribution functions of the near tip fields are derived. Effects of the damage and hardening exponents of materials and the geometric angle of notch/wedge on the near tip quantities are discussed in detail. It is found that damage leads to a weaker dominant singularity of stress, but to little stronger singularities of the dominant and second order terms of strain compared to that for undamaged material. It is also seen that damage has important effect on the angular distribution functions of the near tip stress and strain fields. As special cases, higher order analytical solutions of the crack and rigid flat inclusion tip fields are obtained, respectively, by reducing the notch/wedge tip solutions. Effects of damage and hardening exponents on the dominant and second order terms in the solutions of the crack and inclusion tip fields are discussed.

Higher order asymptotic solutions of V-notch tip fields for damaged nonlinear materials under antiplane shear loading

The higher order solutions of stress and deformation fields near the tip of a sharp V-notch in a power-law hardening material with continuous damage formation are analytically investigated under antiplane shear loading condition. The interaction between a macroscopic sharp notch and distributed microscopic damage is considered by describing the effect of damage in terms of a damage variable in the framework of damage mechanics. A deformation plasticity theory coupled with damage and a damage evolution law are formulated. A hodograph transformation is employed to determine the solution of damaged nonlinear notch problem in the stress plane. Then, inversion of the stress plane solution to the physical plane is performed. Consequently, higher order terms in the asymptotic solutions of the notch tip fields are obtained. Analytical expressions of the dominant and second order singularity exponents and associated angular distribution functions of notch tip stress and strain are presented. Effects of damage and strain hardening exponents and notch angle on the singular behavior of the notch tip quantities are discussed detailly. It is found that damage can lead to a weaker singularity of the dominant term of stress on one hand, but to stronger singularities of the second order term of stress and the dominant and second order terms of strain compared to that for undamaged case on the other. Also, both hardening exponent and notch angle have important effects on the notch tip quantities. Moreover, reduction of the notch tip solutions to a damaged nonlinear crack problem is carried out, and higher order solutions of the crack tip fields are obtained. Effects of damage and hardening exponents on the dominant and second order terms in the crack tip solutions are detailly discussed. Discussions on some other special cases are also presented, which shows that if damage exponent equals to zero, then the present solutions can be easily reduced to the solutions for undamaged cases.

Novel numerical solution technique for evaluating eigenvalues in a plane notch problem

A novel numerical solution technique for evaluating eigenvalues in a plane notch problem is suggested. In both real value and complex value cases, the problem for evaluating the eigenvalue is reduced to finding the roots of a function F(x)=0, and the roots can be evaluated by the well known half-division method in numerical analysis. Finally, two examples with the calculated results are presented. Copyright © 1998 John Wiley & Sons, Ltd.

Novel numerical solution technique for evaluating eigenvalues in a plane notch problem

A novel numerical solution technique for evaluating eigenvalues in a plane notch problem is suggested. In both real value and complex value cases, the problem for evaluating the eigenvalue is reduced to finding the roots of a function F(x)=0, and the roots can be evaluated by the well known half-division method in numerical analysis. Finally, two examples with the calculated results are presented. Copyright © 1998 John Wiley & Sons, Ltd.

Applicability of Neuber’s Rule to the Analysis of Stress and Strain Concentration Under Creep Conditions

A differential form of Neuber’s rule, originally proposed by M. Chaudonneret, has been formulated for a generic viscoplastic notch problem, making extensive use of suitably normalised stress, strain and time. It has been shown that the stress-strain history at the root of a notch in a viscoplastic body can be determined directly from the elastic response, provided far-field viscoplastic strains can be neglected. Neuber’s rule has also been applied to the more general cases of stress and strain concentration at notches under (i) nominal creep conditions (constant nominal stress) and (ii) stress relaxation (constant nominal strain). Predictions are in good agreement with results from finite element analyses. Stress and strain concentration factors have been observed to approach stationary values after long-time loading. The stationary stress concentration factor under stress relaxation falls below that under nominal creep conditions.