Definition
The material impact tester is a mechanical property testing equipment used to determine the toughness or brittleness behavior of materials under high-speed impact loads. It evaluates a material's ability to resist impact failure by measuring the energy absorbed by a specimen during a one-time impact fracture. This performance metric is critical for the safe application of many engineered materials in dynamic load environments.
Principle
The basic principle of impact testing is based on the law of conservation of energy. The core process of the testing machine is to lift the pendulum with a certain mass to a predetermined height to give it the initial potential energy. After release, the pendulum falls freely, impacting and breaking the pre-placed specimen at its lowest point. The specimen fracture consumes part of the energy, causing the pendulum to lose its remaining kinetic energy and its recovery height to be lower than the initial height. By measuring the remaining lift angle after the pendulum impact, the impact energy absorbed by the specimen fracture can be calculated.
The formula for calculating impact absorbed energy (usually denoted by the symbol KU or KV) can be expressed as:
KU = m * g * L * (cos β - cos α)
m is the pendulum mass, g is the gravitational acceleration, L is the pendulum length, α is the initial lift angle, and β is the maximum lifting angle after breaking the specimen.
Measurement method
The standard impact test methods are mainly divided into Charpy impact test and Aizo impact test. The Charpy impact test uses specimens with horizontal support at both ends and notched backward impact edges. The Aizo impact test uses a cantilever beam specimen with a fixed end and a notch facing the impact blade. Both methods require prefabricating standard notches on the specimen to create stress concentrations, which more sensitively reflects the material's resilience to the notch. During testing, it is necessary to prepare specimens, set parameters and operate equipment in strict accordance with relevant standards (such as ISO, ASTM, GB, etc.). The final result is expressed as the impact absorption energy value, sometimes supplemented by cross-sectional topography analysis.
Influencing factors
Impact test results are influenced by a variety of factors. The material itself includes chemical composition, microstructure, fiber orientation, etc. Among the test conditions, the influence of temperature is significant, and many materials will undergo toughness and brittleness with the decrease of temperature. The notch shape and depth of the specimen directly affect the stress concentration degree. In addition, impact velocity, specimen size, and friction loss and energy resolution of the device also have an impact on measurement accuracy. Therefore, the comparative data must be carried out under strict and uniform test conditions.
Application:
Material impact testing is widely used in industrial and scientific research fields where the dynamic toughness of materials needs to be evaluated. In the field of metal materials, it is often used to evaluate the low-temperature toughness of building steel structures, pressure vessel steel, pipelines, and rail transit components. In the field of polymer materials and composite materials, it is used to test the impact resistance of plastics, nylon, fiberglass reinforced steel and other parts. In addition, impact testing is also a routine test item in auto parts, aerospace materials, new energy equipment components, and product quality control and failure analysis.
Selection considerations
When choosing a material impact testing machine, systematic considerations are required. First of all, the standards to be followed for the test should be clarified, which determines the structural type, pendulum energy range and measurement accuracy requirements of the testing machine. Secondly, according to the expected impact energy range of the material to be tested, choose a testing machine with a suitable initial energy level, and consider whether it has the ability to replace the pendulum to accommodate a wider range of energy testing needs. The energy loss of the equipment should be as small as possible, and it should be equipped with a high-precision angle encoder to ensure accurate energy calculations. In addition, it is also necessary to consider whether the safety protection device is complete, whether it has automatic data collection and processing functions, as well as the stability and maintenance convenience of the equipment in long-term use. The final choice should be based on specific testing needs, budget, and laboratory conditions.