System and method for testing true stress and true strain

A system for testing true stress of a specimen, the system comprising:

• a force input machine for imparting a force on the specimen;
• an imaging system comprising:
• a first light source configured to project a first light beam at the specimen in a first direction;
• and
• a first camera aligned with the first light source on an opposite side of the specimen such that the first camera receives a first shadow image of the specimen;
• and
• a computer having a processor configured to:
• determine a minimum diameter of the specimen perpendicular to the first direction at a plurality of points in time over a plurality of points along the specimen such that the processor accounts for changes in position of the minimum diameter along the specimen as the specimen is subjected to the force over a period of time;
• determine a true stress according to the force applied to the specimen at the point in time and the minimum diameter of the specimen perpendicular to the first direction at the point in time;
• and
• generate an image mask to simplify analysis of the first shadow image of the specimen.

An imaging system for a true stress testing system including a force input machine for imparting a force on a specimen, the imaging system comprising:

• a first laser head positioned perpendicular to the force axis and configured to project a first pulsed, single electromagnetic wavelength light beam at the specimen in a first direction;
• a first camera configured to be aligned with the first laser head on an opposite side of the specimen such that the first camera receives a first shadow image of the specimen, the first camera being configured to detect directional light;
• a second laser head positioned perpendicular to the force axis and angled ninety degrees from the first light source, the second laser head being configured to project a second pulsed, single electromagnetic wavelength light beam at the specimen in a second direction;
• a second camera aligned with the second laser head on an opposite side of the specimen such that the second camera receives a second shadow image of the specimen, the second camera being configured to detect directional light;
• a plurality of components configured to be positioned on opposite ends of the specimen to cast shadows on the first camera and the second camera;
• an adjustable plate for aligning the imaging system with the specimen;
• and
• a computer having a processor configured to:
• determine a minimum diameter of the specimen perpendicular to the first direction at a plurality of points in time over a period of time while the force is being applied to the specimen;
• determine a minimum diameter of the specimen perpendicular to the second direction for the plurality of points in time over the period of time;
• determine a true stress of the specimen according to the force applied to the specimen at the plurality of points in time and the minimum diameters of the specimen at the plurality of points in time;
• determine a true strain of the specimen based on a change of spacing between the shadows;
• and
• generate an image mask for simplifying analysis of the first shadow image and the second shadow image of the specimen.