Free edge strain concentrations in real composite laminates: Experimental-theoretical correlation

The magnitude of the maximum shear strain at the free edge of axially loaded theta (2)/-theta(2)(s) and (+ or - theta(2) (s) composite laminates was investigated experimentally and numerically to ascertain the actual value of strain concentration in resin matrix laminates and to determine the accuracy of finite element results. Experimental results using moire interferometry show large, but finite, shear strain concentrations at the free edge of graphite-epoxy and graphite-polyimide laminates. Comparison of the experimental results with those obtained using several different finite element representations showed that a four node isoparametric finite element provided the best and most trouble free numerical results. The results indicate that the ratio of maxium shear strain at the free edge to applied axial strain varies with fiber orientation and does not exceed nine for the most critical angle which is 15 deg

Deformation measurements of composite multi-span beam shear specimens by Moire interferometry

Experimental analyses were performed for determination of in plane deformations and shear strains in unidirectional and quasi-isotropic graphite-epoxy beams. Forty-eight ply beams were subjected to 5 point and 3 point flexure. Whole field measurements were recorded at load levels from about 20% to more than 90% of failure loads. Contour maps of U and W displacement fields were obtained by moire interferometry, using reference gratings of 2400 lines/mm. Clearly defined fringes with fringe orders exceeding 1000 were obtained. Whole field contour maps of shear strains were obtained by a method developed for these tests. Various anomalous effects were detected in the displacement fields. Their analysis indicated excess shear strains in resin rich zones in regions of shear tractions; free edge shear strains in quasi-isotropic specimens in regions of normal stresses; and shear stresses associated with cyclic shear compliances of quasi-isotropic plies in regions of shear tractions. Their contributions could occur independently or in superposition. Qualitative analyses addressed questions of relaxation; influence of contact stress distribution; specimen failure; effect of specimen overhang; nonlinearity; and qualities of 5 and 3 point flexure tests

Measure of displacement around holes in composite plates subjected to quasi-static compression

Contour maps of thickness changes were obtained for three quasi-isotropic graphite-epoxy plates with central holes, loaded in compression. Thickness changes were determined for six load increments from nearly zero to within a few percent of the failure load. The largest change of thickness occurred near the hole but not at the boundary of the hole. Below 90 percent of the failure load, the thickness changes were nearly proportional to load. Irregularities of thickness changes occurred in zones of compressive stresses and they were attributed to localized fiber buckling. A new optical technique was developed to measure thickness changes with high sensitivity. It utilizes a comparatively simple means of holographic interferometry on both sides of the specimen, followed by additive moire to obtain thickness changes as the sum of the out-of-plane displacements. Sensitivity was 12.5 x 10 to the -6 power in. per fringe order. The fringe patterns represent thickness changes uniquely, even when specimen warpage and consequent out-of-plane displacements are very large

Measurements of displacement around holes in composite plates subjected to quasi-static compression

Attempts to develop a whole-field, high sensitivity optical technque for measurement of load induced changes of thickness of composite plates are described. Graphite-epoxy plates of quasi-isotropic layup were used as test specimens. Changes of thickness of three plates, each with a central hole of different size, were measured as a function of applied compressive loads. The first test specimen showed localized zones where no holographic fringes were present, surrounded by zones of low fringe contrast. This was thought to be a result of localized motion or creep. Subsequent tests with an increased time interval between specimen loading and holographic exposure demonstrated no localized zones of absent fringes. No plausible explanation for radical differences in the quality of fringe patterns was found, although the use of specimens having a high quality mirrorized surface provided superior change of thickness patterns. Recommendations for further investigations and changes in test procedure are presented

Elastic-plastic deformation of a metal-matrix composite coupon with a center slot

A comprehensive experimental analysis of deformations of the surface of a metal-matrix specimen is reported. The specimen is a 6-ply 0 + or - 45 sub s boron-aluminum tensile coupon with a central slot. Moire interferometry is used for high-sensitivity whole-field measurements of in-plane displacements. Normal and shear strains are calculated from displacement gradients. Displacement fields are analyzed at various load levels from 15% to 95% of the failure load. Deformations of the boron fibers could be distinguished from those of the matrix. Highly localized plastic slip zones occur tangent to the ends of the slot. Shear strains and concurrent transverse compressive strains in the slip zones reach approximately 10% and 1%, respectively. Upon unloading, elastic recovery in surrounding regions causes a reverse plastic shear strain in the slip zone of about 4%. Longitudinal normal strains on the unslotted ligament peak at the slot boundary at about 1% strain. The strain concentration factor at the end of the slot decreases with load level and the advance of plasticity

