Charpy & Izod Impact Test Virtual Lab

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). Choose "+ Define custom material…" at the bottom of the Material dropdown to add your own material with custom DBTT and energy properties.

The machine modelled here is a standard ISO 148-1 300 J pendulum: a 20.5 kg hammer on an 0.8 m arm, latched at 150°, striking at 5.41 m/s. Below the machine the classical equation E = mgR(cos β − cos α) is drawn directly on the canvas, and its output counts up as the pendulum follows through so you can watch the measurement happen. Below the results you will find three learning panels — Live equations (rendered in proper mathematical notation), a What-if coach, and a Test history table.

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 Control Panel (Place, Release, Reset, the Charpy/Izod and SI/Imperial toggles, and a single Export Results menu) and the controls panel below it (material, notch type, preset, specimen size, notch condition, release angle and temperature).

To run your first test: (1) Pick a material from the dropdown — or choose "+ Define custom material…" to add 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.

Presets: the fastest way in. Pick one from the Preset dropdown and it loads a complete teaching scenario — Liberty Ship @ 0°C (the historic brittle-fracture case), Pipeline spec −40°C, Upper shelf @ 100°C, Cryogenic 304 @ −196°C, Gray cast iron @ 23°C, U-notch comparison and Izod, mild steel @ 23°C. Changing any control by hand returns the dropdown to “Choose a scenario…”, so it never claims a preset is loaded once you have edited something.

Compact controls. Material, notch and preset are dropdowns rather than button rows, so the whole panel is two lines. The notch dropdown states each geometry inline (depth and root radius), and the last material entry, “+ Define custom material…”, opens the custom-material form rather than selecting anything.

Release angle α — and why β has no control. α is the angle the pendulum is raised to before release, measured from hanging vertical. You set it, and it fixes two things at once: the energy the machine stores, E_cap = mgR(1 − cos α), and the speed it strikes at, v = √(2gR(1 − cos α)). The caption beside the slider shows both live and warns when the striking velocity leaves the 5.0–5.5 m/s window ISO 148-1 requires — at the standard 150° latch this machine gives 5.41 m/s and 300 J.

β is deliberately not settable. It is the angle the pendulum swings through after breaking the specimen — the quantity the machine measures. The whole test solves E = mgR(cos β − cos α) for the absorbed energy using the observed β, so a slider on β would be a slider on the answer. The badges label them accordingly: α (set), β (measured).

Lower α and the capacity falls with it. Drop to 120° and the machine holds only 241 J, so a tough specimen that was comfortably valid at 150° can breach the ASTM E23 80 %-of-capacity rule — a quick way to see why capacity selection matters.

Temperature: drag the slider for a sweep, or type an exact value into the number box beside it and press Enter. The [−] and [+] buttons step one degree at a time. The box shows °C or °F depending on the unit toggle and converts your typed value back automatically.

Specimen size. ASTM E23 defines standard sub-size Charpy specimens for when the stock is too thin for a full bar — thin plate, tube wall, weld heat-affected zone, small forgings. Only the struck thickness is reduced (10, 7.5, 6.7, 5, 3.3 or 2.5 mm); the length and the 10 mm notched face stay full size. Absorbed energy scales with the remaining ligament area, so a ½-size bar reads about half the energy of a full-size one on the same material — but impact toughness in J/cm² is unchanged, because that is energy per unit area. Run the same steel at full and ½ size and watch the Joules halve while the J/cm² stays put; that contrast is the whole point.

Acceptance criteria scale with the specimen. A ⅔-size bar is held to ⅔ of the full-size requirement. Applying a flat “27 J minimum” to a sub-size result is the single most common error in Charpy acceptance testing; the inference panel does the scaling for you and says so.

Notch condition. ASTM E23 holds the V-notch root radius to 0.25 ± 0.025 mm and the depth to 2 ± 0.025 mm. Select Blunt root or Shallow notch to see what a badly machined specimen does: the reading goes up, not down. That is the dangerous direction — a poorly prepared notch makes a steel look safer than it is, which is why notch geometry is checked on an optical comparator and why an out-of-tolerance notch invalidates the test rather than being corrected for.

Display Controls: the collapsible panel pinned to the top-left of the graph canvas decides what is drawn. Ten switches in two groups — Machine: energy equation, notch detail inset, dial gauge, digital readout, protractor & angles, safety guard zone, fracture surface inset; Graph: grid, shelf lines & DBTT, test points. Reset Display turns everything back on. Collapse the panel to keep the canvas clear; strip layers away when projecting to a class, then add them back to reveal how the reading was built up.

