Fatigue. Permanent structural change that occurs in a material subjected to fluctuating stress and strain. However, in the case of glass, fatigue is determined by long-term static testing and is analogous to stress rupture in other materials. In general, fatigue failure can occur with stress levels below the elastic limit.

疲劳。是指在承受脉动应力和应变的材料中发生的永久性结构变化。然而，就玻璃而言，其疲劳是由长期静态测试所决定，类似于其他材料的应力断裂。一般而言，当应力水平低于弹性极限时，就会发生疲劳断裂。

Fatigue life. Number of cycles of fluctuating stress and strain of a specified nature that a material will sustain before failure occurs. Fatigue life is a function of the magnitude of the fluctuating stress, geometry of the specimen and test conditions. An S-N diagram is a plot of the fatigue life at various levels of fluctuating stress.

疲劳寿命。是指材料于发生破坏之前所承受的特定性质的脉动应力和应变的循环数。疲劳寿命是脉动应力、试件几何形状和试验条件的函数。其中，S-N图是在不同水平的脉动应力下的疲劳寿命图。

Fatigue limit. Maximum fluctuating stress a material can endure for an infinite number of cycles. It is usually determined from an S-N diagram and is equal to the stress corresponding to the asymptote of the locus of points corresponding to the fatigue life of a number of fatigue test specimens. An alternate term is endurance limit.

疲劳极限。是指材料可以承受无限次循环的最大脉动应力。它通常由S-N图确定，并且等于与若干疲劳试验试件的疲劳寿命对应点轨迹的渐近线所对应的应力。它又叫耐久极限。

Fatigue notch factor. Ratio of fatigue strength of a specimen with no stress concentration to fatigue strength of a specimen with a notch or other stress raisers. Fatigue notch factor is usually lower than the theoretical stress concentration factor because of stress relief due to plastic deformation. An alternate term is strength reduction ratio.

疲劳缺口系数。是指无应力集中的试样的疲劳强度与带有缺口或其他应力集中器的试样的疲劳强度之比。疲劳缺口系数因塑性变形而引起的应力释放，因此通常低于理论应力集中系数。它又称为强度折减比。

Fatigue ratio. Ratio of fatigue strength or fatigue limit to tensile strength. For many materials fatigue ratio may be used to estimate fatigue properties from data obtained in tension tests.

疲劳比。是指疲劳强度或疲劳极限与拉伸强度之比。就许多材料而言，疲劳比可用于将拉伸试验中获得的数据来估计疲劳性能。

Fatigue strength. Magnitude of fluctuating stress required to cause failure in a fatigue test specimen after a specified number of cycles of loading. Usually determined directly from the S-N diagram.

疲劳强度。是指在指定次数的负荷循环后，导致疲劳试验试样失效所需的脉动应力的大小。它通常直接由S-N图确定。

Fatigue strength reduction factor. An alternate term for fatigue notch factor.

疲劳强度折减比。疲劳缺口系数的另一个术语。

Fatigue test. A method for determining the behavior of materials under fluctuating loads. A specified mean load (which may be zero) and an alternating load are applied to a specimen and the number of cycles required to produce failure (fatigue life) is recorded. Generally, the test is repeated with identical specimens and various fluctuating loads. Loads may be applied axially, in torsion or in flexure. Depending on amplitude of the mean and cyclic load, net stress in the specimen may be in one direction through the loading cycle or may reverse direction.

疲劳试验。是一种在脉动负荷作用下确定材料性能的方法。该试验是将指定的平均负荷(可以为零)和交变负荷被施加到一个试样上，并记录产生破坏(疲劳寿命)所需要的循环次数。一般而言，采用相同的试样和各种不同的脉动负荷进行重复试验。其中，负荷可以是轴向的、扭转的或弯曲的。另外，根据平均负荷和循环负荷的幅值，试样的净应力于整个负荷循环中可能是单向的，也可能是反向的。

Data from fatigue testing often are presented in an S-N diagram which is a plot of the number of cycles required to cause failure in a specimen against the amplitude of the cyclical stress developed. The cyclical stress represented may be stress amplitude, maximum stress or minimum stress. Each curve in the diagram represents a constant mean stress.

疲劳试验的数据通常以S-N图的形式呈现，该图显示了导致试样失效所需的循环次数与循环应力幅值之间的关系。其中，所表示的循环应力可以是应力幅值、最大应力或最小应力。图中的每条曲线均表示一个恒定的平均应力。

Most fatigue tests are conducted in flexure, rotating beam or vibratory type machines. Fatigue testing is generally discussed in “Manual on Fatigue Testing,” ASTM STP 91-A and “Mechanical Testing of Materials,” A. J. Fenner, Philosophical Library Inc. ASTM D-671 details a standard procedure for fatigue testing of plastics in flexure.

