Charpy & Izod Impact Test Virtual Lab
Pendulum Impact Toughness Testing — DBTT & Fracture Analysis Simulator
1 Overview
This Impact Testing Simulator lets you perform virtual Charpy and Izod pendulum impact tests on seven built-in materials (plus custom materials you define) at temperatures from −196 to +200°C. Impact testing measures how much energy a material absorbs during rapid fracture. The pendulum swings down, strikes a notched specimen, and the energy absorbed is calculated from the difference in swing angles.
The simulator reproduces the full testing sequence with animated pendulum motion, an impact sound effect on fracture, and real-time results. A built-in SI / Imperial unit toggle switches between J and ft·lbf, °C and °F instantly. After testing, export results as CSV or save the graph as PNG (with watermark). Click "+ Custom" in the material row to define your own material with custom DBTT and energy properties.
2 Setting Up the Job
The simulator opens in Simulate mode with the pendulum machine on the left and the graph on the right. Below the graph you will find the action bar (Place, Release, Reset, Charpy/Izod toggle, CSV, PNG) and the controls panel (material selection, notch type, temperature slider).
To run your first test: (1) Select a material — or click "+ Custom" to define your own. (2) Choose a notch type. (3) Set the temperature. (4) Select Charpy or Izod from the action bar. (5) Click "Place" to position the specimen. (6) Click "Release" to start the test. You will hear an impact sound when the hammer strikes.
Unit Toggle: Click "SI" or "Imperial" in the top bar. All values — energy (J / ft·lbf), temperature (°C / °F), velocity (m/s / ft/s), and exported data — update instantly.
Right-click the graph canvas for quick access to Save PNG, Export CSV, or Reset.
3 Running the Operation
The left canvas shows the pendulum machine with animated swing motion. Watch the pendulum descend, strike the specimen at the bottom of its arc, and continue swinging to a reduced height. The specimen fractures on impact, and the fracture surface appearance changes with temperature: fibrous and shear-type at high temperatures (ductile), granular and bright at low temperatures (brittle), and a mix in the transition zone.
The right canvas displays the energy graph and builds a DBTT curve as you test at different temperatures. Graph badges show absorbed energy (J), impact velocity (m/s), initial angle, and final angle in real time. The results row reveals eight values: absorbed energy, impact toughness (J/cm squared), initial and final angles, impact velocity, percent shear fracture, lateral expansion, and fracture type classification. Try testing the same material at several temperatures (e.g., -100, -50, 0, +23, +100) to map out the full transition curve.
4 Speeds, Feeds & Theory
Switch to Explore mode to study impact testing concepts in depth. Topics are organized into categories covering test methods, specimen geometry, energy calculations, DBTT theory, fracture surface analysis, and standards (ASTM E23, ISO 148). Each concept card includes a description, relevant formula, and a worked example with numerical values.
Key topics include the energy formula E = mgR(cos beta - cos alpha), the difference between Charpy (simply supported beam, struck opposite notch) and Izod (cantilever, struck same side as notch), V-notch vs. U-notch vs. keyhole geometry, and why BCC metals show a DBTT while FCC metals do not. The annotated canvas diagram updates with each selected concept.
5 Try a Problem
Practice mode presents random calculation problems about impact testing. You might need to calculate absorbed energy from pendulum angles, determine impact toughness from energy and specimen cross-section, or convert between different units. Enter your answer, check it, and view the step-by-step solution if needed. Your running score is tracked.
Quiz mode runs five questions per session covering theory (Charpy vs. Izod differences, DBTT concepts, notch effects) and numerical calculations. Answer all five, review your results, and take a new quiz to improve your score. Aim for a perfect 5/5 before moving on.
6 Shop Tips
- Start with mild steel at room temperature (23 degrees C) to see a typical ductile fracture with high energy absorption.
- Then test the same material at -100 degrees C to observe the dramatic drop in absorbed energy as it transitions to brittle behavior.
- Compare BCC metals (mild steel, low-alloy steel) with FCC metals (aluminum, copper) to see that FCC metals remain ductile at cryogenic temperatures.
- The V-notch is the standard for most testing; U-notch and Keyhole give higher energy values because the stress concentration is less severe.
- Pay attention to the percent shear fracture value; it quantifies how much of the fracture surface is ductile vs. brittle.
- Use the temperature slider to collect at least five data points and observe how the DBTT curve builds on the graph canvas.
- In Practice mode, remember the key formula: E = mgR(cos beta - cos alpha). Most problems are variations of this equation.
- Keyboard shortcuts: 1–4 switch modes, Space place or release, R reset.
- Toggle to Imperial to see energy in ft·lbf and temperature in °F — useful for ASTM E23 standards used in the US.
- Click "+ Custom" to define your own material with custom energy, DBTT, upper/lower shelf energy, and density. The unit-aware form adjusts labels for SI or Imperial.
- After a test, click CSV in the action bar to export results (including DBTT test points). Click PNG to save the graph with a mechsimulator.com watermark.
- Right-click the graph canvas for quick export and reset options.
How Does the Charpy & Izod Impact Test Work?
The Charpy and Izod impact tests measure how much energy a material absorbs during rapid fracture. A heavy pendulum is raised to a known height, giving it a specific potential energy. When released, the pendulum swings down and strikes a notched specimen at the bottom of its arc. The specimen fractures, absorbing some of the pendulum's kinetic energy. By measuring how high the pendulum swings after breaking the specimen, the absorbed energy is calculated as the difference between the initial and final potential energies: E = mgR(cosβ − cosα), where α is the initial angle, β is the final swing-through angle, m is the pendulum mass, and R is the pendulum arm length.
