CAFÉ Corporate average fuel economy.
Camera Lucida Device for facilitating the drawing of an image seen in a microscope or other optical instrument. In its simplest form, it consists of a thin plate of unsilvered glass, placed above the eyepiece at an angle of 45° with the axis of the instrument, so as to reflect into the eye of the observer an image of the drawing surface, which is seen simultaneously with the microscope image.
Cellular Characterized by small compartments or bounded areas forming part of a whole such as the basic structural unit of organisms.
Cellulose Acetate An acetic acid ester of cellulose. It is obtained by the action, under rigidly controlled conditions, of acetic acid and acetic anhydride on purified cellulose usually obtained from cotton linters. All three available hydroxyl groups in each glucose unit of the can cellulose be acetylated, but in the material normally used for plastics, it is usual to acetylate fully and then lower the acetyl value (expressed as acetic acid) to 52 to 56% by partial hydrolysis. When compounded with suitable plasticizers, it gives a tough thermoplastic material.
Cellulose Acetate Butyrate An ester of cellulose made by the action of a mixture of acetic and butyric acids and their anhydrides on purified cellulose. It is used in the manufacture of plastics that are similar in general properties to cellulose acetate but are tougher and have better moisture resistance and dimensional stability.
Cellulose Ester A derivative of cellulose in which the free hydroxyl groups attached to the cellulose chain have been replaced wholly or in part by acetic groups; for example, nitrate, acetate, or stearate groups. Esterification is effected by the use of a mixture of an acid with its anhydride in the presence of a catalyst, such as sulfuric acid. Mixed esters of cellulose, such as cellulose acetate butyrate, are prepared by the use of mixed acids and mixed anhydrides. Esters and mixed esters, a wide range of which are known, differ in their compatibility with plasticizers, in molding properties, and in physical characteristics. These esters and mixed esters are used in the manufacture of thermoplastic molding compositions.
Cellulose Nitrate A nitric acid ester of cellulose manufactured by the action of a mixture of sulfuric acid and nitric acid on cellulose, such as purified cotton linters. The type of cellulose nitrate used for celluloid manufacture usually contains 10.8 to 11.1% nitrogen. The latter figure is the nitrogen content of the dinitrate. Also called nitrocellulose.
Cellulose Propionate An ester of cellulose made by the action of propionic acid and its anhydride on purified cellulose. It is used as the basis of a thermoplastic molding material.
Cellulose Plastics Plastics based on cellulose compounds, such as esters (cellulose acetate) and ethers (ethyl cellulose).
Cement In concrete work, the dry powder that, when it has combined chemically with the water in the mix, cements the particles of aggregate together to form concrete.
Centerpoint Point within a circle or sphere equidistant from all points of the circumference or surface, or the point within a regular polygon or polyhedron equidistant from the vertices.
Ceramics Any inorganic, nonmetallic solids processed or used in high temperatures. The wide range of materials that fall within this classification includes ceramics that are composed of clay minerals, cement, and glass. These materials are typically insulative to the passage of electricity and heat, and are more resistant to high temperatures and harsh environments than metals and polymers (plastics). With regards to mechanical behavior, ceramics are hard but very brittle.
Channeling To convey through, as in channeling forces through a structure.
Chord A member of a truss.
Cipher Key to a secret, as in a geometric secret, for example.
Clay Earths that form a paste with water, is isoplastic when wet, and hardens when heated. The US. Department of Agriculture distinguishes clay as having small grains, less than 0.002 millimeters (mm) in diameter, as distinct from silt with grains from 0.002 to 0.05 mm.
Closed Cell Among RMT architectures, a closed cell void array is one in which each void is a separate, discrete entity (see UniSemble). Closed cells can be compared to tiny balloons or pockets. The walls have no holes in them. If the walls are appropriately impermeable, each cell can hold a gas.
Closed Network Any independent combination of intersecting or interconnecting units, such as rods, bars, or lines, which enclose an area or space.
