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Role Of Delamination And Interlaminar Fatigue In The Failure Of Laminates With Ply Dropoffs
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Book Synopsis Role of Delamination and Interlaminar Fatigue in the Failure of Laminates with Ply Dropoffs by : Dong Jin Shim
Download or read book Role of Delamination and Interlaminar Fatigue in the Failure of Laminates with Ply Dropoffs written by Dong Jin Shim and published by . This book was released on 2002 with total page 488 pages. Available in PDF, EPUB and Kindle. Book excerpt: Analytical and experimental investigations were conducted on laminates with ply dropoffs to better understand the interlaminar stress field and delamination/damage characteristics in such laminates, as well as the relationship between the two based on the strength of materials approach. To gain key insights into the mechanisms and structural parameters that cause interlaminar stresses, analytical models for laminates with simple ply dropoff configurations were developed based on a systematic and hierarchical approach. Mathematically, these individual models are formulated using the stress function method in which the form of the admissible stress field is assumed a priori based on the stress field from the classical laminated plate theory and other functional constraints of the problem. The results are validated via comparisons with numerical solutions from previous investigations and as performed in the current work. Various structural parameters such as the taper angle and the location of the terminated plies are found to affect the interlaminar stress distribution. Careful consideration of the characteristics and trends of the interlaminar stresses in such laminates reveals that two fundamental mechanisms give rise to interlaminar stresses: the termination effect, that is caused by the load transfer from the terminated ply group to the continuous plies; and the offset effect, that is caused by the redistribution of the load from the undropped region to the dropped region in the outer continuous plies through an offset in the through thickness direction. These mechanisms, the factors that affect them, and their utility are described and discussed in detail. Factors of particular importance are the magnitudes of the far-field loads in the terminated and the outer continuous ply groups, the offset distance, and the taper angle. Experiments are conducted on unidirectional laminate configurations under static and cyclic loads to establish delamination/damage trends when the number and location of the terminated plies are varied. Under both loading conditions, delamination is found to be the dominant damage mode, although other modes, e.g., ply splits, occur. In certain types of specimens under cyclic loading, delaminations in different regions have different growth characteristics causing delaminations in one region to be a greater concern than in another region because the length of the delaminations increases indefinitely. In general, the experimental observations regarding delamination/damage are consistent with expectations based on the stress analysis. Delaminations are generally observed along interfaces where the interlaminar stresses are greatest, and static delamination loads are higher in laminates with lower interlaminar stresses. Quantitative predictions of the delamination loads using the Quadratic Delamination Criterion with the average stress method do not agree as well with the experimental data because a single value for the averaging length could not be obtained. The possible causes for the apparent non-uniqueness of the averaging length and its implications are further discussed. Based on this investigation, further recommendations for work on laminates with ply dropoffs are proposed.
Book Synopsis Interlaminar Stresses and Fracture Behavior in Thickness-tapered Composite Laminates by : Kan He
Download or read book Interlaminar Stresses and Fracture Behavior in Thickness-tapered Composite Laminates written by Kan He and published by . This book was released on 2002 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Design and manufacture of a variable thickness composite laminate such as a helicopter yoke involves tapering the laminate by dropping individual plies at discrete internal locations, in order to tailor the stiffness of the laminate. The ply drop in the laminate creates large interlaminar stresses and initiates delamination. Therefore, there is a necessity to investigate the fundamental failure mechanisms and controlling parameters that account for the delamination mode of failure in tapered laminates. In this thesis, a numerical and experimental study on interlaminar stresses and delamination in tapered laminates is presented, including a critical and comprehensive review on earlier works on this type of structure. Numerical analyses performed involved development of partial hybrid stress finite elements needed to enhance computational efficiency, and development of a physical concept-based modified shear-lag model that is based on the essential assumptions that both plies and resin layers are treated as carriers of tensile stress and also to act as stress-transfer media. Experimental analysis was attempted to assess the accuracy of the numerical predictions. For this purpose, tapered NCT-301 Graphite/Epoxy specimens were manufactured using a ply in-fill technique for the cured consolidation and tested under quasi-static uniaxial tension. To perform strength and delamination analyses of the tapered laminate, the laminate was modeled as a generalized plane deformation problem, where all the variables involved in the model are independent of the coordinate system. Also quasi-three dimensional partial hybrid finite elements were used to quantify the analysis. In addition to the plies, the inter-ply resin at the critical ply interface was also modeled in order to have direct and realistic interlaminar responses. Stress-based criteria that have proved to be effective in determination of critical location and load of delamination onset were utilized in this study to predict the delamination strength of the laminate. A good correlation between the predictions and experimental results were observed. Evaluation of strain energy release rates of delaminations occurring at the critical interfaces of the tapered laminate was carried out by using the J -integral approach. This was possible because of the path-independence of the J -integral that results in avoiding the need for analyzing the singular stress field near the delamination tip and reducing the computing effort required. Effects of various design parameters on the structural performance of the tapered laminate were studied so as to gain an insight into design considerations for tapered composite structures.
