Reliability analysis of continuous fiber composite laminates

A composite lamina may be viewed as a homogeneous solid whose directional strengths are random variables. Calculation of the lamina reliability under a multi-axial stress state can be approached by either assuming that the strengths act separately (modal or independent action), or that they interact through a quadratic interaction criterion. The independent action reliability may be calculated in closed form, while interactive criteria require simulations; there is currently insufficient data to make a final determination of preference between them. Using independent action for illustration purposes, the lamina reliability may be plotted in either stress space or in a non-dimensional representation. For the typical laminated plate structure, the individual lamina reliabilities may be combined in order to produce formal upper and lower bounds of reliability for the laminate, similar in nature to the bounds on properties produced from variational elastic methods. These bounds are illustrated for a (0/plus or minus 15)sub s Graphite/Epoxy (GR/EP) laminate. And addition, simple physically plausible phenomenological rules are proposed for redistribution of load after a lamina has failed. These rules are illustrated by application to (0/plus or minus 15)sub s and (90/plus or minus 45/0)sub s GR/EP laminates and results are compared with respect to the proposed bounds

The Effects of Modern Band Performance on Enhancing Confidence and Emotional Maturation in Fifth-Grade Students

Current research notes that participation in modern band general music instruction elicits improvements in students’ sense of inclusion in school; however, it is yet to be determined if additional benefits of modern band implementation occur. This applied study aims to investigate the potential for a causal comparison between fifth-grade students’ confidence levels and emotional maturity after exposure to modern band instructional techniques and performance compared to fifth-grade students engaged in music education with an emphasis on vocal instruction. Both qualitative and quantitative approaches were implemented. Data were collected and analyzed by surveying thirty-seven fifth-grade students reporting their confidence levels and emotional maturation over twelve weeks of general music instruction. Seventeen students were instructed in vocal music techniques, and twenty were taught via modern band techniques. Following the eight weeks of instruction, students in both groups participated in a performance. After the study, three students from each group were interviewed regarding their experience. The survey and interview findings determined that those engaged in general music studies through modern band techniques communicated emotional maturity more than those educated in vocal techniques. Those involved in vocal music scored higher in lesson enjoyment. Implications for future studies include analyzing additional characteristics via these musical mediums, varying the age groups studied, and comparing modern band to performance genres concerning confidence and emotional maturity

Probability techniques for reliability analysis of composite materials

Traditional design approaches for composite materials have employed deterministic criteria for failure analysis. New approaches are required to predict the reliability of composite structures since strengths and stresses may be random variables. This report will examine and compare methods used to evaluate the reliability of composite laminae. The two types of methods that will be evaluated are fast probability integration (FPI) methods and Monte Carlo methods. In these methods, reliability is formulated as the probability that an explicit function of random variables is less than a given constant. Using failure criteria developed for composite materials, a function of design variables can be generated which defines a 'failure surface' in probability space. A number of methods are available to evaluate the integration over the probability space bounded by this surface; this integration delivers the required reliability. The methods which will be evaluated are: the first order, second moment FPI methods; second order, second moment FPI methods; the simple Monte Carlo; and an advanced Monte Carlo technique which utilizes importance sampling. The methods are compared for accuracy, efficiency, and for the conservativism of the reliability estimation. The methodology involved in determining the sensitivity of the reliability estimate to the design variables (strength distributions) and importance factors is also presented

Cyclic pressure on compression-moulded bioresorbable phosphate glass fibre reinforced composites

The use of thermoplastic composites based on poly(lactic) acid and phosphate glass fibres over metallic alloys for clinical restorative treatment is highly beneficial due to their biocompatibility and biodegradability. However, difficulties in achieving a thorough melt impregnation at high fibre contents while limiting polymer degradation is one of the main issues encountered during their manufacture. This paper reports for the first time on the effects of pressure cycling on the mechanical properties of compression moulded polylactic acid-phosphate glass fibre composites. The strength of the composites consolidated under pressure cycling were at least 30% higher than those in which conventional static pressure was used. The marked disparity was attributed to the influence of pressure cycling on the fibre preform permeability, the melt viscosity and the capillary pressure, leading to improved fibre wet-out with respect to static pressure. Implementation of a cyclic pressure appeared to promote the occurrence of transcrystallinity in the polymer matrix as suggested by DSC traces. The fibre content influenced PLA thermal degradation since the matrix molecular weight decreased as the fibre content increased on account of the moisture adsorbed by the glass surface. However, this extent of degradation did not impair the matrix mechanical performance in the composites

Advances in computational design and optimization with application to MEMS

In this paper, we will highlight the current research which employs the topology optimization to find the optimal configuration of various smart structures and microstructures, specifically, pressure actuated compliant mechanisms, flextensional transducers, and porous material microstructures with unusual thermoelastic properties. These examples demonstrate that the topology optimization problem involving multiple physics domain is a viable direction for future research, in particular, for sensor and actuator design. Copyright © 2001 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34535/1/271_ftp.pd

Fracture Energy for Short Brittle Fiber/Brittle Matrix Composites With Three-Dimensional Fiber Orientation

Adding brittle fibers to a brittle matrix can create a composite which is substantially tougher than the monolithic matrix by providing mechanisms for energy dissipation during crack propagation. A model based on probabilistic principles has been developed to calculate the increased energy absorption during fracture for a brittle matrix reinforced with very short, poorly bonded fibers. This model, previously developed for planar fiber orientations, is extended to consider the three-dimensional fiber orientations which may occur during composite fabrication. The fiber pull-out energy is assumed to dominate other fracture energy terms, and simple parametric studies are given to demonstrate the effect of fiber orientation, fiber length, fiber diameter, and fiber-matrix interfacial shear stress. In particular, the fiber orientation effects may be grouped into an effective “orientation parameter”. The model predictions compare satisfactorily with the limited data available, and offer a conceptual framework for considering the effect of changing the physical variables on the fracture energy of the composite.</jats:p