Test specimen crack correlator

Claim 2

A test device for determining crack growth rates in test specimens comprising means for cyclically loading a specimen, first means for determining the load applied to a loaded specimen, second means for determining the displacement of a loaded specimen in a region to measure the size of a crack in such a specimen, said first and second means providing analog signals representing load and displacement, means to convert the analog signals from said first and second means to digital form, means to arithmetically compute in digital form a quantity comprising the displacement value divided by the load value, and means to convert the digital output of said means to compute to an analog signal comprising the output of said test device.

Claim 3

The combination as specified in claim 1 and further analog multiplying means to multiply said output by selected factors to provide a correlation of growth of said crack in said specimen.

Claim 4

The combination as specified in claim 2 wherein said analog multiplying means includes means to provide adjustable gain for displacement and load ranges of a specimen being loaded, and to multiply the output by a value equal to the Young's modulus for the material from which a tested specimen is made, and by a scaled value representing the thickness of a specimen being tested to provide a second quantity.

Claim 5

The combination as specified in claim 3 wherein said analog mutliplying means further includes means to utilize the second quantity to provide an analog output representing a third order equation providing an output from the analog multiplying means which is substantially proportional to the crack length divided by the specimen width.

Claim 6

The combination as specified in claim 4 wherein said last mentioned means includes circuitry having a first portion adding a desired gain and an adjustable constant to the analog value of said second quantity, a second portion multiplying said second quantity by itself to provide a signal representing the square of the second quantity, and to multiply said signal representing the square by a constant, and a third portion multiplying the square of the second quantity by the second quantity to provide a signal representing the cube of the second quantity and multiplying the signal representing the cube by a third constant, means to sum the outputs of said first, second and third portions, and means to provide a fourth constant to the summed signals to provide said analog value substantially proportional to crack length divided by specimen width.

Claim 7

The combination as specified in claim 1 wherein one of said first and second means is connected to means for providing a first signal when the output of said one means connected exceeds a first preselected level and is also connected to separate means to provide a second signal when the output of said one means exceeds a second preselected level higher than the first level.

Claim 8

The combination as specified in claim 6 wherein said means to arithmetically compute includes subtractor means receiving the digital values of the outputs of said first and second means, said subtractor means being connected to the output of said means to provide the first signal, and including means to hold the digital values of the outputs of the first and second means when the first signal is received by said subtractor means, said subtractor means subsequently receiving periodic digital values of said first and second means and providing an output comprising the difference between the held values and the subsequent values, the outputs of said subtractor means being provided to a divider, and means connecting said means providing the second signal to said divider and causing an output from said divider in response to said second signal.

Claim 9

A test apparatus for testing a specimen in which crack growth rates are to be studied, and including means to apply a cyclic tension load to a specimen adjacent one edge thereof, a specimen being tested having a thickness represented by B, and a speciment width represented by W, means to determine the force F applied to a specimen being tested, means to determine the displacement V in a crack area of a specimen being tested, a specimen crack having a length a as it propagates across the width of a specimen under loading by said means to load a specimen, the specimen being tested having a known geometry providing a third order polynomial curve when the quantity EBV/F is plotted versus the quantity a/W, where E is Young's modulus for the material from which the specimen is made; the improvement comprising an electronic circuit to provide direct readout of a voltage which is substantially proportional to crack length including means to provide a signal representing the displacement V divided by the force F, (V/F), means to multiply said signal by electrical quantities representative of E and B to provide an output substantially proportional to EBV/F, and a multiplier circuit to receive the separate signal representing the quantity EBV/F including a plurality of portions connected to provide an output signal substantially proportional to a polynomial function of EBV/F which represents the quantity a/W.

Claim 10

A test apparatus for testing a specimen in which crack growth rates are to be studied, and including means to apply a cyclic tension load to a specimen adjacent one edge thereof, a specimen being tested having a thickness represented by B, and a speciment width represented by W, means to determine the force F applied to a specimen being tested, means to determine the displacement V in a crack area of a specimen being tested, a specimen crack having a length a as it propagates across the width of a specimen under loading by said means to load a specimen, the specimen being tested having a known geometry providing a third order polynomial curve when the quantity EBV/F is plotted versus the quantity a/W, where E is Young's modulus for the material from which the specimen is made; the improvement comprising an electronic circuit to provide direct readout of a voltage which is substantially proportional to crack length including means to provide a signal representing the displacement V divided by the force F, (V/F), means to multiply said signal by electrical quantities representative of E and B to provide an output substantially proportional to EBV/F, and a multiplier circuit to receive the separate signal representing the quantity EBV/F including a plurality of portions connected to provide an output signal substantially proportional to a polynomial function of EBV/F which represents the quantity a/W.

