Hammer activated measurement system for testing and evaluating rubber and other materials
Devices and methods are provided for determining whether a laminate structure is in a bonded or debonded state. The devices and methods provide simple, accurate, rapid, cost-effective, and reliable means for assessing the bonding state of such laminated structures.
1 . A device for detecting a bonded state or a debonded state between layers of a laminate structure, the device comprising:
an impulse hammer comprising a hammer head comprising a force sensor; and
a computer having programmed therein a universal profile and a profile threshold;
wherein, when the impulse hammer impacts a region of the laminate for a time period, the force sensor delivers force versus time pulse data to the computer, the force versus time pulse data comprising a plurality of data points spanning fractions of the time period;
the computer normalizes the pulse data to yield a normalized pulse curve, compares the normalized pulse curve to the universal profile, and calculates a root mean square difference (RMSD) between the normalized pulse curve and the universal profile; and
if the RMSD exceeds the profile threshold, the computer provides a notification that the laminate is in a debonded state.
2 . The device of claim 1 , further comprising:
if the RMSD does not exceed the profile threshold, the computer provides a notification that the laminate is in a bonded state.
3 . The device of claim 1 , further comprising an enclosure to house the computer, the computer being attached by a cord to the impulse hammer.
4 . The device of claim 3 , further comprising a battery pack and a signal conditioner housed within the enclosure, and wherein the enclosure has means for being worn by an operator.
5 . The device of claim 1 , wherein the impulse hammer houses the computer, a battery pack, and a signal conditioner.
6 . The device of claim 1 , wherein the laminate structure is a substrate-laminate selected from the group consisting of a submarine hull, a surface ship hull, and an aircraft body.
7 . The device of claim 1 , wherein the force sensor directly measures force and outputs force data.
8 . The device of claim 1 , wherein the force sensor is an accelerometer which directly measures acceleration and outputs acceleration data which may be converted to force data.
9 . The device of claim 1 , wherein the impulse hammer's impulse hammer head is mounted on an air cylinder, the air cylinder being controlled by an air cylinder controller capable of triggering an impact of the impulse hammer head against a laminate structure.
10 . An apparatus comprising a plurality of devices of claim 9 , wherein the impulse hammers form an array, each impulse hammer in the array delivers pulse data from impact to the computer, and for each pulse data the computer determines a bonded state or a debonded state.
11 . The apparatus of claim 10 further comprising means to crawl to at least one additional location after the array has measured impacts at a first location, and optionally further comprising a means of marking debonded regions with visible markings.
12 . A method for determining a bonded state or a debonded state between layers of laminate structure, the method comprising the steps of:
impacting a region of the laminate structure with a device of claim 1 ;
receiving the force versus time pulse data from the pulse hammer;
normalizing the pulse data to produce a normalized pulse curve; and
calculating a pulse RMSD by comparing the normalized pulse curve to a universal profile;
whereby, if the pulse RMSD exceeds a profile threshold, the laminate structure is determined to be in a debonded state, and if the pulse RMSD does not exceed the profile threshold, the laminate structure is determined to be in a bonded state.
13 . The method of claim 12 , wherein the pulse RMSD is calculated according to
R
M
S
D
=
∑
(
f
*
(
t
*
)
-
P
(
t
*
)
)
2
N
wherein f* is a nondimensional force, t* is a nondimensional time, f*(t*) is the normalized pulse curve, P(t*) is the universal profile, and N is a number of time points in the pulse data.
14 . The method of claim 12 , wherein the universal profile is generated by the steps of:
subjecting a plurality of normalized pulse curves to a mathematical regression to establish a plurality of parameters parametrically describing each of the normalized pulse curves;
averaging each of the parameters to produce a working profile;
comparing each normalized pulse curve to the working profile to produce an RMSD for each normalized pulse curve;
generating a working profile histogram comprising the RMSDs;
iteratively eliminating outlier pulse RMSDs to refine the working profile histogram until a confidence level is reached;
wherein the last refined working profile is deemed to be the universal profile.
15 . The method of claim 14 , wherein the mathematical regression is regression selected from the group consisting of a nonlinear regression and a linear regression.
16 . The method of claim 15 , wherein the nonlinear regression is performed according to
f
*
(
t
*
)
=
p
1
+
p
2
sin
(
p
3
t
*
+
p
4
)
e
-
p
5
t
*
wherein f* is a nondimensional force, t* is a nondimensional time, p 1 is a DC offset to long-term equilibrium position, p 2 is a mean-to-peak amplitude, p 3 is a ringdown frequency, p 4 is a phase, and p 5 is an energy dissipation term calculated as a product of a viscous damping ratio and a natural frequency.
17 . The method of claim 14 , wherein the RMSD is calculated according to
R
M
S
D
=
∑
(
f
*
(
t
*
)
-
p
(
t
*
)
)
2
N
wherein f* is a nondimensional force, t* is a nondimensional time, f*(t*) is the normalized pulse curve, p(t*) is the working profile, and N is a number of time points in the pulse data.
18 . The method of claim 12 , wherein the laminate structure is a substrate-laminate selected from the group consisting of a submarine hull, a surface ship hull, and an aircraft body.
19 . The method of claim 18 , wherein a plurality of devices are mounted in an array; each impulse hammer's impulse hammer head is mounted on an air cylinder; the air cylinders are controlled by an air cylinder controller capable of triggering an impact of the impulse hammer head against a laminate structure; and
the method further comprises the step of triggering a plurality of impacts at more than one location of the laminate structure, whereby the bonded or debonded state is determined.
20 . The method of claim 19 , further comprising the step of applying a marking at locations identified as debonded.