1.1 本标准涉及在等温、环境和高温下使用薄壁、圆形截面、管状试样进行的应变控制、轴向、扭转和组合同相和异相轴向扭转疲劳试验。本标准仅限于在组合轴向扭转疲劳试验中具有相同频率的对称、完全反向应变（零平均应变）和轴向和扭转波形。本标准也仅限于用薄壁管状试样表征均质材料，不包括大型部件或结构元件的测试。 1.2 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全和健康实践，并确定监管限制的适用性。 ====意义和用途====== 4.1 多轴力往往会引入独特的变形和损伤机制，与简单单轴加载条件下产生的变形和损伤机制截然不同。由于大多数工程部件受到循环多轴力，因此有必要在此模式下表征材料的变形和疲劳行为。这种特性可以可靠地预测许多工程部件的疲劳寿命。轴向扭转载荷是几种可能的多轴力系统类型之一，本质上是一种双轴载荷。承受轴向扭转载荷的薄壁管状试样可用于探索主应力或应变空间中四个象限中的两个象限中材料的行为。轴向扭转加载比平面内双轴加载更方便，因为应力状态在薄- 有壁管状试样在整个试验段内是恒定的，这是众所周知的。本规程有助于在轴向、扭转以及同相和异相轴向扭转载荷条件下生成均质材料的疲劳寿命和循环变形数据。

1.1 The standard deals with strain-controlled, axial, torsional, and combined in- and out-of-phase axial torsional fatigue testing with thin-walled, circular cross-section, tubular specimens at isothermal, ambient and elevated temperatures. This standard is limited to symmetric, completely-reversed strains (zero mean strains) and axial and torsional waveforms with the same frequency in combined axial-torsional fatigue testing. This standard is also limited to characterization of homogeneous materials with thin-walled tubular specimens and does not cover testing of either large-scale components or structural elements. 1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. ====== Significance And Use ====== 4.1 Multiaxial forces often tend to introduce deformation and damage mechanisms that are unique and quite different from those induced under a simple uniaxial loading condition. Since most engineering components are subjected to cyclic multiaxial forces it is necessary to characterize the deformation and fatigue behaviors of materials in this mode. Such a characterization enables reliable prediction of the fatigue lives of many engineering components. Axial-torsional loading is one of several possible types of multiaxial force systems and is essentially a biaxial type of loading. Thin-walled tubular specimens subjected to axial-torsional loading can be used to explore behavior of materials in two of the four quadrants in principal stress or strain spaces. Axial-torsional loading is more convenient than in-plane biaxial loading because the stress state in the thin-walled tubular specimens is constant over the entire test section and is well-known. This practice is useful for generating fatigue life and cyclic deformation data on homogeneous materials under axial, torsional, and combined in- and out-of-phase axial-torsional loading conditions.