Search results for "Mechanical Engineering & Transports"
showing 10 items of 408 documents
NOX reduction and efficiency improvements by means of the Double Fuel HCCI combustion of natural gas–gasoline mixtures
2016
Abstract Homogeneous Charge Compression Ignition (HCCI) and Double Fuel (DF) combustion represent two innovative processes sharing a strong potential for pollutant emissions and fuel consumption reduction. HCCI regards the auto-ignition of a homogeneous premixed charge of air and fuel, featuring very low NOX emissions and good efficiency. Double Fuel (DF) instead indicates the simultaneous combustion of gasoline and natural gas (or gasoline and LPG), premixed with air by the port injection of both fuels within same engine cycle. Since fuel mixtures enhances the HCCI performances widening the range of possible operating conditions, the authors tested the HCCI combustion process using natural…
Micromechanisms of load transfer in a unidirectional carbon fibre–reinforced epoxy composite due to fibre failures. Part 1: Micromechanisms and 3D an…
2006
This study gives a detailed analysis of load distributions around fibre breaks in a composite and the mechanisms involved in load transfer. In contrast to other studies reported in the literature the analysis considers different configurations of composite damage from the failure of a few fibres to the failure of many. The model considers the elastic case with and without debonding at the broken fibre/matrix interface. In this way, the usual limitations of the finite element approach are overcome so as to take into account the numbers and interactions of broken fibres whilst maintaining an evaluation of the various fields involved, in particular the stress fields associated with fibre failu…
Gradient-enhanced model and its micromorphic regularization for simulation of Lüders-like bands in shape memory alloys
2018
Abstract Shape memory alloys, notably NiTi, often exhibit softening pseudoelastic response that results in formation and propagation of Luders-like bands upon loading, for instance, in uniaxial tension. A common approach to modelling softening and strain localization is to resort to gradient-enhanced formulations that are capable of restoring well-posedness of the boundary-value problem. This approach is also followed in the present paper by introducing a gradient-enhancement into a simple one-dimensional model of pseudoelasticity. In order to facilitate computational treatment, a micromorphic-type regularization of the gradient-enhanced model is subsequently performed. The formulation empl…
Bearing strength and failure behavior of pinned hybrid glass-flax composite laminates
2018
Abstract The aim of the present work is to evaluate the influence of external layers of glass woven fabric on the pin-hole strength of flax/epoxy laminates. Single lap bearing tests were carried out to evaluate the fastened joint performances depending on laminate stacking sequence. In order to better identify the mechanical behavior of the hybrid laminate, full glass and flax laminates were also compared. In particular, bearing stress and failure mechanisms were investigated at varying joint geometry. Furthermore, an experimental failure map, clustering main failure modes of pinned hybrid composite laminate, was used to better clarify the relationship between mechanical failure and geometr…
Low-velocity impact behaviour of green epoxy biocomposite laminates reinforced by sisal fibers
2020
Abstract Due to its good mechanical characteristics, low cost and high availability in the current market, sisal fiber is one of the most used for the manufacturing of biocomposites in various industrial fields (automotive, marine, civil construction etc.). The particular sub-fibrillar structure of the sisal fiber (similar to aramid fibers) and the corresponding anisotropic behavior detected by recent research activities, suggest that such biocomposites should exhibit also high impact strength, in such a way to permit their advantageously use also for the manufacturing of crashworthy components (bumpers, helmets, protection systems etc.), that are at the same time also eco-friendly, lightwe…
Fatigue crack initiation and subsequent crack growth in fillet welded steel joints
2019
Abstract The fatigue damage evolution in fillet welded steel joints where cracks are emanating from the weld toe is investigated. Based on existing experimental data for as-welded joints including crack depth measurements of the early crack growth it is proposed to make a distinction between the crack initiation phase and the subsequent crack growth phase. The welded detail in question is an F class detail with plate thickness 25 mm made of medium strength carbon steel. It is found that the crack initiation phase defined at a crack depth of 0.1 mm is close to 25% of the fatigue life even at a relatively high constant stress range of 150 MPa. At lower stress ranges it is concluded that the i…
A three-dimensional cohesive-frictional grain-boundary micromechanical model for intergranular degradation and failure in polycrystalline materials
2013
Abstract In this study, a novel three-dimensional micro-mechanical crystal-level model for the analysis of intergranular degradation and failure in polycrystalline materials is presented. The polycrystalline microstructures are generated as Voronoi tessellations, that are able to retain the main statistical features of polycrystalline aggregates. The formulation is based on a grain-boundary integral representation of the elastic problem for the aggregate crystals, that are modeled as three-dimensional anisotropic elastic domains with random orientation in the three-dimensional space. The boundary integral representation involves only intergranular variables, namely interface displacement di…
Failure Map of Composite Laminate Mechanical Joint
2007
The aim of this research is to investigate the pin/hole contact stress of a composite laminate and failure modes when submitted to tensile bearing tests. The limit loads and failure modes are evaluated as a function of pin diameter and hole position. Analyzing the joint geometry effect on the fracture mechanisms, a failure map is obtained, identifying three regions of typical failure modes of mechanically fastened joints. A theoretical approach is proposed to identify the field of each fracture mode to obtain a simple experimental methodology to support the design of a particular joint laminate. In addition, a simplified numerical model is proposed to evaluate near the hole the stress/stra…
Microstructural, mechanical and tribological properties of suspension plasma sprayed YSZ/h-BN composite coating
2018
Abstract Brittleness, relative high friction coefficient and wear rate limit the applications of ceramic coatings as wear-resistant layers. However, because embedding additives with ceramic matrix has demonstrated to be an effective way to improve coating performances, different contents and size of h-BN were added into an YSZ suspension. Afterwards, the YSZ/h-BN composite coatings were manufactured by suspension plasma spray and their tribological analysis indicated that: i) the reduction of the friction coefficient and wear rate can be achieved by incorporating h-BN into YSZ coating. ii) finer h-BN particle is more helpful to enhance the tribological properties of the coating. iii) the op…
The control of the residual lifetimes of carbon fibre-reinforced composite pressure vessels
2015
International audience; The understanding of the degradation of carbon fibre composites, with emphasis on the use of these composites in filament-wound pressure vessels, is explored. Earlier studies by many researchers have led to a general appreciation of the mechanisms involved; however, only recently have both computational power and experimental techniques become sufficiently developed to allow for the use of quantitative analyses. It is shown that damage is controlled by fibre failure, and that initially this occurs randomly within the structure. In monotonic loading, the development of clusters of fibre breaks causes rapid failure; however, under maintained loads the kinetics of damag…