Claude Chazal

Viscoelastic crack growth process in wood timbers: An approach by the finite element method for mode I fracture

In this paper the effects of viscoelastic characteristics in wood timbers, on the creep crack growth process are studied through a new finite element approach in the time domain. In order to take into account the linear viscoelastic orthotropic behavior, we present an incremental formulation based on a rheological representation of creep tensor components. By using a relationship between stress and crack opening intensity factors, the general approach of path independent integrals is extended in order to calculate energy release rate and local fracture characteristics. Afterwards, fracture parameters are computed through a coupling process with the incremental viscoelastic behavior. The numerical algorithm is presented and validated through numerical as well as experimental examples.

A Finite Element Analysis of Creep-Crack Growth in Viscoelastic Media

In this paper, the effects of viscoelastic characteristics, on the creep-crack growth process are studied through a finite element approach. The general approach of an independent path integral is extended to crack propagation. Afterwards, fracture parameters are computed through a coupling process with an incremental viscoelastic formulation. Finally, numerical examples are presented in order to demonstrate the independence of the integration domain and the possibility of evaluating fracture characteristics which can be energetic (energy release rate) and local in the vicinity of the crack tip (stress and crack opening intensity factors).

A new incremental formulation in the time domain for crack initiation in an orthotropic linearly viscoelastic solid

The problem of predicting the crack growth initiation in a linearlyviscoelastic material is investigated. A new incremental fractureequations relating viscoelastic stress intensity factors (VSIFs) toviscoelastic opening displacement intensity factors (VODIFs) areestablished. Crack growth initiation is studied in detail by means of acomputational approach based on a modified path independent integral. Itis found that the mechanical and kinematical fields around the crack tipcan be determined using an incremental formulation based on a discretespectrum representation of the viscoelastic compliance functions; thusthe difficulty of computer storage requirements is avoided. Numericalresults are obtained for predicting the time at which propagationinitiates and these are compared with the analytical solution.

Further Development in Thermodynamic Approach for Thermoviscoelastic Materials

In this paper we derive linear and nonlinear theories ofthermoviscoelasticity for thermorheologically simple materials. Thisderivation is based on two theories: the Thermodynamic of IrreversibleTheory and the Generalized Viscoelastic Standard Theory. These twotheories, along with other assumptions, lead to three-dimensionalthermoviscoelastic models. The derivation we give here is an extensionof Schaperys models. We will soon state the relations expressing thebalance of energy, i.e., the specific heat capacity and the heatconduction equation.

Reliability Analysis of Mixed Mode Cracking with Viscoelastic Orthotropic Behaviour

The reliability analysis applied to viscoelastic and orthotropic materials, in the case of mixed mode configuration, is studied in this work. The M integral, separating mixed mode during creep crack initiation in viscoelastic field, is used in the analytical approach. The main development, based on conservative law, and a combination of real and virtual displacement fields, is proposed. In order to provide mixed mode configuration, a Compact Tension Shear (CTS) specimen is used in the numerical process. Simultaneously the fracture and the viscoelastic procedures are coupled with reliability analysis in order to take account for model and parameter uncertainties. In this case, the random parameters related to model factors, elastic constants are defined in the reliability analysis of time dependent fracture materials subjected to complex loading. As results, the reliability levels are computed and discussed according to various mixed-mode loading scenarios

Stress Intensity Factors for Viscoelastic Axisymmetric Problems Applied to Wood

Many materials used in engineering applications obey to time-dependent behaviours and the mechanical fields are affected by the time effects. As a result, the evolution of the stresses and strains in these materials appear still very complex and difficult to study. Among such cases is the situation when the material has an axisymmetric shape and when it is submitted to a complex fracture loading. In this paper, the creep loading is applied on an axisymmetric viscoelastic orthotropic material and the stress intensity factors are computed in the opening mode, in the shear mode and in the mixed mode using to a finite element approach. The uncoupling method is based on M integral, combining the virtual and real mechanical fields. In the same time, the viscoelastic effects are introduced according to the generalized Kelvin-Voigt model composed by four branches. The numerical solution is obtained with an incremental viscoelastic formulation in the time domain. Using a Compact Tension Shear (CTS) specimen, the evolutions of stress intensity factor versus time are posted in each fracture mode configuration. The obtained results demonstrate the efficiency of the proposed model.