A direct method for the assessment of cohesive zone models for thin adhesive layers loaded in mode I, mode II, and mixed-mode I/II

In the context of increasing the strength-to-mass ratio of lightweight structures, the adhesively bonded joining technology appears to be an attractive solution. Nevertheless, this attractiveness of the adhesive bonding is effective only when the structural integrity of joints is ensured. In the literature, the cohesive zone models (CZMs) are shown to be able to predict both the static and fatigue strengths of adhesively bonded joints. The strength prediction is dependent on material laws and associated material parameters, characterizing the bondline behaviour mainly under pure mode I, mode II and mixed-mode I/II. The characterization methods are thus crucial. This paper aims at assessing the capabilities to identify the parameters of a particular CZM for both the inverse method, based on the energy balance associated with the path independent J-integral, and of a direct method described in this present work. The particular CZM has a classical shape based on the definition of a bilinear law for each of both pure modes, associated with pure mode interaction energy laws for initiation and propagation under mixed-mode I/II. The methodology used in this paper is based on a numerical test campaign only, involving the macro-element (ME) technique. A new approach for the fast formulation and implementation of ME modelling of two bonded beams is described

Simplified stress analysis of hybrid (bolted/bonded) joints

The load transfer in hybrid (bolted/bonded) – denoted HBB – single-lap joints is complicated due to the association of two different transfer modes (discrete and continuous) through elements with different stiffnesses. The Finite Element (FE) method can be used to address the stress analysis of those joints. However, analyses based on FE models are computationally expensive and it would be profitable to use simplified approaches enabling extensive parametric studies. Two among the authors of this paper participated in the development of a dedicated 1D-beam approach (Paroissien 2007). This paper presents an extension of this framework enabling (i) the analysis of HBB joints made of dissimilar laminated or monolithic adherends, and (ii) the introduction of non linear material behaviour for both the adhesive layer and the fasteners. The output data are the distributions of displacements and forces in the adherends and fasteners, as well as those of adhesive shear and peeling stresses, allowing for a fast assessment of the material behaviour and strength prediction of HBB joints. The use of this model is illustrated in the identification of the failure mechanisms of HBB joints under quasistatic loadings, based on experimental and numerical tests on single-lap HBB joint. It is worth mentioning that the model can support pure bonded and pure bolted configurations. It can be used during the presizing phase at the design office (possibly independently on commercial software), to obtain quickly mechanical performances and to help in decision making. Moreover, it was shown that the judicious choice of the adhesive material allows for a significant increase of the static and fatigue strength compared to pure bolted or bonded corresponding configurations (Kelly 2006) (Paroissien 2006). The model can then be used to formulate at best adhesive materials to optimize the mechanical performance of HBB joints according to work specifications

An extended semi-analytical formulation for fast and reliable mode I/II stress analysis of adhesively bonded joints

The Finite Element (FE) method is able to address the stress analysis of adhesively bonded joints. However, analyses based on FE models are computationally expansive and it would be profitable to develop simplified approaches enabling extensive parametric studies. Firstly, a 1D-beam simplified model for the bonded joint stress analysis assuming a linear elastic adhesive material is presented. This model, derived from an approach inspired by the Finite Element (FE) method and based on the semi-analytical formulation of a 4-nodes macro-element, is able to simulate entire bonded overlaps at low computational costs. Secondly, a numerical procedure allowing for non-linear adhesive stress–strain relationships to be accounted for is presented. This procedure allows for various non-linear adhesive behaviors (ie. softening, plastic, etc.) to be accounted for with no restriction on the specimen geometry. The possible mixed-mode I/II response of the adhesive layer is introduced through an extension of the classical Cohesive Zone Modeling (CZM) procedure. The aforementioned procedure is then illustrated using a bi-linear softening adhesive behavior. However the procedure is not limited to this particular behavior only. The results obtained are finally compared to those of more time-consuming 2D FE strength predictions. Good agreement is shown

Source tracing of detrital serpentinite in the Oligocene molasse deposits from the western Alps (Barrême basin): implications for relief formation in the internal zone.

