Capacitive extensometer
AssigneeThe United States of America as represented by the Administrator of the National Aeronautics and Space Administration
InventorGail P. Perusek
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Abstract
The present invention provides for measurements of the principal strain magnitudes and directions, and maximum shear strain that occurs in a porous specimen, such as plastic, ceramic or porous metal, when it is loaded (or subjected to a load). In one embodiment the invention includes a capacitive delta extensometer arranged with six sensors in a three piece configuration, with each sensor of each pair spaced apart from each other by a predetermined angle, such as 120 degrees.
Claims13
A capacitive extensometer for sensing the strain of an associated specimen, said extensometer comprising:
- three insertable pins operable for insertion into the specimen;
- and,
- six capacitive sensors mounted across said three pins and each providing a variable capacitance whose value is varied by the strain to which the specimen is subjected, where said six capacitive sensors are grouped into pairs with each pair being arranged on a five sided member having a sensor face along which said pair is attached and spaced apart from each other.
A capacitive extensometer for sensing the strain of a specimen, said extensometer comprising:
- multiple insertable displacement registering devices, each registering device being attached to a mounting member having a first internal side and a second internal side;
- at least one capacitive sensor mounted across each said registering device and providing a variable capacitance whose value is varied by the strain to which the specimen is subjected, where said at least one capacitive sensor is mounted to said first internal side, and where said second internal side is a target face side, and where said at least one capacitive sensor on said mounting members are oriented at a predetermined angle of 120 degrees to each other;
- where each of said capacitive sensors generates an electrical signal which is received by a serial arrangement comprising an amplifier and analog-to-digital converter;
- and
- where said serial arrangement further comprises a linearizing circuit and a low pass filter interposed between said amplifier and said analog-to-digital converter.
A method of measuring strain in an associated specimen, the method comprising the steps of:
- providing a capacitive extensometer that includes multiple displacement registering devices and at least one capacitive sensor mounted across each said registering device which each provide a variable capacitance whose value is varied by the strain to which the specimen is subjected;
- inserting said registering devices into the specimen;
- generating an electrical signal from each of said capacitive sensors;
- routing the electrical signal from each of said capacitive sensors to a serial arrangement comprised of an amplifier and an analog-to-digital converter;
- routing said serial arrangement for each of said capacitive sensors to a processor;
- and,
- using operating routines within said processor to calculate the strain in the specimen.
A method for measuring strain in a specimen comprising the steps of:
- inserting a plurality of pins into a measurement site of said specimen wherein said pins are substantially parallel upon insertion;
- attaching sensing means to at least two pins after said step of inserting said plurality of pins into said measurement site;
- and
- utilizing a drilling guide to determine insertion points on said measurement site prior to said step of inserting said plurality of pins, where points at each apex of an equilateral triangle are utilized to determine said insertion points.
Dependencies are inferred from the claim text.