The Behavior of Structures Composed of Composite Materials
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This invention comes from the idea that modern and future composite materials require a novel building system to take advantage of their phenomenal physical properties. Current building systems are ill equipped to take full advantage of the physical properties of modern composites and future smart materials. Current and future exotic composite materials require an elegant system of construction that will allow the creation of infinite structural diversity. Helixes, spheres, quasicystalline planes, amorphous shapes, branching structures, etc.
Current building systems are not designed to take advantage of the levels of bending stress made available in many composite and smart materials. A structure built of curved elastic elements under stress is better suited to controlled shape morphing than a structure built with straight elements. The level of structural density that defines many current building systems will render them obsolete when the specific strength of future composite materials reach a high enough level.
Additive and reductive changes made to a structure over time is difficult when using existing building systems because of their inflexible nature. Current building systems are diverse in type because they are needed for different applications. An elegantly simple building system using adaptable materials will be best suited to many niches. Current building systems have difficulty adapting to potentially damaging natural phenomena. Building with straight elements is not conducive to flexibility or the benign absorption of external forces.
A building system capable of functioning at many scales is needed in an environment where materials exist that will allow the creation of structures hitherto impossible at many scales.
The Behavior Of Structures Composed Of Composite Materials | SpringerLink
This describes a modular building system tailored to the use of carbon allotrope based composite materials. This modular building system tests the boundary of scale by constructing macroscopic structures based on microscopic construction principles. The products assembled using this system are highly structurally integrated.
The products are structurally fluid and the term growth could describe the construction process. This system of construction has terrestrial, aquatic and aerospace applications. The system is capable of producing isotropic and anisotropic structures. Recent and future advances in material and computer science technologies make this invention feasible. Its goal is to create macro structures that reach or surpass the level of sophistication found in nature at the microscopic level.
This invention is a natural macroscopic development that inversely parallels our exploration and application of nanotechnology. I state that a repertoire of macroscopic composite material modules can function to create a seemingly infinite variety of structural arrangements. The modules are analogous to the organic molecules that make up the matter of life.
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The diversity of organic matter's shape and scale has its roots in the structure of the molecules that comprise it. Like these composite material modules, organic molecules are elastic structures. The elastic energy stored in atomic bonds is potential mechanical energy.
This stored energy enhances the molecule's structural integrity and allows for structural changes in response to intramolecular interactions. This scenario could soon be made available macroscopically by advances in material science. The system I propose is a vehicle for the creation of smart structures built from smart composite materials.
Computer science advances are important to the efficient application of this idea, in particular software and hardware platforms that model the behavior of macromolecular structures. This building system's modular design has a close relationship to the structure of organic cyclic molecules.
It will be used as a tool to help describe the intricacies of this invention. The modules comprising this building system range in their level of complexity. Based on these differences in complexity, the modules are grouped into four families, A,B. C, and D. The most elemental module grouping is family A. Family A is made up of a repertoire of modules that includes the five-sided module depicted in FIG. This module type is similar in structure to the cyclopentane molecule shown in FIG. This six-sided module is structurally analogous to the molecular structure cyclohexane seen in FIG. The chemical family of cycloalkanes shown in FIG.
The corresponding module configurations found in family A mirror the cycloalkanes. Family B modules are similar to family A but have more robust rings. They can be thought of as having single rings composed of all double bonds. The family B modules' best molecular analogy are ringed aromatic compounds, an example being benzene with is depicted in FIGS. The family B module equivalent of benzene is shown in drawing FIG. The hybridization of module families A and B defines module family C.
This group can incorporate any combination of single and double bond configurations within their rings. Their molecular analogy is the family of cycloalkenes. Several cycloalkene molecules shown in FIG. There is a close relationship between the elastic nature of atomic bonds and the elastic nature of the modules comprising this invention. Family D modules have the most complex architecture. This group combines the diverse bond configurations of families A, B and C along with having multiple interconnected rings.
The group's molecular analogy is the polycyclic compounds. Examples are shown in FIGS. The most distinguishing structural feature of this family is the presence of interconnected rings. The number of unique module structures that exist within this family is vast.
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All modules are built from linear component parts and hardware. The basic assembly process is illustrated in FIG. The linear elements' labeled 1 , form intramodular connections within the ring at each focus, labeled 2. The linear elements make sequential bilinear connections as they form the module's central ring.
