1,720,968 research outputs found
Low-cycle Thermal Fatigue and High-cycle Vibration Fatigue Life Estimation of a Diesel Engine Exhaust Manifold
Full text linkThis paper aims at estimating the low-cycle and high-cycle fatigue life of a turbocharged Diesel engine exhaust manifold. First, a decoupled thermo-structural Finite Element analysis has been performed to investigate low-cycle fatigue phenomena due to the thermal loadings applied to the exhaust manifold. High/low temperature cycles causes stress-strain hysteresis loops in the manifold material whose related dissipated energy can be directly correlated to low-cycle thermal fatigue. Afterwards, a dynamic harmonic analysis has been performed aiming at investigating the existence of high-cycle fatigue phenomena due to vibrational loading applied to the exhaust manifold during the duty cycle. Three direction acceleration experimental loadings have been applied to the model. An ad-hoc methodology has been developed to superimpose thermo-structural results to dynamic harmonic analysis results. In particular, quasi-static thermo-structural results have been employed to identify the mean stress values of vibration fatigue cycles, while alternate stress values have been derived from harmonic analysis. Different combinations of frequencies and phases of the acceleration input signals have been considered to create different high-cycle fatigue loadings. Each cyclic load case has been processed employing the multiaxial Dang Van fatigue criterion
Influence of the initial clearance on the peak stress in connecting-rod small ends
No full textThe stress increase that is caused by the presence of an initial clearance within thesmall end of connecting rods for motorbike and car engines is investigated. Plane analyticaland numerical modellings of the dry contact between the small-end and piston pin areadopted. Based upon a recent analytical result, a normalizing parameter is introduced, whichallows the stress concentration factor at the small-end bore sides to be expressed as a functionof a proper combination of the initial clearance between the small end and gudgeon pin, theapplied load, and Young’s modulus, for prescribed aspect ratios of the small end and hollowpin. Design diagrams summarizing the consequences of an initial clearance between the smallendbore and gudgeon pin on the eye peak stress are reported, which cover a wide range ofgeometries, clearances, and loadings. Selected comparisons between two-dimensional andthree-dimensional models are carried out
Contact stresses within a split ring inserted into acircular housing
No full textThe contact problem between a split ring and a circular housing is mechanicallyexamined. This contact is revisited in terms of receding contact, the zones along which the ringbeds over the housing are investigated, and normalizing design parameters are evidenced. Thesplit ring is modelled in terms of a straight, purely flexural beam as well as of a curved, shearelasticbeam; for both models, analytical solutions are obtained. Various easy accessible designdiagrams, useful for estimating the maximum elastic stresses within the split ring and the axialinsertion force, have been prepared with the aid of these two beam models and using finiteelements. The mechanical response of the split ring when its angular width is appreciably lowerthan p is clarified
Influence of different temperature distributions on the fatigue life of a motorcycle piston
Full text linkIn this paper, finite element analyses are performed to evaluate the stresses and the strains in a motorcycle piston. Non-linear finite element models are employed to mimic the piston behaviour when subjected to different loading conditions. In particular, the gas forces, the inertial forces and the piston-to-cylinder contact forces are considered. Appropriate temperature distributions are applied to the model to include the thermal stresses and strains in the analyses. Two different thermal configurations are considered: the first has a standard design of the oil jet hitting the underside zone of the piston crown, while the second presents modified parameters able to increase the heat transfer coefficient appreciably. The different operating temperature distributions related to the two thermal configurations considered strongly influence the pistons thermomechanical behaviour. This paper aims to perform high-cycle fatigue analyses to show how the fatigue life and fatigue-critical points of the component change when moving from the standard configuration to the modified configuration
Influence of the temperature distribution on both high-cycle and low-cycle fatigue life of a motorbike piston
No full textFinite Element analyses are performed to evaluate stresses and strains in a motorbike
piston. Non-linear Finite Element models are employed to mimic the piston behaviour when
subjected to different loading conditions. In particular, gas forces, inertial forces, and piston-tocylinder
contact forces are considered. Temperature distributions formally evaluated and validated
against experimental evidences [1] are applied to the model to include thermal stresses and strains
into the analysis. Two different thermal configurations are considered: the first has a no-optimized
design of the oil jet hitting the underside zone of the piston crown, while the second presents
modified parameters able to appreciably increase the heat transfer coefficient. This aspect causes
different operating temperature distributions that strongly influence the piston behaviour. This
paper aims at performing both low-cycle and high-cycle fatigue analysis to show how the fatigue
life and fatigue-critical points change in the two considered thermal configuration
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Three examples of inadequacy of the Williams asymptotic method in predicting the singularity strength in elastic problems
No full textThree examples are presented for which the Williams asymptotic method
appears to be inadequate in forecasting the strengh of the singularity encountered in elastic
problems. The first case addresses a Kirchhoff plate resting on an irregular linear support;
the second example revisits a classical plane elasticity contact problem; the third case
considers an infinite sheet with a square hole. The reasons of the inadequacy of the Williams
asymptotic method in treating the above situations are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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