friction

摘要： This paper proposes a zero-moment control torque compensation technique.After compensating the gravity and friction of the robot,it must overcome a small inertial force to move in compliance with the external force.The principle of torque balance was used to realise the zero-moment dragging and teaching function of the lightweight collaborative robot.The robot parameter identification based on the least square method was used to accurately identify the robot torque sensitivity and friction parameters.When the robot joint rotates at a low speed,it can approximately satisfy the torque balance equation.The experiment uses the joint position and the current motor value collected during the whole moving process under the low-speed dynamic balance as the excitation signal to realise the parameter identification.After the robot was compensated for gravity and static friction,more precise torque control was realised.The zero-moment dragging and teaching function of the robot was more flexible,and the drag process was smoother.

摘要： Since the global financial crisis in 2008,frictions between China and the United States have been growing,as the backlash against globalization is on the rise.Such frictions,emerging during the Obama administration,became fully public during the Trump administration.After the Biden administration took office,the China-US relations,though more“diplomatic”in appearance,have seen the inherent divisions widening.The China-US conflicts have become an integral part of the entrenched China perception of the Deep State.With the evolution of the international landscape accelerated by COVID-19,the interactions between China and the United States are being shown more visibly than ever to the world.

摘要： The fabrication of boron carbide reinforced aluminum matrix composites(Al-B_(4)C)with various contents of B_(4)C(1wt%,6wt%,15wt%,and 30wt%)was performed by powder metallurgy,and the influence of the content of B_(4)C on their mechanical and tribological behavior was examined.The Al-30B_(4)C composites recorded the highest density(~2.54 g/cm^(3)),lowest porosity(4%),maximum Vickers hardness(HV~75),lowest weight loss(0.4 mg),and lowest specific wear rate(0.00042 mm^(3)/(N·m))under a load of 7 N,with an enhancement of 167%in hardness,a decrease of 75.8%in weight loss,and a decrease of 76.7%in the specific wear rate compared with pure aluminum.In addition,the scanning electron microscope images of the worn surface revealed that the Al-B_(4)C composite has the narrowest wear groove of 0.85 mm at a load of 7 N,and the main wear mechanism was observed as an abrasive wear mechanism.According to the friction analysis,the coefficient of friction between surfaces increased with increasing boron carbide content and with decreasing applied load.In conclusion,B_(4)C is an effective reinforcement material in terms of tribological and mechanical performance of the Al-B_(4)C composites.

摘要： China’s development in just two generations shows how poverty can be tamed with pragmatic projects.WHILE the Western world complains about economic growth slowing down,soaring inflation,supply chain problems,and worsening living standards,China has presented a record of success,notwithstanding the COVID-19 pandemic.China’s GDP grew by 8.1 percent in 2021,and trade in goods increased by 21.4 percent despitethe trade friction with the U.S.The economy is stable,the Chinese market continues to open to foreign enterprises,and Chinese enterprises,especially startups,are encouraged to invest in new innovative products.The market is transforming to support a digital economy,with regulations in place to restrain monopoly and unfair competition.

摘要： To understand the research status of asphalt pavement texture,the related achievements and progress of pavement surface texture were systematically sorted out from three aspects:the characterization of pavement surface texture,the texture measurement and evaluation,and the relationship between texture and the skid resistance.Based on the statistical geometric characteristics,the spectral characteristics,the fractal characteristics and the multifractal characteristics,the characteristics of pavement texture were discussed.The test methods of pavement texture were divided into two categories:direct measurement methods and indirect measurement methods.The advantages and disadvantages of each measurement method were summarized.The effects of macro-texture and micro-texture on asphalt pavement were discussed,respectively.The relationship between texture and skid resistance was studied.This review shows that multifractal theory should be further studied from the aspect of road engineering.High-precision non-contact integrated detection technology should be further studied to meet the needs of complex testing environments.The method of finite element numerical simulation has potential for the analysis of pavement skid resistance.In addition,methods such as big data analysis,neural network,and deep learning should be studied to achieve the intelligent perception and management of the whole state of skid resistance prediction.

