Biaxial measuring device and method for determining normal and shear stress-correlated material parameters

Patent metadata

Field	Value
Publication number	US-9958365-B2
Application number	US-201515505929-A
Country	US
Kind code	B2
Filing date	Jul 24, 2015
Priority date	Aug 26, 2014
Publication date	May 1, 2018
Grant date	May 1, 2018

Abstract

A method for determining material parameters includes applying a character grid over a planar sample, clamping the planar sample in a frame in accordance with directions of orthotropy of the planar sample; collecting a first set of data that describes a first position of the character grid; applying predetermined normal and shear stresses to the planar sample thereby bringing the planar sample into a deformed state and changing the position of the character grid; collecting a second set of data that describes a second position of the character grid, determining a relative position change of the character grid by correlating the collected first set of data and the second set of data; determining a relative displacement and a current distortion state of the planar sample; determining a deformation equilibrium of the deformed state of the planar sample; and calculating the material parameters from the deformation equilibrium.

First claim

The invention claimed is:

1. A method for determining normal stress- and shear stress-correlated material parameters using a biaxial measuring device comprising a frame for clamping a planar sample of a bendable and flexible material, a plurality of drives for applying normal and shear stresses to the sample, and an optical measuring apparatus operatively coupled to a data processing unit, the method comprising:
a) applying a predefined character grid over the planar sample, wherein an orientation of the character grid is either irregular or correlates with directions of orthotropy of the planar sample, and clamping the planar sample in the frame in accordance with the directions of orthotropy of the planar sample,
b) collecting, by the optical measuring apparatus, a first set of data that describes a first position of the character grid and sending the collected first set of data to the data processing unit,
c) applying, simultaneously, predetermined normal and shear stresses to the planar sample by the plurality of drives, thereby bringing the planar sample into a deformed state and changing the position of the character grid,
d) collecting, by the optical measuring apparatus, a second set of data that describes a second position of the character grid and sending the collected second set of data to the data processing unit,
e) determining a relative position change of the character grid by correlating the collected first set of data and the second set of data and determining therefrom, by the data processing unit, a relative displacement and a current distortion state of the planar sample,
f) determining, from the relative displacement and the current distortion state of the planar sample, a deformation equilibrium of the deformed state of the planar sample, wherein the deformation equilibrium correlates with the material parameters, and
g) calculating the material parameters from the deformation equilibrium and outputting the material parameters.

2. The method according to claim 1 , wherein the normal and shear stresses simultaneously applied in step c) to deform the sample are in the non-linear range by virtue of having constantly changing tangent slopes.

3. The method according to claim 1 , wherein, in order to determine the first and or second position of the character grid, distances between three predetermined points on the character grid are detected,
wherein the three predetermined points on the character grid can be joined by lines, and
wherein an angle between the lines of the points on the character grid and a predetermined x- and y-axis of the measuring device can be determined.

4. The method according to claim 1 , further comprising:
g) repeatedly carrying out b) through f) while increasing or reducing the predetermined shear stress and a shear strain with each repetition.

5. A biaxial measuring device comprising:
a frame for clamping a planar sample of a bendable and flexible material, and
a plurality of drives for applying stresses to the clamped sample,
wherein the biaxial measuring device is associated with an optical measuring apparatus operatively coupled to a data processing unit,
wherein, the plurality of drives are configured to simultaneously apply predetermined normal and shear stresses to the clamped sample in normal and parallel directions with respect to directions of orthotropy of the planar sample.

6. The measuring device according to claim 5 , wherein the frame is square, and
wherein the plurality of drives comprises at least eight drives, at least two of the eight drives being arranged along a side edge of the frame, at least one of the at least two drives arranged along a side edge of the frame being a first spindle drive for generating a shear stress, and at least one of the at least two drives arranged along a side edge of the frame being a second spindle drive for generating a shear strain.

7. The measuring device according to 5 , wherein the plurality of drives comprises at least two drives arranged on sides of the frame that face away from one another configured to apply a uniform normal or shear stress to the sample in a predetermined direction of orthotropy.

8. The measuring device according to claim 5 , wherein a rail is arranged within the frame, the rail having an edge portion mounted so as to be linearly displaceable.

9. The measuring device according to claim 5 , wherein the measuring device comprises at least one control unit that is operatively connected to the data processing unit and the plurality of drives and configured to control the plurality of drives in an open- and/or closed-loop manner.

10. The measuring device according to claim 5 , wherein the measuring device comprises a suspension device having a plurality of carriages configured to be connected to an edge portion of the sample.

11. The measuring device according to claim 5 , further comprising a suspension device for the planar sample, the suspension device including at least three carriages that can be connected to an edge portion of the planar sample, at least two of the three carriages being movably mountable on a runner rail and at least one of the carriages being rigidly connectable to the rail.

12. The measuring device according to claim 11 , wherein the suspension device further includes:
a beading around which an edge portion of the planar sample can be placed, the beading being weldable, bondable, or stitchable, to an attachment portion of the planar sample, and
at least three beading, profile blocks each having a recess in which at least portions of the coverable beading can be received, the at least three beading profile blocks being connectable to the at least three carriages.

13. A measurement assembly comprising:
a biaxial measuring device including:
a frame for clamping a planar sample of a bendable and flexible material, and
a plurality of drives for applying stresses to the clamped sample,
wherein the biaxial measuring device is associated with an optical measuring apparatus operatively coupled to a data processing unit,
wherein, the plurality of drives are configured to simultaneously apply predetermined normal and shear stresses to the clamped sample in normal and parallel directions with respect to directions of orthotropy of the planar sample; and

the planar sample of a bendable and flexible material, wherein the planar sample has a planar geometry and/or comprises a character grid predefined on its surface for optically detecting distortions as a result of applicable normal and shear stresses from optically detectable points, wherein an orientation of the character grid correlates with directions of orthotropy of the planar sample.

Assignees

• Karlsruher Inst Technologie

Inventors

• Heinlein Kai
• Mager Arnold
• Wagner Rosemarie

Classifications

• G01N2203/0025

  Shearing · CPC title

• G01N3/24

  by applying steady shearing forces (G01N3/26, G01N3/28 take precedence) · CPC title

• G01N3/08

  by applying steady tensile or compressive forces (G01N3/28 takes precedence) · CPC title

• G01N2203/0282

  Two dimensional, e.g. tapes, webs, sheets, strips, disks or membranes · CPC title

• G01N2203/0641

  using optical, X-ray, ultraviolet, infrared or similar detectors · CPC title