Review Flashcards on Composites and Polymers

Flashcards to assist in exam preparation, covering the material properties, classifications, and processing methods discussed in the lecture notes on composites and polymers.

What are Polymer-Matrix Composites?

Composites reinforced with glass, carbon, and aramid fibers, and are the most common type of composite.

What are Metal-Matrix Composites?

Offer higher service temperatures compared to polymer-matrix composites, and utilize various fiber and whisker types for reinforcement.

What are Ceramic-Matrix Composites?

Aim to increase fracture toughness through interactions between advancing cracks and dispersed phase particles, often employing transformation toughening techniques.

What are Carbon-Carbon Composites?

Composed of carbon fibers embedded in a pyrolyzed carbon matrix, known for high strength and stiffness at elevated temperatures, creep resistance, and good fracture toughness.

What are Hybrid Composites?

Composites containing at least two different fiber types, designed to achieve better all-around sets of properties.

What is Pultrusion?

Involves pulling resin-impregnated fiber tows through a die to form components of continuous length and constant cross-section.

What is a Lay-Up Operation?

A method where prepreg tape plies are laid down on a tooled surface and cured under heat and pressure, commonly used for structural composite applications.

What are Automated Filament Winding Procedures?

Uses resin-coated strands or prepreg tape continuously wound onto a mandrel, followed by curing, and is suitable for fabricating hollow structures.

What are Laminar Composites?

Composites that are virtually isotropic in a two-dimensional plane, achieved by cementing multiple sheets of anisotropic composite with varied high-strength directions.

What are Sandwich Panels?

Consist of two strong, stiff sheet faces separated by a core material or structure, combining high strength and stiffness with low densities.

What are Dispersion-Strengthened Composites?

Composites where improved strength is achieved by extremely small particles of the dispersed phase inhibiting dislocation motion.

How do Large-Particle Composites determine elastic modulus?

Upper and lower elastic modulus values depend on the moduli and volume fractions of matrix and particulate phases according to the rule-of-mixtures expressions.

What is Concrete?

A type of large-particle composite consisting of an aggregate of particles bonded together with cement, commonly using sand and gravel with portland cement.

What are Fiber-Reinforced Composites?

Potential for reinforcement efficiency is greatest for these type of composites.

What is Critical Length in Fiber Composites?

The length which depends on fiber diameter and strength, and fiber-matrix bond strength.

What are Continuous and Aligned Composites?

Composites with mechanical properties that are highly anisotropic; reinforcement and strength are a maximum in the alignment direction and a minimum perpendicular to it.

What are Discontinuous and Aligned Composites?

Composites with significant strengths and stiffnesses possible in the longitudinal direction.

What are Discontinuous and Randomly Oriented Composites?

Composites with properties that are isotropic despite some limitations on reinforcement efficiency.

What are Whiskers?

Extremely strong single crystals with very small diameters.

What are Fibers?

Polymers or ceramics that may be either amorphous or polycrystalline.

What are Wires?

Metals/alloys that have relatively large diameters.

What are Polymers and Metals?

The most common materials used for matrices in composites.

What are the functions of the Matrix Phase?

Binds the fibers together, transmits applied load to the fibers, protects fibers from surface damage, and prevents crack propagation from fiber to fiber.

What occurs during the Crystallization of a Polymer?

Randomly oriented molecules in the liquid phase transform into chain-folded crystallites with ordered and aligned molecular structures.

What occurs during the Melting of Crystalline Regions of a Polymer?

The transformation of a solid material with an ordered structure of aligned molecular chains to a viscous liquid with a highly random structure.

What is the Glass Transition in Polymers?

The gradual transformation from a liquid to a rubbery material, and finally to a rigid solid as temperature decreases, reducing the motion of large segments of molecular chains.

What are ways of classifying Polymeric Materials according to their end use?

Includes plastics, fibers, coatings, adhesives, films, foams, and advanced materials.

What is Addition Polymerization?

Attaching monomer units one at a time in chainlike fashion to form a linear molecule.

What is Condensation Polymerization?

Involves stepwise intermolecular chemical reactions that may include more than a single molecular species.

What are Fillers for Polymers?

Added to improve strength, abrasion resistance, toughness, and thermal/dimensional stability of polymers.

What are Plasticizers for Polymers?

Enhance flexibility, ductility, and toughness when added to polymers.

What are Stabilizers for Polymers?

