ISO 844 Rigid Cellular Plastics Compression Test

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ISO 844 Rigid Cellular Plastics Compression Properties Tester | UnitedTest

UnitedTest manufactures professional ISO 844 compliant compression test machines dedicated to evaluating the compressive mechanical properties of rigid cellular plastics for foam material quality control and laboratory research.

ISO 844 Rigid cellular plastics — Determination of compression properties provides unified, globally standardized test methods for rigid closed-cell and open-cell foam plastics. This standard eliminates inter-laboratory test data discrepancies, enabling accurate and consistent global comparison of rigid foam material compressive performance.

ISO 844 testing captures four essential compressive mechanical indicators: compressive strength, corresponding relative deformation, compressive stress at 10% nominal deformation, and compressive elastic modulus. Designed to deliver stable, repeatable mechanical test data, our ISO 844 compression tester supports precise material grading, product formulation optimization, and industrial performance certification for all types of rigid cellular plastics.

Core Test Principle

Uniaxial compressive force is applied perpendicularly to the two parallel flat faces of a rigid cellular plastic specimen at constant speed. The machine records real-time force (F) and displacement (x) to generate a force-displacement curve.

Procedure A calculates nominal strain from total crosshead travel (includes machine deflection error)

Procedure B calculates true local strain via extensometer readings directly on the foam body

From the linear elastic segment and peak point of the curve, compressive strength, deformation, 10% strain stress, and elastic modulus are calculated via standardized formulas.

ISO 844 Rigid Cellular Plastics Compression Test

Two Specific Test Methods

Procedure A (Crosshead Displacement Method, Nominal Property Test)

Measurement basis: Displacement of the testing machine’s movable crosshead platens (not direct specimen strain measurement)

Target measurable properties:

Compressive strength σₘ + nominal relative deformation ε_Cm at peak load

Compressive stress σ_C10 at 10% nominal relative deformation

Nominal compressive elastic modulus E_C

Procedure B (Extensometer Direct Strain Method, True Property Test)

Measurement basis: Contact/optical extensometer clamped directly on the specimen to capture local foam deformation (eliminates machine frame displacement error)

Target measurable properties:

Compressive strength σₘ + true relative deformation εₘ at peak load

True compressive elastic modulus E (higher accuracy for engineering design)

ISO 844 Compression Test Specimen Information:

Preferred dimensions

Preferred specimen: Square right prism, 100 ±1 mm × 100 ±1 mm base, thickness h₀ = 50 ±1 mm

Alternative allowable shape: Square/circular base; cross-sectional area range 25 cm² ~ 230 cm²

Thickness limits:

General foam: Minimum 20 ±1 mm

Foam with integral molded skins: Full product thickness, minimum 10 mm, thickness ≤ specimen width/diameter

Quantity

At least 5 specimens unless the product specification states otherwise.

Preparation

Cut so the base is normal to the intended compression direction.

Avoid altering cellular structure (use appropriate cutting methods).

ISO 844 Rigid Cellular Plastics Compression Test required Testing Equipment:

Universal Test Machine

Force system compliance: Class 1 per ISO 7500-1

Displacement recording accuracy: ±5% or ±0.1 mm (whichever stricter)

Continuous F-x curve recording function to capture force-displacement data for post-calculation.

Parallel compression platens

Two parallel, polished square/circular steel platens fully covering the specimen base;

Platen specifications: Surface roughness Ra ≤0.4 μm; steel thickness ≥8 mm along loading direction.

Compression deformation meter

For modulus, High‑precision deformation measurement

Key Test Procedures of ISO 844 Rigid Cellular Plastics Compression Test:

1, Pre-condition specimens for ≥6 hours under standardized temperature/humidity.

2, Measure length, width, thickness of each specimen per ISO 1923, record initial cross-sectional area A₀ and initial thickness h₀/gauge length l₀.

3, Mount specimen centrally on compression platens; attach extensometer to specimen if running Procedure B.

4, Set test speed to 10% of original thickness per minute, start machine compression.

5, Synchronously record full force-displacement curve until peak force or 10% nominal deformation is achieved.

6, Stop compression, remove tested specimen, repeat steps 2–5 for all replicate samples.

7, Process curve data: Apply zero-deformation correction as required; identify linear elastic segment (25%–75% max load) via least-square fitting.

