ASTM G39 PDF

Standards Related to G39 – G G Standard ASTM Standards Related to Corrosion Testing of Metals · Annual Book of ASTM Standards Online: Hello everyone, I am looking for ASTM G39 – 99() Standard Practice for Preparation and Use of Bent-Beam Stress- Corrosion Test Specimens. Please. ASTM G39 – 99() – 弯曲梁应力腐蚀试验试样制备和使用标准规程.

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A number in parentheses indicates the year of last reapproval. This practice applicable to specimens of any metal that are stressed to levels less than the elastic limit of the material, and therefore, the applied stress can be accurately calculated or measured see Note 1. Stress calculations atm this practice are not applicable to plastically stressed specimens. NOTE 1—It is the nature of these practices that only the applied stress can be calculated.

Since stress-corrosion cracking is a function of the total stress, for critical applications and proper interpretation of results, the residual stress before applying external stress or the total elastic stress after applying external stress should be determined by appropriate nondestructive methods, such as X-ray diffraction 1.

The inch-pound values in parentheses are provided for information. 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. For plate material the bent-beam specimen is more difficult to use because more rugged specimen holders must be built to accommodate the specimens.

Once cracking has initiated, the state of stress at the tip of the crack as well as in uncracked areas has changed, and therefore, the known or calculated stress or strain values discussed in this practice apply only to the state of stress existing before initiation of cracks. Current edition approved March 1, Originally approved in Last previous edition approved in as G39—99 We expertize in translation of technical documents and also deliver procurement service of Chinese versions.

Information is available from http: Please contact us if you need any help. Presence of cracks can be determined with or without optical, mechanical, or electronic aids.

However, for meaningful interpretation, comparisons should be made only among tests employing crack detection methods of equivalent sensitivity. This excludes corrosion-reduced sections that fail by fast fracture.

3 & 4 POINT BEND FIXTURES – Cortest

It also excludes intercrystalline or transcrystalline corrosion which can disintegrate an alloy without either applied or residual stress.

Summary of Practice 4. The applied stress is determined from the size of the specimen and the bending de? The stressed specimens then are exposed to the ast, environment and the time required for cracks to develop is determined. This cracking time is used as a measure of the stress-corrosion resistance of the material in the test environment at the stress level utilized. The bent-beam specimens are designed for testing at stress levels below the elastic limit of the alloy.

For g9 in the plastic range, U-bend specimens should be employed see Practice G Although it is possible to stress bent-beam specimens into the plastic range, the stress level cannot be calculated for plastically-stressed three- and four-point loaded specimens as well as the double-beam specimens.

Therefore, the use of bent-beam specimens in the plastic range is not recommended for general use. Typical specimen holder con? NOTE 2—The double-beam specimen, more fully described in NOTE 3—Specimen holders can be modi?

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For instance, the loading asgm can be supplanted by a spring or deadweight arrangement to change the mode of loading. In these instances the critical areas should be packed with a hydrophobic? NOTE 5—In atmospheres gas galvanic action between specimen and holder either does not exist or is con? NOTE 4—It should be recognized that many plastics tend to creep when subjected to sustained loads.

If specimen holders or insulators are made of such materials, the applied stress on the specimen may change appreciably with time.

By proper choice of holder and insulator materials, however, many plastics can be used, especially in short-time tests. To stress two-point loaded specimens Fig. A convenient stressing jig is shown in Fig. NOTE 6—The double-beam specimen, described in This is 2 6. In designing a de?

Stressed Coupons

If stenciling is used for identi? Care must be taken to prevent the identi? This procedure is recommended when it is desired to include the effect of surface condition in the test. It is recommended that grinding or machining to a surface? It is desirable to remove the required amount of metal in several steps by alternately grinding opposite surfaces. This practice minimizes warpage due to residual stresses caused by machining.

All edges should be similarly ground or machined to remove cold-worked material from previous shearing. Chemical or electrochemical treatments that produce hydrogen on the specimen surface must not be used on materials that may be subject to embrittlement by hydrogen or that react with hydrogen to form a hydride.

