📋 Table of Contents
- Why Impact Testing is Essential for Plastics
- Three Impact Tests — Quick Comparison
- Dart Impact Testing — Films and Flexible Sheeting
- ASTM D1709: Method A vs Method B
- The Staircase Method — How F50 is Calculated
- Charpy and Izod — Pendulum Impact for Rigid Plastics
- Charpy vs Izod — Key Differences
- Notched vs Unnotched — Why It Matters
- Pendulum Energy Selection
- Standards Reference — ASTM, ISO, IS
- Which Test Do You Need? Decision Guide
- Impact Strength Reference Values for Common Plastics
- Instruments from International Equipments
- Tips for Accurate Impact Testing
- Frequently Asked Questions
Impact strength is the ability of a material to absorb sudden energy without fracturing - yet there is no single "impact test." Dart impact, Charpy, and Izod measure fundamentally different properties, on completely different specimen geometries, in different failure modes. Choosing the wrong test gives meaningless results. This guide covers all three: what each measures, when to use it, and exactly what the numbers mean.
The plastics industry uses dozens of impact test methods, but three dominate: dart impact for flexible films, and Charpy/Izod for rigid plastics. These are so different in principle that comparing results across methods is a category error - yet all three measure some aspect of "impact resistance," which is why confusion persists.
Why Impact Testing is Essential for Plastics
Packaging films
Film bags and pouches must resist puncture from sharp objects in transit. Dart impact quantifies this resistance.
Safety-critical parts
Automotive bumpers, safety helmets, protective housings must not shatter on impact. Charpy/Izod verifies material toughness.
Pipe and fittings
HDPE/PVC pipe fittings must survive installation tool impacts. IS 4984 references falling-weight and impact testing.
Consumer electronics
Plastic casings must survive drop tests. Impact data guides material selection for shells, connectors, and housings.
Cold-temperature service
Many plastics go brittle below 0 degC. Charpy/Izod at -20 degC or -40 degC is essential for outdoor and refrigeration applications.
Engineering components
Gears, levers, brackets in Nylon, POM, ABS - all require impact strength data for structural design.
Three Impact Tests - Quick Comparison
| Test Method | Material type | Loading mode | Result unit | Typical applications | Specimen notes |
|---|---|---|---|---|---|
| Dart Impact (ASTM D1709) | Flexible films and thin sheeting | Drop-weight dart falling onto flat film | F50 in grams | LDPE bags, stretch wrap, BOPP, garbage bags | No specimen machining needed |
| Charpy (ISO 179) | Rigid and semi-rigid plastics | Pendulum strikes centre of horizontal bar | kJ/m² | ABS, PC, PP, Nylon, PVC, filled compounds | Notched or unnotched bar 80x10x4 mm |
| Izod (ISO 180 / ASTM D256) | Rigid and semi-rigid plastics | Pendulum strikes clamped vertical cantilever | J/m | Same as Charpy - complementary method | Notch required for most standards |
Dart Impact Testing - Films and Flexible Sheeting
The dart impact test (ASTM D1709) is a drop-weight test designed specifically for thin flexible plastic films. A flat film specimen is clamped over a 127 mm diameter orifice. A hemispherical dart (38.10 mm diameter, polished) is dropped from a standardised height onto the film centre. The film either punctures (fails) or survives. The test is repeated on multiple specimens at different dart masses using the staircase method to find F50 - the mass causing 50% failure.
Impact Energy by Drop Method
Method A (0.66 m drop)
E = m x g x h = m x 9.81 x 0.66
F50 = 100 g gives E = 0.647 J
Method B (1.50 m drop)
E = m x g x h = m x 9.81 x 1.50
F50 = 100 g gives E = 1.472 J
Method B delivers 2.27x more energy per gram of dart mass than Method A
ASTM D1709: Method A vs Method B
Method A - Standard Drop (0.66 m)
► Drop height: 660 mm
► Dart: 38.10 mm hemispherical
► Weight range: typically 30-500 g
► Increment: 5% of estimated F50
► For: LDPE, cast PP, thin BOPP
► Standard films with moderate toughness
Method B - High Drop (1.50 m)
► Drop height: 1500 mm
► Dart: 38.10 mm hemispherical
► Weight range: typically 200-2000 g
► Increment: 5% of estimated F50
► For: LLDPE, tough PE blends, multilayer films
► 2.27x more energy than Method A per gram
The Staircase Method - How F50 is Calculated
ASTM D1709 uses the statistical staircase (up-and-down) procedure to estimate F50 from the minimum number of specimens. If a specimen FAILS, the next test uses a lighter dart. If it PASSES, the next test uses a heavier dart. After minimum 20 usable specimens, F50 equals the mean dart mass in the staircase series. The weight increment should be 5% of the estimated F50.
