ISO 15024 Mode‑I Interlaminar Fracture Toughness GIC Test for Unidirectional Fibre‑Reinforced Composites

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ISO 15024 DCB Tester | Mode I Interlaminar Fracture Toughness GIC | UnitedTest

ISO 15024 describes the double cantilever beam (DCB) test to measure Mode I interlaminar fracture toughness GIC of unidirectional fibre-reinforced plastic composites. UnitedTest manufactures ISO 15024 compliant DCB test machines for composite delamination resistance evaluation.

ISO 15024 establishes the double‑cantilever‑beam (DCB) test method for determining Mode I interlaminar fracture toughness GIC of unidirectionally fibre-reinforced plastic composites. GIC, also known as critical energy release rate with units J/m², characterizes a composite material’s ability to resist opening-mode delamination crack initiation and crack propagation between composite laminate plies. This test is essential for assessing the interlaminar bonding quality and damage tolerance of fibre composite laminates.

It is widely used in aerospace, automotive, wind energy and advanced composite R&D laboratories for material screening, laminate formulation optimization and structural component qualification. UnitedTest designs and manufactures high-precision ISO 15024 DCB testing machines, delivering stable loading and accurate crack growth monitoring for fibre-reinforced composite specimens.

Test Principle

A DCB specimen contains a thin non-adhesive starter film (≤ 13 µm) at the laminate mid-plane, simulating an initial delamination.

An opening (mode I) load is applied perpendicular to the delamination plane, through load blocks, piano hinges (or insert hinges), under displacement control at constant rate.

The specimen is loaded until the first increment of crack growth from the insert, then unloaded — this creates a sharp mode I precrack (the as-moulded film tip is too blunt to give a representative value).

It is then re-loaded and the stable delamination growth is monitored; load, displacement and delamination length are recorded at defined points.

Data reduction gives initiation values (from the insert and from the precrack) and propagation values, plotted as a delamination-resistance curve (R-curve): G_IC vs. delamination length a. The standard explicitly notes that fibre bridging is the main cause of the rising R-curve shape and may not be representative of the composite itself.

Two Specific Test Methods

Two authorised calculation approaches convert load‑displacement‑crack‑length data to G_IC: Corrected Beam Theory (CBT, Method A) and Modified Compliance Calibration (MCC, Method B). Both apply large‑displacement correction factor F; load‑block correction factor N applies for load‑block fixtures (N=1 for piano hinges).

Three characteristic initiation points are defined on load‑displacement traces:

NL point: Deviation‑from‑linearity point

VIS point: Visually‑observed delamination‑onset point

5 %/MAX point: Whichever occurs first: 5 % compliance increase or maximum load point

PROP points: Discrete stable crack‑propagation points for R‑curve construction (minimum 15 valid PROP points required).

Test Specimen Specifications

Preferred specimen dimensions

Parameter	Carbon‑fibre composite	Glass‑fibre composite	Tolerance
Width b	20 mm	20 mm	± 0.5 mm
Total length l, minimum	125 mm	125 mm	—
Total thickness h	3 mm	5 mm	± 0.1 mm

Insert tip must be ≥ 45 mm from the near end of the load block/hinge; insert length measured on both edges

Minimum 5 valid specimens (invalid ones replaced); 6 recommended when testing a new material or an inexperienced operator.

Required Test Equipment of ISO 15024 DCB Mode I Interlaminar Fracture Toughness (GIC) Testing of Fibre-reinforced plastic composites

Constant-speed Universal Testing Machine (UTM)	Displacement‑controlled, force‑measurement meets ISO 7500‑1 Class 1; displacement‑measurement meets ISO 9513 Class 2; cross‑head speed tolerance ±20 %; machine‑compliance compensation is needed when using cross‑head displacement signal.
Loading fixtures	Three loading alternatives are permitted: - Load blocks (max block length l3=15mm; - Piano hinges; - New flat insert‑hinge fixture (Refer Annex D, no adhesive bonding to specimen) Fixtures must allow free rotation of the specimen end and align with the machine loading axis.
Consumables & auxiliary equipment	Non‑adhesive starter‑insert polymer film (max thickness 13 μm; PTFE for cure < 180 °C; polyimide for cure > 180 °C); Desiccator, release agent, cyanoacrylate / two‑component room‑temperature epoxy adhesive, solvent (acetone / ethanol), ≥ 500‑grit abrasive paper, water‑soluble white marking fluid for specimen edges
Video non-contact extensometer	0–200 mm travel, magnification ≤ ×70, readable to 0.05 mm (can be automated with a position sensor)

