Method for in-situ nondestructive measurement of Young's modulus of plate structures
First Claim
1. A nondestructive method for quantitatively evaluating a material stiffness of a composite laminate plate along an in-plane direction, the plate having a plurality of plies arranged in a balanced symmetric ply lay-up and having opposite major surfaces defining a thickness of the plate therebetween, the method comprising:
- propagating an elastic extensional-mode wave through the plate along said in-plane direction;
determining a velocity of the extensional-mode wave along said in-plane direction of the plate; and
calculating a material stiffness of the plate along said in-plane direction based on the wave velocity.
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Abstract
A method for determining stiffness of a composite laminate plate entails disposing a device for generating an acoustical pulse against a surface of the plate and disposing a detecting device against the same surface spaced a known distance from the pulse-generating device, and using the pulse-generating device to emit a pulse so as to create an extensional wave in the plate. The detecting device is used to determine a time of flight of the wave over the known distance, and the wave velocity is calculated. A Young'"'"'s modulus of the plate is determined based on the wave velocity. Methods for both anisotropic and quasi-isotropic laminates are disclosed.
28 Citations
17 Claims
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1. A nondestructive method for quantitatively evaluating a material stiffness of a composite laminate plate along an in-plane direction, the plate having a plurality of plies arranged in a balanced symmetric ply lay-up and having opposite major surfaces defining a thickness of the plate therebetween, the method comprising:
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propagating an elastic extensional-mode wave through the plate along said in-plane direction;
determining a velocity of the extensional-mode wave along said in-plane direction of the plate; and
calculating a material stiffness of the plate along said in-plane direction based on the wave velocity. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
imparting energy to the plate at a first point located on a first of the major surfaces of the plate so as to cause the extensional-mode wave to originate at said first point and propagate along the plate.
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3. The method of claim 2, wherein determining the wave velocity comprises:
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detecting when the extensional-mode wave reaches a second point located on said first major surface and spaced in said in-plane direction from the first point;
determining a distance d between the first and second points along said first major surface of the plane in said in-plane direction;
measuring an elapsed time t required for the extensional-mode wave to travel the distance d from the first point to the second point; and
calculating the wave velocity based on the distance d and the time t.
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4. The method of claim 3, wherein calculating the material stiffness comprises calculating a Young'"'"'s modulus along said in-plane direction.
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5. The method of claim 4, adapted for evaluating a quasi-isotropic composite laminate plate, wherein the Young'"'"'s modulus E is calculated based on the equation
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6. The method of claim 3, wherein detecting when the extensional-mode wave reaches the second point comprises using an acoustic energy detector disposed against the first major surface of the plate at the second point.
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7. The method of claim 2, wherein imparting energy to the plate comprises using acoustic energy to create the extensional-mode wave.
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8. The method of claim 2, wherein imparting energy to the plate comprises disposing a device for emitting acoustical energy against the first major surface of the plate at the first point and activating the device to emit acoustic energy.
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9. A nondestructive method for quantitatively evaluating Young'"'"'s moduli of a composite laminate plate along two orthogonal in-plane x- and y-directions of the plate, comprising:
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propagating an extensional wave through the plate;
determining a velocity cx of the extensional wave along said x-direction;
determining a velocity cy of the extensional wave along said y-direction;
determining Young'"'"'s moduli Exx and Eyy respectively along the x- and y-directions by solving a set of simultaneous equations relating the extensional wave velocities, the Young'"'"'s moduli, and Poisson'"'"'s ratios and in-plane stiffness parameters for the plate to one another. - View Dependent Claims (10)
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11. A nondestructive method for quantitatively evaluating a change in Young'"'"'s modulus of a composite laminate plate along an in-plane direction, the plate having a plurality of plies arranged in a balanced symmetric ply lay-up and having opposite major surfaces defining a thickness of the plate therebetween, the method comprising:
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(1) performing a first test including steps (a) through (c) comprising;
(a) imparting energy to the plate at a first point located on a first of the major surfaces of the plate so as to cause an extensional-mode wave to originate at said first point and propagate along the plate in said in-plane direction;
(b) detecting when the extensional-mode wave reaches a second point located on said first major surface and spaced a predetermined distance in said in-plane direction from the first point; and
(c) measuring a first elapsed time t1 required for the extensional-mode wave to travel from the first point to the second point;
(2) performing a second test including steps (d) through (f) comprising;
(d) imparting energy to the plate at a third point located on a first of the major surfaces of the plate so as to cause an extensional-mode wave to originate at said third point and propagate along the plate in said in-plane direction;
(e) detecting when the extensional-mode wave reaches a fourth point located on said first major surface and spaced from the third point by the same said predetermined distance along said in-plane direction; and
(f) measuring a second elapsed time t2 required for the extensional-mode wave to travel from the third point to the fourth point; and
(3) calculating a change in Young'"'"'s modulus for the plate along said in-plane direction based on a degree of difference of the times t1 and t2. - View Dependent Claims (12, 13, 14, 15)
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16. A method for quantitatively evaluating a material stiffness of an isotropic or quasi-isotropic plate along an in-plane direction, the method comprising:
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disposing a first device for emitting acoustical energy on a first major surface of the plate and activating the device to cause an elastic extensional-mode wave to be propagated through the plate along said in-plane direction;
disposing a second device for detecting the extensional-mode wave on said first major surface of the plate spaced a distance d from the first device along said in-plane direction and using the second device to detect arrival of the extensional-mode wave;
measuring the elapsed time t between initiation of the extensional-mode wave by the first device and detection of the extensional-mode wave by the second device; and
calculating Young'"'"'s modulus E of the plate along said in plane direction based on the equation - View Dependent Claims (17)
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Specification