Index  

Extension Evaluation

Ver: 0
 

DESCRIPTION

In blow moulding process, and especially during inflation, the parison undergoes large deformations which are basically biaxial or more generally, of a multiaxial type. The amplitude of the extension components can be very large, and their isotropy or non-isotropy may have an influence on the final mechanical properties of the blown product. In extrusion/blow moulding applications, it is rather to evaluate the extension components on the basis of two natural directions considered with respect to the parison axis : the axial and circumferential or hoop directions. The axial component corresponds to the extrusion direction, whilst the circumferential component is perpendicular to the first one and tangent to the parison surface. In thermoforming applications, the both sets of unit vectors may be initially selected along the main axes. Both scalar and vector representations are available for the evaluation of the extensions ; the scalar representation consists of calculating the vector magnitude.

Next to the evaluation of both extension components which indicate the possible non-isotropy of the deformations, it is also relevant to evaluate the area stretch ratio. A continuous representation has been developed, and which takes advantage of the finite element technique presently used and of the Lagrangian formulation. Indeed, each element is considered as a material element ; its current and initial configurations are known, and the ratio of infinitesimal areas respectively considered in both these configurations leads to the area stretch ratio.

  OPTIONS
-1
 Upper level menu
1
 Enable/Disable evaluation of area stretch ratio 
Switches on/off the calculation of the area stretch ratio that is obtained by considering a material surface and by calculating the ratio of its area in the deformed configuration to that in the undeformed one.
2
 Enable/Disable scalar evaluation of extensions 
Switches on/off the scalar evaluation of extensions which is obtained by considering the magnitude changes undergone by two sets of vectors with an initially unit length.
3
 Enable/Disable vector evaluation of extensions 
Switches on/off the vector evaluation of extensions which is obtained by considering the changes in length and orientation undergone by two sets of vectors with an initially unit length.
4
 Modify the reference direction 
In evaluating the extensions, the definition of two sets of unit vectors is necessary. If the user defines a reference direction of the parison (or the flat sheet in thermoforming), the program is able to select the best appropriate sets of unit vectors tangent to the surface. For a parison, this direction should be along the axis. For a flat sheet, the reference direction can coincide with one of the main directions.
5
 Modify the reference point 
A reference point has also to be selected, in order to locate the above direction in the space. The reference point should not be on the initial parison or sheet surface.
SEE ALSO