Le Mans – La Charbonnière

L’opération archéologique qui s’est déroulée durant 5 jours a été programmée dans le cadre des travaux préalables à la construction du Périphérique Est de la ville du Mans. Le site mis en évidence lors d’un diagnostic réalisé en 1998 a fait l’objet d’une évaluation en janvier 1999 par Véronique Gallien (Afan). La nature des vestiges découverts a incité le Service Régional de l’Archéologie à engager une fouille d’urgence pour étudier des vestiges sidérurgiques et miniers, la problématique s’in..

Identifying short-term variation of dynamic friction by means of its frequency response function

A challenging case study of dynamic friction was presented in a previous study (A. Cabboi, J. Woodhouse, Validation of a constitutive law for friction-induced vibration under different wear conditions, Wear 396–397 (2018) 107–125), concerning tests performed with a Polycarbonate pin sliding on a steel disc. Identifying and modelling the frictional frequency response for this system turned out to be rarely possible, since the measurements were affected by significant wear and by intermittent squeal occurrence. To shed light on the observed “capricious” behaviour, an “instantaneous” estimation of the frequency response of dynamic friction was developed, allowing the dynamic friction behaviour to be captured and tracked before, and for few cases during, squeal events. Each “instantaneous” frequency response of dynamic friction was fitted by a rate-and-state model, and variations of the model parameters for different sliding speeds, changing normal forces and at different wear stages were tracked. With direct relevance to squeal predictions, the model parameters identified through the proposed processing and fitting methodology could detect rapid transitions between velocity-strengthening and weakening behaviour. These transitions may occur at different sliding speeds, but they also occur during measurements carried out at a constant sliding speed. Based on the identified model parameters, a first qualitative attempt to predict squeal events by means of rate-and-state models is presented, and shown to give promising correlation with experimental results

La Bazoge – Les Barres

Lors des opérations liées à l’aménagement de l’autoroute A28, deux ateliers sidérurgiques de l’âge du Fer ont été mis au jour, au lieu-dit Les Barres, à proximité d’une minière actuellement attribuée à l’époque gallo-romaine. Le premier atelier a été dégagé sur une surface d’environ 380 m2. On a trouvé 56 bas fourneaux, 14 structures de combustion, 4 concentrations de parois de four (argile cuite scorifiée ou non), 3 fosses charbonneuses. Les bas fourneaux correspondent à une seule technologi..

La Bazoge – L’Aulnay-Truchet

L’ensemble paléosidérurgique qui s’étend au lieu-dit « l’Aunay-Truchet » a été détecté par photographie aérienne. Sept concentrations de scories réparties sur deux parcelles concernées par le futur tracé de l’autoroute A28 s’étalent dans la plaine de la Sarthe, au pied de la butte de La Bazoge où l’extraction de minerai de fer est attestée. Une fouille préventive de six mois a permis d’étudier six de ces terriers et de mettre ainsi au jour des ateliers de traitement et de réduction de minerai..

The frequency response of dynamic friction: Enhanced rate-and-state models

The prediction and control of friction-induced vibration requires a sufficiently accurate constitutive law for dynamic friction at the sliding interface: for linearised stability analysis, this requirement takes the form of a frictional frequency response function. Systematic measurements of this frictional frequency response function are presented for small samples of nylon and polycarbonate sliding against a glass disc. Previous efforts to explain such measurements from a theoretical model have failed, but an enhanced rate-and-state model is presented which is shown to match the measurements remarkably well. The tested parameter space covers a range of normal forces (10–50 N), of sliding speeds (1–10 mm/s) and frequencies (100–2000 Hz). The key new ingredient in the model is the inclusion of contact stiffness to take into account elastic deformations near the interface. A systematic methodology is presented to discriminate among possible variants of the model, and then to identify the model parameter values.Alessandro Cabboi and Thibaut Putelat both acknowledge support from the EPSRC programme grant “Engineering Nonlinearity” (ref. EP/K003836/1).This is the final version of the article. It first appeared from Elsevier via https://doi.org10.1016/j.jmps.2016.03.02

Automatic operational modal analysis: challenges and applications to historic structures and infrastructures

