Model and experiments to determine lubricant film formation and frictional torque in aircraft landing gear pin joints

Pin joints are found in many large articulating structures. They tend to be under high load and articulate slowly; so, the joints typically operate in the boundary or mixed lubrication regimes. This means that the operating torque depends on the respective proportions of liquid and solid contact between the joint mating faces. In this article, a mixed lubrication model of a grease-lubricated landing gear joint is established to determine a theoretical Stribeck curve, frictional torque and lubricant film thickness under different loads. Parameters describing pin joint working conditions, geometry, lubricant properties and pin/bush texture are used. The model can also predict the proportion of the load that is supported by contacting asperities and lubricant film. The changing proportions of these two parts indicate transformations between different lubrication regimes. Experiments on an instrumented pin joint have been carried out to compare with the predicted friction and torque performance. Theoretical calculation results show good consistency with experimental plots at high load. But under low load, the real friction between pin and bush is significantly lower than theoretical predictions

Hardness characterisation of grey cast iron and its tribological performance in a contact lubricated with soybean oil

The effect of hardness of grey cast iron flat specimen on its wear and friction on the contact were characterised with the presence of vegetable oil as biolubricant. Prior to the tribological test, the as - received grey cast iron flat specimen hardness was characterised. Friction and wear tests were then conducted using a ball - on - flat reciprocating sliding contact. The one - way analysis of variance (ANOVA) was used to determine the significance of friction and wear data with a 95% significance level. The wear scars after the test were then characterised by surface roughness and wear mechanism. The microstructure and elemental analysis we re also reported. The average value of hardness was 210 HV with a large difference between minimum (185 HV) and maximum (250 HV) values. The friction and wear performance of grey cast iron specimens with soybean oil varied with its hardness. The specimens with higher hardness gave lower friction coefficient and greater wear resistance than the lower hardness specimens. The difference in coefficient of friction produced between high hardness specimens (COF = 0.122) and low hardness specimens (COF = 0.140) wa s 17%. In terms of mass loss, the low hardness 2 specimens (mass loss = 50.38 mg) and the high hardness specimens (mass loss = 12.90 mg) produced a difference of 74%. It is shown that, with soybean oil lubricant, the grey cast iron specimen can produce wide range of tribological data especially on mass loss due to its hardness distribution. The influence of soybean oil lubrication in this work is less in improving the wear resistance (about 7%), but greater for friction reduction (about 24%) compared to an un lubricated grey cast iron surface. The hardness of grey cast iron specimen is an important parameter that needs to be specifically measured and controlled on the contact due to wide hardness distribution of grey cast iron may produce variation in tribologi cal data

Positive Behavioral Support: Strategies for teachers

Positive behavioral support (PBS) is a comprehensive, research-based proactive approach to behavioral support that endeavors to generate comprehensive change for students with challenging behavior. It involves identifying the purpose of challenging behavior, teaching appropriate alternative responses that serve the same purpose as the challenging behavior, consistently rewarding positive behaviors and minimizing the rewards for challenging behavior, and minimizing the physiological, environmental, and curricular elements that trigger challenging behavior. Proven PBS strategies include altering the classroom environment, increasing predictability and scheduling, increasing choice making, adapting the curriculum, appreciating positive behaviors, and teaching replacement skills. Relevant sources for those interested in implementing PBS are presented