Testing standard
Standard Test Method for Tensile Properties of Reinforced Thermosetting Plastics Using Straight-Sided Specimens
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ASTM D5083 determines the tensile properties of reinforced thermosetting plastics using straight-sided specimens: a coupon of uniform nominal width, up to 14 mm thick, pulled to break under defined pretreatment, temperature, humidity and machine-speed conditions. The specimen is straight-sided because machining a waist through a fibre-reinforced laminate cuts the reinforcement and moves the failure to the radius. The current edition is D5083-26.
A rectangular coupon of reinforced thermoset — a laminate of constant nominal width rather than a moulded dumbbell — is gripped at both ends and pulled along its axis at a controlled rate until it breaks. Force and extension are recorded throughout, so the whole stress–strain response is captured. The specimen is straight-sided on purpose. Machining a waisted profile into a fibre-reinforced laminate cuts through the reinforcement at the radius, and the coupon then fails where the knife went rather than where the material is weakest, which is a measurement of the machining and not of the laminate.
Tensile strength, elongation at break and tensile modulus, in whichever direction the coupon was cut. For a glass-reinforced thermoset those figures belong to a lay-up rather than to a resin, so the same material gives quite different answers along the fibres, across them and at forty-five degrees, and a single number quoted without a direction is close to meaningless. The method exists because the general plastics tensile test does not serve these materials: the scope directs unreinforced and injection-moulded thermoplastics to D638, thin sheeting under 1.0 mm to D882, and unidirectional fibre-reinforced laminates to D3039/D3039M. What is left — hand lay-up, moulded and pressed reinforced thermosets, most of them glass — is what D5083 covers, for quality control, specification and research work.
A laminate coupon, not a moulded dumbbell. Everything that matters about the preparation is about not damaging the reinforcement.
A coupon with a ragged sawn edge or delamination at the cut has a starter crack built into it. The result will be low, repeatable and wrong.
σ = F / A
Based on the original area, so it is a nominal stress rather than a true one.
E = Δσ / Δε over the initial straight portion
Strain must come from an extensometer on the gauge length. Crosshead travel carries grip seating and frame compliance and gives a modulus that is too low.
Extension at rupture divided by the original gauge length, as a percentage
Small for a stiff glass-reinforced laminate, and sensitive to where the coupon actually broke.
A break at the grip line is not a result. It is a tabbing or clamping problem, and repeating the test without changing the set-up simply repeats it.
Self-tightening wedge grips with serrated faces suit thinner laminate coupons. The wedge action rises with load, which is what stops a hard, smooth coupon slipping without needing crushing clamp pressure at the start.
Specifications
For thicker sections and higher loads. Hydraulic closure holds a constant clamping force on a coupon up to 25 mm thick, and the foot-switch operation leaves both hands free to align it — alignment being the thing that decides whether a stiff laminate is pulled or bent.
Specifications
Modulus has to be measured on the gauge length. A clip-on gauge with an activation force under 60 g adds nothing to a stiff laminate, and gets strain from the specimen rather than from the load train.
SpecificationsConsiderably more force than a plastics dumbbell needs. A 25 mm wide glass-reinforced coupon several millimetres thick can carry tens of kilonewtons, so a frame sized for unreinforced plastics will not reach failure — capacity has to be chosen from the section area and the expected strength, not from habit. Force indication must meet ASTM E4. Grips have to hold a thick, hard, slippery laminate without slipping and without crushing it, which in practice means self-tightening wedges with serrated faces, or hydraulic wedges where the section is thick and the load is high. Alignment matters more here than on a ductile plastic: any eccentricity in the load path bends the coupon and the outer surface reaches its strain limit first. Modulus needs an extensometer on the gauge length rather than crosshead travel, since grip seating and machine compliance both appear as extra extension.