Vitrectomy Combined with Cataract Surgery for Retinal Detachment Using a Three-Dimensional Viewing System

Purpose: To evaluate the results of a pars plana vitrectomy (PPV) combined with cataract surgery for primary rhematogenous retinal detachment (RD) using a three-dimensional (3D) viewing system and a conventional microscope (CM). Methods: Medical reports of 82 patients were retrospec-tively reviewed: 26 patients were operated on with 3D and 56 patients were operated on with CM. The main outcome measures were visual acuity, duration of the surgery, and the rate of postoperative complications. Results: No statistically significant differences in pre-and postoperative visual acuity were found between both groups. There was significant improvement in the visual acuity in both groups. The best postoperative visual acuity was achieved with SF6 gas tamponade, followed by C3F8 gas and silicone oil in both groups. The duration of the surgery (60 min vs. 55 min) and the rate of postoperative complications (15% vs. 14%) were similar in both groups. Conclusions: The similar postoperative visual acuity and rate of complications detected using 3D and CM indicate that the 3D viewing system may be advantageous in the treatment of rhematogenous RD with PPV combined with cataract surgery, i.e., a complex procedure involving both anterior and posterior segment manipulations

Ozone-based eye drops activity on ocular epithelial cells and potential pathogens infecting the front of the eye

Confirmation of the biological effectiveness of new ophthalmic preparations introduced in the market is an important element in maintaining the safety of using this type of medications. This study aimed to investigate the activity of Ozodrop® on human corneal and conjunctival epithelial cells, as well as its antibacterial and antifungal activity. Cytotoxicity analyses of ocular surface epithelial cells were performed in vitro by MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide) and Neutral Red uptake assays. The level of nitric oxide released by the cells was assessed by the Griess method. The reduction of the DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical by the tested formulation was analyzed. Microbiological tests were also performed. It was found that the Ozodrop® preparation exhibited biological activity, but was less active than the reference antibiotics and the anti-yeast agent. The cytotoxic activity of the Ozodrop® formulation was dependent on the time of cell exposure to it. No toxic effect was observed in the short-term, for up to 3 h. It appeared after 24 h of exposure of the cells to the preparation. The drops showed antioxidant activity in the specified concentration range. They also stimulated the release of nitric oxide, mainly by corneal epithelial cells. The Ozodrop® formulation exhibits biological activity that can be considered useful in the treatment of infections in the front part of the eye

Double‐needle yamane technique using flanged haptics in ocular trauma—a retrospective survey of visual outcomes and safety

To evaluate visual outcomes and safety of the double‐needle technique using flanged haptics (Yamane technique) in patients with aphakia caused by ocular trauma at a trauma referral center. Retrospective: Consecutive interventional case series of 30 patients who underwent the Yamane technique due to posttraumatic aphakia. The double‐needle technique using flanged haptics was combined with anterior vitrectomy (group A) in 14 patients, and with pars plana vitrectomy (PPV) (group B) due to retinal detachment, nucleus dislocation into the vitreous cavity, or intraocular lens (IOL) displacement in 16 patients. No intraoperative complications were noted. There was significant improvement in the visual acuity in both groups at the second postoperative visit. However, the visual acuity was significantly worse in the group treated with the Yamane technique combined with PPV. Silicone oil tamponade in PPV group was associated with worse visual acuity, whereas post lensectomy status was associated with poor visual function result in the anterior vitrectomy group. There was one case of slight IOL decentration and one retinal detachment during the postoperative follow‐up period in the group with PPV. In this case series, the Yamane technique applied in traumatized eyes was found to be an efficacious and safe procedure. Combining the Yamane technique with PPV due to posterior segment ocular trauma was associated with worse functional results in the follow‐up at three months. Further studies with longer follow‐up evaluations are required to verify long‐term complications