Key Test Parameters & Mandatory Stipulations:

1. Displacement‑rate settings:

Initial loading: 1–5 mm/min (displacement‑controlled).

Unloading rate: maximum 25 mm/min.

Re‑loading rate: same 1‑5 mm/min as initial loading.

2. Crack‑growth control:

Initial pre‑crack growth: stop initial loading after delamination extends 3–5 mm beyond starter‑film tip.

Re‑loading propagation requirement: delamination must propagate ≥ 45 mm past pre‑crack tip (total 50 mm maximum beyond pre‑crack tip).

Crack‑length measurement accuracy: at least ± 0.5 mm.

Validity warning: discard result if delamination migrates away from laminate mid‑plane; report if crack‑tip positions on two specimen edges differ > 2 mm (indicates asymmetric loading).

Step by step Test Procedure of ISO 15024 DCB Mode I Interlaminar Fracture Toughness (GIC) Testing of Fibre-reinforced plastic composites

Specimen preparation: Fabricate composite plate with mid‑plane non‑adhesive insert‑film; machine DCB coupons; measure dimensions; mark edges for crack‑length reading; bond load‑blocks / piano‑hinges (Annex A).
Conditioning: Dry coupons, short‑term desiccator storage before test.
Test setup: Mount specimen on test‑machine fixture under ISO 291 standard laboratory atmosphere.
Initial loading: Apply displacement‑controlled loading (1‑5 mm/min); record continuous load‑displacement; visually track delamination growth; capture VIS‑point; stop loading after stable 3‑5 mm pre‑crack extension; unload at ≤ 25 mm/min; mark pre‑crack tip positions on both specimen edges.
Re‑loading: Re‑load at same 1‑5 mm/min cross‑head speed without intermediate stops; synchronously record load, displacement and delamination‑length at every marked position (dense 1‑mm sampling for first 5 mm and final 5 mm propagation, 5‑mm steps in‑between). Continue until delamination extends to 45‑50 mm past pre‑crack tip; unload; mark final crack‑tip positions.
Data processing: Identify NL, VIS, 5 %/MAX initiation points and stable PROP propagation points. Compute G_IC by either CBT or MCC with correction factors F and N. Generate R‑curve of G_IC against delamination length. Calculate mean, standard deviation and coefficient‑of‑variation for initiation‑point values across replicate specimens.

ISO 15024 DCB Mode I Interlaminar Fracture Toughness (GIC) Testing of Fibre-reinforced plastic composites

Before starting Condition of constant opening

Industrial Application Fields

Aerospace — primary user: G_IC is a material qualification and design-allowable property for damage-tolerance analysis of CFRP structures; OEMs run their own variants (Airbus AITM 1-0005, Boeing BSS 7273 — both using an area method rather than CBT/MCC).
Wind energy — delamination resistance of blade laminates and bondlines; root/spar-cap and adhesive-joint development.
Automotive, rail, marine, pressure vessels/pipes — CFRP/GFRP toughness screening; referenced by EN ISO 23936-4 for composites in oil & gas service.
Materials R&D and QC — quantifying the effect of fibre sizing/surface treatment, matrix toughening (thermoplastic particles, interlayers), fibre volume fraction, processing/cure, moisture and temperature; batch release and supplier comparison.