International audienceWe present the first contribution of tracing the source area of ophiolitic detritus in the Alpine molasses by Raman spectroscopy. The lower Oligocene molasse deposits preserved in the Barrême basin, in the SW foreland of the western Alpine arc, are known for the sudden arrival of the first "exotic" detritus coming from the internal Alpine zones. Among them, the pebbles of serpentinized peridotites have so far not been studied. We show that they only consist of antigorite serpentinite, implying that they originate from erosion of HT-blueschists. In contrast, the upper Oligocene/lower Miocene molasse, shows mixed clasts of serpentine including antigorite and lizardite without any evidence of chrysotile. This suggests that they were derived from a less metamorphosed unit such as the LT-blueschist unit. Taking into account the sediment transport direction in the basin and the varied metamorphic characteristics of the other ocean-derived detritus, we constrain the lithological nature of the source zones and the location of the relief zones, identified as the internal Alps, SE of the Pelvoux external crystalline massif. Available structural data and in situ thermochronological data allow reconstructing the Oligocene to early Miocene collisional geometry of the Paleogene subduction wedge. This phase corresponds to two major phases of uplift evolving from a single relief zone located above the Ivrea body during the early Oligocene and persisting up to the early Miocene; then during the late Oligocene/early Miocene a second relief zone developed above the Briançonnais zone. At that time, the internal western Alps acquired its double vergency

General formulation of macro-elements for the simulation of multi-layered bonded structures

Adhesively bonded joints are often addressed through Finite Element (FE). However, analyses based on FE models are computationally expensive, especially when the number of adherends increases. Simplified approaches are suitable for intensive parametric studies. Firstly, a resolution approach for a 1D-beam simplified model of bonded joint stress analysis under linear elastic material is presented. This approach, named the macro-element (ME) technique, is presented and solved through two different methodologies. Secondly, a new methodology for the formulation of ME stiffness matrices is presented. This methodology offers the ability to easily take into account for the modification of simplifying hypotheses while providing the shape of solutions, which reduced then the computational time. It is illustrated with the 1D-beam ME resolution and compared with the previous ones. Perfect agreement is shown. Thirdly, a 1D-beam multi-layered ME formulation involving various local equilibrium equations and constitutive equations is described. It is able to address the stress analysis of multi-layered structures. It is illustrated on a double lap joint (DLJ) with the presented method

A new subunit vaccine based on nucleoprotein nanoparticles confers partial clinical and virological protection in calves against bovine respiratory syncytial virus

Human and bovine respiratory syncytial viruses (HRSV and BRSV) are two closely related, worldwide prevalent viruses that are the leading cause of severe airway disease in children and calves, respectively. Efficacy of commercial bovine vaccines needs improvement and no human vaccine is licensed yet. We reported that nasal vaccination with the HRSV nucleoprotein produced as recombinant ringshaped nanoparticles (NSRS) protects mice against a viral challenge with HRSV. The aim of this work was to evaluate this new vaccine that uses a conserved viral antigen, in calves, natural hosts for BRSV. Calves, free of colostral or natural anti-BRSV antibodies, were vaccinated with NSRS either intramuscularly, or both intramuscularly and intranasally using MontanideTM ISA71 and IMS4132 as adjuvants and challenged with BRSV. All vaccinated calves developed anti-N antibodies in blood and nasal secretions and N-specific cellular immunity in local lymph nodes. Clinical monitoring post-challenge demonstrated moderate respiratory pathology with local lung tissue consolidations for the non vaccinated calves that were significantly reduced in the vaccinated calves. Vaccinated calves had lower viral loads than the nonvaccinated control calves. Thus NSRS vaccination in calves provided cross-protective immunity against BRSV infection without adverse inflammatory reaction

Direct Translocation as Major Cellular Uptake for CADY Self-Assembling Peptide-Based Nanoparticles