Closest-packing (of equal spheres) The aggregation of identical spheres about a nucleus involving 12 spheres in contact with a central sphere (the nucleus) so that each sphere touches four neighbors in addition to the central sphere. In this arrangement, six spheres surround the central sphere, with three spheres lying in the interstices above and three spheres below. The spheres are grouped in three layers. If the three spheres in the top and bottom layers are oppositely oriented, the spheres are said to be cubically close-packed. If the three spheres in the top and bottom layers are oriented similarly so that a sphere in the bottom layer lies directly beneath a sphere in the top layer, the spheres are said to be hexagonally close-packed.
Coefficient of Thermal Expansion (CTE) A measure of how much a material will lengthen (or shorten upon cooling) based on its original length and the temperature difference it is exposed to. It becomes important when dimensions are critical or when two different materials with different CTE's are attached to each other, such as an unfilled thermoplastic and steel. Stress induced by this difference can become considerable.
Collinear Lying on the same straight line.
Column An upright structural member acting primarily in compression.
Common Designations for Thermoplastics
| ABS |
Acrylonitrile butadiene styrene |
|
Apec
|
Aromatic polyester carbonate |
|
ASA
|
Acrylonitrile styrene acrylate |
|
GPPS
|
General-purpose polystyrene |
|
HDPE
|
High density polyethylene |
|
HIPS
|
High impact polystyrene |
|
LCP
|
Liquid crystal polymer |
|
LDPE
|
Low density polyethylene |
|
PA
|
Polyamide |
|
PB
|
Polybutylene |
|
PBT
|
Polybutylene terephthalate |
|
PC
|
Polycarbonate |
|
PE
|
Polyethylene |
|
PEEK
|
Polyether ether ketone |
|
PEI
|
Polyetherimide |
|
PES
|
Polyethersulfone |
|
PET
|
Polyethylene terephthalate |
|
PMMA
|
Polymethyl methacrylate |
|
POM
|
Polyacetal |
|
PP
|
Polypropylene |
|
PPE
|
Polyphenylene ether |
|
PPO
|
Polyphenylene oxide |
|
PPS
|
Polyphenylene sulphide |
|
PS
|
Polystyrene |
| PSU |
Polysulfone |
|
PVC
|
Polyvinyl chloride |
|
SAN
|
Styrene acrylonitrile |
|
SMA
|
Styrene maleic anhydride |
|
TPU
|
Thermoplastic polyurethane |
Component An element, part or constituent of something larger, such as a structure.
Composite Material Engineered materials which consist of more than one material type. Fiberglass is a familiar example, in which glass fibers are embedded within a polymeric (plastic) material. A composite is designed to display a combination of the best characteristics of each of the component materials. Fiberglass acquires strength from the glass and flexibility from the polymer.
Compression A squeezing force.
Compression Strength (1) The ability of a material to resist a force that tends to crush or buckle. (2) Maximum stress a material can sustain under crush loading. The compressive strength of a material that fails by shattering fracture can be defined within fairly narrow limits as an independent property. However, the compressive strength of materials that do not shatter in compression must be defined as the amount of stress required to distort the material an arbitrary amount. Compressive strength is calculated by dividing the maximum load by the original cross-sectional area of a specimen in a compression test.
Compression Test Method for determining behavior of materials under crushing loads. Specimen is compressed, and deformation at various loads is recorded. Compressive stress and strain are calculated and plotted as a stress-strain diagram, which is used to determine elastic limit, proportional limit, yield point, yield strength, and (for some materials) compressive strength. Standard compression tests are given in ASTM C-773 (high strength ceramics), ASTM E-9 (metals), ASTM E-209 (metals at elevated temperatures) and ASTM D-695 (plastics).
Compressive (or tensile) Stress Compressive or tensile stress “σ” is the force carried per unit of area and is expressed by the equation:
The force (P) produces stresses normal (i.e., perpendicular) to the cross section of the part. If the stress tends to shorten the part, it is called compressive stress. If the stress tends to lengthen the part, it is called tensile stress.
Compressive Yield Strength Stress that causes a material to exhibit a specified deformation. Usually determined from the stress-strain diagram obtained in a compression test. See also Yield Strength.
