Widely used FRP materials are often subjected to impact loads during use, such as the impact of trains when driving and stopping, and the deformation of the car body when the car collides. FRP is widely used in the automotive industry due to its high strength and low price, especially for the production of bumpers and bodywork. According to experts, the impact resistance of these parts of the car is one of the important indicators to measure its mechanical properties. When the composite material is subjected to low-energy impact during use, most of the cases have no obvious visual damage, but the invisible shallow surface delamination is formed on the laminated surface, thereby forming a potential danger, and the existence of internal damage may cause Composite materials, a large loss in strength and stiffness. Experts from China's unsaturated resin network said that extensive and in-depth research has been done on the mechanism and characteristics of low-energy impact damage of composite laminates. Giuseppe Sala and Dai Gil Lee have done a lot of work in this area. Some domestic researchers have done similar work and achieved some results. There are many researches on the optimization design of composite laminates, but there are not many studies on the impact of laminate methods on the impact resistance of composites. According to experts, in order to design and produce more safe and stable FRP products, experts have compared the low-energy impact performance of glass fiber reinforced unsaturated polyester resin composite materials with different lamination processes.
(3) Impact resistance test The quality of the punch that kept the drop weight in the experiment was fixed at 5.7806 kg. According to experts, the impact speed is set as needed to obtain different drop weight heights. According to the law of conservation of energy, the instantaneous maximum impact kinetic energy of the drop hammer is:
Where m is the mass of the drop hammer; Vi is the instantaneous velocity of the drop hammer impact. The energy absorbed when the material is damaged is:
In the formula, Vf is the instantaneous maximum reverse speed after the falling hammer is rebounded by the plate; the kinetic energy obtained by the elastic deformation of the falling hammer due to the impact of the laminated plate.
During the impact process, the impact load calculation formula is:
Where V(t) is the curve of speed versus time.
Test instrument: Dynatup92 type material impact meter produced by INSTRON Company of the United States.
Punch shape: bullet shape.
A 95 mm × 95 mm square test piece was placed on the support surface of the test bench to impact the samples of different layups. A total of 4 groups, 5 test pieces per group, and the test data were taken as the average of 5 samples. Each set of test pieces is selected to have an impact velocity v of incident energy that causes the test piece to undergo a large deformation. According to experts, due to the operation error of manual zero adjustment and the friction error generated by the machine itself during the impact process, v has a certain deviation on the basis of setting, ranging from 0.8 to 0.9 m/s. Different shock load-time and energy-time relationships are obtained.
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