The core of the work turns around the capability to automate Operational Modal Analysis methods for permanent dynamic monitoring systems. In general, the application of OMA methods requires an experienced engineer in experimental dynamics and modal analysis; in addition, a lot of time is usually spent in manual analysis, necessary to ensure the best estimation of modal parameters. Those features are in contrast with permanent dynamic monitoring, which requires algorithms in order to efficiently manage the huge amount of recorded data in short time, ensuring an acceptable quality of results. Therefore, the use of parametric identification methods, like SSI methods, are explored and some recommendations concerning its application are provided. The identification process is combined with the automatic interpretation of stabilization diagrams based on a damping ratio check and on modal complexity inspection. Finally, a clustering method for the identified modes and a modal tracking strategy is suggested and discussed. The whole procedure is validated with a one-month and a one-year set of "manually-identified" modal parameters. This constitutes a quite unique set of validation data in the literature. Two monitoring case studies are studied: a railway iron arch bridge (1889) and a masonry bell-tower (XII century). Within this framework, classical and new strategies to handle the huge amount of recorded and identified data are proposed and compared for structural anomaly detection. The classical strategies are mainly based on the inspection of any irreversible frequency variation. To such purpose, it is mandatory an extensive correlation study with environmental and operational factors which affect the frequency of the vibration modes. Conversely, one of the proposed strategy aims to use alternative dynamic features that are not sensitive to environmental factors, like mode shape or modal complexity, instead of frequency parameters in order to detect any structural anomaly. In addition, a further strategy has the goal to eliminate the environmental-induced effects on frequency without the knowledge and the measurements of such factors. The procedure is mainly based on the combination of a simple regression model with the results obtained by a Principal Component Analysis. Furthermore, two automated Operational Modal Analysis (OMA) procedures are compared for Structural Health Monitoring (SHM) purposes: the first one is based on SSI methods, while the second one involves a non-parametric technique like the Frequency Domain Decomposition method (FDD). In conclusion, a model updating strategy for historic structures using Ambient Vibration Test and long term monitoring results is presented. The main goal is to integrate the information provided by a FE model with those continuously extracted by a dynamic monitoring system, basing so any detection of structural anomalies on the variation of the uncertain structural parameters

Validation of a constitutive law for friction-induced vibration under different wear conditions

Recent work (A. Cabboi, T. Putelat, J. Woodhouse, The frequency response of dynamic friction: Enhanced rate- and-state models, Journal of the Mechanics and Physics of Solids 92 (2016) 210–236) has shown promising agreement between measurements and theoretical modelling of high-frequency dynamic sliding friction. This paper confirms and extends this agreement by presenting results for a wide selection of contacting materials. Additional measurement tech- niques are also introduced, to give independent confirmation of parameter identification and improve the robustness of the identification process. The results show that virtually every individual measurement can be fitted accurately by the pro- posed theoretical model, and that in all cases where rapid wear of the contacting materials was not an issue it was possible to achieve a good global fit to sets of tests at different normal loads and sliding speeds. The evidence suggests that this measurement procedure is able to characterise the dynamic behaviour at a frictional interface up to kiloHertz frequencies, and consequently provide the means to discriminate among, and calibrate, proposed dynamic friction models. Identifying a reliable model could significantly improve the prediction accuracy for friction-induced vibration such as vehicle brake squeal.Financial support was provided by the EPSRC programme grant “Engineering Nonlinearity” (ref. EP/K003836/1 — www.engineeringnonlinearity.ac.uk)

Automated modal identification and tracking: Application to an iron arch bridge

Challenges concerning the automation of modal identification and tracking procedures in permanent monitoring systems for Structural Health Monitoring purposes are discussed. In this context, an automated procedure based on parametric identification methods that involve the interpretation of stabilization diagrams is proposed. The methodology comprehends two key points: (i) automatic analysis of stabilization diagrams, performed through a first check of reasonable damping ratio, a subsequent modal complexity check and a final clustering of structural modes; (ii) automated tracking of the evolution in time of the identified modal properties. The proposed modal clustering and tracking steps exploit the introduction of self-adaptable dynamic thresholds, that do not require any a priori manual tuning for the different recorded data set. Finally, the proposed approach was successfully validated using real data collected on a historic iron arch bridge.This is the author accepted manuscript. The final version is available from Wiley via https://doi.org/10.1002/stc.185

Static and dynamic monitoring of a Cultural Heritage bell-tower in Monza, Italy

A recent survey carried on the historic complex of Santa Maria del Carrobiolo in Monza (Italy) highlighted that the two sides of the bell-tower are directly supported by the load-bearing walls of the apse and South aisle of the neighboring church. After the discovery of the weak structural arrangement of the building, static and dynamic monitoring systems were installed in the tower to address its preservation. After a brief description of the tower and the results of the preliminary survey, the paper presents selected results of the continuous dynamic monitoring as well as the evidences provided by the static monitoring