ISO 34-2 Rubber and Elastomers Tear Test

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Tear & Shear Test evaluates material resistance to tearing and shearing forces, measuring critical strength parameters for quality control. Tear tests (Elmendorf/trouser/trapezoidal) assess resistance to crack propagation in films/fabrics, while shear tests measure resistance to parallel forces in joints/bolts. UnitedTest provides universal testing machines (10KN-600KN) with specialized fixtures for both tests, compliant with ASTM D624/D3164 and ISO standards, serving automotive, packaging and construction industries.

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ISO 34-2 Rubber, vulcanized or thermoplastic. Determination of tear strength. Small (Delft) test pieces

ISO 34-2 specifying tear strength testing for vulcanized and thermoplastic rubber. It defines Delft small rectangular specimens for limited material or tiny finished rubber parts, and test data from the two parts cannot be directly correlated due to distinct specimen configuration and loading mode.

(When the amount of material is limited (small finished products, thin sections, expensive compounds); uses a much smaller rectangular coupon with a pre-cut slit)

Test Principle

Rectangular small specimen with a centered fixed-width internal slit; tensile load pulls specimen to tear across remaining unslit rubber width, record peak tearing force and normalize into standardized tear strength via specified conversion formula accounting for actual specimen thickness and effective torn width (b₃)). Preferred when raw rubber material is scarce or only miniature finished rubber products available for QC inspection.

The force required to tear across the width of a small rectangular coupon (60 × 9 mm) containing a central slit (5.0 ± 0.1 mm long) is measured. The tearing occurs across the remaining uncut ligament b3=W−w≈ 4 mm wide, and the result is normalized to a standard width × thickness reference.

Test Mehods:

Only one uniform testing approach: rectangular specimen with symmetrical central 5.0±0.1 mm slit cut via dedicated die; two official options to calculate effective torn width b₃:

Method1 (Microscope Measurement): Section specimen at slit plane, measure left & right residual rubber width (b₁+b₂)) with travelling microscope (theoretically accurate but operationally complex).

Method2 (Die Dimension Calculation, Default): (b₃=W-w), W=total die width (9.0±0.1 mm), w=slit blade width (5.0±0.1 mm), commonly adopted for routine lab testing; results from two width measurement approaches cannot be cross-compared.

Test Specimen Info

Parameter	Detail
Shape	Rectangular: L = 60 mm, B = 9.0 ± 0.1 mm
Slit	Central slit length b = 5.0 ± 0.1 mm (cut by the die blade)
Thickness	d = 2.0 ± 0.2 mm (strict — thinner/thicker makes the geometry non-standard)
Cutting	Single press stroke / mallet blow onto yielding backing; wet with water/soap; thickness checked in slit region (≥3 readings, no reading >2% from used value)
Grain	Normally cut with grain ⊥ length; evaluate both directions if grain effects matter
Number of specimens	At least 3, preferably 6
measurement — critical:	Method 1 (traveling microscope on cross-sectioned piece — theoretically exact but impractical) vs. b (calculate b3=W-w from die dims — simpler, commonly used). Results from different methods shall NOT be compared.

ISO 34-2 Small (Delft) Specimen Tear Test Required Testing Machine (Similar like ISO 34-1)

Tensile Tensile Testing Machine: Comply fully with ISO5893: Class 1 force measurement accuracy, equipped with low-inertia electronic load cell and auto-recording system (for curve capture required by ISO6133).

Specimen matching tear grips: auto-tightening grips to avoid specimen slippage during tension, symmetric centering alignment structure for all three specimen shapes.

Calibrated Thickness Gauge: Circular foot (~6 mm diameter), applied pressure 22±5 kPa per ISO23529 specification for thickness measurement.

Specimen Cutting Press and dies: Sharp-edged custom dies with dimensional tolerance defined in respective standard drawings; single-stroke press or mallet for punching specimens (rubber can be wetted by water/soap solution for smooth cutting, supported on flexible backing board like leather/cardboard).

