ASTM D3039_Standard Test Methods for Tensile Properties

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Last updated: Feb 08, 2021 by Tommy Tran
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Standards from ASTM’s D3039/D3039M − 17 link to library where ASTM standards are

Symbols to know:

 

Required Equipment

3 Force Indicator—The testing machine force-sensing device should be capable of indicating the total force being carried by the test specimen. Most machines will be computerized and be able to show this information.

 

Grips—Each head of the testing machine has one grip for holding the test specimen in place. The grips need to apply sufficient lateral pressure to prevent slippage between the grip face and the test piece or coupon. If tabs are used the grips should be long enough that they overhang the beveled portion of the tab by approximately 10 to 15 mm [0.5 in.].

Grips can be serrated or smooth.

  • Serration provides good grip on materials without tabs but can cause grip induced failures if they are too large. However, serrations can be rounded to cause less damage to the specimen.

  • Smooth grips are successful with hydraulic grips or with an emery cloth interface or both

  • grips should be wider than specimen

  • grips that cover more area provide better friction

digital image correlation system

 

 

Strain-Indicating Device—Force-strain data is be determined by means of either a strain transducer or an extensometer. Attachment of the strain-indicating device to the coupon shall not cause damage to the specimen surface. If Poisson’s ratio is to be determined, the specimen shall be instrumented to measure strain in both longitudinal and lateral directions. If the modulus of elasticity is to be determined, the longitudinal strain should be simultaneously measured on opposite faces of the specimen to allow for a correction as a result of any bending of the specimen (see 11.6 for further guidance).

Strain transducer - The ST350 Strain Transducer has been designed to quickly and accurately

measure strain on a variety of structures in harsh field environments.

Extensometer - For most purposes, the extensometer gage length should be in the range of 10 to 50 mm [0.5 to 2.0 in.] (Easier to use than strain gauge)

 

Poisson's ratio measures the deformation in the material in a direction perpendicular to the direction of the applied force.

More about Poisson's Ratio

Strain Gauge

A strain gage works to measure the amount of strain on a given object. At its most basic form, a strain gage converts a change in dimension to a change in electrical resistance.

  • An active gauge length of 6mm is recommended

  • Active gauge lengths shouldn’t be less then 3mm

 

Specimen Preparation

Geometry

Tabs

  • Used to help grips hold onto test specimen

  • Tabs must be the same thickness

  • Can most likely be attached with super glue

  • Might not be necessary if the grips are good enough

Bonded Tab Length—When using bonded tabs, estimate the minimum suggested tab length for bonded tabs by the following simple equation.

How to make tabs

Tensile testing video

Composite Tensile Sample Preparation

Procedure

  1. Make the specimen to geometric standards.

  2. Measure the specimen in 3 places in the gauge section and report average thickness and width to 3 sig figs. Determine the specimen area as A = w × h. Record the average area in units of mm2 (in.2 ).

  3. Set speed of testing to effect a nearly constant strain rate in the gage section. (If strain control is not available on the testing machine, this may be approximated by repeated monitoring and adjusting of the rate of force application to maintain a nearly constant strain rate). The strain rate should be selected so as to produce failure within 1 to 10 min.

  4. Determining modulus of elasticity, at least one specimen per like sample should be evaluated with back-to-back axial transducers to evaluate the percent bending using the equation below, at the average axial strain checkpoint value (the mid range of the appropriate chord modulus strain range) shown in Table 3.

  5. Calculate the ultimate tensile strength using Eq 5 below. Report the results to three significant figures. If the tensile modulus is to be calculated, determine the tensile stress at each required data point using Eq 6 also below.

  6. If tensile modulus or ultimate tensile strain is to be calculated, and material response is being determined by an extensometer, determine the tensile strain from the indicated displacement at each required data point using Eq 7 and report the results to three significant figures.

  7. Tensile Chord Modulus of Elasticity—Select the appropriate chord modulus strain range from Table 3. Calculate the tensile chord modulus of elasticity from the stress-strain data using Eq 8 below. If data is not available at the exact strain range end points (as often occurs with digital data), use the closest available data point.

 

8. Poisson’s Ratio By Chord Method—Select the appropriate chord modulus longitudinal strain range from Table 3 above. Determine (by plotting or otherwise) the transverse strain (measured perpendicular to the applied force), εt , at each of the two longitudinal strains (measured parallel to the applied force), εl , strain range end points. If data is not available at the exact strain range end points (as often occurs with digital data), use the closest available data point. Calculate Poisson’s ratio by Eq 9, below, and report to three significant figures. Also report the strain range used.

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