Observation of Damage Growth in Compressively Loaded Laminates

An experimental program to determine tie phenomenological aspects of composite-panel failure under simultaneous compressive n-plane loading and low-velocity transverse impact [C-75 m/s (0-250 ft/s)] is described. High-speed photography coupled with the shadow-moiré technique is used to record the phenomenon of failure propagation. The information gained from these records, supplemented by plate sectioning and observation for interior damage, has provided information regarding the failure-propagation mechanism. The results show that the failure process can be divided roughly into two phases. In the first phase the plane is impacted, and the resulting response causes interlaminar separation. In the second phase the local damage spreads to the undamaged portion of the plate through a combination of laminae buckling and further delamination

Postbuckling delamination of a stiffened composite panel using finite element methods

A combined numerical and experimental study is carried out for the postbuckling behavior of a stiffened composite panel. The panel is rectangular and is subjected to static in-plane compression on two opposite edges to the collapse level. Nonlinear (large deflection) plate theory is employed, together with an experimentally based failure criterion. It is found that the stiffened composite panel can exhibit significant postbuckling strength

A Mechanical Model for Elastic Fiber Microbuckling

A two-dimensional mechanical model is presented to predict the compressive strength of unidirectional fiber composites using technical beam theory and classical elasticity. First, a single fiber resting on a matrix half-plane is considered. Next, a more elaborate analysis of a uniformly laminated, unidirectional fiber composite half-plane is presented. The model configuration incorporates a free edge which introduces a buckling mode that originates at the free edge and decays into the interior of the half-plane. It is demonstrated that for composites of low volume fraction (<0.3), this decay mode furnishes values of buckling strain that are below the values predicted by the Rosen (1965) model. At a higher volume fraction the buckling mode corresponds to a half wavelength that is in violation of the usual assumptions of beam theory. Causes for deviations of the model prediction from existing experimental results are discussed

Scattering from supramacromolecular structures

We study theoretically the scattering imprint of a number of branched supramacromolecular architectures, namely, polydisperse stars and dendrimeric, hyperbranched structures. We show that polydispersity and nature of branching highly influence the intermediate wavevector region of the scattering structure factor, thus providing insight into the morphology of different aggregates formed in polymer solutions.Comment: 20 pages, 8 figures To appear in PR

Internal Stresses in Laminated Construction

This report reviews the procedure employed in an investigation of the sources and influence of internal stresses in laminated construction, and discusses the influence of shrinkage and swelling stresses caused by atmospheric conditions upon the tensile strength across grain in laminated construction with special reference to airplane propellers. The investigation covered three sources of internal stress, namely, the combination of plain-sawed and quarter-sawed material in the same construction, the gluing together of laminations of different moisture contents, and the gluing together of laminations of different densities. Glued specimens and free specimens, made up under various manufacturing conditions, were subjected to various climatic changes inducing internal stresses and then were tested

Visualization of impact damage of composite plates by means of the Moire technique

The phenomenological aspects of propagation damage due to low velocity impact on heavily loaded graphite-epoxy composite laminates were investigated using high speed photography coupled with the moire fringe technique. High speed moire motion records of the impacted specimens are presented. The results provide information on the time scale and sequence of the failure process. While the generation of the initial damage cannot always be separated temporally from the spreading of the damage, the latter takes place on the average with a speed on the order of 200 m/sec

Endothelin stimulates PDGF secretion in cultured human mesangial cells

Endothelin stimulates PDGF secretion in cultured human mesangial cells. Endothelin, a 17-DKa peptide originally described as a potent vasoconstrictor, also stimulates the release of important regulators of glomerular hemodynamics such as atrial natriuretic factor and renin. In the present study we investigated the role of endothelin in the release of another potent vasoconstrictor and mitogen of human mesangial cells, the platelet-derived growth factor. Endothelin stimulated PDGF release at 12 hours and the effect was sustained for 36 hours. This effect was associated with the enhanced induction of mRNAs encoding PDGF A-and B-chain. Endothelin also induced mitogenesis in human mesangial cells which was accompanied by activation of phospholipase C with increased inositol phosphate turnover. These data suggest a mechanism by which endothelin may regulate mesangial cell function in disease states

Damage progression in compressively loaded laminates containing a circular cutout

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76038/1/AIAA-10597-113.pd

Informal Progress Report No. 3 on The Incorporation of Bending into the Buckling Delamination Analysis

In a previous report a one dimensional model of buckling-delamination in a column was summarized. The main assumption made in that report was that the unbuckled portions of the column can be assumed to remain straight. The purpose of this report is to investigate the more general problem in which bending effects are taken into account. We deal here with the case of a single off center delamination in a column. (The case of multi-delaminations in a column can be worked out too under slight modifications.) Following the general procedure outlined in previous reports, consider the column of unit width shown in fig, la, State I represents the unstressed column while state I1 denotes the axially and uniformally compressed column. State III differs from II by allowing the delamination to buckle. Our aim here is to find an expression for the strain energy release rate of state III