Charpy Impact Tester Product

Overview

A Charpy impact tester (also called an impact testing machine) measures the energy absorbed by a notched metal specimen when struck by a swinging pendulum hammer, determining the material's toughness and brittle-to-ductile transition. The machine consists of a pivot-mounted pendulum arm and striking head, a fixed specimen holder with V-notch anvil, a rotary encoder measuring the rebound angle, and a temperature chamber to condition the specimen from -196°C (liquid nitrogen) to +100°C (heated bath). A microcontroller calculates absorbed energy from the difference in pendulum height before and after impact and logs results to USB or LIMS integration.

The Charpy test (ISO 148-1, ASTM E23) is the primary qualification method for structural steels, welds, and composite materials in aerospace, pressure vessels, and shipbuilding. Results are reported as absorbed energy (joules) and often plotted against temperature to identify the ductile-to-brittle transition temperature (DBTT), critical for safe operation in cold climates.

How it works

The Pendulum Hammer is a 2–50 kg mass suspended from a low-friction Pivot Bearing at height, connected to a rigid Swing Arm. The operator loads a notched specimen (10 × 10 × 55 mm) into the Specimen Anvil, which has two support rollers at 45° to the specimen axis.

The Release Mechanism holds the hammer at a fixed initial angle (typically 90°, corresponding to 150 J potential energy). When triggered (solenoid or manual lever), the Latch Pawl retracts, and the hammer swings downward under gravity. Impact occurs at the specimen's notch at a velocity of 5.2 m/s.

During impact, the specimen absorbs energy through plastic deformation and fracture, and the hammer recoils to a lower rebound angle. An Angle Encoder (1024 PPR rotary encoder) mounted on the pivot axis measures the rebound angle to 0.5° accuracy. A microcontroller calculates:

Absorbed Energy (J) = Initial PE − Rebound PE = Mg(h₁ − h₂)

where h₁ is initial height and h₂ is rebound height.

If the specimen fractures in a brittle manner, the hammer rebounds high (low energy absorption). If it deforms plastically (ductile), the hammer loses more energy and rebounds lower. The Display and Logger logs the result in joules and timestamp.

For temperature-dependent testing, the specimen is conditioned in a Temperature Chamber using liquid nitrogen (-196°C) or an immersion heater (+20°C to +100°C) for 10–15 minutes until a Thermocouple confirms the desired temperature. The operator then transfers the heated/cooled specimen to the anvil and executes the impact within 5 seconds to minimize thermal drift.

Specimen preparation and test matrix

Charpy specimens are precision-machined to ISO 148-1 specifications: 10 × 10 × 55 mm bars with a V-notch (2 mm deep, 45° angle) at the center. The notch acts as a stress concentrator, ensuring failure initiates at a known point. Operators typically run a test matrix across 5–10 temperatures (-196°C, -100°C, -50°C, -20°C, +20°C, +50°C) to map the transition from brittle (low energy, high fracture face percentage) to ductile (high energy, shear lip).

After impact, the operator inspects the fracture surface's shear lip percentage (0–100%, measured with optical comparator) and records it alongside the absorbed energy. Some labs photograph or store specimens for post-mortem metallographic analysis.

Ductile-to-brittle transition and material selection

Steels and aluminum alloys exhibit a marked transition from ductile to brittle behavior as temperature drops. The Charpy test identifies this DBTT by plotting energy versus temperature; the inflection point (often defined as the 50% shear appearance temperature or the energy drop from upper to lower shelf) guides engineering decisions. For example, the Titanic's hull steel exhibited poor Charpy impact energy at North Atlantic winter temperatures, contributing to rapid failure after striking the iceberg.

Modern pressure vessel codes (ASME Boiler and Pressure Vessel Code) specify minimum Charpy energy (e.g., 48 J at -20°C) for welds and base materials depending on design temperature and thickness. Aviation and offshore platforms use Charpy testing to qualify weld procedures and material batches before construction.

Automation and data integration

Modern Charpy machines interface with laboratory information management systems (LIMS), auto-recording specimen ID, material batch, test temperature, and results. Some advanced units include high-speed video (1000 fps) to capture the fracture initiation and shear-lip growth, enabling fracture mechanics correlation and fatigue-life prediction.