Dedicated Delft die (fixed W=9.0±0.1 mm, slit blade w=5.0±0.1 mm, die length＜120 mm) as defined in standard; no extra nicking tool required (slit formed during die punching in one step).

ISO 34-2 Rubber and Elastomers Tear Test - Small (Delft) Specimen

Key Fixed Test Parameters Summary

Crosshead Speed	Fixed 500±50 mm/min
Standard Test Temp	Same ISO23529 standard lab temp rule
Effective Grip Span	30 mm free length between two grips (15 mm from slit center on each side)
Thickness tolerance	≥3 thickness readings around slit, individual reading ≤2% vs specimen median; group thickness ≤10% deviation vs batch average
Vulcanization-to-test interval	Governed fully by ISO23529

ISO 34-2 Tear Test Procedure

1, Condition per ISO 23529 (time after vulcanization per ISO 23529 schedule).

2, Cut Delft pieces from sheet with the dedicated punch die; measure thickness & b₃.

3, Mount in tensile machine so free length between grip contact points = 30 mm (each grip 15 mm from the slit), slit centered in the gauge.

4, Pull at 500 mm/min without interruption until the piece tears completely through.

5, Note the maximum force F(N).

6, Calculate tear strength: ISO 34-2 Rubber and Elastomers Tear Test - Small (Delft) Specimen

8=4 mm (nominal b₃)×2 mm (nominal d)— normalizes to standard geometry

b₃= actual uncut width (mm), d= actual thickness (mm)

F₀= tear strength in newtons (N) — note: Delft reports in N, NOT kN/m like ISO 34-1.

7, Report median (or median of two middle values for even N; individual values if only 3), with all metadata.

Side-by-Side Comparison: ISO 34-1 vs. ISO 34-2

Feature	ISO 34-1 (Trouser/Angle/Crescent)	ISO 34-2 (Delft Small)
Material needed	Moderate-to-large (full sheets, larger coupons)	Very little — 60×9 mm strip
Result unit	kN/m (force/thickness)	N (normalized force to std geometry)
Primary physics	Steady-state or initiation-controlled tear propagation	Slit-initiated tear across a narrow ligament (~4 mm)
Grain sensitivity	Explicitly addressed; multiple directions recommended	Explicitly addressed; grain ⊥ length standard
Pull speeds	100 mm/min (trouser) / 500 mm/min (angle/crescent)	500 mm/min
Specimen count	≥5 (ideally 5×2 directions)	≥3, pref. 6
Nick/Cut precision	Critical for angle/crescent (±0.2 mm)	Built into die geometry (±0.1 mm)
When chosen	R&D, specification compliance, adequate material	Small molded parts, thin sections, forensic/field sampling, QC where sheet stock unavailable

Industrial Application Fields

Miniature precision molded rubber parts: electronics small rubber sealing gaskets, tiny watch rubber cushions, micro-sized medical silicone/rubber stoppers (inspect directly from finished small component without cutting large sheet).

R&D with scarce lab synthesized rubber compound (lab small-batch polymer development with limited sample output).

Post-market incoming spot inspection for tiny finished rubber spare parts where large specimen cutting is impossible due to component dimension restriction.

Related Test Standard:

ASTM D624	Standard Test Method for Tear Strength of Conventional Vulcanized Rubber and Thermoplastic Elastomers
JIS K 6252-1	Rubber, vulcanized or thermoplastic -- Determination of tear strength -- Part 1: Trouser, angle and crescent test pieces
GB/T 529	Rubber,vulcanized or thermoplastic - Determination of tear strength（Trouser，angle and crescent test pieces）
ISO 34-1	Rubber, vulcanized or thermoplastic — Determination of tear strength — Part 1: Trouser, angle and crescent test pieces
ISO 6133	Multi-peak ("knotty tear") trace analysis — required for Method A (trouser) to extract the median tearing force from oscillating traces

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.