Staircase Procedure - Example Sequence (estimated F50 = 95 g, increment = 5 g)
| Test # | Dart mass (g) | Result | Next action |
|---|---|---|---|
| 1 | 100 | FAIL | Decrease dart mass next test |
| 2 | 95 | FAIL | Decrease dart mass next test |
| 3 | 90 | PASS | Increase dart mass next test |
| 4 | 95 | FAIL | Decrease dart mass next test |
| 5 | 90 | PASS | Increase dart mass next test |
| 6 | 95 | PASS | Increase dart mass next test |
| 7 | 100 | FAIL | Decrease dart mass next test |
| 8 | 95 | PASS | Continue ... |
After 20+ tests: F50 = ~93-95 g (staircase oscillates around the 50% failure point)
Discard the first specimen result (used only to initiate the sequence). Minimum 20 usable specimens are required for reliable F50 calculation. The staircase oscillates around the true F50 - the mean of all test masses is the F50 estimate.
Charpy and Izod - Pendulum Impact for Rigid Plastics
Both Charpy and Izod use a pendulum that swings from a fixed starting angle, strikes the specimen, and continues through. The angle of follow-through reveals the energy absorbed. The same pendulum tester performs both - only the specimen mounting and striker geometry change.
Pendulum Impact Energy Calculation
E = m x g x (h1 - h2)
h1 = release height, h2 = follow-through height
E = energy absorbed by specimen
Charpy vs Izod - Key Differences
Charpy (ISO 179 / ASTM D6110)
► Specimen horizontal on two supports
► Struck at centre - three-point bending
► Span: 62 mm (ISO 179)
► Result: kJ/m² (energy per notch area)
► Standard in Europe / ISO specifications
► Better for brittle materials
Izod (ISO 180 / ASTM D256)
► Specimen clamped vertically - cantilever
► Struck near free end
► Free length: 22 mm above clamp
► Result: J/m (energy per specimen width)
► Standard in USA / ASTM specifications
► Cannot be compared to Charpy
| Parameter | Charpy | Izod |
|---|---|---|
| Specimen orientation | Horizontal on two supports | Vertical, clamped at base |
| Impact point | Centre of span - three-point bending | Free end - cantilever |
| Span (ISO) | 62 mm between supports | 22 mm free length above clamp |
| Primary standard | ISO 179 / ASTM D6110 | ISO 180 / ASTM D256 |
| Result unit | kJ/m² (energy per notch area) | J/m (energy per specimen width) |
| Advantage | Better for brittle materials | Standard in USA; good for ductile |
| Can be compared? | NO - different stress states | NO - even for the same material |
Notched vs Unnotched - Why It Matters
Notched Specimen
► 45 deg V-notch, depth 2.0 mm, root radius 0.25 mm
► Creates severe stress concentration
► Forces brittle fracture in ductile materials
► Much more sensitive to material quality differences
► Used for ABS, PC, Nylon, POM, filled compounds
► Values 2-10x lower than unnotched
Unnotched Specimen
► No notch - plain bar
► No artificial stress concentration
► Full material toughness expressed
► Less discriminating for ductile materials
► Used for brittle materials (PS) or absolute toughness
► Often results in NB (No Break) for tough plastics
Pendulum Energy Selection
The pendulum must be selected so that the energy absorbed by the specimen is between 10% and 80% of the pendulum available energy. Outside this range, results are unreliable.