Cell penetrating peptides constitute a potent approach to overcome the limitations of in vivo siRNA delivery. We recently proposed a peptide-based nanoparticle system, CADY, for efficient delivery of siRNA into numerous cell lines. CADY is a secondary amphipathic peptide that forms stable complexes with siRNA thereby improving both their cellular uptake and biological response. With the aim of understanding the cellular uptake mechanism of CADY:siRNA complexes, we have combined biochemical, confocal and electron microscopy approaches. In the present work, we provide evidence that the major route for CADY:siRNA cellular uptake involves direct translocation through the membrane but not the endosomal pathway. We have demonstrated that CADY:siRNA complexes do not colocalize with most endosomal markers and remain fully active in the presence of inhibitors of the endosomal pathway. Moreover, neither electrostatic interactions with cell surface heparan sulphates nor membrane potential are essential for CADY:siRNA cell entry. In contrast, we have shown that CADY:siRNA complexes clearly induce a transient cell membrane permeabilization, which is rapidly restored by cell membrane fluidity. Therefore, we propose that direct translocation is the major gate for cell entry of CADY:siRNA complexes. Membrane perturbation and uptake are driven mainly by the ability of CADY to interact with phospholipids within the cell membrane, followed by rapid localization of the complex in the cytoplasm, without affecting cell integrity or viability

An unsupervised approach for health index building and for similarity-based remaining useful life estimation

Predictive maintenance techniques attempt to trigger a maintenance intervention at the right moment by estimating the life expectation. Predictive maintenance is increasingly implemented by automated approaches able to perform diagnostics and prognostics. The main part of recent research in these approaches is focused in machine learning structures whose reasoning is implicit and cannot be easily explained. This poses a problem for their implementation in highly constrained area such as aeronautics. To overcome this constraint, explicit reasoning approaches such as the Similarity-Based Model (SBM) can be implemented. The SBM has been widely used for fault diagnostics and the remaining useful life (RUL) estimation, but the development of SBM includes tasks that often rely on high skilled experts. For instance, data reduction techniques required for SBM are often performed by experts judgment whose outcomes are not always consistent. The produced features from these techniques are used to build the Health Index that can be used to create the degradation trends that serve as a reference for the SBM. To overcome these difficulties, an automatic and unsupervised approach based on the Kernel Principal Component Analysis is proposed to enhance the Health Index creation. It preserves as much of the sensor information as possible improving the similarity-based RUL estimation. Additionally, when estimating the RUL of a system, the most similar degradation trends stored in the SBM library are used to compute individual RULs, the final RUL is obtained by a fusion rule technique that combines all these individual RULs into a consolidated value. For the fusion rule techniques, a self-adaptive method that does not rely on human expertize is proposed. This fusion rule can benefit of the accumulated knowledge over the SBM operation. This unsupervised approach to develop a SBM is validated with promising results against an equivalent and supervised algorithm that came out best in the 2008 prognostic health management challenge

A methodology for the computation of the macro-element stiffness matrix for the stress analysis of a lap joint with functionally graded adhesive properties

The interest of functionally graded adhesives (FGA) is growing as it is a mean to increase a bonded joint strength without any modification of the initial design of the adherends. The behaviour of bonded joints with variable adhesive properties along the overlap can be predicted with a potentially time-costly Finite Element (FE) analysis. Dedicated numerical procedures and design tools for FGA bonded joints would increase. The objective of this paper is to offer a mesh-free method for the analysis of functionally graded joints. The technique is based on the macro-element (ME) method and Taylor expansion in power series (TEPS) are used to approach the shape functions of the ME. The method has been developed so far for 1D-bar and 1D-beam kinematics frameworks. This mesh-free_method and a Finite-Element analysis give similar results

Towards multi-model approaches to predictive maintenance: A systematic literature survey on diagnostics and prognostics

The use of a modern technological system requires a good engineering approach, optimized operations, and proper maintenance in order to keep the system in an optimal state. Predictive maintenance focuses on the organization of maintenance actions according to the actual health state of the system, aiming at giving a precise indication of when a maintenance intervention will be necessary. Predictive maintenance is normally implemented by means of specialized computational systems that incorporate one of several models to fulfil diagnostics and prognostics tasks. As complexity of technological systems increases over time, single-model approaches hardly fulfil all functions and objectives for predictive maintenance systems. It is increasingly common to find research studies that combine different models in multi-model approaches to overcome complexity of predictive maintenance tasks, considering the advantages and disadvantages of each single model and trying to combine the best of them. These multi-model approaches have not been extensively addressed by previous review studies on predictive maintenance. Besides, many of the possible combinations for multi-model approaches remain unexplored in predictive maintenance applications; this offers a vast field of opportunities when architecting new predictive maintenance systems. This systematic survey aims at presenting the current trends in diagnostics and prognostics giving special attention to multi-model approaches and summarizing the current challenges and research opportunities