---
code: "ISO 527-4 / ISO 527-5"
title: "Plastics — Tensile properties of fibre-reinforced composites — Parts 4 and 5"
institution: "ISO"
category: "material-testing"
revision: "2019 / 2009"
scope: "Defines test conditions for determining tensile modulus, strength, and strain of fibre-reinforced plastic composites. ISO 527-4 covers isotropic and orthotropic materials (woven fabrics, chopped strand mats, multi-directional laminates); ISO 527-5 covers unidirectional (UD) fibre composites with mandatory tabbed parallel-sided specimens."
testMethod: "A tabbed or parallel-sided composite coupon is strained at 2 mm/min (1–10 mm/min optional on ISO 527-4) while force and extension are recorded. Modulus is calculated strictly between 0.05% and 0.25% strain using Class 1 (or Class 0.5 for high-stiffness UD) extensometry per ISO 9513; ultimate tensile strength is taken at catastrophic break."
specimenRequirements: "ISO 527-4 Type 1 (controlled thickness, un-tabbed for mats), Type 2 (parallel-sided with tabs for woven fabrics), and Type 3 (dumbbell for structural profiles). ISO 527-5 requires parallel-sided specimens with glued composite or soft-metal tabs at 0° or 90° to the fibre run. Tabs must prevent jaw-crush failure; bonding surfaces require sanding and degreasing before structural epoxy cure."
url: "https://vectorbtc.com.tr/resources/standards/iso-527-4-5/"
---

## Overview

Evaluating the mechanical profile of advanced composite materials requires a testing framework that handles high stiffness, minimal elongation before failure, and strongly anisotropic behaviour. [ISO 527-4](/resources/standards/iso-527-4-5/) and [ISO 527-5](/resources/standards/iso-527-4-5/) are the definitive international standards for tensile properties of fibre-reinforced plastic composites. They extend the general principles of [ISO 527-1](/resources/standards/iso-527-1/) with specimen geometries, tabbing rules, and strain-range requirements specific to laminates and UD tapes.

Running these methods on a [Vector Universal Testing Machine (100–300 kN)](/products/material-testing/universal-testing-systems/universal-testing-machine-300kn/) or [Hydraulic Universal Testing Machine](/products/material-testing/universal-testing-systems/hydraulic-universal-testing-machine/) with **Tesla Test Software** delivers structural alignment verification, precise strain tracking, and compliant calculation of high-modulus composite response.

## Technical architecture and core concepts

### 1. Specimen geometries and tabbing

Composite coupons carry extreme tensile strength along the fibre axis but are highly vulnerable to localized crushing at the grips.

| Standard | Material profile | Specimen types |
| --- | --- | --- |
| ISO 527-4 | Isotropic / orthotropic (woven, mats, multi-directional laminates) | Type 1 (controlled thickness, un-tabbed for mats); Type 2 (parallel-sided with tabs for woven fabrics); Type 3 (dumbbell for structural profiles) |
| ISO 527-5 | Unidirectional (0° or 90° fibre run) | Parallel-sided with **mandatory** glued-on tabs |

**Why tabs matter:** Composite or soft-metal end tabs (*uç takviyeleri*) protect the coupon from hydraulic jaw pressure, preventing premature jaw-break failures and forcing fracture within the central gauge length. On ISO 527-5, tab orientation (0° or 90° composite tabs) must match the fibre direction under test.

### 2. Gripping systems and axis alignment

High force levels on carbon or glass-fibre laminates make sample slippage or bending stress fatal to data validity.

- **Hydraulic wedge grips:** Vector [hydraulic UTMs](/products/material-testing/universal-testing-systems/hydraulic-universal-testing-machine/) and high-capacity [electromechanical frames](/products/material-testing/universal-testing-systems/universal-testing-machine-300kn/) use wedge-action grips that maintain software-regulated clamping pressure throughout the test, accommodating thickness reduction under load.
- **Alignment accuracy:** Load-string alignment should be verified per ASTM E1012 and ISO guidance so bending strain stays below 3–5%. Even minor axial mismatch introduces a shear vector and can cause premature delamination at the grip edge.

### 3. Strain tracking and modulus evaluation

Composites exhibit minimal elongation before catastrophic failure — crosshead displacement alone is unsuitable for modulus.

- **Modulus range:** [Young's modulus](/resources/glossary/youngs-modulus/) must be isolated between **0.05% and 0.25%** strain on both ISO 527-4 and ISO 527-5.
- **Biaxial extensometry:** Capture axial strain (modulus) and transverse strain (Poisson's ratio) with non-contact video extensometers or high-resolution clip-on biaxial sensors, controlled natively by Tesla Test Software on the [50 kN](/products/material-testing/universal-testing-systems/universal-testing-machine-50kn/) and [300 kN](/products/material-testing/universal-testing-systems/universal-testing-machine-300kn/) platforms. [EN ISO 9513 Class 1](/resources/glossary/extensometer/) compliance (Class 0.5 for high-stiffness UD) is mandatory.

