Electricity: measuring and testing – Magnetic – Stress in material measurement
Reexamination Certificate
2000-11-03
2002-07-23
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Stress in material measurement
C324S223000, C073S760000, C073S779000
Reexamination Certificate
active
06424149
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nondestructive test method for quantitatively determining fatigue of ferromagnetic construction materials, or of the structure comprised of such materials.
2. Description of the Related Art
Conventional nondestructive test methods for determining fatigue of materials are generally based on investigation of generation and growth of cracks in the material, and thus, it is highly important to find out as minute cracks as possible. With such a conventional nondestructive test method, it is practically impossible to evaluate metal fatigue of the material before cracks are generated.
There are also other types of nondestructive fatigue test methods known, which can be applied to ferromagnetic construction materials or structures comprised of such construction materials. One of such test methods is for measurement of the coercive force, and another method is for measurement of the magnetic susceptibility of the test material in the range approaching to saturation. It is known that the former method has less measurement sensitivity than the latter method, and such measurement sensitivity of the former method degrades when the materials that have more progressed metal fatigue are measured.
SUMMARY OF THE INVENTION
It is therefore a primary object of the present invention to provide an improved test method for nondestructively determining the metal fatigue of ferromagnetic construction materials, which advantageously eliminates the above-mentioned problems of the prior art.
One aspect of the present invention resides in a method for nondestructively determining metal fatigue of test ferromagnetic construction materials having a known, initial tensile stress &sgr;
0
, by quantifying a change in effective stress due to aging of the materials. The test method according to the present invention comprises the following three steps.
The first step is to measure the coercive force (H
c
) and the magnetic susceptibility (&khgr;
H
) of a test material under a magnetic field having a coercive force(H
c
).
The second step is to determine an effective tensile stress (&sgr;) by putting said coercive force (H
c
) and said magnetic susceptibility (&khgr;
H
) into a following first equation:
&sgr;=
a
(
H
c
/&khgr;
H
)
n
(1)
where a and n are known constants determined by the internal structure of the test material.
Finally, the third step is to determine a change in effective tensile stress of the test material, by comparing said effective tensile stress (&sgr;) of the test material with the initial tensile stress (&sgr;
0
) of the test material.
Another aspect of the present invention resides in an apparatus for nondestructively determining metal fatigue of test ferromagnetic construction materials having a known, initial tensile stress (&sgr;
0
), by quantifying a change in the effective stress due to aging of the test materials. The apparatus according to the present invention comprises:
i) measuring means for measuring the magnetic susceptibility (&khgr;
H
) of a test material in its aged state, under a magnetic field having a coercive force (Hc);
ii) stress calculation means for calculating and thereby determining an effective tensile stress (&sgr;) of the test material, by putting said coercive force (H
c
) and said magnetic susceptibility (&khgr;
H
) into a following first equation:
&sgr;=
a
(
H
c
/&khgr;
H
)
n
(1)
where a and n are known constants determined by the internal structure of the test material; and
iii) evaluation means for determining a change in the effective stress of the test material due to aging thereof, by comparing the current tensile stress (&sgr;) of the test material with its initial tensile stress (&sgr;).
The nondestructive test apparatus according to the present invention, as a whole, may be comprised of a personal computer installed with programs based on the algorithm which enables execution of the above steps.
The principle of the present invention will be described below with reference to the experimental test data. To elucidate the interrelationship between the mechanical and magnetic properties of steel materials, test materials were prepared which consist of a pure iron single crystal, polycrystalline pure iron, and low-alloy steel A533B, respectively. These test materials were formed into samples having shapes as shown in FIGS.
1
(
a
),
1
(
b
) and
1
(
c
), respectively, which are to be subjected to tensile and hysteresis loop tests. The samples as shown in FIG.
1
(
a
) were used for the tensile test, while the samples as shown in FIG.
1
(
b
) or
1
(
c
) were used for the hysteresis loop test. As for the hysteresis loop test, the polycrystalline pure iron and low-alloy steel A533B took the shape of FIG.
1
(
b
) while the pure iron single crystal took the shape of FIG.
1
(
c
). Table 1 below shows the chemical composition of the low-alloy steel A533B submitted to the test.
TABLE 1
A533B
C
Si
Mn
P
S
Cu
Ni
Mo
Al
Wt. %
0.18
0.15
1.5
0.004
0.001
0.03
0.66
0.56
0.01
FIGS. 2
to
4
illustrate the stress-strain characteristics of the test samples, obtained from the tensile test.
FIG. 2
represents the results from Fe single crystal samples, and shows that the strain rate (i.e., extension rate) is 1.5%/min.
FIG. 3
represents the results from Fe polycrystalline samples, and shows that the strain rate is 1.2%/min, and
FIG. 4
represents the results from a low-alloy steel A533B sample, and shows that the strain rate is 1.2%/min.
FIGS. 5 and 6
illustrate the magnetization curves obtained from the hysteresis loop test after the application of stresses.
FIG. 5
shows the hysteresis loop characteristics of Fe single crystal samples with plastic deformation of stresses (0 MPa, 55 MPa, or 115 MPa), while
FIG. 6
shows the hysteresis loop characteristics of Fe polycrystalline samples with plastic deformation of stresses (0 MPa, 550 MPa, or 663 MPa). The applied stresses were chosen to be equal to 0 MPa and the stress that develops just before fracture, both of which had been obtained from a preparatory tensile test, and the above mentioned intermediate stresses had been chosen between these values for plastic deformation.
From the magnetization curve of test materials as depicted in
FIGS. 5 and 6
, it is possible to determine the coercive force Hc (the magnetic field intensity H at the flux density B=0) of the individual test material related to the tensile stress &sgr;.
FIG. 7
is obtained when the coercive force Hc is plotted against the tensile stress &sgr;. The solid triangles (▴), solid circles (&Circlesolid;) and solid diamonds (♦) represent the results obtained from Fe single crystal material, Fe polycrystalline material, and low-alloy steel material, respectively.
Moreover, from the gradient of the magnetization curve of test materials near the flux density B=0 as depicted in
FIGS. 5 and 6
, it is possible to determine the magnetic susceptibility (H corresponds to the coercive force Hc). Thereby,
FIG. 8
is obtained when a ratio of the coercive force Hc and the magnetic susceptibility &khgr;
H
at Hc, A=Hc/&khgr;
H
is calculated, and the logarithmic values of A are plotted in relation to corresponding logarithmic values of the tensile stress &sgr;. The solid triangles (▴), solid circles (&Circlesolid;) and solid diamonds (♦) represent the results obtained from Fe single crystal material, Fe polycrystalline material, and low-alloy steel material, respectively.
From
FIG. 8
, the inventor investigated that the relation of the tensile stress &sgr; and the value A is expressed by the following equation:
log(&sgr;)=log(
a
)+nlog(
A
) (2),
where A=H
c
/&khgr;
H
.
That is, the equation (2) can be expressed by the same form of the equation (1) as follows:
&sgr;=
a
(
A
)
n
(3)
where the constants a and n are determined from the crystal structure of test materials. It is supposed that the single crystal pure iron, polycrystalline pure iron, and
Iwate University
Knobbe, Martens Olson, and Bear, LLP.
Strecker Gerard R.
LandOfFree
Nondestructive fatigue test method for ferromagnetic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Nondestructive fatigue test method for ferromagnetic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Nondestructive fatigue test method for ferromagnetic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2844339