Impact Testing: Izod vs Charpy Pendulum Dynamics & Fracture Mechanics

1. Why This Topic Matters

Polymer components subjected to sudden mechanical impacts (drop impact, collision, shock loading) must resist brittle fracture. Pendulum Impact Testing—via Izod and Charpy methods—measures the energy absorbed during rapid crack propagation across a standardized notched specimen. Understanding notch sensitivity, ductile-to-brittle transition temperature ( $DBTT$ ), and the non-interchangeable differences between ASTM and ISO test standards is critical for automotive bumper and protective helmet material selection.

2. Learning Objectives

By completing this lesson, you will be able to:

Differentiate Izod (cantilever beam) and Charpy (three-point supported beam) testing geometries.
Calculate absorbed impact energy ( $E_{absorbed}$ ) and impact strength.
Compare ASTM D256 ( $ext{J/m}$ ) and ISO 180 / ISO 179 ( $ext{kJ/m}^2$ ) units and notch radii.
Diagnose notch sensitivity and brittle failure modes.

3. Test Geometry & Pendulum Dynamics

Technical Schematic & Mechanism Blueprint: Impact Testing: Izod vs Charpy Pendulum Dynamics & Fracture Mechanics

Impact Testing: Izod vs Charpy Pendulum Dynamics & Fracture Mechanics — Mechanism & Physics Diagram

Analytical SEC Chromatography: Larger hydrodynamic volumes are excluded from porous gel pores and elute first; Mz > Mw > Mn for all polydisperse polymers.

mermaid

graph TD
    A["Pendulum Released from Initial Height h1"] --> B["Impact Striker Strikes Notched Specimen"]
    B --> C{"Testing Configuration"}
    C -->|"Izod Method (ASTM D256 / ISO 180)"| D["Vertical Cantilever Beam (Struck on Notched Face Side)"]
    C -->|"Charpy Method (ISO 179)"| E["Horizontal Simply Supported Beam (Struck Opposite Notch)"]
    D --> F["Pendulum Swings to Reduced Height h2"]
    E --> F
    F --> G["Absorbed Energy E = m*g*(h1 - h2) - Friction Losses"]

4. Equations & Recalculated Impact Energy

Impact Testing: Izod vs Charpy Pendulum Dynamics & Fracture Mechanics — Industrial Process Flow Diagram (PFD)

ISO 10628 Unit Operations & Thermodynamic Control Sequence

ISO 10628 PFD Standard

180°C - 100°C

Raw Material Feed & Metering

Drying to < 0.02% moisture and gravimetric dosing

Output:Conditioned Feed

2220°C - 260°C

Reaction & Polymer Melt Processing

Controlled thermal shear dissipation and phase transition

Output:Homogenous Melt

360 - 120 bar

Shaping & Solidification

Die extrusion or mold cavity pressure packing

Output:Formed Component

4QA Passed

Quality Inspection & Testing

ASTM D638 / ISO 527 tensile & MFI compliance check

Output:Finished Grade

Recycle Loop Stream:Closed-loop sprues and edge-trim regrind re-fed into main hopper at maximum 15% blend ratio.

Standard Indian Industrial Practice (CIPET / Reliance / Supreme Petrochem Protocol)

Pendulum Energy Equation

Potential energy absorbed by specimen fracture:

E_{absorbed} = m \cdot g \cdot (h_1 - h_2) - E_{windage}

Unit Formats: ASTM vs ISO Standards

Engineering Note & Problem Analysis

[!CAUTION] Never Interchange ASTM and ISO Impact Values:

ASTM D256 (Izod) reports impact energy per unit notch length ( $ext{J/m}$ ):

\text{Impact Strength}_{ASTM} = \frac{E_{absorbed}}{b} \quad (\text{J/m})

Engineering Note & Problem Analysis

ISO 180 (Izod) / ISO 179 (Charpy) reports impact energy per unit cross-sectional area under notch ( $ext{kJ/m}^2$ ):

\text{Impact Strength}_{ISO} = \frac{E_{absorbed}}{b \cdot (h - a)} \times 10^3 \quad (\text{kJ/m}^2)

Where $b$ = specimen width ( $0.0032 ext{ m}$ ), $h$ = total thickness ( $0.0127 ext{ m}$ ), $a$ = notch depth ( $0.00254 ext{ m}$ ).