| Pendulum | Available energy | Valid test range | Typical use | Example materials |
|---|---|---|---|---|
| 1 J | 1.0 J | 0.1 - 0.8 J | Very brittle materials | PS, SAN, rigid PVC, unmodified |
| 2.75 J | 2.75 J | 0.28 - 2.2 J | Most engineering plastics | ABS, PP, HDPE, Nylon (notched) |
| 5.5 J | 5.5 J | 0.55 - 4.4 J | Tough materials | PC, PA 66, impact-modified blends |
| 11 J | 11.0 J | 1.1 - 8.8 J | Very tough, often unnotched | Rubber, TPE, tough polyurethane |
| 22 J | 22.0 J | 2.2 - 17.6 J | Highest energy applications | Thick specimens, structural composites |
Standards Reference - ASTM, ISO, IS
| Test | ASTM | ISO | IS | Key Notes |
|---|---|---|---|---|
| Dart Impact - films | ASTM D1709 | ISO 7765-1 | IS 2508 | Drop weight F50; Method A and B; films only |
| Charpy - plastics | ASTM D6110 | ISO 179-1 | IS 13360 | Horizontally supported beam; notched; kJ/m² |
| Charpy - unnotched | ASTM D6110 | ISO 179-1/eU | IS 13360 | Method eU; much higher values than notched |
| Izod - plastics | ASTM D256 | ISO 180 | IS 13360 | Vertical cantilever; notched; J/m |
| Izod - unnotched | ASTM D4812 | ISO 180/U | --- | Higher values; often NB for tough plastics |
| Falling weight - pipes | ASTM D2444 | ISO 3127 | IS 12235 | Drop weight for pipe and fittings installations |
| Tensile impact | ASTM D1822 | ISO 8256 | --- | For rigid films and thin specimens |
Which Test Do You Need? Decision Guide
USE DART IMPACT
Thin flexible film packaging
Films (LDPE bags, LLDPE wrap, BOPP) are flat and flexible - cannot be machined into bars. Dart impact is specifically designed for flat clamped film + hemispherical dart. Per ASTM D1709.
USE CHARPY (ISO 179)
Rigid plastics - European/ISO specs
European norms and ISO standards specify Charpy. Three-point bending geometry. Results in kJ/m-squared. Notched for material comparison; unnotched for maximum energy absorption.
USE IZOD (ASTM D256)
Rigid plastics - US ASTM specs
US-market products and ASTM-certified labs. Cantilever geometry. Results in J/m. Most common in US plastic data sheets for ABS, PC, Nylon, PP.
USE BOTH Charpy + Izod
Full material qualification
Running both allows comparison with global databases covering both ISO and ASTM specifications. Same pendulum tester, same specimen geometry (80x10x4 mm bar).
USE FALLING WEIGHT
Plastic pipes and fittings
Pipes must survive dropping and tool strikes during installation. ASTM D2444 / IS 12235 use a drop-weight to impact pipe specimens - different from pendulum and dart methods.
USE TENSILE IMPACT
Thick rigid films (PET, BOPP >0.2 mm)
Films too thick for dart but not suitable for bar machining: use tensile impact (ASTM D1822) or tensile elongation and energy-to-break from the UTM/tensile tester.
Impact Strength Reference Values for Common Plastics
Dart Impact F50 Values - Flexible Films
| Film / Material | F50 (typical) | Method | Typical Applications |
|---|---|---|---|
| LDPE (standard, 30 um) | 50 - 120 g | Method A | Carrier bags, general packaging |
| LDPE (heavy-duty, 50 um) | 120 - 300 g | Method A | Heavy bags, liners |
| LLDPE blown film (30 um) | 150 - 400 g | Method A | Stretch wrap, lamination films |
| LLDPE stretch film | 300 - 800 g | Method A | Pallet wrap - very high toughness |
| HDPE blown film (25 um) | 30 - 80 g | Method A | Lower toughness, stiff film |
| BOPP (20 um) | 60 - 150 g | Method A | Oriented film, anisotropic |
| Cast PP (CPP, 30 um) | 80 - 200 g | Method A | Sealant layer packaging |
| Nylon/PE coex pouch (75 um) | 400 - 1000 g | Method B | High-toughness retort pouches |
| LDPE heavy-duty liner | 200 - 600 g | Method B | FIBCs, industrial liners |
Notched Izod and Charpy - Rigid Plastics
| Material | Notched Izod (J/m) | Notched Charpy (kJ/m²) | Notes |
|---|---|---|---|
| Polystyrene (GPS) | 20 - 50 | 10 - 20 | Very brittle - fractures easily |
| ABS (medium impact) | 150 - 350 | 8 - 18 | Good impact - most common engineering plastic |
| ABS (high impact) | 400 - 700 | 18 - 35 | Automotive, appliances |
| Polycarbonate (PC) | 600 - 900 | 35 - 80 | Exceptional toughness - helmets, safety glazing |
| PP homopolymer | 40 - 100 | 5 - 12 | Relatively brittle; copolymer is better |
| PP copolymer | 150 - 600 | 12 - 50 | Better cold-temperature toughness |
| Nylon 6 (PA 6) - dry | 50 - 100 | 5 - 12 | Moisture significantly improves toughness |
| Nylon 6 (PA 6) - conditioned | 800+ / NB | 40+ / NB | Moisture-absorbed - very tough |
| HDPE (injection moulded) | 100 - 600 | 8 - 40 | Grade and MFI dependent |
| POM (Acetal) | 75 - 200 | 6 - 15 | Good stiffness/toughness balance |
| PMMA (Acrylic) | 20 - 40 | 5 - 10 | Brittle; impact grades available |
| 30% GF Nylon 66 | 80 - 150 | 8 - 18 | Glass reduces toughness vs unfilled |
Instruments from International Equipments
Essential accessories for Charpy/Izod testing:
Motorized Notch Cutter
Cuts the standardised 45 degree V-notch (depth 2.0 mm, root radius 0.25 mm per ISO 180 Type A) automatically. A hand-cut notch gives wrong and non-reproducible results - the notch cutter is mandatory for ISO/ASTM compliance.
