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1 
A study of compression loading of composite laminatesBerbinau, Pierre J. 03 April 1997 (has links)
The compressive behavior of continuous fiber composites is not as well
understood as their tensile behavior because research and industrial applications have until
recently focused on the latter. Furthermore, most theoretical and experimental studies on
the compression of composites have examined the case of unidirectional specimens with
fibers along the loading direction (0�� fibers). While this is a logical approach since it
isolates the failure mode specific to this geometry (kinking), the study of multidirectional
laminates is essential because these are used in all practical applications. Few theories
model the compressive behavior of multidirectional laminates. None of the theories
account for the stress field or the sequence and interaction of the various observed failure
modes (kinking, delamination, matrix failure) specific to the multidirectional configuration.
The principal objective of this investigation is to construct a realistic theory to
model the compressive behavior of multidirectional composites. Compression
experiments have repeatedly shown that the initial failure mode was inplane kinking of 0��
fibers initiated at the edges of the specimens. We decided to base our compressive failure
theory upon interlaminar stresses because in multidirectional laminates these are known to
exist in a boundary layer along the edges. This required development of an analytical
theory giving the amplitude of these stresses at the free edges. We then incorporated these stresses into a new general microbuckling equation for 0�� fibers. The global laminate failure strain was determined through several fiber and matrix failure criteria. Theoretical predictions were compared with experimental results obtained from compression testing of graphite/thermoplastic laminates with the same ply sequence but different offaxis ply angles. The theory correlated well with experiments and confirmed that inplane kinking was the critical failure mode at low and medium angles, while revealing that outofplane buckling was responsible for failure at high angles. Furthermore, the theory correctly predicted the sequence of various fiber and matrix failure modes. / Graduation date: 1997

2 
Residual strength properties of Gr/BMI composite laminates after constant/cyclic compressionShenoy, Krishnananda 12 November 1993 (has links)
Graduation date: 1994

3 
Design and evaluation of test apparatuses and methods for extensiontwist coupled laminatesHooke, David A. 12 1900 (has links)
No description available.

4 
Impact response of a laminated beam on an elastic foundationTudela, Mark A. 05 1900 (has links)
No description available.

5 
Transverse microcracking in Celion 6000 graphite/PMR15 polymide compositeMills, John Steven 30 October 2008 (has links)
The effects of room temperature tensile loading and five thermal loadings upon the development of transverse microcracks (TVM) in Celion 6000/PMR15 graphiteepoxy laminates were investigated. Microcracks were observed using a replicating technique, microscopy and xray. The mechanical or thermal load at which microcracking initiates and the ply residual stresses were predicted using laminate analysis with stress and temperaturedependent materials. The TVM density as a function of tensile load was predicted using the multiple cracking theory proposed by Garrett, Parvizi and Bailey. Reasonably good correlation between theory and experiment was obtained for both the load at initial failure and the TVM density as a function of tensile load.
It has been shown that TVM density and the load to initiate microcracking are functions of the type of loading and the laminate configuration. Generally, crossply laminates exhibit higher TVM density after thermal loading than do quasiisotropic laminates, but the converse is true for tensile loading. Crossply laminates attain saturation TVM density prior to failure, but the TVM density of quasiisotropic laminates continues to increase until failure. Edge effects have a significant influence on the development of TVM, and TVM present at the free edge of a laminate extend throughout the entire width of the laminate.
<i>[Vita removed Feb. 15, 2011. GMc]</i> / Master of Science

6 
Investigation of constraint effects on flaw growth in composite laminatesYeung, Peter ChunNgok January 1979 (has links)
An investigation was conducted to study the constraint effects on flaw growth in composite laminates. Results were presented for the case of a transverse flaw in an interior ply perpendicular to the loading axis. Two orientations of the flawed ply were examined (0 and 90 degrees), and two distinctly different constraint situations were studied (crossply constraint and biaxial constraint).
Throughout the study, various nondestructive testing methods were employed to evaluate the material response and to determine the damage and damage growth in the specimens. These techniques include replication, ultrasonic cscan, ultrasonic attenuation, acoustic emission, xradiography, thermography and stiffness measurement.
The effects of constraint on the response of composite materials can be classified in two categories: (a) inplane effects and (b) throughthethickness effects. Inplane constraint is the principal contributor to notched strength and changes in notched strength under quasistatic loading. Throughthethickness constraint controls the pattern and spacing of transverse cracks in the offaxis plies to form a characteristic damage state in the laminates. Outofplane stresses produced by constraints are influential on the growth of damage along ply interfaces, especially during cyclic loading.
The mode of damage and the extent of damage in constrained notched plies are governed by the stress state in those plies, as determined by the constraining plies, and the relationship of the stress state to the strength state. Maximum constraint on the flawed ply does not produce minimum damage in the laminate; and the lesser degree of damage (in terms of axial splitting and delamination) does not necessarily result in a higher laminate strength or long fatigue lives. In the design of composite structures, a compromise has to be reached with regard to optimizing material parameters such as strength, stiffness, fatigue life, and residual strength. In maximizing one parameter, one might have to sacrifice other requirements on the other material properties in the design. / Ph. D.

7 
Fatigue response of notched graphiteepoxy laminatesKress, Gerald R. January 1983 (has links)
Changes in the stiffness and strength of notched quasiisotropic graphiteepoxy laminates were recorded and related to the fatigue damage. Two different laminates [0,90,+45,45]s (type A) and [ +45, 90, 45, 0] s (type B) were considered and the effects of stacking sequence were compared. Nondestructive testing techniques such as Xradiography, moire technique, acoustic emission, deply technique, and stiffness change were performed to observe damage development. Static properties and damage initiation were related to an approximate stress analysis.
Results show that the mechanical response and the fatigue damage depend strongly on the stacking sequence of laminates. In general, residual strength increased remarkably for both laminates due to stress redistributions while the continuous stiffness change curve is typical for each laminate and reflects damage characteristics. Buckling effects as well as matrix cracking and delaminations contribute to stiffness changes. / M.S.