Related Test Standard:

ISO 15024	Fibre-reinforced plastic composites. Determination of mode I interlaminar fracture toughness, GIC, for unidirectionally reinforced materials
ASTM D5528	The primary US‑standard DCB Mode‑I test for unidirectional composites, functionally analogous to ISO 15024. Differences: ASTM D5528 uses Compliance‑Calibration (CC) as main evaluation method, whereas ISO 15024 provides CBT and MCC calculation options; ISO 15024 includes mandatory pre‑cracking load‑unload cycle and defines NL‑VIS‑5 %/MAX multiple initiation criteria
GB/T 28891	Fibre-reinforced plastic composites - Determination of mode Ⅰinterlaminar fracture toughness GⅠC for unidirectionally reinforced materials
ISO 15114	Fibre-reinforced plastic composites - Determination of the mode II fracture resistance for unidirectionally reinforced materials using the calibrated end-loaded split (C-ELS) test and an effective crack length approach
GB/T 39484	Fibre-reinforced plastic composites—Determination of the mode Ⅱ fracture resistanc for unidirectionally reinforced materials using the calibrated end-loaded split(C-ELS) test and an effective crack length approach
ISO 25217	DCB‑based Mode‑I test for structural adhesive joints (adhesive fracture energy, for bonded joints, not composite interlaminar delamination)
ASTM D7905	Mode II using the End-Notched Flexure (ENF) test with compliance calibration
ASTM D6671	Mixed-mode I/II interlaminar toughness via Mixed-Mode Bending (MMB); also uses NL and 5 %/Max definitions
ASTM D6115	Mode I fatigue delamination-growth onset (G–N curve) using the same DCB specimen
JIS K 7086	Japanese DCB method for interlaminar fracture toughness of CFRP (modified compliance method)

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WDW Series Computer Control Electronic Universal Testing Machine made by UNITEDTEST range from 100N to 600KN load capacity with various models like single columns, table type, door frame type etc., is used to perform tension, compression, flexure/bending, shearing, peeling etc., test for metal and nonmetal specimens.

Video extensometer, is a non-contact real-time high-precision strain measurement system, which is based on a separate camera and real-time image processing algorithm, by taking images of the experimental process, analyzing image characteristic changes, dynamically measuring the strain changes.

Thin Plastic Film Tensile Testing Fixture is specially designed for tensile strength testing of flexible and soft plastic film specimens. Fully compliant with the ASTM D882 standard for thin film tensile testing, the fixture features premium rubber-coated jaws.

ISO 15024 Mode‑I Interlaminar Fracture Toughness GIC Test for Unidirectional Fibre‑Reinforced Composites | UnitedTest DCB Test Machine

Q1: What is ISO 15024 test?

A: ISO 15024:2023 is an international standard test method that uses a Double Cantilever Beam (DCB) specimen to measure Mode‑I interlaminar fracture toughness G_IC (critical energy release rate, unit J/m²) for unidirectional fibre‑reinforced polymer‑matrix composites. It evaluates a composite’s resistance to opening‑mode delamination crack initiation and crack propagation between laminate plies.

Q2. Why this test matters for the material?

A: Delamination is the dominant life-limiting failure mode of laminates. A composite laminate has essentially no through-thickness reinforcement, so its interlaminar (matrix-dominated) strength is orders of magnitude lower than its in-plane fibre-dominated strength. Impact, ply drops, free edges, bolt holes and manufacturing defects all translate into delaminations that can grow under out-of-plane opening (mode I) — the most damaging and most common driving mode.

G_IC is a geometry-independent material property (J/m²), unlike a strength value, so it can be used directly as a design allowable and as a failure criterion in damage-tolerance and durability analyses, and compared across materials, processes and suppliers.

It is the standard metric for matrix and interface development. Matrix toughening, thermoplastic interlayers, z-pinning/stitching, fibre sizing and cure cycle changes are all judged primarily by the G_IC initiation value they deliver; the R-curve reveals the fibre-bridging contribution that raises apparent toughness with crack length.

It feeds simulation. Cohesive-zone and VCCT delamination models require G_IC (and G_IIC, G_IIIC / mixed-mode data from ISO 15114 and ASTM D6671) as direct inputs — without measured values, virtual testing of impact and compression-after-impact behaviour is not credible.

It is moisture- and temperature-sensitive, which is exactly why the standard mandates drying/conditioning and ISO 291 test atmospheres — guaranteeing that the number reported for a material means the same thing in every laboratory.

