ASTM D2105

What the test does

A length of fibreglass pipe or tube is loaded in tension along the pipe axis until it fails, and the force and the change in length are recorded throughout. The specimen is the pipe itself, not a coupon cut out of it, so the reinforcement architecture the winder or the moulder actually produced is what carries the load. Load is introduced at the ends rather than by clamping the pipe wall between flat jaws, because a jaw closing on a thin filament-wound wall crushes it long before the laminate reaches its axial strength.

Within the method, “fiberglass” pipe means both glass-fibre-reinforced thermosetting-resin pipe, RTRP, and glass-fibre-reinforced polymer mortar pipe, RPMP.

What it measures, and why it matters

The comparative longitudinal tensile properties of the pipe under defined conditions of pretreatment, temperature and testing machine speed. The properties the method deals with are modulus of elasticity, yield stress, elongation beyond the yield point, tensile strength, elongation at break and energy absorption, with the caveat the standard itself makes: materials with a low order of ductility need not show a yield point at all.

Axial strength is the property a buried or above-ground pipeline needs for thrust, for restrained joints, for thermal end load and for handling, and it is emphatically not the same property as hoop strength. A filament-wound pipe is designed with a chosen balance between the two, and the standard is unusually direct about the consequence: producers deliberately offer different balances of resistance to tension, compression, torsion, flexure and internal pressure, so purchaser and seller need a shared understanding of what a D2105 result means for the product before it is used as an acceptance criterion.

The method is equally clear on its limits. The data suit research, design, quality control and acceptance or rejection under a specification, but they cannot be treated as significant for service conditions whose load-time scale differs widely from this test. Impact, creep and fatigue testing answer those questions, not this one.

Specimen and end fittings

The specimen is a length of the pipe as made, not a coupon cut out of it, so the reinforcement architecture the winder actually produced is what carries the load. Everything difficult about this test is at the two ends.

Specimen

A length of fibreglass pipe or tubeBoth RTRP and RPMP are fibreglass pipes within the meaning of this method.

Diameter

Generally limited to 6 in. (150 mm) or smallerLarger sizes may be tested where the necessary apparatus exists — which in practice means a frame with the daylight and the capacity to hold the fittings as well as the pipe.

Load introduction

At the ends, not by clamping the pipe wall between flat jawsPracticeA jaw closing on a thin filament-wound wall crushes it long before the laminate reaches its axial strength, so the load goes in through fittings made to the pipe. The apparatus clause of the current edition governs; this row describes what laboratories build.

Units

Inch-pound values are the standard ones in this methodWorth carrying into the report as tested. Figures rounded twice through a conversion do not always agree with the original.

Cross-sectional area

Computed from wall thickness and diameter measured on the specimen

Measure the wall around the circumference

DakWound and moulded pipe is rarely uniform. A single thickness reading at one clock position sets the area for every stress figure that follows.

Check the fittings are concentric before loading

DakEccentricity between the two ends superimposes bending on the tension, and a thin composite wall fails on the outer fibre well before the laminate reaches its axial strength.

A specimen that fails at or inside an end fitting has measured the fitting. It is not a low result to be averaged in; it is a specimen to be discarded and repeated with the bond or the clamping put right.

Test conditions

The method defines its properties as comparative and ties them explicitly to the conditions used, so the conditions are part of the result rather than a footnote to it.

Speed

A constant, specified testing machine speedThe properties are comparative under defined conditions of pretreatment, temperature and machine speed. Take the speed from the current edition, and from the referring product specification where it names one.

Report the speed used

AlwaysThese materials are rate-sensitive, and a strength quoted without its speed is not comparable with another laboratory's figure.

Pretreatment and temperature

As defined for the test

Agree the conditions before the first lot

DakThe method itself says producer and purchaser need a shared understanding of what a result means for the product. That conversation is cheaper before an acceptance test than after one.

The data suit research, design, quality control and acceptance or rejection under a specification. The method is explicit that they cannot be treated as significant for service conditions whose load-time scale differs widely from this test — impact, creep and fatigue testing answer those questions.

Calculations

Stress is force over the measured wall section, and strain comes from an extension indicator rather than from the crosshead.

How the test runs

1. 01Take the specimen as a length of pipe or tube, of a size the frame and fittings can accommodate.
2. 02Measure wall thickness and diameter on the specimen and compute the cross-sectional area.
3. 03Fit or bond the end fittings so the axial load can be introduced without clamping the pipe wall.
4. 04Allow any bonded fitting to cure fully before loading, following the adhesive's own schedule.
5. 05Mount the specimen so the two fittings are concentric and on the load axis.
6. 06Attach the extension indicator, or bond strain gauges where axial and hoop strain are both wanted.
7. 07Zero the force with the specimen mounted and unloaded.
8. 08Pull at the specified constant machine speed, recording force against extension throughout.
9. 09Record the maximum force and the point at which the specimen failed.
10. 10Note where the failure occurred; discard and repeat anything that failed at or inside a fitting.
11. 11Compute stress on the measured wall area, and modulus from the initial part of the curve.
12. 12Report the mean with the number of specimens and the conditions used.

Alignment is the requirement that decides the result and the one nothing on the trace will confess to. An eccentrically assembled specimen produces a clean, plausible curve at a low breaking load, and reads as a weak pipe.

What the report has to contain

• Reference to ASTM D2105 and the edition used
• Complete identification of the pipe — type (RTRP or RPMP), resin, reinforcement and construction
• Nominal size, and the measured wall thickness and diameter
• The cross-sectional area used in the calculation
• Pretreatment, and the temperature at test
• Testing machine speed
• How the end fittings were made and attached
• How longitudinal strain was measured
• Modulus of elasticity, yield stress where a yield point occurs, tensile strength, elongation at break and energy absorption as applicable
• Location and description of the failure on each specimen
• Number of specimens, the mean, and any specimen discarded with the reason

What the machine must be capable of

Capacity, alignment and enough vertical space for the pipe and its end fittings together. Axial load on a 150 mm pipe is a substantial force, so the frame is sized from the wall section and the expected strength rather than from the pipe's appearance; the load cell should still resolve the low end cleanly, since modulus is taken from the early part of the curve.

Alignment is the requirement that decides the result. Any eccentricity between the two end fittings superimposes bending on the tension, and a thin composite wall in bending fails on the outer fibre well before the laminate reaches its axial strength. The frame must also hold a constant, specified crosshead speed, and the speed used has to be reported with the result because these materials are rate-sensitive.

What goes wrong in practice

End fittings that release before the pipe does, which is a lost specimen rather than a low reading. Failure at or inside the fitting, which measures the fitting. Eccentric assembly, which reads as a weak pipe. Taking axial strain from crosshead travel, which contains the compliance of the fittings and the frame and understates the modulus. And carrying a longitudinal figure into a hoop calculation, which is the most expensive misuse available here because the two are deliberately different by design.

Longitudinal, hoop and coupon

A filament-wound pipe is deliberately designed with a chosen balance between axial and hoop strength. These three methods do not measure the same property and cannot be substituted for one another.

Carrying a longitudinal figure into a hoop calculation is the most expensive misuse available here, because the two are different by design rather than by accident. A pipe wound for pressure and a pipe wound for axial load are the same product family with deliberately different numbers.

Questions we are asked about this test