Overview

MFront comes with a handy and easy-to-use tool called MTest. This tool handles two types of computations:

• the description of a single material point,
• the description of a pipe, subjected to various kinds of loadings. This feature is detailed in a dedicated page.

From various benchmarks, this tool has been found much faster (from ten to several hundred times depending on the test case) than using a full-fledged finite element solver such as Cast3M or code_aster.

The mtest python module, described here, allows much finer control of the computations.

Usage

MTest can be used from the command line as follows:

$ mtest [options] inputfile

If the input file has the ptest extension, MTest will assume that the input files describes a test on a pipe. Otherwise, a test on a material point is assumed.

This can be changed by using the --scheme option that currently accept two values:

• --scheme=mtest to specify that the simulation of a single material point is intended.
• --scheme=ptest to specify that the simulation of a pipe is intended.

Getting help

The --help-keywords-list command line option

The list of available keywords are available thanks to the --help-keywords-list option. By default, this command describes the list of keywords associated with the simulation of a single material point. To see the keywords associated with the simulation of a pipe, use --scheme=ptest option before the --help-keywords-list option.

The --help-keyword option

The --help-keyword displays the help associated with a keyword. If this keyword is specific to the simulation of a pipe, use --scheme=ptest option before the --help-keyword option.

Simulation of a material point

MTest can test the local behaviour of a material, by imposing independent constraints on each component of the driving variables (or deformation gradient or the stress). It is equivalent to the SIMU_POINT_MAT operator available within the Code-Aster finite element solver [1] or to the SiDoLo software [2].

MTest can be used to model various experiments, as far as a stage implying strain localisation is not reached: tensile, compressive or shear tests driven by stresses or deformations, pipe loaded by internal or external pressure, test, etc.

MTest generates a text file containing the evolution of the strains (for small strains behaviours), the stresses and the state variables during the loading history. Other MTest functionalities include:

• the ability to test all the behaviours handled by MFront (small strain and finite strain behaviours, cohesive zone models);
• the ability to test isotropic and orthotropic behaviours;
• the support of various modelling hypotheses, notably the plane stress and axisymmetric generalised imposed plane stress hypotheses;
• many features to evaluate the numerical performances of mechanical behaviours. For example, user can compare the computed tangent consistent operator to a numerical approximation;
• a C++ library and a Python interface [3]. MTest can be embedded in general purpose scientific environment to fit behaviour parameters against experimental data. In particular, MTest can be used in ADAO [4], a module for Data Assimilation and Optimization of the Salome platform [5];
• comparison of the results (strains, stresses, internal state variables) to reference or analytical results. MTest automatically generates XML file using the JUnit format. Those files can be used for reporting using the Jenkins continuous integration application. This functionality is central in the quality assurance procedure of MFront.

Through an appropriate option, a behaviour implementation generated through MFront may create an MTest file in case of integration failure: this MTest file only describes the failed time step with the appropriate initial conditions. This feature is particularly useful to analyze the failure of large simulations which may happen after several hours of computations.

Example

@Behaviour<aster> 'src/libAsterBehaviour.so' 'asterplasticity';
@MaterialProperty<constant> 'YoungModulus'     150.e9;
@MaterialProperty<constant> 'PoissonRatio'       0.3;
@MaterialProperty<constant> 'H'                100.e9;
@MaterialProperty<constant> 's0'               100.e6;
@ExternalStateVariable 'Temperature' {0:293.15,3600.:800};
@ImposedStrain<function> 'EXX' '1.e-3*t';
@Times {0.,1 in 20};

References