Effects of bionic models with simultaneous thermal fatigue and wear resistance

Drum brake is one of important components in braking system. Because of complicated working environment and wrong operation like overload, drum brakes would be damaged earlier than expected(1). According to interdisciplinary research, bionics have great applications in many fields(2), and bionics has had a profound influence on materials science including grey cast iron. Studies have shown that bionic coupling surface could be effectively improved thermal fatigue and wear resistance of grey cast iron.


INTRODUCTION
Drum brake is one of important components in braking system. Because of complicated working environment and wrong operation like overload, drum brakes would be damaged earlier than expected (1). According to interdisciplinary research, bionics have great applications in many fields (2), and bionics has had a profound influence on materials science including grey cast iron. Studies have shown that bionic coupling surface could be effectively improved thermal fatigue and wear resistance of grey cast iron.
In this study, enlightened by leaves and dragonfly wings (3), an idea of processing a similar surface, which is soft part like lamina and membrane, hard part like veins, soft and hard structure could make dragonfly wings flap 40 times per second and leaves exposed in wind and rains without being damaged (4). As such, the bionic coupling surface was processed by pulse laser. The parameters need to be selected for processing good quality bionic coupling unit. A three-level three-factor orthogonal test was designed. However, failure mechanism of drum brake is particular. With regular single model bionic coupling processing cannot perform its powerful function on drum brake(5).
According to the failure mechanism of drum brake in this study, multiple single models were used for various combinations, and the effects of different angles of each double combination model were studied as well. The best double combination model, which was chosen by considering the best performance of thermal fatigue resistance, wear resistance and processing efficiency. Every single model was also selected by the results of thermal fatigue test and wear test, and the bionic coupling drum brake with the best double combination model was then subjected to bench test.

METHDOLOGY
Experimental samples of 40×20×6mm3 were cut by electric spark machine, bionic coupling models were processing by Nd-YAG laser of 1.06 μ m wavelength and maximum power of 800W. Six double combination models were made up of five different angels' stripes (0°, 30°, 45°, 60°, 90°) and a 45°mesh with a frame processed along the four edges of samples. Bionic coupling samples were subjected to thermal fatigue cold cycling at temperatures ranging from 25 ℃ to 700 ℃ , where each was heated and cooled for 180s and 5s, and then bionic coupling samples were tested for wear resistance, using MG-200 wear tester, under the following conditions: load 80N, speed 700 rpm, and wear time 60h, with the friction pair was fabricated from a 45# steel with a hardness of 50 HRC. After above experiments, the best double combination model was processing by pulse laser on the surface of drum brake, and then the bionic coupling drum brake was subjected to bench test, which was speeded up from 0 to 96km/h and then braking to 0, which took 90s as one cycle.

UKHTC2019-
Orthogonal test design constitutes an effective scientific method for performing complex multifactor tests. Therefore, a three-level three-factor orthogonal test for drum brakes was designed in this study. The results shows that current, pulse width, frequency, defocusing amount and moving speed of mechanical arm.

Thermal Fatigue Test
The results showed that fewer cracks formed on the bionic coupling surface but many long cracks appeared on the surface of untreated samples. The stress, material cracking and deformation were led by temperature changes. The surface layer expanded in dimension at the beginning of cooling, the surface layer of sample shrank firstly while temperature of inter was still high, so the compressive stresses were produced. The best model for thermal fatigue resistance is 0 degree angle which was perpendicular to the direction of cracks' growth with 45 degree mesh double combination.

Wear Test
Wear test results showed that less wear tracks on the surface of bionic coupling samples than the normal samples. Due to the higher hardness of the units, hard-soft structure could effectively resist deformation. In addition, the unit itself could eliminate the mechanical stress the generated by graphite as No. Current (A) Pulse Width (ms) Frequency (Hz)