Yazar "Dirikolu, MH" seçeneğine göre listele

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    Analytical and finite element comparisons of stress intensity factors of composite materials
    (Elsevier Sci Ltd, 2000) Dirikolu, MH; Aktas, A
    In this paper, a comparative study regarding the determination of stress intensity factors (SIF) for non-standard thin composite plates is presented. Carbon-epoxy composite plates are considered for the study. Unnotched specimens and specimens containing either 4, 6 or 8 mm diameter holes are prepared and then tested. Based on the experimental data thus obtained, two analytical approaches and a finite element fracture analysis tool called FRANC2DL have been used to compare the critical SIF values for this composite material. (C) 2000 Elsevier Science Ltd. All rights reserved.
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    A computer simulation for estimating lower bound fracture strength of composites using Weibull distribution
    (Elsevier Sci Ltd, 2004) Birgoren, B; Dirikolu, MH
    Estimating confidence lower bound for fracture strength of composites is a key concern in design and manufacture, and the Weibull distribution has been widely used for this purpose. Previous simulation-based studies presented computational tools for these bounds involving tables or parametric equations, which lack generality and may contain simulation and curve-fitting errors. An alternative approach is to present a fast and effective simulation tool that can be directly used by the end-user. Such a tool is developed in this study for estimating the bounds using the Weibull distribution based on maximum likelihood estimation. This is a more versatile approach in that it allows the user to input any desired confidence level, failure probability, and simulation-run number. The tool is demonstrated by using fracture strength data obtained from ASTM D3039 tension tests of 19 identical carbon-epoxy composite specimens. The results are compared with those obtained from previously developed approaches. (C) 2004 Elsevier Ltd. All rights reserved.
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    An experimental and numerical investigation of strength characteristics of carbon-epoxy pinned-joint plates
    (Elsevier Sci Ltd, 2004) Aktas, A; Dirikolu, MH
    An experimental and numerical study has been carried out to investigate the strength of a pinned-joint carbon epoxy composite plate with [0degrees/45degrees/-45degrees/90degrees]s and [90degrees/45degrees/-45degrees/0degrees]s stacking configurations. The experiments were carried out according to the ASTM D953 standard [Standard Test method for Bearing Strength of Plastics, ASTM Designation, 342-346], and the numerical analyses were performed by the finite element method. The ratio of the edge distance to the pin diameter (E/D), and the ratio of the specimen width to the pin diameter (W/D) were systematically varied during analyses. The results from both analyses show firstly that the prepared specimen configurations give bearing mode, secondly that the [90degrees/45degrees/-45degrees/0degrees]s configuration is stronger when compared to [0degrees/45degrees/-45degrees/90degrees]s, and finally that both configurations reach their upper limit bearing strengths when E/D and W/D ratios are equal or greater than 4. (C) 2004 Elsevier Ltd. All rights reserved.
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    Finite element simulation of chip flow in metal machining
    (Pergamon-Elsevier Science Ltd, 2001) Dirikolu, MH; Childs, THC; Maekawa, K
    Finite element studies of machining are becoming ever more sophisticated. A basic approach which removes the need, in an elastic-plastic analysis, to follow the development of chip formation from initial contact between work and tool, is the iterative convergence method (ICM). It develops a steady-state chip formation from an initial state of a fully formed chip loaded against a tool. It relies for its accuracy on the assumption that its simplified loading path coincides with the real developed flow at the end of the simulation. This paper examines the robustness of this assumption by studying the sensitivity of the simulation to changes of detail, within the ICM method, of how the flow develops; and it compares the simulated results with experiments. The experiment involves the turning of three free cutting steels, for which experimental flow stress variations with strain, strain rate and temperature, as well as information about the friction interaction between chip and tool, are available. The changes to the simulation method considered here are the structure of the finite element mesh, the measures of judging when the flow is fully developed, how the chip separates from the work at the cutting edge and the friction laws used during the approach to fully developed flow. It is shown that these do affect the outcomes of the simulation but within the ranges studied only to a minor extent and good agreement with experiment is achieved. (C) 2001 Elsevier Science Ltd. All rights reserved.