Claim 11

The combination of claim 8 wherein said plurality of portions includes a second portion providing an output A 2 (EBV/F) 2 and a third portion providing the quantity A 3 (EBV/F) 3 , and means to sum the outputs of said first and second and third portions and add said first, second and third portions to an electrical signal representing A 0 , to thereby provide an output signal substantially proportional to the quantity a/W where A 0 , A 1 , A 2 and A 3 are constants.

Claim 12

The combination as specified in claim 8 and means to multiply the last mentioned signal representing a/W by an electrical signal proportional to the width of the specimen to provide an analog output representing length of a crack of a specimen being tested.

Claim 13

The combination of claim 10 wherein said means to apply a cyclic tension load includes servo control means, and means to connect the analog output representing the length of a crack to the servo control means to function as a feedback signal in the servo control means.

Claim 14

The combination as specified in claim 8 wherein the means to provide the signal proportional to the quantity V/F includes first and second means to provide analog signals representing the displacement of a specimen being tested and the load on a specimen being tested, respectively, means to convert said analog signals to digital form, and digital divider means to divide selected values of V by selected values of F.

Claim 15

The combination as specified in claim 12 wherein said value of V and the value of F are provided by means detecting a threshold value of said first and second means at a low load point in each operation cycle, and means to subsequently detect a higher value of said first and second means in the same cycle of loading, means to subtract the low values from each of first and second means from the high values of the corresponding means, and means to divide the remainders of the two values in said digital divider.

Claim 16

The combination as specified in claim 12 wherein the means to provide the signal proportional to the quantity V/F includes means to convert the output of said divider into analog form.

Claim 17

A test device for testing specimens wherein values representing selected test parameters must be arithmetically compared or computed and the comparator is desired as an analog signal comprising means for cyclically loading a specimen, means for determining at least two parameters related to loading of the specimen, said means providing analog output signals representing the parameters, means to convert the analog signals to digital form, means to arithmetically compare the parameters in digital form, means to convert the digital value of the compared parameters to an analog signal comprising the output of said test device.

Claim 18

A test device for testing specimens wherein values representing selected test parameters must be arithmetically compared or computed and the comparator is desired as an analog signal comprising means for cyclically loading a specimen, means for determining at least two parameters related to loading of the specimen, said means providing analog output signals representing the parameters, means to convert the analog signals to digital form, means to arithmetically compare the parameters in digital form, means to convert the digital value of the compared parameters to an analog signal comprising the output of said test device.

Claim 19

The test device of claim 15 wherein said means to arithmetically compare includes means to divide the digital value of one parameter by another.

Claim 20

In a test device for testing specimens and obtaining a signal proportional to the displacement of a specimen divided by the load on a specimen and including means to cyclically load a specimen, and signal means to provide separate signals representing the displacement and the load on a specimen, respectively, the improvement comprising threshold detection means connected to said signal means to provide a first signal indicating when a selected one of said displacement and load signals exceeds a first predetermined amount and to provide a second signal when said selected one signal exceeds a second greater amount in the same cycle of loading, means connected to the threshold detection means and to the signal means to determine different values between the value of said displacement and load signals respectively at the time of said first signal and at the time of said second signal and to divide said difference values, one by the other.

Claim 21

In a test device for testing specimens and obtaining a signal proportional to the displacement of a specimen divided by the load on a specimen and including means to cyclically load a specimen, and signal means to provide separate signals representing the displacement and the load on a specimen, respectively, the improvement comprising threshold detection means connected to said signal means to provide a first signal indicating when a selected one of said displacement and load signals exceeds a first predetermined amount and to provide a second signal when said selected one signal exceeds a second greater amount in the same cycle of loading, means connected to the threshold detection means and to the signal means to determine different values between the value of said displacement and load signals respectively at the time of said first signal and at the time of said second signal and to divide said difference values, one by the other.

Claim 22

The device of claim 17 wherein said signal means provide analog signals, means connected to the signal means to convert said analog signals to digital equivalents, and means to connect said means to convert to said means to determine the difference.