Rate of strain hardening. Rate of change of true stress as a function of true strain in a material undergoing plastic deformation. An alternate term is modulus of strain hardening.
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 elevated temperature. It is given as % and is calculated by dividing the difference between height recovered 11/2 hr after load is removed and height after three hr 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 elevated temperature. It is equal to plasticity number minus recovered height. See also Rockwell recovery.
Recovery test. Method for measuring compressibility and recovery of gasket and seal materials. (ASTM F 36).
Reduction of area.. Measure of the ductility of metals obtained in a tension test. It is the difference between original cross section area of a specimen and the area of its smallest cross section after testing. It is usually expressed 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.
Relative modulus. Ratio of the modulus of a rubber at a given temperature to its modulus at 73 F. It is determined in the Gehman torsional test.
Relaxation. Rate of reduction of stress in a material due to creep. An alternate term is stress relaxation.
Repeated bent test. Method for determining ductility of relatively ductile metals such as silicon steel sheet and strip. Specimens about 1 in. wide and 6 in. long are held in jaws and bent 90 deg. Then they are bent back and forth through 180 deg. Results are reported as number of bends (including the original 90 deg bend) required to cause failure. (ASTM A-344).
弯曲疲劳试验。相对易延性金属(如硅钢片和钢带)的韧性测定方法。将约1in.宽和6in.长的s试验置于钳口中，并弯曲90度。然后，将它们前后弯曲180度。其结果记录为导致故障所需的弯曲数(包括最初的90度角弯曲)。(ASTM A- 344)。
Repeated blow impact test. Method for judging impact properties of cast iron. Hammer is dropped on specimen from increasing heights until fracture occurs. Results are reported as height of the last drop prior to fracture (repeated blow impact value). (ASTM A-327).
冲击疲劳试验。铸铁冲击性能的判断方法。该方法是从增加的高度向试样掷锤，直至其断裂。其结果记录为断裂前最后一次下降的高度(重复打击冲击值)。(ASTM A- 327)。
Residual elongation. Measure of ductility of plastics. It is the elongation of a plastic specimen measured 1 min after rupture in a tension test.
Resilience. Measure of recoverable elastic energy in a deformed material. It is the amount of energy released when a load is removed from a specimen. It is equal to deformation energy minus electric hysteresis.
Rockwell hardness number (RHN). Index of indentation hardness measured by a steel ball or diamond cone indentor. RHN is given in various scales (B, C, R, etc.) depending on indentor and scales used. ASTM E-18 details a standard method for determining RHN for metals and gives a table of scale symbols. ASTM D-785 gives standard method for measuring RHN of plastics; ASTM B-294 covers cemented carbides and ASTM A-370, steel products.
洛氏硬度值(RHN)。利用钢球或金刚石圆锥压痕器测定的压痕硬度指数。RHN具有不同的等级(B、C、R级等)，具体取决于压痕器及其所使用的比例。ASTM E-18中详细介绍了测定金属RHN的标准方法，并提供了刻度符号表。ASTM D-785给出了测量塑料RHN的标准方法; 而ASTM B-294则涵盖了硬质合金，ASTM A-370包括钢铁产品。
Rockwell penetration. Measure of indentation hardness of rubber. It is the resistance to penetration by a specified indentor under specified load applied with a Rockwell hardness tester. (ASTM D-530). It usually is reported with Rockwell recovery.
洛氏穿透率。橡胶压痕硬度的测定。它是使用洛氏硬度计在指定负荷作用下，对指定压痕器的穿透阻力。(ASTM D - 530)。它通常记录为洛氏恢复率。
Rockwell recovery. Extent to which hard rubber recovers from indentation. It is obtained in same test as Rockwell penetration (ASTM D-530) and is reported
Rockwell superficial hardness. Measure of surface hardness of thin strip or finished parts on which large test marks cannot be tolerated or shapes that would collapse under normal Rockwell hardness test loads. (ASTM E-18).
Ross flexing machine test. Method for measuring crack growth resistance of rubber by repeatedly bending pierced specimen and measuring growth of crack that develops. (ASTM D-1052).
Ross弯曲机试验。通过对穿孔试样的反复弯曲以及对裂纹扩展的测量来测定橡胶抗裂纹扩展性能的方法。(ASTM D - 1052)。
Rupture resistance. Indication of ability of rubber to withstand tensile loading. It is the load required to rupture a rubber specimen under conditions set out in ASTM D-530.
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.