注1: 塑料应力松弛试验方法已从本标准中撤销，责任已转移到实践中 D2991 . 1.1 这些测试方法包括在近似恒定约束、恒定测试环境和可忽略振动的条件下，确定材料和结构中应力（应力松弛）的时间依赖性。在该程序中，材料或结构最初受到外部作用力的约束，维持该约束所需的外力变化取决于时间。 1.2 A、B、C和D部分分别描述了对承受拉伸、压缩、弯曲和扭转应力的材料进行应力松弛试验的具体方法。这些测试方法还包括对必要测试设备和测试数据分析的建议。 1.3 弯曲应力- 通过使用大块材料加工的环形试样来确定松弛特性的松弛试验已得到充分发展，并广泛用于确定应力松弛特性 ( 1. ) . 2. 这些试验不在这些试验方法的范围内。 1.4 这些类型的测试所需的长时间通常不适合常规测试或材料采购规范。然而，这些测试对于获得受恒定约束、恒定测试环境和可忽略振动影响的材料应力松弛的实际设计信息，以及研究材料的基本行为，都是有价值的工具。 1.5 单位- 以英寸-磅为单位的数值应视为标准值。括号中给出的值是到国际单位制的数学转换，仅供参考，不被视为标准值。 1.6 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、健康和环境实践，并确定监管限制的适用性。 1.7 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 5.1 在设计大多数机械紧固接头时，必须提供应力松弛试验数据，以确保螺栓或铆接组件、压装或热缩配合组件、轧制管等的永久紧密性。其他应用包括预测垫圈紧密性、无焊缠绕连接的环向应力、弹簧约束力的降低，以及预应力混凝土中钢丝束的稳定性。 5.2 可以根据应力松弛数据预测材料在高应力集中（如缺口、夹杂物、裂纹、孔洞和圆角处）松弛的能力。此类测试数据也有助于判断锻件、铸件、焊接件、机加工或冷加工表面等中残余内应力热消除所需的热处理条件。这些方法中概述的测试仅限于近似恒定约束和测试环境的条件。 5.3 一般应力松弛试验是通过向具有固定约束值的试样等温线施加力来进行的。约束保持不变，约束力是时间的函数。应力松弛测试中的主要问题是，恒定约束可能很难保持。对试验结果的影响非常显著，应特别注意最小化约束变化。 此外，实验者应确定并报告每个应力松弛试验中的变化程度，以便将该因素考虑在内。 5.4 进行应力松弛试验的方法有很多，每种方法都有不同的启动程序。然而，通常通过在特定施力速率或特定应变率下施加外力来获得约束。这两种方法将产生如所示的特征行为 图1 当初始应力， σ 0 ，超过比例限制。一些试验机在达到约束值时，既不会产生恒定的施力速率，也不会产生恒定的应变速率，但会产生介于两者之间的结果。然而，数据的一般特征将与所示相似。在任何一种情况下，应力施加速率都应相当快，但不会产生冲击或振动，以便在应力过程中出现任何松弛- 申请期将很短。 5.5 应力松弛试验从零开始， t 0 在里面 图1 . 注2: 该零时间是基准时间，从中可以观察到维持恒定约束的力减少。选择该时间并不意味着施力程序和周期不是重要的试验参数，这在数据应用中很重要。

Note 1: The method of testing for the stress relaxation of plastics has been withdrawn from this standard, and the responsibility has been transferred to Practice D2991 . 1.1 These test methods cover the determination of the time dependence of stress (stress relaxation) in materials and structures under conditions of approximately constant constraint, constant test environment, and negligible vibration. In the procedures, the material or structure is initially constrained by externally applied forces, and the change in the external force necessary to maintain this constraint is determined as a function of time. 1.2 Specific methods for conducting stress-relaxation tests on materials subjected to tension, compression, bending and torsion stresses are described in Parts A, B, C, and D, respectively. These test methods also include recommendations for the necessary testing equipment and for the analysis of the test data. 1.3 Bending stress-relaxation tests to determine relaxation properties by using ring-shaped specimens machined from bulk material have been thoroughly developed and widely used to determine stress-relaxation properties ( 1 ) . 2 These tests are outside the scope of these test methods. 1.4 The long time periods required for these types of tests are often unsuited for routine testing or for specification in the purchase of material. However, these tests are valuable tools in obtaining practical design information on the stress relaxation of materials subjected to constant constraint, constant test environment, and negligible vibration, and in investigations of the fundamental behavior of materials. 1.5 Units— The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard. 1.6 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 Stress-relaxation test data are necessary when designing most mechanically fastened joints to ensure the permanent tightness of bolted or riveted assemblies, press or shrink-fit components, rolled-in tubes, etc. Other applications include predicting the decrease in the tightness of gaskets, in the hoop stress of solderless wrapped connections, in the constraining force of springs, and in the stability of wire tendons in prestressed concrete. 5.2 The ability of a material to relax at high-stress concentrations such as are present at notches, inclusions, cracks, holes, and fillets can be predicted from stress-relaxation data. Such test data are also useful to judge the heat-treatment condition necessary for the thermal relief of residual internal stresses in forgings, castings, weldments, machined or cold-worked surfaces, etc. The tests outlined in these methods are limited to conditions of approximately constant constraint and test environment. 5.3 The general stress-relaxation test is performed by isothermally applying a force to a specimen with fixed value of constraint. The constraint is maintained constant, and the constraining force is determined as a function of time. The major problem in the stress-relaxation test is that constant constraint can be very difficult to maintain. The effects on test results are very significant, and considerable attention shall be given to minimize the constraint variation. Also, experimenters should determine and report the extent of variation in each stress-relaxation test so that this factor can be taken into consideration. 5.4 There are many methods of performing the stress-relaxation test, each with a different starting procedure. However, the constraint is usually obtained initially by the application of an external force at either a specific force-application rate or a specific strain rate. The two methods will produce the characteristic behavior shown in Fig. 1 when the initial stress, σ 0 , exceeds the proportional limit. Some testing machines, while reaching the constraint value, do not produce either a constant force-application rate or constant strain rate, but something in between. However, the general characteristics of the data will be similar to those indicated. The stress-application rate in either case should be reasonably rapid, but without impact or vibration, so that any relaxation during the stress-application period will be small. 5.5 The stress-relaxation test starts at zero time, t 0 , in Fig. 1 . Note 2: This zero time is the reference time from which the observed reduction in force to maintain constant constraint is based. Selection of this time does not imply that the force-application procedure and period are not significant test parameters which are important in the application of the data.