61 research outputs found
Acoustic analysis of an exhaust manifold by Indirect Boundary Element Method
The present work is aimed at the development of a numerical procedure, based on the usage of the Boundary
Element Method (BEM) as implemented in the software LMS Virtual.Lab, for the vibro-acoustics analysis of an exhaust
manifold. The manifold vibrations are induced by two different ways: engine vibrations (transmitted to the manifold
surfaces) and turbulences generated by the air flow in the exhaust system. The indirect BEM (IBEM), with a variational
solution algorithm, is adopted to assess the exhaust manifold acoustic radiation. The modal analysis of the acoustic cavity
is realized by the Finite Element Method (FEM) and the corresponding eigenfrequencies compared with those obtained by
an IBEM forced response analysis and by experimental measurement. Experimental acoustic pressures at the manifold
inlet and outlet are measured in anechoic room in order to compare with corresponding numerical predictions and assess
the accuracy level obtained
BEM Simulation and Experimental Test of a FML Full Scale Aeronautic Panel Undergoing Biaxial Static Load
This paper concerns the numerical and experimental characterization ofthe static and fatigue strength of a flat stiffened panel, designed as a fiber metal laminates (FML) and made of Aluminum alloy and Fiber Glass FRP. The panel is full scale and was tested under both static and fatigue biaxial loads, applied by means of an in house designed and built multi-axial fatigue machine. The static test is simulated by the Boundary Element Method (BEM) in a two-dimensional approach (only allowance
for membrane stresses). The strain gauge outcomes are compared with corresponding numerical results, getting a satisfactory correlation. After the static test, an initial notch is created in the panel and the aforementioned biaxial fatigue load is applied, causing a crack initiation and propagation; the related experimental initiation times and crack growth rates are provided
FEM and BEM Analysis of a Human Mandible with Added Temporomandibular Joints
Mathematical modelling of human mandible and its temporomandibular joints (TMJs) is one of the most
important steps for developing a powerful forecasting tool to analyse the stress/strain behaviour of a human masticatory
system under occlusal loads.
In this work the structural behaviour of a mandible with articular discs, undergoing a unilateral occlusion, is numerically
analysed by means of both Finite Element Method (FEM) and Boundary Element Method (BEM). The mandible is
considered as completely edentulous and its anisotropic and non-homogeneous bone material behaviour is modelled. The
material behaviour of the articular discs was assumed to be either elastic or hyper-elastic. The loads applied to the
mandible are related to the active muscle groups during a unilateral occlusion. The results of FEM and BEM analyses are
presented mainly in terms of stress distribution on the mandible and on the articular discs. Due to the uncertainty in the
determination of the biological parameters, a sensitivity analysis is provided, which demonstrates the impact of the
variation of articular disc stiffness and TMJ friction coefficient on the mandible stress peaks and on the occlusal loads (for
a given intensity of muscle loads). Moreover a comparison between the effectiveness of the BEM and FEM numerical
approaches on this kind of problem is provided
FEM simulation of a crack propagation in a round bar under combined tension and torsion fatigue loading
An edge crack propagation in a steel bar of circular cross-section undergoing multiaxial fatigue loads is simulated by Finite Element Method (FEM). The variation of crack growth behaviour is studied under axial and combined in phase axial+torsional fatigue loading. Results show that the cyclic Mode III loading superimposed on the cyclic Mode I leads to a fatigue life reduction. Numerical calculations are performed using the FEM software ZENCRACK to determine the crack path and fatigue life. The FEM numerical predictions have been compared against corresponding experimental and numerical data, available from literature, getting satisfactory consistencyN/
Hybrid technique to assess the fatigue performance of multiple cracked FSW joints
In this paper a numerical-experimental procedure useful to numerically assess the fatigue performance of friction stir welded aluminium joints is presented. The impact of manufacturing residual stresses on crack propagation in the joint driven by a remote fatigue load can be predicted. The proposed sequential procedure starts with the experimental residual stress assessment by the contour method and proceeds through the multiple crack growth simulation by the Dual Boundary Element Method. In the frame of Linear Elastic Fracture Mechanics, the superposition principle is invoked to provide the mathematical foundation supporting the proposed modelling strategy. In order to validate the proposed procedure, simple specimens are fatigue tested, obtaining multiple crack propagation scenarios that are monitored, in order to compare experimental and predicted crack growth rate
Crack propagation calculations in aircraft engines by coupled FEM-DBEM approach
New generation jet engines are subject to severe reduced fuel consumption requirements. This usually leads to thin components in which damage issues such as thermomechanical fatigue, creep and crack propagation can be quite important. The combination of stresses due to centrifugal loads and thermal stresses usually leads to mixed-mode loading. Consequently, a suitable crack propagation tool must be able to predict mixed-mode crack propagation of arbitrarily curved cracks in three-dimensional space. To tackle this problem a procedure has been developed based on a combined FEM (Finite Element Method) - DBEM (Dual Boundary Element Method) approach. Starting from a three-dimensional FEM mesh for the uncracked structure a subdomain is identified, in which crack initiation and propagation are simulated by DBEM. Such subdomain is extracted from the FEM domain and imported, together with its boundary conditions (calculated by a previous thermal-stress FEM analysis), in a DBEM environment, where a linear elastic crack growth calculation is performed. Once the crack propagation direction is determined a new crack increment can be calculated and for the new crack front the procedure can be repeated until failure. The proposed procedure allows to also consider the spectrum effects and the creep effects: both conditions relieve residual stresses that the crack encounters during its propagation. The procedure has been tested on a gas turbine vane, getting sound results, and can be made fully automatic, thanks to in house made routines needed to facilitate the data exchange between the two adopted codes
Stress Analysis of an Endosseus Dental Implant by BEM and FEM
In this work the Boundary Element Method (BEM) and the Finite Element Method (FEM) have been used for
an elastic-static analysis of both a Branemark dental implant and a generic conic threaded implant, modelled either in the
complete mandible or in a mandibular segment, under axial and lateral loading conditions. Two different hypotheses are
considered with reference to degree of osteo-integration between the implant and the mandibular bone: perfect and partial
osteointegration. The BEM analysis takes advantage of the submodelling technique, applied on the region surrounding the
implant. Such region is extracted from the overall mandible and the boundary conditions for such submodel are obtained
from the stress analysis realised on the complete mandible.
