Radial (1) A figure, such as a line or rod, oriented in the direction of the radius. (2) Arranged like rays or radii, radiating from a common center.
Radiate To spread or move like rays or radii from a center.
Radiolaria Group or order of microscopic organisms having an amoeba like body with radiating pseudopodia and an unusually elaborate skeleton.
Radius The distance from the center of a sphere to its surface or from the center of a circle to its circumference.
Recovery Index of a material's ability to recover from deformation in the compressibility and recovery test (ASTM F-36), the deformation under load test (ASTM D-621) and the plastometer test (ASTM D-926). In the compressibility and recovery test, it usually is reported with compressibility and given as %. It is calculated by dividing the difference between recovered thickness and thickness under load, by the difference between original thickness and thickness under load. In the deformation under load test, it indicates the extent to which a nonrigid plastic recovers from prolonged compressive deformation at an elevated temperature. It is given as %, and is calculated by dividing the difference between height recovered 1-1/2 hours after load is re-moved and height after three hours of loading, by the change in height under load. In the plastometer test, it indicates the extent to which an elastomer recovers from compressive loading at an elevated temperature. It is equal to plasticity number minus recovered height.
Recovery test Method for measuring compressibility and recovery of gasket and seal materials (ASTM F-36).
Rectilinear Consisting of or bound by straight lines: a rectilinear figure.
Reduction of area Measure of the ductility of metals obtained in a tension test. It is the difference between original cross sectional area of a specimen and the area of its smallest cross section after testing. It is usually ex-pressed as % decrease in original cross section. The smallest cross section can be measured at or after fracture. For metals, it usually is measured after fracture and for plastics and elastomers, it is measured at fracture.
Re-engineering Alteration of a design to increase the efficiency of employment of natural resources for human benefit.
Regular Having all faces or sides of equal size and shape.
Reinforcing bar (rebar) A commodity-grade steel used to strengthen concrete in highway and building construction.
Reinforced plastic A plastic with high-strength fibers embedded in the polymer matrix, resulting in increased strength properties superior to those of the base resin.
Reinforced Concrete Concrete work into which steel bars have been embedded to impart tensile strength to the construction.
Reinforcement A strong material incorporated in a material mass, i.e., a matrix, to improve its mechanical properties. Reinforcements are usually long fivers, chopped fibers, whiskers, particulates, and other forms, made of glass, plastics, metals, and ceramics.
Relaxation Rate of reduction of stress in a material due to creep. An alternate term is stress relaxation.
Residual elongation Measure of ductility of plastics. It is the elongation of a plastic specimen measured 1 minute after rupture in a tension test.
Resin (Synthetic) The term is use to designate any polymer that is a basic material for plastics.
Rhombic Dodecahedron Space-filling polyhedron with 12 identical rhombic faces, 14 vertices and 24 edges. It is the dual of the cuboctahedron. It was discovered by the mathematician Johannes Kepler (1571-1630). Buckminster Fuller called it his "spheric."
Rhombus Plane figure with four straight sides of equal length; a parallelogram with equal sides.
Right Angle An angle that is 90°. It is the angle between two lines or planes that are perpendicular to each other. The corner of a square, for example, is a right angle.
Rigid Unbending, inflexible.
RMT Architecture™ See UniSemble.
Rotational Symmetry The rotational symmetry of any figure is determined by counting the number of times it semblance repeats or reproduces itself in one rotation about an axis. Only four kinds of rotational symmetry are possible among regular figure; these are twofold, threefold, fourfold, and sixfold. For example a cube has twofold, threefold and fourfold rotational symmetry.
Rupture strength Nominal stress developed in a material at rupture. It is not necessarily equal to ultimate strength. And, since necking is not taken into account in determining rupture strength, it seldom indicates true stress at rupture.