Impact resistance test of composite materials
1. Test method for low-speed impact
In order to simulate the impact behavior of materials under real conditions, researchers have proposed a large number of experimental methods. According to the actual situation of the impact, the impact is generally divided into high-speed impact and low-speed impact.
High-speed impact is also called ballistic impact. Because high-speed impact has received significant attention in the aerospace and military fields, people have conducted a lot of experimental research on high-speed impact. High-speed impact usually uses a small mass projectile to hit the material at a higher speed, and mainly uses air guns to launch projectiles to study the high-speed impact behavior of composite materials, as shown in the figure:
The low-speed impact test usually simulates the impact of a large-mass object on the surface of the material at a lower speed, such as the accidental drop of a tool during repair, and a drop-weight test device is usually used for experimental simulation.
Figure 2 Drop hammer test device
The research results show that the shape, quality and speed of the projectile will have a significant impact on the failure mechanism of composite materials. For example, researchers have conducted a lot of research on the relationship between the shape of the hammer head and the impact behavior of composite materials. Generally speaking, the sharper the hammer head is used, the more localized the impact damage range of the material, and the main failure mode changes from delamination to matrix failure and damage. Fiber breaks.
2. The influence of environmental factors on low-speed impact performance
Composite structural parts have to experience complex environmental effects during long-term use, such as high temperature, low temperature, damp heat, and thermal cycles. Studies have shown that under the action of these environments, the mechanical properties of composite materials will change significantly. Thermal cycling usually reduces the bending and transverse tensile strength of the composite material, and generates a large number of microcracks in the matrix.
Mainly use environmental pretreatment and environmental simulation tests to study the impact of environmental effects. The so-called environmental pretreatment is to put the composite material to be tested in a certain environment for processing in advance, and then subject the processed material to a low-speed impact test at room temperature. The environmental simulation test is to put the composite material into the environmental chamber while impacting. This method is used to study the impact performance of the components in different service environments.
3. The effect of material properties on low-speed impact performance
Fiber is widely used as a reinforcement in the production of composite materials. At the same time, as the main bearer of the load, the fiber’s performance has a great impact on the overall impact resistance of the composite material. The fibers used in the aerospace industry mainly include carbon fiber, glass fiber and Kevlar fiber. Due to the unique brittleness of carbon fiber, the impact resistance of carbon fiber reinforced resin matrix composites is weaker than that of glass fiber and Kevlar fiber.
The matrix of fiber-reinforced resin-based composite materials plays an extremely important role in composite materials. The resin matrix is inseparable from whether it is to transmit load, maintain the orientation of fibers or maintain the integrity of the material. The results of the study show that although the mechanical properties of thermosetting resins are better than those of thermoplastic resins, the cross-linked molecular structure of thermosetting resins makes them less tough, which makes them more prone to failure under impact load.
The interface plays the role of transferring load to the fiber in the composite material, so the performance of the interface will affect the overall performance of the composite material. The composite material with poor interface bonding between the fiber and the matrix will show lower strength and stiffness, and Too strong bonding will make the material brittle.
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Post time: Oct-14-2021