Compressive Thrust Pushing force in a segmented structure exerted by a component which compresses a contiguous component. The downward load on a segmented arch (one composed of bricks for example) creates lateral and compressive thrust which pushes the brick units against each other in compression. The reaction to the compressive thrust within the arch is provided at the abutments.
Computer-Aided Design (CAD) The use of computer programs and systems to design detailed two- or three-dimensional models of physical objects, such as mechanical parts, buildings, and molecules.
Computer-Aided Engineering (CAE) The use of computers to help with all phases of engineering design work. Like computer aided design, but also involving the conceptual and analytical design steps.
Computer-Aided Manufacturing (CAM) The process of using specialized computers to control, monitor, and adjust tools and machinery in manufacturing.
Concentration Flowing, bringing or drawing to a common center.
Configuration Relative disposition or arrangement of parts or elements of a thing.
Concrete A structural material produced by mixing predetermined amounts of Portland cement, aggregates, and water, and allowing this mixture to cure under controlled conditions.
Congruent Denotes two or more figures that are identical in size and shape. Two circles with the same radius are congruent, and so coincide at all points when superimposed.
Concurrent Engineering A systematic approach to the integrated, concurrent design of products and their related processes, including manufacture and support. This approach is intended to cause the developer, from the outset, to consider all elements of the product lifecycle from concept through disposal, including quality control, cost, scheduling, and user requirements.
Constituent Component.
Continuous Manufacturing The uninterrupted manufacture of a product from raw material to final product.
Copolymer This term usually, but not always, denotes a polymer of two chemically distinct monomers.
Core Central or innermost part of a structure or system; the material sandwiched between two outer layers of veneer.
Counterbalance Equal force acting in opposition; counterpoise.
Crazing An undesirable defect in plastics articles characterized by distinct surface cracks or minute frost-like, internal cracks, resulting from stresses within the article that exceed the tensile strength of the plastic. When a tensile stress is applied to some polymers, the first stage of plastic deformation is the formation of voids in a plane perpendicular to the direction of the applied load. In contrast to metals, these voids do not coalesce into a crack, but instead become stabilized by fibrils containing oriented polymeric material. The resulting region consisting of voids and fibrils is known as craze. Crazes are able to bear loads and also modify the stress field near any neighboring crack. Stress whitening is due to the scattering of light at voids that may be microcrazes, cavities in homogeneous materials, and interphase cracks in heterogeneous materials.
Creep Deformation that occurs over a period of time when a material is subjected to constant stress at constant temperature. In metals, creep usually occurs only at elevated temperatures. Creep at room temperature is more common in plastic materials and is called cold flow or deformation under load. Data obtained in a creep test usually is presented as a plot of creep vs. time with stress and temperature constant. Slope of the curve is creep rate and end point of the curve is time for rupture. As indicated in the accompanying diagram, the creep of a material can be divided into three stages. First stage, or primary creep, starts at a rapid rate and slows with time. Second stage (secondary) creep has a relatively uniform rate. Third stage (tertiary) creep has an accelerating creep rate and terminates by failure of material at time for rupture. See also Stress-Relaxation.
Plastics are viscoelastic – they exhibit both elastic and viscous behavior – and therefore will deform under load with both an immediate response (elastic) and a slower response (viscous). A plastics application may actually change shape slowly to relieve the applied load: it shows a time-dependent increase in deformation or strain, called creep or cold flow, the result of increasing strain over time under a constant load. Creep is the slow and progressive deformation of a material with time under a constant stress. Or, creep is the deformation of a plastic part that takes place over a specified long period of time under controlled conditions while the part is supporting a load. Plastics are very temperature-sensitive to creep. There is no established method of determining creep. ASTM D674 describes a flexural creep method frequently used, although it is not a test method but a "recommended practice for creep tests." It discusses the complications of measuring creep, and the precautions to be taken when using creep data. Complications are largely due to the fact that creep measurements are made over a long period of time – several months to a year or more. Long-term values are extrapolated from relatively short-term results. Since the creep of plastics is dependent upon temperature and load conditions, it is safer to use an apparent modulus for calculating deflections and for design purposes rather than using short-term test data. Apparent modulus can be calculated from isochronous stress-strain curves at chosen temperatures.