Tear fixture ISO 505, ASTM D1004, vise grip or self-tightening roller grips are the most popular for this application and the least expensive. They can be provided with a rubber faced surface to measure the tear resistance strength of flexible plastic film and sheeting.

Electric sample punching machine is a sample preparation device designed based on the punching principle, specifically developed for preparing standard samples of sheet-like, film-like, and thin plate materials.

T-Peel Resistance Test Fixture for Adhesives is based on ASTM D1876 standard, used to measure the adhesion strength of adhesive maeterial. ASTM D1876 peel strength test method is commonly used to measure the strength of adhesive bonds between two sealed materials.

Webbing test fixture used for tensile testing of the webbing, belt test sample, determine the webbing, belt tensile strength, elongation etc., Webbing is a strong fabric woven as a flat strip or tube of varying width and fibres often used in place of rope.

Q1: What is ISO 34-2 and when would I use it instead of ISO 34-1?

A: ISO 34-2 specifies a small-scale tear test using a Delft test piece (60 mm × 9 mm rectangular strip with a 5 mm central slit). You use it when the amount of material available is limited — for example:

Small finished products (O-rings, tiny seals, thin-walled boots)

Forensic or failure analysis where only fragments remain

Expensive or scarce compounds (medical-grade silicones, specialty fluoroelastomers)

Quality control where full sheets cannot be molded

The standard explicitly notes that results do not necessarily agree with ISO 34-1 (trouser/angle/crescent methods). Use ISO 34-2 when you mustwork with small samples, but don’t expect direct numerical comparison with ISO 34-1 data.

Q2: Why is tear strength important for small rubber parts?

A: Even tiny rubber components can experience nicks during installation, handling, or service. A small O-ring with a microscopic surface flaw can tear catastrophically under pressure if the rubber lacks tear resistance. ISO 34-2 lets you quantify that resistance without needing a large molded plaque — making it indispensable for miniaturized or legacy parts where “big” test specimens simply don’t exist.

Q3: How small is the Delft test piece really?

A: Very small. The standard dimensions are:

Dimension	Value
Length (L)	60 mm
Width (B)	9.0 ± 0.1 mm
Slit length (b)	5.0 ± 0.1 mm
Thickness (d)	2.0 ± 0.2 mm

Q4: Why is thickness so strictly controlled at 2.0 ± 0.2 mm?

A: The Delft test relies on a fixed geometric ratio between slit depth and remaining ligament. If the thickness deviates significantly, the stress distribution at the slit tip changes, altering the tear mechanics. The formula’s constant “8” is derived from the nominal dimensions (4 mm × 2 mm). Using a 1 mm-thick piece would halve the ligament cross-section and invalidate the normalization.

Q5: How many test pieces do I need?

A: At least three, preferably six. With only three pieces, you report the individual results. With six, you take the median (odd number) or average of the two middle values (even number). Given tear testing’s natural variability, six is strongly recommended for any serious decision-making.

Q6: Can I cut the test piece from a curved or irregular product?

A: Only if the curvature is gentle. The standard implies flat sheets, but you can cut from curved surfaces provided the internal diameter is >50 mm and the test piece lies flat without distortion. Severely curved or irregular shapes will introduce residual stresses that skew results.

Q7: What unit does ISO 34-2 report, and why is it different from ISO 34-1?

A: ISO 34-2 reports tear strength as F₀ in newtons (N), not kN/m. The formula normalizes the measured force to a standard geometry (4 mm × 2 mm), yielding a force-equivalent value. This is a historical convention for the Delft method and must not be directly compared to ISO 34-1’s kN/m values.

Q8: What failure behavior should I watch for during testing?

A: The standard requires reporting any special tearing behavior (Clause 12.c.8). Look for:

Knotty tear (force oscillates wildly)

Deviation from straight tearing (tear wanders off-axis)

Tearing through the grips (improper mounting)

Premature failure (slit propagates before reaching 30 mm grip separation)

These observations help diagnose whether poor tear strength is due to the material or the test setup.

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