The Charpy Test & Drop Weight Methods
Impact testing determines a material’s toughness or impact strength in the presence of a flaw or notch and fast loading conditions. This destructive test involves fracturing a notched specimen and measuring the amount of energy absorbed by the material during fracture. Impact testing at Laboratory Testing Inc. is performed by two methods:
- Charpy Impact Test including:
- Weld Charpy Test
- Charpy V-notch Test
- Drop Weight Test
Iron and all other body-centered cubic metals undergo a transition from ductile behavior at higher temperatures to brittle behavior at lower temperatures. The impact test is required to evaluate materials used by many industries including steel hull plate for ships, nuclear plant pressure vessels and forgings for electric power plant generator rotors
Our full-service Machine Shop can prepare your impact test specimens on the latest CNC equipment including the charpy V-notch test specimen. LTI is on NIST’s (National Institute of Standards and Technology) Qualified Manufacturers List for Charpy V-notch Impact verification specimens.
The Impact Test Processes
A charpy impact test entails striking notched specimens with a swinging weight or pendulum at a series of temperatures to show the relationship of ductile to brittle transition in absorbed energy. Several machined bar specimens, 1cm x 1cm x 5.5cm with a 2mm deep notch at the middle of a specified flat surface, are required to perform the charpy test. The charpy V-notch test is very common and requires a specimen with a V-shaped notch. The specimens are tested at a series of specified temperatures (e.g. -20ºC, -10ºC, 0ºC, +10ºC, +20ºC) in the range of -452ºF to 500ºF.
Low temperature charpy testing involves placing the specimens in a chamber bath of propylene glycol and dry ice until a calibrated thermocouple records the temperature required for the test. Once a specimen reaches the precise temperature, it is quickly placed into a special holder with the notch oriented vertically and toward the origin of impact. The specimen is struck by a “tup” attached to a swinging pendulum of specific design and weight. The specimen breaks at its notched cross-section upon impact, and the upward swing of the pendulum is used to determine the amount of energy absorbed (notch toughness) in the process.
Watch the process in the Charpy Impact Test Video below.
Drop Weight Test
The drop weight test method subjects each beam specimen in a group at a progression of temperatures to a single impact load from a guided free-falling weight dropped in a vertical direction. The drop weight test determines the maximum temperature at which a specimen breaks or the temperature at which the fracture mode of the steel changes from ductile to brittle (Nil-ductility transition or NDT temperature). The initial test is conducted at a temperature estimated to be near the NDT temperature. The remaining specimens are then tested at a progression of temperature intervals to determine the break and no-break performance temperatures within 10°F or (5°C).
- Test capabilities – charpy impact testing, drop weight testing, weld testing
- Temperature capabilities – -452ºF to 500ºF
- Specimen machining – all charpy test specimens; NIST approved for charpy V-notch test specimens
- ASTM A370
- ASTM E23
- ASTM E208
- ISO 148