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Laminated composites with thermoset matrices are already well established in major engineering fields like automotive and aviation. The primary drawbacks of such thermoset-based composites are the high cycle times required during manufacturing and their limited potential for recycling. Providing an alternative to thermoset-based composites, thermoplastic matrix materials gained more and more momentum by addressing these previously mentioned drawbacks. The preferred manufacturing technique for these materials employs fiber-reinforced thermoplastic tapes consolidated and formed together with a compatible substrate. The most critical aspect for all these applications is the stress or load transfer between the thermoplastic tapes and the substrate. If the interface is too weak and fails prior to the substrate or tape, a high amount of theoretical mechanical performance is lost. The presented research investigates the influence of variations in manufacturing parameters, within the industrially relevant process window, on the interface strength of the final composite. The investigated composite material consists of PPGF UD tapes consolidated on a PPGF mat substrate. In particular, the influence of the consolidation parameters of pressure, temperature, and time are of special interest. The results of this work reveal a 400% increase in the measured mean strain energy release rate upon increasing the consolidation time from 60 s to 120 s at a consolidation temperature of 230 °C and a pressure of one bar. In contrast to this, an increase in the consolidation pressure, at constant temperature and time, leads to a minor improvement in the GC value of 20%. For testing and characterizing the corresponding interface properties, a mandrel peel testing setup was employed. Version of record

The current paper deals with the failure modelling in continuously reinforced composite structures taking into account the material's inherent microstructure. The implementation of a constitutive model for transversely isotropic damage in fibre reinforced composites is presented. Damage initiation in the orthotropic linear elastically modelled composite is governed by the Strain Invariant Failure Theory (SIFT), utilising the first strain invariant and the second deviatoric strain invariant for damage initiation. To phenomenologically account for the material's microstructure, the homogenised macro strain is related to the micro strain by means of strain amplification factors determined from prior simulations of Repeating Unit Cells (RUCs) with different fibre arrangements utilising Periodic Boundary Conditions (PBCs). For validation of the numerically implemented model, experimental tests of composite laminates with varying layups are performed. The conducted experiments are simulated utilising the implemented models and the obtained results are validated with the experimental data.

The current work is aimed at development of a numerical model able to describe complex damage phenomena that occur during an impact event in a sandwich structure having a honeycomb core. The complex material models employed within the research include linear-elastic and elasto-plastic material models having transverse isotropy as well as damage evolution models for both brittle failure and plastic failure. Within this paper remarks concerning the failure of the skins and core components as well as dissipated impact energy and affected regions are done.

Interface damage characterization and interlaminar failure of sandwich specimens with an initial interlaminar delamination in between the face sheet and the core is done by using the digital image correlation method (DIC). Virtual strain gages are emulated at the interface and beneath it, in the polyurethane core and opening strains are measured. Peel tests reveal interesting particularities on damage localization and strain variation while damage is completed. After analyzing the experimentally obtained results, four characteristic domains which describe the opening strain variations in the core are established together with the corresponding variation of the opening strain at the interface. The critical strain at damage initiation, as well as the critical displacement when damage is finalized, is established by DIC in the cohesive zone. After the calibration of the finite element model through experimental results, the use of the cohesive elements together with a linear softening law give in the core a pattern of strain variation similar to the one obtained experimentally.

Static loading and impact tests of ceramic alumina tiles have shown a very interesting behaviour of tough, brittle, and high energy absorbing materials. Strain gauges techniques and data acquisition were used in previous research for static and low velocity impact testing. A static-dynamic equivalence was done through a calibration procedure of the measuring system. The research is continued in this paper by using the digital image correlation method with the complete displacement and strain history acquired till the failure of the ceramic tiles of different compositions, proving the capacity of such materials to be used for particular purpose applications.

Interface damage characterization and interlaminar failure of sandwich specimens with two initial interlaminar defects (inserts) is done by using the digital image correlation method. Mode I tests reveal interesting particularities on damage localization and unstable crack propagation. After analyzing the experimentally obtained results, we propose as a failure parameter the local strain at the crack tip or, alternatively, the crack tip opening displacement which quantifies the non-linear phenomena.

The current paper is describing the implementation of a multiscale numerical model for prediction of stiffness and strength in braided composites. The model is validated by experimental testing of single-layer braided tubes under torsional loading utilising digital image correlation (DIC). For the numerical model the entire braided structure is modelled at yarn detail level, taking into account the yarn behaviour as well as individual yarn-to-yarn interactions by using cohesive contact definitions. By means of Hashin’s failure criteria and cohesive contact damage, failure of the yarns and failure of the yarn-to-yarn interface is being accounted for. Thereby the material failure behaviour can be predicted. For validation of the model, torsion tests of biaxially braided single-layer composite tubes were performed. The strain distribution at the specimen surface was studied using the DIC system ARAMIS in 3D mode.

The applicability and constraints of two fracture mechanics approaches for designing and dimensioning of short fiber reinforced injection molded components are described in the paper. For simplicity, a 3D random short fiber orientation of the component was assumed in the modeling. Based on injection molding and preliminary finite element simulations, the area of interest was selected and mode I stress intensity factors were calculated along the crack front of a corner crack in the component. Furthermore, fiber orientation dependent fracture toughness values were determined at moderate loading rates and at room temperature and compared with the mode I stress intensity factor values. Based on this comparison the occurrence of the crack initiation was predicted. Moreover, welding line formation was observed in the injection molding simulations of this model component and these simulations were verified by computer tomography images. Cohesive elements were embedded at the vicinity of the welding line in the model and the failure evolution was predicted. The existing model assumes constant fracture toughness in the entire ligament and hence constant values for the cohesive zone model. The real fracture toughness, however, depends on the fiber orientation which may vary with the distance and it requires the application of more complex cohesive zone model parameter functions. This is described in a follow-up paper of the authors.

