S-N diagram. Plot of stress (S) against the number of cycles (N) required to cause failure of similar specimens in a fatigue test. Data for each curve on an S-N diagram are obtained by determining fatigue life of a number of specimens subjected to various amounts of fluctuating stress. The stress axis can represent stress amplitude, maximum stress or minimum stress. A log scale is almost always used for the N scale and sometimes for the S scale.
St. Joe flexometer test. Method for measuring compression fatigue characteristics of rubber. Results are reported as time and flexing load required to fail specimen. (ASTM D-623).
St. Joe面料耐挠测试。橡胶压缩疲劳特性的测量方法。结果记录为试验断裂所需的时间和弯曲负荷。(ASTM D - 623)。
Scleroscope hardness. Measure of hardness or impact resilience of metals. A diamond-tipped hammer falls freely against specimen from a fixed height and rebound height is measured. Scleroscope hardness is read on an empirical scale where 100 rep resents average rebound from a quenched high carbon steel specimen. ASTM A-427 contains a table that relates scleroscope hardness to diamond pyramid hardness.
肖氏硬度。测量金属的硬度或冲击回弹性。一个镶金刚石锤从固定高度自由落至试样上，然后测量其回弹高度。肖氏硬度是根据经验刻度读取，其中100 代表淬火高碳钢试样的平均回弹。ASTM A -427包含一张将硬度与金刚石金字塔硬度相联系的表格。
Scratch hardness. Method for determining comparative hardness of materials by measuring width of a scratch made by a scriber drawn across the surface under specified pressure. Often performed on coatings.
Secant modulus of elasticity. Ratio of stress to strain at any point on curve in stress-strain diagram. It is the slope of a line from the origin to any point on stress-strain curve.
Shear modulus of elasticity. Tangent or secant modulus of elasticity of a material subjected to shear loading. Alternate terms are modulus of rigidity and modulus of elasticity in shear. Also, shear modulus of elasticity usually is equal to torsional modulus of elasticity. A method for determining shear modulus of elasticity of structural materials by means of a twisting test is given in ASTM E-143. A method for deter mining shear modulus of structural adhesives is given in ASTM E-229.
切变模量。材料在剪切负荷作用下的正切或正割弹性模量。它又称为刚性模量和剪切弹性模量。另外，切变模量通常等于扭转弹性模量。ASTM E-143中给出了通过扭转试验以测定结构材料切变模量的方法。ASTM E-229中给出了阻止结构粘合剂切变模量的方法。
Shear strength. Maximum shear stress that can be sustained by a material before rupture. It is the ultimate strength of a material subjected to shear loading. It can be determined in a torsion test where it is equal to torsional strength. The shear strength of a plastic is the maximum load required to shear a specimen in such a manner that the resulting pieces are completely clear of each other. It is reported in psi based on the area of the sheared edge. (ASTM D-732). The shear strength of a structural adhesive is the maximum shear stress in the adhesive prior to failure under torsional loading. (ASTM E-229). Methods for deter mining shear strength of timber are given in ASTM D-143 and ASTM D-198.
切变强度。是指材料在断裂前所能承受的最大剪切应力。它是在剪切负荷作用下的材料的极限强度。它也可以在扭转试验中测定，其中，切变强度等于扭转强度。塑料的切变强度是剪切一个试样所需的最大负荷，以使所得碎片彼此完全脱离。最终，根据剪切边缘的面积以psi为单位进行记录。(ASTM D-732)。此外，结构粘合剂的切变强度是在扭转负荷作用下破坏前粘合剂内的最大剪应力。(ASTM E - 229)。ASTM D-143和ASTM D-198中均给出了测定木材切变强度的方法。
Softening point. Temperature at which a uniform fiber of glass elongates under its own weight at a specified rate. (ASTM C-338). The Vicat softening point of plastics is the temperature at which a flat ended needle of 1 sq mm circular or square cross section penetrates a thermoplastic specimen to a depth of 1 mm under load and conditions specified in ASTM D-1525.