Certification and supply-chain control. Aerospace and wind OEM qualification plans, material datasheets and batch acceptance testing all require a standardized, reproducible G_IC — which is why ISO 15024 exists alongside ASTM D5528 and the OEM-specific methods.

Q3: What materials does ISO 15024 apply to? Are multi‑directional laminates allowed?

A: This standard only applies for 0° unidirectional composite laminates with even ply counts, including carbon‑fibre / glass‑fibre thermoset and thermoplastic composites. Multi‑angle / multi‑directional lay‑ups are NOT recommended. Multi‑directional laminates cause anti‑clastic bending and crack branching away from mid‑plane, making test results invalid.

Q4: What starter insert film shall I select?

A: Max thickness ≤ 13 μm.

Curing temperature below 180 °C (epoxy thermoset): use PTFE film.
Curing temperature above 180 °C (polyimide, bismaleimide, high‑temp thermoplastic): use polyimide (Kapton‑type) film. For polyimide film, apply PTFE‑type mould‑release agent and bake twice before embedding into laminate (5.5, Annex B.2).

Q5: How many specimens need to be tested for ISO 15024 test?

A: Minimum 5 valid specimens. Invalid specimens (delamination deviates from mid‑plane, fixture bond failure, asymmetric crack tip > 2 mm difference on two edges) shall be discarded and replaced by new coupons.

Q6: What displacement rate should I run for ISO 15024 DCB test?

A: Loading / re‑loading displacement rate: 1–5 mm/min (displacement‑controlled). Unloading rate maximum 25 mm/min

Q7: What is Mode‑I pre‑cracking? Can I use wedge pre‑cracking?

A: Standard pre‑cracking procedure: initial loading until delamination grows 3‑5 mm beyond starter‑film tip → unload → mark pre‑crack tip → then re‑load for propagation measurement. This is mandatory for ISO 15024. Wedge pre‑cracking is atypical alternative, NOT recommended. If wedge pre‑cracking is used, you must report this deviation explicitly; off‑mid‑plane pre‑crack will invalidate results.

Q8: Two calculation methods: CBT and MCC, which one to choose?

A: ISO 15024 permits either Method A: Corrected Beam Theory (CBT) or Method B: Modified Compliance Calibration (MCC); both produce equivalent results. You need to stick with one method for a complete test batch. Both require large‑displacement correction factor F; load‑block correction factor N applies for load‑block fixtures (N=1 for piano hinges). If F<0.9, note this in your final test report.

Q9: Why does my R‑curve keep rising? Is that abnormal?

A: Rising R‑curve is very common for unidirectional DCB test, mainly caused by fibre‑bridging inside delamination crack. Fibre bridging is test‑induced artefact rather than intrinsic material property. The R‑curve normally rises and plateaus at larger delamination length.

Q10: My specimen shows unstable stick‑slip delamination growth. What to do?

A: Stick‑slip (sudden fast crack jump together with sharp load drop) shall be noted in test report. You cannot collect valid PROP points during unstable crack jump. If most propagation data is lost, the specimen will be invalid.

Q11. What is the difference between ISO 15024 and ASTM D5528?

A: Both use the same DCB specimen and mode I principle, but differ in initiation criteria and data reduction: ISO 15024 reports NL, VIS and 5 %/MAX and reduces data by CBT or MCC; ASTM D5528 uses Compliance Calibration (CC) as its main method and, in its current edition, only the 5 %/MAX compliance criterion for initiation.

Other differences: ISO 15024:2023 adds the flat insert hinge option (Annex D) and requires force to ISO 7500-1 class 1 and displacement to ISO 9513 class 2. In practice most laboratories can satisfy both standards on the same machine with the same fixture set, provided the software can run CBT, MCC and CC. Aerospace OEM methods — Airbus AITM 1-0005 and Boeing BSS 7273 — use a further variant, the area method.

Q12: Can the same machine test mode II and mixed-mode delamination?