8, Calculate target properties using standard formulas:

Compressive strength: σₘ = Fₘ / A₀

10% nominal strain stress: σ_C10 = F₁₀ / A₀

9, Nominal modulus E_C and true modulus E from linear stress-strain slope

Key Test Parameters:

Parameter	Value / Requirement
Test speed	As close as possible to 10 % of original thickness per minute (e.g., 5 mm/min for 50 mm thick specimen)
Temperature/Humidity	Same as conditioning environment
Zero‑deformation point (Procedure A)	Extrapolate steepest straight‑line portion of F‑x curve to zero force; if not feasible, use deformation at stress (250 ± 10) Pa
Toe compensation (Procedure B)	Only if a toe is observed at curve start
Modulus calculation window	Most linear steepest part between 25 % and 75 % of maximum load (least‑square fit)

Specimen centering: Place specimen perfectly centered between two platens to avoid eccentric loading.

Anisotropy control: Separate test batches required for each principal material direction if foam exhibits directional mechanical differences.

Industry Application Fields:

ISO 844 testing is the universal mechanical characterization standard for rigid cellular plastics (rigid PU/PIR insulation, EPS/XPS foam, phenolic foam, structural rigid foam composites):

Construction & Building: Thermal insulation boards, roof/floor foam panels, structural load-bearing foam cores; evaluates compression resistance under floor/wall static load.

Packaging Industry: Rigid protective foam inserts, shock-absorbing transport packaging; verifies cushioning performance under stacking compression.

Automotive & Aerospace: Lightweight structural foam components, energy-absorbing crash foam, interior rigid foam parts; lightweight high-stiffness material screening.

Refrigeration & Cold Chain: Foam insulation for refrigerators, cold storage panels; long-term compressive creep resistance validation.

Industrial Manufacturing & R&D: New foam formulation development, batch quality control, raw material incoming inspection, third-party material certification.

Medical Equipment: Rigid foam medical transport trays, sterile protective packaging.

ISO 844 Rigid Cellular Plastics Compression Test

Related Test Standard

ISO 844	Rigid cellular plastics — Determination of compression properties
ASTM D1621	Standard Test Method for Compressive Properties of Rigid Cellular Plastics
GOST 23206	Rigid cellular plastics. Determination of compression properties
GB/T 8813	Rigid cellular plastics—Determination of compression properties
UNE 53190	Cellular plastics. Determination of tensile properties of rigid materials.
ASTM D695	Standard Test Method for Compressive Properties of Rigid Plastics
AS 2498.3	Methods of testing rigid cellular plastics, Method 3: Determination of compressive stress
ISO 7616	Cellular plastics, rigid-Determination of compressive creep under specified load and temperature conditions
ASTM C365	Standard Test Method for Flatwise Compressive Properties of Sandwich Cores
EN 826	Thermal insulating products for building applications. Determination of compression behaviour
ISO 1856	Flexible cellular polymeric materials - Determination of compression set
DIN 53421	Testing of rigid cellular plastics; compression test

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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.

Compression test fixture is used to investigate the compressive behaviour of the test specimens and for determining the compressive strength, compressive modulus and other aspects of the compressive stress/strain relationship under the conditions defined.

Q1: What is the core purpose of ISO 844 test?

A1: ISO 844 standardizes uniaxial compression testing for rigid foam plastics to measure compressive strength, compressive stress at 10% deformation, and compressive elastic modulus. It provides uniform, repeatable mechanical data for rigid cellular materials to eliminate lab-to-lab test discrepancies.

Q2: What is the difference between Procedure A and Procedure B in ISO 844?

A2: Procedure A uses crosshead displacement for nominal strain calculation, for routine QC and batch screening, simpler operation with lower precision.

Procedure B mounts an extensometer directly on the specimen to capture true local strain, delivering high-accuracy modulus data for engineering design, material R&D and simulation input.

Q3: Can I stack multiple thin foam pieces to reach the standard specimen thickness of 50 mm?

A3: No. ISO 844 explicitly prohibits stacking thin specimens. Stacking creates inconsistent contact friction and uneven load distribution, which leads to inaccurate compressive strength and modulus results. Prepare single solid foam blocks that meet the required thickness range.

Q4: Why must specimens undergo pre-conditioning before ISO 844 compression testing?

A4: Rigid foam’s compressive performance is highly sensitive to temperature and humidity. ISO 291 standardized conditioning removes residual moisture and stabilizes cell structure. Without conditioning, test data will drift, making cross-batch or cross-supplier comparisons invalid. The minimum conditioning time is 6 hours at 23°C / 50% RH as the primary standard atmosphere.

