We use unique materials testing, analysis and optimization methods, based on years of experience in the determination of parameters for the FEM. Whether evaluating a simple tensile test or use of complex planar optimization methods; you will always receive the best possible result.
Conventional testing methods
The figure below illustrates the stress-strain curve of a homogeneous, unidirectional tensile test of a thermoplastic material. An evaluation according to DIN ISO 527-1 gives only a very rough approximation in the initial region of the curve. If one evaluates such a curve, but with our method, there is a very good fit as a function of physical material properties (right image):
- Point- and-click to enlarge
In such a course you might want to use a non-linear elastic or elastoplastic model to receive, depending on the material, more suitable parameters for the FEM.
- We identify the best possible set of material data from one or more tensile tests for your finite element simulation.
A further improvement is achieved by the addition of experimental data in which other stress conditions are taken into account, eg from compression, shear, or biaxial tests. Again, you achieve the best results with our optimization method (see animated graphic). All evaluation methods up to the simultaneous analysis of different types of experimental data sets are implemented in our software FEMCard Basic for a growing number of material models implemented in the most common FEA-Solvers.
- Evaluation of several types of test
Newly invented material testing method
By means of our enhanced testing and evaluation concept FEMCard Pro complete sets of material data for all standard finite element program systems can be determined . We guarantee a manageable amount of time effort with full cost control and for each customer clearly understandable results. By using a e.g. perforated rectangular specimen in tensile testing, a multiaxial strain state around the hole is generated. It is measured with the aid of an optical measurement method at each load step in a resolution of about 1000 up to 3000 measurement points (image on the right).
In the next step the measurement grid is mapped via interpolation on the FE mesh of a corresponding FE model, so that at any load step, the values of the measured displacements can be compared with the related displacements of the simulation (see following pictures).
- Point-and-click to enlarge
Each measurement point on the specimen surface corresponds to a test that causes different proportions of tension, shear and compression inside the material. Therefore a single tensile test on a perforated rectangular specimen represents approximately 1000 up to 3000 load combinations, depending on the measurement resolution (see below).
By means of a global gradient based optimization routine the material properties of the used material model can be adjusted so that the FE-simulation deviates minimal from the optical measurements for the entire deformation range. Hereby our customers receive the complete set of material data for any constitutive law implemented in current FEA-Software within one optimization step.
- Optimization by means of least squares method