Measuring and testing – Specimen stress or strain – or testing by stress or strain... – By loading of specimen
Reexamination Certificate
1999-12-03
2001-12-04
Noori, Max (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
By loading of specimen
Reexamination Certificate
active
06324915
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains generally to methods and systems for measuring forces and, more particularly, to methods and systems for measuring mechanical properties of elastomeric materials.
BACKGROUND OF THE INVENTION
Conventional methods for testing the mechanical properties of elastomeric materials, such as rubber and urethanes, seek to determine elastic and viscous moduli by vibrating specimens at different frequencies. For example, to find the elastic and loss bulk moduli of an elastomeric specimen with dimensions 5 inches in diameter and ½ inch in. thickness (circular disk-flat), these moduli should be functions of excitation frequency over a range of 0-2000 Hz.
As shown in
FIG. 1A
, a typical measuring technique is to use a Universal Test Machine (UTM) loading frame
10
to apply loads and capture data. The UTM
10
includes an upper crosshead
12
that supports a load cell
14
and is connected to a base crosshead
16
, stably affixed to a floor mounted base
18
. A flat disc specimen
20
is placed on top a hydraulic actuator
22
, which imparts a forcing function to the specimen.
Using Fourier analysis, this forcing function can be regarded as comprising a range of excitation frequencies. The forcing function is measured by the load cell
14
as f(t). As seen in
FIG. 1B
, the load cell
14
measures time-varying input motions from a displacement x(t) in the specimen
20
, in order to derive an elastic spring force proportionality rate k, and a viscous damping force proportionality rate c.
Forces generated and transmitted to the load cell are given as:
f
(
t
)=
cx+kx
A Fourier Transform to the frequency domain yields:
F
(&ohgr;)=(
k+j&ohgr;c
)
{overscore (X)}
(&ohgr;)
and a formulation of the Frequency Response Function (FRF):
F
(
ω
)
X
_
(
ω
)
=
k
+
j
ω
c
shows that the real part represents the elastic spring rate and the imaginary part contains the damping rate times the frequency.
This method yields worthwhile results until f(t) begins to contain forces with sources other than those transmitted by the elastomer, for instance mechanical resonances of the machine parts. Results at frequencies above that point are unreliable. Dynamic force measurement (DFM) techniques may be used to remove the resonant effects from the f(t) data. However, neither method yields wide band frequency results directly.
SUMMARY OF THE INVENTION
In view of the difficulties and drawbacks associated with previous methods and apparatuses, there is therefore a need for a test measurement apparatus that can measure results more directly.
There is also a need for a test measurement apparatus that can measure frequency response over a larger frequency range and that is less sensitive to vibrations from external sources.
These needs and others are satisfied by the present invention in which a test measuring device is provided including a base for supporting an elastomeric sample to be measured. A driving point impedance head is provided for imparting a force. A force distributing member receives the imparted force and applies it to the sample. One or more sensors are attached to the force distributing member, for measuring the frequency response of the mass to the imparted force. An analytical device is provided for transforming the frequency response to obtain correlated values representing elastomeric properties of the sample.
As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various respects, all without departing from the invention. Accordingly, the drawing and description are to be regarded as illustrative in nature and not restrictive.
REFERENCES:
patent: 4461177 (1984-07-01), Feng
patent: 4546658 (1985-10-01), Rocha et al.
patent: 4633718 (1987-01-01), Van Engelshoven
patent: 5033308 (1991-07-01), Le Compagnon et al.
patent: 5877428 (1999-03-01), Scolton
Arter & Hadden LLP
Noori Max
Test Measurements Systems Inc.
LandOfFree
Driving point impedance head for measurement of elastomeric... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Driving point impedance head for measurement of elastomeric..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Driving point impedance head for measurement of elastomeric... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2588696