Counteract deteriorative processes due to exposure to light and gaseous species in the atmosphere.

What are Colorants for Polymers?

Used to impart specific colors to polymers.

What are Flame Retardants for Polymers?

Enhance the flammability resistance of polymers.

What are Forming Techniques for Plastics?

Compression, transfer, injection, and blow molding techniques, as well as extrusion and casting.

How are Fibers Fabricated?

Spun from a viscous melt or solution and then plastically elongated during a drawing operation to improve mechanical strength.

How are Films Fabricated?

Formed by extrusion and blowing or by calendering.

What is Curve A?

Polymers that are brittle experience what type of curve?

What is Curve B?

Polymers that are plastic experience what type of curve?

What is Curve C?

Polymers that are highly elastic experience what type of curve?

What is Viscoelastic Deformation?

Displays mechanical behavior intermediate between totally elastic and totally viscous, characterized by the relaxation modulus.

What are Crazes?

Regions of localized deformation and the presence of microvoids that can lead to increased ductility and toughness.

With respect to molecular weight of Semicrystalline Polymers, what are the affects?

Tensile modulus is relatively insensitive, but tensile strength increases with increasing molecular weight

With respect to the degree of crystallinity of Semicrystalline Polymers, what are the affects?

Both tensile modulus and strength increase with increasing percent crystallinity

With respect to Predeformation by drawing of Semicrystalline Polymers, what are the affects?

Stiffness and strength are enhanced by permanently deforming the polymer in tension

With respect to Heat-treating of Semicrystalline Polymers, what are the affects?

Leads to increases in stiffness and strength and a decrease in ductility

What is the deformation of Elastomers?

Corresponds to the unkinking and uncoiling of chains in response to an applied tensile stress.

What does increased crosslinking achieve for Elastomers?

Enhances modulus of elasticity and tensile strength of the elastomer.

How does Diffusion occur in Polymeric Materials?

Small molecules of foreign substances diffuse between molecular chains by an interstitial-type mechanism from one void to an adjacent one.

What is Bifunctional functionality?

A two-dimensional chainlike structure results from a monomer that has two active bonds.

What is Trifunctional functionality?

Three-dimensional network structures form from a monomer that has three active bonds

What are Molecular Entanglements?

Occur when the chains assume twisted, coiled, and kinked shapes or contours as a consequence of chain bond rotations.

What are the four different Polymer Molecular Chain Structures?

linear, branched, crosslinked, and network.

What Molecular Configurations are possible for repeat units that have more than one side atom or groups of atoms bonded to the main chain?

Head-to-head and head-to-tail.

What Differences in spatial arrangements of these side atoms or groups of atoms?

Isotactic, syndiotactic, and atactic stereoisomers.

When a repeat unit contains a double chain bond, what Molecular Configurations are possible?

cis and trans geometrical isomers.

How do Thermoplastic Polymers behave at elevated temperatures?

Soften when heated and harden when cooled.

How do Thermosetting Polymers behave at elevated temperatures?

Once they have hardened, will not soften upon heating; their structures are crosslinked and network.

What are the Co-Polymers?

random, alternating, block, and graft types.

What are Crystalline Regions made up of?

Chains within the platelet are aligned and fold back and forth on themselves, with folds occurring at the faces

What Defects are found in Polymers?

Vacancies, interstitial atoms, and impurity atoms/ions and groups of atoms/ions as interstitials

What are the two prime assets of Glass Materials?

Optical transparency and ease of fabrication.

What are the two properties of Glass-Ceramics that make them superior to glass?

Improved mechanical strengths and lower coefficients of thermal expansion.

What are the Requirements for Refractory Ceramics?

High melting temperature, unreactive/inert when exposed to severe environments, and the ability to provide thermal insulation.

What are the four main Refractory subdivisions, based on composition and application?

Fireclay, silica, basic, and special.

What are the most common abrasive materials?

Diamond, silicon carbide, tungsten carbide, corundum, and silica sand

Subsequent Concrete setting or hardening is a result of what?

Chemical reactions involving the cement particles and occurs at the ambient temperature and hydration for hydraulic cements?

What are Microelectromechanical systems (MEMS)?

Miniaturized mechanical devices integrated with electrical elements on a substrate (normally silicon).

What points represent temperatures that correspond to specific viscosity values because temperature-viscosity behavior is an important consideration

Melting, working, softening, annealing, and strain points represent temperatures that correspond to specific viscosity values.