A: Yes. ISO 15024 shares the same universal testing machine and DCB-style specimen preparation as the other delamination tests — adding the appropriate fixtures lets one frame cover ISO 15114 / ASTM D7905 (mode II) and ASTM D6671 (mixed-mode I/II).

In detail: That is why a modular frame with interchangeable fixtures, a low-capacity load cell and software supporting several data-reduction schemes is the most economical configuration for a composites laboratory. UnitedTest frames are configured this way.

Q13. What capacity of testing machine do I need for ISO 15024?

A: Delamination loads are normally below 500 N, so a 1 kN or 2 kN electromechanical frame fitted with a 100 N–1 kN load cell is the right size. Oversizing the load cell is the most common cause of noisy GIC data.

What matters more than capacity is resolution and control: constant crosshead speed held within ±20 % over 1–5 mm/min, plus unloading at up to 25 mm/min; force accuracy to ISO 7500-1 class 1; displacement to ISO 9513 class 2; and low machine compliance (or compliance compensation) so the recorded opening displacement is trustworthy.

Q14: Why choose UnitedTest ISO 15024 DCB Test Machine, Mode‑I Interlaminar Fracture Toughness G_IC Tester for Unidirectional Fibre‑Reinforced Composites?

A: UnitedTest is professional manufacturer of ISO 15024:2023 DCB (Double Cantilever Beam) test system for measuring Mode‑I interlaminar fracture toughness G_IC of unidirectional CFRP / GFRP composites. Complete DCB fixtures: load‑blocks, piano‑hinges and flat insert‑hinge set, built‑in CBT / MCC calculation algorithm for R‑curve generation, ideal for aerospace, wind‑energy composite lab R&D & QC.

UnitedTest supplies complete turn‑key ISO 15024 DCB test machine for determining Mode‑I interlaminar fracture toughness G_IC, critical energy release rate) for unidirectional fibre‑reinforced polymer composites (carbon‑fibre CFRP, glass‑fibre GFRP thermoset & thermoplastic laminates).

Our composite DCB test system fully complies with latest ISO 15024 international standard, supports three loading configurations: load‑blocks, piano‑hinges and the newly‑added flat insert‑hinge fixture. It can run the full DCB workflow including initial loading, mandatory Mode‑I pre‑cracking, re‑loading crack‑propagation test, synchronous recording load‑displacement and delamination‑length data.

Key Features

✅ Pre‑integrated CBT (Corrected Beam Theory) and MCC (Modified Compliance Calibration) calculation algorithms, automatically compute NL / VIS / 5 %/MAX initiation G_IC values and PROP propagation values; auto‑generate R‑curve (delamination‑resistance curve) and export ISO‑compliant test‑report template.

✅ High‑accuracy force sensor meets ISO 7500‑1 Class 1; displacement resolution satisfies ISO 9513 Class 2; supports machine‑compliance compensation.

✅ Complete ISO‑15024 fixture kit: interchangeable load‑blocks, piano‑hinge assembly, flat insert‑hinge set, specimen marking tools; fixture guarantees free‑rotation of DCB specimen end.

✅ Optional travelling microscope / video crack‑tracking module for accurate delamination‑length measurement (± 0.05 mm reading).

✅ Configurable cross‑head speed range (0.1‑500 mm/min): strictly follows 1‑5 mm/min loading rate requirement of ISO 15024.

✅ Statistical output: mean value, standard deviation, coefficient‑of‑variation CV for replicate specimens, supports batch‑test processing for minimum 5‑specimen‑test requirement.

Application Fields

UnitedTest ISO 15024 DCB test equipment serves composite R&D labs, third‑party testing institutes, aerospace material qualification labs, wind‑turbine blade manufacturers, automotive lightweight composite departments. It is widely used for composite material formulation screening, incoming‑material QC, environmental ageing research and finite‑element‑simulation parameter acquisition for delamination damage modelling.

Compatible comparative standard: also supports ASTM D5528 DCB Mode‑I G_IC test. UnitedTest can customize fixture and software functions according to your laboratory requirement.

We offer customization to meet your specific needs. Our expert team will collaborate with you to develop the perfect product for you