## Quantitative test parameter matrix

| Technical parameter | ISO 527-4 | ISO 527-5 (UD) |
| --- | --- | --- |
| Material profile | Isotropic / orthotropic (woven, mats) | Unidirectional (0° or 90° fibre run) |
| Standard test speed | 2 mm/min (1–10 mm/min optional) | 2 mm/min for strength / modulus |
| Modulus strain limits | 0.05% – 0.25% | 0.05% – 0.25% |
| Extensometer class | Class 1 or better (ISO 9513) | Class 1 or Class 0.5 for high stiffness |
| Load cell accuracy | Class 0.5 per [ISO 7500-1](/resources/standards/iso-7500-1/) | Class 0.5 per ISO 7500-1 |
| Tab configuration | Optional Type 1; mandatory Type 2 / 3 | Mandatory (0° or 90° composite tabs) |

## Process timeline and data capture

1. **Specimen preparation** — Cut laminates cleanly; glue standardized tab blocks with high-shear epoxy after sanding and degreasing bond faces.
2. **Alignment and clamping** — Secure the coupon in hydraulic grips; verify zero pre-load tension on the load cell.
3. **Sensor contact / video calibration** — Attach biaxial clip-on gauges or align Tesla video extensometer target markers across the gauge length.
4. **Automated test run** — Execute at 2 mm/min; Tesla plots [stress vs. strain](/resources/glossary/stress-strain-curve/) and locks the 0.05%–0.25% modulus window.
5. **Break detection** — High-frequency break algorithms register catastrophic failure, compute [ultimate tensile strength](/resources/glossary/ultimate-tensile-strength/), and archive traceable results.

For low-force laminates, coupon films, or R&D coupons below ~10 kN, the [2 kN benchtop UTM](/products/material-testing/universal-testing-systems/universal-testing-machine-2kn/) covers the same ISO strain-range logic at Class 0.5 accuracy.

## Error-prone points and corrective actions

**Misalignment-driven shear failures** — Specimen sits crookedly in the jaws; fracture occurs at the grip edge instead of the gauge section.

*Correction:* Use Vector mechanical grip-alignment fixtures. Discard any test where fracture touches the jaw face; re-check alignment parameters.

**Extensometer slippage on hard matrix surfaces** — Clip-on knife edges slide on glossy epoxy-coated carbon faces during the modulus transition.

*Correction:* Increase spring retention force or switch to the Tesla non-contact video extensometer, which tracks contrast markers without contacting the sample.

**Tab debonding** — Adhesive failure between tab and composite before true ultimate strength.

*Correction:* Sand and degrease both bonding surfaces; use structural epoxy and respect full cure times before testing.

**Incorrect strain range for modulus** — Slope taken across an arbitrary force window instead of the ISO 0.05%–0.25% boundaries.

*Correction:* Tesla Test Software macros lock automatically onto the mandated strain coordinates for repeatable, audit-ready modulus reporting.

## Quick review for lab inspectors

**Why is a high sampling rate mandatory for composites?** Composites fail catastrophically and almost instantly. A low acquisition rate can miss the true peak force and under-report tensile strength. Vector frames sample at up to 5 kHz on the [300 kN platform](/products/material-testing/universal-testing-systems/universal-testing-machine-300kn/).

**What does a low Poisson's ratio indicate in an orthotropic weave?** It reflects fibre orientation — high resistance to lateral contraction along the tested plane.

### Self-test

**Q:** What is the structural distinction between ISO 527-4 and ISO 527-5?

**A:** ISO 527-4 covers multidirectional, woven, or chopped-fibre mats (isotropic/orthotropic). ISO 527-5 applies exclusively to continuous unidirectional designs where alignment with the fibre run is absolute.

**Q:** How does Tesla Test Software protect high-capacity load cells during composite fracture?

**A:** Break-detection algorithms monitor immediate load drop-off; the moment structural failure occurs, hydraulic servo valves relax to absorb the reactive shockwave safely.

## Summary

Mastering composite characterization under ISO 527-4 and ISO 527-5 requires frame rigidity, verified alignment, and Class 1 extensometry. A Vector UTM paired with Tesla Test Software removes grip slippage, axial misalignment, and tracking lag from the measurement chain — giving aerospace, automotive, and wind-energy teams audit-ready tensile data on tabbed composite coupons.