软化点。均匀的玻璃纤维在其自身重量下以一定速率伸长的温度。(ASTM C-338)。塑料的维卡软化点是指根据ASTM D-1525规定的负荷和条件，一个直径为1sq mm的圆形或正方形截面的平头针穿透热塑性试样至1mm深度时的温度。
Splitting resistance. Measure of the ability of felt to withstand tearing. It is the load required to rupture a slit felt specimen by gripping lips of the cut in jaws and pulling them apart. (ASTM D-461). An alternate term is tear resistance.
抗裂性。测量毛毡承受撕裂的能力。它是通过抓住钳口的唇口并将其撕开而使毡制试样破裂所需的负荷。(ASTM D - 461)。它又称为撕裂强度。
Springback. Degree to which a material returns to its original shape after deformation. In plastics and elastomers it is also called recovery.
Stiffness. Measure of resistance of plastics to bending. It includes both plastic and elastic behavior, so it is an apparent value of elastic modulus rather than a true value. (ASTM D-747).
刚性。测量塑料抗弯性能的方法。它既包括塑性行为，又包括弹性行为，因此它是弹性模量的表观值，而不是真实值。(ASTM D - 747)。
Strain. Change per unit length in a linear dimension of a part or specimen, usually expressed in %. Strain as used with most mechanical tests is based on original length of the specimen. True or natural strain is based on instantaneous length and is equal to In l/lo where l is instantaneous length and lo is original length of the specimen. Shear strain is the change in angle between two lines originally at right angles.
应变。零件或试样的线性尺寸中每单位长度的变化，通常以百分比表示。大多数机械试验中所使用的应变是基于试样的原始长度。真实应变或自然应变应以瞬时长度为基础，并且等于In l / lo，其中l是瞬时长度，lo是试样的原始长度。剪切应变是最初成直角的两条线之间的角度变化。
Strain energy. Measure of energy absorption characteristics of a material under load up to fracture. It is equal to the area under the stress strain diagram, and is a measure of the toughness of a material.
Strain hardening exponent. Measure of increase in hardness and strength caused by plastic deformation. It is related to true stress and true strain by the equation: O= oOn where O is true stress, Oo is true stress at unit strain, O is true strain and n is strain hardening exponent.
Strain point. Temperature at which internal stress in glass is substantially relieved in about 1 hr. (ASTM C 336).
应变点。玻璃内应力在大约1小时内得到明显缓解的温度。(ASTM C 336)。
Strain rate. Time rate of elongation.
Strain relaxation. Alternate term for creep of rubber.
Strength reduction ratio. Alternate term for fatigue notch factor.
Stress. Load on a specimen divided by the area through which it acts. As used with most mechanical tests, stress is based on original cross section area without taking into account changes in area due to applied load. This sometimes is called conventional or engineering stress. True stress is equal to the load divided by the instantaneous cross section area through which it acts.
Stress amplitude. One-half the range of fluctuating stress developed in a specimen in a fatigue test. Stress amplitude often is used to construct an S-N diagram.
Stress concentration factor. Ratio of the greatest stress in the area of a notch or other stress raiser to the corresponding nominal stress. It is a theoretical indication of the effect of stress concentrators on mechanical behavior.
Stress concentration factor usually is higher than the empirical fatigue notch factor or strength reduction ratio because it does not take into account stress relief due to local plastic deformation.
Stress corrosion cracking. Failure of a material due to combined effects of corrosion and stress. Generally, stress corrosion cracking refers to the phenomenon by which stress in creases corrosion rate.
Stress ratio. Ratio of minimum stress to maximum stress in one cycle of loading in a fatigue test. Tensile stresses are considered positive and compressive stresses negative.
Stress relaxation. Decrease in stress in a material subjected to prolonged constant strain at a constant temperature. Stress relaxation behavior is determined in a creep test. Data often is presented in the form of a stress vs time plot. Stress relaxation rate is slope of the curve at any point.
Stress rupture strength. Alternate term for creep strength.
Stress-strain diagram. Graph of stress as a function of strain. It can be constructed from data obtained in any mechanical test where a load is applied to a material and continuous measurements of stress and strain are made simultaneously. It is constructed for compression, tension and torsion tests.
Stress-strain ratio. Stress divided by strain at any load or deflection. Below the elastic limit of a material it is equal to tangent modulus of elasticity. An alternate term is secant modulus of elasticity. Stripping strength. Alternate term for peel strength.