Q5: Why is ISO 844 compression test critical for construction rigid foam insulation (XPS/EPS/PIR)?

A5: Building foam boards bear long-term static loads from floors, roofs and wall finishes. ISO 844’s compressive strength and 10% deformation stress data quantify resistance to permanent crushing. Insulation failing this test will sag, lose thermal performance and cause structural flatness defects after years of service; construction product certifications globally require ISO 844 reports.

Q6: What test speed is mandatory under ISO 844?

A6: The compression crosshead speed must equal 10% of the specimen’s original thickness per minute. For a standard 50 mm thick sample, the speed is fixed at 5 mm/min. Fixed speed ensures uniform strain rate across all labs and materials.

Q7: How many replicate specimens are required for one material batch?

A7: A minimum of 5 identical specimens shall be tested per material group. If the foam is anisotropic (different compression performance along different production directions), prepare separate 5-specimen sets for each principal loading axis.

Q8: What is the difference between ISO 844 and ASTM D1621?

A8: Both test compressive properties of rigid cellular plastics, but they differ in key parameters:

ISO 844 uses 10% thickness/min test speed; ASTM D1621 uses 0.1 in/min fixed speed regardless of specimen size.

ISO 844 defines two test procedures for nominal/true modulus; ASTM D1621 only provides a single compression method.

Pre-conditioning environments and specimen dimension tolerances have separate requirements. Data from the two standards cannot be directly interchanged.

Q9: Can ISO 844 be used for flexible polyurethane foam?

A9: No. ISO 844 exclusively targets rigid closed-cell / open-cell cellular plastics. Flexible soft foams use ISO 1856 (compression set) or ASTM D3574 instead, as their deformation and failure mechanisms do not match rigid foam test logic.

Q10: Why do we need the compressive stress value at 10% nominal deformation?

A10: Most foam insulation and packaging materials are not allowed to deform more than 10% under long-term service loads. This parameter predicts the material’s anti-crushing performance under normal working load, rather than ultimate breaking strength, making it more relevant for real-world service life assessment.

Q11: Why is ISO 844 important for rigid foam materials?

A11: Because rigid cellular plastics are widely used as insulation, wall sheathing, roofing, packaging cushioning, and structural sandwich cores, their behaviour under compressive load directly decides whether a product is safe and fit for purpose. ISO 844 gives a single, internationally agreed method to measure:

Compressive strength (σₘ) – the maximum load the foam can bear

Relative deformation at that strength (εₘ / ε_Cm) – how much it crushes

Compressive stress at 10 % nominal strain (σ₁₀) – a design-relevant working point

Compressive modulus (E / E_C) – stiffness for structural calculation

These data feed directly into R&D formulation optimization, incoming material QC, batch-to-batch consistency checks, and compliance with building/product specifications. Without a harmonised method, suppliers and buyers would have no common language to compare foam grades .

Q12: Why is specimen parallelism strictly controlled in ISO 844?

A12: Uneven, non-parallel specimen faces create eccentric loading during compression. Eccentric force causes local stress concentration, prematurely breaking the foam sample and lowering measured compressive strength and modulus, resulting in false low performance results. The thickness variation between opposite faces cannot exceed 1% of total thickness.

Q13: How does ISO 844 data support lightweight automotive foam component design?

A13: Procedure B’s high-precision elastic modulus values are used as input parameters for finite element (FEA) crash and structural simulations. Engineers rely on ISO 844 data to balance lightweight foam weight with crash energy absorption and static load bearing capacity for automotive interior and bumper foam parts.

Q14: What if one specimen’s test result deviates more than 10% from the group average?

A14: ISO 844 requires all individual specimen values to be fully listed in the final test report, not only the average value. Technicians must inspect the outlier sample for cutting damage, surface defects or off-center loading to identify the root cause of deviation.

Q15: Is ISO 844 identical to EN 826?

A15: Yes. BS EN ISO 844 (EN 826) is the European regional identical adoption of the global ISO 844 standard under the CEN-Vienna Agreement. Test methods, specimen rules and calculation formulas are fully consistent, so ISO 844 reports are accepted for EU construction material CE marking.

Q16: What is "toe compensation" and when is it needed?

A16: At the start of a compression curve, a non-linear "toe" region can appear due to minor gaps or seating effects. For Procedure A, the steepest straight-line portion is extrapolated to zero force to define the zero-deformation point; if no clear straight portion exists, use the deformation at (250 ± 10) Pa stress. For Procedure B, toe compensation is applied only when a toe is actually observed.

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