ASTM G38-01(R2021) pdf free download

ASTM G38-01(R2021) pdf free download.Standard Practice for Making and Using C-Ring Stress-Corrosion Test Specimens
1. Scope
1.1 This practice covers the essential features of the design and machining, and procedures for stressing, exposing, and inspecting C-ring type of stress-corrosion test specimens. An analysis is given of the state and distribution of stress in the C-ring. 1.2 Specific considerations relating to the sampling process and to the selection of appropriate test environments are outside the scope of this practice. 1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard. 1.4 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 appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.5 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
4. Significance and Use
4.1 The C-ring is a versatile, economical specimen for quantitatively determining the susceptibility to stress-corrosion cracking of all types of alloys in a wide variety of product forms. It is particularly suitable for making transverse tests of tubing and rod and for making short-transverse tests of various products as illustrated for plate in Fig. 1.
5. Sampling
5.1 Test specimens shall be taken from a location and with an orientation so that they adequately represent the material to be tested. 5.2 In testing thick sections that have a directional grain structure, it is essential that the C-ring be oriented in the section so that the direction of principal stress (parallel to the stressing bolt) is in the direction of minimum resistance to stress-corrosion cracking. For example, in the case of alumi- num alloys (1), 3 this is the short-transverse direction relative to the grain structure. If the ring is not so oriented it will tend to crack off-center at a location where the stress is unknown.
6. Specimen Design
6.1 Sizes for C-rings may be varied over a wide range, but C-rings with an outside diameter less than about 16 mm ( 5 ⁄ 8 in.) are not recommended because of increased difficulties in machining and decreased precision in stressing. The dimen- sions of the ring can affect the stress state, and these consid- erations are discussed in Section 7. A typical shop drawing for the manufacture of a C-ring is shown in Fig. 2.
7.2 Another characteristic of the stress system in the C-ring is the presence of biaxial stresses; that is, transverse as well as circumferential stresses are developed on the critical test section. The transverse stress will vary from a maximum at the mid-width to zero at the edges, and will be the same sign as the circumferential stress. In general, the transverse stress may be expected to decrease with decreasing width to thickness and increasing diameter to thickness ratios. An example is shown in Fig. 4 where the transverse tensile stress at the mid-width of a 19.00 mm (0.748 in.) outside diameter by 1.537 mm (0.0605 in.) thick by 19.0 mm (0.75 in.) wide C-ring ofaluminum alloy 7075-T6 was equal to about one third of the circumferential tensile stress. In this example the circumferential stress was uniform over most of the width of the C-ring; measurements were not made at the extreme edge. 7.3 In the case of the notched C-ring (Fig. 3(d)) a triaxial stress state is present adjacent to the root of the notch (5). In addition, the circumferential stress at the root of the notch will be greater than the nominal stress and generally may be expected to be in the plastic range. 7.4 The possibility of residual stress should always be considered, especially when C-rings are machined from prod- ucts that contain appreciable residual stress or when C-rings over about 6.35 mm ( 1 ⁄ 4 in.) thick are heat treated after being machined. It is generally not advisable to heat treat finish- machined C-rings because of the likelihood of developing residual stresses in the ring. N OTE 1—When specimens are exposed to corrosive media at elevated temperatures, the possibility of relaxation of stress during the exposure period should be investigated. Relaxation can be estimated from known creep data for both the ring and the stressing bolt.