The elements run bilinearly tangent to the ring in opposite directions. The linear elements join to form potential intermodular connection points around the module's periphery and labeled 3. The three-sided module seen in FIG. It has three intramodular connection points 2 , three intermodular connection points 3 and is made up of three linear elements 1.
Linear element connection points are analogous to the atomic bonds that form between or within ringed molecules. Connections between modules intermodular are not as strong as the connections that make up the central ring structure intramodular. Intermodular and intramodular connections have different elastic properties that need to be explored.
Each linear element can be thought of as being an atom. This module's structural elasticity is analogous to the benzene molecule's internal forces. There is a general relationship between each module's geometric proportions and the golden ratio as seen in FIG. There is evidence that this phi relationship exists within the molecular geometries of all ringed carbon based compounds.
In nature bond lengths and strengths depend on the elements involved. For this reason the modules' geometry references only organic chemistry. As mentioned, modules within family A are made up of linear elements. These elements are symmetrically positioned within each modular assembly. In this case each linear element has the same stress placed on it within the modular assembly. All the modules within family A and B are built using linear elements of identical length like those labeled 1 in FIG. Those linear elements after becoming assembled into a module are also labeled as 1.
The linear elements are straight prior to becoming the curved structure of the module. Because the elements are elastic, the module contains stored energy.
The linear elements are assembled sequentially into a ring. The ring is punctuated by arms that tangentially exit the structure at specific angles around the ring's periphery 4. These linear elements affix to one another intramodularly at foci located around the ring 2. Modules will interconnect at intermodular connection points labeled 3. Module connections require hardware shown in FIG. The foci connection hardware labeled 7 holds the elements in place.
The hardware connectors labeled 8 allow modules to interconnect. When smart materials are used, 7 and 8 type connectors act to electrically isolate the elements from one another. The hardware labeled 7 and 8 may incorporate electronic components that relate to the use and control of smart materials. The addressing and stimulation of the individual smart material elements within a module may involve electronics that are located within the hardware.
The four linear elements labeled 1 in figure FIG. An alternative to assembling the modules from individual elements could involve the use of modern casting, molding or 3D printing techniques, forming integrated modules with or without individual parts. Molding and 3D printing are better adapted to gross production, greater structural complexity and control circuit integration.
All unit module types are anisotropic structures. Module families are grouped based on structural similarity and complexity. Any combination of intra or extra familial module connections is possible. The various module types can have any number of connection points and representative linear elements.
The modules' linear elements described to this point have had a solid circular cross section.
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The modules can also be constructed of linear elements that are hollow solids cellular solids or solid with asymmetric and symmetric cross sections as shown in FIG. When compared to elements with symmetric cross sections, those with asymmetric cross sections would change the structural and behavioral characteristics of the module.
The modules of family A are radially symmetric structures composed of linear elements of identical lengths. In FIG. Within family A the foci that punctuate each module's central ring are equidistant. The linear elements emerge from each focus in opposite directions tangent to the ring. Two intersecting adjacent linear elements join to create each intermodular connection point.
The ratio of the distance between two adjacent foci and the distance from each focus and its parent connection point approximates phi. Each module type within family A maintains the same geometric proportions regardless of scale or material composition. The modules of family B are radially symmetric structures composed of linear elements of identical length. It provides the information for an understanding o This title is no longer available locally, but in stock internationally — usually ships weeks.
This title is firm sale. Please select carefully as returns are not accepted. Shell structures are used in all phases of structures, from space vehicles to deep submergence hulls, from nuclear reactors to domes on sport arenas and civic buildings. With new materials and manufacturing methods, curved thin walled structures are being used increasingly.
This text is a graduate course in the theory of shells. It covers shells of isotropic materials, such as metal alloys and plastics, and shells of composite materials, such as fibre reinforced polymer, metal or ceramic matrix materials. It provides the essential information for an understanding of the underlying theory, and solution of some of the basic problems. It also provides a basis to study the voluminous shell literature. Beyond being primarily a textbook, it is intended also for self study by practising engineers who would like to learn more about the behaviour of shells.
The book has two parts: Part I deals with shells of isotropic materials. In this part the mathematical formulations are introduced involving curvilinear coordinates. Recently, 3D graphene structures also called graphene foam have also been employed as core structures. A recent review by Khurram and Xu et al. Although the two phases are chemically equivalent, semi-crystalline polymers can be described both quantitatively and qualitatively as composite materials. The crystalline portion has a higher elastic modulus and provides reinforcement for the less stiff, amorphous phase.