Osteoarticular diseases account for approximately 10% of all diseases occurring inFrance each year. The difficulties in identifying their causes are also due to a deficiency inunderstanding the lubrication mechanism of healthy synovial joint.In this context, the first objective of the present study was to analyze the discontinuousstructure of synovial fluid samples from healthy animals and to reproduce it using commercialbiomolecular components in order to understand the lubrication mechanism in the healthycase. The second objective of this thesis was to analyze the evolution of the structure andthe lubricating properties of synovial fluid in the early stage of non-inflammatory andinflammatory diseases using pathological human fluid samples. In order to study moreprecisely the evolution of pathological lubrication this work aimed to develop lubricantmodels obtained from cell cultures of human synoviocytes adding the action of pathologicalinflammatory factors (cytokines). All together the results show the importance of the supramolecular structure of thesynovial fluid in obtaining good lubricating properties what may be a key parameter in theearly diagnosis of joint diseases and even more a chance to develop therapeutic fluids basedon nanostructured lubricants; Les maladies ostéoarticulaires représentent environ 10% de l’ensemble des pathologiessurvenant en France chaque année. Les difficultés pour identifier les causes de ces maladiesproviennent pour une part d’un manque de compréhension du mécanisme de lubrificationd’une articulation synoviale saine. Dans ce contexte, un premier objectif de ce travail a été d’analyser la structurediscontinue du liquide synovial à partir de prélèvements animaux sains et de la reproduire àpartir de composants biomoléculaires commerciaux afin de comprendre le mécanisme delubrification dans le cas sain. Le deuxième objectif de cette thèse a été d’analyser l’évolution de la structure et despropriétés lubrifiantes du liquide synovial dans le stade précoce de pathologies noninflammatoiresou inflammatoires à partir de prélèvements pathologiques humains. Afind’étudier plus finement l’évolution de la lubrification pathologique cette thèse a visé àdévelopper aussi des modèles de lubrifiants obtenus à partir de cultures cellulaires desynoviocytes humains en combinant l’action de facteurs inflammatoire (cytokines).L’ensemble des résultats montre l’importance de la structure supramoléculaire duliquide synovial dans l’obtention de bonnes propriétés lubrifiantes ; cette relation devraitconstituer d’une part un paramètre clé dans le diagnostic précoce des pathologies articulaireset d’autre part une voie de développement de liquides thérapeutiques à base de lubrifiantsnanostructurés

Osteoarticular diseases account for approximately 10% of all diseases occurring inFrance each year. The difficulties in identifying their causes are also due to a deficiency inunderstanding the lubrication mechanism of healthy synovial joint.In this context, the first objective of the present study was to analyze the discontinuousstructure of synovial fluid samples from healthy animals and to reproduce it using commercialbiomolecular components in order to understand the lubrication mechanism in the healthycase. The second objective of this thesis was to analyze the evolution of the structure andthe lubricating properties of synovial fluid in the early stage of non-inflammatory andinflammatory diseases using pathological human fluid samples. In order to study moreprecisely the evolution of pathological lubrication this work aimed to develop lubricantmodels obtained from cell cultures of human synoviocytes adding the action of pathologicalinflammatory factors (cytokines). All together the results show the importance of the supramolecular structure of thesynovial fluid in obtaining good lubricating properties what may be a key parameter in theearly diagnosis of joint diseases and even more a chance to develop therapeutic fluids basedon nanostructured lubricants; Les maladies ostéoarticulaires représentent environ 10% de l’ensemble des pathologiessurvenant en France chaque année. Les difficultés pour identifier les causes de ces maladiesproviennent pour une part d’un manque de compréhension du mécanisme de lubrificationd’une articulation synoviale saine. Dans ce contexte, un premier objectif de ce travail a été d’analyser la structurediscontinue du liquide synovial à partir de prélèvements animaux sains et de la reproduire àpartir de composants biomoléculaires commerciaux afin de comprendre le mécanisme delubrification dans le cas sain. Le deuxième objectif de cette thèse a été d’analyser l’évolution de la structure et despropriétés lubrifiantes du liquide synovial dans le stade précoce de pathologies noninflammatoiresou inflammatoires à partir de prélèvements pathologiques humains. Afind’étudier plus finement l’évolution de la lubrification pathologique cette thèse a visé àdévelopper aussi des modèles de lubrifiants obtenus à partir de cultures cellulaires desynoviocytes humains en combinant l’action de facteurs inflammatoire (cytokines).L’ensemble des résultats montre l’importance de la structure supramoléculaire duliquide synovial dans l’obtention de bonnes propriétés lubrifiantes ; cette relation devraitconstituer d’une part un paramètre clé dans le diagnostic précoce des pathologies articulaireset d’autre part une voie de développement de liquides thérapeutiques à base de lubrifiantsnanostructurés

International audience

International audience

http://www-lpmcn.univ-lyon1.fr/workshop_biolub/index.html

International audience