8 
Improved testing methods for measurement of extensiontwist couplingSchliesman, Michael Dean 05 1900 (has links)
No description available.

9 
Nondestructive inspection of load induced damage in fiber reinforced polyphenylene sulfideFields, Richard Elliot January 1982 (has links)
The present work presents the results of an investigation of properties of polyphenylene sulfide (PPS) reinforced with random, continuous glass fibers, approximately 30% by weight. The investigation included both characterization of the mechanical properties and nondestructive inspection of the material. The objectives of the nondestructive inspection program were twofold: i) to determine nondestructive testing techniques were most responsive to developing damage and ii) to identify the damage modes using the nondestructive testing methods.
The mechanical testing program involved the study of three types of specimens: straight sided tensile coupon, dogbone, and streamline. The streamline specimen typically fails in the narrow region and therefore appears to be relatively unaffected by stress concentrations induced by the specimen geometry. Results are given for all three specimen types and comparisons made for the measured mechanical properties.
Several nondestructive testing methods, including Cscan, ultrasonic attenuation, acoustic emission, Xray radiography, and edge replication, were applied to study the damage developed under quasistatic tension loading of this material. The Cscan, edge replication, and Xray radiography tests were performed both initially and after intermediate stages of loading. These three tests appear to be unresponsive to the developing damage. That is, these techniques were unable to detect any distinctive patterns around the regions of final failure. The most responsive NDT techniques are ultrasonic attenuation and acoustic emission. Both of these methods yield quite distinct changes with increasing load. The acoustic emission tests, for example, show an extremely rapid rise in count rate at loads of about twothirds of ultimate. The ultrasonic attenuation measurements display maxima and minima when taken in realtime as the specimen is loaded.
In an effort to determine the damage mechanisms in the material and to understand the results of the NDE tests, virgin and damaged specimens were destructively examined with the aid of a scanning electron microscope (SEM). The SEM appears to show that the acoustic emission production is corning from cracking of the transverse glass fibers. The results of all tests to date are presented together with recommendations and conclusions for the application of nondestructive test methods to PPS. / Master of Science

10 
Buckling response of symmetrically laminated composite plates having a trapezoidal planform areaRadloff, Harold David 11 June 2009 (has links)
The focus of this work is the buckling response of symmetrically laminated composite plates having a planform area in the shape of an isosceles trapezoid. The loading is assumed to be inplane and applied perpendicular to the parallel ends of the plate. The tapered edges of the plate are assumed to have simply supported boundary conditions, while the parallel ends are assumed to have either simply supported or clamped boundary conditions. Plates with one end being up to 3 times narrower than the other end, and the plate being up to 3 time longer than the width of the wide end are considered. A semianalytic closedform solution based on energy principles and the Trefftz stability criterion is derived and solutions are obtained using the RayleighRitz method. Intrinsic in this solution is a simplified prebuckling analysis which approximates the inplane force resultant distributions by the forms N<sub>x</sub>=P/W(x) and N<sub>y</sub>=N<sub>xy</sub>=0, where P is the applied load and W(x) is the plate width which, for the trapezoidal planform, varies linearly with the lengthwise coordinate x. The outof plane displacement is approximated by a double trigonometric series. This analysis is posed in terms of four nondimensional parameters representing orthotropic and anisotropic material properties, and two nondimensional parameters representing geometric properties. With nondimensionalization, the analysis is well suited for parametric studies. The analysis uses standard eigenvalue extraction routines and converges using 5 terms in the outofplane displacement series. It appears that this analysis captures the buckling response of plates having tapered planform and should be a useful design tool. For comparison purposes, a number of specific plate geometry, ply orientation, and stacking sequence combinations are investigated using the general purpose finite element code ABAQUS. Comparison of buckling coefficients calculated using the semianalytical model and the finite element model show agreement within 5%, in general, and within 15% for the worst cases. In addition to the good agreement between the semianalytical analysis and the finite element results, the finite element model also suggests that the simplified inplane force resultant distribution assumed in the analysis is valid. In order to verify both the finite element and semianalytical analyses, buckling loads are measured for graphite/epoxy plates having a wide range of plate geometries and stacking sequences. Test fixtures, instrumentation system, and experimental technique are described. Experimental results for the buckling load, the buckled mode shape, and the prebuckling plate stiffness are presented and show good agreement with the analytical results regarding the buckling load and the prebuckling plate stiffness. However, the experimental results show that for some cases the analysis underpredicts the number of halfwaves in the buckled mode shape. In the context of the definitions of taper ratio and aspect ratio used in this study, it is concluded that the buckling load always increases as taper ratio increases for a given aspect ratio for plates having simply supported boundary conditions on the parallel ends. There are combinations of plate geometry and ply stacking sequences, however, that reverse this trend for plates having clamped boundary conditions on the parallel ends such that an increase in the taper ratio causes a decrease in the buckling load. The clamped boundary conditions on the parallel ends of the plate are shown to increase the buckling load compared to simply supported boundary conditions. Also, anisotropy (the D₁₆ and D₂₆ terms) is shown to decrease the buckling load and skew the buckled mode shape for both the simply supported and clamped boundary conditions. / Master of Science

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