Compression failure of angle-ply laminates

The present work deals with modes and mechanisms of failure in compression of angle-ply laminates. Experimental results were obtained from 42 angle-ply IM7/8551-7a specimens with a lay-up of ((plus or minus theta)/(plus or minus theta)) sub 6s where theta, the off-axis angle, ranged from 0 degrees to 90 degrees. The results showed four failure modes, these modes being a function of off-axis angle. Failure modes include fiber compression, inplane transverse tension, inplane shear, and inplane transverse compression. Excessive interlaminar shear strain was also considered as an important mode of failure. At low off-axis angles, experimentally observed values were considerably lower than published strengths. It was determined that laminate imperfections in the form of layer waviness could be a major factor in reducing compression strength. Previously developed linear buckling and geometrically nonlinear theories were used, with modifications and enhancements, to examine the influence of layer waviness on compression response. The wavy layer is described by a wave amplitude and a wave length. Linear elastic stress-strain response is assumed. The geometrically nonlinear theory, in conjunction with the maximum stress failure criterion, was used to predict compression failure and failure modes for the angle-ply laminates. A range of wave length and amplitudes were used. It was found that for 0 less than or equal to theta less than or equal to 15 degrees failure was most likely due to fiber compression. For 15 degrees less than theta less than or equal to 35 degrees, failure was most likely due to inplane transverse tension. For 35 degrees less than theta less than or equal to 70 degrees, failure was most likely due to inplane shear. For theta less than 70 degrees, failure was most likely due to inplane transverse compression. The fiber compression and transverse tension failure modes depended more heavily on wave length than on wave amplitude. Thus using a single parameter, such as a ratio of wave amplitude to wave length, to describe waviness in a laminate would be inaccurate. Throughout, results for AS4/3502, studied previously, are included for comparison. At low off-axis angles, the AS4/3502 material system was found to be less sensitive to layer waviness than IM7/8551-7a. Analytical predictions were also obtained for laminates with waviness in only some of the layers. For this type of waviness, laminate compression strength could also be considered a function of which layers in the laminate were wavy, and where those wavy layers were. Overall, the geometrically nonlinear model correlates well with experimental results

BATCH FABRICATION OF FIBER-REINFORCED ELASTOMER PREPREG ABSTRACT

Heightened interest in flexible (elastomeric) composite applications such as bio-mechanical devices, flexible underwater vehicles, and inflatable space structures highlight the need of improved fabrication techniques for fiber-reinforced elastomeric materials (FRE). Previous methods have generally been limited to a fairly low percentage of fibers in an elastomeric matrix, or used calendering manufacturing methods that are not generally suitable for non-tire fiber-rein-forced elastomeric composites applications. Other researchers have noted problems with fiber-elastomer adhesion. The current work demonstrates a method for making small batches of high quality fiber-reinforced elastomer pre-preg. Strengths of the current work include excellent fiber adhesion, medium to high fiber volume fractions, highly parallel fibers, use of traditional advanced composites fabrication methodologies, and reproducible ply thicknesses. The method combines standard techniques of filament winding, wet lay-up techniques, and autoclave curing with pertinent knowledge of elastomers to produce fiber-reinforced elastomer prepreg. Fiber-elastomer adhesion was enhanced by the proper choice of fibers, autoclave pressure, and the application of a primer. Fiber parallelism and straightness were accomplished by use of a fila-ment winder. Fiber-reinforced elastomer prepreg and laminated specimens with fiber volume fractions of 12 % to 62 % were fabricated using fiberglass and cotton fibers, respectively. Manu-facturing quality was verified by tensile tests on fabricated specimens. Nonlinear material proper-Accepted for publication in the Journal of Advanced Materials, Sept. 5, 1998 1 ties from the tests are being used to calibrate a modified nonlinear laminated plate model. Complete test results and nonlinear predictions are being reported separately

On Bayesian analysis of mixtures with an unknown number of components - Discussion

New methodology for fully Bayesian mixture analysis is developed, making use of reversible jump Markov chain Monte Carlo methods that are capable of jumping between the parameter subspaces corresponding to different numbers of components in the mixture. A sample from the full joint distribution of all unknown variables is thereby generated, and this can be used as a basis for a thorough presentation of many aspects of the posterior distribution. The methodology is applied here to the analysis of univariate normal mixtures, using a hierarchical prior model that offers an approach to dealing with weak prior information while avoiding the mathematical pitfalls of using improper priors in the mixture context

Magistrates, magistrates courts, and social change

New Yor