The key difference between the two methods lies in specimen orientation. In the Charpy test (ASTM E23, ISO 148), the specimen is supported as a simply supported beam and struck on the face opposite the notch. In the Izod test (ASTM E23, ISO 180), the specimen is clamped vertically as a cantilever and struck on the same side as the notch, above the clamp. Both methods yield absorbed energy values in Joules (J), which can be converted to impact toughness by dividing by the cross-sectional area at the notch.
Understanding the Ductile-Brittle Transition Temperature (DBTT)
Many metals, particularly those with body-centered cubic (BCC) crystal structures like carbon steel and low-alloy steels, undergo a dramatic change in fracture behavior as temperature decreases. At high temperatures, they fracture in a ductile manner with significant energy absorption, producing a fibrous, shear-type fracture surface. At low temperatures, the same material fractures in a brittle, cleavage mode with very little energy absorption, producing a bright, granular fracture surface. The temperature range over which this transition occurs is called the ductile-brittle transition temperature (DBTT), and it appears as a sigmoid curve when absorbed energy is plotted against temperature. Face-centered cubic (FCC) metals like aluminum and copper do not exhibit this transition and remain ductile even at cryogenic temperatures, making them suitable for low-temperature applications.
Specimen Preparation and Notch Types
Standard Charpy specimens are 10 mm × 10 mm × 55 mm bars with a machined notch at the midpoint. Three notch geometries are commonly used: the V-notch (2 mm deep, 45° included angle, 0.25 mm root radius) specified in ASTM E23 and ISO 148-1, the U-notch (5 mm deep, 1 mm root radius) used in some European standards, and the keyhole notch (deeper with a drilled hole at the root) used for certain cast irons and polymers. The V-notch is the most widely used because it provides the sharpest stress concentration and greatest sensitivity to material toughness differences. Precise machining of the notch is critical, as variations in notch depth, angle, or root radius directly affect the measured impact energy.
The Liberty Ship Lesson — Why Impact Testing Exists
During World War II, 2700 Liberty Ships were built as fast as possible by welding (rather than the traditional riveting) plate steel together. By 1946, almost 1500 of them had developed serious cracks; nearly 200 had broken catastrophically — some snapping completely in half in calm sea. The investigation pointed to a single cause: ordinary low-carbon steel, which behaved ductile at room temperature, became brittle below about 5 °C. North Atlantic winter convoys regularly saw water temperatures of 0−4 °C. The steel was simply too brittle at service temperature.
Before the Liberty Ships, impact testing was a research curiosity. After them, it became mandatory for every structural steel destined for cold-temperature service. The Charpy V-notch test at the lowest expected operating temperature is now written into ASTM A20, A516, A537 and dozens of other pressure-vessel and shipbuilding standards. The story is repeated in every materials-engineering course because the lesson is stark: a property you do not measure cannot save you from a failure you did not predict.
The Ductile-Brittle Transition — What the Numbers Mean in Service
Take mild steel: at 20 °C it absorbs about 40−60 J in a Charpy test. At −40 °C it might absorb 5 J. Same metal, ten times less toughness. The transition is sigmoid: a gentle decline from high temperature to about the “mid-transition” temperature, then a rapid fall over 20−40 °C, then a low brittle shelf at low temperatures.
Engineering codes set thresholds. ASME pressure-vessel code requires steel to absorb a minimum of 18 J at the lowest service temperature; pipeline codes for sub-Arctic service require 40 J at −30 °C. Specifying the wrong steel for a cold-temperature application is the most common materials-engineering error and the easiest to avoid with Charpy data.
References for Impact Testing
- ASTM E23-18 — Standard Test Methods for Notched Bar Impact Testing of Metallic Materials.
- ISO 148-1:2016 — Metallic materials — Charpy pendulum impact test.
- ASTM A370 — Standard Test Methods and Definitions for Mechanical Testing of Steel Products.
- Anderson, T. L. — Fracture Mechanics: Fundamentals and Applications, 4th ed.
Charpy Impact Test — Key Formulas
| Parameter | Formula | Description |
|---|---|---|
| Absorbed Energy | E = m × g × (h1 − h2) | Energy absorbed by specimen fracture (J) |
| Initial Height | h1 = R(1 − cos α) | Pendulum release height from swing angle α |
| Final Height | h2 = R(1 − cos β) | Pendulum follow-through height after fracture |
| Impact Toughness | K = E / A | Absorbed energy per unit cross-section area (J/m²) |
Typical Charpy V-Notch Impact Energies (at 20 °C)
| Material | Impact Energy (J) | Fracture Type |
|---|---|---|
| Mild Steel (AISI 1018) | 100 – 150 | Ductile (cup-cone) |
| Stainless Steel (304) | 150 – 200 | Ductile |
| Aluminium 6061-T6 | 20 – 30 | Ductile |
| Cast Iron (grey) | 3 – 8 | Brittle (granular) |
| Tool Steel (D2) | 12 – 20 | Brittle to semi-brittle |
| Brass (C26000) | 40 – 60 | Ductile |
| Nylon 6/6 | 50 – 80 | Ductile |
Explore Related Simulators
If you found this Impact Testing simulator helpful, explore our Fatigue Testing simulator, Hardness Testing simulator, Universal Testing Machine simulator, and Stress–Strain Curve simulator for more hands-on practice.