The obtained results provide the localisation of the most stressed areas at the bone-implant interface and at the mandibular
canal (containing the alveolar nerve) which represent the most critical areas during mastication.
This methodology, enriched with the tools necessary for the numerical mandible reconstruction, is useful to realise
sensitivity analysis of the stress field against a variation of the localisation, inclination and typology of the considered
implant, in order to assess the optimal implant conditions for each patient under treatment.
Due to the high flexibility in the pre- and post-processing phase and accuracy in reproducing superficial stress gradients,
BEM is more efficient than FEM in facing this kind of problem, especially when a linear elastic constitutive material law
is adopted
FEM sensitivity analyses on the stress levels in a human mandible with a varying ATM modelling complexity
Abstract: In this work the structural behaviour of a mandible considering a unilateral occlusion is numerically analysed
by means of the Finite Element Method (FEM). The mandible, considered as completely edentolous, is modelled together
with its articular disks, whose material behaviour is assumed as elastic or hyper-elastic. The mandible model is obtained
by computer tomography scans. The anisotropic and non homogeneous bone material behaviour is considered and the
loads applied to the mandible are those related to the active muscle groups during unilateral occlusion. The results of FEM
analysis are presented mainly in terms of stress distribution on the mandible. Because of uncertainty on the determination
of the adopted parameters, a sensitivity analysis is provided, showing the way in which the variation of articular disc
stiffness and temporomandibular joint friction coefficient has an impact on the mandible stress peak and occlusal force
MSD Crack propagation on a repaired aeronautic panel by DBEM, Advances in Engineering Software
This paper focuses on the use of the Dual Boundary Element Method (DBEM), as implemented in a commercial code (BEASY), to investigate the damage tolerance performance of a riveted repair flat aeronautic panel, realised and tested in the context of the European project ''IARCAS'' (VI framework). Such panel is assembled in such a way to simulate the in service repairs, with doublers riveted over corresponding cut-out. The panels, repair patches and rivets are modelled in a two-dimensional analysis with no allowance for out-of-plane bending, with edge-cracks initiated from some skin rivet holes and growing due to fatigue load. In the model, the layers representative of each component are overlapped but distinct, providing no allowance for the existing offset. The two-dimensional approximation for this problem is not detrimental to the accuracy of numerical-experimental correlation, so it turn out to be useful to study varying repair configurations, where reduced run times and a lean pre-processing phase are prerequisites
Advanced Design Concepts and Maintenance by Integrated Risk Evaluation for Aerostructures
This paper presents an overview of the
achievements of a research and development project
sponsored by the European Commission in the general
area of Key Actions and New Perspectives in Aeronautics.
The project was coordinated by Alenia and involved
partners from major European Aircraft and Helicopter
manufactures as well as research institutions and universities.
The project was in support of EU policies on energy
and environment, in addition to those on transport,
economic and social cohesion, industry and, of course,
research and technology.
The overall objective of Advanced Design concepts and
Maintenance by Integrated risk Evaluation for aerostructures
(ADMIRE) was “to develop a probabilistic foundation
for the application of damage tolerant design of
metallic aircraft structures taking into account the innovative
investigations on the initial flaw concept, crack
growth evaluation improvements and residual strength in
complex geometries”.
The innovation provided by this project was the development
of an overall approach capable of evaluating the
damage tolerance of the structure on a probabilistic basis.
This global risk analysis took into account the stochastic
nature of structural parameters, their variation and
their effects on the design and response properties of aircraft
structural components, in order to estimate structural
safety on a probabilistic basis while providing information
on the confidence to be given to the predicted behavior.
It also incorporated the investigations on the initial
flaw concept, crack growth evaluation improvements
and residual strength in complex geometries
- …