Book Synopsis Interlaminar Response of Composite Materials by : N.J. Pagano
Download or read book Interlaminar Response of Composite Materials written by N.J. Pagano and published by Elsevier. This book was released on 2012-12-02 with total page 268 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents the topics of major importance toward understanding the most feared failure mode in composite laminates, namely delamination. There are few books at present that describe the phenomenon of composite laminate failure by delamination in such detail.Written by pioneers and principal researchers in various aspects of composite delamination, starting from basic principles to the most current research findings, the work provides a complete study of the theoretical and experimental aspects of composite delamination in one volume.
Book Synopsis Proceedings of the American Society for Composites, Seventeenth Technical Conference by : C. T. Sun
Download or read book Proceedings of the American Society for Composites, Seventeenth Technical Conference written by C. T. Sun and published by CRC Press. This book was released on 2002-10-24 with total page 1685 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Fracture Mechanics of Matrix Cracking and Delamination in Glass/epoxy Laminates by : M. Caslini
Download or read book Fracture Mechanics of Matrix Cracking and Delamination in Glass/epoxy Laminates written by M. Caslini and published by . This book was released on 1986 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt: This study focused on characterizing matrix cracking and delamination behavior in multidirectional laminates. Static tension and tension-tension fatigue tests were conducted on two different layups. Damage onset, accumulation, and residual properties were measured. Matrix cracking was shown to have a considerable influence on residual stiffness of glass epoxy laminates, and could be predicted reasonably well for cracks in 90 deg plies using a simple shear lag analysis. A fracture mechanics analysis for the strain energy release rate associated with 90 deg ply matrix crack formation was developed and was shown to correlate the onset of 90 deg ply cracks in different laminates. The linear degradation of laminate modulus with delamination area, previously observed for graphite epoxy laminates, was predicted for glass epoxy laminates using a simple rule of mixtures analysis. The strain energy release rate associated with edge delamination formation under static and cyclic loading was difficult to analyze because of the presence of several contemporary damage phenomena. Keywords: Fatigue(Mechanics), and Stiffness loss.
Book Synopsis Analysis of Interlaminar Stresses in Thick Composite Laminates with and Without Edge Delamination by :
Download or read book Analysis of Interlaminar Stresses in Thick Composite Laminates with and Without Edge Delamination written by and published by . This book was released on 1984 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Fatigue Strength Calculation by : A. Buch
Download or read book Fatigue Strength Calculation written by A. Buch and published by Trans Tech Publications Ltd. This book was released on 1988-01-01 with total page 478 pages. Available in PDF, EPUB and Kindle. Book excerpt: Optimal design using advanced materials is an ever more progressive and challenging domain within applied mechanics. Here is an invaluable self-contained source of information concerning methods of calculation of fatigue limits and lifetimes of structural elements. While in most texts the treatment of this subject is confined merely to a phenomenological approach, this book provides the essential knowledge for an analytical treatment of design problems as well as a unique collection of appropriate data sheets which are required for the quantitative application of accepted design recommendations.
Book Synopsis Fatigue Delamination Onset Prediction in Tapered Composite Laminates by :
Download or read book Fatigue Delamination Onset Prediction in Tapered Composite Laminates written by and published by . This book was released on 1989 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Advanced Fatigue Damage Development in Graphite Epoxy Laminates by : Russell Douglas Jamison
Download or read book Advanced Fatigue Damage Development in Graphite Epoxy Laminates written by Russell Douglas Jamison and published by . This book was released on 1982 with total page 238 pages. Available in PDF, EPUB and Kindle. Book excerpt: Results of an experimental investigation of damage development in T300/5208 graphite epoxy laminates subjected to tension-tension cyclic loading are reported. The concept of laminate stiffness reduction as a damage analogue is shown to be a valuable means of test control and damage interpretation. The relationship between stiffness and number of cycles is shown to be unique for each laminate type studied, each possessing three distinct stages, but markedly different among the laminate types. By using two complementary nondestructive evaluation (NDE) techniques, edge replication and penetrant-enhanced stereo X- ray radiography along with a method for deploying fatigue-damaged specimens, the stages of stiffness reduction were found to correspond variously to the predominance of matrix cracking or delamination or interactions of these matrix damage modes. A number of subordinate matrix damage modes including interior delamination, microcracking, and longitudinal splitting are identified with the matrix cracks which produce them.
Book Synopsis The Effect of Thickness on Interlaminar Stresses and Delamination in Straight-Edged Laminates by : P. Lagace
Download or read book The Effect of Thickness on Interlaminar Stresses and Delamination in Straight-Edged Laminates written by P. Lagace and published by . This book was released on 1987 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: The effect of ply and laminate thickness on the fracture of graphite/epoxy laminates induced by delamination was investigated. Five laminate types were manufactured from AS1/3501-6 graphite/epoxy and tested: [±15n]s, [±15n/0n]s, [0n/±15n]s, [±45n/0n]s, and [[0/±15]s]n. "Effective ply thickness" was varied by stacking several plies of the same angular orientation together. It was found that an increase in effective ply thickness caused a decrease in fracture stress resulting from delamination in all cases. Interlaminar stress calculations indicate that this results from the fact that the region of high interlaminar stresses increases as the effective ply thickness increases. These calculations also suggest that interlaminar shear stresses are at least as important in causing delamination as interlaminar normal stresses. "Back-to-back" [[0/±15]s]n laminates were found to have the same strength for values of n from one to three. This indicates that reductions in strength are not simply a laminate thickness phenomenon but are related to the effective ply thickness.