Worked Numerical Example:

Engineering Note & Problem Analysis

Problem Statement:

Problem: A Polycarbonate notched Izod specimen ( $b = 3.20\text{ mm} = 0.0032\text{ m}$ , depth under notch $h - a = 10.16\text{ mm} = 0.01016\text{ m}$ ) absorbs $E_{absorbed} = 2.10\text{ Joules}$ during fracture. Calculate impact strength under both ASTM D256 and ISO 180 formats.

Engineering Note & Problem Analysis

Solution Step:

Solution:

Calculate ASTM D256 Impact Strength ( $ext{J/m}$ ):

\text{Impact Strength}_{ASTM} = \frac{2.10\text{ J}}{0.00320\text{ m}} = 656.25\text{ J/m}

Calculate ISO 180 Impact Strength ( $ext{kJ/m}^2$ ):

\text{Cross-Section Area} = 0.00320 \times 0.01016 = 3.2512 \times 10^{-5}\text{ m}^2

\text{Impact Strength}_{ISO} = \frac{2.10\text{ J}}{3.2512 \times 10^{-5}\text{ m}^2} = 64,591.5\text{ J/m}^2 = 64.59\text{ kJ/m}^2

5. Industrial Applications

Impact Testing: Izod vs Charpy Pendulum Dynamics & Fracture Mechanics — CAD Tooling & Machine Geometry Blueprint

DWG NO: DWG-POLY-2026-232SCALE: 1:1 (FULL)MATERIAL: P20 Tool Steel / Hardened Alloy (HRC 48-52)

Critical Geometric Dimensions & Tolerances (GD&T)

Primary Processing Tolerance:± 0.02 mm (ISO 20457 Class M1)
Thermal Expansion Allowance:1.5% (Volumetric Shrinkage)
Draft Angle Minimum:1.0° - 1.5° (Core/Cavity Ejection)

Tooling Fabrication Notes

• Fabricated according to ISO 20457 plastic molding tolerance standards.
• EDM finish SPI C-1 applied across cavity optical contact faces.
• Conformal cooling lines pressure tested at 12 bar water flow.

Automotive Bumper Compound Validation: Polypropylene-EPDM tough impact testing at $-30^circ ext{C}$ in Chennai auto testing lab. (Illustrative Indian industry scenario based on automotive polymer testing).

6. Key Takeaways & Glossary

Notch Sensitivity: Susceptibility of material to brittle fracture caused by stress concentration at sharp notch roots ( $R = 0.25 ext{ mm}$ ).
DBTT: Ductile-to-Brittle Transition Temperature where impact strength drops sharply.

7. Sources & Standard References

ASTM D256-23 — Standard Test Methods for Determining the Izod Pendulum Impact Resistance of Plastics, ASTM.
ISO 179-1:2023 — Plastics — Determination of Charpy impact properties, ISO.

Impact Testing: Izod vs Charpy Pendulum Dynamics & Fracture Mechanics

01 · Why This Matters in Industry & GATE XE5

Impact Testing: Izod vs Charpy Pendulum Dynamics & Fracture Mechanics

1. Why This Topic Matters

2. Learning Objectives

3. Test Geometry & Pendulum Dynamics

4. Equations & Recalculated Impact Energy

Impact Testing: Izod vs Charpy Pendulum Dynamics & Fracture Mechanics — Industrial Process Flow Diagram (PFD)

Raw Material Feed & Metering

Reaction & Polymer Melt Processing

Shaping & Solidification

Quality Inspection & Testing

Pendulum Energy Equation

Unit Formats: ASTM vs ISO Standards

Worked Numerical Example:

5. Industrial Applications

Impact Testing: Izod vs Charpy Pendulum Dynamics & Fracture Mechanics — CAD Tooling & Machine Geometry Blueprint

Critical Geometric Dimensions & Tolerances (GD&T)

Tooling Fabrication Notes

6. Key Takeaways & Glossary

7. Sources & Standard References

Impact Testing: Izod vs Charpy Pendulum Dynamics & Fracture Mechanics · Engineering Triad

Acrylonitrile Butadiene Styrene (ABS)

Computerized Servo-Universal Testing Machine (UTM 50kN)

Consumer Electronics Enclosures & Crash Helmets

Test Your Conceptual Understanding

Personal Lesson Notes