Search results for "Damage Tolerance"

Numerical modelling of low velocity multi-impact test on different stacking sequences

2019

The use of composite materials in the industrial field has been growing significantly for many years. This increase is explained by the fact that the industry, especially aeronautics which was pioneering in this field, is interested in the lightening of structures in order to be able to take up the new environmental challenges. Whether in the aeronautical field or in the land transport sector, structural elements may undergo multi-impactsor impact. Even at low velocitypose a threat to the integrity of the material and the structure itself. The objective of this work is to propose a numerical model to determine the damage within a composite structure subjected to low energy multi-impact. The…

Impact behaviour of flax/epoxy composite plates

2015

This paper presents an experimental investigation of the impact behaviour of flax/epoxy composite plates submitted to low-velocity transverse impact. Low energy drop-weight impact tests have been performed on two types of quasi-isotropic flax/epoxy composites, rectangularly shaped with edges lengths of 142 mm × 94 mm and 2.85 mm thick. Residual properties have been assessed by compression after impact tests. A detailed description of damage development, especially the increase of the rear face crack with respect to the impact energy is given by the microscopic observation. The influence of impact damage on the residual strength is described. A loss of 15%–30% in compression resistance was n…

Inspection Policies in Service of Fatigued Aircraft Structures

2011

Fatigue is one of the most important problems of aircraft arising from their nature as multiple-component structures, subjected to random dynamic loads. For guaranteeing safety, the structural life ceiling limits of the fleet aircraft are defined from three distinct approaches: Safe-Life, Fail-Safe, and Damage Tolerance approaches. The common objectives to define fleet aircraft lives by the three approaches are to ensure safety while at the same time reducing total ownership costs. In this paper, the damage tolerance approach is considered and the focus is on the inspection scheme with decreasing intervals between inspections. The paper proposes an analysis methodology to determine appropri…

ANALISI E SVILUPPO DI UN SETUP SPERIMENTALE PER LA DETERMINAZIONE DELLA TENACITÀ A FRATTURA A MODO II NEI MATERIALI COMPOSITI E IBRIDI

Il presente lavoro di Tesi si propone a compimento del percorso previsto dal Ciclo XXVI del corso di Dottorato di Ricerca in Ingegneria Civile e Ambientale – Indirizzo Materiali – seguito durante il triennio Gennaio 2013- Dicembre 2015 presso l’Università degli Studi di Palermo. L’elaborato si sviluppa in due principali sezioni. Dopo un’introduzione all’argomento affrontato, nella prima parte del lavoro, viene analizzato, sia sperimentalmente che numericamente, un setup tipicamente utilizzato nell’industria aeronautica per la caratterizzazione delle delaminazione a MODO II nei materiali compositi (Transverse Crack Tensile test – TCT-test). A partire dai risultati ottenuti dalle analisi prel…

Adaptive Planning in-Service Inspections of Fatigued Structures in Damage Tolerance Situations via Observations of Crack Growth Process

2017

From an engineering standpoint the fatigue life of a fatigued structure consists of two periods: (i) crack initiation period, which starts with the first load cycle and ends when a technically detectable crack is presented, and (ii) crack propagation period, which starts with a technically detectable crack and ends when the remaining cross section can no longer withstand the loads applied and fails statically. The main aim of this paper is to present more accurate innovative stochastic fatigue model for adaptive planning inspections of fatigued structures in damage tolerance situations via observations of crack growth process during a crack propagation period. A new crack growth equation is…

EGFP Reporters for Direct and Sensitive Detection of Mutagenic Bypass of DNA Lesions

2020

The sustainment of replication and transcription of damaged DNA is essential for cell survival under genotoxic stress

Improved Planning In-Service Inspections of Fatigued Aircraft Structures Under Parametric Uncertainty of Underlying Lifetime Models

2014

Certain fatigued structures must be inspected in order to detect fatigue damages that would otherwise not be apparent. A technique for obtaining optimal inspection strategies is proposed for situations where it is difficult to quantify the costs associated with inspections and undetected failure. For fatigued structures for which fatigue damages are only detected at the time of inspection, it is important to be able to determine the optimal times of inspection. Fewer inspections will lead to lower fatigue reliability of the structure upon demand, and frequent inspection will lead to higher cost. When there is a fatigue reliability requirement, the problem is usually to develop an inspection…

Investigation of buckling characteristics of cracked variable stiffness composite plates by an eXtended Ritz approach

2021

Abstract Variable Angle Tow (VAT) composite plates are characterized by in-plane variable stiffness properties, which opens to new concepts of stiffness tailoring and optimization to achieve higher structural performance for advanced lightweight structures where damage tolerance consideration are often mandatory. In this paper, a single-domain eXtended Ritz formulation is proposed to study the buckling behaviour of variable stiffness laminated cracked plates. The plate behaviour is described by the first order shear deformation theory whose generalized displacements, namely reference plane translations and rotations, are expressed via suitable admissible trial functions. These consist of a …