Book Synopsis An Analytical and Experimental Investigation of Edge Delamination in Laminates Subjected to Tension, Bending, and Torsion by :
Download or read book An Analytical and Experimental Investigation of Edge Delamination in Laminates Subjected to Tension, Bending, and Torsion written by and published by . This book was released on 1989 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Experimental and Analytical Study of Fatigue Damage in Notched Graphite/epoxy Laminates by :
Download or read book Experimental and Analytical Study of Fatigue Damage in Notched Graphite/epoxy Laminates written by and published by . This book was released on 1979 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author :National Aeronautics and Space Administration (NASA) Publisher :Createspace Independent Publishing Platform ISBN 13 :9781722617707 Total Pages :58 pages Book Rating :4.6/5 (177 download)
Book Synopsis Local Delamination in Laminates with Angle Ply Matrix Cracks. Part 2 by : National Aeronautics and Space Administration (NASA)
Download or read book Local Delamination in Laminates with Angle Ply Matrix Cracks. Part 2 written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-08 with total page 58 pages. Available in PDF, EPUB and Kindle. Book excerpt: Constant amplitude tension-tension fatigue tests were conducted on AS4/3501-6 graphite/epoxy (02/ theta sub 2/ -(theta sub 2))sub s laminates, where theta was 15, 20, 25, or 30 degrees. Fatigue tests were conducted at a frequency of 5 Hz and an R-ratio of 0.1. Dye penetrant enhanced x-radiography was used to document the onset of matrix cracking in the central -(theta) degree plies, and the subsequent onset of local delaminations in the theta/ -(theta) interface at the intersection of the matrix cracks and the free edge, as a function of the number of fatigue cycles. Two strain energy release rate solutions for local delamination from matrix cracks were derived: one for a local delamination growing from an angle ply matrix crack with a uniform delamination growing from an angle ply matrix crack with a triangular shaped delamination area that extended only partially into the laminate width from the free edge. Plots of G(max) vs. N were generated to assess the accuracy of these G solutions. The influence of residual thermal and moisture stresses on G were also quantified. However, a detailed analysis of the G components and a mixed-mode fatigue failure criterion for this material may be needed to predict the fatigue behavior of these laminates. Obrien, T. Kevin Langley Research Center...
Book Synopsis Local Delamination in Laminates with Angle Ply Matrix Cracks. Part 1: Tension Tests and Stress Analysis by :
Download or read book Local Delamination in Laminates with Angle Ply Matrix Cracks. Part 1: Tension Tests and Stress Analysis written by and published by . This book was released on 1991 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Delamination of Composite Laminates Stimulated by Interlaminar Shear by : RY. Kim
Download or read book Delamination of Composite Laminates Stimulated by Interlaminar Shear written by RY. Kim and published by . This book was released on 1986 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: Although interlaminar shear stresses become very large in composite laminates, in the literature there is no conclusive demonstration of the onset of delamination in composites due to interlaminar shear. The present work addresses the title problem by accurate stress analysis, application of an average stress failure criterion over a predominant stress component, and testing chosen laminates made of T300/1034-C graphite epoxy to the onset of delamination. The stress analysis has been used to define the laminate stacking sequence and the required loading direction to eliminate modes of failure other than that stimulated by interlaminar shear stress. The predicted strains at the onset of delamination are close to experimental values in some of the laminates, and the predicted interfaces of delamination are the same as experimentally observed delaminated interfaces. This work leads to an understanding of validity of average stress failure criterion and probable causes of difference between the predicted and experimental values.
Book Synopsis Tension Fatigue of Glass/epoxy and Graphite/epoxy Tapered Laminates by :
Download or read book Tension Fatigue of Glass/epoxy and Graphite/epoxy Tapered Laminates written by and published by . This book was released on 1990 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Virtual Crack Closure Technique: History, Approach and Applications by : Ronald Krueger
Download or read book The Virtual Crack Closure Technique: History, Approach and Applications written by Ronald Krueger and published by . This book was released on 2002 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt: An overview of the virtual crack closure technique is presented. The approach used is discussed, the history summarized, and insight into its applications provided. Equations for two-dimensional quadrilateral elements with linear and quadratic shape functions are given. Formula for applying the technique in conjuction with three-dimensional solid elements as well as plate/shell elements are also provided. Necessary modifications for the use of the method with geometrically nonlinear finite element analysis and corrections required for elements at the crack tip with different lengths and widths are discussed. The problems associated with cracks or delaminations propagating between different materials are mentioned briefly, as well as a strategy to minimize these problems. Due to an increased interest in using a fracture mechanics based approach to assess the damage tolerance of composite structures in the design phase and during certification, the engineering problems selected as examples and given as references focus on the application of the technique to components made of composite materials.
