Test specimen crack correlator
AssigneeMTS Systems Corporation
InventorWilliam D. Juusola
Life of this patent
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Abstract
A testing apparatus for cyclically loading specimens of a known configuration to determine properties of materials from propagation or growth of a crack through the specimen including means to provide a direct output which is a function of crack length derived from measurements of the load and the displacement of the specimen.
Claims18
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.
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.
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.
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.
Dependencies are inferred from the claim text.