Effects of angle formation between melted zone and friction direction on thermal fatigue and wear resistance of truck drum brake

The failure of grey cast iron drum brake is mainly caused by thermal fatigue crack running through the top along the axial direction, which has the characteristics of regional failure. By using the advantages of laser fabrication technology, the single models with five different angles combined with the anti-crack ring were designed. The optical microscope, scanning electron microscope and X-ray diffraction were used to characterize the microstructure and phase of the drum brake material grey cast iron and the bionic coupling unit. Both single models and double combination models were tested for thermal fatigue and wear after thermal fatigue, respectively. The effects of angle on the thermal fatigue and wear resistance of the bionic coupling models were investigated. Experimental results show that the microstructure of the unit was better than that of the base grey cast iron due to the appearance of ledeburite, martensite and residual austenite after laser treatment. Besides, thermal fatigue crack has a great influence on wear performance. The thermal fatigue crack and wear loss weight are the least in the model with anti-crack ring + 45°angle, the main crack length is the shortest. The service life of the drum brake with the double combination bionic coupling model is increased by 50% compared with that of the untreated drum brake in bench test.

Numerical investigation of aerodynamic and acoustic characteristics of bionic airfoils inspired by bird wing

Airfoil is the basic element of fluid machinery and aircraft, and the noise generated from that is an important research aspect. Aiming to reduce the aerodynamic noise around the airfoil, this study proposes an airfoil inspired by the long-eared owl wing and another airfoil coupled with the bionic airfoil profile, leading edge waves, and trailing edge serrations. Numerical simulations dependent on the large eddy simulation method coupled with the wall-adapting local eddy-viscosity model and the Ffowcs Williams and Hawkings equation are conducted to compare the aerodynamic and acoustic characteristics of two types of bionic airfoils at low Reynolds number condition. The simulations reveal the dipole characteristic of acoustic source and sound pressure level distribution at various frequencies. Two types of bionic airfoils show lower noise compared with the conventional NACA 0012 airfoil with a similar relative thickness of 12%. Compared with the bionic airfoil, the average value of sound pressure level at the monitoring points around the bionic coupling airfoil is decreased by 9.94 dB, meanwhile the lift-to-drag ratio also keep higher. The bionic coupling airfoil exerts a suppression of sound pressure fluctuation on the airfoil surfaces, which result from that the range and size of separation vortices are reduced and the distance between vortices and airfoil surface are increased. The tube-shaped vortices in the wake of airfoil are effectively restrained and split into small scale vortices, which are important to cause less aerodynamic noise around the bionic coupling airfoil. Consequently, a novel bionic coupling airfoil is developed with the excellent aerodynamic and acoustic performance.