摘要： Themain goal of this work is to study the ballistic performance ofmulti-layered moderately-thick metallic targets.Several target configurations have been considered in thiswork,with various types of interlayer connection(spaced,contacted and adhesive)and the number of layers(four and eight),and the influence of target configurations on ballistic performance has been studied experimentally and numerically.In the experiments,the targets were impacted by 12.7-mm projectiles at a velocity around 820 m/s.The experimental results show that,with similar total thickness,the contacted and adhesive targets exhibit better ballistic performance than the monolithic targets,and the four-layered targets are better than the eight-layered targets with the same connection type.To explore the ballistic resistance mechanism,numerical method has been used to simulate the penetration process of each target.The numerical results indicate that petal formation and friction have significant influence on targets’ballistic performance.Friction has stronger influence on themulti-layered targets than on themonolithic ones.According to the numerical results,about 14%of projectile’s initial kinetic energy is dissipated by friction during penetrating the four-layered contacted target,which is proved to be the most effective type of target studied in thiswork.The results also indicate that,in contrast to common understanding,friction plays an important role even when the impact velocity is significantly higher than the ballistic limit.The outcome of this work may provide useful information for a better understanding of ballistic resistant mechanisms and more efficient utilization of multi-layered metallic targets in armor structural design.

摘要： Unlike most fluids,granular materials include coexisting solid,liquid or gaseous regions,which produce a rich variety of complex flows.Dense flows of grains driven by gravity down inclines occur in nature and in industrialprocesses.To describe the granular flow on an inclined surface,several studies were carried out.We can cite in particular the description of Saint-Venant which considers a dry granular flow,without cohesion and it only takes into account the substance-substrate friction,this model proposes a simplified form of the granular flow,which depends on the one side on the angle of inclination of the substrate with respect to the horizontal plane and on the other side on the thickness of the substance H.The numerical simulation we have developed is first based on the Saint-Venant model,it allowed us to visualize the variation of the speed according to the thickness of the substance(from 0 to H)and to deduce the average speed of the substance on an inclined plane.However,this restrictive model does not take into account the effect of particle friction on the flow and considers that the thickness H is constant.To make our simulation more realistic,we opted for the Savage-Hatter model.We took into account the variation of the thickness on the particles speed,in addition we have studied the effect of the variation of many parameters on the granular flow,namely the temperature and the roughness of the substrate,the density and the compactness of the substance,we found that the speed of the particles increases and the treatment time decreases with an increase in temperature.

摘要： Due to an array of negative factors,such as the COVID-19 pandemic,trade frictions,geopolitical tensions,diplomatic conflicts,and natural disasters,the global industrial and supply chain is now in a bind.With the most complete industrial chain and being among the biggest exporters and importers in the world,China is under close watch by the rest of the world.In the first half of this year(H1),in response to resurging COVID-19 cases,Beijing and Shanghai enforced a strict dynamic zero-COVID-19 policy,triggering concerns across the world over China’s role in the global industrial and supply chain.

摘要： Surface chemistry of solids is the fundamental for processes on solid surfaces and properties of solid surfaces,such as heterogeneous catalysis,electrochemistry,corrosion,thin film growth,sensing,friction and lubrication[1].Understanding surface chemistry of solids is not only of great scientific interest,but also of important technological value for optimizing surface properties and processes.Due to the complexity of solid surface structures,it is challenging to unambiguously elucidate the surface chemistry of surface properties and processes at a molecular level.

摘要： Charles William Johns has recently published a concise treatise of ontology entitled The Irreducible Reality of the Object:Phenomenological and Speculative Theories of Eqipment.1 This title suggests Johns’s intellectual proximity to Object-Oriented Ontology(OOO),and Johns is perfectly open about those points where he agrees with OOO:indeed,the book is dedicated to me and Tristan Garcia,whose own philosophy of things is located not so far from mine.2 But as is often the case in works of this kind,Johns’s points of friction with his neighbors are of even more interest than his agreements.This becomes clear from a chapter entitled“The New Reality of the Object,”to which we now turn.