Unit Toggle: Click "SI" or "Imperial" in the Control Panel, beside the Charpy/Izod toggle. All values — energy (J / ft·lbf), temperature (°C / °F), velocity (m/s / ft/s), the learning panels, and exported data — update instantly.

Right-click the graph canvas for quick access to Save PNG, Export CSV, or Reset.

How the specimen is supported. In Charpy the bar lies across two anvils whose inner faces set the 40 mm span — that span is the dimension called out on the canvas, measured between those faces. Each anvil has a 1 mm radius on its striking edge and is relieved outward behind it, and small back stops locate the bar fore and aft. The gap between the anvils is deliberately open: it is the space the specimen bends into and that the striker passes through, and it is where the notch sits. A 55 mm bar on a 40 mm span overhangs 7.5 mm each side, which is what you see.

Which face gets struck. Watch the specimen closely — the two methods are not just different fixtures. In Charpy the bar lies across two anvils and the notch is cut into the bottom face, so the hammer strikes the face opposite the notch and the notch sits on the tension side where the crack opens. In Izod the bar is clamped upright in a vice and the notch faces towards the incoming hammer, level with the top of the vice jaws, so the notched face is the struck face. The magnified "Notch Detail" inset states which arrangement is active.

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.

Validity check. Under the results a coloured note applies the ASTM E23 rule that a quantitative result must fall below roughly 80 percent of the machine's capacity — 240 J on this 300 J pendulum. Green means the value is usable; amber means friction and vibration losses are no longer negligible; red means the pendulum ran out of energy and the specimen did not separate, which must be reported as "did not break" rather than as a number.

Two graphs, and you choose. The Graph selector above the badges switches between Pendulum Swing and the DBTT Curve. Pendulum Swing plots the real angle against time in seconds — it is integrated from the pendulum equation, so the marked impact time and the follow-through angle are genuine, not decorative. The DBTT Curve plots absorbed energy against temperature and gains a point with every test. The view switches to the DBTT curve automatically once the hammer has passed through (the caption tells you when it did that), and you can switch back at any time.

Inference panel. Directly under the two canvases, "What This Result Tells You" reads the completed test back in plain language: what the energy figure means, what the fracture surface would look like in the hand, where the temperature sits relative to the DBTT, whether the value can be checked against code minima, and which temperature to test next. It also warns when a U-notch, keyhole or Izod reading is being compared against acceptance criteria that are written for Charpy V-notch.

Learning panels. Expand Live equations to see the impact velocity, the energy balance and the toughness division typeset with your current values substituted in. The What-if coach reads the current material, temperature, notch and method and explains what they mean — whether you are on the lower shelf, in the scatter-prone transition zone or on the upper shelf, how the notch geometry is affecting the reading, and whether the expected energy clears typical ASME and pipeline code minima. Test history tabulates every point plotted on the DBTT curve and can clear them.

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.

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.

• 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. Load the U-notch comparison preset and run it against a V-notch test on the same steel: the blunter 1 mm root relieves crack-tip constraint, so a ductile specimen absorbs roughly 50 percent more energy. Repeat the comparison at -100 degrees C and the advantage almost vanishes, because cleavage fracture barely cares how sharp the notch is.
• Run the Izod, mild steel preset straight after the Charpy test at the same temperature. Izod reads about 20 percent lower for the same material because the specimen is a clamped cantilever struck on the notched face. Never quote an Izod figure against a Charpy specification.
• 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.
• Choose "+ Define custom material…" from the Material dropdown to add 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, open Export Results in the Control Panel. CSV data gives the result plus every DBTT point collected, Graph PNG saves the current chart with a mechsimulator.com watermark, and Test report opens a printable certificate.
• Right-click the graph canvas for quick export and reset options.
• Run the same specimen at α = 150° and again at 120°. The absorbed energy barely changes — it is a property of the material — but β and the validity verdict both move, because the machine now stores far less energy.
• Run mild steel full-size, then at ½ size. The Joules halve but the J/cm² toughness is identical — energy depends on how much material you broke, toughness is the material property.
• Set Blunt root and re-run: the energy rises by about 20 % on a ductile specimen. A notch error flatters the material, which is why it invalidates the test rather than merely adding scatter.
• Use the presets row to jump straight to a teaching scenario, then nudge the temperature stepper by one degree at a time to find exactly where the transition begins.
• If the validity note turns amber or red, the number is not usable as reported data — that is the same judgement a real test house makes before signing a certificate.
• Open Display Controls on the graph canvas and switch off the dial, digital readout and protractor to leave a clean machine diagram for a worksheet screenshot — then Reset Display to bring everything back.