Only chemicals appropriate for the given metal or alloy should be used. Care must be exercised not to contaminate cleaned specimens. Also, it is suggested that specimens be examined for cracks before exposure to the test environment. At stresses above the elastic limit, astn below the engineering yield strength 0.

Asym equations must not be used above the yield strength of the material. The following paragraphs give asstm used to calculate the maximum longitudinal stress in the outer? Calculations for transverse stress or edge-to-edge variation of longitudinal stress are not given; the specimen dimensions are chosen to minimize these stresses consistent with convenient 3 FIG. Due to high stresses in a specimen, these pieces may leave the specimen at high velocity and can be dangerous.

Personnel installing and examining specimens should be cognizant of this possibility and be protected against injury.

The specimen dimensions given here can be modi? However, if this is done, the approximate specimen proportions should be preserved to give a similar stress distribution for instance, if the length is doubled the width should be doubled also. Relaxation can be estimated from known creep data for the specimen, holder, and insulating materials.

Stressed Coupons

Differences in thermal expansion also should be considered. Thus, the errors in the applied stress are related to those inherent in the use of measuring instruments micrometers, de?

The calculated stress applies only to the state of stress before initiation of cracks. Once cracking is initiated, the stress at the tip of the crack, as well as in uncracked areas, has changed. The specimens shall be approximately 25 by mm 1- by in. To facilitate calculations, a computer can be used to generate a table for a axtm of strain? The other quantities are given in This relationship can be used as a simple check to ensure that the maximum stress does not exceed the proportional limit.

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If it should exceed the proportional limit, the measured de?

The common parameter in these equations is the modulus k of the elliptic integrals. Thus, the following procedure can be used to determine the specimen length L that is required to produce a given maximum stress s: This equation can be solved by computer, by trial and error, or by using a series expansion of the sine function.

A specimen thickness of about 0. However, if this is done, approximate dimensional proportions shall be preserved. Since this corrosion site is very close to the point of highest tension stress, it may cathodically protect the specimen and prevent possible crack formation or cause hydrogen embrittlement. Furthermore, the pressure of the central support at the point of highest load introduces biaxial stresses at the area of contact and could introduce tension stresses where normally compression stresses are present.

NOTE 7—Occasionally two-point loaded specimens having a nonuniform cross section are used for special purposes. A description of such a specimen is given by Wilson and Spier 5. The thickness of the specimen is usually dictated by the mechanical properties of the material and the product form available. Support the specimen at the ends and bend the specimen by forcing a screw equipped with a ball or knife-edge tip against it at the point halfway between the end supports in a fashion shown in Fig.

In sheet-gage, bent-beam specimens the de? To obtain more accurate stress values, use a prototype specimen, equipped with strain gages, for calibration. This prototype should have the same dimensions as the test specimens and should be stressed in the same way. Support the specimen at the ends and bend the specimen by forcing two inner supports against it in a fashion shown in Fig.

The two inner supports shall be located symmetrically around the midpoint between the outer supports. This equation is a special case of In sheet-gage bent-beam specimens the de? To obtain more accurate stress values, use for calibration a prototype specimen equipped with strain gages. This prototype specimen should have the same dimensions as the test specimens and should be stressed in the same way.

From the inner supports the stress decreases linearly toward zero at the outer supports. Bend the strips against each other over a centrally located spacer until both ends of the specimens touch. Hold them in this position by welding the ends together as shown in Fig. An equivalent procedure for bolted specimens is described on pp. NOTE 8—If the test is to be conducted in an electrolyte, the spacer shall be made of the same material as the specimen or of an electrically nonconducting material such as glass, ceramic, and so forth to prevent galvanic action between specimen and spacer.

The prototype specimen should have the same dimensions as the test specimens and should be stressed in the same way. G39 — 99 From the contact with the spacer the stress decreases linearly toward zero at the ends of specimens. Choice of Test Conditions