Charpy Impact Tester Evaluates Brittle Fracture of Carbon Fiber Plates

Introduction

In the field of materials science, evaluating the fracture behavior of plates under dynamic loads is a common need. As a classic method, the impact test of simply supported beams is widely used to determine the fracture resistance of materials under high-speed impact. This paper will take carbon fiber plate as an example to discuss how to evaluate the brittle fracture characteristics of carbon fiber plate by a simple beam impact tester, and analyze the relevant technical points and data interpretation methods.

Test principle

The basic principle of the impact test of the simply supported beam is to place the specimen horizontally on two support points to form a simple supported beam structure. By releasing the pendulum, it hits the middle of the specimen at a specified speed, causing the specimen to break in a three-point bending state. By measuring the energy difference between the impact of the pendulum and the impact, the energy absorbed by the fracture of the specimen can be calculated, which is often used to characterize the toughness or brittleness tendency of the material. For composites such as carbon fiber plates, the fracture behavior is significantly affected by fiber orientation, layer structure and matrix characteristics, and the impact energy value can reflect the ability of the material to resist crack propagation.

The fracture absorption energy A of the specimen can be calculated by the following formula:
A = m * g * (h₁ - h₂)
where m is the mass of the pendulum, g is the acceleration of gravity, h₁is the initial height of the pendulum, h₂The pendulum is raised after impact.

Sample preparation

The preparation of carbon fiber plate specimens requires strict adherence to relevant standards to ensure comparable results. Usually the specimen is a rectangular strip, and the length, width and thickness need to be precisely cut according to the standard. The edges of the specimen should be flat and free of burrs to avoid data bias caused by stress concentration. For carbon fiber plates with obvious anisotropy, the specimen orientation (e.g., along the fiber direction or vertical direction) should be indicated and clearly recorded in the report.

Experimental process

Before the test, the impact testing machine needs to be calibrated to ensure that the energy loss of the pendulum is within the specified range. Place the specimen accurately on the support base so that the impact blade is aligned with the center of the specimen. Release the pendulum to complete the impact and record the energy indication. Each set of trials should contain a sufficient number of specimens to obtain statistically significant data. The temperature and humidity of the test environment should be recorded and controlled, because the mechanical properties of carbon fiber composites may be affected by environmental conditions.

Data & Discussion

The impact test data of carbon fiber plates usually includes impact absorption energy, fracture morphology observation, etc. Low impact energy value is often accompanied by flat fracture surfaces, which is a typical feature of brittle fractures. while higher energy values may be accompanied by complex failure modes such as fiber pullout and delamination, showing a certain degree of toughness. By systematically testing plates with different ply designs or processes, the differences in brittle fracture tendencies can be compared.

The following is an example data sheet showing a summary of the test results for two different carbon fiber sheets:

Note: The data are examples only, and the actual value needs to be determined by repeated experiments.

Influencing factors

There are various factors that influence the impact test results of carbon fiber sheets. The material itself factors include fiber type, resin system, interfacial bond strength, and layer order. Test parameters such as impact velocity, support span and specimen size also directly affect the results. In addition, the processing quality of the specimen, whether there are preset notches, and the status of the testing machine need to be strictly controlled to ensure data reliability.

Conclusion

The impact test of the simply supported beam provides an effective means to evaluate the brittle fracture of carbon fiber plates. Through standardized sample preparation, rigorous testing process and comprehensive data analysis, quantitative indicators reflecting the dynamic fracture behavior of materials can be obtained. The results of this method are helpful for material research and development and quality control, and provide a basis for optimizing the impact resistance of plates. In the future, combined with fracture microanalysis and other technologies, the understanding of fracture mechanism can be further deepened.

References

1. The introduction and test principle part refers to the standard text of the International Organization for Standardization on the impact test of plastic simply supported beams.
2. The sample preparation and testing process partly draws on the relevant technical literature on the physical property test method of composite materials.
3. Data Discussion and Influencing Factors section synthesizes several research papers on the impact behavior of fiber-reinforced polymers.