Creep Deformation The change in strain over time with a constant load.
Creep Recovery (1) A time-dependent decrease in strain after removal of stress, also known as "relaxation." (2) Rate of decrease in deformation that occurs when load is removed after prolonged application in a creep test. Constant temperature is maintained to eliminate effects of thermal expansion, and measurements are taken from time load is zero to eliminate elastic effects.
Creep Rupture Strength Stress required to cause fracture in a creep test within a specified time. Alternate term is stress rupture strength.
Creep Strength Maximum stress required to cause a specified amount of creep in a specified time. Also used to describe maximum stress that can be generated in a material at constant temperature under which creep rate decreases with time. An alternate term is creep limit.
Creep Test Method for determining creep or stress relaxation behavior. To determine creep properties, material is subjected to prolonged constant tension or compression loading at constant temperature. Deformation is recorded at specified time intervals and a creep vs. time diagram is plotted. Slope of curve at any point is creep rate. If failure occurs, it terminates test and time for rupture is recorded. If specimen does not fracture within test period, creep recovery may be measured. To determine stress relaxation of material, specimen is deformed a given amount and decrease in stress over prolonged period of exposure at constant temperature is recorded. Standard creep testing procedures are detailed in ASTM E-139, ASTM D-2990 and D-2991 (plastics) and ASTM D-2294 (adhesives).
Cross Linking The forming of strong covalent bonds in a polymer chain that can only be broken at high temperatures.
Crush Press or squeeze with a force that deforms or destroys, as in to break in compression.
Crushing Load Maximum compressive force applied during a compression or crushing test. For materials that do not shatter, crushing load is defined as the force required to produce a specified type of failure.
Crushing Strength Compressive load required to cause a crack to form in a sintered metal powder bearing (ASTM B-438 and B-439). Cold crushing strength of refractory bricks and shapes is the gross compressive stress required to cause fracture. (ASTM C-133).
Crystal Solid with a regular geometric shape, having a characteristic internal structure and enclosed by symmetrically arranged plane surfaces, intersecting at definite and characteristic angles. In crystals the particles (atoms, ions, or molecules) have a regular three-dimensional repeating arrangement in space. This is called the crystal structure. The crystal lattice is the arrangement of points in space at which the particles are positioned.
Cube A solid figure that has six square faces. The cube is invariant under rotation about an axis through the center of two opposite faces under four rotations of 90°, 180°, 270° and 360°. This is called fourfold rotational symmetry of the cube and the axis is known as a fourfold axis of rotational symmetry. This axis corresponds to a face-on view of the cube. The three fourfold axes of the cube are responsible for a total of nine rotations in addition to the identity transformation which leaves the cube unchanged (or rotates it 360°). The cube also has four threefold axes (responsible for eight rotations) through opposite vertices which result in a vertex-on view of the cube, and six twofold axes (responsible for six rotations) through the centers of opposite edges, resulting in an edge-on view. With 13 rotational axes, the cube has a total of 24 rotations (including the identity transformation) that leave its configuration invariant.
Cubic Symmetry Characterized by twofold, threefold and fourfold axes of rotation. The cube has three axes of fourfold symmetry, four axes of threefold symmetry and six axes of twofold symmetry.
Cubically Close-packed The closest packing of equal spheres is cubically close-packed when the result of connecting the centers of the spheres surrounding the center sphere with straight lines is the framework of a cuboctahedron.
Cuboctahedron Polyhedron with eight regular triangular and six square faces, 12 vertices and 24 edges. It is an amalgam of the cube and the octahedron. It is one of 13 semiregular, or Archimedean, polyhedra. It is the only polyhedron with an edge length equal to the radius from its center to all of its 12 vertices, so all of its angles -- both radial and circumferential -- are equal, specifically 60°. Its dual is the rhombic dodecahedron. Buckminster Fuller called the cuboctahedron his "Vector Equilibrium."
Curtain Wall An exterior building wall that has no structural function. It is supported entirely by the frame of the building, rather than being self-supporting or load bearing.
Curve Set of points forming a continuous line without angles.
Curvilinear Consisting of or bound by curved lines: a curvilinear figure.