大多数疲劳试验是在挠曲、旋转梁或振动式机器中进行的。疲劳试验一般在《疲劳试验手册》、ASTM STP 91-A和《材料的机械试验》 A. J. Fenner, Philosophical Library Inc. 中展开讨论。另外，ASTM D-671详细说明了塑料弯曲疲劳试验的标准程序。

Fiber stress. Stress through a point in a part in which stress distribution is not uniform. For example, the stress in a beam under bending load varies from compression to tension across the beam. It is more meaningful in determining the properties of the beam material to consider the maximum stress generated in the outer fibers of the beam. Similarly, stress in a beam under twist loading is a maximum in the material furthest from the axis of twist.

纤维应力。是指在应力分布不均匀的零件中穿过某一点所产生的应力。例如，在弯曲负荷下的横梁的应力从压缩到整条横梁的张力会有所不同。因此，当确定横梁材料性能时，考虑横梁外部纤维所产生的最大应力更有意义。同样，在扭转负荷作用下，横梁离扭轴最远，其材料的应力最大。

File hardness. Simple determination of the comparative hardness of a metal. It is a statement as to whether a file does or does not bite into a material.

锉刀硬度。是指金属相对硬度的简单测定。这是关于锉刀是否咬入或不咬入材料的声明。

Firestone flexometer test. Method for determining compression fatigue characteristics of rubber. A pyramidal rubber specimen is subjected to an oscillating compressive load and the number of load cycles required to produce a specified deflection is reported. (ASTM D-623).

费尔斯通屈挠试验机试验(疲劳强度试验)。它是橡胶压缩疲劳特性的测定方法。该试验记录锥体橡胶试样承受的振荡压缩负荷及其产生指定挠度所需的负荷循环数。(ASTM D - 623)。

Flare test. Method for determining ductility of tubing material. It is similar to an expansion test and a pin test.

扩口试验。是指管材韧性的测定方法。它类似于膨胀试验和插销试验。

Flattening test. Measure of the ductility of metal pipe. A short section of pipe is crushed diametrically between parallel plates to a specified extent and examined for failure.

压扁试验。是指金属管韧性的测定方法。该试验是在平行板之间沿直径方向将一小段管道压碎至指定程度，并检查是否有故障。

Flex resistance. Ability of foam rubber to sustain repeated compressive loads without damage to cell structure. (ASTM D-1055).

抗弯性。是指泡沫橡胶能够承受反复多次压缩载荷而不损坏孔结构的能力。(ASTM D- 1055)。

Flexural modulus of elasticity. Alternate term for modulus in bending.

弯曲弹性模量。弯曲模量的另一种术语。

Flexural strength. Maximum fiber stress developed in a specimen just before it cracks or breaks in a flexure test. Flexural yield strength is reported instead of flexural strength for materials that do not crack in the flexure test. An alternate term is modulus of rupture.

弯曲强度。弯曲试验中，试样在开裂或断裂前产生的最大纤维应力。它在弯曲试验中记录为材料弯曲屈服强度而非其弯曲强度。它又称为断裂模量。

Flexure test. Method for measuring behavior of materials subjected to simple beam loading. It is also called a transverse beam test with some materials. Specimen is supported on two knife edges as a simple beam and load is applied at its midpoint. Maximum fiber stress and maximum strain are calculated for increments of load. Results are plotted in a stress-strain diagram, and maximum fiber stress at failure is flexural strength. Flexural yield strength is reported for materials that do not crack. Standard test procedures are given in ASTM D 790 (plastics), ASTM C-328 and ASTM C-369 (fired whiteware), ASTM D-797 (elastomers), ASTM A-438 (cast iron) and ASTM C-158 (glass).

弯曲试验。是指测定承受简单横梁负荷的材料性能的方法。这也称为对某些材料进行横梁试验。其中，试样作为简单横梁支承在两个刀口上，并在其中点施加负荷。然后，计算最大纤维应力和最大应变以增加负荷。其结果被绘制于一幅应力应变图，并且最大纤维应力在横梁破坏时即为抗弯强度。而抗弯屈服强度则记录为材料不开裂。此外，关于标准测试程序已在ASTM D 790(塑料)、ASTM C-328和ASTM C-369(烧制白陶)、ASTM D-797(弹性体)、ASTM A-438(铸铁)和ASTM C-158(玻璃)中给出。

Flow stress. Stress required to cause plastic deformation.

流度应力。是指引起塑性变形所需的应力。

Fluting diameter. Smallest diameter about which sheet metal can be bent to form a smooth curve rather than a series of planes with a fluted appearance.

开槽直径。是指钣金能弯曲成一条平滑曲线而不是一系列表面有凹槽的平面的最小直径。

Fracture stress. True stress generated in a material at fracture.

断裂应力。材料在断裂处产生的真实应力。

Fracture test. Visual test wherein a specimen is fractured and examined for grain size, case depth, etc.

断裂试验。当试样断裂时，检查晶粒大小、外壳深度等的目视试验。

Fracture toughness. Ability of a material to resist crack propagation when subjected to shock load as in an impact test.

断裂韧性。冲击试验中，材料在冲击负荷作用下抵抗裂纹扩展的能力