Numerical analysis of timber fracture due to mechanical and thermal loads: an approach based on invariant integral

International audienc

Stochastic analysis of mixed mode fracture in timber material using polynomial chaos expansion

International audienc

Numerical fracture analysis coupling thermo-hygro mechanical and viscoelastic behaviour

International audienc

On analytical formulation integrating mixed mode fracture and climate change in wood material

International audienc

Investigation of a Staphylococcus aureus sequence type 72 food poisoning outbreak associated with food-handler contamination in Italy

On August 2019 a staphylococcal food poisoning outbreak occurred in an elderly home in Piedmont, Italy. The epidemiological investigation performed among the per- sons that consumed the meal identified chicken salad as the most likely source of the outbreak. Staphylococcus aureus was isolated from a total of seven samples, namely one vomit sample from a guest of the nursing home, two food samples (chicken salad with and without mayonnaise) and nasal swabs collected from a total of four persons working in the kitchen of the nursing home. The maximum likelihood tree obtained using single nucleotide polymorphisms analysis revealed that the isolates from the aforementioned samples clustered together. Multilocus sequence typing revealed that they belonged to Sequence Type 72. Fourier transform infrared spectroscopy (FTIR) was used in parallel to single nucleotide polymorphisms and whole genome sequencing for the determination of the degree of relatedness of the isolates. The results of the FTIR showed the same clustering obtained with single nucleotide poly- morphisms and whole genome sequencing and revealed the source of infection. This study underlines the importance of both laboratory evidence and epidemiological data for outbreak investigation and further confirms that FTIR is a suitable support for the short-term epidemiological investigation on source attribution in case of a S. aureus infection

ANR JCJC2013 Projet CLIMBOIS : Essais de fissuration du bois en fluage sous environnement variable

National audienc

Numerical study of crack path by MMCG specimen using M integral

The mixed mode loading configuration occurs in many civil engineering and mechanical applications. In wood material, the study of this problem is very important due to the orthotropic character and the heterogeneity of the material. In order to study the mixed mode loading in wood material, Moutou Pitti et al [1] have proposed a new specimen called Mixed Mode Crack Growth (MMCG). The main goal of this geometry is to propose a decrease of the energy release rate during the crack growth process. In this case, the fracture parameters can be decoupled into Mode I and Mode II in order to determine the impact of time during creep crack test. The present work proposes to study the crack path stability in MMCG specimen for different sizes and thicknesses. The M? integral, combining real and virtual mechanical displacement fields is used in order to separate numerically mode I and mode II in the mixed mode ratio. The stability is shown for the opening mode (Mode I), the shear mode (Mode II), and the mixed mode of 15°, 30°, 45°, 60°, 75° by computing the energy release rate versus the crack length. Finally, it is shown that the MMCG specimen can be reduced in various shape and used for example in small climate chamber in order to perform creep test at different temperature and moisture content levels

On Numerical Evaluation of Mixed Mode Crack Propagation Coupling Mechanical and Thermal Loads in Wood Material

The mixed-mode crack growth coupling mechanical and thermal loads in wood material is investigated in this numerical work. The analytical formulation the crack driving force, namely the energy release rate, is introduced by T-integral that takes into account mixed mode fracture, thermal process in orthotropic material and pressure applied on the crack lips. This new formulation is based on Nother’s theorem and the definition of the strain energy density according to Lagrangian’s and Eulerian’s configurations. Moreover, this analytical formulation is implemented in finite element software Cast3m. First of all, several numerical examples, dealing with isotropic material, are provided to illustrate the accuracy of the FEM model. Then, the crack resistance of a timber CTS (Compact Tension Specimen) is investigated to show the efficiency of the proposed approach in the case of orthotropic material

Numerical Fracture Analysis Under Temperature Variation by Energetic Method

It is known that temperature change can induce sudden crack propagation especially when the material is composed of fibers. In this fact, the crack growth process under mixed-mode coupling mechanical and thermal loads in orthotropic materials like wood is investigated in this work. The analytical formulation of A integral’s combines the real and virtual mechanical and thermal stress/strain fields under transient diet in 2D. The Mixed Mode Crack Growth specimen providing the decrease of energy release rate during crack propagation is considered in order to compute the various mixed mode ratios. By using three specific routines, the analytical formulation is implemented in finite element software Cast3m. The efficiency of the proposed model is justified by showing the evolution of energy release rate and the stress intensity factors versus crack length and versus temperature variation in time dependent materia