Different processing techniques can be employed to vary the percent crystallinity in these materials and thus the mechanical properties of these materials as described in the physical properties section. This effect is seen in a variety of places from industrial plastics like polyethylene shopping bags to spiders which can produce silks with different mechanical properties. However they can also be engineered to be anisotropic and act more like fiber reinforced composites. Composite fabrication usually involves wetting, mixing or saturating the reinforcement with the matrix , and then causing the matrix to bind together with heat or a chemical reaction into a rigid structure.
The operation is usually [ citation needed ] done in an open or closed forming mold, but the order and ways of introducing the ingredients varies considerably. Within a mold, the reinforcing and matrix materials are combined, compacted, and cured processed to undergo a melding event.
After the melding event, the part shape is essentially set, although it can deform under certain process conditions. For a thermoset polymer matrix material, the melding event is a curing reaction that is initiated by the application of additional heat or chemical reactivity such as an organic peroxide.
For a thermoplastic polymeric matrix material, the melding event is a solidification from the melted state. For a metal matrix material such as titanium foil, the melding event is a fusing at high pressure and a temperature near the melting point. For many moulding methods, it is convenient to refer to one mould piece as a "lower" mould and another mould piece as an "upper" mould. Lower and upper refer to the different faces of the moulded panel, not the mould's configuration in space.
In this convention, there is always a lower mould, and sometimes an upper mould. Part construction begins by applying materials to the lower mould. Lower mould and upper mould are more generalized descriptors than more common and specific terms such as male side, female side, a-side, b-side, tool side, bowl, hat, mandrel, etc. Continuous manufacturing uses a different nomenclature. The moulded product is often referred to as a panel.
For certain geometries and material combinations, it can be referred to as a casting. For certain continuous processes, it can be referred to as a profile. Vacuum bag moulding uses a flexible film to enclose the part and seal it from outside air. Vacuum bag material is available in a tube shape or a sheet of material. A vacuum is then drawn on the vacuum bag and atmospheric pressure compresses the part during the cure.
When a tube shaped bag is used, the entire part can be enclosed within the bag. When using sheet bagging materials, the edges of the vacuum bag are sealed against the edges of the mould surface to enclose the part against an air-tight mould. When bagged in this way, the lower mold is a rigid structure and the upper surface of the part is formed by the flexible membrane vacuum bag. The flexible membrane can be a reusable silicone material or an extruded polymer film. After sealing the part inside the vacuum bag, a vacuum is drawn on the part and held during cure. This process can be performed at either ambient or elevated temperature with ambient atmospheric pressure acting upon the vacuum bag.
A vacuum pump is typically used to draw a vacuum. An economical method of drawing a vacuum is with a venturi vacuum and air compressor. A vacuum bag is a bag made of strong rubber -coated fabric or a polymer film used to compress the part during cure or hardening. In some applications the bag encloses the entire material, or in other applications a mold is used to form one face of the laminate with the bag being a single layer to seal to the outer edge of the mold face.
When using a tube shaped bag, the ends of the bag are sealed and the air is drawn out of the bag through a nipple using a vacuum pump.
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As a result, uniform pressure approaching one atmosphere is applied to the surfaces of the object inside the bag, holding parts together while the adhesive cures. The entire bag may be placed in a temperature-controlled oven, oil bath or water bath and gently heated to accelerate curing. Vacuum bagging is widely used in the composites industry as well. In commercial woodworking facilities, vacuum bags are used to laminate curved and irregular shaped workpieces.
Typically, polyurethane or vinyl materials are used to make the bag. A tube shaped bag is open at both ends. The piece, or pieces to be glued are placed into the bag and the ends sealed. One method of sealing the open ends of the bag is by placing a clamp on each end of the bag.
A plastic rod is laid across the end of the bag, the bag is then folded over the rod. A plastic sleeve with an opening in it, is then snapped over the rod. This procedure forms a seal at both ends of the bag, when the vacuum is ready to be drawn. A "platen" is sometimes used inside the bag for the piece being glued to lie on. The platen has a series of small slots cut into it, to allow the air under it to be evacuated. The platen must have rounded edges and corners to prevent the vacuum from tearing the bag.