Failure inside the grips, which is the classic invalid result and is usually a tab problem or a clamping-pressure problem rather than a material one. Slipping, which produces a curve that looks soft and destroys the modulus. Cutting the coupon without regard to the fibre direction, so that a nominally identical set of specimens is really several different materials. Testing a laminate with a delaminated or ragged sawn edge. And quoting a figure with no direction, no thickness and no conditioning attached to it, which is the commonest way a valid test becomes an unusable number.
| ASTM D5083 | ASTM D638 | ASTM D3039 | ASTM D882 | |
|---|---|---|---|---|
| Material | Reinforced thermosets | Unreinforced and moulded thermoplastics | Unidirectional fibre-reinforced laminates | Thin sheeting and film |
| Specimen | Straight-sided coupon | Dumbbell | Straight-sided tabbed coupon | Strip |
| Thickness | Up to 14 mm | As tabulated by type | As the laminate | Under 1.0 mm |
| Result belongs to | A lay-up direction | The material | A lay-up direction | A machine direction |
The scope names D638, D882 and D3039/D3039M explicitly and sends material to each of them. ISO 527-4 and ISO 527-5 are the international counterparts and are comparable rather than equivalent: geometry, speed and modulus evaluation differ, so results do not transfer between the two families without checking.
It is the ASTM method for the tensile properties of reinforced thermosetting plastics using straight-sided specimens. A coupon of uniform nominal width is pulled to break under defined pretreatment, temperature, humidity and machine-speed conditions, and tensile strength, modulus and elongation are reported. The current edition is D5083-26, which supersedes D5083-17.
Because machining a waist into a fibre-reinforced laminate cuts through the reinforcement at the radius. The coupon then fails where the cutter went rather than where the material is weakest, which measures the machining and not the laminate. A straight-sided coupon leaves the fibres continuous through the gauge length, and the clamping problem it creates is solved with end tabs instead.
For unreinforced and injection-moulded thermoplastics, which the scope of D5083 explicitly directs to D638. D882 takes over for sheeting under 1.0 mm thick, and D3039/D3039M is the method for unidirectional fibre-reinforced laminates. D5083 covers what is left: moulded, pressed and laid-up reinforced thermosets, most of them glass-reinforced.
Any thickness up to 14 mm (0.55 in.). The method does not recommend testing material thicker than that. Thickness matters for more than the scope limit: a thick, strong coupon needs both a frame with the capacity to break it and grips that will hold it without crushing the fibres under the jaws.
Not always, but they solve the commonest problem with the method. A straight-sided coupon has to be clamped hard enough not to slip, and on a thick or high-strength laminate that clamping crushes the fibres under the jaw and starts the failure there. Bonded tabs spread the load into the coupon and move the break back into the gauge length where it belongs.
Because a reinforced laminate has no single tensile strength. The same material gives quite different figures along the fibres, across them and at forty-five degrees, so strength, modulus and elongation all belong to a direction rather than to the material. A figure quoted with no direction, thickness or conditioning attached to it cannot be used for anything.
No, not usefully. Crosshead travel includes grip seating, tab compliance and the elastic stretch of the whole load train, all of which appear as extra extension and make the modulus too low. Modulus needs an extensometer fixed on the gauge length of the coupon itself.
They are counterparts, not equivalents. The scope names them as comparable standards, but specimen geometry, test speed and the way modulus is evaluated differ between the ASTM and ISO families, so a result generated under one should not be quoted against a specification written to the other without checking those three things first.
Dak verifies against whichever standard the method names, and where a class applies our frames sit a class tighter than it asks.
| The method asks for | Dak supplies | |
|---|---|---|
| Capacity | Not prescribed. Chosen from the section area and the expected strength — a 25 mm wide glass-reinforced coupon a few millimetres thick reaches tens of kilonewtons, beyond what a frame sized for unreinforced plastics will deliver. | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | Force verification to Practices E4, which the method references | ISO 7500-1 Class 0.5, verified to ASTM E4, DIN 51221 and BS 1610 |
| Strain measurement | An extensometer to Practice E83, class as the material specification requires, gauge length unknown — the specimen table is paywalled and no gauge length could be corroborated from two independent sources | Certified to ISO 9513 Class 1 and ASTM E83 — non-contact video, clip-on and high-elongation |
| Gripping | Self-tightening or hydraulic wedge grips with serrated faces; bonded end tabs on thick or high-strength coupons | Our self-tightening serrated wedge grips, with V-jaws for round specimens, built to the specimen |
| Environment | Defined pretreatment, temperature and humidity, reported with the result; Practice D618 conditioning is referenced | 3009 series chambers, −150 °C to +400 °C — temperature only |
This page describes the method as practised. The governing text is the current edition from the issuing body. Tell us what you are testing and we will answer with the machine, the fixture and a quotation.