View product →Micro-meter Jig
Verifies notch depth, specimen width, and specimen thickness before testing. Dimensional errors in the notch directly affect impact results. Catches out-of-tolerance specimens before they invalidate an entire test series.
View product →🔗 Related Products:
- → Dart Impact Tester — ASTM D1709 Method A and B
- → Izod/Charpy Impact Tester — ISO 179 / ISO 180 / ASTM D256 / ASTM D6110
- → Motorized Notch Cutter — ISO 180 Type A notch - mandatory for valid results
- → Micro-meter Jig — Specimen dimension verification
Tips for Accurate Impact Testing
Dart Impact Testing Tips
- 1Condition specimens at 23 degC / 50% RH for 24 hours. Temperature and humidity significantly affect dart impact values for PE films - a 5 degC difference can shift F50 by 10-20%.
- 2Start near the expected F50. Use supplier data or previous test records. The first specimen result is discarded per ASTM D1709 - starting far from F50 wastes material.
- 3Use the correct weight increment: 5% of estimated F50. Too large reduces statistical accuracy; too small requires excessive specimens.
- 4Inspect the dart after every 50 drops. Scratches or flat spots on the hemispherical surface change contact geometry and invalidate results.
- 5Test minimum 20 usable specimens. With fewer specimens the statistical confidence interval is too wide for most quality specifications.
Charpy / Izod Impact Testing Tips
- 1Always use the Motorized Notch Cutter. The notch root radius (0.25 mm) is critical - a 0.05 mm variation can change impact result by 15-30%. Never notch specimens by hand.
- 2Verify specimen dimensions with the Micro-meter Jig before every test. Width, depth, and notch depth must be within ISO 180 / ASTM D256 tolerances.
- 3Select the right pendulum: 10-80% energy absorption. Below 10% - friction errors dominate. Above 80% - risk of pendulum rebound. Record NB if specimen does not break.
- 4Test at the temperature specified in the product standard. Ductile-brittle transition in PP occurs around 0 degC; in Nylon around -20 degC. Room-temperature and cold-temperature results are not interchangeable.
- 5Run minimum 10 specimens and report mean plus standard deviation. Impact testing has high natural scatter. If SD > 20% of mean, investigate specimen preparation and conditioning.
Key Takeaways
- ✓Dart impact (ASTM D1709) tests flexible films only - the F50 value (grams) from the staircase method. Method A (0.66 m) and Method B (1.50 m) deliver different energy levels and cannot be compared.
- ✓Charpy (ISO 179) and Izod (ISO 180 / ASTM D256) test rigid plastics using a pendulum. Results in kJ/m-squared (Charpy) and J/m (Izod) cannot be compared even for the same material.
- ✓Notched specimens give lower, more discriminating results. Unnotched give higher values, often NB for tough plastics. Always specify which was tested.
- ✓Select pendulum energy so absorbed energy is 10-80% of available capacity. Below 10% = friction error; above 80% = rebound error.
- ✓The Motorized Notch Cutter and Micro-meter Jig are mandatory for valid Charpy/Izod testing - not optional accessories.
- ✓International Equipments manufactures both the Dart Impact Tester (ASTM D1709) and the Izod/Charpy Impact Tester (ISO 179/180, ASTM D256/D6110), plus the Motorized Notch Cutter and Micro-meter Jig - all CE and ISO certified with calibration documentation.
Frequently Asked Questions
Common questions about dart impact, Charpy, and Izod testing methods and equipment.