When a curved part is to be glued in a vacuum bag, it is important that the pieces being glued be placed over a solidly built form, or have an air bladder placed under the form. This air bladder has access to "free air" outside the bag. It is used to create an equal pressure under the form, preventing it from being crushed. This process is related to vacuum bag molding in exactly the same way as it sounds.
A solid female mold is used along with a flexible male mold. The reinforcement is placed inside the female mold with just enough resin to allow the fabric to stick in place wet lay up. A measured amount of resin is then liberally brushed indiscriminately into the mold and the mold is then clamped to a machine that contains the male flexible mold. The flexible male membrane is then inflated with heated compressed air or possibly steam. The female mold can also be heated. Excess resin is forced out along with trapped air. This process is extensively used in the production of composite helmets due to the lower cost of unskilled labor.
Cycle times for a helmet bag moulding machine vary from 20 to 45 minutes, but the finished shells require no further curing if the molds are heated. A process using a two-sided mould set that forms both surfaces of the panel. On the lower side is a rigid mould and on the upper side is a flexible membrane made from silicone or an extruded polymer film such as nylon. Reinforcement materials can be placed manually or robotically. They include continuous fibre forms fashioned into textile constructions.
Most often, they are pre-impregnated with the resin in the form of prepreg fabrics or unidirectional tapes. In some instances, a resin film is placed upon the lower mould and dry reinforcement is placed above. The upper mould is installed and vacuum is applied to the mould cavity. The assembly is placed into an autoclave. This process is generally performed at both elevated pressure and elevated temperature. The use of elevated pressure facilitates a high fibre volume fraction and low void content for maximum structural efficiency. RTM is a process using a rigid two-sided mould set that forms both surfaces of the panel.
The mould is typically constructed from aluminum or steel, but composite molds are sometimes used. The two sides fit together to produce a mould cavity. The distinguishing feature of resin transfer moulding is that the reinforcement materials are placed into this cavity and the mould set is closed prior to the introduction of matrix material. Resin transfer moulding includes numerous varieties which differ in the mechanics of how the resin is introduced to the reinforcement in the mould cavity.
These variations include everything from the RTM methods used in out of autoclave composite manufacturing for high-tech aerospace components to vacuum infusion for resin infusion see also boat building to vacuum assisted resin transfer moulding VARTM. This process can be performed at either ambient or elevated temperature and is suitable for manufacturing high performance composite components in medium volumes 1,s to 10,s of parts. A vacuum holds mold A and mold B together to result in two finished sides with fixed thickness levels. Vacuum rings around the tools hold the molds together for this process after dry fiber reinforcements are loaded into mold A before joining with mold B.
The air is vacuumed out of the molds with a lower vacuum level, separate from the tooling. After the air is removed the resin is injected into the part. The vacuum remains in effect into the resin is cured. Other types of fabrication include press moulding, transfer moulding , pultrusion moulding, filament winding , casting , centrifugal casting, continuous casting and slip forming. There are also forming capabilities including CNC filament winding, vacuum infusion, wet lay-up, compression moulding , and thermoplastic moulding, to name a few.
The use of curing ovens and paint booths is also needed for some projects. The finishing of the composite parts is also critical in the final design. Many of these finishes will include rain-erosion coatings or polyurethane coatings. The mold and mold inserts are referred to as "tooling.
Tooling materials include invar , steel, aluminium , reinforced silicone rubber , nickel , and carbon fibre. Selection of the tooling material is typically based on, but not limited to, the coefficient of thermal expansion , expected number of cycles, end item tolerance, desired or required surface condition, method of cure, glass transition temperature of the material being moulded, moulding method, matrix, cost and a variety of other considerations. The physical properties of composite materials are generally not isotropic independent of direction of applied force in nature, but they are typically anisotropic different depending on the direction of the applied force or load.
The behavior of structures composed of composite materials /
The strength of a composite is bounded by two loading conditions as shown in the plot to the right. If both the fibres and matrix are aligned parallel to the loading direction, the deformation of both phases will be the same assuming there is no delamination at the fibre-matrix interface. This isostrain condition provides the upper bound for composite strength, and is determined by the rule of mixtures:.
The lower bound is dictated by the isostress condition, in which the fibres and matrix are oriented perpendicularly to the loading direction:. Comparatively, under isostress conditions both phases will feel the same stress but the strains will differ between each phase. Though composite stiffness is maximized when fibres are aligned with the loading direction, so is the possibility of fibre tensile fracture, assuming the tensile strength exceeds that of the matrix.