摘要:

A theoretical formulation for predicting fatigue strength and life in composite laminates is proposed. First, the Tsai‐Hill failure criterion is modified to become the extended Tsai‐Hill fatigue failure criterion for the prediction of fatigue characteristics of unidirectional laminates. The fatigue data of [0]16, [90]16, and [45]16coupons are the base‐line data involved in the parametric study to estimate fatigue strengths and lives of other off‐axis laminates. The predicted values are found satisfactorily close to the empirical data. In association with classical lamination plate theory (CLPT), the extended Tsai‐Hill fatigue failure criterion can also be applied to quasi‐isotropic [0/45/‐45/90]2Sand cross‐ply [0/90]4Slaminates. Nevertheless the difference is larger for [±45]4Slaminates because of the coupling effect of plastic deformation and friction among the layers of relative slippage. Next, based on Marco‐Starkey theory we develop the nonlinear cumulative damage as well as the reduced non‐damage theory associated with four damage parameters and the failure criterion of multi‐block fatigue loading to predict the life due to variable cyclic loadings. The difference in cycle fraction between two damage loading conditions is generated, so that we can easily shift to a different damage curve and predict the life due to a multi‐block cyclic loading. Fatigue tests of two‐step and multi‐block loading are also discussed. The measured lives are in good agreement with those predicted by our proposed four models.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670463

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Fatigue crack propagation tests under a high stress intensity range have been carried out on a low alloy structural steel BS 4360 Grade 50B. Crack growth rates ranging from about 10‐5mm/cycleto over 0.1mm/cyclehave been recorded. Fatigue tests took on three kinds of control modes to achieve vastly different loading histories. Two specimen geometries which have markedly different yielding constraints and slip line field patterns have been employed. These tests aim at examining the ability of various fracture mechanics parameters to give a unifying quantitative correlation of fatigue crack growth rate from predominantly elastic to elastic‐plastic regimes. An effective cyclic‐J integral with crack closure being taken into account has been shown to be able to rationalize quantitatively the growth data under the different conditions investigated.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670464

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This paper provides an analytical exact closed‐form solution for a partially reinforced elliptic hole embedded in an infinite isotropic medium under a remote uniform heat flow. Based on the method of analytical continuation and the technique of conformal mapping, the full field solutions for the temperature and stresses are obtained in compact complex form. The rotation angle of a reinforced portion on the hole due to the application of a remote uniform heat flow is determined analytically and is dependent of the material property, geometric configuration and the magnitude of applied loading. The stress intensity factors are also obtained and displayed in graphic form. Comparison of the present results with the existing ones shows that our derived solutions are exact and general.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670465

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In this study, a higher order asymptotic expansion of anti‐plane crack tip fields is investigated for dynamic transient crack growth. A six term and a three term expansion for the shear stresses around the crack tip are obtained for cracks propagating at constant and nonuniform velocity, respectively. In order to compare with the near tip field solution derived in this study, an exact transient solution of propagating cracks with constant velocity is examined. The result shows that the use of the singular field to represent the actual stress field should be carefully considered, especially in the early stages of the dynamic transient field.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670466

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Previous findings have shown that, under certain conditions, the stress concentration factorKtin an anisotropic material can be written as 1+FmFswhere the material factorFmand the shape factorFsare uncoupled. For illustration, the stress concentration problem of an elliptic hole is briefly discussed and the correspondingFmandFsare identified. The shape factor of a slot is proposed by interpolating two limiting values in an isotropic material. The accuracy of this expression is demonstrated by comparing the present predictions with the existing numerical values ofKtin isotropic and orthotropic materials.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670467

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Effects of truncations of computational domains have been studied for the development of a flow past a circular cylinder. Of particular interest is the separated flow at low Reynolds numbers. The results reveal some interesting features. The linear relation between the length of the recirculating region and the Reynolds number doesn't exist for a severe truncation, in contrast to the linear situation in an unbounded flow. In particular, when the truncation factor, defined as the ratio of the width of the computational domain to the diameter of the cylinder, exceeds 0.2, the linear relation is destroyed and a more complicated one takes place. In addition, the domain truncation also strongly affects the Reynolds number above which the flow separates from the cylinder.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670468

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

There are three purposes for this study. The first one is to develop a computer simulation model to predict the temperature profiles and the associated thermal stresses of an exhaust oxygen sensor during the warm‐up stage. The second is to evaluate the applicability of two kinds of ceramic material, PSZ and TTZ, based on warm‐up performance and thermal stress magnitude. And the third is to identify the causes of test failures and propose improvements in design. A finite element model was built, which included a zirconia sensor body, a platinum heater and alumina insulating layers. The area with the embedded heater in the coating was considered a composite plate. A single layer was used to approximate the Al2O3/platinum/Al2O3layers. A transient heat transfer analysis was performed first to obtain the thermal response of the exhaust oxygen sensor. The analysis simulated the electrical circuit behavior and thermomechanical interactions of a vertically supported oxygen sensor powered by a constant voltage during a warm‐up test. In the simulation, the electrical resistance, convective coefficient and radiative emissivity were considered temperature dependent. Using ABAQUS (1994) finite element code, a user subroutine DFLUX was developed to interface with the source code to calculate the electric power density of each heater element. Another user subroutine, FILM, was developed to compute the combined convective and radiative heat transfer coefficient on the sensor surface. With the simulated temperature distributions, a follow‐up stress analysis was conducted for the associated thermal stresses. The above procedures were applied to PSZ and TTZ sensors to select the better sensor substrate.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670469

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A double diffusive natural convection in an enclosure filled with a porous medium is investigated numerically. To enhance the heat transfer rate of a heat wall, the heat wall is wetted with a thin water film, then sensible and latent heat transfer occur simultaneously. The Darcy‐Brinkman‐Forchheimer model is used and the factors of heat flux, porosity and diameter of bead are taken into consideration. The SIMPLEC method with iterative processes is adopted to solve the governing equations. The results show that the effect of evaporation on the heat transfer rate is apparent, and the latent heat transfer plays an important role in the high Darcy‐Rayleigh number situations. The averaged Nusselt numberNuis approximately 2.5 whenRa*<4. In the range of 4<Ra*<4469, the relationship of the averaged Nusselt number with the Darcy‐Rayleigh number is linear in logarithmic scale.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670470

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Accurate finite difference schemes in phase space for solving the Vlasov‐Poisson system are presented for the simulation of various stability problems of one‐dimensional inhomogeneous electron plasma. Applications of the present method to the simulations of long time evolution of two‐stream instability, strong Landau damping andNhole Bernstein‐Greene‐Kruskal structure are illustrated.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670471

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The convergence of a general algorithm for limit analysis involving rate‐sensitive materials is proved. The application of this combined smoothing and successive approximation (CSSA) algorithm was extended to deal with plasticity problems involving rate‐sensitive materials. A plasticity problem was stated by the upper bound formulation derived rigorously from the lower bound formulation. Applying a finite‐element discretization, we then employed the CSSA algorithm to solve the resulting optimization problem iteratively. Finally, the Holder inequality was adopted to prove the convergence of the CSSA algorithm. Moreover, it is the familiar Cauchy‐Schwarz inequality, a reduced form of the Hölder inequality, which is utilized to prove the convergence of the CSSA algorithm applied to plasticity problems involving rate‐insensitive materials.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670472

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor