Modeling 3D Fiber Reinforced Foam Core Sandwich Structures Using a Multi-Scale Finite Element Approach.

An engineering challenge of composite sandwich structures is quantifying their ability to tolerate damage, particularly in launch vehicles and spacecraft, where mission assurance is critical. Recently, there has been a development of new core materials that may alter their damage tolerance through the use of a three-dimensional, truss-like network of reinforcing fibers inside a lightweight foam core. This research focuses on the testing and developing a multi-scale approach to model 3D Fiber Reinforced Foam Core (3DFRFC) sandwich composites with defects across typical operating temperatures. Details of the 3DFRFC measured directly from the microstructure were utilized to develop a parametric code for generating detailed embedded element models. These models were used for direct detailed modeling of fracture, edgewise compression, flatwise tension, flatwise compression, and three point bending test specimens. The embedded element models were also used as the cornerstone of a new method of developing effective homogenized properties for 3DFRFCs based on the details of the microstructure. Improved homogenization techniques developed by including the local interaction between the facesheet and the core are also included. The development of a new bonded double cantilever beam (BDCB) specimen for testing the Mode I fracture of a 3DFRFC sandwich structures is presented. The BDCB specimens exhibited relatively smooth crack propagation and produced GIc values similar to honeycomb sandwich structures and significantly higher than comparable foam structures. A full fabrication, testing, and evaluation of 3DFRFC specimens with differing sizes of facesheet-to-core interface debonds is also presented. The analysis methods were able to predict the failure load and modes within 5%. The 3DFRFC proved to be tolerant to facesheet-to-core debonds with only the largest debond demonstrating a statistically significant reduction of 22%. Finally, a detailed investigation of the through thickness behavior of a 3DFRFC composite under ambient and cold conditions is included demonstrating better through thickness ambient performance than unreinforced cores and relatively small reductions in strength at cold temperatures. The investigation into the performance of 3DFRFC composite structures highlights the robust behavior of the structure to cold environments while underscoring the importance of loading direction on the structural response of these highly orthotropic composites.PhDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111577/1/ztkier_1.pd

Competitive Interactions among Symbiotic Fungi of the Southern Pine Beetle

The southern pine beetle, a damaging pest of conifers, is intimately linked to three symbiotic fungi. Two fungi, Ceratocystiopsis ranaculosus and Entomocorticium sp. A, are transported within specialized structures (mycangia) in the beetle exoskeleton and are mutualists of the beetle. A third fungus, Ophiostoma minus, is transported externally on the beetle exoskeleton (phoretically) and is an antagonist of the beetle. This study examined competitive interactions among these three fungi. The results of de Wit replacement series and primary and secondary resource capture assays with these fungi provide strong evidence for differential competition between the phoretic and mycangial fungi. O. minus was the most able to capture both uncolonized and colonized resources. Entomocorticium sp. A and C. ranaculosus, although equal to one another in compet- itive abilities, differed in their ability to compete with O. minus. Entomocorticium sp. A was able to maintain space free of O. minus to a much greater degree than was C. ranaculosus. The outcome of such competitive interactions may have significant impacts on the biology of this ecologically and economically important beetle

Determining Effective Interface Fracture Properties of 3D Fiber Reinforced Foam Core Sandwich Structures

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106494/1/AIAA2013-1547.pd

A non-intrusive nonlinear aeroelastic extension of loads packages with application to long range transport aircraft configuration

A new method for constructing geometrically-nonlinear aeroelastic systems from standard linear models is applied to an industry-level aircraft configuration. The new approach seamlessly integrates with current aeroelastic load packages performing linear analysis based on generic finite-element models (FEMs) and aerodynamic influence coefficient matrices (AICs). We generalize the methodology to incorporate control inputs, find the trimmed aircraft state, or generate gusts disturbances, which can be employed separately or combined to obtain a simplified flight dynamics model for load analysis. An initial study of the aeroelastic response of a long range aircraft is presented. Linear and nonlinear results are introduced in static and dynamic computations of manoeuvres, trim, and gust disturbances. These are compared to commercial software calculations, showing the need for geometrically nonlinear analysis in the production environment of airplanes with ultra high aspect ratio wings

Micromechanical Modeling and Design Optimization of 2-D Triaxial Braided Composites

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97106/1/AIAA2012-1257.pd

Effects of Ply Stacking Sequence in 3D Fiber Reinforced Foam Core Sandwich Structures with Defects

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140407/1/6.2014-0504.pd

Computing Aggregate Properties of Preimages for 2D Cellular Automata

Computing properties of the set of precursors of a given configuration is a common problem underlying many important questions about cellular automata. Unfortunately, such computations quickly become intractable in dimension greater than one. This paper presents an algorithm --- incremental aggregation --- that can compute aggregate properties of the set of precursors exponentially faster than na{\"i}ve approaches. The incremental aggregation algorithm is demonstrated on two problems from the two-dimensional binary Game of Life cellular automaton: precursor count distributions and higher-order mean field theory coefficients. In both cases, incremental aggregation allows us to obtain new results that were previously beyond reach

Ontogeny of mantle musculature and implications for jet locomotion in oval squid Sepioteuthis lessoniana

SUMMARY We examined the relationship between mantle muscle structure and mantle kinematics in an ontogenetic series (5-85 mm dorsal mantle length) of oval squid, Sepioteuthis lessoniana. Thick filament length increased during growth in the mantle muscle fibres that power jet locomotion (i.e. the circular muscles). The thick filament length of both the superficial mitochondria-rich (SMR; analogous to vertebrate red muscle fibres) and central mitochondria-poor (CMP; analogous to vertebrate white muscle fibres) circular muscles increased significantly during ontogeny. Thick filaments in the SMR circular muscle fibres of newly hatched squid (N=5) ranged from 0.7 to 1.4 μm and averaged 1.0 μm, while the thick filaments of the SMR fibres of the largest squids (N=4) studied ranged from 1.2 to 3.4μ m and averaged 1.9 μm. The ontogeny of thick filament length in the CMP circular muscle fibres showed a similar trend. The range for hatchling CMP circular muscles was 0.7-1.4 μm, with an average of 1.0 μm, whereas the range and average for the largest squids studied were 0.9-2.2 μm and 1.5μ m, respectively. Within an individual hatchling, we noted no significant differences between the thick filament lengths of the SMR and CMP fibres. Within an individual juvenile, the thick filaments of the SMR fibres were∼ 25% longer than the CMP fibres. The change in thick filament length may alter the contractile properties of the circular muscles and may also result in a decrease in the rate of mantle contraction during jetting. In escape-jet locomotion, the maximum rate of mantle contraction was highest in newly hatched squid and declined during ontogeny. The maximum rate of mantle contraction varied from 7-13 muscle lengths per second in newly hatched squid (N=14) and from 3-5 muscle lengths per second in the largest squids (N=35) studied

Antagonisms, mutualisms and commensalisms affect outbreak dynamics of the southern pine beetle

Feedback from community interactions involving mutualisms are a rarely explored mechanism for generating complex population dynamics. We examined the effects of two linked mutualisms on the population dynamics of a beetle that exhibits outbreak dynamics. One mutualism involves an obligate association between the bark beetle, Dendroctonus frontalis and two mycangial fungi. The second mutualism involves Tarsonemus mites that are phoretic on D. frontalis ( commensal ), and a blue-staining fungus, Ophiostoma minus. The presence of O. minus reduces beetle larval survival ( antagonistic ) by outcompeting beetle-mutualistic fungi within trees yet supports mite populations by acting as a nutritional mutualist. These linked interactions potentially create an interaction system with the form of an endogenous negative feedback loop. We address four hypotheses: (1) Direct negative feedback: Beetles directly increase the abundance of O. minus, which reduces per capita reproduction of beetles. (2) Indirect negative feedback: Beetles indirectly increase mite abundance, which increases O. minus, which decreases beetle reproduction. (3) The effect of O. minus on beetles depends on mites, but mite abundance is independent of beetle abundance. (4) The effect of O. minus on beetles is independent of beetle and mite abundance. High Tarsonemus and O. minus abundances were strongly correlated with the decline and eventual local extinction of beetle populations. Manipulation experiments revealed strong negative effects of O. minus on beetles, but falsified the hypothesis that horizontal transmission of O. minus generates negative feedback. Surveys of beetle populations revealed that reproductive rates of Tarsonemus, O. minus, and beetles covaried in a manner consistent with strong indirect interactions between organisms. Co-occurrence of mutualisms embedded within a community may have stabilizing effects if both mutualisms limit each other. However, delays and/ or non-linearities in the interaction systems may result in large population fluctuations. © Springer-Verlag 2005

The length-force behavior and operating length range of squid muscle vary as a function of position in the mantle wall

Hollow cylindrical muscular organs are widespread in animals and are effective in providing support for locomotion and movement, yet are subject to significant non-uniformities in circumferential muscle strain. During contraction of the mantle of squid, the circular muscle fibers along the inner (lumen) surface of the mantle experience circumferential strains 1.3 to 1.6 times greater than fibers along the outer surface of the mantle. This transmural gradient of strain may require the circular muscle fibers near the inner and outer surfaces of the mantle to operate in different regions of the length-tension curve during a given mantle contraction cycle. We tested the hypothesis that circular muscle contractile properties vary transmurally in the mantle of the Atlantic longfin squid, Doryteuthis pealeii. We found that both the length-twitch force and length-tetanic force relationships of the obliquely striated, central mitochondria-poor (CMP) circular muscle fibers varied with radial position in the mantle wall. CMP circular fibers near the inner surface of the mantle produced higher force relative to maximum isometric tetanic force, P0, at all points along the ascending limb of the length-tension curve than CMP circular fibers near the outer surface of the mantle. The mean ± s.d. maximum isometric tetanic stresses at L₀ (the preparation length that produced the maximum isometric tetanic force) of 212 ± 105 and 290 ± 166 kN m(-2) for the fibers from the outer and inner surfaces of the mantle, respectively, did not differ significantly (P=0.29). The mean twitch:tetanus ratios for the outer and inner preparations, 0.60 ± 0.085 and 0.58 ± 0.10, respectively, did not differ significantly (P=0.67). The circular fibers did not exhibit length-dependent changes in contraction kinetics when given a twitch stimulus. As the stimulation frequency increased, L₀ was approximately 1.06 times longer than LTW, the mean preparation length that yielded maximum isometric twitch force. Sonomicrometry experiments revealed that the CMP circular muscle fibers operated in vivo primarily along the ascending limb of the length-tension curve. The CMP fibers functioned routinely over muscle lengths at which force output ranged from only 85% to 40% of P₀, and during escape jets from 100% to 30% of P₀. Our work shows that the functional diversity of obliquely striated muscles is much greater than previously recognized