Assembly and method for determining the coefficient of thermal expansion of a workpiece

Claim 2

An assembly suitable for determining a coefficient of thermal expansion of a workpiece having opposite ends, the assembly comprising: (a) a chamber which surrounds and is spaced apart from the workpiece; (b) means for locating the workpiece in the chamber including a first imaging device attachable to one end of the workpiece to move with said one end and a second imaging device attachable to the other end of the workpiece to move with said other end; (c) means for selectively changing and monitoring the temperature of the workpiece; (d) a dual channel laser interferometer system including a source of first and second measurement laser beams of different frequencies placed in operative association with the workpiece so that, under testing conditions, the first beam is reflected off said first imaging device and the second beam is reflected off said second imaging device, said imaging devices moving with said ends to induce frequency shifts in said beams from which information concerning the length of the workpiece is obtained; and (e) a data acquisition system for computing the coefficient of thermal expansion of the workpiece based on the temperature and length of the workpiece under test.

Claim 3

An assembly according to claim 1, wherein the chamber comprises inner and outer walls which form a water jacket for heating and cooling the workpiece.

Claim 4

An assembly according to claim 1, wherein the means for changing the temperature of the workpiece comprises: (a) a constant temperature bath and circulator; and (b) pump means for evacuating the chamber.

Claim 5

An assembly according to claim 3, wherein the constant temperature bath is controlled to within ±0.5° F.

Claim 6

An assembly according to claim 4, wherein the constant temperature bath is controlled to within ±0.041° F.

Claim 7

An assembly according to claim 3, wherein the chamber is evacuated to below 1×10 -1 Torr.

Claim 8

An assembly according to claim 6, wherein the chamber is evacuated to below 1×10 -2 Torr.

Claim 9

An assembly according to claim 1, comprising at least one temperature sensing device.

Claim 10

An assembly according to claim 8, wherein the means for monitoring the temperature of the workpiece comprises at least one thermistor attachable to the workpiece.

Claim 11

An assembly as in claim 1, wherein said first imaging device comprises a device having a center, first and third quadrants positioned diagonally oppositely about said center, and first and second specular reflector portions respectively located in said first and third quadrants and having corresponding parts separated by a 180° angle; and said dual channel laser interferometer system is placed in operative association with the workpiece so that the first beam is serially reflected first from said first portion, then from said second portion.

Claim 12

An assembly as in claim 10, wherein said first imaging device further comprises second and fourth quadrants positioned diagonally oppositely about said center and first and second non-reflective portions respectively located in said second and fourth quadrants and having corresponding parts separated by a 180° angle; and said dual channel laser interferometer system is placed in operative association with the workpiece so that the second beam is serially reflected by said second imaging device first through said first non-reflective portion of said first imaging device, then through said second non-reflective portion.

Claim 13

An assembly as in claim 10, wherein said means for locating the workpiece further comprises first and second flexure systems which engage respective ends of said workpiece by way of said first and second imaging devices.

Claim 14

An assembly suitable for determining a coefficient of thermal expansion of a workpiece, the assembly comprising: (a) a chamber which surrounds and is spaced apart from the workpiece; (b) means for locating the workpiece comprising a rail assembly; a first and second flexure system connected to the rail assembly; and means for engaging the workpiece to the first and second flexure system; (c) means for selectively changing and monitoring the temperature of the workpiece; (d) a dual channel laser interferometer system placed in operative association with the workpiece so that, under testing conditions, information concerning the length of the workpiece is obtained; and (e) a data acquisition system for computing the coefficient of thermal expansion of the workpiece based on the temperature and length of the workpiece under test.

Claim 15

An assembly suitable for determining a coefficient of thermal expansion of a workpiece, the assembly comprising: (a) a chamber which surrounds and is spaced apart from the workpiece; (b) means for locating the workpiece comprising a rail assembly; a first and second flexure system connected to the rail assembly; and means for engaging the workpiece to the first and second flexure system; (c) means for selectively changing and monitoring the temperature of the workpiece; (d) a dual channel laser interferometer system placed in operative association with the workpiece so that, under testing conditions, information concerning the length of the workpiece is obtained; and (e) a data acquisition system for computing the coefficient of thermal expansion of the workpiece based on the temperature and length of the workpiece under test.

Claim 16

An assembly suitable for determining a coefficient of thermal expansion of a workpiece, the assembly comprising: (a) a chamber which surrounds and is spaced apart from the workpiece; (b) means for locating the workpiece in the chamber; (c) means for selectively changing and monitoring the temperature of the workpiece; (d) a dual channel laser interferometer system placed in operative association with the workpiece so that, under testing conditions, information concerning the length of the workpiece is obtained; and (e) a data acquisition system for computing the coefficient of thermal expansion of the workpiece based on the temperature and length of the workpiece under test; wherein the dual channel laser interferometer system comprises: a two-frequency laser beam; a dilatometer converter for splitting the laser beam into a first frequency measurement beam and a second frequency measurement beam; a remote interferometer comprising a first and second reflector for optically processing the first and second frequency measurement beams respectively; a plane mirror converter for optically processing the beams outputted by the remote interferometer; and (i) a first imaging device comprising a first and second specular reflector for reflecting the first frequency measurement beam to the interferometer first and second reflectors, the first imaging device attachable to the workpiece at a first location, and capable of moving with the workpiece as the workpiece expands or contracts in response to a changing temperature; and (ii) a second imaging device comprising a specular reflector for reflecting the second frequency measurement beam to the first and second interferometer reflectors, the second imaging device attachable to the workpiece at a second location, and capable of moving with the workpiece as the workpiece expands or contracts in response to a changing temperature.

Claim 17

An assembly suitable for determining a coefficient of thermal expansion of a workpiece, the assembly comprising: (a) a chamber which surrounds and is spaced apart from the workpiece; (b) means for locating the workpiece in the chamber; (c) means for selectively changing and monitoring the temperature of the workpiece; (d) a dual channel laser interferometer system placed in operative association with the workpiece so that, under testing conditions, information concerning the length of the workpiece is obtained; and (e) a data acquisition system for computing the coefficient of thermal expansion of the workpiece based on the temperature and length of the workpiece under test; wherein the dual channel laser interferometer system comprises: a two-frequency laser beam; a dilatometer converter for splitting the laser beam into a first frequency measurement beam and a second frequency measurement beam; a remote interferometer comprising a first and second reflector for optically processing the first and second frequency measurement beams respectively; a plane mirror converter for optically processing the beams outputted by the remote interferometer; and (i) a first imaging device comprising a first and second specular reflector for reflecting the first frequency measurement beam to the interferometer first and second reflectors, the first imaging device attachable to the workpiece at a first location, and capable of moving with the workpiece as the workpiece expands or contracts in response to a changing temperature; and (ii) a second imaging device comprising a specular reflector for reflecting the second frequency measurement beam to the first and second interferometer reflectors, the second imaging device attachable to the workpiece at a second location, and capable of moving with the workpiece as the workpiece expands or contracts in response to a changing temperature.

Claim 18

An assembly according to claim 14, wherein the duel channel laser interferometer system further comprises means: (i) for detecting frequency shifts in the first and second frequency measurement beams respectively induced by movements of the workpiece; (ii) for converting the respective frequency shifts into displacement parameters; and (iii) for computing the relative displacement between the first and second imaging devices based on the displacement parameters.

Claim 21

A method according to claim 16, wherein the workpiece comprises a composite.

Claim 22

A method according to claim 17, wherein the composite comprises graphite/epoxy.