Experimental and numerical investigation into effect of elevated temperature on fretting fatigue behavior

Fretting fatigue damage occurs in contacting parts when they are subjected to fluctuating loadings and sliding movements at the same time. This phenomenon may occur in many applications such as bearings/ shafts, bolted and riveted connections, steel cables, and steam and gas turbines. In this paper, the effect of elevated temperature on fretting fatigue life of Al7075-T6 is investigated using a new device for fretting fatigue tests with variable crank shaft mechanism. Also a finite element modeling method was used to estimate crack propagation lifetime in aluminum alloy, Al7075-T6 specimens at elevated temperature under fretting condition. In this method, shear and normal stresses that are caused by contact load are updated at each crack growth increment. Finally, a comparison between the experimental and numerical results is done in order to evaluate the FE simulation. Department of mechanical engineering, Islamic Azad University, Takestan Branch, Takestan, Iran The experimental results show that: (i) fretting fatigue life of the material increases with temperature up to 350°C by 180% for low stresses and decreases by 40% for high stresses, (ii) this fashion of variation of fretting fatigue life versus temperature is believed to be due to degradation of material properties which occurs by overaging and wear resistance increase due to oxidation of aluminum alloy. While overaging gives rise to degradation of mechanical strength of material and hence the reduction of its fretting fatigue life, surface oxidation of the specimens brings some improvement of fatigue behavior of the material. Metallurgical examination of the specimens reveals that temperature results in precipitation of impurities of al-7075-T6. The size of precipitated impurities and their distances gets bigger as temperature increases. This could be a reason for material degradation of specimens which are exposed to heating for longer time duration

Efectividad de los cepillos laterales para barrido de calles

Se estudia experimentalmente la efectividad de los cepillos laterales para barrido de calles para remover varios tipos de basura. Se usa un cepillo cortador y un cepillo F128 bajo diversas condiciones de operación. Se identifican combinaciones apropiadas y óptimas de los parámetros de operación para varios tipos de basura. Se concluye que la gravilla mediana es de fácil remoción, mientras que las partículas pequeñas se tienden a quedar en las irregularidades de la vía y la basura húmeda delgada tiende a adherirse al cepillo y a quedarse en la vía. El cepillo F128 presenta mejor efectividad que el cortador

Desarrollos recientes en equipos de barrido de calles

El barrido de calles es una actividad necesaria para remover la contaminación de las calles y mantener en ellas una buena apariencia. Sin embargo, la cantidad de investigación sobre barredoras de calles es muy poca, y la literatura sugiere que las barredoras de calles no han sido muy eficientes en su operación. Debido a esto, en los últimos años se han desarrollado nuevas tecnologías que permiten a las barredoras tener mejor acceso a las basuras, remover más contaminación, reducir las emisiones de polvo a la atmósfera y aumentar la vida del equipo. Este artículo presenta brevemente la investigación que se ha efectuado sobre barredoras de calles, habla sobre los desarrollos recientes en estos vehículos y discute las necesidades de investigación con el fin de mejorar su desempeño

Modeling of an oscillatory freely-rotating cutting brush for street sweeping

A dynamic model of a novel oscillatory cutting brush for street sweeping in free rotation is developed. The bristles are modelled as cantilever beams. The equation of motion is determined through the theory of forced transverse vibrations of beams, and the solution is based on the normal-mode method. A sinusoidal angular speed function and a novel function, named VAP, are studied. The model is validated through finite element analyses. The effects of brush parameters on brush dynamics are identified. Notably, for the VAP function, a condition similar to resonance tends to occur in the stronger plane for bending deflections, when the frequency of the brush is an odd fraction of a natural frequency of the bristle for that plane. The model can also be applied to study the dynamics of a small-deflection cantilever beam, when the transverse external force is a squared, sinusoidal, triangle, or VAP wave

Determination of the Rayleigh damping coefficients of steel bristles and clusters of bristles of gutter brushes

Street sweeping is an important service that is usually performed by lorry-type vehicles that have a gutter brush, which is comprised of clusters of steel bristles that sweep the debris found in the road gutter. Effective operation of this brush is important, as most of the debris on roads is located in the gutter. In order to model a gutter brush by means of finite element dynamic analyses, it is necessary to determine appropriate values of the Rayleigh damping coefficients of both individual bristles and clusters of bristles. This paper presents the methodology and results of experimental tests that have been conducted to determine these coefficients. The results obtained are useful when studying the performance of conventional and oscillatory street sweeper gutter brushes by means of dynamic finite element modeling

Desarrollos recientes en equipos de barrido de calles

El barrido de calles es una actividad necesaria para remover la contaminación de las calles y mantener en ellas una buena apariencia. Sin embargo, la cantidad de investigación sobre barredoras de calles es muy poca, y la literatura sugiere que las barredoras de calles no han sido muy eficientes en su operación. Debido a esto, en los últimos años se han desarrollado nuevas tecnologías que permiten a las barredoras tener mejor acceso a las basuras, remover más contaminación, reducir las emisiones de polvo a la atmósfera y aumentar la vida del equipo. Este artículo presenta brevemente la investigación que se ha efectuado sobre barredoras de calles, habla sobre los desarrollos recientes en estos vehículos y discute las necesidades de investigación con el fin de mejorar su desempeño